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