LBFactory.php

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<?php
namespace Wikimedia\Rdbms;
 
use BagOStuff;
use EmptyBagOStuff;
use Exception;
use Generator;
use LogicException;
use Psr\Log\LoggerInterface;
use Psr\Log\NullLogger;
use RuntimeException;
use Throwable;
use WANObjectCache;
use Wikimedia\RequestTimeout\CriticalSectionProvider;
use Wikimedia\ScopedCallback;
 
abstract class LBFactory implements ILBFactory {
    private $chronProt;
    private $csProvider;
    private $profiler;
    private $trxProfiler;
    private $replLogger;
    private $connLogger;
    private $queryLogger;
    private $perfLogger;
    private $errorLogger;
    private $deprecationLogger;
 
    protected $cpStash;
    protected $srvCache;
    protected $wanCache;
 
    protected $localDomain;
 
    private $requestInfo;
    private $cliMode;
    private $agent;
    private $secret;
 
    private $tableAliases = [];
    private $indexAliases = [];
    private $domainAliases = [];
    private $replicationWaitCallbacks = [];
 
    private $ticket;
    private $trxRoundId = false;
    private $trxRoundStage = self::ROUND_CURSORY;
    private $replicationWaitTimeout;
 
    protected $readOnlyReason = false;
 
    private $defaultGroup = null;
 
    protected $maxLag;
 
    private $nonLocalDomainCache = [];
 
    private const ROUND_CURSORY = 'cursory';
    private const ROUND_BEGINNING = 'within-begin';
    private const ROUND_COMMITTING = 'within-commit';
    private const ROUND_ROLLING_BACK = 'within-rollback';
    private const ROUND_COMMIT_CALLBACKS = 'within-commit-callbacks';
    private const ROUND_ROLLBACK_CALLBACKS = 'within-rollback-callbacks';
    private const ROUND_ROLLBACK_SESSIONS = 'within-rollback-session';
 
    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->cpStash = $conf['cpStash'] ?? new EmptyBagOStuff();
        $this->srvCache = $conf['srvCache'] ?? new EmptyBagOStuff();
        $this->wanCache = $conf['wanCache'] ?? WANObjectCache::newEmpty();
 
        foreach ( self::$loggerFields as $key ) {
            $this->$key = $conf[$key] ?? new NullLogger();
        }
        $this->errorLogger = $conf['errorLogger'] ?? static function ( Throwable $e ) {
            trigger_error( get_class( $e ) . ': ' . $e->getMessage(), E_USER_WARNING );
        };
        $this->deprecationLogger = $conf['deprecationLogger'] ?? static function ( $msg ) {
            trigger_error( $msg, E_USER_DEPRECATED );
        };
 
        $this->profiler = $conf['profiler'] ?? null;
        $this->trxProfiler = $conf['trxProfiler'] ?? new TransactionProfiler();
 
        $this->csProvider = $conf['criticalSectionProvider'] ?? null;
 
        $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->agent = $conf['agent'] ?? '';
        $this->defaultGroup = $conf['defaultGroup'] ?? null;
        $this->secret = $conf['secret'] ?? '';
        $this->replicationWaitTimeout = $this->cliMode ? 60 : 1;
 
        static $nextTicket;
        $this->ticket = $nextTicket = ( is_int( $nextTicket ) ? $nextTicket++ : mt_rand() );
    }
 
    public function destroy() {
        $scope = ScopedCallback::newScopedIgnoreUserAbort();
 
        foreach ( $this->getLBsForOwner() as $lb ) {
            $lb->disable( __METHOD__ );
        }
    }
 
    public function getLocalDomainID() {
        return $this->localDomain->getId();
    }
 
    public function resolveDomainID( $domain ) {
        return $this->resolveDomainInstance( $domain )->getId();
    }
 
    final protected function resolveDomainInstance( $domain ) {
        if ( $domain instanceof DatabaseDomain ) {
            return $domain; // already a domain instance
        } elseif ( $domain === false || $domain === $this->localDomain->getId() ) {
            return $this->localDomain;
        } elseif ( isset( $this->domainAliases[$domain] ) ) {
            // This array acts as both the original map and as instance cache.
            // Instances pass-through DatabaseDomain::newFromId as-is.
            $this->domainAliases[$domain] =
                DatabaseDomain::newFromId( $this->domainAliases[$domain] );
 
            return $this->domainAliases[$domain];
        }
 
        $cachedDomain = $this->nonLocalDomainCache[$domain] ?? null;
        if ( $cachedDomain === null ) {
            $cachedDomain = DatabaseDomain::newFromId( $domain );
            $this->nonLocalDomainCache = [ $domain => $cachedDomain ];
        }
 
        return $cachedDomain;
    }
 
    public function shutdown(
        $flags = self::SHUTDOWN_NORMAL,
        callable $workCallback = null,
        &$cpIndex = null,
        &$cpClientId = null
    ) {
        $scope = ScopedCallback::newScopedIgnoreUserAbort();
 
        $chronProt = $this->getChronologyProtector();
        if ( ( $flags & self::SHUTDOWN_NO_CHRONPROT ) != self::SHUTDOWN_NO_CHRONPROT ) {
            $this->shutdownChronologyProtector( $chronProt, $workCallback, $cpIndex );
            $this->replLogger->debug( __METHOD__ . ': finished ChronologyProtector shutdown' );
        }
        $cpClientId = $chronProt->getClientId();
 
        $this->commitPrimaryChanges( __METHOD__ );
 
        $this->replLogger->debug( 'LBFactory shutdown completed' );
    }
 
    public function getAllLBs() {
        foreach ( $this->getLBsForOwner() as $lb ) {
            yield $lb;
        }
    }
 
    abstract protected function getLBsForOwner();
 
    public function flushReplicaSnapshots( $fname = __METHOD__ ) {
        if ( $this->trxRoundId !== false && $this->trxRoundId !== $fname ) {
            $this->queryLogger->warning(
                "$fname: transaction round '{$this->trxRoundId}' still running",
                [ 'exception' => new RuntimeException() ]
            );
        }
        foreach ( $this->getLBsForOwner() as $lb ) {
            $lb->flushReplicaSnapshots( $fname );
        }
    }
 
    final public function commitAll( $fname = __METHOD__, array $options = [] ) {
        $this->commitPrimaryChanges( $fname, $options );
        foreach ( $this->getLBsForOwner() as $lb ) {
            $lb->flushPrimarySessions( $fname );
        }
        foreach ( $this->getLBsForOwner() as $lb ) {
            $lb->flushReplicaSnapshots( $fname );
        }
    }
 
    final public function beginPrimaryChanges( $fname = __METHOD__ ) {
        $this->assertTransactionRoundStage( self::ROUND_CURSORY );
        $scope = ScopedCallback::newScopedIgnoreUserAbort();
 
        $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
        foreach ( $this->getLBsForOwner() as $lb ) {
            $lb->beginPrimaryChanges( $fname );
        }
        $this->trxRoundStage = self::ROUND_CURSORY;
    }
 
    final public function commitPrimaryChanges( $fname = __METHOD__, array $options = [] ) {
        $this->assertTransactionRoundStage( self::ROUND_CURSORY );
        $scope = ScopedCallback::newScopedIgnoreUserAbort();
 
        $this->trxRoundStage = self::ROUND_COMMITTING;
        if ( $this->trxRoundId !== false && $this->trxRoundId !== $fname ) {
            throw new DBTransactionError(
                null,
                "$fname: transaction round '{$this->trxRoundId}' still running"
            );
        }
        // Run pre-commit callbacks and suppress post-commit callbacks, aborting on failure
        do {
            $count = 0; // number of callbacks executed this iteration
            foreach ( $this->getLBsForOwner() as $lb ) {
                $count += $lb->finalizePrimaryChanges( $fname );
            }
        } while ( $count > 0 );
        $this->trxRoundId = false;
        // Perform pre-commit checks, aborting on failure
        foreach ( $this->getLBsForOwner() as $lb ) {
            $lb->approvePrimaryChanges( $options, $fname );
        }
        // Log the DBs and methods involved in multi-DB transactions
        $this->logIfMultiDbTransaction();
        // Actually perform the commit on all primary DB connections and revert DBO_TRX
        foreach ( $this->getLBsForOwner() as $lb ) {
            $lb->commitPrimaryChanges( $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 rollbackPrimaryChanges( $fname = __METHOD__ ) {
        $scope = ScopedCallback::newScopedIgnoreUserAbort();
 
        $this->trxRoundStage = self::ROUND_ROLLING_BACK;
        $this->trxRoundId = false;
        // Actually perform the rollback on all primary DB connections and revert DBO_TRX
        foreach ( $this->getLBsForOwner() as $lb ) {
            $lb->rollbackPrimaryChanges( $fname );
        }
        // Run all post-commit callbacks in a separate step
        $this->trxRoundStage = self::ROUND_ROLLBACK_CALLBACKS;
        $this->executePostTransactionCallbacks();
        $this->trxRoundStage = self::ROUND_CURSORY;
    }
 
    final public function flushPrimarySessions( $fname = __METHOD__ ) {
        $scope = ScopedCallback::newScopedIgnoreUserAbort();
 
        // Release named locks and table locks on all primary DB connections
        $this->trxRoundStage = self::ROUND_ROLLBACK_SESSIONS;
        foreach ( $this->getLBsForOwner() as $lb ) {
            $lb->flushPrimarySessions( $fname );
        }
        $this->trxRoundStage = self::ROUND_CURSORY;
    }
 
    private function executePostTransactionCallbacks() {
        $fname = __METHOD__;
        // Run all post-commit callbacks until new ones stop getting added
        $e = null; // first callback exception
        do {
            foreach ( $this->getLBsForOwner() as $lb ) {
                $ex = $lb->runPrimaryTransactionIdleCallbacks( $fname );
                $e = $e ?: $ex;
            }
        } while ( $this->hasPrimaryChanges() );
        // Run all listener callbacks once
        foreach ( $this->getLBsForOwner() as $lb ) {
            $ex = $lb->runPrimaryTransactionListenerCallbacks( $fname );
            $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 = [];
        foreach ( $this->getLBsForOwner() as $lb ) {
            $primaryName = $lb->getServerName( $lb->getWriterIndex() );
            $callers = $lb->pendingPrimaryChangeCallers();
            if ( $callers ) {
                $callersByDB[$primaryName] = $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 hasPrimaryChanges() {
        foreach ( $this->getLBsForOwner() as $lb ) {
            if ( $lb->hasPrimaryChanges() ) {
                return true;
            }
        }
        return false;
    }
 
    public function laggedReplicaUsed() {
        foreach ( $this->getLBsForOwner() as $lb ) {
            if ( $lb->laggedReplicaUsed() ) {
                return true;
            }
        }
        return false;
    }
 
    public function hasOrMadeRecentPrimaryChanges( $age = null ) {
        foreach ( $this->getLBsForOwner() as $lb ) {
            if ( $lb->hasOrMadeRecentPrimaryChanges( $age ) ) {
                return true;
            }
        }
        return false;
    }
 
    public function waitForReplication( array $opts = [] ) {
        $opts += [
            'domain' => false,
            'cluster' => false,
            'timeout' => $this->replicationWaitTimeout,
            '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 {
            foreach ( $this->getAllLBs() as $lb ) {
                $lbs[] = $lb;
            }
            if ( !$lbs ) {
                return true; // nothing actually used
            }
        }
 
        // Get all the primary DB 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.
        $primaryPositions = array_fill( 0, count( $lbs ), false );
        foreach ( $lbs as $i => $lb ) {
            if (
                // No writes to wait on getting replicated
                !$lb->hasPrimaryConnection() ||
                // No replication; avoid getPrimaryPos() permissions errors (T29975)
                !$lb->hasStreamingReplicaServers() ||
                // No writes since the last replication wait
                (
                    $opts['ifWritesSince'] &&
                    $lb->lastPrimaryChangeTimestamp() < $opts['ifWritesSince']
                )
            ) {
                continue; // no need to wait
            }
 
            $primaryPositions[$i] = $lb->getPrimaryPos();
        }
 
        // 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 ( $primaryPositions[$i] ) {
                // The RDBMS may not support getPrimaryPos()
                if ( !$lb->waitForAll( $primaryPositions[$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->hasPrimaryChanges() ) {
            $this->queryLogger->error(
                __METHOD__ . ": $fname does not have outer scope",
                [ 'exception' => new RuntimeException() ]
            );
 
            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",
                [ 'exception' => new RuntimeException() ]
            );
 
            return false;
        }
 
        // 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->commitPrimaryChanges( $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->beginPrimaryChanges( $fnameEffective );
        }
 
        return $waitSucceeded;
    }
 
    public function getChronologyProtectorTouched( $domain = false ) {
        return $this->getChronologyProtector()->getTouched( $this->getMainLB( $domain ) );
    }
 
    public function disableChronologyProtection() {
        $this->getChronologyProtector()->setEnabled( false );
    }
 
    protected function getChronologyProtector() {
        if ( $this->chronProt ) {
            return $this->chronProt;
        }
 
        $this->chronProt = new ChronologyProtector(
            $this->cpStash,
            [
                'ip' => $this->requestInfo['IPAddress'],
                'agent' => $this->requestInfo['UserAgent'],
                'clientId' => $this->requestInfo['ChronologyClientId'] ?: null
            ],
            $this->requestInfo['ChronologyPositionIndex'],
            $this->secret
        );
        $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->cpStash instanceof EmptyBagOStuff ) {
            // No where to store any DB positions and wait for them to appear
            $this->chronProt->setEnabled( false );
            $this->replLogger->debug( 'Cannot use ChronologyProtector with EmptyBagOStuff' );
        }
 
        $this->replLogger->debug(
            __METHOD__ . ': request info ' .
            json_encode( $this->requestInfo, JSON_PRETTY_PRINT )
        );
 
        return $this->chronProt;
    }
 
    protected function shutdownChronologyProtector(
        ChronologyProtector $cp, $workCallback, &$cpIndex = null
    ) {
        // Remark all of the relevant DB primary positions
        foreach ( $this->getLBsForOwner() as $lb ) {
            $cp->stageSessionReplicationPosition( $lb );
        }
        // Write the positions to the persistent stash
        $unsavedPositions = $cp->persistSessionReplicationPositions( $cpIndex );
        if ( $unsavedPositions && $workCallback ) {
            // Invoke callback in case it did not cache the result yet
            $workCallback();
        }
        // If the positions failed to write to the stash, then wait on the local datacenter
        // replica DBs to catch up before sending an HTTP response. As long as the request that
        // caused such DB writes occurred in the primary datacenter, and clients are temporarily
        // pinned to the primary datacenter after causing DB writes, then this should suffice.
        foreach ( $this->getLBsForOwner() as $lb ) {
            $primaryName = $lb->getServerName( $lb->getWriterIndex() );
            if ( isset( $unsavedPositions[$primaryName] ) ) {
                $lb->waitForAll( $unsavedPositions[$primaryName] );
            }
        }
    }
 
    final protected function baseLoadBalancerParams() {
        if ( $this->trxRoundStage === self::ROUND_COMMIT_CALLBACKS ) {
            $initStage = ILoadBalancerForOwner::STAGE_POSTCOMMIT_CALLBACKS;
        } elseif ( $this->trxRoundStage === self::ROUND_ROLLBACK_CALLBACKS ) {
            $initStage = ILoadBalancerForOwner::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,
            'perfLogger' => $this->perfLogger,
            'errorLogger' => $this->errorLogger,
            'deprecationLogger' => $this->deprecationLogger,
            '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()->applySessionReplicationPosition( $lb );
            },
            'roundStage' => $initStage,
            'criticalSectionProvider' => $this->csProvider
        ];
    }
 
    protected function initLoadBalancer( ILoadBalancerForOwner $lb ) {
        if ( $this->trxRoundId !== false ) {
            $lb->beginPrimaryChanges( $this->trxRoundId ); // set DBO_TRX
        }
 
        $lb->setTableAliases( $this->tableAliases );
        $lb->setIndexAliases( $this->indexAliases );
        $lb->setDomainAliases( $this->domainAliases );
    }
 
    public function setTableAliases( array $aliases ) {
        $this->tableAliases = $aliases;
    }
 
    public function setIndexAliases( array $aliases ) {
        $this->indexAliases = $aliases;
    }
 
    public function setDomainAliases( array $aliases ) {
        $this->domainAliases = $aliases;
    }
 
    public function getTransactionProfiler(): TransactionProfiler {
        return $this->trxProfiler;
    }
 
    public function setLocalDomainPrefix( $prefix ) {
        $this->localDomain = new DatabaseDomain(
            $this->localDomain->getDatabase(),
            $this->localDomain->getSchema(),
            $prefix
        );
 
        foreach ( $this->getLBsForOwner() as $lb ) {
            $lb->setLocalDomainPrefix( $prefix );
        }
    }
 
    public function redefineLocalDomain( $domain ) {
        $this->closeAll( __METHOD__ );
 
        $this->localDomain = DatabaseDomain::newFromId( $domain );
 
        foreach ( $this->getLBsForOwner() as $lb ) {
            $lb->redefineLocalDomain( $this->localDomain );
        }
    }
 
    public function closeAll( $fname = __METHOD__ ) {
        $scope = ScopedCallback::newScopedIgnoreUserAbort();
 
        foreach ( $this->getLBsForOwner() as $lb ) {
            $lb->closeAll( $fname );
        }
    }
 
    public function setAgentName( $agent ) {
        $this->agent = $agent;
    }
 
    public function appendShutdownCPIndexAsQuery( $url, $index ) {
        foreach ( $this->getLBsForOwner() as $lb ) {
            if ( $lb->hasStreamingReplicaServers() ) {
                return strpos( $url, '?' ) === false
                    ? "$url?cpPosIndex=$index" : "$url&cpPosIndex=$index";
            }
        }
        return $url; // no primary/replica clusters touched
    }
 
    public function getChronologyProtectorClientId() {
        return $this->getChronologyProtector()->getClientId();
    }
 
    public static function makeCookieValueFromCPIndex(
        int $writeIndex,
        int $time,
        string $clientId
    ) {
        // Format is "<write index>@<write timestamp>#<client ID hash>"
        return "{$writeIndex}@{$time}#{$clientId}";
    }
 
    public static function getCPInfoFromCookieValue( ?string $value, int $minTimestamp ) {
        static $placeholder = [ 'index' => null, 'clientId' => null ];
 
        if ( $value === null ) {
            return $placeholder; // not set
        }
 
        // Format is "<write index>@<write timestamp>#<client ID hash>"
        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;
    }
 
    public function setDefaultReplicationWaitTimeout( $seconds ) {
        $old = $this->replicationWaitTimeout;
        $this->replicationWaitTimeout = max( 1, (int)$seconds );
 
        return $old;
    }
 
    private function assertTransactionRoundStage( $stage ) {
        if ( $this->trxRoundStage !== $stage ) {
            throw new DBTransactionError(
                null,
                "Transaction round stage must be '$stage' (not '{$this->trxRoundStage}')"
            );
        }
    }
 
    public function __destruct() {
        $this->destroy();
    }
 
    public function setMockTime( &$time ) {
        $this->getChronologyProtector()->setMockTime( $time );
    }
}