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::getMainWANInstance()
  46  *   Purpose: Memory cache.
  47  *   Stored in the local data-center's main cache (uses different cache keys).
  48  *   Delete events are broadcasted to other DCs. See WANObjectCache for details.
  49  *
  50  * - ObjectCache::getLocalServerInstance( $fallbackType )
  51  *   Purpose: Memory cache for very hot keys.
  52  *   Stored only on the individual web server (often EmptyBagOStuff in CLI mode).
  53  *   Not replicated to the other servers.
  54  *
  55  * - ObjectCache::getLocalClusterInstance()
  56  *   Purpose: Memory storage for per-cluster coordination and tracking.
  57  *   A typical use case would be a rate limit counter or cache regeneration mutex.
  58  *   Stored centrally within the local data-center. Not replicated to other DCs.
  59  *   Also known as $wgMemc. Configured by $wgMainCacheType.
  60  *
  61  * - ObjectCache::getMainStashInstance()
  62  *   Purpose: Ephemeral global storage.
  63  *   Stored centrally within the primary data-center.
  64  *   Changes are applied there first and replicated to other DCs (best-effort).
  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  * - ObjectCache::getInstance( $cacheType )
  69  *   Purpose: Special cases (like tiered memory/disk caches).
  70  *   Get a specific cache type by key in $wgObjectCaches.
  71  *
  72  * All the above cache instances (BagOStuff and WANObjectCache) have their makeKey()
  73  * method scoped to the *current* wiki ID. Use makeGlobalKey() to avoid this scoping
  74  * when using keys that need to be shared amongst wikis.
  75  *
  76  * @ingroup Cache
  77  */
  78 class ObjectCache {
  79         /** @var BagOStuff[] Map of (id => BagOStuff) */
  80         public static $instances = array();
  81         /** @var WANObjectCache[] Map of (id => WANObjectCache) */
  82         public static $wanInstances = array();
  83
  84         /**
  85          * Get a cached instance of the specified type of cache object.
  86          *
  87          * @param string $id A key in $wgObjectCaches.
  88          * @return BagOStuff
  89          */
  90         public static function getInstance( $id ) {
  91                 if ( !isset( self::$instances[$id] ) ) {
  92                         self::$instances[$id] = self::newFromId( $id );
  93                 }
  94
  95                 return self::$instances[$id];
  96         }
  97
  98         /**
  99          * Get a cached instance of the specified type of WAN cache object.
 100          *
 101          * @since 1.26
 102          * @param string $id A key in $wgWANObjectCaches.
 103          * @return WANObjectCache
 104          */
 105         public static function getWANInstance( $id ) {
 106                 if ( !isset( self::$wanInstances[$id] ) ) {
 107                         self::$wanInstances[$id] = self::newWANCacheFromId( $id );
 108                 }
 109
 110                 return self::$wanInstances[$id];
 111         }
 112
 113         /**
 114          * Create a new cache object of the specified type.
 115          *
 116          * @param string $id A key in $wgObjectCaches.
 117          * @return BagOStuff
 118          * @throws MWException
 119          */
 120         public static function newFromId( $id ) {
 121                 global $wgObjectCaches;
 122
 123                 if ( !isset( $wgObjectCaches[$id] ) ) {
 124                         throw new MWException( "Invalid object cache type \"$id\" requested. " .
 125                                 "It is not present in \$wgObjectCaches." );
 126                 }
 127
 128                 return self::newFromParams( $wgObjectCaches[$id] );
 129         }
 130
 131         /**
 132          * Get the default keyspace for this wiki.
 133          *
 134          * This is either the value of the `CachePrefix` configuration variable,
 135          * or (if the former is unset) the `DBname` configuration variable, with
 136          * `DBprefix` (if defined).
 137          *
 138          * @return string
 139          */
 140         public static function getDefaultKeyspace() {
 141                 global $wgCachePrefix, $wgDBname, $wgDBprefix;
 142
 143                 $keyspace = $wgCachePrefix;
 144                 if ( is_string( $keyspace ) && $keyspace !== '' ) {
 145                         return $keyspace;
 146                 }
 147
 148                 $keyspace = $wgDBname;
 149                 if ( is_string( $wgDBprefix ) && $wgDBprefix !== '' ) {
 150                         $keyspace .= '-' . $wgDBprefix;
 151                 }
 152
 153                 return $keyspace;
 154         }
 155
 156         /**
 157          * Create a new cache object from parameters.
 158          *
 159          * @param array $params Must have 'factory' or 'class' property.
 160          *  - factory: Callback passed $params that returns BagOStuff.
 161          *  - class: BagOStuff subclass constructed with $params.
 162          *  - loggroup: Alias to set 'logger' key with LoggerFactory group.
 163          *  - .. Other parameters passed to factory or class.
 164          * @return BagOStuff
 165          * @throws MWException
 166          */
 167         public static function newFromParams( $params ) {
 168                 if ( isset( $params['loggroup'] ) ) {
 169                         $params['logger'] = LoggerFactory::getInstance( $params['loggroup'] );
 170                 } else {
 171                         $params['logger'] = LoggerFactory::getInstance( 'objectcache' );
 172                 }
 173                 if ( !isset( $params['keyspace'] ) ) {
 174                         $params['keyspace'] = self::getDefaultKeyspace();
 175                 }
 176                 if ( isset( $params['factory'] ) ) {
 177                         return call_user_func( $params['factory'], $params );
 178                 } elseif ( isset( $params['class'] ) ) {
 179                         $class = $params['class'];
 180                         // Automatically set the 'async' update handler
 181                         if ( $class === 'MultiWriteBagOStuff' ) {
 182                                 $params['asyncHandler'] = isset( $params['asyncHandler'] )
 183                                         ? $params['asyncHandler']
 184                                         : 'DeferredUpdates::addCallableUpdate';
 185                         }
 186                         // Do b/c logic for MemcachedBagOStuff
 187                         if ( is_subclass_of( $class, 'MemcachedBagOStuff' ) ) {
 188                                 if ( !isset( $params['servers'] ) ) {
 189                                         $params['servers'] = $GLOBALS['wgMemCachedServers'];
 190                                 }
 191                                 if ( !isset( $params['debug'] ) ) {
 192                                         $params['debug'] = $GLOBALS['wgMemCachedDebug'];
 193                                 }
 194                                 if ( !isset( $params['persistent'] ) ) {
 195                                         $params['persistent'] = $GLOBALS['wgMemCachedPersistent'];
 196                                 }
 197                                 if ( !isset( $params['timeout'] ) ) {
 198                                         $params['timeout'] = $GLOBALS['wgMemCachedTimeout'];
 199                                 }
 200                         }
 201                         return new $class( $params );
 202                 } else {
 203                         throw new MWException( "The definition of cache type \""
 204                                 . print_r( $params, true ) . "\" lacks both "
 205                                 . "factory and class parameters." );
 206                 }
 207         }
 208
 209         /**
 210          * Factory function for CACHE_ANYTHING (referenced from DefaultSettings.php)
 211          *
 212          * CACHE_ANYTHING means that stuff has to be cached, not caching is not an option.
 213          * If a caching method is configured for any of the main caches ($wgMainCacheType,
 214          * $wgMessageCacheType, $wgParserCacheType), then CACHE_ANYTHING will effectively
 215          * be an alias to the configured cache choice for that.
 216          * If no cache choice is configured (by default $wgMainCacheType is CACHE_NONE),
 217          * then CACHE_ANYTHING will forward to CACHE_DB.
 218          *
 219          * @param array $params
 220          * @return BagOStuff
 221          */
 222         public static function newAnything( $params ) {
 223                 global $wgMainCacheType, $wgMessageCacheType, $wgParserCacheType;
 224                 $candidates = array( $wgMainCacheType, $wgMessageCacheType, $wgParserCacheType );
 225                 foreach ( $candidates as $candidate ) {
 226                         if ( $candidate !== CACHE_NONE && $candidate !== CACHE_ANYTHING ) {
 227                                 return self::getInstance( $candidate );
 228                         }
 229                 }
 230                 return self::getInstance( CACHE_DB );
 231         }
 232
 233         /**
 234          * Factory function for CACHE_ACCEL (referenced from DefaultSettings.php)
 235          *
 236          * This will look for any APC style server-local cache.
 237          * A fallback cache can be specified if none is found.
 238          *
 239          *     // Direct calls
 240          *     ObjectCache::getLocalServerInstance( $fallbackType );
 241          *
 242          *     // From $wgObjectCaches via newFromParams()
 243          *     ObjectCache::getLocalServerInstance( array( 'fallback' => $fallbackType ) );
 244          *
 245          * @param int|string|array $fallback Fallback cache or parameter map with 'fallback'
 246          * @return BagOStuff
 247          * @throws MWException
 248          * @since 1.27
 249          */
 250         public static function getLocalServerInstance( $fallback = CACHE_NONE ) {
 251                 if ( function_exists( 'apc_fetch' ) ) {
 252                         $id = 'apc';
 253                 } elseif ( function_exists( 'xcache_get' ) && wfIniGetBool( 'xcache.var_size' ) ) {
 254                         $id = 'xcache';
 255                 } elseif ( function_exists( 'wincache_ucache_get' ) ) {
 256                         $id = 'wincache';
 257                 } else {
 258                         if ( is_array( $fallback ) ) {
 259                                 $id = isset( $fallback['fallback'] ) ? $fallback['fallback'] : CACHE_NONE;
 260                         } else {
 261                                 $id = $fallback;
 262                         }
 263                 }
 264
 265                 return self::getInstance( $id );
 266         }
 267
 268         /**
 269          * @param array $params [optional] Array key 'fallback' for $fallback.
 270          * @param int|string $fallback Fallback cache, e.g. (CACHE_NONE, "hash") (since 1.24)
 271          * @return BagOStuff
 272          * @deprecated 1.27
 273          */
 274         public static function newAccelerator( $params = array(), $fallback = null ) {
 275                 if ( $fallback === null ) {
 276                         // The is_array check here is needed because in PHP 5.3:
 277                         // $a = 'hash'; isset( $params['fallback'] ); yields true
 278                         if ( is_array( $params ) && isset( $params['fallback'] ) ) {
 279                                 $fallback = $params['fallback'];
 280                         } elseif ( !is_array( $params ) ) {
 281                                 $fallback = $params;
 282                         }
 283                 }
 284
 285                 return self::getLocalServerInstance( $fallback );
 286         }
 287
 288         /**
 289          * Create a new cache object of the specified type.
 290          *
 291          * @since 1.26
 292          * @param string $id A key in $wgWANObjectCaches.
 293          * @return WANObjectCache
 294          * @throws MWException
 295          */
 296         public static function newWANCacheFromId( $id ) {
 297                 global $wgWANObjectCaches;
 298
 299                 if ( !isset( $wgWANObjectCaches[$id] ) ) {
 300                         throw new MWException( "Invalid object cache type \"$id\" requested. " .
 301                                 "It is not present in \$wgWANObjectCaches." );
 302                 }
 303
 304                 $params = $wgWANObjectCaches[$id];
 305                 $class = $params['relayerConfig']['class'];
 306                 $params['relayer'] = new $class( $params['relayerConfig'] );
 307                 $params['cache'] = self::newFromId( $params['cacheId'] );
 308                 if ( isset( $params['loggroup'] ) ) {
 309                         $params['logger'] = LoggerFactory::getInstance( $params['loggroup'] );
 310                 } else {
 311                         $params['logger'] = LoggerFactory::getInstance( 'objectcache' );
 312                 }
 313                 $class = $params['class'];
 314
 315                 return new $class( $params );
 316         }
 317
 318         /**
 319          * Get the main cluster-local cache object.
 320          *
 321          * @since 1.27
 322          * @return BagOStuff
 323          */
 324         public static function getLocalClusterInstance() {
 325                 global $wgMainCacheType;
 326
 327                 return self::getInstance( $wgMainCacheType );
 328         }
 329
 330         /**
 331          * Get the main WAN cache object.
 332          *
 333          * @since 1.26
 334          * @return WANObjectCache
 335          */
 336         public static function getMainWANInstance() {
 337                 global $wgMainWANCache;
 338
 339                 return self::getWANInstance( $wgMainWANCache );
 340         }
 341
 342         /**
 343          * Get the cache object for the main stash.
 344          *
 345          * Stash objects are BagOStuff instances suitable for storing light
 346          * weight data that is not canonically stored elsewhere (such as RDBMS).
 347          * Stashes should be configured to propagate changes to all data-centers.
 348          *
 349          * Callers should be prepared for:
 350          *   - a) Writes to be slower in non-"primary" (e.g. HTTP GET/HEAD only) DCs
 351          *   - b) Reads to be eventually consistent, e.g. for get()/getMulti()
 352          * In general, this means avoiding updates on idempotent HTTP requests and
 353          * avoiding an assumption of perfect serializability (or accepting anomalies).
 354          * Reads may be eventually consistent or data might rollback as nodes flap.
 355          * Callers can use BagOStuff:READ_LATEST to see the latest available data.
 356          *
 357          * @return BagOStuff
 358          * @since 1.26
 359          */
 360         public static function getMainStashInstance() {
 361                 global $wgMainStash;
 362
 363                 return self::getInstance( $wgMainStash );
 364         }
 365
 366         /**
 367          * Clear all the cached instances.
 368          */
 369         public static function clear() {
 370                 self::$instances = array();
 371                 self::$wanInstances = array();
 372         }
 373 }