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 use \MediaWiki\MediaWikiServices;
  25 use \Wikimedia\WaitConditionLoop;
  26
  27 /**
  28  * Class to store objects in the database
  29  *
  30  * @ingroup Cache
  31  */
  32 class SqlBagOStuff extends BagOStuff {
  33         /** @var array[] (server index => server config) */
  34         protected $serverInfos;
  35         /** @var string[] (server index => tag/host name) */
  36         protected $serverTags;
  37         /** @var int */
  38         protected $numServers;
  39         /** @var int */
  40         protected $lastExpireAll = 0;
  41         /** @var int */
  42         protected $purgePeriod = 100;
  43         /** @var int */
  44         protected $shards = 1;
  45         /** @var string */
  46         protected $tableName = 'objectcache';
  47         /** @var bool */
  48         protected $replicaOnly = false;
  49         /** @var int */
  50         protected $syncTimeout = 3;
  51
  52         /** @var LoadBalancer|null */
  53         protected $separateMainLB;
  54         /** @var array */
  55         protected $conns;
  56         /** @var array UNIX timestamps */
  57         protected $connFailureTimes = [];
  58         /** @var array Exceptions */
  59         protected $connFailureErrors = [];
  60
  61         /**
  62          * Constructor. Parameters are:
  63          *   - server:      A server info structure in the format required by each
  64          *                  element in $wgDBServers.
  65          *
  66          *   - servers:     An array of server info structures describing a set of database servers
  67          *                  to distribute keys to. If this is specified, the "server" option will be
  68          *                  ignored. If string keys are used, then they will be used for consistent
  69          *                  hashing *instead* of the host name (from the server config). This is useful
  70          *                  when a cluster is replicated to another site (with different host names)
  71          *                  but each server has a corresponding replica in the other cluster.
  72          *
  73          *   - purgePeriod: The average number of object cache requests in between
  74          *                  garbage collection operations, where expired entries
  75          *                  are removed from the database. Or in other words, the
  76          *                  reciprocal of the probability of purging on any given
  77          *                  request. If this is set to zero, purging will never be
  78          *                  done.
  79          *
  80          *   - tableName:   The table name to use, default is "objectcache".
  81          *
  82          *   - shards:      The number of tables to use for data storage on each server.
  83          *                  If this is more than 1, table names will be formed in the style
  84          *                  objectcacheNNN where NNN is the shard index, between 0 and
  85          *                  shards-1. The number of digits will be the minimum number
  86          *                  required to hold the largest shard index. Data will be
  87          *                  distributed across all tables by key hash. This is for
  88          *                  MySQL bugs 61735 and 61736.
  89          *   - slaveOnly:   Whether to only use replica DBs and avoid triggering
  90          *                  garbage collection logic of expired items. This only
  91          *                  makes sense if the primary DB is used and only if get()
  92          *                  calls will be used. This is used by ReplicatedBagOStuff.
  93          *   - syncTimeout: Max seconds to wait for replica DBs to catch up for WRITE_SYNC.
  94          *
  95          * @param array $params
  96          */
  97         public function __construct( $params ) {
  98                 parent::__construct( $params );
  99
 100                 $this->attrMap[self::ATTR_EMULATION] = self::QOS_EMULATION_SQL;
 101                 $this->attrMap[self::ATTR_SYNCWRITES] = self::QOS_SYNCWRITES_NONE;
 102
 103                 if ( isset( $params['servers'] ) ) {
 104                         $this->serverInfos = [];
 105                         $this->serverTags = [];
 106                         $this->numServers = count( $params['servers'] );
 107                         $index = 0;
 108                         foreach ( $params['servers'] as $tag => $info ) {
 109                                 $this->serverInfos[$index] = $info;
 110                                 if ( is_string( $tag ) ) {
 111                                         $this->serverTags[$index] = $tag;
 112                                 } else {
 113                                         $this->serverTags[$index] = isset( $info['host'] ) ? $info['host'] : "#$index";
 114                                 }
 115                                 ++$index;
 116                         }
 117                 } elseif ( isset( $params['server'] ) ) {
 118                         $this->serverInfos = [ $params['server'] ];
 119                         $this->numServers = count( $this->serverInfos );
 120                 } else {
 121                         // Default to using the main wiki's database servers
 122                         $this->serverInfos = false;
 123                         $this->numServers = 1;
 124                         $this->attrMap[self::ATTR_SYNCWRITES] = self::QOS_SYNCWRITES_BE;
 125                 }
 126                 if ( isset( $params['purgePeriod'] ) ) {
 127                         $this->purgePeriod = intval( $params['purgePeriod'] );
 128                 }
 129                 if ( isset( $params['tableName'] ) ) {
 130                         $this->tableName = $params['tableName'];
 131                 }
 132                 if ( isset( $params['shards'] ) ) {
 133                         $this->shards = intval( $params['shards'] );
 134                 }
 135                 if ( isset( $params['syncTimeout'] ) ) {
 136                         $this->syncTimeout = $params['syncTimeout'];
 137                 }
 138                 $this->replicaOnly = !empty( $params['slaveOnly'] );
 139         }
 140
 141         protected function getSeparateMainLB() {
 142                 global $wgDBtype;
 143
 144                 if ( $wgDBtype === 'mysql' && $this->usesMainDB() ) {
 145                         if ( !$this->separateMainLB ) {
 146                                 // We must keep a separate connection to MySQL in order to avoid deadlocks
 147                                 $lbFactory = MediaWikiServices::getInstance()->getDBLoadBalancerFactory();
 148                                 $this->separateMainLB = $lbFactory->newMainLB();
 149                         }
 150                         return $this->separateMainLB;
 151                 } else {
 152                         // However, SQLite has an opposite behavior. And PostgreSQL needs to know
 153                         // if we are in transaction or not (@TODO: find some PostgreSQL work-around).
 154                         return null;
 155                 }
 156         }
 157
 158         /**
 159          * Get a connection to the specified database
 160          *
 161          * @param int $serverIndex
 162          * @return IDatabase
 163          * @throws MWException
 164          */
 165         protected function getDB( $serverIndex ) {
 166                 if ( !isset( $this->conns[$serverIndex] ) ) {
 167                         if ( $serverIndex >= $this->numServers ) {
 168                                 throw new MWException( __METHOD__ . ": Invalid server index \"$serverIndex\"" );
 169                         }
 170
 171                         # Don't keep timing out trying to connect for each call if the DB is down
 172                         if ( isset( $this->connFailureErrors[$serverIndex] )
 173                                 && ( time() - $this->connFailureTimes[$serverIndex] ) < 60
 174                         ) {
 175                                 throw $this->connFailureErrors[$serverIndex];
 176                         }
 177
 178                         # If server connection info was given, use that
 179                         if ( $this->serverInfos ) {
 180                                 $info = $this->serverInfos[$serverIndex];
 181                                 $type = isset( $info['type'] ) ? $info['type'] : 'mysql';
 182                                 $host = isset( $info['host'] ) ? $info['host'] : '[unknown]';
 183                                 $this->logger->debug( __CLASS__ . ": connecting to $host" );
 184                                 // Use a blank trx profiler to ignore expections as this is a cache
 185                                 $info['trxProfiler'] = new TransactionProfiler();
 186                                 $db = Database::factory( $type, $info );
 187                                 $db->clearFlag( DBO_TRX );
 188                         } else {
 189                                 $index = $this->replicaOnly ? DB_REPLICA : DB_MASTER;
 190                                 if ( $this->getSeparateMainLB() ) {
 191                                         $db = $this->getSeparateMainLB()->getConnection( $index );
 192                                         $db->clearFlag( DBO_TRX ); // auto-commit mode
 193                                 } else {
 194                                         $db = wfGetDB( $index );
 195                                         // Can't mess with transaction rounds (DBO_TRX) :(
 196                                 }
 197                         }
 198                         $this->logger->debug( sprintf( "Connection %s will be used for SqlBagOStuff", $db ) );
 199                         $this->conns[$serverIndex] = $db;
 200                 }
 201
 202                 return $this->conns[$serverIndex];
 203         }
 204
 205         /**
 206          * Get the server index and table name for a given key
 207          * @param string $key
 208          * @return array Server index and table name
 209          */
 210         protected function getTableByKey( $key ) {
 211                 if ( $this->shards > 1 ) {
 212                         $hash = hexdec( substr( md5( $key ), 0, 8 ) ) & 0x7fffffff;
 213                         $tableIndex = $hash % $this->shards;
 214                 } else {
 215                         $tableIndex = 0;
 216                 }
 217                 if ( $this->numServers > 1 ) {
 218                         $sortedServers = $this->serverTags;
 219                         ArrayUtils::consistentHashSort( $sortedServers, $key );
 220                         reset( $sortedServers );
 221                         $serverIndex = key( $sortedServers );
 222                 } else {
 223                         $serverIndex = 0;
 224                 }
 225                 return [ $serverIndex, $this->getTableNameByShard( $tableIndex ) ];
 226         }
 227
 228         /**
 229          * Get the table name for a given shard index
 230          * @param int $index
 231          * @return string
 232          */
 233         protected function getTableNameByShard( $index ) {
 234                 if ( $this->shards > 1 ) {
 235                         $decimals = strlen( $this->shards - 1 );
 236                         return $this->tableName .
 237                                 sprintf( "%0{$decimals}d", $index );
 238                 } else {
 239                         return $this->tableName;
 240                 }
 241         }
 242
 243         protected function doGet( $key, $flags = 0 ) {
 244                 $casToken = null;
 245
 246                 return $this->getWithToken( $key, $casToken, $flags );
 247         }
 248
 249         protected function getWithToken( $key, &$casToken, $flags = 0 ) {
 250                 $values = $this->getMulti( [ $key ] );
 251                 if ( array_key_exists( $key, $values ) ) {
 252                         $casToken = $values[$key];
 253                         return $values[$key];
 254                 }
 255                 return false;
 256         }
 257
 258         public function getMulti( array $keys, $flags = 0 ) {
 259                 $values = []; // array of (key => value)
 260
 261                 $keysByTable = [];
 262                 foreach ( $keys as $key ) {
 263                         list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
 264                         $keysByTable[$serverIndex][$tableName][] = $key;
 265                 }
 266
 267                 $this->garbageCollect(); // expire old entries if any
 268
 269                 $dataRows = [];
 270                 foreach ( $keysByTable as $serverIndex => $serverKeys ) {
 271                         try {
 272                                 $db = $this->getDB( $serverIndex );
 273                                 foreach ( $serverKeys as $tableName => $tableKeys ) {
 274                                         $res = $db->select( $tableName,
 275                                                 [ 'keyname', 'value', 'exptime' ],
 276                                                 [ 'keyname' => $tableKeys ],
 277                                                 __METHOD__,
 278                                                 // Approximate write-on-the-fly BagOStuff API via blocking.
 279                                                 // This approximation fails if a ROLLBACK happens (which is rare).
 280                                                 // We do not want to flush the TRX as that can break callers.
 281                                                 $db->trxLevel() ? [ 'LOCK IN SHARE MODE' ] : []
 282                                         );
 283                                         if ( $res === false ) {
 284                                                 continue;
 285                                         }
 286                                         foreach ( $res as $row ) {
 287                                                 $row->serverIndex = $serverIndex;
 288                                                 $row->tableName = $tableName;
 289                                                 $dataRows[$row->keyname] = $row;
 290                                         }
 291                                 }
 292                         } catch ( DBError $e ) {
 293                                 $this->handleReadError( $e, $serverIndex );
 294                         }
 295                 }
 296
 297                 foreach ( $keys as $key ) {
 298                         if ( isset( $dataRows[$key] ) ) { // HIT?
 299                                 $row = $dataRows[$key];
 300                                 $this->debug( "get: retrieved data; expiry time is " . $row->exptime );
 301                                 $db = null;
 302                                 try {
 303                                         $db = $this->getDB( $row->serverIndex );
 304                                         if ( $this->isExpired( $db, $row->exptime ) ) { // MISS
 305                                                 $this->debug( "get: key has expired" );
 306                                         } else { // HIT
 307                                                 $values[$key] = $this->unserialize( $db->decodeBlob( $row->value ) );
 308                                         }
 309                                 } catch ( DBQueryError $e ) {
 310                                         $this->handleWriteError( $e, $db, $row->serverIndex );
 311                                 }
 312                         } else { // MISS
 313                                 $this->debug( 'get: no matching rows' );
 314                         }
 315                 }
 316
 317                 return $values;
 318         }
 319
 320         public function setMulti( array $data, $expiry = 0 ) {
 321                 $keysByTable = [];
 322                 foreach ( $data as $key => $value ) {
 323                         list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
 324                         $keysByTable[$serverIndex][$tableName][] = $key;
 325                 }
 326
 327                 $this->garbageCollect(); // expire old entries if any
 328
 329                 $result = true;
 330                 $exptime = (int)$expiry;
 331                 foreach ( $keysByTable as $serverIndex => $serverKeys ) {
 332                         $db = null;
 333                         try {
 334                                 $db = $this->getDB( $serverIndex );
 335                         } catch ( DBError $e ) {
 336                                 $this->handleWriteError( $e, $db, $serverIndex );
 337                                 $result = false;
 338                                 continue;
 339                         }
 340
 341                         if ( $exptime < 0 ) {
 342                                 $exptime = 0;
 343                         }
 344
 345                         if ( $exptime == 0 ) {
 346                                 $encExpiry = $this->getMaxDateTime( $db );
 347                         } else {
 348                                 $exptime = $this->convertExpiry( $exptime );
 349                                 $encExpiry = $db->timestamp( $exptime );
 350                         }
 351                         foreach ( $serverKeys as $tableName => $tableKeys ) {
 352                                 $rows = [];
 353                                 foreach ( $tableKeys as $key ) {
 354                                         $rows[] = [
 355                                                 'keyname' => $key,
 356                                                 'value' => $db->encodeBlob( $this->serialize( $data[$key] ) ),
 357                                                 'exptime' => $encExpiry,
 358                                         ];
 359                                 }
 360
 361                                 try {
 362                                         $db->replace(
 363                                                 $tableName,
 364                                                 [ 'keyname' ],
 365                                                 $rows,
 366                                                 __METHOD__
 367                                         );
 368                                 } catch ( DBError $e ) {
 369                                         $this->handleWriteError( $e, $db, $serverIndex );
 370                                         $result = false;
 371                                 }
 372
 373                         }
 374
 375                 }
 376
 377                 return $result;
 378         }
 379
 380         public function set( $key, $value, $exptime = 0, $flags = 0 ) {
 381                 $ok = $this->setMulti( [ $key => $value ], $exptime );
 382                 if ( ( $flags & self::WRITE_SYNC ) == self::WRITE_SYNC ) {
 383                         $ok = $this->waitForReplication() && $ok;
 384                 }
 385
 386                 return $ok;
 387         }
 388
 389         protected function cas( $casToken, $key, $value, $exptime = 0 ) {
 390                 list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
 391                 $db = null;
 392                 try {
 393                         $db = $this->getDB( $serverIndex );
 394                         $exptime = intval( $exptime );
 395
 396                         if ( $exptime < 0 ) {
 397                                 $exptime = 0;
 398                         }
 399
 400                         if ( $exptime == 0 ) {
 401                                 $encExpiry = $this->getMaxDateTime( $db );
 402                         } else {
 403                                 $exptime = $this->convertExpiry( $exptime );
 404                                 $encExpiry = $db->timestamp( $exptime );
 405                         }
 406                         // (bug 24425) use a replace if the db supports it instead of
 407                         // delete/insert to avoid clashes with conflicting keynames
 408                         $db->update(
 409                                 $tableName,
 410                                 [
 411                                         'keyname' => $key,
 412                                         'value' => $db->encodeBlob( $this->serialize( $value ) ),
 413                                         'exptime' => $encExpiry
 414                                 ],
 415                                 [
 416                                         'keyname' => $key,
 417                                         'value' => $db->encodeBlob( $this->serialize( $casToken ) )
 418                                 ],
 419                                 __METHOD__
 420                         );
 421                 } catch ( DBQueryError $e ) {
 422                         $this->handleWriteError( $e, $db, $serverIndex );
 423
 424                         return false;
 425                 }
 426
 427                 return (bool)$db->affectedRows();
 428         }
 429
 430         public function delete( $key ) {
 431                 list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
 432                 $db = null;
 433                 try {
 434                         $db = $this->getDB( $serverIndex );
 435                         $db->delete(
 436                                 $tableName,
 437                                 [ 'keyname' => $key ],
 438                                 __METHOD__ );
 439                 } catch ( DBError $e ) {
 440                         $this->handleWriteError( $e, $db, $serverIndex );
 441                         return false;
 442                 }
 443
 444                 return true;
 445         }
 446
 447         public function incr( $key, $step = 1 ) {
 448                 list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
 449                 $db = null;
 450                 try {
 451                         $db = $this->getDB( $serverIndex );
 452                         $step = intval( $step );
 453                         $row = $db->selectRow(
 454                                 $tableName,
 455                                 [ 'value', 'exptime' ],
 456                                 [ 'keyname' => $key ],
 457                                 __METHOD__,
 458                                 [ 'FOR UPDATE' ] );
 459                         if ( $row === false ) {
 460                                 // Missing
 461
 462                                 return null;
 463                         }
 464                         $db->delete( $tableName, [ 'keyname' => $key ], __METHOD__ );
 465                         if ( $this->isExpired( $db, $row->exptime ) ) {
 466                                 // Expired, do not reinsert
 467
 468                                 return null;
 469                         }
 470
 471                         $oldValue = intval( $this->unserialize( $db->decodeBlob( $row->value ) ) );
 472                         $newValue = $oldValue + $step;
 473                         $db->insert( $tableName,
 474                                 [
 475                                         'keyname' => $key,
 476                                         'value' => $db->encodeBlob( $this->serialize( $newValue ) ),
 477                                         'exptime' => $row->exptime
 478                                 ], __METHOD__, 'IGNORE' );
 479
 480                         if ( $db->affectedRows() == 0 ) {
 481                                 // Race condition. See bug 28611
 482                                 $newValue = null;
 483                         }
 484                 } catch ( DBError $e ) {
 485                         $this->handleWriteError( $e, $db, $serverIndex );
 486                         return null;
 487                 }
 488
 489                 return $newValue;
 490         }
 491
 492         public function merge( $key, callable $callback, $exptime = 0, $attempts = 10, $flags = 0 ) {
 493                 $ok = $this->mergeViaCas( $key, $callback, $exptime, $attempts );
 494                 if ( ( $flags & self::WRITE_SYNC ) == self::WRITE_SYNC ) {
 495                         $ok = $this->waitForReplication() && $ok;
 496                 }
 497
 498                 return $ok;
 499         }
 500
 501         public function changeTTL( $key, $expiry = 0 ) {
 502                 list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
 503                 $db = null;
 504                 try {
 505                         $db = $this->getDB( $serverIndex );
 506                         $db->update(
 507                                 $tableName,
 508                                 [ 'exptime' => $db->timestamp( $this->convertExpiry( $expiry ) ) ],
 509                                 [ 'keyname' => $key, 'exptime > ' . $db->addQuotes( $db->timestamp( time() ) ) ],
 510                                 __METHOD__
 511                         );
 512                         if ( $db->affectedRows() == 0 ) {
 513                                 return false;
 514                         }
 515                 } catch ( DBError $e ) {
 516                         $this->handleWriteError( $e, $db, $serverIndex );
 517                         return false;
 518                 }
 519
 520                 return true;
 521         }
 522
 523         /**
 524          * @param IDatabase $db
 525          * @param string $exptime
 526          * @return bool
 527          */
 528         protected function isExpired( $db, $exptime ) {
 529                 return $exptime != $this->getMaxDateTime( $db ) && wfTimestamp( TS_UNIX, $exptime ) < time();
 530         }
 531
 532         /**
 533          * @param IDatabase $db
 534          * @return string
 535          */
 536         protected function getMaxDateTime( $db ) {
 537                 if ( time() > 0x7fffffff ) {
 538                         return $db->timestamp( 1 << 62 );
 539                 } else {
 540                         return $db->timestamp( 0x7fffffff );
 541                 }
 542         }
 543
 544         protected function garbageCollect() {
 545                 if ( !$this->purgePeriod || $this->replicaOnly ) {
 546                         // Disabled
 547                         return;
 548                 }
 549                 // Only purge on one in every $this->purgePeriod requests.
 550                 if ( $this->purgePeriod !== 1 && mt_rand( 0, $this->purgePeriod - 1 ) ) {
 551                         return;
 552                 }
 553                 $now = time();
 554                 // Avoid repeating the delete within a few seconds
 555                 if ( $now > ( $this->lastExpireAll + 1 ) ) {
 556                         $this->lastExpireAll = $now;
 557                         $this->expireAll();
 558                 }
 559         }
 560
 561         public function expireAll() {
 562                 $this->deleteObjectsExpiringBefore( wfTimestampNow() );
 563         }
 564
 565         /**
 566          * Delete objects from the database which expire before a certain date.
 567          * @param string $timestamp
 568          * @param bool|callable $progressCallback
 569          * @return bool
 570          */
 571         public function deleteObjectsExpiringBefore( $timestamp, $progressCallback = false ) {
 572                 for ( $serverIndex = 0; $serverIndex < $this->numServers; $serverIndex++ ) {
 573                         $db = null;
 574                         try {
 575                                 $db = $this->getDB( $serverIndex );
 576                                 $dbTimestamp = $db->timestamp( $timestamp );
 577                                 $totalSeconds = false;
 578                                 $baseConds = [ 'exptime < ' . $db->addQuotes( $dbTimestamp ) ];
 579                                 for ( $i = 0; $i < $this->shards; $i++ ) {
 580                                         $maxExpTime = false;
 581                                         while ( true ) {
 582                                                 $conds = $baseConds;
 583                                                 if ( $maxExpTime !== false ) {
 584                                                         $conds[] = 'exptime > ' . $db->addQuotes( $maxExpTime );
 585                                                 }
 586                                                 $rows = $db->select(
 587                                                         $this->getTableNameByShard( $i ),
 588                                                         [ 'keyname', 'exptime' ],
 589                                                         $conds,
 590                                                         __METHOD__,
 591                                                         [ 'LIMIT' => 100, 'ORDER BY' => 'exptime' ] );
 592                                                 if ( $rows === false || !$rows->numRows() ) {
 593                                                         break;
 594                                                 }
 595                                                 $keys = [];
 596                                                 $row = $rows->current();
 597                                                 $minExpTime = $row->exptime;
 598                                                 if ( $totalSeconds === false ) {
 599                                                         $totalSeconds = wfTimestamp( TS_UNIX, $timestamp )
 600                                                                 - wfTimestamp( TS_UNIX, $minExpTime );
 601                                                 }
 602                                                 foreach ( $rows as $row ) {
 603                                                         $keys[] = $row->keyname;
 604                                                         $maxExpTime = $row->exptime;
 605                                                 }
 606
 607                                                 $db->delete(
 608                                                         $this->getTableNameByShard( $i ),
 609                                                         [
 610                                                                 'exptime >= ' . $db->addQuotes( $minExpTime ),
 611                                                                 'exptime < ' . $db->addQuotes( $dbTimestamp ),
 612                                                                 'keyname' => $keys
 613                                                         ],
 614                                                         __METHOD__ );
 615
 616                                                 if ( $progressCallback ) {
 617                                                         if ( intval( $totalSeconds ) === 0 ) {
 618                                                                 $percent = 0;
 619                                                         } else {
 620                                                                 $remainingSeconds = wfTimestamp( TS_UNIX, $timestamp )
 621                                                                         - wfTimestamp( TS_UNIX, $maxExpTime );
 622                                                                 if ( $remainingSeconds > $totalSeconds ) {
 623                                                                         $totalSeconds = $remainingSeconds;
 624                                                                 }
 625                                                                 $processedSeconds = $totalSeconds - $remainingSeconds;
 626                                                                 $percent = ( $i + $processedSeconds / $totalSeconds )
 627                                                                         / $this->shards * 100;
 628                                                         }
 629                                                         $percent = ( $percent / $this->numServers )
 630                                                                 + ( $serverIndex / $this->numServers * 100 );
 631                                                         call_user_func( $progressCallback, $percent );
 632                                                 }
 633                                         }
 634                                 }
 635                         } catch ( DBError $e ) {
 636                                 $this->handleWriteError( $e, $db, $serverIndex );
 637                                 return false;
 638                         }
 639                 }
 640                 return true;
 641         }
 642
 643         /**
 644          * Delete content of shard tables in every server.
 645          * Return true if the operation is successful, false otherwise.
 646          * @return bool
 647          */
 648         public function deleteAll() {
 649                 for ( $serverIndex = 0; $serverIndex < $this->numServers; $serverIndex++ ) {
 650                         $db = null;
 651                         try {
 652                                 $db = $this->getDB( $serverIndex );
 653                                 for ( $i = 0; $i < $this->shards; $i++ ) {
 654                                         $db->delete( $this->getTableNameByShard( $i ), '*', __METHOD__ );
 655                                 }
 656                         } catch ( DBError $e ) {
 657                                 $this->handleWriteError( $e, $db, $serverIndex );
 658                                 return false;
 659                         }
 660                 }
 661                 return true;
 662         }
 663
 664         /**
 665          * Serialize an object and, if possible, compress the representation.
 666          * On typical message and page data, this can provide a 3X decrease
 667          * in storage requirements.
 668          *
 669          * @param mixed $data
 670          * @return string
 671          */
 672         protected function serialize( &$data ) {
 673                 $serial = serialize( $data );
 674
 675                 if ( function_exists( 'gzdeflate' ) ) {
 676                         return gzdeflate( $serial );
 677                 } else {
 678                         return $serial;
 679                 }
 680         }
 681
 682         /**
 683          * Unserialize and, if necessary, decompress an object.
 684          * @param string $serial
 685          * @return mixed
 686          */
 687         protected function unserialize( $serial ) {
 688                 if ( function_exists( 'gzinflate' ) ) {
 689                         MediaWiki\suppressWarnings();
 690                         $decomp = gzinflate( $serial );
 691                         MediaWiki\restoreWarnings();
 692
 693                         if ( false !== $decomp ) {
 694                                 $serial = $decomp;
 695                         }
 696                 }
 697
 698                 $ret = unserialize( $serial );
 699
 700                 return $ret;
 701         }
 702
 703         /**
 704          * Handle a DBError which occurred during a read operation.
 705          *
 706          * @param DBError $exception
 707          * @param int $serverIndex
 708          */
 709         protected function handleReadError( DBError $exception, $serverIndex ) {
 710                 if ( $exception instanceof DBConnectionError ) {
 711                         $this->markServerDown( $exception, $serverIndex );
 712                 }
 713                 $this->logger->error( "DBError: {$exception->getMessage()}" );
 714                 if ( $exception instanceof DBConnectionError ) {
 715                         $this->setLastError( BagOStuff::ERR_UNREACHABLE );
 716                         $this->logger->debug( __METHOD__ . ": ignoring connection error" );
 717                 } else {
 718                         $this->setLastError( BagOStuff::ERR_UNEXPECTED );
 719                         $this->logger->debug( __METHOD__ . ": ignoring query error" );
 720                 }
 721         }
 722
 723         /**
 724          * Handle a DBQueryError which occurred during a write operation.
 725          *
 726          * @param DBError $exception
 727          * @param IDatabase|null $db DB handle or null if connection failed
 728          * @param int $serverIndex
 729          * @throws Exception
 730          */
 731         protected function handleWriteError( DBError $exception, IDatabase $db = null, $serverIndex ) {
 732                 if ( !$db ) {
 733                         $this->markServerDown( $exception, $serverIndex );
 734                 } elseif ( $db->wasReadOnlyError() ) {
 735                         if ( $db->trxLevel() && $this->usesMainDB() ) {
 736                                 // Errors like deadlocks and connection drops already cause rollback.
 737                                 // For consistency, we have no choice but to throw an error and trigger
 738                                 // complete rollback if the main DB is also being used as the cache DB.
 739                                 throw $exception;
 740                         }
 741                 }
 742
 743                 $this->logger->error( "DBError: {$exception->getMessage()}" );
 744                 if ( $exception instanceof DBConnectionError ) {
 745                         $this->setLastError( BagOStuff::ERR_UNREACHABLE );
 746                         $this->logger->debug( __METHOD__ . ": ignoring connection error" );
 747                 } else {
 748                         $this->setLastError( BagOStuff::ERR_UNEXPECTED );
 749                         $this->logger->debug( __METHOD__ . ": ignoring query error" );
 750                 }
 751         }
 752
 753         /**
 754          * Mark a server down due to a DBConnectionError exception
 755          *
 756          * @param DBError $exception
 757          * @param int $serverIndex
 758          */
 759         protected function markServerDown( DBError $exception, $serverIndex ) {
 760                 unset( $this->conns[$serverIndex] ); // bug T103435
 761
 762                 if ( isset( $this->connFailureTimes[$serverIndex] ) ) {
 763                         if ( time() - $this->connFailureTimes[$serverIndex] >= 60 ) {
 764                                 unset( $this->connFailureTimes[$serverIndex] );
 765                                 unset( $this->connFailureErrors[$serverIndex] );
 766                         } else {
 767                                 $this->logger->debug( __METHOD__ . ": Server #$serverIndex already down" );
 768                                 return;
 769                         }
 770                 }
 771                 $now = time();
 772                 $this->logger->info( __METHOD__ . ": Server #$serverIndex down until " . ( $now + 60 ) );
 773                 $this->connFailureTimes[$serverIndex] = $now;
 774                 $this->connFailureErrors[$serverIndex] = $exception;
 775         }
 776
 777         /**
 778          * Create shard tables. For use from eval.php.
 779          */
 780         public function createTables() {
 781                 for ( $serverIndex = 0; $serverIndex < $this->numServers; $serverIndex++ ) {
 782                         $db = $this->getDB( $serverIndex );
 783                         if ( $db->getType() !== 'mysql' ) {
 784                                 throw new MWException( __METHOD__ . ' is not supported on this DB server' );
 785                         }
 786
 787                         for ( $i = 0; $i < $this->shards; $i++ ) {
 788                                 $db->query(
 789                                         'CREATE TABLE ' . $db->tableName( $this->getTableNameByShard( $i ) ) .
 790                                         ' LIKE ' . $db->tableName( 'objectcache' ),
 791                                         __METHOD__ );
 792                         }
 793                 }
 794         }
 795
 796         /**
 797          * @return bool Whether the main DB is used, e.g. wfGetDB( DB_MASTER )
 798          */
 799         protected function usesMainDB() {
 800                 return !$this->serverInfos;
 801         }
 802
 803         protected function waitForReplication() {
 804                 if ( !$this->usesMainDB() ) {
 805                         // Custom DB server list; probably doesn't use replication
 806                         return true;
 807                 }
 808
 809                 $lb = $this->getSeparateMainLB()
 810                         ?: MediaWikiServices::getInstance()->getDBLoadBalancer();
 811
 812                 if ( $lb->getServerCount() <= 1 ) {
 813                         return true; // no replica DBs
 814                 }
 815
 816                 // Main LB is used; wait for any replica DBs to catch up
 817                 $masterPos = $lb->getMasterPos();
 818
 819                 $loop = new WaitConditionLoop(
 820                         function () use ( $lb, $masterPos ) {
 821                                 return $lb->waitForAll( $masterPos, 1 );
 822                         },
 823                         $this->syncTimeout,
 824                         $this->busyCallbacks
 825                 );
 826
 827                 return ( $loop->invoke() === $loop::CONDITION_REACHED );
 828         }
 829 }