Basic DB load monitor with no external dependencies. More...

Inheritance diagram for Wikimedia\Rdbms\LoadMonitor:

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Collaboration diagram for Wikimedia\Rdbms\LoadMonitor:

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Public Member Functions
	__construct (ILoadBalancer $lb, BagOStuff $srvCache, WANObjectCache $wCache, array $options=[])

	getLagTimes (array $serverIndexes, $domain)
	Get an estimate of replication lag (in seconds) for each server.

	scaleLoads (array &$weightByServer, $domain)
	Perform load ratio adjustment before deciding which server to use.

	setLogger (LoggerInterface $logger)

	setMockTime (&$time)

	setStatsdDataFactory (StatsdDataFactoryInterface $statsFactory)
	Sets a StatsdDataFactory instance on the object.

Protected Member Functions
	computeServerStates (array $serverIndexes, $domain, $priorStates)

	getCurrentTime ()

	getNewScaleViaMovingAve ( $lastScale, $naiveScale, $movAveRatio)
	Get the moving average weight scale given a naive and the last iteration value.

	getServerStates (array $serverIndexes, $domain)

	getWeightScale ( $index, IDatabase $conn=null)

Protected Attributes
ILoadBalancer	$lb

LoggerInterface	$replLogger

BagOStuff	$srvCache

StatsdDataFactoryInterface	$statsd

WANObjectCache	$wanCache

Detailed Description

Basic DB load monitor with no external dependencies.

Uses both server-local and shared caches for server state information.

The "domain" parameters are unused, though they might be used in the future. Therefore, at present, this assumes one channel of replication per server.

Definition at line 41 of file LoadMonitor.php.

Constructor & Destructor Documentation

◆ __construct()

Wikimedia\Rdbms\LoadMonitor::__construct	(	ILoadBalancer	$lb,
		BagOStuff	$srvCache,
		WANObjectCache	$wCache,
		array	$options = [] )

Parameters

ILoadBalancer	$lb
BagOStuff	$srvCache
WANObjectCache	$wCache
array	$options	movingAveRatio: moving average constant for server weight updates based on lag lagWarnThreshold: how many seconds of lag trigger warnings

Implements Wikimedia\Rdbms\ILoadMonitor.

Reimplemented in Wikimedia\Rdbms\LoadMonitorMySQL.

Definition at line 81 of file LoadMonitor.php.

References Wikimedia\Rdbms\LoadMonitor\$lb, Wikimedia\Rdbms\LoadMonitor\$srvCache, and Wikimedia\Rdbms\LoadBalancer\MAX_LAG_DEFAULT.

Member Function Documentation

◆ computeServerStates()

Wikimedia\Rdbms\LoadMonitor::computeServerStates	(	array	$serverIndexes,
			$domain,
			$priorStates )

protected

Parameters

array	$serverIndexes
string \| false	$domain
array \| false	$priorStates

Returns: array

Exceptions

DBAccessError

Definition at line 208 of file LoadMonitor.php.

References Wikimedia\Rdbms\ILoadBalancer\CONN_SILENCE_ERRORS, Wikimedia\Rdbms\ILoadBalancer\CONN_TRX_AUTOCOMMIT, Wikimedia\Rdbms\ILoadBalancer\DOMAIN_ANY, Wikimedia\Rdbms\LoadMonitor\getCurrentTime(), Wikimedia\Rdbms\LoadMonitor\getNewScaleViaMovingAve(), and Wikimedia\Rdbms\LoadMonitor\getWeightScale().

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

◆ getCurrentTime()

Wikimedia\Rdbms\LoadMonitor::getCurrentTime ( )

protected

Returns: float UNIX timestamp

Definition at line 407 of file LoadMonitor.php.

Referenced by Wikimedia\Rdbms\LoadMonitor\computeServerStates(), and Wikimedia\Rdbms\LoadMonitor\getServerStates().

◆ getLagTimes()

Wikimedia\Rdbms\LoadMonitor::getLagTimes	(	array	$serverIndexes,
			$domain )

final

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

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

Parameters

int[]	$serverIndexes
string	$domain

Returns: array Map of (server index => float|int|false)

Implements Wikimedia\Rdbms\ILoadMonitor.

Definition at line 116 of file LoadMonitor.php.

References Wikimedia\Rdbms\LoadMonitor\getServerStates().

◆ getNewScaleViaMovingAve()

Wikimedia\Rdbms\LoadMonitor::getNewScaleViaMovingAve	(	$lastScale,
		$naiveScale,
		$movAveRatio )

protected

Get the moving average weight scale given a naive and the last iteration value.

One case of particular note is if a server totally cannot have its state queried. Ideally, the scale should be able to drop from 1.0 to a miniscule amount (say 0.001) fairly quickly. To get the time to reach 0.001, some calculations can be done:

SCALE = $naiveScale * $movAveRatio + $lastScale * (1 - $movAveRatio) SCALE = 0 * $movAveRatio + $lastScale * (1 - $movAveRatio) SCALE = $lastScale * (1 - $movAveRatio)

Given a starting weight scale of 1.0: 1.0 * (1 - $movAveRatio)^(# iterations) = 0.001 ceil( log<1 - $movAveRatio>(0.001) ) = (# iterations) t = (# iterations) * (POLL_PERIOD + SHARED_CACHE_TTL) t = (# iterations) * (1e3 * POLL_PERIOD_MS + SHARED_CACHE_TTL)

If $movAveRatio is 0.5, then: t = ceil( log<0.5>(0.01) ) * 1.5 = 7 * 1.5 = 10.5 seconds [for 1% scale] t = ceil( log<0.5>(0.001) ) * 1.5 = 10 * 1.5 = 15 seconds [for 0.1% scale]

If $movAveRatio is 0.8, then: t = ceil( log<0.2>(0.01) ) * 1.5 = 3 * 1.5 = 4.5 seconds [for 1% scale] t = ceil( log<0.2>(0.001) ) * 1.5 = 5 * 1.5 = 7.5 seconds [for 0.1% scale]

Use of connection failure rate can greatly speed this process up

Parameters

float	$lastScale	Current moving average of scaling factors
float	$naiveScale	New scaling factor
float	$movAveRatio	Weight given to the new value

Returns: float

Since: 1.35

Definition at line 368 of file LoadMonitor.php.

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

◆ getServerStates()

Wikimedia\Rdbms\LoadMonitor::getServerStates	(	array	$serverIndexes,
			$domain )

protected

Parameters

array	$serverIndexes
string \| false	$domain

Returns: array

Exceptions

DBAccessError

Definition at line 126 of file LoadMonitor.php.

References Wikimedia\Rdbms\LoadMonitor\computeServerStates(), and Wikimedia\Rdbms\LoadMonitor\getCurrentTime().

Referenced by Wikimedia\Rdbms\LoadMonitor\getLagTimes(), and Wikimedia\Rdbms\LoadMonitor\scaleLoads().

◆ getWeightScale()

Wikimedia\Rdbms\LoadMonitor::getWeightScale	(		$index,
		IDatabase	$conn = null )

protected

Parameters

int	$index	Server index
IDatabase \| null	$conn	Connection handle or null on connection failure

Returns: float

Since: 1.28

Reimplemented in Wikimedia\Rdbms\LoadMonitorMySQL.

Definition at line 331 of file LoadMonitor.php.

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

◆ scaleLoads()

Wikimedia\Rdbms\LoadMonitor::scaleLoads	(	array &	$weightByServer,
			$domain )

final

Perform load ratio adjustment before deciding which server to use.

Parameters

int[]	&$weightByServer	Map of (server index => float weight)
string \| false	$domain

Implements Wikimedia\Rdbms\ILoadMonitor.

Definition at line 102 of file LoadMonitor.php.

References Wikimedia\Rdbms\LoadMonitor\getServerStates().

◆ setLogger()

Wikimedia\Rdbms\LoadMonitor::setLogger ( LoggerInterface $logger )

Definition at line 94 of file LoadMonitor.php.

◆ setMockTime()

Wikimedia\Rdbms\LoadMonitor::setMockTime ( & $time )

Parameters

float | null &$time Mock UNIX timestamp for testing

Definition at line 415 of file LoadMonitor.php.

◆ setStatsdDataFactory()

Wikimedia\Rdbms\LoadMonitor::setStatsdDataFactory ( StatsdDataFactoryInterface $statsFactory )

Sets a StatsdDataFactory instance on the object.

Parameters

StatsdDataFactoryInterface $statsFactory

Returns: null

Implements StatsdAwareInterface.

Definition at line 98 of file LoadMonitor.php.

Member Data Documentation

◆ $lb

ILoadBalancer Wikimedia\Rdbms\LoadMonitor::$lb

protected

Definition at line 43 of file LoadMonitor.php.

Referenced by Wikimedia\Rdbms\LoadMonitor\__construct(), and Wikimedia\Rdbms\LoadMonitorMySQL\__construct().

◆ $replLogger

LoggerInterface Wikimedia\Rdbms\LoadMonitor::$replLogger

protected

Definition at line 49 of file LoadMonitor.php.

◆ $srvCache

BagOStuff Wikimedia\Rdbms\LoadMonitor::$srvCache

protected

Definition at line 45 of file LoadMonitor.php.

Referenced by Wikimedia\Rdbms\LoadMonitor\__construct(), and Wikimedia\Rdbms\LoadMonitorMySQL\__construct().

◆ $statsd

StatsdDataFactoryInterface Wikimedia\Rdbms\LoadMonitor::$statsd

protected

Definition at line 51 of file LoadMonitor.php.

◆ $wanCache

WANObjectCache Wikimedia\Rdbms\LoadMonitor::$wanCache

protected

Definition at line 47 of file LoadMonitor.php.

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

includes/libs/rdbms/loadmonitor/LoadMonitor.php

Public Member Functions

Protected Member Functions

Protected Attributes

Detailed Description

Constructor & Destructor Documentation

◆ __construct()

Member Function Documentation

◆ computeServerStates()

◆ getCurrentTime()

◆ getLagTimes()

◆ getNewScaleViaMovingAve()

◆ getServerStates()

◆ getWeightScale()

◆ scaleLoads()

◆ setLogger()

◆ setMockTime()

◆ setStatsdDataFactory()

Member Data Documentation

◆ $lb

◆ $replLogger

◆ $srvCache

◆ $statsd

◆ $wanCache