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         protected $serverInfos;
  31
  32         /** @var array */
  33         protected $serverNames;
  34
  35         /** @var int */
  36         protected $numServers;
  37
  38         /** @var array */
  39         protected $conns;
  40
  41         /** @var int */
  42         protected $lastExpireAll = 0;
  43
  44         /** @var int */
  45         protected $purgePeriod = 100;
  46
  47         /** @var int */
  48         protected $shards = 1;
  49
  50         /** @var string */
  51         protected $tableName = 'objectcache';
  52
  53         /** @var array UNIX timestamps */
  54         protected $connFailureTimes = array();
  55
  56         /** @var array Exceptions */
  57         protected $connFailureErrors = array();
  58
  59         /**
  60          * Constructor. Parameters are:
  61          *   - server:      A server info structure in the format required by each
  62          *                  element in $wgDBServers.
  63          *
  64          *   - servers:     An array of server info structures describing a set of
  65          *                  database servers to distribute keys to. If this is
  66          *                  specified, the "server" option will be ignored.
  67          *
  68          *   - purgePeriod: The average number of object cache requests in between
  69          *                  garbage collection operations, where expired entries
  70          *                  are removed from the database. Or in other words, the
  71          *                  reciprocal of the probability of purging on any given
  72          *                  request. If this is set to zero, purging will never be
  73          *                  done.
  74          *
  75          *   - tableName:   The table name to use, default is "objectcache".
  76          *
  77          *   - shards:      The number of tables to use for data storage on each server.
  78          *                  If this is more than 1, table names will be formed in the style
  79          *                  objectcacheNNN where NNN is the shard index, between 0 and
  80          *                  shards-1. The number of digits will be the minimum number
  81          *                  required to hold the largest shard index. Data will be
  82          *                  distributed across all tables by key hash. This is for
  83          *                  MySQL bugs 61735 and 61736.
  84          *
  85          * @param array $params
  86          */
  87         public function __construct( $params ) {
  88                 if ( isset( $params['servers'] ) ) {
  89                         $this->serverInfos = $params['servers'];
  90                         $this->numServers = count( $this->serverInfos );
  91                         $this->serverNames = array();
  92                         foreach ( $this->serverInfos as $i => $info ) {
  93                                 $this->serverNames[$i] = isset( $info['host'] ) ? $info['host'] : "#$i";
  94                         }
  95                 } elseif ( isset( $params['server'] ) ) {
  96                         $this->serverInfos = array( $params['server'] );
  97                         $this->numServers = count( $this->serverInfos );
  98                 } else {
  99                         $this->serverInfos = false;
 100                         $this->numServers = 1;
 101                 }
 102                 if ( isset( $params['purgePeriod'] ) ) {
 103                         $this->purgePeriod = intval( $params['purgePeriod'] );
 104                 }
 105                 if ( isset( $params['tableName'] ) ) {
 106                         $this->tableName = $params['tableName'];
 107                 }
 108                 if ( isset( $params['shards'] ) ) {
 109                         $this->shards = intval( $params['shards'] );
 110                 }
 111         }
 112
 113         /**
 114          * Get a connection to the specified database
 115          *
 116          * @param int $serverIndex
 117          * @return DatabaseBase
 118          */
 119         protected function getDB( $serverIndex ) {
 120                 global $wgDebugDBTransactions;
 121
 122                 if ( !isset( $this->conns[$serverIndex] ) ) {
 123                         if ( $serverIndex >= $this->numServers ) {
 124                                 throw new MWException( __METHOD__ . ": Invalid server index \"$serverIndex\"" );
 125                         }
 126
 127                         # Don't keep timing out trying to connect for each call if the DB is down
 128                         if ( isset( $this->connFailureErrors[$serverIndex] )
 129                                 && ( time() - $this->connFailureTimes[$serverIndex] ) < 60
 130                         ) {
 131                                 throw $this->connFailureErrors[$serverIndex];
 132                         }
 133
 134                         # If server connection info was given, use that
 135                         if ( $this->serverInfos ) {
 136                                 if ( $wgDebugDBTransactions ) {
 137                                         wfDebug( "Using provided serverInfo for SqlBagOStuff\n" );
 138                                 }
 139                                 $info = $this->serverInfos[$serverIndex];
 140                                 $type = isset( $info['type'] ) ? $info['type'] : 'mysql';
 141                                 $host = isset( $info['host'] ) ? $info['host'] : '[unknown]';
 142                                 wfDebug( __CLASS__ . ": connecting to $host\n" );
 143                                 $db = DatabaseBase::factory( $type, $info );
 144                                 $db->clearFlag( DBO_TRX );
 145                         } else {
 146                                 // We must keep a separate connection to MySQL in order to avoid deadlocks
 147                                 // However, SQLite has an opposite behavior.
 148                                 // @todo get this trick to work on PostgreSQL too
 149                                 if ( wfGetDB( DB_MASTER )->getType() == 'mysql' ) {
 150                                         $lb = wfGetLBFactory()->newMainLB();
 151                                         $db = $lb->getConnection( DB_MASTER );
 152                                         $db->clearFlag( DBO_TRX ); // auto-commit mode
 153                                 } else {
 154                                         $db = wfGetDB( DB_MASTER );
 155                                 }
 156                         }
 157                         if ( $wgDebugDBTransactions ) {
 158                                 wfDebug( sprintf( "Connection %s will be used for SqlBagOStuff\n", $db ) );
 159                         }
 160                         $this->conns[$serverIndex] = $db;
 161                 }
 162
 163                 return $this->conns[$serverIndex];
 164         }
 165
 166         /**
 167          * Get the server index and table name for a given key
 168          * @param string $key
 169          * @return array Server index and table name
 170          */
 171         protected function getTableByKey( $key ) {
 172                 if ( $this->shards > 1 ) {
 173                         $hash = hexdec( substr( md5( $key ), 0, 8 ) ) & 0x7fffffff;
 174                         $tableIndex = $hash % $this->shards;
 175                 } else {
 176                         $tableIndex = 0;
 177                 }
 178                 if ( $this->numServers > 1 ) {
 179                         $sortedServers = $this->serverNames;
 180                         ArrayUtils::consistentHashSort( $sortedServers, $key );
 181                         reset( $sortedServers );
 182                         $serverIndex = key( $sortedServers );
 183                 } else {
 184                         $serverIndex = 0;
 185                 }
 186                 return array( $serverIndex, $this->getTableNameByShard( $tableIndex ) );
 187         }
 188
 189         /**
 190          * Get the table name for a given shard index
 191          * @param int $index
 192          * @return string
 193          */
 194         protected function getTableNameByShard( $index ) {
 195                 if ( $this->shards > 1 ) {
 196                         $decimals = strlen( $this->shards - 1 );
 197                         return $this->tableName .
 198                                 sprintf( "%0{$decimals}d", $index );
 199                 } else {
 200                         return $this->tableName;
 201                 }
 202         }
 203
 204         /**
 205          * @param string $key
 206          * @param mixed $casToken [optional]
 207          * @return mixed
 208          */
 209         public function get( $key, &$casToken = null ) {
 210                 $values = $this->getMulti( array( $key ) );
 211                 if ( array_key_exists( $key, $values ) ) {
 212                         $casToken = $values[$key];
 213                         return $values[$key];
 214                 }
 215                 return false;
 216         }
 217
 218         /**
 219          * @param array $keys
 220          * @return array
 221          */
 222         public function getMulti( array $keys ) {
 223                 $values = array(); // array of (key => value)
 224
 225                 $keysByTable = array();
 226                 foreach ( $keys as $key ) {
 227                         list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
 228                         $keysByTable[$serverIndex][$tableName][] = $key;
 229                 }
 230
 231                 $this->garbageCollect(); // expire old entries if any
 232
 233                 $dataRows = array();
 234                 foreach ( $keysByTable as $serverIndex => $serverKeys ) {
 235                         try {
 236                                 $db = $this->getDB( $serverIndex );
 237                                 foreach ( $serverKeys as $tableName => $tableKeys ) {
 238                                         $res = $db->select( $tableName,
 239                                                 array( 'keyname', 'value', 'exptime' ),
 240                                                 array( 'keyname' => $tableKeys ),
 241                                                 __METHOD__,
 242                                                 // Approximate write-on-the-fly BagOStuff API via blocking.
 243                                                 // This approximation fails if a ROLLBACK happens (which is rare).
 244                                                 // We do not want to flush the TRX as that can break callers.
 245                                                 $db->trxLevel() ? array( 'LOCK IN SHARE MODE' ) : array()
 246                                         );
 247                                         if ( $res === false ) {
 248                                                 continue;
 249                                         }
 250                                         foreach ( $res as $row ) {
 251                                                 $row->serverIndex = $serverIndex;
 252                                                 $row->tableName = $tableName;
 253                                                 $dataRows[$row->keyname] = $row;
 254                                         }
 255                                 }
 256                         } catch ( DBError $e ) {
 257                                 $this->handleReadError( $e, $serverIndex );
 258                         }
 259                 }
 260
 261                 foreach ( $keys as $key ) {
 262                         if ( isset( $dataRows[$key] ) ) { // HIT?
 263                                 $row = $dataRows[$key];
 264                                 $this->debug( "get: retrieved data; expiry time is " . $row->exptime );
 265                                 try {
 266                                         $db = $this->getDB( $row->serverIndex );
 267                                         if ( $this->isExpired( $db, $row->exptime ) ) { // MISS
 268                                                 $this->debug( "get: key has expired, deleting" );
 269                                                 # Put the expiry time in the WHERE condition to avoid deleting a
 270                                                 # newly-inserted value
 271                                                 $db->delete( $row->tableName,
 272                                                         array( 'keyname' => $key, 'exptime' => $row->exptime ),
 273                                                         __METHOD__ );
 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                                 $this->debug( 'get: no matching rows' );
 282                         }
 283                 }
 284
 285                 return $values;
 286         }
 287
 288         /**
 289          * @param array $data
 290          * @param int $expiry
 291          * @return bool
 292          */
 293         public function setMulti( array $data, $expiry = 0 ) {
 294                 $keysByTable = array();
 295                 foreach ( $data as $key => $value ) {
 296                         list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
 297                         $keysByTable[$serverIndex][$tableName][] = $key;
 298                 }
 299
 300                 $this->garbageCollect(); // expire old entries if any
 301
 302                 $result = true;
 303                 $exptime = (int)$expiry;
 304                 foreach ( $keysByTable as $serverIndex => $serverKeys ) {
 305                         try {
 306                                 $db = $this->getDB( $serverIndex );
 307                         } catch ( DBError $e ) {
 308                                 $this->handleWriteError( $e, $serverIndex );
 309                                 $result = false;
 310                                 continue;
 311                         }
 312
 313                         if ( $exptime < 0 ) {
 314                                 $exptime = 0;
 315                         }
 316
 317                         if ( $exptime == 0 ) {
 318                                 $encExpiry = $this->getMaxDateTime( $db );
 319                         } else {
 320                                 if ( $exptime < 3.16e8 ) { # ~10 years
 321                                         $exptime += time();
 322                                 }
 323                                 $encExpiry = $db->timestamp( $exptime );
 324                         }
 325                         foreach ( $serverKeys as $tableName => $tableKeys ) {
 326                                 $rows = array();
 327                                 foreach ( $tableKeys as $key ) {
 328                                         $rows[] = array(
 329                                                 'keyname' => $key,
 330                                                 'value' => $db->encodeBlob( $this->serialize( $data[$key] ) ),
 331                                                 'exptime' => $encExpiry,
 332                                         );
 333                                 }
 334
 335                                 try {
 336                                         $db->replace(
 337                                                 $tableName,
 338                                                 array( 'keyname' ),
 339                                                 $rows,
 340                                                 __METHOD__
 341                                         );
 342                                 } catch ( DBError $e ) {
 343                                         $this->handleWriteError( $e, $serverIndex );
 344                                         $result = false;
 345                                 }
 346
 347                         }
 348
 349                 }
 350
 351                 return $result;
 352         }
 353
 354
 355
 356         /**
 357          * @param string $key
 358          * @param mixed $value
 359          * @param int $exptime
 360          * @return bool
 361          */
 362         public function set( $key, $value, $exptime = 0 ) {
 363                 list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
 364                 try {
 365                         $db = $this->getDB( $serverIndex );
 366                         $exptime = intval( $exptime );
 367
 368                         if ( $exptime < 0 ) {
 369                                 $exptime = 0;
 370                         }
 371
 372                         if ( $exptime == 0 ) {
 373                                 $encExpiry = $this->getMaxDateTime( $db );
 374                         } else {
 375                                 if ( $exptime < 3.16e8 ) { # ~10 years
 376                                         $exptime += time();
 377                                 }
 378
 379                                 $encExpiry = $db->timestamp( $exptime );
 380                         }
 381                         // (bug 24425) use a replace if the db supports it instead of
 382                         // delete/insert to avoid clashes with conflicting keynames
 383                         $db->replace(
 384                                 $tableName,
 385                                 array( 'keyname' ),
 386                                 array(
 387                                         'keyname' => $key,
 388                                         'value' => $db->encodeBlob( $this->serialize( $value ) ),
 389                                         'exptime' => $encExpiry
 390                                 ), __METHOD__ );
 391                 } catch ( DBError $e ) {
 392                         $this->handleWriteError( $e, $serverIndex );
 393                         return false;
 394                 }
 395
 396                 return true;
 397         }
 398
 399         /**
 400          * @param mixed $casToken
 401          * @param string $key
 402          * @param mixed $value
 403          * @param int $exptime
 404          * @return bool
 405          */
 406         public function cas( $casToken, $key, $value, $exptime = 0 ) {
 407                 list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
 408                 try {
 409                         $db = $this->getDB( $serverIndex );
 410                         $exptime = intval( $exptime );
 411
 412                         if ( $exptime < 0 ) {
 413                                 $exptime = 0;
 414                         }
 415
 416                         if ( $exptime == 0 ) {
 417                                 $encExpiry = $this->getMaxDateTime( $db );
 418                         } else {
 419                                 if ( $exptime < 3.16e8 ) { # ~10 years
 420                                         $exptime += time();
 421                                 }
 422                                 $encExpiry = $db->timestamp( $exptime );
 423                         }
 424                         // (bug 24425) use a replace if the db supports it instead of
 425                         // delete/insert to avoid clashes with conflicting keynames
 426                         $db->update(
 427                                 $tableName,
 428                                 array(
 429                                         'keyname' => $key,
 430                                         'value' => $db->encodeBlob( $this->serialize( $value ) ),
 431                                         'exptime' => $encExpiry
 432                                 ),
 433                                 array(
 434                                         'keyname' => $key,
 435                                         'value' => $db->encodeBlob( $this->serialize( $casToken ) )
 436                                 ),
 437                                 __METHOD__
 438                         );
 439                 } catch ( DBQueryError $e ) {
 440                         $this->handleWriteError( $e, $serverIndex );
 441
 442                         return false;
 443                 }
 444
 445                 return (bool)$db->affectedRows();
 446         }
 447
 448         /**
 449          * @param string $key
 450          * @param int $time
 451          * @return bool
 452          */
 453         public function delete( $key, $time = 0 ) {
 454                 list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
 455                 try {
 456                         $db = $this->getDB( $serverIndex );
 457                         $db->delete(
 458                                 $tableName,
 459                                 array( 'keyname' => $key ),
 460                                 __METHOD__ );
 461                 } catch ( DBError $e ) {
 462                         $this->handleWriteError( $e, $serverIndex );
 463                         return false;
 464                 }
 465
 466                 return true;
 467         }
 468
 469         /**
 470          * @param string $key
 471          * @param int $step
 472          * @return int|null
 473          */
 474         public function incr( $key, $step = 1 ) {
 475                 list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
 476                 try {
 477                         $db = $this->getDB( $serverIndex );
 478                         $step = intval( $step );
 479                         $row = $db->selectRow(
 480                                 $tableName,
 481                                 array( 'value', 'exptime' ),
 482                                 array( 'keyname' => $key ),
 483                                 __METHOD__,
 484                                 array( 'FOR UPDATE' ) );
 485                         if ( $row === false ) {
 486                                 // Missing
 487
 488                                 return null;
 489                         }
 490                         $db->delete( $tableName, array( 'keyname' => $key ), __METHOD__ );
 491                         if ( $this->isExpired( $db, $row->exptime ) ) {
 492                                 // Expired, do not reinsert
 493
 494                                 return null;
 495                         }
 496
 497                         $oldValue = intval( $this->unserialize( $db->decodeBlob( $row->value ) ) );
 498                         $newValue = $oldValue + $step;
 499                         $db->insert( $tableName,
 500                                 array(
 501                                         'keyname' => $key,
 502                                         'value' => $db->encodeBlob( $this->serialize( $newValue ) ),
 503                                         'exptime' => $row->exptime
 504                                 ), __METHOD__, 'IGNORE' );
 505
 506                         if ( $db->affectedRows() == 0 ) {
 507                                 // Race condition. See bug 28611
 508                                 $newValue = null;
 509                         }
 510                 } catch ( DBError $e ) {
 511                         $this->handleWriteError( $e, $serverIndex );
 512                         return null;
 513                 }
 514
 515                 return $newValue;
 516         }
 517
 518         /**
 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                                                                 $percent = ( $i + $remainingSeconds / $totalSeconds )
 619                                                                         / $this->shards * 100;
 620                                                         }
 621                                                         $percent = ( $percent / $this->numServers )
 622                                                                 + ( $serverIndex / $this->numServers * 100 );
 623                                                         call_user_func( $progressCallback, $percent );
 624                                                 }
 625                                         }
 626                                 }
 627                         } catch ( DBError $e ) {
 628                                 $this->handleWriteError( $e, $serverIndex );
 629                                 return false;
 630                         }
 631                 }
 632                 return true;
 633         }
 634
 635         public function deleteAll() {
 636                 for ( $serverIndex = 0; $serverIndex < $this->numServers; $serverIndex++ ) {
 637                         try {
 638                                 $db = $this->getDB( $serverIndex );
 639                                 for ( $i = 0; $i < $this->shards; $i++ ) {
 640                                         $db->delete( $this->getTableNameByShard( $i ), '*', __METHOD__ );
 641                                 }
 642                         } catch ( DBError $e ) {
 643                                 $this->handleWriteError( $e, $serverIndex );
 644                                 return false;
 645                         }
 646                 }
 647                 return true;
 648         }
 649
 650         /**
 651          * Serialize an object and, if possible, compress the representation.
 652          * On typical message and page data, this can provide a 3X decrease
 653          * in storage requirements.
 654          *
 655          * @param mixed $data
 656          * @return string
 657          */
 658         protected function serialize( &$data ) {
 659                 $serial = serialize( $data );
 660
 661                 if ( function_exists( 'gzdeflate' ) ) {
 662                         return gzdeflate( $serial );
 663                 } else {
 664                         return $serial;
 665                 }
 666         }
 667
 668         /**
 669          * Unserialize and, if necessary, decompress an object.
 670          * @param string $serial
 671          * @return mixed
 672          */
 673         protected function unserialize( $serial ) {
 674                 if ( function_exists( 'gzinflate' ) ) {
 675                         wfSuppressWarnings();
 676                         $decomp = gzinflate( $serial );
 677                         wfRestoreWarnings();
 678
 679                         if ( false !== $decomp ) {
 680                                 $serial = $decomp;
 681                         }
 682                 }
 683
 684                 $ret = unserialize( $serial );
 685
 686                 return $ret;
 687         }
 688
 689         /**
 690          * Handle a DBError which occurred during a read operation.
 691          *
 692          * @param DBError $exception
 693          * @param int $serverIndex
 694          */
 695         protected function handleReadError( DBError $exception, $serverIndex ) {
 696                 if ( $exception instanceof DBConnectionError ) {
 697                         $this->markServerDown( $exception, $serverIndex );
 698                 }
 699                 wfDebugLog( 'SQLBagOStuff', "DBError: {$exception->getMessage()}" );
 700                 if ( $exception instanceof DBConnectionError ) {
 701                         $this->setLastError( BagOStuff::ERR_UNREACHABLE );
 702                         wfDebug( __METHOD__ . ": ignoring connection error\n" );
 703                 } else {
 704                         $this->setLastError( BagOStuff::ERR_UNEXPECTED );
 705                         wfDebug( __METHOD__ . ": ignoring query error\n" );
 706                 }
 707         }
 708
 709         /**
 710          * Handle a DBQueryError which occurred during a write operation.
 711          *
 712          * @param DBError $exception
 713          * @param int $serverIndex
 714          */
 715         protected function handleWriteError( DBError $exception, $serverIndex ) {
 716                 if ( $exception instanceof DBConnectionError ) {
 717                         $this->markServerDown( $exception, $serverIndex );
 718                 }
 719                 if ( $exception->db && $exception->db->wasReadOnlyError() ) {
 720                         try {
 721                                 $exception->db->rollback( __METHOD__ );
 722                         } catch ( DBError $e ) {
 723                         }
 724                 }
 725                 wfDebugLog( 'SQLBagOStuff', "DBError: {$exception->getMessage()}" );
 726                 if ( $exception instanceof DBConnectionError ) {
 727                         $this->setLastError( BagOStuff::ERR_UNREACHABLE );
 728                         wfDebug( __METHOD__ . ": ignoring connection error\n" );
 729                 } else {
 730                         $this->setLastError( BagOStuff::ERR_UNEXPECTED );
 731                         wfDebug( __METHOD__ . ": ignoring query error\n" );
 732                 }
 733         }
 734
 735         /**
 736          * Mark a server down due to a DBConnectionError exception
 737          *
 738          * @param DBError $exception
 739          * @param int $serverIndex
 740          */
 741         protected function markServerDown( $exception, $serverIndex ) {
 742                 if ( isset( $this->connFailureTimes[$serverIndex] ) ) {
 743                         if ( time() - $this->connFailureTimes[$serverIndex] >= 60 ) {
 744                                 unset( $this->connFailureTimes[$serverIndex] );
 745                                 unset( $this->connFailureErrors[$serverIndex] );
 746                         } else {
 747                                 wfDebug( __METHOD__ . ": Server #$serverIndex already down\n" );
 748                                 return;
 749                         }
 750                 }
 751                 $now = time();
 752                 wfDebug( __METHOD__ . ": Server #$serverIndex down until " . ( $now + 60 ) . "\n" );
 753                 $this->connFailureTimes[$serverIndex] = $now;
 754                 $this->connFailureErrors[$serverIndex] = $exception;
 755         }
 756
 757         /**
 758          * Create shard tables. For use from eval.php.
 759          */
 760         public function createTables() {
 761                 for ( $serverIndex = 0; $serverIndex < $this->numServers; $serverIndex++ ) {
 762                         $db = $this->getDB( $serverIndex );
 763                         if ( $db->getType() !== 'mysql' ) {
 764                                 throw new MWException( __METHOD__ . ' is not supported on this DB server' );
 765                         }
 766
 767                         for ( $i = 0; $i < $this->shards; $i++ ) {
 768                                 $db->query(
 769                                         'CREATE TABLE ' . $db->tableName( $this->getTableNameByShard( $i ) ) .
 770                                         ' LIKE ' . $db->tableName( 'objectcache' ),
 771                                         __METHOD__ );
 772                         }
 773                 }
 774         }
 775 }
 776
 777 /**
 778  * Backwards compatibility alias
 779  */
 780 class MediaWikiBagOStuff extends SqlBagOStuff {
 781 }