LoadBalancer.php

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<?php
class LoadBalancer {
        private $mServers, $mConns, $mLoads, $mGroupLoads;
        private $mErrorConnection;
        private $mReadIndex, $mAllowLagged;
        private $mWaitForPos, $mWaitTimeout;
        private $mLaggedSlaveMode, $mLastError = 'Unknown error';
        private $mParentInfo, $mLagTimes;
        private $mLoadMonitorClass, $mLoadMonitor;

        function __construct( $params ) {
                if ( !isset( $params['servers'] ) ) {
                        throw new MWException( __CLASS__ . ': missing servers parameter' );
                }
                $this->mServers = $params['servers'];

                if ( isset( $params['waitTimeout'] ) ) {
                        $this->mWaitTimeout = $params['waitTimeout'];
                } else {
                        $this->mWaitTimeout = 10;
                }

                $this->mReadIndex = -1;
                $this->mWriteIndex = -1;
                $this->mConns = array(
                        'local' => array(),
                        'foreignUsed' => array(),
                        'foreignFree' => array() );
                $this->mLoads = array();
                $this->mWaitForPos = false;
                $this->mLaggedSlaveMode = false;
                $this->mErrorConnection = false;
                $this->mAllowLagged = false;

                if ( isset( $params['loadMonitor'] ) ) {
                        $this->mLoadMonitorClass = $params['loadMonitor'];
                } else {
                        $master = reset( $params['servers'] );
                        if ( isset( $master['type'] ) && $master['type'] === 'mysql' ) {
                                $this->mLoadMonitorClass = 'LoadMonitor_MySQL';
                        } else {
                                $this->mLoadMonitorClass = 'LoadMonitor_Null';
                        }
                }

                foreach( $params['servers'] as $i => $server ) {
                        $this->mLoads[$i] = $server['load'];
                        if ( isset( $server['groupLoads'] ) ) {
                                foreach ( $server['groupLoads'] as $group => $ratio ) {
                                        if ( !isset( $this->mGroupLoads[$group] ) ) {
                                                $this->mGroupLoads[$group] = array();
                                        }
                                        $this->mGroupLoads[$group][$i] = $ratio;
                                }
                        }
                }
        }

        function getLoadMonitor() {
                if ( !isset( $this->mLoadMonitor ) ) {
                        $class = $this->mLoadMonitorClass;
                        $this->mLoadMonitor = new $class( $this );
                }
                return $this->mLoadMonitor;
        }

        function parentInfo( $x = null ) {
                return wfSetVar( $this->mParentInfo, $x );
        }

        function pickRandom( $weights ) {
                return ArrayUtils::pickRandom( $weights );
        }

        function getRandomNonLagged( $loads, $wiki = false ) {
                # Unset excessively lagged servers
                $lags = $this->getLagTimes( $wiki );
                foreach ( $lags as $i => $lag ) {
                        if ( $i != 0 ) {
                                if ( $lag === false ) {
                                        wfDebugLog( 'replication', "Server #$i is not replicating\n" );
                                        unset( $loads[$i] );
                                } elseif ( isset( $this->mServers[$i]['max lag'] ) && $lag > $this->mServers[$i]['max lag'] ) {
                                        wfDebugLog( 'replication', "Server #$i is excessively lagged ($lag seconds)\n" );
                                        unset( $loads[$i] );
                                }
                        }
                }

                # Find out if all the slaves with non-zero load are lagged
                $sum = 0;
                foreach ( $loads as $load ) {
                        $sum += $load;
                }
                if ( $sum == 0 ) {
                        # No appropriate DB servers except maybe the master and some slaves with zero load
                        # Do NOT use the master
                        # Instead, this function will return false, triggering read-only mode,
                        # and a lagged slave will be used instead.
                        return false;
                }

                if ( count( $loads ) == 0 ) {
                        return false;
                }

                #wfDebugLog( 'connect', var_export( $loads, true ) );

                # Return a random representative of the remainder
                return $this->pickRandom( $loads );
        }

        function getReaderIndex( $group = false, $wiki = false ) {
                global $wgReadOnly, $wgDBClusterTimeout, $wgDBAvgStatusPoll, $wgDBtype;

                # @todo FIXME: For now, only go through all this for mysql databases
                if ( $wgDBtype != 'mysql' ) {
                        return $this->getWriterIndex();
                }

                if ( count( $this->mServers ) == 1 ) {
                        # Skip the load balancing if there's only one server
                        return 0;
                } elseif ( $group === false and $this->mReadIndex >= 0 ) {
                        # Shortcut if generic reader exists already
                        return $this->mReadIndex;
                }

                wfProfileIn( __METHOD__ );

                $totalElapsed = 0;

                # convert from seconds to microseconds
                $timeout = $wgDBClusterTimeout * 1e6;

                # Find the relevant load array
                if ( $group !== false ) {
                        if ( isset( $this->mGroupLoads[$group] ) ) {
                                $nonErrorLoads = $this->mGroupLoads[$group];
                        } else {
                                # No loads for this group, return false and the caller can use some other group
                                wfDebug( __METHOD__ . ": no loads for group $group\n" );
                                wfProfileOut( __METHOD__ );
                                return false;
                        }
                } else {
                        $nonErrorLoads = $this->mLoads;
                }

                if ( !$nonErrorLoads ) {
                        throw new MWException( "Empty server array given to LoadBalancer" );
                }

                # Scale the configured load ratios according to the dynamic load (if the load monitor supports it)
                $this->getLoadMonitor()->scaleLoads( $nonErrorLoads, $group, $wiki );

                $laggedSlaveMode = false;

                # First try quickly looking through the available servers for a server that
                # meets our criteria
                do {
                        $totalThreadsConnected = 0;
                        $overloadedServers = 0;
                        $currentLoads = $nonErrorLoads;
                        while ( count( $currentLoads ) ) {
                                if ( $wgReadOnly || $this->mAllowLagged || $laggedSlaveMode ) {
                                        $i = $this->pickRandom( $currentLoads );
                                } else {
                                        $i = $this->getRandomNonLagged( $currentLoads, $wiki );
                                        if ( $i === false && count( $currentLoads ) != 0 ) {
                                                # All slaves lagged. Switch to read-only mode
                                                wfDebugLog( 'replication', "All slaves lagged. Switch to read-only mode\n" );
                                                $wgReadOnly = 'The database has been automatically locked ' .
                                                        'while the slave database servers catch up to the master';
                                                $i = $this->pickRandom( $currentLoads );
                                                $laggedSlaveMode = true;
                                        }
                                }

                                if ( $i === false ) {
                                        # pickRandom() returned false
                                        # This is permanent and means the configuration or the load monitor
                                        # wants us to return false.
                                        wfDebugLog( 'connect', __METHOD__ . ": pickRandom() returned false\n" );
                                        wfProfileOut( __METHOD__ );
                                        return false;
                                }

                                wfDebugLog( 'connect', __METHOD__ . ": Using reader #$i: {$this->mServers[$i]['host']}...\n" );
                                $conn = $this->openConnection( $i, $wiki );

                                if ( !$conn ) {
                                        wfDebugLog( 'connect', __METHOD__ . ": Failed connecting to $i/$wiki\n" );
                                        unset( $nonErrorLoads[$i] );
                                        unset( $currentLoads[$i] );
                                        continue;
                                }

                                // Perform post-connection backoff
                                $threshold = isset( $this->mServers[$i]['max threads'] )
                                        ? $this->mServers[$i]['max threads'] : false;
                                $backoff = $this->getLoadMonitor()->postConnectionBackoff( $conn, $threshold );

                                // Decrement reference counter, we are finished with this connection.
                                // It will be incremented for the caller later.
                                if ( $wiki !== false ) {
                                        $this->reuseConnection( $conn );
                                }

                                if ( $backoff ) {
                                        # Post-connection overload, don't use this server for now
                                        $totalThreadsConnected += $backoff;
                                        $overloadedServers++;
                                        unset( $currentLoads[$i] );
                                } else {
                                        # Return this server
                                        break 2;
                                }
                        }

                        # No server found yet
                        $i = false;

                        # If all servers were down, quit now
                        if ( !count( $nonErrorLoads ) ) {
                                wfDebugLog( 'connect', "All servers down\n" );
                                break;
                        }

                        # Some servers must have been overloaded
                        if ( $overloadedServers == 0 ) {
                                throw new MWException( __METHOD__ . ": unexpectedly found no overloaded servers" );
                        }
                        # Back off for a while
                        # Scale the sleep time by the number of connected threads, to produce a
                        # roughly constant global poll rate
                        $avgThreads = $totalThreadsConnected / $overloadedServers;
                        $totalElapsed += $this->sleep( $wgDBAvgStatusPoll * $avgThreads );
                } while ( $totalElapsed < $timeout );

                if ( $totalElapsed >= $timeout ) {
                        wfDebugLog( 'connect', "All servers busy\n" );
                        $this->mErrorConnection = false;
                        $this->mLastError = 'All servers busy';
                }

                if ( $i !== false ) {
                        # Slave connection successful
                        # Wait for the session master pos for a short time
                        if ( $this->mWaitForPos && $i > 0 ) {
                                if ( !$this->doWait( $i ) ) {
                                        $this->mServers[$i]['slave pos'] = $conn->getSlavePos();
                                }
                        }
                        if ( $this->mReadIndex <= 0 && $this->mLoads[$i] > 0 && $i !== false ) {
                                $this->mReadIndex = $i;
                        }
                }
                wfProfileOut( __METHOD__ );
                return $i;
        }

        function sleep( $t ) {
                wfProfileIn( __METHOD__ );
                wfDebug( __METHOD__ . ": waiting $t us\n" );
                usleep( $t );
                wfProfileOut( __METHOD__ );
                return $t;
        }

        public function waitFor( $pos ) {
                wfProfileIn( __METHOD__ );
                $this->mWaitForPos = $pos;
                $i = $this->mReadIndex;

                if ( $i > 0 ) {
                        if ( !$this->doWait( $i ) ) {
                                $this->mServers[$i]['slave pos'] = $this->getAnyOpenConnection( $i )->getSlavePos();
                                $this->mLaggedSlaveMode = true;
                        }
                }
                wfProfileOut( __METHOD__ );
        }

        public function waitForAll( $pos ) {
                wfProfileIn( __METHOD__ );
                $this->mWaitForPos = $pos;
                for ( $i = 1; $i < count( $this->mServers ); $i++ ) {
                        $this->doWait( $i, true );
                }
                wfProfileOut( __METHOD__ );
        }

        function getAnyOpenConnection( $i ) {
                foreach ( $this->mConns as $conns ) {
                        if ( !empty( $conns[$i] ) ) {
                                return reset( $conns[$i] );
                        }
                }
                return false;
        }

        function doWait( $index, $open = false ) {
                # Find a connection to wait on
                $conn = $this->getAnyOpenConnection( $index );
                if ( !$conn ) {
                        if ( !$open ) {
                                wfDebug( __METHOD__ . ": no connection open\n" );
                                return false;
                        } else {
                                $conn = $this->openConnection( $index );
                                if ( !$conn ) {
                                        wfDebug( __METHOD__ . ": failed to open connection\n" );
                                        return false;
                                }
                        }
                }

                wfDebug( __METHOD__ . ": Waiting for slave #$index to catch up...\n" );
                $result = $conn->masterPosWait( $this->mWaitForPos, $this->mWaitTimeout );

                if ( $result == -1 || is_null( $result ) ) {
                        # Timed out waiting for slave, use master instead
                        wfDebug( __METHOD__ . ": Timed out waiting for slave #$index pos {$this->mWaitForPos}\n" );
                        return false;
                } else {
                        wfDebug( __METHOD__ . ": Done\n" );
                        return true;
                }
        }

        public function &getConnection( $i, $groups = array(), $wiki = false ) {
                wfProfileIn( __METHOD__ );

                if ( $i == DB_LAST ) {
                        throw new MWException( 'Attempt to call ' . __METHOD__ . ' with deprecated server index DB_LAST' );
                } elseif ( $i === null || $i === false ) {
                        throw new MWException( 'Attempt to call ' . __METHOD__ . ' with invalid server index' );
                }

                if ( $wiki === wfWikiID() ) {
                        $wiki = false;
                }

                # Query groups
                if ( $i == DB_MASTER ) {
                        $i = $this->getWriterIndex();
                } elseif ( !is_array( $groups ) ) {
                        $groupIndex = $this->getReaderIndex( $groups, $wiki );
                        if ( $groupIndex !== false ) {
                                $serverName = $this->getServerName( $groupIndex );
                                wfDebug( __METHOD__ . ": using server $serverName for group $groups\n" );
                                $i = $groupIndex;
                        }
                } else {
                        foreach ( $groups as $group ) {
                                $groupIndex = $this->getReaderIndex( $group, $wiki );
                                if ( $groupIndex !== false ) {
                                        $serverName = $this->getServerName( $groupIndex );
                                        wfDebug( __METHOD__ . ": using server $serverName for group $group\n" );
                                        $i = $groupIndex;
                                        break;
                                }
                        }
                }

                # Operation-based index
                if ( $i == DB_SLAVE ) {
                        $i = $this->getReaderIndex( false, $wiki );
                        # Couldn't find a working server in getReaderIndex()?
                        if ( $i === false ) {
                                $this->mLastError = 'No working slave server: ' . $this->mLastError;
                                wfProfileOut( __METHOD__ );
                                return $this->reportConnectionError();
                        }
                }

                # Now we have an explicit index into the servers array
                $conn = $this->openConnection( $i, $wiki );
                if ( !$conn ) {
                        wfProfileOut( __METHOD__ );
                        return $this->reportConnectionError();
                }

                wfProfileOut( __METHOD__ );
                return $conn;
        }

        public function reuseConnection( $conn ) {
                $serverIndex = $conn->getLBInfo( 'serverIndex' );
                $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
                $dbName = $conn->getDBname();
                $prefix = $conn->tablePrefix();
                if ( strval( $prefix ) !== '' ) {
                        $wiki = "$dbName-$prefix";
                } else {
                        $wiki = $dbName;
                }
                if ( $serverIndex === null || $refCount === null ) {
                        wfDebug( __METHOD__ . ": this connection was not opened as a foreign connection\n" );
                        return;
                }
                if ( $this->mConns['foreignUsed'][$serverIndex][$wiki] !== $conn ) {
                        throw new MWException( __METHOD__ . ": connection not found, has the connection been freed already?" );
                }
                $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
                if ( $refCount <= 0 ) {
                        $this->mConns['foreignFree'][$serverIndex][$wiki] = $conn;
                        unset( $this->mConns['foreignUsed'][$serverIndex][$wiki] );
                        wfDebug( __METHOD__ . ": freed connection $serverIndex/$wiki\n" );
                } else {
                        wfDebug( __METHOD__ . ": reference count for $serverIndex/$wiki reduced to $refCount\n" );
                }
        }

        function openConnection( $i, $wiki = false ) {
                wfProfileIn( __METHOD__ );
                if ( $wiki !== false ) {
                        $conn = $this->openForeignConnection( $i, $wiki );
                        wfProfileOut( __METHOD__ );
                        return $conn;
                }
                if ( isset( $this->mConns['local'][$i][0] ) ) {
                        $conn = $this->mConns['local'][$i][0];
                } else {
                        $server = $this->mServers[$i];
                        $server['serverIndex'] = $i;
                        $conn = $this->reallyOpenConnection( $server, false );
                        if ( $conn->isOpen() ) {
                                wfDebug( "Connected to database $i at {$this->mServers[$i]['host']}\n" );
                                $this->mConns['local'][$i][0] = $conn;
                        } else {
                                wfDebug( "Failed to connect to database $i at {$this->mServers[$i]['host']}\n" );
                                $this->mErrorConnection = $conn;
                                $conn = false;
                        }
                }
                wfProfileOut( __METHOD__ );
                return $conn;
        }

        function openForeignConnection( $i, $wiki ) {
                wfProfileIn( __METHOD__ );
                list( $dbName, $prefix ) = wfSplitWikiID( $wiki );
                if ( isset( $this->mConns['foreignUsed'][$i][$wiki] ) ) {
                        // Reuse an already-used connection
                        $conn = $this->mConns['foreignUsed'][$i][$wiki];
                        wfDebug( __METHOD__ . ": reusing connection $i/$wiki\n" );
                } elseif ( isset( $this->mConns['foreignFree'][$i][$wiki] ) ) {
                        // Reuse a free connection for the same wiki
                        $conn = $this->mConns['foreignFree'][$i][$wiki];
                        unset( $this->mConns['foreignFree'][$i][$wiki] );
                        $this->mConns['foreignUsed'][$i][$wiki] = $conn;
                        wfDebug( __METHOD__ . ": reusing free connection $i/$wiki\n" );
                } elseif ( !empty( $this->mConns['foreignFree'][$i] ) ) {
                        // Reuse a connection from another wiki
                        $conn = reset( $this->mConns['foreignFree'][$i] );
                        $oldWiki = key( $this->mConns['foreignFree'][$i] );

                        if ( !$conn->selectDB( $dbName ) ) {
                                $this->mLastError = "Error selecting database $dbName on server " .
                                        $conn->getServer() . " from client host " . wfHostname() . "\n";
                                $this->mErrorConnection = $conn;
                                $conn = false;
                        } else {
                                $conn->tablePrefix( $prefix );
                                unset( $this->mConns['foreignFree'][$i][$oldWiki] );
                                $this->mConns['foreignUsed'][$i][$wiki] = $conn;
                                wfDebug( __METHOD__ . ": reusing free connection from $oldWiki for $wiki\n" );
                        }
                } else {
                        // Open a new connection
                        $server = $this->mServers[$i];
                        $server['serverIndex'] = $i;
                        $server['foreignPoolRefCount'] = 0;
                        $conn = $this->reallyOpenConnection( $server, $dbName );
                        if ( !$conn->isOpen() ) {
                                wfDebug( __METHOD__ . ": error opening connection for $i/$wiki\n" );
                                $this->mErrorConnection = $conn;
                                $conn = false;
                        } else {
                                $conn->tablePrefix( $prefix );
                                $this->mConns['foreignUsed'][$i][$wiki] = $conn;
                                wfDebug( __METHOD__ . ": opened new connection for $i/$wiki\n" );
                        }
                }

                // Increment reference count
                if ( $conn ) {
                        $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
                        $conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
                }
                wfProfileOut( __METHOD__ );
                return $conn;
        }

        function isOpen( $index ) {
                if( !is_integer( $index ) ) {
                        return false;
                }
                return (bool)$this->getAnyOpenConnection( $index );
        }

        function reallyOpenConnection( $server, $dbNameOverride = false ) {
                if( !is_array( $server ) ) {
                        throw new MWException( 'You must update your load-balancing configuration. ' .
                                'See DefaultSettings.php entry for $wgDBservers.' );
                }

                if ( $dbNameOverride !== false ) {
                        $server['dbname'] = $dbNameOverride;
                }

                # Create object
                try {
                        $db = DatabaseBase::factory( $server['type'], $server );
                } catch ( DBConnectionError $e ) {
                        // FIXME: This is probably the ugliest thing I have ever done to
                        // PHP. I'm half-expecting it to segfault, just out of disgust. -- TS
                        $db = $e->db;
                }

                $db->setLBInfo( $server );
                if ( isset( $server['fakeSlaveLag'] ) ) {
                        $db->setFakeSlaveLag( $server['fakeSlaveLag'] );
                }
                if ( isset( $server['fakeMaster'] ) ) {
                        $db->setFakeMaster( true );
                }
                return $db;
        }

        private function reportConnectionError() {
                $conn = $this->mErrorConnection; // The connection which caused the error

                if ( !is_object( $conn ) ) {
                        // No last connection, probably due to all servers being too busy
                        wfLogDBError( "LB failure with no last connection. Connection error: {$this->mLastError}\n" );

                        // If all servers were busy, mLastError will contain something sensible
                        throw new DBConnectionError( null, $this->mLastError );
                } else {
                        $server = $conn->getProperty( 'mServer' );
                        wfLogDBError( "Connection error: {$this->mLastError} ({$server})\n" );
                        $conn->reportConnectionError( "{$this->mLastError} ({$server})" ); // throws DBConnectionError
                }
                return false; /* not reached */
        }

        function getWriterIndex() {
                return 0;
        }

        function haveIndex( $i ) {
                return array_key_exists( $i, $this->mServers );
        }

        function isNonZeroLoad( $i ) {
                return array_key_exists( $i, $this->mServers ) && $this->mLoads[$i] != 0;
        }

        function getServerCount() {
                return count( $this->mServers );
        }

        function getServerName( $i ) {
                if ( isset( $this->mServers[$i]['hostName'] ) ) {
                        return $this->mServers[$i]['hostName'];
                } elseif ( isset( $this->mServers[$i]['host'] ) ) {
                        return $this->mServers[$i]['host'];
                } else {
                        return '';
                }
        }

        function getServerInfo( $i ) {
                if ( isset( $this->mServers[$i] ) ) {
                        return $this->mServers[$i];
                } else {
                        return false;
                }
        }

        function setServerInfo( $i, $serverInfo ) {
                $this->mServers[$i] = $serverInfo;
        }

        function getMasterPos() {
                # If this entire request was served from a slave without opening a connection to the
                # master (however unlikely that may be), then we can fetch the position from the slave.
                $masterConn = $this->getAnyOpenConnection( 0 );
                if ( !$masterConn ) {
                        for ( $i = 1; $i < count( $this->mServers ); $i++ ) {
                                $conn = $this->getAnyOpenConnection( $i );
                                if ( $conn ) {
                                        wfDebug( "Master pos fetched from slave\n" );
                                        return $conn->getSlavePos();
                                }
                        }
                } else {
                        wfDebug( "Master pos fetched from master\n" );
                        return $masterConn->getMasterPos();
                }
                return false;
        }

        function closeAll() {
                foreach ( $this->mConns as $conns2 ) {
                        foreach  ( $conns2 as $conns3 ) {
                                foreach ( $conns3 as $conn ) {
                                        $conn->close();
                                }
                        }
                }
                $this->mConns = array(
                        'local' => array(),
                        'foreignFree' => array(),
                        'foreignUsed' => array(),
                );
        }

        function closeConnecton( $conn ) {
                wfDeprecated( __METHOD__, '1.18' );
                $this->closeConnection( $conn );
        }

        function closeConnection( $conn ) {
                $done = false;
                foreach ( $this->mConns as $i1 => $conns2 ) {
                        foreach ( $conns2 as $i2 => $conns3 ) {
                                foreach ( $conns3 as $i3 => $candidateConn ) {
                                        if ( $conn === $candidateConn ) {
                                                $conn->close();
                                                unset( $this->mConns[$i1][$i2][$i3] );
                                                $done = true;
                                                break;
                                        }
                                }
                        }
                }
                if ( !$done ) {
                        $conn->close();
                }
        }

        function commitAll() {
                foreach ( $this->mConns as $conns2 ) {
                        foreach ( $conns2 as $conns3 ) {
                                foreach ( $conns3 as $conn ) {
                                        if ( $conn->trxLevel() ) {
                                                $conn->commit( __METHOD__, 'flush' );
                                        }
                                }
                        }
                }
        }

        function commitMasterChanges() {
                // Always 0, but who knows.. :)
                $masterIndex = $this->getWriterIndex();
                foreach ( $this->mConns as $conns2 ) {
                        if ( empty( $conns2[$masterIndex] ) ) {
                                continue;
                        }
                        foreach ( $conns2[$masterIndex] as $conn ) {
                                if ( $conn->trxLevel() && $conn->writesOrCallbacksPending() ) {
                                        $conn->commit( __METHOD__, 'flush' );
                                }
                        }
                }
        }

        function waitTimeout( $value = null ) {
                return wfSetVar( $this->mWaitTimeout, $value );
        }

        function getLaggedSlaveMode() {
                return $this->mLaggedSlaveMode;
        }

        function allowLagged( $mode = null ) {
                if ( $mode === null ) {
                        return $this->mAllowLagged;
                }
                $this->mAllowLagged = $mode;
                return $this->mAllowLagged;
        }

        function pingAll() {
                $success = true;
                foreach ( $this->mConns as $conns2 ) {
                        foreach ( $conns2 as $conns3 ) {
                                foreach ( $conns3 as $conn ) {
                                        if ( !$conn->ping() ) {
                                                $success = false;
                                        }
                                }
                        }
                }
                return $success;
        }

        function forEachOpenConnection( $callback, $params = array() ) {
                foreach ( $this->mConns as $conns2 ) {
                        foreach ( $conns2 as $conns3 ) {
                                foreach ( $conns3 as $conn ) {
                                        $mergedParams = array_merge( array( $conn ), $params );
                                        call_user_func_array( $callback, $mergedParams );
                                }
                        }
                }
        }

        function getMaxLag( $wiki = false ) {
                $maxLag = -1;
                $host = '';
                $maxIndex = 0;
                if ( $this->getServerCount() > 1 ) { // no replication = no lag
                        foreach ( $this->mServers as $i => $conn ) {
                                $conn = false;
                                if ( $wiki === false ) {
                                        $conn = $this->getAnyOpenConnection( $i );
                                }
                                if ( !$conn ) {
                                        $conn = $this->openConnection( $i, $wiki );
                                }
                                if ( !$conn ) {
                                        continue;
                                }
                                $lag = $conn->getLag();
                                if ( $lag > $maxLag ) {
                                        $maxLag = $lag;
                                        $host = $this->mServers[$i]['host'];
                                        $maxIndex = $i;
                                }
                        }
                }
                return array( $host, $maxLag, $maxIndex );
        }

        function getLagTimes( $wiki = false ) {
                # Try process cache
                if ( isset( $this->mLagTimes ) ) {
                        return $this->mLagTimes;
                }
                if ( $this->getServerCount() == 1 ) {
                        # No replication
                        $this->mLagTimes = array( 0 => 0 );
                } else {
                        # Send the request to the load monitor
                        $this->mLagTimes = $this->getLoadMonitor()->getLagTimes(
                                array_keys( $this->mServers ), $wiki );
                }
                return $this->mLagTimes;
        }

        function safeGetLag( $conn ) {
                if ( $this->getServerCount() == 1 ) {
                        return 0;
                } else {
                        return $conn->getLag();
                }
        }

        function clearLagTimeCache() {
                $this->mLagTimes = null;
        }
}