PHPSessionHandler: Implement SessionHandlerInterface

[mediawiki.git] / includes / db / loadbalancer / LBFactory.php

<?php
/**
 * Generator of database load balancing objects.
 *
 * 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 Database
 */

use Psr\Log\LoggerInterface;
use MediaWiki\Logger\LoggerFactory;

/**
 * An interface for generating database load balancers
 * @ingroup Database
 */
abstract class LBFactory {
        /** @var ChronologyProtector */
        protected $chronProt;

        /** @var TransactionProfiler */
        protected $trxProfiler;

        /** @var LoggerInterface */
        protected $logger;

        /** @var LBFactory */
        private static $instance;

        /** @var string|bool Reason all LBs are read-only or false if not */
        protected $readOnlyReason = false;

        const SHUTDOWN_NO_CHRONPROT = 1; // don't save ChronologyProtector positions (for async code)

        /**
         * Construct a factory based on a configuration array (typically from $wgLBFactoryConf)
         * @param array $conf
         */
        public function __construct( array $conf ) {
                if ( isset( $conf['readOnlyReason'] ) && is_string( $conf['readOnlyReason'] ) ) {
                        $this->readOnlyReason = $conf['readOnlyReason'];
                }

                $this->chronProt = $this->newChronologyProtector();
                $this->trxProfiler = Profiler::instance()->getTransactionProfiler();
                $this->logger = LoggerFactory::getInstance( 'DBTransaction' );
        }

        /**
         * Disables all access to the load balancer, will cause all database access
         * to throw a DBAccessError
         */
        public static function disableBackend() {
                global $wgLBFactoryConf;
                self::$instance = new LBFactoryFake( $wgLBFactoryConf );
        }

        /**
         * Get an LBFactory instance
         *
         * @return LBFactory
         */
        public static function singleton() {
                global $wgLBFactoryConf;

                if ( is_null( self::$instance ) ) {
                        $class = self::getLBFactoryClass( $wgLBFactoryConf );
                        $config = $wgLBFactoryConf;
                        if ( !isset( $config['readOnlyReason'] ) ) {
                                $config['readOnlyReason'] = wfConfiguredReadOnlyReason();
                        }
                        self::$instance = new $class( $config );
                }

                return self::$instance;
        }

        /**
         * Returns the LBFactory class to use and the load balancer configuration.
         *
         * @param array $config (e.g. $wgLBFactoryConf)
         * @return string Class name
         */
        public static function getLBFactoryClass( array $config ) {
                // For configuration backward compatibility after removing
                // underscores from class names in MediaWiki 1.23.
                $bcClasses = array(
                        'LBFactory_Simple' => 'LBFactorySimple',
                        'LBFactory_Single' => 'LBFactorySingle',
                        'LBFactory_Multi' => 'LBFactoryMulti',
                        'LBFactory_Fake' => 'LBFactoryFake',
                );

                $class = $config['class'];

                if ( isset( $bcClasses[$class] ) ) {
                        $class = $bcClasses[$class];
                        wfDeprecated(
                                '$wgLBFactoryConf must be updated. See RELEASE-NOTES for details',
                                '1.23'
                        );
                }

                return $class;
        }

        /**
         * Shut down, close connections and destroy the cached instance.
         */
        public static function destroyInstance() {
                if ( self::$instance ) {
                        self::$instance->shutdown();
                        self::$instance->forEachLBCallMethod( 'closeAll' );
                        self::$instance = null;
                }
        }

        /**
         * Set the instance to be the given object
         *
         * @param LBFactory $instance
         */
        public static function setInstance( $instance ) {
                self::destroyInstance();
                self::$instance = $instance;
        }

        /**
         * Create a new load balancer object. The resulting object will be untracked,
         * not chronology-protected, and the caller is responsible for cleaning it up.
         *
         * @param bool|string $wiki Wiki ID, or false for the current wiki
         * @return LoadBalancer
         */
        abstract public function newMainLB( $wiki = false );

        /**
         * Get a cached (tracked) load balancer object.
         *
         * @param bool|string $wiki Wiki ID, or false for the current wiki
         * @return LoadBalancer
         */
        abstract public function getMainLB( $wiki = false );

        /**
         * Create a new load balancer for external storage. The resulting object will be
         * untracked, not chronology-protected, and the caller is responsible for
         * cleaning it up.
         *
         * @param string $cluster External storage cluster, or false for core
         * @param bool|string $wiki Wiki ID, or false for the current wiki
         * @return LoadBalancer
         */
        abstract protected function newExternalLB( $cluster, $wiki = false );

        /**
         * Get a cached (tracked) load balancer for external storage
         *
         * @param string $cluster External storage cluster, or false for core
         * @param bool|string $wiki Wiki ID, or false for the current wiki
         * @return LoadBalancer
         */
        abstract public function &getExternalLB( $cluster, $wiki = false );

        /**
         * Execute a function for each tracked load balancer
         * The callback is called with the load balancer as the first parameter,
         * and $params passed as the subsequent parameters.
         *
         * @param callable $callback
         * @param array $params
         */
        abstract public function forEachLB( $callback, array $params = array() );

        /**
         * Prepare all tracked load balancers for shutdown
         * @param integer $flags Supports SHUTDOWN_* flags
         * STUB
         */
        public function shutdown( $flags = 0 ) {
        }

        /**
         * Call a method of each tracked load balancer
         *
         * @param string $methodName
         * @param array $args
         */
        private function forEachLBCallMethod( $methodName, array $args = array() ) {
                $this->forEachLB(
                        function ( LoadBalancer $loadBalancer, $methodName, array $args ) {
                                call_user_func_array( array( $loadBalancer, $methodName ), $args );
                        },
                        array( $methodName, $args )
                );
        }

        /**
         * Commit on all connections. Done for two reasons:
         * 1. To commit changes to the masters.
         * 2. To release the snapshot on all connections, master and slave.
         * @param string $fname Caller name
         */
        public function commitAll( $fname = __METHOD__ ) {
                $this->logMultiDbTransaction();

                $start = microtime( true );
                $this->forEachLBCallMethod( 'commitAll', array( $fname ) );
                $timeMs = 1000 * ( microtime( true ) - $start );

                RequestContext::getMain()->getStats()->timing( "db.commit-all", $timeMs );
        }

        /**
         * Commit changes on all master connections
         * @param string $fname Caller name
         * @param array $options Options map:
         *   - maxWriteDuration: abort if more than this much time was spent in write queries
         */
        public function commitMasterChanges( $fname = __METHOD__, array $options = array() ) {
                $limit = isset( $options['maxWriteDuration'] ) ? $options['maxWriteDuration'] : 0;

                $this->logMultiDbTransaction();
                $this->forEachLB( function ( LoadBalancer $lb ) use ( $limit ) {
                        $lb->forEachOpenConnection( function ( IDatabase $db ) use ( $limit ) {
                                $time = $db->pendingWriteQueryDuration();
                                if ( $limit > 0 && $time > $limit ) {
                                        throw new DBTransactionError(
                                                $db,
                                                wfMessage( 'transaction-duration-limit-exceeded', $time, $limit )->text()
                                        );
                                }
                        } );
                } );

                $start = microtime( true );
                $this->forEachLBCallMethod( 'commitMasterChanges', array( $fname ) );
                $timeMs = 1000 * ( microtime( true ) - $start );

                RequestContext::getMain()->getStats()->timing( "db.commit-masters", $timeMs );
        }

        /**
         * Rollback changes on all master connections
         * @param string $fname Caller name
         * @since 1.23
         */
        public function rollbackMasterChanges( $fname = __METHOD__ ) {
                $this->forEachLBCallMethod( 'rollbackMasterChanges', array( $fname ) );
        }

        /**
         * Log query info if multi DB transactions are going to be committed now
         */
        private function logMultiDbTransaction() {
                $callersByDB = array();
                $this->forEachLB( function ( LoadBalancer $lb ) use ( &$callersByDB ) {
                        $masterName = $lb->getServerName( $lb->getWriterIndex() );
                        $callers = $lb->pendingMasterChangeCallers();
                        if ( $callers ) {
                                $callersByDB[$masterName] = $callers;
                        }
                } );

                if ( count( $callersByDB ) >= 2 ) {
                        $dbs = implode( ', ', array_keys( $callersByDB ) );
                        $msg = "Multi-DB transaction [{$dbs}]:\n";
                        foreach ( $callersByDB as $db => $callers ) {
                                $msg .= "$db: " . implode( '; ', $callers ) . "\n";
                        }
                        $this->logger->info( $msg );
                }
        }

        /**
         * Determine if any master connection has pending changes
         * @return bool
         * @since 1.23
         */
        public function hasMasterChanges() {
                $ret = false;
                $this->forEachLB( function ( LoadBalancer $lb ) use ( &$ret ) {
                        $ret = $ret || $lb->hasMasterChanges();
                } );

                return $ret;
        }

        /**
         * Detemine if any lagged slave connection was used
         * @since 1.27
         * @return bool
         */
        public function laggedSlaveUsed() {
                $ret = false;
                $this->forEachLB( function ( LoadBalancer $lb ) use ( &$ret ) {
                        $ret = $ret || $lb->laggedSlaveUsed();
                } );

                return $ret;
        }

        /**
         * Determine if any master connection has pending/written changes from this request
         * @return bool
         * @since 1.27
         */
        public function hasOrMadeRecentMasterChanges() {
                $ret = false;
                $this->forEachLB( function ( LoadBalancer $lb ) use ( &$ret ) {
                        $ret = $ret || $lb->hasOrMadeRecentMasterChanges();
                } );
                return $ret;
        }

        /**
         * Waits for the slave DBs to catch up to the current master position
         *
         * Use this when updating very large numbers of rows, as in maintenance scripts,
         * to avoid causing too much lag. Of course, this is a no-op if there are no slaves.
         *
         * By default this waits on all DB clusters actually used in this request.
         * This makes sense when lag being waiting on is caused by the code that does this check.
         * In that case, setting "ifWritesSince" can avoid the overhead of waiting for clusters
         * that were not changed since the last wait check. To forcefully wait on a specific cluster
         * for a given wiki, use the 'wiki' parameter. To forcefully wait on an "external" cluster,
         * use the "cluster" parameter.
         *
         * Never call this function after a large DB write that is *still* in a transaction.
         * It only makes sense to call this after the possible lag inducing changes were committed.
         *
         * @param array $opts Optional fields that include:
         *   - wiki : wait on the load balancer DBs that handles the given wiki
         *   - cluster : wait on the given external load balancer DBs
         *   - timeout : Max wait time. Default: ~60 seconds
         *   - ifWritesSince: Only wait if writes were done since this UNIX timestamp
         * @throws DBReplicationWaitError If a timeout or error occured waiting on a DB cluster
         * @since 1.27
         */
        public function waitForReplication( array $opts = array() ) {
                $opts += array(
                        'wiki' => false,
                        'cluster' => false,
                        'timeout' => 60,
                        'ifWritesSince' => null
                );

                // Figure out which clusters need to be checked
                /** @var LoadBalancer[] $lbs */
                $lbs = array();
                if ( $opts['cluster'] !== false ) {
                        $lbs[] = $this->getExternalLB( $opts['cluster'] );
                } elseif ( $opts['wiki'] !== false ) {
                        $lbs[] = $this->getMainLB( $opts['wiki'] );
                } else {
                        $this->forEachLB( function ( LoadBalancer $lb ) use ( &$lbs ) {
                                $lbs[] = $lb;
                        } );
                        if ( !$lbs ) {
                                return; // nothing actually used
                        }
                }

                // Get all the master positions of applicable DBs right now.
                // This can be faster since waiting on one cluster reduces the
                // time needed to wait on the next clusters.
                $masterPositions = array_fill( 0, count( $lbs ), false );
                foreach ( $lbs as $i => $lb ) {
                        if ( $lb->getServerCount() <= 1 ) {
                                // Bug 27975 - Don't try to wait for slaves if there are none
                                // Prevents permission error when getting master position
                                continue;
                        } elseif ( $opts['ifWritesSince']
                                && $lb->lastMasterChangeTimestamp() < $opts['ifWritesSince']
                        ) {
                                continue; // no writes since the last wait
                        }
                        $masterPositions[$i] = $lb->getMasterPos();
                }

                $failed = array();
                foreach ( $lbs as $i => $lb ) {
                        if ( $masterPositions[$i] ) {
                                // The DBMS may not support getMasterPos() or the whole
                                // load balancer might be fake (e.g. $wgAllDBsAreLocalhost).
                                if ( !$lb->waitForAll( $masterPositions[$i], $opts['timeout'] ) ) {
                                        $failed[] = $lb->getServerName( $lb->getWriterIndex() );
                                }
                        }
                }

                if ( $failed ) {
                        throw new DBReplicationWaitError(
                                "Could not wait for slaves to catch up to " .
                                implode( ', ', $failed )
                        );
                }
        }

        /**
         * Disable the ChronologyProtector for all load balancers
         *
         * This can be called at the start of special API entry points
         *
         * @since 1.27
         */
        public function disableChronologyProtection() {
                $this->chronProt->setEnabled( false );
        }

        /**
         * @return ChronologyProtector
         */
        protected function newChronologyProtector() {
                $request = RequestContext::getMain()->getRequest();
                $chronProt = new ChronologyProtector(
                        ObjectCache::getMainStashInstance(),
                        array(
                                'ip' => $request->getIP(),
                                'agent' => $request->getHeader( 'User-Agent' )
                        )
                );
                if ( PHP_SAPI === 'cli' ) {
                        $chronProt->setEnabled( false );
                } elseif ( $request->getHeader( 'ChronologyProtection' ) === 'false' ) {
                        // Request opted out of using position wait logic. This is useful for requests
                        // done by the job queue or background ETL that do not have a meaningful session.
                        $chronProt->setWaitEnabled( false );
                }

                return $chronProt;
        }

        /**
         * @param ChronologyProtector $cp
         */
        protected function shutdownChronologyProtector( ChronologyProtector $cp ) {
                // Get all the master positions needed
                $this->forEachLB( function ( LoadBalancer $lb ) use ( $cp ) {
                        $cp->shutdownLB( $lb );
                } );
                // Write them to the stash
                $unsavedPositions = $cp->shutdown();
                // If the positions failed to write to the stash, at least wait on local datacenter
                // slaves to catch up before responding. Even if there are several DCs, this increases
                // the chance that the user will see their own changes immediately afterwards. As long
                // as the sticky DC cookie applies (same domain), this is not even an issue.
                $this->forEachLB( function ( LoadBalancer $lb ) use ( $unsavedPositions ) {
                        $masterName = $lb->getServerName( $lb->getWriterIndex() );
                        if ( isset( $unsavedPositions[$masterName] ) ) {
                                $lb->waitForAll( $unsavedPositions[$masterName] );
                        }
                } );
        }
}

/**
 * Exception class for attempted DB access
 */
class DBAccessError extends MWException {
        public function __construct() {
                parent::__construct( "Mediawiki tried to access the database via wfGetDB(). " .
                        "This is not allowed." );
        }
}

/**
 * Exception class for replica DB wait timeouts
 */
class DBReplicationWaitError extends Exception {
}