includes/objectcache/ObjectCache.php

   1 <?php
   2 /**
   3  * Functions to get cache objects.
   4  *
   5  * This program is free software; you can redistribute it and/or modify
   6  * it under the terms of the GNU General Public License as published by
   7  * the Free Software Foundation; either version 2 of the License, or
   8  * (at your option) any later version.
   9  *
  10  * This program is distributed in the hope that it will be useful,
  11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  13  * GNU General Public License for more details.
  14  *
  15  * You should have received a copy of the GNU General Public License along
  16  * with this program; if not, write to the Free Software Foundation, Inc.,
  17  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
  18  * http://www.gnu.org/copyleft/gpl.html
  19  *
  20  * @file
  21  * @ingroup Cache
  22  */
  23
  24 use MediaWiki\Logger\LoggerFactory;
  25
  26 /**
  27  * Functions to get cache objects
  28  *
  29  * The word "cache" has two main dictionary meanings, and both
  30  * are used in this factory class. They are:
  31  *
  32  *   - a) Cache (the computer science definition).
  33  *        A place to store copies or computations on existing data for
  34  *        higher access speeds.
  35  *   - b) Storage.
  36  *        A place to store lightweight data that is not canonically
  37  *        stored anywhere else (e.g. a "hoard" of objects).
  38  *
  39  * The former should always use strongly consistent stores, so callers don't
  40  * have to deal with stale reads. The later may be eventually consistent, but
  41  * callers can use BagOStuff:READ_LATEST to see the latest available data.
  42  *
  43  * Primary entry points:
  44  *
  45  * - ObjectCache::newAccelerator( $fallbackType )
  46  *   Purpose: Cache for very hot keys.
  47  *   Stored only on the individual web server.
  48  *   Not associated with other servers.
  49  *
  50  * - ObjectCache::getMainClusterInstance()
  51  *   Purpose: Memory storage for per-cluster coordination and tracking.
  52  *   Stored centrally within the local data-center.
  53  *   Not replicated to other DCs.
  54  *   Also known as $wgMemc. Configured by $wgMainCacheType.
  55  *
  56  * - ObjectCache::getMainWANInstance()
  57  *   Purpose: Cache.
  58  *   Stored in the local data-center's main cache (uses different cache keys).
  59  *   Delete events are broadcasted to other DCs. See WANObjectCache for details.
  60  *
  61  * - ObjectCache::getMainStashInstance()
  62  *   Purpose: Ephemeral storage.
  63  *   Stored centrally within the local data-center.
  64  *   Changes are replicated to other DCs (eventually consistent).
  65  *   To retrieve the latest value (e.g. not from a slave), use BagOStuff:READ_LATEST.
  66  *   This store may be subject to LRU style evictions.
  67  *
  68  * - wfGetCache( $cacheType )
  69  *   Get a specific cache type by key in $wgObjectCaches.
  70  *
  71  * @ingroup Cache
  72  */
  73 class ObjectCache {
  74         /** @var BagOStuff[] Map of (id => BagOStuff) */
  75         public static $instances = array();
  76         /** @var WANObjectCache[] Map of (id => WANObjectCache) */
  77         public static $wanInstances = array();
  78
  79         /**
  80          * Get a cached instance of the specified type of cache object.
  81          *
  82          * @param string $id A key in $wgObjectCaches.
  83          * @return BagOStuff
  84          */
  85         public static function getInstance( $id ) {
  86                 if ( !isset( self::$instances[$id] ) ) {
  87                         self::$instances[$id] = self::newFromId( $id );
  88                 }
  89
  90                 return self::$instances[$id];
  91         }
  92
  93         /**
  94          * Get a cached instance of the specified type of WAN cache object.
  95          *
  96          * @since 1.26
  97          * @param string $id A key in $wgWANObjectCaches.
  98          * @return WANObjectCache
  99          */
 100         public static function getWANInstance( $id ) {
 101                 if ( !isset( self::$wanInstances[$id] ) ) {
 102                         self::$wanInstances[$id] = self::newWANCacheFromId( $id );
 103                 }
 104
 105                 return self::$wanInstances[$id];
 106         }
 107
 108         /**
 109          * Create a new cache object of the specified type.
 110          *
 111          * @param string $id A key in $wgObjectCaches.
 112          * @return BagOStuff
 113          * @throws MWException
 114          */
 115         public static function newFromId( $id ) {
 116                 global $wgObjectCaches;
 117
 118                 if ( !isset( $wgObjectCaches[$id] ) ) {
 119                         throw new MWException( "Invalid object cache type \"$id\" requested. " .
 120                                 "It is not present in \$wgObjectCaches." );
 121                 }
 122
 123                 return self::newFromParams( $wgObjectCaches[$id] );
 124         }
 125
 126         /**
 127          * Create a new cache object from parameters.
 128          *
 129          * @param array $params Must have 'factory' or 'class' property.
 130          *  - factory: Callback passed $params that returns BagOStuff.
 131          *  - class: BagOStuff subclass constructed with $params.
 132          *  - loggroup: Alias to set 'logger' key with LoggerFactory group.
 133          *  - .. Other parameters passed to factory or class.
 134          * @return BagOStuff
 135          * @throws MWException
 136          */
 137         public static function newFromParams( $params ) {
 138                 if ( isset( $params['loggroup'] ) ) {
 139                         $params['logger'] = LoggerFactory::getInstance( $params['loggroup'] );
 140                 } else {
 141                         // For backwards-compatability with custom parameters, lets not
 142                         // have all logging suddenly disappear
 143                         $params['logger'] = LoggerFactory::getInstance( 'objectcache' );
 144                 }
 145                 if ( isset( $params['factory'] ) ) {
 146                         return call_user_func( $params['factory'], $params );
 147                 } elseif ( isset( $params['class'] ) ) {
 148                         $class = $params['class'];
 149                         return new $class( $params );
 150                 } else {
 151                         throw new MWException( "The definition of cache type \""
 152                                 . print_r( $params, true ) . "\" lacks both "
 153                                 . "factory and class parameters." );
 154                 }
 155         }
 156
 157         /**
 158          * Factory function for CACHE_ANYTHING (referenced from DefaultSettings.php)
 159          *
 160          * CACHE_ANYTHING means that stuff has to be cached, not caching is not an option.
 161          * If a caching method is configured for any of the main caches ($wgMainCacheType,
 162          * $wgMessageCacheType, $wgParserCacheType), then CACHE_ANYTHING will effectively
 163          * be an alias to the configured cache choice for that.
 164          * If no cache choice is configured (by default $wgMainCacheType is CACHE_NONE),
 165          * then CACHE_ANYTHING will forward to CACHE_DB.
 166          *
 167          * @param array $params
 168          * @return BagOStuff
 169          */
 170         public static function newAnything( $params ) {
 171                 global $wgMainCacheType, $wgMessageCacheType, $wgParserCacheType;
 172                 $candidates = array( $wgMainCacheType, $wgMessageCacheType, $wgParserCacheType );
 173                 foreach ( $candidates as $candidate ) {
 174                         if ( $candidate !== CACHE_NONE && $candidate !== CACHE_ANYTHING ) {
 175                                 return self::getInstance( $candidate );
 176                         }
 177                 }
 178                 return self::getInstance( CACHE_DB );
 179         }
 180
 181         /**
 182          * Factory function for CACHE_ACCEL (referenced from DefaultSettings.php)
 183          *
 184          * This will look for any APC style server-local cache.
 185          * A fallback cache can be specified if none is found.
 186          *
 187          *     // Direct calls
 188          *     ObjectCache::newAccelerator( $fallbackType );
 189          *
 190          *     // From $wgObjectCaches via newFromParams()
 191          *     ObjectCache::newAccelerator( array( 'fallback' => $fallbackType ) );
 192          *
 193          * @param array $params [optional] Array key 'fallback' for $fallback.
 194          * @param int|string $fallback Fallback cache, e.g. (CACHE_NONE, "hash") (since 1.24)
 195          * @return BagOStuff
 196          * @throws MWException
 197          */
 198         public static function newAccelerator( $params = array(), $fallback = null ) {
 199                 if ( $fallback === null ) {
 200                         // The is_array check here is needed because in PHP 5.3:
 201                         // $a = 'hash'; isset( $params['fallback'] ); yields true
 202                         if ( is_array( $params ) && isset( $params['fallback'] ) ) {
 203                                 $fallback = $params['fallback'];
 204                         } elseif ( !is_array( $params ) ) {
 205                                 $fallback = $params;
 206                         }
 207                 }
 208                 if ( function_exists( 'apc_fetch' ) ) {
 209                         $id = 'apc';
 210                 } elseif ( function_exists( 'xcache_get' ) && wfIniGetBool( 'xcache.var_size' ) ) {
 211                         $id = 'xcache';
 212                 } elseif ( function_exists( 'wincache_ucache_get' ) ) {
 213                         $id = 'wincache';
 214                 } else {
 215                         if ( $fallback === null ) {
 216                                 throw new MWException( 'CACHE_ACCEL requested but no suitable object ' .
 217                                         'cache is present. You may want to install APC.' );
 218                         }
 219                         $id = $fallback;
 220                 }
 221                 return self::newFromId( $id );
 222         }
 223
 224         /**
 225          * Factory function that creates a memcached client object.
 226          *
 227          * This always uses the PHP client, since the PECL client has a different
 228          * hashing scheme and a different interpretation of the flags bitfield, so
 229          * switching between the two clients randomly would be disastrous.
 230          *
 231          * @param array $params
 232          * @return MemcachedPhpBagOStuff
 233          */
 234         public static function newMemcached( $params ) {
 235                 return new MemcachedPhpBagOStuff( $params );
 236         }
 237
 238         /**
 239          * Create a new cache object of the specified type.
 240          *
 241          * @since 1.26
 242          * @param string $id A key in $wgWANObjectCaches.
 243          * @return WANObjectCache
 244          * @throws MWException
 245          */
 246         public static function newWANCacheFromId( $id ) {
 247                 global $wgWANObjectCaches;
 248
 249                 if ( !isset( $wgWANObjectCaches[$id] ) ) {
 250                         throw new MWException( "Invalid object cache type \"$id\" requested. " .
 251                                 "It is not present in \$wgWANObjectCaches." );
 252                 }
 253
 254                 $params = $wgWANObjectCaches[$id];
 255                 $class = $params['relayerConfig']['class'];
 256                 $params['relayer'] = new $class( $params['relayerConfig'] );
 257                 $params['cache'] = self::newFromId( $params['cacheId'] );
 258                 $class = $params['class'];
 259
 260                 return new $class( $params );
 261         }
 262
 263         /**
 264          * Get the main cluster-local cache object.
 265          *
 266          * @since 1.27
 267          * @return BagOStuff
 268          */
 269         public static function getMainClusterInstance() {
 270                 $config = RequestContext::getMain()->getConfig();
 271                 $id = $config->get( 'MainCacheType' );
 272                 return self::getInstance( $id );
 273         }
 274
 275         /**
 276          * Get the main WAN cache object.
 277          *
 278          * @since 1.26
 279          * @return WANObjectCache
 280          */
 281         public static function getMainWANInstance() {
 282                 global $wgMainWANCache;
 283
 284                 return self::getWANInstance( $wgMainWANCache );
 285         }
 286
 287         /**
 288          * Get the cache object for the main stash.
 289          *
 290          * Stash objects are BagOStuff instances suitable for storing light
 291          * weight data that is not canonically stored elsewhere (such as RDBMS).
 292          * Stashes should be configured to propagate changes to all data-centers.
 293          *
 294          * Callers should be prepared for:
 295          *   - a) Writes to be slower in non-"primary" (e.g. HTTP GET/HEAD only) DCs
 296          *   - b) Reads to be eventually consistent, e.g. for get()/getMulti()
 297          * In general, this means avoiding updates on idempotent HTTP requests and
 298          * avoiding an assumption of perfect serializability (or accepting anomalies).
 299          * Reads may be eventually consistent or data might rollback as nodes flap.
 300          * Callers can use BagOStuff:READ_LATEST to see the latest available data.
 301          *
 302          * @return BagOStuff
 303          * @since 1.26
 304          */
 305         public static function getMainStashInstance() {
 306                 global $wgMainStash;
 307
 308                 return self::getInstance( $wgMainStash );
 309         }
 310
 311         /**
 312          * Clear all the cached instances.
 313          */
 314         public static function clear() {
 315                 self::$instances = array();
 316                 self::$wanInstances = array();
 317         }
 318 }