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          * @throws MWException
 122          */
 123         protected function getDB( $serverIndex ) {
 124                 global $wgDebugDBTransactions;
 125
 126                 if ( !isset( $this->conns[$serverIndex] ) ) {
 127                         if ( $serverIndex >= $this->numServers ) {
 128                                 throw new MWException( __METHOD__ . ": Invalid server index \"$serverIndex\"" );
 129                         }
 130
 131                         # Don't keep timing out trying to connect for each call if the DB is down
 132                         if ( isset( $this->connFailureErrors[$serverIndex] )
 133                                 && ( time() - $this->connFailureTimes[$serverIndex] ) < 60
 134                         ) {
 135                                 throw $this->connFailureErrors[$serverIndex];
 136                         }
 137
 138                         # If server connection info was given, use that
 139                         if ( $this->serverInfos ) {
 140                                 if ( $wgDebugDBTransactions ) {
 141                                         wfDebug( "Using provided serverInfo for SqlBagOStuff\n" );
 142                                 }
 143                                 $info = $this->serverInfos[$serverIndex];
 144                                 $type = isset( $info['type'] ) ? $info['type'] : 'mysql';
 145                                 $host = isset( $info['host'] ) ? $info['host'] : '[unknown]';
 146                                 wfDebug( __CLASS__ . ": connecting to $host\n" );
 147                                 $db = DatabaseBase::factory( $type, $info );
 148                                 $db->clearFlag( DBO_TRX );
 149                         } else {
 150                                 /*
 151                                  * We must keep a separate connection to MySQL in order to avoid deadlocks
 152                                  * However, SQLite has an opposite behavior. And PostgreSQL needs to know
 153                                  * if we are in transaction or no
 154                                  */
 155                                 if ( wfGetDB( DB_MASTER )->getType() == 'mysql' ) {
 156                                         $this->lb = wfGetLBFactory()->newMainLB();
 157                                         $db = $this->lb->getConnection( DB_MASTER );
 158                                         $db->clearFlag( DBO_TRX ); // auto-commit mode
 159                                 } else {
 160                                         $db = wfGetDB( DB_MASTER );
 161                                 }
 162                         }
 163                         if ( $wgDebugDBTransactions ) {
 164                                 wfDebug( sprintf( "Connection %s will be used for SqlBagOStuff\n", $db ) );
 165                         }
 166                         $this->conns[$serverIndex] = $db;
 167                 }
 168
 169                 return $this->conns[$serverIndex];
 170         }
 171
 172         /**
 173          * Get the server index and table name for a given key
 174          * @param string $key
 175          * @return array Server index and table name
 176          */
 177         protected function getTableByKey( $key ) {
 178                 if ( $this->shards > 1 ) {
 179                         $hash = hexdec( substr( md5( $key ), 0, 8 ) ) & 0x7fffffff;
 180                         $tableIndex = $hash % $this->shards;
 181                 } else {
 182                         $tableIndex = 0;
 183                 }
 184                 if ( $this->numServers > 1 ) {
 185                         $sortedServers = $this->serverNames;
 186                         ArrayUtils::consistentHashSort( $sortedServers, $key );
 187                         reset( $sortedServers );
 188                         $serverIndex = key( $sortedServers );
 189                 } else {
 190                         $serverIndex = 0;
 191                 }
 192                 return array( $serverIndex, $this->getTableNameByShard( $tableIndex ) );
 193         }
 194
 195         /**
 196          * Get the table name for a given shard index
 197          * @param int $index
 198          * @return string
 199          */
 200         protected function getTableNameByShard( $index ) {
 201                 if ( $this->shards > 1 ) {
 202                         $decimals = strlen( $this->shards - 1 );
 203                         return $this->tableName .
 204                                 sprintf( "%0{$decimals}d", $index );
 205                 } else {
 206                         return $this->tableName;
 207                 }
 208         }
 209
 210         /**
 211          * @param string $key
 212          * @param mixed $casToken [optional]
 213          * @return mixed
 214          */
 215         public function get( $key, &$casToken = null ) {
 216                 $values = $this->getMulti( array( $key ) );
 217                 if ( array_key_exists( $key, $values ) ) {
 218                         $casToken = $values[$key];
 219                         return $values[$key];
 220                 }
 221                 return false;
 222         }
 223
 224         /**
 225          * @param array $keys
 226          * @return array
 227          */
 228         public function getMulti( array $keys ) {
 229                 $values = array(); // array of (key => value)
 230
 231                 $keysByTable = array();
 232                 foreach ( $keys as $key ) {
 233                         list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
 234                         $keysByTable[$serverIndex][$tableName][] = $key;
 235                 }
 236
 237                 $this->garbageCollect(); // expire old entries if any
 238
 239                 $dataRows = array();
 240                 foreach ( $keysByTable as $serverIndex => $serverKeys ) {
 241                         try {
 242                                 $db = $this->getDB( $serverIndex );
 243                                 foreach ( $serverKeys as $tableName => $tableKeys ) {
 244                                         $res = $db->select( $tableName,
 245                                                 array( 'keyname', 'value', 'exptime' ),
 246                                                 array( 'keyname' => $tableKeys ),
 247                                                 __METHOD__,
 248                                                 // Approximate write-on-the-fly BagOStuff API via blocking.
 249                                                 // This approximation fails if a ROLLBACK happens (which is rare).
 250                                                 // We do not want to flush the TRX as that can break callers.
 251                                                 $db->trxLevel() ? array( 'LOCK IN SHARE MODE' ) : array()
 252                                         );
 253                                         if ( $res === false ) {
 254                                                 continue;
 255                                         }
 256                                         foreach ( $res as $row ) {
 257                                                 $row->serverIndex = $serverIndex;
 258                                                 $row->tableName = $tableName;
 259                                                 $dataRows[$row->keyname] = $row;
 260                                         }
 261                                 }
 262                         } catch ( DBError $e ) {
 263                                 $this->handleReadError( $e, $serverIndex );
 264                         }
 265                 }
 266
 267                 foreach ( $keys as $key ) {
 268                         if ( isset( $dataRows[$key] ) ) { // HIT?
 269                                 $row = $dataRows[$key];
 270                                 $this->debug( "get: retrieved data; expiry time is " . $row->exptime );
 271                                 try {
 272                                         $db = $this->getDB( $row->serverIndex );
 273                                         if ( $this->isExpired( $db, $row->exptime ) ) { // MISS
 274                                                 $this->debug( "get: key has expired, deleting" );
 275                                                 # Put the expiry time in the WHERE condition to avoid deleting a
 276                                                 # newly-inserted value
 277                                                 $db->delete( $row->tableName,
 278                                                         array( 'keyname' => $key, 'exptime' => $row->exptime ),
 279                                                         __METHOD__ );
 280                                         } else { // HIT
 281                                                 $values[$key] = $this->unserialize( $db->decodeBlob( $row->value ) );
 282                                         }
 283                                 } catch ( DBQueryError $e ) {
 284                                         $this->handleWriteError( $e, $row->serverIndex );
 285                                 }
 286                         } else { // MISS
 287                                 $this->debug( 'get: no matching rows' );
 288                         }
 289                 }
 290
 291                 return $values;
 292         }
 293
 294         /**
 295          * @param array $data
 296          * @param int $expiry
 297          * @return bool
 298          */
 299         public function setMulti( array $data, $expiry = 0 ) {
 300                 $keysByTable = array();
 301                 foreach ( $data as $key => $value ) {
 302                         list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
 303                         $keysByTable[$serverIndex][$tableName][] = $key;
 304                 }
 305
 306                 $this->garbageCollect(); // expire old entries if any
 307
 308                 $result = true;
 309                 $exptime = (int)$expiry;
 310                 foreach ( $keysByTable as $serverIndex => $serverKeys ) {
 311                         try {
 312                                 $db = $this->getDB( $serverIndex );
 313                         } catch ( DBError $e ) {
 314                                 $this->handleWriteError( $e, $serverIndex );
 315                                 $result = false;
 316                                 continue;
 317                         }
 318
 319                         if ( $exptime < 0 ) {
 320                                 $exptime = 0;
 321                         }
 322
 323                         if ( $exptime == 0 ) {
 324                                 $encExpiry = $this->getMaxDateTime( $db );
 325                         } else {
 326                                 $exptime = $this->convertExpiry( $exptime );
 327                                 $encExpiry = $db->timestamp( $exptime );
 328                         }
 329                         foreach ( $serverKeys as $tableName => $tableKeys ) {
 330                                 $rows = array();
 331                                 foreach ( $tableKeys as $key ) {
 332                                         $rows[] = array(
 333                                                 'keyname' => $key,
 334                                                 'value' => $db->encodeBlob( $this->serialize( $data[$key] ) ),
 335                                                 'exptime' => $encExpiry,
 336                                         );
 337                                 }
 338
 339                                 try {
 340                                         $db->replace(
 341                                                 $tableName,
 342                                                 array( 'keyname' ),
 343                                                 $rows,
 344                                                 __METHOD__
 345                                         );
 346                                 } catch ( DBError $e ) {
 347                                         $this->handleWriteError( $e, $serverIndex );
 348                                         $result = false;
 349                                 }
 350
 351                         }
 352
 353                 }
 354
 355                 return $result;
 356         }
 357
 358
 359
 360         /**
 361          * @param string $key
 362          * @param mixed $value
 363          * @param int $exptime
 364          * @return bool
 365          */
 366         public function set( $key, $value, $exptime = 0 ) {
 367                 list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
 368                 try {
 369                         $db = $this->getDB( $serverIndex );
 370                         $exptime = intval( $exptime );
 371
 372                         if ( $exptime < 0 ) {
 373                                 $exptime = 0;
 374                         }
 375
 376                         if ( $exptime == 0 ) {
 377                                 $encExpiry = $this->getMaxDateTime( $db );
 378                         } else {
 379                                 $exptime = $this->convertExpiry( $exptime );
 380                                 $encExpiry = $db->timestamp( $exptime );
 381                         }
 382                         // (bug 24425) use a replace if the db supports it instead of
 383                         // delete/insert to avoid clashes with conflicting keynames
 384                         $db->replace(
 385                                 $tableName,
 386                                 array( 'keyname' ),
 387                                 array(
 388                                         'keyname' => $key,
 389                                         'value' => $db->encodeBlob( $this->serialize( $value ) ),
 390                                         'exptime' => $encExpiry
 391                                 ), __METHOD__ );
 392                 } catch ( DBError $e ) {
 393                         $this->handleWriteError( $e, $serverIndex );
 394                         return false;
 395                 }
 396
 397                 return true;
 398         }
 399
 400         /**
 401          * @param mixed $casToken
 402          * @param string $key
 403          * @param mixed $value
 404          * @param int $exptime
 405          * @return bool
 406          */
 407         public function cas( $casToken, $key, $value, $exptime = 0 ) {
 408                 list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
 409                 try {
 410                         $db = $this->getDB( $serverIndex );
 411                         $exptime = intval( $exptime );
 412
 413                         if ( $exptime < 0 ) {
 414                                 $exptime = 0;
 415                         }
 416
 417                         if ( $exptime == 0 ) {
 418                                 $encExpiry = $this->getMaxDateTime( $db );
 419                         } else {
 420                                 $exptime = $this->convertExpiry( $exptime );
 421                                 $encExpiry = $db->timestamp( $exptime );
 422                         }
 423                         // (bug 24425) use a replace if the db supports it instead of
 424                         // delete/insert to avoid clashes with conflicting keynames
 425                         $db->update(
 426                                 $tableName,
 427                                 array(
 428                                         'keyname' => $key,
 429                                         'value' => $db->encodeBlob( $this->serialize( $value ) ),
 430                                         'exptime' => $encExpiry
 431                                 ),
 432                                 array(
 433                                         'keyname' => $key,
 434                                         'value' => $db->encodeBlob( $this->serialize( $casToken ) )
 435                                 ),
 436                                 __METHOD__
 437                         );
 438                 } catch ( DBQueryError $e ) {
 439                         $this->handleWriteError( $e, $serverIndex );
 440
 441                         return false;
 442                 }
 443
 444                 return (bool)$db->affectedRows();
 445         }
 446
 447         /**
 448          * @param string $key
 449          * @param int $time
 450          * @return bool
 451          */
 452         public function delete( $key, $time = 0 ) {
 453                 list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
 454                 try {
 455                         $db = $this->getDB( $serverIndex );
 456                         $db->delete(
 457                                 $tableName,
 458                                 array( 'keyname' => $key ),
 459                                 __METHOD__ );
 460                 } catch ( DBError $e ) {
 461                         $this->handleWriteError( $e, $serverIndex );
 462                         return false;
 463                 }
 464
 465                 return true;
 466         }
 467
 468         /**
 469          * @param string $key
 470          * @param int $step
 471          * @return int|null
 472          */
 473         public function incr( $key, $step = 1 ) {
 474                 list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
 475                 try {
 476                         $db = $this->getDB( $serverIndex );
 477                         $step = intval( $step );
 478                         $row = $db->selectRow(
 479                                 $tableName,
 480                                 array( 'value', 'exptime' ),
 481                                 array( 'keyname' => $key ),
 482                                 __METHOD__,
 483                                 array( 'FOR UPDATE' ) );
 484                         if ( $row === false ) {
 485                                 // Missing
 486
 487                                 return null;
 488                         }
 489                         $db->delete( $tableName, array( 'keyname' => $key ), __METHOD__ );
 490                         if ( $this->isExpired( $db, $row->exptime ) ) {
 491                                 // Expired, do not reinsert
 492
 493                                 return null;
 494                         }
 495
 496                         $oldValue = intval( $this->unserialize( $db->decodeBlob( $row->value ) ) );
 497                         $newValue = $oldValue + $step;
 498                         $db->insert( $tableName,
 499                                 array(
 500                                         'keyname' => $key,
 501                                         'value' => $db->encodeBlob( $this->serialize( $newValue ) ),
 502                                         'exptime' => $row->exptime
 503                                 ), __METHOD__, 'IGNORE' );
 504
 505                         if ( $db->affectedRows() == 0 ) {
 506                                 // Race condition. See bug 28611
 507                                 $newValue = null;
 508                         }
 509                 } catch ( DBError $e ) {
 510                         $this->handleWriteError( $e, $serverIndex );
 511                         return null;
 512                 }
 513
 514                 return $newValue;
 515         }
 516
 517         /**
 518          * @param DatabaseBase $db
 519          * @param string $exptime
 520          * @return bool
 521          */
 522         protected function isExpired( $db, $exptime ) {
 523                 return $exptime != $this->getMaxDateTime( $db ) && wfTimestamp( TS_UNIX, $exptime ) < time();
 524         }
 525
 526         /**
 527          * @param DatabaseBase $db
 528          * @return string
 529          */
 530         protected function getMaxDateTime( $db ) {
 531                 if ( time() > 0x7fffffff ) {
 532                         return $db->timestamp( 1 << 62 );
 533                 } else {
 534                         return $db->timestamp( 0x7fffffff );
 535                 }
 536         }
 537
 538         protected function garbageCollect() {
 539                 if ( !$this->purgePeriod ) {
 540                         // Disabled
 541                         return;
 542                 }
 543                 // Only purge on one in every $this->purgePeriod requests.
 544                 if ( $this->purgePeriod !== 1 && mt_rand( 0, $this->purgePeriod - 1 ) ) {
 545                         return;
 546                 }
 547                 $now = time();
 548                 // Avoid repeating the delete within a few seconds
 549                 if ( $now > ( $this->lastExpireAll + 1 ) ) {
 550                         $this->lastExpireAll = $now;
 551                         $this->expireAll();
 552                 }
 553         }
 554
 555         public function expireAll() {
 556                 $this->deleteObjectsExpiringBefore( wfTimestampNow() );
 557         }
 558
 559         /**
 560          * Delete objects from the database which expire before a certain date.
 561          * @param string $timestamp
 562          * @param bool|callable $progressCallback
 563          * @return bool
 564          */
 565         public function deleteObjectsExpiringBefore( $timestamp, $progressCallback = false ) {
 566                 for ( $serverIndex = 0; $serverIndex < $this->numServers; $serverIndex++ ) {
 567                         try {
 568                                 $db = $this->getDB( $serverIndex );
 569                                 $dbTimestamp = $db->timestamp( $timestamp );
 570                                 $totalSeconds = false;
 571                                 $baseConds = array( 'exptime < ' . $db->addQuotes( $dbTimestamp ) );
 572                                 for ( $i = 0; $i < $this->shards; $i++ ) {
 573                                         $maxExpTime = false;
 574                                         while ( true ) {
 575                                                 $conds = $baseConds;
 576                                                 if ( $maxExpTime !== false ) {
 577                                                         $conds[] = 'exptime > ' . $db->addQuotes( $maxExpTime );
 578                                                 }
 579                                                 $rows = $db->select(
 580                                                         $this->getTableNameByShard( $i ),
 581                                                         array( 'keyname', 'exptime' ),
 582                                                         $conds,
 583                                                         __METHOD__,
 584                                                         array( 'LIMIT' => 100, 'ORDER BY' => 'exptime' ) );
 585                                                 if ( $rows === false || !$rows->numRows() ) {
 586                                                         break;
 587                                                 }
 588                                                 $keys = array();
 589                                                 $row = $rows->current();
 590                                                 $minExpTime = $row->exptime;
 591                                                 if ( $totalSeconds === false ) {
 592                                                         $totalSeconds = wfTimestamp( TS_UNIX, $timestamp )
 593                                                                 - wfTimestamp( TS_UNIX, $minExpTime );
 594                                                 }
 595                                                 foreach ( $rows as $row ) {
 596                                                         $keys[] = $row->keyname;
 597                                                         $maxExpTime = $row->exptime;
 598                                                 }
 599
 600                                                 $db->delete(
 601                                                         $this->getTableNameByShard( $i ),
 602                                                         array(
 603                                                                 'exptime >= ' . $db->addQuotes( $minExpTime ),
 604                                                                 'exptime < ' . $db->addQuotes( $dbTimestamp ),
 605                                                                 'keyname' => $keys
 606                                                         ),
 607                                                         __METHOD__ );
 608
 609                                                 if ( $progressCallback ) {
 610                                                         if ( intval( $totalSeconds ) === 0 ) {
 611                                                                 $percent = 0;
 612                                                         } else {
 613                                                                 $remainingSeconds = wfTimestamp( TS_UNIX, $timestamp )
 614                                                                         - wfTimestamp( TS_UNIX, $maxExpTime );
 615                                                                 if ( $remainingSeconds > $totalSeconds ) {
 616                                                                         $totalSeconds = $remainingSeconds;
 617                                                                 }
 618                                                                 $processedSeconds = $totalSeconds - $remainingSeconds;
 619                                                                 $percent = ( $i + $processedSeconds / $totalSeconds )
 620                                                                         / $this->shards * 100;
 621                                                         }
 622                                                         $percent = ( $percent / $this->numServers )
 623                                                                 + ( $serverIndex / $this->numServers * 100 );
 624                                                         call_user_func( $progressCallback, $percent );
 625                                                 }
 626                                         }
 627                                 }
 628                         } catch ( DBError $e ) {
 629                                 $this->handleWriteError( $e, $serverIndex );
 630                                 return false;
 631                         }
 632                 }
 633                 return true;
 634         }
 635
 636         /**
 637          * Delete content of shard tables in every server.
 638          * Return true if the operation is successful, false otherwise.
 639          * @return bool
 640          */
 641         public function deleteAll() {
 642                 for ( $serverIndex = 0; $serverIndex < $this->numServers; $serverIndex++ ) {
 643                         try {
 644                                 $db = $this->getDB( $serverIndex );
 645                                 for ( $i = 0; $i < $this->shards; $i++ ) {
 646                                         $db->delete( $this->getTableNameByShard( $i ), '*', __METHOD__ );
 647                                 }
 648                         } catch ( DBError $e ) {
 649                                 $this->handleWriteError( $e, $serverIndex );
 650                                 return false;
 651                         }
 652                 }
 653                 return true;
 654         }
 655
 656         /**
 657          * Serialize an object and, if possible, compress the representation.
 658          * On typical message and page data, this can provide a 3X decrease
 659          * in storage requirements.
 660          *
 661          * @param mixed $data
 662          * @return string
 663          */
 664         protected function serialize( &$data ) {
 665                 $serial = serialize( $data );
 666
 667                 if ( function_exists( 'gzdeflate' ) ) {
 668                         return gzdeflate( $serial );
 669                 } else {
 670                         return $serial;
 671                 }
 672         }
 673
 674         /**
 675          * Unserialize and, if necessary, decompress an object.
 676          * @param string $serial
 677          * @return mixed
 678          */
 679         protected function unserialize( $serial ) {
 680                 if ( function_exists( 'gzinflate' ) ) {
 681                         wfSuppressWarnings();
 682                         $decomp = gzinflate( $serial );
 683                         wfRestoreWarnings();
 684
 685                         if ( false !== $decomp ) {
 686                                 $serial = $decomp;
 687                         }
 688                 }
 689
 690                 $ret = unserialize( $serial );
 691
 692                 return $ret;
 693         }
 694
 695         /**
 696          * Handle a DBError which occurred during a read operation.
 697          *
 698          * @param DBError $exception
 699          * @param int $serverIndex
 700          */
 701         protected function handleReadError( DBError $exception, $serverIndex ) {
 702                 if ( $exception instanceof DBConnectionError ) {
 703                         $this->markServerDown( $exception, $serverIndex );
 704                 }
 705                 wfDebugLog( 'SQLBagOStuff', "DBError: {$exception->getMessage()}" );
 706                 if ( $exception instanceof DBConnectionError ) {
 707                         $this->setLastError( BagOStuff::ERR_UNREACHABLE );
 708                         wfDebug( __METHOD__ . ": ignoring connection error\n" );
 709                 } else {
 710                         $this->setLastError( BagOStuff::ERR_UNEXPECTED );
 711                         wfDebug( __METHOD__ . ": ignoring query error\n" );
 712                 }
 713         }
 714
 715         /**
 716          * Handle a DBQueryError which occurred during a write operation.
 717          *
 718          * @param DBError $exception
 719          * @param int $serverIndex
 720          */
 721         protected function handleWriteError( DBError $exception, $serverIndex ) {
 722                 if ( $exception instanceof DBConnectionError ) {
 723                         $this->markServerDown( $exception, $serverIndex );
 724                 }
 725                 if ( $exception->db && $exception->db->wasReadOnlyError() ) {
 726                         try {
 727                                 $exception->db->rollback( __METHOD__ );
 728                         } catch ( DBError $e ) {
 729                         }
 730                 }
 731                 wfDebugLog( 'SQLBagOStuff', "DBError: {$exception->getMessage()}" );
 732                 if ( $exception instanceof DBConnectionError ) {
 733                         $this->setLastError( BagOStuff::ERR_UNREACHABLE );
 734                         wfDebug( __METHOD__ . ": ignoring connection error\n" );
 735                 } else {
 736                         $this->setLastError( BagOStuff::ERR_UNEXPECTED );
 737                         wfDebug( __METHOD__ . ": ignoring query error\n" );
 738                 }
 739         }
 740
 741         /**
 742          * Mark a server down due to a DBConnectionError exception
 743          *
 744          * @param DBError $exception
 745          * @param int $serverIndex
 746          */
 747         protected function markServerDown( $exception, $serverIndex ) {
 748                 if ( isset( $this->connFailureTimes[$serverIndex] ) ) {
 749                         if ( time() - $this->connFailureTimes[$serverIndex] >= 60 ) {
 750                                 unset( $this->connFailureTimes[$serverIndex] );
 751                                 unset( $this->connFailureErrors[$serverIndex] );
 752                         } else {
 753                                 wfDebug( __METHOD__ . ": Server #$serverIndex already down\n" );
 754                                 return;
 755                         }
 756                 }
 757                 $now = time();
 758                 wfDebug( __METHOD__ . ": Server #$serverIndex down until " . ( $now + 60 ) . "\n" );
 759                 $this->connFailureTimes[$serverIndex] = $now;
 760                 $this->connFailureErrors[$serverIndex] = $exception;
 761         }
 762
 763         /**
 764          * Create shard tables. For use from eval.php.
 765          */
 766         public function createTables() {
 767                 for ( $serverIndex = 0; $serverIndex < $this->numServers; $serverIndex++ ) {
 768                         $db = $this->getDB( $serverIndex );
 769                         if ( $db->getType() !== 'mysql' ) {
 770                                 throw new MWException( __METHOD__ . ' is not supported on this DB server' );
 771                         }
 772
 773                         for ( $i = 0; $i < $this->shards; $i++ ) {
 774                                 $db->query(
 775                                         'CREATE TABLE ' . $db->tableName( $this->getTableNameByShard( $i ) ) .
 776                                         ' LIKE ' . $db->tableName( 'objectcache' ),
 777                                         __METHOD__ );
 778                         }
 779                 }
 780         }
 781 }
 782
 783 /**
 784  * Backwards compatibility alias
 785  */
 786 class MediaWikiBagOStuff extends SqlBagOStuff {
 787 }