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::getMainWANInstance()
  51  *   Purpose: Cache.
  52  *   Stored in the local data-center's main cache (uses different cache keys).
  53  *   Delete events are broadcasted to other DCs. See WANObjectCache for details.
  54  *
  55  * - ObjectCache::getMainStashInstance()
  56  *   Purpose: Ephemeral storage.
  57  *   Stored centrally within the primary data-center.
  58  *   Changes are applied there first and replicated to other DCs (best-effort).
  59  *   To retrieve the latest value (e.g. not from a slave), use BagOStuff:READ_LATEST.
  60  *   This store may be subject to LRU style evictions.
  61  *
  62  * - ObjectCache::getLocalClusterInstance()
  63  *   Purpose: Memory storage for per-cluster coordination and tracking.
  64  *   A typical use case would be a rate limit counter or cache regeneration mutex.
  65  *   Stored centrally within the local data-center. Not replicated to other DCs.
  66  *   Also known as $wgMemc. Configured by $wgMainCacheType.
  67  *
  68  * - wfGetCache( $cacheType )
  69  *   Get a specific cache type by key in $wgObjectCaches.
  70  *
  71  * All the above cache instances (BagOStuff and WANObjectCache) have their makeKey()
  72  * method scoped to the *current* wiki ID. Use makeGlobalKey() to avoid this scoping
  73  * when using keys that need to be shared amongst wikis.
  74  *
  75  * @ingroup Cache
  76  */
  77 class ObjectCache {
  78         /** @var BagOStuff[] Map of (id => BagOStuff) */
  79         public static $instances = array();
  80         /** @var WANObjectCache[] Map of (id => WANObjectCache) */
  81         public static $wanInstances = array();
  82
  83         /**
  84          * Get a cached instance of the specified type of cache object.
  85          *
  86          * @param string $id A key in $wgObjectCaches.
  87          * @return BagOStuff
  88          */
  89         public static function getInstance( $id ) {
  90                 if ( !isset( self::$instances[$id] ) ) {
  91                         self::$instances[$id] = self::newFromId( $id );
  92                 }
  93
  94                 return self::$instances[$id];
  95         }
  96
  97         /**
  98          * Get a cached instance of the specified type of WAN cache object.
  99          *
 100          * @since 1.26
 101          * @param string $id A key in $wgWANObjectCaches.
 102          * @return WANObjectCache
 103          */
 104         public static function getWANInstance( $id ) {
 105                 if ( !isset( self::$wanInstances[$id] ) ) {
 106                         self::$wanInstances[$id] = self::newWANCacheFromId( $id );
 107                 }
 108
 109                 return self::$wanInstances[$id];
 110         }
 111
 112         /**
 113          * Create a new cache object of the specified type.
 114          *
 115          * @param string $id A key in $wgObjectCaches.
 116          * @return BagOStuff
 117          * @throws MWException
 118          */
 119         public static function newFromId( $id ) {
 120                 global $wgObjectCaches;
 121
 122                 if ( !isset( $wgObjectCaches[$id] ) ) {
 123                         throw new MWException( "Invalid object cache type \"$id\" requested. " .
 124                                 "It is not present in \$wgObjectCaches." );
 125                 }
 126
 127                 return self::newFromParams( $wgObjectCaches[$id] );
 128         }
 129
 130         /**
 131          * Get the default keyspace for this wiki.
 132          *
 133          * This is either the value of the `CachePrefix` configuration variable,
 134          * or (if the former is unset) the `DBname` configuration variable, with
 135          * `DBprefix` (if defined).
 136          *
 137          * @return string
 138          */
 139         public static function getDefaultKeyspace() {
 140                 global $wgCachePrefix;
 141
 142                 $keyspace = $wgCachePrefix;
 143                 if ( is_string( $keyspace ) && $keyspace !== '' ) {
 144                         return $keyspace;
 145                 }
 146
 147                 return wfWikiID();
 148         }
 149
 150         /**
 151          * Create a new cache object from parameters.
 152          *
 153          * @param array $params Must have 'factory' or 'class' property.
 154          *  - factory: Callback passed $params that returns BagOStuff.
 155          *  - class: BagOStuff subclass constructed with $params.
 156          *  - loggroup: Alias to set 'logger' key with LoggerFactory group.
 157          *  - .. Other parameters passed to factory or class.
 158          * @return BagOStuff
 159          * @throws MWException
 160          */
 161         public static function newFromParams( $params ) {
 162                 if ( isset( $params['loggroup'] ) ) {
 163                         $params['logger'] = LoggerFactory::getInstance( $params['loggroup'] );
 164                 } else {
 165                         $params['logger'] = LoggerFactory::getInstance( 'objectcache' );
 166                 }
 167                 if ( !isset( $params['keyspace'] ) ) {
 168                         $params['keyspace'] = self::getDefaultKeyspace();
 169                 }
 170                 if ( isset( $params['factory'] ) ) {
 171                         return call_user_func( $params['factory'], $params );
 172                 } elseif ( isset( $params['class'] ) ) {
 173                         $class = $params['class'];
 174                         // Automatically set the 'async' update handler
 175                         if ( $class === 'MultiWriteBagOStuff' ) {
 176                                 $params['asyncHandler'] = isset( $params['asyncHandler'] )
 177                                         ? $params['asyncHandler']
 178                                         : 'DeferredUpdates::addCallableUpdate';
 179                         }
 180                         // Do b/c logic for MemcachedBagOStuff
 181                         if ( is_subclass_of( $class, 'MemcachedBagOStuff' ) ) {
 182                                 if ( !isset( $params['servers'] ) ) {
 183                                         $params['servers'] = $GLOBALS['wgMemCachedServers'];
 184                                 }
 185                                 if ( !isset( $params['debug'] ) ) {
 186                                         $params['debug'] = $GLOBALS['wgMemCachedDebug'];
 187                                 }
 188                                 if ( !isset( $params['persistent'] ) ) {
 189                                         $params['persistent'] = $GLOBALS['wgMemCachedPersistent'];
 190                                 }
 191                                 if ( !isset( $params['timeout'] ) ) {
 192                                         $params['timeout'] = $GLOBALS['wgMemCachedTimeout'];
 193                                 }
 194                         }
 195                         return new $class( $params );
 196                 } else {
 197                         throw new MWException( "The definition of cache type \""
 198                                 . print_r( $params, true ) . "\" lacks both "
 199                                 . "factory and class parameters." );
 200                 }
 201         }
 202
 203         /**
 204          * Factory function for CACHE_ANYTHING (referenced from DefaultSettings.php)
 205          *
 206          * CACHE_ANYTHING means that stuff has to be cached, not caching is not an option.
 207          * If a caching method is configured for any of the main caches ($wgMainCacheType,
 208          * $wgMessageCacheType, $wgParserCacheType), then CACHE_ANYTHING will effectively
 209          * be an alias to the configured cache choice for that.
 210          * If no cache choice is configured (by default $wgMainCacheType is CACHE_NONE),
 211          * then CACHE_ANYTHING will forward to CACHE_DB.
 212          *
 213          * @param array $params
 214          * @return BagOStuff
 215          */
 216         public static function newAnything( $params ) {
 217                 global $wgMainCacheType, $wgMessageCacheType, $wgParserCacheType;
 218                 $candidates = array( $wgMainCacheType, $wgMessageCacheType, $wgParserCacheType );
 219                 foreach ( $candidates as $candidate ) {
 220                         if ( $candidate !== CACHE_NONE && $candidate !== CACHE_ANYTHING ) {
 221                                 return self::getInstance( $candidate );
 222                         }
 223                 }
 224                 return self::getInstance( CACHE_DB );
 225         }
 226
 227         /**
 228          * Factory function for CACHE_ACCEL (referenced from DefaultSettings.php)
 229          *
 230          * This will look for any APC style server-local cache.
 231          * A fallback cache can be specified if none is found.
 232          *
 233          *     // Direct calls
 234          *     ObjectCache::newAccelerator( $fallbackType );
 235          *
 236          *     // From $wgObjectCaches via newFromParams()
 237          *     ObjectCache::newAccelerator( array( 'fallback' => $fallbackType ) );
 238          *
 239          * @param array $params [optional] Array key 'fallback' for $fallback.
 240          * @param int|string $fallback Fallback cache, e.g. (CACHE_NONE, "hash") (since 1.24)
 241          * @return BagOStuff
 242          * @throws MWException
 243          */
 244         public static function newAccelerator( $params = array(), $fallback = null ) {
 245                 if ( $fallback === null ) {
 246                         // The is_array check here is needed because in PHP 5.3:
 247                         // $a = 'hash'; isset( $params['fallback'] ); yields true
 248                         if ( is_array( $params ) && isset( $params['fallback'] ) ) {
 249                                 $fallback = $params['fallback'];
 250                         } elseif ( !is_array( $params ) ) {
 251                                 $fallback = $params;
 252                         }
 253                 }
 254                 if ( function_exists( 'apc_fetch' ) ) {
 255                         $id = 'apc';
 256                 } elseif ( function_exists( 'xcache_get' ) && wfIniGetBool( 'xcache.var_size' ) ) {
 257                         $id = 'xcache';
 258                 } elseif ( function_exists( 'wincache_ucache_get' ) ) {
 259                         $id = 'wincache';
 260                 } else {
 261                         if ( $fallback === null ) {
 262                                 throw new MWException( 'CACHE_ACCEL requested but no suitable object ' .
 263                                         'cache is present. You may want to install APC.' );
 264                         }
 265                         $id = $fallback;
 266                 }
 267                 return self::getInstance( $id );
 268         }
 269
 270         /**
 271          * Create a new cache object of the specified type.
 272          *
 273          * @since 1.26
 274          * @param string $id A key in $wgWANObjectCaches.
 275          * @return WANObjectCache
 276          * @throws MWException
 277          */
 278         public static function newWANCacheFromId( $id ) {
 279                 global $wgWANObjectCaches;
 280
 281                 if ( !isset( $wgWANObjectCaches[$id] ) ) {
 282                         throw new MWException( "Invalid object cache type \"$id\" requested. " .
 283                                 "It is not present in \$wgWANObjectCaches." );
 284                 }
 285
 286                 $params = $wgWANObjectCaches[$id];
 287                 $class = $params['relayerConfig']['class'];
 288                 $params['relayer'] = new $class( $params['relayerConfig'] );
 289                 $params['cache'] = self::newFromId( $params['cacheId'] );
 290                 if ( isset( $params['loggroup'] ) ) {
 291                         $params['logger'] = LoggerFactory::getInstance( $params['loggroup'] );
 292                 } else {
 293                         $params['logger'] = LoggerFactory::getInstance( 'objectcache' );
 294                 }
 295                 $class = $params['class'];
 296
 297                 return new $class( $params );
 298         }
 299
 300         /**
 301          * Get the main cluster-local cache object.
 302          *
 303          * @since 1.27
 304          * @return BagOStuff
 305          */
 306         public static function getLocalClusterInstance() {
 307                 global $wgMainCacheType;
 308
 309                 return self::getInstance( $wgMainCacheType );
 310         }
 311
 312         /**
 313          * Get the main WAN cache object.
 314          *
 315          * @since 1.26
 316          * @return WANObjectCache
 317          */
 318         public static function getMainWANInstance() {
 319                 global $wgMainWANCache;
 320
 321                 return self::getWANInstance( $wgMainWANCache );
 322         }
 323
 324         /**
 325          * Get the cache object for the main stash.
 326          *
 327          * Stash objects are BagOStuff instances suitable for storing light
 328          * weight data that is not canonically stored elsewhere (such as RDBMS).
 329          * Stashes should be configured to propagate changes to all data-centers.
 330          *
 331          * Callers should be prepared for:
 332          *   - a) Writes to be slower in non-"primary" (e.g. HTTP GET/HEAD only) DCs
 333          *   - b) Reads to be eventually consistent, e.g. for get()/getMulti()
 334          * In general, this means avoiding updates on idempotent HTTP requests and
 335          * avoiding an assumption of perfect serializability (or accepting anomalies).
 336          * Reads may be eventually consistent or data might rollback as nodes flap.
 337          * Callers can use BagOStuff:READ_LATEST to see the latest available data.
 338          *
 339          * @return BagOStuff
 340          * @since 1.26
 341          */
 342         public static function getMainStashInstance() {
 343                 global $wgMainStash;
 344
 345                 return self::getInstance( $wgMainStash );
 346         }
 347
 348         /**
 349          * Clear all the cached instances.
 350          */
 351         public static function clear() {
 352                 self::$instances = array();
 353                 self::$wanInstances = array();
 354         }
 355 }