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
 368         /**
 369          * @param string $key
 370          * @param mixed $value
 371          * @param int $exptime
 372          * @return bool
 373          */
 374         public function set( $key, $value, $exptime = 0 ) {
 375                 list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
 376                 try {
 377                         $db = $this->getDB( $serverIndex );
 378                         $exptime = intval( $exptime );
 379
 380                         if ( $exptime < 0 ) {
 381                                 $exptime = 0;
 382                         }
 383
 384                         if ( $exptime == 0 ) {
 385                                 $encExpiry = $this->getMaxDateTime( $db );
 386                         } else {
 387                                 $exptime = $this->convertExpiry( $exptime );
 388                                 $encExpiry = $db->timestamp( $exptime );
 389                         }
 390                         // (bug 24425) use a replace if the db supports it instead of
 391                         // delete/insert to avoid clashes with conflicting keynames
 392                         $db->replace(
 393                                 $tableName,
 394                                 array( 'keyname' ),
 395                                 array(
 396                                         'keyname' => $key,
 397                                         'value' => $db->encodeBlob( $this->serialize( $value ) ),
 398                                         'exptime' => $encExpiry
 399                                 ), __METHOD__ );
 400                 } catch ( DBError $e ) {
 401                         $this->handleWriteError( $e, $serverIndex );
 402                         return false;
 403                 }
 404
 405                 return true;
 406         }
 407
 408         /**
 409          * @param mixed $casToken
 410          * @param string $key
 411          * @param mixed $value
 412          * @param int $exptime
 413          * @return bool
 414          */
 415         protected function cas( $casToken, $key, $value, $exptime = 0 ) {
 416                 list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
 417                 try {
 418                         $db = $this->getDB( $serverIndex );
 419                         $exptime = intval( $exptime );
 420
 421                         if ( $exptime < 0 ) {
 422                                 $exptime = 0;
 423                         }
 424
 425                         if ( $exptime == 0 ) {
 426                                 $encExpiry = $this->getMaxDateTime( $db );
 427                         } else {
 428                                 $exptime = $this->convertExpiry( $exptime );
 429                                 $encExpiry = $db->timestamp( $exptime );
 430                         }
 431                         // (bug 24425) use a replace if the db supports it instead of
 432                         // delete/insert to avoid clashes with conflicting keynames
 433                         $db->update(
 434                                 $tableName,
 435                                 array(
 436                                         'keyname' => $key,
 437                                         'value' => $db->encodeBlob( $this->serialize( $value ) ),
 438                                         'exptime' => $encExpiry
 439                                 ),
 440                                 array(
 441                                         'keyname' => $key,
 442                                         'value' => $db->encodeBlob( $this->serialize( $casToken ) )
 443                                 ),
 444                                 __METHOD__
 445                         );
 446                 } catch ( DBQueryError $e ) {
 447                         $this->handleWriteError( $e, $serverIndex );
 448
 449                         return false;
 450                 }
 451
 452                 return (bool)$db->affectedRows();
 453         }
 454
 455         /**
 456          * @param string $key
 457          * @return bool
 458          */
 459         public function delete( $key ) {
 460                 list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
 461                 try {
 462                         $db = $this->getDB( $serverIndex );
 463                         $db->delete(
 464                                 $tableName,
 465                                 array( 'keyname' => $key ),
 466                                 __METHOD__ );
 467                 } catch ( DBError $e ) {
 468                         $this->handleWriteError( $e, $serverIndex );
 469                         return false;
 470                 }
 471
 472                 return true;
 473         }
 474
 475         /**
 476          * @param string $key
 477          * @param int $step
 478          * @return int|null
 479          */
 480         public function incr( $key, $step = 1 ) {
 481                 list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
 482                 try {
 483                         $db = $this->getDB( $serverIndex );
 484                         $step = intval( $step );
 485                         $row = $db->selectRow(
 486                                 $tableName,
 487                                 array( 'value', 'exptime' ),
 488                                 array( 'keyname' => $key ),
 489                                 __METHOD__,
 490                                 array( 'FOR UPDATE' ) );
 491                         if ( $row === false ) {
 492                                 // Missing
 493
 494                                 return null;
 495                         }
 496                         $db->delete( $tableName, array( 'keyname' => $key ), __METHOD__ );
 497                         if ( $this->isExpired( $db, $row->exptime ) ) {
 498                                 // Expired, do not reinsert
 499
 500                                 return null;
 501                         }
 502
 503                         $oldValue = intval( $this->unserialize( $db->decodeBlob( $row->value ) ) );
 504                         $newValue = $oldValue + $step;
 505                         $db->insert( $tableName,
 506                                 array(
 507                                         'keyname' => $key,
 508                                         'value' => $db->encodeBlob( $this->serialize( $newValue ) ),
 509                                         'exptime' => $row->exptime
 510                                 ), __METHOD__, 'IGNORE' );
 511
 512                         if ( $db->affectedRows() == 0 ) {
 513                                 // Race condition. See bug 28611
 514                                 $newValue = null;
 515                         }
 516                 } catch ( DBError $e ) {
 517                         $this->handleWriteError( $e, $serverIndex );
 518                         return null;
 519                 }
 520
 521                 return $newValue;
 522         }
 523
 524         public function merge( $key, $callback, $exptime = 0, $attempts = 10 ) {
 525                 if ( !is_callable( $callback ) ) {
 526                         throw new Exception( "Got invalid callback." );
 527                 }
 528
 529                 return $this->mergeViaCas( $key, $callback, $exptime, $attempts );
 530         }
 531
 532         /**
 533          * @param DatabaseBase $db
 534          * @param string $exptime
 535          * @return bool
 536          */
 537         protected function isExpired( $db, $exptime ) {
 538                 return $exptime != $this->getMaxDateTime( $db ) && wfTimestamp( TS_UNIX, $exptime ) < time();
 539         }
 540
 541         /**
 542          * @param DatabaseBase $db
 543          * @return string
 544          */
 545         protected function getMaxDateTime( $db ) {
 546                 if ( time() > 0x7fffffff ) {
 547                         return $db->timestamp( 1 << 62 );
 548                 } else {
 549                         return $db->timestamp( 0x7fffffff );
 550                 }
 551         }
 552
 553         protected function garbageCollect() {
 554                 if ( !$this->purgePeriod || $this->slaveOnly ) {
 555                         // Disabled
 556                         return;
 557                 }
 558                 // Only purge on one in every $this->purgePeriod requests.
 559                 if ( $this->purgePeriod !== 1 && mt_rand( 0, $this->purgePeriod - 1 ) ) {
 560                         return;
 561                 }
 562                 $now = time();
 563                 // Avoid repeating the delete within a few seconds
 564                 if ( $now > ( $this->lastExpireAll + 1 ) ) {
 565                         $this->lastExpireAll = $now;
 566                         $this->expireAll();
 567                 }
 568         }
 569
 570         public function expireAll() {
 571                 $this->deleteObjectsExpiringBefore( wfTimestampNow() );
 572         }
 573
 574         /**
 575          * Delete objects from the database which expire before a certain date.
 576          * @param string $timestamp
 577          * @param bool|callable $progressCallback
 578          * @return bool
 579          */
 580         public function deleteObjectsExpiringBefore( $timestamp, $progressCallback = false ) {
 581                 for ( $serverIndex = 0; $serverIndex < $this->numServers; $serverIndex++ ) {
 582                         try {
 583                                 $db = $this->getDB( $serverIndex );
 584                                 $dbTimestamp = $db->timestamp( $timestamp );
 585                                 $totalSeconds = false;
 586                                 $baseConds = array( 'exptime < ' . $db->addQuotes( $dbTimestamp ) );
 587                                 for ( $i = 0; $i < $this->shards; $i++ ) {
 588                                         $maxExpTime = false;
 589                                         while ( true ) {
 590                                                 $conds = $baseConds;
 591                                                 if ( $maxExpTime !== false ) {
 592                                                         $conds[] = 'exptime > ' . $db->addQuotes( $maxExpTime );
 593                                                 }
 594                                                 $rows = $db->select(
 595                                                         $this->getTableNameByShard( $i ),
 596                                                         array( 'keyname', 'exptime' ),
 597                                                         $conds,
 598                                                         __METHOD__,
 599                                                         array( 'LIMIT' => 100, 'ORDER BY' => 'exptime' ) );
 600                                                 if ( $rows === false || !$rows->numRows() ) {
 601                                                         break;
 602                                                 }
 603                                                 $keys = array();
 604                                                 $row = $rows->current();
 605                                                 $minExpTime = $row->exptime;
 606                                                 if ( $totalSeconds === false ) {
 607                                                         $totalSeconds = wfTimestamp( TS_UNIX, $timestamp )
 608                                                                 - wfTimestamp( TS_UNIX, $minExpTime );
 609                                                 }
 610                                                 foreach ( $rows as $row ) {
 611                                                         $keys[] = $row->keyname;
 612                                                         $maxExpTime = $row->exptime;
 613                                                 }
 614
 615                                                 $db->delete(
 616                                                         $this->getTableNameByShard( $i ),
 617                                                         array(
 618                                                                 'exptime >= ' . $db->addQuotes( $minExpTime ),
 619                                                                 'exptime < ' . $db->addQuotes( $dbTimestamp ),
 620                                                                 'keyname' => $keys
 621                                                         ),
 622                                                         __METHOD__ );
 623
 624                                                 if ( $progressCallback ) {
 625                                                         if ( intval( $totalSeconds ) === 0 ) {
 626                                                                 $percent = 0;
 627                                                         } else {
 628                                                                 $remainingSeconds = wfTimestamp( TS_UNIX, $timestamp )
 629                                                                         - wfTimestamp( TS_UNIX, $maxExpTime );
 630                                                                 if ( $remainingSeconds > $totalSeconds ) {
 631                                                                         $totalSeconds = $remainingSeconds;
 632                                                                 }
 633                                                                 $processedSeconds = $totalSeconds - $remainingSeconds;
 634                                                                 $percent = ( $i + $processedSeconds / $totalSeconds )
 635                                                                         / $this->shards * 100;
 636                                                         }
 637                                                         $percent = ( $percent / $this->numServers )
 638                                                                 + ( $serverIndex / $this->numServers * 100 );
 639                                                         call_user_func( $progressCallback, $percent );
 640                                                 }
 641                                         }
 642                                 }
 643                         } catch ( DBError $e ) {
 644                                 $this->handleWriteError( $e, $serverIndex );
 645                                 return false;
 646                         }
 647                 }
 648                 return true;
 649         }
 650
 651         /**
 652          * Delete content of shard tables in every server.
 653          * Return true if the operation is successful, false otherwise.
 654          * @return bool
 655          */
 656         public function deleteAll() {
 657                 for ( $serverIndex = 0; $serverIndex < $this->numServers; $serverIndex++ ) {
 658                         try {
 659                                 $db = $this->getDB( $serverIndex );
 660                                 for ( $i = 0; $i < $this->shards; $i++ ) {
 661                                         $db->delete( $this->getTableNameByShard( $i ), '*', __METHOD__ );
 662                                 }
 663                         } catch ( DBError $e ) {
 664                                 $this->handleWriteError( $e, $serverIndex );
 665                                 return false;
 666                         }
 667                 }
 668                 return true;
 669         }
 670
 671         /**
 672          * Serialize an object and, if possible, compress the representation.
 673          * On typical message and page data, this can provide a 3X decrease
 674          * in storage requirements.
 675          *
 676          * @param mixed $data
 677          * @return string
 678          */
 679         protected function serialize( &$data ) {
 680                 $serial = serialize( $data );
 681
 682                 if ( function_exists( 'gzdeflate' ) ) {
 683                         return gzdeflate( $serial );
 684                 } else {
 685                         return $serial;
 686                 }
 687         }
 688
 689         /**
 690          * Unserialize and, if necessary, decompress an object.
 691          * @param string $serial
 692          * @return mixed
 693          */
 694         protected function unserialize( $serial ) {
 695                 if ( function_exists( 'gzinflate' ) ) {
 696                         wfSuppressWarnings();
 697                         $decomp = gzinflate( $serial );
 698                         wfRestoreWarnings();
 699
 700                         if ( false !== $decomp ) {
 701                                 $serial = $decomp;
 702                         }
 703                 }
 704
 705                 $ret = unserialize( $serial );
 706
 707                 return $ret;
 708         }
 709
 710         /**
 711          * Handle a DBError which occurred during a read operation.
 712          *
 713          * @param DBError $exception
 714          * @param int $serverIndex
 715          */
 716         protected function handleReadError( DBError $exception, $serverIndex ) {
 717                 if ( $exception instanceof DBConnectionError ) {
 718                         $this->markServerDown( $exception, $serverIndex );
 719                 }
 720                 $this->logger->error( "DBError: {$exception->getMessage()}" );
 721                 if ( $exception instanceof DBConnectionError ) {
 722                         $this->setLastError( BagOStuff::ERR_UNREACHABLE );
 723                         $this->logger->debug( __METHOD__ . ": ignoring connection error" );
 724                 } else {
 725                         $this->setLastError( BagOStuff::ERR_UNEXPECTED );
 726                         $this->logger->debug( __METHOD__ . ": ignoring query error" );
 727                 }
 728         }
 729
 730         /**
 731          * Handle a DBQueryError which occurred during a write operation.
 732          *
 733          * @param DBError $exception
 734          * @param int $serverIndex
 735          */
 736         protected function handleWriteError( DBError $exception, $serverIndex ) {
 737                 if ( $exception instanceof DBConnectionError ) {
 738                         $this->markServerDown( $exception, $serverIndex );
 739                 }
 740                 if ( $exception->db && $exception->db->wasReadOnlyError() ) {
 741                         if ( $exception->db->trxLevel() ) {
 742                                 try {
 743                                         $exception->db->rollback( __METHOD__ );
 744                                 } catch ( DBError $e ) {
 745                                 }
 746                         }
 747                 }
 748
 749                 $this->logger->error( "DBError: {$exception->getMessage()}" );
 750                 if ( $exception instanceof DBConnectionError ) {
 751                         $this->setLastError( BagOStuff::ERR_UNREACHABLE );
 752                         $this->logger->debug( __METHOD__ . ": ignoring connection error" );
 753                 } else {
 754                         $this->setLastError( BagOStuff::ERR_UNEXPECTED );
 755                         $this->logger->debug( __METHOD__ . ": ignoring query error" );
 756                 }
 757         }
 758
 759         /**
 760          * Mark a server down due to a DBConnectionError exception
 761          *
 762          * @param DBError $exception
 763          * @param int $serverIndex
 764          */
 765         protected function markServerDown( $exception, $serverIndex ) {
 766                 if ( isset( $this->connFailureTimes[$serverIndex] ) ) {
 767                         if ( time() - $this->connFailureTimes[$serverIndex] >= 60 ) {
 768                                 unset( $this->connFailureTimes[$serverIndex] );
 769                                 unset( $this->connFailureErrors[$serverIndex] );
 770                         } else {
 771                                 $this->logger->debug( __METHOD__ . ": Server #$serverIndex already down" );
 772                                 return;
 773                         }
 774                 }
 775                 $now = time();
 776                 $this->logger->info( __METHOD__ . ": Server #$serverIndex down until " . ( $now + 60 ) );
 777                 $this->connFailureTimes[$serverIndex] = $now;
 778                 $this->connFailureErrors[$serverIndex] = $exception;
 779         }
 780
 781         /**
 782          * Create shard tables. For use from eval.php.
 783          */
 784         public function createTables() {
 785                 for ( $serverIndex = 0; $serverIndex < $this->numServers; $serverIndex++ ) {
 786                         $db = $this->getDB( $serverIndex );
 787                         if ( $db->getType() !== 'mysql' ) {
 788                                 throw new MWException( __METHOD__ . ' is not supported on this DB server' );
 789                         }
 790
 791                         for ( $i = 0; $i < $this->shards; $i++ ) {
 792                                 $db->query(
 793                                         'CREATE TABLE ' . $db->tableName( $this->getTableNameByShard( $i ) ) .
 794                                         ' LIKE ' . $db->tableName( 'objectcache' ),
 795                                         __METHOD__ );
 796                         }
 797                 }
 798         }
 799 }