Create and track the database connections and transactions for a given database cluster. More...

Inheritance diagram for Wikimedia\Rdbms\ILoadBalancer:

[legend]

Public Member Functions
	closeConnection (IDatabase $conn)
	Close a connection.

	explicitTrxActive ()
	Determine whether an explicit transaction is active on any open primary connection.

	getAnyOpenConnection ( $i, $flags=0)
	Get an existing DB handle to the given server index (on any domain)

	getClusterName ()
	Get the logical name of the database cluster.

	getConnection ( $i, $groups=[], $domain=false, $flags=0)
	Get a lazy-connecting database handle for a specific or virtual (DB_PRIMARY/DB_REPLICA) server index.

	getConnectionInternal ( $i, $groups=[], $domain=false, $flags=0)

	getConnectionRef ( $i, $groups=[], $domain=false, $flags=0)

	getLaggedReplicaMode ( $domain=false)

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

	getLazyConnectionRef ( $i, $groups=[], $domain=false, $flags=0)
	Get a lazy-connecting database handle for a server index.

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

	getMaintenanceConnectionRef ( $i, $groups=[], $domain=false, $flags=0)
	Get a DB handle, suitable for migrations and schema changes, for a server index.

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

	getPrimaryPos ()
	Get the current primary replication position.

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

	getReadOnlyReason ( $domain=false)

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

	getServerAttributes ( $i)
	Get basic attributes of the server with the specified index without connecting.

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

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

	getServerInfo ( $i)
	Return the server configuration map for the server with the specified index.

	getServerName ( $i)
	Get the readable name of the server with the specified index.

	getServerType ( $i)
	Get the RDBMS type of the server with the specified index (e.g.

	getWriterIndex ()
	Get the specific server index of the primary server.

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

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

	hasPrimaryConnection ()

	hasReplicaServers ()
	Whether there are any replica servers configured.

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

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

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

	pingAll ()

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

	resolveDomainID ( $domain)

	reuseConnection (IDatabase $conn)

	reuseConnectionInternal (IDatabase $conn)

	setDomainAliases (array $aliases)
	Convert certain database domains to alternative ones.

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

	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.

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

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

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

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

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

Public Attributes
const	CONN_INTENT_WRITABLE = 4
	Caller is requesting the primary DB server for possibly writes.

const	CONN_REFRESH_READ_ONLY = 8
	Bypass and update any server-side read-only mode state cache.

const	CONN_SILENCE_ERRORS = 2
	Return null on connection failure instead of throwing an exception.

const	CONN_TRX_AUTOCOMMIT = 1
	DB handle should have DBO_TRX disabled and the caller will leave it as such.

const	DB_MASTER = self::DB_PRIMARY
	Request a primary, write-enabled DB connection.

const	DB_PRIMARY = -2
	Request a primary, write-enabled DB connection.

const	DB_REPLICA = -1
	Request a replica DB connection.

const	DOMAIN_ANY = ''
	Domain specifier when no specific database needs to be selected.

const	GROUP_GENERIC = ''
	The generic query group.

Detailed Description

Create and track the database connections and transactions for a given database cluster.

This class is a delegate to ILBFactory for a given database cluster (separated for the LBFactoryMulti use case).

A "cluster" is defined as a primary database with zero or more replica databases. Typically, the replica DBs replicate from the primary asynchronously. The first node in the "servers" configuration array is always considered the "primary". However, this class can still be used when all or some of the "replica" DBs are multi-primary peers of the primary or even when all the DBs are non-replicating clones of each other holding read-only data. Thus, the role of "primary" 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 commitPrimaryChanges() or rollbackPrimaryChanges() is called. The application must have some point where it calls commitPrimaryChanges() near the end of the PHP request. Every iteration of beginPrimaryChanges()/commitPrimaryChanges() is called a "transaction round". Rounds are useful on the primary 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 foreign 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 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:

Primary + 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 primary 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 77 of file ILoadBalancer.php.

Member Function Documentation

◆ 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.

◆ explicitTrxActive()

Wikimedia\Rdbms\ILoadBalancer::explicitTrxActive ( )

Determine whether an explicit transaction is active on any open primary connection.

Returns: bool

Since: 1.39

Implemented in Wikimedia\Rdbms\LoadBalancer.

◆ getAnyOpenConnection()

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

Get an existing DB handle to the given server index (on any domain)

Use the CONN_TRX_AUTOCOMMIT flag to only look for connections opened with that flag.

Avoid the use of begin()/commit() and startAtomic()/endAtomic() on any handle returned. This method is intended for internal RDBMS callers that issue queries that do not affect any current transaction.

Access: internal: For use by Rdbms classes only

Parameters

int	$i	Specific or virtual (DB_PRIMARY/DB_REPLICA) server index
int	$flags	Bitfield of CONN_* class constants

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

Implemented in Wikimedia\Rdbms\LoadBalancer.

◆ getClusterName()

Wikimedia\Rdbms\ILoadBalancer::getClusterName ( )

Get the logical name of the database cluster.

This is useful for identifying a cluster or replicated dataset, even when:

The primary server is sometimes swapped with another one
The cluster/dataset is replicated among multiple datacenters, with one "primary" datacenter having the writable primary server and the other datacenters having a read-only replica in the "primary" server slot
The dataset is replicated among multiple datacenters, via circular replication, with each datacenter having its own "primary" server

Returns: string

Since: 1.36

Implemented in Wikimedia\Rdbms\LoadBalancer.

Referenced by Wikimedia\Rdbms\ChronologyProtector\applySessionReplicationPosition(), Wikimedia\Rdbms\ChronologyProtector\getTouched(), and Wikimedia\Rdbms\ChronologyProtector\stageSessionReplicationPosition().

◆ getConnection()

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

Get a lazy-connecting database handle for a specific or virtual (DB_PRIMARY/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 primary 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_PRIMARY: the primary 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.

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_PRIMARY 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.

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

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

Implemented in Wikimedia\Rdbms\LoadBalancer.

◆ getConnectionInternal()

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

Access: internal: Only to be used by DBConnRef

Parameters

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

Returns: IDatabase

Implemented in Wikimedia\Rdbms\LoadBalancer.

◆ getConnectionRef()

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

Deprecated: since 1.39, use ILoadBalancer::getConnection() instead.

Parameters

int	$i	Specific or virtual (DB_PRIMARY/DB_REPLICA) server index
string[] \| string	$groups	Query group(s) in preference order; [] for the default group
string \| false	$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.

◆ getLaggedReplicaMode()

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

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

Parameters

string | false $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 | false $domain

Returns: float[]|int[]|false[] Map of (server index => lag) in order of server index

Implemented in Wikimedia\Rdbms\LoadBalancer.

◆ getLazyConnectionRef()

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

Get a lazy-connecting database handle for a 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.

Deprecated: since 1.38, use ILoadBalancer::getConnectionRef() instead.

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

Parameters

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

Returns: IDatabase

Implemented in Wikimedia\Rdbms\LoadBalancer.

◆ 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 DB handle, suitable for migrations and schema changes, for a server index.

The DBConnRef methods simply proxy an underlying IDatabase object 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	Specific or virtual (DB_PRIMARY/DB_REPLICA) server index
string[] \| string	$groups	Query group(s) in preference order; [] for the default group
string \| false	$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.

◆ getMaxLag()

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

Get the name 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

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

Returns: array{0:string,1:float|int|false,2:int} (host, max lag, index of max lagged host)

Implemented in Wikimedia\Rdbms\LoadBalancer.

◆ getPrimaryPos()

Wikimedia\Rdbms\ILoadBalancer::getPrimaryPos ( )

Get the current primary replication position.

Returns: DBPrimaryPos|false Returns false if not applicable

Exceptions

DBError

Since: 1.37

Implemented in Wikimedia\Rdbms\LoadBalancer.

◆ getReaderIndex()

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

Get the specific 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 (usually 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 \| false	$group	Query group or false for the generic group
string \| false	$domain	DB domain ID or false for the local domain

Returns: int|false Specific server index, or false if no DB 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 | false $domain DB domain ID or false for the local domain

Returns: string|false Reason the primary 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 primary 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 across multiple HTTP requests or CLI script instances.

Returns: DBPrimaryPos|false Replication position or false if not applicable

Since: 1.34

Implemented in Wikimedia\Rdbms\LoadBalancer.

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

◆ getServerAttributes()

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

Get basic attributes of the server with the specified index without connecting.

Parameters

int $i Specific 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 DB handle for a specific server index.

This is an internal utility method for methods like LoadBalancer::getConnectionInternal() and DBConnRef to create the underlying connection to a concrete server.

The following is the responsibility of the caller:

translate any virtual server indexes (DB_PRIMARY/DB_REPLICA) to a real server index.
enforce read-only mode on primary DB handle if there is high replication lag.

See also: ILoadBalancer::getConnection()

Access: internal: Only for use within ILoadBalancer/ILoadMonitor

Parameters

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

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

Exceptions

DBError If no DB handle could be obtained and CONN_SILENCE_ERRORS is not set

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 configuration map for the server with the specified index.

Parameters

int $i Specific server index

Returns: array|false Server configuration map; false if the index is invalid

Since: 1.31

Implemented in Wikimedia\Rdbms\LoadBalancer.

◆ getServerName()

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

Get the readable name of the server with the specified index.

Parameters

int $i Specific server index

Returns: string Readable server name, falling back to the hostname or IP address

Implemented in Wikimedia\Rdbms\LoadBalancer.

Referenced by Wikimedia\Rdbms\ChronologyProtector\applySessionReplicationPosition(), and Wikimedia\Rdbms\ChronologyProtector\stageSessionReplicationPosition().

◆ getServerType()

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

Get the RDBMS type of the server with the specified index (e.g.

"mysql", "sqlite")

Parameters

int $i Specific server index

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 specific server index of the primary server.

Returns: int

Implemented in Wikimedia\Rdbms\LoadBalancer.

Referenced by Wikimedia\Rdbms\ChronologyProtector\applySessionReplicationPosition(), and Wikimedia\Rdbms\ChronologyProtector\stageSessionReplicationPosition().

◆ hasOrMadeRecentPrimaryChanges()

Wikimedia\Rdbms\ILoadBalancer::hasOrMadeRecentPrimaryChanges ( $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

Since: 1.37

Implemented in Wikimedia\Rdbms\LoadBalancer.

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

◆ hasPrimaryChanges()

Wikimedia\Rdbms\ILoadBalancer::hasPrimaryChanges ( )

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

Returns: bool

Since: 1.37

Implemented in Wikimedia\Rdbms\LoadBalancer.

◆ hasPrimaryConnection()

Wikimedia\Rdbms\ILoadBalancer::hasPrimaryConnection ( )

Returns: bool Whether a primary connection is already open

Since: 1.37

Implemented in Wikimedia\Rdbms\LoadBalancer.

◆ hasReplicaServers()

Wikimedia\Rdbms\ILoadBalancer::hasReplicaServers ( )

Whether there are any replica servers configured.

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

Returns: bool

Since: 1.34

Implemented in Wikimedia\Rdbms\LoadBalancer.

◆ hasStreamingReplicaServers()

Wikimedia\Rdbms\ILoadBalancer::hasStreamingReplicaServers ( )

Whether any replica servers use streaming replication from the primary 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 false, this means that there is generally no reason to execute replication wait logic for session consistency and lag reduction.

Returns: bool

Since: 1.34

Implemented in Wikimedia\Rdbms\LoadBalancer.

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

◆ laggedReplicaUsed()

Wikimedia\Rdbms\ILoadBalancer::laggedReplicaUsed ( )

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

a) Already chosen 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.

◆ lastPrimaryChangeTimestamp()

Wikimedia\Rdbms\ILoadBalancer::lastPrimaryChangeTimestamp ( )

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

Returns: float|false UNIX timestamp or false

Since: 1.37

Implemented in Wikimedia\Rdbms\LoadBalancer.

◆ 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.

◆ resolveDomainID()

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

Parameters

DatabaseDomain | string | false $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 )

Deprecated: since 1.39 noop

Parameters

IDatabase $conn

Implemented in Wikimedia\Rdbms\LoadBalancer.

◆ reuseConnectionInternal()

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

Access: internal: Only for use within DBConnRef

Parameters

IDatabase $conn

Implemented in Wikimedia\Rdbms\LoadBalancer.

◆ setDomainAliases()

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

Convert certain database domains to alternative ones.

This can be used for backwards compatibility logic.

Parameters

DatabaseDomain[] | string[] $aliases Map of (domain alias => domain)

Since: 1.35

Implemented in Wikimedia\Rdbms\LoadBalancer.

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

◆ 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().

◆ 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 primary 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 primary position to reach before the next generic group DB 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. This is useful for discouraging clients from taking further actions if session consistency could not be maintained with respect to their last actions.

Parameters

DBPrimaryPos | false $pos Primary position or false

Implemented in Wikimedia\Rdbms\LoadBalancer.

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

◆ waitForAll()

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

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

This method is only intended for use a throttling mechanism for high-volume updates. Unlike waitFor(), failure does not effect getLaggedReplicaMode()/laggedReplicaUsed().

Parameters

DBPrimaryPos \| false	$pos	Primary 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.

◆ waitForPrimaryPos()

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

Wait for a replica DB to reach a specified primary 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 primary server to get an accurate position.

Parameters

IDatabase	$conn	Replica DB
DBPrimaryPos \| false	$pos	Primary position; default: current position
int	$timeout	Timeout in seconds [optional]

Returns: bool Success

Since: 1.37

Implemented in Wikimedia\Rdbms\LoadBalancer.

Member Data Documentation

◆ CONN_INTENT_WRITABLE

const Wikimedia\Rdbms\ILoadBalancer::CONN_INTENT_WRITABLE = 4

Caller is requesting the primary DB server for possibly writes.

Definition at line 104 of file ILoadBalancer.php.

◆ CONN_REFRESH_READ_ONLY

const Wikimedia\Rdbms\ILoadBalancer::CONN_REFRESH_READ_ONLY = 8

Bypass and update any server-side read-only mode state cache.

Definition at line 106 of file ILoadBalancer.php.

◆ CONN_SILENCE_ERRORS

const Wikimedia\Rdbms\ILoadBalancer::CONN_SILENCE_ERRORS = 2

Return null on connection failure instead of throwing an exception.

Definition at line 102 of file ILoadBalancer.php.

Referenced by Wikimedia\Rdbms\LoadMonitor\computeServerStates().

◆ CONN_TRX_AUTOCOMMIT

const Wikimedia\Rdbms\ILoadBalancer::CONN_TRX_AUTOCOMMIT = 1

DB handle should have DBO_TRX disabled and the caller will leave it as such.

Definition at line 100 of file ILoadBalancer.php.

Referenced by Wikimedia\Rdbms\LoadMonitor\computeServerStates().

◆ DB_MASTER

const Wikimedia\Rdbms\ILoadBalancer::DB_MASTER = self::DB_PRIMARY

Request a primary, write-enabled DB connection.

Deprecated: since 1.36, Use DB_PRIMARY instead

Definition at line 91 of file ILoadBalancer.php.

◆ DB_PRIMARY

const Wikimedia\Rdbms\ILoadBalancer::DB_PRIMARY = -2

Request a primary, write-enabled DB connection.

Since: 1.36

Definition at line 84 of file ILoadBalancer.php.

Referenced by Wikimedia\Rdbms\DBConnRef\query(), and Wikimedia\Rdbms\DBConnRef\queryMulti().

◆ DB_REPLICA

const Wikimedia\Rdbms\ILoadBalancer::DB_REPLICA = -1

Request a replica DB connection.

Definition at line 79 of file ILoadBalancer.php.

◆ DOMAIN_ANY

const Wikimedia\Rdbms\ILoadBalancer::DOMAIN_ANY = ''

Domain specifier when no specific database needs to be selected.

Definition at line 95 of file ILoadBalancer.php.

Referenced by Wikimedia\Rdbms\LoadMonitor\computeServerStates().

◆ GROUP_GENERIC

const Wikimedia\Rdbms\ILoadBalancer::GROUP_GENERIC = ''

The generic query group.

Definition at line 97 of file ILoadBalancer.php.

Referenced by Wikimedia\Rdbms\LBFactoryMulti\__construct().

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

includes/libs/rdbms/loadbalancer/ILoadBalancer.php

Public Member Functions

Public Attributes

Detailed Description

Member Function Documentation

◆ closeConnection()

◆ explicitTrxActive()

◆ getAnyOpenConnection()

◆ getClusterName()

◆ getConnection()

◆ getConnectionInternal()

◆ getConnectionRef()

◆ getLaggedReplicaMode()

◆ getLagTimes()

◆ getLazyConnectionRef()

◆ getLocalDomainID()

◆ getMaintenanceConnectionRef()

◆ getMaxLag()

◆ getPrimaryPos()

◆ getReaderIndex()

◆ getReadOnlyReason()

◆ getReplicaResumePos()

◆ getServerAttributes()

◆ getServerConnection()

◆ getServerCount()

◆ getServerInfo()

◆ getServerName()

◆ getServerType()

◆ getWriterIndex()

◆ hasOrMadeRecentPrimaryChanges()

◆ hasPrimaryChanges()

◆ hasPrimaryConnection()

◆ hasReplicaServers()

◆ hasStreamingReplicaServers()

◆ laggedReplicaUsed()

◆ lastPrimaryChangeTimestamp()

◆ pingAll()

◆ redefineLocalDomain()

◆ resolveDomainID()

◆ reuseConnection()

◆ reuseConnectionInternal()

◆ setDomainAliases()

◆ setIndexAliases()

◆ setTableAliases()

◆ setTempTablesOnlyMode()

◆ setTransactionListener()

◆ waitFor()

◆ waitForAll()

◆ waitForPrimaryPos()

Member Data Documentation

◆ CONN_INTENT_WRITABLE

◆ CONN_REFRESH_READ_ONLY

◆ CONN_SILENCE_ERRORS

◆ CONN_TRX_AUTOCOMMIT

◆ DB_MASTER

◆ DB_PRIMARY

◆ DB_REPLICA

◆ DOMAIN_ANY

◆ GROUP_GENERIC