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 /**
  25  * Class to store objects in the database
  26  *
  27  * @ingroup Cache
  28  */
  29 class SqlBagOStuff extends BagOStuff {
  30         /** @var array[] (server index => server config) */
  31         protected $serverInfos;
  32         /** @var string[] (server index => tag/host name) */
  33         protected $serverTags;
  34         /** @var int */
  35         protected $numServers;
  36         /** @var int */
  37         protected $lastExpireAll = 0;
  38         /** @var int */
  39         protected $purgePeriod = 100;
  40         /** @var int */
  41         protected $shards = 1;
  42         /** @var string */
  43         protected $tableName = 'objectcache';
  44         /** @var bool */
  45         protected $slaveOnly = false;
  46         /** @var int */
  47         protected $syncTimeout = 3;
  48
  49         /** @var array */
  50         protected $conns;
  51         /** @var array UNIX timestamps */
  52         protected $connFailureTimes = [];
  53         /** @var array Exceptions */
  54         protected $connFailureErrors = [];
  55
  56         /**
  57          * Constructor. Parameters are:
  58          *   - server:      A server info structure in the format required by each
  59          *                  element in $wgDBServers.
  60          *
  61          *   - servers:     An array of server info structures describing a set of database servers
  62          *                  to distribute keys to. If this is specified, the "server" option will be
  63          *                  ignored. If string keys are used, then they will be used for consistent
  64          *                  hashing *instead* of the host name (from the server config). This is useful
  65          *                  when a cluster is replicated to another site (with different host names)
  66          *                  but each server has a corresponding replica in the other cluster.
  67          *
  68          *   - purgePeriod: The average number of object cache requests in between
  69          *                  garbage collection operations, where expired entries
  70          *                  are removed from the database. Or in other words, the
  71          *                  reciprocal of the probability of purging on any given
  72          *                  request. If this is set to zero, purging will never be
  73          *                  done.
  74          *
  75          *   - tableName:   The table name to use, default is "objectcache".
  76          *
  77          *   - shards:      The number of tables to use for data storage on each server.
  78          *                  If this is more than 1, table names will be formed in the style
  79          *                  objectcacheNNN where NNN is the shard index, between 0 and
  80          *                  shards-1. The number of digits will be the minimum number
  81          *                  required to hold the largest shard index. Data will be
  82          *                  distributed across all tables by key hash. This is for
  83          *                  MySQL bugs 61735 and 61736.
  84          *   - slaveOnly:   Whether to only use slave DBs and avoid triggering
  85          *                  garbage collection logic of expired items. This only
  86          *                  makes sense if the primary DB is used and only if get()
  87          *                  calls will be used. This is used by ReplicatedBagOStuff.
  88          *   - syncTimeout: Max seconds to wait for slaves to catch up for WRITE_SYNC.
  89          *
  90          * @param array $params
  91          */
  92         public function __construct( $params ) {
  93                 parent::__construct( $params );
  94
  95                 $this->attrMap[self::ATTR_EMULATION] = self::QOS_EMULATION_SQL;
  96
  97                 if ( isset( $params['servers'] ) ) {
  98                         $this->serverInfos = [];
  99                         $this->serverTags = [];
 100                         $this->numServers = count( $params['servers'] );
 101                         $index = 0;
 102                         foreach ( $params['servers'] as $tag => $info ) {
 103                                 $this->serverInfos[$index] = $info;
 104                                 if ( is_string( $tag ) ) {
 105                                         $this->serverTags[$index] = $tag;
 106                                 } else {
 107                                         $this->serverTags[$index] = isset( $info['host'] ) ? $info['host'] : "#$index";
 108                                 }
 109                                 ++$index;
 110                         }
 111                 } elseif ( isset( $params['server'] ) ) {
 112                         $this->serverInfos = [ $params['server'] ];
 113                         $this->numServers = count( $this->serverInfos );
 114                 } else {
 115                         $this->serverInfos = false;
 116                         $this->numServers = 1;
 117                 }
 118                 if ( isset( $params['purgePeriod'] ) ) {
 119                         $this->purgePeriod = intval( $params['purgePeriod'] );
 120                 }
 121                 if ( isset( $params['tableName'] ) ) {
 122                         $this->tableName = $params['tableName'];
 123                 }
 124                 if ( isset( $params['shards'] ) ) {
 125                         $this->shards = intval( $params['shards'] );
 126                 }
 127                 if ( isset( $params['syncTimeout'] ) ) {
 128                         $this->syncTimeout = $params['syncTimeout'];
 129                 }
 130                 $this->slaveOnly = !empty( $params['slaveOnly'] );
 131         }
 132
 133         /**
 134          * Get a connection to the specified database
 135          *
 136          * @param int $serverIndex
 137          * @return IDatabase
 138          * @throws MWException
 139          */
 140         protected function getDB( $serverIndex ) {
 141                 if ( !isset( $this->conns[$serverIndex] ) ) {
 142                         if ( $serverIndex >= $this->numServers ) {
 143                                 throw new MWException( __METHOD__ . ": Invalid server index \"$serverIndex\"" );
 144                         }
 145
 146                         # Don't keep timing out trying to connect for each call if the DB is down
 147                         if ( isset( $this->connFailureErrors[$serverIndex] )
 148                                 && ( time() - $this->connFailureTimes[$serverIndex] ) < 60
 149                         ) {
 150                                 throw $this->connFailureErrors[$serverIndex];
 151                         }
 152
 153                         # If server connection info was given, use that
 154                         if ( $this->serverInfos ) {
 155                                 $info = $this->serverInfos[$serverIndex];
 156                                 $type = isset( $info['type'] ) ? $info['type'] : 'mysql';
 157                                 $host = isset( $info['host'] ) ? $info['host'] : '[unknown]';
 158                                 $this->logger->debug( __CLASS__ . ": connecting to $host" );
 159                                 // Use a blank trx profiler to ignore expections as this is a cache
 160                                 $info['trxProfiler'] = new TransactionProfiler();
 161                                 $db = DatabaseBase::factory( $type, $info );
 162                                 $db->clearFlag( DBO_TRX );
 163                         } else {
 164                                 // We must keep a separate connection to MySQL in order to avoid deadlocks
 165                                 // However, SQLite has an opposite behavior. And PostgreSQL needs to know
 166                                 // if we are in transaction or not (@TODO: find some work-around).
 167                                 $index = $this->slaveOnly ? DB_SLAVE : DB_MASTER;
 168                                 if ( wfGetDB( $index )->getType() == 'mysql' ) {
 169                                         $lb = wfGetLBFactory()->newMainLB();
 170                                         $db = $lb->getConnection( $index );
 171                                         $db->clearFlag( DBO_TRX ); // auto-commit mode
 172                                 } else {
 173                                         $db = wfGetDB( $index );
 174                                 }
 175                         }
 176                         $this->logger->debug( sprintf( "Connection %s will be used for SqlBagOStuff", $db ) );
 177                         $this->conns[$serverIndex] = $db;
 178                 }
 179
 180                 return $this->conns[$serverIndex];
 181         }
 182
 183         /**
 184          * Get the server index and table name for a given key
 185          * @param string $key
 186          * @return array Server index and table name
 187          */
 188         protected function getTableByKey( $key ) {
 189                 if ( $this->shards > 1 ) {
 190                         $hash = hexdec( substr( md5( $key ), 0, 8 ) ) & 0x7fffffff;
 191                         $tableIndex = $hash % $this->shards;
 192                 } else {
 193                         $tableIndex = 0;
 194                 }
 195                 if ( $this->numServers > 1 ) {
 196                         $sortedServers = $this->serverTags;
 197                         ArrayUtils::consistentHashSort( $sortedServers, $key );
 198                         reset( $sortedServers );
 199                         $serverIndex = key( $sortedServers );
 200                 } else {
 201                         $serverIndex = 0;
 202                 }
 203                 return [ $serverIndex, $this->getTableNameByShard( $tableIndex ) ];
 204         }
 205
 206         /**
 207          * Get the table name for a given shard index
 208          * @param int $index
 209          * @return string
 210          */
 211         protected function getTableNameByShard( $index ) {
 212                 if ( $this->shards > 1 ) {
 213                         $decimals = strlen( $this->shards - 1 );
 214                         return $this->tableName .
 215                                 sprintf( "%0{$decimals}d", $index );
 216                 } else {
 217                         return $this->tableName;
 218                 }
 219         }
 220
 221         protected function doGet( $key, $flags = 0 ) {
 222                 $casToken = null;
 223
 224                 return $this->getWithToken( $key, $casToken, $flags );
 225         }
 226
 227         protected function getWithToken( $key, &$casToken, $flags = 0 ) {
 228                 $values = $this->getMulti( [ $key ] );
 229                 if ( array_key_exists( $key, $values ) ) {
 230                         $casToken = $values[$key];
 231                         return $values[$key];
 232                 }
 233                 return false;
 234         }
 235
 236         public function getMulti( array $keys, $flags = 0 ) {
 237                 $values = []; // array of (key => value)
 238
 239                 $keysByTable = [];
 240                 foreach ( $keys as $key ) {
 241                         list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
 242                         $keysByTable[$serverIndex][$tableName][] = $key;
 243                 }
 244
 245                 $this->garbageCollect(); // expire old entries if any
 246
 247                 $dataRows = [];
 248                 foreach ( $keysByTable as $serverIndex => $serverKeys ) {
 249                         try {
 250                                 $db = $this->getDB( $serverIndex );
 251                                 foreach ( $serverKeys as $tableName => $tableKeys ) {
 252                                         $res = $db->select( $tableName,
 253                                                 [ 'keyname', 'value', 'exptime' ],
 254                                                 [ 'keyname' => $tableKeys ],
 255                                                 __METHOD__,
 256                                                 // Approximate write-on-the-fly BagOStuff API via blocking.
 257                                                 // This approximation fails if a ROLLBACK happens (which is rare).
 258                                                 // We do not want to flush the TRX as that can break callers.
 259                                                 $db->trxLevel() ? [ 'LOCK IN SHARE MODE' ] : []
 260                                         );
 261                                         if ( $res === false ) {
 262                                                 continue;
 263                                         }
 264                                         foreach ( $res as $row ) {
 265                                                 $row->serverIndex = $serverIndex;
 266                                                 $row->tableName = $tableName;
 267                                                 $dataRows[$row->keyname] = $row;
 268                                         }
 269                                 }
 270                         } catch ( DBError $e ) {
 271                                 $this->handleReadError( $e, $serverIndex );
 272                         }
 273                 }
 274
 275                 foreach ( $keys as $key ) {
 276                         if ( isset( $dataRows[$key] ) ) { // HIT?
 277                                 $row = $dataRows[$key];
 278                                 $this->debug( "get: retrieved data; expiry time is " . $row->exptime );
 279                                 try {
 280                                         $db = $this->getDB( $row->serverIndex );
 281                                         if ( $this->isExpired( $db, $row->exptime ) ) { // MISS
 282                                                 $this->debug( "get: key has expired" );
 283                                         } else { // HIT
 284                                                 $values[$key] = $this->unserialize( $db->decodeBlob( $row->value ) );
 285                                         }
 286                                 } catch ( DBQueryError $e ) {
 287                                         $this->handleWriteError( $e, $row->serverIndex );
 288                                 }
 289                         } else { // MISS
 290                                 $this->debug( 'get: no matching rows' );
 291                         }
 292                 }
 293
 294                 return $values;
 295         }
 296
 297         public function setMulti( array $data, $expiry = 0 ) {
 298                 $keysByTable = [];
 299                 foreach ( $data as $key => $value ) {
 300                         list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
 301                         $keysByTable[$serverIndex][$tableName][] = $key;
 302                 }
 303
 304                 $this->garbageCollect(); // expire old entries if any
 305
 306                 $result = true;
 307                 $exptime = (int)$expiry;
 308                 foreach ( $keysByTable as $serverIndex => $serverKeys ) {
 309                         try {
 310                                 $db = $this->getDB( $serverIndex );
 311                         } catch ( DBError $e ) {
 312                                 $this->handleWriteError( $e, $serverIndex );
 313                                 $result = false;
 314                                 continue;
 315                         }
 316
 317                         if ( $exptime < 0 ) {
 318                                 $exptime = 0;
 319                         }
 320
 321                         if ( $exptime == 0 ) {
 322                                 $encExpiry = $this->getMaxDateTime( $db );
 323                         } else {
 324                                 $exptime = $this->convertExpiry( $exptime );
 325                                 $encExpiry = $db->timestamp( $exptime );
 326                         }
 327                         foreach ( $serverKeys as $tableName => $tableKeys ) {
 328                                 $rows = [];
 329                                 foreach ( $tableKeys as $key ) {
 330                                         $rows[] = [
 331                                                 'keyname' => $key,
 332                                                 'value' => $db->encodeBlob( $this->serialize( $data[$key] ) ),
 333                                                 'exptime' => $encExpiry,
 334                                         ];
 335                                 }
 336
 337                                 try {
 338                                         $db->replace(
 339                                                 $tableName,
 340                                                 [ 'keyname' ],
 341                                                 $rows,
 342                                                 __METHOD__
 343                                         );
 344                                 } catch ( DBError $e ) {
 345                                         $this->handleWriteError( $e, $serverIndex );
 346                                         $result = false;
 347                                 }
 348
 349                         }
 350
 351                 }
 352
 353                 return $result;
 354         }
 355
 356         public function set( $key, $value, $exptime = 0, $flags = 0 ) {
 357                 $ok = $this->setMulti( [ $key => $value ], $exptime );
 358                 if ( ( $flags & self::WRITE_SYNC ) == self::WRITE_SYNC ) {
 359                         $ok = $ok && $this->waitForSlaves();
 360                 }
 361
 362                 return $ok;
 363         }
 364
 365         protected function cas( $casToken, $key, $value, $exptime = 0 ) {
 366                 list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
 367                 try {
 368                         $db = $this->getDB( $serverIndex );
 369                         $exptime = intval( $exptime );
 370
 371                         if ( $exptime < 0 ) {
 372                                 $exptime = 0;
 373                         }
 374
 375                         if ( $exptime == 0 ) {
 376                                 $encExpiry = $this->getMaxDateTime( $db );
 377                         } else {
 378                                 $exptime = $this->convertExpiry( $exptime );
 379                                 $encExpiry = $db->timestamp( $exptime );
 380                         }
 381                         // (bug 24425) use a replace if the db supports it instead of
 382                         // delete/insert to avoid clashes with conflicting keynames
 383                         $db->update(
 384                                 $tableName,
 385                                 [
 386                                         'keyname' => $key,
 387                                         'value' => $db->encodeBlob( $this->serialize( $value ) ),
 388                                         'exptime' => $encExpiry
 389                                 ],
 390                                 [
 391                                         'keyname' => $key,
 392                                         'value' => $db->encodeBlob( $this->serialize( $casToken ) )
 393                                 ],
 394                                 __METHOD__
 395                         );
 396                 } catch ( DBQueryError $e ) {
 397                         $this->handleWriteError( $e, $serverIndex );
 398
 399                         return false;
 400                 }
 401
 402                 return (bool)$db->affectedRows();
 403         }
 404
 405         public function delete( $key ) {
 406                 list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
 407                 try {
 408                         $db = $this->getDB( $serverIndex );
 409                         $db->delete(
 410                                 $tableName,
 411                                 [ 'keyname' => $key ],
 412                                 __METHOD__ );
 413                 } catch ( DBError $e ) {
 414                         $this->handleWriteError( $e, $serverIndex );
 415                         return false;
 416                 }
 417
 418                 return true;
 419         }
 420
 421         public function incr( $key, $step = 1 ) {
 422                 list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
 423                 try {
 424                         $db = $this->getDB( $serverIndex );
 425                         $step = intval( $step );
 426                         $row = $db->selectRow(
 427                                 $tableName,
 428                                 [ 'value', 'exptime' ],
 429                                 [ 'keyname' => $key ],
 430                                 __METHOD__,
 431                                 [ 'FOR UPDATE' ] );
 432                         if ( $row === false ) {
 433                                 // Missing
 434
 435                                 return null;
 436                         }
 437                         $db->delete( $tableName, [ 'keyname' => $key ], __METHOD__ );
 438                         if ( $this->isExpired( $db, $row->exptime ) ) {
 439                                 // Expired, do not reinsert
 440
 441                                 return null;
 442                         }
 443
 444                         $oldValue = intval( $this->unserialize( $db->decodeBlob( $row->value ) ) );
 445                         $newValue = $oldValue + $step;
 446                         $db->insert( $tableName,
 447                                 [
 448                                         'keyname' => $key,
 449                                         'value' => $db->encodeBlob( $this->serialize( $newValue ) ),
 450                                         'exptime' => $row->exptime
 451                                 ], __METHOD__, 'IGNORE' );
 452
 453                         if ( $db->affectedRows() == 0 ) {
 454                                 // Race condition. See bug 28611
 455                                 $newValue = null;
 456                         }
 457                 } catch ( DBError $e ) {
 458                         $this->handleWriteError( $e, $serverIndex );
 459                         return null;
 460                 }
 461
 462                 return $newValue;
 463         }
 464
 465         public function merge( $key, callable $callback, $exptime = 0, $attempts = 10, $flags = 0 ) {
 466                 $ok = $this->mergeViaCas( $key, $callback, $exptime, $attempts );
 467                 if ( ( $flags & self::WRITE_SYNC ) == self::WRITE_SYNC ) {
 468                         $ok = $ok && $this->waitForSlaves();
 469                 }
 470
 471                 return $ok;
 472         }
 473
 474         public function changeTTL( $key, $expiry = 0 ) {
 475                 list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
 476                 try {
 477                         $db = $this->getDB( $serverIndex );
 478                         $db->update(
 479                                 $tableName,
 480                                 [ 'exptime' => $db->timestamp( $this->convertExpiry( $expiry ) ) ],
 481                                 [ 'keyname' => $key, 'exptime > ' . $db->addQuotes( $db->timestamp( time() ) ) ],
 482                                 __METHOD__
 483                         );
 484                         if ( $db->affectedRows() == 0 ) {
 485                                 return false;
 486                         }
 487                 } catch ( DBError $e ) {
 488                         $this->handleWriteError( $e, $serverIndex );
 489                         return false;
 490                 }
 491
 492                 return true;
 493         }
 494
 495         /**
 496          * @param IDatabase $db
 497          * @param string $exptime
 498          * @return bool
 499          */
 500         protected function isExpired( $db, $exptime ) {
 501                 return $exptime != $this->getMaxDateTime( $db ) && wfTimestamp( TS_UNIX, $exptime ) < time();
 502         }
 503
 504         /**
 505          * @param IDatabase $db
 506          * @return string
 507          */
 508         protected function getMaxDateTime( $db ) {
 509                 if ( time() > 0x7fffffff ) {
 510                         return $db->timestamp( 1 << 62 );
 511                 } else {
 512                         return $db->timestamp( 0x7fffffff );
 513                 }
 514         }
 515
 516         protected function garbageCollect() {
 517                 if ( !$this->purgePeriod || $this->slaveOnly ) {
 518                         // Disabled
 519                         return;
 520                 }
 521                 // Only purge on one in every $this->purgePeriod requests.
 522                 if ( $this->purgePeriod !== 1 && mt_rand( 0, $this->purgePeriod - 1 ) ) {
 523                         return;
 524                 }
 525                 $now = time();
 526                 // Avoid repeating the delete within a few seconds
 527                 if ( $now > ( $this->lastExpireAll + 1 ) ) {
 528                         $this->lastExpireAll = $now;
 529                         $this->expireAll();
 530                 }
 531         }
 532
 533         public function expireAll() {
 534                 $this->deleteObjectsExpiringBefore( wfTimestampNow() );
 535         }
 536
 537         /**
 538          * Delete objects from the database which expire before a certain date.
 539          * @param string $timestamp
 540          * @param bool|callable $progressCallback
 541          * @return bool
 542          */
 543         public function deleteObjectsExpiringBefore( $timestamp, $progressCallback = false ) {
 544                 for ( $serverIndex = 0; $serverIndex < $this->numServers; $serverIndex++ ) {
 545                         try {
 546                                 $db = $this->getDB( $serverIndex );
 547                                 $dbTimestamp = $db->timestamp( $timestamp );
 548                                 $totalSeconds = false;
 549                                 $baseConds = [ 'exptime < ' . $db->addQuotes( $dbTimestamp ) ];
 550                                 for ( $i = 0; $i < $this->shards; $i++ ) {
 551                                         $maxExpTime = false;
 552                                         while ( true ) {
 553                                                 $conds = $baseConds;
 554                                                 if ( $maxExpTime !== false ) {
 555                                                         $conds[] = 'exptime > ' . $db->addQuotes( $maxExpTime );
 556                                                 }
 557                                                 $rows = $db->select(
 558                                                         $this->getTableNameByShard( $i ),
 559                                                         [ 'keyname', 'exptime' ],
 560                                                         $conds,
 561                                                         __METHOD__,
 562                                                         [ 'LIMIT' => 100, 'ORDER BY' => 'exptime' ] );
 563                                                 if ( $rows === false || !$rows->numRows() ) {
 564                                                         break;
 565                                                 }
 566                                                 $keys = [];
 567                                                 $row = $rows->current();
 568                                                 $minExpTime = $row->exptime;
 569                                                 if ( $totalSeconds === false ) {
 570                                                         $totalSeconds = wfTimestamp( TS_UNIX, $timestamp )
 571                                                                 - wfTimestamp( TS_UNIX, $minExpTime );
 572                                                 }
 573                                                 foreach ( $rows as $row ) {
 574                                                         $keys[] = $row->keyname;
 575                                                         $maxExpTime = $row->exptime;
 576                                                 }
 577
 578                                                 $db->delete(
 579                                                         $this->getTableNameByShard( $i ),
 580                                                         [
 581                                                                 'exptime >= ' . $db->addQuotes( $minExpTime ),
 582                                                                 'exptime < ' . $db->addQuotes( $dbTimestamp ),
 583                                                                 'keyname' => $keys
 584                                                         ],
 585                                                         __METHOD__ );
 586
 587                                                 if ( $progressCallback ) {
 588                                                         if ( intval( $totalSeconds ) === 0 ) {
 589                                                                 $percent = 0;
 590                                                         } else {
 591                                                                 $remainingSeconds = wfTimestamp( TS_UNIX, $timestamp )
 592                                                                         - wfTimestamp( TS_UNIX, $maxExpTime );
 593                                                                 if ( $remainingSeconds > $totalSeconds ) {
 594                                                                         $totalSeconds = $remainingSeconds;
 595                                                                 }
 596                                                                 $processedSeconds = $totalSeconds - $remainingSeconds;
 597                                                                 $percent = ( $i + $processedSeconds / $totalSeconds )
 598                                                                         / $this->shards * 100;
 599                                                         }
 600                                                         $percent = ( $percent / $this->numServers )
 601                                                                 + ( $serverIndex / $this->numServers * 100 );
 602                                                         call_user_func( $progressCallback, $percent );
 603                                                 }
 604                                         }
 605                                 }
 606                         } catch ( DBError $e ) {
 607                                 $this->handleWriteError( $e, $serverIndex );
 608                                 return false;
 609                         }
 610                 }
 611                 return true;
 612         }
 613
 614         /**
 615          * Delete content of shard tables in every server.
 616          * Return true if the operation is successful, false otherwise.
 617          * @return bool
 618          */
 619         public function deleteAll() {
 620                 for ( $serverIndex = 0; $serverIndex < $this->numServers; $serverIndex++ ) {
 621                         try {
 622                                 $db = $this->getDB( $serverIndex );
 623                                 for ( $i = 0; $i < $this->shards; $i++ ) {
 624                                         $db->delete( $this->getTableNameByShard( $i ), '*', __METHOD__ );
 625                                 }
 626                         } catch ( DBError $e ) {
 627                                 $this->handleWriteError( $e, $serverIndex );
 628                                 return false;
 629                         }
 630                 }
 631                 return true;
 632         }
 633
 634         /**
 635          * Serialize an object and, if possible, compress the representation.
 636          * On typical message and page data, this can provide a 3X decrease
 637          * in storage requirements.
 638          *
 639          * @param mixed $data
 640          * @return string
 641          */
 642         protected function serialize( &$data ) {
 643                 $serial = serialize( $data );
 644
 645                 if ( function_exists( 'gzdeflate' ) ) {
 646                         return gzdeflate( $serial );
 647                 } else {
 648                         return $serial;
 649                 }
 650         }
 651
 652         /**
 653          * Unserialize and, if necessary, decompress an object.
 654          * @param string $serial
 655          * @return mixed
 656          */
 657         protected function unserialize( $serial ) {
 658                 if ( function_exists( 'gzinflate' ) ) {
 659                         MediaWiki\suppressWarnings();
 660                         $decomp = gzinflate( $serial );
 661                         MediaWiki\restoreWarnings();
 662
 663                         if ( false !== $decomp ) {
 664                                 $serial = $decomp;
 665                         }
 666                 }
 667
 668                 $ret = unserialize( $serial );
 669
 670                 return $ret;
 671         }
 672
 673         /**
 674          * Handle a DBError which occurred during a read operation.
 675          *
 676          * @param DBError $exception
 677          * @param int $serverIndex
 678          */
 679         protected function handleReadError( DBError $exception, $serverIndex ) {
 680                 if ( $exception instanceof DBConnectionError ) {
 681                         $this->markServerDown( $exception, $serverIndex );
 682                 }
 683                 $this->logger->error( "DBError: {$exception->getMessage()}" );
 684                 if ( $exception instanceof DBConnectionError ) {
 685                         $this->setLastError( BagOStuff::ERR_UNREACHABLE );
 686                         $this->logger->debug( __METHOD__ . ": ignoring connection error" );
 687                 } else {
 688                         $this->setLastError( BagOStuff::ERR_UNEXPECTED );
 689                         $this->logger->debug( __METHOD__ . ": ignoring query error" );
 690                 }
 691         }
 692
 693         /**
 694          * Handle a DBQueryError which occurred during a write operation.
 695          *
 696          * @param DBError $exception
 697          * @param int $serverIndex
 698          * @throws Exception
 699          */
 700         protected function handleWriteError( DBError $exception, $serverIndex ) {
 701                 if ( $exception instanceof DBConnectionError ) {
 702                         $this->markServerDown( $exception, $serverIndex );
 703                 }
 704                 if ( $exception->db && $exception->db->wasReadOnlyError() ) {
 705                         if ( $exception->db->trxLevel() ) {
 706                                 if ( !$this->serverInfos ) {
 707                                         // Errors like deadlocks and connection drops already cause rollback.
 708                                         // For consistency, we have no choice but to throw an error and trigger
 709                                         // complete rollback if the main DB is also being used as the cache DB.
 710                                         throw $exception;
 711                                 }
 712
 713                                 try {
 714                                         $exception->db->rollback( __METHOD__ );
 715                                 } catch ( DBError $e ) {
 716                                 }
 717                         }
 718                 }
 719
 720                 $this->logger->error( "DBError: {$exception->getMessage()}" );
 721                 if ( $exception instanceof DBConnectionError ) {
 722                         $this->setLastError( BagOStuff::ERR_UNREACHABLE );
 723                         $this->logger->debug( __METHOD__ . ": ignoring connection error" );
 724                 } else {
 725                         $this->setLastError( BagOStuff::ERR_UNEXPECTED );
 726                         $this->logger->debug( __METHOD__ . ": ignoring query error" );
 727                 }
 728         }
 729
 730         /**
 731          * Mark a server down due to a DBConnectionError exception
 732          *
 733          * @param DBError $exception
 734          * @param int $serverIndex
 735          */
 736         protected function markServerDown( $exception, $serverIndex ) {
 737                 unset( $this->conns[$serverIndex] ); // bug T103435
 738
 739                 if ( isset( $this->connFailureTimes[$serverIndex] ) ) {
 740                         if ( time() - $this->connFailureTimes[$serverIndex] >= 60 ) {
 741                                 unset( $this->connFailureTimes[$serverIndex] );
 742                                 unset( $this->connFailureErrors[$serverIndex] );
 743                         } else {
 744                                 $this->logger->debug( __METHOD__ . ": Server #$serverIndex already down" );
 745                                 return;
 746                         }
 747                 }
 748                 $now = time();
 749                 $this->logger->info( __METHOD__ . ": Server #$serverIndex down until " . ( $now + 60 ) );
 750                 $this->connFailureTimes[$serverIndex] = $now;
 751                 $this->connFailureErrors[$serverIndex] = $exception;
 752         }
 753
 754         /**
 755          * Create shard tables. For use from eval.php.
 756          */
 757         public function createTables() {
 758                 for ( $serverIndex = 0; $serverIndex < $this->numServers; $serverIndex++ ) {
 759                         $db = $this->getDB( $serverIndex );
 760                         if ( $db->getType() !== 'mysql' ) {
 761                                 throw new MWException( __METHOD__ . ' is not supported on this DB server' );
 762                         }
 763
 764                         for ( $i = 0; $i < $this->shards; $i++ ) {
 765                                 $db->query(
 766                                         'CREATE TABLE ' . $db->tableName( $this->getTableNameByShard( $i ) ) .
 767                                         ' LIKE ' . $db->tableName( 'objectcache' ),
 768                                         __METHOD__ );
 769                         }
 770                 }
 771         }
 772
 773         protected function waitForSlaves() {
 774                 if ( !$this->serverInfos ) {
 775                         // Main LB is used; wait for any slaves to catch up
 776                         try {
 777                                 wfGetLBFactory()->waitForReplication( [ 'wiki' => wfWikiID() ] );
 778                                 return true;
 779                         } catch ( DBReplicationWaitError $e ) {
 780                                 return false;
 781                         }
 782                 } else {
 783                         // Custom DB server list; probably doesn't use replication
 784                         return true;
 785                 }
 786         }
 787 }