includes/libs/objectcache/MultiWriteBagOStuff.php

   1 <?php
   2 /**
   3  * Wrapper for object caching in different caches.
   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 use Wikimedia\ObjectFactory;
  24
  25 /**
  26  * A cache class that replicates all writes to multiple child caches. Reads
  27  * are implemented by reading from the caches in the order they are given in
  28  * the configuration until a cache gives a positive result.
  29  *
  30  * Note that cache key construction will use the first cache backend in the list,
  31  * so make sure that the other backends can handle such keys (e.g. via encoding).
  32  *
  33  * @ingroup Cache
  34  */
  35 class MultiWriteBagOStuff extends BagOStuff {
  36         /** @var BagOStuff[] */
  37         protected $caches;
  38         /** @var bool Use async secondary writes */
  39         protected $asyncWrites = false;
  40         /** @var int[] List of all backing cache indexes */
  41         protected $cacheIndexes = [];
  42
  43         /** @var int TTL when a key is copied to a higher cache tier */
  44         private static $UPGRADE_TTL = 3600;
  45
  46         /**
  47          * $params include:
  48          *   - caches: A numbered array of either ObjectFactory::getObjectFromSpec
  49          *      arrays yeilding BagOStuff objects or direct BagOStuff objects.
  50          *      If using the former, the 'args' field *must* be set.
  51          *      The first cache is the primary one, being the first to
  52          *      be read in the fallback chain. Writes happen to all stores
  53          *      in the order they are defined. However, lock()/unlock() calls
  54          *      only use the primary store.
  55          *   - replication: Either 'sync' or 'async'. This controls whether writes
  56          *      to secondary stores are deferred when possible. Async writes
  57          *      require setting 'asyncHandler'. HHVM register_postsend_function() function.
  58          *      Async writes can increase the chance of some race conditions
  59          *      or cause keys to expire seconds later than expected. It is
  60          *      safe to use for modules when cached values: are immutable,
  61          *      invalidation uses logical TTLs, invalidation uses etag/timestamp
  62          *      validation against the DB, or merge() is used to handle races.
  63          * @param array $params
  64          * @throws InvalidArgumentException
  65          */
  66         public function __construct( $params ) {
  67                 parent::__construct( $params );
  68
  69                 if ( empty( $params['caches'] ) || !is_array( $params['caches'] ) ) {
  70                         throw new InvalidArgumentException(
  71                                 __METHOD__ . ': "caches" parameter must be an array of caches'
  72                         );
  73                 }
  74
  75                 $this->caches = [];
  76                 foreach ( $params['caches'] as $cacheInfo ) {
  77                         if ( $cacheInfo instanceof BagOStuff ) {
  78                                 $this->caches[] = $cacheInfo;
  79                         } else {
  80                                 if ( !isset( $cacheInfo['args'] ) ) {
  81                                         // B/C for when $cacheInfo was for ObjectCache::newFromParams().
  82                                         // Callers intenting this to be for ObjectFactory::getObjectFromSpec
  83                                         // should have set "args" per the docs above. Doings so avoids extra
  84                                         // (likely harmless) params (factory/class/calls) ending up in "args".
  85                                         $cacheInfo['args'] = [ $cacheInfo ];
  86                                 }
  87                                 $this->caches[] = ObjectFactory::getObjectFromSpec( $cacheInfo );
  88                         }
  89                 }
  90                 $this->mergeFlagMaps( $this->caches );
  91
  92                 $this->asyncWrites = (
  93                         isset( $params['replication'] ) &&
  94                         $params['replication'] === 'async' &&
  95                         is_callable( $this->asyncHandler )
  96                 );
  97
  98                 $this->cacheIndexes = array_keys( $this->caches );
  99         }
 100
 101         public function setDebug( $enabled ) {
 102                 parent::setDebug( $enabled );
 103                 foreach ( $this->caches as $cache ) {
 104                         $cache->setDebug( $enabled );
 105                 }
 106         }
 107
 108         public function get( $key, $flags = 0 ) {
 109                 if ( $this->fieldHasFlags( $flags, self::READ_LATEST ) ) {
 110                         // If the latest write was a delete(), we do NOT want to fallback
 111                         // to the other tiers and possibly see the old value. Also, this
 112                         // is used by merge(), which only needs to hit the primary.
 113                         return $this->caches[0]->get( $key, $flags );
 114                 }
 115
 116                 $value = false;
 117                 $missIndexes = []; // backends checked
 118                 foreach ( $this->caches as $i => $cache ) {
 119                         $value = $cache->get( $key, $flags );
 120                         if ( $value !== false ) {
 121                                 break;
 122                         }
 123                         $missIndexes[] = $i;
 124                 }
 125
 126                 if (
 127                         $value !== false &&
 128                         $this->fieldHasFlags( $flags, self::READ_VERIFIED ) &&
 129                         $missIndexes
 130                 ) {
 131                         // Backfill the value to the higher (and often faster/smaller) cache tiers
 132                         $this->doWrite(
 133                                 $missIndexes,
 134                                 $this->asyncWrites,
 135                                 'set',
 136                                 // @TODO: consider using self::WRITE_ALLOW_SEGMENTS here?
 137                                 [ $key, $value, self::$UPGRADE_TTL ]
 138                         );
 139                 }
 140
 141                 return $value;
 142         }
 143
 144         public function set( $key, $value, $exptime = 0, $flags = 0 ) {
 145                 return $this->doWrite(
 146                         $this->cacheIndexes,
 147                         $this->usesAsyncWritesGivenFlags( $flags ),
 148                         __FUNCTION__,
 149                         func_get_args()
 150                 );
 151         }
 152
 153         public function delete( $key, $flags = 0 ) {
 154                 return $this->doWrite(
 155                         $this->cacheIndexes,
 156                         $this->usesAsyncWritesGivenFlags( $flags ),
 157                         __FUNCTION__,
 158                         func_get_args()
 159                 );
 160         }
 161
 162         public function add( $key, $value, $exptime = 0, $flags = 0 ) {
 163                 // Try the write to the top-tier cache
 164                 $ok = $this->doWrite(
 165                         [ 0 ],
 166                         $this->usesAsyncWritesGivenFlags( $flags ),
 167                         __FUNCTION__,
 168                         func_get_args()
 169                 );
 170
 171                 if ( $ok ) {
 172                         // Relay the add() using set() if it succeeded. This is meant to handle certain
 173                         // migration scenarios where the same store might get written to twice for certain
 174                         // keys. In that case, it does not make sense to return false due to "self-conflicts".
 175                         return $this->doWrite(
 176                                 array_slice( $this->cacheIndexes, 1 ),
 177                                 $this->usesAsyncWritesGivenFlags( $flags ),
 178                                 'set',
 179                                 [ $key, $value, $exptime, $flags ]
 180                         );
 181                 }
 182
 183                 return false;
 184         }
 185
 186         public function merge( $key, callable $callback, $exptime = 0, $attempts = 10, $flags = 0 ) {
 187                 return $this->doWrite(
 188                         $this->cacheIndexes,
 189                         $this->usesAsyncWritesGivenFlags( $flags ),
 190                         __FUNCTION__,
 191                         func_get_args()
 192                 );
 193         }
 194
 195         public function changeTTL( $key, $exptime = 0, $flags = 0 ) {
 196                 return $this->doWrite(
 197                         $this->cacheIndexes,
 198                         $this->usesAsyncWritesGivenFlags( $flags ),
 199                         __FUNCTION__,
 200                         func_get_args()
 201                 );
 202         }
 203
 204         public function lock( $key, $timeout = 6, $expiry = 6, $rclass = '' ) {
 205                 // Only need to lock the first cache; also avoids deadlocks
 206                 return $this->caches[0]->lock( $key, $timeout, $expiry, $rclass );
 207         }
 208
 209         public function unlock( $key ) {
 210                 // Only the first cache is locked
 211                 return $this->caches[0]->unlock( $key );
 212         }
 213
 214         public function deleteObjectsExpiringBefore(
 215                 $timestamp,
 216                 callable $progress = null,
 217                 $limit = INF
 218         ) {
 219                 $ret = false;
 220                 foreach ( $this->caches as $cache ) {
 221                         if ( $cache->deleteObjectsExpiringBefore( $timestamp, $progress, $limit ) ) {
 222                                 $ret = true;
 223                         }
 224                 }
 225
 226                 return $ret;
 227         }
 228
 229         public function getMulti( array $keys, $flags = 0 ) {
 230                 // Just iterate over each key in order to handle all the backfill logic
 231                 $res = [];
 232                 foreach ( $keys as $key ) {
 233                         $val = $this->get( $key, $flags );
 234                         if ( $val !== false ) {
 235                                 $res[$key] = $val;
 236                         }
 237                 }
 238
 239                 return $res;
 240         }
 241
 242         public function setMulti( array $data, $exptime = 0, $flags = 0 ) {
 243                 return $this->doWrite(
 244                         $this->cacheIndexes,
 245                         $this->usesAsyncWritesGivenFlags( $flags ),
 246                         __FUNCTION__,
 247                         func_get_args()
 248                 );
 249         }
 250
 251         public function deleteMulti( array $data, $flags = 0 ) {
 252                 return $this->doWrite(
 253                         $this->cacheIndexes,
 254                         $this->usesAsyncWritesGivenFlags( $flags ),
 255                         __FUNCTION__,
 256                         func_get_args()
 257                 );
 258         }
 259
 260         public function changeTTLMulti( array $keys, $exptime, $flags = 0 ) {
 261                 return $this->doWrite(
 262                         $this->cacheIndexes,
 263                         $this->usesAsyncWritesGivenFlags( $flags ),
 264                         __FUNCTION__,
 265                         func_get_args()
 266                 );
 267         }
 268
 269         public function incr( $key, $value = 1, $flags = 0 ) {
 270                 return $this->doWrite(
 271                         $this->cacheIndexes,
 272                         $this->asyncWrites,
 273                         __FUNCTION__,
 274                         func_get_args()
 275                 );
 276         }
 277
 278         public function decr( $key, $value = 1, $flags = 0 ) {
 279                 return $this->doWrite(
 280                         $this->cacheIndexes,
 281                         $this->asyncWrites,
 282                         __FUNCTION__,
 283                         func_get_args()
 284                 );
 285         }
 286
 287         public function incrWithInit( $key, $exptime, $value = 1, $init = null, $flags = 0 ) {
 288                 return $this->doWrite(
 289                         $this->cacheIndexes,
 290                         $this->asyncWrites,
 291                         __FUNCTION__,
 292                         func_get_args()
 293                 );
 294         }
 295
 296         public function getLastError() {
 297                 return $this->caches[0]->getLastError();
 298         }
 299
 300         public function clearLastError() {
 301                 $this->caches[0]->clearLastError();
 302         }
 303
 304         /**
 305          * Apply a write method to the backing caches specified by $indexes (in order)
 306          *
 307          * @param int[] $indexes List of backing cache indexes
 308          * @param bool $asyncWrites
 309          * @param string $method Method name of backing caches
 310          * @param array $args Arguments to the method of backing caches
 311          * @return bool
 312          */
 313         protected function doWrite( $indexes, $asyncWrites, $method, array $args ) {
 314                 $ret = true;
 315
 316                 if ( array_diff( $indexes, [ 0 ] ) && $asyncWrites && $method !== 'merge' ) {
 317                         // Deep-clone $args to prevent misbehavior when something writes an
 318                         // object to the BagOStuff then modifies it afterwards, e.g. T168040.
 319                         $args = unserialize( serialize( $args ) );
 320                 }
 321
 322                 foreach ( $indexes as $i ) {
 323                         $cache = $this->caches[$i];
 324                         if ( $i == 0 || !$asyncWrites ) {
 325                                 // First store or in sync mode: write now and get result
 326                                 if ( !$cache->$method( ...$args ) ) {
 327                                         $ret = false;
 328                                 }
 329                         } else {
 330                                 // Secondary write in async mode: do not block this HTTP request
 331                                 $logger = $this->logger;
 332                                 ( $this->asyncHandler )(
 333                                         function () use ( $cache, $method, $args, $logger ) {
 334                                                 if ( !$cache->$method( ...$args ) ) {
 335                                                         $logger->warning( "Async $method op failed" );
 336                                                 }
 337                                         }
 338                                 );
 339                         }
 340                 }
 341
 342                 return $ret;
 343         }
 344
 345         /**
 346          * @param int $flags
 347          * @return bool
 348          */
 349         protected function usesAsyncWritesGivenFlags( $flags ) {
 350                 return $this->fieldHasFlags( $flags, self::WRITE_SYNC ) ? false : $this->asyncWrites;
 351         }
 352
 353         public function makeKeyInternal( $keyspace, $args ) {
 354                 return $this->caches[0]->makeKeyInternal( $keyspace, $args );
 355         }
 356
 357         public function makeKey( $class, ...$components ) {
 358                 return $this->caches[0]->makeKey( ...func_get_args() );
 359         }
 360
 361         public function makeGlobalKey( $class, ...$components ) {
 362                 return $this->caches[0]->makeGlobalKey( ...func_get_args() );
 363         }
 364
 365         public function addBusyCallback( callable $workCallback ) {
 366                 $this->caches[0]->addBusyCallback( $workCallback );
 367         }
 368
 369         public function setMockTime( &$time ) {
 370                 parent::setMockTime( $time );
 371                 foreach ( $this->caches as $cache ) {
 372                         $cache->setMockTime( $time );
 373                         $cache->setMockTime( $time );
 374                 }
 375         }
 376 }