/includes/objectcache/SqlBagOStuff.php

<?php

/**
 * Class to store objects in the database
 *
 * @ingroup Cache
 */
class SqlBagOStuff extends BagOStuff {

	/**
	 * @var LoadBalancer
	 */
	var $lb;

	/**
	 * @var DatabaseBase
	 */
	var $db;
	var $serverInfo;
	var $lastExpireAll = 0;
	var $purgePeriod = 100;
	var $shards = 1;
	var $tableName = 'objectcache';

	/**
	 * Constructor. Parameters are:
	 *   - server:   A server info structure in the format required by each 
	 *               element in $wgDBServers.
	 *
	 *   - purgePeriod: The average number of object cache requests in between 
	 *                  garbage collection operations, where expired entries 
	 *                  are removed from the database. Or in other words, the 
	 *                  reciprocal of the probability of purging on any given 
	 *                  request. If this is set to zero, purging will never be 
	 *                  done.
	 *
	 *   - tableName:   The table name to use, default is "objectcache".
	 *
	 *   - shards:      The number of tables to use for data storage. If this is 
	 *                  more than 1, table names will be formed in the style 
	 *                  objectcacheNNN where NNN is the shard index, between 0 and 
	 *                  shards-1. The number of digits will be the minimum number 
	 *                  required to hold the largest shard index. Data will be 
	 *                  distributed across all tables by key hash. This is for 
	 *                  MySQL bugs 61735 and 61736.
	 *
	 * @param $params array
	 */
	public function __construct( $params ) {
		if ( isset( $params['server'] ) ) {
			$this->serverInfo = $params['server'];
			$this->serverInfo['load'] = 1;
		}
		if ( isset( $params['purgePeriod'] ) ) {
			$this->purgePeriod = intval( $params['purgePeriod'] );
		}
		if ( isset( $params['tableName'] ) ) {
			$this->tableName = $params['tableName'];
		}
		if ( isset( $params['shards'] ) ) {
			$this->shards = intval( $params['shards'] );
		}
	}

	/**
	 * @return DatabaseBase
	 */
	protected function getDB() {
		if ( !isset( $this->db ) ) {
			# If server connection info was given, use that
			if ( $this->serverInfo ) {
				$this->lb = new LoadBalancer( array(
					'servers' => array( $this->serverInfo ) ) );
				$this->db = $this->lb->getConnection( DB_MASTER );
				$this->db->clearFlag( DBO_TRX );
			} else {
				# We must keep a separate connection to MySQL in order to avoid deadlocks
				# However, SQLite has an opposite behaviour.
				# @todo Investigate behaviour for other databases
				if ( wfGetDB( DB_MASTER )->getType() == 'sqlite' ) {
					$this->db = wfGetDB( DB_MASTER );
				} else {
					$this->lb = wfGetLBFactory()->newMainLB();
					$this->db = $this->lb->getConnection( DB_MASTER );
					$this->db->clearFlag( DBO_TRX );
				}
			}
		}

		return $this->db;
	}

	/**
	 * Get the table name for a given key
	 */
	protected function getTableByKey( $key ) {
		if ( $this->shards > 1 ) {
			$hash = hexdec( substr( md5( $key ), 0, 8 ) ) & 0x7fffffff;
			return $this->getTableByShard( $hash % $this->shards );
		} else {
			return $this->tableName;
		}
	}

	/**
	 * Get the table name for a given shard index
	 */
	protected function getTableByShard( $index ) {
		if ( $this->shards > 1 ) {
			$decimals = strlen( $this->shards - 1 );
			return $this->tableName . 
				sprintf( "%0{$decimals}d", $index );
		} else {
			return $this->tableName;
		}
	}

	public function get( $key ) {
		# expire old entries if any
		$this->garbageCollect();
		$db = $this->getDB();
		$tableName = $this->getTableByKey( $key );
		$row = $db->selectRow( $tableName, array( 'value', 'exptime' ),
			array( 'keyname' => $key ), __METHOD__ );

		if ( !$row ) {
			$this->debug( 'get: no matching rows' );
			return false;
		}

		$this->debug( "get: retrieved data; expiry time is " . $row->exptime );

		if ( $this->isExpired( $row->exptime ) ) {
			$this->debug( "get: key has expired, deleting" );
			try {
				$db->begin();
				# Put the expiry time in the WHERE condition to avoid deleting a
				# newly-inserted value
				$db->delete( $tableName,
					array(
						'keyname' => $key,
						'exptime' => $row->exptime
					), __METHOD__ );
				$db->commit();
			} catch ( DBQueryError $e ) {
				$this->handleWriteError( $e );
			}

			return false;
		}

		return $this->unserialize( $db->decodeBlob( $row->value ) );
	}

	public function set( $key, $value, $exptime = 0 ) {
		$db = $this->getDB();
		$exptime = intval( $exptime );

		if ( $exptime < 0 ) {
			$exptime = 0;
		}

		if ( $exptime == 0 ) {
			$encExpiry = $this->getMaxDateTime();
		} else {
			if ( $exptime < 3.16e8 ) { # ~10 years
				$exptime += time();
			}

			$encExpiry = $db->timestamp( $exptime );
		}
		try {
			$db->begin();
			// (bug 24425) use a replace if the db supports it instead of
			// delete/insert to avoid clashes with conflicting keynames
			$db->replace( 
				$this->getTableByKey( $key ), 
				array( 'keyname' ),
				array(
					'keyname' => $key,
					'value' => $db->encodeBlob( $this->serialize( $value ) ),
					'exptime' => $encExpiry
				), __METHOD__ );
			$db->commit();
		} catch ( DBQueryError $e ) {
			$this->handleWriteError( $e );

			return false;
		}

		return true;
	}

	public function delete( $key, $time = 0 ) {
		$db = $this->getDB();

		try {
			$db->begin();
			$db->delete( 
				$this->getTableByKey( $key ), 
				array( 'keyname' => $key ), 
				__METHOD__ );
			$db->commit();
		} catch ( DBQueryError $e ) {
			$this->handleWriteError( $e );

			return false;
		}

		return true;
	}

	public function incr( $key, $step = 1 ) {
		$db = $this->getDB();
		$tableName = $this->getTableByKey( $key );
		$step = intval( $step );

		try {
			$db->begin();
			$row = $db->selectRow( 
				$tableName, 
				array( 'value', 'exptime' ),
				array( 'keyname' => $key ), 
				__METHOD__, 
				array( 'FOR UPDATE' ) );
			if ( $row === false ) {
				// Missing
				$db->commit();

				return null;
			}
			$db->delete( $tableName, array( 'keyname' => $key ), __METHOD__ );
			if ( $this->isExpired( $row->exptime ) ) {
				// Expired, do not reinsert
				$db->commit();

				return null;
			}

			$oldValue = intval( $this->unserialize( $db->decodeBlob( $row->value ) ) );
			$newValue = $oldValue + $step;
			$db->insert( $tableName,
				array(
					'keyname' => $key,
					'value' => $db->encodeBlob( $this->serialize( $newValue ) ),
					'exptime' => $row->exptime
				), __METHOD__, 'IGNORE' );
			
			if ( $db->affectedRows() == 0 ) {
				// Race condition. See bug 28611
				$newValue = null;
			}
			$db->commit();
		} catch ( DBQueryError $e ) {
			$this->handleWriteError( $e );

			return null;
		}

		return $newValue;
	}

	public function keys() {
		$db = $this->getDB();
		$result = array();

		for ( $i = 0; $i < $this->shards; $i++ ) {
			$res = $db->select( $this->getTableByShard( $i ), 
				array( 'keyname' ), false, __METHOD__ );
			foreach ( $res as $row ) {
				$result[] = $row->keyname;
			}
		}

		return $result;
	}

	protected function isExpired( $exptime ) {
		return $exptime != $this->getMaxDateTime() && wfTimestamp( TS_UNIX, $exptime ) < time();
	}

	protected function getMaxDateTime() {
		if ( time() > 0x7fffffff ) {
			return $this->getDB()->timestamp( 1 << 62 );
		} else {
			return $this->getDB()->timestamp( 0x7fffffff );
		}
	}

	protected function garbageCollect() {
		if ( !$this->purgePeriod ) {
			// Disabled
			return;
		}
		// Only purge on one in every $this->purgePeriod requests.
		if ( $this->purgePeriod !== 1 && mt_rand( 0, $this->purgePeriod - 1 ) ) {
			return;
		}
		$now = time();
		// Avoid repeating the delete within a few seconds
		if ( $now > ( $this->lastExpireAll + 1 ) ) {
			$this->lastExpireAll = $now;
			$this->expireAll();
		}
	}

	public function expireAll() {
		$db = $this->getDB();
		$now = $db->timestamp();

		try {
			for ( $i = 0; $i < $this->shards; $i++ ) {
				$db->begin();
				$db->delete(
					$this->getTableByShard( $i ), 
					array( 'exptime < ' . $db->addQuotes( $now ) ), 
					__METHOD__ );
				$db->commit();
			}
		} catch ( DBQueryError $e ) {
			$this->handleWriteError( $e );
		}
	}

	public function deleteAll() {
		$db = $this->getDB();

		try {
			for ( $i = 0; $i < $this->shards; $i++ ) {
				$db->begin();
				$db->delete( $this->getTableByShard( $i ), '*', __METHOD__ );
				$db->commit();
			}
		} catch ( DBQueryError $e ) {
			$this->handleWriteError( $e );
		}
	}

	/**
	 * Serialize an object and, if possible, compress the representation.
	 * On typical message and page data, this can provide a 3X decrease
	 * in storage requirements.
	 *
	 * @param $data mixed
	 * @return string
	 */
	protected function serialize( &$data ) {
		$serial = serialize( $data );

		if ( function_exists( 'gzdeflate' ) ) {
			return gzdeflate( $serial );
		} else {
			return $serial;
		}
	}

	/**
	 * Unserialize and, if necessary, decompress an object.
	 * @param $serial string
	 * @return mixed
	 */
	protected function unserialize( $serial ) {
		if ( function_exists( 'gzinflate' ) ) {
			wfSuppressWarnings();
			$decomp = gzinflate( $serial );
			wfRestoreWarnings();

			if ( false !== $decomp ) {
				$serial = $decomp;
			}
		}

		$ret = unserialize( $serial );

		return $ret;
	}

	/**
	 * Handle a DBQueryError which occurred during a write operation.
	 * Ignore errors which are due to a read-only database, rethrow others.
	 */
	protected function handleWriteError( $exception ) {
		$db = $this->getDB();

		if ( !$db->wasReadOnlyError() ) {
			throw $exception;
		}

		try {
			$db->rollback();
		} catch ( DBQueryError $e ) {
		}

		wfDebug( __METHOD__ . ": ignoring query error\n" );
		$db->ignoreErrors( false );
	}

	/**
	 * Create shard tables. For use from eval.php.
	 */
	public function createTables() {
		$db = $this->getDB();
		if ( $db->getType() !== 'mysql'
			|| version_compare( $db->getServerVersion(), '4.1.0', '<' ) )
		{
			throw new MWException( __METHOD__ . ' is not supported on this DB server' );
		}

		for ( $i = 0; $i < $this->shards; $i++ ) {
			$db->begin();
			$db->query(
				'CREATE TABLE ' . $db->tableName( $this->getTableByShard( $i ) ) .
				' LIKE ' . $db->tableName( 'objectcache' ),
				__METHOD__ );
			$db->commit();
		}
	}
}

/**
 * Backwards compatibility alias
 */
class MediaWikiBagOStuff extends SqlBagOStuff { }