includes/objectcache/SqlBagOStuff.php

   1 <?php
   2 /**
   3  * Object caching using a SQL database.
   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\MediaWikiServices;
  25 use Wikimedia\Rdbms\Database;
  26 use Wikimedia\Rdbms\IDatabase;
  27 use Wikimedia\Rdbms\DBError;
  28 use Wikimedia\Rdbms\DBQueryError;
  29 use Wikimedia\Rdbms\DBConnectionError;
  30 use Wikimedia\Rdbms\LoadBalancer;
  31 use Wikimedia\ScopedCallback;
  32 use Wikimedia\WaitConditionLoop;
  33
  34 /**
  35  * Class to store objects in the database
  36  *
  37  * @ingroup Cache
  38  */
  39 class SqlBagOStuff extends BagOStuff {
  40         /** @var array[] (server index => server config) */
  41         protected $serverInfos;
  42         /** @var string[] (server index => tag/host name) */
  43         protected $serverTags;
  44         /** @var int */
  45         protected $numServers;
  46         /** @var int */
  47         protected $lastExpireAll = 0;
  48         /** @var int */
  49         protected $purgePeriod = 10;
  50         /** @var int */
  51         protected $purgeLimit = 100;
  52         /** @var int */
  53         protected $shards = 1;
  54         /** @var string */
  55         protected $tableName = 'objectcache';
  56         /** @var bool */
  57         protected $replicaOnly = false;
  58         /** @var int */
  59         protected $syncTimeout = 3;
  60
  61         /** @var LoadBalancer|null */
  62         protected $separateMainLB;
  63         /** @var array */
  64         protected $conns;
  65         /** @var array UNIX timestamps */
  66         protected $connFailureTimes = [];
  67         /** @var array Exceptions */
  68         protected $connFailureErrors = [];
  69
  70         /**
  71          * Constructor. Parameters are:
  72          *   - server:      A server info structure in the format required by each
  73          *                  element in $wgDBServers.
  74          *
  75          *   - servers:     An array of server info structures describing a set of database servers
  76          *                  to distribute keys to. If this is specified, the "server" option will be
  77          *                  ignored. If string keys are used, then they will be used for consistent
  78          *                  hashing *instead* of the host name (from the server config). This is useful
  79          *                  when a cluster is replicated to another site (with different host names)
  80          *                  but each server has a corresponding replica in the other cluster.
  81          *
  82          *   - purgePeriod: The average number of object cache writes in between
  83          *                  garbage collection operations, where expired entries
  84          *                  are removed from the database. Or in other words, the
  85          *                  reciprocal of the probability of purging on any given
  86          *                  write. If this is set to zero, purging will never be done.
  87          *
  88          *   - purgeLimit:  Maximum number of rows to purge at once.
  89          *
  90          *   - tableName:   The table name to use, default is "objectcache".
  91          *
  92          *   - shards:      The number of tables to use for data storage on each server.
  93          *                  If this is more than 1, table names will be formed in the style
  94          *                  objectcacheNNN where NNN is the shard index, between 0 and
  95          *                  shards-1. The number of digits will be the minimum number
  96          *                  required to hold the largest shard index. Data will be
  97          *                  distributed across all tables by key hash. This is for
  98          *                  MySQL bugs 61735 <https://bugs.mysql.com/bug.php?id=61735>
  99          *                  and 61736 <https://bugs.mysql.com/bug.php?id=61736>.
 100          *
 101          *   - slaveOnly:   Whether to only use replica DBs and avoid triggering
 102          *                  garbage collection logic of expired items. This only
 103          *                  makes sense if the primary DB is used and only if get()
 104          *                  calls will be used. This is used by ReplicatedBagOStuff.
 105          *   - syncTimeout: Max seconds to wait for replica DBs to catch up for WRITE_SYNC.
 106          *
 107          * @param array $params
 108          */
 109         public function __construct( $params ) {
 110                 parent::__construct( $params );
 111
 112                 $this->attrMap[self::ATTR_EMULATION] = self::QOS_EMULATION_SQL;
 113                 $this->attrMap[self::ATTR_SYNCWRITES] = self::QOS_SYNCWRITES_NONE;
 114
 115                 if ( isset( $params['servers'] ) ) {
 116                         $this->serverInfos = [];
 117                         $this->serverTags = [];
 118                         $this->numServers = count( $params['servers'] );
 119                         $index = 0;
 120                         foreach ( $params['servers'] as $tag => $info ) {
 121                                 $this->serverInfos[$index] = $info;
 122                                 if ( is_string( $tag ) ) {
 123                                         $this->serverTags[$index] = $tag;
 124                                 } else {
 125                                         $this->serverTags[$index] = $info['host'] ?? "#$index";
 126                                 }
 127                                 ++$index;
 128                         }
 129                 } elseif ( isset( $params['server'] ) ) {
 130                         $this->serverInfos = [ $params['server'] ];
 131                         $this->numServers = count( $this->serverInfos );
 132                 } else {
 133                         // Default to using the main wiki's database servers
 134                         $this->serverInfos = false;
 135                         $this->numServers = 1;
 136                         $this->attrMap[self::ATTR_SYNCWRITES] = self::QOS_SYNCWRITES_BE;
 137                 }
 138                 if ( isset( $params['purgePeriod'] ) ) {
 139                         $this->purgePeriod = intval( $params['purgePeriod'] );
 140                 }
 141                 if ( isset( $params['purgeLimit'] ) ) {
 142                         $this->purgeLimit = intval( $params['purgeLimit'] );
 143                 }
 144                 if ( isset( $params['tableName'] ) ) {
 145                         $this->tableName = $params['tableName'];
 146                 }
 147                 if ( isset( $params['shards'] ) ) {
 148                         $this->shards = intval( $params['shards'] );
 149                 }
 150                 if ( isset( $params['syncTimeout'] ) ) {
 151                         $this->syncTimeout = $params['syncTimeout'];
 152                 }
 153                 $this->replicaOnly = !empty( $params['slaveOnly'] );
 154         }
 155
 156         /**
 157          * Get a connection to the specified database
 158          *
 159          * @param int $serverIndex
 160          * @return Database
 161          * @throws MWException
 162          */
 163         protected function getDB( $serverIndex ) {
 164                 if ( !isset( $this->conns[$serverIndex] ) ) {
 165                         if ( $serverIndex >= $this->numServers ) {
 166                                 throw new MWException( __METHOD__ . ": Invalid server index \"$serverIndex\"" );
 167                         }
 168
 169                         # Don't keep timing out trying to connect for each call if the DB is down
 170                         if ( isset( $this->connFailureErrors[$serverIndex] )
 171                                 && ( time() - $this->connFailureTimes[$serverIndex] ) < 60
 172                         ) {
 173                                 throw $this->connFailureErrors[$serverIndex];
 174                         }
 175
 176                         if ( $this->serverInfos ) {
 177                                 // Use custom database defined by server connection info
 178                                 $info = $this->serverInfos[$serverIndex];
 179                                 $type = $info['type'] ?? 'mysql';
 180                                 $host = $info['host'] ?? '[unknown]';
 181                                 $this->logger->debug( __CLASS__ . ": connecting to $host" );
 182                                 $db = Database::factory( $type, $info );
 183                                 $db->clearFlag( DBO_TRX ); // auto-commit mode
 184                         } else {
 185                                 // Use the main LB database
 186                                 $lb = MediaWikiServices::getInstance()->getDBLoadBalancer();
 187                                 $index = $this->replicaOnly ? DB_REPLICA : DB_MASTER;
 188                                 if ( $lb->getServerType( $lb->getWriterIndex() ) !== 'sqlite' ) {
 189                                         // Keep a separate connection to avoid contention and deadlocks
 190                                         $db = $lb->getConnection( $index, [], false, $lb::CONN_TRX_AUTOCOMMIT );
 191                                 } else {
 192                                         // However, SQLite has the opposite behavior due to DB-level locking.
 193                                         // Stock sqlite MediaWiki installs use a separate sqlite cache DB instead.
 194                                         $db = $lb->getConnection( $index );
 195                                 }
 196                         }
 197
 198                         $this->logger->debug( sprintf( "Connection %s will be used for SqlBagOStuff", $db ) );
 199                         $this->conns[$serverIndex] = $db;
 200                 }
 201
 202                 return $this->conns[$serverIndex];
 203         }
 204
 205         /**
 206          * Get the server index and table name for a given key
 207          * @param string $key
 208          * @return array Server index and table name
 209          */
 210         protected function getTableByKey( $key ) {
 211                 if ( $this->shards > 1 ) {
 212                         $hash = hexdec( substr( md5( $key ), 0, 8 ) ) & 0x7fffffff;
 213                         $tableIndex = $hash % $this->shards;
 214                 } else {
 215                         $tableIndex = 0;
 216                 }
 217                 if ( $this->numServers > 1 ) {
 218                         $sortedServers = $this->serverTags;
 219                         ArrayUtils::consistentHashSort( $sortedServers, $key );
 220                         reset( $sortedServers );
 221                         $serverIndex = key( $sortedServers );
 222                 } else {
 223                         $serverIndex = 0;
 224                 }
 225                 return [ $serverIndex, $this->getTableNameByShard( $tableIndex ) ];
 226         }
 227
 228         /**
 229          * Get the table name for a given shard index
 230          * @param int $index
 231          * @return string
 232          */
 233         protected function getTableNameByShard( $index ) {
 234                 if ( $this->shards > 1 ) {
 235                         $decimals = strlen( $this->shards - 1 );
 236                         return $this->tableName .
 237                                 sprintf( "%0{$decimals}d", $index );
 238                 } else {
 239                         return $this->tableName;
 240                 }
 241         }
 242
 243         protected function doGet( $key, $flags = 0, &$casToken = null ) {
 244                 $casToken = null;
 245
 246                 $blobs = $this->fetchBlobMulti( [ $key ] );
 247                 if ( array_key_exists( $key, $blobs ) ) {
 248                         $blob = $blobs[$key];
 249                         $value = $this->unserialize( $blob );
 250
 251                         $casToken = ( $value !== false ) ? $blob : null;
 252
 253                         return $value;
 254                 }
 255
 256                 return false;
 257         }
 258
 259         protected function doGetMulti( array $keys, $flags = 0 ) {
 260                 $values = [];
 261
 262                 $blobs = $this->fetchBlobMulti( $keys );
 263                 foreach ( $blobs as $key => $blob ) {
 264                         $values[$key] = $this->unserialize( $blob );
 265                 }
 266
 267                 return $values;
 268         }
 269
 270         protected function fetchBlobMulti( array $keys, $flags = 0 ) {
 271                 $values = []; // array of (key => value)
 272
 273                 $keysByTable = [];
 274                 foreach ( $keys as $key ) {
 275                         list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
 276                         $keysByTable[$serverIndex][$tableName][] = $key;
 277                 }
 278
 279                 $dataRows = [];
 280                 foreach ( $keysByTable as $serverIndex => $serverKeys ) {
 281                         try {
 282                                 $db = $this->getDB( $serverIndex );
 283                                 foreach ( $serverKeys as $tableName => $tableKeys ) {
 284                                         $res = $db->select( $tableName,
 285                                                 [ 'keyname', 'value', 'exptime' ],
 286                                                 [ 'keyname' => $tableKeys ],
 287                                                 __METHOD__,
 288                                                 // Approximate write-on-the-fly BagOStuff API via blocking.
 289                                                 // This approximation fails if a ROLLBACK happens (which is rare).
 290                                                 // We do not want to flush the TRX as that can break callers.
 291                                                 $db->trxLevel() ? [ 'LOCK IN SHARE MODE' ] : []
 292                                         );
 293                                         if ( $res === false ) {
 294                                                 continue;
 295                                         }
 296                                         foreach ( $res as $row ) {
 297                                                 $row->serverIndex = $serverIndex;
 298                                                 $row->tableName = $tableName;
 299                                                 $dataRows[$row->keyname] = $row;
 300                                         }
 301                                 }
 302                         } catch ( DBError $e ) {
 303                                 $this->handleReadError( $e, $serverIndex );
 304                         }
 305                 }
 306
 307                 foreach ( $keys as $key ) {
 308                         if ( isset( $dataRows[$key] ) ) { // HIT?
 309                                 $row = $dataRows[$key];
 310                                 $this->debug( "get: retrieved data; expiry time is " . $row->exptime );
 311                                 $db = null;
 312                                 try {
 313                                         $db = $this->getDB( $row->serverIndex );
 314                                         if ( $this->isExpired( $db, $row->exptime ) ) { // MISS
 315                                                 $this->debug( "get: key has expired" );
 316                                         } else { // HIT
 317                                                 $values[$key] = $db->decodeBlob( $row->value );
 318                                         }
 319                                 } catch ( DBQueryError $e ) {
 320                                         $this->handleWriteError( $e, $db, $row->serverIndex );
 321                                 }
 322                         } else { // MISS
 323                                 $this->debug( 'get: no matching rows' );
 324                         }
 325                 }
 326
 327                 return $values;
 328         }
 329
 330         public function setMulti( array $data, $expiry = 0, $flags = 0 ) {
 331                 return $this->insertMulti( $data, $expiry, $flags, true );
 332         }
 333
 334         private function insertMulti( array $data, $expiry, $flags, $replace ) {
 335                 $keysByTable = [];
 336                 foreach ( $data as $key => $value ) {
 337                         list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
 338                         $keysByTable[$serverIndex][$tableName][] = $key;
 339                 }
 340
 341                 $this->garbageCollect(); // expire old entries if any
 342
 343                 $result = true;
 344                 $exptime = (int)$expiry;
 345                 /** @noinspection PhpUnusedLocalVariableInspection */
 346                 $silenceScope = $this->silenceTransactionProfiler();
 347                 foreach ( $keysByTable as $serverIndex => $serverKeys ) {
 348                         $db = null;
 349                         try {
 350                                 $db = $this->getDB( $serverIndex );
 351                         } catch ( DBError $e ) {
 352                                 $this->handleWriteError( $e, $db, $serverIndex );
 353                                 $result = false;
 354                                 continue;
 355                         }
 356
 357                         if ( $exptime < 0 ) {
 358                                 $exptime = 0;
 359                         }
 360
 361                         if ( $exptime == 0 ) {
 362                                 $encExpiry = $this->getMaxDateTime( $db );
 363                         } else {
 364                                 $exptime = $this->convertToExpiry( $exptime );
 365                                 $encExpiry = $db->timestamp( $exptime );
 366                         }
 367                         foreach ( $serverKeys as $tableName => $tableKeys ) {
 368                                 $rows = [];
 369                                 foreach ( $tableKeys as $key ) {
 370                                         $rows[] = [
 371                                                 'keyname' => $key,
 372                                                 'value' => $db->encodeBlob( $this->serialize( $data[$key] ) ),
 373                                                 'exptime' => $encExpiry,
 374                                         ];
 375                                 }
 376
 377                                 try {
 378                                         if ( $replace ) {
 379                                                 $db->replace( $tableName, [ 'keyname' ], $rows, __METHOD__ );
 380                                         } else {
 381                                                 $db->insert( $tableName, $rows, __METHOD__, [ 'IGNORE' ] );
 382                                                 $result = ( $db->affectedRows() > 0 && $result );
 383                                         }
 384                                 } catch ( DBError $e ) {
 385                                         $this->handleWriteError( $e, $db, $serverIndex );
 386                                         $result = false;
 387                                 }
 388
 389                         }
 390                 }
 391
 392                 if ( ( $flags & self::WRITE_SYNC ) == self::WRITE_SYNC ) {
 393                         $result = $this->waitForReplication() && $result;
 394                 }
 395
 396                 return $result;
 397         }
 398
 399         protected function doSet( $key, $value, $exptime = 0, $flags = 0 ) {
 400                 $ok = $this->insertMulti( [ $key => $value ], $exptime, $flags, true );
 401
 402                 return $ok;
 403         }
 404
 405         public function add( $key, $value, $exptime = 0, $flags = 0 ) {
 406                 $added = $this->insertMulti( [ $key => $value ], $exptime, $flags, false );
 407
 408                 return $added;
 409         }
 410
 411         protected function cas( $casToken, $key, $value, $exptime = 0, $flags = 0 ) {
 412                 list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
 413                 $db = null;
 414                 /** @noinspection PhpUnusedLocalVariableInspection */
 415                 $silenceScope = $this->silenceTransactionProfiler();
 416                 try {
 417                         $db = $this->getDB( $serverIndex );
 418                         $exptime = intval( $exptime );
 419
 420                         if ( $exptime < 0 ) {
 421                                 $exptime = 0;
 422                         }
 423
 424                         if ( $exptime == 0 ) {
 425                                 $encExpiry = $this->getMaxDateTime( $db );
 426                         } else {
 427                                 $exptime = $this->convertToExpiry( $exptime );
 428                                 $encExpiry = $db->timestamp( $exptime );
 429                         }
 430                         // (T26425) use a replace if the db supports it instead of
 431                         // delete/insert to avoid clashes with conflicting keynames
 432                         $db->update(
 433                                 $tableName,
 434                                 [
 435                                         'keyname' => $key,
 436                                         'value' => $db->encodeBlob( $this->serialize( $value ) ),
 437                                         'exptime' => $encExpiry
 438                                 ],
 439                                 [
 440                                         'keyname' => $key,
 441                                         'value' => $db->encodeBlob( $casToken )
 442                                 ],
 443                                 __METHOD__
 444                         );
 445                 } catch ( DBQueryError $e ) {
 446                         $this->handleWriteError( $e, $db, $serverIndex );
 447
 448                         return false;
 449                 }
 450
 451                 return (bool)$db->affectedRows();
 452         }
 453
 454         public function deleteMulti( array $keys, $flags = 0 ) {
 455                 return $this->purgeMulti( $keys, $flags );
 456         }
 457
 458         public function purgeMulti( array $keys, $flags = 0 ) {
 459                 $keysByTable = [];
 460                 foreach ( $keys as $key ) {
 461                         list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
 462                         $keysByTable[$serverIndex][$tableName][] = $key;
 463                 }
 464
 465                 $result = true;
 466                 /** @noinspection PhpUnusedLocalVariableInspection */
 467                 $silenceScope = $this->silenceTransactionProfiler();
 468                 foreach ( $keysByTable as $serverIndex => $serverKeys ) {
 469                         $db = null;
 470                         try {
 471                                 $db = $this->getDB( $serverIndex );
 472                         } catch ( DBError $e ) {
 473                                 $this->handleWriteError( $e, $db, $serverIndex );
 474                                 $result = false;
 475                                 continue;
 476                         }
 477
 478                         foreach ( $serverKeys as $tableName => $tableKeys ) {
 479                                 try {
 480                                         $db->delete( $tableName, [ 'keyname' => $tableKeys ], __METHOD__ );
 481                                 } catch ( DBError $e ) {
 482                                         $this->handleWriteError( $e, $db, $serverIndex );
 483                                         $result = false;
 484                                 }
 485
 486                         }
 487                 }
 488
 489                 if ( ( $flags & self::WRITE_SYNC ) == self::WRITE_SYNC ) {
 490                         $result = $this->waitForReplication() && $result;
 491                 }
 492
 493                 return $result;
 494         }
 495
 496         protected function doDelete( $key, $flags = 0 ) {
 497                 $ok = $this->purgeMulti( [ $key ], $flags );
 498
 499                 return $ok;
 500         }
 501
 502         public function incr( $key, $step = 1 ) {
 503                 list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
 504                 $db = null;
 505                 /** @noinspection PhpUnusedLocalVariableInspection */
 506                 $silenceScope = $this->silenceTransactionProfiler();
 507                 try {
 508                         $db = $this->getDB( $serverIndex );
 509                         $step = intval( $step );
 510                         $row = $db->selectRow(
 511                                 $tableName,
 512                                 [ 'value', 'exptime' ],
 513                                 [ 'keyname' => $key ],
 514                                 __METHOD__,
 515                                 [ 'FOR UPDATE' ]
 516                         );
 517                         if ( $row === false ) {
 518                                 // Missing
 519                                 return false;
 520                         }
 521                         $db->delete( $tableName, [ 'keyname' => $key ], __METHOD__ );
 522                         if ( $this->isExpired( $db, $row->exptime ) ) {
 523                                 // Expired, do not reinsert
 524                                 return false;
 525                         }
 526
 527                         $oldValue = intval( $this->unserialize( $db->decodeBlob( $row->value ) ) );
 528                         $newValue = $oldValue + $step;
 529                         $db->insert(
 530                                 $tableName,
 531                                 [
 532                                         'keyname' => $key,
 533                                         'value' => $db->encodeBlob( $this->serialize( $newValue ) ),
 534                                         'exptime' => $row->exptime
 535                                 ],
 536                                 __METHOD__,
 537                                 [ 'IGNORE' ]
 538                         );
 539
 540                         if ( $db->affectedRows() == 0 ) {
 541                                 // Race condition. See T30611
 542                                 $newValue = false;
 543                         }
 544                 } catch ( DBError $e ) {
 545                         $this->handleWriteError( $e, $db, $serverIndex );
 546                         return false;
 547                 }
 548
 549                 return $newValue;
 550         }
 551
 552         public function merge( $key, callable $callback, $exptime = 0, $attempts = 10, $flags = 0 ) {
 553                 $ok = $this->mergeViaCas( $key, $callback, $exptime, $attempts, $flags );
 554                 if ( ( $flags & self::WRITE_SYNC ) == self::WRITE_SYNC ) {
 555                         $ok = $this->waitForReplication() && $ok;
 556                 }
 557
 558                 return $ok;
 559         }
 560
 561         public function changeTTL( $key, $exptime = 0, $flags = 0 ) {
 562                 list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
 563                 $db = null;
 564                 /** @noinspection PhpUnusedLocalVariableInspection */
 565                 $silenceScope = $this->silenceTransactionProfiler();
 566                 try {
 567                         $db = $this->getDB( $serverIndex );
 568                         if ( $exptime == 0 ) {
 569                                 $timestamp = $this->getMaxDateTime( $db );
 570                         } else {
 571                                 $timestamp = $db->timestamp( $this->convertToExpiry( $exptime ) );
 572                         }
 573                         $db->update(
 574                                 $tableName,
 575                                 [ 'exptime' => $timestamp ],
 576                                 [ 'keyname' => $key, 'exptime > ' . $db->addQuotes( $db->timestamp( time() ) ) ],
 577                                 __METHOD__
 578                         );
 579                         if ( $db->affectedRows() == 0 ) {
 580                                 $exists = (bool)$db->selectField(
 581                                         $tableName,
 582                                         1,
 583                                         [ 'keyname' => $key, 'exptime' => $timestamp ],
 584                                         __METHOD__,
 585                                         [ 'FOR UPDATE' ]
 586                                 );
 587
 588                                 return $exists;
 589                         }
 590                 } catch ( DBError $e ) {
 591                         $this->handleWriteError( $e, $db, $serverIndex );
 592                         return false;
 593                 }
 594
 595                 return true;
 596         }
 597
 598         /**
 599          * @param IDatabase $db
 600          * @param string $exptime
 601          * @return bool
 602          */
 603         protected function isExpired( $db, $exptime ) {
 604                 return $exptime != $this->getMaxDateTime( $db ) && wfTimestamp( TS_UNIX, $exptime ) < time();
 605         }
 606
 607         /**
 608          * @param IDatabase $db
 609          * @return string
 610          */
 611         protected function getMaxDateTime( $db ) {
 612                 if ( time() > 0x7fffffff ) {
 613                         return $db->timestamp( 1 << 62 );
 614                 } else {
 615                         return $db->timestamp( 0x7fffffff );
 616                 }
 617         }
 618
 619         protected function garbageCollect() {
 620                 if ( !$this->purgePeriod || $this->replicaOnly ) {
 621                         // Disabled
 622                         return;
 623                 }
 624                 // Only purge on one in every $this->purgePeriod writes
 625                 if ( $this->purgePeriod !== 1 && mt_rand( 0, $this->purgePeriod - 1 ) ) {
 626                         return;
 627                 }
 628                 $now = time();
 629                 // Avoid repeating the delete within a few seconds
 630                 if ( $now > ( $this->lastExpireAll + 1 ) ) {
 631                         $this->lastExpireAll = $now;
 632                         $this->deleteObjectsExpiringBefore(
 633                                 wfTimestamp( TS_MW, $now ),
 634                                 false,
 635                                 $this->purgeLimit
 636                         );
 637                 }
 638         }
 639
 640         public function expireAll() {
 641                 $this->deleteObjectsExpiringBefore( wfTimestampNow() );
 642         }
 643
 644         public function deleteObjectsExpiringBefore(
 645                 $timestamp,
 646                 $progressCallback = false,
 647                 $limit = INF
 648         ) {
 649                 /** @noinspection PhpUnusedLocalVariableInspection */
 650                 $silenceScope = $this->silenceTransactionProfiler();
 651
 652                 $count = 0;
 653                 for ( $serverIndex = 0; $serverIndex < $this->numServers; $serverIndex++ ) {
 654                         $db = null;
 655                         try {
 656                                 $db = $this->getDB( $serverIndex );
 657                                 $dbTimestamp = $db->timestamp( $timestamp );
 658                                 $totalSeconds = false;
 659                                 $baseConds = [ 'exptime < ' . $db->addQuotes( $dbTimestamp ) ];
 660                                 for ( $i = 0; $i < $this->shards; $i++ ) {
 661                                         $maxExpTime = false;
 662                                         while ( true ) {
 663                                                 $conds = $baseConds;
 664                                                 if ( $maxExpTime !== false ) {
 665                                                         $conds[] = 'exptime >= ' . $db->addQuotes( $maxExpTime );
 666                                                 }
 667                                                 $rows = $db->select(
 668                                                         $this->getTableNameByShard( $i ),
 669                                                         [ 'keyname', 'exptime' ],
 670                                                         $conds,
 671                                                         __METHOD__,
 672                                                         [ 'LIMIT' => 100, 'ORDER BY' => 'exptime' ]
 673                                                 );
 674                                                 if ( $rows === false || !$rows->numRows() ) {
 675                                                         break;
 676                                                 }
 677                                                 $keys = [];
 678                                                 $row = $rows->current();
 679                                                 $minExpTime = $row->exptime;
 680                                                 if ( $totalSeconds === false ) {
 681                                                         $totalSeconds = wfTimestamp( TS_UNIX, $timestamp )
 682                                                                 - wfTimestamp( TS_UNIX, $minExpTime );
 683                                                 }
 684                                                 foreach ( $rows as $row ) {
 685                                                         $keys[] = $row->keyname;
 686                                                         $maxExpTime = $row->exptime;
 687                                                 }
 688
 689                                                 $db->delete(
 690                                                         $this->getTableNameByShard( $i ),
 691                                                         [
 692                                                                 'exptime >= ' . $db->addQuotes( $minExpTime ),
 693                                                                 'exptime < ' . $db->addQuotes( $dbTimestamp ),
 694                                                                 'keyname' => $keys
 695                                                         ],
 696                                                         __METHOD__
 697                                                 );
 698                                                 $count += $db->affectedRows();
 699                                                 if ( $count >= $limit ) {
 700                                                         return true;
 701                                                 }
 702
 703                                                 if ( is_callable( $progressCallback ) ) {
 704                                                         if ( intval( $totalSeconds ) === 0 ) {
 705                                                                 $percent = 0;
 706                                                         } else {
 707                                                                 $remainingSeconds = wfTimestamp( TS_UNIX, $timestamp )
 708                                                                         - wfTimestamp( TS_UNIX, $maxExpTime );
 709                                                                 if ( $remainingSeconds > $totalSeconds ) {
 710                                                                         $totalSeconds = $remainingSeconds;
 711                                                                 }
 712                                                                 $processedSeconds = $totalSeconds - $remainingSeconds;
 713                                                                 $percent = ( $i + $processedSeconds / $totalSeconds )
 714                                                                         / $this->shards * 100;
 715                                                         }
 716                                                         $percent = ( $percent / $this->numServers )
 717                                                                 + ( $serverIndex / $this->numServers * 100 );
 718                                                         call_user_func( $progressCallback, $percent );
 719                                                 }
 720                                         }
 721                                 }
 722                         } catch ( DBError $e ) {
 723                                 $this->handleWriteError( $e, $db, $serverIndex );
 724                                 return false;
 725                         }
 726                 }
 727
 728                 return true;
 729         }
 730
 731         /**
 732          * Delete content of shard tables in every server.
 733          * Return true if the operation is successful, false otherwise.
 734          * @return bool
 735          */
 736         public function deleteAll() {
 737                 /** @noinspection PhpUnusedLocalVariableInspection */
 738                 $silenceScope = $this->silenceTransactionProfiler();
 739                 for ( $serverIndex = 0; $serverIndex < $this->numServers; $serverIndex++ ) {
 740                         $db = null;
 741                         try {
 742                                 $db = $this->getDB( $serverIndex );
 743                                 for ( $i = 0; $i < $this->shards; $i++ ) {
 744                                         $db->delete( $this->getTableNameByShard( $i ), '*', __METHOD__ );
 745                                 }
 746                         } catch ( DBError $e ) {
 747                                 $this->handleWriteError( $e, $db, $serverIndex );
 748                                 return false;
 749                         }
 750                 }
 751                 return true;
 752         }
 753
 754         public function lock( $key, $timeout = 6, $expiry = 6, $rclass = '' ) {
 755                 // Avoid deadlocks and allow lock reentry if specified
 756                 if ( isset( $this->locks[$key] ) ) {
 757                         if ( $rclass != '' && $this->locks[$key]['class'] === $rclass ) {
 758                                 ++$this->locks[$key]['depth'];
 759                                 return true;
 760                         } else {
 761                                 return false;
 762                         }
 763                 }
 764
 765                 list( $serverIndex ) = $this->getTableByKey( $key );
 766                 try {
 767                         $db = $this->getDB( $serverIndex );
 768                         $ok = $db->lock( $key, __METHOD__, $timeout );
 769                         if ( $ok ) {
 770                                 $this->locks[$key] = [ 'class' => $rclass, 'depth' => 1 ];
 771                         }
 772
 773                         $this->logger->warning(
 774                                 __METHOD__ . " failed due to timeout for {key}.",
 775                                 [ 'key' => $key, 'timeout' => $timeout ]
 776                         );
 777
 778                         return $ok;
 779                 } catch ( DBError $e ) {
 780                         $this->handleWriteError( $e, $db, $serverIndex );
 781                         $ok = false;
 782                 }
 783
 784                 return $ok;
 785         }
 786
 787         public function unlock( $key ) {
 788                 if ( !isset( $this->locks[$key] ) ) {
 789                         return false;
 790                 }
 791
 792                 if ( --$this->locks[$key]['depth'] <= 0 ) {
 793                         unset( $this->locks[$key] );
 794
 795                         list( $serverIndex ) = $this->getTableByKey( $key );
 796                         try {
 797                                 $db = $this->getDB( $serverIndex );
 798                                 $ok = $db->unlock( $key, __METHOD__ );
 799                                 if ( !$ok ) {
 800                                         $this->logger->warning(
 801                                                 __METHOD__ . ' failed to release lock for {key}.',
 802                                                 [ 'key' => $key ]
 803                                         );
 804                                 }
 805                         } catch ( DBError $e ) {
 806                                 $this->handleWriteError( $e, $db, $serverIndex );
 807                                 $ok = false;
 808                         }
 809                 } else {
 810                         $ok = false;
 811                 }
 812
 813                 return $ok;
 814         }
 815
 816         /**
 817          * Serialize an object and, if possible, compress the representation.
 818          * On typical message and page data, this can provide a 3X decrease
 819          * in storage requirements.
 820          *
 821          * @param mixed $data
 822          * @return string
 823          */
 824         protected function serialize( $data ) {
 825                 $serial = serialize( $data );
 826
 827                 if ( function_exists( 'gzdeflate' ) ) {
 828                         return gzdeflate( $serial );
 829                 } else {
 830                         return $serial;
 831                 }
 832         }
 833
 834         /**
 835          * Unserialize and, if necessary, decompress an object.
 836          * @param string $serial
 837          * @return mixed
 838          */
 839         protected function unserialize( $serial ) {
 840                 if ( function_exists( 'gzinflate' ) ) {
 841                         Wikimedia\suppressWarnings();
 842                         $decomp = gzinflate( $serial );
 843                         Wikimedia\restoreWarnings();
 844
 845                         if ( $decomp !== false ) {
 846                                 $serial = $decomp;
 847                         }
 848                 }
 849
 850                 $ret = unserialize( $serial );
 851
 852                 return $ret;
 853         }
 854
 855         /**
 856          * Handle a DBError which occurred during a read operation.
 857          *
 858          * @param DBError $exception
 859          * @param int $serverIndex
 860          */
 861         protected function handleReadError( DBError $exception, $serverIndex ) {
 862                 if ( $exception instanceof DBConnectionError ) {
 863                         $this->markServerDown( $exception, $serverIndex );
 864                 }
 865
 866                 $this->setAndLogDBError( $exception );
 867         }
 868
 869         /**
 870          * Handle a DBQueryError which occurred during a write operation.
 871          *
 872          * @param DBError $exception
 873          * @param IDatabase|null $db DB handle or null if connection failed
 874          * @param int $serverIndex
 875          * @throws Exception
 876          */
 877         protected function handleWriteError( DBError $exception, $db, $serverIndex ) {
 878                 if ( !( $db instanceof IDatabase ) ) {
 879                         $this->markServerDown( $exception, $serverIndex );
 880                 }
 881
 882                 $this->setAndLogDBError( $exception );
 883         }
 884
 885         /**
 886          * @param DBError $exception
 887          */
 888         private function setAndLogDBError( DBError $exception ) {
 889                 $this->logger->error( "DBError: {$exception->getMessage()}" );
 890                 if ( $exception instanceof DBConnectionError ) {
 891                         $this->setLastError( BagOStuff::ERR_UNREACHABLE );
 892                         $this->logger->debug( __METHOD__ . ": ignoring connection error" );
 893                 } else {
 894                         $this->setLastError( BagOStuff::ERR_UNEXPECTED );
 895                         $this->logger->debug( __METHOD__ . ": ignoring query error" );
 896                 }
 897         }
 898
 899         /**
 900          * Mark a server down due to a DBConnectionError exception
 901          *
 902          * @param DBError $exception
 903          * @param int $serverIndex
 904          */
 905         protected function markServerDown( DBError $exception, $serverIndex ) {
 906                 unset( $this->conns[$serverIndex] ); // bug T103435
 907
 908                 if ( isset( $this->connFailureTimes[$serverIndex] ) ) {
 909                         if ( time() - $this->connFailureTimes[$serverIndex] >= 60 ) {
 910                                 unset( $this->connFailureTimes[$serverIndex] );
 911                                 unset( $this->connFailureErrors[$serverIndex] );
 912                         } else {
 913                                 $this->logger->debug( __METHOD__ . ": Server #$serverIndex already down" );
 914                                 return;
 915                         }
 916                 }
 917                 $now = time();
 918                 $this->logger->info( __METHOD__ . ": Server #$serverIndex down until " . ( $now + 60 ) );
 919                 $this->connFailureTimes[$serverIndex] = $now;
 920                 $this->connFailureErrors[$serverIndex] = $exception;
 921         }
 922
 923         /**
 924          * Create shard tables. For use from eval.php.
 925          */
 926         public function createTables() {
 927                 for ( $serverIndex = 0; $serverIndex < $this->numServers; $serverIndex++ ) {
 928                         $db = $this->getDB( $serverIndex );
 929                         if ( $db->getType() !== 'mysql' ) {
 930                                 throw new MWException( __METHOD__ . ' is not supported on this DB server' );
 931                         }
 932
 933                         for ( $i = 0; $i < $this->shards; $i++ ) {
 934                                 $db->query(
 935                                         'CREATE TABLE ' . $db->tableName( $this->getTableNameByShard( $i ) ) .
 936                                         ' LIKE ' . $db->tableName( 'objectcache' ),
 937                                         __METHOD__ );
 938                         }
 939                 }
 940         }
 941
 942         /**
 943          * @return bool Whether the main DB is used, e.g. wfGetDB( DB_MASTER )
 944          */
 945         protected function usesMainDB() {
 946                 return !$this->serverInfos;
 947         }
 948
 949         protected function waitForReplication() {
 950                 if ( !$this->usesMainDB() ) {
 951                         // Custom DB server list; probably doesn't use replication
 952                         return true;
 953                 }
 954
 955                 $lb = MediaWikiServices::getInstance()->getDBLoadBalancer();
 956                 if ( $lb->getServerCount() <= 1 ) {
 957                         return true; // no replica DBs
 958                 }
 959
 960                 // Main LB is used; wait for any replica DBs to catch up
 961                 try {
 962                         $masterPos = $lb->getMasterPos();
 963                         if ( !$masterPos ) {
 964                                 return true; // not applicable
 965                         }
 966
 967                         $loop = new WaitConditionLoop(
 968                                 function () use ( $lb, $masterPos ) {
 969                                         return $lb->waitForAll( $masterPos, 1 );
 970                                 },
 971                                 $this->syncTimeout,
 972                                 $this->busyCallbacks
 973                         );
 974
 975                         return ( $loop->invoke() === $loop::CONDITION_REACHED );
 976                 } catch ( DBError $e ) {
 977                         $this->setAndLogDBError( $e );
 978
 979                         return false;
 980                 }
 981         }
 982
 983         /**
 984          * Returns a ScopedCallback which resets the silence flag in the transaction profiler when it is
 985          * destroyed on the end of a scope, for example on return or throw
 986          * @return ScopedCallback
 987          * @since 1.32
 988          */
 989         protected function silenceTransactionProfiler() {
 990                 $trxProfiler = Profiler::instance()->getTransactionProfiler();
 991                 $oldSilenced = $trxProfiler->setSilenced( true );
 992                 return new ScopedCallback( function () use ( $trxProfiler, $oldSilenced ) {
 993                         $trxProfiler->setSilenced( $oldSilenced );
 994                 } );
 995         }
 996 }