LBFactory.php

Go to the documentation of this file.

<?php
use Psr\Log\LoggerInterface;
use MediaWiki\Logger\LoggerFactory;

abstract class LBFactory {
    protected $chronProt;

    protected $trxProfiler;

    protected $logger;

    private static $instance;

    protected $readOnlyReason = false;

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

    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' );
    }

    public static function disableBackend() {
        global $wgLBFactoryConf;
        self::$instance = new LBFactoryFake( $wgLBFactoryConf );
    }

    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;
    }

    public static function getLBFactoryClass( array $config ) {
        // For configuration backward compatibility after removing
        // underscores from class names in MediaWiki 1.23.
        $bcClasses = [
            '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;
    }

    public static function destroyInstance() {
        if ( self::$instance ) {
            self::$instance->shutdown();
            self::$instance->forEachLBCallMethod( 'closeAll' );
            self::$instance = null;
        }
    }

    public static function setInstance( $instance ) {
        self::destroyInstance();
        self::$instance = $instance;
    }

    abstract public function newMainLB( $wiki = false );

    abstract public function getMainLB( $wiki = false );

    abstract protected function newExternalLB( $cluster, $wiki = false );

    abstract public function &getExternalLB( $cluster, $wiki = false );

    abstract public function forEachLB( $callback, array $params = [] );

    public function shutdown( $flags = 0 ) {
    }

    private function forEachLBCallMethod( $methodName, array $args = [] ) {
        $this->forEachLB(
            function ( LoadBalancer $loadBalancer, $methodName, array $args ) {
                call_user_func_array( [ $loadBalancer, $methodName ], $args );
            },
            [ $methodName, $args ]
        );
    }

    public function commitAll( $fname = __METHOD__ ) {
        $this->logMultiDbTransaction();

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

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

    public function commitMasterChanges( $fname = __METHOD__, array $options = [] ) {
        $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()
                    );
                }
            } );
        } );

        $this->forEachLBCallMethod( 'commitMasterChanges', [ $fname ] );
    }

    public function rollbackMasterChanges( $fname = __METHOD__ ) {
        $this->forEachLBCallMethod( 'rollbackMasterChanges', [ $fname ] );
    }

    private function logMultiDbTransaction() {
        $callersByDB = [];
        $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 );
        }
    }

    public function hasMasterChanges() {
        $ret = false;
        $this->forEachLB( function ( LoadBalancer $lb ) use ( &$ret ) {
            $ret = $ret || $lb->hasMasterChanges();
        } );

        return $ret;
    }

    public function laggedSlaveUsed() {
        $ret = false;
        $this->forEachLB( function ( LoadBalancer $lb ) use ( &$ret ) {
            $ret = $ret || $lb->laggedSlaveUsed();
        } );

        return $ret;
    }

    public function hasOrMadeRecentMasterChanges() {
        $ret = false;
        $this->forEachLB( function ( LoadBalancer $lb ) use ( &$ret ) {
            $ret = $ret || $lb->hasOrMadeRecentMasterChanges();
        } );
        return $ret;
    }

    public function waitForReplication( array $opts = [] ) {
        $opts += [
            'wiki' => false,
            'cluster' => false,
            'timeout' => 60,
            'ifWritesSince' => null
        ];

        // Figure out which clusters need to be checked
        $lbs = [];
        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 = [];
        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 )
            );
        }
    }

    public function disableChronologyProtection() {
        $this->chronProt->setEnabled( false );
    }

    protected function newChronologyProtector() {
        $request = RequestContext::getMain()->getRequest();
        $chronProt = new ChronologyProtector(
            ObjectCache::getMainStashInstance(),
            [
                '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;
    }

    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] );
            }
        } );
    }
}

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

class DBReplicationWaitError extends Exception {
}