845e5b24c4
* Use ProfileSection * Removed redundant doc blocks * Added method visibility Change-Id: I76cd666c28b8bea7d5997a9f2b7d1c39539f7c5e
149 lines
4.1 KiB
PHP
149 lines
4.1 KiB
PHP
<?php
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/**
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* Database load monitoring.
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License along
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* with this program; if not, write to the Free Software Foundation, Inc.,
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* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
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* http://www.gnu.org/copyleft/gpl.html
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*
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* @file
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* @ingroup Database
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*/
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/**
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* An interface for database load monitoring
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*
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* @ingroup Database
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*/
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interface LoadMonitor {
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/**
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* Construct a new LoadMonitor with a given LoadBalancer parent
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*
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* @param LoadBalancer $parent
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*/
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public function __construct( $parent );
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/**
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* Perform pre-connection load ratio adjustment.
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* @param array $loads
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* @param string|bool $group The selected query group. Default: false
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* @param string|bool $wiki Default: false
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*/
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public function scaleLoads( &$loads, $group = false, $wiki = false );
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/**
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* Return an estimate of replication lag for each server
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*
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* @param array $serverIndexes
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* @param string $wiki
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*
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* @return array
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*/
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public function getLagTimes( $serverIndexes, $wiki );
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}
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class LoadMonitorNull implements LoadMonitor {
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public function __construct( $parent ) {
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}
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public function scaleLoads( &$loads, $group = false, $wiki = false ) {
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}
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public function getLagTimes( $serverIndexes, $wiki ) {
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return array_fill_keys( $serverIndexes, 0 );
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}
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}
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/**
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* Basic MySQL load monitor with no external dependencies
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* Uses memcached to cache the replication lag for a short time
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*
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* @ingroup Database
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*/
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class LoadMonitorMySQL implements LoadMonitor {
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/** @var LoadBalancer */
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public $parent;
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public function __construct( $parent ) {
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$this->parent = $parent;
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}
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public function scaleLoads( &$loads, $group = false, $wiki = false ) {
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}
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public function getLagTimes( $serverIndexes, $wiki ) {
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if ( count( $serverIndexes ) == 1 && reset( $serverIndexes ) == 0 ) {
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// Single server only, just return zero without caching
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return array( 0 => 0 );
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}
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$section = new ProfileSection( __METHOD__ );
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$expiry = 5;
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$requestRate = 10;
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global $wgMemc;
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if ( empty( $wgMemc ) ) {
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$wgMemc = wfGetMainCache();
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}
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$masterName = $this->parent->getServerName( 0 );
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$memcKey = wfMemcKey( 'lag_times', $masterName );
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$times = $wgMemc->get( $memcKey );
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if ( is_array( $times ) ) {
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# Randomly recache with probability rising over $expiry
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$elapsed = time() - $times['timestamp'];
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$chance = max( 0, ( $expiry - $elapsed ) * $requestRate );
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if ( mt_rand( 0, $chance ) != 0 ) {
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unset( $times['timestamp'] ); // hide from caller
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return $times;
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}
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wfIncrStats( 'lag_cache_miss_expired' );
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} else {
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wfIncrStats( 'lag_cache_miss_absent' );
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}
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# Cache key missing or expired
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if ( $wgMemc->add( "$memcKey:lock", 1, 10 ) ) {
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# Let this process alone update the cache value
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$unlocker = new ScopedCallback( function () use ( $wgMemc, $memcKey ) {
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$wgMemc->delete( $memcKey );
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} );
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} elseif ( is_array( $times ) ) {
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# Could not acquire lock but an old cache exists, so use it
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unset( $times['timestamp'] ); // hide from caller
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return $times;
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}
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$times = array();
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foreach ( $serverIndexes as $i ) {
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if ( $i == 0 ) { # Master
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$times[$i] = 0;
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} elseif ( false !== ( $conn = $this->parent->getAnyOpenConnection( $i ) ) ) {
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$times[$i] = $conn->getLag();
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} elseif ( false !== ( $conn = $this->parent->openConnection( $i, $wiki ) ) ) {
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$times[$i] = $conn->getLag();
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}
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}
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# Add a timestamp key so we know when it was cached
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$times['timestamp'] = time();
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$wgMemc->set( $memcKey, $times, $expiry + 10 );
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unset( $times['timestamp'] ); // hide from caller
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return $times;
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}
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}
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