/Community.CsharpSqlite/src/btree_c.cs

using System;
using System.Diagnostics;
using System.Text;

using i64 = System.Int64;
using u8 = System.Byte;
using u16 = System.UInt16;
using u32 = System.UInt32;
using u64 = System.UInt64;
using sqlite3_int64 = System.Int64;
using Pgno = System.UInt32;

namespace Community.CsharpSqlite
{
  using DbPage = Sqlite3.PgHdr;

  public partial class Sqlite3
  {
/*
** 2004 April 6
**
** The author disclaims copyright to this source code.  In place of
** a legal notice, here is a blessing:
**
**    May you do good and not evil.
**    May you find forgiveness for yourself and forgive others.
**    May you share freely, never taking more than you give.
**
** This file implements a external (disk-based) database using BTrees.
** See the header comment on "btreeInt.h" for additional information.
** Including a description of file format and an overview of operation.
*************************************************************************
**  Included in SQLite3 port to C#-SQLite;  2008 Noah B Hart
**  C#-SQLite is an independent reimplementation of the SQLite software library
**
**  SQLITE_SOURCE_ID: 2011-06-23 19:49:22 4374b7e83ea0a3fbc3691f9c0c936272862f32f2 
**
*************************************************************************
*/
//#include "btreeInt.h"

/*
** The header string that appears at the beginning of every
** SQLite database.
*/
static byte[] zMagicHeader = Encoding.UTF8.GetBytes( SQLITE_FILE_HEADER );

/*
** Set this global variable to 1 to enable tracing using the TRACE
** macro.
*/
#if TRACE 
static bool sqlite3BtreeTrace=false;  /* True to enable tracing */
//# define TRACE(X)  if(sqlite3BtreeTrace){printf X;fflush(stdout);}
static void TRACE(string X, params object[] ap) { if (sqlite3BtreeTrace)  printf(X, ap); }
#else
//# define TRACE(X)
static void TRACE( string X, params object[] ap )
{
}
#endif



/*
** Extract a 2-byte big-endian integer from an array of unsigned bytes.
** But if the value is zero, make it 65536.
**
** This routine is used to extract the "offset to cell content area" value
** from the header of a btree page.  If the page size is 65536 and the page
** is empty, the offset should be 65536, but the 2-byte value stores zero.
** This routine makes the necessary adjustment to 65536.
*/
//#define get2byteNotZero(X)  (((((int)get2byte(X))-1)&0xffff)+1)
static int get2byteNotZero( byte[] X, int offset )
{
  return ( ( ( ( (int)get2byte( X, offset ) ) - 1 ) & 0xffff ) + 1 );
}

#if !SQLITE_OMIT_SHARED_CACHE
/*
** A list of BtShared objects that are eligible for participation
** in shared cache.  This variable has file scope during normal builds,
** but the test harness needs to access it so we make it global for
** test builds.
**
** Access to this variable is protected by SQLITE_MUTEX_STATIC_MASTER.
*/
#if SQLITE_TEST
BtShared *SQLITE_WSD sqlite3SharedCacheList = 0;
#else
static BtShared *SQLITE_WSD sqlite3SharedCacheList = 0;
#endif
#endif //* SQLITE_OMIT_SHARED_CACHE */

#if !SQLITE_OMIT_SHARED_CACHE
/*
** Enable or disable the shared pager and schema features.
**
** This routine has no effect on existing database connections.
** The shared cache setting effects only future calls to
** sqlite3_open(), sqlite3_open16(), or sqlite3_open_v2().
*/
int sqlite3_enable_shared_cache(int enable){
sqlite3GlobalConfig.sharedCacheEnabled = enable;
return SQLITE_OK;
}
#endif



#if SQLITE_OMIT_SHARED_CACHE
/*
** The functions querySharedCacheTableLock(), setSharedCacheTableLock(),
** and clearAllSharedCacheTableLocks()
** manipulate entries in the BtShared.pLock linked list used to store
** shared-cache table level locks. If the library is compiled with the
** shared-cache feature disabled, then there is only ever one user
** of each BtShared structure and so this locking is not necessary.
** So define the lock related functions as no-ops.
*/
//#define querySharedCacheTableLock(a,b,c) SQLITE_OK
static int querySharedCacheTableLock( Btree p, Pgno iTab, u8 eLock )
{
  return SQLITE_OK;
}

//#define setSharedCacheTableLock(a,b,c) SQLITE_OK
//#define clearAllSharedCacheTableLocks(a)
static void clearAllSharedCacheTableLocks( Btree a )
{
}
//#define downgradeAllSharedCacheTableLocks(a)
static void downgradeAllSharedCacheTableLocks( Btree a )
{
}
//#define hasSharedCacheTableLock(a,b,c,d) 1
static bool hasSharedCacheTableLock( Btree a, Pgno b, int c, int d )
{
  return true;
}
//#define hasReadConflicts(a, b) 0
static bool hasReadConflicts( Btree a, Pgno b )
{
  return false;
}
#endif

#if !SQLITE_OMIT_SHARED_CACHE

#if SQLITE_DEBUG
/*
**** This function is only used as part of an assert() statement. ***
**
** Check to see if pBtree holds the required locks to read or write to the 
** table with root page iRoot.   Return 1 if it does and 0 if not.
**
** For example, when writing to a table with root-page iRoot via 
** Btree connection pBtree:
**
**    assert( hasSharedCacheTableLock(pBtree, iRoot, 0, WRITE_LOCK) );
**
** When writing to an index that resides in a sharable database, the 
** caller should have first obtained a lock specifying the root page of
** the corresponding table. This makes things a bit more complicated,
** as this module treats each table as a separate structure. To determine
** the table corresponding to the index being written, this
** function has to search through the database schema.
**
** Instead of a lock on the table/index rooted at page iRoot, the caller may
** hold a write-lock on the schema table (root page 1). This is also
** acceptable.
*/
static int hasSharedCacheTableLock(
Btree pBtree,         /* Handle that must hold lock */
Pgno iRoot,            /* Root page of b-tree */
int isIndex,           /* True if iRoot is the root of an index b-tree */
int eLockType          /* Required lock type (READ_LOCK or WRITE_LOCK) */
){
Schema pSchema = (Schema *)pBtree.pBt.pSchema;
Pgno iTab = 0;
BtLock pLock;

/* If this database is not shareable, or if the client is reading
** and has the read-uncommitted flag set, then no lock is required. 
** Return true immediately.
*/
if( (pBtree.sharable==null)
|| (eLockType==READ_LOCK && (pBtree.db.flags & SQLITE_ReadUncommitted))
){
return 1;
}

/* If the client is reading  or writing an index and the schema is
** not loaded, then it is too difficult to actually check to see if
** the correct locks are held.  So do not bother - just return true.
** This case does not come up very often anyhow.
*/
if( isIndex && (!pSchema || (pSchema->flags&DB_SchemaLoaded)==0) ){
return 1;
}

/* Figure out the root-page that the lock should be held on. For table
** b-trees, this is just the root page of the b-tree being read or
** written. For index b-trees, it is the root page of the associated
** table.  */
if( isIndex ){
HashElem p;
for(p=sqliteHashFirst(pSchema.idxHash); p!=null; p=sqliteHashNext(p)){
Index pIdx = (Index *)sqliteHashData(p);
if( pIdx.tnum==(int)iRoot ){
iTab = pIdx.pTable.tnum;
}
}
}else{
iTab = iRoot;
}

/* Search for the required lock. Either a write-lock on root-page iTab, a
** write-lock on the schema table, or (if the client is reading) a
** read-lock on iTab will suffice. Return 1 if any of these are found.  */
for(pLock=pBtree.pBt.pLock; pLock; pLock=pLock.pNext){
if( pLock.pBtree==pBtree
&& (pLock.iTable==iTab || (pLock.eLock==WRITE_LOCK && pLock.iTable==1))
&& pLock.eLock>=eLockType
){
return 1;
}
}

/* Failed to find the required lock. */
return 0;
}

#endif //* SQLITE_DEBUG */

#if SQLITE_DEBUG
/*
** This function may be used as part of assert() statements only. ****
**
** Return true if it would be illegal for pBtree to write into the
** table or index rooted at iRoot because other shared connections are
** simultaneously reading that same table or index.
**
** It is illegal for pBtree to write if some other Btree object that
** shares the same BtShared object is currently reading or writing
** the iRoot table.  Except, if the other Btree object has the
** read-uncommitted flag set, then it is OK for the other object to
** have a read cursor.
**
** For example, before writing to any part of the table or index
** rooted at page iRoot, one should call:
**
**    assert( !hasReadConflicts(pBtree, iRoot) );
*/
static int hasReadConflicts(Btree pBtree, Pgno iRoot){
BtCursor p;
for(p=pBtree.pBt.pCursor; p!=null; p=p.pNext){
if( p.pgnoRoot==iRoot
&& p.pBtree!=pBtree
&& 0==(p.pBtree.db.flags & SQLITE_ReadUncommitted)
){
return 1;
}
}
return 0;
}
#endif    //* #if SQLITE_DEBUG */

/*
** Query to see if Btree handle p may obtain a lock of type eLock
** (READ_LOCK or WRITE_LOCK) on the table with root-page iTab. Return
** SQLITE_OK if the lock may be obtained (by calling
** setSharedCacheTableLock()), or SQLITE_LOCKED if not.
*/
static int querySharedCacheTableLock(Btree p, Pgno iTab, u8 eLock){
BtShared pBt = p.pBt;
BtLock pIter;

Debug.Assert( sqlite3BtreeHoldsMutex(p) );
Debug.Assert( eLock==READ_LOCK || eLock==WRITE_LOCK );
Debug.Assert( p.db!=null );
Debug.Assert( !(p.db.flags&SQLITE_ReadUncommitted)||eLock==WRITE_LOCK||iTab==1 );

/* If requesting a write-lock, then the Btree must have an open write
** transaction on this file. And, obviously, for this to be so there
** must be an open write transaction on the file itself.
*/
Debug.Assert( eLock==READ_LOCK || (p==pBt.pWriter && p.inTrans==TRANS_WRITE) );
Debug.Assert( eLock==READ_LOCK || pBt.inTransaction==TRANS_WRITE );

/* This routine is a no-op if the shared-cache is not enabled */
if( !p.sharable ){
return SQLITE_OK;
}

/* If some other connection is holding an exclusive lock, the
** requested lock may not be obtained.
*/
if( pBt.pWriter!=p && pBt.isExclusive ){
sqlite3ConnectionBlocked(p.db, pBt.pWriter.db);
return SQLITE_LOCKED_SHAREDCACHE;
}

for(pIter=pBt.pLock; pIter; pIter=pIter.pNext){
/* The condition (pIter.eLock!=eLock) in the following if(...)
** statement is a simplification of:
**
**   (eLock==WRITE_LOCK || pIter.eLock==WRITE_LOCK)
**
** since we know that if eLock==WRITE_LOCK, then no other connection
** may hold a WRITE_LOCK on any table in this file (since there can
** only be a single writer).
*/
Debug.Assert( pIter.eLock==READ_LOCK || pIter.eLock==WRITE_LOCK );
Debug.Assert( eLock==READ_LOCK || pIter.pBtree==p || pIter.eLock==READ_LOCK);
if( pIter.pBtree!=p && pIter.iTable==iTab && pIter.eLock!=eLock ){
sqlite3ConnectionBlocked(p.db, pIter.pBtree.db);
if( eLock==WRITE_LOCK ){
Debug.Assert( p==pBt.pWriter );
pBt.isPending = 1;
}
return SQLITE_LOCKED_SHAREDCACHE;
}
}
return SQLITE_OK;
}
#endif //* !SQLITE_OMIT_SHARED_CACHE */

#if !SQLITE_OMIT_SHARED_CACHE
/*
** Add a lock on the table with root-page iTable to the shared-btree used
** by Btree handle p. Parameter eLock must be either READ_LOCK or 
** WRITE_LOCK.
**
** This function assumes the following:
**
**   (a) The specified Btree object p is connected to a sharable
**       database (one with the BtShared.sharable flag set), and
**
**   (b) No other Btree objects hold a lock that conflicts
**       with the requested lock (i.e. querySharedCacheTableLock() has
**       already been called and returned SQLITE_OK).
**
** SQLITE_OK is returned if the lock is added successfully. SQLITE_NOMEM 
** is returned if a malloc attempt fails.
*/
static int setSharedCacheTableLock(Btree p, Pgno iTable, u8 eLock){
BtShared pBt = p.pBt;
BtLock pLock = 0;
BtLock pIter;

Debug.Assert( sqlite3BtreeHoldsMutex(p) );
Debug.Assert( eLock==READ_LOCK || eLock==WRITE_LOCK );
Debug.Assert( p.db!=null );

/* A connection with the read-uncommitted flag set will never try to
** obtain a read-lock using this function. The only read-lock obtained
** by a connection in read-uncommitted mode is on the sqlite_master
** table, and that lock is obtained in BtreeBeginTrans().  */
Debug.Assert( 0==(p.db.flags&SQLITE_ReadUncommitted) || eLock==WRITE_LOCK );

/* This function should only be called on a sharable b-tree after it
** has been determined that no other b-tree holds a conflicting lock.  */
Debug.Assert( p.sharable );
Debug.Assert( SQLITE_OK==querySharedCacheTableLock(p, iTable, eLock) );

/* First search the list for an existing lock on this table. */
for(pIter=pBt.pLock; pIter; pIter=pIter.pNext){
if( pIter.iTable==iTable && pIter.pBtree==p ){
pLock = pIter;
break;
}
}

/* If the above search did not find a BtLock struct associating Btree p
** with table iTable, allocate one and link it into the list.
*/
if( !pLock ){
pLock = (BtLock *)sqlite3MallocZero(sizeof(BtLock));
if( !pLock ){
return SQLITE_NOMEM;
}
pLock.iTable = iTable;
pLock.pBtree = p;
pLock.pNext = pBt.pLock;
pBt.pLock = pLock;
}

/* Set the BtLock.eLock variable to the maximum of the current lock
** and the requested lock. This means if a write-lock was already held
** and a read-lock requested, we don't incorrectly downgrade the lock.
*/
Debug.Assert( WRITE_LOCK>READ_LOCK );
if( eLock>pLock.eLock ){
pLock.eLock = eLock;
}

return SQLITE_OK;
}
#endif //* !SQLITE_OMIT_SHARED_CACHE */

#if !SQLITE_OMIT_SHARED_CACHE
/*
** Release all the table locks (locks obtained via calls to
** the setSharedCacheTableLock() procedure) held by Btree object p.
**
** This function assumes that Btree p has an open read or write 
** transaction. If it does not, then the BtShared.isPending variable
** may be incorrectly cleared.
*/
static void clearAllSharedCacheTableLocks(Btree p){
BtShared pBt = p.pBt;
BtLock **ppIter = &pBt.pLock;

Debug.Assert( sqlite3BtreeHoldsMutex(p) );
Debug.Assert( p.sharable || 0==*ppIter );
Debug.Assert( p.inTrans>0 );

while( ppIter ){
BtLock pLock = ppIter;
Debug.Assert( pBt.isExclusive==null || pBt.pWriter==pLock.pBtree );
Debug.Assert( pLock.pBtree.inTrans>=pLock.eLock );
if( pLock.pBtree==p ){
ppIter = pLock.pNext;
Debug.Assert( pLock.iTable!=1 || pLock==&p.lock );
if( pLock.iTable!=1 ){
pLock=null;//sqlite3_free(ref pLock);
}
}else{
ppIter = &pLock.pNext;
}
}

Debug.Assert( pBt.isPending==null || pBt.pWriter );
if( pBt.pWriter==p ){
pBt.pWriter = 0;
pBt.isExclusive = 0;
pBt.isPending = 0;
}else if( pBt.nTransaction==2 ){
/* This function is called when Btree p is concluding its 
** transaction. If there currently exists a writer, and p is not
** that writer, then the number of locks held by connections other
** than the writer must be about to drop to zero. In this case
** set the isPending flag to 0.
**
** If there is not currently a writer, then BtShared.isPending must
** be zero already. So this next line is harmless in that case.
*/
pBt.isPending = 0;
}
}

/*
** This function changes all write-locks held by Btree p into read-locks.
*/
static void downgradeAllSharedCacheTableLocks(Btree p){
BtShared pBt = p.pBt;
if( pBt.pWriter==p ){
BtLock pLock;
pBt.pWriter = 0;
pBt.isExclusive = 0;
pBt.isPending = 0;
for(pLock=pBt.pLock; pLock; pLock=pLock.pNext){
Debug.Assert( pLock.eLock==READ_LOCK || pLock.pBtree==p );
pLock.eLock = READ_LOCK;
}
}
}

#endif //* SQLITE_OMIT_SHARED_CACHE */

//static void releasePage(MemPage pPage);  /* Forward reference */

/*
***** This routine is used inside of assert() only ****
**
** Verify that the cursor holds the mutex on its BtShared
*/
#if SQLITE_DEBUG
static bool cursorHoldsMutex( BtCursor p )
{
  return sqlite3_mutex_held( p.pBt.mutex );
}
#else
static bool cursorHoldsMutex(BtCursor p) { return true; }
#endif


#if !SQLITE_OMIT_INCRBLOB
/*
** Invalidate the overflow page-list cache for cursor pCur, if any.
*/
static void invalidateOverflowCache(BtCursor pCur){
Debug.Assert( cursorHoldsMutex(pCur) );
//sqlite3_free(ref pCur.aOverflow);
pCur.aOverflow = null;
}

/*
** Invalidate the overflow page-list cache for all cursors opened
** on the shared btree structure pBt.
*/
static void invalidateAllOverflowCache(BtShared pBt){
BtCursor p;
Debug.Assert( sqlite3_mutex_held(pBt.mutex) );
for(p=pBt.pCursor; p!=null; p=p.pNext){
invalidateOverflowCache(p);
}
}

/*
** This function is called before modifying the contents of a table
** to invalidate any incrblob cursors that are open on the
** row or one of the rows being modified.
**
** If argument isClearTable is true, then the entire contents of the
** table is about to be deleted. In this case invalidate all incrblob
** cursors open on any row within the table with root-page pgnoRoot.
**
** Otherwise, if argument isClearTable is false, then the row with
** rowid iRow is being replaced or deleted. In this case invalidate
** only those incrblob cursors open on that specific row.
*/
static void invalidateIncrblobCursors(
Btree pBtree,          /* The database file to check */
i64 iRow,               /* The rowid that might be changing */
int isClearTable        /* True if all rows are being deleted */
){
BtCursor p;
BtShared pBt = pBtree.pBt;
Debug.Assert( sqlite3BtreeHoldsMutex(pBtree) );
for(p=pBt.pCursor; p!=null; p=p.pNext){
if( p.isIncrblobHandle && (isClearTable || p.info.nKey==iRow) ){
p.eState = CURSOR_INVALID;
}
}
}

#else
/* Stub functions when INCRBLOB is omitted */
//#define invalidateOverflowCache(x)
static void invalidateOverflowCache( BtCursor pCur )
{
}
//#define invalidateAllOverflowCache(x)
static void invalidateAllOverflowCache( BtShared pBt )
{
}
//#define invalidateIncrblobCursors(x,y,z)
static void invalidateIncrblobCursors( Btree x, i64 y, int z )
{
}
#endif //* SQLITE_OMIT_INCRBLOB */

/*
** Set bit pgno of the BtShared.pHasContent bitvec. This is called
** when a page that previously contained data becomes a free-list leaf
** page.
**
** The BtShared.pHasContent bitvec exists to work around an obscure
** bug caused by the interaction of two useful IO optimizations surrounding
** free-list leaf pages:
**
**   1) When all data is deleted from a page and the page becomes
**      a free-list leaf page, the page is not written to the database
**      (as free-list leaf pages contain no meaningful data). Sometimes
**      such a page is not even journalled (as it will not be modified,
**      why bother journalling it?).
**
**   2) When a free-list leaf page is reused, its content is not read
**      from the database or written to the journal file (why should it
**      be, if it is not at all meaningful?).
**
** By themselves, these optimizations work fine and provide a handy
** performance boost to bulk delete or insert operations. However, if
** a page is moved to the free-list and then reused within the same
** transaction, a problem comes up. If the page is not journalled when
** it is moved to the free-list and it is also not journalled when it
** is extracted from the free-list and reused, then the original data
** may be lost. In the event of a rollback, it may not be possible
** to restore the database to its original configuration.
**
** The solution is the BtShared.pHasContent bitvec. Whenever a page is
** moved to become a free-list leaf page, the corresponding bit is
** set in the bitvec. Whenever a leaf page is extracted from the free-list,
** optimization 2 above is omitted if the corresponding bit is already
** set in BtShared.pHasContent. The contents of the bitvec are cleared
** at the end of every transaction.
*/
static int btreeSetHasContent( BtShared pBt, Pgno pgno )
{
  int rc = SQLITE_OK;
  if ( null == pBt.pHasContent )
  {
    Debug.Assert( pgno <= pBt.nPage );
    pBt.pHasContent = sqlite3BitvecCreate( pBt.nPage );
    //if ( null == pBt.pHasContent )
    //{
    //  rc = SQLITE_NOMEM;
    //}
  }
  if ( rc == SQLITE_OK && pgno <= sqlite3BitvecSize( pBt.pHasContent ) )
  {
    rc = sqlite3BitvecSet( pBt.pHasContent, pgno );
  }
  return rc;
}

/*
** Query the BtShared.pHasContent vector.
**
** This function is called when a free-list leaf page is removed from the
** free-list for reuse. It returns false if it is safe to retrieve the
** page from the pager layer with the 'no-content' flag set. True otherwise.
*/
static bool btreeGetHasContent( BtShared pBt, Pgno pgno )
{
  Bitvec p = pBt.pHasContent;
  return ( p != null && ( pgno > sqlite3BitvecSize( p ) || sqlite3BitvecTest( p, pgno ) != 0 ) );
}

/*
** Clear (destroy) the BtShared.pHasContent bitvec. This should be
** invoked at the conclusion of each write-transaction.
*/
static void btreeClearHasContent( BtShared pBt )
{
  sqlite3BitvecDestroy( ref pBt.pHasContent );
  pBt.pHasContent = null;
}

/*
** Save the current cursor position in the variables BtCursor.nKey
** and BtCursor.pKey. The cursor's state is set to CURSOR_REQUIRESEEK.
**
** The caller must ensure that the cursor is valid (has eState==CURSOR_VALID)
** prior to calling this routine.
*/
static int saveCursorPosition( BtCursor pCur )
{
  int rc;

  Debug.Assert( CURSOR_VALID == pCur.eState );
  Debug.Assert( null == pCur.pKey );
  Debug.Assert( cursorHoldsMutex( pCur ) );

  rc = sqlite3BtreeKeySize( pCur, ref pCur.nKey );
  Debug.Assert( rc == SQLITE_OK );  /* KeySize() cannot fail */

  /* If this is an intKey table, then the above call to BtreeKeySize()
  ** stores the integer key in pCur.nKey. In this case this value is
  ** all that is required. Otherwise, if pCur is not open on an intKey
  ** table, then malloc space for and store the pCur.nKey bytes of key
  ** data.
  */
  if ( 0 == pCur.apPage[0].intKey )
  {
    byte[] pKey = sqlite3Malloc( (int)pCur.nKey );
    //if( pKey !=null){
    rc = sqlite3BtreeKey( pCur, 0, (u32)pCur.nKey, pKey );
    if ( rc == SQLITE_OK )
    {
      pCur.pKey = pKey;
    }
    //else{
    //  sqlite3_free(ref pKey);
    //}
    //}else{
    //  rc = SQLITE_NOMEM;
    //}
  }
  Debug.Assert( 0 == pCur.apPage[0].intKey || null == pCur.pKey );

  if ( rc == SQLITE_OK )
  {
    int i;
    for ( i = 0; i <= pCur.iPage; i++ )
    {
      releasePage( pCur.apPage[i] );
      pCur.apPage[i] = null;
    }
    pCur.iPage = -1;
    pCur.eState = CURSOR_REQUIRESEEK;
  }

  invalidateOverflowCache( pCur );
  return rc;
}

/*
** Save the positions of all cursors (except pExcept) that are open on
** the table  with root-page iRoot. Usually, this is called just before cursor
** pExcept is used to modify the table (BtreeDelete() or BtreeInsert()).
*/
static int saveAllCursors( BtShared pBt, Pgno iRoot, BtCursor pExcept )
{
  BtCursor p;
  Debug.Assert( sqlite3_mutex_held( pBt.mutex ) );
  Debug.Assert( pExcept == null || pExcept.pBt == pBt );
  for ( p = pBt.pCursor; p != null; p = p.pNext )
  {
    if ( p != pExcept && ( 0 == iRoot || p.pgnoRoot == iRoot ) &&
    p.eState == CURSOR_VALID )
    {
      int rc = saveCursorPosition( p );
      if ( SQLITE_OK != rc )
      {
        return rc;
      }
    }
  }
  return SQLITE_OK;
}

/*
** Clear the current cursor position.
*/
static void sqlite3BtreeClearCursor( BtCursor pCur )
{
  Debug.Assert( cursorHoldsMutex( pCur ) );
  sqlite3_free( ref pCur.pKey );
  pCur.eState = CURSOR_INVALID;
}

/*
** In this version of BtreeMoveto, pKey is a packed index record
** such as is generated by the OP_MakeRecord opcode.  Unpack the
** record and then call BtreeMovetoUnpacked() to do the work.
*/
static int btreeMoveto(
BtCursor pCur,     /* Cursor open on the btree to be searched */
byte[] pKey,       /* Packed key if the btree is an index */
i64 nKey,          /* Integer key for tables.  Size of pKey for indices */
int bias,          /* Bias search to the high end */
ref int pRes       /* Write search results here */
)
{
  int rc;                    /* Status code */
  UnpackedRecord pIdxKey;   /* Unpacked index key */
  UnpackedRecord aSpace = new UnpackedRecord();//char aSpace[150]; /* Temp space for pIdxKey - to avoid a malloc */

  if ( pKey != null )
  {
    Debug.Assert( nKey == (i64)(int)nKey );
    pIdxKey = sqlite3VdbeRecordUnpack( pCur.pKeyInfo, (int)nKey, pKey,
    aSpace, 16 );//sizeof( aSpace ) );
    //if ( pIdxKey == null )
    //  return SQLITE_NOMEM;
  }
  else
  {
    pIdxKey = null;
  }
  rc = sqlite3BtreeMovetoUnpacked( pCur, pIdxKey, nKey, bias != 0 ? 1 : 0, ref pRes );

  if ( pKey != null )
  {
    sqlite3VdbeDeleteUnpackedRecord( pIdxKey );
  }
  return rc;
}

/*
** Restore the cursor to the position it was in (or as close to as possible)
** when saveCursorPosition() was called. Note that this call deletes the
** saved position info stored by saveCursorPosition(), so there can be
** at most one effective restoreCursorPosition() call after each
** saveCursorPosition().
*/
static int btreeRestoreCursorPosition( BtCursor pCur )
{
  int rc;
  Debug.Assert( cursorHoldsMutex( pCur ) );
  Debug.Assert( pCur.eState >= CURSOR_REQUIRESEEK );
  if ( pCur.eState == CURSOR_FAULT )
  {
    return pCur.skipNext;
  }
  pCur.eState = CURSOR_INVALID;
  rc = btreeMoveto( pCur, pCur.pKey, pCur.nKey, 0, ref pCur.skipNext );
  if ( rc == SQLITE_OK )
  {
    //sqlite3_free(ref pCur.pKey);
    pCur.pKey = null;
    Debug.Assert( pCur.eState == CURSOR_VALID || pCur.eState == CURSOR_INVALID );
  }
  return rc;
}

//#define restoreCursorPosition(p) \
//  (p.eState>=CURSOR_REQUIRESEEK ? \
//         btreeRestoreCursorPosition(p) : \
//         SQLITE_OK)
static int restoreCursorPosition( BtCursor pCur )
{
  if ( pCur.eState >= CURSOR_REQUIRESEEK )
    return btreeRestoreCursorPosition( pCur );
  else
    return SQLITE_OK;
}

/*
** Determine whether or not a cursor has moved from the position it
** was last placed at.  Cursors can move when the row they are pointing
** at is deleted out from under them.
**
** This routine returns an error code if something goes wrong.  The
** integer pHasMoved is set to one if the cursor has moved and 0 if not.
*/
static int sqlite3BtreeCursorHasMoved( BtCursor pCur, ref int pHasMoved )
{
  int rc;

  rc = restoreCursorPosition( pCur );
  if ( rc != 0 )
  {
    pHasMoved = 1;
    return rc;
  }
  if ( pCur.eState != CURSOR_VALID || pCur.skipNext != 0 )
  {
    pHasMoved = 1;
  }
  else
  {
    pHasMoved = 0;
  }
  return SQLITE_OK;
}

#if !SQLITE_OMIT_AUTOVACUUM
/*
** Given a page number of a regular database page, return the page
** number for the pointer-map page that contains the entry for the
** input page number.
**
** Return 0 (not a valid page) for pgno==1 since there is
** no pointer map associated with page 1.  The integrity_check logic
** requires that ptrmapPageno(*,1)!=1.
*/
static Pgno ptrmapPageno( BtShared pBt, Pgno pgno )
{
  int nPagesPerMapPage;
  Pgno iPtrMap, ret;
  Debug.Assert( sqlite3_mutex_held( pBt.mutex ) );
  if ( pgno < 2 )
    return 0;
  nPagesPerMapPage = (int)( pBt.usableSize / 5 + 1 );
  iPtrMap = (Pgno)( ( pgno - 2 ) / nPagesPerMapPage );
  ret = (Pgno)( iPtrMap * nPagesPerMapPage ) + 2;
  if ( ret == PENDING_BYTE_PAGE( pBt ) )
  {
    ret++;
  }
  return ret;
}

/*
** Write an entry into the pointer map.
**
** This routine updates the pointer map entry for page number 'key'
** so that it maps to type 'eType' and parent page number 'pgno'.
**
** If pRC is initially non-zero (non-SQLITE_OK) then this routine is
** a no-op.  If an error occurs, the appropriate error code is written
** into pRC.
*/
static void ptrmapPut( BtShared pBt, Pgno key, u8 eType, Pgno parent, ref int pRC )
{
  PgHdr pDbPage = new PgHdr(); /* The pointer map page */
  u8[] pPtrmap;                 /* The pointer map data */
  Pgno iPtrmap;                 /* The pointer map page number */
  int offset;                   /* Offset in pointer map page */
  int rc;                       /* Return code from subfunctions */

  if ( pRC != 0 )
    return;

  Debug.Assert( sqlite3_mutex_held( pBt.mutex ) );
  /* The master-journal page number must never be used as a pointer map page */
  Debug.Assert( false == PTRMAP_ISPAGE( pBt, PENDING_BYTE_PAGE( pBt ) ) );

  Debug.Assert( pBt.autoVacuum );
  if ( key == 0 )
  {
    pRC = SQLITE_CORRUPT_BKPT();
    return;
  }
  iPtrmap = PTRMAP_PAGENO( pBt, key );
  rc = sqlite3PagerGet( pBt.pPager, iPtrmap, ref pDbPage );
  if ( rc != SQLITE_OK )
  {
    pRC = rc;
    return;
  }
  offset = (int)PTRMAP_PTROFFSET( iPtrmap, key );
  if ( offset < 0 )
  {
    pRC = SQLITE_CORRUPT_BKPT();
    goto ptrmap_exit;
  }
  Debug.Assert( offset <= (int)pBt.usableSize - 5 );
  pPtrmap = sqlite3PagerGetData( pDbPage );

  if ( eType != pPtrmap[offset] || sqlite3Get4byte( pPtrmap, offset + 1 ) != parent )
  {
    TRACE( "PTRMAP_UPDATE: %d->(%d,%d)\n", key, eType, parent );
    pRC = rc = sqlite3PagerWrite( pDbPage );
    if ( rc == SQLITE_OK )
    {
      pPtrmap[offset] = eType;
      sqlite3Put4byte( pPtrmap, offset + 1, parent );
    }
  }

ptrmap_exit:
  sqlite3PagerUnref( pDbPage );
}

/*
** Read an entry from the pointer map.
**
** This routine retrieves the pointer map entry for page 'key', writing
** the type and parent page number to pEType and pPgno respectively.
** An error code is returned if something goes wrong, otherwise SQLITE_OK.
*/
static int ptrmapGet( BtShared pBt, Pgno key, ref u8 pEType, ref Pgno pPgno )
{
  PgHdr pDbPage = new PgHdr();/* The pointer map page */
  int iPtrmap;                 /* Pointer map page index */
  u8[] pPtrmap;                /* Pointer map page data */
  int offset;                  /* Offset of entry in pointer map */
  int rc;

  Debug.Assert( sqlite3_mutex_held( pBt.mutex ) );

  iPtrmap = (int)PTRMAP_PAGENO( pBt, key );
  rc = sqlite3PagerGet( pBt.pPager, (u32)iPtrmap, ref pDbPage );
  if ( rc != 0 )
  {
    return rc;
  }
  pPtrmap = sqlite3PagerGetData( pDbPage );

  offset = (int)PTRMAP_PTROFFSET( (u32)iPtrmap, key );
  if ( offset < 0 )
  {
    sqlite3PagerUnref( pDbPage );
    return SQLITE_CORRUPT_BKPT();
  }
  Debug.Assert( offset <= (int)pBt.usableSize - 5 );
  // Under C# pEType will always exist. No need to test; //
  //Debug.Assert( pEType != 0 );
  pEType = pPtrmap[offset];
  // Under C# pPgno will always exist. No need to test; //
  //if ( pPgno != 0 )
  pPgno = sqlite3Get4byte( pPtrmap, offset + 1 );

  sqlite3PagerUnref( pDbPage );
  if ( pEType < 1 || pEType > 5 )
    return SQLITE_CORRUPT_BKPT();
  return SQLITE_OK;
}

#else //* if defined SQLITE_OMIT_AUTOVACUUM */
//#define ptrmapPut(w,x,y,z,rc)
//#define ptrmapGet(w,x,y,z) SQLITE_OK
//#define ptrmapPutOvflPtr(x, y, rc)
#endif

/*
** Given a btree page and a cell index (0 means the first cell on
** the page, 1 means the second cell, and so forth) return a pointer
** to the cell content.
**
** This routine works only for pages that do not contain overflow cells.
*/
//#define findCell(P,I) \
//  ((P).aData + ((P).maskPage & get2byte((P).aData[(P).cellOffset+2*(I)])))
static int findCell( MemPage pPage, int iCell )
{
  return get2byte( pPage.aData, pPage.cellOffset + 2 * ( iCell ) );
}

//#define findCellv2(D,M,O,I) (D+(M&get2byte(D+(O+2*(I)))))
static u8[] findCellv2( u8[] pPage, u16 iCell, u16 O, int I )
{
  Debugger.Break();
  return pPage;
}


/*
** This a more complex version of findCell() that works for
** pages that do contain overflow cells.
*/
static int findOverflowCell( MemPage pPage, int iCell )
{
  int i;
  Debug.Assert( sqlite3_mutex_held( pPage.pBt.mutex ) );
  for ( i = pPage.nOverflow - 1; i >= 0; i-- )
  {
    int k;
    _OvflCell pOvfl;
    pOvfl = pPage.aOvfl[i];
    k = pOvfl.idx;
    if ( k <= iCell )
    {
      if ( k == iCell )
      {
        //return pOvfl.pCell;
        return -i - 1; // Negative Offset means overflow cells
      }
      iCell--;
    }
  }
  return findCell( pPage, iCell );
}

/*
** Parse a cell content block and fill in the CellInfo structure.  There
** are two versions of this function.  btreeParseCell() takes a
** cell index as the second argument and btreeParseCellPtr()
** takes a pointer to the body of the cell as its second argument.
**
** Within this file, the parseCell() macro can be called instead of
** btreeParseCellPtr(). Using some compilers, this will be faster.
*/
//OVERLOADS
static void btreeParseCellPtr(
MemPage pPage,        /* Page containing the cell */
int iCell,            /* Pointer to the cell text. */
ref CellInfo pInfo    /* Fill in this structure */
)
{
  btreeParseCellPtr( pPage, pPage.aData, iCell, ref pInfo );
}
static void btreeParseCellPtr(
MemPage pPage,        /* Page containing the cell */
byte[] pCell,         /* The actual data */
ref CellInfo pInfo    /* Fill in this structure */
)
{
  btreeParseCellPtr( pPage, pCell, 0, ref pInfo );
}
static void btreeParseCellPtr(
MemPage pPage,         /* Page containing the cell */
u8[] pCell,            /* Pointer to the cell text. */
int iCell,             /* Pointer to the cell text. */
ref CellInfo pInfo     /* Fill in this structure */
)
{
  u16 n;               /* Number bytes in cell content header */
  u32 nPayload = 0;    /* Number of bytes of cell payload */

  Debug.Assert( sqlite3_mutex_held( pPage.pBt.mutex ) );

  if ( pInfo.pCell != pCell )
    pInfo.pCell = pCell;
  pInfo.iCell = iCell;
  Debug.Assert( pPage.leaf == 0 || pPage.leaf == 1 );
  n = pPage.childPtrSize;
  Debug.Assert( n == 4 - 4 * pPage.leaf );
  if ( pPage.intKey != 0 )
  {
    if ( pPage.hasData != 0 )
    {
      n += (u16)getVarint32( pCell, iCell + n, out nPayload );
    }
    else
    {
      nPayload = 0;
    }
    n += (u16)getVarint( pCell, iCell + n, out pInfo.nKey );
    pInfo.nData = nPayload;
  }
  else
  {
    pInfo.nData = 0;
    n += (u16)getVarint32( pCell, iCell + n, out nPayload );
    pInfo.nKey = nPayload;
  }
  pInfo.nPayload = nPayload;
  pInfo.nHeader = n;
  testcase( nPayload == pPage.maxLocal );
  testcase( nPayload == pPage.maxLocal + 1 );
  if ( likely( nPayload <= pPage.maxLocal ) )
  {
    /* This is the (easy) common case where the entire payload fits
    ** on the local page.  No overflow is required.
    */
    if ( ( pInfo.nSize = (u16)( n + nPayload ) ) < 4 )
      pInfo.nSize = 4;
    pInfo.nLocal = (u16)nPayload;
    pInfo.iOverflow = 0;
  }
  else
  {
    /* If the payload will not fit completely on the local page, we have
    ** to decide how much to store locally and how much to spill onto
    ** overflow pages.  The strategy is to minimize the amount of unused
    ** space on overflow pages while keeping the amount of local storage
    ** in between minLocal and maxLocal.
    **
    ** Warning:  changing the way overflow payload is distributed in any
    ** way will result in an incompatible file format.
    */
    int minLocal;  /* Minimum amount of payload held locally */
    int maxLocal;  /* Maximum amount of payload held locally */
    int surplus;   /* Overflow payload available for local storage */

    minLocal = pPage.minLocal;
    maxLocal = pPage.maxLocal;
    surplus = (int)( minLocal + ( nPayload - minLocal ) % ( pPage.pBt.usableSize - 4 ) );
    testcase( surplus == maxLocal );
    testcase( surplus == maxLocal + 1 );
    if ( surplus <= maxLocal )
    {
      pInfo.nLocal = (u16)surplus;
    }
    else
    {
      pInfo.nLocal = (u16)minLocal;
    }
    pInfo.iOverflow = (u16)( pInfo.nLocal + n );
    pInfo.nSize = (u16)( pInfo.iOverflow + 4 );
  }
}
//#define parseCell(pPage, iCell, pInfo) \
//  btreeParseCellPtr((pPage), findCell((pPage), (iCell)), (pInfo))
static void parseCell( MemPage pPage, int iCell, ref CellInfo pInfo )
{
  btreeParseCellPtr( pPage, findCell( pPage, iCell ), ref pInfo );
}

static void btreeParseCell(
MemPage pPage,         /* Page containing the cell */
int iCell,              /* The cell index.  First cell is 0 */
ref CellInfo pInfo         /* Fill in this structure */
)
{
  parseCell( pPage, iCell, ref pInfo );
}

/*
** Compute the total number of bytes that a Cell needs in the cell
** data area of the btree-page.  The return number includes the cell
** data header and the local payload, but not any overflow page or
** the space used by the cell pointer.
*/
// Alternative form for C#
static u16 cellSizePtr( MemPage pPage, int iCell )
{
  CellInfo info = new CellInfo();
  byte[] pCell = new byte[13];
  // Minimum Size = (2 bytes of Header  or (4) Child Pointer) + (maximum of) 9 bytes data
  if ( iCell < 0 )// Overflow Cell
    Buffer.BlockCopy( pPage.aOvfl[-( iCell + 1 )].pCell, 0, pCell, 0, pCell.Length < pPage.aOvfl[-( iCell + 1 )].pCell.Length ? pCell.Length : pPage.aOvfl[-( iCell + 1 )].pCell.Length );
  else if ( iCell >= pPage.aData.Length + 1 - pCell.Length )
    Buffer.BlockCopy( pPage.aData, iCell, pCell, 0, pPage.aData.Length - iCell );
  else
    Buffer.BlockCopy( pPage.aData, iCell, pCell, 0, pCell.Length );
  btreeParseCellPtr( pPage, pCell, ref info );
  return info.nSize;
}

// Alternative form for C#
static u16 cellSizePtr( MemPage pPage, byte[] pCell, int offset )
{
  CellInfo info = new CellInfo();
  info.pCell = sqlite3Malloc( pCell.Length );
  Buffer.BlockCopy( pCell, offset, info.pCell, 0, pCell.Length - offset );
  btreeParseCellPtr( pPage, info.pCell, ref info );
  return info.nSize;
}

static u16 cellSizePtr( MemPage pPage, u8[] pCell )
{
  int _pIter = pPage.childPtrSize; //u8 pIter = &pCell[pPage.childPtrSize];
  u32 nSize = 0;

#if SQLITE_DEBUG || DEBUG
  /* The value returned by this function should always be the same as
** the (CellInfo.nSize) value found by doing a full parse of the
** cell. If SQLITE_DEBUG is defined, an Debug.Assert() at the bottom of
** this function verifies that this invariant is not violated. */
  CellInfo debuginfo = new CellInfo();
  btreeParseCellPtr( pPage, pCell, ref debuginfo );
#else
CellInfo debuginfo = new CellInfo();
#endif

  if ( pPage.intKey != 0 )
  {
    int pEnd;
    if ( pPage.hasData != 0 )
    {
      _pIter += getVarint32( pCell, out nSize );// pIter += getVarint32( pIter, out nSize );
    }
    else
    {
      nSize = 0;
    }

    /* pIter now points at the 64-bit integer key value, a variable length
    ** integer. The following block moves pIter to point at the first byte
    ** past the end of the key value. */
    pEnd = _pIter + 9;//pEnd = &pIter[9];
    while ( ( ( pCell[_pIter++] ) & 0x80 ) != 0 && _pIter < pEnd )
      ;//while( (pIter++)&0x80 && pIter<pEnd );
  }
  else
  {
    _pIter += getVarint32( pCell, _pIter, out nSize ); //pIter += getVarint32( pIter, out nSize );
  }

  testcase( nSize == pPage.maxLocal );
  testcase( nSize == pPage.maxLocal + 1 );
  if ( nSize > pPage.maxLocal )
  {
    int minLocal = pPage.minLocal;
    nSize = (u32)( minLocal + ( nSize - minLocal ) % ( pPage.pBt.usableSize - 4 ) );
    testcase( nSize == pPage.maxLocal );
    testcase( nSize == pPage.maxLocal + 1 );
    if ( nSize > pPage.maxLocal )
    {
      nSize = (u32)minLocal;
    }
    nSize += 4;
  }
  nSize += (uint)_pIter;//nSize += (u32)(pIter - pCell);

  /* The minimum size of any cell is 4 bytes. */
  if ( nSize < 4 )
  {
    nSize = 4;
  }

  Debug.Assert( nSize == debuginfo.nSize );
  return (u16)nSize;
}

#if SQLITE_DEBUG
/* This variation on cellSizePtr() is used inside of assert() statements
** only. */
static u16 cellSize( MemPage pPage, int iCell )
{
  return cellSizePtr( pPage, findCell( pPage, iCell ) );
}
#else
static int cellSize(MemPage pPage, int iCell) { return -1; }
#endif

#if !SQLITE_OMIT_AUTOVACUUM
/*
** If the cell pCell, part of page pPage contains a pointer
** to an overflow page, insert an entry into the pointer-map
** for the overflow page.
*/
static void ptrmapPutOvflPtr( MemPage pPage, int pCell, ref int pRC )
{
  if ( pRC != 0 )
    return;
  CellInfo info = new CellInfo();
  Debug.Assert( pCell != 0 );
  btreeParseCellPtr( pPage, pCell, ref info );
  Debug.Assert( ( info.nData + ( pPage.intKey != 0 ? 0 : info.nKey ) ) == info.nPayload );
  if ( info.iOverflow != 0 )
  {
    Pgno ovfl = sqlite3Get4byte( pPage.aData, pCell, info.iOverflow );
    ptrmapPut( pPage.pBt, ovfl, PTRMAP_OVERFLOW1, pPage.pgno, ref pRC );
  }
}

static void ptrmapPutOvflPtr( MemPage pPage, u8[] pCell, ref int pRC )
{
  if ( pRC != 0 )
    return;
  CellInfo info = new CellInfo();
  Debug.Assert( pCell != null );
  btreeParseCellPtr( pPage, pCell, ref info );
  Debug.Assert( ( info.nData + ( pPage.intKey != 0 ? 0 : info.nKey ) ) == info.nPayload );
  if ( info.iOverflow != 0 )
  {
    Pgno ovfl = sqlite3Get4byte( pCell, info.iOverflow );
    ptrmapPut( pPage.pBt, ovfl, PTRMAP_OVERFLOW1, pPage.pgno, ref pRC );
  }
}
#endif


/*
** Defragment the page given.  All Cells are moved to the
** end of the page and all free space is collected into one
** big FreeBlk that occurs in between the header and cell
** pointer array and the cell content area.
*/
static int defragmentPage( MemPage pPage )
{
  int i;                     /* Loop counter */
  int pc;                    /* Address of a i-th cell */
  int addr;                  /* Offset of first byte after cell pointer array */
  int hdr;                   /* Offset to the page header */
  int size;                  /* Size of a cell */
  int usableSize;            /* Number of usable bytes on a page */
  int cellOffset;            /* Offset to the cell pointer array */
  int cbrk;                  /* Offset to the cell content area */
  int nCell;                 /* Number of cells on the page */
  byte[] data;               /* The page data */
  byte[] temp;               /* Temp area for cell content */
  int iCellFirst;            /* First allowable cell index */
  int iCellLast;             /* Last possible cell index */


  Debug.Assert( sqlite3PagerIswriteable( pPage.pDbPage ) );
  Debug.Assert( pPage.pBt != null );
  Debug.Assert( pPage.pBt.usableSize <= SQLITE_MAX_PAGE_SIZE );
  Debug.Assert( pPage.nOverflow == 0 );
  Debug.Assert( sqlite3_mutex_held( pPage.pBt.mutex ) );
  temp = sqlite3PagerTempSpace( pPage.pBt.pPager );
  data = pPage.aData;
  hdr = pPage.hdrOffset;
  cellOffset = pPage.cellOffset;
  nCell = pPage.nCell;
  Debug.Assert( nCell == get2byte( data, hdr + 3 ) );
  usableSize = (int)pPage.pBt.usableSize;
  cbrk = get2byte( data, hdr + 5 );
  Buffer.BlockCopy( data, cbrk, temp, cbrk, usableSize - cbrk );//memcpy( temp[cbrk], ref data[cbrk], usableSize - cbrk );
  cbrk = usableSize;
  iCellFirst = cellOffset + 2 * nCell;
  iCellLast = usableSize - 4;
  for ( i = 0; i < nCell; i++ )
  {
    int pAddr;     /* The i-th cell pointer */
    pAddr = cellOffset + i * 2; // &data[cellOffset + i * 2];
    pc = get2byte( data, pAddr );
    testcase( pc == iCellFirst );
    testcase( pc == iCellLast );
#if !(SQLITE_ENABLE_OVERSIZE_CELL_CHECK)
    /* These conditions have already been verified in btreeInitPage()
** if SQLITE_ENABLE_OVERSIZE_CELL_CHECK is defined
*/
    if ( pc < iCellFirst || pc > iCellLast )
    {
      return SQLITE_CORRUPT_BKPT();
    }
#endif
    Debug.Assert( pc >= iCellFirst && pc <= iCellLast );
    size = cellSizePtr( pPage, temp, pc );
    cbrk -= size;
#if (SQLITE_ENABLE_OVERSIZE_CELL_CHECK)
    if ( cbrk < iCellFirst || pc + size > usableSize )
    {
      return SQLITE_CORRUPT_BKPT();
    }
#else
    if ( cbrk < iCellFirst || pc + size > usableSize )
    {
      return SQLITE_CORRUPT_BKPT();
    }
#endif
    Debug.Assert( cbrk + size <= usableSize && cbrk >= iCellFirst );
    testcase( cbrk + size == usableSize );
    testcase( pc + size == usableSize );
    Buffer.BlockCopy( temp, pc, data, cbrk, size );//memcpy(data[cbrk], ref temp[pc], size);
    put2byte( data, pAddr, cbrk );
  }
  Debug.Assert( cbrk >= iCellFirst );
  put2byte( data, hdr + 5, cbrk );
  data[hdr + 1] = 0;
  data[hdr + 2] = 0;
  data[hdr + 7] = 0;
  addr = cellOffset + 2 * nCell;
  Array.Clear( data, addr, cbrk - addr );  //memset(data[iCellFirst], 0, cbrk-iCellFirst);
  Debug.Assert( sqlite3PagerIswriteable( pPage.pDbPage ) );
  if ( cbrk - iCellFirst != pPage.nFree )
  {
    return SQLITE_CORRUPT_BKPT();
  }
  return SQLITE_OK;
}

/*
** Allocate nByte bytes of space from within the B-Tree page passed
** as the first argument. Write into pIdx the index into pPage.aData[]
** of the first byte of allocated space. Return either SQLITE_OK or
** an error code (usually SQLITE_CORRUPT).
**
** The caller guarantees that there is sufficient space to make the
** allocation.  This routine might need to defragment in order to bring
** all the space together, however.  This routine will avoid using
** the first two bytes past the cell pointer area since presumably this
** allocation is being made in order to insert a new cell, so we will
** also end up needing a new cell pointer.
*/
static int allocateSpace( MemPage pPage, int nByte, ref int pIdx )
{
  int hdr = pPage.hdrOffset;  /* Local cache of pPage.hdrOffset */
  u8[] data = pPage.aData;    /* Local cache of pPage.aData */
  int nFrag;                  /* Number of fragmented bytes on pPage */
  int top;                    /* First byte of cell content area */
  int gap;                    /* First byte of gap between cell pointers and cell content */
  int rc;                     /* Integer return code */
  u32 usableSize;             /* Usable size of the page */

  Debug.Assert( sqlite3PagerIswriteable( pPage.pDbPage ) );
  Debug.Assert( pPage.pBt != null );
  Debug.Assert( sqlite3_mutex_held( pPage.pBt.mutex ) );
  Debug.Assert( nByte >= 0 );  /* Minimum cell size is 4 */
  Debug.Assert( pPage.nFree >= nByte );
  Debug.Assert( pPage.nOverflow == 0 );
  usableSize = pPage.pBt.usableSize;
  Debug.Assert( nByte < usableSize - 8 );

  nFrag = data[hdr + 7];
  Debug.Assert( pPage.cellOffset == hdr + 12 - 4 * pPage.leaf );
  gap = pPage.cellOffset + 2 * pPage.nCell;
  top = get2byteNotZero( data, hdr + 5 );
  if ( gap > top )
    return SQLITE_CORRUPT_BKPT();
  testcase( gap + 2 == top );
  testcase( gap + 1 == top );
  testcase( gap == top );

  if ( nFrag >= 60 )
  {
    /* Always defragment highly fragmented pages */
    rc = defragmentPage( pPage );
    if ( rc != 0 )
      return rc;
    top = get2byteNotZero( data, hdr + 5 );
  }
  else if ( gap + 2 <= top )
  {
    /* Search the freelist looking for a free slot big enough to satisfy
    ** the request. The allocation is made from the first free slot in
    ** the list that is large enough to accomadate it.
    */
    int pc, addr;
    for ( addr = hdr + 1; ( pc = get2byte( data, addr ) ) > 0; addr = pc )
    {
      int size;     /* Size of free slot */
      if ( pc > usableSize - 4 || pc < addr + 4 )
      {
        return SQLITE_CORRUPT_BKPT();
      }
      size = get2byte( data, pc + 2 );
      if ( size >= nByte )
      {
        int x = size - nByte;
        testcase( x == 4 );
        testcase( x == 3 );
        if ( x < 4 )
        {
          /* Remove the slot from the free-list. Update the number of
          ** fragmented bytes within the page. */
          data[addr + 0] = data[pc + 0];
          data[addr + 1] = data[pc + 1]; //memcpy( data[addr], ref data[pc], 2 );
          data[hdr + 7] = (u8)( nFrag + x );
        }
        else if ( size + pc > usableSize )
        {
          return SQLITE_CORRUPT_BKPT();
        }
        else
        {
          /* The slot remains on the free-list. Reduce its size to account
          ** for the portion used by the new allocation. */
          put2byte( data, pc + 2, x );
        }
        pIdx = pc + x;
        return SQLITE_OK;
      }
    }
  }

  /* Check to make sure there is enough space in the gap to satisfy
  ** the allocation.  If not, defragment.
  */
  testcase( gap + 2 + nByte == top );
  if ( gap + 2 + nByte > top )
  {
    rc = defragmentPage( pPage );
    if ( rc != 0 )
      return rc;
    top = get2byteNotZero( data, hdr + 5 );
    Debug.Assert( gap + nByte <= top );
  }


  /* Allocate memory from the gap in between the cell pointer array
  ** and the cell content area.  The btreeInitPage() call has already
  ** validated the freelist.  Given that the freelist is valid, there
  ** is no way that the allocation can extend off the end of the page.
  ** The Debug.Assert() below verifies the previous sentence.
  */
  top -= nByte;
  put2byte( data, hdr + 5, top );
  Debug.Assert( top + nByte <= (int)pPage.pBt.usableSize );
  pIdx = top;
  return SQLITE_OK;
}

/*
** Return a section of the pPage.aData to the freelist.
** The first byte of the new free block is pPage.aDisk[start]
** and the size of the block is "size" bytes.
**
** Most of the effort here is involved in coalesing adjacent
** free blocks into a single big free block.
*/
static int freeSpace( MemPage pPage, u32 start, int size )
{
  return freeSpace( pPage, (int)start, size );
}
static int freeSpace( MemPage pPage, int start, int size )
{
  int addr, pbegin, hdr;
  int iLast;                        /* Largest possible freeblock offset */
  byte[] data = pPage.aData;

  Debug.Assert( pPage.pBt != null );
  Debug.Assert( sqlite3PagerIswriteable( pPage.pDbPage ) );
  Debug.Assert( start >= pPage.hdrOffset + 6 + pPage.childPtrSize );
  Debug.Assert( ( start + size ) <= (int)pPage.pBt.usableSize );
  Debug.Assert( sqlite3_mutex_held( pPage.pBt.mutex ) );
  Debug.Assert( size >= 0 );   /* Minimum cell size is 4 */

  if ( pPage.pBt.secureDelete )
  {
    /* Overwrite deleted information with zeros when the secure_delete
    ** option is enabled */
    Array.Clear( data, start, size );// memset(&data[start], 0, size);
  }

  /* Add the space back into the linked list of freeblocks.  Note that
  ** even though the freeblock list was checked by btreeInitPage(),
  ** btreeInitPage() did not detect overlapping cells or
  ** freeblocks that overlapped cells.   Nor does it detect when the
  ** cell content area exceeds the value in the page header.  If these
  ** situations arise, then subsequent insert operations might corrupt
  ** the freelist.  So we do need to check for corruption while scanning
  ** the freelist.
  */
  hdr = pPage.hdrOffset;
  addr = hdr + 1;
  iLast = (int)pPage.pBt.usableSize - 4;
  Debug.Assert( start <= iLast );
  while ( ( pbegin = get2byte( data, addr ) ) < start && pbegin > 0 )
  {
    if ( pbegin < addr + 4 )
    {
      return SQLITE_CORRUPT_BKPT();
    }
    addr = pbegin;
  }
  if ( pbegin > iLast )
  {
    return SQLITE_CORRUPT_BKPT();
  }
  Debug.Assert( pbegin > addr || pbegin == 0 );
  put2byte( data, addr, start );
  put2byte( data, start, pbegin );
  put2byte( data, start + 2, size );
  pPage.nFree = (u16)( pPage.nFree + size );

  /* Coalesce adjacent free blocks */
  addr = hdr + 1;
  while ( ( pbegin = get2byte( data, addr ) ) > 0 )
  {
    int pnext, psize, x;
    Debug.Assert( pbegin > addr );
    Debug.Assert( pbegin <= (int)pPage.pBt.usableSize - 4 );
    pnext = get2byte( data, pbegin );
    psize = get2byte( data, pbegin + 2 );
    if ( pbegin + psize + 3 >= pnext && pnext > 0 )
    {
      int frag = pnext - ( pbegin + psize );
      if ( ( frag < 0 ) || ( frag > (int)data[hdr + 7] ) )
      {
        return SQLITE_CORRUPT_BKPT();
      }
      data[hdr + 7] -= (u8)frag;
      x = get2byte( data, pnext );
      put2byte( data, pbegin, x );
      x = pnext + get2byte( data, pnext + 2 ) - pbegin;
      put2byte( data, pbegin + 2, x );
    }
    else
    {
      addr = pbegin;
    }
  }

  /* If the cell content area begins with a freeblock, remove it. */
  if ( data[hdr + 1] == data[hdr + 5] && data[hdr + 2] == data[hdr + 6] )
  {
    int top;
    pbegin = get2byte( data, hdr + 1 );
    put2byte( data, hdr + 1, get2byte( data, pbegin ) ); //memcpy( data[hdr + 1], ref data[pbegin], 2 );
    top = get2byte( data, hdr + 5 ) + get2byte( data, pbegin + 2 );
    put2byte( data, hdr + 5, top );
  }
  Debug.Assert( sqlite3PagerIswriteable( pPage.pDbPage ) );
  return SQLITE_OK;
}

/*
** Decode the flags byte (the first byte of the header) for a page
** and initialize fields of the MemPage structure accordingly.
**
** Only the following combinations are supported.  Anything different
** indicates a corrupt database files:
**
**         PTF_ZERODATA
**         PTF_ZERODATA | PTF_LEAF
**         PTF_LEAFDATA | PTF_INTKEY
**         PTF_LEAFDATA | PTF_INTKEY | PTF_LEAF
*/
static int decodeFlags( MemPage pPage, int flagByte )
{
  BtShared pBt;     /* A copy of pPage.pBt */

  Debug.Assert( pPage.hdrOffset == ( pPage.pgno == 1 ? 100 : 0 ) );
  Debug.Assert( sqlite3_mutex_held( pPage.pBt.mutex ) );
  pPage.leaf = (u8)( flagByte >> 3 );
  Debug.Assert( PTF_LEAF == 1 << 3 );
  flagByte &= ~PTF_LEAF;
  pPage.childPtrSize = (u8)( 4 - 4 * pPage.leaf );
  pBt = pPage.pBt;
  if ( flagByte == ( PTF_LEAFDATA | PTF_INTKEY ) )
  {
    pPage.intKey = 1;
    pPage.hasData = pPage.leaf;
    pPage.maxLocal = pBt.maxLeaf;
    pPage.minLocal = pBt.minLeaf;
  }
  else if ( flagByte == PTF_ZERODATA )
  {
    pPage.intKey = 0;
    pPage.hasData = 0;
    pPage.maxLocal = pBt.maxLocal;
    pPage.minLocal = pBt.minLocal;
  }
  else
  {
    return SQLITE_CORRUPT_BKPT();
  }
  return SQLITE_OK;
}

/*
** Initialize the auxiliary information for a disk block.
**
** Return SQLITE_OK on success.  If we see that the page does
** not contain a well-formed database page, then return
** SQLITE_CORRUPT.  Note that a return of SQLITE_OK does not
** guarantee that the page is well-formed.  It only shows that
** we failed to detect any corruption.
*/
static int btreeInitPage( MemPage pPage )
{

  Debug.Assert( pPage.pBt != null );
  Debug.Assert( sqlite3_mutex_held( pPage.pBt.mutex ) );
  Debug.Assert( pPage.pgno == sqlite3PagerPagenumber( pPage.pDbPage ) );
  Debug.Assert( pPage == sqlite3PagerGetExtra( pPage.pDbPage ) );
  Debug.Assert( pPage.aData == sqlite3PagerGetData( pPage.pDbPage ) );

  if ( 0 == pPage.isInit )
  {
    u16 pc;            /* Address of a freeblock within pPage.aData[] */
    u8 hdr;            /* Offset to beginning of page header */
    u8[] data;         /* Equal to pPage.aData */
    BtShared pBt;      /* The main btree structure */
    int usableSize;    /* Amount of usable space on each page */
    u16 cellOffset;    /* Offset from start of page to first cell pointer */
    int nFree;         /* Number of unused bytes on the page */
    int top;           /* First byte of the cell content area */
    int iCellFirst;    /* First allowable cell or freeblock offset */
    int iCellLast;     /* Last possible cell or freeblock offset */

    pBt = pPage.pBt;

    hdr = pPage.hdrOffset;
    data = pPage.aData;
    if ( decodeFlags( pPage, data[hdr] ) != 0 )
      return SQLITE_CORRUPT_BKPT();
    Debug.Assert( pBt.pageSize >= 512 && pBt.pageSize <= 65536 );
    pPage.maskPage = (u16)( pBt.pageSize - 1 );
    pPage.nOverflow = 0;
    usableSize = (int)pBt.usableSize;
    pPage.cellOffset = ( cellOffset = (u16)( hdr + 12 - 4 * pPage.leaf ) );
    top = get2byteNotZero( data, hdr + 5 );
    pPage.nCell = (u16)( get2byte( data, hdr + 3 ) );
    if ( pPage.nCell > MX_CELL( pBt ) )
    {
      /* To many cells for a single page.  The page must be corrupt */
      return SQLITE_CORRUPT_BKPT();
    }
    testcase( pPage.nCell == MX_CELL( pBt ) );

    /* A malformed database page might cause us to read past the end
    ** of page when parsing a cell.
    **
    ** The following block of code checks early to see if a cell extends
    ** past the end of a page boundary and causes SQLITE_CORRUPT to be
    ** returned if it does.
    */
    iCellFirst = cellOffset + 2 * pPage.nCell;
    iCellLast = usableSize - 4;
#if (SQLITE_ENABLE_OVERSIZE_CELL_CHECK)
    {
      int i;            /* Index into the cell pointer array */
      int sz;           /* Size of a cell */

      if ( 0 == pPage.leaf )
        iCellLast--;
      for ( i = 0; i < pPage.nCell; i++ )
      {
        pc = (u16)get2byte( data, cellOffset + i * 2 );
        testcase( pc == iCellFirst );
        testcase( pc == iCellLast );
        if ( pc < iCellFirst || pc > iCellLast )
        {
          return SQLITE_CORRUPT_BKPT();
        }
        sz = cellSizePtr( pPage, data, pc );
        testcase( pc + sz == usableSize );
        if ( pc + sz > usableSize )
        {
          return SQLITE_CORRUPT_BKPT();
        }
      }
      if ( 0 == pPage.leaf )
        iCellLast++;
    }
#endif

    /* Compute the total free space on the page */
    pc = (u16)get2byte( data, hdr + 1 );
    nFree = (u16)( data[hdr + 7] + top );
    while ( pc > 0 )
    {
      u16 next, size;
      if ( pc < iCellFirst || pc > iCellLast )
      {
        /* Start of free block is off the page */
        return SQLITE_CORRUPT_BKPT();
      }
      next = (u16)get2byte( data, pc );
      size = (u16)get2byte( data, pc + 2 );
      if ( ( next > 0 && next <= pc + size + 3 ) || pc + size > usableSize )
      {
        /* Free blocks must be in ascending order. And the last byte of
        ** the free-block must lie on the database page.  */
        return SQLITE_CORRUPT_BKPT();
      }
      nFree = (u16)( nFree + size );
      pc = next;
    }

    /* At this point, nFree contains the sum of the offset to the start
    ** of the cell-content area plus the number of free bytes within
    ** the cell-content area. If this is greater than the usable-size
    ** of the page, then the page must be corrupted. This check also
    ** serves to verify that the offset to the start of the cell-content
    ** area, according to the page header, lies within the page.
    */
    if ( nFree > usableSize )
    {
      return SQLITE_CORRUPT_BKPT();
    }
    pPage.nFree = (u16)( nFree - iCellFirst );
    pPage.isInit = 1;
  }
  return SQLITE_OK;
}

/*
** Set up a raw page so that it looks like a database page holding
** no entries.
*/
static void zeroPage( MemPage pPage, int flags )
{
  byte[] data = pPage.aData;
  BtShared pBt = pPage.pBt;
  u8 hdr = pPage.hdrOffset;
  u16 first;

  Debug.Assert( sqlite3PagerPagenumber( pPage.pDbPage ) == pPage.pgno );
  Debug.Assert( sqlite3PagerGetExtra( pPage.pDbPage ) == pPage );
  Debug.Assert( sqlite3PagerGetData( pPage.pDbPage ) == data );
  Debug.Assert( sqlite3PagerIswriteable( pPage.pDbPage ) );
  Debug.Assert( sqlite3_mutex_held( pBt.mutex ) );
  if ( pBt.secureDelete )
  {
    Array.Clear( data, hdr, (int)( pBt.usableSize - hdr ) );//memset(&data[hdr], 0, pBt->usableSize - hdr);
  }

  data[hdr] = (u8)flags;
  first = (u16)( hdr + 8 + 4 * ( ( flags & PTF_LEAF ) == 0 ? 1 : 0 ) );
  Array.Clear( data, hdr + 1, 4 );//memset(data[hdr+1], 0, 4);
  data[hdr + 7] = 0;
  put2byte( data, hdr + 5, pBt.usableSize );
  pPage.nFree = (u16)( pBt.usableSize - first );
  decodeFlags( pPage, flags );
  pPage.hdrOffset = hdr;
  pPage.cellOffset = first;
  pPage.nOverflow = 0;
  Debug.Assert( pBt.pageSize >= 512 && pBt.pageSize <= 65536 );
  pPage.maskPage = (u16)( pBt.pageSize - 1 );
  pPage.nCell = 0;
  pPage.isInit = 1;
}


/*
** Convert a DbPage obtained from the pager into a MemPage used by
** the btree layer.
*/
static MemPage btreePageFromDbPage( DbPage pDbPage, Pgno pgno, BtShared pBt )
{
  MemPage pPage = (MemPage)sqlite3PagerGetExtra( pDbPage );
  pPage.aData = sqlite3PagerGetData( pDbPage );
  pPage.pDbPage = pDbPage;
  pPage.pBt = pBt;
  pPage.pgno = pgno;
  pPage.hdrOffset = (u8)( pPage.pgno == 1 ? 100 : 0 );
  return pPage;
}

/*
** Get a page from the pager.  Initialize the MemPage.pBt and
** MemPage.aData elements if needed.
**
** If the noContent flag is set, it means that we do not care about
** the content of the page at this time.  So do not go to the disk
** to fetch the content.  Just fill in the content with zeros for now.
** If in the future we call sqlite3PagerWrite() on this page, that
** means we have started to be concerned about content and the disk
** read should occur at that point.
*/
static int btreeGetPage(
BtShared pBt,        /* The btree */
Pgno pgno,           /* Number of the page to fetch */
ref MemPage ppPage,  /* Return the page in this parameter */
int noContent        /* Do not load page content if true */
)
{
  int rc;
  DbPage pDbPage = null;

  Debug.Assert( sqlite3_mutex_held( pBt.mutex ) );
  rc = sqlite3PagerAcquire( pBt.pPager, pgno, ref pDbPage, (u8)noContent );
  if ( rc != 0 )
    return rc;
  ppPage = btreePageFromDbPage( pDbPage, pgno, pBt );
  return SQLITE_OK;
}

/*
** Retrieve a page from the pager cache. If the requested page is not
** already in the pager cache return NULL. Initialize the MemPage.pBt and
** MemPage.aData elements if needed.
*/
static MemPage btreePageLookup( BtShared pBt, Pgno pgno )
{
  DbPage pDbPage;
  Debug.Assert( sqlite3_mutex_held( pBt.mutex ) );
  pDbPage = sqlite3PagerLookup( pBt.pPager, pgno );
  if ( pDbPage )
  {
    return btreePageFromDbPage( pDbPage, pgno, pBt );
  }
  return null;
}

/*
** Return the size of the database file in pages. If there is any kind of
** error, return ((unsigned int)-1).
*/
static Pgno btreePagecount( BtShared pBt )
{
  return pBt.nPage;
}
static Pgno sqlite3BtreeLastPage( Btree p )
{
  Debug.Assert( sqlite3BtreeHoldsMutex( p ) );
  Debug.Assert( ( ( p.pBt.nPage ) & 0x8000000 ) == 0 );
  return (Pgno)btreePagecount( p.pBt );
}



/*
** Get a page from the pager and initialize it.  This routine is just a
** convenience wrapper around separate calls to btreeGetPage() and
** btreeInitPage().
**
** If an error occurs, then the value ppPage is set to is undefined. It
** may remain unchanged, or it may be set to an invalid value.
*/
static int getAndInitPage(
BtShared pBt,          /* The database file */
Pgno pgno,             /* Number of the page to get */
ref MemPage ppPage     /* Write the page pointer here */
)
{
  int rc;
  Debug.Assert( sqlite3_mutex_held( pBt.mutex ) );

  if ( pgno > btreePagecount( pBt ) )
  {
    rc = SQLITE_CORRUPT_BKPT();
  }
  else
  {
    rc = btreeGetPage( pBt, pgno, ref ppPage, 0 );
    if ( rc == SQLITE_OK )
    {
      rc = btreeInitPage( ppPage );
      if ( rc != SQLITE_OK )
      {
        releasePage( ppPage );
      }
    }
  }

  testcase( pgno == 0 );
  Debug.Assert( pgno != 0 || rc == SQLITE_CORRUPT );

  return rc;
}

/*
** Release a MemPage.  This should be called once for each prior
** call to btreeGetPage.
*/
static void releasePage( MemPage pPage )
{
  if ( pPage != null )
  {
    Debug.Assert( pPage.aData != null );
    Debug.Assert( pPage.pBt != null );
    //TODO -- find out why corrupt9 & diskfull fail on this tests 
    //Debug.Assert( sqlite3PagerGetExtra( pPage.pDbPage ) == pPage );
    //Debug.Assert( sqlite3PagerGetData( pPage.pDbPage ) == pPage.aData );
    Debug.Assert( sqlite3_mutex_held( pPage.pBt.mutex ) );
    sqlite3PagerUnref( pPage.pDbPage );
  }
}

/*
** During a rollback, when the pager reloads information into the cache
** so that the cache is restored to its original state at the start of
** the transaction, for each page restored this routine is called.
**
** This routine needs to reset the extra data section at the end of the
** page to agree with the restored data.
*/
static void pageReinit( DbPage pData )
{
  MemPage pPage;
  pPage = sqlite3PagerGetExtra( pData );
  Debug.Assert( sqlite3PagerPageRefcount( pData ) > 0 );
  if ( pPage.isInit != 0 )
  {
    Debug.Assert( sqlite3_mutex_held( pPage.pBt.mutex ) );
    pPage.isInit = 0;
    if ( sqlite3PagerPageRefcount( pData ) > 1 )
    {
      /* pPage might not be a btree page;  it might be an overflow page
      ** or ptrmap page or a free page.  In those cases, the following
      ** call to btreeInitPage() will likely return SQLITE_CORRUPT.
      ** But no harm is done by this.  And it is very important that
      ** btreeInitPage() be called on every btree page so we make
      ** the call for every page that comes in for re-initing. */
      btreeInitPage( pPage );
    }
  }
}

/*
** Invoke the busy handler for a btree.
*/
static int btreeInvokeBusyHandler( object pArg )
{
  BtShared pBt = (BtShared)pArg;
  Debug.Assert( pBt.db != null );
  Debug.Assert( sqlite3_mutex_held( pBt.db.mutex ) );
  return sqlite3InvokeBusyHandler( pBt.db.busyHandler );
}

/*
** Open a database file.
** 
** zFilename is the name of the database file.  If zFilename is NULL
** then an ephemeral database is created.  The ephemeral database might
** be exclusively in memory, or it might use a disk-based memory cache.
** Either way, the ephemeral database will be automatically deleted 
** when sqlite3BtreeClose() is called.
**
** If zFilename is ":memory:" then an in-memory database is created
** that is automatically destroyed when it is closed.
**
** The "flags" parameter is a bitmask that might contain bits
** BTREE_OMIT_JOURNAL and/or BTREE_NO_READLOCK.  The BTREE_NO_READLOCK
** bit is also set if the SQLITE_NoReadlock flags is set in db->flags.
** These flags are passed through into sqlite3PagerOpen() and must
** be the same values as PAGER_OMIT_JOURNAL and PAGER_NO_READLOCK.
**
** If the database is already opened in the same database connection
** and we are in shared cache mode, then the open will fail with an
** SQLITE_CONSTRAINT error.  We cannot allow two or more BtShared
** objects in the same database connection since doing so will lead
** to problems with locking.
*/
static int sqlite3BtreeOpen(
sqlite3_vfs pVfs,       /* VFS to use for this b-tree */
string zFilename,       /* Name of the file containing the BTree database */
sqlite3 db,             /* Associated database handle */
ref Btree ppBtree,      /* Pointer to new Btree object written here */
int flags,              /* Options */
int vfsFlags            /* Flags passed through to sqlite3_vfs.xOpen() */
)
{
  BtShared pBt = null;          /* Shared part of btree structure */
  Btree p;                      /* Handle to return */
  sqlite3_mutex mutexOpen = null;  /* Prevents a race condition. Ticket #3537 */
  int rc = SQLITE_OK;            /* Result code from this function */
  u8 nReserve;                   /* Byte of unused space on each page */
  byte[] zDbHeader = new byte[100]; /* Database header content */

  /* True if opening an ephemeral, temporary database */
  bool isTempDb = String.IsNullOrEmpty( zFilename );//zFilename==0 || zFilename[0]==0;

  /* Set the variable isMemdb to true for an in-memory database, or 
  ** false for a file-based database.
  */
#if SQLITE_OMIT_MEMORYDB
bool isMemdb = false;
#else
  bool isMemdb = ( zFilename == ":memory:" )
  || ( isTempDb && sqlite3TempInMemory( db ) );

#endif

  Debug.Assert( db != null );
  Debug.Assert( pVfs != null );
  Debug.Assert( sqlite3_mutex_held( db.mutex ) );
  Debug.Assert( ( flags & 0xff ) == flags );   /* flags fit in 8 bits */

  /* Only a BTREE_SINGLE database can be BTREE_UNORDERED */
  Debug.Assert( ( flags & BTREE_UNORDERED ) == 0 || ( flags & BTREE_SINGLE ) != 0 );

  /* A BTREE_SINGLE database is always a temporary and/or ephemeral */
  Debug.Assert( ( flags & BTREE_SINGLE ) == 0 || isTempDb );

  if ( ( db.flags & SQLITE_NoReadlock ) != 0 )
  {
    flags |= BTREE_NO_READLOCK;
  }
  if ( isMemdb )
  {
    flags |= BTREE_MEMORY;
  }
  if ( ( vfsFlags & SQLITE_OPEN_MAIN_DB ) != 0 && ( isMemdb || isTempDb ) )
  {
    vfsFlags = ( vfsFlags & ~SQLITE_OPEN_MAIN_DB ) | SQLITE_OPEN_TEMP_DB;
  }

  p = new Btree();//sqlite3MallocZero(sizeof(Btree));
  //if( !p ){
  //  return SQLITE_NOMEM;
  //}
  p.inTrans = TRANS_NONE;
  p.db = db;
#if !SQLITE_OMIT_SHARED_CACHE
p.lock.pBtree = p;
p.lock.iTable = 1;
#endif

#if !(SQLITE_OMIT_SHARED_CACHE) && !(SQLITE_OMIT_DISKIO)
/*
** If this Btree is a candidate for shared cache, try to find an
** existing BtShared object that we can share with
*/
if( !isMemdb && !isTempDb ){
if( vfsFlags & SQLITE_OPEN_SHAREDCACHE ){
int nFullPathname = pVfs.mxPathname+1;
string zFullPathname = sqlite3Malloc(nFullPathname);
sqlite3_mutex *mutexShared;
p.sharable = 1;
if( !zFullPathname ){
p = null;//sqlite3_free(ref p);
return SQLITE_NOMEM;
}
sqlite3OsFullPathname(pVfs, zFilename, nFullPathname, zFullPathname);
mutexOpen = sqlite3MutexAlloc(SQLITE_MUTEX_STATIC_OPEN);
sqlite3_mutex_enter(mutexOpen);
mutexShared = sqlite3MutexAlloc(SQLITE_MUTEX_STATIC_MASTER);
sqlite3_mutex_enter(mutexShared);
for(pBt=GLOBAL(BtShared*,sqlite3SharedCacheList); pBt; pBt=pBt.pNext){
Debug.Assert( pBt.nRef>0 );
if( 0==strcmp(zFullPathname, sqlite3PagerFilename(pBt.pPager))
&& sqlite3PagerVfs(pBt.pPager)==pVfs ){
int iDb;
for(iDb=db.nDb-1; iDb>=0; iDb--){
Btree pExisting = db.aDb[iDb].pBt;
if( pExisting && pExisting.pBt==pBt ){
sqlite3_mutex_leave(mutexShared);
sqlite3_mutex_leave(mutexOpen);
zFullPathname = null;//sqlite3_free(ref zFullPathname);
p=null;//sqlite3_free(ref p);
return SQLITE_CONSTRAINT;
}
}
p.pBt = pBt;
pBt.nRef++;
break;
}
}
sqlite3_mutex_leave(mutexShared);
zFullPathname=null;//sqlite3_free(ref zFullPathname);
}
#if SQLITE_DEBUG
else{
/* In debug mode, we mark all persistent databases as sharable
** even when they are not.  This exercises the locking code and
** gives more opportunity for asserts(sqlite3_mutex_held())
** statements to find locking problems.
*/
p.sharable = 1;
}
#endif
}
#endif
  if ( pBt == null )
  {
    /*
    ** The following asserts make sure that structures used by the btree are
    ** the right size.  This is to guard against size changes that result
    ** when compiling on a different architecture.
    */
    Debug.Assert( sizeof( i64 ) == 8 || sizeof( i64 ) == 4 );
    Debug.Assert( sizeof( u64 ) == 8 || sizeof( u64 ) == 4 );
    Debug.Assert( sizeof( u32 ) == 4 );
    Debug.Assert( sizeof( u16 ) == 2 );
    Debug.Assert( sizeof( Pgno ) == 4 );

    pBt = new BtShared();//sqlite3MallocZero( sizeof(pBt) );
    //if( pBt==null ){
    //  rc = SQLITE_NOMEM;
    //  goto btree_open_out;
    //}
    rc = sqlite3PagerOpen( pVfs, out pBt.pPager, zFilename,
    EXTRA_SIZE, flags, vfsFlags, pageReinit );
    if ( rc == SQLITE_OK )
    {
      rc = sqlite3PagerReadFileheader( pBt.pPager, zDbHeader.Length, zDbHeader );
    }
    if ( rc != SQLITE_OK )
    {
      goto btree_open_out;
    }
    pBt.openFlags = (u8)flags;
    pBt.db = db;
    sqlite3PagerSetBusyhandler( pBt.pPager, btreeInvokeBusyHandler, pBt );
    p.pBt = pBt;

    pBt.pCursor = null;
    pBt.pPage1 = null;
    pBt.readOnly = sqlite3PagerIsreadonly( pBt.pPager );
#if SQLITE_SECURE_DELETE
pBt.secureDelete = true;
#endif
    pBt.pageSize = (u32)( ( zDbHeader[16] << 8 ) | ( zDbHeader[17] << 16 ) );
    if ( pBt.pageSize < 512 || pBt.pageSize > SQLITE_MAX_PAGE_SIZE
    || ( ( pBt.pageSize - 1 ) & pBt.pageSize ) != 0 )
    {
      pBt.pageSize = 0;
#if !SQLITE_OMIT_AUTOVACUUM
      /* If the magic name ":memory:" will create an in-memory database, then
** leave the autoVacuum mode at 0 (do not auto-vacuum), even if
** SQLITE_DEFAULT_AUTOVACUUM is true. On the other hand, if
** SQLITE_OMIT_MEMORYDB has been defined, then ":memory:" is just a
** regular file-name. In this case the auto-vacuum applies as per normal.
*/
      if ( zFilename != "" && !isMemdb )
      {
        pBt.autoVacuum = ( SQLITE_DEFAULT_AUTOVACUUM != 0 );
        pBt.incrVacuum = ( SQLITE_DEFAULT_AUTOVACUUM == 2 );
      }
#endif
      nReserve = 0;
    }
    else
    {
      nReserve = zDbHeader[20];
      pBt.pageSizeFixed = true;
#if !SQLITE_OMIT_AUTOVACUUM
      pBt.autoVacuum = sqlite3Get4byte( zDbHeader, 36 + 4 * 4 ) != 0;
      pBt.incrVacuum = sqlite3Get4byte( zDbHeader, 36 + 7 * 4 ) != 0;
#endif
    }
    rc = sqlite3PagerSetPagesize( pBt.pPager, ref pBt.pageSize, nReserve );
    if ( rc != 0 )
      goto btree_open_out;
    pBt.usableSize = (u16)( pBt.pageSize - nReserve );
    Debug.Assert( ( pBt.pageSize & 7 ) == 0 );  /* 8-byte alignment of pageSize */

#if !(SQLITE_OMIT_SHARED_CACHE) && !(SQLITE_OMIT_DISKIO)
/* Add the new BtShared object to the linked list sharable BtShareds.
*/
if( p.sharable ){
sqlite3_mutex *mutexShared;
pBt.nRef = 1;
mutexShared = sqlite3MutexAlloc(SQLITE_MUTEX_STATIC_MASTER);
if( SQLITE_THREADSAFE && sqlite3GlobalConfig.bCoreMutex ){
pBt.mutex = sqlite3MutexAlloc(SQLITE_MUTEX_FAST);
if( pBt.mutex==null ){
rc = SQLITE_NOMEM;
db.mallocFailed = 0;
goto btree_open_out;
}
}
sqlite3_mutex_enter(mutexShared);
pBt.pNext = GLOBAL(BtShared*,sqlite3SharedCacheList);
GLOBAL(BtShared*,sqlite3SharedCacheList) = pBt;
sqlite3_mutex_leave(mutexShared);
}
#endif
  }

#if !(SQLITE_OMIT_SHARED_CACHE) && !(SQLITE_OMIT_DISKIO)
/* If the new Btree uses a sharable pBtShared, then link the new
** Btree into the list of all sharable Btrees for the same connection.
** The list is kept in ascending order by pBt address.
*/
if( p.sharable ){
int i;
Btree pSib;
for(i=0; i<db.nDb; i++){
if( (pSib = db.aDb[i].pBt)!=null && pSib.sharable ){
while( pSib.pPrev ){ pSib = pSib.pPrev; }
if( p.pBt<pSib.pBt ){
p.pNext = pSib;
p.pPrev = 0;
pSib.pPrev = p;
}else{
while( pSib.pNext && pSib.pNext.pBt<p.pBt ){
pSib = pSib.pNext;
}
p.pNext = pSib.pNext;
p.pPrev = pSib;
if( p.pNext ){
p.pNext.pPrev = p;
}
pSib.pNext = p;
}
break;
}
}
}
#endif
  ppBtree = p;

btree_open_out:
  if ( rc != SQLITE_OK )
  {
    if ( pBt != null && pBt.pPager != null )
    {
      sqlite3PagerClose( pBt.pPager );
    }
    pBt = null; //    sqlite3_free(ref pBt);
    p = null; //    sqlite3_free(ref p);
    ppBtree = null;
  }
  else
  {
    /* If the B-Tree was successfully opened, set the pager-cache size to the
    ** default value. Except, when opening on an existing shared pager-cache,
    ** do not change the pager-cache size.
    */
    if ( sqlite3BtreeSchema( p, 0, null ) == null )
    {
      sqlite3PagerSetCachesize( p.pBt.pPager, SQLITE_DEFAULT_CACHE_SIZE );
    }

  }
  if ( mutexOpen != null )
  {
    Debug.Assert( sqlite3_mutex_held( mutexOpen ) );
    sqlite3_mutex_leave( mutexOpen );
  }
  return rc;
}

/*
** Decrement the BtShared.nRef counter.  When it reaches zero,
** remove the BtShared structure from the sharing list.  Return
** true if the BtShared.nRef counter reaches zero and return
** false if it is still positive.
*/
static bool removeFromSharingList( BtShared pBt )
{
#if !SQLITE_OMIT_SHARED_CACHE
sqlite3_mutex pMaster;
BtShared pList;
bool removed = false;

Debug.Assert( sqlite3_mutex_notheld(pBt.mutex) );
pMaster = sqlite3MutexAlloc(SQLITE_MUTEX_STATIC_MASTER);
sqlite3_mutex_enter(pMaster);
pBt.nRef--;
if( pBt.nRef<=0 ){
if( GLOBAL(BtShared*,sqlite3SharedCacheList)==pBt ){
GLOBAL(BtShared*,sqlite3SharedCacheList) = pBt.pNext;
}else{
pList = GLOBAL(BtShared*,sqlite3SharedCacheList);
while( ALWAYS(pList) && pList.pNext!=pBt ){
pList=pList.pNext;
}
if( ALWAYS(pList) ){
pList.pNext = pBt.pNext;
}
}
if( SQLITE_THREADSAFE ){
sqlite3_mutex_free(pBt.mutex);
}
removed = true;
}
sqlite3_mutex_leave(pMaster);
return removed;
#else
  return true;
#endif
}

/*
** Make sure pBt.pTmpSpace points to an allocation of
** MX_CELL_SIZE(pBt) bytes.
*/
static void allocateTempSpace( BtShared pBt )
{
  if ( null == pBt.pTmpSpace )
  {
    pBt.pTmpSpace = sqlite3Malloc( pBt.pageSize );
  }
}

/*
** Free the pBt.pTmpSpace allocation
*/
static void freeTempSpace( BtShared pBt )
{
  sqlite3PageFree( ref pBt.pTmpSpace );
}

/*
** Close an open database and invalidate all cursors.
*/
static int sqlite3BtreeClose( ref Btree p )
{
  BtShared pBt = p.pBt;
  BtCursor pCur;

  /* Close all cursors opened via this handle.  */
  Debug.Assert( sqlite3_mutex_held( p.db.mutex ) );
  sqlite3BtreeEnter( p );
  pCur = pBt.pCursor;
  while ( pCur != null )
  {
    BtCursor pTmp = pCur;
    pCur = pCur.pNext;
    if ( pTmp.pBtree == p )
    {
      sqlite3BtreeCloseCursor( pTmp );
    }
  }

  /* Rollback any active transaction and free the handle structure.
  ** The call to sqlite3BtreeRollback() drops any table-locks held by
  ** this handle.
  */
  sqlite3BtreeRollback( p );
  sqlite3BtreeLeave( p );

  /* If there are still other outstanding references to the shared-btree
  ** structure, return now. The remainder of this procedure cleans
  ** up the shared-btree.
  */
  Debug.Assert( p.wantToLock == 0 && !p.locked );
  if ( !p.sharable || removeFromSharingList( pBt ) )
  {
    /* The pBt is no longer on the sharing list, so we can access
    ** it without having to hold the mutex.
    **
    ** Clean out and delete the BtShared object.
    */
    Debug.Assert( null == pBt.pCursor );
    sqlite3PagerClose( pBt.pPager );
    if ( pBt.xFreeSchema != null && pBt.pSchema != null )
    {
      pBt.xFreeSchema( pBt.pSchema );
    }
    pBt.pSchema = null;// sqlite3DbFree(0, pBt->pSchema);
    //freeTempSpace(pBt);
    pBt = null; //sqlite3_free(ref pBt);
  }

#if !SQLITE_OMIT_SHARED_CACHE
Debug.Assert( p.wantToLock==null );
Debug.Assert( p.locked==null );
if( p.pPrev ) p.pPrev.pNext = p.pNext;
if( p.pNext ) p.pNext.pPrev = p.pPrev;
#endif

  //sqlite3_free(ref p);
  return SQLITE_OK;
}

/*
** Change the limit on the number of pages allowed in the cache.
**
** The maximum number of cache pages is set to the absolute
** value of mxPage.  If mxPage is negative, the pager will
** operate asynchronously - it will not stop to do fsync()s
** to insure data is written to the disk surface before
** continuing.  Transactions still work if synchronous is off,
** and the database cannot be corrupted if this program
** crashes.  But if the operating system crashes or there is
** an abrupt power failure when synchronous is off, the database
** could be left in an inconsistent and unrecoverable state.
** Synchronous is on by default so database corruption is not
** normally a worry.
*/
static int sqlite3BtreeSetCacheSize( Btree p, int mxPage )
{
  BtShared pBt = p.pBt;
  Debug.Assert( sqlite3_mutex_held( p.db.mutex ) );
  sqlite3BtreeEnter( p );
  sqlite3PagerSetCachesize( pBt.pPager, mxPage );
  sqlite3BtreeLeave( p );
  return SQLITE_OK;
}

/*
** Change the way data is synced to disk in order to increase or decrease
** how well the database resists damage due to OS crashes and power
** failures.  Level 1 is the same as asynchronous (no syncs() occur and
** there is a high probability of damage)  Level 2 is the default.  There
** is a very low but non-zero probability of damage.  Level 3 reduces the
** probability of damage to near zero but with a write performance reduction.
*/
#if !SQLITE_OMIT_PAGER_PRAGMAS
static int sqlite3BtreeSetSafetyLevel(
Btree p,               /* The btree to set the safety level on */
int level,             /* PRAGMA synchronous.  1=OFF, 2=NORMAL, 3=FULL */
int fullSync,          /* PRAGMA fullfsync. */
int ckptFullSync       /* PRAGMA checkpoint_fullfync */
)
{
  BtShared pBt = p.pBt;
  Debug.Assert( sqlite3_mutex_held( p.db.mutex ) );
  Debug.Assert( level >= 1 && level <= 3 );
  sqlite3BtreeEnter( p );
  sqlite3PagerSetSafetyLevel( pBt.pPager, level, fullSync, ckptFullSync );
  sqlite3BtreeLeave( p );
  return SQLITE_OK;
}
#endif

/*
** Return TRUE if the given btree is set to safety level 1.  In other
** words, return TRUE if no sync() occurs on the disk files.
*/
static int sqlite3BtreeSyncDisabled( Btree p )
{
  BtShared pBt = p.pBt;
  int rc;
  Debug.Assert( sqlite3_mutex_held( p.db.mutex ) );
  sqlite3BtreeEnter( p );
  Debug.Assert( pBt != null && pBt.pPager != null );
  rc = sqlite3PagerNosync( pBt.pPager ) ? 1 : 0;
  sqlite3BtreeLeave( p );
  return rc;
}

/*
** Change the default pages size and the number of reserved bytes per page.
** Or, if the page size has already been fixed, return SQLITE_READONLY
** without changing anything.
**
** The page size must be a power of 2 between 512 and 65536.  If the page
** size supplied does not meet this constraint then the page size is not
** changed.
**
** Page sizes are constrained to be a power of two so that the region
** of the database file used for locking (beginning at PENDING_BYTE,
** the first byte past the 1GB boundary, 0x40000000) needs to occur
** at the beginning of a page.
**
** If parameter nReserve is less than zero, then the number of reserved
** bytes per page is left unchanged.
**
** If iFix!=0 then the pageSizeFixed flag is set so that the page size
** and autovacuum mode can no longer be changed.
*/
static int sqlite3BtreeSetPageSize( Btree p, int pageSize, int nReserve, int iFix )
{
  int rc = SQLITE_OK;
  BtShared pBt = p.pBt;
  Debug.Assert( nReserve >= -1 && nReserve <= 255 );
  sqlite3BtreeEnter( p );
  if ( pBt.pageSizeFixed )
  {
    sqlite3BtreeLeave( p );
    return SQLITE_READONLY;
  }
  if ( nReserve < 0 )
  {
    nReserve = (int)( pBt.pageSize - pBt.usableSize );
  }
  Debug.Assert( nReserve >= 0 && nReserve <= 255 );
  if ( pageSize >= 512 && pageSize <= SQLITE_MAX_PAGE_SIZE &&
  ( ( pageSize - 1 ) & pageSize ) == 0 )
  {
    Debug.Assert( ( pageSize & 7 ) == 0 );
    Debug.Assert( null == pBt.pPage1 && null == pBt.pCursor );
    pBt.pageSize = (u32)pageSize;
    //        freeTempSpace(pBt);
  }
  rc = sqlite3PagerSetPagesize( pBt.pPager, ref pBt.pageSize, nReserve );
  pBt.usableSize = (u16)( pBt.pageSize - nReserve );
  if ( iFix != 0 )
    pBt.pageSizeFixed = true;
  sqlite3BtreeLeave( p );
  return rc;
}

/*
** Return the currently defined page size
*/
static int sqlite3BtreeGetPageSize( Btree p )
{
  return (int)p.pBt.pageSize;
}

#if !(SQLITE_OMIT_PAGER_PRAGMAS) || !(SQLITE_OMIT_VACUUM)
/*
** Return the number of bytes of space at the end of every page that
** are intentually left unused.  This is the "reserved" space that is
** sometimes used by extensions.
*/
static int sqlite3BtreeGetReserve( Btree p )
{
  int n;
  sqlite3BtreeEnter( p );
  n = (int)( p.pBt.pageSize - p.pBt.usableSize );
  sqlite3BtreeLeave( p );
  return n;
}

/*
** Set the maximum page count for a database if mxPage is positive.
** No changes are made if mxPage is 0 or negative.
** Regardless of the value of mxPage, return the maximum page count.
*/
static Pgno sqlite3BtreeMaxPageCount( Btree p, int mxPage )
{
  Pgno n;
  sqlite3BtreeEnter( p );
  n = sqlite3PagerMaxPageCount( p.pBt.pPager, mxPage );
  sqlite3BtreeLeave( p );
  return n;
}

/*
** Set the secureDelete flag if newFlag is 0 or 1.  If newFlag is -1,
** then make no changes.  Always return the value of the secureDelete
** setting after the change.
*/
static int sqlite3BtreeSecureDelete( Btree p, int newFlag )
{
  int b;
  if ( p == null )
    return 0;
  sqlite3BtreeEnter( p );
  if ( newFlag >= 0 )
  {
    p.pBt.secureDelete = ( newFlag != 0 );
  }
  b = p.pBt.secureDelete ? 1 : 0;
  sqlite3BtreeLeave( p );
  return b;
}
#endif //* !(SQLITE_OMIT_PAGER_PRAGMAS) || !(SQLITE_OMIT_VACUUM) */

/*
** Change the 'auto-vacuum' property of the database. If the 'autoVacuum'
** parameter is non-zero, then auto-vacuum mode is enabled. If zero, it
** is disabled. The default value for the auto-vacuum property is
** determined by the SQLITE_DEFAULT_AUTOVACUUM macro.
*/
static int sqlite3BtreeSetAutoVacuum( Btree p, int autoVacuum )
{
#if SQLITE_OMIT_AUTOVACUUM
return SQLITE_READONLY;
#else
  BtShared pBt = p.pBt;
  int rc = SQLITE_OK;
  u8 av = (u8)autoVacuum;

  sqlite3BtreeEnter( p );
  if ( pBt.pageSizeFixed && ( av != 0 ) != pBt.autoVacuum )
  {
    rc = SQLITE_READONLY;
  }
  else
  {
    pBt.autoVacuum = av != 0;
    pBt.incrVacuum = av == 2;
  }
  sqlite3BtreeLeave( p );
  return rc;
#endif
}

/*
** Return the value of the 'auto-vacuum' property. If auto-vacuum is
** enabled 1 is returned. Otherwise 0.
*/
static int sqlite3BtreeGetAutoVacuum( Btree p )
{
#if SQLITE_OMIT_AUTOVACUUM
return BTREE_AUTOVACUUM_NONE;
#else
  int rc;
  sqlite3BtreeEnter( p );
  rc = (
  ( !p.pBt.autoVacuum ) ? BTREE_AUTOVACUUM_NONE :
  ( !p.pBt.incrVacuum ) ? BTREE_AUTOVACUUM_FULL :
  BTREE_AUTOVACUUM_INCR
  );
  sqlite3BtreeLeave( p );
  return rc;
#endif
}


/*
** Get a reference to pPage1 of the database file.  This will
** also acquire a readlock on that file.
**
** SQLITE_OK is returned on success.  If the file is not a
** well-formed database file, then SQLITE_CORRUPT is returned.
** SQLITE_BUSY is returned if the database is locked.  SQLITE_NOMEM
** is returned if we run out of memory.
*/
static int lockBtree( BtShared pBt )
{
  int rc;                /* Result code from subfunctions */
  MemPage pPage1 = null; /* Page 1 of the database file */
  Pgno nPage;            /* Number of pages in the database */
  Pgno nPageFile = 0;    /* Number of pages in the database file */
  ////Pgno nPageHeader;      /* Number of pages in the database according to hdr */

  Debug.Assert( sqlite3_mutex_held( pBt.mutex ) );
  Debug.Assert( pBt.pPage1 == null );
  rc = sqlite3PagerSharedLock( pBt.pPager );
  if ( rc != SQLITE_OK )
    return rc;
  rc = btreeGetPage( pBt, 1, ref pPage1, 0 );
  if ( rc != SQLITE_OK )
    return rc;

  /* Do some checking to help insure the file we opened really is
  ** a valid database file.
  */
  nPage = sqlite3Get4byte( pPage1.aData, 28 );//get4byte(28+(u8*)pPage1->aData);
  sqlite3PagerPagecount( pBt.pPager, out nPageFile );
  if ( nPage == 0 || memcmp( pPage1.aData, 24, pPage1.aData, 92, 4 ) != 0 )//memcmp(24 + (u8*)pPage1.aData, 92 + (u8*)pPage1.aData, 4) != 0)
  {
    nPage = nPageFile;
  }
  if ( nPage > 0 )
  {
    u32 pageSize;
    u32 usableSize;
    u8[] page1 = pPage1.aData;
    rc = SQLITE_NOTADB;
    if ( memcmp( page1, zMagicHeader, 16 ) != 0 )
    {
      goto page1_init_failed;
    }

#if SQLITE_OMIT_WAL
    if ( page1[18] > 1 )
    {
      pBt.readOnly = true;
    }
    if ( page1[19] > 1 )
    {
      pBt.pSchema.file_format = page1[19];
      goto page1_init_failed;
    }
#else
if( page1[18]>2 ){
pBt.readOnly = true;
}
if( page1[19]>2 ){
goto page1_init_failed;
}

/* If the write version is set to 2, this database should be accessed
** in WAL mode. If the log is not already open, open it now. Then 
** return SQLITE_OK and return without populating BtShared.pPage1.
** The caller detects this and calls this function again. This is
** required as the version of page 1 currently in the page1 buffer
** may not be the latest version - there may be a newer one in the log
** file.
*/
if( page1[19]==2 && pBt.doNotUseWAL==false ){
int isOpen = 0;
rc = sqlite3PagerOpenWal(pBt.pPager, ref isOpen);
if( rc!=SQLITE_OK ){
goto page1_init_failed;
}else if( isOpen==0 ){
releasePage(pPage1);
return SQLITE_OK;
}
rc = SQLITE_NOTADB;
}
#endif

    /* The maximum embedded fraction must be exactly 25%.  And the minimum
** embedded fraction must be 12.5% for both leaf-data and non-leaf-data.
** The original design allowed these amounts to vary, but as of
** version 3.6.0, we require them to be fixed.
*/
    if ( memcmp( page1, 21, "\x0040\x0020\x0020", 3 ) != 0 )//   "\100\040\040"
    {
      goto page1_init_failed;
    }
    pageSize = (u32)( ( page1[16] << 8 ) | ( page1[17] << 16 ) );
    if ( ( ( pageSize - 1 ) & pageSize ) != 0
    || pageSize > SQLITE_MAX_PAGE_SIZE
    || pageSize <= 256
    )
    {
      goto page1_init_failed;
    }
    Debug.Assert( ( pageSize & 7 ) == 0 );
    usableSize = pageSize - page1[20];
    if ( pageSize != pBt.pageSize )
    {
      /* After reading the first page of the database assuming a page size
      ** of BtShared.pageSize, we have discovered that the page-size is
      ** actually pageSize. Unlock the database, leave pBt.pPage1 at
      ** zero and return SQLITE_OK. The caller will call this function
      ** again with the correct page-size.
      */
      releasePage( pPage1 );
      pBt.usableSize = usableSize;
      pBt.pageSize = pageSize;
      //          freeTempSpace(pBt);
      rc = sqlite3PagerSetPagesize( pBt.pPager, ref pBt.pageSize,
      (int)( pageSize - usableSize ) );
      return rc;
    }
    if ( ( pBt.db.flags & SQLITE_RecoveryMode ) == 0 && nPage > nPageFile )
    {
      rc = SQLITE_CORRUPT_BKPT();
      goto page1_init_failed;
    }
    if ( usableSize < 480 )
    {
      goto page1_init_failed;
    }
    pBt.pageSize = pageSize;
    pBt.usableSize = usableSize;
#if !SQLITE_OMIT_AUTOVACUUM
    pBt.autoVacuum = ( sqlite3Get4byte( page1, 36 + 4 * 4 ) != 0 );
    pBt.incrVacuum = ( sqlite3Get4byte( page1, 36 + 7 * 4 ) != 0 );
#endif
  }

  /* maxLocal is the maximum amount of payload to store locally for
  ** a cell.  Make sure it is small enough so that at least minFanout
  ** cells can will fit on one page.  We assume a 10-byte page header.
  ** Besides the payload, the cell must store:
  **     2-byte pointer to the cell
  **     4-byte child pointer
  **     9-byte nKey value
  **     4-byte nData value
  **     4-byte overflow page pointer
  ** So a cell consists of a 2-byte pointer, a header which is as much as
  ** 17 bytes long, 0 to N bytes of payload, and an optional 4 byte overflow
  ** page pointer.
  */
  pBt.maxLocal = (u16)( ( pBt.usableSize - 12 ) * 64 / 255 - 23 );
  pBt.minLocal = (u16)( ( pBt.usableSize - 12 ) * 32 / 255 - 23 );
  pBt.maxLeaf = (u16)( pBt.usableSize - 35 );
  pBt.minLeaf = (u16)( ( pBt.usableSize - 12 ) * 32 / 255 - 23 );
  Debug.Assert( pBt.maxLeaf + 23 <= MX_CELL_SIZE( pBt ) );
  pBt.pPage1 = pPage1;
  pBt.nPage = nPage;
  return SQLITE_OK;

page1_init_failed:
  releasePage( pPage1 );
  pBt.pPage1 = null;
  return rc;
}

/*
** If there are no outstanding cursors and we are not in the middle
** of a transaction but there is a read lock on the database, then
** this routine unrefs the first page of the database file which
** has the effect of releasing the read lock.
**
** If there is a transaction in progress, this routine is a no-op.
*/
static void unlockBtreeIfUnused( BtShared pBt )
{
  Debug.Assert( sqlite3_mutex_held( pBt.mutex ) );
  Debug.Assert( pBt.pCursor == null || pBt.inTransaction > TRANS_NONE );
  if ( pBt.inTransaction == TRANS_NONE && pBt.pPage1 != null )
  {
    Debug.Assert( pBt.pPage1.aData != null );
    //Debug.Assert( sqlite3PagerRefcount( pBt.pPager ) == 1 );
    releasePage( pBt.pPage1 );
    pBt.pPage1 = null;
  }
}

/*
** If pBt points to an empty file then convert that empty file
** into a new empty database by initializing the first page of
** the database.
*/
static int newDatabase( BtShared pBt )
{
  MemPage pP1;
  byte[] data;
  int rc;

  Debug.Assert( sqlite3_mutex_held( pBt.mutex ) );
  if ( pBt.nPage > 0 )
  {
    return SQLITE_OK;
  }
  pP1 = pBt.pPage1;
  Debug.Assert( pP1 != null );
  data = pP1.aData;
  rc = sqlite3PagerWrite( pP1.pDbPage );
  if ( rc != 0 )
    return rc;
  Buffer.BlockCopy( zMagicHeader, 0, data, 0, 16 );// memcpy(data, zMagicHeader, sizeof(zMagicHeader));
  Debug.Assert( zMagicHeader.Length == 16 );
  data[16] = (u8)( ( pBt.pageSize >> 8 ) & 0xff );
  data[17] = (u8)( ( pBt.pageSize >> 16 ) & 0xff );
  data[18] = 1;
  data[19] = 1;
  Debug.Assert( pBt.usableSize <= pBt.pageSize && pBt.usableSize + 255 >= pBt.pageSize );
  data[20] = (u8)( pBt.pageSize - pBt.usableSize );
  data[21] = 64;
  data[22] = 32;
  data[23] = 32;
  //memset(&data[24], 0, 100-24);
  zeroPage( pP1, PTF_INTKEY | PTF_LEAF | PTF_LEAFDATA );
  pBt.pageSizeFixed = true;
#if !SQLITE_OMIT_AUTOVACUUM
  Debug.Assert( pBt.autoVacuum == true || pBt.autoVacuum == false );
  Debug.Assert( pBt.incrVacuum == true || pBt.incrVacuum == false );
  sqlite3Put4byte( data, 36 + 4 * 4, pBt.autoVacuum ? 1 : 0 );
  sqlite3Put4byte( data, 36 + 7 * 4, pBt.incrVacuum ? 1 : 0 );
#endif
  pBt.nPage = 1;
  data[31] = 1;
  return SQLITE_OK;
}

/*
** Attempt to start a new transaction. A write-transaction
** is started if the second argument is nonzero, otherwise a read-
** transaction.  If the second argument is 2 or more and exclusive
** transaction is started, meaning that no other process is allowed
** to access the database.  A preexisting transaction may not be
** upgraded to exclusive by calling this routine a second time - the
** exclusivity flag only works for a new transaction.
**
** A write-transaction must be started before attempting any
** changes to the database.  None of the following routines
** will work unless a transaction is started first:
**
**      sqlite3BtreeCreateTable()
**      sqlite3BtreeCreateIndex()
**      sqlite3BtreeClearTable()
**      sqlite3BtreeDropTable()
**      sqlite3BtreeInsert()
**      sqlite3BtreeDelete()
**      sqlite3BtreeUpdateMeta()
**
** If an initial attempt to acquire the lock fails because of lock contention
** and the database was previously unlocked, then invoke the busy handler
** if there is one.  But if there was previously a read-lock, do not
** invoke the busy handler - just return SQLITE_BUSY.  SQLITE_BUSY is
** returned when there is already a read-lock in order to avoid a deadlock.
**
** Suppose there are two processes A and B.  A has a read lock and B has
** a reserved lock.  B tries to promote to exclusive but is blocked because
** of A's read lock.  A tries to promote to reserved but is blocked by B.
** One or the other of the two processes must give way or there can be
** no progress.  By returning SQLITE_BUSY and not invoking the busy callback
** when A already has a read lock, we encourage A to give up and let B
** proceed.
*/
static int sqlite3BtreeBeginTrans( Btree p, int wrflag )
{
  BtShared pBt = p.pBt;
  int rc = SQLITE_OK;

  sqlite3BtreeEnter( p );
  btreeIntegrity( p );

  /* If the btree is already in a write-transaction, or it
  ** is already in a read-transaction and a read-transaction
  ** is requested, this is a no-op.
  */
  if ( p.inTrans == TRANS_WRITE || ( p.inTrans == TRANS_READ && 0 == wrflag ) )
  {
    goto trans_begun;
  }

  /* Write transactions are not possible on a read-only database */
  if ( pBt.readOnly && wrflag != 0 )
  {
    rc = SQLITE_READONLY;
    goto trans_begun;
  }

#if !SQLITE_OMIT_SHARED_CACHE
/* If another database handle has already opened a write transaction
** on this shared-btree structure and a second write transaction is
** requested, return SQLITE_LOCKED.
*/
if( (wrflag && pBt.inTransaction==TRANS_WRITE) || pBt.isPending ){
sqlite3 pBlock = pBt.pWriter.db;
}else if( wrflag>1 ){
BtLock pIter;
for(pIter=pBt.pLock; pIter; pIter=pIter.pNext){
if( pIter.pBtree!=p ){
pBlock = pIter.pBtree.db;
break;
}
}
}
if( pBlock ){
sqlite3ConnectionBlocked(p.db, pBlock);
rc = SQLITE_LOCKED_SHAREDCACHE;
goto trans_begun;
}
#endif

  /* Any read-only or read-write transaction implies a read-lock on
** page 1. So if some other shared-cache client already has a write-lock
** on page 1, the transaction cannot be opened. */
  rc = querySharedCacheTableLock( p, MASTER_ROOT, READ_LOCK );
  if ( SQLITE_OK != rc )
    goto trans_begun;

  pBt.initiallyEmpty = pBt.nPage == 0;
  do
  {
    /* Call lockBtree() until either pBt.pPage1 is populated or
    ** lockBtree() returns something other than SQLITE_OK. lockBtree()
    ** may return SQLITE_OK but leave pBt.pPage1 set to 0 if after
    ** reading page 1 it discovers that the page-size of the database
    ** file is not pBt.pageSize. In this case lockBtree() will update
    ** pBt.pageSize to the page-size of the file on disk.
    */
    while ( pBt.pPage1 == null && SQLITE_OK == ( rc = lockBtree( pBt ) ) )
      ;

    if ( rc == SQLITE_OK && wrflag != 0 )
    {
      if ( pBt.readOnly )
      {
        rc = SQLITE_READONLY;
      }
      else
      {
        rc = sqlite3PagerBegin( pBt.pPager, wrflag > 1, sqlite3TempInMemory( p.db ) ? 1 : 0 );
        if ( rc == SQLITE_OK )
        {
          rc = newDatabase( pBt );
        }
      }
    }

    if ( rc != SQLITE_OK )
    {
      unlockBtreeIfUnused( pBt );
    }
  } while ( ( rc & 0xFF ) == SQLITE_BUSY && pBt.inTransaction == TRANS_NONE &&
  btreeInvokeBusyHandler( pBt ) != 0 );

  if ( rc == SQLITE_OK )
  {
    if ( p.inTrans == TRANS_NONE )
    {
      pBt.nTransaction++;
#if !SQLITE_OMIT_SHARED_CACHE
if( p.sharable ){
Debug.Assert( p.lock.pBtree==p && p.lock.iTable==1 );
p.lock.eLock = READ_LOCK;
p.lock.pNext = pBt.pLock;
pBt.pLock = &p.lock;
}
#endif
    }
    p.inTrans = ( wrflag != 0 ? TRANS_WRITE : TRANS_READ );
    if ( p.inTrans > pBt.inTransaction )
    {
      pBt.inTransaction = p.inTrans;
    }
    if ( wrflag != 0 )
    {
      MemPage pPage1 = pBt.pPage1;
#if !SQLITE_OMIT_SHARED_CACHE
Debug.Assert( !pBt.pWriter );
pBt.pWriter = p;
pBt.isExclusive = (u8)(wrflag>1);
#endif
      /* If the db-size header field is incorrect (as it may be if an old
** client has been writing the database file), update it now. Doing
** this sooner rather than later means the database size can safely 
** re-read the database size from page 1 if a savepoint or transaction
** rollback occurs within the transaction.
*/
      if ( pBt.nPage != sqlite3Get4byte( pPage1.aData, 28 ) )
      {
        rc = sqlite3PagerWrite( pPage1.pDbPage );
        if ( rc == SQLITE_OK )
        {
          sqlite3Put4byte( pPage1.aData, (u32)28, pBt.nPage );
        }
      }
    }
  }


trans_begun:
  if ( rc == SQLITE_OK && wrflag != 0 )
  {
    /* This call makes sure that the pager has the correct number of
    ** open savepoints. If the second parameter is greater than 0 and
    ** the sub-journal is not already open, then it will be opened here.
    */
    rc = sqlite3PagerOpenSavepoint( pBt.pPager, p.db.nSavepoint );
  }

  btreeIntegrity( p );
  sqlite3BtreeLeave( p );
  return rc;
}

#if !SQLITE_OMIT_AUTOVACUUM

/*
** Set the pointer-map entries for all children of page pPage. Also, if
** pPage contains cells that point to overflow pages, set the pointer
** map entries for the overflow pages as well.
*/
static int setChildPtrmaps( MemPage pPage )
{
  int i;                             /* Counter variable */
  int nCell;                         /* Number of cells in page pPage */
  int rc;                            /* Return code */
  BtShared pBt = pPage.pBt;
  u8 isInitOrig = pPage.isInit;
  Pgno pgno = pPage.pgno;

  Debug.Assert( sqlite3_mutex_held( pPage.pBt.mutex ) );
  rc = btreeInitPage( pPage );
  if ( rc != SQLITE_OK )
  {
    goto set_child_ptrmaps_out;
  }
  nCell = pPage.nCell;

  for ( i = 0; i < nCell; i++ )
  {
    int pCell = findCell( pPage, i );

    ptrmapPutOvflPtr( pPage, pCell, ref rc );

    if ( 0 == pPage.leaf )
    {
      Pgno childPgno = sqlite3Get4byte( pPage.aData, pCell );
      ptrmapPut( pBt, childPgno, PTRMAP_BTREE, pgno, ref rc );
    }
  }

  if ( 0 == pPage.leaf )
  {
    Pgno childPgno = sqlite3Get4byte( pPage.aData, pPage.hdrOffset + 8 );
    ptrmapPut( pBt, childPgno, PTRMAP_BTREE, pgno, ref rc );
  }

set_child_ptrmaps_out:
  pPage.isInit = isInitOrig;
  return rc;
}

/*
** Somewhere on pPage is a pointer to page iFrom.  Modify this pointer so
** that it points to iTo. Parameter eType describes the type of pointer to
** be modified, as  follows:
**
** PTRMAP_BTREE:     pPage is a btree-page. The pointer points at a child
**                   page of pPage.
**
** PTRMAP_OVERFLOW1: pPage is a btree-page. The pointer points at an overflow
**                   page pointed to by one of the cells on pPage.
**
** PTRMAP_OVERFLOW2: pPage is an overflow-page. The pointer points at the next
**                   overflow page in the list.
*/
static int modifyPagePointer( MemPage pPage, Pgno iFrom, Pgno iTo, u8 eType )
{
  Debug.Assert( sqlite3_mutex_held( pPage.pBt.mutex ) );
  Debug.Assert( sqlite3PagerIswriteable( pPage.pDbPage ) );
  if ( eType == PTRMAP_OVERFLOW2 )
  {
    /* The pointer is always the first 4 bytes of the page in this case.  */
    if ( sqlite3Get4byte( pPage.aData ) != iFrom )
    {
      return SQLITE_CORRUPT_BKPT();
    }
    sqlite3Put4byte( pPage.aData, iTo );
  }
  else
  {
    u8 isInitOrig = pPage.isInit;
    int i;
    int nCell;

    btreeInitPage( pPage );
    nCell = pPage.nCell;

    for ( i = 0; i < nCell; i++ )
    {
      int pCell = findCell( pPage, i );
      if ( eType == PTRMAP_OVERFLOW1 )
      {
        CellInfo info = new CellInfo();
        btreeParseCellPtr( pPage, pCell, ref info );
        if ( info.iOverflow != 0 )
        {
          if ( iFrom == sqlite3Get4byte( pPage.aData, pCell, info.iOverflow ) )
          {
            sqlite3Put4byte( pPage.aData, pCell + info.iOverflow, (int)iTo );
            break;
          }
        }
      }
      else
      {
        if ( sqlite3Get4byte( pPage.aData, pCell ) == iFrom )
        {
          sqlite3Put4byte( pPage.aData, pCell, (int)iTo );
          break;
        }
      }
    }

    if ( i == nCell )
    {
      if ( eType != PTRMAP_BTREE ||
      sqlite3Get4byte( pPage.aData, pPage.hdrOffset + 8 ) != iFrom )
      {
        return SQLITE_CORRUPT_BKPT();
      }
      sqlite3Put4byte( pPage.aData, pPage.hdrOffset + 8, iTo );
    }

    pPage.isInit = isInitOrig;
  }
  return SQLITE_OK;
}


/*
** Move the open database page pDbPage to location iFreePage in the
** database. The pDbPage reference remains valid.
**
** The isCommit flag indicates that there is no need to remember that
** the journal needs to be sync()ed before database page pDbPage.pgno
** can be written to. The caller has already promised not to write to that
** page.
*/
static int relocatePage(
BtShared pBt,           /* Btree */
MemPage pDbPage,        /* Open page to move */
u8 eType,                /* Pointer map 'type' entry for pDbPage */
Pgno iPtrPage,           /* Pointer map 'page-no' entry for pDbPage */
Pgno iFreePage,          /* The location to move pDbPage to */
int isCommit             /* isCommit flag passed to sqlite3PagerMovepage */
)
{
  MemPage pPtrPage = new MemPage();   /* The page that contains a pointer to pDbPage */
  Pgno iDbPage = pDbPage.pgno;
  Pager pPager = pBt.pPager;
  int rc;

  Debug.Assert( eType == PTRMAP_OVERFLOW2 || eType == PTRMAP_OVERFLOW1 ||
  eType == PTRMAP_BTREE || eType == PTRMAP_ROOTPAGE );
  Debug.Assert( sqlite3_mutex_held( pBt.mutex ) );
  Debug.Assert( pDbPage.pBt == pBt );

  /* Move page iDbPage from its current location to page number iFreePage */
  TRACE( "AUTOVACUUM: Moving %d to free page %d (ptr page %d type %d)\n",
  iDbPage, iFreePage, iPtrPage, eType );
  rc = sqlite3PagerMovepage( pPager, pDbPage.pDbPage, iFreePage, isCommit );
  if ( rc != SQLITE_OK )
  {
    return rc;
  }
  pDbPage.pgno = iFreePage;

  /* If pDbPage was a btree-page, then it may have child pages and/or cells
  ** that point to overflow pages. The pointer map entries for all these
  ** pages need to be changed.
  **
  ** If pDbPage is an overflow page, then the first 4 bytes may store a
  ** pointer to a subsequent overflow page. If this is the case, then
  ** the pointer map needs to be updated for the subsequent overflow page.
  */
  if ( eType == PTRMAP_BTREE || eType == PTRMAP_ROOTPAGE )
  {
    rc = setChildPtrmaps( pDbPage );
    if ( rc != SQLITE_OK )
    {
      return rc;
    }
  }
  else
  {
    Pgno nextOvfl = sqlite3Get4byte( pDbPage.aData );
    if ( nextOvfl != 0 )
    {
      ptrmapPut( pBt, nextOvfl, PTRMAP_OVERFLOW2, iFreePage, ref rc );
      if ( rc != SQLITE_OK )
      {
        return rc;
      }
    }
  }

  /* Fix the database pointer on page iPtrPage that pointed at iDbPage so
  ** that it points at iFreePage. Also fix the pointer map entry for
  ** iPtrPage.
  */
  if ( eType != PTRMAP_ROOTPAGE )
  {
    rc = btreeGetPage( pBt, iPtrPage, ref pPtrPage, 0 );
    if ( rc != SQLITE_OK )
    {
      return rc;
    }
    rc = sqlite3PagerWrite( pPtrPage.pDbPage );
    if ( rc != SQLITE_OK )
    {
      releasePage( pPtrPage );
      return rc;
    }
    rc = modifyPagePointer( pPtrPage, iDbPage, iFreePage, eType );
    releasePage( pPtrPage );
    if ( rc == SQLITE_OK )
    {
      ptrmapPut( pBt, iFreePage, eType, iPtrPage, ref rc );
    }
  }
  return rc;
}

/* Forward declaration required by incrVacuumStep(). */
//static int allocateBtreePage(BtShared *, MemPage **, Pgno *, Pgno, u8);

/*
** Perform a single step of an incremental-vacuum. If successful,
** return SQLITE_OK. If there is no work to do (and therefore no
** point in calling this function again), return SQLITE_DONE.
**
** More specificly, this function attempts to re-organize the
** database so that the last page of the file currently in use
** is no longer in use.
**
** If the nFin parameter is non-zero, this function assumes
** that the caller will keep calling incrVacuumStep() until
** it returns SQLITE_DONE or an error, and that nFin is the
** number of pages the database file will contain after this
** process is complete.  If nFin is zero, it is assumed that
** incrVacuumStep() will be called a finite amount of times
** which may or may not empty the freelist.  A full autovacuum
** has nFin>0.  A "PRAGMA incremental_vacuum" has nFin==null.
*/
static int incrVacuumStep( BtShared pBt, Pgno nFin, Pgno iLastPg )
{
  Pgno nFreeList;           /* Number of pages still on the free-list */
  int rc;

  Debug.Assert( sqlite3_mutex_held( pBt.mutex ) );
  Debug.Assert( iLastPg > nFin );

  if ( !PTRMAP_ISPAGE( pBt, iLastPg ) && iLastPg != PENDING_BYTE_PAGE( pBt ) )
  {
    u8 eType = 0;
    Pgno iPtrPage = 0;

    nFreeList = sqlite3Get4byte( pBt.pPage1.aData, 36 );
    if ( nFreeList == 0 )
    {
      return SQLITE_DONE;
    }

    rc = ptrmapGet( pBt, iLastPg, ref eType, ref iPtrPage );
    if ( rc != SQLITE_OK )
    {
      return rc;
    }
    if ( eType == PTRMAP_ROOTPAGE )
    {
      return SQLITE_CORRUPT_BKPT();
    }

    if ( eType == PTRMAP_FREEPAGE )
    {
      if ( nFin == 0 )
      {
        /* Remove the page from the files free-list. This is not required
        ** if nFin is non-zero. In that case, the free-list will be
        ** truncated to zero after this function returns, so it doesn't
        ** matter if it still contains some garbage entries.
        */
        Pgno iFreePg = 0;
        MemPage pFreePg = new MemPage();
        rc = allocateBtreePage( pBt, ref pFreePg, ref iFreePg, iLastPg, 1 );
        if ( rc != SQLITE_OK )
        {
          return rc;
        }
        Debug.Assert( iFreePg == iLastPg );
        releasePage( pFreePg );
      }
    }
    else
    {
      Pgno iFreePg = 0;             /* Index of free page to move pLastPg to */
      MemPage pLastPg = new MemPage();

      rc = btreeGetPage( pBt, iLastPg, ref pLastPg, 0 );
      if ( rc != SQLITE_OK )
      {
        return rc;
      }

      /* If nFin is zero, this loop runs exactly once and page pLastPg
      ** is swapped with the first free page pulled off the free list.
      **
      ** On the other hand, if nFin is greater than zero, then keep
      ** looping until a free-page located within the first nFin pages
      ** of the file is found.
      */
      do
      {
        MemPage pFreePg = new MemPage();
        rc = allocateBtreePage( pBt, ref pFreePg, ref iFreePg, 0, 0 );
        if ( rc != SQLITE_OK )
        {
          releasePage( pLastPg );
          return rc;
        }
        releasePage( pFreePg );
      } while ( nFin != 0 && iFreePg > nFin );
      Debug.Assert( iFreePg < iLastPg );

      rc = sqlite3PagerWrite( pLastPg.pDbPage );
      if ( rc == SQLITE_OK )
      {
        rc = relocatePage( pBt, pLastPg, eType, iPtrPage, iFreePg, ( nFin != 0 ) ? 1 : 0 );
      }
      releasePage( pLastPg );
      if ( rc != SQLITE_OK )
      {
        return rc;
      }
    }
  }

  if ( nFin == 0 )
  {
    iLastPg--;
    while ( iLastPg == PENDING_BYTE_PAGE( pBt ) || PTRMAP_ISPAGE( pBt, iLastPg ) )
    {
      if ( PTRMAP_ISPAGE( pBt, iLastPg ) )
      {
        MemPage pPg = new MemPage();
        rc = btreeGetPage( pBt, iLastPg, ref pPg, 0 );
        if ( rc != SQLITE_OK )
        {
          return rc;
        }
        rc = sqlite3PagerWrite( pPg.pDbPage );
        releasePage( pPg );
        if ( rc != SQLITE_OK )
        {
          return rc;
        }
      }
      iLastPg--;
    }
    sqlite3PagerTruncateImage( pBt.pPager, iLastPg );
    pBt.nPage = iLastPg;
  }
  return SQLITE_OK;
}

/*
** A write-transaction must be opened before calling this function.
** It performs a single unit of work towards an incremental vacuum.
**
** If the incremental vacuum is finished after this function has run,
** SQLITE_DONE is returned. If it is not finished, but no error occurred,
** SQLITE_OK is returned. Otherwise an SQLite error code.
*/
static int sqlite3BtreeIncrVacuum( Btree p )
{
  int rc;
  BtShared pBt = p.pBt;

  sqlite3BtreeEnter( p );
  Debug.Assert( pBt.inTransaction == TRANS_WRITE && p.inTrans == TRANS_WRITE );
  if ( !pBt.autoVacuum )
  {
    rc = SQLITE_DONE;
  }
  else
  {
    invalidateAllOverflowCache( pBt );
    rc = incrVacuumStep( pBt, 0, btreePagecount( pBt ) );
    if ( rc == SQLITE_OK )
    {
      rc = sqlite3PagerWrite( pBt.pPage1.pDbPage );
      sqlite3Put4byte( pBt.pPage1.aData, (u32)28, pBt.nPage );//put4byte(&pBt->pPage1->aData[28], pBt->nPage);
    }
  }
  sqlite3BtreeLeave( p );
  return rc;
}

/*
** This routine is called prior to sqlite3PagerCommit when a transaction
** is commited for an auto-vacuum database.
**
** If SQLITE_OK is returned, then pnTrunc is set to the number of pages
** the database file should be truncated to during the commit process.
** i.e. the database has been reorganized so that only the first pnTrunc
** pages are in use.
*/
static int autoVacuumCommit( BtShared pBt )
{
  int rc = SQLITE_OK;
  Pager pPager = pBt.pPager;
  // VVA_ONLY( int nRef = sqlite3PagerRefcount(pPager) );
#if !NDEBUG || DEBUG
  int nRef = sqlite3PagerRefcount( pPager );
#else
int nRef=0;
#endif


  Debug.Assert( sqlite3_mutex_held( pBt.mutex ) );
  invalidateAllOverflowCache( pBt );
  Debug.Assert( pBt.autoVacuum );
  if ( !pBt.incrVacuum )
  {
    Pgno nFin;         /* Number of pages in database after autovacuuming */
    Pgno nFree;        /* Number of pages on the freelist initially */
    Pgno nPtrmap;      /* Number of PtrMap pages to be freed */
    Pgno iFree;        /* The next page to be freed */
    int nEntry;        /* Number of entries on one ptrmap page */
    Pgno nOrig;        /* Database size before freeing */

    nOrig = btreePagecount( pBt );
    if ( PTRMAP_ISPAGE( pBt, nOrig ) || nOrig == PENDING_BYTE_PAGE( pBt ) )
    {
      /* It is not possible to create a database for which the final page
      ** is either a pointer-map page or the pending-byte page. If one
      ** is encountered, this indicates corruption.
      */
      return SQLITE_CORRUPT_BKPT();
    }

    nFree = sqlite3Get4byte( pBt.pPage1.aData, 36 );
    nEntry = (int)pBt.usableSize / 5;
    nPtrmap = (Pgno)( ( nFree - nOrig + PTRMAP_PAGENO( pBt, nOrig ) + (Pgno)nEntry ) / nEntry );
    nFin = nOrig - nFree - nPtrmap;
    if ( nOrig > PENDING_BYTE_PAGE( pBt ) && nFin < PENDING_BYTE_PAGE( pBt ) )
    {
      nFin--;
    }
    while ( PTRMAP_ISPAGE( pBt, nFin ) || nFin == PENDING_BYTE_PAGE( pBt ) )
    {
      nFin--;
    }
    if ( nFin > nOrig )
      return SQLITE_CORRUPT_BKPT();

    for ( iFree = nOrig; iFree > nFin && rc == SQLITE_OK; iFree-- )
    {
      rc = incrVacuumStep( pBt, nFin, iFree );
    }
    if ( ( rc == SQLITE_DONE || rc == SQLITE_OK ) && nFree > 0 )
    {
      rc = sqlite3PagerWrite( pBt.pPage1.pDbPage );
      sqlite3Put4byte( pBt.pPage1.aData, 32, 0 );
      sqlite3Put4byte( pBt.pPage1.aData, 36, 0 );
      sqlite3Put4byte( pBt.pPage1.aData, (u32)28, nFin );
      sqlite3PagerTruncateImage( pBt.pPager, nFin );
      pBt.nPage = nFin;
    }
    if ( rc != SQLITE_OK )
    {
      sqlite3PagerRollback( pPager );
    }
  }

  Debug.Assert( nRef == sqlite3PagerRefcount( pPager ) );
  return rc;
}

#else //* ifndef SQLITE_OMIT_AUTOVACUUM */
//# define setChildPtrmaps(x) SQLITE_OK
#endif

/*
** This routine does the first phase of a two-phase commit.  This routine
** causes a rollback journal to be created (if it does not already exist)
** and populated with enough information so that if a power loss occurs
** the database can be restored to its original state by playing back
** the journal.  Then the contents of the journal are flushed out to
** the disk.  After the journal is safely on oxide, the changes to the
** database are written into the database file and flushed to oxide.
** At the end of this call, the rollback journal still exists on the
** disk and we are still holding all locks, so the transaction has not
** committed.  See sqlite3BtreeCommitPhaseTwo() for the second phase of the
** commit process.
**
** This call is a no-op if no write-transaction is currently active on pBt.
**
** Otherwise, sync the database file for the btree pBt. zMaster points to
** the name of a master journal file that should be written into the
** individual journal file, or is NULL, indicating no master journal file
** (single database transaction).
**
** When this is called, the master journal should already have been
** created, populated with this journal pointer and synced to disk.
**
** Once this is routine has returned, the only thing required to commit
** the write-transaction for this database file is to delete the journal.
*/
static int sqlite3BtreeCommitPhaseOne( Btree p, string zMaster )
{
  int rc = SQLITE_OK;
  if ( p.inTrans == TRANS_WRITE )
  {
    BtShared pBt = p.pBt;
    sqlite3BtreeEnter( p );
#if !SQLITE_OMIT_AUTOVACUUM
    if ( pBt.autoVacuum )
    {
      rc = autoVacuumCommit( pBt );
      if ( rc != SQLITE_OK )
      {
        sqlite3BtreeLeave( p );
        return rc;
      }
    }
#endif
    rc = sqlite3PagerCommitPhaseOne( pBt.pPager, zMaster, false );
    sqlite3BtreeLeave( p );
  }
  return rc;
}

/*
** This function is called from both BtreeCommitPhaseTwo() and BtreeRollback()
** at the conclusion of a transaction.
*/
static void btreeEndTransaction( Btree p )
{
  BtShared pBt = p.pBt;
  Debug.Assert( sqlite3BtreeHoldsMutex( p ) );

  btreeClearHasContent( pBt );
  if ( p.inTrans > TRANS_NONE && p.db.activeVdbeCnt > 1 )
  {
    /* If there are other active statements that belong to this database
    ** handle, downgrade to a read-only transaction. The other statements
    ** may still be reading from the database.  */

    downgradeAllSharedCacheTableLocks( p );
    p.inTrans = TRANS_READ;
  }
  else
  {
    /* If the handle had any kind of transaction open, decrement the
    ** transaction count of the shared btree. If the transaction count
    ** reaches 0, set the shared state to TRANS_NONE. The unlockBtreeIfUnused()
    ** call below will unlock the pager.  */
    if ( p.inTrans != TRANS_NONE )
    {
      clearAllSharedCacheTableLocks( p );
      pBt.nTransaction--;
      if ( 0 == pBt.nTransaction )
      {
        pBt.inTransaction = TRANS_NONE;
      }
    }

    /* Set the current transaction state to TRANS_NONE and unlock the
    ** pager if this call closed the only read or write transaction.  */
    p.inTrans = TRANS_NONE;
    unlockBtreeIfUnused( pBt );
  }

  btreeIntegrity( p );
}

/*
** Commit the transaction currently in progress.
**
** This routine implements the second phase of a 2-phase commit.  The
** sqlite3BtreeCommitPhaseOne() routine does the first phase and should
** be invoked prior to calling this routine.  The sqlite3BtreeCommitPhaseOne()
** routine did all the work of writing information out to disk and flushing the
** contents so that they are written onto the disk platter.  All this
** routine has to do is delete or truncate or zero the header in the
** the rollback journal (which causes the transaction to commit) and
** drop locks.
**
** Normally, if an error occurs while the pager layer is attempting to 
** finalize the underlying journal file, this function returns an error and
** the upper layer will attempt a rollback. However, if the second argument
** is non-zero then this b-tree transaction is part of a multi-file 
** transaction. In this case, the transaction has already been committed 
** (by deleting a master journal file) and the caller will ignore this 
** functions return code. So, even if an error occurs in the pager layer,
** reset the b-tree objects internal state to indicate that the write
** transaction has been closed. This is quite safe, as the pager will have
** transitioned to the error state.
**
** This will release the write lock on the database file.  If there
** are no active cursors, it also releases the read lock.
*/
static int sqlite3BtreeCommitPhaseTwo( Btree p, int bCleanup)
{
  if ( p.inTrans == TRANS_NONE )
    return SQLITE_OK;
  sqlite3BtreeEnter( p );
  btreeIntegrity( p );

  /* If the handle has a write-transaction open, commit the shared-btrees
  ** transaction and set the shared state to TRANS_READ.
  */
  if ( p.inTrans == TRANS_WRITE )
  {
    int rc;
    BtShared pBt = p.pBt;
    Debug.Assert( pBt.inTransaction == TRANS_WRITE );
    Debug.Assert( pBt.nTransaction > 0 );
    rc = sqlite3PagerCommitPhaseTwo( pBt.pPager );
    if ( rc != SQLITE_OK && bCleanup == 0 )
    {
      sqlite3BtreeLeave( p );
      return rc;
    }
    pBt.inTransaction = TRANS_READ;
  }

  btreeEndTransaction( p );
  sqlite3BtreeLeave( p );
  return SQLITE_OK;
}

/*
** Do both phases of a commit.
*/
static int sqlite3BtreeCommit( Btree p )
{
  int rc;
  sqlite3BtreeEnter( p );
  rc = sqlite3BtreeCommitPhaseOne( p, null );
  if ( rc == SQLITE_OK )
  {
    rc = sqlite3BtreeCommitPhaseTwo( p, 0 );
  }
  sqlite3BtreeLeave( p );
  return rc;
}

#if !NDEBUG || DEBUG
/*
** Return the number of write-cursors open on this handle. This is for use
** in Debug.Assert() expressions, so it is only compiled if NDEBUG is not
** defined.
**
** For the purposes of this routine, a write-cursor is any cursor that
** is capable of writing to the databse.  That means the cursor was
** originally opened for writing and the cursor has not be disabled
** by having its state changed to CURSOR_FAULT.
*/
static int countWriteCursors( BtShared pBt )
{
  BtCursor pCur;
  int r = 0;
  for ( pCur = pBt.pCursor; pCur != null; pCur = pCur.pNext )
  {
    if ( pCur.wrFlag != 0 && pCur.eState != CURSOR_FAULT )
      r++;
  }
  return r;
}
#else
static int countWriteCursors(BtShared pBt) { return -1; }
#endif

/*
** This routine sets the state to CURSOR_FAULT and the error
** code to errCode for every cursor on BtShared that pBtree
** references.
**
** Every cursor is tripped, including cursors that belong
** to other database connections that happen to be sharing
** the cache with pBtree.
**
** This routine gets called when a rollback occurs.
** All cursors using the same cache must be tripped
** to prevent them from trying to use the btree after
** the rollback.  The rollback may have deleted tables
** or moved root pages, so it is not sufficient to
** save the state of the cursor.  The cursor must be
** invalidated.
*/
static void sqlite3BtreeTripAllCursors( Btree pBtree, int errCode )
{
  BtCursor p;
  sqlite3BtreeEnter( pBtree );
  for ( p = pBtree.pBt.pCursor; p != null; p = p.pNext )
  {
    int i;
    sqlite3BtreeClearCursor( p );
    p.eState = CURSOR_FAULT;
    p.skipNext = errCode;
    for ( i = 0; i <= p.iPage; i++ )
    {
      releasePage( p.apPage[i] );
      p.apPage[i] = null;
    }
  }
  sqlite3BtreeLeave( pBtree );
}

/*
** Rollback the transaction in progress.  All cursors will be
** invalided by this operation.  Any attempt to use a cursor
** that was open at the beginning of this operation will result
** in an error.
**
** This will release the write lock on the database file.  If there
** are no active cursors, it also releases the read lock.
*/
static int sqlite3BtreeRollback( Btree p )
{
  int rc;
  BtShared pBt = p.pBt;
  MemPage pPage1 = new MemPage();

  sqlite3BtreeEnter( p );
  rc = saveAllCursors( pBt, 0, null );
#if !SQLITE_OMIT_SHARED_CACHE
if( rc!=SQLITE_OK ){
/* This is a horrible situation. An IO or malloc() error occurred whilst
** trying to save cursor positions. If this is an automatic rollback (as
** the result of a constraint, malloc() failure or IO error) then
** the cache may be internally inconsistent (not contain valid trees) so
** we cannot simply return the error to the caller. Instead, abort
** all queries that may be using any of the cursors that failed to save.
*/
sqlite3BtreeTripAllCursors(p, rc);
}
#endif
  btreeIntegrity( p );

  if ( p.inTrans == TRANS_WRITE )
  {
    int rc2;

    Debug.Assert( TRANS_WRITE == pBt.inTransaction );
    rc2 = sqlite3PagerRollback( pBt.pPager );
    if ( rc2 != SQLITE_OK )
    {
      rc = rc2;
    }

    /* The rollback may have destroyed the pPage1.aData value.  So
    ** call btreeGetPage() on page 1 again to make
    ** sure pPage1.aData is set correctly. */
    if ( btreeGetPage( pBt, 1, ref pPage1, 0 ) == SQLITE_OK )
    {
      Pgno nPage = sqlite3Get4byte( pPage1.aData, 28 );
      testcase( nPage == 0 );
      if ( nPage == 0 )
        sqlite3PagerPagecount( pBt.pPager, out nPage );
      testcase( pBt.nPage != nPage );
      pBt.nPage = nPage;
      releasePage( pPage1 );
    }
    Debug.Assert( countWriteCursors( pBt ) == 0 );
    pBt.inTransaction = TRANS_READ;
  }

  btreeEndTransaction( p );
  sqlite3BtreeLeave( p );
  return rc;
}

/*
** Start a statement subtransaction. The subtransaction can can be rolled
** back independently of the main transaction. You must start a transaction
** before starting a subtransaction. The subtransaction is ended automatically
** if the main transaction commits or rolls back.
**
** Statement subtransactions are used around individual SQL statements
** that are contained within a BEGIN...COMMIT block.  If a constraint
** error occurs within the statement, the effect of that one statement
** can be rolled back without having to rollback the entire transaction.
**
** A statement sub-transaction is implemented as an anonymous savepoint. The
** value passed as the second parameter is the total number of savepoints,
** including the new anonymous savepoint, open on the B-Tree. i.e. if there
** are no active savepoints and no other statement-transactions open,
** iStatement is 1. This anonymous savepoint can be released or rolled back
** using the sqlite3BtreeSavepoint() function.
*/
static int sqlite3BtreeBeginStmt( Btree p, int iStatement )
{
  int rc;
  BtShared pBt = p.pBt;
  sqlite3BtreeEnter( p );
  Debug.Assert( p.inTrans == TRANS_WRITE );
  Debug.Assert( !pBt.readOnly );
  Debug.Assert( iStatement > 0 );
  Debug.Assert( iStatement > p.db.nSavepoint );
  Debug.Assert( pBt.inTransaction == TRANS_WRITE );
  /* At the pager level, a statement transaction is a savepoint with
  ** an index greater than all savepoints created explicitly using
  ** SQL statements. It is illegal to open, release or rollback any
  ** such savepoints while the statement transaction savepoint is active.
  */
  rc = sqlite3PagerOpenSavepoint( pBt.pPager, iStatement );
  sqlite3BtreeLeave( p );
  return rc;
}

/*
** The second argument to this function, op, is always SAVEPOINT_ROLLBACK
** or SAVEPOINT_RELEASE. This function either releases or rolls back the
** savepoint identified by parameter iSavepoint, depending on the value
** of op.
**
** Normally, iSavepoint is greater than or equal to zero. However, if op is
** SAVEPOINT_ROLLBACK, then iSavepoint may also be -1. In this case the
** contents of the entire transaction are rolled back. This is different
** from a normal transaction rollback, as no locks are released and the
** transaction remains open.
*/
static int sqlite3BtreeSavepoint( Btree p, int op, int iSavepoint )
{
  int rc = SQLITE_OK;
  if ( p != null && p.inTrans == TRANS_WRITE )
  {
    BtShared pBt = p.pBt;
    Debug.Assert( op == SAVEPOINT_RELEASE || op == SAVEPOINT_ROLLBACK );
    Debug.Assert( iSavepoint >= 0 || ( iSavepoint == -1 && op == SAVEPOINT_ROLLBACK ) );
    sqlite3BtreeEnter( p );
    rc = sqlite3PagerSavepoint( pBt.pPager, op, iSavepoint );
    if ( rc == SQLITE_OK )
    {
      if ( iSavepoint < 0 && pBt.initiallyEmpty )
        pBt.nPage = 0;
      rc = newDatabase( pBt );
      pBt.nPage = sqlite3Get4byte( pBt.pPage1.aData, 28 );
      /* The database size was written into the offset 28 of the header
      ** when the transaction started, so we know that the value at offset
      ** 28 is nonzero. */
      Debug.Assert( pBt.nPage > 0 );
    }
    sqlite3BtreeLeave( p );
  }
  return rc;
}

/*
** Create a new cursor for the BTree whose root is on the page
** iTable. If a read-only cursor is requested, it is assumed that
** the caller already has at least a read-only transaction open
** on the database already. If a write-cursor is requested, then
** the caller is assumed to have an open write transaction.
**
** If wrFlag==null, then the cursor can only be used for reading.
** If wrFlag==1, then the cursor can be used for reading or for
** writing if other conditions for writing are also met.  These
** are the conditions that must be met in order for writing to
** be allowed:
**
** 1:  The cursor must have been opened with wrFlag==1
**
** 2:  Other database connections that share the same pager cache
**     but which are not in the READ_UNCOMMITTED state may not have
**     cursors open with wrFlag==null on the same table.  Otherwise
**     the changes made by this write cursor would be visible to
**     the read cursors in the other database connection.
**
** 3:  The database must be writable (not on read-only media)
**
** 4:  There must be an active transaction.
**
** No checking is done to make sure that page iTable really is the
** root page of a b-tree.  If it is not, then the cursor acquired
** will not work correctly.
**
** It is assumed that the sqlite3BtreeCursorZero() has been called
** on pCur to initialize the memory space prior to invoking this routine.
*/
static int btreeCursor(
Btree p,                              /* The btree */
int iTable,                           /* Root page of table to open */
int wrFlag,                           /* 1 to write. 0 read-only */
KeyInfo pKeyInfo,                     /* First arg to comparison function */
BtCursor pCur                         /* Space for new cursor */
)
{
  BtShared pBt = p.pBt;                 /* Shared b-tree handle */

  Debug.Assert( sqlite3BtreeHoldsMutex( p ) );
  Debug.Assert( wrFlag == 0 || wrFlag == 1 );

  /* The following Debug.Assert statements verify that if this is a sharable
  ** b-tree database, the connection is holding the required table locks,
  ** and that no other connection has any open cursor that conflicts with
  ** this lock.  */
  Debug.Assert( hasSharedCacheTableLock( p, (u32)iTable, pKeyInfo != null ? 1 : 0, wrFlag + 1 ) );
  Debug.Assert( wrFlag == 0 || !hasReadConflicts( p, (u32)iTable ) );

  /* Assert that the caller has opened the required transaction. */
  Debug.Assert( p.inTrans > TRANS_NONE );
  Debug.Assert( wrFlag == 0 || p.inTrans == TRANS_WRITE );
  Debug.Assert( pBt.pPage1 != null && pBt.pPage1.aData != null );

  if ( NEVER( wrFlag != 0 && pBt.readOnly ) )
  {
    return SQLITE_READONLY;
  }
  if ( iTable == 1 && btreePagecount( pBt ) == 0 )
  {
    return SQLITE_EMPTY;
  }

  /* Now that no other errors can occur, finish filling in the BtCursor
  ** variables and link the cursor into the BtShared list.  */
  pCur.pgnoRoot = (Pgno)iTable;
  pCur.iPage = -1;
  pCur.pKeyInfo = pKeyInfo;
  pCur.pBtree = p;
  pCur.pBt = pBt;
  pCur.wrFlag = (u8)wrFlag;
  pCur.pNext = pBt.pCursor;
  if ( pCur.pNext != null )
  {
    pCur.pNext.pPrev = pCur;
  }
  pBt.pCursor = pCur;
  pCur.eState = CURSOR_INVALID;
  pCur.cachedRowid = 0;
  return SQLITE_OK;
}
static int sqlite3BtreeCursor(
Btree p,                                   /* The btree */
int iTable,                                /* Root page of table to open */
int wrFlag,                                /* 1 to write. 0 read-only */
KeyInfo pKeyInfo,                          /* First arg to xCompare() */
BtCursor pCur                              /* Write new cursor here */
)
{
  int rc;
  sqlite3BtreeEnter( p );
  rc = btreeCursor( p, iTable, wrFlag, pKeyInfo, pCur );
  sqlite3BtreeLeave( p );
  return rc;
}

/*
** Return the size of a BtCursor object in bytes.
**
** This interfaces is needed so that users of cursors can preallocate
** sufficient storage to hold a cursor.  The BtCursor object is opaque
** to users so they cannot do the sizeof() themselves - they must call
** this routine.
*/
static int sqlite3BtreeCursorSize()
{
  return -1; // Not Used --  return ROUND8(sizeof(BtCursor));
}

/*
** Initialize memory that will be converted into a BtCursor object.
**
** The simple approach here would be to memset() the entire object
** to zero.  But it turns out that the apPage[] and aiIdx[] arrays
** do not need to be zeroed and they are large, so we can save a lot
** of run-time by skipping the initialization of those elements.
*/
static void sqlite3BtreeCursorZero( BtCursor p )
{
  p.Clear(); // memset( p, 0, offsetof( BtCursor, iPage ) );
}

/*
** Set the cached rowid value of every cursor in the same database file
** as pCur and having the same root page number as pCur.  The value is
** set to iRowid.
**
** Only positive rowid values are considered valid for this cache.
** The cache is initialized to zero, indicating an invalid cache.
** A btree will work fine with zero or negative rowids.  We just cannot
** cache zero or negative rowids, which means tables that use zero or
** negative rowids might run a little slower.  But in practice, zero
** or negative rowids are very uncommon so this should not be a problem.
*/
static void sqlite3BtreeSetCachedRowid( BtCursor pCur, sqlite3_int64 iRowid )
{
  BtCursor p;
  for ( p = pCur.pBt.pCursor; p != null; p = p.pNext )
  {
    if ( p.pgnoRoot == pCur.pgnoRoot )
      p.cachedRowid = iRowid;
  }
  Debug.Assert( pCur.cachedRowid == iRowid );
}

/*
** Return the cached rowid for the given cursor.  A negative or zero
** return value indicates that the rowid cache is invalid and should be
** ignored.  If the rowid cache has never before been set, then a
** zero is returned.
*/
static sqlite3_int64 sqlite3BtreeGetCachedRowid( BtCursor pCur )
{
  return pCur.cachedRowid;
}

/*
** Close a cursor.  The read lock on the database file is released
** when the last cursor is closed.
*/
static int sqlite3BtreeCloseCursor( BtCursor pCur )
{
  Btree pBtree = pCur.pBtree;
  if ( pBtree != null )
  {
    int i;
    BtShared pBt = pCur.pBt;
    sqlite3BtreeEnter( pBtree );
    sqlite3BtreeClearCursor( pCur );
    if ( pCur.pPrev != null )
    {
      pCur.pPrev.pNext = pCur.pNext;
    }
    else
    {
      pBt.pCursor = pCur.pNext;
    }
    if ( pCur.pNext != null )
    {
      pCur.pNext.pPrev = pCur.pPrev;
    }
    for ( i = 0; i <= pCur.iPage; i++ )
    {
      releasePage( pCur.apPage[i] );
    }
    unlockBtreeIfUnused( pBt );
    invalidateOverflowCache( pCur );
    /* sqlite3_free(ref pCur); */
    sqlite3BtreeLeave( pBtree );
  }
  return SQLITE_OK;
}

/*
** Make sure the BtCursor* given in the argument has a valid
** BtCursor.info structure.  If it is not already valid, call
** btreeParseCell() to fill it in.
**
** BtCursor.info is a cache of the information in the current cell.
** Using this cache reduces the number of calls to btreeParseCell().
**
** 2007-06-25:  There is a bug in some versions of MSVC that cause the
** compiler to crash when getCellInfo() is implemented as a macro.
** But there is a measureable speed advantage to using the macro on gcc
** (when less compiler optimizations like -Os or -O0 are used and the
** compiler is not doing agressive inlining.)  So we use a real function
** for MSVC and a macro for everything else.  Ticket #2457.
*/
#if !NDEBUG
static void assertCellInfo( BtCursor pCur )
{
  CellInfo info;
  int iPage = pCur.iPage;
  info = new CellInfo();//memset(info, 0, sizeof(info));
  btreeParseCell( pCur.apPage[iPage], pCur.aiIdx[iPage], ref info );
  Debug.Assert( info.GetHashCode() == pCur.info.GetHashCode() || info.Equals( pCur.info ) );//memcmp(info, pCur.info, sizeof(info))==0 );
}
#else
//  #define assertCellInfo(x)
static void assertCellInfo(BtCursor pCur) { }
#endif
#if _MSC_VER
/* Use a real function in MSVC to work around bugs in that compiler. */
static void getCellInfo( BtCursor pCur )
{
  if ( pCur.info.nSize == 0 )
  {
    int iPage = pCur.iPage;
    btreeParseCell( pCur.apPage[iPage], pCur.aiIdx[iPage], ref pCur.info );
    pCur.validNKey = true;
  }
  else
  {
    assertCellInfo( pCur );
  }
}
#else //* if not _MSC_VER */
/* Use a macro in all other compilers so that the function is inlined */
//#define getCellInfo(pCur)                                                      \
//  if( pCur.info.nSize==null ){                                                   \
//    int iPage = pCur.iPage;                                                   \
//    btreeParseCell(pCur.apPage[iPage],pCur.aiIdx[iPage],&pCur.info); \
//    pCur.validNKey = true;                                                       \
//  }else{                                                                       \
//    assertCellInfo(pCur);                                                      \
//  }
#endif //* _MSC_VER */

#if !NDEBUG  //* The next routine used only within Debug.Assert() statements */
/*
** Return true if the given BtCursor is valid.  A valid cursor is one
** that is currently pointing to a row in a (non-empty) table.
** This is a verification routine is used only within Debug.Assert() statements.
*/
static bool sqlite3BtreeCursorIsValid( BtCursor pCur )
{
  return pCur != null && pCur.eState == CURSOR_VALID;
}
#else
static bool sqlite3BtreeCursorIsValid(BtCursor pCur) { return true; }
#endif //* NDEBUG */

/*
** Set pSize to the size of the buffer needed to hold the value of
** the key for the current entry.  If the cursor is not pointing
** to a valid entry, pSize is set to 0.
**
** For a table with the INTKEY flag set, this routine returns the key
** itself, not the number of bytes in the key.
**
** The caller must position the cursor prior to invoking this routine.
**
** This routine cannot fail.  It always returns SQLITE_OK.
*/
static int sqlite3BtreeKeySize( BtCursor pCur, ref i64 pSize )
{
  Debug.Assert( cursorHoldsMutex( pCur ) );
  Debug.Assert( pCur.eState == CURSOR_INVALID || pCur.eState == CURSOR_VALID );
  if ( pCur.eState != CURSOR_VALID )
  {
    pSize = 0;
  }
  else
  {
    getCellInfo( pCur );
    pSize = pCur.info.nKey;
  }
  return SQLITE_OK;
}

/*
** Set pSize to the number of bytes of data in the entry the
** cursor currently points to.
**
** The caller must guarantee that the cursor is pointing to a non-NULL
** valid entry.  In other words, the calling procedure must guarantee
** that the cursor has Cursor.eState==CURSOR_VALID.
**
** Failure is not possible.  This function always returns SQLITE_OK.
** It might just as well be a procedure (returning void) but we continue
** to return an integer result code for historical reasons.
*/
static int sqlite3BtreeDataSize( BtCursor pCur, ref u32 pSize )
{
  Debug.Assert( cursorHoldsMutex( pCur ) );
  Debug.Assert( pCur.eState == CURSOR_VALID );
  getCellInfo( pCur );
  pSize = pCur.info.nData;
  return SQLITE_OK;
}

/*
** Given the page number of an overflow page in the database (parameter
** ovfl), this function finds the page number of the next page in the
** linked list of overflow pages. If possible, it uses the auto-vacuum
** pointer-map data instead of reading the content of page ovfl to do so.
**
** If an error occurs an SQLite error code is returned. Otherwise:
**
** The page number of the next overflow page in the linked list is
** written to pPgnoNext. If page ovfl is the last page in its linked
** list, pPgnoNext is set to zero.
**
** If ppPage is not NULL, and a reference to the MemPage object corresponding
** to page number pOvfl was obtained, then ppPage is set to point to that
** reference. It is the responsibility of the caller to call releasePage()
** on ppPage to free the reference. In no reference was obtained (because
** the pointer-map was used to obtain the value for pPgnoNext), then
** ppPage is set to zero.
*/
static int getOverflowPage(
BtShared pBt,               /* The database file */
Pgno ovfl,                  /* Current overflow page number */
out MemPage ppPage,         /* OUT: MemPage handle (may be NULL) */
out Pgno pPgnoNext          /* OUT: Next overflow page number */
)
{
  Pgno next = 0;
  MemPage pPage = null;
  ppPage = null;
  int rc = SQLITE_OK;

  Debug.Assert( sqlite3_mutex_held( pBt.mutex ) );
  // Debug.Assert( pPgnoNext);

#if !SQLITE_OMIT_AUTOVACUUM
  /* Try to find the next page in the overflow list using the
** autovacuum pointer-map pages. Guess that the next page in
** the overflow list is page number (ovfl+1). If that guess turns
** out to be wrong, fall back to loading the data of page
** number ovfl to determine the next page number.
*/
  if ( pBt.autoVacuum )
  {
    Pgno pgno = 0;
    Pgno iGuess = ovfl + 1;
    u8 eType = 0;

    while ( PTRMAP_ISPAGE( pBt, iGuess ) || iGuess == PENDING_BYTE_PAGE( pBt ) )
    {
      iGuess++;
    }

    if ( iGuess <= btreePagecount( pBt ) )
    {
      rc = ptrmapGet( pBt, iGuess, ref eType, ref pgno );
      if ( rc == SQLITE_OK && eType == PTRMAP_OVERFLOW2 && pgno == ovfl )
      {
        next = iGuess;
        rc = SQLITE_DONE;
      }
    }
  }
#endif

  Debug.Assert( next == 0 || rc == SQLITE_DONE );
  if ( rc == SQLITE_OK )
  {
    rc = btreeGetPage( pBt, ovfl, ref pPage, 0 );
    Debug.Assert( rc == SQLITE_OK || pPage == null );
    if ( rc == SQLITE_OK )
    {
      next = sqlite3Get4byte( pPage.aData );
    }
  }

  pPgnoNext = next;
  if ( ppPage != null )
  {
    ppPage = pPage;
  }
  else
  {
    releasePage( pPage );
  }
  return ( rc == SQLITE_DONE ? SQLITE_OK : rc );
}

/*
** Copy data from a buffer to a page, or from a page to a buffer.
**
** pPayload is a pointer to data stored on database page pDbPage.
** If argument eOp is false, then nByte bytes of data are copied
** from pPayload to the buffer pointed at by pBuf. If eOp is true,
** then sqlite3PagerWrite() is called on pDbPage and nByte bytes
** of data are copied from the buffer pBuf to pPayload.
**
** SQLITE_OK is returned on success, otherwise an error code.
*/
static int copyPayload(
byte[] pPayload,           /* Pointer to page data */
u32 payloadOffset,         /* Offset into page data */
byte[] pBuf,               /* Pointer to buffer */
u32 pBufOffset,            /* Offset into buffer */
u32 nByte,                 /* Number of bytes to copy */
int eOp,                   /* 0 . copy from page, 1 . copy to page */
DbPage pDbPage             /* Page containing pPayload */
)
{
  if ( eOp != 0 )
  {
    /* Copy data from buffer to page (a write operation) */
    int rc = sqlite3PagerWrite( pDbPage );
    if ( rc != SQLITE_OK )
    {
      return rc;
    }
    Buffer.BlockCopy( pBuf, (int)pBufOffset, pPayload, (int)payloadOffset, (int)nByte );// memcpy( pPayload, pBuf, nByte );
  }
  else
  {
    /* Copy data from page to buffer (a read operation) */
    Buffer.BlockCopy( pPayload, (int)payloadOffset, pBuf, (int)pBufOffset, (int)nByte );//memcpy(pBuf, pPayload, nByte);
  }
  return SQLITE_OK;
}
//static int copyPayload(
//  byte[] pPayload,           /* Pointer to page data */
//  byte[] pBuf,               /* Pointer to buffer */
//  int nByte,                 /* Number of bytes to copy */
//  int eOp,                   /* 0 -> copy from page, 1 -> copy to page */
//  DbPage pDbPage             /* Page containing pPayload */
//){
//  if( eOp!=0 ){
//    /* Copy data from buffer to page (a write operation) */
//    int rc = sqlite3PagerWrite(pDbPage);
//    if( rc!=SQLITE_OK ){
//      return rc;
//    }
//    memcpy(pPayload, pBuf, nByte);
//  }else{
//    /* Copy data from page to buffer (a read operation) */
//    memcpy(pBuf, pPayload, nByte);
//  }
//  return SQLITE_OK;
//}

/*
** This function is used to read or overwrite payload information
** for the entry that the pCur cursor is pointing to. If the eOp
** parameter is 0, this is a read operation (data copied into
** buffer pBuf). If it is non-zero, a write (data copied from
** buffer pBuf).
**
** A total of "amt" bytes are read or written beginning at "offset".
** Data is read to or from the buffer pBuf.
**
** The content being read or written might appear on the main page
** or be scattered out on multiple overflow pages.
**
** If the BtCursor.isIncrblobHandle flag is set, and the current
** cursor entry uses one or more overflow pages, this function
** allocates space for and lazily popluates the overflow page-list
** cache array (BtCursor.aOverflow). Subsequent calls use this
** cache to make seeking to the supplied offset more efficient.
**
** Once an overflow page-list cache has been allocated, it may be
** invalidated if some other cursor writes to the same table, or if
** the cursor is moved to a different row. Additionally, in auto-vacuum
** mode, the following events may invalidate an overflow page-list cache.
**
**   * An incremental vacuum,
**   * A commit in auto_vacuum="full" mode,
**   * Creating a table (may require moving an overflow page).
*/
static int accessPayload(
BtCursor pCur,      /* Cursor pointing to entry to read from */
u32 offset,         /* Begin reading this far into payload */
u32 amt,            /* Read this many bytes */
byte[] pBuf,        /* Write the bytes into this buffer */
int eOp             /* zero to read. non-zero to write. */
)
{
  u32 pBufOffset = 0;
  byte[] aPayload;
  int rc = SQLITE_OK;
  u32 nKey;
  int iIdx = 0;
  MemPage pPage = pCur.apPage[pCur.iPage]; /* Btree page of current entry */
  BtShared pBt = pCur.pBt;                  /* Btree this cursor belongs to */

  Debug.Assert( pPage != null );
  Debug.Assert( pCur.eState == CURSOR_VALID );
  Debug.Assert( pCur.aiIdx[pCur.iPage] < pPage.nCell );
  Debug.Assert( cursorHoldsMutex( pCur ) );

  getCellInfo( pCur );
  aPayload = pCur.info.pCell; //pCur.info.pCell + pCur.info.nHeader;
  nKey = (u32)( pPage.intKey != 0 ? 0 : (int)pCur.info.nKey );

  if ( NEVER( offset + amt > nKey + pCur.info.nData )
  || pCur.info.nLocal > pBt.usableSize//&aPayload[pCur.info.nLocal] > &pPage.aData[pBt.usableSize]
  )
  {
    /* Trying to read or write past the end of the data is an error */
    return SQLITE_CORRUPT_BKPT();
  }

  /* Check if data must be read/written to/from the btree page itself. */
  if ( offset < pCur.info.nLocal )
  {
    int a = (int)amt;
    if ( a + offset > pCur.info.nLocal )
    {
      a = (int)( pCur.info.nLocal - offset );
    }
    rc = copyPayload( aPayload, (u32)( offset + pCur.info.iCell + pCur.info.nHeader ), pBuf, pBufOffset, (u32)a, eOp, pPage.pDbPage );
    offset = 0;
    pBufOffset += (u32)a; //pBuf += a;
    amt -= (u32)a;
  }
  else
  {
    offset -= pCur.info.nLocal;
  }

  if ( rc == SQLITE_OK && amt > 0 )
  {
    u32 ovflSize = (u32)( pBt.usableSize - 4 );  /* Bytes content per ovfl page */
    Pgno nextPage;

    nextPage = sqlite3Get4byte( aPayload, pCur.info.nLocal + pCur.info.iCell + pCur.info.nHeader );

#if !SQLITE_OMIT_INCRBLOB
/* If the isIncrblobHandle flag is set and the BtCursor.aOverflow[]
** has not been allocated, allocate it now. The array is sized at
** one entry for each overflow page in the overflow chain. The
** page number of the first overflow page is stored in aOverflow[0],
** etc. A value of 0 in the aOverflow[] array means "not yet known"
** (the cache is lazily populated).
*/
if( pCur.isIncrblobHandle && !pCur.aOverflow ){
int nOvfl = (pCur.info.nPayload-pCur.info.nLocal+ovflSize-1)/ovflSize;
pCur.aOverflow = (Pgno *)sqlite3MallocZero(sizeof(Pgno)*nOvfl);
/* nOvfl is always positive.  If it were zero, fetchPayload would have
** been used instead of this routine. */
if( ALWAYS(nOvfl) && !pCur.aOverflow ){
rc = SQLITE_NOMEM;
}
}

/* If the overflow page-list cache has been allocated and the
** entry for the first required overflow page is valid, skip
** directly to it.
*/
if( pCur.aOverflow && pCur.aOverflow[offset/ovflSize] ){
iIdx = (offset/ovflSize);
nextPage = pCur.aOverflow[iIdx];
offset = (offset%ovflSize);
}
#endif

    for ( ; rc == SQLITE_OK && amt > 0 && nextPage != 0; iIdx++ )
    {

#if !SQLITE_OMIT_INCRBLOB
/* If required, populate the overflow page-list cache. */
if( pCur.aOverflow ){
Debug.Assert(!pCur.aOverflow[iIdx] || pCur.aOverflow[iIdx]==nextPage);
pCur.aOverflow[iIdx] = nextPage;
}
#endif

      MemPage MemPageDummy = null;
      if ( offset >= ovflSize )
      {
        /* The only reason to read this page is to obtain the page
        ** number for the next page in the overflow chain. The page
        ** data is not required. So first try to lookup the overflow
        ** page-list cache, if any, then fall back to the getOverflowPage()
        ** function.
        */
#if !SQLITE_OMIT_INCRBLOB
if( pCur.aOverflow && pCur.aOverflow[iIdx+1] ){
nextPage = pCur.aOverflow[iIdx+1];
} else
#endif
        rc = getOverflowPage( pBt, nextPage, out MemPageDummy, out nextPage );
        offset -= ovflSize;
      }
      else
      {
        /* Need to read this page properly. It contains some of the
        ** range of data that is being read (eOp==null) or written (eOp!=null).
        */
        PgHdr pDbPage = new PgHdr();
        int a = (int)amt;
        rc = sqlite3PagerGet( pBt.pPager, nextPage, ref pDbPage );
        if ( rc == SQLITE_OK )
        {
          aPayload = sqlite3PagerGetData( pDbPage );
          nextPage = sqlite3Get4byte( aPayload );
          if ( a + offset > ovflSize )
          {
            a = (int)( ovflSize - offset );
          }
          rc = copyPayload( aPayload, offset + 4, pBuf, pBufOffset, (u32)a, eOp, pDbPage );
          sqlite3PagerUnref( pDbPage );
          offset = 0;
          amt -= (u32)a;
          pBufOffset += (u32)a;//pBuf += a;
        }
      }
    }
  }

  if ( rc == SQLITE_OK && amt > 0 )
  {
    return SQLITE_CORRUPT_BKPT();
  }
  return rc;
}

/*
** Read part of the key associated with cursor pCur.  Exactly
** "amt" bytes will be transfered into pBuf[].  The transfer
** begins at "offset".
**
** The caller must ensure that pCur is pointing to a valid row
** in the table.
**
** Return SQLITE_OK on success or an error code if anything goes
** wrong.  An error is returned if "offset+amt" is larger than
** the available payload.
*/
static int sqlite3BtreeKey( BtCursor pCur, u32 offset, u32 amt, byte[] pBuf )
{
  Debug.Assert( cursorHoldsMutex( pCur ) );
  Debug.Assert( pCur.eState == CURSOR_VALID );
  Debug.Assert( pCur.iPage >= 0 && pCur.apPage[pCur.iPage] != null );
  Debug.Assert( pCur.aiIdx[pCur.iPage] < pCur.apPage[pCur.iPage].nCell );
  return accessPayload( pCur, offset, amt, pBuf, 0 );
}

/*
** Read part of the data associated with cursor pCur.  Exactly
** "amt" bytes will be transfered into pBuf[].  The transfer
** begins at "offset".
**
** Return SQLITE_OK on success or an error code if anything goes
** wrong.  An error is returned if "offset+amt" is larger than
** the available payload.
*/
static int sqlite3BtreeData( BtCursor pCur, u32 offset, u32 amt, byte[] pBuf )
{
  int rc;

#if !SQLITE_OMIT_INCRBLOB
if ( pCur.eState==CURSOR_INVALID ){
return SQLITE_ABORT;
}
#endif

  Debug.Assert( cursorHoldsMutex( pCur ) );
  rc = restoreCursorPosition( pCur );
  if ( rc == SQLITE_OK )
  {
    Debug.Assert( pCur.eState == CURSOR_VALID );
    Debug.Assert( pCur.iPage >= 0 && pCur.apPage[pCur.iPage] != null );
    Debug.Assert( pCur.aiIdx[pCur.iPage] < pCur.apPage[pCur.iPage].nCell );
    rc = accessPayload( pCur, offset, amt, pBuf, 0 );
  }
  return rc;
}

/*
** Return a pointer to payload information from the entry that the
** pCur cursor is pointing to.  The pointer is to the beginning of
** the key if skipKey==null and it points to the beginning of data if
** skipKey==1.  The number of bytes of available key/data is written
** into pAmt.  If pAmt==null, then the value returned will not be
** a valid pointer.
**
** This routine is an optimization.  It is common for the entire key
** and data to fit on the local page and for there to be no overflow
** pages.  When that is so, this routine can be used to access the
** key and data without making a copy.  If the key and/or data spills
** onto overflow pages, then accessPayload() must be used to reassemble
** the key/data and copy it into a preallocated buffer.
**
** The pointer returned by this routine looks directly into the cached
** page of the database.  The data might change or move the next time
** any btree routine is called.
*/
static byte[] fetchPayload(
BtCursor pCur,   /* Cursor pointing to entry to read from */
ref int pAmt,    /* Write the number of available bytes here */
ref int outOffset, /* Offset into Buffer */
bool skipKey    /* read beginning at data if this is true */
)
{
  byte[] aPayload;
  MemPage pPage;
  u32 nKey;
  u32 nLocal;

  Debug.Assert( pCur != null && pCur.iPage >= 0 && pCur.apPage[pCur.iPage] != null );
  Debug.Assert( pCur.eState == CURSOR_VALID );
  Debug.Assert( cursorHoldsMutex( pCur ) );
  outOffset = -1;
  pPage = pCur.apPage[pCur.iPage];
  Debug.Assert( pCur.aiIdx[pCur.iPage] < pPage.nCell );
  if ( NEVER( pCur.info.nSize == 0 ) )
  {
    btreeParseCell( pCur.apPage[pCur.iPage], pCur.aiIdx[pCur.iPage],
    ref pCur.info );
  }
  //aPayload = pCur.info.pCell;
  //aPayload += pCur.info.nHeader;
  aPayload = sqlite3Malloc( pCur.info.nSize - pCur.info.nHeader );
  if ( pPage.intKey != 0 )
  {
    nKey = 0;
  }
  else
  {
    nKey = (u32)pCur.info.nKey;
  }
  if ( skipKey )
  {
    //aPayload += nKey;
    outOffset = (int)( pCur.info.iCell + pCur.info.nHeader + nKey );
    Buffer.BlockCopy( pCur.info.pCell, outOffset, aPayload, 0, (int)( pCur.info.nSize - pCur.info.nHeader - nKey ) );
    nLocal = pCur.info.nLocal - nKey;
  }
  else
  {
    outOffset = (int)( pCur.info.iCell + pCur.info.nHeader );
    Buffer.BlockCopy( pCur.info.pCell, outOffset, aPayload, 0, pCur.info.nSize - pCur.info.nHeader );
    nLocal = pCur.info.nLocal;
    Debug.Assert( nLocal <= nKey );
  }
  pAmt = (int)nLocal;
  return aPayload;
}

/*
** For the entry that cursor pCur is point to, return as
** many bytes of the key or data as are available on the local
** b-tree page.  Write the number of available bytes into pAmt.
**
** The pointer returned is ephemeral.  The key/data may move
** or be destroyed on the next call to any Btree routine,
** including calls from other threads against the same cache.
** Hence, a mutex on the BtShared should be held prior to calling
** this routine.
**
** These routines is used to get quick access to key and data
** in the common case where no overflow pages are used.
*/
static byte[] sqlite3BtreeKeyFetch( BtCursor pCur, ref int pAmt, ref int outOffset )
{
  byte[] p = null;
  Debug.Assert( sqlite3_mutex_held( pCur.pBtree.db.mutex ) );
  Debug.Assert( cursorHoldsMutex( pCur ) );
  if ( ALWAYS( pCur.eState == CURSOR_VALID ) )
  {
    p = fetchPayload( pCur, ref pAmt, ref outOffset, false );
  }
  return p;
}
static byte[] sqlite3BtreeDataFetch( BtCursor pCur, ref int pAmt, ref int outOffset )
{
  byte[] p = null;
  Debug.Assert( sqlite3_mutex_held( pCur.pBtree.db.mutex ) );
  Debug.Assert( cursorHoldsMutex( pCur ) );
  if ( ALWAYS( pCur.eState == CURSOR_VALID ) )
  {
    p = fetchPayload( pCur, ref pAmt, ref outOffset, true );
  }
  return p;
}

/*
** Move the cursor down to a new child page.  The newPgno argument is the
** page number of the child page to move to.
**
** This function returns SQLITE_CORRUPT if the page-header flags field of
** the new child page does not match the flags field of the parent (i.e.
** if an intkey page appears to be the parent of a non-intkey page, or
** vice-versa).
*/
static int moveToChild( BtCursor pCur, u32 newPgno )
{
  int rc;
  int i = pCur.iPage;
  MemPage pNewPage = new MemPage();
  BtShared pBt = pCur.pBt;

  Debug.Assert( cursorHoldsMutex( pCur ) );
  Debug.Assert( pCur.eState == CURSOR_VALID );
  Debug.Assert( pCur.iPage < BTCURSOR_MAX_DEPTH );
  if ( pCur.iPage >= ( BTCURSOR_MAX_DEPTH - 1 ) )
  {
    return SQLITE_CORRUPT_BKPT();
  }
  rc = getAndInitPage( pBt, newPgno, ref pNewPage );
  if ( rc != 0 )
    return rc;
  pCur.apPage[i + 1] = pNewPage;
  pCur.aiIdx[i + 1] = 0;
  pCur.iPage++;

  pCur.info.nSize = 0;
  pCur.validNKey = false;
  if ( pNewPage.nCell < 1 || pNewPage.intKey != pCur.apPage[i].intKey )
  {
    return SQLITE_CORRUPT_BKPT();
  }
  return SQLITE_OK;
}

#if !NDEBUG
/*
** Page pParent is an internal (non-leaf) tree page. This function
** asserts that page number iChild is the left-child if the iIdx'th
** cell in page pParent. Or, if iIdx is equal to the total number of
** cells in pParent, that page number iChild is the right-child of
** the page.
*/
static void assertParentIndex( MemPage pParent, int iIdx, Pgno iChild )
{
  Debug.Assert( iIdx <= pParent.nCell );
  if ( iIdx == pParent.nCell )
  {
    Debug.Assert( sqlite3Get4byte( pParent.aData, pParent.hdrOffset + 8 ) == iChild );
  }
  else
  {
    Debug.Assert( sqlite3Get4byte( pParent.aData, findCell( pParent, iIdx ) ) == iChild );
  }
}
#else
//#  define assertParentIndex(x,y,z)
static void assertParentIndex(MemPage pParent, int iIdx, Pgno iChild) { }
#endif

/*
** Move the cursor up to the parent page.
**
** pCur.idx is set to the cell index that contains the pointer
** to the page we are coming from.  If we are coming from the
** right-most child page then pCur.idx is set to one more than
** the largest cell index.
*/
static void moveToParent( BtCursor pCur )
{
  Debug.Assert( cursorHoldsMutex( pCur ) );
  Debug.Assert( pCur.eState == CURSOR_VALID );
  Debug.Assert( pCur.iPage > 0 );
  Debug.Assert( pCur.apPage[pCur.iPage] != null );
  assertParentIndex(
  pCur.apPage[pCur.iPage - 1],
  pCur.aiIdx[pCur.iPage - 1],
  pCur.apPage[pCur.iPage].pgno
  );
  releasePage( pCur.apPage[pCur.iPage] );
  pCur.iPage--;
  pCur.info.nSize = 0;
  pCur.validNKey = false;
}

/*
** Move the cursor to point to the root page of its b-tree structure.
**
** If the table has a virtual root page, then the cursor is moved to point
** to the virtual root page instead of the actual root page. A table has a
** virtual root page when the actual root page contains no cells and a
** single child page. This can only happen with the table rooted at page 1.
**
** If the b-tree structure is empty, the cursor state is set to
** CURSOR_INVALID. Otherwise, the cursor is set to point to the first
** cell located on the root (or virtual root) page and the cursor state
** is set to CURSOR_VALID.
**
** If this function returns successfully, it may be assumed that the
** page-header flags indicate that the [virtual] root-page is the expected
** kind of b-tree page (i.e. if when opening the cursor the caller did not
** specify a KeyInfo structure the flags byte is set to 0x05 or 0x0D,
** indicating a table b-tree, or if the caller did specify a KeyInfo
** structure the flags byte is set to 0x02 or 0x0A, indicating an index
** b-tree).
*/
static int moveToRoot( BtCursor pCur )
{
  MemPage pRoot;
  int rc = SQLITE_OK;
  Btree p = pCur.pBtree;
  BtShared pBt = p.pBt;

  Debug.Assert( cursorHoldsMutex( pCur ) );
  Debug.Assert( CURSOR_INVALID < CURSOR_REQUIRESEEK );
  Debug.Assert( CURSOR_VALID < CURSOR_REQUIRESEEK );
  Debug.Assert( CURSOR_FAULT > CURSOR_REQUIRESEEK );
  if ( pCur.eState >= CURSOR_REQUIRESEEK )
  {
    if ( pCur.eState == CURSOR_FAULT )
    {
      Debug.Assert( pCur.skipNext != SQLITE_OK );
      return pCur.skipNext;
    }
    sqlite3BtreeClearCursor( pCur );
  }

  if ( pCur.iPage >= 0 )
  {
    int i;
    for ( i = 1; i <= pCur.iPage; i++ )
    {
      releasePage( pCur.apPage[i] );
    }
    pCur.iPage = 0;
  }
  else
  {
    rc = getAndInitPage( pBt, pCur.pgnoRoot, ref pCur.apPage[0] );
    if ( rc != SQLITE_OK )
    {
      pCur.eState = CURSOR_INVALID;
      return rc;
    }
    pCur.iPage = 0;

    /* If pCur.pKeyInfo is not NULL, then the caller that opened this cursor
    ** expected to open it on an index b-tree. Otherwise, if pKeyInfo is
    ** NULL, the caller expects a table b-tree. If this is not the case,
    ** return an SQLITE_CORRUPT error.  */
    Debug.Assert( pCur.apPage[0].intKey == 1 || pCur.apPage[0].intKey == 0 );
    if ( ( pCur.pKeyInfo == null ) != ( pCur.apPage[0].intKey != 0 ) )
    {
      return SQLITE_CORRUPT_BKPT();
    }
  }

  /* Assert that the root page is of the correct type. This must be the
  ** case as the call to this function that loaded the root-page (either
  ** this call or a previous invocation) would have detected corruption
  ** if the assumption were not true, and it is not possible for the flags
  ** byte to have been modified while this cursor is holding a reference
  ** to the page.  */
  pRoot = pCur.apPage[0];
  Debug.Assert( pRoot.pgno == pCur.pgnoRoot );
  Debug.Assert( pRoot.isInit != 0 && ( pCur.pKeyInfo == null ) == ( pRoot.intKey != 0 ) );

  pCur.aiIdx[0] = 0;
  pCur.info.nSize = 0;
  pCur.atLast = 0;
  pCur.validNKey = false;

  if ( pRoot.nCell == 0 && 0 == pRoot.leaf )
  {
    Pgno subpage;
    if ( pRoot.pgno != 1 )
      return SQLITE_CORRUPT_BKPT();
    subpage = sqlite3Get4byte( pRoot.aData, pRoot.hdrOffset + 8 );
    pCur.eState = CURSOR_VALID;
    rc = moveToChild( pCur, subpage );
  }
  else
  {
    pCur.eState = ( ( pRoot.nCell > 0 ) ? CURSOR_VALID : CURSOR_INVALID );
  }
  return rc;
}

/*
** Move the cursor down to the left-most leaf entry beneath the
** entry to which it is currently pointing.
**
** The left-most leaf is the one with the smallest key - the first
** in ascending order.
*/
static int moveToLeftmost( BtCursor pCur )
{
  Pgno pgno;
  int rc = SQLITE_OK;
  MemPage pPage;

  Debug.Assert( cursorHoldsMutex( pCur ) );
  Debug.Assert( pCur.eState == CURSOR_VALID );
  while ( rc == SQLITE_OK && 0 == ( pPage = pCur.apPage[pCur.iPage] ).leaf )
  {
    Debug.Assert( pCur.aiIdx[pCur.iPage] < pPage.nCell );
    pgno = sqlite3Get4byte( pPage.aData, findCell( pPage, pCur.aiIdx[pCur.iPage] ) );
    rc = moveToChild( pCur, pgno );
  }
  return rc;
}

/*
** Move the cursor down to the right-most leaf entry beneath the
** page to which it is currently pointing.  Notice the difference
** between moveToLeftmost() and moveToRightmost().  moveToLeftmost()
** finds the left-most entry beneath the *entry* whereas moveToRightmost()
** finds the right-most entry beneath the page*.
**
** The right-most entry is the one with the largest key - the last
** key in ascending order.
*/
static int moveToRightmost( BtCursor pCur )
{
  Pgno pgno;
  int rc = SQLITE_OK;
  MemPage pPage = null;

  Debug.Assert( cursorHoldsMutex( pCur ) );
  Debug.Assert( pCur.eState == CURSOR_VALID );
  while ( rc == SQLITE_OK && 0 == ( pPage = pCur.apPage[pCur.iPage] ).leaf )
  {
    pgno = sqlite3Get4byte( pPage.aData, pPage.hdrOffset + 8 );
    pCur.aiIdx[pCur.iPage] = pPage.nCell;
    rc = moveToChild( pCur, pgno );
  }
  if ( rc == SQLITE_OK )
  {
    pCur.aiIdx[pCur.iPage] = (u16)( pPage.nCell - 1 );
    pCur.info.nSize = 0;
    pCur.validNKey = false;
  }
  return rc;
}

/* Move the cursor to the first entry in the table.  Return SQLITE_OK
** on success.  Set pRes to 0 if the cursor actually points to something
** or set pRes to 1 if the table is empty.
*/
static int sqlite3BtreeFirst( BtCursor pCur, ref int pRes )
{
  int rc;

  Debug.Assert( cursorHoldsMutex( pCur ) );
  Debug.Assert( sqlite3_mutex_held( pCur.pBtree.db.mutex ) );
  rc = moveToRoot( pCur );
  if ( rc == SQLITE_OK )
  {
    if ( pCur.eState == CURSOR_INVALID )
    {
      Debug.Assert( pCur.apPage[pCur.iPage].nCell == 0 );
      pRes = 1;
    }
    else
    {
      Debug.Assert( pCur.apPage[pCur.iPage].nCell > 0 );
      pRes = 0;
      rc = moveToLeftmost( pCur );
    }
  }
  return rc;
}

/* Move the cursor to the last entry in the table.  Return SQLITE_OK
** on success.  Set pRes to 0 if the cursor actually points to something
** or set pRes to 1 if the table is empty.
*/
static int sqlite3BtreeLast( BtCursor pCur, ref int pRes )
{
  int rc;

  Debug.Assert( cursorHoldsMutex( pCur ) );
  Debug.Assert( sqlite3_mutex_held( pCur.pBtree.db.mutex ) );

  /* If the cursor already points to the last entry, this is a no-op. */
  if ( CURSOR_VALID == pCur.eState && pCur.atLast != 0 )
  {
#if SQLITE_DEBUG
    /* This block serves to Debug.Assert() that the cursor really does point
** to the last entry in the b-tree. */
    int ii;
    for ( ii = 0; ii < pCur.iPage; ii++ )
    {
      Debug.Assert( pCur.aiIdx[ii] == pCur.apPage[ii].nCell );
    }
    Debug.Assert( pCur.aiIdx[pCur.iPage] == pCur.apPage[pCur.iPage].nCell - 1 );
    Debug.Assert( pCur.apPage[pCur.iPage].leaf != 0 );
#endif
    return SQLITE_OK;
  }

  rc = moveToRoot( pCur );
  if ( rc == SQLITE_OK )
  {
    if ( CURSOR_INVALID == pCur.eState )
    {
      Debug.Assert( pCur.apPage[pCur.iPage].nCell == 0 );
      pRes = 1;
    }
    else
    {
      Debug.Assert( pCur.eState == CURSOR_VALID );
      pRes = 0;
      rc = moveToRightmost( pCur );
      pCur.atLast = (u8)( rc == SQLITE_OK ? 1 : 0 );
    }
  }
  return rc;
}

/* Move the cursor so that it points to an entry near the key
** specified by pIdxKey or intKey.   Return a success code.
**
** For INTKEY tables, the intKey parameter is used.  pIdxKey
** must be NULL.  For index tables, pIdxKey is used and intKey
** is ignored.
**
** If an exact match is not found, then the cursor is always
** left pointing at a leaf page which would hold the entry if it
** were present.  The cursor might point to an entry that comes
** before or after the key.
**
** An integer is written into pRes which is the result of
** comparing the key with the entry to which the cursor is
** pointing.  The meaning of the integer written into
** pRes is as follows:
**
**     pRes<0      The cursor is left pointing at an entry that
**                  is smaller than intKey/pIdxKey or if the table is empty
**                  and the cursor is therefore left point to nothing.
**
**     pRes==null     The cursor is left pointing at an entry that
**                  exactly matches intKey/pIdxKey.
**
**     pRes>0      The cursor is left pointing at an entry that
**                  is larger than intKey/pIdxKey.
**
*/
static int sqlite3BtreeMovetoUnpacked(
BtCursor pCur,           /* The cursor to be moved */
UnpackedRecord pIdxKey,  /* Unpacked index key */
i64 intKey,              /* The table key */
int biasRight,           /* If true, bias the search to the high end */
ref int pRes             /* Write search results here */
)
{
  int rc;

  Debug.Assert( cursorHoldsMutex( pCur ) );
  Debug.Assert( sqlite3_mutex_held( pCur.pBtree.db.mutex ) );
  // Not needed in C# // Debug.Assert( pRes != 0 );
  Debug.Assert( ( pIdxKey == null ) == ( pCur.pKeyInfo == null ) );

  /* If the cursor is already positioned at the point we are trying
  ** to move to, then just return without doing any work */
  if ( pCur.eState == CURSOR_VALID && pCur.validNKey
  && pCur.apPage[0].intKey != 0
  )
  {
    if ( pCur.info.nKey == intKey )
    {
      pRes = 0;
      return SQLITE_OK;
    }
    if ( pCur.atLast != 0 && pCur.info.nKey < intKey )
    {
      pRes = -1;
      return SQLITE_OK;
    }
  }

  rc = moveToRoot( pCur );
  if ( rc != 0 )
  {
    return rc;
  }
  Debug.Assert( pCur.apPage[pCur.iPage] != null );
  Debug.Assert( pCur.apPage[pCur.iPage].isInit != 0 );
  Debug.Assert( pCur.apPage[pCur.iPage].nCell > 0 || pCur.eState == CURSOR_INVALID );
  if ( pCur.eState == CURSOR_INVALID )
  {
    pRes = -1;
    Debug.Assert( pCur.apPage[pCur.iPage].nCell == 0 );
    return SQLITE_OK;
  }
  Debug.Assert( pCur.apPage[0].intKey != 0 || pIdxKey != null );
  for ( ; ; )
  {
    int lwr, upr, idx;
    Pgno chldPg;
    MemPage pPage = pCur.apPage[pCur.iPage];
    int c;

    /* pPage.nCell must be greater than zero. If this is the root-page
    ** the cursor would have been INVALID above and this for(;;) loop
    ** not run. If this is not the root-page, then the moveToChild() routine
    ** would have already detected db corruption. Similarly, pPage must
    ** be the right kind (index or table) of b-tree page. Otherwise
    ** a moveToChild() or moveToRoot() call would have detected corruption.  */
    Debug.Assert( pPage.nCell > 0 );
    Debug.Assert( pPage.intKey == ( ( pIdxKey == null ) ? 1 : 0 ) );
    lwr = 0;
    upr = pPage.nCell - 1;
    if ( biasRight != 0 )
    {
      pCur.aiIdx[pCur.iPage] = (u16)( idx = upr );
    }
    else
    {
      pCur.aiIdx[pCur.iPage] = (u16)( idx = ( upr + lwr ) / 2 );
    }
    for ( ; ; )
    {
      int pCell;                        /* Pointer to current cell in pPage */

      Debug.Assert( idx == pCur.aiIdx[pCur.iPage] );
      pCur.info.nSize = 0;
      pCell = findCell( pPage, idx ) + pPage.childPtrSize;
      if ( pPage.intKey != 0 )
      {
        i64 nCellKey = 0;
        if ( pPage.hasData != 0 )
        {
          u32 Dummy0 = 0;
          pCell += getVarint32( pPage.aData, pCell, out Dummy0 );
        }
        getVarint( pPage.aData, pCell, out nCellKey );
        if ( nCellKey == intKey )
        {
          c = 0;
        }
        else if ( nCellKey < intKey )
        {
          c = -1;
        }
        else
        {
          Debug.Assert( nCellKey > intKey );
          c = +1;
        }
        pCur.validNKey = true;
        pCur.info.nKey = nCellKey;
      }
      else
      {
        /* The maximum supported page-size is 65536 bytes. This means that
        ** the maximum number of record bytes stored on an index B-Tree
        ** page is less than 16384 bytes and may be stored as a 2-byte
        ** varint. This information is used to attempt to avoid parsing
        ** the entire cell by checking for the cases where the record is
        ** stored entirely within the b-tree page by inspecting the first
        ** 2 bytes of the cell.
        */
        int nCell = pPage.aData[pCell + 0]; //pCell[0];
        if ( 0 == ( nCell & 0x80 ) && nCell <= pPage.maxLocal )
        {
          /* This branch runs if the record-size field of the cell is a
          ** single byte varint and the record fits entirely on the main
          ** b-tree page.  */
          c = sqlite3VdbeRecordCompare( nCell, pPage.aData, pCell + 1, pIdxKey ); //c = sqlite3VdbeRecordCompare( nCell, (void*)&pCell[1], pIdxKey );
        }
        else if ( 0 == ( pPage.aData[pCell + 1] & 0x80 )//!(pCell[1] & 0x80)
        && ( nCell = ( ( nCell & 0x7f ) << 7 ) + pPage.aData[pCell + 1] ) <= pPage.maxLocal//pCell[1])<=pPage.maxLocal
        )
        {
          /* The record-size field is a 2 byte varint and the record
          ** fits entirely on the main b-tree page.  */
          c = sqlite3VdbeRecordCompare( nCell, pPage.aData, pCell + 2, pIdxKey ); //c = sqlite3VdbeRecordCompare( nCell, (void*)&pCell[2], pIdxKey );
        }
        else
        {
          /* The record flows over onto one or more overflow pages. In
          ** this case the whole cell needs to be parsed, a buffer allocated
          ** and accessPayload() used to retrieve the record into the
          ** buffer before VdbeRecordCompare() can be called. */
          u8[] pCellKey;
          u8[] pCellBody = new u8[pPage.aData.Length - pCell + pPage.childPtrSize];
          Buffer.BlockCopy( pPage.aData, pCell - pPage.childPtrSize, pCellBody, 0, pCellBody.Length );//          u8 * const pCellBody = pCell - pPage->childPtrSize;
          btreeParseCellPtr( pPage, pCellBody, ref pCur.info );
          nCell = (int)pCur.info.nKey;
          pCellKey = sqlite3Malloc( nCell );
          //if ( pCellKey == null )
          //{
          //  rc = SQLITE_NOMEM;
          //  goto moveto_finish;
          //}
          rc = accessPayload( pCur, 0, (u32)nCell, pCellKey, 0 );
          if ( rc != 0 )
          {
            pCellKey = null;// sqlite3_free(ref pCellKey );
            goto moveto_finish;
          }
          c = sqlite3VdbeRecordCompare( nCell, pCellKey, pIdxKey );
          pCellKey = null;// sqlite3_free(ref pCellKey );
        }
      }
      if ( c == 0 )
      {
        if ( pPage.intKey != 0 && 0 == pPage.leaf )
        {
          lwr = idx;
          upr = lwr - 1;
          break;
        }
        else
        {
          pRes = 0;
          rc = SQLITE_OK;
          goto moveto_finish;
        }
      }
      if ( c < 0 )
      {
        lwr = idx + 1;
      }
      else
      {
        upr = idx - 1;
      }
      if ( lwr > upr )
      {
        break;
      }
      pCur.aiIdx[pCur.iPage] = (u16)( idx = ( lwr + upr ) / 2 );
    }
    Debug.Assert( lwr == upr + 1 );
    Debug.Assert( pPage.isInit != 0 );
    if ( pPage.leaf != 0 )
    {
      chldPg = 0;
    }
    else if ( lwr >= pPage.nCell )
    {
      chldPg = sqlite3Get4byte( pPage.aData, pPage.hdrOffset + 8 );
    }
    else
    {
      chldPg = sqlite3Get4byte( pPage.aData, findCell( pPage, lwr ) );
    }
    if ( chldPg == 0 )
    {
      Debug.Assert( pCur.aiIdx[pCur.iPage] < pCur.apPage[pCur.iPage].nCell );
      pRes = c;
      rc = SQLITE_OK;
      goto moveto_finish;
    }
    pCur.aiIdx[pCur.iPage] = (u16)lwr;
    pCur.info.nSize = 0;
    pCur.validNKey = false;
    rc = moveToChild( pCur, chldPg );
    if ( rc != 0 )
      goto moveto_finish;
  }
moveto_finish:
  return rc;
}


/*
** Return TRUE if the cursor is not pointing at an entry of the table.
**
** TRUE will be returned after a call to sqlite3BtreeNext() moves
** past the last entry in the table or sqlite3BtreePrev() moves past
** the first entry.  TRUE is also returned if the table is empty.
*/
static bool sqlite3BtreeEof( BtCursor pCur )
{
  /* TODO: What if the cursor is in CURSOR_REQUIRESEEK but all table entries
  ** have been deleted? This API will need to change to return an error code
  ** as well as the boolean result value.
  */
  return ( CURSOR_VALID != pCur.eState );
}

/*
** Advance the cursor to the next entry in the database.  If
** successful then set pRes=0.  If the cursor
** was already pointing to the last entry in the database before
** this routine was called, then set pRes=1.
*/
static int sqlite3BtreeNext( BtCursor pCur, ref int pRes )
{
  int rc;
  int idx;
  MemPage pPage;

  Debug.Assert( cursorHoldsMutex( pCur ) );
  rc = restoreCursorPosition( pCur );
  if ( rc != SQLITE_OK )
  {
    return rc;
  }
  // Not needed in C# // Debug.Assert( pRes != 0 );
  if ( CURSOR_INVALID == pCur.eState )
  {
    pRes = 1;
    return SQLITE_OK;
  }
  if ( pCur.skipNext > 0 )
  {
    pCur.skipNext = 0;
    pRes = 0;
    return SQLITE_OK;
  }
  pCur.skipNext = 0;

  pPage = pCur.apPage[pCur.iPage];
  idx = ++pCur.aiIdx[pCur.iPage];
  Debug.Assert( pPage.isInit != 0 );
  Debug.Assert( idx <= pPage.nCell );

  pCur.info.nSize = 0;
  pCur.validNKey = false;
  if ( idx >= pPage.nCell )
  {
    if ( 0 == pPage.leaf )
    {
      rc = moveToChild( pCur, sqlite3Get4byte( pPage.aData, pPage.hdrOffset + 8 ) );
      if ( rc != 0 )
        return rc;
      rc = moveToLeftmost( pCur );
      pRes = 0;
      return rc;
    }
    do
    {
      if ( pCur.iPage == 0 )
      {
        pRes = 1;
        pCur.eState = CURSOR_INVALID;
        return SQLITE_OK;
      }
      moveToParent( pCur );
      pPage = pCur.apPage[pCur.iPage];
    } while ( pCur.aiIdx[pCur.iPage] >= pPage.nCell );
    pRes = 0;
    if ( pPage.intKey != 0 )
    {
      rc = sqlite3BtreeNext( pCur, ref pRes );
    }
    else
    {
      rc = SQLITE_OK;
    }
    return rc;
  }
  pRes = 0;
  if ( pPage.leaf != 0 )
  {
    return SQLITE_OK;
  }
  rc = moveToLeftmost( pCur );
  return rc;
}


/*
** Step the cursor to the back to the previous entry in the database.  If
** successful then set pRes=0.  If the cursor
** was already pointing to the first entry in the database before
** this routine was called, then set pRes=1.
*/
static int sqlite3BtreePrevious( BtCursor pCur, ref int pRes )
{
  int rc;
  MemPage pPage;

  Debug.Assert( cursorHoldsMutex( pCur ) );
  rc = restoreCursorPosition( pCur );
  if ( rc != SQLITE_OK )
  {
    return rc;
  }
  pCur.atLast = 0;
  if ( CURSOR_INVALID == pCur.eState )
  {
    pRes = 1;
    return SQLITE_OK;
  }
  if ( pCur.skipNext < 0 )
  {
    pCur.skipNext = 0;
    pRes = 0;
    return SQLITE_OK;
  }
  pCur.skipNext = 0;

  pPage = pCur.apPage[pCur.iPage];
  Debug.Assert( pPage.isInit != 0 );
  if ( 0 == pPage.leaf )
  {
    int idx = pCur.aiIdx[pCur.iPage];
    rc = moveToChild( pCur, sqlite3Get4byte( pPage.aData, findCell( pPage, idx ) ) );
    if ( rc != 0 )
    {
      return rc;
    }
    rc = moveToRightmost( pCur );
  }
  else
  {
    while ( pCur.aiIdx[pCur.iPage] == 0 )
    {
      if ( pCur.iPage == 0 )
      {
        pCur.eState = CURSOR_INVALID;
        pRes = 1;
        return SQLITE_OK;
      }
      moveToParent( pCur );
    }
    pCur.info.nSize = 0;
    pCur.validNKey = false;

    pCur.aiIdx[pCur.iPage]--;
    pPage = pCur.apPage[pCur.iPage];
    if ( pPage.intKey != 0 && 0 == pPage.leaf )
    {
      rc = sqlite3BtreePrevious( pCur, ref pRes );
    }
    else
    {
      rc = SQLITE_OK;
    }
  }
  pRes = 0;
  return rc;
}

/*
** Allocate a new page from the database file.
**
** The new page is marked as dirty.  (In other words, sqlite3PagerWrite()
** has already been called on the new page.)  The new page has also
** been referenced and the calling routine is responsible for calling
** sqlite3PagerUnref() on the new page when it is done.
**
** SQLITE_OK is returned on success.  Any other return value indicates
** an error.  ppPage and pPgno are undefined in the event of an error.
** Do not invoke sqlite3PagerUnref() on ppPage if an error is returned.
**
** If the "nearby" parameter is not 0, then a (feeble) effort is made to
** locate a page close to the page number "nearby".  This can be used in an
** attempt to keep related pages close to each other in the database file,
** which in turn can make database access faster.
**
** If the "exact" parameter is not 0, and the page-number nearby exists
** anywhere on the free-list, then it is guarenteed to be returned. This
** is only used by auto-vacuum databases when allocating a new table.
*/
static int allocateBtreePage(
BtShared pBt,
ref MemPage ppPage,
ref Pgno pPgno,
Pgno nearby,
u8 exact
)
{
  MemPage pPage1;
  int rc;
  u32 n;     /* Number of pages on the freelist */
  u32 k;     /* Number of leaves on the trunk of the freelist */
  MemPage pTrunk = null;
  MemPage pPrevTrunk = null;
  Pgno mxPage;     /* Total size of the database file */

  Debug.Assert( sqlite3_mutex_held( pBt.mutex ) );
  pPage1 = pBt.pPage1;
  mxPage = btreePagecount( pBt );
  n = sqlite3Get4byte( pPage1.aData, 36 );
  testcase( n == mxPage - 1 );
  if ( n >= mxPage )
  {
    return SQLITE_CORRUPT_BKPT();
  }
  if ( n > 0 )
  {
    /* There are pages on the freelist.  Reuse one of those pages. */
    Pgno iTrunk;
    u8 searchList = 0; /* If the free-list must be searched for 'nearby' */

    /* If the 'exact' parameter was true and a query of the pointer-map
    ** shows that the page 'nearby' is somewhere on the free-list, then
    ** the entire-list will be searched for that page.
    */
#if !SQLITE_OMIT_AUTOVACUUM
    if ( exact != 0 && nearby <= mxPage )
    {
      u8 eType = 0;
      Debug.Assert( nearby > 0 );
      Debug.Assert( pBt.autoVacuum );
      u32 Dummy0 = 0;
      rc = ptrmapGet( pBt, nearby, ref eType, ref Dummy0 );
      if ( rc != 0 )
        return rc;
      if ( eType == PTRMAP_FREEPAGE )
      {
        searchList = 1;
      }
      pPgno = nearby;
    }
#endif

    /* Decrement the free-list count by 1. Set iTrunk to the index of the
** first free-list trunk page. iPrevTrunk is initially 1.
*/
    rc = sqlite3PagerWrite( pPage1.pDbPage );
    if ( rc != 0 )
      return rc;
    sqlite3Put4byte( pPage1.aData, (u32)36, n - 1 );

    /* The code within this loop is run only once if the 'searchList' variable
    ** is not true. Otherwise, it runs once for each trunk-page on the
    ** free-list until the page 'nearby' is located.
    */
    do
    {
      pPrevTrunk = pTrunk;
      if ( pPrevTrunk != null )
      {
        iTrunk = sqlite3Get4byte( pPrevTrunk.aData, 0 );
      }
      else
      {
        iTrunk = sqlite3Get4byte( pPage1.aData, 32 );
      }
      testcase( iTrunk == mxPage );
      if ( iTrunk > mxPage )
      {
        rc = SQLITE_CORRUPT_BKPT();
      }
      else
      {
        rc = btreeGetPage( pBt, iTrunk, ref pTrunk, 0 );
      }
      if ( rc != 0 )
      {
        pTrunk = null;
        goto end_allocate_page;
      }

      k = sqlite3Get4byte( pTrunk.aData, 4 ); /* # of leaves on this trunk page */
      if ( k == 0 && 0 == searchList )
      {
        /* The trunk has no leaves and the list is not being searched.
        ** So extract the trunk page itself and use it as the newly
        ** allocated page */
        Debug.Assert( pPrevTrunk == null );
        rc = sqlite3PagerWrite( pTrunk.pDbPage );
        if ( rc != 0 )
        {
          goto end_allocate_page;
        }
        pPgno = iTrunk;
        Buffer.BlockCopy( pTrunk.aData, 0, pPage1.aData, 32, 4 );//memcpy( pPage1.aData[32], ref pTrunk.aData[0], 4 );
        ppPage = pTrunk;
        pTrunk = null;
        TRACE( "ALLOCATE: %d trunk - %d free pages left\n", pPgno, n - 1 );
      }
      else if ( k > (u32)( pBt.usableSize / 4 - 2 ) )
      {
        /* Value of k is out of range.  Database corruption */
        rc = SQLITE_CORRUPT_BKPT();
        goto end_allocate_page;
#if !SQLITE_OMIT_AUTOVACUUM
      }
      else if ( searchList != 0 && nearby == iTrunk )
      {
        /* The list is being searched and this trunk page is the page
        ** to allocate, regardless of whether it has leaves.
        */
        Debug.Assert( pPgno == iTrunk );
        ppPage = pTrunk;
        searchList = 0;
        rc = sqlite3PagerWrite( pTrunk.pDbPage );
        if ( rc != 0 )
        {
          goto end_allocate_page;
        }
        if ( k == 0 )
        {
          if ( null == pPrevTrunk )
          {
            //memcpy(pPage1.aData[32], pTrunk.aData[0], 4);
            pPage1.aData[32 + 0] = pTrunk.aData[0 + 0];
            pPage1.aData[32 + 1] = pTrunk.aData[0 + 1];
            pPage1.aData[32 + 2] = pTrunk.aData[0 + 2];
            pPage1.aData[32 + 3] = pTrunk.aData[0 + 3];
          }
          else
          {
            rc = sqlite3PagerWrite( pPrevTrunk.pDbPage );
            if ( rc != SQLITE_OK )
            {
              goto end_allocate_page;
            }
            //memcpy(pPrevTrunk.aData[0], pTrunk.aData[0], 4);
            pPrevTrunk.aData[0 + 0] = pTrunk.aData[0 + 0];
            pPrevTrunk.aData[0 + 1] = pTrunk.aData[0 + 1];
            pPrevTrunk.aData[0 + 2] = pTrunk.aData[0 + 2];
            pPrevTrunk.aData[0 + 3] = pTrunk.aData[0 + 3];
          }
        }
        else
        {
          /* The trunk page is required by the caller but it contains
          ** pointers to free-list leaves. The first leaf becomes a trunk
          ** page in this case.
          */
          MemPage pNewTrunk = new MemPage();
          Pgno iNewTrunk = sqlite3Get4byte( pTrunk.aData, 8 );
          if ( iNewTrunk > mxPage )
          {
            rc = SQLITE_CORRUPT_BKPT();
            goto end_allocate_page;
          }
          testcase( iNewTrunk == mxPage );
          rc = btreeGetPage( pBt, iNewTrunk, ref pNewTrunk, 0 );
          if ( rc != SQLITE_OK )
          {
            goto end_allocate_page;
          }
          rc = sqlite3PagerWrite( pNewTrunk.pDbPage );
          if ( rc != SQLITE_OK )
          {
            releasePage( pNewTrunk );
            goto end_allocate_page;
          }
          //memcpy(pNewTrunk.aData[0], pTrunk.aData[0], 4);
          pNewTrunk.aData[0 + 0] = pTrunk.aData[0 + 0];
          pNewTrunk.aData[0 + 1] = pTrunk.aData[0 + 1];
          pNewTrunk.aData[0 + 2] = pTrunk.aData[0 + 2];
          pNewTrunk.aData[0 + 3] = pTrunk.aData[0 + 3];
          sqlite3Put4byte( pNewTrunk.aData, (u32)4, (u32)( k - 1 ) );
          Buffer.BlockCopy( pTrunk.aData, 12, pNewTrunk.aData, 8, (int)( k - 1 ) * 4 );//memcpy( pNewTrunk.aData[8], ref pTrunk.aData[12], ( k - 1 ) * 4 );
          releasePage( pNewTrunk );
          if ( null == pPrevTrunk )
          {
            Debug.Assert( sqlite3PagerIswriteable( pPage1.pDbPage ) );
            sqlite3Put4byte( pPage1.aData, (u32)32, iNewTrunk );
          }
          else
          {
            rc = sqlite3PagerWrite( pPrevTrunk.pDbPage );
            if ( rc != 0 )
            {
              goto end_allocate_page;
            }
            sqlite3Put4byte( pPrevTrunk.aData, (u32)0, iNewTrunk );
          }
        }
        pTrunk = null;
        TRACE( "ALLOCATE: %d trunk - %d free pages left\n", pPgno, n - 1 );
#endif
      }
      else if ( k > 0 )
      {
        /* Extract a leaf from the trunk */
        u32 closest;
        Pgno iPage;
        byte[] aData = pTrunk.aData;
        if ( nearby > 0 )
        {
          u32 i;
          int dist;
          closest = 0;
          dist = sqlite3AbsInt32( (int)(sqlite3Get4byte( aData, 8 ) - nearby ));
          for ( i = 1; i < k; i++ )
          {
            int d2 = sqlite3AbsInt32( (int)(sqlite3Get4byte( aData, 8 + i * 4 ) - nearby ));
            if ( d2 < dist )
            {
              closest = i;
              dist = d2;
            }
          }
        }
        else
        {
          closest = 0;
        }

        iPage = sqlite3Get4byte( aData, 8 + closest * 4 );
        testcase( iPage == mxPage );
        if ( iPage > mxPage )
        {
          rc = SQLITE_CORRUPT_BKPT();
          goto end_allocate_page;
        }
        testcase( iPage == mxPage );
        if ( 0 == searchList || iPage == nearby )
        {
          int noContent;
          pPgno = iPage;
          TRACE( "ALLOCATE: %d was leaf %d of %d on trunk %d" +
          ": %d more free pages\n",
          pPgno, closest + 1, k, pTrunk.pgno, n - 1 );
          rc = sqlite3PagerWrite( pTrunk.pDbPage );
          if ( rc != 0)
            goto end_allocate_page;
          if ( closest < k - 1 )
          {
            Buffer.BlockCopy( aData, (int)( 4 + k * 4 ), aData, 8 + (int)closest * 4, 4 );//memcpy( aData[8 + closest * 4], ref aData[4 + k * 4], 4 );
          }
          sqlite3Put4byte( aData, (u32)4, ( k - 1 ) );// sqlite3Put4byte( aData, 4, k - 1 );
          noContent = !btreeGetHasContent( pBt, pPgno ) ? 1 : 0;
          rc = btreeGetPage( pBt, pPgno, ref ppPage, noContent );
          if ( rc == SQLITE_OK )
          {
            rc = sqlite3PagerWrite( ( ppPage ).pDbPage );
            if ( rc != SQLITE_OK )
            {
              releasePage( ppPage );
            }
          }
          searchList = 0;
        }
      }
      releasePage( pPrevTrunk );
      pPrevTrunk = null;
    } while ( searchList != 0 );
  }
  else
  {
    /* There are no pages on the freelist, so create a new page at the
    ** end of the file */
    rc = sqlite3PagerWrite( pBt.pPage1.pDbPage );
    if ( rc != 0 )
      return rc;
    pBt.nPage++;
    if ( pBt.nPage == PENDING_BYTE_PAGE( pBt ) )
      pBt.nPage++;

#if !SQLITE_OMIT_AUTOVACUUM
    if ( pBt.autoVacuum && PTRMAP_ISPAGE( pBt, pBt.nPage ) )
    {
      /* If pPgno refers to a pointer-map page, allocate two new pages
      ** at the end of the file instead of one. The first allocated page
      ** becomes a new pointer-map page, the second is used by the caller.
      */
      MemPage pPg = null;
      TRACE( "ALLOCATE: %d from end of file (pointer-map page)\n", pPgno );
      Debug.Assert( pBt.nPage != PENDING_BYTE_PAGE( pBt ) );
      rc = btreeGetPage( pBt, pBt.nPage, ref pPg, 1 );
      if ( rc == SQLITE_OK )
      {
        rc = sqlite3PagerWrite( pPg.pDbPage );
        releasePage( pPg );
      }
      if ( rc != 0 )
        return rc;
      pBt.nPage++;
      if ( pBt.nPage == PENDING_BYTE_PAGE( pBt ) )
      {
        pBt.nPage++;
      }
    }
#endif
    sqlite3Put4byte( pBt.pPage1.aData, (u32)28, pBt.nPage );
    pPgno = pBt.nPage;

    Debug.Assert( pPgno != PENDING_BYTE_PAGE( pBt ) );
    rc = btreeGetPage( pBt, pPgno, ref ppPage, 1 );
    if ( rc != 0 )
      return rc;
    rc = sqlite3PagerWrite( ( ppPage ).pDbPage );
    if ( rc != SQLITE_OK )
    {
      releasePage( ppPage );
    }
    TRACE( "ALLOCATE: %d from end of file\n", pPgno );
  }

  Debug.Assert( pPgno != PENDING_BYTE_PAGE( pBt ) );

end_allocate_page:
  releasePage( pTrunk );
  releasePage( pPrevTrunk );
  if ( rc == SQLITE_OK )
  {
    if ( sqlite3PagerPageRefcount( ( ppPage ).pDbPage ) > 1 )
    {
      releasePage( ppPage );
      return SQLITE_CORRUPT_BKPT();
    }
    ( ppPage ).isInit = 0;
  }
  else
  {
    ppPage = null;
  }
  Debug.Assert( rc != SQLITE_OK || sqlite3PagerIswriteable( ( ppPage ).pDbPage ) );
  return rc;
}

/*
** This function is used to add page iPage to the database file free-list.
** It is assumed that the page is not already a part of the free-list.
**
** The value passed as the second argument to this function is optional.
** If the caller happens to have a pointer to the MemPage object
** corresponding to page iPage handy, it may pass it as the second value.
** Otherwise, it may pass NULL.
**
** If a pointer to a MemPage object is passed as the second argument,
** its reference count is not altered by this function.
*/
static int freePage2( BtShared pBt, MemPage pMemPage, Pgno iPage )
{
  MemPage pTrunk = null;                /* Free-list trunk page */
  Pgno iTrunk = 0;                      /* Page number of free-list trunk page */
  MemPage pPage1 = pBt.pPage1;          /* Local reference to page 1 */
  MemPage pPage;                        /* Page being freed. May be NULL. */
  int rc;                               /* Return Code */
  int nFree;                           /* Initial number of pages on free-list */

  Debug.Assert( sqlite3_mutex_held( pBt.mutex ) );
  Debug.Assert( iPage > 1 );
  Debug.Assert( null == pMemPage || pMemPage.pgno == iPage );

  if ( pMemPage != null )
  {
    pPage = pMemPage;
    sqlite3PagerRef( pPage.pDbPage );
  }
  else
  {
    pPage = btreePageLookup( pBt, iPage );
  }

  /* Increment the free page count on pPage1 */
  rc = sqlite3PagerWrite( pPage1.pDbPage );
  if ( rc != 0 )
    goto freepage_out;
  nFree = (int)sqlite3Get4byte( pPage1.aData, 36 );
  sqlite3Put4byte( pPage1.aData, 36, nFree + 1 );

  if ( pBt.secureDelete )
  {
    /* If the secure_delete option is enabled, then
    ** always fully overwrite deleted information with zeros.
    */
    if ( ( null == pPage && ( ( rc = btreeGetPage( pBt, iPage, ref pPage, 0 ) ) != 0 ) )
    || ( ( rc = sqlite3PagerWrite( pPage.pDbPage ) ) != 0 )
    )
    {
      goto freepage_out;
    }
    Array.Clear( pPage.aData, 0, (int)pPage.pBt.pageSize );//memset(pPage->aData, 0, pPage->pBt->pageSize);
  }

  /* If the database supports auto-vacuum, write an entry in the pointer-map
  ** to indicate that the page is free.
  */
#if !SQLITE_OMIT_AUTOVACUUM //   if ( ISAUTOVACUUM )
  if ( pBt.autoVacuum )
#else
if (false)
#endif
  {
    ptrmapPut( pBt, iPage, PTRMAP_FREEPAGE, 0, ref rc );
    if ( rc != 0 )
      goto freepage_out;
  }

  /* Now manipulate the actual database free-list structure. There are two
  ** possibilities. If the free-list is currently empty, or if the first
  ** trunk page in the free-list is full, then this page will become a
  ** new free-list trunk page. Otherwise, it will become a leaf of the
  ** first trunk page in the current free-list. This block tests if it
  ** is possible to add the page as a new free-list leaf.
  */
  if ( nFree != 0 )
  {
    u32 nLeaf;                /* Initial number of leaf cells on trunk page */

    iTrunk = sqlite3Get4byte( pPage1.aData, 32 );
    rc = btreeGetPage( pBt, iTrunk, ref pTrunk, 0 );
    if ( rc != SQLITE_OK )
    {
      goto freepage_out;
    }

    nLeaf = sqlite3Get4byte( pTrunk.aData, 4 );
    Debug.Assert( pBt.usableSize > 32 );
    if ( nLeaf > (u32)pBt.usableSize / 4 - 2 )
    {
      rc = SQLITE_CORRUPT_BKPT();
      goto freepage_out;
    }
    if ( nLeaf < (u32)pBt.usableSize / 4 - 8 )
    {
      /* In this case there is room on the trunk page to insert the page
      ** being freed as a new leaf.
      **
      ** Note that the trunk page is not really full until it contains
      ** usableSize/4 - 2 entries, not usableSize/4 - 8 entries as we have
      ** coded.  But due to a coding error in versions of SQLite prior to
      ** 3.6.0, databases with freelist trunk pages holding more than
      ** usableSize/4 - 8 entries will be reported as corrupt.  In order
      ** to maintain backwards compatibility with older versions of SQLite,
      ** we will continue to restrict the number of entries to usableSize/4 - 8
      ** for now.  At some point in the future (once everyone has upgraded
      ** to 3.6.0 or later) we should consider fixing the conditional above
      ** to read "usableSize/4-2" instead of "usableSize/4-8".
      */
      rc = sqlite3PagerWrite( pTrunk.pDbPage );
      if ( rc == SQLITE_OK )
      {
        sqlite3Put4byte( pTrunk.aData, (u32)4, nLeaf + 1 );
        sqlite3Put4byte( pTrunk.aData, (u32)8 + nLeaf * 4, iPage );
        if ( pPage != null && !pBt.secureDelete )
        {
          sqlite3PagerDontWrite( pPage.pDbPage );
        }
        rc = btreeSetHasContent( pBt, iPage );
      }
      TRACE( "FREE-PAGE: %d leaf on trunk page %d\n", iPage, pTrunk.pgno );
      goto freepage_out;
    }
  }

  /* If control flows to this point, then it was not possible to add the
  ** the page being freed as a leaf page of the first trunk in the free-list.
  ** Possibly because the free-list is empty, or possibly because the
  ** first trunk in the free-list is full. Either way, the page being freed
  ** will become the new first trunk page in the free-list.
  */
  if ( pPage == null && SQLITE_OK != ( rc = btreeGetPage( pBt, iPage, ref pPage, 0 ) ) )
  {
    goto freepage_out;
  }
  rc = sqlite3PagerWrite( pPage.pDbPage );
  if ( rc != SQLITE_OK )
  {
    goto freepage_out;
  }
  sqlite3Put4byte( pPage.aData, iTrunk );
  sqlite3Put4byte( pPage.aData, 4, 0 );
  sqlite3Put4byte( pPage1.aData, (u32)32, iPage );
  TRACE( "FREE-PAGE: %d new trunk page replacing %d\n", pPage.pgno, iTrunk );

freepage_out:
  if ( pPage != null )
  {
    pPage.isInit = 0;
  }
  releasePage( pPage );
  releasePage( pTrunk );
  return rc;
}
static void freePage( MemPage pPage, ref int pRC )
{
  if ( ( pRC ) == SQLITE_OK )
  {
    pRC = freePage2( pPage.pBt, pPage, pPage.pgno );
  }
}

/*
** Free any overflow pages associated with the given Cell.
*/
static int clearCell( MemPage pPage, int pCell )
{
  BtShared pBt = pPage.pBt;
  CellInfo info = new CellInfo();
  Pgno ovflPgno;
  int rc;
  int nOvfl;
  u32 ovflPageSize;

  Debug.Assert( sqlite3_mutex_held( pPage.pBt.mutex ) );
  btreeParseCellPtr( pPage, pCell, ref info );
  if ( info.iOverflow == 0 )
  {
    return SQLITE_OK;  /* No overflow pages. Return without doing anything */
  }
  ovflPgno = sqlite3Get4byte( pPage.aData, pCell, info.iOverflow );
  Debug.Assert( pBt.usableSize > 4 );
  ovflPageSize = (u16)( pBt.usableSize - 4 );
  nOvfl = (int)( ( info.nPayload - info.nLocal + ovflPageSize - 1 ) / ovflPageSize );
  Debug.Assert( ovflPgno == 0 || nOvfl > 0 );
  while ( nOvfl-- != 0 )
  {
    Pgno iNext = 0;
    MemPage pOvfl = null;
    if ( ovflPgno < 2 || ovflPgno > btreePagecount( pBt ) )
    {
      /* 0 is not a legal page number and page 1 cannot be an
      ** overflow page. Therefore if ovflPgno<2 or past the end of the
      ** file the database must be corrupt. */
      return SQLITE_CORRUPT_BKPT();
    }
    if ( nOvfl != 0 )
    {
      rc = getOverflowPage( pBt, ovflPgno, out pOvfl, out iNext );
      if ( rc != 0 )
        return rc;
    }

    if ( ( pOvfl != null || ( ( pOvfl = btreePageLookup( pBt, ovflPgno ) ) != null ) )
    && sqlite3PagerPageRefcount( pOvfl.pDbPage ) != 1
    )
    {
      /* There is no reason any cursor should have an outstanding reference 
      ** to an overflow page belonging to a cell that is being deleted/updated.
      ** So if there exists more than one reference to this page, then it 
      ** must not really be an overflow page and the database must be corrupt. 
      ** It is helpful to detect this before calling freePage2(), as 
      ** freePage2() may zero the page contents if secure-delete mode is
      ** enabled. If this 'overflow' page happens to be a page that the
      ** caller is iterating through or using in some other way, this
      ** can be problematic.
      */
      rc = SQLITE_CORRUPT_BKPT();
    }
    else
    {
      rc = freePage2( pBt, pOvfl, ovflPgno );
    }
    if ( pOvfl != null )
    {
      sqlite3PagerUnref( pOvfl.pDbPage );
    }
    if ( rc != 0 )
      return rc;
    ovflPgno = iNext;
  }
  return SQLITE_OK;
}

/*
** Create the byte sequence used to represent a cell on page pPage
** and write that byte sequence into pCell[].  Overflow pages are
** allocated and filled in as necessary.  The calling procedure
** is responsible for making sure sufficient space has been allocated
** for pCell[].
**
** Note that pCell does not necessary need to point to the pPage.aData
** area.  pCell might point to some temporary storage.  The cell will
** be constructed in this temporary area then copied into pPage.aData
** later.
*/
static int fillInCell(
MemPage pPage,            /* The page that contains the cell */
byte[] pCell,             /* Complete text of the cell */
byte[] pKey, i64 nKey,    /* The key */
byte[] pData, int nData,  /* The data */
int nZero,                /* Extra zero bytes to append to pData */
ref int pnSize            /* Write cell size here */
)
{
  int nPayload;
  u8[] pSrc;
  int pSrcIndex = 0;
  int nSrc, n, rc;
  int spaceLeft;
  MemPage pOvfl = null;
  MemPage pToRelease = null;
  byte[] pPrior;
  int pPriorIndex = 0;
  byte[] pPayload;
  int pPayloadIndex = 0;
  BtShared pBt = pPage.pBt;
  Pgno pgnoOvfl = 0;
  int nHeader;
  CellInfo info = new CellInfo();

  Debug.Assert( sqlite3_mutex_held( pPage.pBt.mutex ) );

  /* pPage is not necessarily writeable since pCell might be auxiliary
  ** buffer space that is separate from the pPage buffer area */
  // TODO -- Determine if the following Assert is needed under c#
  //Debug.Assert( pCell < pPage.aData || pCell >= &pPage.aData[pBt.pageSize]
  //          || sqlite3PagerIswriteable(pPage.pDbPage) );

  /* Fill in the header. */
  nHeader = 0;
  if ( 0 == pPage.leaf )
  {
    nHeader += 4;
  }
  if ( pPage.hasData != 0 )
  {
    nHeader += (int)putVarint( pCell, nHeader, (int)( nData + nZero ) ); //putVarint( pCell[nHeader], nData + nZero );
  }
  else
  {
    nData = nZero = 0;
  }
  nHeader += putVarint( pCell, nHeader, (u64)nKey ); //putVarint( pCell[nHeader], *(u64*)&nKey );
  btreeParseCellPtr( pPage, pCell, ref info );
  Debug.Assert( info.nHeader == nHeader );
  Debug.Assert( info.nKey == nKey );
  Debug.Assert( info.nData == (u32)( nData + nZero ) );

  /* Fill in the payload */
  nPayload = nData + nZero;
  if ( pPage.intKey != 0 )
  {
    pSrc = pData;
    nSrc = nData;
    nData = 0;
  }
  else
  {
    if ( NEVER( nKey > 0x7fffffff || pKey == null ) )
    {
      return SQLITE_CORRUPT_BKPT();
    }
    nPayload += (int)nKey;
    pSrc = pKey;
    nSrc = (int)nKey;
  }
  pnSize = info.nSize;
  spaceLeft = info.nLocal;
  //  pPayload = &pCell[nHeader];
  pPayload = pCell;
  pPayloadIndex = nHeader;
  //  pPrior = &pCell[info.iOverflow];
  pPrior = pCell;
  pPriorIndex = info.iOverflow;

  while ( nPayload > 0 )
  {
    if ( spaceLeft == 0 )
    {
#if !SQLITE_OMIT_AUTOVACUUM
      Pgno pgnoPtrmap = pgnoOvfl; /* Overflow page pointer-map entry page */
      if ( pBt.autoVacuum )
      {
        do
        {
          pgnoOvfl++;
        } while (
        PTRMAP_ISPAGE( pBt, pgnoOvfl ) || pgnoOvfl == PENDING_BYTE_PAGE( pBt )
        );
      }
#endif
      rc = allocateBtreePage( pBt, ref pOvfl, ref pgnoOvfl, pgnoOvfl, 0 );
#if !SQLITE_OMIT_AUTOVACUUM
      /* If the database supports auto-vacuum, and the second or subsequent
** overflow page is being allocated, add an entry to the pointer-map
** for that page now.
**
** If this is the first overflow page, then write a partial entry
** to the pointer-map. If we write nothing to this pointer-map slot,
** then the optimistic overflow chain processing in clearCell()
** may misinterpret the uninitialised values and delete the
** wrong pages from the database.
*/
      if ( pBt.autoVacuum && rc == SQLITE_OK )
      {
        u8 eType = (u8)( pgnoPtrmap != 0 ? PTRMAP_OVERFLOW2 : PTRMAP_OVERFLOW1 );
        ptrmapPut( pBt, pgnoOvfl, eType, pgnoPtrmap, ref rc );
        if ( rc != 0 )
        {
          releasePage( pOvfl );
        }
      }
#endif
      if ( rc != 0 )
      {
        releasePage( pToRelease );
        return rc;
      }

      /* If pToRelease is not zero than pPrior points into the data area
      ** of pToRelease.  Make sure pToRelease is still writeable. */
      Debug.Assert( pToRelease == null || sqlite3PagerIswriteable( pToRelease.pDbPage ) );

      /* If pPrior is part of the data area of pPage, then make sure pPage
      ** is still writeable */
      // TODO -- Determine if the following Assert is needed under c#
      //Debug.Assert( pPrior < pPage.aData || pPrior >= &pPage.aData[pBt.pageSize]
      //      || sqlite3PagerIswriteable(pPage.pDbPage) );

      sqlite3Put4byte( pPrior, pPriorIndex, pgnoOvfl );
      releasePage( pToRelease );
      pToRelease = pOvfl;
      pPrior = pOvfl.aData;
      pPriorIndex = 0;
      sqlite3Put4byte( pPrior, 0 );
      pPayload = pOvfl.aData;
      pPayloadIndex = 4; //&pOvfl.aData[4];
      spaceLeft = (int)pBt.usableSize - 4;
    }
    n = nPayload;
    if ( n > spaceLeft )
      n = spaceLeft;

    /* If pToRelease is not zero than pPayload points into the data area
    ** of pToRelease.  Make sure pToRelease is still writeable. */
    Debug.Assert( pToRelease == null || sqlite3PagerIswriteable( pToRelease.pDbPage ) );

    /* If pPayload is part of the data area of pPage, then make sure pPage
    ** is still writeable */
    // TODO -- Determine if the following Assert is needed under c#
    //Debug.Assert( pPayload < pPage.aData || pPayload >= &pPage.aData[pBt.pageSize]
    //        || sqlite3PagerIswriteable(pPage.pDbPage) );

    if ( nSrc > 0 )
    {
      if ( n > nSrc )
        n = nSrc;
      Debug.Assert( pSrc != null );
      Buffer.BlockCopy( pSrc, pSrcIndex, pPayload, pPayloadIndex, n );//memcpy(pPayload, pSrc, n);
    }
    else
    {
      byte[] pZeroBlob = sqlite3Malloc( n ); // memset(pPayload, 0, n);
      Buffer.BlockCopy( pZeroBlob, 0, pPayload, pPayloadIndex, n );
    }
    nPayload -= n;
    pPayloadIndex += n;// pPayload += n;
    pSrcIndex += n;// pSrc += n;
    nSrc -= n;
    spaceLeft -= n;
    if ( nSrc == 0 )
    {
      nSrc = nData;
      pSrc = pData;
    }
  }
  releasePage( pToRelease );
  return SQLITE_OK;
}

/*
** Remove the i-th cell from pPage.  This routine effects pPage only.
** The cell content is not freed or deallocated.  It is assumed that
** the cell content has been copied someplace else.  This routine just
** removes the reference to the cell from pPage.
**
** "sz" must be the number of bytes in the cell.
*/
static void dropCell( MemPage pPage, int idx, int sz, ref int pRC )
{
  u32 pc;         /* Offset to cell content of cell being deleted */
  u8[] data;      /* pPage.aData */
  int ptr;        /* Used to move bytes around within data[] */
  int endPtr;     /* End of loop */
  int rc;         /* The return code */
  int hdr;        /* Beginning of the header.  0 most pages.  100 page 1 */

  if ( pRC != 0 )
    return;

  Debug.Assert( idx >= 0 && idx < pPage.nCell );
#if SQLITE_DEBUG
  Debug.Assert( sz == cellSize( pPage, idx ) );
#endif
  Debug.Assert( sqlite3PagerIswriteable( pPage.pDbPage ) );
  Debug.Assert( sqlite3_mutex_held( pPage.pBt.mutex ) );
  data = pPage.aData;
  ptr = pPage.cellOffset + 2 * idx; //ptr = &data[pPage.cellOffset + 2 * idx];
  pc = (u32)get2byte( data, ptr );
  hdr = pPage.hdrOffset;
  testcase( pc == get2byte( data, hdr + 5 ) );
  testcase( pc + sz == pPage.pBt.usableSize );
  if ( pc < (u32)get2byte( data, hdr + 5 ) || pc + sz > pPage.pBt.usableSize )
  {
    pRC = SQLITE_CORRUPT_BKPT();
    return;
  }
  rc = freeSpace( pPage, pc, sz );
  if ( rc != 0 )
  {
    pRC = rc;
    return;
  }
  //endPtr = &data[pPage->cellOffset + 2*pPage->nCell - 2];
  //assert( (SQLITE_PTR_TO_INT(ptr)&1)==0 );  /* ptr is always 2-byte aligned */
  //while( ptr<endPtr ){
  //  *(u16*)ptr = *(u16*)&ptr[2];
  //  ptr += 2;
  Buffer.BlockCopy( data, ptr + 2, data, ptr, ( pPage.nCell - 1 - idx ) * 2 );
  pPage.nCell--;
  data[pPage.hdrOffset + 3] = (byte)( pPage.nCell >> 8 );
  data[pPage.hdrOffset + 4] = (byte)( pPage.nCell ); //put2byte( data, hdr + 3, pPage.nCell );
  pPage.nFree += 2;
}

/*
** Insert a new cell on pPage at cell index "i".  pCell points to the
** content of the cell.
**
** If the cell content will fit on the page, then put it there.  If it
** will not fit, then make a copy of the cell content into pTemp if
** pTemp is not null.  Regardless of pTemp, allocate a new entry
** in pPage.aOvfl[] and make it point to the cell content (either
** in pTemp or the original pCell) and also record its index.
** Allocating a new entry in pPage.aCell[] implies that
** pPage.nOverflow is incremented.
**
** If nSkip is non-zero, then do not copy the first nSkip bytes of the
** cell. The caller will overwrite them after this function returns. If
** nSkip is non-zero, then pCell may not point to an invalid memory location
** (but pCell+nSkip is always valid).
*/
static void insertCell(
MemPage pPage,      /* Page into which we are copying */
int i,              /* New cell becomes the i-th cell of the page */
u8[] pCell,         /* Content of the new cell */
int sz,             /* Bytes of content in pCell */
u8[] pTemp,         /* Temp storage space for pCell, if needed */
Pgno iChild,        /* If non-zero, replace first 4 bytes with this value */
ref int pRC         /* Read and write return code from here */
)
{
  int idx = 0;      /* Where to write new cell content in data[] */
  int j;            /* Loop counter */
  int end;          /* First byte past the last cell pointer in data[] */
  int ins;          /* Index in data[] where new cell pointer is inserted */
  int cellOffset;   /* Address of first cell pointer in data[] */
  u8[] data;        /* The content of the whole page */
  u8 ptr;           /* Used for moving information around in data[] */
  u8 endPtr;        /* End of the loop */

  int nSkip = ( iChild != 0 ? 4 : 0 );

  if ( pRC != 0 )
    return;

  Debug.Assert( i >= 0 && i <= pPage.nCell + pPage.nOverflow );
  Debug.Assert( pPage.nCell <= MX_CELL( pPage.pBt ) && MX_CELL( pPage.pBt ) <= 10921 );
  Debug.Assert( pPage.nOverflow <= ArraySize( pPage.aOvfl ) );
  Debug.Assert( sqlite3_mutex_held( pPage.pBt.mutex ) );
  /* The cell should normally be sized correctly.  However, when moving a
  ** malformed cell from a leaf page to an interior page, if the cell size
  ** wanted to be less than 4 but got rounded up to 4 on the leaf, then size
  ** might be less than 8 (leaf-size + pointer) on the interior node.  Hence
  ** the term after the || in the following assert(). */
  Debug.Assert( sz == cellSizePtr( pPage, pCell ) || ( sz == 8 && iChild > 0 ) );
  if ( pPage.nOverflow != 0 || sz + 2 > pPage.nFree )
  {
    if ( pTemp != null )
    {
      Buffer.BlockCopy( pCell, nSkip, pTemp, nSkip, sz - nSkip );//memcpy(pTemp+nSkip, pCell+nSkip, sz-nSkip);
      pCell = pTemp;
    }
    if ( iChild != 0 )
    {
      sqlite3Put4byte( pCell, iChild );
    }
    j = pPage.nOverflow++;
    Debug.Assert( j < pPage.aOvfl.Length );//(int)(sizeof(pPage.aOvfl)/sizeof(pPage.aOvfl[0])) );
    pPage.aOvfl[j].pCell = pCell;
    pPage.aOvfl[j].idx = (u16)i;
  }
  else
  {
    int rc = sqlite3PagerWrite( pPage.pDbPage );
    if ( rc != SQLITE_OK )
    {
      pRC = rc;
      return;
    }
    Debug.Assert( sqlite3PagerIswriteable( pPage.pDbPage ) );
    data = pPage.aData;
    cellOffset = pPage.cellOffset;
    end = cellOffset + 2 * pPage.nCell;
    ins = cellOffset + 2 * i;
    rc = allocateSpace( pPage, sz, ref idx );
    if ( rc != 0 )
    {
      pRC = rc;
      return;
    }
    /* The allocateSpace() routine guarantees the following two properties
    ** if it returns success */
    Debug.Assert( idx >= end + 2 );
    Debug.Assert( idx + sz <= (int)pPage.pBt.usableSize );
    pPage.nCell++;
    pPage.nFree -= (u16)( 2 + sz );
    Buffer.BlockCopy( pCell, nSkip, data, idx + nSkip, sz - nSkip ); //memcpy( data[idx + nSkip], pCell + nSkip, sz - nSkip );
    if ( iChild != 0 )
    {
      sqlite3Put4byte( data, idx, iChild );
    }
    //ptr = &data[end];
    //endPtr = &data[ins];
    //assert( ( SQLITE_PTR_TO_INT( ptr ) & 1 ) == 0 );  /* ptr is always 2-byte aligned */
    //while ( ptr > endPtr )
    //{
    //  *(u16*)ptr = *(u16*)&ptr[-2];
    //  ptr -= 2;
    //}
    for ( j = end; j > ins; j -= 2 )
    {
      data[j + 0] = data[j - 2];
      data[j + 1] = data[j - 1];
    }
    put2byte( data, ins, idx );
    put2byte( data, pPage.hdrOffset + 3, pPage.nCell );
#if !SQLITE_OMIT_AUTOVACUUM
    if ( pPage.pBt.autoVacuum )
    {
      /* The cell may contain a pointer to an overflow page. If so, write
      ** the entry for the overflow page into the pointer map.
      */
      ptrmapPutOvflPtr( pPage, pCell, ref pRC );
    }
#endif
  }
}

/*
** Add a list of cells to a page.  The page should be initially empty.
** The cells are guaranteed to fit on the page.
*/
static void assemblePage(
MemPage pPage,    /* The page to be assemblied */
int nCell,        /* The number of cells to add to this page */
u8[] apCell,      /* Pointer to a single the cell bodies */
int[] aSize       /* Sizes of the cells bodie*/
)
{
  int i;            /* Loop counter */
  int pCellptr;     /* Address of next cell pointer */
  int cellbody;     /* Address of next cell body */
  byte[] data = pPage.aData;          /* Pointer to data for pPage */
  int hdr = pPage.hdrOffset;          /* Offset of header on pPage */
  int nUsable = (int)pPage.pBt.usableSize; /* Usable size of page */

  Debug.Assert( pPage.nOverflow == 0 );
  Debug.Assert( sqlite3_mutex_held( pPage.pBt.mutex ) );
  Debug.Assert( nCell >= 0 && nCell <= (int)MX_CELL( pPage.pBt )
        && (int)MX_CELL( pPage.pBt ) <= 10921 );

  Debug.Assert( sqlite3PagerIswriteable( pPage.pDbPage ) );

  /* Check that the page has just been zeroed by zeroPage() */
  Debug.Assert( pPage.nCell == 0 );
  Debug.Assert( get2byteNotZero( data, hdr + 5 ) == nUsable );

  pCellptr = pPage.cellOffset + nCell * 2; //data[pPage.cellOffset + nCell * 2];
  cellbody = nUsable;
  for ( i = nCell - 1; i >= 0; i-- )
  {
    u16 sz = (u16)aSize[i];
    pCellptr -= 2;
    cellbody -= sz;
    put2byte( data, pCellptr, cellbody );
    Buffer.BlockCopy( apCell, 0, data, cellbody, sz );// memcpy(&data[cellbody], apCell[i], sz);
  }
  put2byte( data, hdr + 3, nCell );
  put2byte( data, hdr + 5, cellbody );
  pPage.nFree -= (u16)( nCell * 2 + nUsable - cellbody );
  pPage.nCell = (u16)nCell;
}
static void assemblePage(
MemPage pPage,    /* The page to be assemblied */
int nCell,        /* The number of cells to add to this page */
u8[][] apCell,    /* Pointers to cell bodies */
u16[] aSize,      /* Sizes of the cells */
int offset        /* Offset into the cell bodies, for c#  */
)
{
  int i;            /* Loop counter */
  int pCellptr;      /* Address of next cell pointer */
  int cellbody;     /* Address of next cell body */
  byte[] data = pPage.aData;          /* Pointer to data for pPage */
  int hdr = pPage.hdrOffset;          /* Offset of header on pPage */
  int nUsable = (int)pPage.pBt.usableSize; /* Usable size of page */

  Debug.Assert( pPage.nOverflow == 0 );
  Debug.Assert( sqlite3_mutex_held( pPage.pBt.mutex ) );
  Debug.Assert( nCell >= 0 && nCell <= MX_CELL( pPage.pBt ) && MX_CELL( pPage.pBt ) <= 5460 );
  Debug.Assert( sqlite3PagerIswriteable( pPage.pDbPage ) );

  /* Check that the page has just been zeroed by zeroPage() */
  Debug.Assert( pPage.nCell == 0 );
  Debug.Assert( get2byte( data, hdr + 5 ) == nUsable );

  pCellptr = pPage.cellOffset + nCell * 2; //data[pPage.cellOffset + nCell * 2];
  cellbody = nUsable;
  for ( i = nCell - 1; i >= 0; i-- )
  {
    pCellptr -= 2;
    cellbody -= aSize[i + offset];
    put2byte( data, pCellptr, cellbody );
    Buffer.BlockCopy( apCell[offset + i], 0, data, cellbody, aSize[i + offset] );//          memcpy(&data[cellbody], apCell[i], aSize[i]);
  }
  put2byte( data, hdr + 3, nCell );
  put2byte( data, hdr + 5, cellbody );
  pPage.nFree -= (u16)( nCell * 2 + nUsable - cellbody );
  pPage.nCell = (u16)nCell;
}

static void assemblePage(
MemPage pPage,    /* The page to be assemblied */
int nCell,        /* The number of cells to add to this page */
u8[] apCell,      /* Pointers to cell bodies */
u16[] aSize       /* Sizes of the cells */
)
{
  int i;            /* Loop counter */
  int pCellptr;     /* Address of next cell pointer */
  int cellbody;     /* Address of next cell body */
  u8[] data = pPage.aData;             /* Pointer to data for pPage */
  int hdr = pPage.hdrOffset;           /* Offset of header on pPage */
  int nUsable = (int)pPage.pBt.usableSize; /* Usable size of page */

  Debug.Assert( pPage.nOverflow == 0 );
  Debug.Assert( sqlite3_mutex_held( pPage.pBt.mutex ) );
  Debug.Assert( nCell >= 0 && nCell <= MX_CELL( pPage.pBt ) && MX_CELL( pPage.pBt ) <= 5460 );
  Debug.Assert( sqlite3PagerIswriteable( pPage.pDbPage ) );

  /* Check that the page has just been zeroed by zeroPage() */
  Debug.Assert( pPage.nCell == 0 );
  Debug.Assert( get2byte( data, hdr + 5 ) == nUsable );

  pCellptr = pPage.cellOffset + nCell * 2; //&data[pPage.cellOffset + nCell * 2];
  cellbody = nUsable;
  for ( i = nCell - 1; i >= 0; i-- )
  {
    pCellptr -= 2;
    cellbody -= aSize[i];
    put2byte( data, pCellptr, cellbody );
    Buffer.BlockCopy( apCell, 0, data, cellbody, aSize[i] );//memcpy( data[cellbody], apCell[i], aSize[i] );
  }
  put2byte( data, hdr + 3, nCell );
  put2byte( data, hdr + 5, cellbody );
  pPage.nFree -= (u16)( nCell * 2 + nUsable - cellbody );
  pPage.nCell = (u16)nCell;
}

/*
** The following parameters determine how many adjacent pages get involved
** in a balancing operation.  NN is the number of neighbors on either side
** of the page that participate in the balancing operation.  NB is the
** total number of pages that participate, including the target page and
** NN neighbors on either side.
**
** The minimum value of NN is 1 (of course).  Increasing NN above 1
** (to 2 or 3) gives a modest improvement in SELECT and DELETE performance
** in exchange for a larger degradation in INSERT and UPDATE performance.
** The value of NN appears to give the best results overall.
*/
static int NN = 1;              /* Number of neighbors on either side of pPage */
static int NB = ( NN * 2 + 1 );   /* Total pages involved in the balance */

#if !SQLITE_OMIT_QUICKBALANCE
/*
** This version of balance() handles the common special case where
** a new entry is being inserted on the extreme right-end of the
** tree, in other words, when the new entry will become the largest
** entry in the tree.
**
** Instead of trying to balance the 3 right-most leaf pages, just add
** a new page to the right-hand side and put the one new entry in
** that page.  This leaves the right side of the tree somewhat
** unbalanced.  But odds are that we will be inserting new entries
** at the end soon afterwards so the nearly empty page will quickly
** fill up.  On average.
**
** pPage is the leaf page which is the right-most page in the tree.
** pParent is its parent.  pPage must have a single overflow entry
** which is also the right-most entry on the page.
**
** The pSpace buffer is used to store a temporary copy of the divider
** cell that will be inserted into pParent. Such a cell consists of a 4
** byte page number followed by a variable length integer. In other
** words, at most 13 bytes. Hence the pSpace buffer must be at
** least 13 bytes in size.
*/
static int balance_quick( MemPage pParent, MemPage pPage, u8[] pSpace )
{
  BtShared pBt = pPage.pBt;    /* B-Tree Database */
  MemPage pNew = new MemPage();/* Newly allocated page */
  int rc;                      /* Return Code */
  Pgno pgnoNew = 0;              /* Page number of pNew */

  Debug.Assert( sqlite3_mutex_held( pPage.pBt.mutex ) );
  Debug.Assert( sqlite3PagerIswriteable( pParent.pDbPage ) );
  Debug.Assert( pPage.nOverflow == 1 );

  /* This error condition is now caught prior to reaching this function */
  if ( pPage.nCell <= 0 )
    return SQLITE_CORRUPT_BKPT();

  /* Allocate a new page. This page will become the right-sibling of
  ** pPage. Make the parent page writable, so that the new divider cell
  ** may be inserted. If both these operations are successful, proceed.
  */
  rc = allocateBtreePage( pBt, ref pNew, ref pgnoNew, 0, 0 );

  if ( rc == SQLITE_OK )
  {

    int pOut = 4;//u8 pOut = &pSpace[4];
    u8[] pCell = pPage.aOvfl[0].pCell;
    int[] szCell = new int[1];
    szCell[0] = cellSizePtr( pPage, pCell );
    int pStop;

    Debug.Assert( sqlite3PagerIswriteable( pNew.pDbPage ) );
    Debug.Assert( pPage.aData[0] == ( PTF_INTKEY | PTF_LEAFDATA | PTF_LEAF ) );
    zeroPage( pNew, PTF_INTKEY | PTF_LEAFDATA | PTF_LEAF );
    assemblePage( pNew, 1, pCell, szCell );

    /* If this is an auto-vacuum database, update the pointer map
    ** with entries for the new page, and any pointer from the
    ** cell on the page to an overflow page. If either of these
    ** operations fails, the return code is set, but the contents
    ** of the parent page are still manipulated by thh code below.
    ** That is Ok, at this point the parent page is guaranteed to
    ** be marked as dirty. Returning an error code will cause a
    ** rollback, undoing any changes made to the parent page.
    */
#if !SQLITE_OMIT_AUTOVACUUM //   if ( ISAUTOVACUUM )
    if ( pBt.autoVacuum )
#else
if (false)
#endif
    {
      ptrmapPut( pBt, pgnoNew, PTRMAP_BTREE, pParent.pgno, ref rc );
      if ( szCell[0] > pNew.minLocal )
      {
        ptrmapPutOvflPtr( pNew, pCell, ref rc );
      }
    }

    /* Create a divider cell to insert into pParent. The divider cell
    ** consists of a 4-byte page number (the page number of pPage) and
    ** a variable length key value (which must be the same value as the
    ** largest key on pPage).
    **
    ** To find the largest key value on pPage, first find the right-most
    ** cell on pPage. The first two fields of this cell are the
    ** record-length (a variable length integer at most 32-bits in size)
    ** and the key value (a variable length integer, may have any value).
    ** The first of the while(...) loops below skips over the record-length
    ** field. The second while(...) loop copies the key value from the
    ** cell on pPage into the pSpace buffer.
    */
    int iCell = findCell( pPage, pPage.nCell - 1 ); //pCell = findCell( pPage, pPage.nCell - 1 );
    pCell = pPage.aData;
    int _pCell = iCell;
    pStop = _pCell + 9; //pStop = &pCell[9];
    while ( ( ( pCell[_pCell++] ) & 0x80 ) != 0 && _pCell < pStop )
      ; //while ( ( *( pCell++ ) & 0x80 ) && pCell < pStop ) ;
    pStop = _pCell + 9;//pStop = &pCell[9];
    while ( ( ( pSpace[pOut++] = pCell[_pCell++] ) & 0x80 ) != 0 && _pCell < pStop )
      ; //while ( ( ( *( pOut++ ) = *( pCell++ ) ) & 0x80 ) && pCell < pStop ) ;

    /* Insert the new divider cell into pParent. */
    insertCell( pParent, pParent.nCell, pSpace, pOut, //(int)(pOut-pSpace),
    null, pPage.pgno, ref rc );

    /* Set the right-child pointer of pParent to point to the new page. */
    sqlite3Put4byte( pParent.aData, pParent.hdrOffset + 8, pgnoNew );

    /* Release the reference to the new page. */
    releasePage( pNew );
  }

  return rc;
}
#endif //* SQLITE_OMIT_QUICKBALANCE */

#if FALSE
/*
** This function does not contribute anything to the operation of SQLite.
** it is sometimes activated temporarily while debugging code responsible
** for setting pointer-map entries.
*/
static int ptrmapCheckPages(MemPage **apPage, int nPage){
int i, j;
for(i=0; i<nPage; i++){
Pgno n;
u8 e;
MemPage pPage = apPage[i];
BtShared pBt = pPage.pBt;
Debug.Assert( pPage.isInit!=0 );

for(j=0; j<pPage.nCell; j++){
CellInfo info;
u8 *z;

z = findCell(pPage, j);
btreeParseCellPtr(pPage, z,  info);
if( info.iOverflow ){
Pgno ovfl = sqlite3Get4byte(z[info.iOverflow]);
ptrmapGet(pBt, ovfl, ref e, ref n);
Debug.Assert( n==pPage.pgno && e==PTRMAP_OVERFLOW1 );
}
if( 0==pPage.leaf ){
Pgno child = sqlite3Get4byte(z);
ptrmapGet(pBt, child, ref e, ref n);
Debug.Assert( n==pPage.pgno && e==PTRMAP_BTREE );
}
}
if( 0==pPage.leaf ){
Pgno child = sqlite3Get4byte(pPage.aData,pPage.hdrOffset+8]);
ptrmapGet(pBt, child, ref e, ref n);
Debug.Assert( n==pPage.pgno && e==PTRMAP_BTREE );
}
}
return 1;
}
#endif

/*
** This function is used to copy the contents of the b-tree node stored
** on page pFrom to page pTo. If page pFrom was not a leaf page, then
** the pointer-map entries for each child page are updated so that the
** parent page stored in the pointer map is page pTo. If pFrom contained
** any cells with overflow page pointers, then the corresponding pointer
** map entries are also updated so that the parent page is page pTo.
**
** If pFrom is currently carrying any overflow cells (entries in the
** MemPage.aOvfl[] array), they are not copied to pTo.
**
** Before returning, page pTo is reinitialized using btreeInitPage().
**
** The performance of this function is not critical. It is only used by
** the balance_shallower() and balance_deeper() procedures, neither of
** which are called often under normal circumstances.
*/
static void copyNodeContent( MemPage pFrom, MemPage pTo, ref int pRC )
{
  if ( ( pRC ) == SQLITE_OK )
  {
    BtShared pBt = pFrom.pBt;
    u8[] aFrom = pFrom.aData;
    u8[] aTo = pTo.aData;
    int iFromHdr = pFrom.hdrOffset;
    int iToHdr = ( ( pTo.pgno == 1 ) ? 100 : 0 );
    int rc;
    int iData;


    Debug.Assert( pFrom.isInit != 0 );
    Debug.Assert( pFrom.nFree >= iToHdr );
    Debug.Assert( get2byte( aFrom, iFromHdr + 5 ) <= (int)pBt.usableSize );

    /* Copy the b-tree node content from page pFrom to page pTo. */
    iData = get2byte( aFrom, iFromHdr + 5 );
    Buffer.BlockCopy( aFrom, iData, aTo, iData, (int)pBt.usableSize - iData );//memcpy(aTo[iData], ref aFrom[iData], pBt.usableSize-iData);
    Buffer.BlockCopy( aFrom, iFromHdr, aTo, iToHdr, pFrom.cellOffset + 2 * pFrom.nCell );//memcpy(aTo[iToHdr], ref aFrom[iFromHdr], pFrom.cellOffset + 2*pFrom.nCell);

    /* Reinitialize page pTo so that the contents of the MemPage structure
    ** match the new data. The initialization of pTo can actually fail under
    ** fairly obscure circumstances, even though it is a copy of initialized 
    ** page pFrom.
    */
    pTo.isInit = 0;
    rc = btreeInitPage( pTo );
    if ( rc != SQLITE_OK )
    {
      pRC = rc;
      return;
    }

    /* If this is an auto-vacuum database, update the pointer-map entries
    ** for any b-tree or overflow pages that pTo now contains the pointers to.
    */
#if !SQLITE_OMIT_AUTOVACUUM //   if ( ISAUTOVACUUM )
    if ( pBt.autoVacuum )
#else
if (false)
#endif
    {
      pRC = setChildPtrmaps( pTo );
    }
  }
}

/*
** This routine redistributes cells on the iParentIdx'th child of pParent
** (hereafter "the page") and up to 2 siblings so that all pages have about the
** same amount of free space. Usually a single sibling on either side of the
** page are used in the balancing, though both siblings might come from one
** side if the page is the first or last child of its parent. If the page
** has fewer than 2 siblings (something which can only happen if the page
** is a root page or a child of a root page) then all available siblings
** participate in the balancing.
**
** The number of siblings of the page might be increased or decreased by
** one or two in an effort to keep pages nearly full but not over full.
**
** Note that when this routine is called, some of the cells on the page
** might not actually be stored in MemPage.aData[]. This can happen
** if the page is overfull. This routine ensures that all cells allocated
** to the page and its siblings fit into MemPage.aData[] before returning.
**
** In the course of balancing the page and its siblings, cells may be
** inserted into or removed from the parent page (pParent). Doing so
** may cause the parent page to become overfull or underfull. If this
** happens, it is the responsibility of the caller to invoke the correct
** balancing routine to fix this problem (see the balance() routine).
**
** If this routine fails for any reason, it might leave the database
** in a corrupted state. So if this routine fails, the database should
** be rolled back.
**
** The third argument to this function, aOvflSpace, is a pointer to a
** buffer big enough to hold one page. If while inserting cells into the parent
** page (pParent) the parent page becomes overfull, this buffer is
** used to store the parent's overflow cells. Because this function inserts
** a maximum of four divider cells into the parent page, and the maximum
** size of a cell stored within an internal node is always less than 1/4
** of the page-size, the aOvflSpace[] buffer is guaranteed to be large
** enough for all overflow cells.
**
** If aOvflSpace is set to a null pointer, this function returns
** SQLITE_NOMEM.
*/

// under C#; Try to reuse Memory

static int balance_nonroot(
MemPage pParent,               /* Parent page of siblings being balanced */
int iParentIdx,                /* Index of "the page" in pParent */
u8[] aOvflSpace,               /* page-size bytes of space for parent ovfl */
int isRoot                     /* True if pParent is a root-page */
)
{
  MemPage[] apOld = new MemPage[NB];    /* pPage and up to two siblings */
  MemPage[] apCopy = new MemPage[NB];   /* Private copies of apOld[] pages */
  MemPage[] apNew = new MemPage[NB + 2];/* pPage and up to NB siblings after balancing */
  int[] apDiv = new int[NB - 1];        /* Divider cells in pParent */
  int[] cntNew = new int[NB + 2];       /* Index in aCell[] of cell after i-th page */
  int[] szNew = new int[NB + 2];        /* Combined size of cells place on i-th page */
  u16[] szCell = new u16[1];            /* Local size of all cells in apCell[] */
  BtShared pBt;                /* The whole database */
  int nCell = 0;               /* Number of cells in apCell[] */
  int nMaxCells = 0;           /* Allocated size of apCell, szCell, aFrom. */
  int nNew = 0;                /* Number of pages in apNew[] */
  int nOld;                    /* Number of pages in apOld[] */
  int i, j, k;                 /* Loop counters */
  int nxDiv;                   /* Next divider slot in pParent.aCell[] */
  int rc = SQLITE_OK;          /* The return code */
  u16 leafCorrection;          /* 4 if pPage is a leaf.  0 if not */
  int leafData;                /* True if pPage is a leaf of a LEAFDATA tree */
  int usableSpace;             /* Bytes in pPage beyond the header */
  int pageFlags;               /* Value of pPage.aData[0] */
  int subtotal;                /* Subtotal of bytes in cells on one page */
  //int iSpace1 = 0;             /* First unused byte of aSpace1[] */
  int iOvflSpace = 0;          /* First unused byte of aOvflSpace[] */
  int szScratch;               /* Size of scratch memory requested */
  int pRight;                  /* Location in parent of right-sibling pointer */
  u8[][] apCell = null;                 /* All cells begin balanced */
  //u16[] szCell;                         /* Local size of all cells in apCell[] */
  //u8[] aSpace1;                         /* Space for copies of dividers cells */
  Pgno pgno;                   /* Temp var to store a page number in */

  pBt = pParent.pBt;
  Debug.Assert( sqlite3_mutex_held( pBt.mutex ) );
  Debug.Assert( sqlite3PagerIswriteable( pParent.pDbPage ) );

#if FALSE
TRACE("BALANCE: begin page %d child of %d\n", pPage.pgno, pParent.pgno);
#endif

  /* At this point pParent may have at most one overflow cell. And if
** this overflow cell is present, it must be the cell with
** index iParentIdx. This scenario comes about when this function
** is called (indirectly) from sqlite3BtreeDelete().
*/
  Debug.Assert( pParent.nOverflow == 0 || pParent.nOverflow == 1 );
  Debug.Assert( pParent.nOverflow == 0 || pParent.aOvfl[0].idx == iParentIdx );

  //if( !aOvflSpace ){
  //  return SQLITE_NOMEM;
  //}

  /* Find the sibling pages to balance. Also locate the cells in pParent
  ** that divide the siblings. An attempt is made to find NN siblings on
  ** either side of pPage. More siblings are taken from one side, however,
  ** if there are fewer than NN siblings on the other side. If pParent
  ** has NB or fewer children then all children of pParent are taken.
  **
  ** This loop also drops the divider cells from the parent page. This
  ** way, the remainder of the function does not have to deal with any
  ** overflow cells in the parent page, since if any existed they will
  ** have already been removed.
  */
  i = pParent.nOverflow + pParent.nCell;
  if ( i < 2 )
  {
    nxDiv = 0;
    nOld = i + 1;
  }
  else
  {
    nOld = 3;
    if ( iParentIdx == 0 )
    {
      nxDiv = 0;
    }
    else if ( iParentIdx == i )
    {
      nxDiv = i - 2;
    }
    else
    {
      nxDiv = iParentIdx - 1;
    }
    i = 2;
  }
  if ( ( i + nxDiv - pParent.nOverflow ) == pParent.nCell )
  {
    pRight = pParent.hdrOffset + 8; //&pParent.aData[pParent.hdrOffset + 8];
  }
  else
  {
    pRight = findCell( pParent, i + nxDiv - pParent.nOverflow );
  }
  pgno = sqlite3Get4byte( pParent.aData, pRight );
  while ( true )
  {
    rc = getAndInitPage( pBt, pgno, ref apOld[i] );
    if ( rc != 0 )
    {
      //memset(apOld, 0, (i+1)*sizeof(MemPage*));
      goto balance_cleanup;
    }
    nMaxCells += 1 + apOld[i].nCell + apOld[i].nOverflow;
    if ( ( i-- ) == 0 )
      break;

    if ( i + nxDiv == pParent.aOvfl[0].idx && pParent.nOverflow != 0 )
    {
      apDiv[i] = 0;// = pParent.aOvfl[0].pCell;
      pgno = sqlite3Get4byte( pParent.aOvfl[0].pCell, apDiv[i] );
      szNew[i] = cellSizePtr( pParent, apDiv[i] );
      pParent.nOverflow = 0;
    }
    else
    {
      apDiv[i] = findCell( pParent, i + nxDiv - pParent.nOverflow );
      pgno = sqlite3Get4byte( pParent.aData, apDiv[i] );
      szNew[i] = cellSizePtr( pParent, apDiv[i] );

      /* Drop the cell from the parent page. apDiv[i] still points to
      ** the cell within the parent, even though it has been dropped.
      ** This is safe because dropping a cell only overwrites the first
      ** four bytes of it, and this function does not need the first
      ** four bytes of the divider cell. So the pointer is safe to use
      ** later on.
      **
      ** Unless SQLite is compiled in secure-delete mode. In this case,
      ** the dropCell() routine will overwrite the entire cell with zeroes.
      ** In this case, temporarily copy the cell into the aOvflSpace[]
      ** buffer. It will be copied out again as soon as the aSpace[] buffer
      ** is allocated.  */
      //if (pBt.secureDelete)
      //{
      //  int iOff = (int)(apDiv[i]) - (int)(pParent.aData); //SQLITE_PTR_TO_INT(apDiv[i]) - SQLITE_PTR_TO_INT(pParent.aData);
      //         if( (iOff+szNew[i])>(int)pBt->usableSize )
      //  {
      //    rc = SQLITE_CORRUPT_BKPT();
      //    Array.Clear(apOld[0].aData,0,apOld[0].aData.Length); //memset(apOld, 0, (i + 1) * sizeof(MemPage*));
      //    goto balance_cleanup;
      //  }
      //  else
      //  {
      //    memcpy(&aOvflSpace[iOff], apDiv[i], szNew[i]);
      //    apDiv[i] = &aOvflSpace[apDiv[i] - pParent.aData];
      //  }
      //}
      dropCell( pParent, i + nxDiv - pParent.nOverflow, szNew[i], ref rc );
    }
  }

  /* Make nMaxCells a multiple of 4 in order to preserve 8-byte
  ** alignment */
  nMaxCells = ( nMaxCells + 3 ) & ~3;

  /*
  ** Allocate space for memory structures
  */
  //k = pBt.pageSize + ROUND8(sizeof(MemPage));
  //szScratch =
  //     nMaxCells*sizeof(u8*)                       /* apCell */
  //   + nMaxCells*sizeof(u16)                       /* szCell */
  //   + pBt.pageSize                               /* aSpace1 */
  //   + k*nOld;                                     /* Page copies (apCopy) */
  apCell = sqlite3ScratchMalloc( apCell, nMaxCells );
  //if( apCell==null ){
  //  rc = SQLITE_NOMEM;
  //  goto balance_cleanup;
  //}
  if ( szCell.Length < nMaxCells )
    Array.Resize( ref szCell, nMaxCells ); //(u16*)&apCell[nMaxCells];
  //aSpace1 = new byte[pBt.pageSize * (nMaxCells)];//  aSpace1 = (u8*)&szCell[nMaxCells];
  //Debug.Assert( EIGHT_BYTE_ALIGNMENT(aSpace1) );

  /*
  ** Load pointers to all cells on sibling pages and the divider cells
  ** into the local apCell[] array.  Make copies of the divider cells
  ** into space obtained from aSpace1[] and remove the the divider Cells
  ** from pParent.
  **
  ** If the siblings are on leaf pages, then the child pointers of the
  ** divider cells are stripped from the cells before they are copied
  ** into aSpace1[].  In this way, all cells in apCell[] are without
  ** child pointers.  If siblings are not leaves, then all cell in
  ** apCell[] include child pointers.  Either way, all cells in apCell[]
  ** are alike.
  **
  ** leafCorrection:  4 if pPage is a leaf.  0 if pPage is not a leaf.
  **       leafData:  1 if pPage holds key+data and pParent holds only keys.
  */
  leafCorrection = (u16)( apOld[0].leaf * 4 );
  leafData = apOld[0].hasData;
  for ( i = 0; i < nOld; i++ )
  {
    int limit;

    /* Before doing anything else, take a copy of the i'th original sibling
    ** The rest of this function will use data from the copies rather
    ** that the original pages since the original pages will be in the
    ** process of being overwritten.  */
    //MemPage pOld = apCopy[i] = (MemPage*)&aSpace1[pBt.pageSize + k*i];
    //memcpy(pOld, apOld[i], sizeof(MemPage));
    //pOld.aData = (void*)&pOld[1];
    //memcpy(pOld.aData, apOld[i].aData, pBt.pageSize);
    MemPage pOld = apCopy[i] = apOld[i].Copy();

    limit = pOld.nCell + pOld.nOverflow;
    if( pOld.nOverflow>0 || true){
    for ( j = 0; j < limit; j++ )
    {
      Debug.Assert( nCell < nMaxCells );
      //apCell[nCell] = findOverflowCell( pOld, j );
      //szCell[nCell] = cellSizePtr( pOld, apCell, nCell );
      int iFOFC = findOverflowCell( pOld, j );
      szCell[nCell] = cellSizePtr( pOld, iFOFC );
      // Copy the Data Locally
      if ( apCell[nCell] == null )
        apCell[nCell] = new u8[szCell[nCell]];
      else if ( apCell[nCell].Length < szCell[nCell] )
        Array.Resize( ref apCell[nCell], szCell[nCell] );
      if ( iFOFC < 0 )  // Overflow Cell
        Buffer.BlockCopy( pOld.aOvfl[-( iFOFC + 1 )].pCell, 0, apCell[nCell], 0, szCell[nCell] );
      else
        Buffer.BlockCopy( pOld.aData, iFOFC, apCell[nCell], 0, szCell[nCell] );
      nCell++;
    }
    }
    else
    {
      u8[] aData = pOld.aData;
      u16 maskPage = pOld.maskPage;
      u16 cellOffset = pOld.cellOffset;
      for ( j = 0; j < limit; j++ )
      {
        Debugger.Break();
        Debug.Assert( nCell < nMaxCells );
        apCell[nCell] = findCellv2( aData, maskPage, cellOffset, j );
        szCell[nCell] = cellSizePtr( pOld, apCell[nCell] );
        nCell++;
      }
    }
    if ( i < nOld - 1 && 0 == leafData )
    {
      u16 sz = (u16)szNew[i];
      byte[] pTemp = sqlite3Malloc( sz + leafCorrection );
      Debug.Assert( nCell < nMaxCells );
      szCell[nCell] = sz;
      //pTemp = &aSpace1[iSpace1];
      //iSpace1 += sz;
      Debug.Assert( sz <= pBt.maxLocal + 23 );
      //Debug.Assert(iSpace1 <= (int)pBt.pageSize);
      Buffer.BlockCopy( pParent.aData, apDiv[i], pTemp, 0, sz );//memcpy( pTemp, apDiv[i], sz );
      if ( apCell[nCell] == null || apCell[nCell].Length < sz )
        Array.Resize( ref apCell[nCell], sz );
      Buffer.BlockCopy( pTemp, leafCorrection, apCell[nCell], 0, sz );//apCell[nCell] = pTemp + leafCorrection;
      Debug.Assert( leafCorrection == 0 || leafCorrection == 4 );
      szCell[nCell] = (u16)( szCell[nCell] - leafCorrection );
      if ( 0 == pOld.leaf )
      {
        Debug.Assert( leafCorrection == 0 );
        Debug.Assert( pOld.hdrOffset == 0 );
        /* The right pointer of the child page pOld becomes the left
        ** pointer of the divider cell */
        Buffer.BlockCopy( pOld.aData, 8, apCell[nCell], 0, 4 );//memcpy( apCell[nCell], ref pOld.aData[8], 4 );
      }
      else
      {
        Debug.Assert( leafCorrection == 4 );
        if ( szCell[nCell] < 4 )
        {
          /* Do not allow any cells smaller than 4 bytes. */
          szCell[nCell] = 4;
        }
      }
      nCell++;
    }
  }

  /*
  ** Figure out the number of pages needed to hold all nCell cells.
  ** Store this number in "k".  Also compute szNew[] which is the total
  ** size of all cells on the i-th page and cntNew[] which is the index
  ** in apCell[] of the cell that divides page i from page i+1.
  ** cntNew[k] should equal nCell.
  **
  ** Values computed by this block:
  **
  **           k: The total number of sibling pages
  **    szNew[i]: Spaced used on the i-th sibling page.
  **   cntNew[i]: Index in apCell[] and szCell[] for the first cell to
  **              the right of the i-th sibling page.
  ** usableSpace: Number of bytes of space available on each sibling.
  **
  */
  usableSpace = (int)pBt.usableSize - 12 + leafCorrection;
  for ( subtotal = k = i = 0; i < nCell; i++ )
  {
    Debug.Assert( i < nMaxCells );
    subtotal += szCell[i] + 2;
    if ( subtotal > usableSpace )
    {
      szNew[k] = subtotal - szCell[i];
      cntNew[k] = i;
      if ( leafData != 0 )
      {
        i--;
      }
      subtotal = 0;
      k++;
      if ( k > NB + 1 )
      {
        rc = SQLITE_CORRUPT_BKPT();
        goto balance_cleanup;
      }
    }
  }
  szNew[k] = subtotal;
  cntNew[k] = nCell;
  k++;

  /*
  ** The packing computed by the previous block is biased toward the siblings
  ** on the left side.  The left siblings are always nearly full, while the
  ** right-most sibling might be nearly empty.  This block of code attempts
  ** to adjust the packing of siblings to get a better balance.
  **
  ** This adjustment is more than an optimization.  The packing above might
  ** be so out of balance as to be illegal.  For example, the right-most
  ** sibling might be completely empty.  This adjustment is not optional.
  */
  for ( i = k - 1; i > 0; i-- )
  {
    int szRight = szNew[i];  /* Size of sibling on the right */
    int szLeft = szNew[i - 1]; /* Size of sibling on the left */
    int r;              /* Index of right-most cell in left sibling */
    int d;              /* Index of first cell to the left of right sibling */

    r = cntNew[i - 1] - 1;
    d = r + 1 - leafData;
    Debug.Assert( d < nMaxCells );
    Debug.Assert( r < nMaxCells );
    while ( szRight == 0 || szRight + szCell[d] + 2 <= szLeft - ( szCell[r] + 2 ) )
    {
      szRight += szCell[d] + 2;
      szLeft -= szCell[r] + 2;
      cntNew[i - 1]--;
      r = cntNew[i - 1] - 1;
      d = r + 1 - leafData;
    }
    szNew[i] = szRight;
    szNew[i - 1] = szLeft;
  }

  /* Either we found one or more cells (cntnew[0])>0) or pPage is
  ** a virtual root page.  A virtual root page is when the real root
  ** page is page 1 and we are the only child of that page.
  */
  Debug.Assert( cntNew[0] > 0 || ( pParent.pgno == 1 && pParent.nCell == 0 ) );

  TRACE( "BALANCE: old: %d %d %d  ",
  apOld[0].pgno,
  nOld >= 2 ? apOld[1].pgno : 0,
  nOld >= 3 ? apOld[2].pgno : 0
  );

  /*
  ** Allocate k new pages.  Reuse old pages where possible.
  */
  if ( apOld[0].pgno <= 1 )
  {
    rc = SQLITE_CORRUPT_BKPT();
    goto balance_cleanup;
  }
  pageFlags = apOld[0].aData[0];
  for ( i = 0; i < k; i++ )
  {
    MemPage pNew = new MemPage();
    if ( i < nOld )
    {
      pNew = apNew[i] = apOld[i];
      apOld[i] = null;
      rc = sqlite3PagerWrite( pNew.pDbPage );
      nNew++;
      if ( rc != 0 )
        goto balance_cleanup;
    }
    else
    {
      Debug.Assert( i > 0 );
      rc = allocateBtreePage( pBt, ref pNew, ref pgno, pgno, 0 );
      if ( rc != 0 )
        goto balance_cleanup;
      apNew[i] = pNew;
      nNew++;

      /* Set the pointer-map entry for the new sibling page. */
#if !SQLITE_OMIT_AUTOVACUUM //   if ( ISAUTOVACUUM )
      if ( pBt.autoVacuum )
#else
if (false)
#endif
      {
        ptrmapPut( pBt, pNew.pgno, PTRMAP_BTREE, pParent.pgno, ref rc );
        if ( rc != SQLITE_OK )
        {
          goto balance_cleanup;
        }
      }
    }
  }

  /* Free any old pages that were not reused as new pages.
  */
  while ( i < nOld )
  {
    freePage( apOld[i], ref rc );
    if ( rc != 0 )
      goto balance_cleanup;
    releasePage( apOld[i] );
    apOld[i] = null;
    i++;
  }

  /*
  ** Put the new pages in accending order.  This helps to
  ** keep entries in the disk file in order so that a scan
  ** of the table is a linear scan through the file.  That
  ** in turn helps the operating system to deliver pages
  ** from the disk more rapidly.
  **
  ** An O(n^2) insertion sort algorithm is used, but since
  ** n is never more than NB (a small constant), that should
  ** not be a problem.
  **
  ** When NB==3, this one optimization makes the database
  ** about 25% faster for large insertions and deletions.
  */
  for ( i = 0; i < k - 1; i++ )
  {
    int minV = (int)apNew[i].pgno;
    int minI = i;
    for ( j = i + 1; j < k; j++ )
    {
      if ( apNew[j].pgno < (u32)minV )
      {
        minI = j;
        minV = (int)apNew[j].pgno;
      }
    }
    if ( minI > i )
    {
      MemPage pT;
      pT = apNew[i];
      apNew[i] = apNew[minI];
      apNew[minI] = pT;
    }
  }
  TRACE( "new: %d(%d) %d(%d) %d(%d) %d(%d) %d(%d)\n",
  apNew[0].pgno, szNew[0],
  nNew >= 2 ? apNew[1].pgno : 0, nNew >= 2 ? szNew[1] : 0,
  nNew >= 3 ? apNew[2].pgno : 0, nNew >= 3 ? szNew[2] : 0,
  nNew >= 4 ? apNew[3].pgno : 0, nNew >= 4 ? szNew[3] : 0,
  nNew >= 5 ? apNew[4].pgno : 0, nNew >= 5 ? szNew[4] : 0 );

  Debug.Assert( sqlite3PagerIswriteable( pParent.pDbPage ) );
  sqlite3Put4byte( pParent.aData, pRight, apNew[nNew - 1].pgno );

  /*
  ** Evenly distribute the data in apCell[] across the new pages.
  ** Insert divider cells into pParent as necessary.
  */
  j = 0;
  for ( i = 0; i < nNew; i++ )
  {
    /* Assemble the new sibling page. */
    MemPage pNew = apNew[i];
    Debug.Assert( j < nMaxCells );
    zeroPage( pNew, pageFlags );
    assemblePage( pNew, cntNew[i] - j, apCell, szCell, j );
    Debug.Assert( pNew.nCell > 0 || ( nNew == 1 && cntNew[0] == 0 ) );
    Debug.Assert( pNew.nOverflow == 0 );

    j = cntNew[i];

    /* If the sibling page assembled above was not the right-most sibling,
    ** insert a divider cell into the parent page.
    */
    Debug.Assert( i < nNew - 1 || j == nCell );
    if ( j < nCell )
    {
      u8[] pCell;
      u8[] pTemp;
      int sz;

      Debug.Assert( j < nMaxCells );
      pCell = apCell[j];
      sz = szCell[j] + leafCorrection;
      pTemp = sqlite3Malloc( sz );//&aOvflSpace[iOvflSpace];
      if ( 0 == pNew.leaf )
      {
        Buffer.BlockCopy( pCell, 0, pNew.aData, 8, 4 );//memcpy( pNew.aData[8], pCell, 4 );
      }
      else if ( leafData != 0 )
      {
        /* If the tree is a leaf-data tree, and the siblings are leaves,
        ** then there is no divider cell in apCell[]. Instead, the divider
        ** cell consists of the integer key for the right-most cell of
        ** the sibling-page assembled above only.
        */
        CellInfo info = new CellInfo();
        j--;
        btreeParseCellPtr( pNew, apCell[j], ref info );
        pCell = pTemp;
        sz = 4 + putVarint( pCell, 4, (u64)info.nKey );
        pTemp = null;
      }
      else
      {
        //------------ pCell -= 4;
        byte[] _pCell_4 = sqlite3Malloc( pCell.Length + 4 );
        Buffer.BlockCopy( pCell, 0, _pCell_4, 4, pCell.Length );
        pCell = _pCell_4;
        //
        /* Obscure case for non-leaf-data trees: If the cell at pCell was
        ** previously stored on a leaf node, and its reported size was 4
        ** bytes, then it may actually be smaller than this
        ** (see btreeParseCellPtr(), 4 bytes is the minimum size of
        ** any cell). But it is important to pass the correct size to
        ** insertCell(), so reparse the cell now.
        **
        ** Note that this can never happen in an SQLite data file, as all
        ** cells are at least 4 bytes. It only happens in b-trees used
        ** to evaluate "IN (SELECT ...)" and similar clauses.
        */
        if ( szCell[j] == 4 )
        {
          Debug.Assert( leafCorrection == 4 );
          sz = cellSizePtr( pParent, pCell );
        }
      }
      iOvflSpace += sz;
      Debug.Assert( sz <= pBt.maxLocal + 23 );
      Debug.Assert( iOvflSpace <= (int)pBt.pageSize );
      insertCell( pParent, nxDiv, pCell, sz, pTemp, pNew.pgno, ref rc );
      if ( rc != SQLITE_OK )
        goto balance_cleanup;
      Debug.Assert( sqlite3PagerIswriteable( pParent.pDbPage ) );

      j++;
      nxDiv++;
    }
  }
  Debug.Assert( j == nCell );
  Debug.Assert( nOld > 0 );
  Debug.Assert( nNew > 0 );
  if ( ( pageFlags & PTF_LEAF ) == 0 )
  {
    Buffer.BlockCopy( apCopy[nOld - 1].aData, 8, apNew[nNew - 1].aData, 8, 4 ); //u8* zChild = &apCopy[nOld - 1].aData[8];
    //memcpy( apNew[nNew - 1].aData[8], zChild, 4 );
  }

  if ( isRoot != 0 && pParent.nCell == 0 && pParent.hdrOffset <= apNew[0].nFree )
  {
    /* The root page of the b-tree now contains no cells. The only sibling
    ** page is the right-child of the parent. Copy the contents of the
    ** child page into the parent, decreasing the overall height of the
    ** b-tree structure by one. This is described as the "balance-shallower"
    ** sub-algorithm in some documentation.
    **
    ** If this is an auto-vacuum database, the call to copyNodeContent()
    ** sets all pointer-map entries corresponding to database image pages
    ** for which the pointer is stored within the content being copied.
    **
    ** The second Debug.Assert below verifies that the child page is defragmented
    ** (it must be, as it was just reconstructed using assemblePage()). This
    ** is important if the parent page happens to be page 1 of the database
    ** image.  */
    Debug.Assert( nNew == 1 );
    Debug.Assert( apNew[0].nFree ==
    ( get2byte( apNew[0].aData, 5 ) - apNew[0].cellOffset - apNew[0].nCell * 2 )
    );
    copyNodeContent( apNew[0], pParent, ref rc );
    freePage( apNew[0], ref rc );
  }
  else
#if !SQLITE_OMIT_AUTOVACUUM //   if ( ISAUTOVACUUM )
    if ( pBt.autoVacuum )
#else
if (false)
#endif
    {
      /* Fix the pointer-map entries for all the cells that were shifted around.
      ** There are several different types of pointer-map entries that need to
      ** be dealt with by this routine. Some of these have been set already, but
      ** many have not. The following is a summary:
      **
      **   1) The entries associated with new sibling pages that were not
      **      siblings when this function was called. These have already
      **      been set. We don't need to worry about old siblings that were
      **      moved to the free-list - the freePage() code has taken care
      **      of those.
      **
      **   2) The pointer-map entries associated with the first overflow
      **      page in any overflow chains used by new divider cells. These
      **      have also already been taken care of by the insertCell() code.
      **
      **   3) If the sibling pages are not leaves, then the child pages of
      **      cells stored on the sibling pages may need to be updated.
      **
      **   4) If the sibling pages are not internal intkey nodes, then any
      **      overflow pages used by these cells may need to be updated
      **      (internal intkey nodes never contain pointers to overflow pages).
      **
      **   5) If the sibling pages are not leaves, then the pointer-map
      **      entries for the right-child pages of each sibling may need
      **      to be updated.
      **
      ** Cases 1 and 2 are dealt with above by other code. The next
      ** block deals with cases 3 and 4 and the one after that, case 5. Since
      ** setting a pointer map entry is a relatively expensive operation, this
      ** code only sets pointer map entries for child or overflow pages that have
      ** actually moved between pages.  */
      MemPage pNew = apNew[0];
      MemPage pOld = apCopy[0];
      int nOverflow = pOld.nOverflow;
      int iNextOld = pOld.nCell + nOverflow;
      int iOverflow = ( nOverflow != 0 ? pOld.aOvfl[0].idx : -1 );
      j = 0;                             /* Current 'old' sibling page */
      k = 0;                             /* Current 'new' sibling page */
      for ( i = 0; i < nCell; i++ )
      {
        int isDivider = 0;
        while ( i == iNextOld )
        {
          /* Cell i is the cell immediately following the last cell on old
          ** sibling page j. If the siblings are not leaf pages of an
          ** intkey b-tree, then cell i was a divider cell. */
          pOld = apCopy[++j];
          iNextOld = i + ( 0 == leafData ? 1 : 0 ) + pOld.nCell + pOld.nOverflow;
          if ( pOld.nOverflow != 0 )
          {
            nOverflow = pOld.nOverflow;
            iOverflow = i + ( 0 == leafData ? 1 : 0 ) + pOld.aOvfl[0].idx;
          }
          isDivider = 0 == leafData ? 1 : 0;
        }

        Debug.Assert( nOverflow > 0 || iOverflow < i );
        Debug.Assert( nOverflow < 2 || pOld.aOvfl[0].idx == pOld.aOvfl[1].idx - 1 );
        Debug.Assert( nOverflow < 3 || pOld.aOvfl[1].idx == pOld.aOvfl[2].idx - 1 );
        if ( i == iOverflow )
        {
          isDivider = 1;
          if ( ( --nOverflow ) > 0 )
          {
            iOverflow++;
          }
        }

        if ( i == cntNew[k] )
        {
          /* Cell i is the cell immediately following the last cell on new
          ** sibling page k. If the siblings are not leaf pages of an
          ** intkey b-tree, then cell i is a divider cell.  */
          pNew = apNew[++k];
          if ( 0 == leafData )
            continue;
        }
        Debug.Assert( j < nOld );
        Debug.Assert( k < nNew );

        /* If the cell was originally divider cell (and is not now) or
        ** an overflow cell, or if the cell was located on a different sibling
        ** page before the balancing, then the pointer map entries associated
        ** with any child or overflow pages need to be updated.  */
        if ( isDivider != 0 || pOld.pgno != pNew.pgno )
        {
          if ( 0 == leafCorrection )
          {
            ptrmapPut( pBt, sqlite3Get4byte( apCell[i] ), PTRMAP_BTREE, pNew.pgno, ref rc );
          }
          if ( szCell[i] > pNew.minLocal )
          {
            ptrmapPutOvflPtr( pNew, apCell[i], ref rc );
          }
        }
      }

      if ( 0 == leafCorrection )
      {
        for ( i = 0; i < nNew; i++ )
        {
          u32 key = sqlite3Get4byte( apNew[i].aData, 8 );
          ptrmapPut( pBt, key, PTRMAP_BTREE, apNew[i].pgno, ref rc );
        }
      }

#if FALSE
/* The ptrmapCheckPages() contains Debug.Assert() statements that verify that
** all pointer map pages are set correctly. This is helpful while
** debugging. This is usually disabled because a corrupt database may
** cause an Debug.Assert() statement to fail.  */
ptrmapCheckPages(apNew, nNew);
ptrmapCheckPages(pParent, 1);
#endif
    }

  Debug.Assert( pParent.isInit != 0 );
  TRACE( "BALANCE: finished: old=%d new=%d cells=%d\n",
  nOld, nNew, nCell );

/*
** Cleanup before returning.
*/
balance_cleanup:
  sqlite3ScratchFree( apCell );
  for ( i = 0; i < nOld; i++ )
  {
    releasePage( apOld[i] );
  }
  for ( i = 0; i < nNew; i++ )
  {
    releasePage( apNew[i] );
  }

  return rc;
}


/*
** This function is called when the root page of a b-tree structure is
** overfull (has one or more overflow pages).
**
** A new child page is allocated and the contents of the current root
** page, including overflow cells, are copied into the child. The root
** page is then overwritten to make it an empty page with the right-child
** pointer pointing to the new page.
**
** Before returning, all pointer-map entries corresponding to pages
** that the new child-page now contains pointers to are updated. The
** entry corresponding to the new right-child pointer of the root
** page is also updated.
**
** If successful, ppChild is set to contain a reference to the child
** page and SQLITE_OK is returned. In this case the caller is required
** to call releasePage() on ppChild exactly once. If an error occurs,
** an error code is returned and ppChild is set to 0.
*/
static int balance_deeper( MemPage pRoot, ref MemPage ppChild )
{
  int rc;                        /* Return value from subprocedures */
  MemPage pChild = null;           /* Pointer to a new child page */
  Pgno pgnoChild = 0;            /* Page number of the new child page */
  BtShared pBt = pRoot.pBt;    /* The BTree */

  Debug.Assert( pRoot.nOverflow > 0 );
  Debug.Assert( sqlite3_mutex_held( pBt.mutex ) );

  /* Make pRoot, the root page of the b-tree, writable. Allocate a new
  ** page that will become the new right-child of pPage. Copy the contents
  ** of the node stored on pRoot into the new child page.
  */
  rc = sqlite3PagerWrite( pRoot.pDbPage );
  if ( rc == SQLITE_OK )
  {
    rc = allocateBtreePage( pBt, ref pChild, ref pgnoChild, pRoot.pgno, 0 );
    copyNodeContent( pRoot, pChild, ref rc );
#if !SQLITE_OMIT_AUTOVACUUM //   if ( ISAUTOVACUUM )
    if ( pBt.autoVacuum )
#else
if (false)
#endif
    {
      ptrmapPut( pBt, pgnoChild, PTRMAP_BTREE, pRoot.pgno, ref rc );
    }
  }
  if ( rc != 0 )
  {
    ppChild = null;
    releasePage( pChild );
    return rc;
  }
  Debug.Assert( sqlite3PagerIswriteable( pChild.pDbPage ) );
  Debug.Assert( sqlite3PagerIswriteable( pRoot.pDbPage ) );
  Debug.Assert( pChild.nCell == pRoot.nCell );

  TRACE( "BALANCE: copy root %d into %d\n", pRoot.pgno, pChild.pgno );

  /* Copy the overflow cells from pRoot to pChild */
  Array.Copy( pRoot.aOvfl, pChild.aOvfl, pRoot.nOverflow );//memcpy(pChild.aOvfl, pRoot.aOvfl, pRoot.nOverflow*sizeof(pRoot.aOvfl[0]));
  pChild.nOverflow = pRoot.nOverflow;

  /* Zero the contents of pRoot. Then install pChild as the right-child. */
  zeroPage( pRoot, pChild.aData[0] & ~PTF_LEAF );
  sqlite3Put4byte( pRoot.aData, pRoot.hdrOffset + 8, pgnoChild );

  ppChild = pChild;
  return SQLITE_OK;
}

/*
** The page that pCur currently points to has just been modified in
** some way. This function figures out if this modification means the
** tree needs to be balanced, and if so calls the appropriate balancing
** routine. Balancing routines are:
**
**   balance_quick()
**   balance_deeper()
**   balance_nonroot()
*/
static u8[] aBalanceQuickSpace = new u8[13];
static int balance( BtCursor pCur )
{
  int rc = SQLITE_OK;
  int nMin = (int)pCur.pBt.usableSize * 2 / 3;

  //u8[] pFree = null;

#if !NDEBUG || SQLITE_COVERAGE_TEST || DEBUG
  int balance_quick_called = 0;//TESTONLY( int balance_quick_called = 0 );
  int balance_deeper_called = 0;//TESTONLY( int balance_deeper_called = 0 );
#else
int balance_quick_called = 0;
int balance_deeper_called = 0;
#endif

  do
  {
    int iPage = pCur.iPage;
    MemPage pPage = pCur.apPage[iPage];

    if ( iPage == 0 )
    {
      if ( pPage.nOverflow != 0 )
      {
        /* The root page of the b-tree is overfull. In this case call the
        ** balance_deeper() function to create a new child for the root-page
        ** and copy the current contents of the root-page to it. The
        ** next iteration of the do-loop will balance the child page.
        */
        Debug.Assert( ( balance_deeper_called++ ) == 0 );
        rc = balance_deeper( pPage, ref pCur.apPage[1] );
        if ( rc == SQLITE_OK )
        {
          pCur.iPage = 1;
          pCur.aiIdx[0] = 0;
          pCur.aiIdx[1] = 0;
          Debug.Assert( pCur.apPage[1].nOverflow != 0 );
        }
      }
      else
      {
        break;
      }
    }
    else if ( pPage.nOverflow == 0 && pPage.nFree <= nMin )
    {
      break;
    }
    else
    {
      MemPage pParent = pCur.apPage[iPage - 1];
      int iIdx = pCur.aiIdx[iPage - 1];

      rc = sqlite3PagerWrite( pParent.pDbPage );
      if ( rc == SQLITE_OK )
      {
#if !SQLITE_OMIT_QUICKBALANCE
        if ( pPage.hasData != 0
        && pPage.nOverflow == 1
        && pPage.aOvfl[0].idx == pPage.nCell
        && pParent.pgno != 1
        && pParent.nCell == iIdx
        )
        {
          /* Call balance_quick() to create a new sibling of pPage on which
          ** to store the overflow cell. balance_quick() inserts a new cell
          ** into pParent, which may cause pParent overflow. If this
          ** happens, the next interation of the do-loop will balance pParent
          ** use either balance_nonroot() or balance_deeper(). Until this
          ** happens, the overflow cell is stored in the aBalanceQuickSpace[]
          ** buffer.
          **
          ** The purpose of the following Debug.Assert() is to check that only a
          ** single call to balance_quick() is made for each call to this
          ** function. If this were not verified, a subtle bug involving reuse
          ** of the aBalanceQuickSpace[] might sneak in.
          */
          Debug.Assert( ( balance_quick_called++ ) == 0 );
          rc = balance_quick( pParent, pPage, aBalanceQuickSpace );
        }
        else
#endif
        {
          /* In this case, call balance_nonroot() to redistribute cells
          ** between pPage and up to 2 of its sibling pages. This involves
          ** modifying the contents of pParent, which may cause pParent to
          ** become overfull or underfull. The next iteration of the do-loop
          ** will balance the parent page to correct this.
          **
          ** If the parent page becomes overfull, the overflow cell or cells
          ** are stored in the pSpace buffer allocated immediately below.
          ** A subsequent iteration of the do-loop will deal with this by
          ** calling balance_nonroot() (balance_deeper() may be called first,
          ** but it doesn't deal with overflow cells - just moves them to a
          ** different page). Once this subsequent call to balance_nonroot()
          ** has completed, it is safe to release the pSpace buffer used by
          ** the previous call, as the overflow cell data will have been
          ** copied either into the body of a database page or into the new
          ** pSpace buffer passed to the latter call to balance_nonroot().
          */
          ////u8[] pSpace = new u8[pCur.pBt.pageSize];// u8 pSpace = sqlite3PageMalloc( pCur.pBt.pageSize );
          rc = balance_nonroot( pParent, iIdx, null, iPage == 1 ? 1 : 0 );
          //if (pFree != null)
          //{
          //  /* If pFree is not NULL, it points to the pSpace buffer used
          //  ** by a previous call to balance_nonroot(). Its contents are
          //  ** now stored either on real database pages or within the
          //  ** new pSpace buffer, so it may be safely freed here. */
          //  sqlite3PageFree(ref pFree);
          //}

          /* The pSpace buffer will be freed after the next call to
          ** balance_nonroot(), or just before this function returns, whichever
          ** comes first. */
          //pFree = pSpace;
        }
      }

      pPage.nOverflow = 0;

      /* The next iteration of the do-loop balances the parent page. */
      releasePage( pPage );
      pCur.iPage--;
    }
  } while ( rc == SQLITE_OK );

  //if (pFree != null)
  //{
  //  sqlite3PageFree(ref pFree);
  //}
  return rc;
}


/*
** Insert a new record into the BTree.  The key is given by (pKey,nKey)
** and the data is given by (pData,nData).  The cursor is used only to
** define what table the record should be inserted into.  The cursor
** is left pointing at a random location.
**
** For an INTKEY table, only the nKey value of the key is used.  pKey is
** ignored.  For a ZERODATA table, the pData and nData are both ignored.
**
** If the seekResult parameter is non-zero, then a successful call to
** MovetoUnpacked() to seek cursor pCur to (pKey, nKey) has already
** been performed. seekResult is the search result returned (a negative
** number if pCur points at an entry that is smaller than (pKey, nKey), or
** a positive value if pCur points at an etry that is larger than
** (pKey, nKey)).
**
** If the seekResult parameter is non-zero, then the caller guarantees that
** cursor pCur is pointing at the existing copy of a row that is to be
** overwritten.  If the seekResult parameter is 0, then cursor pCur may
** point to any entry or to no entry at all and so this function has to seek
** the cursor before the new key can be inserted.
*/
static int sqlite3BtreeInsert(
BtCursor pCur,                /* Insert data into the table of this cursor */
byte[] pKey, i64 nKey,        /* The key of the new record */
byte[] pData, int nData,      /* The data of the new record */
int nZero,                    /* Number of extra 0 bytes to append to data */
int appendBias,               /* True if this is likely an append */
int seekResult                /* Result of prior MovetoUnpacked() call */
)
{
  int rc;
  int loc = seekResult;       /* -1: before desired location  +1: after */
  int szNew = 0;
  int idx;
  MemPage pPage;
  Btree p = pCur.pBtree;
  BtShared pBt = p.pBt;
  int oldCell;
  byte[] newCell = null;

  if ( pCur.eState == CURSOR_FAULT )
  {
    Debug.Assert( pCur.skipNext != SQLITE_OK );
    return pCur.skipNext;
  }

  Debug.Assert( cursorHoldsMutex( pCur ) );
  Debug.Assert( pCur.wrFlag != 0 && pBt.inTransaction == TRANS_WRITE && !pBt.readOnly );
  Debug.Assert( hasSharedCacheTableLock( p, pCur.pgnoRoot, pCur.pKeyInfo != null ? 1 : 0, 2 ) );

  /* Assert that the caller has been consistent. If this cursor was opened
  ** expecting an index b-tree, then the caller should be inserting blob
  ** keys with no associated data. If the cursor was opened expecting an
  ** intkey table, the caller should be inserting integer keys with a
  ** blob of associated data.  */
  Debug.Assert( ( pKey == null ) == ( pCur.pKeyInfo == null ) );

  /* If this is an insert into a table b-tree, invalidate any incrblob
  ** cursors open on the row being replaced (assuming this is a replace
  ** operation - if it is not, the following is a no-op).  */
  if ( pCur.pKeyInfo == null )
  {
    invalidateIncrblobCursors( p, nKey, 0 );
  }

  /* Save the positions of any other cursors open on this table.
  **
  ** In some cases, the call to btreeMoveto() below is a no-op. For
  ** example, when inserting data into a table with auto-generated integer
  ** keys, the VDBE layer invokes sqlite3BtreeLast() to figure out the
  ** integer key to use. It then calls this function to actually insert the
  ** data into the intkey B-Tree. In this case btreeMoveto() recognizes
  ** that the cursor is already where it needs to be and returns without
  ** doing any work. To avoid thwarting these optimizations, it is important
  ** not to clear the cursor here.
  */
  rc = saveAllCursors( pBt, pCur.pgnoRoot, pCur );
  if ( rc != 0 )
    return rc;
  if ( 0 == loc )
  {
    rc = btreeMoveto( pCur, pKey, nKey, appendBias, ref loc );
    if ( rc != 0 )
      return rc;
  }
  Debug.Assert( pCur.eState == CURSOR_VALID || ( pCur.eState == CURSOR_INVALID && loc != 0 ) );

  pPage = pCur.apPage[pCur.iPage];
  Debug.Assert( pPage.intKey != 0 || nKey >= 0 );
  Debug.Assert( pPage.leaf != 0 || 0 == pPage.intKey );

  TRACE( "INSERT: table=%d nkey=%lld ndata=%d page=%d %s\n",
  pCur.pgnoRoot, nKey, nData, pPage.pgno,
  loc == 0 ? "overwrite" : "new entry" );
  Debug.Assert( pPage.isInit != 0 );
  allocateTempSpace( pBt );
  newCell = pBt.pTmpSpace;
  //if (newCell == null) return SQLITE_NOMEM;
  rc = fillInCell( pPage, newCell, pKey, nKey, pData, nData, nZero, ref szNew );
  if ( rc != 0 )
    goto end_insert;
  Debug.Assert( szNew == cellSizePtr( pPage, newCell ) );
  Debug.Assert( szNew <= MX_CELL_SIZE( pBt ) );
  idx = pCur.aiIdx[pCur.iPage];
  if ( loc == 0 )
  {
    u16 szOld;
    Debug.Assert( idx < pPage.nCell );
    rc = sqlite3PagerWrite( pPage.pDbPage );
    if ( rc != 0 )
    {
      goto end_insert;
    }
    oldCell = findCell( pPage, idx );
    if ( 0 == pPage.leaf )
    {
      //memcpy(newCell, oldCell, 4);
      newCell[0] = pPage.aData[oldCell + 0];
      newCell[1] = pPage.aData[oldCell + 1];
      newCell[2] = pPage.aData[oldCell + 2];
      newCell[3] = pPage.aData[oldCell + 3];
    }
    szOld = cellSizePtr( pPage, oldCell );
    rc = clearCell( pPage, oldCell );
    dropCell( pPage, idx, szOld, ref rc );
    if ( rc != 0 )
      goto end_insert;
  }
  else if ( loc < 0 && pPage.nCell > 0 )
  {
    Debug.Assert( pPage.leaf != 0 );
    idx = ++pCur.aiIdx[pCur.iPage];
  }
  else
  {
    Debug.Assert( pPage.leaf != 0 );
  }
  insertCell( pPage, idx, newCell, szNew, null, 0, ref rc );
  Debug.Assert( rc != SQLITE_OK || pPage.nCell > 0 || pPage.nOverflow > 0 );

  /* If no error has occured and pPage has an overflow cell, call balance()
  ** to redistribute the cells within the tree. Since balance() may move
  ** the cursor, zero the BtCursor.info.nSize and BtCursor.validNKey
  ** variables.
  **
  ** Previous versions of SQLite called moveToRoot() to move the cursor
  ** back to the root page as balance() used to invalidate the contents
  ** of BtCursor.apPage[] and BtCursor.aiIdx[]. Instead of doing that,
  ** set the cursor state to "invalid". This makes common insert operations
  ** slightly faster.
  **
  ** There is a subtle but important optimization here too. When inserting
  ** multiple records into an intkey b-tree using a single cursor (as can
  ** happen while processing an "INSERT INTO ... SELECT" statement), it
  ** is advantageous to leave the cursor pointing to the last entry in
  ** the b-tree if possible. If the cursor is left pointing to the last
  ** entry in the table, and the next row inserted has an integer key
  ** larger than the largest existing key, it is possible to insert the
  ** row without seeking the cursor. This can be a big performance boost.
  */
  pCur.info.nSize = 0;
  pCur.validNKey = false;
  if ( rc == SQLITE_OK && pPage.nOverflow != 0 )
  {
    rc = balance( pCur );

    /* Must make sure nOverflow is reset to zero even if the balance()
    ** fails. Internal data structure corruption will result otherwise.
    ** Also, set the cursor state to invalid. This stops saveCursorPosition()
    ** from trying to save the current position of the cursor.  */
    pCur.apPage[pCur.iPage].nOverflow = 0;
    pCur.eState = CURSOR_INVALID;
  }
  Debug.Assert( pCur.apPage[pCur.iPage].nOverflow == 0 );

end_insert:
  return rc;
}

/*
** Delete the entry that the cursor is pointing to.  The cursor
** is left pointing at a arbitrary location.
*/
static int sqlite3BtreeDelete( BtCursor pCur )
{
  Btree p = pCur.pBtree;
  BtShared pBt = p.pBt;
  int rc;                             /* Return code */
  MemPage pPage;                      /* Page to delete cell from */
  int pCell;                          /* Pointer to cell to delete */
  int iCellIdx;                       /* Index of cell to delete */
  int iCellDepth;                     /* Depth of node containing pCell */

  Debug.Assert( cursorHoldsMutex( pCur ) );
  Debug.Assert( pBt.inTransaction == TRANS_WRITE );
  Debug.Assert( !pBt.readOnly );
  Debug.Assert( pCur.wrFlag != 0 );
  Debug.Assert( hasSharedCacheTableLock( p, pCur.pgnoRoot, pCur.pKeyInfo != null ? 1 : 0, 2 ) );
  Debug.Assert( !hasReadConflicts( p, pCur.pgnoRoot ) );

  if ( NEVER( pCur.aiIdx[pCur.iPage] >= pCur.apPage[pCur.iPage].nCell )
  || NEVER( pCur.eState != CURSOR_VALID )
  )
  {
    return SQLITE_ERROR;  /* Something has gone awry. */
  }

  /* If this is a delete operation to remove a row from a table b-tree,
  ** invalidate any incrblob cursors open on the row being deleted.  */
  if ( pCur.pKeyInfo == null )
  {
    invalidateIncrblobCursors( p, pCur.info.nKey, 0 );
  }

  iCellDepth = pCur.iPage;
  iCellIdx = pCur.aiIdx[iCellDepth];
  pPage = pCur.apPage[iCellDepth];
  pCell = findCell( pPage, iCellIdx );

  /* If the page containing the entry to delete is not a leaf page, move
  ** the cursor to the largest entry in the tree that is smaller than
  ** the entry being deleted. This cell will replace the cell being deleted
  ** from the internal node. The 'previous' entry is used for this instead
  ** of the 'next' entry, as the previous entry is always a part of the
  ** sub-tree headed by the child page of the cell being deleted. This makes
  ** balancing the tree following the delete operation easier.  */
  if ( 0 == pPage.leaf )
  {
    int notUsed = 0;
    rc = sqlite3BtreePrevious( pCur, ref notUsed );
    if ( rc != 0 )
      return rc;
  }

  /* Save the positions of any other cursors open on this table before
  ** making any modifications. Make the page containing the entry to be
  ** deleted writable. Then free any overflow pages associated with the
  ** entry and finally remove the cell itself from within the page.
  */
  rc = saveAllCursors( pBt, pCur.pgnoRoot, pCur );
  if ( rc != 0 )
    return rc;
  rc = sqlite3PagerWrite( pPage.pDbPage );
  if ( rc != 0 )
    return rc;
  rc = clearCell( pPage, pCell );
  dropCell( pPage, iCellIdx, cellSizePtr( pPage, pCell ), ref rc );
  if ( rc != 0 )
    return rc;

  /* If the cell deleted was not located on a leaf page, then the cursor
  ** is currently pointing to the largest entry in the sub-tree headed
  ** by the child-page of the cell that was just deleted from an internal
  ** node. The cell from the leaf node needs to be moved to the internal
  ** node to replace the deleted cell.  */
  if ( 0 == pPage.leaf )
  {
    MemPage pLeaf = pCur.apPage[pCur.iPage];
    int nCell;
    Pgno n = pCur.apPage[iCellDepth + 1].pgno;
    //byte[] pTmp;

    pCell = findCell( pLeaf, pLeaf.nCell - 1 );
    nCell = cellSizePtr( pLeaf, pCell );
    Debug.Assert( MX_CELL_SIZE( pBt ) >= nCell );

    //allocateTempSpace(pBt);
    //pTmp = pBt.pTmpSpace;

    rc = sqlite3PagerWrite( pLeaf.pDbPage );
    byte[] pNext_4 = sqlite3Malloc( nCell + 4 );
    Buffer.BlockCopy( pLeaf.aData, pCell - 4, pNext_4, 0, nCell + 4 );
    insertCell( pPage, iCellIdx, pNext_4, nCell + 4, null, n, ref rc ); //insertCell( pPage, iCellIdx, pCell - 4, nCell + 4, pTmp, n, ref rc );
    dropCell( pLeaf, pLeaf.nCell - 1, nCell, ref rc );
    if ( rc != 0 )
      return rc;
  }

  /* Balance the tree. If the entry deleted was located on a leaf page,
  ** then the cursor still points to that page. In this case the first
  ** call to balance() repairs the tree, and the if(...) condition is
  ** never true.
  **
  ** Otherwise, if the entry deleted was on an internal node page, then
  ** pCur is pointing to the leaf page from which a cell was removed to
  ** replace the cell deleted from the internal node. This is slightly
  ** tricky as the leaf node may be underfull, and the internal node may
  ** be either under or overfull. In this case run the balancing algorithm
  ** on the leaf node first. If the balance proceeds far enough up the
  ** tree that we can be sure that any problem in the internal node has
  ** been corrected, so be it. Otherwise, after balancing the leaf node,
  ** walk the cursor up the tree to the internal node and balance it as
  ** well.  */
  rc = balance( pCur );
  if ( rc == SQLITE_OK && pCur.iPage > iCellDepth )
  {
    while ( pCur.iPage > iCellDepth )
    {
      releasePage( pCur.apPage[pCur.iPage--] );
    }
    rc = balance( pCur );
  }

  if ( rc == SQLITE_OK )
  {
    moveToRoot( pCur );
  }
  return rc;
}

/*
** Create a new BTree table.  Write into piTable the page
** number for the root page of the new table.
**
** The type of type is determined by the flags parameter.  Only the
** following values of flags are currently in use.  Other values for
** flags might not work:
**
**     BTREE_INTKEY|BTREE_LEAFDATA     Used for SQL tables with rowid keys
**     BTREE_ZERODATA                  Used for SQL indices
*/
static int btreeCreateTable( Btree p, ref int piTable, int createTabFlags )
{
  BtShared pBt = p.pBt;
  MemPage pRoot = new MemPage();
  Pgno pgnoRoot = 0;
  int rc;
  int ptfFlags;          /* Page-type flage for the root page of new table */

  Debug.Assert( sqlite3BtreeHoldsMutex( p ) );
  Debug.Assert( pBt.inTransaction == TRANS_WRITE );
  Debug.Assert( !pBt.readOnly );

#if SQLITE_OMIT_AUTOVACUUM
rc = allocateBtreePage(pBt, ref pRoot, ref pgnoRoot, 1, 0);
if( rc !=0){
return rc;
}
#else
  if ( pBt.autoVacuum )
  {
    Pgno pgnoMove = 0;                    /* Move a page here to make room for the root-page */
    MemPage pPageMove = new MemPage();  /* The page to move to. */

    /* Creating a new table may probably require moving an existing database
    ** to make room for the new tables root page. In case this page turns
    ** out to be an overflow page, delete all overflow page-map caches
    ** held by open cursors.
    */
    invalidateAllOverflowCache( pBt );

    /* Read the value of meta[3] from the database to determine where the
    ** root page of the new table should go. meta[3] is the largest root-page
    ** created so far, so the new root-page is (meta[3]+1).
    */
    sqlite3BtreeGetMeta( p, BTREE_LARGEST_ROOT_PAGE, ref pgnoRoot );
    pgnoRoot++;

    /* The new root-page may not be allocated on a pointer-map page, or the
    ** PENDING_BYTE page.
    */
    while ( pgnoRoot == PTRMAP_PAGENO( pBt, pgnoRoot ) ||
    pgnoRoot == PENDING_BYTE_PAGE( pBt ) )
    {
      pgnoRoot++;
    }
    Debug.Assert( pgnoRoot >= 3 );

    /* Allocate a page. The page that currently resides at pgnoRoot will
    ** be moved to the allocated page (unless the allocated page happens
    ** to reside at pgnoRoot).
    */
    rc = allocateBtreePage( pBt, ref pPageMove, ref pgnoMove, pgnoRoot, 1 );
    if ( rc != SQLITE_OK )
    {
      return rc;
    }

    if ( pgnoMove != pgnoRoot )
    {
      /* pgnoRoot is the page that will be used for the root-page of
      ** the new table (assuming an error did not occur). But we were
      ** allocated pgnoMove. If required (i.e. if it was not allocated
      ** by extending the file), the current page at position pgnoMove
      ** is already journaled.
      */
      u8 eType = 0;
      Pgno iPtrPage = 0;

      releasePage( pPageMove );

      /* Move the page currently at pgnoRoot to pgnoMove. */
      rc = btreeGetPage( pBt, pgnoRoot, ref pRoot, 0 );
      if ( rc != SQLITE_OK )
      {
        return rc;
      }
      rc = ptrmapGet( pBt, pgnoRoot, ref eType, ref iPtrPage );
      if ( eType == PTRMAP_ROOTPAGE || eType == PTRMAP_FREEPAGE )
      {
        rc = SQLITE_CORRUPT_BKPT();
      }
      if ( rc != SQLITE_OK )
      {
        releasePage( pRoot );
        return rc;
      }
      Debug.Assert( eType != PTRMAP_ROOTPAGE );
      Debug.Assert( eType != PTRMAP_FREEPAGE );
      rc = relocatePage( pBt, pRoot, eType, iPtrPage, pgnoMove, 0 );
      releasePage( pRoot );

      /* Obtain the page at pgnoRoot */
      if ( rc != SQLITE_OK )
      {
        return rc;
      }
      rc = btreeGetPage( pBt, pgnoRoot, ref pRoot, 0 );
      if ( rc != SQLITE_OK )
      {
        return rc;
      }
      rc = sqlite3PagerWrite( pRoot.pDbPage );
      if ( rc != SQLITE_OK )
      {
        releasePage( pRoot );
        return rc;
      }
    }
    else
    {
      pRoot = pPageMove;
    }

    /* Update the pointer-map and meta-data with the new root-page number. */
    ptrmapPut( pBt, pgnoRoot, PTRMAP_ROOTPAGE, 0, ref rc );
    if ( rc != 0 )
    {
      releasePage( pRoot );
      return rc;
    }

    /* When the new root page was allocated, page 1 was made writable in
    ** order either to increase the database filesize, or to decrement the
    ** freelist count.  Hence, the sqlite3BtreeUpdateMeta() call cannot fail.
    */
    Debug.Assert( sqlite3PagerIswriteable( pBt.pPage1.pDbPage ) );
    rc = sqlite3BtreeUpdateMeta( p, 4, pgnoRoot );
    if ( NEVER( rc != 0 ) )
    {
      releasePage( pRoot );
      return rc;
    }

  }
  else
  {
    rc = allocateBtreePage( pBt, ref pRoot, ref pgnoRoot, 1, 0 );
    if ( rc != 0 )
      return rc;
  }
#endif
  Debug.Assert( sqlite3PagerIswriteable( pRoot.pDbPage ) );
  if ( ( createTabFlags & BTREE_INTKEY ) != 0 )
  {
    ptfFlags = PTF_INTKEY | PTF_LEAFDATA | PTF_LEAF;
  }
  else
  {
    ptfFlags = PTF_ZERODATA | PTF_LEAF;
  }
  zeroPage( pRoot, ptfFlags );
  sqlite3PagerUnref( pRoot.pDbPage );
  Debug.Assert( ( pBt.openFlags & BTREE_SINGLE ) == 0 || pgnoRoot == 2 );
  piTable = (int)pgnoRoot;
  return SQLITE_OK;
}
static int sqlite3BtreeCreateTable( Btree p, ref int piTable, int flags )
{
  int rc;
  sqlite3BtreeEnter( p );
  rc = btreeCreateTable( p, ref piTable, flags );
  sqlite3BtreeLeave( p );
  return rc;
}

/*
** Erase the given database page and all its children.  Return
** the page to the freelist.
*/
static int clearDatabasePage(
BtShared pBt,         /* The BTree that contains the table */
Pgno pgno,            /* Page number to clear */
int freePageFlag,     /* Deallocate page if true */
ref int pnChange      /* Add number of Cells freed to this counter */
)
{
  MemPage pPage = new MemPage();
  int rc;
  byte[] pCell;
  int i;

  Debug.Assert( sqlite3_mutex_held( pBt.mutex ) );
  if ( pgno > btreePagecount( pBt ) )
  {
    return SQLITE_CORRUPT_BKPT();
  }

  rc = getAndInitPage( pBt, pgno, ref pPage );
  if ( rc != 0 )
    return rc;
  for ( i = 0; i < pPage.nCell; i++ )
  {
    int iCell = findCell( pPage, i );
    pCell = pPage.aData; //        pCell = findCell( pPage, i );
    if ( 0 == pPage.leaf )
    {
      rc = clearDatabasePage( pBt, sqlite3Get4byte( pCell, iCell ), 1, ref pnChange );
      if ( rc != 0 )
        goto cleardatabasepage_out;
    }
    rc = clearCell( pPage, iCell );
    if ( rc != 0 )
      goto cleardatabasepage_out;
  }
  if ( 0 == pPage.leaf )
  {
    rc = clearDatabasePage( pBt, sqlite3Get4byte( pPage.aData, 8 ), 1, ref pnChange );
    if ( rc != 0 )
      goto cleardatabasepage_out;
  }
  else //if (pnChange != 0)
  {
    //Debug.Assert(pPage.intKey != 0);
    pnChange += pPage.nCell;
  }
  if ( freePageFlag != 0 )
  {
    freePage( pPage, ref rc );
  }
  else if ( ( rc = sqlite3PagerWrite( pPage.pDbPage ) ) == 0 )
  {
    zeroPage( pPage, pPage.aData[0] | PTF_LEAF );
  }

cleardatabasepage_out:
  releasePage( pPage );
  return rc;
}

/*
** Delete all information from a single table in the database.  iTable is
** the page number of the root of the table.  After this routine returns,
** the root page is empty, but still exists.
**
** This routine will fail with SQLITE_LOCKED if there are any open
** read cursors on the table.  Open write cursors are moved to the
** root of the table.
**
** If pnChange is not NULL, then table iTable must be an intkey table. The
** integer value pointed to by pnChange is incremented by the number of
** entries in the table.
*/
static int sqlite3BtreeClearTable( Btree p, int iTable, ref int pnChange )
{
  int rc;
  BtShared pBt = p.pBt;
  sqlite3BtreeEnter( p );
  Debug.Assert( p.inTrans == TRANS_WRITE );

  /* Invalidate all incrblob cursors open on table iTable (assuming iTable
  ** is the root of a table b-tree - if it is not, the following call is
  ** a no-op).  */
  invalidateIncrblobCursors( p, 0, 1 );

  rc = saveAllCursors( pBt, (Pgno)iTable, null );
  if ( SQLITE_OK == rc )
  {
    rc = clearDatabasePage( pBt, (Pgno)iTable, 0, ref pnChange );
  }
  sqlite3BtreeLeave( p );
  return rc;
}

/*
** Erase all information in a table and add the root of the table to
** the freelist.  Except, the root of the principle table (the one on
** page 1) is never added to the freelist.
**
** This routine will fail with SQLITE_LOCKED if there are any open
** cursors on the table.
**
** If AUTOVACUUM is enabled and the page at iTable is not the last
** root page in the database file, then the last root page
** in the database file is moved into the slot formerly occupied by
** iTable and that last slot formerly occupied by the last root page
** is added to the freelist instead of iTable.  In this say, all
** root pages are kept at the beginning of the database file, which
** is necessary for AUTOVACUUM to work right.  piMoved is set to the
** page number that used to be the last root page in the file before
** the move.  If no page gets moved, piMoved is set to 0.
** The last root page is recorded in meta[3] and the value of
** meta[3] is updated by this procedure.
*/
static int btreeDropTable( Btree p, Pgno iTable, ref int piMoved )
{
  int rc;
  MemPage pPage = null;
  BtShared pBt = p.pBt;

  Debug.Assert( sqlite3BtreeHoldsMutex( p ) );
  Debug.Assert( p.inTrans == TRANS_WRITE );

  /* It is illegal to drop a table if any cursors are open on the
  ** database. This is because in auto-vacuum mode the backend may
  ** need to move another root-page to fill a gap left by the deleted
  ** root page. If an open cursor was using this page a problem would
  ** occur.
  **
  ** This error is caught long before control reaches this point.
  */
  if ( NEVER( pBt.pCursor ) )
  {
    sqlite3ConnectionBlocked( p.db, pBt.pCursor.pBtree.db );
    return SQLITE_LOCKED_SHAREDCACHE;
  }

  rc = btreeGetPage( pBt, (Pgno)iTable, ref pPage, 0 );
  if ( rc != 0 )
    return rc;
  int Dummy0 = 0;
  rc = sqlite3BtreeClearTable( p, (int)iTable, ref Dummy0 );
  if ( rc != 0 )
  {
    releasePage( pPage );
    return rc;
  }

  piMoved = 0;

  if ( iTable > 1 )
  {
#if SQLITE_OMIT_AUTOVACUUM
freePage(pPage, ref rc);
releasePage(pPage);
#else
    if ( pBt.autoVacuum )
    {
      Pgno maxRootPgno = 0;
      sqlite3BtreeGetMeta( p, BTREE_LARGEST_ROOT_PAGE, ref maxRootPgno );

      if ( iTable == maxRootPgno )
      {
        /* If the table being dropped is the table with the largest root-page
        ** number in the database, put the root page on the free list.
        */
        freePage( pPage, ref rc );
        releasePage( pPage );
        if ( rc != SQLITE_OK )
        {
          return rc;
        }
      }
      else
      {
        /* The table being dropped does not have the largest root-page
        ** number in the database. So move the page that does into the
        ** gap left by the deleted root-page.
        */
        MemPage pMove = new MemPage();
        releasePage( pPage );
        rc = btreeGetPage( pBt, maxRootPgno, ref pMove, 0 );
        if ( rc != SQLITE_OK )
        {
          return rc;
        }
        rc = relocatePage( pBt, pMove, PTRMAP_ROOTPAGE, 0, iTable, 0 );
        releasePage( pMove );
        if ( rc != SQLITE_OK )
        {
          return rc;
        }
        pMove = null;
        rc = btreeGetPage( pBt, maxRootPgno, ref pMove, 0 );
        freePage( pMove, ref rc );
        releasePage( pMove );
        if ( rc != SQLITE_OK )
        {
          return rc;
        }
        piMoved = (int)maxRootPgno;
      }

      /* Set the new 'max-root-page' value in the database header. This
      ** is the old value less one, less one more if that happens to
      ** be a root-page number, less one again if that is the
      ** PENDING_BYTE_PAGE.
      */
      maxRootPgno--;
      while ( maxRootPgno == PENDING_BYTE_PAGE( pBt )
      || PTRMAP_ISPAGE( pBt, maxRootPgno ) )
      {
        maxRootPgno--;
      }
      Debug.Assert( maxRootPgno != PENDING_BYTE_PAGE( pBt ) );

      rc = sqlite3BtreeUpdateMeta( p, 4, maxRootPgno );
    }
    else
    {
      freePage( pPage, ref rc );
      releasePage( pPage );
    }
#endif
  }
  else
  {
    /* If sqlite3BtreeDropTable was called on page 1.
    ** This really never should happen except in a corrupt
    ** database.
    */
    zeroPage( pPage, PTF_INTKEY | PTF_LEAF );
    releasePage( pPage );
  }
  return rc;
}
static int sqlite3BtreeDropTable( Btree p, int iTable, ref int piMoved )
{
  int rc;
  sqlite3BtreeEnter( p );
  rc = btreeDropTable( p, (u32)iTable, ref piMoved );
  sqlite3BtreeLeave( p );
  return rc;
}


/*
** This function may only be called if the b-tree connection already
** has a read or write transaction open on the database.
**
** Read the meta-information out of a database file.  Meta[0]
** is the number of free pages currently in the database.  Meta[1]
** through meta[15] are available for use by higher layers.  Meta[0]
** is read-only, the others are read/write.
**
** The schema layer numbers meta values differently.  At the schema
** layer (and the SetCookie and ReadCookie opcodes) the number of
** free pages is not visible.  So Cookie[0] is the same as Meta[1].
*/
static void sqlite3BtreeGetMeta( Btree p, int idx, ref u32 pMeta )
{
  BtShared pBt = p.pBt;

  sqlite3BtreeEnter( p );
  Debug.Assert( p.inTrans > TRANS_NONE );
  Debug.Assert( SQLITE_OK == querySharedCacheTableLock( p, MASTER_ROOT, READ_LOCK ) );
  Debug.Assert( pBt.pPage1 != null );
  Debug.Assert( idx >= 0 && idx <= 15 );

  pMeta = sqlite3Get4byte( pBt.pPage1.aData, 36 + idx * 4 );

  /* If auto-vacuum is disabled in this build and this is an auto-vacuum
  ** database, mark the database as read-only.  */
#if SQLITE_OMIT_AUTOVACUUM
if( idx==BTREE_LARGEST_ROOT_PAGE && pMeta>0 ) pBt.readOnly = 1;
#endif

  sqlite3BtreeLeave( p );
}

/*
** Write meta-information back into the database.  Meta[0] is
** read-only and may not be written.
*/
static int sqlite3BtreeUpdateMeta( Btree p, int idx, u32 iMeta )
{
  BtShared pBt = p.pBt;
  byte[] pP1;
  int rc;
  Debug.Assert( idx >= 1 && idx <= 15 );
  sqlite3BtreeEnter( p );
  Debug.Assert( p.inTrans == TRANS_WRITE );
  Debug.Assert( pBt.pPage1 != null );
  pP1 = pBt.pPage1.aData;
  rc = sqlite3PagerWrite( pBt.pPage1.pDbPage );
  if ( rc == SQLITE_OK )
  {
    sqlite3Put4byte( pP1, 36 + idx * 4, iMeta );
#if !SQLITE_OMIT_AUTOVACUUM
    if ( idx == BTREE_INCR_VACUUM )
    {
      Debug.Assert( pBt.autoVacuum || iMeta == 0 );
      Debug.Assert( iMeta == 0 || iMeta == 1 );
      pBt.incrVacuum = iMeta != 0;
    }
#endif
  }
  sqlite3BtreeLeave( p );
  return rc;
}

#if !SQLITE_OMIT_BTREECOUNT
/*
** The first argument, pCur, is a cursor opened on some b-tree. Count the
** number of entries in the b-tree and write the result to pnEntry.
**
** SQLITE_OK is returned if the operation is successfully executed.
** Otherwise, if an error is encountered (i.e. an IO error or database
** corruption) an SQLite error code is returned.
*/
static int sqlite3BtreeCount( BtCursor pCur, ref i64 pnEntry )
{
  i64 nEntry = 0;                      /* Value to return in pnEntry */
  int rc;                              /* Return code */
  rc = moveToRoot( pCur );

  /* Unless an error occurs, the following loop runs one iteration for each
  ** page in the B-Tree structure (not including overflow pages).
  */
  while ( rc == SQLITE_OK )
  {
    int iIdx;                          /* Index of child node in parent */
    MemPage pPage;                    /* Current page of the b-tree */

    /* If this is a leaf page or the tree is not an int-key tree, then
    ** this page contains countable entries. Increment the entry counter
    ** accordingly.
    */
    pPage = pCur.apPage[pCur.iPage];
    if ( pPage.leaf != 0 || 0 == pPage.intKey )
    {
      nEntry += pPage.nCell;
    }

    /* pPage is a leaf node. This loop navigates the cursor so that it
    ** points to the first interior cell that it points to the parent of
    ** the next page in the tree that has not yet been visited. The
    ** pCur.aiIdx[pCur.iPage] value is set to the index of the parent cell
    ** of the page, or to the number of cells in the page if the next page
    ** to visit is the right-child of its parent.
    **
    ** If all pages in the tree have been visited, return SQLITE_OK to the
    ** caller.
    */
    if ( pPage.leaf != 0 )
    {
      do
      {
        if ( pCur.iPage == 0 )
        {
          /* All pages of the b-tree have been visited. Return successfully. */
          pnEntry = nEntry;
          return SQLITE_OK;
        }
        moveToParent( pCur );
      } while ( pCur.aiIdx[pCur.iPage] >= pCur.apPage[pCur.iPage].nCell );

      pCur.aiIdx[pCur.iPage]++;
      pPage = pCur.apPage[pCur.iPage];
    }

    /* Descend to the child node of the cell that the cursor currently
    ** points at. This is the right-child if (iIdx==pPage.nCell).
    */
    iIdx = pCur.aiIdx[pCur.iPage];
    if ( iIdx == pPage.nCell )
    {
      rc = moveToChild( pCur, sqlite3Get4byte( pPage.aData, pPage.hdrOffset + 8 ) );
    }
    else
    {
      rc = moveToChild( pCur, sqlite3Get4byte( pPage.aData, findCell( pPage, iIdx ) ) );
    }
  }

  /* An error has occurred. Return an error code. */
  return rc;
}
#endif

/*
** Return the pager associated with a BTree.  This routine is used for
** testing and debugging only.
*/
static Pager sqlite3BtreePager( Btree p )
{
  return p.pBt.pPager;
}

#if !SQLITE_OMIT_INTEGRITY_CHECK
/*
** Append a message to the error message string.
*/
static void checkAppendMsg(
IntegrityCk pCheck,
string zMsg1,
string zFormat,
params object[] ap
)
{
  if ( 0 == pCheck.mxErr )
    return;
  //va_list ap;
  lock ( lock_va_list )
  {
    pCheck.mxErr--;
    pCheck.nErr++;
    va_start( ap, zFormat );
    if ( pCheck.errMsg.zText.Length != 0 )
    {
      sqlite3StrAccumAppend( pCheck.errMsg, "\n", 1 );
    }
    if ( zMsg1.Length > 0 )
    {
      sqlite3StrAccumAppend( pCheck.errMsg, zMsg1.ToString(), -1 );
    }
    sqlite3VXPrintf( pCheck.errMsg, 1, zFormat, ap );
    va_end( ref ap );
  }
}

static void checkAppendMsg(
IntegrityCk pCheck,
StringBuilder zMsg1,
string zFormat,
params object[] ap
)
{
  if ( 0 == pCheck.mxErr )
    return;
  //va_list ap;
  lock ( lock_va_list )
  {
    pCheck.mxErr--;
    pCheck.nErr++;
    va_start( ap, zFormat );
    if ( pCheck.errMsg.zText.Length != 0 )
    {
      sqlite3StrAccumAppend( pCheck.errMsg, "\n", 1 );
    }
    if ( zMsg1.Length > 0 )
    {
      sqlite3StrAccumAppend( pCheck.errMsg, zMsg1.ToString(), -1 );
    }
    sqlite3VXPrintf( pCheck.errMsg, 1, zFormat, ap );
    va_end( ref ap );
  }      
  //if( pCheck.errMsg.mallocFailed ){
  //  pCheck.mallocFailed = 1;
  //}
}
#endif //* SQLITE_OMIT_INTEGRITY_CHECK */

#if !SQLITE_OMIT_INTEGRITY_CHECK
/*
** Add 1 to the reference count for page iPage.  If this is the second
** reference to the page, add an error message to pCheck.zErrMsg.
** Return 1 if there are 2 ore more references to the page and 0 if
** if this is the first reference to the page.
**
** Also check that the page number is in bounds.
*/
static int checkRef( IntegrityCk pCheck, Pgno iPage, string zContext )
{
  if ( iPage == 0 )
    return 1;
  if ( iPage > pCheck.nPage )
  {
    checkAppendMsg( pCheck, zContext, "invalid page number %d", iPage );
    return 1;
  }
  if ( pCheck.anRef[iPage] == 1 )
  {
    checkAppendMsg( pCheck, zContext, "2nd reference to page %d", iPage );
    return 1;
  }
  return ( ( pCheck.anRef[iPage]++ ) > 1 ) ? 1 : 0;
}

#if !SQLITE_OMIT_AUTOVACUUM
/*
** Check that the entry in the pointer-map for page iChild maps to
** page iParent, pointer type ptrType. If not, append an error message
** to pCheck.
*/
static void checkPtrmap(
IntegrityCk pCheck,    /* Integrity check context */
Pgno iChild,           /* Child page number */
u8 eType,              /* Expected pointer map type */
Pgno iParent,          /* Expected pointer map parent page number */
string zContext /* Context description (used for error msg) */
)
{
  int rc;
  u8 ePtrmapType = 0;
  Pgno iPtrmapParent = 0;

  rc = ptrmapGet( pCheck.pBt, iChild, ref ePtrmapType, ref iPtrmapParent );
  if ( rc != SQLITE_OK )
  {
    //if( rc==SQLITE_NOMEM || rc==SQLITE_IOERR_NOMEM ) pCheck.mallocFailed = 1;
    checkAppendMsg( pCheck, zContext, "Failed to read ptrmap key=%d", iChild );
    return;
  }

  if ( ePtrmapType != eType || iPtrmapParent != iParent )
  {
    checkAppendMsg( pCheck, zContext,
    "Bad ptr map entry key=%d expected=(%d,%d) got=(%d,%d)",
    iChild, eType, iParent, ePtrmapType, iPtrmapParent );
  }
}
#endif

/*
** Check the integrity of the freelist or of an overflow page list.
** Verify that the number of pages on the list is N.
*/
static void checkList(
IntegrityCk pCheck,  /* Integrity checking context */
int isFreeList,       /* True for a freelist.  False for overflow page list */
int iPage,            /* Page number for first page in the list */
int N,                /* Expected number of pages in the list */
string zContext        /* Context for error messages */
)
{
  int i;
  int expected = N;
  int iFirst = iPage;
  while ( N-- > 0 && pCheck.mxErr != 0 )
  {
    PgHdr pOvflPage = new PgHdr();
    byte[] pOvflData;
    if ( iPage < 1 )
    {
      checkAppendMsg( pCheck, zContext,
      "%d of %d pages missing from overflow list starting at %d",
      N + 1, expected, iFirst );
      break;
    }
    if ( checkRef( pCheck, (u32)iPage, zContext ) != 0 )
      break;
    if ( sqlite3PagerGet( pCheck.pPager, (Pgno)iPage, ref pOvflPage ) != 0 )
    {
      checkAppendMsg( pCheck, zContext, "failed to get page %d", iPage );
      break;
    }
    pOvflData = sqlite3PagerGetData( pOvflPage );
    if ( isFreeList != 0 )
    {
      int n = (int)sqlite3Get4byte( pOvflData, 4 );
#if !SQLITE_OMIT_AUTOVACUUM
      if ( pCheck.pBt.autoVacuum )
      {
        checkPtrmap( pCheck, (u32)iPage, PTRMAP_FREEPAGE, 0, zContext );
      }
#endif
      if ( n > (int)pCheck.pBt.usableSize / 4 - 2 )
      {
        checkAppendMsg( pCheck, zContext,
        "freelist leaf count too big on page %d", iPage );
        N--;
      }
      else
      {
        for ( i = 0; i < n; i++ )
        {
          Pgno iFreePage = sqlite3Get4byte( pOvflData, 8 + i * 4 );
#if !SQLITE_OMIT_AUTOVACUUM
          if ( pCheck.pBt.autoVacuum )
          {
            checkPtrmap( pCheck, iFreePage, PTRMAP_FREEPAGE, 0, zContext );
          }
#endif
          checkRef( pCheck, iFreePage, zContext );
        }
        N -= n;
      }
    }
#if !SQLITE_OMIT_AUTOVACUUM
    else
    {
      /* If this database supports auto-vacuum and iPage is not the last
      ** page in this overflow list, check that the pointer-map entry for
      ** the following page matches iPage.
      */
      if ( pCheck.pBt.autoVacuum && N > 0 )
      {
        i = (int)sqlite3Get4byte( pOvflData );
        checkPtrmap( pCheck, (u32)i, PTRMAP_OVERFLOW2, (u32)iPage, zContext );
      }
    }
#endif
    iPage = (int)sqlite3Get4byte( pOvflData );
    sqlite3PagerUnref( pOvflPage );
  }
}
#endif //* SQLITE_OMIT_INTEGRITY_CHECK */

#if !SQLITE_OMIT_INTEGRITY_CHECK
/*
** Do various sanity checks on a single page of a tree.  Return
** the tree depth.  Root pages return 0.  Parents of root pages
** return 1, and so forth.
**
** These checks are done:
**
**      1.  Make sure that cells and freeblocks do not overlap
**          but combine to completely cover the page.
**  NO  2.  Make sure cell keys are in order.
**  NO  3.  Make sure no key is less than or equal to zLowerBound.
**  NO  4.  Make sure no key is greater than or equal to zUpperBound.
**      5.  Check the integrity of overflow pages.
**      6.  Recursively call checkTreePage on all children.
**      7.  Verify that the depth of all children is the same.
**      8.  Make sure this page is at least 33% full or else it is
**          the root of the tree.
*/

static i64 refNULL = 0;   //Dummy for C# ref NULL

static int checkTreePage(
IntegrityCk pCheck,    /* Context for the sanity check */
int iPage,             /* Page number of the page to check */
string zParentContext, /* Parent context */
ref i64 pnParentMinKey,
ref i64 pnParentMaxKey,
object _pnParentMinKey, /* C# Needed to determine if content passed*/
object _pnParentMaxKey  /* C# Needed to determine if content passed*/
)
{
  MemPage pPage = new MemPage();
  int i, rc, depth, d2, pgno, cnt;
  int hdr, cellStart;
  int nCell;
  u8[] data;
  BtShared pBt;
  int usableSize;
  StringBuilder zContext = new StringBuilder( 100 );
  byte[] hit = null;
  i64 nMinKey = 0;
  i64 nMaxKey = 0;


  sqlite3_snprintf( 200, zContext, "Page %d: ", iPage );

  /* Check that the page exists
  */
  pBt = pCheck.pBt;
  usableSize = (int)pBt.usableSize;
  if ( iPage == 0 )
    return 0;
  if ( checkRef( pCheck, (u32)iPage, zParentContext ) != 0 )
    return 0;
  if ( ( rc = btreeGetPage( pBt, (Pgno)iPage, ref pPage, 0 ) ) != 0 )
  {
    checkAppendMsg( pCheck, zContext.ToString(),
    "unable to get the page. error code=%d", rc );
    return 0;
  }

  /* Clear MemPage.isInit to make sure the corruption detection code in
  ** btreeInitPage() is executed.  */
  pPage.isInit = 0;
  if ( ( rc = btreeInitPage( pPage ) ) != 0 )
  {
    Debug.Assert( rc == SQLITE_CORRUPT );  /* The only possible error from InitPage */
    checkAppendMsg( pCheck, zContext.ToString(),
    "btreeInitPage() returns error code %d", rc );
    releasePage( pPage );
    return 0;
  }

  /* Check out all the cells.
  */
  depth = 0;
  for ( i = 0; i < pPage.nCell && pCheck.mxErr != 0; i++ )
  {
    u8[] pCell;
    u32 sz;
    CellInfo info = new CellInfo();

    /* Check payload overflow pages
    */
    sqlite3_snprintf( 200, zContext,
    "On tree page %d cell %d: ", iPage, i );
    int iCell = findCell( pPage, i ); //pCell = findCell( pPage, i );
    pCell = pPage.aData;
    btreeParseCellPtr( pPage, iCell, ref info ); //btreeParseCellPtr( pPage, pCell, info );
    sz = info.nData;
    if ( 0 == pPage.intKey )
      sz += (u32)info.nKey;
    /* For intKey pages, check that the keys are in order.
    */
    else if ( i == 0 )
      nMinKey = nMaxKey = info.nKey;
    else
    {
      if ( info.nKey <= nMaxKey )
      {
        checkAppendMsg( pCheck, zContext.ToString(),
        "Rowid %lld out of order (previous was %lld)", info.nKey, nMaxKey );
      }
      nMaxKey = info.nKey;
    }
    Debug.Assert( sz == info.nPayload );
    if ( ( sz > info.nLocal )
      //&& (pCell[info.iOverflow]<=&pPage.aData[pBt.usableSize])
    )
    {
      int nPage = (int)( sz - info.nLocal + usableSize - 5 ) / ( usableSize - 4 );
      Pgno pgnoOvfl = sqlite3Get4byte( pCell, iCell, info.iOverflow );
#if !SQLITE_OMIT_AUTOVACUUM
      if ( pBt.autoVacuum )
      {
        checkPtrmap( pCheck, pgnoOvfl, PTRMAP_OVERFLOW1, (u32)iPage, zContext.ToString() );
      }
#endif
      checkList( pCheck, 0, (int)pgnoOvfl, nPage, zContext.ToString() );
    }

    /* Check sanity of left child page.
    */
    if ( 0 == pPage.leaf )
    {
      pgno = (int)sqlite3Get4byte( pCell, iCell ); //sqlite3Get4byte( pCell );
#if !SQLITE_OMIT_AUTOVACUUM
      if ( pBt.autoVacuum )
      {
        checkPtrmap( pCheck, (u32)pgno, PTRMAP_BTREE, (u32)iPage, zContext.ToString() );
      }
#endif
      if ( i == 0 )
        d2 = checkTreePage( pCheck, pgno, zContext.ToString(), ref nMinKey, ref refNULL, pCheck, null );
      else
        d2 = checkTreePage( pCheck, pgno, zContext.ToString(), ref nMinKey, ref nMaxKey, pCheck, pCheck );

      if ( i > 0 && d2 != depth )
      {
        checkAppendMsg( pCheck, zContext, "Child page depth differs" );
      }
      depth = d2;
    }
  }
  if ( 0 == pPage.leaf )
  {
    pgno = (int)sqlite3Get4byte( pPage.aData, pPage.hdrOffset + 8 );
    sqlite3_snprintf( 200, zContext,
    "On page %d at right child: ", iPage );
#if !SQLITE_OMIT_AUTOVACUUM
    if ( pBt.autoVacuum )
    {
      checkPtrmap( pCheck, (u32)pgno, PTRMAP_BTREE, (u32)iPage, zContext.ToString() );
    }
#endif
    //    checkTreePage(pCheck, pgno, zContext, NULL, !pPage->nCell ? NULL : &nMaxKey);
    if ( 0 == pPage.nCell )
      checkTreePage( pCheck, pgno, zContext.ToString(), ref refNULL, ref refNULL, null, null );
    else
      checkTreePage( pCheck, pgno, zContext.ToString(), ref refNULL, ref nMaxKey, null, pCheck );
  }

  /* For intKey leaf pages, check that the min/max keys are in order
  ** with any left/parent/right pages.
  */
  if ( pPage.leaf != 0 && pPage.intKey != 0 )
  {
    /* if we are a left child page */
    if ( _pnParentMinKey != null )
    {
      /* if we are the left most child page */
      if ( _pnParentMaxKey == null )
      {
        if ( nMaxKey > pnParentMinKey )
        {
          checkAppendMsg( pCheck, zContext,
          "Rowid %lld out of order (max larger than parent min of %lld)",
          nMaxKey, pnParentMinKey );
        }
      }
      else
      {
        if ( nMinKey <= pnParentMinKey )
        {
          checkAppendMsg( pCheck, zContext,
          "Rowid %lld out of order (min less than parent min of %lld)",
          nMinKey, pnParentMinKey );
        }
        if ( nMaxKey > pnParentMaxKey )
        {
          checkAppendMsg( pCheck, zContext,
          "Rowid %lld out of order (max larger than parent max of %lld)",
          nMaxKey, pnParentMaxKey );
        }
        pnParentMinKey = nMaxKey;
      }
      /* else if we're a right child page */
    }
    else if ( _pnParentMaxKey != null )
    {
      if ( nMinKey <= pnParentMaxKey )
      {
        checkAppendMsg( pCheck, zContext,
        "Rowid %lld out of order (min less than parent max of %lld)",
        nMinKey, pnParentMaxKey );
      }
    }
  }

  /* Check for complete coverage of the page
  */
  data = pPage.aData;
  hdr = pPage.hdrOffset;
  hit = sqlite3Malloc( pBt.pageSize );
  //if( hit==null ){
  //  pCheck.mallocFailed = 1;
  //}else
  {
    int contentOffset = get2byteNotZero( data, hdr + 5 );
    Debug.Assert( contentOffset <= usableSize );  /* Enforced by btreeInitPage() */
    Array.Clear( hit, contentOffset, usableSize - contentOffset );//memset(hit+contentOffset, 0, usableSize-contentOffset);
    for ( int iLoop = contentOffset - 1; iLoop >= 0; iLoop-- )
      hit[iLoop] = 1;//memset(hit, 1, contentOffset);
    nCell = get2byte( data, hdr + 3 );
    cellStart = hdr + 12 - 4 * pPage.leaf;
    for ( i = 0; i < nCell; i++ )
    {
      int pc = get2byte( data, cellStart + i * 2 );
      u32 size = 65536;
      int j;
      if ( pc <= usableSize - 4 )
      {
        size = cellSizePtr( pPage, data, pc );
      }
      if ( (int)( pc + size - 1 ) >= usableSize )
      {
        checkAppendMsg( pCheck, "",
        "Corruption detected in cell %d on page %d", i, iPage );
      }
      else
      {
        for ( j = (int)( pc + size - 1 ); j >= pc; j-- )
          hit[j]++;
      }
    }
    i = get2byte( data, hdr + 1 );
    while ( i > 0 )
    {
      int size, j;
      Debug.Assert( i <= usableSize - 4 );     /* Enforced by btreeInitPage() */
      size = get2byte( data, i + 2 );
      Debug.Assert( i + size <= usableSize );  /* Enforced by btreeInitPage() */
      for ( j = i + size - 1; j >= i; j-- )
        hit[j]++;
      j = get2byte( data, i );
      Debug.Assert( j == 0 || j > i + size );  /* Enforced by btreeInitPage() */
      Debug.Assert( j <= usableSize - 4 );   /* Enforced by btreeInitPage() */
      i = j;
    }
    for ( i = cnt = 0; i < usableSize; i++ )
    {
      if ( hit[i] == 0 )
      {
        cnt++;
      }
      else if ( hit[i] > 1 )
      {
        checkAppendMsg( pCheck, "",
        "Multiple uses for byte %d of page %d", i, iPage );
        break;
      }
    }
    if ( cnt != data[hdr + 7] )
    {
      checkAppendMsg( pCheck, "",
      "Fragmentation of %d bytes reported as %d on page %d",
      cnt, data[hdr + 7], iPage );
    }
  }
  sqlite3PageFree( ref hit );
  releasePage( pPage );
  return depth + 1;
}
#endif //* SQLITE_OMIT_INTEGRITY_CHECK */

#if !SQLITE_OMIT_INTEGRITY_CHECK
/*
** This routine does a complete check of the given BTree file.  aRoot[] is
** an array of pages numbers were each page number is the root page of
** a table.  nRoot is the number of entries in aRoot.
**
** A read-only or read-write transaction must be opened before calling
** this function.
**
** Write the number of error seen in pnErr.  Except for some memory
** allocation errors,  an error message held in memory obtained from
** malloc is returned if pnErr is non-zero.  If pnErr==null then NULL is
** returned.  If a memory allocation error occurs, NULL is returned.
*/
static string sqlite3BtreeIntegrityCheck(
Btree p,       /* The btree to be checked */
int[] aRoot,   /* An array of root pages numbers for individual trees */
int nRoot,     /* Number of entries in aRoot[] */
int mxErr,     /* Stop reporting errors after this many */
ref int pnErr  /* Write number of errors seen to this variable */
)
{
  Pgno i;
  int nRef;
  IntegrityCk sCheck = new IntegrityCk();
  BtShared pBt = p.pBt;

  sqlite3BtreeEnter( p );
  Debug.Assert( p.inTrans > TRANS_NONE && pBt.inTransaction > TRANS_NONE );
  nRef = sqlite3PagerRefcount( pBt.pPager );
  sCheck.pBt = pBt;
  sCheck.pPager = pBt.pPager;
  sCheck.nPage = btreePagecount( sCheck.pBt );
  sCheck.mxErr = mxErr;
  sCheck.nErr = 0;
  //sCheck.mallocFailed = 0;
  pnErr = 0;
  if ( sCheck.nPage == 0 )
  {
    sqlite3BtreeLeave( p );
    return "";
  }
  sCheck.anRef = sqlite3Malloc( sCheck.anRef, (int)sCheck.nPage + 1 );
  //if( !sCheck.anRef ){
  //  pnErr = 1;
  //  sqlite3BtreeLeave(p);
  //  return 0;
  //}
  // for (i = 0; i <= sCheck.nPage; i++) { sCheck.anRef[i] = 0; }
  i = PENDING_BYTE_PAGE( pBt );
  if ( i <= sCheck.nPage )
  {
    sCheck.anRef[i] = 1;
  }
  sqlite3StrAccumInit( sCheck.errMsg, null, 1000, 20000 );
  //sCheck.errMsg.useMalloc = 2;

  /* Check the integrity of the freelist
  */
  checkList( sCheck, 1, (int)sqlite3Get4byte( pBt.pPage1.aData, 32 ),
  (int)sqlite3Get4byte( pBt.pPage1.aData, 36 ), "Main freelist: " );

  /* Check all the tables.
  */
  for ( i = 0; (int)i < nRoot && sCheck.mxErr != 0; i++ )
  {
    if ( aRoot[i] == 0 )
      continue;
#if !SQLITE_OMIT_AUTOVACUUM
    if ( pBt.autoVacuum && aRoot[i] > 1 )
    {
      checkPtrmap( sCheck, (u32)aRoot[i], PTRMAP_ROOTPAGE, 0, "" );
    }
#endif
    checkTreePage( sCheck, aRoot[i], "List of tree roots: ", ref refNULL, ref refNULL, null, null );
  }

  /* Make sure every page in the file is referenced
  */
  for ( i = 1; i <= sCheck.nPage && sCheck.mxErr != 0; i++ )
  {
#if SQLITE_OMIT_AUTOVACUUM
if( sCheck.anRef[i]==null ){
checkAppendMsg(sCheck, 0, "Page %d is never used", i);
}
#else
    /* If the database supports auto-vacuum, make sure no tables contain
** references to pointer-map pages.
*/
    if ( sCheck.anRef[i] == 0 &&
    ( PTRMAP_PAGENO( pBt, i ) != i || !pBt.autoVacuum ) )
    {
      checkAppendMsg( sCheck, "", "Page %d is never used", i );
    }
    if ( sCheck.anRef[i] != 0 &&
    ( PTRMAP_PAGENO( pBt, i ) == i && pBt.autoVacuum ) )
    {
      checkAppendMsg( sCheck, "", "Pointer map page %d is referenced", i );
    }
#endif
  }

  /* Make sure this analysis did not leave any unref() pages.
  ** This is an internal consistency check; an integrity check
  ** of the integrity check.
  */
  if ( NEVER( nRef != sqlite3PagerRefcount( pBt.pPager ) ) )
  {
    checkAppendMsg( sCheck, "",
    "Outstanding page count goes from %d to %d during this analysis",
    nRef, sqlite3PagerRefcount( pBt.pPager )
    );
  }

  /* Clean  up and report errors.
  */
  sqlite3BtreeLeave( p );
  sCheck.anRef = null;// sqlite3_free( ref sCheck.anRef );
  //if( sCheck.mallocFailed ){
  //  sqlite3StrAccumReset(sCheck.errMsg);
  //  pnErr = sCheck.nErr+1;
  //  return 0;
  //}
  pnErr = sCheck.nErr;
  if ( sCheck.nErr == 0 )
    sqlite3StrAccumReset( sCheck.errMsg );
  return sqlite3StrAccumFinish( sCheck.errMsg );
}
#endif //* SQLITE_OMIT_INTEGRITY_CHECK */

/*
** Return the full pathname of the underlying database file.
**
** The pager filename is invariant as long as the pager is
** open so it is safe to access without the BtShared mutex.
*/
static string sqlite3BtreeGetFilename( Btree p )
{
  Debug.Assert( p.pBt.pPager != null );
  return sqlite3PagerFilename( p.pBt.pPager );
}

/*
** Return the pathname of the journal file for this database. The return
** value of this routine is the same regardless of whether the journal file
** has been created or not.
**
** The pager journal filename is invariant as long as the pager is
** open so it is safe to access without the BtShared mutex.
*/
static string sqlite3BtreeGetJournalname( Btree p )
{
  Debug.Assert( p.pBt.pPager != null );
  return sqlite3PagerJournalname( p.pBt.pPager );
}

/*
** Return non-zero if a transaction is active.
*/
static bool sqlite3BtreeIsInTrans( Btree p )
{
  Debug.Assert( p == null || sqlite3_mutex_held( p.db.mutex ) );
  return ( p != null && ( p.inTrans == TRANS_WRITE ) );
}

#if !SQLITE_OMIT_WAL
/*
** Run a checkpoint on the Btree passed as the first argument.
**
** Return SQLITE_LOCKED if this or any other connection has an open 
** transaction on the shared-cache the argument Btree is connected to.
**
** Parameter eMode is one of SQLITE_CHECKPOINT_PASSIVE, FULL or RESTART.
*/
static int sqlite3BtreeCheckpointBtree *p, int eMode, int *pnLog, int *pnCkpt){
int rc = SQLITE_OK;
if( p != null){
BtShared pBt = p.pBt;
sqlite3BtreeEnter(p);
if( pBt.inTransaction!=TRANS_NONE ){
rc = SQLITE_LOCKED;
}else{
rc = sqlite3PagerCheckpoint(pBt.pPager, eMode, pnLog, pnCkpt);
}
sqlite3BtreeLeave(p);
}
return rc;
}
#endif

/*
** Return non-zero if a read (or write) transaction is active.
*/
static bool sqlite3BtreeIsInReadTrans( Btree p )
{
  Debug.Assert( p != null );
  Debug.Assert( sqlite3_mutex_held( p.db.mutex ) );
  return p.inTrans != TRANS_NONE;
}

static bool sqlite3BtreeIsInBackup( Btree p )
{
  Debug.Assert( p != null );
  Debug.Assert( sqlite3_mutex_held( p.db.mutex ) );
  return p.nBackup != 0;
}

/*
** This function returns a pointer to a blob of memory associated with
** a single shared-btree. The memory is used by client code for its own
** purposes (for example, to store a high-level schema associated with
** the shared-btree). The btree layer manages reference counting issues.
**
** The first time this is called on a shared-btree, nBytes bytes of memory
** are allocated, zeroed, and returned to the caller. For each subsequent
** call the nBytes parameter is ignored and a pointer to the same blob
** of memory returned.
**
** If the nBytes parameter is 0 and the blob of memory has not yet been
** allocated, a null pointer is returned. If the blob has already been
** allocated, it is returned as normal.
**
** Just before the shared-btree is closed, the function passed as the 
** xFree argument when the memory allocation was made is invoked on the 
** blob of allocated memory. The xFree function should not call sqlite3_free()
** on the memory, the btree layer does that.
*/
static Schema sqlite3BtreeSchema( Btree p, int nBytes, dxFreeSchema xFree )
{
  BtShared pBt = p.pBt;
  sqlite3BtreeEnter( p );
  if ( null == pBt.pSchema && nBytes != 0 )
  {
    pBt.pSchema = new Schema();//sqlite3DbMallocZero(0, nBytes);
    pBt.xFreeSchema = xFree;
  }
  sqlite3BtreeLeave( p );
  return pBt.pSchema;
}

/*
** Return SQLITE_LOCKED_SHAREDCACHE if another user of the same shared
** btree as the argument handle holds an exclusive lock on the
** sqlite_master table. Otherwise SQLITE_OK.
*/
static int sqlite3BtreeSchemaLocked( Btree p )
{
  int rc;
  Debug.Assert( sqlite3_mutex_held( p.db.mutex ) );
  sqlite3BtreeEnter( p );
  rc = querySharedCacheTableLock( p, MASTER_ROOT, READ_LOCK );
  Debug.Assert( rc == SQLITE_OK || rc == SQLITE_LOCKED_SHAREDCACHE );
  sqlite3BtreeLeave( p );
  return rc;
}


#if !SQLITE_OMIT_SHARED_CACHE
/*
** Obtain a lock on the table whose root page is iTab.  The
** lock is a write lock if isWritelock is true or a read lock
** if it is false.
*/
int sqlite3BtreeLockTable(Btree p, int iTab, u8 isWriteLock){
int rc = SQLITE_OK;
Debug.Assert( p.inTrans!=TRANS_NONE );
if( p.sharable ){
u8 lockType = READ_LOCK + isWriteLock;
Debug.Assert( READ_LOCK+1==WRITE_LOCK );
Debug.Assert( isWriteLock==null || isWriteLock==1 );

sqlite3BtreeEnter(p);
rc = querySharedCacheTableLock(p, iTab, lockType);
if( rc==SQLITE_OK ){
rc = setSharedCacheTableLock(p, iTab, lockType);
}
sqlite3BtreeLeave(p);
}
return rc;
}
#endif

#if !SQLITE_OMIT_INCRBLOB
/*
** Argument pCsr must be a cursor opened for writing on an
** INTKEY table currently pointing at a valid table entry.
** This function modifies the data stored as part of that entry.
**
** Only the data content may only be modified, it is not possible to
** change the length of the data stored. If this function is called with
** parameters that attempt to write past the end of the existing data,
** no modifications are made and SQLITE_CORRUPT is returned.
*/
int sqlite3BtreePutData(BtCursor pCsr, u32 offset, u32 amt, void *z){
int rc;
Debug.Assert( cursorHoldsMutex(pCsr) );
Debug.Assert( sqlite3_mutex_held(pCsr.pBtree.db.mutex) );
Debug.Assert( pCsr.isIncrblobHandle );

rc = restoreCursorPosition(pCsr);
if( rc!=SQLITE_OK ){
return rc;
}
Debug.Assert( pCsr.eState!=CURSOR_REQUIRESEEK );
if( pCsr.eState!=CURSOR_VALID ){
return SQLITE_ABORT;
}

/* Check some assumptions:
**   (a) the cursor is open for writing,
**   (b) there is a read/write transaction open,
**   (c) the connection holds a write-lock on the table (if required),
**   (d) there are no conflicting read-locks, and
**   (e) the cursor points at a valid row of an intKey table.
*/
if( !pCsr.wrFlag ){
return SQLITE_READONLY;
}
Debug.Assert( !pCsr.pBt.readOnly && pCsr.pBt.inTransaction==TRANS_WRITE );
Debug.Assert( hasSharedCacheTableLock(pCsr.pBtree, pCsr.pgnoRoot, 0, 2) );
Debug.Assert( !hasReadConflicts(pCsr.pBtree, pCsr.pgnoRoot) );
Debug.Assert( pCsr.apPage[pCsr.iPage].intKey );

return accessPayload(pCsr, offset, amt, (byte[] *)z, 1);
}

/*
** Set a flag on this cursor to cache the locations of pages from the
** overflow list for the current row. This is used by cursors opened
** for incremental blob IO only.
**
** This function sets a flag only. The actual page location cache
** (stored in BtCursor.aOverflow[]) is allocated and used by function
** accessPayload() (the worker function for sqlite3BtreeData() and
** sqlite3BtreePutData()).
*/
static void sqlite3BtreeCacheOverflow(BtCursor pCur){
Debug.Assert( cursorHoldsMutex(pCur) );
Debug.Assert( sqlite3_mutex_held(pCur.pBtree.db.mutex) );
invalidateOverflowCache(pCur)
pCur.isIncrblobHandle = 1;
}
#endif

/*
** Set both the "read version" (single byte at byte offset 18) and 
** "write version" (single byte at byte offset 19) fields in the database
** header to iVersion.
*/
static int sqlite3BtreeSetVersion( Btree pBtree, int iVersion )
{
  BtShared pBt = pBtree.pBt;
  int rc;                         /* Return code */

  Debug.Assert( pBtree.inTrans == TRANS_NONE );
  Debug.Assert( iVersion == 1 || iVersion == 2 );

  /* If setting the version fields to 1, do not automatically open the
  ** WAL connection, even if the version fields are currently set to 2.
  */
  pBt.doNotUseWAL = iVersion == 1;

  rc = sqlite3BtreeBeginTrans( pBtree, 0 );
  if ( rc == SQLITE_OK )
  {
    u8[] aData = pBt.pPage1.aData;
    if ( aData[18] != (u8)iVersion || aData[19] != (u8)iVersion )
    {
      rc = sqlite3BtreeBeginTrans( pBtree, 2 );
      if ( rc == SQLITE_OK )
      {
        rc = sqlite3PagerWrite( pBt.pPage1.pDbPage );
        if ( rc == SQLITE_OK )
        {
          aData[18] = (u8)iVersion;
          aData[19] = (u8)iVersion;
        }
      }
    }
  }

  pBt.doNotUseWAL = false;
  return rc;
}
  }
}