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 array */
  31         protected $serverInfos;
  32         /** @var array */
  33         protected $serverNames;
  34         /** @var int */
  35         protected $numServers;
  36         /** @var int */
  37         protected $lastExpireAll = 0;
  38         /** @var int */
  39         protected $purgePeriod = 100;
  40         /** @var int */
  41         protected $shards = 1;
  42         /** @var string */
  43         protected $tableName = 'objectcache';
  44         /** @var bool */
  45         protected $slaveOnly = false;
  46         /** @var int */
  47         protected $syncTimeout = 3;
  48
  49         /** @var array */
  50         protected $conns;
  51         /** @var array UNIX timestamps */
  52         protected $connFailureTimes = [];
  53         /** @var array Exceptions */
  54         protected $connFailureErrors = [];
  55
  56         /**
  57          * Constructor. Parameters are:
  58          *   - server:      A server info structure in the format required by each
  59          *                  element in $wgDBServers.
  60          *
  61          *   - servers:     An array of server info structures describing a set of
  62          *                  database servers to distribute keys to. If this is
  63          *                  specified, the "server" option will be ignored.
  64          *
  65          *   - purgePeriod: The average number of object cache requests in between
  66          *                  garbage collection operations, where expired entries
  67          *                  are removed from the database. Or in other words, the
  68          *                  reciprocal of the probability of purging on any given
  69          *                  request. If this is set to zero, purging will never be
  70          *                  done.
  71          *
  72          *   - tableName:   The table name to use, default is "objectcache".
  73          *
  74          *   - shards:      The number of tables to use for data storage on each server.
  75          *                  If this is more than 1, table names will be formed in the style
  76          *                  objectcacheNNN where NNN is the shard index, between 0 and
  77          *                  shards-1. The number of digits will be the minimum number
  78          *                  required to hold the largest shard index. Data will be
  79          *                  distributed across all tables by key hash. This is for
  80          *                  MySQL bugs 61735 and 61736.
  81          *   - slaveOnly:   Whether to only use slave DBs and avoid triggering
  82          *                  garbage collection logic of expired items. This only
  83          *                  makes sense if the primary DB is used and only if get()
  84          *                  calls will be used. This is used by ReplicatedBagOStuff.
  85          *   - syncTimeout: Max seconds to wait for slaves to catch up for WRITE_SYNC.
  86          *
  87          * @param array $params
  88          */
  89         public function __construct( $params ) {
  90                 parent::__construct( $params );
  91                 if ( isset( $params['servers'] ) ) {
  92                         $this->serverInfos = $params['servers'];
  93                         $this->numServers = count( $this->serverInfos );
  94                         $this->serverNames = [];
  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 = [ $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                 if ( isset( $params['syncTimeout'] ) ) {
 115                         $this->syncTimeout = $params['syncTimeout'];
 116                 }
 117                 $this->slaveOnly = !empty( $params['slaveOnly'] );
 118         }
 119
 120         /**
 121          * Get a connection to the specified database
 122          *
 123          * @param int $serverIndex
 124          * @return IDatabase
 125          * @throws MWException
 126          */
 127         protected function getDB( $serverIndex ) {
 128                 if ( !isset( $this->conns[$serverIndex] ) ) {
 129                         if ( $serverIndex >= $this->numServers ) {
 130                                 throw new MWException( __METHOD__ . ": Invalid server index \"$serverIndex\"" );
 131                         }
 132
 133                         # Don't keep timing out trying to connect for each call if the DB is down
 134                         if ( isset( $this->connFailureErrors[$serverIndex] )
 135                                 && ( time() - $this->connFailureTimes[$serverIndex] ) < 60
 136                         ) {
 137                                 throw $this->connFailureErrors[$serverIndex];
 138                         }
 139
 140                         # If server connection info was given, use that
 141                         if ( $this->serverInfos ) {
 142                                 $info = $this->serverInfos[$serverIndex];
 143                                 $type = isset( $info['type'] ) ? $info['type'] : 'mysql';
 144                                 $host = isset( $info['host'] ) ? $info['host'] : '[unknown]';
 145                                 $this->logger->debug( __CLASS__ . ": connecting to $host" );
 146                                 // Use a blank trx profiler to ignore expections as this is a cache
 147                                 $info['trxProfiler'] = new TransactionProfiler();
 148                                 $db = DatabaseBase::factory( $type, $info );
 149                                 $db->clearFlag( DBO_TRX );
 150                         } else {
 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 not (@TODO: find some work-around).
 154                                 $index = $this->slaveOnly ? DB_SLAVE : DB_MASTER;
 155                                 if ( wfGetDB( $index )->getType() == 'mysql' ) {
 156                                         $lb = wfGetLBFactory()->newMainLB();
 157                                         $db = $lb->getConnection( $index );
 158                                         $db->clearFlag( DBO_TRX ); // auto-commit mode
 159                                 } else {
 160                                         $db = wfGetDB( $index );
 161                                 }
 162                         }
 163                         $this->logger->debug( sprintf( "Connection %s will be used for SqlBagOStuff", $db ) );
 164                         $this->conns[$serverIndex] = $db;
 165                 }
 166
 167                 return $this->conns[$serverIndex];
 168         }
 169
 170         /**
 171          * Get the server index and table name for a given key
 172          * @param string $key
 173          * @return array Server index and table name
 174          */
 175         protected function getTableByKey( $key ) {
 176                 if ( $this->shards > 1 ) {
 177                         $hash = hexdec( substr( md5( $key ), 0, 8 ) ) & 0x7fffffff;
 178                         $tableIndex = $hash % $this->shards;
 179                 } else {
 180                         $tableIndex = 0;
 181                 }
 182                 if ( $this->numServers > 1 ) {
 183                         $sortedServers = $this->serverNames;
 184                         ArrayUtils::consistentHashSort( $sortedServers, $key );
 185                         reset( $sortedServers );
 186                         $serverIndex = key( $sortedServers );
 187                 } else {
 188                         $serverIndex = 0;
 189                 }
 190                 return [ $serverIndex, $this->getTableNameByShard( $tableIndex ) ];
 191         }
 192
 193         /**
 194          * Get the table name for a given shard index
 195          * @param int $index
 196          * @return string
 197          */
 198         protected function getTableNameByShard( $index ) {
 199                 if ( $this->shards > 1 ) {
 200                         $decimals = strlen( $this->shards - 1 );
 201                         return $this->tableName .
 202                                 sprintf( "%0{$decimals}d", $index );
 203                 } else {
 204                         return $this->tableName;
 205                 }
 206         }
 207
 208         protected function doGet( $key, $flags = 0 ) {
 209                 $casToken = null;
 210
 211                 return $this->getWithToken( $key, $casToken, $flags );
 212         }
 213
 214         protected function getWithToken( $key, &$casToken, $flags = 0 ) {
 215                 $values = $this->getMulti( [ $key ] );
 216                 if ( array_key_exists( $key, $values ) ) {
 217                         $casToken = $values[$key];
 218                         return $values[$key];
 219                 }
 220                 return false;
 221         }
 222
 223         public function getMulti( array $keys, $flags = 0 ) {
 224                 $values = []; // array of (key => value)
 225
 226                 $keysByTable = [];
 227                 foreach ( $keys as $key ) {
 228                         list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
 229                         $keysByTable[$serverIndex][$tableName][] = $key;
 230                 }
 231
 232                 $this->garbageCollect(); // expire old entries if any
 233
 234                 $dataRows = [];
 235                 foreach ( $keysByTable as $serverIndex => $serverKeys ) {
 236                         try {
 237                                 $db = $this->getDB( $serverIndex );
 238                                 foreach ( $serverKeys as $tableName => $tableKeys ) {
 239                                         $res = $db->select( $tableName,
 240                                                 [ 'keyname', 'value', 'exptime' ],
 241                                                 [ 'keyname' => $tableKeys ],
 242                                                 __METHOD__,
 243                                                 // Approximate write-on-the-fly BagOStuff API via blocking.
 244                                                 // This approximation fails if a ROLLBACK happens (which is rare).
 245                                                 // We do not want to flush the TRX as that can break callers.
 246                                                 $db->trxLevel() ? [ 'LOCK IN SHARE MODE' ] : []
 247                                         );
 248                                         if ( $res === false ) {
 249                                                 continue;
 250                                         }
 251                                         foreach ( $res as $row ) {
 252                                                 $row->serverIndex = $serverIndex;
 253                                                 $row->tableName = $tableName;
 254                                                 $dataRows[$row->keyname] = $row;
 255                                         }
 256                                 }
 257                         } catch ( DBError $e ) {
 258                                 $this->handleReadError( $e, $serverIndex );
 259                         }
 260                 }
 261
 262                 foreach ( $keys as $key ) {
 263                         if ( isset( $dataRows[$key] ) ) { // HIT?
 264                                 $row = $dataRows[$key];
 265                                 $this->debug( "get: retrieved data; expiry time is " . $row->exptime );
 266                                 try {
 267                                         $db = $this->getDB( $row->serverIndex );
 268                                         if ( $this->isExpired( $db, $row->exptime ) ) { // MISS
 269                                                 $this->debug( "get: key has expired" );
 270                                         } else { // HIT
 271                                                 $values[$key] = $this->unserialize( $db->decodeBlob( $row->value ) );
 272                                         }
 273                                 } catch ( DBQueryError $e ) {
 274                                         $this->handleWriteError( $e, $row->serverIndex );
 275                                 }
 276                         } else { // MISS
 277                                 $this->debug( 'get: no matching rows' );
 278                         }
 279                 }
 280
 281                 return $values;
 282         }
 283
 284         public function setMulti( array $data, $expiry = 0 ) {
 285                 $keysByTable = [];
 286                 foreach ( $data as $key => $value ) {
 287                         list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
 288                         $keysByTable[$serverIndex][$tableName][] = $key;
 289                 }
 290
 291                 $this->garbageCollect(); // expire old entries if any
 292
 293                 $result = true;
 294                 $exptime = (int)$expiry;
 295                 foreach ( $keysByTable as $serverIndex => $serverKeys ) {
 296                         try {
 297                                 $db = $this->getDB( $serverIndex );
 298                         } catch ( DBError $e ) {
 299                                 $this->handleWriteError( $e, $serverIndex );
 300                                 $result = false;
 301                                 continue;
 302                         }
 303
 304                         if ( $exptime < 0 ) {
 305                                 $exptime = 0;
 306                         }
 307
 308                         if ( $exptime == 0 ) {
 309                                 $encExpiry = $this->getMaxDateTime( $db );
 310                         } else {
 311                                 $exptime = $this->convertExpiry( $exptime );
 312                                 $encExpiry = $db->timestamp( $exptime );
 313                         }
 314                         foreach ( $serverKeys as $tableName => $tableKeys ) {
 315                                 $rows = [];
 316                                 foreach ( $tableKeys as $key ) {
 317                                         $rows[] = [
 318                                                 'keyname' => $key,
 319                                                 'value' => $db->encodeBlob( $this->serialize( $data[$key] ) ),
 320                                                 'exptime' => $encExpiry,
 321                                         ];
 322                                 }
 323
 324                                 try {
 325                                         $db->replace(
 326                                                 $tableName,
 327                                                 [ 'keyname' ],
 328                                                 $rows,
 329                                                 __METHOD__
 330                                         );
 331                                 } catch ( DBError $e ) {
 332                                         $this->handleWriteError( $e, $serverIndex );
 333                                         $result = false;
 334                                 }
 335
 336                         }
 337
 338                 }
 339
 340                 return $result;
 341         }
 342
 343         public function set( $key, $value, $exptime = 0, $flags = 0 ) {
 344                 $ok = $this->setMulti( [ $key => $value ], $exptime );
 345                 if ( ( $flags & self::WRITE_SYNC ) == self::WRITE_SYNC ) {
 346                         $ok = $ok && $this->waitForSlaves();
 347                 }
 348
 349                 return $ok;
 350         }
 351
 352         protected function cas( $casToken, $key, $value, $exptime = 0 ) {
 353                 list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
 354                 try {
 355                         $db = $this->getDB( $serverIndex );
 356                         $exptime = intval( $exptime );
 357
 358                         if ( $exptime < 0 ) {
 359                                 $exptime = 0;
 360                         }
 361
 362                         if ( $exptime == 0 ) {
 363                                 $encExpiry = $this->getMaxDateTime( $db );
 364                         } else {
 365                                 $exptime = $this->convertExpiry( $exptime );
 366                                 $encExpiry = $db->timestamp( $exptime );
 367                         }
 368                         // (bug 24425) use a replace if the db supports it instead of
 369                         // delete/insert to avoid clashes with conflicting keynames
 370                         $db->update(
 371                                 $tableName,
 372                                 [
 373                                         'keyname' => $key,
 374                                         'value' => $db->encodeBlob( $this->serialize( $value ) ),
 375                                         'exptime' => $encExpiry
 376                                 ],
 377                                 [
 378                                         'keyname' => $key,
 379                                         'value' => $db->encodeBlob( $this->serialize( $casToken ) )
 380                                 ],
 381                                 __METHOD__
 382                         );
 383                 } catch ( DBQueryError $e ) {
 384                         $this->handleWriteError( $e, $serverIndex );
 385
 386                         return false;
 387                 }
 388
 389                 return (bool)$db->affectedRows();
 390         }
 391
 392         public function delete( $key ) {
 393                 list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
 394                 try {
 395                         $db = $this->getDB( $serverIndex );
 396                         $db->delete(
 397                                 $tableName,
 398                                 [ 'keyname' => $key ],
 399                                 __METHOD__ );
 400                 } catch ( DBError $e ) {
 401                         $this->handleWriteError( $e, $serverIndex );
 402                         return false;
 403                 }
 404
 405                 return true;
 406         }
 407
 408         public function incr( $key, $step = 1 ) {
 409                 list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
 410                 try {
 411                         $db = $this->getDB( $serverIndex );
 412                         $step = intval( $step );
 413                         $row = $db->selectRow(
 414                                 $tableName,
 415                                 [ 'value', 'exptime' ],
 416                                 [ 'keyname' => $key ],
 417                                 __METHOD__,
 418                                 [ 'FOR UPDATE' ] );
 419                         if ( $row === false ) {
 420                                 // Missing
 421
 422                                 return null;
 423                         }
 424                         $db->delete( $tableName, [ 'keyname' => $key ], __METHOD__ );
 425                         if ( $this->isExpired( $db, $row->exptime ) ) {
 426                                 // Expired, do not reinsert
 427
 428                                 return null;
 429                         }
 430
 431                         $oldValue = intval( $this->unserialize( $db->decodeBlob( $row->value ) ) );
 432                         $newValue = $oldValue + $step;
 433                         $db->insert( $tableName,
 434                                 [
 435                                         'keyname' => $key,
 436                                         'value' => $db->encodeBlob( $this->serialize( $newValue ) ),
 437                                         'exptime' => $row->exptime
 438                                 ], __METHOD__, 'IGNORE' );
 439
 440                         if ( $db->affectedRows() == 0 ) {
 441                                 // Race condition. See bug 28611
 442                                 $newValue = null;
 443                         }
 444                 } catch ( DBError $e ) {
 445                         $this->handleWriteError( $e, $serverIndex );
 446                         return null;
 447                 }
 448
 449                 return $newValue;
 450         }
 451
 452         public function merge( $key, $callback, $exptime = 0, $attempts = 10, $flags = 0 ) {
 453                 if ( !is_callable( $callback ) ) {
 454                         throw new Exception( "Got invalid callback." );
 455                 }
 456
 457                 $ok = $this->mergeViaCas( $key, $callback, $exptime, $attempts );
 458                 if ( ( $flags & self::WRITE_SYNC ) == self::WRITE_SYNC ) {
 459                         $ok = $ok && $this->waitForSlaves();
 460                 }
 461
 462                 return $ok;
 463         }
 464
 465         /**
 466          * @param IDatabase $db
 467          * @param string $exptime
 468          * @return bool
 469          */
 470         protected function isExpired( $db, $exptime ) {
 471                 return $exptime != $this->getMaxDateTime( $db ) && wfTimestamp( TS_UNIX, $exptime ) < time();
 472         }
 473
 474         /**
 475          * @param IDatabase $db
 476          * @return string
 477          */
 478         protected function getMaxDateTime( $db ) {
 479                 if ( time() > 0x7fffffff ) {
 480                         return $db->timestamp( 1 << 62 );
 481                 } else {
 482                         return $db->timestamp( 0x7fffffff );
 483                 }
 484         }
 485
 486         protected function garbageCollect() {
 487                 if ( !$this->purgePeriod || $this->slaveOnly ) {
 488                         // Disabled
 489                         return;
 490                 }
 491                 // Only purge on one in every $this->purgePeriod requests.
 492                 if ( $this->purgePeriod !== 1 && mt_rand( 0, $this->purgePeriod - 1 ) ) {
 493                         return;
 494                 }
 495                 $now = time();
 496                 // Avoid repeating the delete within a few seconds
 497                 if ( $now > ( $this->lastExpireAll + 1 ) ) {
 498                         $this->lastExpireAll = $now;
 499                         $this->expireAll();
 500                 }
 501         }
 502
 503         public function expireAll() {
 504                 $this->deleteObjectsExpiringBefore( wfTimestampNow() );
 505         }
 506
 507         /**
 508          * Delete objects from the database which expire before a certain date.
 509          * @param string $timestamp
 510          * @param bool|callable $progressCallback
 511          * @return bool
 512          */
 513         public function deleteObjectsExpiringBefore( $timestamp, $progressCallback = false ) {
 514                 for ( $serverIndex = 0; $serverIndex < $this->numServers; $serverIndex++ ) {
 515                         try {
 516                                 $db = $this->getDB( $serverIndex );
 517                                 $dbTimestamp = $db->timestamp( $timestamp );
 518                                 $totalSeconds = false;
 519                                 $baseConds = [ 'exptime < ' . $db->addQuotes( $dbTimestamp ) ];
 520                                 for ( $i = 0; $i < $this->shards; $i++ ) {
 521                                         $maxExpTime = false;
 522                                         while ( true ) {
 523                                                 $conds = $baseConds;
 524                                                 if ( $maxExpTime !== false ) {
 525                                                         $conds[] = 'exptime > ' . $db->addQuotes( $maxExpTime );
 526                                                 }
 527                                                 $rows = $db->select(
 528                                                         $this->getTableNameByShard( $i ),
 529                                                         [ 'keyname', 'exptime' ],
 530                                                         $conds,
 531                                                         __METHOD__,
 532                                                         [ 'LIMIT' => 100, 'ORDER BY' => 'exptime' ] );
 533                                                 if ( $rows === false || !$rows->numRows() ) {
 534                                                         break;
 535                                                 }
 536                                                 $keys = [];
 537                                                 $row = $rows->current();
 538                                                 $minExpTime = $row->exptime;
 539                                                 if ( $totalSeconds === false ) {
 540                                                         $totalSeconds = wfTimestamp( TS_UNIX, $timestamp )
 541                                                                 - wfTimestamp( TS_UNIX, $minExpTime );
 542                                                 }
 543                                                 foreach ( $rows as $row ) {
 544                                                         $keys[] = $row->keyname;
 545                                                         $maxExpTime = $row->exptime;
 546                                                 }
 547
 548                                                 $db->delete(
 549                                                         $this->getTableNameByShard( $i ),
 550                                                         [
 551                                                                 'exptime >= ' . $db->addQuotes( $minExpTime ),
 552                                                                 'exptime < ' . $db->addQuotes( $dbTimestamp ),
 553                                                                 'keyname' => $keys
 554                                                         ],
 555                                                         __METHOD__ );
 556
 557                                                 if ( $progressCallback ) {
 558                                                         if ( intval( $totalSeconds ) === 0 ) {
 559                                                                 $percent = 0;
 560                                                         } else {
 561                                                                 $remainingSeconds = wfTimestamp( TS_UNIX, $timestamp )
 562                                                                         - wfTimestamp( TS_UNIX, $maxExpTime );
 563                                                                 if ( $remainingSeconds > $totalSeconds ) {
 564                                                                         $totalSeconds = $remainingSeconds;
 565                                                                 }
 566                                                                 $processedSeconds = $totalSeconds - $remainingSeconds;
 567                                                                 $percent = ( $i + $processedSeconds / $totalSeconds )
 568                                                                         / $this->shards * 100;
 569                                                         }
 570                                                         $percent = ( $percent / $this->numServers )
 571                                                                 + ( $serverIndex / $this->numServers * 100 );
 572                                                         call_user_func( $progressCallback, $percent );
 573                                                 }
 574                                         }
 575                                 }
 576                         } catch ( DBError $e ) {
 577                                 $this->handleWriteError( $e, $serverIndex );
 578                                 return false;
 579                         }
 580                 }
 581                 return true;
 582         }
 583
 584         /**
 585          * Delete content of shard tables in every server.
 586          * Return true if the operation is successful, false otherwise.
 587          * @return bool
 588          */
 589         public function deleteAll() {
 590                 for ( $serverIndex = 0; $serverIndex < $this->numServers; $serverIndex++ ) {
 591                         try {
 592                                 $db = $this->getDB( $serverIndex );
 593                                 for ( $i = 0; $i < $this->shards; $i++ ) {
 594                                         $db->delete( $this->getTableNameByShard( $i ), '*', __METHOD__ );
 595                                 }
 596                         } catch ( DBError $e ) {
 597                                 $this->handleWriteError( $e, $serverIndex );
 598                                 return false;
 599                         }
 600                 }
 601                 return true;
 602         }
 603
 604         /**
 605          * Serialize an object and, if possible, compress the representation.
 606          * On typical message and page data, this can provide a 3X decrease
 607          * in storage requirements.
 608          *
 609          * @param mixed $data
 610          * @return string
 611          */
 612         protected function serialize( &$data ) {
 613                 $serial = serialize( $data );
 614
 615                 if ( function_exists( 'gzdeflate' ) ) {
 616                         return gzdeflate( $serial );
 617                 } else {
 618                         return $serial;
 619                 }
 620         }
 621
 622         /**
 623          * Unserialize and, if necessary, decompress an object.
 624          * @param string $serial
 625          * @return mixed
 626          */
 627         protected function unserialize( $serial ) {
 628                 if ( function_exists( 'gzinflate' ) ) {
 629                         MediaWiki\suppressWarnings();
 630                         $decomp = gzinflate( $serial );
 631                         MediaWiki\restoreWarnings();
 632
 633                         if ( false !== $decomp ) {
 634                                 $serial = $decomp;
 635                         }
 636                 }
 637
 638                 $ret = unserialize( $serial );
 639
 640                 return $ret;
 641         }
 642
 643         /**
 644          * Handle a DBError which occurred during a read operation.
 645          *
 646          * @param DBError $exception
 647          * @param int $serverIndex
 648          */
 649         protected function handleReadError( DBError $exception, $serverIndex ) {
 650                 if ( $exception instanceof DBConnectionError ) {
 651                         $this->markServerDown( $exception, $serverIndex );
 652                 }
 653                 $this->logger->error( "DBError: {$exception->getMessage()}" );
 654                 if ( $exception instanceof DBConnectionError ) {
 655                         $this->setLastError( BagOStuff::ERR_UNREACHABLE );
 656                         $this->logger->debug( __METHOD__ . ": ignoring connection error" );
 657                 } else {
 658                         $this->setLastError( BagOStuff::ERR_UNEXPECTED );
 659                         $this->logger->debug( __METHOD__ . ": ignoring query error" );
 660                 }
 661         }
 662
 663         /**
 664          * Handle a DBQueryError which occurred during a write operation.
 665          *
 666          * @param DBError $exception
 667          * @param int $serverIndex
 668          */
 669         protected function handleWriteError( DBError $exception, $serverIndex ) {
 670                 if ( $exception instanceof DBConnectionError ) {
 671                         $this->markServerDown( $exception, $serverIndex );
 672                 }
 673                 if ( $exception->db && $exception->db->wasReadOnlyError() ) {
 674                         if ( $exception->db->trxLevel() ) {
 675                                 try {
 676                                         $exception->db->rollback( __METHOD__ );
 677                                 } catch ( DBError $e ) {
 678                                 }
 679                         }
 680                 }
 681
 682                 $this->logger->error( "DBError: {$exception->getMessage()}" );
 683                 if ( $exception instanceof DBConnectionError ) {
 684                         $this->setLastError( BagOStuff::ERR_UNREACHABLE );
 685                         $this->logger->debug( __METHOD__ . ": ignoring connection error" );
 686                 } else {
 687                         $this->setLastError( BagOStuff::ERR_UNEXPECTED );
 688                         $this->logger->debug( __METHOD__ . ": ignoring query error" );
 689                 }
 690         }
 691
 692         /**
 693          * Mark a server down due to a DBConnectionError exception
 694          *
 695          * @param DBError $exception
 696          * @param int $serverIndex
 697          */
 698         protected function markServerDown( $exception, $serverIndex ) {
 699                 unset( $this->conns[$serverIndex] ); // bug T103435
 700
 701                 if ( isset( $this->connFailureTimes[$serverIndex] ) ) {
 702                         if ( time() - $this->connFailureTimes[$serverIndex] >= 60 ) {
 703                                 unset( $this->connFailureTimes[$serverIndex] );
 704                                 unset( $this->connFailureErrors[$serverIndex] );
 705                         } else {
 706                                 $this->logger->debug( __METHOD__ . ": Server #$serverIndex already down" );
 707                                 return;
 708                         }
 709                 }
 710                 $now = time();
 711                 $this->logger->info( __METHOD__ . ": Server #$serverIndex down until " . ( $now + 60 ) );
 712                 $this->connFailureTimes[$serverIndex] = $now;
 713                 $this->connFailureErrors[$serverIndex] = $exception;
 714         }
 715
 716         /**
 717          * Create shard tables. For use from eval.php.
 718          */
 719         public function createTables() {
 720                 for ( $serverIndex = 0; $serverIndex < $this->numServers; $serverIndex++ ) {
 721                         $db = $this->getDB( $serverIndex );
 722                         if ( $db->getType() !== 'mysql' ) {
 723                                 throw new MWException( __METHOD__ . ' is not supported on this DB server' );
 724                         }
 725
 726                         for ( $i = 0; $i < $this->shards; $i++ ) {
 727                                 $db->query(
 728                                         'CREATE TABLE ' . $db->tableName( $this->getTableNameByShard( $i ) ) .
 729                                         ' LIKE ' . $db->tableName( 'objectcache' ),
 730                                         __METHOD__ );
 731                         }
 732                 }
 733         }
 734
 735         protected function waitForSlaves() {
 736                 if ( !$this->serverInfos ) {
 737                         // Main LB is used; wait for any slaves to catch up
 738                         try {
 739                                 wfGetLBFactory()->waitForReplication( [ 'wiki' => wfWikiID() ] );
 740                                 return true;
 741                         } catch ( DBReplicationWaitError $e ) {
 742                                 return false;
 743                         }
 744                 } else {
 745                         // Custom DB server list; probably doesn't use replication
 746                         return true;
 747                 }
 748         }
 749 }