Database cluster connection, tracking, load balancing, and transaction manager interface. More...

Inheritance diagram for Wikimedia\Rdbms\ILoadBalancer:

Public Member Functions
	__construct (array $params)
	Construct a manager of IDatabase connection objects. More...

	allowLagged ( $mode=null)
	Disables/enables lag checks. More...

	approveMasterChanges (array $options, $fname, $owner=null)
	Perform all pre-commit checks for things like replication safety. More...

	beginMasterChanges ( $fname=__METHOD__, $owner=null)
	Flush any master transaction snapshots and set DBO_TRX (if DBO_DEFAULT is set) More...

	closeAll ( $fname=__METHOD__, $owner=null)
	Close all open connections. More...

	closeConnection (IDatabase $conn)
	Close a connection. More...

	commitAll ( $fname=__METHOD__, $owner=null)
	Commit transactions on all open connections. More...

	commitMasterChanges ( $fname=__METHOD__, $owner=null)
	Issue COMMIT on all open master connections to flush changes and view snapshots. More...

	disable ( $fname=__METHOD__, $owner=null)
	Close all connections and disable this load balancer. More...

	finalizeMasterChanges ( $fname=__METHOD__, $owner=null)
	Run pre-commit callbacks and defer execution of post-commit callbacks. More...

	flushMasterSnapshots ( $fname=__METHOD__, $owner=null)
	Commit all master DB transactions so as to flush any REPEATABLE-READ or SSI snapshots. More...

	flushReplicaSnapshots ( $fname=__METHOD__, $owner=null)
	Commit all replica DB transactions so as to flush any REPEATABLE-READ or SSI snapshots. More...

	forEachOpenConnection ( $callback, array $params=[])
	Call a function with each open connection object. More...

	forEachOpenMasterConnection ( $callback, array $params=[])
	Call a function with each open connection object to a master. More...

	forEachOpenReplicaConnection ( $callback, array $params=[])
	Call a function with each open replica DB connection object. More...

	getAnyOpenConnection ( $i, $flags=0)
	Get any open connection to a given server index, local or foreign. More...

	getConnection ( $i, $groups=[], $domain=false, $flags=0)
	Get a live handle for a real or virtual (DB_MASTER/DB_REPLICA) server index. More...

	getConnectionRef ( $i, $groups=[], $domain=false, $flags=0)
	Get a live database handle reference for a real or virtual (DB_MASTER/DB_REPLICA) server index. More...

	getLaggedReplicaMode ( $domain=false)

	getLagTimes ( $domain=false)
	Get an estimate of replication lag (in seconds) for each server. More...

	getLazyConnectionRef ( $i, $groups=[], $domain=false, $flags=0)
	Get a database handle reference for a real or virtual (DB_MASTER/DB_REPLICA) server index. More...

	getLocalDomainID ()
	Get the local (and default) database domain ID of connection handles. More...

	getMaintenanceConnectionRef ( $i, $groups=[], $domain=false, $flags=0)
	Get a live database handle for a real or virtual (DB_MASTER/DB_REPLICA) server index that can be used for data migrations and schema changes. More...

	getMasterPos ()
	Get the current master replication position. More...

	getMaxLag ( $domain=false)
	Get the hostname and lag time of the most-lagged replica server. More...

	getReaderIndex ( $group=false, $domain=false)
	Get the server index of the reader connection for a given group. More...

	getReadOnlyReason ( $domain=false)

	getReplicaResumePos ()
	Get the highest DB replication position for chronology control purposes. More...

	getServerAttributes ( $i)

	getServerConnection ( $i, $domain, $flags=0)
	Get a live handle for a server index. More...

	getServerCount ()
	Get the number of servers defined in configuration. More...

	getServerInfo ( $i)
	Return the server info structure for a given index or false if the index is invalid. More...

	getServerName ( $i)
	Get the host name or IP address of the server with the specified index. More...

	getServerType ( $i)
	Get DB type of the server with the specified index. More...

	getWriterIndex ()
	Get the server index of the master server. More...

	hasMasterChanges ()
	Whether there are pending changes or callbacks in a transaction by this thread. More...

	hasMasterConnection ()

	hasOrMadeRecentMasterChanges ( $age=null)
	Check if this load balancer object had any recent or still pending writes issued against it by this PHP thread. More...

	hasReplicaServers ()
	Whether there are any replica servers configured. More...

	hasStreamingReplicaServers ()
	Whether any replica servers use streaming replication from the master server. More...

	laggedReplicaUsed ()
	Checks whether the database for generic connections this request was both: More...

	lastMasterChangeTimestamp ()
	Get the timestamp of the latest write query done by this thread. More...

	pendingMasterChangeCallers ()
	Get the list of callers that have pending master changes. More...

	pingAll ()

	redefineLocalDomain ( $domain)
	Close all connection and redefine the local domain for testing or schema creation. More...

	resolveDomainID ( $domain)

	reuseConnection (IDatabase $conn)
	Mark a live handle as being available for reuse under a different database domain. More...

	rollbackMasterChanges ( $fname=__METHOD__, $owner=null)
	Issue ROLLBACK only on master, only if queries were done on connection. More...

	runMasterTransactionIdleCallbacks ( $fname=__METHOD__, $owner=null)
	Consume and run all pending post-COMMIT/ROLLBACK callbacks and commit dangling transactions. More...

	runMasterTransactionListenerCallbacks ( $fname=__METHOD__, $owner=null)
	Run all recurring post-COMMIT/ROLLBACK listener callbacks. More...

	setIndexAliases (array $aliases)
	Convert certain index names to alternative names before querying the DB. More...

	setLocalDomainPrefix ( $prefix)
	Set a new table prefix for the existing local domain ID for testing. More...

	setTableAliases (array $aliases)
	Make certain table names use their own database, schema, and table prefix when passed into SQL queries pre-escaped and without a qualified database name. More...

	setTempTablesOnlyMode ( $value, $domain)
	Indicate whether the tables on this domain are only temporary tables for testing. More...

	setTransactionListener ( $name, callable $callback=null)
	Set a callback via IDatabase::setTransactionListener() on all current and future master connections of this load balancer. More...

	waitFor ( $pos)
	Set the master position to reach before the next generic group DB handle query. More...

	waitForAll ( $pos, $timeout=null)
	Set the master wait position and wait for ALL replica DBs to catch up to it. More...

	waitForMasterPos (IDatabase $conn, $pos=false, $timeout=10)
	Wait for a replica DB to reach a specified master position. More...

	waitForOne ( $pos, $timeout=null)
	Set the master wait position and wait for a generic replica DB to catch up to it. More...

Detailed Description

Database cluster connection, tracking, load balancing, and transaction manager interface.

A "cluster" is considered to be one master database and zero or more replica databases. Typically, the replica DBs replicate from the master asynchronously. The first node in the "servers" configuration array is always considered the "master". However, this class can still be used when all or some of the "replica" DBs are multi-master peers of the master or even when all the DBs are non-replicating clones of each other holding read-only data. Thus, the role of "master" is in some cases merely nominal.

By default, each DB server uses DBO_DEFAULT for its 'flags' setting, unless explicitly set otherwise in configuration. DBO_DEFAULT behavior depends on whether 'cliMode' is set:

In CLI mode, the flag has no effect with regards to LoadBalancer.
In non-CLI mode, the flag causes implicit transactions to be used; the first query on a database starts a transaction on that database. The transactions are meant to remain pending until either commitMasterChanges() or rollbackMasterChanges() is called. The application must have some point where it calls commitMasterChanges() near the end of the PHP request. Every iteration of beginMasterChanges()/commitMasterChanges() is called a "transaction round". Rounds are useful on the master DB connections because they make single-DB (and by and large multi-DB) updates in web requests all-or-nothing. Also, transactions on replica DBs are useful when REPEATABLE-READ or SERIALIZABLE isolation is used because all foriegn keys and constraints hold across separate queries in the DB transaction since the data appears within a consistent point-in-time snapshot.

The typical caller will use LoadBalancer::getConnection( DB_* ) to yield a live database connection handle. The choice of which DB server to use is based on pre-defined loads for weighted random selection, adjustments thereof by LoadMonitor, and the amount of replication lag on each DB server. Lag checks might cause problems in certain setups, so they should be tuned in the server configuration maps as follows:

Master + N Replica(s): set 'max lag' to an appropriate threshold for avoiding any database lagged by this much or more. If all DBs are this lagged, then the load balancer considers the cluster to be read-only.
Galera Cluster: Seconds_Behind_Master will be 0, so there probably is nothing to tune. Note that lag is still possible depending on how wsrep-sync-wait is set server-side.
Read-only archive clones: set 'is static' in the server configuration maps. This will treat all such DBs as having 0 lag.
Externally updated dataset clones: set 'is static' in the server configuration maps. This will treat all such DBs as having 0 lag.
SQL load balancing proxy: any proxy should handle lag checks on its own, so the 'max lag' parameter should probably be set to INF in the server configuration maps. This will make the load balancer ignore whatever it detects as the lag of the logical replica is (which would probably just randomly bounce around).

If using a SQL proxy service, it would probably be best to have two proxy hosts for the load balancer to talk to. One would be the 'host' of the master server entry and another for the (logical) replica server entry. The proxy could map the load balancer's "replica" DB to any number of physical replica DBs.

Since: 1.28

Definition at line 81 of file ILoadBalancer.php.

Constructor & Destructor Documentation

◆ __construct()

Wikimedia\Rdbms\ILoadBalancer::__construct ( array $params )

Construct a manager of IDatabase connection objects.

Parameters

array

$params

Parameter map with keys:

servers : List of server info structures
localDomain: A DatabaseDomain or domain ID string
loadMonitor : Name of a class used to fetch server lag and load
readOnlyReason : Reason the master DB is read-only if so [optional]
waitTimeout : Maximum time to wait for replicas for consistency [optional]
maxLag: Try to avoid DB replicas with lag above this many seconds [optional]
srvCache : BagOStuff object for server cache [optional]
wanCache : WANObjectCache object [optional]
chronologyCallback: Callback to run before the first connection attempt [optional]
defaultGroup: Default query group; the generic group if not specified [optional]
hostname : The name of the current server [optional]
cliMode: Whether the execution context is a CLI script [optional]
profiler : Class name or instance with profileIn()/profileOut() methods [optional]
trxProfiler: TransactionProfiler instance [optional]
replLogger: PSR-3 logger instance [optional]
connLogger: PSR-3 logger instance [optional]
queryLogger: PSR-3 logger instance [optional]
perfLogger: PSR-3 logger instance [optional]
errorLogger : Callback that takes an Exception and logs it [optional]
deprecationLogger: Callback to log a deprecation warning [optional]
roundStage: STAGE_POSTCOMMIT_* class constant; for internal use [optional]
ownerId: integer ID of an LBFactory instance that manages this instance [optional]

Exceptions

InvalidArgumentException

Implemented in Wikimedia\Rdbms\LoadBalancer, and Wikimedia\Rdbms\LoadBalancerSingle.

Member Function Documentation

◆ allowLagged()

Wikimedia\Rdbms\ILoadBalancer::allowLagged ( $mode = null )

Disables/enables lag checks.

Parameters

null | bool $mode

Returns: bool

Implemented in Wikimedia\Rdbms\LoadBalancer.

◆ approveMasterChanges()

Wikimedia\Rdbms\ILoadBalancer::approveMasterChanges	(	array	$options,
			$fname,
			$owner = `null`
	)

Perform all pre-commit checks for things like replication safety.

Use this only for mutli-database commits

Parameters

array	$options	Includes: maxWriteDuration : max write query duration time in seconds
string	$fname	Caller name
int \| null	$owner	ID of the calling instance (e.g. the LBFactory ID)

Exceptions

DBTransactionError

Implemented in Wikimedia\Rdbms\LoadBalancer.

◆ beginMasterChanges()

Wikimedia\Rdbms\ILoadBalancer::beginMasterChanges	(	$fname = `__METHOD__`,
		$owner = `null`
	)

Flush any master transaction snapshots and set DBO_TRX (if DBO_DEFAULT is set)

The DBO_TRX setting will be reverted to the default in each of these methods:

commitMasterChanges()
rollbackMasterChanges()
commitAll() This allows for custom transaction rounds from any outer transaction scope.

Parameters

string	$fname	Caller name
int \| null	$owner	ID of the calling instance (e.g. the LBFactory ID)

Exceptions

DBExpectedError

Implemented in Wikimedia\Rdbms\LoadBalancer.

Referenced by Wikimedia\Rdbms\LBFactory\initLoadBalancer().

◆ closeAll()

Wikimedia\Rdbms\ILoadBalancer::closeAll	(	$fname = `__METHOD__`,
		$owner = `null`
	)

Close all open connections.

Parameters

string	$fname	Caller name
int \| null	$owner	ID of the calling instance (e.g. the LBFactory ID)

Implemented in Wikimedia\Rdbms\LoadBalancer.

◆ closeConnection()

Wikimedia\Rdbms\ILoadBalancer::closeConnection ( IDatabase $conn )

Close a connection.

Using this function makes sure the LoadBalancer knows the connection is closed. If you use $conn->close() directly, the load balancer won't update its state.

Parameters

IDatabase $conn

Implemented in Wikimedia\Rdbms\LoadBalancer.

◆ commitAll()

Wikimedia\Rdbms\ILoadBalancer::commitAll	(	$fname = `__METHOD__`,
		$owner = `null`
	)

Commit transactions on all open connections.

Parameters

string	$fname	Caller name
int \| null	$owner	ID of the calling instance (e.g. the LBFactory ID)

Exceptions

DBExpectedError

Implemented in Wikimedia\Rdbms\LoadBalancer.

◆ commitMasterChanges()

Wikimedia\Rdbms\ILoadBalancer::commitMasterChanges	(	$fname = `__METHOD__`,
		$owner = `null`
	)

Issue COMMIT on all open master connections to flush changes and view snapshots.

Parameters

string	$fname	Caller name
int \| null	$owner	ID of the calling instance (e.g. the LBFactory ID)

Exceptions

DBExpectedError

Implemented in Wikimedia\Rdbms\LoadBalancer.

◆ disable()

Wikimedia\Rdbms\ILoadBalancer::disable	(	$fname = `__METHOD__`,
		$owner = `null`
	)

Close all connections and disable this load balancer.

Any attempt to open a new connection will result in a DBAccessError.

Parameters

string	$fname	Caller name
int \| null	$owner	ID of the calling instance (e.g. the LBFactory ID)

Implemented in Wikimedia\Rdbms\LoadBalancer.

◆ finalizeMasterChanges()

Wikimedia\Rdbms\ILoadBalancer::finalizeMasterChanges	(	$fname = `__METHOD__`,
		$owner = `null`
	)

Run pre-commit callbacks and defer execution of post-commit callbacks.

Use this only for mutli-database commits

Parameters

string	$fname	Caller name
int \| null	$owner	ID of the calling instance (e.g. the LBFactory ID)

Returns: int Number of pre-commit callbacks run (since 1.32)

Implemented in Wikimedia\Rdbms\LoadBalancer.

Referenced by Wikimedia\Rdbms\LBFactory\commitMasterChanges().

◆ flushMasterSnapshots()

Wikimedia\Rdbms\ILoadBalancer::flushMasterSnapshots	(	$fname = `__METHOD__`,
		$owner = `null`
	)

Commit all master DB transactions so as to flush any REPEATABLE-READ or SSI snapshots.

An error will be thrown if a connection has pending writes or callbacks

Parameters

string	$fname	Caller name
int \| null	$owner	ID of the calling instance (e.g. the LBFactory ID)

Implemented in Wikimedia\Rdbms\LoadBalancer.

◆ flushReplicaSnapshots()

Wikimedia\Rdbms\ILoadBalancer::flushReplicaSnapshots	(	$fname = `__METHOD__`,
		$owner = `null`
	)

Commit all replica DB transactions so as to flush any REPEATABLE-READ or SSI snapshots.

Parameters

string	$fname	Caller name
int \| null	$owner	ID of the calling instance (e.g. the LBFactory ID)

Implemented in Wikimedia\Rdbms\LoadBalancer.

◆ forEachOpenConnection()

Wikimedia\Rdbms\ILoadBalancer::forEachOpenConnection	(		$callback,
		array	$params = `[]`
	)

Call a function with each open connection object.

Parameters

callable	$callback
array	$params

Implemented in Wikimedia\Rdbms\LoadBalancer.

◆ forEachOpenMasterConnection()

Wikimedia\Rdbms\ILoadBalancer::forEachOpenMasterConnection	(		$callback,
		array	$params = `[]`
	)

Call a function with each open connection object to a master.

Parameters

callable	$callback
array	$params

Implemented in Wikimedia\Rdbms\LoadBalancer.

◆ forEachOpenReplicaConnection()

Wikimedia\Rdbms\ILoadBalancer::forEachOpenReplicaConnection	(		$callback,
		array	$params = `[]`
	)

Call a function with each open replica DB connection object.

Parameters

callable	$callback
array	$params

Implemented in Wikimedia\Rdbms\LoadBalancer.

◆ getAnyOpenConnection()

Wikimedia\Rdbms\ILoadBalancer::getAnyOpenConnection	(	$i,
		$flags = `0`
	)

Get any open connection to a given server index, local or foreign.

Use CONN_TRX_AUTOCOMMIT to only look for connections opened with that flag. Avoid the use of transaction methods like IDatabase::begin() or IDatabase::startAtomic() on any such connections.

Parameters

int	$i	Server index or DB_MASTER/DB_REPLICA
int	$flags	Bitfield of CONN_* class constants

Returns: Database|bool False if no such connection is open

Implemented in Wikimedia\Rdbms\LoadBalancer.

◆ getConnection()

Wikimedia\Rdbms\ILoadBalancer::getConnection	(	$i,
		$groups = `[]`,
		$domain = `false`,
		$flags = `0`
	)

Get a live handle for a real or virtual (DB_MASTER/DB_REPLICA) server index.

The server index, $i, can be one of the following:

DB_REPLICA: a server index will be selected by the load balancer based on read weight, connectivity, and replication lag. Note that the master server might be configured with read weight. If $groups is empty then it means "the generic group", in which case all servers defined with read weight will be considered. Additional query groups can be configured, having their own list of server indexes and read weights. If a query group list is provided in $groups, then each recognized group will be tried, left-to-right, until server index selection succeeds or all groups have been tried, in which case the generic group will be tried.
DB_MASTER: the master server index will be used; the same as getWriterIndex(). The value of $groups should be [] when using this server index.
Specific server index: a positive integer can be provided to use the server with that index. An error will be thrown in no such server index is recognized. This server selection method is usually only useful for internal load balancing logic. The value of $groups should be [] when using a specific server index.

Handles acquired by this method, getConnectionRef(), getLazyConnectionRef(), and getMaintenanceConnectionRef() use the same set of shared connection pools. Callers that get a local DB domain handle for the same server will share one handle for all of those callers using CONN_TRX_AUTOCOMMIT (via $flags) and one handle for all of those callers not using CONN_TRX_AUTOCOMMIT. Callers that get a foreign DB domain handle (via $domain) will share any handle that has the right CONN_TRX_AUTOCOMMIT mode and is already on the right DB domain. Otherwise, one of the "free for reuse" handles will be claimed or a new handle will be made if there are none.

Handle sharing is particularly useful when callers get local DB domain (the default), transaction round aware (the default), DB_MASTER handles. All such callers will operate within a single database transaction as a consequence. Handle sharing is also useful when callers get local DB domain (the default), transaction round aware (the default), samely query grouped (the default), DB_REPLICA handles. All such callers will operate within a single database transaction as a consequence.

Calling functions that use $domain must call reuseConnection() once the last query of the function is executed. This lets the load balancer share this handle with other callers requesting connections on different database domains.

Use CONN_TRX_AUTOCOMMIT to use a separate pool of only auto-commit handles. This flag is ignored for databases with ATTR_DB_LEVEL_LOCKING (e.g. sqlite) in order to avoid deadlocks. getServerAttributes() can be used to check such attributes beforehand. Avoid using IDatabase::begin() and IDatabase::commit() on such handles. If it is not possible to avoid using methods like IDatabase::startAtomic() and IDatabase::endAtomic(), callers should at least make sure that the atomic sections are closed on failure via try/catch and IDatabase::cancelAtomic().

See also: ILoadBalancer::reuseConnection(); ILoadBalancer::getServerAttributes()

Parameters

int	$i	Server index (overrides $groups) or DB_MASTER/DB_REPLICA
string[] \| string	$groups	Query group(s) in preference order; [] for the default group
string \| bool	$domain	DB domain ID or false for the local domain
int	$flags	Bitfield of CONN_* class constants

Note: This method throws DBAccessError if ILoadBalancer::disable() was called

Returns: IDatabase|bool This returns false on failure if CONN_SILENCE_ERRORS is set

Exceptions

DBError	If no live handle can be obtained and CONN_SILENCE_ERRORS is not set
DBAccessError	If disable() was previously called
InvalidArgumentException

Implemented in Wikimedia\Rdbms\LoadBalancer.

◆ getConnectionRef()

Wikimedia\Rdbms\ILoadBalancer::getConnectionRef	(	$i,
		$groups = `[]`,
		$domain = `false`,
		$flags = `0`
	)

Get a live database handle reference for a real or virtual (DB_MASTER/DB_REPLICA) server index.

The CONN_TRX_AUTOCOMMIT flag is ignored for databases with ATTR_DB_LEVEL_LOCKING (e.g. sqlite) in order to avoid deadlocks. getServerAttributes() can be used to check such flags beforehand. Avoid the use of begin() or startAtomic() on any CONN_TRX_AUTOCOMMIT connections.

See also: ILoadBalancer::getConnection() for parameter information

Parameters

int	$i	Server index or DB_MASTER/DB_REPLICA
string[] \| string	$groups	Query group(s) in preference order; [] for the default group
string \| bool	$domain	DB domain ID or false for the local domain
int	$flags	Bitfield of CONN_* class constants (e.g. CONN_TRX_AUTOCOMMIT)

Returns: DBConnRef

Implemented in Wikimedia\Rdbms\LoadBalancer.

Referenced by ImportableOldRevisionImporter\import().

◆ getLaggedReplicaMode()

Wikimedia\Rdbms\ILoadBalancer::getLaggedReplicaMode ( $domain = false )

Note: This method will trigger a DB connection if not yet done

Parameters

string | bool $domain DB domain ID or false for the local domain

Returns: bool Whether the database for generic connections this request is highly "lagged"

Implemented in Wikimedia\Rdbms\LoadBalancer.

◆ getLagTimes()

Wikimedia\Rdbms\ILoadBalancer::getLagTimes ( $domain = false )

Get an estimate of replication lag (in seconds) for each server.

Results are cached for a short time in memcached/process cache

Values may be "false" if replication is too broken to estimate

Parameters

string | bool $domain

Returns: int[] Map of (server index => float|int|bool)

Implemented in Wikimedia\Rdbms\LoadBalancer.

◆ getLazyConnectionRef()

Wikimedia\Rdbms\ILoadBalancer::getLazyConnectionRef	(	$i,
		$groups = `[]`,
		$domain = `false`,
		$flags = `0`
	)

Get a database handle reference for a real or virtual (DB_MASTER/DB_REPLICA) server index.

The handle's methods simply proxy to those of an underlying IDatabase handle which takes care of the actual connection and query logic.

The CONN_TRX_AUTOCOMMIT flag is ignored for databases with ATTR_DB_LEVEL_LOCKING (e.g. sqlite) in order to avoid deadlocks. getServerAttributes() can be used to check such flags beforehand. Avoid the use of begin() or startAtomic() on any CONN_TRX_AUTOCOMMIT connections.

See also: ILoadBalancer::getConnection() for parameter information

Parameters

int	$i	Server index or DB_MASTER/DB_REPLICA
string[] \| string	$groups	Query group(s) in preference order; [] for the default group
string \| bool	$domain	DB domain ID or false for the local domain
int	$flags	Bitfield of CONN_* class constants (e.g. CONN_TRX_AUTOCOMMIT)

Returns: DBConnRef

Implemented in Wikimedia\Rdbms\LoadBalancer.

Referenced by SearchDatabase\__construct().

◆ getLocalDomainID()

Wikimedia\Rdbms\ILoadBalancer::getLocalDomainID ( )

Get the local (and default) database domain ID of connection handles.

See also: DatabaseDomain

Returns: string Database domain ID; this specifies DB name, schema, and table prefix

Since: 1.31

Implemented in Wikimedia\Rdbms\LoadBalancer.

◆ getMaintenanceConnectionRef()

Wikimedia\Rdbms\ILoadBalancer::getMaintenanceConnectionRef	(	$i,
		$groups = `[]`,
		$domain = `false`,
		$flags = `0`
	)

Get a live database handle for a real or virtual (DB_MASTER/DB_REPLICA) server index that can be used for data migrations and schema changes.

The handle's methods simply proxy to those of an underlying IDatabase handle which takes care of the actual connection and query logic.

The CONN_TRX_AUTOCOMMIT flag is ignored for databases with ATTR_DB_LEVEL_LOCKING (e.g. sqlite) in order to avoid deadlocks. getServerAttributes() can be used to check such flags beforehand. Avoid the use of begin() or startAtomic() on any CONN_TRX_AUTOCOMMIT connections.

See also: ILoadBalancer::getConnection() for parameter information

Parameters

int	$i	Server index or DB_MASTER/DB_REPLICA
string[] \| string	$groups	Query group(s) in preference order; [] for the default group
string \| bool	$domain	DB domain ID or false for the local domain
int	$flags	Bitfield of CONN_* class constants (e.g. CONN_TRX_AUTOCOMMIT)

Returns: MaintainableDBConnRef

Implemented in Wikimedia\Rdbms\LoadBalancer.

◆ getMasterPos()

Wikimedia\Rdbms\ILoadBalancer::getMasterPos ( )

Get the current master replication position.

Returns: DBMasterPos|bool Returns false if not applicable

Exceptions

DBError

Implemented in Wikimedia\Rdbms\LoadBalancer.

◆ getMaxLag()

Wikimedia\Rdbms\ILoadBalancer::getMaxLag ( $domain = false )

Get the hostname and lag time of the most-lagged replica server.

This is useful for maintenance scripts that need to throttle their updates. May attempt to open connections to replica DBs on the default DB. If there is no lag, the maximum lag will be reported as -1.

Parameters

bool | string $domain Domain ID or false for the default database

Returns: array ( host, max lag, index of max lagged host )

Implemented in Wikimedia\Rdbms\LoadBalancer.

◆ getReaderIndex()

Wikimedia\Rdbms\ILoadBalancer::getReaderIndex	(	$group = `false`,
		$domain = `false`
	)

Get the server index of the reader connection for a given group.

This takes into account load ratios and lag times. It should return a consistent index during the life time of the load balancer. This initially checks replica DBs for connectivity to avoid returning an unusable server. This means that connections might be attempted by calling this method (usally one at the most but possibly more). Subsequent calls with the same $group will not need to make new connection attempts since the acquired connection for each group is preserved.

Parameters

string \| bool	$group	Query group or false for the generic group
string \| bool	$domain	DB domain ID or false for the local domain

Returns: int|bool Returns false if no live handle can be obtained

Implemented in Wikimedia\Rdbms\LoadBalancer.

◆ getReadOnlyReason()

Wikimedia\Rdbms\ILoadBalancer::getReadOnlyReason ( $domain = false )

Note: This method may trigger a DB connection if not yet done

Parameters

string | bool $domain DB domain ID or false for the local domain

Returns: string|bool Reason the master is read-only or false if it is not

Implemented in Wikimedia\Rdbms\LoadBalancer.

◆ getReplicaResumePos()

Wikimedia\Rdbms\ILoadBalancer::getReplicaResumePos ( )

Get the highest DB replication position for chronology control purposes.

If there is only a master server then this returns false. If replication is present and correctly configured, then this returns the highest replication position of any server with an open connection. That position can later be passed to waitFor() on a new load balancer instance to make sure that queries on the new connections see data at least as up-to-date as queries (prior to this method call) on the old connections.

This can be useful for implementing session consistency, where the session will be resumed accross multiple HTTP requests or CLI script instances.

Returns: DBMasterPos|bool Replication position or false if not applicable

Since: 1.34

Implemented in Wikimedia\Rdbms\LoadBalancer.

Referenced by Wikimedia\Rdbms\ChronologyProtector\storeSessionReplicationPosition().

◆ getServerAttributes()

Wikimedia\Rdbms\ILoadBalancer::getServerAttributes ( $i )

Parameters

int $i Server index

Returns: array (Database::ATTRIBUTE_* constant => value) for all such constants

Since: 1.31

Implemented in Wikimedia\Rdbms\LoadBalancer.

◆ getServerConnection()

Wikimedia\Rdbms\ILoadBalancer::getServerConnection	(	$i,
		$domain,
		$flags = `0`
	)

Get a live handle for a server index.

This is a simpler version of getConnection() that does not accept virtual server indexes (e.g. DB_MASTER/DB_REPLICA), does not assure that master DB handles have read-only mode when there is high replication lag, and can only trigger attempts to connect to a single server (the one with the specified server index).

See also: ILoadBalancer::getConnection()

Parameters

int	$i	Specific server index
string	$domain	Resolved DB domain
int	$flags	Bitfield of class CONN_* constants

Returns: IDatabase|bool

Implemented in Wikimedia\Rdbms\LoadBalancer.

◆ getServerCount()

Wikimedia\Rdbms\ILoadBalancer::getServerCount ( )

Get the number of servers defined in configuration.

Returns: int

Implemented in Wikimedia\Rdbms\LoadBalancer.

◆ getServerInfo()

Wikimedia\Rdbms\ILoadBalancer::getServerInfo ( $i )

Return the server info structure for a given index or false if the index is invalid.

Parameters

int $i

Returns: array|bool

Since: 1.31

Implemented in Wikimedia\Rdbms\LoadBalancer.

◆ getServerName()

Wikimedia\Rdbms\ILoadBalancer::getServerName ( $i )

Get the host name or IP address of the server with the specified index.

Parameters

int $i

Returns: string Readable name if available or IP/host otherwise

Implemented in Wikimedia\Rdbms\LoadBalancer.

Referenced by Wikimedia\Rdbms\ChronologyProtector\applySessionReplicationPosition(), Wikimedia\Rdbms\LBFactory\logIfMultiDbTransaction(), Wikimedia\Rdbms\LBFactory\shutdownChronologyProtector(), and Wikimedia\Rdbms\ChronologyProtector\storeSessionReplicationPosition().

◆ getServerType()

Wikimedia\Rdbms\ILoadBalancer::getServerType ( $i )

Get DB type of the server with the specified index.

Parameters

int $i

Returns: string One of (mysql,postgres,sqlite,...) or "unknown" for bad indexes

Since: 1.30

Implemented in Wikimedia\Rdbms\LoadBalancer.

◆ getWriterIndex()

Wikimedia\Rdbms\ILoadBalancer::getWriterIndex ( )

Get the server index of the master server.

Returns: int

Implemented in Wikimedia\Rdbms\LoadBalancer.

Referenced by Wikimedia\Rdbms\ChronologyProtector\applySessionReplicationPosition(), Wikimedia\Rdbms\LBFactory\logIfMultiDbTransaction(), Wikimedia\Rdbms\LBFactory\shutdownChronologyProtector(), and Wikimedia\Rdbms\ChronologyProtector\storeSessionReplicationPosition().

◆ hasMasterChanges()

Wikimedia\Rdbms\ILoadBalancer::hasMasterChanges ( )

Whether there are pending changes or callbacks in a transaction by this thread.

Returns: bool

Implemented in Wikimedia\Rdbms\LoadBalancer.

Referenced by Wikimedia\Rdbms\LBFactory\hasMasterChanges().

◆ hasMasterConnection()

Wikimedia\Rdbms\ILoadBalancer::hasMasterConnection ( )

Returns: bool Whether a master connection is already open

Implemented in Wikimedia\Rdbms\LoadBalancer.

◆ hasOrMadeRecentMasterChanges()

Wikimedia\Rdbms\ILoadBalancer::hasOrMadeRecentMasterChanges ( $age = null )

Check if this load balancer object had any recent or still pending writes issued against it by this PHP thread.

Parameters

float | null $age How many seconds ago is "recent" [defaults to mWaitTimeout]

Returns: bool

Implemented in Wikimedia\Rdbms\LoadBalancer.

Referenced by Wikimedia\Rdbms\LBFactory\hasOrMadeRecentMasterChanges(), and Wikimedia\Rdbms\ChronologyProtector\storeSessionReplicationPosition().

◆ hasReplicaServers()

Wikimedia\Rdbms\ILoadBalancer::hasReplicaServers ( )

Whether there are any replica servers configured.

This counts both servers using streaming replication from the master server and servers that just have a clone of the static dataset found on the master server

Returns: int

Since: 1.34

Implemented in Wikimedia\Rdbms\LoadBalancer.

◆ hasStreamingReplicaServers()

Wikimedia\Rdbms\ILoadBalancer::hasStreamingReplicaServers ( )

Whether any replica servers use streaming replication from the master server.

Generally this is one less than getServerCount(), though it might otherwise return a lower number if some of the servers are configured with "is static". That flag is used when both the server has no active replication setup and the dataset is either read-only or occasionally updated out-of-band. For example, a script might import a new geographic information dataset each week by writing it to each server and later directing the application to use the new version.

It is possible for some replicas to be configured with "is static" but not others, though it generally should either be set for all or none of the replicas.

If this returns zero, this means that there is generally no reason to execute replication wait logic for session consistency and lag reduction.

Returns: int

Since: 1.34

Implemented in Wikimedia\Rdbms\LoadBalancer.

Referenced by Wikimedia\Rdbms\LBFactory\appendShutdownCPIndexAsQuery(), and Wikimedia\Rdbms\ChronologyProtector\storeSessionReplicationPosition().

◆ laggedReplicaUsed()

Wikimedia\Rdbms\ILoadBalancer::laggedReplicaUsed ( )

Checks whether the database for generic connections this request was both:

a) Already choosen due to a prior connection attempt
b) Considered highly "lagged"

Note: This method will never cause a new DB connection

Returns: bool

Implemented in Wikimedia\Rdbms\LoadBalancer.

Referenced by Wikimedia\Rdbms\LBFactory\laggedReplicaUsed().

◆ lastMasterChangeTimestamp()

Wikimedia\Rdbms\ILoadBalancer::lastMasterChangeTimestamp ( )

Get the timestamp of the latest write query done by this thread.

Returns: float|bool UNIX timestamp or false

Implemented in Wikimedia\Rdbms\LoadBalancer.

◆ pendingMasterChangeCallers()

Wikimedia\Rdbms\ILoadBalancer::pendingMasterChangeCallers ( )

Get the list of callers that have pending master changes.

Returns: string[] List of method names

Implemented in Wikimedia\Rdbms\LoadBalancer.

Referenced by Wikimedia\Rdbms\LBFactory\logIfMultiDbTransaction().

◆ pingAll()

Wikimedia\Rdbms\ILoadBalancer::pingAll ( )

Returns: bool

Implemented in Wikimedia\Rdbms\LoadBalancer.

◆ redefineLocalDomain()

Wikimedia\Rdbms\ILoadBalancer::redefineLocalDomain ( $domain )

Close all connection and redefine the local domain for testing or schema creation.

Parameters

DatabaseDomain | string $domain

Since: 1.33

Implemented in Wikimedia\Rdbms\LoadBalancer.

Referenced by Wikimedia\Rdbms\LBFactory\redefineLocalDomain().

◆ resolveDomainID()

Wikimedia\Rdbms\ILoadBalancer::resolveDomainID ( $domain )

Parameters

DatabaseDomain | string | bool $domain Database domain

Returns: string Value of $domain if it is foreign or the local domain otherwise

Since: 1.32

Implemented in Wikimedia\Rdbms\LoadBalancer.

◆ reuseConnection()

Wikimedia\Rdbms\ILoadBalancer::reuseConnection ( IDatabase $conn )

Mark a live handle as being available for reuse under a different database domain.

This mechanism is reference-counted, and must be called the same number of times as getConnection() to work. Never call this on handles acquired via getConnectionRef(), getLazyConnectionRef(), and getMaintenanceConnectionRef(), as they already manage the logic of calling this method when they fall out of scope in PHP.

See also: ILoadBalancer::getConnection()

Parameters

IDatabase $conn

Exceptions

LogicException

Implemented in Wikimedia\Rdbms\LoadBalancer.

◆ rollbackMasterChanges()

Wikimedia\Rdbms\ILoadBalancer::rollbackMasterChanges	(	$fname = `__METHOD__`,
		$owner = `null`
	)

Issue ROLLBACK only on master, only if queries were done on connection.

Parameters

string	$fname	Caller name
int \| null	$owner	ID of the calling instance (e.g. the LBFactory ID)

Exceptions

DBExpectedError

Implemented in Wikimedia\Rdbms\LoadBalancer.

◆ runMasterTransactionIdleCallbacks()

Wikimedia\Rdbms\ILoadBalancer::runMasterTransactionIdleCallbacks	(	$fname = `__METHOD__`,
		$owner = `null`
	)

Consume and run all pending post-COMMIT/ROLLBACK callbacks and commit dangling transactions.

Parameters

string	$fname	Caller name
int \| null	$owner	ID of the calling instance (e.g. the LBFactory ID)

Returns: Exception|null The first exception or null if there were none

Implemented in Wikimedia\Rdbms\LoadBalancer.

Referenced by Wikimedia\Rdbms\LBFactory\executePostTransactionCallbacks().

◆ runMasterTransactionListenerCallbacks()

Wikimedia\Rdbms\ILoadBalancer::runMasterTransactionListenerCallbacks	(	$fname = `__METHOD__`,
		$owner = `null`
	)

Run all recurring post-COMMIT/ROLLBACK listener callbacks.

Parameters

string	$fname	Caller name
int \| null	$owner	ID of the calling instance (e.g. the LBFactory ID)

Returns: Exception|null The first exception or null if there were none

Implemented in Wikimedia\Rdbms\LoadBalancer.

Referenced by Wikimedia\Rdbms\LBFactory\executePostTransactionCallbacks().

◆ setIndexAliases()

Wikimedia\Rdbms\ILoadBalancer::setIndexAliases ( array $aliases )

Convert certain index names to alternative names before querying the DB.

Note that this applies to indexes regardless of the table they belong to.

This can be employed when an index was renamed X => Y in code, but the new Y-named indexes were not yet built on all DBs. After all the Y-named ones are added by the DBA, the aliases can be removed, and then the old X-named indexes dropped.

Parameters

string[] $aliases

Since: 1.31

Implemented in Wikimedia\Rdbms\LoadBalancer.

Referenced by Wikimedia\Rdbms\LBFactory\initLoadBalancer().

◆ setLocalDomainPrefix()

Wikimedia\Rdbms\ILoadBalancer::setLocalDomainPrefix ( $prefix )

Set a new table prefix for the existing local domain ID for testing.

Parameters

string $prefix

Since: 1.33

Implemented in Wikimedia\Rdbms\LoadBalancer.

Referenced by Wikimedia\Rdbms\LBFactory\setLocalDomainPrefix().

◆ setTableAliases()

Wikimedia\Rdbms\ILoadBalancer::setTableAliases ( array $aliases )

Make certain table names use their own database, schema, and table prefix when passed into SQL queries pre-escaped and without a qualified database name.

For example, "user" can be converted to "myschema.mydbname.user" for convenience. Appearances like user, somedb.user, somedb.someschema.user will used literally.

Calling this twice will completely clear any old table aliases. Also, note that callers are responsible for making sure the schemas and databases actually exist.

Parameters

array[] $aliases Map of (table => (dbname, schema, prefix) map)

Implemented in Wikimedia\Rdbms\LoadBalancer.

Referenced by Wikimedia\Rdbms\LBFactory\initLoadBalancer().

◆ setTempTablesOnlyMode()

Wikimedia\Rdbms\ILoadBalancer::setTempTablesOnlyMode	(	$value,
		$domain
	)

Indicate whether the tables on this domain are only temporary tables for testing.

In "temporary tables mode", the ILoadBalancer::CONN_TRX_AUTOCOMMIT flag is ignored

Parameters

bool	$value
string	$domain

Returns: bool Whether "temporary tables mode" was active

Since: 1.34

Implemented in Wikimedia\Rdbms\LoadBalancer.

◆ setTransactionListener()

Wikimedia\Rdbms\ILoadBalancer::setTransactionListener	(		$name,
		callable	$callback = `null`
	)

Set a callback via IDatabase::setTransactionListener() on all current and future master connections of this load balancer.

Parameters

string	$name	Callback name
callable \| null	$callback

Implemented in Wikimedia\Rdbms\LoadBalancer.

◆ waitFor()

Wikimedia\Rdbms\ILoadBalancer::waitFor ( $pos )

Set the master position to reach before the next generic group DB handle query.

If a generic replica DB connection is already open then this immediately waits for that DB to catch up to the specified replication position. Otherwise, it will do so once such a connection is opened.

If a timeout happens when waiting, then getLaggedReplicaMode()/laggedReplicaUsed() will return true.

Parameters

DBMasterPos | bool $pos Master position or false

Implemented in Wikimedia\Rdbms\LoadBalancer.

Referenced by Wikimedia\Rdbms\ChronologyProtector\applySessionReplicationPosition().

◆ waitForAll()

Wikimedia\Rdbms\ILoadBalancer::waitForAll	(	$pos,
		$timeout = `null`
	)

Set the master wait position and wait for ALL replica DBs to catch up to it.

Parameters

DBMasterPos \| bool	$pos	Master position or false
int \| null	$timeout	Max seconds to wait; default is mWaitTimeout

Returns: bool Success (able to connect and no timeouts reached)

Implemented in Wikimedia\Rdbms\LoadBalancer.

Referenced by Wikimedia\Rdbms\LBFactory\shutdownChronologyProtector().

◆ waitForMasterPos()

Wikimedia\Rdbms\ILoadBalancer::waitForMasterPos	(	IDatabase	$conn,
			$pos = `false`,
			$timeout = `10`
	)

Wait for a replica DB to reach a specified master position.

If $conn is not a replica server connection, then this will return true. Otherwise, if $pos is not provided, this will connect to the master server to get an accurate position.

Parameters

IDatabase	$conn	Replica DB
DBMasterPos \| bool	$pos	Master position; default: current position
int	$timeout	Timeout in seconds [optional]

Returns: bool Success

Since: 1.34

Implemented in Wikimedia\Rdbms\LoadBalancer.

◆ waitForOne()

Wikimedia\Rdbms\ILoadBalancer::waitForOne	(	$pos,
		$timeout = `null`
	)

Set the master wait position and wait for a generic replica DB to catch up to it.

This can be used a faster proxy for waitForAll()

Parameters

DBMasterPos \| bool	$pos	Master position or false
int \| null	$timeout	Max seconds to wait; default is mWaitTimeout

Returns: bool Success (able to connect and no timeouts reached)

Implemented in Wikimedia\Rdbms\LoadBalancer.

The documentation for this interface was generated from the following file:

includes/libs/rdbms/loadbalancer/ILoadBalancer.php

Public Member Functions

Detailed Description

Constructor & Destructor Documentation

◆ __construct()

Member Function Documentation

◆ allowLagged()

◆ approveMasterChanges()

◆ beginMasterChanges()

◆ closeAll()

◆ closeConnection()

◆ commitAll()

◆ commitMasterChanges()

◆ disable()

◆ finalizeMasterChanges()

◆ flushMasterSnapshots()

◆ flushReplicaSnapshots()

◆ forEachOpenConnection()

◆ forEachOpenMasterConnection()

◆ forEachOpenReplicaConnection()

◆ getAnyOpenConnection()

◆ getConnection()

◆ getConnectionRef()

◆ getLaggedReplicaMode()

◆ getLagTimes()

◆ getLazyConnectionRef()

◆ getLocalDomainID()

◆ getMaintenanceConnectionRef()

◆ getMasterPos()

◆ getMaxLag()

◆ getReaderIndex()

◆ getReadOnlyReason()

◆ getReplicaResumePos()

◆ getServerAttributes()

◆ getServerConnection()

◆ getServerCount()

◆ getServerInfo()

◆ getServerName()

◆ getServerType()

◆ getWriterIndex()

◆ hasMasterChanges()

◆ hasMasterConnection()

◆ hasOrMadeRecentMasterChanges()

◆ hasReplicaServers()

◆ hasStreamingReplicaServers()

◆ laggedReplicaUsed()

◆ lastMasterChangeTimestamp()

◆ pendingMasterChangeCallers()

◆ pingAll()

◆ redefineLocalDomain()

◆ resolveDomainID()

◆ reuseConnection()

◆ rollbackMasterChanges()

◆ runMasterTransactionIdleCallbacks()

◆ runMasterTransactionListenerCallbacks()

◆ setIndexAliases()

◆ setLocalDomainPrefix()

◆ setTableAliases()

◆ setTempTablesOnlyMode()

◆ setTransactionListener()

◆ waitFor()

◆ waitForAll()

◆ waitForMasterPos()

◆ waitForOne()