X-Git-Url: https://git.heureux-cyclage.org/?p=lhc%2Fweb%2Fwiklou.git;a=blobdiff_plain;f=includes%2Flibs%2Frdbms%2Floadbalancer%2FLoadBalancer.php;h=8393e2bcfeaca928b1851064af0309469d937f52;hp=0b70010e19c973f4578d130044896174ddbae325;hb=36f4daf32c591d6b7e2435629fc6e431398b641a;hpb=0e25b050286bed143ed5a23e87d5543fe71ce5dd

diff --git a/includes/libs/rdbms/loadbalancer/LoadBalancer.php b/includes/libs/rdbms/loadbalancer/LoadBalancer.php
index 0b70010e19..eb288dd63d 100644
--- a/includes/libs/rdbms/loadbalancer/LoadBalancer.php
+++ b/includes/libs/rdbms/loadbalancer/LoadBalancer.php
@@ -18,7 +18,6 @@
  * http://www.gnu.org/copyleft/gpl.html
  *
  * @file
- * @ingroup Database
  */
 namespace Wikimedia\Rdbms;
 
@@ -41,7 +40,7 @@ use Exception;
 class LoadBalancer implements ILoadBalancer {
 	/** @var array[] Map of (server index => server config array) */
 	private $mServers;
-	/** @var Database[][][] Map of local/foreignUsed/foreignFree => server index => IDatabase array */
+	/** @var Database[][][] Map of (connection category => server index => IDatabase[]) */
 	private $mConns;
 	/** @var float[] Map of (server index => weight) */
 	private $mLoads;
@@ -49,7 +48,7 @@ class LoadBalancer implements ILoadBalancer {
 	private $mGroupLoads;
 	/** @var bool Whether to disregard replica DB lag as a factor in replica DB selection */
 	private $mAllowLagged;
-	/** @var integer Seconds to spend waiting on replica DB lag to resolve */
+	/** @var int Seconds to spend waiting on replica DB lag to resolve */
 	private $mWaitTimeout;
 	/** @var array The LoadMonitor configuration */
 	private $loadMonitorConfig;
@@ -62,8 +61,6 @@ class LoadBalancer implements ILoadBalancer {
 	private $chronProt;
 	/** @var BagOStuff */
 	private $srvCache;
-	/** @var BagOStuff */
-	private $memCache;
 	/** @var WANObjectCache */
 	private $wanCache;
 	/** @var object|string Class name or object With profileIn/profileOut methods */
@@ -81,7 +78,7 @@ class LoadBalancer implements ILoadBalancer {
 
 	/** @var Database DB connection object that caused a problem */
 	private $errorConnection;
-	/** @var integer The generic (not query grouped) replica DB index (of $mServers) */
+	/** @var int The generic (not query grouped) replica DB index (of $mServers) */
 	private $mReadIndex;
 	/** @var bool|DBMasterPos False if not set */
 	private $mWaitForPos;
@@ -93,7 +90,7 @@ class LoadBalancer implements ILoadBalancer {
 	private $mLastError = 'Unknown error';
 	/** @var string|bool Reason the LB is read-only or false if not */
 	private $readOnlyReason = false;
-	/** @var integer Total connections opened */
+	/** @var int Total connections opened */
 	private $connsOpened = 0;
 	/** @var string|bool String if a requested DBO_TRX transaction round is active */
 	private $trxRoundId = false;
@@ -113,24 +110,41 @@ class LoadBalancer implements ILoadBalancer {
 	/** @var callable Exception logger */
 	private $errorLogger;
 
-	/** @var boolean */
+	/** @var bool */
 	private $disabled = false;
-	/** @var boolean */
+	/** @var bool */
 	private $chronProtInitialized = false;
+	/** @var int */
+	private $maxLag = self::MAX_LAG_DEFAULT;
 
-	/** @var integer Warn when this many connection are held */
+	/** @var int Warn when this many connection are held */
 	const CONN_HELD_WARN_THRESHOLD = 10;
 
-	/** @var integer Default 'max lag' when unspecified */
+	/** @var int Default 'maxLag' when unspecified */
 	const MAX_LAG_DEFAULT = 10;
-	/** @var integer Seconds to cache master server read-only status */
+	/** @var int Seconds to cache master server read-only status */
 	const TTL_CACHE_READONLY = 5;
 
+	const KEY_LOCAL = 'local';
+	const KEY_FOREIGN_FREE = 'foreignFree';
+	const KEY_FOREIGN_INUSE = 'foreignInUse';
+
+	const KEY_LOCAL_NOROUND = 'localAutoCommit';
+	const KEY_FOREIGN_FREE_NOROUND = 'foreignFreeAutoCommit';
+	const KEY_FOREIGN_INUSE_NOROUND = 'foreignInUseAutoCommit';
+
 	public function __construct( array $params ) {
 		if ( !isset( $params['servers'] ) ) {
 			throw new InvalidArgumentException( __CLASS__ . ': missing servers parameter' );
 		}
 		$this->mServers = $params['servers'];
+		foreach ( $this->mServers as $i => $server ) {
+			if ( $i == 0 ) {
+				$this->mServers[$i]['master'] = true;
+			} else {
+				$this->mServers[$i]['replica'] = true;
+			}
+		}
 
 		$this->localDomain = isset( $params['localDomain'] )
 			? DatabaseDomain::newFromId( $params['localDomain'] )
@@ -148,9 +162,14 @@ class LoadBalancer implements ILoadBalancer {
 
 		$this->mReadIndex = -1;
 		$this->mConns = [
-			'local'       => [],
-			'foreignUsed' => [],
-			'foreignFree' => []
+			// Connection were transaction rounds may be applied
+			self::KEY_LOCAL => [],
+			self::KEY_FOREIGN_INUSE => [],
+			self::KEY_FOREIGN_FREE => [],
+			// Auto-committing counterpart connections that ignore transaction rounds
+			self::KEY_LOCAL_NOROUND => [],
+			self::KEY_FOREIGN_INUSE_NOROUND => [],
+			self::KEY_FOREIGN_FREE_NOROUND => []
 		];
 		$this->mLoads = [];
 		$this->mWaitForPos = false;
@@ -160,11 +179,16 @@ class LoadBalancer implements ILoadBalancer {
 			$this->readOnlyReason = $params['readOnlyReason'];
 		}
 
+		if ( isset( $params['maxLag'] ) ) {
+			$this->maxLag = $params['maxLag'];
+		}
+
 		if ( isset( $params['loadMonitor'] ) ) {
 			$this->loadMonitorConfig = $params['loadMonitor'];
 		} else {
 			$this->loadMonitorConfig = [ 'class' => 'LoadMonitorNull' ];
 		}
+		$this->loadMonitorConfig += [ 'lagWarnThreshold' => $this->maxLag ];
 
 		foreach ( $params['servers'] as $i => $server ) {
 			$this->mLoads[$i] = $server['load'];
@@ -183,11 +207,6 @@ class LoadBalancer implements ILoadBalancer {
 		} else {
 			$this->srvCache = new EmptyBagOStuff();
 		}
-		if ( isset( $params['memCache'] ) ) {
-			$this->memCache = $params['memCache'];
-		} else {
-			$this->memCache = new EmptyBagOStuff();
-		}
 		if ( isset( $params['wanCache'] ) ) {
 			$this->wanCache = $params['wanCache'];
 		} else {
@@ -240,7 +259,7 @@ class LoadBalancer implements ILoadBalancer {
 			}
 
 			$this->loadMonitor = new $class(
-				$this, $this->srvCache, $this->memCache, $this->loadMonitorConfig );
+				$this, $this->srvCache, $this->wanCache, $this->loadMonitorConfig );
 			$this->loadMonitor->setLogger( $this->replLogger );
 		}
 
@@ -262,7 +281,7 @@ class LoadBalancer implements ILoadBalancer {
 				# How much lag this server nominally is allowed to have
 				$maxServerLag = isset( $this->mServers[$i]['max lag'] )
 					? $this->mServers[$i]['max lag']
-					: self::MAX_LAG_DEFAULT; // default
+					: $this->maxLag; // default
 				# Constrain that futher by $maxLag argument
 				$maxServerLag = min( $maxServerLag, $maxLag );
 
@@ -272,7 +291,7 @@ class LoadBalancer implements ILoadBalancer {
 						"Server {host} is not replicating?", [ 'host' => $host ] );
 					unset( $loads[$i] );
 				} elseif ( $lag > $maxServerLag ) {
-					$this->replLogger->warning(
+					$this->replLogger->info(
 						"Server {host} has {lag} seconds of lag (>= {maxlag})",
 						[ 'host' => $host, 'lag' => $lag, 'maxlag' => $maxServerLag ]
 					);
@@ -371,9 +390,9 @@ class LoadBalancer implements ILoadBalancer {
 			throw new InvalidArgumentException( "Empty server array given to LoadBalancer" );
 		}
 
-		/** @var $i int|bool Index of selected server */
+		/** @var int|bool $i Index of selected server */
 		$i = false;
-		/** @var $laggedReplicaMode bool Whether server is considered lagged */
+		/** @var bool $laggedReplicaMode Whether server is considered lagged */
 		$laggedReplicaMode = false;
 
 		// Quickly look through the available servers for a server that meets criteria...
@@ -525,7 +544,7 @@ class LoadBalancer implements ILoadBalancer {
 	public function getAnyOpenConnection( $i ) {
 		foreach ( $this->mConns as $connsByServer ) {
 			if ( !empty( $connsByServer[$i] ) ) {
-				/** @var $serverConns IDatabase[] */
+				/** @var IDatabase[] $serverConns */
 				$serverConns = $connsByServer[$i];
 
 				return reset( $serverConns );
@@ -555,7 +574,8 @@ class LoadBalancer implements ILoadBalancer {
 			$knownReachedPos->hasReached( $this->mWaitForPos )
 		) {
 			$this->replLogger->debug( __METHOD__ .
-				": replica DB $server known to be caught up (pos >= $knownReachedPos)." );
+				': replica DB {dbserver} known to be caught up (pos >= $knownReachedPos).',
+				[ 'dbserver' => $server ] );
 			return true;
 		}
 
@@ -563,13 +583,15 @@ class LoadBalancer implements ILoadBalancer {
 		$conn = $this->getAnyOpenConnection( $index );
 		if ( !$conn ) {
 			if ( !$open ) {
-				$this->replLogger->debug( __METHOD__ . ": no connection open for $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 $server" );
+					$this->replLogger->warning( __METHOD__ . ': failed to connect to {dbserver}',
+						[ 'dbserver' => $server ] );
 
 					return false;
 				}
@@ -579,15 +601,16 @@ class LoadBalancer implements ILoadBalancer {
 			}
 		}
 
-		$this->replLogger->info( __METHOD__ . ": Waiting for replica DB $server to catch up..." );
+		$this->replLogger->info( __METHOD__ . ': Waiting for replica DB {dbserver} to catch up...',
+			[ 'dbserver' => $server ] );
 		$timeout = $timeout ?: $this->mWaitTimeout;
 		$result = $conn->masterPosWait( $this->mWaitForPos, $timeout );
 
 		if ( $result == -1 || is_null( $result ) ) {
 			// Timed out waiting for replica DB, use master instead
 			$this->replLogger->warning(
-				__METHOD__ . ": Timed out waiting on {host} pos {$this->mWaitForPos}",
-				[ 'host' => $server ]
+				__METHOD__ . ': Timed out waiting on {host} pos {pos}',
+				[ 'host' => $server, 'pos' => $this->mWaitForPos ]
 			);
 			$ok = false;
 		} else {
@@ -604,16 +627,7 @@ class LoadBalancer implements ILoadBalancer {
 		return $ok;
 	}
 
-	/**
-	 * @see ILoadBalancer::getConnection()
-	 *
-	 * @param int $i
-	 * @param array $groups
-	 * @param bool $domain
-	 * @return Database
-	 * @throws DBConnectionError
-	 */
-	public function getConnection( $i, $groups = [], $domain = false ) {
+	public function getConnection( $i, $groups = [], $domain = false, $flags = 0 ) {
 		if ( $i === null || $i === false ) {
 			throw new InvalidArgumentException( 'Attempt to call ' . __METHOD__ .
 				' with invalid server index' );
@@ -631,6 +645,12 @@ class LoadBalancer implements ILoadBalancer {
 		$oldConnsOpened = $this->connsOpened; // connections open now
 
 		if ( $i == self::DB_MASTER ) {
+			if ( $flags & self::CONN_NO_WRITE ) {
+				throw new InvalidArgumentException(
+					'Cannot set CONN_NO_WRITE flag on master connection!'
+				);
+			}
+
 			$i = $this->getWriterIndex();
 		} else {
 			# Try to find an available server in any the query groups (in order)
@@ -641,6 +661,9 @@ class LoadBalancer implements ILoadBalancer {
 					break;
 				}
 			}
+
+			// Request no-write connection, even if $i == $this->getWriterIndex().
+			$flags |= self::CONN_NO_WRITE;
 		}
 
 		# Operation-based index
@@ -657,10 +680,13 @@ class LoadBalancer implements ILoadBalancer {
 				$this->reportConnectionError();
 				return null; // not reached
 			}
+
+			// Request no-write connection, even if $i == $this->getWriterIndex().
+			$flags |= self::CONN_NO_WRITE;
 		}
 
 		# Now we have an explicit index into the servers array
-		$conn = $this->openConnection( $i, $domain );
+		$conn = $this->openConnection( $i, $domain, $flags );
 		if ( !$conn ) {
 			// Throw an exception
 			$this->reportConnectionError();
@@ -710,20 +736,29 @@ class LoadBalancer implements ILoadBalancer {
 			return; // DBConnRef handle probably survived longer than the LoadBalancer
 		}
 
+		if ( $conn->getLBInfo( 'autoCommitOnly' ) ) {
+			$connFreeKey = self::KEY_FOREIGN_FREE_NOROUND;
+			$connInUseKey = self::KEY_FOREIGN_INUSE_NOROUND;
+		} else {
+			$connFreeKey = self::KEY_FOREIGN_FREE;
+			$connInUseKey = self::KEY_FOREIGN_INUSE;
+		}
+
 		$domain = $conn->getDomainID();
-		if ( !isset( $this->mConns['foreignUsed'][$serverIndex][$domain] ) ) {
+		if ( !isset( $this->mConns[$connInUseKey][$serverIndex][$domain] ) ) {
 			throw new InvalidArgumentException( __METHOD__ .
 				": connection $serverIndex/$domain not found; it may have already been freed." );
-		} elseif ( $this->mConns['foreignUsed'][$serverIndex][$domain] !== $conn ) {
+		} elseif ( $this->mConns[$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 ) {
-			$this->mConns['foreignFree'][$serverIndex][$domain] = $conn;
-			unset( $this->mConns['foreignUsed'][$serverIndex][$domain] );
-			if ( !$this->mConns['foreignUsed'][$serverIndex] ) {
-				unset( $this->mConns[ 'foreignUsed' ][$serverIndex] ); // clean up
+			$this->mConns[$connFreeKey][$serverIndex][$domain] = $conn;
+			unset( $this->mConns[$connInUseKey][$serverIndex][$domain] );
+			if ( !$this->mConns[$connInUseKey][$serverIndex] ) {
+				unset( $this->mConns[$connInUseKey][$serverIndex] ); // clean up
 			}
 			$this->connLogger->debug( __METHOD__ . ": freed connection $serverIndex/$domain" );
 		} else {
@@ -732,33 +767,26 @@ class LoadBalancer implements ILoadBalancer {
 		}
 	}
 
-	public function getConnectionRef( $db, $groups = [], $domain = false ) {
+	public function getConnectionRef( $db, $groups = [], $domain = false, $flags = 0 ) {
 		$domain = ( $domain !== false ) ? $domain : $this->localDomain;
 
-		return new DBConnRef( $this, $this->getConnection( $db, $groups, $domain ) );
+		return new DBConnRef( $this, $this->getConnection( $db, $groups, $domain, $flags ) );
 	}
 
-	public function getLazyConnectionRef( $db, $groups = [], $domain = false ) {
+	public function getLazyConnectionRef( $db, $groups = [], $domain = false, $flags = 0 ) {
 		$domain = ( $domain !== false ) ? $domain : $this->localDomain;
 
-		return new DBConnRef( $this, [ $db, $groups, $domain ] );
+		return new DBConnRef( $this, [ $db, $groups, $domain, $flags ] );
 	}
 
-	public function getMaintenanceConnectionRef( $db, $groups = [], $domain = false ) {
+	public function getMaintenanceConnectionRef( $db, $groups = [], $domain = false, $flags = 0 ) {
 		$domain = ( $domain !== false ) ? $domain : $this->localDomain;
 
-		return new MaintainableDBConnRef( $this, $this->getConnection( $db, $groups, $domain ) );
+		return new MaintainableDBConnRef(
+			$this, $this->getConnection( $db, $groups, $domain, $flags ) );
 	}
 
-	/**
-	 * @see ILoadBalancer::openConnection()
-	 *
-	 * @param int $i
-	 * @param bool $domain
-	 * @return bool|Database
-	 * @throws DBAccessError
-	 */
-	public function openConnection( $i, $domain = false ) {
+	public function openConnection( $i, $domain = false, $flags = 0 ) {
 		if ( $this->localDomain->equals( $domain ) || $domain === $this->localDomainIdAlias ) {
 			$domain = false; // local connection requested
 		}
@@ -770,26 +798,46 @@ class LoadBalancer implements ILoadBalancer {
 			$this->chronProt->initLB( $this );
 		}
 
+		// Check if an auto-commit connection is being requested. If so, it will not reuse the
+		// main set of DB connections but rather its own pool since:
+		// a) those are usually set to implicitly use transaction rounds via DBO_TRX
+		// b) those must support the use of explicit transaction rounds via beginMasterChanges()
+		$autoCommit = ( ( $flags & self::CONN_TRX_AUTO ) == self::CONN_TRX_AUTO );
+		$noWrite = ( ( $flags & self::CONN_NO_WRITE ) == self::CONN_NO_WRITE );
+
+		if ( $noWrite && $i === $this->getWriterIndex() ) {
+			// We can't disable writes on the master connection!
+			// TODO: Wrap the master connection, so write operations fail!
+			$noWrite = false;
+		}
+
 		if ( $domain !== false ) {
-			$conn = $this->openForeignConnection( $i, $domain );
-		} elseif ( isset( $this->mConns['local'][$i][0] ) ) {
-			$conn = $this->mConns['local'][$i][0];
+			// Connection is to a foreign domain
+			$conn = $this->openForeignConnection( $i, $domain, $flags );
 		} else {
-			if ( !isset( $this->mServers[$i] ) || !is_array( $this->mServers[$i] ) ) {
-				throw new InvalidArgumentException( "No server with index '$i'." );
-			}
-			// Open a new connection
-			$server = $this->mServers[$i];
-			$server['serverIndex'] = $i;
-			$conn = $this->reallyOpenConnection( $server, false );
-			$serverName = $this->getServerName( $i );
-			if ( $conn->isOpen() ) {
-				$this->connLogger->debug( "Connected to database $i at '$serverName'." );
-				$this->mConns['local'][$i][0] = $conn;
+			// 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];
 			} else {
-				$this->connLogger->warning( "Failed to connect to database $i at '$serverName'." );
-				$this->errorConnection = $conn;
-				$conn = false;
+				if ( !isset( $this->mServers[$i] ) || !is_array( $this->mServers[$i] ) ) {
+					throw new InvalidArgumentException( "No server with index '$i'." );
+				}
+				// Open a new connection
+				$server = $this->mServers[$i];
+				$server['serverIndex'] = $i;
+				$server['noWrite'] = $noWrite;
+				$server['autoCommitOnly'] = $autoCommit;
+				$conn = $this->reallyOpenConnection( $server, false );
+				$host = $this->getServerName( $i );
+				if ( $conn->isOpen() ) {
+					$this->connLogger->debug( "Connected to database $i at '$host'." );
+					$this->mConns[$connKey][$i][0] = $conn;
+				} else {
+					$this->connLogger->warning( "Failed to connect to database $i at '$host'." );
+					$this->errorConnection = $conn;
+					$conn = false;
+				}
 			}
 		}
 
@@ -802,6 +850,10 @@ class LoadBalancer implements ILoadBalancer {
 			$conn = false;
 		}
 
+		if ( $autoCommit && $conn instanceof IDatabase ) {
+			$conn->clearFlag( $conn::DBO_TRX ); // auto-commit mode
+		}
+
 		return $conn;
 	}
 
@@ -823,27 +875,44 @@ class LoadBalancer implements ILoadBalancer {
 	 *
 	 * @param int $i Server index
 	 * @param string $domain Domain ID to open
+	 * @param int $flags Class CONN_* constant bitfield
 	 * @return Database
 	 */
-	private function openForeignConnection( $i, $domain ) {
+	private function openForeignConnection( $i, $domain, $flags = 0 ) {
 		$domainInstance = DatabaseDomain::newFromId( $domain );
 		$dbName = $domainInstance->getDatabase();
 		$prefix = $domainInstance->getTablePrefix();
+		$autoCommit = ( ( $flags & self::CONN_TRX_AUTO ) == self::CONN_TRX_AUTO );
+		$noWrite = ( ( $flags & self::CONN_NO_WRITE ) == self::CONN_NO_WRITE );
+
+		if ( $noWrite && $i === $this->getWriterIndex() ) {
+			// We can't disable writes on the master connection!
+			// TODO: Wrap the master connection, so write operations fail!
+			$noWrite = false;
+		}
+
+		if ( $autoCommit ) {
+			$connFreeKey = self::KEY_FOREIGN_FREE_NOROUND;
+			$connInUseKey = self::KEY_FOREIGN_INUSE_NOROUND;
+		} else {
+			$connFreeKey = self::KEY_FOREIGN_FREE;
+			$connInUseKey = self::KEY_FOREIGN_INUSE;
+		}
 
-		if ( isset( $this->mConns['foreignUsed'][$i][$domain] ) ) {
-			// Reuse an already-used connection
-			$conn = $this->mConns['foreignUsed'][$i][$domain];
+		if ( isset( $this->mConns[$connInUseKey][$i][$domain] ) ) {
+			// Reuse an in-use connection for the same domain
+			$conn = $this->mConns[$connInUseKey][$i][$domain];
 			$this->connLogger->debug( __METHOD__ . ": reusing connection $i/$domain" );
-		} elseif ( isset( $this->mConns['foreignFree'][$i][$domain] ) ) {
+		} elseif ( isset( $this->mConns[$connFreeKey][$i][$domain] ) ) {
 			// Reuse a free connection for the same domain
-			$conn = $this->mConns['foreignFree'][$i][$domain];
-			unset( $this->mConns['foreignFree'][$i][$domain] );
-			$this->mConns['foreignUsed'][$i][$domain] = $conn;
+			$conn = $this->mConns[$connFreeKey][$i][$domain];
+			unset( $this->mConns[$connFreeKey][$i][$domain] );
+			$this->mConns[$connInUseKey][$i][$domain] = $conn;
 			$this->connLogger->debug( __METHOD__ . ": reusing free connection $i/$domain" );
-		} elseif ( !empty( $this->mConns['foreignFree'][$i] ) ) {
-			// Reuse a connection from another domain
-			$conn = reset( $this->mConns['foreignFree'][$i] );
-			$oldDomain = key( $this->mConns['foreignFree'][$i] );
+		} elseif ( !empty( $this->mConns[$connFreeKey][$i] ) ) {
+			// Reuse a free connection from another domain
+			$conn = reset( $this->mConns[$connFreeKey][$i] );
+			$oldDomain = key( $this->mConns[$connFreeKey][$i] );
 			// The empty string as a DB name means "don't care".
 			// DatabaseMysqlBase::open() already handle this on connection.
 			if ( strlen( $dbName ) && !$conn->selectDB( $dbName ) ) {
@@ -853,8 +922,8 @@ class LoadBalancer implements ILoadBalancer {
 				$conn = false;
 			} else {
 				$conn->tablePrefix( $prefix );
-				unset( $this->mConns['foreignFree'][$i][$oldDomain] );
-				$this->mConns['foreignUsed'][$i][$domain] = $conn;
+				unset( $this->mConns[$connFreeKey][$i][$oldDomain] );
+				$this->mConns[$connInUseKey][$i][$domain] = $conn;
 				$this->connLogger->debug( __METHOD__ .
 					": reusing free connection from $oldDomain for $domain" );
 			}
@@ -867,6 +936,8 @@ class LoadBalancer implements ILoadBalancer {
 			$server['serverIndex'] = $i;
 			$server['foreignPoolRefCount'] = 0;
 			$server['foreign'] = true;
+			$server['autoCommitOnly'] = $autoCommit;
+			$server['noWrite'] = $noWrite;
 			$conn = $this->reallyOpenConnection( $server, $dbName );
 			if ( !$conn->isOpen() ) {
 				$this->connLogger->warning( __METHOD__ . ": connection error for $i/$domain" );
@@ -874,7 +945,7 @@ class LoadBalancer implements ILoadBalancer {
 				$conn = false;
 			} else {
 				$conn->tablePrefix( $prefix );
-				$this->mConns['foreignUsed'][$i][$domain] = $conn;
+				$this->mConns[$connInUseKey][$i][$domain] = $conn;
 				$this->connLogger->debug( __METHOD__ . ": opened new connection for $i/$domain" );
 			}
 		}
@@ -1033,6 +1104,10 @@ class LoadBalancer implements ILoadBalancer {
 		return ( $name != '' ) ? $name : 'localhost';
 	}
 
+	public function getServerType( $i ) {
+		return isset( $this->mServers[$i]['type'] ) ? $this->mServers[$i]['type'] : 'unknown';
+	}
+
 	/**
 	 * @deprecated Since 1.30, no alternative
 	 */
@@ -1085,9 +1160,12 @@ class LoadBalancer implements ILoadBalancer {
 		} );
 
 		$this->mConns = [
-			'local' => [],
-			'foreignFree' => [],
-			'foreignUsed' => [],
+			self::KEY_LOCAL => [],
+			self::KEY_FOREIGN_INUSE => [],
+			self::KEY_FOREIGN_FREE => [],
+			self::KEY_LOCAL_NOROUND => [],
+			self::KEY_FOREIGN_INUSE_NOROUND => [],
+			self::KEY_FOREIGN_FREE_NOROUND => []
 		];
 		$this->connsOpened = 0;
 	}
@@ -1168,7 +1246,7 @@ class LoadBalancer implements ILoadBalancer {
 			if ( $limit > 0 && $time > $limit ) {
 				throw new DBTransactionSizeError(
 					$conn,
-					"Transaction spent $time second(s) in writes, exceeding the $limit limit.",
+					"Transaction spent $time second(s) in writes, exceeding the limit of $limit.",
 					[ $time, $limit ]
 				);
 			}
@@ -1307,6 +1385,10 @@ class LoadBalancer implements ILoadBalancer {
 	 * @param IDatabase $conn
 	 */
 	private function applyTransactionRoundFlags( IDatabase $conn ) {
+		if ( $conn->getLBInfo( 'autoCommitOnly' ) ) {
+			return; // transaction rounds do not apply to these connections
+		}
+
 		if ( $conn->getFlag( $conn::DBO_DEFAULT ) ) {
 			// DBO_TRX is controlled entirely by CLI mode presence with DBO_DEFAULT.
 			// Force DBO_TRX even in CLI mode since a commit round is expected soon.
@@ -1321,6 +1403,10 @@ class LoadBalancer implements ILoadBalancer {
 	 * @param IDatabase $conn
 	 */
 	private function undoTransactionRoundFlags( IDatabase $conn ) {
+		if ( $conn->getLBInfo( 'autoCommitOnly' ) ) {
+			return; // transaction rounds do not apply to these connections
+		}
+
 		if ( $conn->getFlag( $conn::DBO_DEFAULT ) ) {
 			$conn->restoreFlags( $conn::RESTORE_PRIOR );
 		}
@@ -1588,16 +1674,18 @@ class LoadBalancer implements ILoadBalancer {
 		if ( $pos instanceof DBMasterPos ) {
 			$result = $conn->masterPosWait( $pos, $timeout );
 			if ( $result == -1 || is_null( $result ) ) {
-				$msg = __METHOD__ . ": Timed out waiting on {$conn->getServer()} pos {$pos}";
-				$this->replLogger->warning( "$msg" );
+				$msg = __METHOD__ . ': Timed out waiting on {host} pos {pos}';
+				$this->replLogger->warning( $msg,
+					[ 'host' => $conn->getServer(), 'pos' => $pos ] );
 				$ok = false;
 			} else {
-				$this->replLogger->info( __METHOD__ . ": Done" );
+				$this->replLogger->info( __METHOD__ . ': Done' );
 				$ok = true;
 			}
 		} else {
 			$ok = false; // something is misconfigured
-			$this->replLogger->error( "Could not get master pos for {$conn->getServer()}." );
+			$this->replLogger->error( 'Could not get master pos for {host}',
+				[ 'host' => $conn->getServer() ] );
 		}
 
 		return $ok;
@@ -1621,13 +1709,19 @@ class LoadBalancer implements ILoadBalancer {
 	}
 
 	public function setDomainPrefix( $prefix ) {
-		if ( $this->mConns['foreignUsed'] ) {
-			// Do not switch connections to explicit foreign domains unless marked as free
-			$domains = [];
-			foreach ( $this->mConns['foreignUsed'] as $i => $connsByDomain ) {
-				$domains = array_merge( $domains, array_keys( $connsByDomain ) );
+		// Find connections to explicit foreign domains still marked as in-use...
+		$domainsInUse = [];
+		$this->forEachOpenConnection( function ( IDatabase $conn ) use ( &$domainsInUse ) {
+			// Once reuseConnection() is called on a handle, its reference count goes from 1 to 0.
+			// Until then, it is still in use by the caller (explicitly or via DBConnRef scope).
+			if ( $conn->getLBInfo( 'foreignPoolRefCount' ) > 0 ) {
+				$domainsInUse[] = $conn->getDomainID();
 			}
-			$domains = implode( ', ', $domains );
+		} );
+
+		// Do not switch connections to explicit foreign domains unless marked as safe
+		if ( $domainsInUse ) {
+			$domains = implode( ', ', $domainsInUse );
 			throw new DBUnexpectedError( null,
 				"Foreign domain connections are still in use ($domains)." );
 		}