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         /**
  31          * @var LoadBalancer
  32          */
  33         var $lb;
  34
  35         var $serverInfos;
  36         var $serverNames;
  37         var $numServers;
  38         var $conns;
  39         var $lastExpireAll = 0;
  40         var $purgePeriod = 100;
  41         var $shards = 1;
  42         var $tableName = 'objectcache';
  43
  44         protected $connFailureTimes = array(); // UNIX timestamps
  45         protected $connFailureErrors = array(); // exceptions
  46
  47         /**
  48          * Constructor. Parameters are:
  49          *   - server:      A server info structure in the format required by each
  50          *                  element in $wgDBServers.
  51          *
  52          *   - servers:     An array of server info structures describing a set of
  53          *                  database servers to distribute keys to. If this is
  54          *                  specified, the "server" option will be ignored.
  55          *
  56          *   - purgePeriod: The average number of object cache requests in between
  57          *                  garbage collection operations, where expired entries
  58          *                  are removed from the database. Or in other words, the
  59          *                  reciprocal of the probability of purging on any given
  60          *                  request. If this is set to zero, purging will never be
  61          *                  done.
  62          *
  63          *   - tableName:   The table name to use, default is "objectcache".
  64          *
  65          *   - shards:      The number of tables to use for data storage on each server.
  66          *                  If this is more than 1, table names will be formed in the style
  67          *                  objectcacheNNN where NNN is the shard index, between 0 and
  68          *                  shards-1. The number of digits will be the minimum number
  69          *                  required to hold the largest shard index. Data will be
  70          *                  distributed across all tables by key hash. This is for
  71          *                  MySQL bugs 61735 and 61736.
  72          *
  73          * @param $params array
  74          */
  75         public function __construct( $params ) {
  76                 if ( isset( $params['servers'] ) ) {
  77                         $this->serverInfos = $params['servers'];
  78                         $this->numServers = count( $this->serverInfos );
  79                         $this->serverNames = array();
  80                         foreach ( $this->serverInfos as $i => $info ) {
  81                                 $this->serverNames[$i] = isset( $info['host'] ) ? $info['host'] : "#$i";
  82                         }
  83                 } elseif ( isset( $params['server'] ) ) {
  84                         $this->serverInfos = array( $params['server'] );
  85                         $this->numServers = count( $this->serverInfos );
  86                 } else {
  87                         $this->serverInfos = false;
  88                         $this->numServers = 1;
  89                 }
  90                 if ( isset( $params['purgePeriod'] ) ) {
  91                         $this->purgePeriod = intval( $params['purgePeriod'] );
  92                 }
  93                 if ( isset( $params['tableName'] ) ) {
  94                         $this->tableName = $params['tableName'];
  95                 }
  96                 if ( isset( $params['shards'] ) ) {
  97                         $this->shards = intval( $params['shards'] );
  98                 }
  99         }
 100
 101         /**
 102          * Get a connection to the specified database
 103          *
 104          * @param $serverIndex integer
 105          * @return DatabaseBase
 106          */
 107         protected function getDB( $serverIndex ) {
 108                 global $wgDebugDBTransactions;
 109
 110                 if ( !isset( $this->conns[$serverIndex] ) ) {
 111                         if ( $serverIndex >= $this->numServers ) {
 112                                 throw new MWException( __METHOD__ . ": Invalid server index \"$serverIndex\"" );
 113                         }
 114
 115                         # Don't keep timing out trying to connect for each call if the DB is down
 116                         if ( isset( $this->connFailureErrors[$serverIndex] )
 117                                 && ( time() - $this->connFailureTimes[$serverIndex] ) < 60 )
 118                         {
 119                                 throw $this->connFailureErrors[$serverIndex];
 120                         }
 121
 122                         # If server connection info was given, use that
 123                         if ( $this->serverInfos ) {
 124                                 if ( $wgDebugDBTransactions ) {
 125                                         wfDebug( "Using provided serverInfo for SqlBagOStuff\n" );
 126                                 }
 127                                 $info = $this->serverInfos[$serverIndex];
 128                                 $type = isset( $info['type'] ) ? $info['type'] : 'mysql';
 129                                 $host = isset( $info['host'] ) ? $info['host'] : '[unknown]';
 130                                 wfDebug( __CLASS__ . ": connecting to $host\n" );
 131                                 $db = DatabaseBase::factory( $type, $info );
 132                                 $db->clearFlag( DBO_TRX );
 133                         } else {
 134                                 /*
 135                                  * We must keep a separate connection to MySQL in order to avoid deadlocks
 136                                  * However, SQLite has an opposite behavior. And PostgreSQL needs to know
 137                                  * if we are in transaction or no
 138                                  */
 139                                 if ( wfGetDB( DB_MASTER )->getType() == 'mysql' ) {
 140                                         $this->lb = wfGetLBFactory()->newMainLB();
 141                                         $db = $this->lb->getConnection( DB_MASTER );
 142                                         $db->clearFlag( DBO_TRX ); // auto-commit mode
 143                                 } else {
 144                                         $db = wfGetDB( DB_MASTER );
 145                                 }
 146                         }
 147                         if ( $wgDebugDBTransactions ) {
 148                                 wfDebug( sprintf( "Connection %s will be used for SqlBagOStuff\n", $db ) );
 149                         }
 150                         $this->conns[$serverIndex] = $db;
 151                 }
 152
 153                 return $this->conns[$serverIndex];
 154         }
 155
 156         /**
 157          * Get the server index and table name for a given key
 158          * @param $key string
 159          * @return Array: server index and table name
 160          */
 161         protected function getTableByKey( $key ) {
 162                 if ( $this->shards > 1 ) {
 163                         $hash = hexdec( substr( md5( $key ), 0, 8 ) ) & 0x7fffffff;
 164                         $tableIndex = $hash % $this->shards;
 165                 } else {
 166                         $tableIndex = 0;
 167                 }
 168                 if ( $this->numServers > 1 ) {
 169                         $sortedServers = $this->serverNames;
 170                         ArrayUtils::consistentHashSort( $sortedServers, $key );
 171                         reset( $sortedServers );
 172                         $serverIndex = key( $sortedServers );
 173                 } else {
 174                         $serverIndex = 0;
 175                 }
 176                 return array( $serverIndex, $this->getTableNameByShard( $tableIndex ) );
 177         }
 178
 179         /**
 180          * Get the table name for a given shard index
 181          * @param $index int
 182          * @return string
 183          */
 184         protected function getTableNameByShard( $index ) {
 185                 if ( $this->shards > 1 ) {
 186                         $decimals = strlen( $this->shards - 1 );
 187                         return $this->tableName .
 188                                 sprintf( "%0{$decimals}d", $index );
 189                 } else {
 190                         return $this->tableName;
 191                 }
 192         }
 193
 194         /**
 195          * @param $key string
 196          * @param $casToken[optional] mixed
 197          * @return mixed
 198          */
 199         public function get( $key, &$casToken = null ) {
 200                 $values = $this->getMulti( array( $key ) );
 201                 if ( array_key_exists( $key, $values ) ) {
 202                         $casToken = $values[$key];
 203                         return $values[$key];
 204                 }
 205                 return false;
 206         }
 207
 208         /**
 209          * @param $keys array
 210          * @return Array
 211          */
 212         public function getMulti( array $keys ) {
 213                 $values = array(); // array of (key => value)
 214
 215                 $keysByTable = array();
 216                 foreach ( $keys as $key ) {
 217                         list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
 218                         $keysByTable[$serverIndex][$tableName][] = $key;
 219                 }
 220
 221                 $this->garbageCollect(); // expire old entries if any
 222
 223                 $dataRows = array();
 224                 foreach ( $keysByTable as $serverIndex => $serverKeys ) {
 225                         try {
 226                                 $db = $this->getDB( $serverIndex );
 227                                 foreach ( $serverKeys as $tableName => $tableKeys ) {
 228                                         $res = $db->select( $tableName,
 229                                                 array( 'keyname', 'value', 'exptime' ),
 230                                                 array( 'keyname' => $tableKeys ),
 231                                                 __METHOD__ );
 232                                         foreach ( $res as $row ) {
 233                                                 $row->serverIndex = $serverIndex;
 234                                                 $row->tableName = $tableName;
 235                                                 $dataRows[$row->keyname] = $row;
 236                                         }
 237                                 }
 238                         } catch ( DBError $e ) {
 239                                 $this->handleReadError( $e, $serverIndex );
 240                         }
 241                 }
 242
 243                 foreach ( $keys as $key ) {
 244                         if ( isset( $dataRows[$key] ) ) { // HIT?
 245                                 $row = $dataRows[$key];
 246                                 $this->debug( "get: retrieved data; expiry time is " . $row->exptime );
 247                                 try {
 248                                         $db = $this->getDB( $row->serverIndex );
 249                                         if ( $this->isExpired( $db, $row->exptime ) ) { // MISS
 250                                                 $this->debug( "get: key has expired, deleting" );
 251                                                 $db->begin( __METHOD__ );
 252                                                 # Put the expiry time in the WHERE condition to avoid deleting a
 253                                                 # newly-inserted value
 254                                                 $db->delete( $row->tableName,
 255                                                         array( 'keyname' => $key, 'exptime' => $row->exptime ),
 256                                                         __METHOD__ );
 257                                                 $db->commit( __METHOD__ );
 258                                                 $values[$key] = false;
 259                                         } else { // HIT
 260                                                 $values[$key] = $this->unserialize( $db->decodeBlob( $row->value ) );
 261                                         }
 262                                 } catch ( DBQueryError $e ) {
 263                                         $this->handleWriteError( $e, $row->serverIndex );
 264                                 }
 265                         } else { // MISS
 266                                 $values[$key] = false;
 267                                 $this->debug( 'get: no matching rows' );
 268                         }
 269                 }
 270
 271                 return $values;
 272         }
 273
 274         /**
 275          * @param $key string
 276          * @param $value mixed
 277          * @param $exptime int
 278          * @return bool
 279          */
 280         public function set( $key, $value, $exptime = 0 ) {
 281                 list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
 282                 try {
 283                         $db = $this->getDB( $serverIndex );
 284                         $exptime = intval( $exptime );
 285
 286                         if ( $exptime < 0 ) {
 287                                 $exptime = 0;
 288                         }
 289
 290                         if ( $exptime == 0 ) {
 291                                 $encExpiry = $this->getMaxDateTime( $db );
 292                         } else {
 293                                 if ( $exptime < 3.16e8 ) { # ~10 years
 294                                         $exptime += time();
 295                                 }
 296
 297                                 $encExpiry = $db->timestamp( $exptime );
 298                         }
 299                         $db->begin( __METHOD__ );
 300                         // (bug 24425) use a replace if the db supports it instead of
 301                         // delete/insert to avoid clashes with conflicting keynames
 302                         $db->replace(
 303                                 $tableName,
 304                                 array( 'keyname' ),
 305                                 array(
 306                                         'keyname' => $key,
 307                                         'value' => $db->encodeBlob( $this->serialize( $value ) ),
 308                                         'exptime' => $encExpiry
 309                                 ), __METHOD__ );
 310                         $db->commit( __METHOD__ );
 311                 } catch ( DBError $e ) {
 312                         $this->handleWriteError( $e, $serverIndex );
 313                         return false;
 314                 }
 315
 316                 return true;
 317         }
 318
 319         /**
 320          * @param $casToken mixed
 321          * @param $key string
 322          * @param $value mixed
 323          * @param $exptime int
 324          * @return bool
 325          */
 326         public function cas( $casToken, $key, $value, $exptime = 0 ) {
 327                 list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
 328                 try {
 329                         $db = $this->getDB( $serverIndex );
 330                         $exptime = intval( $exptime );
 331
 332                         if ( $exptime < 0 ) {
 333                                 $exptime = 0;
 334                         }
 335
 336                         if ( $exptime == 0 ) {
 337                                 $encExpiry = $this->getMaxDateTime( $db );
 338                         } else {
 339                                 if ( $exptime < 3.16e8 ) { # ~10 years
 340                                         $exptime += time();
 341                                 }
 342                                 $encExpiry = $db->timestamp( $exptime );
 343                         }
 344                         $db->begin( __METHOD__ );
 345                         // (bug 24425) use a replace if the db supports it instead of
 346                         // delete/insert to avoid clashes with conflicting keynames
 347                         $db->update(
 348                                 $tableName,
 349                                 array(
 350                                         'keyname' => $key,
 351                                         'value' => $db->encodeBlob( $this->serialize( $value ) ),
 352                                         'exptime' => $encExpiry
 353                                 ),
 354                                 array(
 355                                         'keyname' => $key,
 356                                         'value' => $db->encodeBlob( $this->serialize( $casToken ) )
 357                                 ),
 358                                 __METHOD__
 359                         );
 360                         $db->commit( __METHOD__ );
 361                 } catch ( DBQueryError $e ) {
 362                         $this->handleWriteError( $e, $serverIndex );
 363
 364                         return false;
 365                 }
 366
 367                 return (bool)$db->affectedRows();
 368         }
 369
 370         /**
 371          * @param $key string
 372          * @param $time int
 373          * @return bool
 374          */
 375         public function delete( $key, $time = 0 ) {
 376                 list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
 377                 try {
 378                         $db = $this->getDB( $serverIndex );
 379                         $db->begin( __METHOD__ );
 380                         $db->delete(
 381                                 $tableName,
 382                                 array( 'keyname' => $key ),
 383                                 __METHOD__ );
 384                         $db->commit( __METHOD__ );
 385                 } catch ( DBError $e ) {
 386                         $this->handleWriteError( $e, $serverIndex );
 387                         return false;
 388                 }
 389
 390                 return true;
 391         }
 392
 393         /**
 394          * @param $key string
 395          * @param $step int
 396          * @return int|null
 397          */
 398         public function incr( $key, $step = 1 ) {
 399                 list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
 400                 try {
 401                         $db = $this->getDB( $serverIndex );
 402                         $step = intval( $step );
 403                         $db->begin( __METHOD__ );
 404                         $row = $db->selectRow(
 405                                 $tableName,
 406                                 array( 'value', 'exptime' ),
 407                                 array( 'keyname' => $key ),
 408                                 __METHOD__,
 409                                 array( 'FOR UPDATE' ) );
 410                         if ( $row === false ) {
 411                                 // Missing
 412                                 $db->commit( __METHOD__ );
 413
 414                                 return null;
 415                         }
 416                         $db->delete( $tableName, array( 'keyname' => $key ), __METHOD__ );
 417                         if ( $this->isExpired( $db, $row->exptime ) ) {
 418                                 // Expired, do not reinsert
 419                                 $db->commit( __METHOD__ );
 420
 421                                 return null;
 422                         }
 423
 424                         $oldValue = intval( $this->unserialize( $db->decodeBlob( $row->value ) ) );
 425                         $newValue = $oldValue + $step;
 426                         $db->insert( $tableName,
 427                                 array(
 428                                         'keyname' => $key,
 429                                         'value' => $db->encodeBlob( $this->serialize( $newValue ) ),
 430                                         'exptime' => $row->exptime
 431                                 ), __METHOD__, 'IGNORE' );
 432
 433                         if ( $db->affectedRows() == 0 ) {
 434                                 // Race condition. See bug 28611
 435                                 $newValue = null;
 436                         }
 437                         $db->commit( __METHOD__ );
 438                 } catch ( DBError $e ) {
 439                         $this->handleWriteError( $e, $serverIndex );
 440                         return null;
 441                 }
 442
 443                 return $newValue;
 444         }
 445
 446         /**
 447          * @param $exptime string
 448          * @return bool
 449          */
 450         protected function isExpired( $db, $exptime ) {
 451                 return $exptime != $this->getMaxDateTime( $db ) && wfTimestamp( TS_UNIX, $exptime ) < time();
 452         }
 453
 454         /**
 455          * @return string
 456          */
 457         protected function getMaxDateTime( $db ) {
 458                 if ( time() > 0x7fffffff ) {
 459                         return $db->timestamp( 1 << 62 );
 460                 } else {
 461                         return $db->timestamp( 0x7fffffff );
 462                 }
 463         }
 464
 465         protected function garbageCollect() {
 466                 if ( !$this->purgePeriod ) {
 467                         // Disabled
 468                         return;
 469                 }
 470                 // Only purge on one in every $this->purgePeriod requests.
 471                 if ( $this->purgePeriod !== 1 && mt_rand( 0, $this->purgePeriod - 1 ) ) {
 472                         return;
 473                 }
 474                 $now = time();
 475                 // Avoid repeating the delete within a few seconds
 476                 if ( $now > ( $this->lastExpireAll + 1 ) ) {
 477                         $this->lastExpireAll = $now;
 478                         $this->expireAll();
 479                 }
 480         }
 481
 482         public function expireAll() {
 483                 $this->deleteObjectsExpiringBefore( wfTimestampNow() );
 484         }
 485
 486         /**
 487          * Delete objects from the database which expire before a certain date.
 488          * @param $timestamp string
 489          * @param $progressCallback bool|callback
 490          * @return bool
 491          */
 492         public function deleteObjectsExpiringBefore( $timestamp, $progressCallback = false ) {
 493                 for ( $serverIndex = 0; $serverIndex < $this->numServers; $serverIndex++ ) {
 494                         try {
 495                                 $db = $this->getDB( $serverIndex );
 496                                 $dbTimestamp = $db->timestamp( $timestamp );
 497                                 $totalSeconds = false;
 498                                 $baseConds = array( 'exptime < ' . $db->addQuotes( $dbTimestamp ) );
 499                                 for ( $i = 0; $i < $this->shards; $i++ ) {
 500                                         $maxExpTime = false;
 501                                         while ( true ) {
 502                                                 $conds = $baseConds;
 503                                                 if ( $maxExpTime !== false ) {
 504                                                         $conds[] = 'exptime > ' . $db->addQuotes( $maxExpTime );
 505                                                 }
 506                                                 $rows = $db->select(
 507                                                         $this->getTableNameByShard( $i ),
 508                                                         array( 'keyname', 'exptime' ),
 509                                                         $conds,
 510                                                         __METHOD__,
 511                                                         array( 'LIMIT' => 100, 'ORDER BY' => 'exptime' ) );
 512                                                 if ( !$rows->numRows() ) {
 513                                                         break;
 514                                                 }
 515                                                 $keys = array();
 516                                                 $row = $rows->current();
 517                                                 $minExpTime = $row->exptime;
 518                                                 if ( $totalSeconds === false ) {
 519                                                         $totalSeconds = wfTimestamp( TS_UNIX, $timestamp )
 520                                                                 - wfTimestamp( TS_UNIX, $minExpTime );
 521                                                 }
 522                                                 foreach ( $rows as $row ) {
 523                                                         $keys[] = $row->keyname;
 524                                                         $maxExpTime = $row->exptime;
 525                                                 }
 526
 527                                                 $db->begin( __METHOD__ );
 528                                                 $db->delete(
 529                                                         $this->getTableNameByShard( $i ),
 530                                                         array(
 531                                                                 'exptime >= ' . $db->addQuotes( $minExpTime ),
 532                                                                 'exptime < ' . $db->addQuotes( $dbTimestamp ),
 533                                                                 'keyname' => $keys
 534                                                         ),
 535                                                         __METHOD__ );
 536                                                 $db->commit( __METHOD__ );
 537
 538                                                 if ( $progressCallback ) {
 539                                                         if ( intval( $totalSeconds ) === 0 ) {
 540                                                                 $percent = 0;
 541                                                         } else {
 542                                                                 $remainingSeconds = wfTimestamp( TS_UNIX, $timestamp )
 543                                                                         - wfTimestamp( TS_UNIX, $maxExpTime );
 544                                                                 if ( $remainingSeconds > $totalSeconds ) {
 545                                                                         $totalSeconds = $remainingSeconds;
 546                                                                 }
 547                                                                 $percent = ( $i + $remainingSeconds / $totalSeconds )
 548                                                                         / $this->shards * 100;
 549                                                         }
 550                                                         $percent = ( $percent / $this->numServers )
 551                                                                 + ( $serverIndex / $this->numServers * 100 );
 552                                                         call_user_func( $progressCallback, $percent );
 553                                                 }
 554                                         }
 555                                 }
 556                         } catch ( DBError $e ) {
 557                                 $this->handleWriteError( $e, $serverIndex );
 558                                 return false;
 559                         }
 560                 }
 561                 return true;
 562         }
 563
 564         public function deleteAll() {
 565                 for ( $serverIndex = 0; $serverIndex < $this->numServers; $serverIndex++ ) {
 566                         try {
 567                                 $db = $this->getDB( $serverIndex );
 568                                 for ( $i = 0; $i < $this->shards; $i++ ) {
 569                                         $db->begin( __METHOD__ );
 570                                         $db->delete( $this->getTableNameByShard( $i ), '*', __METHOD__ );
 571                                         $db->commit( __METHOD__ );
 572                                 }
 573                         } catch ( DBError $e ) {
 574                                 $this->handleWriteError( $e, $serverIndex );
 575                                 return false;
 576                         }
 577                 }
 578                 return true;
 579         }
 580
 581         /**
 582          * Serialize an object and, if possible, compress the representation.
 583          * On typical message and page data, this can provide a 3X decrease
 584          * in storage requirements.
 585          *
 586          * @param $data mixed
 587          * @return string
 588          */
 589         protected function serialize( &$data ) {
 590                 $serial = serialize( $data );
 591
 592                 if ( function_exists( 'gzdeflate' ) ) {
 593                         return gzdeflate( $serial );
 594                 } else {
 595                         return $serial;
 596                 }
 597         }
 598
 599         /**
 600          * Unserialize and, if necessary, decompress an object.
 601          * @param $serial string
 602          * @return mixed
 603          */
 604         protected function unserialize( $serial ) {
 605                 if ( function_exists( 'gzinflate' ) ) {
 606                         wfSuppressWarnings();
 607                         $decomp = gzinflate( $serial );
 608                         wfRestoreWarnings();
 609
 610                         if ( false !== $decomp ) {
 611                                 $serial = $decomp;
 612                         }
 613                 }
 614
 615                 $ret = unserialize( $serial );
 616
 617                 return $ret;
 618         }
 619
 620         /**
 621          * Handle a DBError which occurred during a read operation.
 622          */
 623         protected function handleReadError( DBError $exception, $serverIndex ) {
 624                 if ( $exception instanceof DBConnectionError ) {
 625                         $this->markServerDown( $exception, $serverIndex );
 626                 }
 627                 wfDebugLog( 'SQLBagOStuff', "DBError: {$exception->getMessage()}" );
 628                 if ( $exception instanceof DBConnectionError ) {
 629                         wfDebug( __METHOD__ . ": ignoring connection error\n" );
 630                 } else {
 631                         wfDebug( __METHOD__ . ": ignoring query error\n" );
 632                 }
 633         }
 634
 635         /**
 636          * Handle a DBQueryError which occurred during a write operation.
 637          */
 638         protected function handleWriteError( DBError $exception, $serverIndex ) {
 639                 if ( $exception instanceof DBConnectionError ) {
 640                         $this->markServerDown( $exception, $serverIndex );
 641                 }
 642                 if ( $exception->db && $exception->db->wasReadOnlyError() ) {
 643                         try {
 644                                 $exception->db->rollback( __METHOD__ );
 645                         } catch ( DBError $e ) {}
 646                 }
 647                 wfDebugLog( 'SQLBagOStuff', "DBError: {$exception->getMessage()}" );
 648                 if ( $exception instanceof DBConnectionError ) {
 649                         wfDebug( __METHOD__ . ": ignoring connection error\n" );
 650                 } else {
 651                         wfDebug( __METHOD__ . ": ignoring query error\n" );
 652                 }
 653         }
 654
 655         /**
 656          * Mark a server down due to a DBConnectionError exception
 657          */
 658         protected function markServerDown( $exception, $serverIndex ) {
 659                 if ( isset( $this->connFailureTimes[$serverIndex] ) ) {
 660                         if ( time() - $this->connFailureTimes[$serverIndex] >= 60 ) {
 661                                 unset( $this->connFailureTimes[$serverIndex] );
 662                                 unset( $this->connFailureErrors[$serverIndex] );
 663                         } else {
 664                                 wfDebug( __METHOD__ . ": Server #$serverIndex already down\n" );
 665                                 return;
 666                         }
 667                 }
 668                 $now = time();
 669                 wfDebug( __METHOD__ . ": Server #$serverIndex down until " . ( $now + 60 ) . "\n" );
 670                 $this->connFailureTimes[$serverIndex] = $now;
 671                 $this->connFailureErrors[$serverIndex] = $exception;
 672         }
 673
 674         /**
 675          * Create shard tables. For use from eval.php.
 676          */
 677         public function createTables() {
 678                 for ( $serverIndex = 0; $serverIndex < $this->numServers; $serverIndex++ ) {
 679                         $db = $this->getDB( $serverIndex );
 680                         if ( $db->getType() !== 'mysql'
 681                                 || version_compare( $db->getServerVersion(), '4.1.0', '<' ) )
 682                         {
 683                                 throw new MWException( __METHOD__ . ' is not supported on this DB server' );
 684                         }
 685
 686                         for ( $i = 0; $i < $this->shards; $i++ ) {
 687                                 $db->begin( __METHOD__ );
 688                                 $db->query(
 689                                         'CREATE TABLE ' . $db->tableName( $this->getTableNameByShard( $i ) ) .
 690                                         ' LIKE ' . $db->tableName( 'objectcache' ),
 691                                         __METHOD__ );
 692                                 $db->commit( __METHOD__ );
 693                         }
 694                 }
 695         }
 696 }
 697
 698 /**
 699  * Backwards compatibility alias
 700  */
 701 class MediaWikiBagOStuff extends SqlBagOStuff { }