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 DatabaseBase
 131          * @throws MWException
 132          */
 133         protected function getDB( $serverIndex ) {
 134                 global $wgDebugDBTransactions;
 135
 136                 if ( !isset( $this->conns[$serverIndex] ) ) {
 137                         if ( $serverIndex >= $this->numServers ) {
 138                                 throw new MWException( __METHOD__ . ": Invalid server index \"$serverIndex\"" );
 139                         }
 140
 141                         # Don't keep timing out trying to connect for each call if the DB is down
 142                         if ( isset( $this->connFailureErrors[$serverIndex] )
 143                                 && ( time() - $this->connFailureTimes[$serverIndex] ) < 60
 144                         ) {
 145                                 throw $this->connFailureErrors[$serverIndex];
 146                         }
 147
 148                         # If server connection info was given, use that
 149                         if ( $this->serverInfos ) {
 150                                 if ( $wgDebugDBTransactions ) {
 151                                         $this->logger->debug( "Using provided serverInfo for SqlBagOStuff" );
 152                                 }
 153                                 $info = $this->serverInfos[$serverIndex];
 154                                 $type = isset( $info['type'] ) ? $info['type'] : 'mysql';
 155                                 $host = isset( $info['host'] ) ? $info['host'] : '[unknown]';
 156                                 $this->logger->debug( __CLASS__ . ": connecting to $host" );
 157                                 // Use a blank trx profiler to ignore expections as this is a cache
 158                                 $info['trxProfiler'] = new TransactionProfiler();
 159                                 $db = DatabaseBase::factory( $type, $info );
 160                                 $db->clearFlag( DBO_TRX );
 161                         } else {
 162                                 /*
 163                                  * We must keep a separate connection to MySQL in order to avoid deadlocks
 164                                  * However, SQLite has an opposite behavior. And PostgreSQL needs to know
 165                                  * if we are in transaction or no
 166                                  */
 167                                 $index = $this->slaveOnly ? DB_SLAVE : DB_MASTER;
 168                                 if ( wfGetDB( $index )->getType() == 'mysql' ) {
 169                                         $this->lb = wfGetLBFactory()->newMainLB();
 170                                         $db = $this->lb->getConnection( $index );
 171                                         $db->clearFlag( DBO_TRX ); // auto-commit mode
 172                                 } else {
 173                                         $db = wfGetDB( $index );
 174                                 }
 175                         }
 176                         if ( $wgDebugDBTransactions ) {
 177                                 $this->logger->debug( sprintf( "Connection %s will be used for SqlBagOStuff", $db ) );
 178                         }
 179                         $this->conns[$serverIndex] = $db;
 180                 }
 181
 182                 return $this->conns[$serverIndex];
 183         }
 184
 185         /**
 186          * Get the server index and table name for a given key
 187          * @param string $key
 188          * @return array Server index and table name
 189          */
 190         protected function getTableByKey( $key ) {
 191                 if ( $this->shards > 1 ) {
 192                         $hash = hexdec( substr( md5( $key ), 0, 8 ) ) & 0x7fffffff;
 193                         $tableIndex = $hash % $this->shards;
 194                 } else {
 195                         $tableIndex = 0;
 196                 }
 197                 if ( $this->numServers > 1 ) {
 198                         $sortedServers = $this->serverNames;
 199                         ArrayUtils::consistentHashSort( $sortedServers, $key );
 200                         reset( $sortedServers );
 201                         $serverIndex = key( $sortedServers );
 202                 } else {
 203                         $serverIndex = 0;
 204                 }
 205                 return array( $serverIndex, $this->getTableNameByShard( $tableIndex ) );
 206         }
 207
 208         /**
 209          * Get the table name for a given shard index
 210          * @param int $index
 211          * @return string
 212          */
 213         protected function getTableNameByShard( $index ) {
 214                 if ( $this->shards > 1 ) {
 215                         $decimals = strlen( $this->shards - 1 );
 216                         return $this->tableName .
 217                                 sprintf( "%0{$decimals}d", $index );
 218                 } else {
 219                         return $this->tableName;
 220                 }
 221         }
 222
 223         /**
 224          * @param string $key
 225          * @param mixed $casToken [optional]
 226          * @return mixed
 227          */
 228         public function get( $key, &$casToken = null ) {
 229                 $values = $this->getMulti( array( $key ) );
 230                 if ( array_key_exists( $key, $values ) ) {
 231                         $casToken = $values[$key];
 232                         return $values[$key];
 233                 }
 234                 return false;
 235         }
 236
 237         /**
 238          * @param array $keys
 239          * @return array
 240          */
 241         public function getMulti( array $keys ) {
 242                 $values = array(); // array of (key => value)
 243
 244                 $keysByTable = array();
 245                 foreach ( $keys as $key ) {
 246                         list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
 247                         $keysByTable[$serverIndex][$tableName][] = $key;
 248                 }
 249
 250                 $this->garbageCollect(); // expire old entries if any
 251
 252                 $dataRows = array();
 253                 foreach ( $keysByTable as $serverIndex => $serverKeys ) {
 254                         try {
 255                                 $db = $this->getDB( $serverIndex );
 256                                 foreach ( $serverKeys as $tableName => $tableKeys ) {
 257                                         $res = $db->select( $tableName,
 258                                                 array( 'keyname', 'value', 'exptime' ),
 259                                                 array( 'keyname' => $tableKeys ),
 260                                                 __METHOD__,
 261                                                 // Approximate write-on-the-fly BagOStuff API via blocking.
 262                                                 // This approximation fails if a ROLLBACK happens (which is rare).
 263                                                 // We do not want to flush the TRX as that can break callers.
 264                                                 $db->trxLevel() ? array( 'LOCK IN SHARE MODE' ) : array()
 265                                         );
 266                                         if ( $res === false ) {
 267                                                 continue;
 268                                         }
 269                                         foreach ( $res as $row ) {
 270                                                 $row->serverIndex = $serverIndex;
 271                                                 $row->tableName = $tableName;
 272                                                 $dataRows[$row->keyname] = $row;
 273                                         }
 274                                 }
 275                         } catch ( DBError $e ) {
 276                                 $this->handleReadError( $e, $serverIndex );
 277                         }
 278                 }
 279
 280                 foreach ( $keys as $key ) {
 281                         if ( isset( $dataRows[$key] ) ) { // HIT?
 282                                 $row = $dataRows[$key];
 283                                 $this->debug( "get: retrieved data; expiry time is " . $row->exptime );
 284                                 try {
 285                                         $db = $this->getDB( $row->serverIndex );
 286                                         if ( $this->isExpired( $db, $row->exptime ) ) { // MISS
 287                                                 $this->debug( "get: key has expired" );
 288                                         } else { // HIT
 289                                                 $values[$key] = $this->unserialize( $db->decodeBlob( $row->value ) );
 290                                         }
 291                                 } catch ( DBQueryError $e ) {
 292                                         $this->handleWriteError( $e, $row->serverIndex );
 293                                 }
 294                         } else { // MISS
 295                                 $this->debug( 'get: no matching rows' );
 296                         }
 297                 }
 298
 299                 return $values;
 300         }
 301
 302         /**
 303          * @param array $data
 304          * @param int $expiry
 305          * @return bool
 306          */
 307         public function setMulti( array $data, $expiry = 0 ) {
 308                 $keysByTable = array();
 309                 foreach ( $data as $key => $value ) {
 310                         list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
 311                         $keysByTable[$serverIndex][$tableName][] = $key;
 312                 }
 313
 314                 $this->garbageCollect(); // expire old entries if any
 315
 316                 $result = true;
 317                 $exptime = (int)$expiry;
 318                 foreach ( $keysByTable as $serverIndex => $serverKeys ) {
 319                         try {
 320                                 $db = $this->getDB( $serverIndex );
 321                         } catch ( DBError $e ) {
 322                                 $this->handleWriteError( $e, $serverIndex );
 323                                 $result = false;
 324                                 continue;
 325                         }
 326
 327                         if ( $exptime < 0 ) {
 328                                 $exptime = 0;
 329                         }
 330
 331                         if ( $exptime == 0 ) {
 332                                 $encExpiry = $this->getMaxDateTime( $db );
 333                         } else {
 334                                 $exptime = $this->convertExpiry( $exptime );
 335                                 $encExpiry = $db->timestamp( $exptime );
 336                         }
 337                         foreach ( $serverKeys as $tableName => $tableKeys ) {
 338                                 $rows = array();
 339                                 foreach ( $tableKeys as $key ) {
 340                                         $rows[] = array(
 341                                                 'keyname' => $key,
 342                                                 'value' => $db->encodeBlob( $this->serialize( $data[$key] ) ),
 343                                                 'exptime' => $encExpiry,
 344                                         );
 345                                 }
 346
 347                                 try {
 348                                         $db->replace(
 349                                                 $tableName,
 350                                                 array( 'keyname' ),
 351                                                 $rows,
 352                                                 __METHOD__
 353                                         );
 354                                 } catch ( DBError $e ) {
 355                                         $this->handleWriteError( $e, $serverIndex );
 356                                         $result = false;
 357                                 }
 358
 359                         }
 360
 361                 }
 362
 363                 return $result;
 364         }
 365
 366         /**
 367          * @param string $key
 368          * @param mixed $value
 369          * @param int $exptime
 370          * @return bool
 371          */
 372         public function set( $key, $value, $exptime = 0 ) {
 373                 return $this->setMulti( array( $key => $value ), $exptime );
 374         }
 375
 376         /**
 377          * @param mixed $casToken
 378          * @param string $key
 379          * @param mixed $value
 380          * @param int $exptime
 381          * @return bool
 382          */
 383         protected function cas( $casToken, $key, $value, $exptime = 0 ) {
 384                 list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
 385                 try {
 386                         $db = $this->getDB( $serverIndex );
 387                         $exptime = intval( $exptime );
 388
 389                         if ( $exptime < 0 ) {
 390                                 $exptime = 0;
 391                         }
 392
 393                         if ( $exptime == 0 ) {
 394                                 $encExpiry = $this->getMaxDateTime( $db );
 395                         } else {
 396                                 $exptime = $this->convertExpiry( $exptime );
 397                                 $encExpiry = $db->timestamp( $exptime );
 398                         }
 399                         // (bug 24425) use a replace if the db supports it instead of
 400                         // delete/insert to avoid clashes with conflicting keynames
 401                         $db->update(
 402                                 $tableName,
 403                                 array(
 404                                         'keyname' => $key,
 405                                         'value' => $db->encodeBlob( $this->serialize( $value ) ),
 406                                         'exptime' => $encExpiry
 407                                 ),
 408                                 array(
 409                                         'keyname' => $key,
 410                                         'value' => $db->encodeBlob( $this->serialize( $casToken ) )
 411                                 ),
 412                                 __METHOD__
 413                         );
 414                 } catch ( DBQueryError $e ) {
 415                         $this->handleWriteError( $e, $serverIndex );
 416
 417                         return false;
 418                 }
 419
 420                 return (bool)$db->affectedRows();
 421         }
 422
 423         /**
 424          * @param string $key
 425          * @return bool
 426          */
 427         public function delete( $key ) {
 428                 list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
 429                 try {
 430                         $db = $this->getDB( $serverIndex );
 431                         $db->delete(
 432                                 $tableName,
 433                                 array( 'keyname' => $key ),
 434                                 __METHOD__ );
 435                 } catch ( DBError $e ) {
 436                         $this->handleWriteError( $e, $serverIndex );
 437                         return false;
 438                 }
 439
 440                 return true;
 441         }
 442
 443         /**
 444          * @param string $key
 445          * @param int $step
 446          * @return int|null
 447          */
 448         public function incr( $key, $step = 1 ) {
 449                 list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
 450                 try {
 451                         $db = $this->getDB( $serverIndex );
 452                         $step = intval( $step );
 453                         $row = $db->selectRow(
 454                                 $tableName,
 455                                 array( 'value', 'exptime' ),
 456                                 array( 'keyname' => $key ),
 457                                 __METHOD__,
 458                                 array( 'FOR UPDATE' ) );
 459                         if ( $row === false ) {
 460                                 // Missing
 461
 462                                 return null;
 463                         }
 464                         $db->delete( $tableName, array( 'keyname' => $key ), __METHOD__ );
 465                         if ( $this->isExpired( $db, $row->exptime ) ) {
 466                                 // Expired, do not reinsert
 467
 468                                 return null;
 469                         }
 470
 471                         $oldValue = intval( $this->unserialize( $db->decodeBlob( $row->value ) ) );
 472                         $newValue = $oldValue + $step;
 473                         $db->insert( $tableName,
 474                                 array(
 475                                         'keyname' => $key,
 476                                         'value' => $db->encodeBlob( $this->serialize( $newValue ) ),
 477                                         'exptime' => $row->exptime
 478                                 ), __METHOD__, 'IGNORE' );
 479
 480                         if ( $db->affectedRows() == 0 ) {
 481                                 // Race condition. See bug 28611
 482                                 $newValue = null;
 483                         }
 484                 } catch ( DBError $e ) {
 485                         $this->handleWriteError( $e, $serverIndex );
 486                         return null;
 487                 }
 488
 489                 return $newValue;
 490         }
 491
 492         public function merge( $key, $callback, $exptime = 0, $attempts = 10 ) {
 493                 if ( !is_callable( $callback ) ) {
 494                         throw new Exception( "Got invalid callback." );
 495                 }
 496
 497                 return $this->mergeViaCas( $key, $callback, $exptime, $attempts );
 498         }
 499
 500         /**
 501          * @param DatabaseBase $db
 502          * @param string $exptime
 503          * @return bool
 504          */
 505         protected function isExpired( $db, $exptime ) {
 506                 return $exptime != $this->getMaxDateTime( $db ) && wfTimestamp( TS_UNIX, $exptime ) < time();
 507         }
 508
 509         /**
 510          * @param DatabaseBase $db
 511          * @return string
 512          */
 513         protected function getMaxDateTime( $db ) {
 514                 if ( time() > 0x7fffffff ) {
 515                         return $db->timestamp( 1 << 62 );
 516                 } else {
 517                         return $db->timestamp( 0x7fffffff );
 518                 }
 519         }
 520
 521         protected function garbageCollect() {
 522                 if ( !$this->purgePeriod || $this->slaveOnly ) {
 523                         // Disabled
 524                         return;
 525                 }
 526                 // Only purge on one in every $this->purgePeriod requests.
 527                 if ( $this->purgePeriod !== 1 && mt_rand( 0, $this->purgePeriod - 1 ) ) {
 528                         return;
 529                 }
 530                 $now = time();
 531                 // Avoid repeating the delete within a few seconds
 532                 if ( $now > ( $this->lastExpireAll + 1 ) ) {
 533                         $this->lastExpireAll = $now;
 534                         $this->expireAll();
 535                 }
 536         }
 537
 538         public function expireAll() {
 539                 $this->deleteObjectsExpiringBefore( wfTimestampNow() );
 540         }
 541
 542         /**
 543          * Delete objects from the database which expire before a certain date.
 544          * @param string $timestamp
 545          * @param bool|callable $progressCallback
 546          * @return bool
 547          */
 548         public function deleteObjectsExpiringBefore( $timestamp, $progressCallback = false ) {
 549                 for ( $serverIndex = 0; $serverIndex < $this->numServers; $serverIndex++ ) {
 550                         try {
 551                                 $db = $this->getDB( $serverIndex );
 552                                 $dbTimestamp = $db->timestamp( $timestamp );
 553                                 $totalSeconds = false;
 554                                 $baseConds = array( 'exptime < ' . $db->addQuotes( $dbTimestamp ) );
 555                                 for ( $i = 0; $i < $this->shards; $i++ ) {
 556                                         $maxExpTime = false;
 557                                         while ( true ) {
 558                                                 $conds = $baseConds;
 559                                                 if ( $maxExpTime !== false ) {
 560                                                         $conds[] = 'exptime > ' . $db->addQuotes( $maxExpTime );
 561                                                 }
 562                                                 $rows = $db->select(
 563                                                         $this->getTableNameByShard( $i ),
 564                                                         array( 'keyname', 'exptime' ),
 565                                                         $conds,
 566                                                         __METHOD__,
 567                                                         array( 'LIMIT' => 100, 'ORDER BY' => 'exptime' ) );
 568                                                 if ( $rows === false || !$rows->numRows() ) {
 569                                                         break;
 570                                                 }
 571                                                 $keys = array();
 572                                                 $row = $rows->current();
 573                                                 $minExpTime = $row->exptime;
 574                                                 if ( $totalSeconds === false ) {
 575                                                         $totalSeconds = wfTimestamp( TS_UNIX, $timestamp )
 576                                                                 - wfTimestamp( TS_UNIX, $minExpTime );
 577                                                 }
 578                                                 foreach ( $rows as $row ) {
 579                                                         $keys[] = $row->keyname;
 580                                                         $maxExpTime = $row->exptime;
 581                                                 }
 582
 583                                                 $db->delete(
 584                                                         $this->getTableNameByShard( $i ),
 585                                                         array(
 586                                                                 'exptime >= ' . $db->addQuotes( $minExpTime ),
 587                                                                 'exptime < ' . $db->addQuotes( $dbTimestamp ),
 588                                                                 'keyname' => $keys
 589                                                         ),
 590                                                         __METHOD__ );
 591
 592                                                 if ( $progressCallback ) {
 593                                                         if ( intval( $totalSeconds ) === 0 ) {
 594                                                                 $percent = 0;
 595                                                         } else {
 596                                                                 $remainingSeconds = wfTimestamp( TS_UNIX, $timestamp )
 597                                                                         - wfTimestamp( TS_UNIX, $maxExpTime );
 598                                                                 if ( $remainingSeconds > $totalSeconds ) {
 599                                                                         $totalSeconds = $remainingSeconds;
 600                                                                 }
 601                                                                 $processedSeconds = $totalSeconds - $remainingSeconds;
 602                                                                 $percent = ( $i + $processedSeconds / $totalSeconds )
 603                                                                         / $this->shards * 100;
 604                                                         }
 605                                                         $percent = ( $percent / $this->numServers )
 606                                                                 + ( $serverIndex / $this->numServers * 100 );
 607                                                         call_user_func( $progressCallback, $percent );
 608                                                 }
 609                                         }
 610                                 }
 611                         } catch ( DBError $e ) {
 612                                 $this->handleWriteError( $e, $serverIndex );
 613                                 return false;
 614                         }
 615                 }
 616                 return true;
 617         }
 618
 619         /**
 620          * Delete content of shard tables in every server.
 621          * Return true if the operation is successful, false otherwise.
 622          * @return bool
 623          */
 624         public function deleteAll() {
 625                 for ( $serverIndex = 0; $serverIndex < $this->numServers; $serverIndex++ ) {
 626                         try {
 627                                 $db = $this->getDB( $serverIndex );
 628                                 for ( $i = 0; $i < $this->shards; $i++ ) {
 629                                         $db->delete( $this->getTableNameByShard( $i ), '*', __METHOD__ );
 630                                 }
 631                         } catch ( DBError $e ) {
 632                                 $this->handleWriteError( $e, $serverIndex );
 633                                 return false;
 634                         }
 635                 }
 636                 return true;
 637         }
 638
 639         /**
 640          * Serialize an object and, if possible, compress the representation.
 641          * On typical message and page data, this can provide a 3X decrease
 642          * in storage requirements.
 643          *
 644          * @param mixed $data
 645          * @return string
 646          */
 647         protected function serialize( &$data ) {
 648                 $serial = serialize( $data );
 649
 650                 if ( function_exists( 'gzdeflate' ) ) {
 651                         return gzdeflate( $serial );
 652                 } else {
 653                         return $serial;
 654                 }
 655         }
 656
 657         /**
 658          * Unserialize and, if necessary, decompress an object.
 659          * @param string $serial
 660          * @return mixed
 661          */
 662         protected function unserialize( $serial ) {
 663                 if ( function_exists( 'gzinflate' ) ) {
 664                         MediaWiki\suppressWarnings();
 665                         $decomp = gzinflate( $serial );
 666                         MediaWiki\restoreWarnings();
 667
 668                         if ( false !== $decomp ) {
 669                                 $serial = $decomp;
 670                         }
 671                 }
 672
 673                 $ret = unserialize( $serial );
 674
 675                 return $ret;
 676         }
 677
 678         /**
 679          * Handle a DBError which occurred during a read operation.
 680          *
 681          * @param DBError $exception
 682          * @param int $serverIndex
 683          */
 684         protected function handleReadError( DBError $exception, $serverIndex ) {
 685                 if ( $exception instanceof DBConnectionError ) {
 686                         $this->markServerDown( $exception, $serverIndex );
 687                 }
 688                 $this->logger->error( "DBError: {$exception->getMessage()}" );
 689                 if ( $exception instanceof DBConnectionError ) {
 690                         $this->setLastError( BagOStuff::ERR_UNREACHABLE );
 691                         $this->logger->debug( __METHOD__ . ": ignoring connection error" );
 692                 } else {
 693                         $this->setLastError( BagOStuff::ERR_UNEXPECTED );
 694                         $this->logger->debug( __METHOD__ . ": ignoring query error" );
 695                 }
 696         }
 697
 698         /**
 699          * Handle a DBQueryError which occurred during a write operation.
 700          *
 701          * @param DBError $exception
 702          * @param int $serverIndex
 703          */
 704         protected function handleWriteError( DBError $exception, $serverIndex ) {
 705                 if ( $exception instanceof DBConnectionError ) {
 706                         $this->markServerDown( $exception, $serverIndex );
 707                 }
 708                 if ( $exception->db && $exception->db->wasReadOnlyError() ) {
 709                         if ( $exception->db->trxLevel() ) {
 710                                 try {
 711                                         $exception->db->rollback( __METHOD__ );
 712                                 } catch ( DBError $e ) {
 713                                 }
 714                         }
 715                 }
 716
 717                 $this->logger->error( "DBError: {$exception->getMessage()}" );
 718                 if ( $exception instanceof DBConnectionError ) {
 719                         $this->setLastError( BagOStuff::ERR_UNREACHABLE );
 720                         $this->logger->debug( __METHOD__ . ": ignoring connection error" );
 721                 } else {
 722                         $this->setLastError( BagOStuff::ERR_UNEXPECTED );
 723                         $this->logger->debug( __METHOD__ . ": ignoring query error" );
 724                 }
 725         }
 726
 727         /**
 728          * Mark a server down due to a DBConnectionError exception
 729          *
 730          * @param DBError $exception
 731          * @param int $serverIndex
 732          */
 733         protected function markServerDown( $exception, $serverIndex ) {
 734                 unset( $this->conns[$serverIndex] ); // bug T103435
 735
 736                 if ( isset( $this->connFailureTimes[$serverIndex] ) ) {
 737                         if ( time() - $this->connFailureTimes[$serverIndex] >= 60 ) {
 738                                 unset( $this->connFailureTimes[$serverIndex] );
 739                                 unset( $this->connFailureErrors[$serverIndex] );
 740                         } else {
 741                                 $this->logger->debug( __METHOD__ . ": Server #$serverIndex already down" );
 742                                 return;
 743                         }
 744                 }
 745                 $now = time();
 746                 $this->logger->info( __METHOD__ . ": Server #$serverIndex down until " . ( $now + 60 ) );
 747                 $this->connFailureTimes[$serverIndex] = $now;
 748                 $this->connFailureErrors[$serverIndex] = $exception;
 749         }
 750
 751         /**
 752          * Create shard tables. For use from eval.php.
 753          */
 754         public function createTables() {
 755                 for ( $serverIndex = 0; $serverIndex < $this->numServers; $serverIndex++ ) {
 756                         $db = $this->getDB( $serverIndex );
 757                         if ( $db->getType() !== 'mysql' ) {
 758                                 throw new MWException( __METHOD__ . ' is not supported on this DB server' );
 759                         }
 760
 761                         for ( $i = 0; $i < $this->shards; $i++ ) {
 762                                 $db->query(
 763                                         'CREATE TABLE ' . $db->tableName( $this->getTableNameByShard( $i ) ) .
 764                                         ' LIKE ' . $db->tableName( 'objectcache' ),
 765                                         __METHOD__ );
 766                         }
 767                 }
 768         }
 769 }