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 use MediaWiki\MediaWikiServices;
  26 use MediaWiki\Services\ServiceDisabledException;
  27
  28 /**
  29  * Functions to get cache objects
  30  *
  31  * The word "cache" has two main dictionary meanings, and both
  32  * are used in this factory class. They are:
  33  *
  34  *   - a) Cache (the computer science definition).
  35  *        A place to store copies or computations on existing data for
  36  *        higher access speeds.
  37  *   - b) Storage.
  38  *        A place to store lightweight data that is not canonically
  39  *        stored anywhere else (e.g. a "hoard" of objects).
  40  *
  41  * The former should always use strongly consistent stores, so callers don't
  42  * have to deal with stale reads. The later may be eventually consistent, but
  43  * callers can use BagOStuff:READ_LATEST to see the latest available data.
  44  *
  45  * Primary entry points:
  46  *
  47  * - ObjectCache::getMainWANInstance()
  48  *   Purpose: Memory cache.
  49  *   Stored in the local data-center's main cache (keyspace different from local-cluster cache).
  50  *   Delete events are broadcasted to other DCs main cache. See WANObjectCache for details.
  51  *
  52  * - ObjectCache::getLocalServerInstance( $fallbackType )
  53  *   Purpose: Memory cache for very hot keys.
  54  *   Stored only on the individual web server (typically APC for web requests,
  55  *   and EmptyBagOStuff in CLI mode).
  56  *   Not replicated to the other servers.
  57  *
  58  * - ObjectCache::getLocalClusterInstance()
  59  *   Purpose: Memory storage for per-cluster coordination and tracking.
  60  *   A typical use case would be a rate limit counter or cache regeneration mutex.
  61  *   Stored centrally within the local data-center. Not replicated to other DCs.
  62  *   Configured by $wgMainCacheType.
  63  *
  64  * - ObjectCache::getMainStashInstance()
  65  *   Purpose: Ephemeral global storage.
  66  *   Stored centrally within the primary data-center.
  67  *   Changes are applied there first and replicated to other DCs (best-effort).
  68  *   To retrieve the latest value (e.g. not from a slave), use BagOStuff::READ_LATEST.
  69  *   This store may be subject to LRU style evictions.
  70  *
  71  * - ObjectCache::getInstance( $cacheType )
  72  *   Purpose: Special cases (like tiered memory/disk caches).
  73  *   Get a specific cache type by key in $wgObjectCaches.
  74  *
  75  * All the above cache instances (BagOStuff and WANObjectCache) have their makeKey()
  76  * method scoped to the *current* wiki ID. Use makeGlobalKey() to avoid this scoping
  77  * when using keys that need to be shared amongst wikis.
  78  *
  79  * @ingroup Cache
  80  */
  81 class ObjectCache {
  82         /** @var BagOStuff[] Map of (id => BagOStuff) */
  83         public static $instances = [];
  84         /** @var WANObjectCache[] Map of (id => WANObjectCache) */
  85         public static $wanInstances = [];
  86
  87         /**
  88          * Get a cached instance of the specified type of cache object.
  89          *
  90          * @param string $id A key in $wgObjectCaches.
  91          * @return BagOStuff
  92          */
  93         public static function getInstance( $id ) {
  94                 if ( !isset( self::$instances[$id] ) ) {
  95                         self::$instances[$id] = self::newFromId( $id );
  96                 }
  97
  98                 return self::$instances[$id];
  99         }
 100
 101         /**
 102          * Get a cached instance of the specified type of WAN cache object.
 103          *
 104          * @since 1.26
 105          * @param string $id A key in $wgWANObjectCaches.
 106          * @return WANObjectCache
 107          */
 108         public static function getWANInstance( $id ) {
 109                 if ( !isset( self::$wanInstances[$id] ) ) {
 110                         self::$wanInstances[$id] = self::newWANCacheFromId( $id );
 111                 }
 112
 113                 return self::$wanInstances[$id];
 114         }
 115
 116         /**
 117          * Create a new cache object of the specified type.
 118          *
 119          * @param string $id A key in $wgObjectCaches.
 120          * @return BagOStuff
 121          * @throws MWException
 122          */
 123         public static function newFromId( $id ) {
 124                 global $wgObjectCaches;
 125
 126                 if ( !isset( $wgObjectCaches[$id] ) ) {
 127                         throw new MWException( "Invalid object cache type \"$id\" requested. " .
 128                                 "It is not present in \$wgObjectCaches." );
 129                 }
 130
 131                 return self::newFromParams( $wgObjectCaches[$id] );
 132         }
 133
 134         /**
 135          * Get the default keyspace for this wiki.
 136          *
 137          * This is either the value of the `CachePrefix` configuration variable,
 138          * or (if the former is unset) the `DBname` configuration variable, with
 139          * `DBprefix` (if defined).
 140          *
 141          * @return string
 142          */
 143         public static function getDefaultKeyspace() {
 144                 global $wgCachePrefix;
 145
 146                 $keyspace = $wgCachePrefix;
 147                 if ( is_string( $keyspace ) && $keyspace !== '' ) {
 148                         return $keyspace;
 149                 }
 150
 151                 return wfWikiID();
 152         }
 153
 154         /**
 155          * Create a new cache object from parameters.
 156          *
 157          * @param array $params Must have 'factory' or 'class' property.
 158          *  - factory: Callback passed $params that returns BagOStuff.
 159          *  - class: BagOStuff subclass constructed with $params.
 160          *  - loggroup: Alias to set 'logger' key with LoggerFactory group.
 161          *  - .. Other parameters passed to factory or class.
 162          * @return BagOStuff
 163          * @throws MWException
 164          */
 165         public static function newFromParams( $params ) {
 166                 if ( isset( $params['loggroup'] ) ) {
 167                         $params['logger'] = LoggerFactory::getInstance( $params['loggroup'] );
 168                 } else {
 169                         $params['logger'] = LoggerFactory::getInstance( 'objectcache' );
 170                 }
 171                 if ( !isset( $params['keyspace'] ) ) {
 172                         $params['keyspace'] = self::getDefaultKeyspace();
 173                 }
 174                 if ( isset( $params['factory'] ) ) {
 175                         return call_user_func( $params['factory'], $params );
 176                 } elseif ( isset( $params['class'] ) ) {
 177                         $class = $params['class'];
 178                         // Automatically set the 'async' update handler
 179                         $params['asyncHandler'] = isset( $params['asyncHandler'] )
 180                                 ? $params['asyncHandler']
 181                                 : 'DeferredUpdates::addCallableUpdate';
 182                         // Enable reportDupes by default
 183                         $params['reportDupes'] = isset( $params['reportDupes'] )
 184                                 ? $params['reportDupes']
 185                                 : true;
 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 = [ $wgMainCacheType, $wgMessageCacheType, $wgParserCacheType ];
 225                 foreach ( $candidates as $candidate ) {
 226                         if ( $candidate !== CACHE_NONE && $candidate !== CACHE_ANYTHING ) {
 227                                 return self::getInstance( $candidate );
 228                         }
 229                 }
 230
 231                 try {
 232                         // Make sure we actually have a DB backend before falling back to CACHE_DB
 233                         MediaWikiServices::getInstance()->getDBLoadBalancer();
 234                         $candidate = CACHE_DB;
 235                 } catch ( ServiceDisabledException $e ) {
 236                         // The LoadBalancer is disabled, probably because
 237                         // MediaWikiServices::disableStorageBackend was called.
 238                         $candidate = CACHE_NONE;
 239                 }
 240
 241                 return self::getInstance( $candidate );
 242         }
 243
 244         /**
 245          * Factory function for CACHE_ACCEL (referenced from DefaultSettings.php)
 246          *
 247          * This will look for any APC style server-local cache.
 248          * A fallback cache can be specified if none is found.
 249          *
 250          *     // Direct calls
 251          *     ObjectCache::getLocalServerInstance( $fallbackType );
 252          *
 253          *     // From $wgObjectCaches via newFromParams()
 254          *     ObjectCache::getLocalServerInstance( array( 'fallback' => $fallbackType ) );
 255          *
 256          * @param int|string|array $fallback Fallback cache or parameter map with 'fallback'
 257          * @return BagOStuff
 258          * @throws MWException
 259          * @since 1.27
 260          */
 261         public static function getLocalServerInstance( $fallback = CACHE_NONE ) {
 262                 if ( function_exists( 'apc_fetch' ) ) {
 263                         $id = 'apc';
 264                 } elseif ( function_exists( 'xcache_get' ) && wfIniGetBool( 'xcache.var_size' ) ) {
 265                         $id = 'xcache';
 266                 } elseif ( function_exists( 'wincache_ucache_get' ) ) {
 267                         $id = 'wincache';
 268                 } else {
 269                         if ( is_array( $fallback ) ) {
 270                                 $id = isset( $fallback['fallback'] ) ? $fallback['fallback'] : CACHE_NONE;
 271                         } else {
 272                                 $id = $fallback;
 273                         }
 274                 }
 275
 276                 return self::getInstance( $id );
 277         }
 278
 279         /**
 280          * @param array $params [optional] Array key 'fallback' for $fallback.
 281          * @param int|string $fallback Fallback cache, e.g. (CACHE_NONE, "hash") (since 1.24)
 282          * @return BagOStuff
 283          * @deprecated 1.27
 284          */
 285         public static function newAccelerator( $params = [], $fallback = null ) {
 286                 if ( $fallback === null ) {
 287                         if ( is_array( $params ) && isset( $params['fallback'] ) ) {
 288                                 $fallback = $params['fallback'];
 289                         } elseif ( !is_array( $params ) ) {
 290                                 $fallback = $params;
 291                         }
 292                 }
 293
 294                 return self::getLocalServerInstance( $fallback );
 295         }
 296
 297         /**
 298          * Create a new cache object of the specified type.
 299          *
 300          * @since 1.26
 301          * @param string $id A key in $wgWANObjectCaches.
 302          * @return WANObjectCache
 303          * @throws MWException
 304          */
 305         public static function newWANCacheFromId( $id ) {
 306                 global $wgWANObjectCaches;
 307
 308                 if ( !isset( $wgWANObjectCaches[$id] ) ) {
 309                         throw new MWException( "Invalid object cache type \"$id\" requested. " .
 310                                 "It is not present in \$wgWANObjectCaches." );
 311                 }
 312
 313                 $params = $wgWANObjectCaches[$id];
 314                 foreach ( $params['channels'] as $action => $channel ) {
 315                         $params['relayers'][$action] = MediaWikiServices::getInstance()->getEventRelayerGroup()
 316                                 ->getRelayer( $channel );
 317                         $params['channels'][$action] = $channel;
 318                 }
 319                 $params['cache'] = self::newFromId( $params['cacheId'] );
 320                 if ( isset( $params['loggroup'] ) ) {
 321                         $params['logger'] = LoggerFactory::getInstance( $params['loggroup'] );
 322                 } else {
 323                         $params['logger'] = LoggerFactory::getInstance( 'objectcache' );
 324                 }
 325                 $class = $params['class'];
 326
 327                 return new $class( $params );
 328         }
 329
 330         /**
 331          * Get the main cluster-local cache object.
 332          *
 333          * @since 1.27
 334          * @return BagOStuff
 335          */
 336         public static function getLocalClusterInstance() {
 337                 global $wgMainCacheType;
 338
 339                 return self::getInstance( $wgMainCacheType );
 340         }
 341
 342         /**
 343          * Get the main WAN cache object.
 344          *
 345          * @since 1.26
 346          * @return WANObjectCache
 347          */
 348         public static function getMainWANInstance() {
 349                 global $wgMainWANCache;
 350
 351                 return self::getWANInstance( $wgMainWANCache );
 352         }
 353
 354         /**
 355          * Get the cache object for the main stash.
 356          *
 357          * Stash objects are BagOStuff instances suitable for storing light
 358          * weight data that is not canonically stored elsewhere (such as RDBMS).
 359          * Stashes should be configured to propagate changes to all data-centers.
 360          *
 361          * Callers should be prepared for:
 362          *   - a) Writes to be slower in non-"primary" (e.g. HTTP GET/HEAD only) DCs
 363          *   - b) Reads to be eventually consistent, e.g. for get()/getMulti()
 364          * In general, this means avoiding updates on idempotent HTTP requests and
 365          * avoiding an assumption of perfect serializability (or accepting anomalies).
 366          * Reads may be eventually consistent or data might rollback as nodes flap.
 367          * Callers can use BagOStuff:READ_LATEST to see the latest available data.
 368          *
 369          * @return BagOStuff
 370          * @since 1.26
 371          */
 372         public static function getMainStashInstance() {
 373                 global $wgMainStash;
 374
 375                 return self::getInstance( $wgMainStash );
 376         }
 377
 378         /**
 379          * Clear all the cached instances.
 380          */
 381         public static function clear() {
 382                 self::$instances = [];
 383                 self::$wanInstances = [];
 384         }
 385 }