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                                 [ $key, $value, self::UPGRADE_TTL ]
 134                         );
 135                 }
 136
 137                 return $value;
 138         }
 139
 140         public function set( $key, $value, $exptime = 0, $flags = 0 ) {
 141                 return $this->doWrite(
 142                         $this->cacheIndexes,
 143                         $this->usesAsyncWritesGivenFlags( $flags ),
 144                         __FUNCTION__,
 145                         func_get_args()
 146                 );
 147         }
 148
 149         public function delete( $key, $flags = 0 ) {
 150                 return $this->doWrite(
 151                         $this->cacheIndexes,
 152                         $this->usesAsyncWritesGivenFlags( $flags ),
 153                         __FUNCTION__,
 154                         func_get_args()
 155                 );
 156         }
 157
 158         public function add( $key, $value, $exptime = 0, $flags = 0 ) {
 159                 // Try the write to the top-tier cache
 160                 $ok = $this->doWrite(
 161                         [ 0 ],
 162                         $this->usesAsyncWritesGivenFlags( $flags ),
 163                         __FUNCTION__,
 164                         func_get_args()
 165                 );
 166
 167                 if ( $ok ) {
 168                         // Relay the add() using set() if it succeeded. This is meant to handle certain
 169                         // migration scenarios where the same store might get written to twice for certain
 170                         // keys. In that case, it does not make sense to return false due to "self-conflicts".
 171                         return $this->doWrite(
 172                                 array_slice( $this->cacheIndexes, 1 ),
 173                                 $this->usesAsyncWritesGivenFlags( $flags ),
 174                                 'set',
 175                                 [ $key, $value, $exptime, $flags ]
 176                         );
 177                 }
 178
 179                 return false;
 180         }
 181
 182         public function merge( $key, callable $callback, $exptime = 0, $attempts = 10, $flags = 0 ) {
 183                 return $this->doWrite(
 184                         $this->cacheIndexes,
 185                         $this->usesAsyncWritesGivenFlags( $flags ),
 186                         __FUNCTION__,
 187                         func_get_args()
 188                 );
 189         }
 190
 191         public function changeTTL( $key, $exptime = 0, $flags = 0 ) {
 192                 return $this->doWrite(
 193                         $this->cacheIndexes,
 194                         $this->usesAsyncWritesGivenFlags( $flags ),
 195                         __FUNCTION__,
 196                         func_get_args()
 197                 );
 198         }
 199
 200         public function lock( $key, $timeout = 6, $expiry = 6, $rclass = '' ) {
 201                 // Only need to lock the first cache; also avoids deadlocks
 202                 return $this->caches[0]->lock( $key, $timeout, $expiry, $rclass );
 203         }
 204
 205         public function unlock( $key ) {
 206                 // Only the first cache is locked
 207                 return $this->caches[0]->unlock( $key );
 208         }
 209
 210         /**
 211          * Delete objects expiring before a certain date.
 212          *
 213          * Succeed if any of the child caches succeed.
 214          * @param string $date
 215          * @param bool|callable $progressCallback
 216          * @return bool
 217          */
 218         public function deleteObjectsExpiringBefore( $date, $progressCallback = false ) {
 219                 $ret = false;
 220                 foreach ( $this->caches as $cache ) {
 221                         if ( $cache->deleteObjectsExpiringBefore( $date, $progressCallback ) ) {
 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 incr( $key, $value = 1 ) {
 261                 return $this->doWrite(
 262                         $this->cacheIndexes,
 263                         $this->asyncWrites,
 264                         __FUNCTION__,
 265                         func_get_args()
 266                 );
 267         }
 268
 269         public function decr( $key, $value = 1 ) {
 270                 return $this->doWrite(
 271                         $this->cacheIndexes,
 272                         $this->asyncWrites,
 273                         __FUNCTION__,
 274                         func_get_args()
 275                 );
 276         }
 277
 278         public function incrWithInit( $key, $ttl, $value = 1, $init = 1 ) {
 279                 return $this->doWrite(
 280                         $this->cacheIndexes,
 281                         $this->asyncWrites,
 282                         __FUNCTION__,
 283                         func_get_args()
 284                 );
 285         }
 286
 287         public function getLastError() {
 288                 return $this->caches[0]->getLastError();
 289         }
 290
 291         public function clearLastError() {
 292                 $this->caches[0]->clearLastError();
 293         }
 294
 295         /**
 296          * Apply a write method to the backing caches specified by $indexes (in order)
 297          *
 298          * @param int[] $indexes List of backing cache indexes
 299          * @param bool $asyncWrites
 300          * @param string $method Method name of backing caches
 301          * @param array[] $args Arguments to the method of backing caches
 302          * @return bool
 303          */
 304         protected function doWrite( $indexes, $asyncWrites, $method, array $args ) {
 305                 $ret = true;
 306
 307                 if ( array_diff( $indexes, [ 0 ] ) && $asyncWrites && $method !== 'merge' ) {
 308                         // Deep-clone $args to prevent misbehavior when something writes an
 309                         // object to the BagOStuff then modifies it afterwards, e.g. T168040.
 310                         $args = unserialize( serialize( $args ) );
 311                 }
 312
 313                 foreach ( $indexes as $i ) {
 314                         $cache = $this->caches[$i];
 315                         if ( $i == 0 || !$asyncWrites ) {
 316                                 // First store or in sync mode: write now and get result
 317                                 if ( !$cache->$method( ...$args ) ) {
 318                                         $ret = false;
 319                                 }
 320                         } else {
 321                                 // Secondary write in async mode: do not block this HTTP request
 322                                 $logger = $this->logger;
 323                                 ( $this->asyncHandler )(
 324                                         function () use ( $cache, $method, $args, $logger ) {
 325                                                 if ( !$cache->$method( ...$args ) ) {
 326                                                         $logger->warning( "Async $method op failed" );
 327                                                 }
 328                                         }
 329                                 );
 330                         }
 331                 }
 332
 333                 return $ret;
 334         }
 335
 336         /**
 337          * @param int $flags
 338          * @return bool
 339          */
 340         protected function usesAsyncWritesGivenFlags( $flags ) {
 341                 return ( ( $flags & self::WRITE_SYNC ) == self::WRITE_SYNC ) ? false : $this->asyncWrites;
 342         }
 343
 344         public function makeKeyInternal( $keyspace, $args ) {
 345                 return $this->caches[0]->makeKeyInternal( ...func_get_args() );
 346         }
 347
 348         public function makeKey( $class, $component = null ) {
 349                 return $this->caches[0]->makeKey( ...func_get_args() );
 350         }
 351
 352         public function makeGlobalKey( $class, $component = null ) {
 353                 return $this->caches[0]->makeGlobalKey( ...func_get_args() );
 354         }
 355
 356         protected function doGet( $key, $flags = 0, &$casToken = null ) {
 357                 throw new LogicException( __METHOD__ . ': proxy class does not need this method.' );
 358         }
 359 }