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, $wgDBname, $wgDBprefix;
 141
 142                 $keyspace = $wgCachePrefix;
 143                 if ( is_string( $keyspace ) && $keyspace !== '' ) {
 144                         return $keyspace;
 145                 }
 146
 147                 $keyspace = $wgDBname;
 148                 if ( is_string( $wgDBprefix ) && $wgDBprefix !== '' ) {
 149                         $keyspace .= '-' . $wgDBprefix;
 150                 }
 151
 152                 return $keyspace;
 153         }
 154
 155         /**
 156          * Create a new cache object from parameters.
 157          *
 158          * @param array $params Must have 'factory' or 'class' property.
 159          *  - factory: Callback passed $params that returns BagOStuff.
 160          *  - class: BagOStuff subclass constructed with $params.
 161          *  - loggroup: Alias to set 'logger' key with LoggerFactory group.
 162          *  - .. Other parameters passed to factory or class.
 163          * @return BagOStuff
 164          * @throws MWException
 165          */
 166         public static function newFromParams( $params ) {
 167                 if ( isset( $params['loggroup'] ) ) {
 168                         $params['logger'] = LoggerFactory::getInstance( $params['loggroup'] );
 169                 } else {
 170                         // For backwards-compatability with custom parameters, lets not
 171                         // have all logging suddenly disappear
 172                         $params['logger'] = LoggerFactory::getInstance( 'objectcache' );
 173                 }
 174                 if ( !isset( $params['keyspace'] ) ) {
 175                         $params['keyspace'] = self::getDefaultKeyspace();
 176                 }
 177                 if ( isset( $params['factory'] ) ) {
 178                         return call_user_func( $params['factory'], $params );
 179                 } elseif ( isset( $params['class'] ) ) {
 180                         $class = $params['class'];
 181                         return new $class( $params );
 182                 } else {
 183                         throw new MWException( "The definition of cache type \""
 184                                 . print_r( $params, true ) . "\" lacks both "
 185                                 . "factory and class parameters." );
 186                 }
 187         }
 188
 189         /**
 190          * Factory function for CACHE_ANYTHING (referenced from DefaultSettings.php)
 191          *
 192          * CACHE_ANYTHING means that stuff has to be cached, not caching is not an option.
 193          * If a caching method is configured for any of the main caches ($wgMainCacheType,
 194          * $wgMessageCacheType, $wgParserCacheType), then CACHE_ANYTHING will effectively
 195          * be an alias to the configured cache choice for that.
 196          * If no cache choice is configured (by default $wgMainCacheType is CACHE_NONE),
 197          * then CACHE_ANYTHING will forward to CACHE_DB.
 198          *
 199          * @param array $params
 200          * @return BagOStuff
 201          */
 202         public static function newAnything( $params ) {
 203                 global $wgMainCacheType, $wgMessageCacheType, $wgParserCacheType;
 204                 $candidates = array( $wgMainCacheType, $wgMessageCacheType, $wgParserCacheType );
 205                 foreach ( $candidates as $candidate ) {
 206                         if ( $candidate !== CACHE_NONE && $candidate !== CACHE_ANYTHING ) {
 207                                 return self::getInstance( $candidate );
 208                         }
 209                 }
 210                 return self::getInstance( CACHE_DB );
 211         }
 212
 213         /**
 214          * Factory function for CACHE_ACCEL (referenced from DefaultSettings.php)
 215          *
 216          * This will look for any APC style server-local cache.
 217          * A fallback cache can be specified if none is found.
 218          *
 219          *     // Direct calls
 220          *     ObjectCache::newAccelerator( $fallbackType );
 221          *
 222          *     // From $wgObjectCaches via newFromParams()
 223          *     ObjectCache::newAccelerator( array( 'fallback' => $fallbackType ) );
 224          *
 225          * @param array $params [optional] Array key 'fallback' for $fallback.
 226          * @param int|string $fallback Fallback cache, e.g. (CACHE_NONE, "hash") (since 1.24)
 227          * @return BagOStuff
 228          * @throws MWException
 229          */
 230         public static function newAccelerator( $params = array(), $fallback = null ) {
 231                 if ( $fallback === null ) {
 232                         // The is_array check here is needed because in PHP 5.3:
 233                         // $a = 'hash'; isset( $params['fallback'] ); yields true
 234                         if ( is_array( $params ) && isset( $params['fallback'] ) ) {
 235                                 $fallback = $params['fallback'];
 236                         } elseif ( !is_array( $params ) ) {
 237                                 $fallback = $params;
 238                         }
 239                 }
 240                 if ( function_exists( 'apc_fetch' ) ) {
 241                         $id = 'apc';
 242                 } elseif ( function_exists( 'xcache_get' ) && wfIniGetBool( 'xcache.var_size' ) ) {
 243                         $id = 'xcache';
 244                 } elseif ( function_exists( 'wincache_ucache_get' ) ) {
 245                         $id = 'wincache';
 246                 } else {
 247                         if ( $fallback === null ) {
 248                                 throw new MWException( 'CACHE_ACCEL requested but no suitable object ' .
 249                                         'cache is present. You may want to install APC.' );
 250                         }
 251                         $id = $fallback;
 252                 }
 253                 return self::newFromId( $id );
 254         }
 255
 256         /**
 257          * Factory function that creates a memcached client object.
 258          *
 259          * This always uses the PHP client, since the PECL client has a different
 260          * hashing scheme and a different interpretation of the flags bitfield, so
 261          * switching between the two clients randomly would be disastrous.
 262          *
 263          * @param array $params
 264          * @return MemcachedPhpBagOStuff
 265          */
 266         public static function newMemcached( $params ) {
 267                 return new MemcachedPhpBagOStuff( $params );
 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                 $class = $params['class'];
 291
 292                 return new $class( $params );
 293         }
 294
 295         /**
 296          * Get the main cluster-local cache object.
 297          *
 298          * @since 1.27
 299          * @return BagOStuff
 300          */
 301         public static function getLocalClusterInstance() {
 302                 global $wgMainCacheType;
 303
 304                 return self::getInstance( $wgMainCacheType );
 305         }
 306
 307         /**
 308          * Get the main WAN cache object.
 309          *
 310          * @since 1.26
 311          * @return WANObjectCache
 312          */
 313         public static function getMainWANInstance() {
 314                 global $wgMainWANCache;
 315
 316                 return self::getWANInstance( $wgMainWANCache );
 317         }
 318
 319         /**
 320          * Get the cache object for the main stash.
 321          *
 322          * Stash objects are BagOStuff instances suitable for storing light
 323          * weight data that is not canonically stored elsewhere (such as RDBMS).
 324          * Stashes should be configured to propagate changes to all data-centers.
 325          *
 326          * Callers should be prepared for:
 327          *   - a) Writes to be slower in non-"primary" (e.g. HTTP GET/HEAD only) DCs
 328          *   - b) Reads to be eventually consistent, e.g. for get()/getMulti()
 329          * In general, this means avoiding updates on idempotent HTTP requests and
 330          * avoiding an assumption of perfect serializability (or accepting anomalies).
 331          * Reads may be eventually consistent or data might rollback as nodes flap.
 332          * Callers can use BagOStuff:READ_LATEST to see the latest available data.
 333          *
 334          * @return BagOStuff
 335          * @since 1.26
 336          */
 337         public static function getMainStashInstance() {
 338                 global $wgMainStash;
 339
 340                 return self::getInstance( $wgMainStash );
 341         }
 342
 343         /**
 344          * Clear all the cached instances.
 345          */
 346         public static function clear() {
 347                 self::$instances = array();
 348                 self::$wanInstances = array();
 349         }
 350 }