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         protected $serverInfos;
  34
  35         /** @var array */
  36         protected $serverNames;
  37
  38         /** @var int */
  39         protected $numServers;
  40
  41         /** @var array */
  42         protected $conns;
  43
  44         /** @var int */
  45         protected $lastExpireAll = 0;
  46
  47         /** @var int */
  48         protected $purgePeriod = 100;
  49
  50         /** @var int */
  51         protected $shards = 1;
  52
  53         /** @var string */
  54         protected $tableName = 'objectcache';
  55
  56         /** @var array UNIX timestamps */
  57         protected $connFailureTimes = array();
  58
  59         /** @var array Exceptions */
  60         protected $connFailureErrors = array();
  61
  62         /**
  63          * Constructor. Parameters are:
  64          *   - server:      A server info structure in the format required by each
  65          *                  element in $wgDBServers.
  66          *
  67          *   - servers:     An array of server info structures describing a set of
  68          *                  database servers to distribute keys to. If this is
  69          *                  specified, the "server" option will be ignored.
  70          *
  71          *   - purgePeriod: The average number of object cache requests in between
  72          *                  garbage collection operations, where expired entries
  73          *                  are removed from the database. Or in other words, the
  74          *                  reciprocal of the probability of purging on any given
  75          *                  request. If this is set to zero, purging will never be
  76          *                  done.
  77          *
  78          *   - tableName:   The table name to use, default is "objectcache".
  79          *
  80          *   - shards:      The number of tables to use for data storage on each server.
  81          *                  If this is more than 1, table names will be formed in the style
  82          *                  objectcacheNNN where NNN is the shard index, between 0 and
  83          *                  shards-1. The number of digits will be the minimum number
  84          *                  required to hold the largest shard index. Data will be
  85          *                  distributed across all tables by key hash. This is for
  86          *                  MySQL bugs 61735 and 61736.
  87          *
  88          * @param array $params
  89          */
  90         public function __construct( $params ) {
  91                 if ( isset( $params['servers'] ) ) {
  92                         $this->serverInfos = $params['servers'];
  93                         $this->numServers = count( $this->serverInfos );
  94                         $this->serverNames = array();
  95                         foreach ( $this->serverInfos as $i => $info ) {
  96                                 $this->serverNames[$i] = isset( $info['host'] ) ? $info['host'] : "#$i";
  97                         }
  98                 } elseif ( isset( $params['server'] ) ) {
  99                         $this->serverInfos = array( $params['server'] );
 100                         $this->numServers = count( $this->serverInfos );
 101                 } else {
 102                         $this->serverInfos = false;
 103                         $this->numServers = 1;
 104                 }
 105                 if ( isset( $params['purgePeriod'] ) ) {
 106                         $this->purgePeriod = intval( $params['purgePeriod'] );
 107                 }
 108                 if ( isset( $params['tableName'] ) ) {
 109                         $this->tableName = $params['tableName'];
 110                 }
 111                 if ( isset( $params['shards'] ) ) {
 112                         $this->shards = intval( $params['shards'] );
 113                 }
 114         }
 115
 116         /**
 117          * Get a connection to the specified database
 118          *
 119          * @param int $serverIndex
 120          * @return DatabaseBase
 121          */
 122         protected function getDB( $serverIndex ) {
 123                 global $wgDebugDBTransactions;
 124
 125                 if ( !isset( $this->conns[$serverIndex] ) ) {
 126                         if ( $serverIndex >= $this->numServers ) {
 127                                 throw new MWException( __METHOD__ . ": Invalid server index \"$serverIndex\"" );
 128                         }
 129
 130                         # Don't keep timing out trying to connect for each call if the DB is down
 131                         if ( isset( $this->connFailureErrors[$serverIndex] )
 132                                 && ( time() - $this->connFailureTimes[$serverIndex] ) < 60
 133                         ) {
 134                                 throw $this->connFailureErrors[$serverIndex];
 135                         }
 136
 137                         # If server connection info was given, use that
 138                         if ( $this->serverInfos ) {
 139                                 if ( $wgDebugDBTransactions ) {
 140                                         wfDebug( "Using provided serverInfo for SqlBagOStuff\n" );
 141                                 }
 142                                 $info = $this->serverInfos[$serverIndex];
 143                                 $type = isset( $info['type'] ) ? $info['type'] : 'mysql';
 144                                 $host = isset( $info['host'] ) ? $info['host'] : '[unknown]';
 145                                 wfDebug( __CLASS__ . ": connecting to $host\n" );
 146                                 $db = DatabaseBase::factory( $type, $info );
 147                                 $db->clearFlag( DBO_TRX );
 148                         } else {
 149                                 /*
 150                                  * We must keep a separate connection to MySQL in order to avoid deadlocks
 151                                  * However, SQLite has an opposite behavior. And PostgreSQL needs to know
 152                                  * if we are in transaction or no
 153                                  */
 154                                 if ( wfGetDB( DB_MASTER )->getType() == 'mysql' ) {
 155                                         $this->lb = wfGetLBFactory()->newMainLB();
 156                                         $db = $this->lb->getConnection( DB_MASTER );
 157                                         $db->clearFlag( DBO_TRX ); // auto-commit mode
 158                                 } else {
 159                                         $db = wfGetDB( DB_MASTER );
 160                                 }
 161                         }
 162                         if ( $wgDebugDBTransactions ) {
 163                                 wfDebug( sprintf( "Connection %s will be used for SqlBagOStuff\n", $db ) );
 164                         }
 165                         $this->conns[$serverIndex] = $db;
 166                 }
 167
 168                 return $this->conns[$serverIndex];
 169         }
 170
 171         /**
 172          * Get the server index and table name for a given key
 173          * @param string $key
 174          * @return array Server index and table name
 175          */
 176         protected function getTableByKey( $key ) {
 177                 if ( $this->shards > 1 ) {
 178                         $hash = hexdec( substr( md5( $key ), 0, 8 ) ) & 0x7fffffff;
 179                         $tableIndex = $hash % $this->shards;
 180                 } else {
 181                         $tableIndex = 0;
 182                 }
 183                 if ( $this->numServers > 1 ) {
 184                         $sortedServers = $this->serverNames;
 185                         ArrayUtils::consistentHashSort( $sortedServers, $key );
 186                         reset( $sortedServers );
 187                         $serverIndex = key( $sortedServers );
 188                 } else {
 189                         $serverIndex = 0;
 190                 }
 191                 return array( $serverIndex, $this->getTableNameByShard( $tableIndex ) );
 192         }
 193
 194         /**
 195          * Get the table name for a given shard index
 196          * @param int $index
 197          * @return string
 198          */
 199         protected function getTableNameByShard( $index ) {
 200                 if ( $this->shards > 1 ) {
 201                         $decimals = strlen( $this->shards - 1 );
 202                         return $this->tableName .
 203                                 sprintf( "%0{$decimals}d", $index );
 204                 } else {
 205                         return $this->tableName;
 206                 }
 207         }
 208
 209         /**
 210          * @param string $key
 211          * @param mixed $casToken [optional]
 212          * @return mixed
 213          */
 214         public function get( $key, &$casToken = null ) {
 215                 $values = $this->getMulti( array( $key ) );
 216                 if ( array_key_exists( $key, $values ) ) {
 217                         $casToken = $values[$key];
 218                         return $values[$key];
 219                 }
 220                 return false;
 221         }
 222
 223         /**
 224          * @param array $keys
 225          * @return array
 226          */
 227         public function getMulti( array $keys ) {
 228                 $values = array(); // array of (key => value)
 229
 230                 $keysByTable = array();
 231                 foreach ( $keys as $key ) {
 232                         list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
 233                         $keysByTable[$serverIndex][$tableName][] = $key;
 234                 }
 235
 236                 $this->garbageCollect(); // expire old entries if any
 237
 238                 $dataRows = array();
 239                 foreach ( $keysByTable as $serverIndex => $serverKeys ) {
 240                         try {
 241                                 $db = $this->getDB( $serverIndex );
 242                                 foreach ( $serverKeys as $tableName => $tableKeys ) {
 243                                         $res = $db->select( $tableName,
 244                                                 array( 'keyname', 'value', 'exptime' ),
 245                                                 array( 'keyname' => $tableKeys ),
 246                                                 __METHOD__ );
 247                                         foreach ( $res as $row ) {
 248                                                 $row->serverIndex = $serverIndex;
 249                                                 $row->tableName = $tableName;
 250                                                 $dataRows[$row->keyname] = $row;
 251                                         }
 252                                 }
 253                         } catch ( DBError $e ) {
 254                                 $this->handleReadError( $e, $serverIndex );
 255                         }
 256                 }
 257
 258                 foreach ( $keys as $key ) {
 259                         if ( isset( $dataRows[$key] ) ) { // HIT?
 260                                 $row = $dataRows[$key];
 261                                 $this->debug( "get: retrieved data; expiry time is " . $row->exptime );
 262                                 try {
 263                                         $db = $this->getDB( $row->serverIndex );
 264                                         if ( $this->isExpired( $db, $row->exptime ) ) { // MISS
 265                                                 $this->debug( "get: key has expired, deleting" );
 266                                                 $db->commit( __METHOD__, 'flush' );
 267                                                 # Put the expiry time in the WHERE condition to avoid deleting a
 268                                                 # newly-inserted value
 269                                                 $db->delete( $row->tableName,
 270                                                         array( 'keyname' => $key, 'exptime' => $row->exptime ),
 271                                                         __METHOD__ );
 272                                                 $db->commit( __METHOD__, 'flush' );
 273                                                 $values[$key] = false;
 274                                         } else { // HIT
 275                                                 $values[$key] = $this->unserialize( $db->decodeBlob( $row->value ) );
 276                                         }
 277                                 } catch ( DBQueryError $e ) {
 278                                         $this->handleWriteError( $e, $row->serverIndex );
 279                                 }
 280                         } else { // MISS
 281                                 $values[$key] = false;
 282                                 $this->debug( 'get: no matching rows' );
 283                         }
 284                 }
 285
 286                 return $values;
 287         }
 288
 289         /**
 290          * @param array $data
 291          * @param int $expiry
 292          * @return bool
 293          */
 294         public function setMulti( array $data, $expiry = 0 ) {
 295                 $keysByTable = array();
 296                 foreach ( $data as $key => $value ) {
 297                         list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
 298                         $keysByTable[$serverIndex][$tableName][] = $key;
 299                 }
 300
 301                 $this->garbageCollect(); // expire old entries if any
 302
 303                 $result = true;
 304                 $exptime = (int)$expiry;
 305                 foreach ( $keysByTable as $serverIndex => $serverKeys ) {
 306                         try {
 307                                 $db = $this->getDB( $serverIndex );
 308                         } catch ( DBError $e ) {
 309                                 $this->handleWriteError( $e, $serverIndex );
 310                                 $result = false;
 311                                 continue;
 312                         }
 313
 314                         if ( $exptime < 0 ) {
 315                                 $exptime = 0;
 316                         }
 317
 318                         if ( $exptime == 0 ) {
 319                                 $encExpiry = $this->getMaxDateTime( $db );
 320                         } else {
 321                                 if ( $exptime < 3.16e8 ) { # ~10 years
 322                                         $exptime += time();
 323                                 }
 324                                 $encExpiry = $db->timestamp( $exptime );
 325                         }
 326                         foreach ( $serverKeys as $tableName => $tableKeys ) {
 327                                 $rows = array();
 328                                 foreach ( $tableKeys as $key ) {
 329                                         $rows[] = array(
 330                                                 'keyname' => $key,
 331                                                 'value' => $db->encodeBlob( $this->serialize( $data[$key] ) ),
 332                                                 'exptime' => $encExpiry,
 333                                         );
 334                                 }
 335
 336                                 try {
 337                                         $db->commit( __METHOD__, 'flush' );
 338                                         $db->replace(
 339                                                 $tableName,
 340                                                 array( 'keyname' ),
 341                                                 $rows,
 342                                                 __METHOD__
 343                                         );
 344                                         $db->commit( __METHOD__, 'flush' );
 345                                 } catch ( DBError $e ) {
 346                                         $this->handleWriteError( $e, $serverIndex );
 347                                         $result = false;
 348                                 }
 349
 350                         }
 351
 352                 }
 353
 354                 return $result;
 355         }
 356
 357
 358
 359         /**
 360          * @param string $key
 361          * @param mixed $value
 362          * @param int $exptime
 363          * @return bool
 364          */
 365         public function set( $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                                 if ( $exptime < 3.16e8 ) { # ~10 years
 379                                         $exptime += time();
 380                                 }
 381
 382                                 $encExpiry = $db->timestamp( $exptime );
 383                         }
 384                         $db->commit( __METHOD__, 'flush' );
 385                         // (bug 24425) use a replace if the db supports it instead of
 386                         // delete/insert to avoid clashes with conflicting keynames
 387                         $db->replace(
 388                                 $tableName,
 389                                 array( 'keyname' ),
 390                                 array(
 391                                         'keyname' => $key,
 392                                         'value' => $db->encodeBlob( $this->serialize( $value ) ),
 393                                         'exptime' => $encExpiry
 394                                 ), __METHOD__ );
 395                         $db->commit( __METHOD__, 'flush' );
 396                 } catch ( DBError $e ) {
 397                         $this->handleWriteError( $e, $serverIndex );
 398                         return false;
 399                 }
 400
 401                 return true;
 402         }
 403
 404         /**
 405          * @param mixed $casToken
 406          * @param string $key
 407          * @param mixed $value
 408          * @param int $exptime
 409          * @return bool
 410          */
 411         public function cas( $casToken, $key, $value, $exptime = 0 ) {
 412                 list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
 413                 try {
 414                         $db = $this->getDB( $serverIndex );
 415                         $exptime = intval( $exptime );
 416
 417                         if ( $exptime < 0 ) {
 418                                 $exptime = 0;
 419                         }
 420
 421                         if ( $exptime == 0 ) {
 422                                 $encExpiry = $this->getMaxDateTime( $db );
 423                         } else {
 424                                 if ( $exptime < 3.16e8 ) { # ~10 years
 425                                         $exptime += time();
 426                                 }
 427                                 $encExpiry = $db->timestamp( $exptime );
 428                         }
 429                         $db->commit( __METHOD__, 'flush' );
 430                         // (bug 24425) use a replace if the db supports it instead of
 431                         // delete/insert to avoid clashes with conflicting keynames
 432                         $db->update(
 433                                 $tableName,
 434                                 array(
 435                                         'keyname' => $key,
 436                                         'value' => $db->encodeBlob( $this->serialize( $value ) ),
 437                                         'exptime' => $encExpiry
 438                                 ),
 439                                 array(
 440                                         'keyname' => $key,
 441                                         'value' => $db->encodeBlob( $this->serialize( $casToken ) )
 442                                 ),
 443                                 __METHOD__
 444                         );
 445                         $db->commit( __METHOD__, 'flush' );
 446                 } catch ( DBQueryError $e ) {
 447                         $this->handleWriteError( $e, $serverIndex );
 448
 449                         return false;
 450                 }
 451
 452                 return (bool)$db->affectedRows();
 453         }
 454
 455         /**
 456          * @param string $key
 457          * @param int $time
 458          * @return bool
 459          */
 460         public function delete( $key, $time = 0 ) {
 461                 list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
 462                 try {
 463                         $db = $this->getDB( $serverIndex );
 464                         $db->commit( __METHOD__, 'flush' );
 465                         $db->delete(
 466                                 $tableName,
 467                                 array( 'keyname' => $key ),
 468                                 __METHOD__ );
 469                         $db->commit( __METHOD__, 'flush' );
 470                 } catch ( DBError $e ) {
 471                         $this->handleWriteError( $e, $serverIndex );
 472                         return false;
 473                 }
 474
 475                 return true;
 476         }
 477
 478         /**
 479          * @param string $key
 480          * @param int $step
 481          * @return int|null
 482          */
 483         public function incr( $key, $step = 1 ) {
 484                 list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
 485                 try {
 486                         $db = $this->getDB( $serverIndex );
 487                         $step = intval( $step );
 488                         $db->commit( __METHOD__, 'flush' );
 489                         $row = $db->selectRow(
 490                                 $tableName,
 491                                 array( 'value', 'exptime' ),
 492                                 array( 'keyname' => $key ),
 493                                 __METHOD__,
 494                                 array( 'FOR UPDATE' ) );
 495                         if ( $row === false ) {
 496                                 // Missing
 497                                 $db->commit( __METHOD__, 'flush' );
 498
 499                                 return null;
 500                         }
 501                         $db->delete( $tableName, array( 'keyname' => $key ), __METHOD__ );
 502                         if ( $this->isExpired( $db, $row->exptime ) ) {
 503                                 // Expired, do not reinsert
 504                                 $db->commit( __METHOD__, 'flush' );
 505
 506                                 return null;
 507                         }
 508
 509                         $oldValue = intval( $this->unserialize( $db->decodeBlob( $row->value ) ) );
 510                         $newValue = $oldValue + $step;
 511                         $db->insert( $tableName,
 512                                 array(
 513                                         'keyname' => $key,
 514                                         'value' => $db->encodeBlob( $this->serialize( $newValue ) ),
 515                                         'exptime' => $row->exptime
 516                                 ), __METHOD__, 'IGNORE' );
 517
 518                         if ( $db->affectedRows() == 0 ) {
 519                                 // Race condition. See bug 28611
 520                                 $newValue = null;
 521                         }
 522                         $db->commit( __METHOD__, 'flush' );
 523                 } catch ( DBError $e ) {
 524                         $this->handleWriteError( $e, $serverIndex );
 525                         return null;
 526                 }
 527
 528                 return $newValue;
 529         }
 530
 531         /**
 532          * @param string $exptime
 533          * @return bool
 534          */
 535         protected function isExpired( $db, $exptime ) {
 536                 return $exptime != $this->getMaxDateTime( $db ) && wfTimestamp( TS_UNIX, $exptime ) < time();
 537         }
 538
 539         /**
 540          * @param DatabaseBase $db
 541          * @return string
 542          */
 543         protected function getMaxDateTime( $db ) {
 544                 if ( time() > 0x7fffffff ) {
 545                         return $db->timestamp( 1 << 62 );
 546                 } else {
 547                         return $db->timestamp( 0x7fffffff );
 548                 }
 549         }
 550
 551         protected function garbageCollect() {
 552                 if ( !$this->purgePeriod ) {
 553                         // Disabled
 554                         return;
 555                 }
 556                 // Only purge on one in every $this->purgePeriod requests.
 557                 if ( $this->purgePeriod !== 1 && mt_rand( 0, $this->purgePeriod - 1 ) ) {
 558                         return;
 559                 }
 560                 $now = time();
 561                 // Avoid repeating the delete within a few seconds
 562                 if ( $now > ( $this->lastExpireAll + 1 ) ) {
 563                         $this->lastExpireAll = $now;
 564                         $this->expireAll();
 565                 }
 566         }
 567
 568         public function expireAll() {
 569                 $this->deleteObjectsExpiringBefore( wfTimestampNow() );
 570         }
 571
 572         /**
 573          * Delete objects from the database which expire before a certain date.
 574          * @param string $timestamp
 575          * @param bool|callable $progressCallback
 576          * @return bool
 577          */
 578         public function deleteObjectsExpiringBefore( $timestamp, $progressCallback = false ) {
 579                 for ( $serverIndex = 0; $serverIndex < $this->numServers; $serverIndex++ ) {
 580                         try {
 581                                 $db = $this->getDB( $serverIndex );
 582                                 $dbTimestamp = $db->timestamp( $timestamp );
 583                                 $totalSeconds = false;
 584                                 $baseConds = array( 'exptime < ' . $db->addQuotes( $dbTimestamp ) );
 585                                 for ( $i = 0; $i < $this->shards; $i++ ) {
 586                                         $maxExpTime = false;
 587                                         while ( true ) {
 588                                                 $conds = $baseConds;
 589                                                 if ( $maxExpTime !== false ) {
 590                                                         $conds[] = 'exptime > ' . $db->addQuotes( $maxExpTime );
 591                                                 }
 592                                                 $rows = $db->select(
 593                                                         $this->getTableNameByShard( $i ),
 594                                                         array( 'keyname', 'exptime' ),
 595                                                         $conds,
 596                                                         __METHOD__,
 597                                                         array( 'LIMIT' => 100, 'ORDER BY' => 'exptime' ) );
 598                                                 if ( !$rows->numRows() ) {
 599                                                         break;
 600                                                 }
 601                                                 $keys = array();
 602                                                 $row = $rows->current();
 603                                                 $minExpTime = $row->exptime;
 604                                                 if ( $totalSeconds === false ) {
 605                                                         $totalSeconds = wfTimestamp( TS_UNIX, $timestamp )
 606                                                                 - wfTimestamp( TS_UNIX, $minExpTime );
 607                                                 }
 608                                                 foreach ( $rows as $row ) {
 609                                                         $keys[] = $row->keyname;
 610                                                         $maxExpTime = $row->exptime;
 611                                                 }
 612
 613                                                 $db->commit( __METHOD__, 'flush' );
 614                                                 $db->delete(
 615                                                         $this->getTableNameByShard( $i ),
 616                                                         array(
 617                                                                 'exptime >= ' . $db->addQuotes( $minExpTime ),
 618                                                                 'exptime < ' . $db->addQuotes( $dbTimestamp ),
 619                                                                 'keyname' => $keys
 620                                                         ),
 621                                                         __METHOD__ );
 622                                                 $db->commit( __METHOD__, 'flush' );
 623
 624                                                 if ( $progressCallback ) {
 625                                                         if ( intval( $totalSeconds ) === 0 ) {
 626                                                                 $percent = 0;
 627                                                         } else {
 628                                                                 $remainingSeconds = wfTimestamp( TS_UNIX, $timestamp )
 629                                                                         - wfTimestamp( TS_UNIX, $maxExpTime );
 630                                                                 if ( $remainingSeconds > $totalSeconds ) {
 631                                                                         $totalSeconds = $remainingSeconds;
 632                                                                 }
 633                                                                 $percent = ( $i + $remainingSeconds / $totalSeconds )
 634                                                                         / $this->shards * 100;
 635                                                         }
 636                                                         $percent = ( $percent / $this->numServers )
 637                                                                 + ( $serverIndex / $this->numServers * 100 );
 638                                                         call_user_func( $progressCallback, $percent );
 639                                                 }
 640                                         }
 641                                 }
 642                         } catch ( DBError $e ) {
 643                                 $this->handleWriteError( $e, $serverIndex );
 644                                 return false;
 645                         }
 646                 }
 647                 return true;
 648         }
 649
 650         public function deleteAll() {
 651                 for ( $serverIndex = 0; $serverIndex < $this->numServers; $serverIndex++ ) {
 652                         try {
 653                                 $db = $this->getDB( $serverIndex );
 654                                 for ( $i = 0; $i < $this->shards; $i++ ) {
 655                                         $db->commit( __METHOD__, 'flush' );
 656                                         $db->delete( $this->getTableNameByShard( $i ), '*', __METHOD__ );
 657                                         $db->commit( __METHOD__, 'flush' );
 658                                 }
 659                         } catch ( DBError $e ) {
 660                                 $this->handleWriteError( $e, $serverIndex );
 661                                 return false;
 662                         }
 663                 }
 664                 return true;
 665         }
 666
 667         /**
 668          * Serialize an object and, if possible, compress the representation.
 669          * On typical message and page data, this can provide a 3X decrease
 670          * in storage requirements.
 671          *
 672          * @param mixed $data
 673          * @return string
 674          */
 675         protected function serialize( &$data ) {
 676                 $serial = serialize( $data );
 677
 678                 if ( function_exists( 'gzdeflate' ) ) {
 679                         return gzdeflate( $serial );
 680                 } else {
 681                         return $serial;
 682                 }
 683         }
 684
 685         /**
 686          * Unserialize and, if necessary, decompress an object.
 687          * @param string $serial
 688          * @return mixed
 689          */
 690         protected function unserialize( $serial ) {
 691                 if ( function_exists( 'gzinflate' ) ) {
 692                         wfSuppressWarnings();
 693                         $decomp = gzinflate( $serial );
 694                         wfRestoreWarnings();
 695
 696                         if ( false !== $decomp ) {
 697                                 $serial = $decomp;
 698                         }
 699                 }
 700
 701                 $ret = unserialize( $serial );
 702
 703                 return $ret;
 704         }
 705
 706         /**
 707          * Handle a DBError which occurred during a read operation.
 708          *
 709          * @param DBError $exception
 710          * @param int $serverIndex
 711          */
 712         protected function handleReadError( DBError $exception, $serverIndex ) {
 713                 if ( $exception instanceof DBConnectionError ) {
 714                         $this->markServerDown( $exception, $serverIndex );
 715                 }
 716                 wfDebugLog( 'SQLBagOStuff', "DBError: {$exception->getMessage()}" );
 717                 if ( $exception instanceof DBConnectionError ) {
 718                         $this->setLastError( BagOStuff::ERR_UNREACHABLE );
 719                         wfDebug( __METHOD__ . ": ignoring connection error\n" );
 720                 } else {
 721                         $this->setLastError( BagOStuff::ERR_UNEXPECTED );
 722                         wfDebug( __METHOD__ . ": ignoring query error\n" );
 723                 }
 724         }
 725
 726         /**
 727          * Handle a DBQueryError which occurred during a write operation.
 728          *
 729          * @param DBError $exception
 730          * @param int $serverIndex
 731          */
 732         protected function handleWriteError( DBError $exception, $serverIndex ) {
 733                 if ( $exception instanceof DBConnectionError ) {
 734                         $this->markServerDown( $exception, $serverIndex );
 735                 }
 736                 if ( $exception->db && $exception->db->wasReadOnlyError() ) {
 737                         try {
 738                                 $exception->db->rollback( __METHOD__ );
 739                         } catch ( DBError $e ) {
 740                         }
 741                 }
 742                 wfDebugLog( 'SQLBagOStuff', "DBError: {$exception->getMessage()}" );
 743                 if ( $exception instanceof DBConnectionError ) {
 744                         $this->setLastError( BagOStuff::ERR_UNREACHABLE );
 745                         wfDebug( __METHOD__ . ": ignoring connection error\n" );
 746                 } else {
 747                         $this->setLastError( BagOStuff::ERR_UNEXPECTED );
 748                         wfDebug( __METHOD__ . ": ignoring query error\n" );
 749                 }
 750         }
 751
 752         /**
 753          * Mark a server down due to a DBConnectionError exception
 754          *
 755          * @param DBError $exception
 756          * @param int $serverIndex
 757          */
 758         protected function markServerDown( $exception, $serverIndex ) {
 759                 if ( isset( $this->connFailureTimes[$serverIndex] ) ) {
 760                         if ( time() - $this->connFailureTimes[$serverIndex] >= 60 ) {
 761                                 unset( $this->connFailureTimes[$serverIndex] );
 762                                 unset( $this->connFailureErrors[$serverIndex] );
 763                         } else {
 764                                 wfDebug( __METHOD__ . ": Server #$serverIndex already down\n" );
 765                                 return;
 766                         }
 767                 }
 768                 $now = time();
 769                 wfDebug( __METHOD__ . ": Server #$serverIndex down until " . ( $now + 60 ) . "\n" );
 770                 $this->connFailureTimes[$serverIndex] = $now;
 771                 $this->connFailureErrors[$serverIndex] = $exception;
 772         }
 773
 774         /**
 775          * Create shard tables. For use from eval.php.
 776          */
 777         public function createTables() {
 778                 for ( $serverIndex = 0; $serverIndex < $this->numServers; $serverIndex++ ) {
 779                         $db = $this->getDB( $serverIndex );
 780                         if ( $db->getType() !== 'mysql' ) {
 781                                 throw new MWException( __METHOD__ . ' is not supported on this DB server' );
 782                         }
 783
 784                         for ( $i = 0; $i < $this->shards; $i++ ) {
 785                                 $db->commit( __METHOD__, 'flush' );
 786                                 $db->query(
 787                                         'CREATE TABLE ' . $db->tableName( $this->getTableNameByShard( $i ) ) .
 788                                         ' LIKE ' . $db->tableName( 'objectcache' ),
 789                                         __METHOD__ );
 790                                 $db->commit( __METHOD__, 'flush' );
 791                         }
 792                 }
 793         }
 794 }
 795
 796 /**
 797  * Backwards compatibility alias
 798  */
 799 class MediaWikiBagOStuff extends SqlBagOStuff {
 800 }