cb862afaf3
Also corrected some ObjectCache docs Change-Id: I322f4cbd72fbd5d4c6887d90ee75d0baddb6ac25
350 lines
11 KiB
PHP
350 lines
11 KiB
PHP
<?php
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/**
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* Functions to get cache objects.
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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 Cache
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*/
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use MediaWiki\Logger\LoggerFactory;
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/**
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* Functions to get cache objects
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*
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* The word "cache" has two main dictionary meanings, and both
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* are used in this factory class. They are:
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*
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* - a) Cache (the computer science definition).
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* A place to store copies or computations on existing data for
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* higher access speeds.
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* - b) Storage.
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* A place to store lightweight data that is not canonically
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* stored anywhere else (e.g. a "hoard" of objects).
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*
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* The former should always use strongly consistent stores, so callers don't
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* have to deal with stale reads. The later may be eventually consistent, but
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* callers can use BagOStuff:READ_LATEST to see the latest available data.
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*
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* Primary entry points:
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*
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* - ObjectCache::newAccelerator( $fallbackType )
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* Purpose: Cache for very hot keys.
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* Stored only on the individual web server.
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* Not associated with other servers.
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*
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* - ObjectCache::getMainWANInstance()
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* Purpose: Cache.
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* Stored in the local data-center's main cache (uses different cache keys).
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* Delete events are broadcasted to other DCs. See WANObjectCache for details.
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*
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* - ObjectCache::getMainStashInstance()
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* Purpose: Ephemeral storage.
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* Stored centrally within the primary data-center.
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* Changes are applied there first and replicated to other DCs (best-effort).
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* To retrieve the latest value (e.g. not from a slave), use BagOStuff:READ_LATEST.
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* This store may be subject to LRU style evictions.
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*
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* - ObjectCache::getLocalClusterInstance()
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* Purpose: Memory storage for per-cluster coordination and tracking.
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* A typical use case would be a rate limit counter or cache regeneration mutex.
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* Stored centrally within the local data-center. Not replicated to other DCs.
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* Also known as $wgMemc. Configured by $wgMainCacheType.
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*
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* - wfGetCache( $cacheType )
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* Get a specific cache type by key in $wgObjectCaches.
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*
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* All the above cache instances (BagOStuff and WANObjectCache) have their makeKey()
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* method scoped to the *current* wiki ID. Use makeGlobalKey() to avoid this scoping
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* when using keys that need to be shared amongst wikis.
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*
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* @ingroup Cache
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*/
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class ObjectCache {
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/** @var BagOStuff[] Map of (id => BagOStuff) */
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public static $instances = array();
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/** @var WANObjectCache[] Map of (id => WANObjectCache) */
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public static $wanInstances = array();
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/**
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* Get a cached instance of the specified type of cache object.
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*
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* @param string $id A key in $wgObjectCaches.
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* @return BagOStuff
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*/
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public static function getInstance( $id ) {
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if ( !isset( self::$instances[$id] ) ) {
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self::$instances[$id] = self::newFromId( $id );
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}
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return self::$instances[$id];
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}
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/**
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* Get a cached instance of the specified type of WAN cache object.
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*
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* @since 1.26
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* @param string $id A key in $wgWANObjectCaches.
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* @return WANObjectCache
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*/
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public static function getWANInstance( $id ) {
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if ( !isset( self::$wanInstances[$id] ) ) {
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self::$wanInstances[$id] = self::newWANCacheFromId( $id );
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}
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return self::$wanInstances[$id];
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}
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/**
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* Create a new cache object of the specified type.
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*
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* @param string $id A key in $wgObjectCaches.
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* @return BagOStuff
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* @throws MWException
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*/
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public static function newFromId( $id ) {
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global $wgObjectCaches;
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if ( !isset( $wgObjectCaches[$id] ) ) {
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throw new MWException( "Invalid object cache type \"$id\" requested. " .
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"It is not present in \$wgObjectCaches." );
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}
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return self::newFromParams( $wgObjectCaches[$id] );
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}
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/**
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* Get the default keyspace for this wiki.
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*
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* This is either the value of the `CachePrefix` configuration variable,
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* or (if the former is unset) the `DBname` configuration variable, with
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* `DBprefix` (if defined).
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*
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* @return string
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*/
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public static function getDefaultKeyspace() {
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global $wgCachePrefix, $wgDBname, $wgDBprefix;
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$keyspace = $wgCachePrefix;
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if ( is_string( $keyspace ) && $keyspace !== '' ) {
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return $keyspace;
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}
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$keyspace = $wgDBname;
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if ( is_string( $wgDBprefix ) && $wgDBprefix !== '' ) {
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$keyspace .= '-' . $wgDBprefix;
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}
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return $keyspace;
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}
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/**
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* Create a new cache object from parameters.
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*
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* @param array $params Must have 'factory' or 'class' property.
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* - factory: Callback passed $params that returns BagOStuff.
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* - class: BagOStuff subclass constructed with $params.
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* - loggroup: Alias to set 'logger' key with LoggerFactory group.
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* - .. Other parameters passed to factory or class.
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* @return BagOStuff
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* @throws MWException
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*/
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public static function newFromParams( $params ) {
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if ( isset( $params['loggroup'] ) ) {
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$params['logger'] = LoggerFactory::getInstance( $params['loggroup'] );
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} else {
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// For backwards-compatability with custom parameters, lets not
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// have all logging suddenly disappear
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$params['logger'] = LoggerFactory::getInstance( 'objectcache' );
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}
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if ( !isset( $params['keyspace'] ) ) {
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$params['keyspace'] = self::getDefaultKeyspace();
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}
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if ( isset( $params['factory'] ) ) {
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return call_user_func( $params['factory'], $params );
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} elseif ( isset( $params['class'] ) ) {
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$class = $params['class'];
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return new $class( $params );
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} else {
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throw new MWException( "The definition of cache type \""
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. print_r( $params, true ) . "\" lacks both "
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. "factory and class parameters." );
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}
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}
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/**
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* Factory function for CACHE_ANYTHING (referenced from DefaultSettings.php)
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*
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* CACHE_ANYTHING means that stuff has to be cached, not caching is not an option.
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* If a caching method is configured for any of the main caches ($wgMainCacheType,
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* $wgMessageCacheType, $wgParserCacheType), then CACHE_ANYTHING will effectively
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* be an alias to the configured cache choice for that.
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* If no cache choice is configured (by default $wgMainCacheType is CACHE_NONE),
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* then CACHE_ANYTHING will forward to CACHE_DB.
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*
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* @param array $params
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* @return BagOStuff
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*/
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public static function newAnything( $params ) {
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global $wgMainCacheType, $wgMessageCacheType, $wgParserCacheType;
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$candidates = array( $wgMainCacheType, $wgMessageCacheType, $wgParserCacheType );
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foreach ( $candidates as $candidate ) {
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if ( $candidate !== CACHE_NONE && $candidate !== CACHE_ANYTHING ) {
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return self::getInstance( $candidate );
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}
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}
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return self::getInstance( CACHE_DB );
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}
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/**
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* Factory function for CACHE_ACCEL (referenced from DefaultSettings.php)
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*
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* This will look for any APC style server-local cache.
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* A fallback cache can be specified if none is found.
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*
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* // Direct calls
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* ObjectCache::newAccelerator( $fallbackType );
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*
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* // From $wgObjectCaches via newFromParams()
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* ObjectCache::newAccelerator( array( 'fallback' => $fallbackType ) );
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*
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* @param array $params [optional] Array key 'fallback' for $fallback.
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* @param int|string $fallback Fallback cache, e.g. (CACHE_NONE, "hash") (since 1.24)
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* @return BagOStuff
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* @throws MWException
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*/
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public static function newAccelerator( $params = array(), $fallback = null ) {
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if ( $fallback === null ) {
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// The is_array check here is needed because in PHP 5.3:
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// $a = 'hash'; isset( $params['fallback'] ); yields true
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if ( is_array( $params ) && isset( $params['fallback'] ) ) {
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$fallback = $params['fallback'];
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} elseif ( !is_array( $params ) ) {
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$fallback = $params;
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}
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}
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if ( function_exists( 'apc_fetch' ) ) {
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$id = 'apc';
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} elseif ( function_exists( 'xcache_get' ) && wfIniGetBool( 'xcache.var_size' ) ) {
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$id = 'xcache';
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} elseif ( function_exists( 'wincache_ucache_get' ) ) {
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$id = 'wincache';
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} else {
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if ( $fallback === null ) {
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throw new MWException( 'CACHE_ACCEL requested but no suitable object ' .
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'cache is present. You may want to install APC.' );
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}
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$id = $fallback;
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}
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return self::newFromId( $id );
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}
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/**
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* Factory function that creates a memcached client object.
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*
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* This always uses the PHP client, since the PECL client has a different
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* hashing scheme and a different interpretation of the flags bitfield, so
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* switching between the two clients randomly would be disastrous.
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*
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* @param array $params
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* @return MemcachedPhpBagOStuff
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*/
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public static function newMemcached( $params ) {
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return new MemcachedPhpBagOStuff( $params );
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}
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/**
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* Create a new cache object of the specified type.
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*
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* @since 1.26
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* @param string $id A key in $wgWANObjectCaches.
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* @return WANObjectCache
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* @throws MWException
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*/
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public static function newWANCacheFromId( $id ) {
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global $wgWANObjectCaches;
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if ( !isset( $wgWANObjectCaches[$id] ) ) {
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throw new MWException( "Invalid object cache type \"$id\" requested. " .
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"It is not present in \$wgWANObjectCaches." );
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}
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$params = $wgWANObjectCaches[$id];
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$class = $params['relayerConfig']['class'];
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$params['relayer'] = new $class( $params['relayerConfig'] );
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$params['cache'] = self::newFromId( $params['cacheId'] );
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$class = $params['class'];
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return new $class( $params );
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}
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/**
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* Get the main cluster-local cache object.
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*
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* @since 1.27
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* @return BagOStuff
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*/
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public static function getLocalClusterInstance() {
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global $wgMainCacheType;
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return self::getInstance( $wgMainCacheType );
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}
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/**
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* Get the main WAN cache object.
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*
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* @since 1.26
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* @return WANObjectCache
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*/
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public static function getMainWANInstance() {
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global $wgMainWANCache;
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return self::getWANInstance( $wgMainWANCache );
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}
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/**
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* Get the cache object for the main stash.
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*
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* Stash objects are BagOStuff instances suitable for storing light
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* weight data that is not canonically stored elsewhere (such as RDBMS).
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* Stashes should be configured to propagate changes to all data-centers.
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*
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* Callers should be prepared for:
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* - a) Writes to be slower in non-"primary" (e.g. HTTP GET/HEAD only) DCs
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* - b) Reads to be eventually consistent, e.g. for get()/getMulti()
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* In general, this means avoiding updates on idempotent HTTP requests and
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* avoiding an assumption of perfect serializability (or accepting anomalies).
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* Reads may be eventually consistent or data might rollback as nodes flap.
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* Callers can use BagOStuff:READ_LATEST to see the latest available data.
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*
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* @return BagOStuff
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* @since 1.26
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*/
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public static function getMainStashInstance() {
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global $wgMainStash;
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return self::getInstance( $wgMainStash );
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}
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/**
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* Clear all the cached instances.
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*/
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public static function clear() {
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self::$instances = array();
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self::$wanInstances = array();
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}
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}
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