LBFactory.php

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<?php
namespace Wikimedia\Rdbms;

use Psr\Log\LoggerInterface;
use Wikimedia\ScopedCallback;
use BagOStuff;
use EmptyBagOStuff;
use WANObjectCache;
use Exception;
use RuntimeException;
use LogicException;

abstract class LBFactory implements ILBFactory {
    private $chronProt;
    private $profiler;
    private $trxProfiler;
    private $replLogger;
    private $connLogger;
    private $queryLogger;
    private $perfLogger;
    private $errorLogger;
    private $deprecationLogger;

    protected $srvCache;
    protected $memStash;
    protected $wanCache;

    protected $localDomain;

    private $hostname;
    private $requestInfo;
    private $cliMode;
    private $agent;

    private $tableAliases = [];
    private $indexAliases = [];
    private $replicationWaitCallbacks = [];

    private $ticket;
    private $trxRoundId = false;
    private $trxRoundStage = self::ROUND_CURSORY;

    protected $readOnlyReason = false;

    private $defaultGroup = null;

    protected $maxLag;

    const ROUND_CURSORY = 'cursory';
    const ROUND_BEGINNING = 'within-begin';
    const ROUND_COMMITTING = 'within-commit';
    const ROUND_ROLLING_BACK = 'within-rollback';
    const ROUND_COMMIT_CALLBACKS = 'within-commit-callbacks';
    const ROUND_ROLLBACK_CALLBACKS = 'within-rollback-callbacks';

    private static $loggerFields =
        [ 'replLogger', 'connLogger', 'queryLogger', 'perfLogger' ];

    public function __construct( array $conf ) {
        $this->localDomain = isset( $conf['localDomain'] )
            ? DatabaseDomain::newFromId( $conf['localDomain'] )
            : DatabaseDomain::newUnspecified();

        $this->maxLag = $conf['maxLag'] ?? null;
        if ( isset( $conf['readOnlyReason'] ) && is_string( $conf['readOnlyReason'] ) ) {
            $this->readOnlyReason = $conf['readOnlyReason'];
        }

        $this->srvCache = $conf['srvCache'] ?? new EmptyBagOStuff();
        $this->memStash = $conf['memStash'] ?? new EmptyBagOStuff();
        $this->wanCache = $conf['wanCache'] ?? WANObjectCache::newEmpty();

        foreach ( self::$loggerFields as $key ) {
            $this->$key = $conf[$key] ?? new \Psr\Log\NullLogger();
        }
        $this->errorLogger = $conf['errorLogger'] ?? function ( Exception $e ) {
            trigger_error( get_class( $e ) . ': ' . $e->getMessage(), E_USER_WARNING );
        };
        $this->deprecationLogger = $conf['deprecationLogger'] ?? function ( $msg ) {
            trigger_error( $msg, E_USER_DEPRECATED );
        };

        $this->profiler = $conf['profiler'] ?? null;
        $this->trxProfiler = $conf['trxProfiler'] ?? new TransactionProfiler();

        $this->requestInfo = [
            'IPAddress' => $_SERVER[ 'REMOTE_ADDR' ] ?? '',
            'UserAgent' => $_SERVER['HTTP_USER_AGENT'] ?? '',
            // Headers application can inject via LBFactory::setRequestInfo()
            'ChronologyProtection' => null,
            'ChronologyClientId' => null, // prior $cpClientId value from LBFactory::shutdown()
            'ChronologyPositionIndex' => null // prior $cpIndex value from LBFactory::shutdown()
        ];

        $this->cliMode = $conf['cliMode'] ?? ( PHP_SAPI === 'cli' || PHP_SAPI === 'phpdbg' );
        $this->hostname = $conf['hostname'] ?? gethostname();
        $this->agent = $conf['agent'] ?? '';
        $this->defaultGroup = $conf['defaultGroup'] ?? null;

        $this->ticket = mt_rand();
    }

    public function destroy() {
        $this->shutdown( self::SHUTDOWN_NO_CHRONPROT );
        $this->forEachLBCallMethod( 'disable' );
    }

    public function getLocalDomainID() {
        return $this->localDomain->getId();
    }

    public function resolveDomainID( $domain ) {
        return ( $domain !== false ) ? (string)$domain : $this->getLocalDomainID();
    }

    public function shutdown(
        $mode = self::SHUTDOWN_CHRONPROT_SYNC,
        callable $workCallback = null,
        &$cpIndex = null,
        &$cpClientId = null
    ) {
        $chronProt = $this->getChronologyProtector();
        if ( $mode === self::SHUTDOWN_CHRONPROT_SYNC ) {
            $this->shutdownChronologyProtector( $chronProt, $workCallback, 'sync', $cpIndex );
        } elseif ( $mode === self::SHUTDOWN_CHRONPROT_ASYNC ) {
            $this->shutdownChronologyProtector( $chronProt, null, 'async', $cpIndex );
        }

        $cpClientId = $chronProt->getClientId();

        $this->commitMasterChanges( __METHOD__ ); // sanity
    }

    abstract public function newMainLB( $domain = false );

    abstract public function getMainLB( $domain = false );

    abstract public function newExternalLB( $cluster );

    abstract public function getExternalLB( $cluster );

    protected function forEachLBCallMethod( $methodName, array $args = [] ) {
        $this->forEachLB(
            function ( ILoadBalancer $loadBalancer, $methodName, array $args ) {
                $loadBalancer->$methodName( ...$args );
            },
            [ $methodName, $args ]
        );
    }

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

    final public function commitAll( $fname = __METHOD__, array $options = [] ) {
        $this->commitMasterChanges( $fname, $options );
        $this->forEachLBCallMethod( 'flushMasterSnapshots', [ $fname ] );
        $this->forEachLBCallMethod( 'flushReplicaSnapshots', [ $fname ] );
    }

    final public function beginMasterChanges( $fname = __METHOD__ ) {
        $this->assertTransactionRoundStage( self::ROUND_CURSORY );
        $this->trxRoundStage = self::ROUND_BEGINNING;
        if ( $this->trxRoundId !== false ) {
            throw new DBTransactionError(
                null,
                "$fname: transaction round '{$this->trxRoundId}' already started."
            );
        }
        $this->trxRoundId = $fname;
        // Set DBO_TRX flags on all appropriate DBs
        $this->forEachLBCallMethod( 'beginMasterChanges', [ $fname ] );
        $this->trxRoundStage = self::ROUND_CURSORY;
    }

    final public function commitMasterChanges( $fname = __METHOD__, array $options = [] ) {
        $this->assertTransactionRoundStage( self::ROUND_CURSORY );
        $this->trxRoundStage = self::ROUND_COMMITTING;
        if ( $this->trxRoundId !== false && $this->trxRoundId !== $fname ) {
            throw new DBTransactionError(
                null,
                "$fname: transaction round '{$this->trxRoundId}' still running."
            );
        }
        $scope = ScopedCallback::newScopedIgnoreUserAbort(); // try to ignore client aborts
        // Run pre-commit callbacks and suppress post-commit callbacks, aborting on failure
        do {
            $count = 0; // number of callbacks executed this iteration
            $this->forEachLB( function ( ILoadBalancer $lb ) use ( &$count ) {
                $count += $lb->finalizeMasterChanges();
            } );
        } while ( $count > 0 );
        $this->trxRoundId = false;
        // Perform pre-commit checks, aborting on failure
        $this->forEachLBCallMethod( 'approveMasterChanges', [ $options ] );
        // Log the DBs and methods involved in multi-DB transactions
        $this->logIfMultiDbTransaction();
        // Actually perform the commit on all master DB connections and revert DBO_TRX
        $this->forEachLBCallMethod( 'commitMasterChanges', [ $fname ] );
        // Run all post-commit callbacks in a separate step
        $this->trxRoundStage = self::ROUND_COMMIT_CALLBACKS;
        $e = $this->executePostTransactionCallbacks();
        $this->trxRoundStage = self::ROUND_CURSORY;
        // Throw any last post-commit callback error
        if ( $e instanceof Exception ) {
            throw $e;
        }
    }

    final public function rollbackMasterChanges( $fname = __METHOD__ ) {
        $this->trxRoundStage = self::ROUND_ROLLING_BACK;
        $this->trxRoundId = false;
        // Actually perform the rollback on all master DB connections and revert DBO_TRX
        $this->forEachLBCallMethod( 'rollbackMasterChanges', [ $fname ] );
        // Run all post-commit callbacks in a separate step
        $this->trxRoundStage = self::ROUND_ROLLBACK_CALLBACKS;
        $this->executePostTransactionCallbacks();
        $this->trxRoundStage = self::ROUND_CURSORY;
    }

    private function executePostTransactionCallbacks() {
        // Run all post-commit callbacks until new ones stop getting added
        $e = null; // first callback exception
        do {
            $this->forEachLB( function ( ILoadBalancer $lb ) use ( &$e ) {
                $ex = $lb->runMasterTransactionIdleCallbacks();
                $e = $e ?: $ex;
            } );
        } while ( $this->hasMasterChanges() );
        // Run all listener callbacks once
        $this->forEachLB( function ( ILoadBalancer $lb ) use ( &$e ) {
            $ex = $lb->runMasterTransactionListenerCallbacks();
            $e = $e ?: $ex;
        } );

        return $e;
    }

    public function hasTransactionRound() {
        return ( $this->trxRoundId !== false );
    }

    public function isReadyForRoundOperations() {
        return ( $this->trxRoundStage === self::ROUND_CURSORY );
    }

    private function logIfMultiDbTransaction() {
        $callersByDB = [];
        $this->forEachLB( function ( ILoadBalancer $lb ) use ( &$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->queryLogger->info( $msg );
        }
    }

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

        return $ret;
    }

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

        return $ret;
    }

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

    public function waitForReplication( array $opts = [] ) {
        $opts += [
            'domain' => false,
            'cluster' => false,
            'timeout' => $this->cliMode ? 60 : 1,
            'ifWritesSince' => null
        ];

        if ( $opts['domain'] === false && isset( $opts['wiki'] ) ) {
            $opts['domain'] = $opts['wiki']; // b/c
        }

        // Figure out which clusters need to be checked
        $lbs = [];
        if ( $opts['cluster'] !== false ) {
            $lbs[] = $this->getExternalLB( $opts['cluster'] );
        } elseif ( $opts['domain'] !== false ) {
            $lbs[] = $this->getMainLB( $opts['domain'] );
        } else {
            $this->forEachLB( function ( ILoadBalancer $lb ) use ( &$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 ) {
                // T29975 - Don't try to wait for replica DBs 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();
        }

        // Run any listener callbacks *after* getting the DB positions. The more
        // time spent in the callbacks, the less time is spent in waitForAll().
        foreach ( $this->replicationWaitCallbacks as $callback ) {
            $callback();
        }

        $failed = [];
        foreach ( $lbs as $i => $lb ) {
            if ( $masterPositions[$i] ) {
                // The RDBMS may not support getMasterPos()
                if ( !$lb->waitForAll( $masterPositions[$i], $opts['timeout'] ) ) {
                    $failed[] = $lb->getServerName( $lb->getWriterIndex() );
                }
            }
        }

        return !$failed;
    }

    public function setWaitForReplicationListener( $name, callable $callback = null ) {
        if ( $callback ) {
            $this->replicationWaitCallbacks[$name] = $callback;
        } else {
            unset( $this->replicationWaitCallbacks[$name] );
        }
    }

    public function getEmptyTransactionTicket( $fname ) {
        if ( $this->hasMasterChanges() ) {
            $this->queryLogger->error( __METHOD__ . ": $fname does not have outer scope.\n" .
                ( new RuntimeException() )->getTraceAsString() );

            return null;
        }

        return $this->ticket;
    }

    final public function commitAndWaitForReplication( $fname, $ticket, array $opts = [] ) {
        if ( $ticket !== $this->ticket ) {
            $this->perfLogger->error( __METHOD__ . ": $fname does not have outer scope.\n" .
                ( new RuntimeException() )->getTraceAsString() );

            return;
        }

        // The transaction owner and any caller with the empty transaction ticket can commit
        // so that getEmptyTransactionTicket() callers don't risk seeing DBTransactionError.
        if ( $this->trxRoundId !== false && $fname !== $this->trxRoundId ) {
            $this->queryLogger->info( "$fname: committing on behalf of {$this->trxRoundId}." );
            $fnameEffective = $this->trxRoundId;
        } else {
            $fnameEffective = $fname;
        }

        $this->commitMasterChanges( $fnameEffective );
        $waitSucceeded = $this->waitForReplication( $opts );
        // If a nested caller committed on behalf of $fname, start another empty $fname
        // transaction, leaving the caller with the same empty transaction state as before.
        if ( $fnameEffective !== $fname ) {
            $this->beginMasterChanges( $fnameEffective );
        }
        return $waitSucceeded;
    }

    public function getChronologyProtectorTouched( $dbName ) {
        return $this->getChronologyProtector()->getTouched( $dbName );
    }

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

    protected function getChronologyProtector() {
        if ( $this->chronProt ) {
            return $this->chronProt;
        }

        $this->chronProt = new ChronologyProtector(
            $this->memStash,
            [
                'ip' => $this->requestInfo['IPAddress'],
                'agent' => $this->requestInfo['UserAgent'],
                'clientId' => $this->requestInfo['ChronologyClientId']
            ],
            $this->requestInfo['ChronologyPositionIndex']
        );
        $this->chronProt->setLogger( $this->replLogger );

        if ( $this->cliMode ) {
            $this->chronProt->setEnabled( false );
        } elseif ( $this->requestInfo['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.
            $this->chronProt->setWaitEnabled( false );
        } elseif ( $this->memStash instanceof EmptyBagOStuff ) {
            // No where to store any DB positions and wait for them to appear
            $this->chronProt->setEnabled( false );
            $this->replLogger->info( 'Cannot use ChronologyProtector with EmptyBagOStuff.' );
        }

        $this->replLogger->debug( __METHOD__ . ': using request info ' .
            json_encode( $this->requestInfo, JSON_PRETTY_PRINT ) );

        return $this->chronProt;
    }

    protected function shutdownChronologyProtector(
        ChronologyProtector $cp, $workCallback, $mode, &$cpIndex = null
    ) {
        // Record all the master positions needed
        $this->forEachLB( function ( ILoadBalancer $lb ) use ( $cp ) {
            $cp->shutdownLB( $lb );
        } );
        // Write them to the persistent stash. Try to do something useful by running $work
        // while ChronologyProtector waits for the stash write to replicate to all DCs.
        $unsavedPositions = $cp->shutdown( $workCallback, $mode, $cpIndex );
        if ( $unsavedPositions && $workCallback ) {
            // Invoke callback in case it did not cache the result yet
            $workCallback(); // work now to block for less time in waitForAll()
        }
        // If the positions failed to write to the stash, at least wait on local datacenter
        // replica DBs 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 ( ILoadBalancer $lb ) use ( $unsavedPositions ) {
            $masterName = $lb->getServerName( $lb->getWriterIndex() );
            if ( isset( $unsavedPositions[$masterName] ) ) {
                $lb->waitForAll( $unsavedPositions[$masterName] );
            }
        } );
    }

    final protected function baseLoadBalancerParams() {
        if ( $this->trxRoundStage === self::ROUND_COMMIT_CALLBACKS ) {
            $initStage = ILoadBalancer::STAGE_POSTCOMMIT_CALLBACKS;
        } elseif ( $this->trxRoundStage === self::ROUND_ROLLBACK_CALLBACKS ) {
            $initStage = ILoadBalancer::STAGE_POSTROLLBACK_CALLBACKS;
        } else {
            $initStage = null;
        }

        return [
            'localDomain' => $this->localDomain,
            'readOnlyReason' => $this->readOnlyReason,
            'srvCache' => $this->srvCache,
            'wanCache' => $this->wanCache,
            'profiler' => $this->profiler,
            'trxProfiler' => $this->trxProfiler,
            'queryLogger' => $this->queryLogger,
            'connLogger' => $this->connLogger,
            'replLogger' => $this->replLogger,
            'errorLogger' => $this->errorLogger,
            'deprecationLogger' => $this->deprecationLogger,
            'hostname' => $this->hostname,
            'cliMode' => $this->cliMode,
            'agent' => $this->agent,
            'maxLag' => $this->maxLag,
            'defaultGroup' => $this->defaultGroup,
            'chronologyCallback' => function ( ILoadBalancer $lb ) {
                // Defer ChronologyProtector construction in case setRequestInfo() ends up
                // being called later (but before the first connection attempt) (T192611)
                $this->getChronologyProtector()->initLB( $lb );
            },
            'roundStage' => $initStage
        ];
    }

    protected function initLoadBalancer( ILoadBalancer $lb ) {
        if ( $this->trxRoundId !== false ) {
            $lb->beginMasterChanges( $this->trxRoundId ); // set DBO_TRX
        }

        $lb->setTableAliases( $this->tableAliases );
        $lb->setIndexAliases( $this->indexAliases );
    }

    public function setTableAliases( array $aliases ) {
        $this->tableAliases = $aliases;
    }

    public function setIndexAliases( array $aliases ) {
        $this->indexAliases = $aliases;
    }

    public function setDomainPrefix( $prefix ) {
        $this->setLocalDomainPrefix( $prefix );
    }

    public function setLocalDomainPrefix( $prefix ) {
        $this->localDomain = new DatabaseDomain(
            $this->localDomain->getDatabase(),
            null,
            $prefix
        );

        $this->forEachLB( function ( ILoadBalancer $lb ) use ( $prefix ) {
            $lb->setLocalDomainPrefix( $prefix );
        } );
    }

    public function redefineLocalDomain( $domain ) {
        $this->closeAll();

        $this->localDomain = DatabaseDomain::newFromId( $domain );

        $this->forEachLB( function ( ILoadBalancer $lb ) {
            $lb->redefineLocalDomain( $this->localDomain );
        } );
    }

    public function closeAll() {
        $this->forEachLBCallMethod( 'closeAll', [] );
    }

    public function setAgentName( $agent ) {
        $this->agent = $agent;
    }

    public function appendShutdownCPIndexAsQuery( $url, $index ) {
        $usedCluster = 0;
        $this->forEachLB( function ( ILoadBalancer $lb ) use ( &$usedCluster ) {
            $usedCluster |= ( $lb->getServerCount() > 1 );
        } );

        if ( !$usedCluster ) {
            return $url; // no master/replica clusters touched
        }

        return strpos( $url, '?' ) === false ? "$url?cpPosIndex=$index" : "$url&cpPosIndex=$index";
    }

    public static function makeCookieValueFromCPIndex( $index, $time, $clientId ) {
        return "$index@$time#$clientId";
    }

    public static function getCPInfoFromCookieValue( $value, $minTimestamp ) {
        static $placeholder = [ 'index' => null, 'clientId' => null ];

        if ( !preg_match( '/^(\d+)@(\d+)#([0-9a-f]{32})$/', $value, $m ) ) {
            return $placeholder; // invalid
        }

        $index = (int)$m[1];
        if ( $index <= 0 ) {
            return $placeholder; // invalid
        } elseif ( isset( $m[2] ) && $m[2] !== '' && (int)$m[2] < $minTimestamp ) {
            return $placeholder; // expired
        }

        $clientId = ( isset( $m[3] ) && $m[3] !== '' ) ? $m[3] : null;

        return [ 'index' => $index, 'clientId' => $clientId ];
    }

    public function setRequestInfo( array $info ) {
        if ( $this->chronProt ) {
            throw new LogicException( 'ChronologyProtector already initialized.' );
        }

        $this->requestInfo = $info + $this->requestInfo;
    }

    private function assertTransactionRoundStage( $stage ) {
        if ( $this->trxRoundStage !== $stage ) {
            throw new DBTransactionError(
                null,
                "Transaction round stage must be '$stage' (not '{$this->trxRoundStage}')"
            );
        }
    }

    function __destruct() {
        $this->destroy();
    }
}