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

Inheritance diagram for 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)
	Perform all pre-commit checks for things like replication safety. More...

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

	closeAll ()
	Close all open connections. More...

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

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

	commitMasterChanges ($fname=__METHOD__)
	Issue COMMIT on all master connections where writes where done. More...

	disable ()
	Disable this load balancer. More...

	finalizeMasterChanges ()
	Perform all pre-commit callbacks that remain part of the atomic transactions and disable any post-commit callbacks until runMasterPostTrxCallbacks() More...

	flushReplicaSnapshots ($fname=__METHOD__)
	Commit all replica DB transactions so as to flush any REPEATABLE-READ or SSI snapshot. 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)
	Get any open connection to a given server index, local or foreign Returns false if there is no connection open. More...

	getConnection ($i, $groups=[], $domain=false)
	Get a connection by index This is the main entry point for this class. More...

	getConnectionRef ($db, $groups=[], $domain=false)
	Get a database connection handle reference. More...

	getLaggedReplicaMode ($domain=false)

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

	getLazyConnectionRef ($db, $groups=[], $domain=false)
	Get a database connection handle reference without connecting yet. More...

	getMasterPos ()
	Get the current master position for chronology control purposes. More...

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

	getReaderIndex ($group=false, $domain=false)
	Get the index of the reader connection, which may be a replica DB This takes into account load ratios and lag times. More...

	getReadOnlyReason ($domain=false, IDatabase $conn=null)

	getServerCount ()
	Get the number of defined servers (not the number of open connections) 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 Prefer a readable name if available. More...

	getWriterIndex ()

	hasMasterChanges ()
	Determine if there are pending changes 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...

	haveIndex ($i)
	Returns true if the specified index is a valid server index. More...

	isNonZeroLoad ($i)
	Returns true if the specified index is valid and has non-zero load. More...

	laggedReplicaUsed ()

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

	openConnection ($i, $domain=false)
	Open a connection to the server given by the specified index Index must be an actual index into the array. More...

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

	pingAll ()

	reuseConnection ($conn)
	Mark a foreign connection as being available for reuse under a different DB name or prefix. More...

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

	runMasterPostTrxCallbacks ($type)
	Issue all pending post-COMMIT/ROLLBACK callbacks. More...

	safeGetLag (IDatabase $conn)
	Get the lag in seconds for a given connection, or zero if this load balancer does not have replication enabled. More...

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

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

	setServerInfo ($i, array $serverInfo)
	Sets the server info structure for the given index. 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...

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

	suppressTransactionEndCallbacks ()
	Suppress all pending post-COMMIT/ROLLBACK callbacks. More...

	waitFor ($pos)
	Set the master wait position If a DB_REPLICA connection has been opened already, waits Otherwise sets a variable telling it to wait if such a connection is opened. More...

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

Constructor & Destructor Documentation

ILoadBalancer::__construct ( array $params )

Construct a manager of IDatabase connection objects.

Parameters

array

$params

Parameter map with keys:

servers : Required. Array 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]
srvCache : BagOStuff object for server cache [optional]
memCache : BagOStuff object for cluster memory cache [optional]
wanCache : WANObjectCache object [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]

Exceptions

InvalidArgumentException

Implemented in LoadBalancer, and LoadBalancerSingle.

Member Function Documentation

ILoadBalancer::allowLagged ( $mode = null )

Disables/enables lag checks.

Parameters

null | bool $mode

Returns: bool

Implemented in LoadBalancer.

ILoadBalancer::approveMasterChanges ( array $options )

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

Exceptions

DBTransactionError

Implemented in LoadBalancer.

ILoadBalancer::beginMasterChanges ( $fname = __METHOD__ )

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

Exceptions

DBExpectedError

Implemented in LoadBalancer.

Referenced by LBFactory\initLoadBalancer().

ILoadBalancer::closeAll ( )

Close all open connections.

Implemented in LoadBalancer.

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 LoadBalancer.

ILoadBalancer::commitAll ( $fname = __METHOD__ )

Commit transactions on all open connections.

Parameters

string $fname Caller name

Exceptions

DBExpectedError

Implemented in LoadBalancer.

ILoadBalancer::commitMasterChanges ( $fname = __METHOD__ )

Issue COMMIT on all master connections where writes where done.

Parameters

string $fname Caller name

Exceptions

DBExpectedError

Implemented in LoadBalancer.

ILoadBalancer::disable ( )

Disable this load balancer.

All connections are closed, and any attempt to open a new connection will result in a DBAccessError.

Implemented in LoadBalancer.

ILoadBalancer::finalizeMasterChanges ( )

Perform all pre-commit callbacks that remain part of the atomic transactions and disable any post-commit callbacks until runMasterPostTrxCallbacks()

Use this only for mutli-database commits

Implemented in LoadBalancer.

ILoadBalancer::flushReplicaSnapshots ( $fname = __METHOD__ )

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

Parameters

string $fname Caller name

Implemented in LoadBalancer.

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

Call a function with each open connection object.

Parameters

callable	$callback
array	$params

Implemented in LoadBalancer.

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

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

Parameters

callable	$callback
array	$params

Implemented in LoadBalancer.

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

Call a function with each open replica DB connection object.

Parameters

callable	$callback
array	$params

Implemented in LoadBalancer.

ILoadBalancer::getAnyOpenConnection ( $i )

Get any open connection to a given server index, local or foreign Returns false if there is no connection open.

Parameters

int $i Server index

Returns: IDatabase|bool False on failure

Implemented in LoadBalancer.

ILoadBalancer::getConnection	(	$i,
		$groups = `[]`,
		$domain = `false`
	)

Get a connection by index This is the main entry point for this class.

Parameters

int	$i	Server index
array \| string \| bool	$groups	Query group(s), or false for the generic reader
string \| bool	$domain	Domain ID, or false for the current domain

Exceptions

DBError

Returns: IDatabase

Implemented in LoadBalancer.

ILoadBalancer::getConnectionRef	(	$db,
		$groups = `[]`,
		$domain = `false`
	)

Get a database connection handle reference.

The handle's methods wrap simply wrap those of a IDatabase handle

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

Parameters

int	$db
array \| string \| bool	$groups	Query group(s), or false for the generic reader
string \| bool	$domain	Domain ID, or false for the current domain

Returns: DBConnRef

Implemented in LoadBalancer.

ILoadBalancer::getLaggedReplicaMode ( $domain = false )

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

Parameters

string | bool $domain Domain ID, or false for the current domain

Returns: bool Whether the generic connection for reads is highly "lagged"

Implemented in LoadBalancer.

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 LoadBalancer.

ILoadBalancer::getLazyConnectionRef	(	$db,
		$groups = `[]`,
		$domain = `false`
	)

Get a database connection handle reference without connecting yet.

The handle's methods wrap simply wrap those of a IDatabase handle

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

Parameters

int	$db
array \| string \| bool	$groups	Query group(s), or false for the generic reader
string \| bool	$domain	Domain ID, or false for the current domain

Returns: DBConnRef

Implemented in LoadBalancer.

ILoadBalancer::getMasterPos ( )

Get the current master position for chronology control purposes.

Returns: DBMasterPos|bool Returns false if not applicable

Implemented in LoadBalancer.

Referenced by ChronologyProtector\shutdownLB().

ILoadBalancer::getMaxLag ( $domain = false )

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

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 LoadBalancer.

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

Get the index of the reader connection, which may be a replica DB This takes into account load ratios and lag times.

It should always return a consistent index during a given invocation

Side effect: opens connections to databases

Parameters

string \| bool	$group	Query group, or false for the generic reader
string \| bool	$domain	Domain ID, or false for the current domain

Exceptions

DBError

Returns: bool|int|string

Implemented in LoadBalancer.

ILoadBalancer::getReadOnlyReason	(		$domain = `false`,
		IDatabase	$conn = `null`
	)

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

Parameters

string \| bool	$domain	Domain ID, or false for the current domain
	IDatabase\|null	DB master connection; used to avoid loops [optional]

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

Implemented in LoadBalancer.

ILoadBalancer::getServerCount ( )

Get the number of defined servers (not the number of open connections)

Returns: int

Implemented in LoadBalancer.

Referenced by LBFactory\appendPreShutdownTimeAsQuery(), ChronologyProtector\initLB(), and ChronologyProtector\shutdownLB().

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

Implemented in LoadBalancer.

ILoadBalancer::getServerName ( $i )

Get the host name or IP address of the server with the specified index Prefer a readable name if available.

Parameters

string $i

Returns: string

Implemented in LoadBalancer.

Referenced by ChronologyProtector\initLB(), LBFactory\logIfMultiDbTransaction(), LBFactory\shutdownChronologyProtector(), and ChronologyProtector\shutdownLB().

ILoadBalancer::getWriterIndex ( )

Returns: int

Implemented in LoadBalancer.

Referenced by ChronologyProtector\initLB(), LBFactory\logIfMultiDbTransaction(), LBFactory\shutdownChronologyProtector(), and ChronologyProtector\shutdownLB().

ILoadBalancer::hasMasterChanges ( )

Determine if there are pending changes in a transaction by this thread.

Returns: bool

Implemented in LoadBalancer.

Referenced by LBFactory\hasMasterChanges().

ILoadBalancer::hasMasterConnection ( )

Returns: bool Whether a master connection is already open

Implemented in LoadBalancer.

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

Returns: bool

Implemented in LoadBalancer.

Referenced by LBFactory\hasOrMadeRecentMasterChanges(), and ChronologyProtector\shutdownLB().

ILoadBalancer::haveIndex ( $i )

Returns true if the specified index is a valid server index.

Parameters

string $i

Returns: bool

Implemented in LoadBalancer.

ILoadBalancer::isNonZeroLoad ( $i )

Returns true if the specified index is valid and has non-zero load.

Parameters

string $i

Returns: bool

Implemented in LoadBalancer.

ILoadBalancer::laggedReplicaUsed ( )

Note: This method will never cause a new DB connection

Returns: bool Whether any generic connection used for reads was highly "lagged"

Implemented in LoadBalancer.

Referenced by LBFactory\laggedReplicaUsed().

ILoadBalancer::lastMasterChangeTimestamp ( )

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

Returns: float|bool UNIX timestamp or false

Implemented in LoadBalancer.

ILoadBalancer::openConnection	(	$i,
		$domain = `false`
	)

Open a connection to the server given by the specified index Index must be an actual index into the array.

If the server is already open, returns it.

On error, returns false, and the connection which caused the error will be available via $this->mErrorConnection.

Note: If disable() was called on this LoadBalancer, this method will throw a DBAccessError.

Parameters

int	$i	Server index
string \| bool	$domain	Domain ID, or false for the current domain

Returns: IDatabase|bool Returns false on errors

Exceptions

DBAccessError

Implemented in LoadBalancer.

ILoadBalancer::pendingMasterChangeCallers ( )

Get the list of callers that have pending master changes.

Returns: string[] List of method names

Implemented in LoadBalancer.

Referenced by LBFactory\logIfMultiDbTransaction().

ILoadBalancer::pingAll ( )

Returns: bool

Implemented in LoadBalancer.

ILoadBalancer::reuseConnection ( $conn )

Mark a foreign connection as being available for reuse under a different DB name or prefix.

This mechanism is reference-counted, and must be called the same number of times as getConnection() to work.

Parameters

IDatabase $conn

Exceptions

InvalidArgumentException

Implemented in LoadBalancer.

ILoadBalancer::rollbackMasterChanges ( $fname = __METHOD__ )

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

Parameters

string $fname Caller name

Exceptions

DBExpectedError

Implemented in LoadBalancer.

ILoadBalancer::runMasterPostTrxCallbacks ( $type )

Issue all pending post-COMMIT/ROLLBACK callbacks.

Use this only for mutli-database commits

Parameters

integer $type IDatabase::TRIGGER_* constant

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

Implemented in LoadBalancer.

Referenced by LBFactory\commitMasterChanges(), and LBFactory\rollbackMasterChanges().

ILoadBalancer::safeGetLag ( IDatabase $conn )

Get the lag in seconds for a given connection, or zero if this load balancer does not have replication enabled.

This should be used in preference to Database::getLag() in cases where replication may not be in use, since there is no way to determine if replication is in use at the connection level without running potentially restricted queries such as SHOW SLAVE STATUS. Using this function instead of Database::getLag() avoids a fatal error in this case on many installations.

Parameters

IDatabase $conn

Returns: int|bool Returns false on error

Implemented in LoadBalancer.

ILoadBalancer::safeWaitForMasterPos	(	IDatabase	$conn,
			$pos = `false`,
			$timeout = `null`
	)

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

This will connect to the master to get an accurate position if $pos is not given

Parameters

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

Returns: bool Success

Implemented in LoadBalancer.

ILoadBalancer::setDomainPrefix ( $prefix )

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

Parameters

string $prefix

Implemented in LoadBalancer.

Referenced by LBFactory\setDomainPrefix().

ILoadBalancer::setServerInfo	(		$i,
		array	$serverInfo
	)

Sets the server info structure for the given index.

Entry at index $i is created if it doesn't exist

Parameters

int	$i
array	$serverInfo

Implemented in LoadBalancer.

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 LoadBalancer.

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 LoadBalancer.

ILoadBalancer::suppressTransactionEndCallbacks ( )

Suppress all pending post-COMMIT/ROLLBACK callbacks.

Use this only for mutli-database commits

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

Implemented in LoadBalancer.

ILoadBalancer::waitFor ( $pos )

Set the master wait position If a DB_REPLICA connection has been opened already, waits Otherwise sets a variable telling it to wait if such a connection is opened.

Parameters

DBMasterPos $pos

Implemented in LoadBalancer.

Referenced by ChronologyProtector\initLB().

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

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

Parameters

DBMasterPos	$pos
int	$timeout	Max seconds to wait; default is mWaitTimeout

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

Implemented in LoadBalancer.

Referenced by LBFactory\shutdownChronologyProtector().

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	$pos
int	$timeout	Max seconds to wait; default is mWaitTimeout

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

Implemented in 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

Member Function Documentation