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[mediawiki.git] / includes / objectcache / SqlBagOStuff.php

<?php
/**
 * Object caching using a SQL database.
 *
 * 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
 * @ingroup Cache
 */

/**
 * 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
         * @return string
         */
        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
         * @return string
         */
        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 ) {
                $values = $this->getMulti( array( $key ) );
                return $values[$key];
        }

        public function getMulti( array $keys ) {
                $values = array(); // array of (key => value)

                $keysByTableName = array();
                foreach ( $keys as $key ) {
                        $tableName = $this->getTableByKey( $key );
                        if ( !isset( $keysByTableName[$tableName] ) ) {
                                $keysByTableName[$tableName] = array();
                        }
                        $keysByTableName[$tableName][] = $key;
                }

                $db = $this->getDB();
                $this->garbageCollect(); // expire old entries if any

                $dataRows = array();
                foreach ( $keysByTableName as $tableName => $tableKeys ) {
                        $res = $db->select( $tableName,
                                array( 'keyname', 'value', 'exptime' ),
                                array( 'keyname' => $tableKeys ),
                                __METHOD__ );
                        foreach ( $res as $row ) {
                                $dataRows[$row->keyname] = $row;
                        }
                }

                foreach ( $keys as $key ) {
                        if ( isset( $dataRows[$key] ) ) { // HIT?
                                $row = $dataRows[$key];
                                $this->debug( "get: retrieved data; expiry time is " . $row->exptime );
                                if ( $this->isExpired( $row->exptime ) ) { // MISS
                                        $this->debug( "get: key has expired, deleting" );
                                        try {
                                                $db->begin( __METHOD__ );
                                                # Put the expiry time in the WHERE condition to avoid deleting a
                                                # newly-inserted value
                                                $db->delete( $this->getTableByKey( $key ),
                                                        array( 'keyname' => $key, 'exptime' => $row->exptime ),
                                                        __METHOD__ );
                                                $db->commit( __METHOD__ );
                                        } catch ( DBQueryError $e ) {
                                                $this->handleWriteError( $e );
                                        }
                                        $values[$key] = false;
                                } else { // HIT
                                        $values[$key] = $this->unserialize( $db->decodeBlob( $row->value ) );
                                }
                        } else { // MISS
                                $values[$key] = false;
                                $this->debug( 'get: no matching rows' );
                        }
                }

                return $values;
        }

        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( __METHOD__ );
                        // (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( __METHOD__ );
                } catch ( DBQueryError $e ) {
                        $this->handleWriteError( $e );

                        return false;
                }

                return true;
        }

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

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

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

                                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( __METHOD__ );
                } 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() {
                $this->deleteObjectsExpiringBefore( wfTimestampNow() );
        }

        /**
         * Delete objects from the database which expire before a certain date.
         * @return bool
         */
        public function deleteObjectsExpiringBefore( $timestamp, $progressCallback = false ) {
                $db = $this->getDB();
                $dbTimestamp = $db->timestamp( $timestamp );
                $totalSeconds = false;
                $baseConds = array( 'exptime < ' . $db->addQuotes( $dbTimestamp ) );

                try {
                        for ( $i = 0; $i < $this->shards; $i++ ) {
                                $maxExpTime = false;
                                while ( true ) {
                                        $conds = $baseConds;
                                        if ( $maxExpTime !== false ) {
                                                $conds[] = 'exptime > ' . $db->addQuotes( $maxExpTime );
                                        }
                                        $rows = $db->select(
                                                $this->getTableByShard( $i ),
                                                array( 'keyname', 'exptime' ),
                                                $conds,
                                                __METHOD__,
                                                array( 'LIMIT' => 100, 'ORDER BY' => 'exptime' ) );
                                        if ( !$rows->numRows() ) {
                                                break;
                                        }
                                        $keys = array();
                                        $row = $rows->current();
                                        $minExpTime = $row->exptime;
                                        if ( $totalSeconds === false ) {
                                                $totalSeconds = wfTimestamp( TS_UNIX, $timestamp )
                                                        - wfTimestamp( TS_UNIX, $minExpTime );
                                        }
                                        foreach ( $rows as $row ) {
                                                $keys[] = $row->keyname;
                                                $maxExpTime = $row->exptime;
                                        }

                                        $db->begin( __METHOD__ );
                                        $db->delete(
                                                $this->getTableByShard( $i ),
                                                array(
                                                        'exptime >= ' . $db->addQuotes( $minExpTime ),
                                                        'exptime < ' . $db->addQuotes( $dbTimestamp ),
                                                        'keyname' => $keys
                                                ),
                                                __METHOD__ );
                                        $db->commit( __METHOD__ );

                                        if ( $progressCallback ) {
                                                if ( intval( $totalSeconds ) === 0 ) {
                                                        $percent = 0;
                                                } else {
                                                        $remainingSeconds = wfTimestamp( TS_UNIX, $timestamp )
                                                                - wfTimestamp( TS_UNIX, $maxExpTime );
                                                        if ( $remainingSeconds > $totalSeconds ) {
                                                                $totalSeconds = $remainingSeconds;
                                                        }
                                                        $percent = ( $i + $remainingSeconds / $totalSeconds )
                                                                / $this->shards * 100;
                                                }
                                                call_user_func( $progressCallback, $percent );
                                        }
                                }
                        }
                } catch ( DBQueryError $e ) {
                        $this->handleWriteError( $e );
                }
                return true;
        }

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

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

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