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