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 yielding 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          * @phan-param array{caches:array<int,array|BagOStuff>,replication:string} $params
  65          * @throws InvalidArgumentException
  66          */
  67         public function __construct( $params ) {
  68                 parent::__construct( $params );
  69
  70                 if ( empty( $params['caches'] ) || !is_array( $params['caches'] ) ) {
  71                         throw new InvalidArgumentException(
  72                                 __METHOD__ . ': "caches" parameter must be an array of caches'
  73                         );
  74                 }
  75
  76                 $this->caches = [];
  77                 foreach ( $params['caches'] as $cacheInfo ) {
  78                         if ( $cacheInfo instanceof BagOStuff ) {
  79                                 $this->caches[] = $cacheInfo;
  80                         } else {
  81                                 if ( !isset( $cacheInfo['args'] ) ) {
  82                                         // B/C for when $cacheInfo was for ObjectCache::newFromParams().
  83                                         // Callers intenting this to be for ObjectFactory::getObjectFromSpec
  84                                         // should have set "args" per the docs above. Doings so avoids extra
  85                                         // (likely harmless) params (factory/class/calls) ending up in "args".
  86                                         $cacheInfo['args'] = [ $cacheInfo ];
  87                                 }
  88                                 $this->caches[] = ObjectFactory::getObjectFromSpec( $cacheInfo );
  89                         }
  90                 }
  91                 $this->mergeFlagMaps( $this->caches );
  92
  93                 $this->asyncWrites = (
  94                         isset( $params['replication'] ) &&
  95                         $params['replication'] === 'async' &&
  96                         is_callable( $this->asyncHandler )
  97                 );
  98
  99                 $this->cacheIndexes = array_keys( $this->caches );
 100         }
 101
 102         public function setDebug( $enabled ) {
 103                 parent::setDebug( $enabled );
 104                 foreach ( $this->caches as $cache ) {
 105                         $cache->setDebug( $enabled );
 106                 }
 107         }
 108
 109         public function get( $key, $flags = 0 ) {
 110                 if ( $this->fieldHasFlags( $flags, self::READ_LATEST ) ) {
 111                         // If the latest write was a delete(), we do NOT want to fallback
 112                         // to the other tiers and possibly see the old value. Also, this
 113                         // is used by merge(), which only needs to hit the primary.
 114                         return $this->caches[0]->get( $key, $flags );
 115                 }
 116
 117                 $value = false;
 118                 $missIndexes = []; // backends checked
 119                 foreach ( $this->caches as $i => $cache ) {
 120                         $value = $cache->get( $key, $flags );
 121                         if ( $value !== false ) {
 122                                 break;
 123                         }
 124                         $missIndexes[] = $i;
 125                 }
 126
 127                 if (
 128                         $value !== false &&
 129                         $this->fieldHasFlags( $flags, self::READ_VERIFIED ) &&
 130                         $missIndexes
 131                 ) {
 132                         // Backfill the value to the higher (and often faster/smaller) cache tiers
 133                         $this->doWrite(
 134                                 $missIndexes,
 135                                 $this->asyncWrites,
 136                                 'set',
 137                                 // @TODO: consider using self::WRITE_ALLOW_SEGMENTS here?
 138                                 [ $key, $value, self::$UPGRADE_TTL ]
 139                         );
 140                 }
 141
 142                 return $value;
 143         }
 144
 145         public function set( $key, $value, $exptime = 0, $flags = 0 ) {
 146                 return $this->doWrite(
 147                         $this->cacheIndexes,
 148                         $this->usesAsyncWritesGivenFlags( $flags ),
 149                         __FUNCTION__,
 150                         func_get_args()
 151                 );
 152         }
 153
 154         public function delete( $key, $flags = 0 ) {
 155                 return $this->doWrite(
 156                         $this->cacheIndexes,
 157                         $this->usesAsyncWritesGivenFlags( $flags ),
 158                         __FUNCTION__,
 159                         func_get_args()
 160                 );
 161         }
 162
 163         public function add( $key, $value, $exptime = 0, $flags = 0 ) {
 164                 // Try the write to the top-tier cache
 165                 $ok = $this->doWrite(
 166                         [ 0 ],
 167                         $this->usesAsyncWritesGivenFlags( $flags ),
 168                         __FUNCTION__,
 169                         func_get_args()
 170                 );
 171
 172                 if ( $ok ) {
 173                         // Relay the add() using set() if it succeeded. This is meant to handle certain
 174                         // migration scenarios where the same store might get written to twice for certain
 175                         // keys. In that case, it does not make sense to return false due to "self-conflicts".
 176                         return $this->doWrite(
 177                                 array_slice( $this->cacheIndexes, 1 ),
 178                                 $this->usesAsyncWritesGivenFlags( $flags ),
 179                                 'set',
 180                                 [ $key, $value, $exptime, $flags ]
 181                         );
 182                 }
 183
 184                 return false;
 185         }
 186
 187         public function merge( $key, callable $callback, $exptime = 0, $attempts = 10, $flags = 0 ) {
 188                 return $this->doWrite(
 189                         $this->cacheIndexes,
 190                         $this->usesAsyncWritesGivenFlags( $flags ),
 191                         __FUNCTION__,
 192                         func_get_args()
 193                 );
 194         }
 195
 196         public function changeTTL( $key, $exptime = 0, $flags = 0 ) {
 197                 return $this->doWrite(
 198                         $this->cacheIndexes,
 199                         $this->usesAsyncWritesGivenFlags( $flags ),
 200                         __FUNCTION__,
 201                         func_get_args()
 202                 );
 203         }
 204
 205         public function lock( $key, $timeout = 6, $expiry = 6, $rclass = '' ) {
 206                 // Only need to lock the first cache; also avoids deadlocks
 207                 return $this->caches[0]->lock( $key, $timeout, $expiry, $rclass );
 208         }
 209
 210         public function unlock( $key ) {
 211                 // Only the first cache is locked
 212                 return $this->caches[0]->unlock( $key );
 213         }
 214
 215         public function deleteObjectsExpiringBefore(
 216                 $timestamp,
 217                 callable $progress = null,
 218                 $limit = INF
 219         ) {
 220                 $ret = false;
 221                 foreach ( $this->caches as $cache ) {
 222                         if ( $cache->deleteObjectsExpiringBefore( $timestamp, $progress, $limit ) ) {
 223                                 $ret = true;
 224                         }
 225                 }
 226
 227                 return $ret;
 228         }
 229
 230         public function getMulti( array $keys, $flags = 0 ) {
 231                 // Just iterate over each key in order to handle all the backfill logic
 232                 $res = [];
 233                 foreach ( $keys as $key ) {
 234                         $val = $this->get( $key, $flags );
 235                         if ( $val !== false ) {
 236                                 $res[$key] = $val;
 237                         }
 238                 }
 239
 240                 return $res;
 241         }
 242
 243         public function setMulti( array $data, $exptime = 0, $flags = 0 ) {
 244                 return $this->doWrite(
 245                         $this->cacheIndexes,
 246                         $this->usesAsyncWritesGivenFlags( $flags ),
 247                         __FUNCTION__,
 248                         func_get_args()
 249                 );
 250         }
 251
 252         public function deleteMulti( array $data, $flags = 0 ) {
 253                 return $this->doWrite(
 254                         $this->cacheIndexes,
 255                         $this->usesAsyncWritesGivenFlags( $flags ),
 256                         __FUNCTION__,
 257                         func_get_args()
 258                 );
 259         }
 260
 261         public function changeTTLMulti( array $keys, $exptime, $flags = 0 ) {
 262                 return $this->doWrite(
 263                         $this->cacheIndexes,
 264                         $this->usesAsyncWritesGivenFlags( $flags ),
 265                         __FUNCTION__,
 266                         func_get_args()
 267                 );
 268         }
 269
 270         public function incr( $key, $value = 1, $flags = 0 ) {
 271                 return $this->doWrite(
 272                         $this->cacheIndexes,
 273                         $this->asyncWrites,
 274                         __FUNCTION__,
 275                         func_get_args()
 276                 );
 277         }
 278
 279         public function decr( $key, $value = 1, $flags = 0 ) {
 280                 return $this->doWrite(
 281                         $this->cacheIndexes,
 282                         $this->asyncWrites,
 283                         __FUNCTION__,
 284                         func_get_args()
 285                 );
 286         }
 287
 288         public function incrWithInit( $key, $exptime, $value = 1, $init = null, $flags = 0 ) {
 289                 return $this->doWrite(
 290                         $this->cacheIndexes,
 291                         $this->asyncWrites,
 292                         __FUNCTION__,
 293                         func_get_args()
 294                 );
 295         }
 296
 297         public function getLastError() {
 298                 return $this->caches[0]->getLastError();
 299         }
 300
 301         public function clearLastError() {
 302                 $this->caches[0]->clearLastError();
 303         }
 304
 305         /**
 306          * Apply a write method to the backing caches specified by $indexes (in order)
 307          *
 308          * @param int[] $indexes List of backing cache indexes
 309          * @param bool $asyncWrites
 310          * @param string $method Method name of backing caches
 311          * @param array $args Arguments to the method of backing caches
 312          * @return bool
 313          */
 314         protected function doWrite( $indexes, $asyncWrites, $method, array $args ) {
 315                 $ret = true;
 316
 317                 if ( array_diff( $indexes, [ 0 ] ) && $asyncWrites && $method !== 'merge' ) {
 318                         // Deep-clone $args to prevent misbehavior when something writes an
 319                         // object to the BagOStuff then modifies it afterwards, e.g. T168040.
 320                         $args = unserialize( serialize( $args ) );
 321                 }
 322
 323                 foreach ( $indexes as $i ) {
 324                         $cache = $this->caches[$i];
 325                         if ( $i == 0 || !$asyncWrites ) {
 326                                 // First store or in sync mode: write now and get result
 327                                 if ( !$cache->$method( ...$args ) ) {
 328                                         $ret = false;
 329                                 }
 330                         } else {
 331                                 // Secondary write in async mode: do not block this HTTP request
 332                                 $logger = $this->logger;
 333                                 ( $this->asyncHandler )(
 334                                         function () use ( $cache, $method, $args, $logger ) {
 335                                                 if ( !$cache->$method( ...$args ) ) {
 336                                                         $logger->warning( "Async $method op failed" );
 337                                                 }
 338                                         }
 339                                 );
 340                         }
 341                 }
 342
 343                 return $ret;
 344         }
 345
 346         /**
 347          * @param int $flags
 348          * @return bool
 349          */
 350         protected function usesAsyncWritesGivenFlags( $flags ) {
 351                 return $this->fieldHasFlags( $flags, self::WRITE_SYNC ) ? false : $this->asyncWrites;
 352         }
 353
 354         public function makeKeyInternal( $keyspace, $args ) {
 355                 return $this->caches[0]->makeKeyInternal( $keyspace, $args );
 356         }
 357
 358         public function makeKey( $class, ...$components ) {
 359                 return $this->caches[0]->makeKey( ...func_get_args() );
 360         }
 361
 362         public function makeGlobalKey( $class, ...$components ) {
 363                 return $this->caches[0]->makeGlobalKey( ...func_get_args() );
 364         }
 365
 366         public function addBusyCallback( callable $workCallback ) {
 367                 $this->caches[0]->addBusyCallback( $workCallback );
 368         }
 369
 370         public function setMockTime( &$time ) {
 371                 parent::setMockTime( $time );
 372                 foreach ( $this->caches as $cache ) {
 373                         $cache->setMockTime( $time );
 374                         $cache->setMockTime( $time );
 375                 }
 376         }
 377 }