rdbms: minor improvements to LoadBalancer logging
[lhc/web/wiklou.git] / includes / libs / rdbms / loadbalancer / LoadBalancer.php
index 864e6f0..e95e23f 100644 (file)
@@ -39,17 +39,17 @@ use Exception;
  */
 class LoadBalancer implements ILoadBalancer {
        /** @var array[] Map of (server index => server config array) */
-       private $mServers;
+       private $servers;
        /** @var Database[][][] Map of (connection category => server index => IDatabase[]) */
-       private $mConns;
+       private $conns;
        /** @var float[] Map of (server index => weight) */
-       private $mLoads;
+       private $loads;
        /** @var array[] Map of (group => server index => weight) */
-       private $mGroupLoads;
+       private $groupLoads;
        /** @var bool Whether to disregard replica DB lag as a factor in replica DB selection */
-       private $mAllowLagged;
+       private $allowLagged;
        /** @var int Seconds to spend waiting on replica DB lag to resolve */
-       private $mWaitTimeout;
+       private $waitTimeout;
        /** @var array The LoadMonitor configuration */
        private $loadMonitorConfig;
        /** @var array[] $aliases Map of (table => (dbname, schema, prefix) map) */
@@ -79,15 +79,15 @@ class LoadBalancer implements ILoadBalancer {
        /** @var Database DB connection object that caused a problem */
        private $errorConnection;
        /** @var int The generic (not query grouped) replica DB index (of $mServers) */
-       private $mReadIndex;
+       private $readIndex;
        /** @var bool|DBMasterPos False if not set */
-       private $mWaitForPos;
+       private $waitForPos;
        /** @var bool Whether the generic reader fell back to a lagged replica DB */
        private $laggedReplicaMode = false;
        /** @var bool Whether the generic reader fell back to a lagged replica DB */
        private $allReplicasDownMode = false;
        /** @var string The last DB selection or connection error */
-       private $mLastError = 'Unknown error';
+       private $lastError = 'Unknown error';
        /** @var string|bool Reason the LB is read-only or false if not */
        private $readOnlyReason = false;
        /** @var int Total connections opened */
@@ -122,6 +122,8 @@ class LoadBalancer implements ILoadBalancer {
 
        /** @var int Default 'maxLag' when unspecified */
        const MAX_LAG_DEFAULT = 10;
+       /** @var int Default 'waitTimeout' when unspecified */
+       const MAX_WAIT_DEFAULT = 10;
        /** @var int Seconds to cache master server read-only status */
        const TTL_CACHE_READONLY = 5;
 
@@ -137,12 +139,12 @@ class LoadBalancer implements ILoadBalancer {
                if ( !isset( $params['servers'] ) ) {
                        throw new InvalidArgumentException( __CLASS__ . ': missing servers parameter' );
                }
-               $this->mServers = $params['servers'];
-               foreach ( $this->mServers as $i => $server ) {
+               $this->servers = $params['servers'];
+               foreach ( $this->servers as $i => $server ) {
                        if ( $i == 0 ) {
-                               $this->mServers[$i]['master'] = true;
+                               $this->servers[$i]['master'] = true;
                        } else {
-                               $this->mServers[$i]['replica'] = true;
+                               $this->servers[$i]['replica'] = true;
                        }
                }
 
@@ -151,10 +153,12 @@ class LoadBalancer implements ILoadBalancer {
                        : DatabaseDomain::newUnspecified();
                $this->setLocalDomain( $localDomain );
 
-               $this->mWaitTimeout = isset( $params['waitTimeout'] ) ? $params['waitTimeout'] : 10;
+               $this->waitTimeout = isset( $params['waitTimeout'] )
+                       ? $params['waitTimeout']
+                       : self::MAX_WAIT_DEFAULT;
 
-               $this->mReadIndex = -1;
-               $this->mConns = [
+               $this->readIndex = -1;
+               $this->conns = [
                        // Connection were transaction rounds may be applied
                        self::KEY_LOCAL => [],
                        self::KEY_FOREIGN_INUSE => [],
@@ -164,9 +168,9 @@ class LoadBalancer implements ILoadBalancer {
                        self::KEY_FOREIGN_INUSE_NOROUND => [],
                        self::KEY_FOREIGN_FREE_NOROUND => []
                ];
-               $this->mLoads = [];
-               $this->mWaitForPos = false;
-               $this->mAllowLagged = false;
+               $this->loads = [];
+               $this->waitForPos = false;
+               $this->allowLagged = false;
 
                if ( isset( $params['readOnlyReason'] ) && is_string( $params['readOnlyReason'] ) ) {
                        $this->readOnlyReason = $params['readOnlyReason'];
@@ -184,13 +188,13 @@ class LoadBalancer implements ILoadBalancer {
                $this->loadMonitorConfig += [ 'lagWarnThreshold' => $this->maxLag ];
 
                foreach ( $params['servers'] as $i => $server ) {
-                       $this->mLoads[$i] = $server['load'];
+                       $this->loads[$i] = $server['load'];
                        if ( isset( $server['groupLoads'] ) ) {
                                foreach ( $server['groupLoads'] as $group => $ratio ) {
-                                       if ( !isset( $this->mGroupLoads[$group] ) ) {
-                                               $this->mGroupLoads[$group] = [];
+                                       if ( !isset( $this->groupLoads[$group] ) ) {
+                                               $this->groupLoads[$group] = [];
                                        }
-                                       $this->mGroupLoads[$group][$i] = $ratio;
+                                       $this->groupLoads[$group][$i] = $ratio;
                                }
                        }
                }
@@ -285,8 +289,8 @@ class LoadBalancer implements ILoadBalancer {
                foreach ( $lags as $i => $lag ) {
                        if ( $i != 0 ) {
                                # How much lag this server nominally is allowed to have
-                               $maxServerLag = isset( $this->mServers[$i]['max lag'] )
-                                       ? $this->mServers[$i]['max lag']
+                               $maxServerLag = isset( $this->servers[$i]['max lag'] )
+                                       ? $this->servers[$i]['max lag']
                                        : $this->maxLag; // default
                                # Constrain that futher by $maxLag argument
                                $maxServerLag = min( $maxServerLag, $maxLag );
@@ -294,11 +298,13 @@ class LoadBalancer implements ILoadBalancer {
                                $host = $this->getServerName( $i );
                                if ( $lag === false && !is_infinite( $maxServerLag ) ) {
                                        $this->replLogger->error(
-                                               "Server {host} is not replicating?", [ 'host' => $host ] );
+                                               __METHOD__ .
+                                               ": server {host} is not replicating?", [ 'host' => $host ] );
                                        unset( $loads[$i] );
                                } elseif ( $lag > $maxServerLag ) {
                                        $this->replLogger->info(
-                                               "Server {host} has {lag} seconds of lag (>= {maxlag})",
+                                               __METHOD__ .
+                                               ": server {host} has {lag} seconds of lag (>= {maxlag})",
                                                [ 'host' => $host, 'lag' => $lag, 'maxlag' => $maxServerLag ]
                                        );
                                        unset( $loads[$i] );
@@ -328,18 +334,18 @@ class LoadBalancer implements ILoadBalancer {
        }
 
        public function getReaderIndex( $group = false, $domain = false ) {
-               if ( count( $this->mServers ) == 1 ) {
+               if ( count( $this->servers ) == 1 ) {
                        // Skip the load balancing if there's only one server
                        return $this->getWriterIndex();
-               } elseif ( $group === false && $this->mReadIndex >= 0 ) {
+               } elseif ( $group === false && $this->readIndex >= 0 ) {
                        // Shortcut if the generic reader index was already cached
-                       return $this->mReadIndex;
+                       return $this->readIndex;
                }
 
                if ( $group !== false ) {
                        // Use the server weight array for this load group
-                       if ( isset( $this->mGroupLoads[$group] ) ) {
-                               $loads = $this->mGroupLoads[$group];
+                       if ( isset( $this->groupLoads[$group] ) ) {
+                               $loads = $this->groupLoads[$group];
                        } else {
                                // No loads for this group, return false and the caller can use some other group
                                $this->connLogger->info( __METHOD__ . ": no loads for group $group" );
@@ -348,7 +354,7 @@ class LoadBalancer implements ILoadBalancer {
                        }
                } else {
                        // Use the generic load group
-                       $loads = $this->mLoads;
+                       $loads = $this->loads;
                }
 
                // Scale the configured load ratios according to each server's load and state
@@ -361,7 +367,7 @@ class LoadBalancer implements ILoadBalancer {
                        return false;
                }
 
-               if ( $this->mWaitForPos && $i != $this->getWriterIndex() ) {
+               if ( $this->waitForPos && $i != $this->getWriterIndex() ) {
                        // Before any data queries are run, wait for the server to catch up to the
                        // specified position. This is used to improve session consistency. Note that
                        // when LoadBalancer::waitFor() sets mWaitForPos, the waiting triggers here,
@@ -371,9 +377,9 @@ class LoadBalancer implements ILoadBalancer {
                        }
                }
 
-               if ( $this->mReadIndex <= 0 && $this->mLoads[$i] > 0 && $group === false ) {
+               if ( $this->readIndex <= 0 && $this->loads[$i] > 0 && $group === false ) {
                        // Cache the generic reader index for future ungrouped DB_REPLICA handles
-                       $this->mReadIndex = $i;
+                       $this->readIndex = $i;
                        // Record if the generic reader index is in "lagged replica DB" mode
                        if ( $laggedReplicaMode ) {
                                $this->laggedReplicaMode = true;
@@ -404,15 +410,15 @@ class LoadBalancer implements ILoadBalancer {
                // Quickly look through the available servers for a server that meets criteria...
                $currentLoads = $loads;
                while ( count( $currentLoads ) ) {
-                       if ( $this->mAllowLagged || $laggedReplicaMode ) {
+                       if ( $this->allowLagged || $laggedReplicaMode ) {
                                $i = ArrayUtils::pickRandom( $currentLoads );
                        } else {
                                $i = false;
-                               if ( $this->mWaitForPos && $this->mWaitForPos->asOfTime() ) {
+                               if ( $this->waitForPos && $this->waitForPos->asOfTime() ) {
                                        // ChronologyProtecter sets mWaitForPos for session consistency.
                                        // This triggers doWait() after connect, so it's especially good to
                                        // avoid lagged servers so as to avoid excessive delay in that method.
-                                       $ago = microtime( true ) - $this->mWaitForPos->asOfTime();
+                                       $ago = microtime( true ) - $this->waitForPos->asOfTime();
                                        // Aim for <= 1 second of waiting (being too picky can backfire)
                                        $i = $this->getRandomNonLagged( $currentLoads, $domain, $ago + 1 );
                                }
@@ -422,7 +428,8 @@ class LoadBalancer implements ILoadBalancer {
                                }
                                if ( $i === false && count( $currentLoads ) != 0 ) {
                                        // All replica DBs lagged. Switch to read-only mode
-                                       $this->replLogger->error( "All replica DBs lagged. Switch to read-only mode" );
+                                       $this->replLogger->error(
+                                               __METHOD__ . ": all replica DBs lagged. Switch to read-only mode" );
                                        $i = ArrayUtils::pickRandom( $currentLoads );
                                        $laggedReplicaMode = true;
                                }
@@ -460,18 +467,18 @@ class LoadBalancer implements ILoadBalancer {
 
                // If all servers were down, quit now
                if ( !count( $currentLoads ) ) {
-                       $this->connLogger->error( "All servers down" );
+                       $this->connLogger->error( __METHOD__ . ": all servers down" );
                }
 
                return [ $i, $laggedReplicaMode ];
        }
 
        public function waitFor( $pos ) {
-               $oldPos = $this->mWaitForPos;
+               $oldPos = $this->waitForPos;
                try {
-                       $this->mWaitForPos = $pos;
+                       $this->waitForPos = $pos;
                        // If a generic reader connection was already established, then wait now
-                       $i = $this->mReadIndex;
+                       $i = $this->readIndex;
                        if ( $i > 0 ) {
                                if ( !$this->doWait( $i ) ) {
                                        $this->laggedReplicaMode = true;
@@ -484,14 +491,14 @@ class LoadBalancer implements ILoadBalancer {
        }
 
        public function waitForOne( $pos, $timeout = null ) {
-               $oldPos = $this->mWaitForPos;
+               $oldPos = $this->waitForPos;
                try {
-                       $this->mWaitForPos = $pos;
+                       $this->waitForPos = $pos;
 
-                       $i = $this->mReadIndex;
+                       $i = $this->readIndex;
                        if ( $i <= 0 ) {
                                // Pick a generic replica DB if there isn't one yet
-                               $readLoads = $this->mLoads;
+                               $readLoads = $this->loads;
                                unset( $readLoads[$this->getWriterIndex()] ); // replica DBs only
                                $readLoads = array_filter( $readLoads ); // with non-zero load
                                $i = ArrayUtils::pickRandom( $readLoads );
@@ -504,25 +511,25 @@ class LoadBalancer implements ILoadBalancer {
                        }
                } finally {
                        # Restore the old position, as this is not used for lag-protection but for throttling
-                       $this->mWaitForPos = $oldPos;
+                       $this->waitForPos = $oldPos;
                }
 
                return $ok;
        }
 
        public function waitForAll( $pos, $timeout = null ) {
-               $timeout = $timeout ?: $this->mWaitTimeout;
+               $timeout = $timeout ?: $this->waitTimeout;
 
-               $oldPos = $this->mWaitForPos;
+               $oldPos = $this->waitForPos;
                try {
-                       $this->mWaitForPos = $pos;
-                       $serverCount = count( $this->mServers );
+                       $this->waitForPos = $pos;
+                       $serverCount = count( $this->servers );
 
                        $ok = true;
                        for ( $i = 1; $i < $serverCount; $i++ ) {
-                               if ( $this->mLoads[$i] > 0 ) {
+                               if ( $this->loads[$i] > 0 ) {
                                        $start = microtime( true );
-                                       $ok = $this->doWait( $i, true, max( 1, (int)$timeout ) ) && $ok;
+                                       $ok = $this->doWait( $i, true, $timeout ) && $ok;
                                        $timeout -= ( microtime( true ) - $start );
                                        if ( $timeout <= 0 ) {
                                                break; // timeout reached
@@ -531,7 +538,7 @@ class LoadBalancer implements ILoadBalancer {
                        }
                } finally {
                        # Restore the old position, as this is not used for lag-protection but for throttling
-                       $this->mWaitForPos = $oldPos;
+                       $this->waitForPos = $oldPos;
                }
 
                return $ok;
@@ -545,8 +552,8 @@ class LoadBalancer implements ILoadBalancer {
                        return;
                }
 
-               if ( !$this->mWaitForPos || $pos->hasReached( $this->mWaitForPos ) ) {
-                       $this->mWaitForPos = $pos;
+               if ( !$this->waitForPos || $pos->hasReached( $this->waitForPos ) ) {
+                       $this->waitForPos = $pos;
                }
        }
 
@@ -555,7 +562,7 @@ class LoadBalancer implements ILoadBalancer {
         * @return IDatabase|bool
         */
        public function getAnyOpenConnection( $i ) {
-               foreach ( $this->mConns as $connsByServer ) {
+               foreach ( $this->conns as $connsByServer ) {
                        if ( !empty( $connsByServer[$i] ) ) {
                                /** @var IDatabase[] $serverConns */
                                $serverConns = $connsByServer[$i];
@@ -571,11 +578,11 @@ class LoadBalancer implements ILoadBalancer {
         * Wait for a given replica DB to catch up to the master pos stored in $this
         * @param int $index Server index
         * @param bool $open Check the server even if a new connection has to be made
-        * @param int $timeout Max seconds to wait; default is mWaitTimeout
+        * @param int $timeout Max seconds to wait; default is "waitTimeout" given to __construct()
         * @return bool
         */
        protected function doWait( $index, $open = false, $timeout = null ) {
-               $close = false; // close the connection afterwards
+               $timeout = max( 1, $timeout ?: $this->waitTimeout );
 
                // Check if we already know that the DB has reached this point
                $server = $this->getServerName( $index );
@@ -584,27 +591,34 @@ class LoadBalancer implements ILoadBalancer {
                $knownReachedPos = $this->srvCache->get( $key );
                if (
                        $knownReachedPos instanceof DBMasterPos &&
-                       $knownReachedPos->hasReached( $this->mWaitForPos )
+                       $knownReachedPos->hasReached( $this->waitForPos )
                ) {
-                       $this->replLogger->debug( __METHOD__ .
+                       $this->replLogger->debug(
+                               __METHOD__ .
                                ': replica DB {dbserver} known to be caught up (pos >= $knownReachedPos).',
-                               [ 'dbserver' => $server ] );
+                               [ 'dbserver' => $server ]
+                       );
                        return true;
                }
 
                // Find a connection to wait on, creating one if needed and allowed
+               $close = false; // close the connection afterwards
                $conn = $this->getAnyOpenConnection( $index );
                if ( !$conn ) {
                        if ( !$open ) {
-                               $this->replLogger->debug( __METHOD__ . ': no connection open for {dbserver}',
-                                       [ 'dbserver' => $server ] );
+                               $this->replLogger->debug(
+                                       __METHOD__ . ': no connection open for {dbserver}',
+                                       [ 'dbserver' => $server ]
+                               );
 
                                return false;
                        } else {
                                $conn = $this->openConnection( $index, self::DOMAIN_ANY );
                                if ( !$conn ) {
-                                       $this->replLogger->warning( __METHOD__ . ': failed to connect to {dbserver}',
-                                               [ 'dbserver' => $server ] );
+                                       $this->replLogger->warning(
+                                               __METHOD__ . ': failed to connect to {dbserver}',
+                                               [ 'dbserver' => $server ]
+                                       );
 
                                        return false;
                                }
@@ -614,23 +628,39 @@ class LoadBalancer implements ILoadBalancer {
                        }
                }
 
-               $this->replLogger->info( __METHOD__ . ': Waiting for replica DB {dbserver} to catch up...',
-                       [ 'dbserver' => $server ] );
-               $timeout = $timeout ?: $this->mWaitTimeout;
-               $result = $conn->masterPosWait( $this->mWaitForPos, $timeout );
+               $this->replLogger->info(
+                       __METHOD__ .
+                       ': waiting for replica DB {dbserver} to catch up...',
+                       [ 'dbserver' => $server ]
+               );
+
+               $result = $conn->masterPosWait( $this->waitForPos, $timeout );
 
-               if ( $result == -1 || is_null( $result ) ) {
-                       // Timed out waiting for replica DB, use master instead
+               if ( $result === null ) {
+                       $this->replLogger->warning(
+                               __METHOD__ . ': Errored out waiting on {host} pos {pos}',
+                               [
+                                       'host' => $server,
+                                       'pos' => $this->waitForPos,
+                                       'trace' => ( new RuntimeException() )->getTraceAsString()
+                               ]
+                       );
+                       $ok = false;
+               } elseif ( $result == -1 ) {
                        $this->replLogger->warning(
                                __METHOD__ . ': Timed out waiting on {host} pos {pos}',
-                               [ 'host' => $server, 'pos' => $this->mWaitForPos ]
+                               [
+                                       'host' => $server,
+                                       'pos' => $this->waitForPos,
+                                       'trace' => ( new RuntimeException() )->getTraceAsString()
+                               ]
                        );
                        $ok = false;
                } else {
-                       $this->replLogger->info( __METHOD__ . ": Done" );
+                       $this->replLogger->debug( __METHOD__ . ": done waiting" );
                        $ok = true;
                        // Remember that the DB reached this point
-                       $this->srvCache->set( $key, $this->mWaitForPos, BagOStuff::TTL_DAY );
+                       $this->srvCache->set( $key, $this->waitForPos, BagOStuff::TTL_DAY );
                }
 
                if ( $close ) {
@@ -672,14 +702,14 @@ class LoadBalancer implements ILoadBalancer {
 
                # Operation-based index
                if ( $i == self::DB_REPLICA ) {
-                       $this->mLastError = 'Unknown error'; // reset error string
+                       $this->lastError = 'Unknown error'; // reset error string
                        # Try the general server pool if $groups are unavailable.
                        $i = ( $groups === [ false ] )
                                ? false // don't bother with this if that is what was tried above
                                : $this->getReaderIndex( false, $domain );
                        # Couldn't find a working server in getReaderIndex()?
                        if ( $i === false ) {
-                               $this->mLastError = 'No working replica DB server: ' . $this->mLastError;
+                               $this->lastError = 'No working replica DB server: ' . $this->lastError;
                                // Throw an exception
                                $this->reportConnectionError();
                                return null; // not reached
@@ -727,7 +757,8 @@ class LoadBalancer implements ILoadBalancer {
                } elseif ( $conn instanceof DBConnRef ) {
                        // DBConnRef already handles calling reuseConnection() and only passes the live
                        // Database instance to this method. Any caller passing in a DBConnRef is broken.
-                       $this->connLogger->error( __METHOD__ . ": got DBConnRef instance.\n" .
+                       $this->connLogger->error(
+                               __METHOD__ . ": got DBConnRef instance.\n" .
                                ( new RuntimeException() )->getTraceAsString() );
 
                        return;
@@ -746,20 +777,20 @@ class LoadBalancer implements ILoadBalancer {
                }
 
                $domain = $conn->getDomainID();
-               if ( !isset( $this->mConns[$connInUseKey][$serverIndex][$domain] ) ) {
+               if ( !isset( $this->conns[$connInUseKey][$serverIndex][$domain] ) ) {
                        throw new InvalidArgumentException( __METHOD__ .
                                ": connection $serverIndex/$domain not found; it may have already been freed." );
-               } elseif ( $this->mConns[$connInUseKey][$serverIndex][$domain] !== $conn ) {
+               } elseif ( $this->conns[$connInUseKey][$serverIndex][$domain] !== $conn ) {
                        throw new InvalidArgumentException( __METHOD__ .
                                ": connection $serverIndex/$domain mismatched; it may have already been freed." );
                }
 
                $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
                if ( $refCount <= 0 ) {
-                       $this->mConns[$connFreeKey][$serverIndex][$domain] = $conn;
-                       unset( $this->mConns[$connInUseKey][$serverIndex][$domain] );
-                       if ( !$this->mConns[$connInUseKey][$serverIndex] ) {
-                               unset( $this->mConns[$connInUseKey][$serverIndex] ); // clean up
+                       $this->conns[$connFreeKey][$serverIndex][$domain] = $conn;
+                       unset( $this->conns[$connInUseKey][$serverIndex][$domain] );
+                       if ( !$this->conns[$connInUseKey][$serverIndex] ) {
+                               unset( $this->conns[$connInUseKey][$serverIndex] ); // clean up
                        }
                        $this->connLogger->debug( __METHOD__ . ": freed connection $serverIndex/$domain" );
                } else {
@@ -811,14 +842,14 @@ class LoadBalancer implements ILoadBalancer {
                } else {
                        // Connection is to the local domain
                        $connKey = $autoCommit ? self::KEY_LOCAL_NOROUND : self::KEY_LOCAL;
-                       if ( isset( $this->mConns[$connKey][$i][0] ) ) {
-                               $conn = $this->mConns[$connKey][$i][0];
+                       if ( isset( $this->conns[$connKey][$i][0] ) ) {
+                               $conn = $this->conns[$connKey][$i][0];
                        } else {
-                               if ( !isset( $this->mServers[$i] ) || !is_array( $this->mServers[$i] ) ) {
+                               if ( !isset( $this->servers[$i] ) || !is_array( $this->servers[$i] ) ) {
                                        throw new InvalidArgumentException( "No server with index '$i'." );
                                }
                                // Open a new connection
-                               $server = $this->mServers[$i];
+                               $server = $this->servers[$i];
                                $server['serverIndex'] = $i;
                                $server['autoCommitOnly'] = $autoCommit;
                                if ( $this->localDomain->getDatabase() !== null ) {
@@ -828,10 +859,12 @@ class LoadBalancer implements ILoadBalancer {
                                $conn = $this->reallyOpenConnection( $server, $this->localDomain );
                                $host = $this->getServerName( $i );
                                if ( $conn->isOpen() ) {
-                                       $this->connLogger->debug( "Connected to database $i at '$host'." );
-                                       $this->mConns[$connKey][$i][0] = $conn;
+                                       $this->connLogger->debug(
+                                               __METHOD__ . ": connected to database $i at '$host'." );
+                                       $this->conns[$connKey][$i][0] = $conn;
                                } else {
-                                       $this->connLogger->warning( "Failed to connect to database $i at '$host'." );
+                                       $this->connLogger->warning(
+                                               __METHOD__ . ": failed to connect to database $i at '$host'." );
                                        $this->errorConnection = $conn;
                                        $conn = false;
                                }
@@ -889,39 +922,39 @@ class LoadBalancer implements ILoadBalancer {
                        $connInUseKey = self::KEY_FOREIGN_INUSE;
                }
 
-               if ( isset( $this->mConns[$connInUseKey][$i][$domain] ) ) {
+               if ( isset( $this->conns[$connInUseKey][$i][$domain] ) ) {
                        // Reuse an in-use connection for the same domain
-                       $conn = $this->mConns[$connInUseKey][$i][$domain];
+                       $conn = $this->conns[$connInUseKey][$i][$domain];
                        $this->connLogger->debug( __METHOD__ . ": reusing connection $i/$domain" );
-               } elseif ( isset( $this->mConns[$connFreeKey][$i][$domain] ) ) {
+               } elseif ( isset( $this->conns[$connFreeKey][$i][$domain] ) ) {
                        // Reuse a free connection for the same domain
-                       $conn = $this->mConns[$connFreeKey][$i][$domain];
-                       unset( $this->mConns[$connFreeKey][$i][$domain] );
-                       $this->mConns[$connInUseKey][$i][$domain] = $conn;
+                       $conn = $this->conns[$connFreeKey][$i][$domain];
+                       unset( $this->conns[$connFreeKey][$i][$domain] );
+                       $this->conns[$connInUseKey][$i][$domain] = $conn;
                        $this->connLogger->debug( __METHOD__ . ": reusing free connection $i/$domain" );
-               } elseif ( !empty( $this->mConns[$connFreeKey][$i] ) ) {
+               } elseif ( !empty( $this->conns[$connFreeKey][$i] ) ) {
                        // Reuse a free connection from another domain
-                       $conn = reset( $this->mConns[$connFreeKey][$i] );
-                       $oldDomain = key( $this->mConns[$connFreeKey][$i] );
+                       $conn = reset( $this->conns[$connFreeKey][$i] );
+                       $oldDomain = key( $this->conns[$connFreeKey][$i] );
                        if ( strlen( $dbName ) && !$conn->selectDB( $dbName ) ) {
-                               $this->mLastError = "Error selecting database '$dbName' on server " .
+                               $this->lastError = "Error selecting database '$dbName' on server " .
                                        $conn->getServer() . " from client host {$this->host}";
                                $this->errorConnection = $conn;
                                $conn = false;
                        } else {
                                $conn->tablePrefix( $prefix );
-                               unset( $this->mConns[$connFreeKey][$i][$oldDomain] );
+                               unset( $this->conns[$connFreeKey][$i][$oldDomain] );
                                // Note that if $domain is an empty string, getDomainID() might not match it
-                               $this->mConns[$connInUseKey][$i][$conn->getDomainId()] = $conn;
+                               $this->conns[$connInUseKey][$i][$conn->getDomainId()] = $conn;
                                $this->connLogger->debug( __METHOD__ .
                                        ": reusing free connection from $oldDomain for $domain" );
                        }
                } else {
-                       if ( !isset( $this->mServers[$i] ) || !is_array( $this->mServers[$i] ) ) {
+                       if ( !isset( $this->servers[$i] ) || !is_array( $this->servers[$i] ) ) {
                                throw new InvalidArgumentException( "No server with index '$i'." );
                        }
                        // Open a new connection
-                       $server = $this->mServers[$i];
+                       $server = $this->servers[$i];
                        $server['serverIndex'] = $i;
                        $server['foreignPoolRefCount'] = 0;
                        $server['foreign'] = true;
@@ -934,7 +967,7 @@ class LoadBalancer implements ILoadBalancer {
                        } else {
                                $conn->tablePrefix( $prefix ); // as specified
                                // Note that if $domain is an empty string, getDomainID() might not match it
-                               $this->mConns[$connInUseKey][$i][$conn->getDomainID()] = $conn;
+                               $this->conns[$connInUseKey][$i][$conn->getDomainID()] = $conn;
                                $this->connLogger->debug( __METHOD__ . ": opened new connection for $i/$domain" );
                        }
                }
@@ -979,7 +1012,17 @@ class LoadBalancer implements ILoadBalancer {
                        throw new DBAccessError();
                }
 
-               if ( $domainOverride->getDatabase() !== null ) {
+               // Handle $domainOverride being a specified or an unspecified domain
+               if ( $domainOverride->getDatabase() === null ) {
+                       // Normally, an RDBMS requires a DB name specified on connection and the $server
+                       // configuration array is assumed to already specify an appropriate DB name.
+                       if ( $server['type'] === 'mysql' ) {
+                               // For MySQL, DATABASE and SCHEMA are synonyms, connections need not specify a DB,
+                               // and the DB name in $server might not exist due to legacy reasons (the default
+                               // domain used to ignore the local LB domain, even when mismatched).
+                               $server['dbname'] = null;
+                       }
+               } else {
                        $server['dbname'] = $domainOverride->getDatabase();
                        $server['schema'] = $domainOverride->getSchema();
                }
@@ -1042,27 +1085,28 @@ class LoadBalancer implements ILoadBalancer {
                $conn = $this->errorConnection; // the connection which caused the error
                $context = [
                        'method' => __METHOD__,
-                       'last_error' => $this->mLastError,
+                       'last_error' => $this->lastError,
                ];
 
                if ( $conn instanceof IDatabase ) {
                        $context['db_server'] = $conn->getServer();
                        $this->connLogger->warning(
-                               "Connection error: {last_error} ({db_server})",
+                               __METHOD__ . ": connection error: {last_error} ({db_server})",
                                $context
                        );
 
                        // throws DBConnectionError
-                       $conn->reportConnectionError( "{$this->mLastError} ({$context['db_server']})" );
+                       $conn->reportConnectionError( "{$this->lastError} ({$context['db_server']})" );
                } else {
                        // No last connection, probably due to all servers being too busy
                        $this->connLogger->error(
-                               "LB failure with no last connection. Connection error: {last_error}",
+                               __METHOD__ .
+                               ": LB failure with no last connection. Connection error: {last_error}",
                                $context
                        );
 
                        // If all servers were busy, mLastError will contain something sensible
-                       throw new DBConnectionError( null, $this->mLastError );
+                       throw new DBConnectionError( null, $this->lastError );
                }
        }
 
@@ -1071,22 +1115,22 @@ class LoadBalancer implements ILoadBalancer {
        }
 
        public function haveIndex( $i ) {
-               return array_key_exists( $i, $this->mServers );
+               return array_key_exists( $i, $this->servers );
        }
 
        public function isNonZeroLoad( $i ) {
-               return array_key_exists( $i, $this->mServers ) && $this->mLoads[$i] != 0;
+               return array_key_exists( $i, $this->servers ) && $this->loads[$i] != 0;
        }
 
        public function getServerCount() {
-               return count( $this->mServers );
+               return count( $this->servers );
        }
 
        public function getServerName( $i ) {
-               if ( isset( $this->mServers[$i]['hostName'] ) ) {
-                       $name = $this->mServers[$i]['hostName'];
-               } elseif ( isset( $this->mServers[$i]['host'] ) ) {
-                       $name = $this->mServers[$i]['host'];
+               if ( isset( $this->servers[$i]['hostName'] ) ) {
+                       $name = $this->servers[$i]['hostName'];
+               } elseif ( isset( $this->servers[$i]['host'] ) ) {
+                       $name = $this->servers[$i]['host'];
                } else {
                        $name = '';
                }
@@ -1095,7 +1139,7 @@ class LoadBalancer implements ILoadBalancer {
        }
 
        public function getServerType( $i ) {
-               return isset( $this->mServers[$i]['type'] ) ? $this->mServers[$i]['type'] : 'unknown';
+               return isset( $this->servers[$i]['type'] ) ? $this->servers[$i]['type'] : 'unknown';
        }
 
        public function getMasterPos() {
@@ -1103,7 +1147,7 @@ class LoadBalancer implements ILoadBalancer {
                # master (however unlikely that may be), then we can fetch the position from the replica DB.
                $masterConn = $this->getAnyOpenConnection( $this->getWriterIndex() );
                if ( !$masterConn ) {
-                       $serverCount = count( $this->mServers );
+                       $serverCount = count( $this->servers );
                        for ( $i = 1; $i < $serverCount; $i++ ) {
                                $conn = $this->getAnyOpenConnection( $i );
                                if ( $conn ) {
@@ -1125,11 +1169,12 @@ class LoadBalancer implements ILoadBalancer {
        public function closeAll() {
                $this->forEachOpenConnection( function ( IDatabase $conn ) {
                        $host = $conn->getServer();
-                       $this->connLogger->debug( "Closing connection to database '$host'." );
+                       $this->connLogger->debug(
+                               __METHOD__ . ": closing connection to database '$host'." );
                        $conn->close();
                } );
 
-               $this->mConns = [
+               $this->conns = [
                        self::KEY_LOCAL => [],
                        self::KEY_FOREIGN_INUSE => [],
                        self::KEY_FOREIGN_FREE => [],
@@ -1142,7 +1187,7 @@ class LoadBalancer implements ILoadBalancer {
 
        public function closeConnection( IDatabase $conn ) {
                $serverIndex = $conn->getLBInfo( 'serverIndex' ); // second index level of mConns
-               foreach ( $this->mConns as $type => $connsByServer ) {
+               foreach ( $this->conns as $type => $connsByServer ) {
                        if ( !isset( $connsByServer[$serverIndex] ) ) {
                                continue;
                        }
@@ -1150,8 +1195,9 @@ class LoadBalancer implements ILoadBalancer {
                        foreach ( $connsByServer[$serverIndex] as $i => $trackedConn ) {
                                if ( $conn === $trackedConn ) {
                                        $host = $this->getServerName( $i );
-                                       $this->connLogger->debug( "Closing connection to database $i at '$host'." );
-                                       unset( $this->mConns[$type][$serverIndex][$i] );
+                                       $this->connLogger->debug(
+                                               __METHOD__ . ": closing connection to database $i at '$host'." );
+                                       unset( $this->conns[$type][$serverIndex][$i] );
                                        --$this->connsOpened;
                                        break 2;
                                }
@@ -1335,7 +1381,7 @@ class LoadBalancer implements ILoadBalancer {
                $this->trxRoundId = false;
                $this->forEachOpenMasterConnection(
                        function ( IDatabase $conn ) use ( $fname, $restore ) {
-                               if ( $conn->writesOrCallbacksPending() ) {
+                               if ( $conn->writesOrCallbacksPending() || $conn->explicitTrxActive() ) {
                                        $conn->rollback( $fname, $conn::FLUSHING_ALL_PEERS );
                                }
                                if ( $restore ) {
@@ -1411,7 +1457,7 @@ class LoadBalancer implements ILoadBalancer {
        }
 
        public function hasOrMadeRecentMasterChanges( $age = null ) {
-               $age = ( $age === null ) ? $this->mWaitTimeout : $age;
+               $age = ( $age === null ) ? $this->waitTimeout : $age;
 
                return ( $this->hasMasterChanges()
                        || $this->lastMasterChangeTimestamp() > microtime( true ) - $age );
@@ -1515,11 +1561,11 @@ class LoadBalancer implements ILoadBalancer {
 
        public function allowLagged( $mode = null ) {
                if ( $mode === null ) {
-                       return $this->mAllowLagged;
+                       return $this->allowLagged;
                }
-               $this->mAllowLagged = $mode;
+               $this->allowLagged = $mode;
 
-               return $this->mAllowLagged;
+               return $this->allowLagged;
        }
 
        public function pingAll() {
@@ -1534,7 +1580,7 @@ class LoadBalancer implements ILoadBalancer {
        }
 
        public function forEachOpenConnection( $callback, array $params = [] ) {
-               foreach ( $this->mConns as $connsByServer ) {
+               foreach ( $this->conns as $connsByServer ) {
                        foreach ( $connsByServer as $serverConns ) {
                                foreach ( $serverConns as $conn ) {
                                        $mergedParams = array_merge( [ $conn ], $params );
@@ -1546,7 +1592,7 @@ class LoadBalancer implements ILoadBalancer {
 
        public function forEachOpenMasterConnection( $callback, array $params = [] ) {
                $masterIndex = $this->getWriterIndex();
-               foreach ( $this->mConns as $connsByServer ) {
+               foreach ( $this->conns as $connsByServer ) {
                        if ( isset( $connsByServer[$masterIndex] ) ) {
                                /** @var IDatabase $conn */
                                foreach ( $connsByServer[$masterIndex] as $conn ) {
@@ -1558,7 +1604,7 @@ class LoadBalancer implements ILoadBalancer {
        }
 
        public function forEachOpenReplicaConnection( $callback, array $params = [] ) {
-               foreach ( $this->mConns as $connsByServer ) {
+               foreach ( $this->conns as $connsByServer ) {
                        foreach ( $connsByServer as $i => $serverConns ) {
                                if ( $i === $this->getWriterIndex() ) {
                                        continue; // skip master
@@ -1582,9 +1628,9 @@ class LoadBalancer implements ILoadBalancer {
 
                $lagTimes = $this->getLagTimes( $domain );
                foreach ( $lagTimes as $i => $lag ) {
-                       if ( $this->mLoads[$i] > 0 && $lag > $maxLag ) {
+                       if ( $this->loads[$i] > 0 && $lag > $maxLag ) {
                                $maxLag = $lag;
-                               $host = $this->mServers[$i]['host'];
+                               $host = $this->servers[$i]['host'];
                                $maxIndex = $i;
                        }
                }
@@ -1599,7 +1645,7 @@ class LoadBalancer implements ILoadBalancer {
 
                $knownLagTimes = []; // map of (server index => 0 seconds)
                $indexesWithLag = [];
-               foreach ( $this->mServers as $i => $server ) {
+               foreach ( $this->servers as $i => $server ) {
                        if ( empty( $server['is static'] ) ) {
                                $indexesWithLag[] = $i; // DB server might have replication lag
                        } else {
@@ -1621,10 +1667,12 @@ class LoadBalancer implements ILoadBalancer {
        /**
         * @param IDatabase $conn
         * @param DBMasterPos|bool $pos
-        * @param int $timeout
+        * @param int|null $timeout
         * @return bool
         */
-       public function safeWaitForMasterPos( IDatabase $conn, $pos = false, $timeout = 10 ) {
+       public function safeWaitForMasterPos( IDatabase $conn, $pos = false, $timeout = null ) {
+               $timeout = max( 1, $timeout ?: $this->waitTimeout );
+
                if ( $this->getServerCount() <= 1 || !$conn->getLBInfo( 'replica' ) ) {
                        return true; // server is not a replica DB
                }
@@ -1644,18 +1692,26 @@ class LoadBalancer implements ILoadBalancer {
                if ( $pos instanceof DBMasterPos ) {
                        $result = $conn->masterPosWait( $pos, $timeout );
                        if ( $result == -1 || is_null( $result ) ) {
-                               $msg = __METHOD__ . ': Timed out waiting on {host} pos {pos}';
-                               $this->replLogger->warning( $msg,
-                                       [ 'host' => $conn->getServer(), 'pos' => $pos ] );
+                               $msg = __METHOD__ . ': timed out waiting on {host} pos {pos}';
+                               $this->replLogger->warning( $msg, [
+                                       'host' => $conn->getServer(),
+                                       'pos' => $pos,
+                                       'trace' => ( new RuntimeException() )->getTraceAsString()
+                               ] );
                                $ok = false;
                        } else {
-                               $this->replLogger->info( __METHOD__ . ': Done' );
+                               $this->replLogger->debug( __METHOD__ . ': done waiting' );
                                $ok = true;
                        }
                } else {
                        $ok = false; // something is misconfigured
-                       $this->replLogger->error( 'Could not get master pos for {host}',
-                               [ 'host' => $conn->getServer() ] );
+                       $this->replLogger->error(
+                               __METHOD__ . ': could not get master pos for {host}',
+                               [
+                                       'host' => $conn->getServer(),
+                                       'trace' => ( new RuntimeException() )->getTraceAsString()
+                               ]
+                       );
                }
 
                return $ok;