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          * Get the default keyspace for this wiki.
 128          *
 129          * This is either the value of the `CachePrefix` configuration variable,
 130          * or (if the former is unset) the `DBname` configuration variable, with
 131          * `DBprefix` (if defined).
 132          *
 133          * @return string
 134          */
 135         public static function getDefaultKeyspace() {
 136                 global $wgCachePrefix, $wgDBname, $wgDBprefix;
 137
 138                 $keyspace = $wgCachePrefix;
 139                 if ( is_string( $keyspace ) && $keyspace !== '' ) {
 140                         return $keyspace;
 141                 }
 142
 143                 $keyspace = $wgDBname;
 144                 if ( is_string( $wgDBprefix ) && $wgDBprefix !== '' ) {
 145                         $keyspace .= '-' . $wgDBprefix;
 146                 }
 147
 148                 return $keyspace;
 149         }
 150
 151         /**
 152          * Create a new cache object from parameters.
 153          *
 154          * @param array $params Must have 'factory' or 'class' property.
 155          *  - factory: Callback passed $params that returns BagOStuff.
 156          *  - class: BagOStuff subclass constructed with $params.
 157          *  - loggroup: Alias to set 'logger' key with LoggerFactory group.
 158          *  - .. Other parameters passed to factory or class.
 159          * @return BagOStuff
 160          * @throws MWException
 161          */
 162         public static function newFromParams( $params ) {
 163                 if ( isset( $params['loggroup'] ) ) {
 164                         $params['logger'] = LoggerFactory::getInstance( $params['loggroup'] );
 165                 } else {
 166                         // For backwards-compatability with custom parameters, lets not
 167                         // have all logging suddenly disappear
 168                         $params['logger'] = LoggerFactory::getInstance( 'objectcache' );
 169                 }
 170                 if ( !isset( $params['keyspace'] ) ) {
 171                         $params['keyspace'] = self::getDefaultKeyspace();
 172                 }
 173                 if ( isset( $params['factory'] ) ) {
 174                         return call_user_func( $params['factory'], $params );
 175                 } elseif ( isset( $params['class'] ) ) {
 176                         $class = $params['class'];
 177                         return new $class( $params );
 178                 } else {
 179                         throw new MWException( "The definition of cache type \""
 180                                 . print_r( $params, true ) . "\" lacks both "
 181                                 . "factory and class parameters." );
 182                 }
 183         }
 184
 185         /**
 186          * Factory function for CACHE_ANYTHING (referenced from DefaultSettings.php)
 187          *
 188          * CACHE_ANYTHING means that stuff has to be cached, not caching is not an option.
 189          * If a caching method is configured for any of the main caches ($wgMainCacheType,
 190          * $wgMessageCacheType, $wgParserCacheType), then CACHE_ANYTHING will effectively
 191          * be an alias to the configured cache choice for that.
 192          * If no cache choice is configured (by default $wgMainCacheType is CACHE_NONE),
 193          * then CACHE_ANYTHING will forward to CACHE_DB.
 194          *
 195          * @param array $params
 196          * @return BagOStuff
 197          */
 198         public static function newAnything( $params ) {
 199                 global $wgMainCacheType, $wgMessageCacheType, $wgParserCacheType;
 200                 $candidates = array( $wgMainCacheType, $wgMessageCacheType, $wgParserCacheType );
 201                 foreach ( $candidates as $candidate ) {
 202                         if ( $candidate !== CACHE_NONE && $candidate !== CACHE_ANYTHING ) {
 203                                 return self::getInstance( $candidate );
 204                         }
 205                 }
 206                 return self::getInstance( CACHE_DB );
 207         }
 208
 209         /**
 210          * Factory function for CACHE_ACCEL (referenced from DefaultSettings.php)
 211          *
 212          * This will look for any APC style server-local cache.
 213          * A fallback cache can be specified if none is found.
 214          *
 215          *     // Direct calls
 216          *     ObjectCache::newAccelerator( $fallbackType );
 217          *
 218          *     // From $wgObjectCaches via newFromParams()
 219          *     ObjectCache::newAccelerator( array( 'fallback' => $fallbackType ) );
 220          *
 221          * @param array $params [optional] Array key 'fallback' for $fallback.
 222          * @param int|string $fallback Fallback cache, e.g. (CACHE_NONE, "hash") (since 1.24)
 223          * @return BagOStuff
 224          * @throws MWException
 225          */
 226         public static function newAccelerator( $params = array(), $fallback = null ) {
 227                 if ( $fallback === null ) {
 228                         // The is_array check here is needed because in PHP 5.3:
 229                         // $a = 'hash'; isset( $params['fallback'] ); yields true
 230                         if ( is_array( $params ) && isset( $params['fallback'] ) ) {
 231                                 $fallback = $params['fallback'];
 232                         } elseif ( !is_array( $params ) ) {
 233                                 $fallback = $params;
 234                         }
 235                 }
 236                 if ( function_exists( 'apc_fetch' ) ) {
 237                         $id = 'apc';
 238                 } elseif ( function_exists( 'xcache_get' ) && wfIniGetBool( 'xcache.var_size' ) ) {
 239                         $id = 'xcache';
 240                 } elseif ( function_exists( 'wincache_ucache_get' ) ) {
 241                         $id = 'wincache';
 242                 } else {
 243                         if ( $fallback === null ) {
 244                                 throw new MWException( 'CACHE_ACCEL requested but no suitable object ' .
 245                                         'cache is present. You may want to install APC.' );
 246                         }
 247                         $id = $fallback;
 248                 }
 249                 return self::newFromId( $id );
 250         }
 251
 252         /**
 253          * Factory function that creates a memcached client object.
 254          *
 255          * This always uses the PHP client, since the PECL client has a different
 256          * hashing scheme and a different interpretation of the flags bitfield, so
 257          * switching between the two clients randomly would be disastrous.
 258          *
 259          * @param array $params
 260          * @return MemcachedPhpBagOStuff
 261          */
 262         public static function newMemcached( $params ) {
 263                 return new MemcachedPhpBagOStuff( $params );
 264         }
 265
 266         /**
 267          * Create a new cache object of the specified type.
 268          *
 269          * @since 1.26
 270          * @param string $id A key in $wgWANObjectCaches.
 271          * @return WANObjectCache
 272          * @throws MWException
 273          */
 274         public static function newWANCacheFromId( $id ) {
 275                 global $wgWANObjectCaches;
 276
 277                 if ( !isset( $wgWANObjectCaches[$id] ) ) {
 278                         throw new MWException( "Invalid object cache type \"$id\" requested. " .
 279                                 "It is not present in \$wgWANObjectCaches." );
 280                 }
 281
 282                 $params = $wgWANObjectCaches[$id];
 283                 $class = $params['relayerConfig']['class'];
 284                 $params['relayer'] = new $class( $params['relayerConfig'] );
 285                 $params['cache'] = self::newFromId( $params['cacheId'] );
 286                 $class = $params['class'];
 287
 288                 return new $class( $params );
 289         }
 290
 291         /**
 292          * Get the main cluster-local cache object.
 293          *
 294          * @since 1.27
 295          * @return BagOStuff
 296          */
 297         public static function getMainClusterInstance() {
 298                 global $wgMainCacheType;
 299
 300                 return self::getInstance( $wgMainCacheType );
 301         }
 302
 303         /**
 304          * Get the main WAN cache object.
 305          *
 306          * @since 1.26
 307          * @return WANObjectCache
 308          */
 309         public static function getMainWANInstance() {
 310                 global $wgMainWANCache;
 311
 312                 return self::getWANInstance( $wgMainWANCache );
 313         }
 314
 315         /**
 316          * Get the cache object for the main stash.
 317          *
 318          * Stash objects are BagOStuff instances suitable for storing light
 319          * weight data that is not canonically stored elsewhere (such as RDBMS).
 320          * Stashes should be configured to propagate changes to all data-centers.
 321          *
 322          * Callers should be prepared for:
 323          *   - a) Writes to be slower in non-"primary" (e.g. HTTP GET/HEAD only) DCs
 324          *   - b) Reads to be eventually consistent, e.g. for get()/getMulti()
 325          * In general, this means avoiding updates on idempotent HTTP requests and
 326          * avoiding an assumption of perfect serializability (or accepting anomalies).
 327          * Reads may be eventually consistent or data might rollback as nodes flap.
 328          * Callers can use BagOStuff:READ_LATEST to see the latest available data.
 329          *
 330          * @return BagOStuff
 331          * @since 1.26
 332          */
 333         public static function getMainStashInstance() {
 334                 global $wgMainStash;
 335
 336                 return self::getInstance( $wgMainStash );
 337         }
 338
 339         /**
 340          * Clear all the cached instances.
 341          */
 342         public static function clear() {
 343                 self::$instances = array();
 344                 self::$wanInstances = array();
 345         }
 346 }