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