/includes/cache/BacklinkCache.php
PHP | 493 lines | 253 code | 56 blank | 184 comment | 49 complexity | 3fa031e2adae76c04d0793921d2dfe19 MD5 | raw file
Possible License(s): Apache-2.0, MIT, GPL-2.0
- <?php
- /**
- * Class for fetching backlink lists, approximate backlink counts and
- * partitions.
- *
- * This program is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License as published by
- * the Free Software Foundation; either version 2 of the License, or
- * (at your option) any later version.
- *
- * This program is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
- * GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License along
- * with this program; if not, write to the Free Software Foundation, Inc.,
- * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
- * http://www.gnu.org/copyleft/gpl.html
- *
- * @file
- * @author Tim Starling
- * @author Aaron Schulz
- * @copyright © 2009, Tim Starling, Domas Mituzas
- * @copyright © 2010, Max Sem
- * @copyright © 2011, Antoine Musso
- */
- /**
- * Class for fetching backlink lists, approximate backlink counts and
- * partitions. This is a shared cache.
- *
- * Instances of this class should typically be fetched with the method
- * $title->getBacklinkCache().
- *
- * Ideally you should only get your backlinks from here when you think
- * there is some advantage in caching them. Otherwise it's just a waste
- * of memory.
- *
- * Introduced by r47317
- *
- * @internal documentation reviewed on 18 Mar 2011 by hashar
- */
- class BacklinkCache {
- /** @var ProcessCacheLRU */
- protected static $cache;
- /**
- * Multi dimensions array representing batches. Keys are:
- * > (string) links table name
- * > (int) batch size
- * > 'numRows' : Number of rows for this link table
- * > 'batches' : array( $start, $end )
- *
- * @see BacklinkCache::partitionResult()
- *
- * Cleared with BacklinkCache::clear()
- */
- protected $partitionCache = array();
- /**
- * Contains the whole links from a database result.
- * This is raw data that will be partitioned in $partitionCache
- *
- * Initialized with BacklinkCache::getLinks()
- * Cleared with BacklinkCache::clear()
- */
- protected $fullResultCache = array();
- /**
- * Local copy of a database object.
- *
- * Accessor: BacklinkCache::getDB()
- * Mutator : BacklinkCache::setDB()
- * Cleared with BacklinkCache::clear()
- */
- protected $db;
- /**
- * Local copy of a Title object
- */
- protected $title;
- const CACHE_EXPIRY = 3600;
- /**
- * Create a new BacklinkCache
- *
- * @param Title $title : Title object to create a backlink cache for
- */
- public function __construct( Title $title ) {
- $this->title = $title;
- }
- /**
- * Create a new BacklinkCache or reuse any existing one.
- * Currently, only one cache instance can exist; callers that
- * need multiple backlink cache objects should keep them in scope.
- *
- * @param Title $title Title object to get a backlink cache for
- * @return BacklinkCache
- */
- public static function get( Title $title ) {
- if ( !self::$cache ) { // init cache
- self::$cache = new ProcessCacheLRU( 1 );
- }
- $dbKey = $title->getPrefixedDBkey();
- if ( !self::$cache->has( $dbKey, 'obj', 3600 ) ) {
- self::$cache->set( $dbKey, 'obj', new self( $title ) );
- }
- return self::$cache->get( $dbKey, 'obj' );
- }
- /**
- * Serialization handler, diasallows to serialize the database to prevent
- * failures after this class is deserialized from cache with dead DB
- * connection.
- *
- * @return array
- */
- function __sleep() {
- return array( 'partitionCache', 'fullResultCache', 'title' );
- }
- /**
- * Clear locally stored data and database object.
- */
- public function clear() {
- $this->partitionCache = array();
- $this->fullResultCache = array();
- unset( $this->db );
- }
- /**
- * Set the Database object to use
- *
- * @param DatabaseBase $db
- */
- public function setDB( $db ) {
- $this->db = $db;
- }
- /**
- * Get the slave connection to the database
- * When non existing, will initialize the connection.
- * @return DatabaseBase
- */
- protected function getDB() {
- if ( !isset( $this->db ) ) {
- $this->db = wfGetDB( DB_SLAVE );
- }
- return $this->db;
- }
- /**
- * Get the backlinks for a given table. Cached in process memory only.
- * @param string $table
- * @param int|bool $startId
- * @param int|bool $endId
- * @param int|INF $max
- * @return TitleArrayFromResult
- */
- public function getLinks( $table, $startId = false, $endId = false, $max = INF ) {
- return TitleArray::newFromResult( $this->queryLinks( $table, $startId, $endId, $max ) );
- }
- /**
- * Get the backlinks for a given table. Cached in process memory only.
- * @param string $table
- * @param int|bool $startId
- * @param int|bool $endId
- * @param int|INF $max
- * @param string $select 'all' or 'ids'
- * @return ResultWrapper
- */
- protected function queryLinks( $table, $startId, $endId, $max, $select = 'all' ) {
- wfProfileIn( __METHOD__ );
- $fromField = $this->getPrefix( $table ) . '_from';
- if ( !$startId && !$endId && is_infinite( $max )
- && isset( $this->fullResultCache[$table] )
- ) {
- wfDebug( __METHOD__ . ": got results from cache\n" );
- $res = $this->fullResultCache[$table];
- } else {
- wfDebug( __METHOD__ . ": got results from DB\n" );
- $conds = $this->getConditions( $table );
- // Use the from field in the condition rather than the joined page_id,
- // because databases are stupid and don't necessarily propagate indexes.
- if ( $startId ) {
- $conds[] = "$fromField >= " . intval( $startId );
- }
- if ( $endId ) {
- $conds[] = "$fromField <= " . intval( $endId );
- }
- $options = array( 'ORDER BY' => $fromField );
- if ( is_finite( $max ) && $max > 0 ) {
- $options['LIMIT'] = $max;
- }
- if ( $select === 'ids' ) {
- // Just select from the backlink table and ignore the page JOIN
- $res = $this->getDB()->select(
- $table,
- array( $this->getPrefix( $table ) . '_from AS page_id' ),
- array_filter( $conds, function ( $clause ) { // kind of janky
- return !preg_match( '/(\b|=)page_id(\b|=)/', $clause );
- } ),
- __METHOD__,
- $options
- );
- } else {
- // Select from the backlink table and JOIN with page title information
- $res = $this->getDB()->select(
- array( $table, 'page' ),
- array( 'page_namespace', 'page_title', 'page_id' ),
- $conds,
- __METHOD__,
- array_merge( array( 'STRAIGHT_JOIN' ), $options )
- );
- }
- if ( $select === 'all' && !$startId && !$endId && $res->numRows() < $max ) {
- // The full results fit within the limit, so cache them
- $this->fullResultCache[$table] = $res;
- } else {
- wfDebug( __METHOD__ . ": results from DB were uncacheable\n" );
- }
- }
- wfProfileOut( __METHOD__ );
- return $res;
- }
- /**
- * Get the field name prefix for a given table
- * @param string $table
- * @throws MWException
- * @return null|string
- */
- protected function getPrefix( $table ) {
- static $prefixes = array(
- 'pagelinks' => 'pl',
- 'imagelinks' => 'il',
- 'categorylinks' => 'cl',
- 'templatelinks' => 'tl',
- 'redirect' => 'rd',
- );
- if ( isset( $prefixes[$table] ) ) {
- return $prefixes[$table];
- } else {
- $prefix = null;
- wfRunHooks( 'BacklinkCacheGetPrefix', array( $table, &$prefix ) );
- if ( $prefix ) {
- return $prefix;
- } else {
- throw new MWException( "Invalid table \"$table\" in " . __CLASS__ );
- }
- }
- }
- /**
- * Get the SQL condition array for selecting backlinks, with a join
- * on the page table.
- * @param string $table
- * @throws MWException
- * @return array|null
- */
- protected function getConditions( $table ) {
- $prefix = $this->getPrefix( $table );
- switch ( $table ) {
- case 'pagelinks':
- case 'templatelinks':
- $conds = array(
- "{$prefix}_namespace" => $this->title->getNamespace(),
- "{$prefix}_title" => $this->title->getDBkey(),
- "page_id={$prefix}_from"
- );
- break;
- case 'redirect':
- $conds = array(
- "{$prefix}_namespace" => $this->title->getNamespace(),
- "{$prefix}_title" => $this->title->getDBkey(),
- $this->getDb()->makeList( array(
- "{$prefix}_interwiki" => '',
- "{$prefix}_interwiki IS NULL",
- ), LIST_OR ),
- "page_id={$prefix}_from"
- );
- break;
- case 'imagelinks':
- case 'categorylinks':
- $conds = array(
- "{$prefix}_to" => $this->title->getDBkey(),
- "page_id={$prefix}_from"
- );
- break;
- default:
- $conds = null;
- wfRunHooks( 'BacklinkCacheGetConditions', array( $table, $this->title, &$conds ) );
- if ( !$conds ) {
- throw new MWException( "Invalid table \"$table\" in " . __CLASS__ );
- }
- }
- return $conds;
- }
- /**
- * Check if there are any backlinks
- * @param string $table
- * @return bool
- */
- public function hasLinks( $table ) {
- return ( $this->getNumLinks( $table, 1 ) > 0 );
- }
- /**
- * Get the approximate number of backlinks
- * @param string $table
- * @param int|INF $max Only count up to this many backlinks
- * @return int
- */
- public function getNumLinks( $table, $max = INF ) {
- global $wgMemc, $wgUpdateRowsPerJob;
- // 1) try partition cache ...
- if ( isset( $this->partitionCache[$table] ) ) {
- $entry = reset( $this->partitionCache[$table] );
- return min( $max, $entry['numRows'] );
- }
- // 2) ... then try full result cache ...
- if ( isset( $this->fullResultCache[$table] ) ) {
- return min( $max, $this->fullResultCache[$table]->numRows() );
- }
- $memcKey = wfMemcKey( 'numbacklinks', md5( $this->title->getPrefixedDBkey() ), $table );
- // 3) ... fallback to memcached ...
- $count = $wgMemc->get( $memcKey );
- if ( $count ) {
- return min( $max, $count );
- }
- // 4) fetch from the database ...
- if ( is_infinite( $max ) ) { // no limit at all
- // Use partition() since it will batch the query and skip the JOIN.
- // Use $wgUpdateRowsPerJob just to encourage cache reuse for jobs.
- $this->partition( $table, $wgUpdateRowsPerJob ); // updates $this->partitionCache
- return $this->partitionCache[$table][$wgUpdateRowsPerJob]['numRows'];
- } else { // probably some sane limit
- // Fetch the full title info, since the caller will likely need it next
- $count = $this->getLinks( $table, false, false, $max )->count();
- if ( $count < $max ) { // full count
- $wgMemc->set( $memcKey, $count, self::CACHE_EXPIRY );
- }
- }
- return min( $max, $count );
- }
- /**
- * Partition the backlinks into batches.
- * Returns an array giving the start and end of each range. The first
- * batch has a start of false, and the last batch has an end of false.
- *
- * @param string $table The links table name
- * @param int $batchSize
- * @return array
- */
- public function partition( $table, $batchSize ) {
- global $wgMemc;
- // 1) try partition cache ...
- if ( isset( $this->partitionCache[$table][$batchSize] ) ) {
- wfDebug( __METHOD__ . ": got from partition cache\n" );
- return $this->partitionCache[$table][$batchSize]['batches'];
- }
- $this->partitionCache[$table][$batchSize] = false;
- $cacheEntry =& $this->partitionCache[$table][$batchSize];
- // 2) ... then try full result cache ...
- if ( isset( $this->fullResultCache[$table] ) ) {
- $cacheEntry = $this->partitionResult( $this->fullResultCache[$table], $batchSize );
- wfDebug( __METHOD__ . ": got from full result cache\n" );
- return $cacheEntry['batches'];
- }
- $memcKey = wfMemcKey(
- 'backlinks',
- md5( $this->title->getPrefixedDBkey() ),
- $table,
- $batchSize
- );
- // 3) ... fallback to memcached ...
- $memcValue = $wgMemc->get( $memcKey );
- if ( is_array( $memcValue ) ) {
- $cacheEntry = $memcValue;
- wfDebug( __METHOD__ . ": got from memcached $memcKey\n" );
- return $cacheEntry['batches'];
- }
- // 4) ... finally fetch from the slow database :(
- $cacheEntry = array( 'numRows' => 0, 'batches' => array() ); // final result
- // Do the selects in batches to avoid client-side OOMs (bug 43452).
- // Use a LIMIT that plays well with $batchSize to keep equal sized partitions.
- $selectSize = max( $batchSize, 200000 - ( 200000 % $batchSize ) );
- $start = false;
- do {
- $res = $this->queryLinks( $table, $start, false, $selectSize, 'ids' );
- $partitions = $this->partitionResult( $res, $batchSize, false );
- // Merge the link count and range partitions for this chunk
- $cacheEntry['numRows'] += $partitions['numRows'];
- $cacheEntry['batches'] = array_merge( $cacheEntry['batches'], $partitions['batches'] );
- if ( count( $partitions['batches'] ) ) {
- list( , $lEnd ) = end( $partitions['batches'] );
- $start = $lEnd + 1; // pick up after this inclusive range
- }
- } while ( $partitions['numRows'] >= $selectSize );
- // Make sure the first range has start=false and the last one has end=false
- if ( count( $cacheEntry['batches'] ) ) {
- $cacheEntry['batches'][0][0] = false;
- $cacheEntry['batches'][count( $cacheEntry['batches'] ) - 1][1] = false;
- }
- // Save partitions to memcached
- $wgMemc->set( $memcKey, $cacheEntry, self::CACHE_EXPIRY );
- // Save backlink count to memcached
- $memcKey = wfMemcKey( 'numbacklinks', md5( $this->title->getPrefixedDBkey() ), $table );
- $wgMemc->set( $memcKey, $cacheEntry['numRows'], self::CACHE_EXPIRY );
- wfDebug( __METHOD__ . ": got from database\n" );
- return $cacheEntry['batches'];
- }
- /**
- * Partition a DB result with backlinks in it into batches
- * @param ResultWrapper $res Database result
- * @param int $batchSize
- * @param bool $isComplete Whether $res includes all the backlinks
- * @throws MWException
- * @return array
- */
- protected function partitionResult( $res, $batchSize, $isComplete = true ) {
- $batches = array();
- $numRows = $res->numRows();
- $numBatches = ceil( $numRows / $batchSize );
- for ( $i = 0; $i < $numBatches; $i++ ) {
- if ( $i == 0 && $isComplete ) {
- $start = false;
- } else {
- $rowNum = $i * $batchSize;
- $res->seek( $rowNum );
- $row = $res->fetchObject();
- $start = (int)$row->page_id;
- }
- if ( $i == ( $numBatches - 1 ) && $isComplete ) {
- $end = false;
- } else {
- $rowNum = min( $numRows - 1, ( $i + 1 ) * $batchSize - 1 );
- $res->seek( $rowNum );
- $row = $res->fetchObject();
- $end = (int)$row->page_id;
- }
- # Sanity check order
- if ( $start && $end && $start > $end ) {
- throw new MWException( __METHOD__ . ': Internal error: query result out of order' );
- }
- $batches[] = array( $start, $end );
- }
- return array( 'numRows' => $numRows, 'batches' => $batches );
- }
- }