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 Wikimedia\Rdbms\Database;
  25 use Wikimedia\Rdbms\IDatabase;
  26 use \MediaWiki\MediaWikiServices;
  27 use \Wikimedia\WaitConditionLoop;
  28 use \Wikimedia\Rdbms\TransactionProfiler;
  29 use Wikimedia\Rdbms\LoadBalancer;
  30
  31 /**
  32  * Class to store objects in the database
  33  *
  34  * @ingroup Cache
  35  */
  36 class SqlBagOStuff extends BagOStuff {
  37         /** @var array[] (server index => server config) */
  38         protected $serverInfos;
  39         /** @var string[] (server index => tag/host name) */
  40         protected $serverTags;
  41         /** @var int */
  42         protected $numServers;
  43         /** @var int */
  44         protected $lastExpireAll = 0;
  45         /** @var int */
  46         protected $purgePeriod = 100;
  47         /** @var int */
  48         protected $shards = 1;
  49         /** @var string */
  50         protected $tableName = 'objectcache';
  51         /** @var bool */
  52         protected $replicaOnly = false;
  53         /** @var int */
  54         protected $syncTimeout = 3;
  55
  56         /** @var LoadBalancer|null */
  57         protected $separateMainLB;
  58         /** @var array */
  59         protected $conns;
  60         /** @var array UNIX timestamps */
  61         protected $connFailureTimes = [];
  62         /** @var array Exceptions */
  63         protected $connFailureErrors = [];
  64
  65         /**
  66          * Constructor. Parameters are:
  67          *   - server:      A server info structure in the format required by each
  68          *                  element in $wgDBServers.
  69          *
  70          *   - servers:     An array of server info structures describing a set of database servers
  71          *                  to distribute keys to. If this is specified, the "server" option will be
  72          *                  ignored. If string keys are used, then they will be used for consistent
  73          *                  hashing *instead* of the host name (from the server config). This is useful
  74          *                  when a cluster is replicated to another site (with different host names)
  75          *                  but each server has a corresponding replica in the other cluster.
  76          *
  77          *   - purgePeriod: The average number of object cache requests in between
  78          *                  garbage collection operations, where expired entries
  79          *                  are removed from the database. Or in other words, the
  80          *                  reciprocal of the probability of purging on any given
  81          *                  request. If this is set to zero, purging will never be
  82          *                  done.
  83          *
  84          *   - tableName:   The table name to use, default is "objectcache".
  85          *
  86          *   - shards:      The number of tables to use for data storage on each server.
  87          *                  If this is more than 1, table names will be formed in the style
  88          *                  objectcacheNNN where NNN is the shard index, between 0 and
  89          *                  shards-1. The number of digits will be the minimum number
  90          *                  required to hold the largest shard index. Data will be
  91          *                  distributed across all tables by key hash. This is for
  92          *                  MySQL bugs 61735 and 61736.
  93          *   - slaveOnly:   Whether to only use replica DBs and avoid triggering
  94          *                  garbage collection logic of expired items. This only
  95          *                  makes sense if the primary DB is used and only if get()
  96          *                  calls will be used. This is used by ReplicatedBagOStuff.
  97          *   - syncTimeout: Max seconds to wait for replica DBs to catch up for WRITE_SYNC.
  98          *
  99          * @param array $params
 100          */
 101         public function __construct( $params ) {
 102                 parent::__construct( $params );
 103
 104                 $this->attrMap[self::ATTR_EMULATION] = self::QOS_EMULATION_SQL;
 105                 $this->attrMap[self::ATTR_SYNCWRITES] = self::QOS_SYNCWRITES_NONE;
 106
 107                 if ( isset( $params['servers'] ) ) {
 108                         $this->serverInfos = [];
 109                         $this->serverTags = [];
 110                         $this->numServers = count( $params['servers'] );
 111                         $index = 0;
 112                         foreach ( $params['servers'] as $tag => $info ) {
 113                                 $this->serverInfos[$index] = $info;
 114                                 if ( is_string( $tag ) ) {
 115                                         $this->serverTags[$index] = $tag;
 116                                 } else {
 117                                         $this->serverTags[$index] = isset( $info['host'] ) ? $info['host'] : "#$index";
 118                                 }
 119                                 ++$index;
 120                         }
 121                 } elseif ( isset( $params['server'] ) ) {
 122                         $this->serverInfos = [ $params['server'] ];
 123                         $this->numServers = count( $this->serverInfos );
 124                 } else {
 125                         // Default to using the main wiki's database servers
 126                         $this->serverInfos = false;
 127                         $this->numServers = 1;
 128                         $this->attrMap[self::ATTR_SYNCWRITES] = self::QOS_SYNCWRITES_BE;
 129                 }
 130                 if ( isset( $params['purgePeriod'] ) ) {
 131                         $this->purgePeriod = intval( $params['purgePeriod'] );
 132                 }
 133                 if ( isset( $params['tableName'] ) ) {
 134                         $this->tableName = $params['tableName'];
 135                 }
 136                 if ( isset( $params['shards'] ) ) {
 137                         $this->shards = intval( $params['shards'] );
 138                 }
 139                 if ( isset( $params['syncTimeout'] ) ) {
 140                         $this->syncTimeout = $params['syncTimeout'];
 141                 }
 142                 $this->replicaOnly = !empty( $params['slaveOnly'] );
 143         }
 144
 145         protected function getSeparateMainLB() {
 146                 global $wgDBtype;
 147
 148                 if ( $wgDBtype === 'mysql' && $this->usesMainDB() ) {
 149                         if ( !$this->separateMainLB ) {
 150                                 // We must keep a separate connection to MySQL in order to avoid deadlocks
 151                                 $lbFactory = MediaWikiServices::getInstance()->getDBLoadBalancerFactory();
 152                                 $this->separateMainLB = $lbFactory->newMainLB();
 153                         }
 154                         return $this->separateMainLB;
 155                 } else {
 156                         // However, SQLite has an opposite behavior. And PostgreSQL needs to know
 157                         // if we are in transaction or not (@TODO: find some PostgreSQL work-around).
 158                         return null;
 159                 }
 160         }
 161
 162         /**
 163          * Get a connection to the specified database
 164          *
 165          * @param int $serverIndex
 166          * @return IDatabase
 167          * @throws MWException
 168          */
 169         protected function getDB( $serverIndex ) {
 170                 if ( !isset( $this->conns[$serverIndex] ) ) {
 171                         if ( $serverIndex >= $this->numServers ) {
 172                                 throw new MWException( __METHOD__ . ": Invalid server index \"$serverIndex\"" );
 173                         }
 174
 175                         # Don't keep timing out trying to connect for each call if the DB is down
 176                         if ( isset( $this->connFailureErrors[$serverIndex] )
 177                                 && ( time() - $this->connFailureTimes[$serverIndex] ) < 60
 178                         ) {
 179                                 throw $this->connFailureErrors[$serverIndex];
 180                         }
 181
 182                         # If server connection info was given, use that
 183                         if ( $this->serverInfos ) {
 184                                 $info = $this->serverInfos[$serverIndex];
 185                                 $type = isset( $info['type'] ) ? $info['type'] : 'mysql';
 186                                 $host = isset( $info['host'] ) ? $info['host'] : '[unknown]';
 187                                 $this->logger->debug( __CLASS__ . ": connecting to $host" );
 188                                 // Use a blank trx profiler to ignore expections as this is a cache
 189                                 $info['trxProfiler'] = new TransactionProfiler();
 190                                 $db = Database::factory( $type, $info );
 191                                 $db->clearFlag( DBO_TRX );
 192                         } else {
 193                                 $index = $this->replicaOnly ? DB_REPLICA : DB_MASTER;
 194                                 if ( $this->getSeparateMainLB() ) {
 195                                         $db = $this->getSeparateMainLB()->getConnection( $index );
 196                                         $db->clearFlag( DBO_TRX ); // auto-commit mode
 197                                 } else {
 198                                         $db = wfGetDB( $index );
 199                                         // Can't mess with transaction rounds (DBO_TRX) :(
 200                                 }
 201                         }
 202                         $this->logger->debug( sprintf( "Connection %s will be used for SqlBagOStuff", $db ) );
 203                         $this->conns[$serverIndex] = $db;
 204                 }
 205
 206                 return $this->conns[$serverIndex];
 207         }
 208
 209         /**
 210          * Get the server index and table name for a given key
 211          * @param string $key
 212          * @return array Server index and table name
 213          */
 214         protected function getTableByKey( $key ) {
 215                 if ( $this->shards > 1 ) {
 216                         $hash = hexdec( substr( md5( $key ), 0, 8 ) ) & 0x7fffffff;
 217                         $tableIndex = $hash % $this->shards;
 218                 } else {
 219                         $tableIndex = 0;
 220                 }
 221                 if ( $this->numServers > 1 ) {
 222                         $sortedServers = $this->serverTags;
 223                         ArrayUtils::consistentHashSort( $sortedServers, $key );
 224                         reset( $sortedServers );
 225                         $serverIndex = key( $sortedServers );
 226                 } else {
 227                         $serverIndex = 0;
 228                 }
 229                 return [ $serverIndex, $this->getTableNameByShard( $tableIndex ) ];
 230         }
 231
 232         /**
 233          * Get the table name for a given shard index
 234          * @param int $index
 235          * @return string
 236          */
 237         protected function getTableNameByShard( $index ) {
 238                 if ( $this->shards > 1 ) {
 239                         $decimals = strlen( $this->shards - 1 );
 240                         return $this->tableName .
 241                                 sprintf( "%0{$decimals}d", $index );
 242                 } else {
 243                         return $this->tableName;
 244                 }
 245         }
 246
 247         protected function doGet( $key, $flags = 0 ) {
 248                 $casToken = null;
 249
 250                 return $this->getWithToken( $key, $casToken, $flags );
 251         }
 252
 253         protected function getWithToken( $key, &$casToken, $flags = 0 ) {
 254                 $values = $this->getMulti( [ $key ] );
 255                 if ( array_key_exists( $key, $values ) ) {
 256                         $casToken = $values[$key];
 257                         return $values[$key];
 258                 }
 259                 return false;
 260         }
 261
 262         public function getMulti( array $keys, $flags = 0 ) {
 263                 $values = []; // array of (key => value)
 264
 265                 $keysByTable = [];
 266                 foreach ( $keys as $key ) {
 267                         list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
 268                         $keysByTable[$serverIndex][$tableName][] = $key;
 269                 }
 270
 271                 $this->garbageCollect(); // expire old entries if any
 272
 273                 $dataRows = [];
 274                 foreach ( $keysByTable as $serverIndex => $serverKeys ) {
 275                         try {
 276                                 $db = $this->getDB( $serverIndex );
 277                                 foreach ( $serverKeys as $tableName => $tableKeys ) {
 278                                         $res = $db->select( $tableName,
 279                                                 [ 'keyname', 'value', 'exptime' ],
 280                                                 [ 'keyname' => $tableKeys ],
 281                                                 __METHOD__,
 282                                                 // Approximate write-on-the-fly BagOStuff API via blocking.
 283                                                 // This approximation fails if a ROLLBACK happens (which is rare).
 284                                                 // We do not want to flush the TRX as that can break callers.
 285                                                 $db->trxLevel() ? [ 'LOCK IN SHARE MODE' ] : []
 286                                         );
 287                                         if ( $res === false ) {
 288                                                 continue;
 289                                         }
 290                                         foreach ( $res as $row ) {
 291                                                 $row->serverIndex = $serverIndex;
 292                                                 $row->tableName = $tableName;
 293                                                 $dataRows[$row->keyname] = $row;
 294                                         }
 295                                 }
 296                         } catch ( DBError $e ) {
 297                                 $this->handleReadError( $e, $serverIndex );
 298                         }
 299                 }
 300
 301                 foreach ( $keys as $key ) {
 302                         if ( isset( $dataRows[$key] ) ) { // HIT?
 303                                 $row = $dataRows[$key];
 304                                 $this->debug( "get: retrieved data; expiry time is " . $row->exptime );
 305                                 $db = null;
 306                                 try {
 307                                         $db = $this->getDB( $row->serverIndex );
 308                                         if ( $this->isExpired( $db, $row->exptime ) ) { // MISS
 309                                                 $this->debug( "get: key has expired" );
 310                                         } else { // HIT
 311                                                 $values[$key] = $this->unserialize( $db->decodeBlob( $row->value ) );
 312                                         }
 313                                 } catch ( DBQueryError $e ) {
 314                                         $this->handleWriteError( $e, $db, $row->serverIndex );
 315                                 }
 316                         } else { // MISS
 317                                 $this->debug( 'get: no matching rows' );
 318                         }
 319                 }
 320
 321                 return $values;
 322         }
 323
 324         public function setMulti( array $data, $expiry = 0 ) {
 325                 $keysByTable = [];
 326                 foreach ( $data as $key => $value ) {
 327                         list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
 328                         $keysByTable[$serverIndex][$tableName][] = $key;
 329                 }
 330
 331                 $this->garbageCollect(); // expire old entries if any
 332
 333                 $result = true;
 334                 $exptime = (int)$expiry;
 335                 foreach ( $keysByTable as $serverIndex => $serverKeys ) {
 336                         $db = null;
 337                         try {
 338                                 $db = $this->getDB( $serverIndex );
 339                         } catch ( DBError $e ) {
 340                                 $this->handleWriteError( $e, $db, $serverIndex );
 341                                 $result = false;
 342                                 continue;
 343                         }
 344
 345                         if ( $exptime < 0 ) {
 346                                 $exptime = 0;
 347                         }
 348
 349                         if ( $exptime == 0 ) {
 350                                 $encExpiry = $this->getMaxDateTime( $db );
 351                         } else {
 352                                 $exptime = $this->convertExpiry( $exptime );
 353                                 $encExpiry = $db->timestamp( $exptime );
 354                         }
 355                         foreach ( $serverKeys as $tableName => $tableKeys ) {
 356                                 $rows = [];
 357                                 foreach ( $tableKeys as $key ) {
 358                                         $rows[] = [
 359                                                 'keyname' => $key,
 360                                                 'value' => $db->encodeBlob( $this->serialize( $data[$key] ) ),
 361                                                 'exptime' => $encExpiry,
 362                                         ];
 363                                 }
 364
 365                                 try {
 366                                         $db->replace(
 367                                                 $tableName,
 368                                                 [ 'keyname' ],
 369                                                 $rows,
 370                                                 __METHOD__
 371                                         );
 372                                 } catch ( DBError $e ) {
 373                                         $this->handleWriteError( $e, $db, $serverIndex );
 374                                         $result = false;
 375                                 }
 376
 377                         }
 378
 379                 }
 380
 381                 return $result;
 382         }
 383
 384         public function set( $key, $value, $exptime = 0, $flags = 0 ) {
 385                 $ok = $this->setMulti( [ $key => $value ], $exptime );
 386                 if ( ( $flags & self::WRITE_SYNC ) == self::WRITE_SYNC ) {
 387                         $ok = $this->waitForReplication() && $ok;
 388                 }
 389
 390                 return $ok;
 391         }
 392
 393         protected function cas( $casToken, $key, $value, $exptime = 0 ) {
 394                 list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
 395                 $db = null;
 396                 try {
 397                         $db = $this->getDB( $serverIndex );
 398                         $exptime = intval( $exptime );
 399
 400                         if ( $exptime < 0 ) {
 401                                 $exptime = 0;
 402                         }
 403
 404                         if ( $exptime == 0 ) {
 405                                 $encExpiry = $this->getMaxDateTime( $db );
 406                         } else {
 407                                 $exptime = $this->convertExpiry( $exptime );
 408                                 $encExpiry = $db->timestamp( $exptime );
 409                         }
 410                         // (T26425) use a replace if the db supports it instead of
 411                         // delete/insert to avoid clashes with conflicting keynames
 412                         $db->update(
 413                                 $tableName,
 414                                 [
 415                                         'keyname' => $key,
 416                                         'value' => $db->encodeBlob( $this->serialize( $value ) ),
 417                                         'exptime' => $encExpiry
 418                                 ],
 419                                 [
 420                                         'keyname' => $key,
 421                                         'value' => $db->encodeBlob( $this->serialize( $casToken ) )
 422                                 ],
 423                                 __METHOD__
 424                         );
 425                 } catch ( DBQueryError $e ) {
 426                         $this->handleWriteError( $e, $db, $serverIndex );
 427
 428                         return false;
 429                 }
 430
 431                 return (bool)$db->affectedRows();
 432         }
 433
 434         public function delete( $key ) {
 435                 list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
 436                 $db = null;
 437                 try {
 438                         $db = $this->getDB( $serverIndex );
 439                         $db->delete(
 440                                 $tableName,
 441                                 [ 'keyname' => $key ],
 442                                 __METHOD__ );
 443                 } catch ( DBError $e ) {
 444                         $this->handleWriteError( $e, $db, $serverIndex );
 445                         return false;
 446                 }
 447
 448                 return true;
 449         }
 450
 451         public function incr( $key, $step = 1 ) {
 452                 list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
 453                 $db = null;
 454                 try {
 455                         $db = $this->getDB( $serverIndex );
 456                         $step = intval( $step );
 457                         $row = $db->selectRow(
 458                                 $tableName,
 459                                 [ 'value', 'exptime' ],
 460                                 [ 'keyname' => $key ],
 461                                 __METHOD__,
 462                                 [ 'FOR UPDATE' ] );
 463                         if ( $row === false ) {
 464                                 // Missing
 465
 466                                 return null;
 467                         }
 468                         $db->delete( $tableName, [ 'keyname' => $key ], __METHOD__ );
 469                         if ( $this->isExpired( $db, $row->exptime ) ) {
 470                                 // Expired, do not reinsert
 471
 472                                 return null;
 473                         }
 474
 475                         $oldValue = intval( $this->unserialize( $db->decodeBlob( $row->value ) ) );
 476                         $newValue = $oldValue + $step;
 477                         $db->insert( $tableName,
 478                                 [
 479                                         'keyname' => $key,
 480                                         'value' => $db->encodeBlob( $this->serialize( $newValue ) ),
 481                                         'exptime' => $row->exptime
 482                                 ], __METHOD__, 'IGNORE' );
 483
 484                         if ( $db->affectedRows() == 0 ) {
 485                                 // Race condition. See T30611
 486                                 $newValue = null;
 487                         }
 488                 } catch ( DBError $e ) {
 489                         $this->handleWriteError( $e, $db, $serverIndex );
 490                         return null;
 491                 }
 492
 493                 return $newValue;
 494         }
 495
 496         public function merge( $key, callable $callback, $exptime = 0, $attempts = 10, $flags = 0 ) {
 497                 $ok = $this->mergeViaCas( $key, $callback, $exptime, $attempts );
 498                 if ( ( $flags & self::WRITE_SYNC ) == self::WRITE_SYNC ) {
 499                         $ok = $this->waitForReplication() && $ok;
 500                 }
 501
 502                 return $ok;
 503         }
 504
 505         public function changeTTL( $key, $expiry = 0 ) {
 506                 list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
 507                 $db = null;
 508                 try {
 509                         $db = $this->getDB( $serverIndex );
 510                         $db->update(
 511                                 $tableName,
 512                                 [ 'exptime' => $db->timestamp( $this->convertExpiry( $expiry ) ) ],
 513                                 [ 'keyname' => $key, 'exptime > ' . $db->addQuotes( $db->timestamp( time() ) ) ],
 514                                 __METHOD__
 515                         );
 516                         if ( $db->affectedRows() == 0 ) {
 517                                 return false;
 518                         }
 519                 } catch ( DBError $e ) {
 520                         $this->handleWriteError( $e, $db, $serverIndex );
 521                         return false;
 522                 }
 523
 524                 return true;
 525         }
 526
 527         /**
 528          * @param IDatabase $db
 529          * @param string $exptime
 530          * @return bool
 531          */
 532         protected function isExpired( $db, $exptime ) {
 533                 return $exptime != $this->getMaxDateTime( $db ) && wfTimestamp( TS_UNIX, $exptime ) < time();
 534         }
 535
 536         /**
 537          * @param IDatabase $db
 538          * @return string
 539          */
 540         protected function getMaxDateTime( $db ) {
 541                 if ( time() > 0x7fffffff ) {
 542                         return $db->timestamp( 1 << 62 );
 543                 } else {
 544                         return $db->timestamp( 0x7fffffff );
 545                 }
 546         }
 547
 548         protected function garbageCollect() {
 549                 if ( !$this->purgePeriod || $this->replicaOnly ) {
 550                         // Disabled
 551                         return;
 552                 }
 553                 // Only purge on one in every $this->purgePeriod requests.
 554                 if ( $this->purgePeriod !== 1 && mt_rand( 0, $this->purgePeriod - 1 ) ) {
 555                         return;
 556                 }
 557                 $now = time();
 558                 // Avoid repeating the delete within a few seconds
 559                 if ( $now > ( $this->lastExpireAll + 1 ) ) {
 560                         $this->lastExpireAll = $now;
 561                         $this->expireAll();
 562                 }
 563         }
 564
 565         public function expireAll() {
 566                 $this->deleteObjectsExpiringBefore( wfTimestampNow() );
 567         }
 568
 569         /**
 570          * Delete objects from the database which expire before a certain date.
 571          * @param string $timestamp
 572          * @param bool|callable $progressCallback
 573          * @return bool
 574          */
 575         public function deleteObjectsExpiringBefore( $timestamp, $progressCallback = false ) {
 576                 for ( $serverIndex = 0; $serverIndex < $this->numServers; $serverIndex++ ) {
 577                         $db = null;
 578                         try {
 579                                 $db = $this->getDB( $serverIndex );
 580                                 $dbTimestamp = $db->timestamp( $timestamp );
 581                                 $totalSeconds = false;
 582                                 $baseConds = [ 'exptime < ' . $db->addQuotes( $dbTimestamp ) ];
 583                                 for ( $i = 0; $i < $this->shards; $i++ ) {
 584                                         $maxExpTime = false;
 585                                         while ( true ) {
 586                                                 $conds = $baseConds;
 587                                                 if ( $maxExpTime !== false ) {
 588                                                         $conds[] = 'exptime > ' . $db->addQuotes( $maxExpTime );
 589                                                 }
 590                                                 $rows = $db->select(
 591                                                         $this->getTableNameByShard( $i ),
 592                                                         [ 'keyname', 'exptime' ],
 593                                                         $conds,
 594                                                         __METHOD__,
 595                                                         [ 'LIMIT' => 100, 'ORDER BY' => 'exptime' ] );
 596                                                 if ( $rows === false || !$rows->numRows() ) {
 597                                                         break;
 598                                                 }
 599                                                 $keys = [];
 600                                                 $row = $rows->current();
 601                                                 $minExpTime = $row->exptime;
 602                                                 if ( $totalSeconds === false ) {
 603                                                         $totalSeconds = wfTimestamp( TS_UNIX, $timestamp )
 604                                                                 - wfTimestamp( TS_UNIX, $minExpTime );
 605                                                 }
 606                                                 foreach ( $rows as $row ) {
 607                                                         $keys[] = $row->keyname;
 608                                                         $maxExpTime = $row->exptime;
 609                                                 }
 610
 611                                                 $db->delete(
 612                                                         $this->getTableNameByShard( $i ),
 613                                                         [
 614                                                                 'exptime >= ' . $db->addQuotes( $minExpTime ),
 615                                                                 'exptime < ' . $db->addQuotes( $dbTimestamp ),
 616                                                                 'keyname' => $keys
 617                                                         ],
 618                                                         __METHOD__ );
 619
 620                                                 if ( $progressCallback ) {
 621                                                         if ( intval( $totalSeconds ) === 0 ) {
 622                                                                 $percent = 0;
 623                                                         } else {
 624                                                                 $remainingSeconds = wfTimestamp( TS_UNIX, $timestamp )
 625                                                                         - wfTimestamp( TS_UNIX, $maxExpTime );
 626                                                                 if ( $remainingSeconds > $totalSeconds ) {
 627                                                                         $totalSeconds = $remainingSeconds;
 628                                                                 }
 629                                                                 $processedSeconds = $totalSeconds - $remainingSeconds;
 630                                                                 $percent = ( $i + $processedSeconds / $totalSeconds )
 631                                                                         / $this->shards * 100;
 632                                                         }
 633                                                         $percent = ( $percent / $this->numServers )
 634                                                                 + ( $serverIndex / $this->numServers * 100 );
 635                                                         call_user_func( $progressCallback, $percent );
 636                                                 }
 637                                         }
 638                                 }
 639                         } catch ( DBError $e ) {
 640                                 $this->handleWriteError( $e, $db, $serverIndex );
 641                                 return false;
 642                         }
 643                 }
 644                 return true;
 645         }
 646
 647         /**
 648          * Delete content of shard tables in every server.
 649          * Return true if the operation is successful, false otherwise.
 650          * @return bool
 651          */
 652         public function deleteAll() {
 653                 for ( $serverIndex = 0; $serverIndex < $this->numServers; $serverIndex++ ) {
 654                         $db = null;
 655                         try {
 656                                 $db = $this->getDB( $serverIndex );
 657                                 for ( $i = 0; $i < $this->shards; $i++ ) {
 658                                         $db->delete( $this->getTableNameByShard( $i ), '*', __METHOD__ );
 659                                 }
 660                         } catch ( DBError $e ) {
 661                                 $this->handleWriteError( $e, $db, $serverIndex );
 662                                 return false;
 663                         }
 664                 }
 665                 return true;
 666         }
 667
 668         /**
 669          * Serialize an object and, if possible, compress the representation.
 670          * On typical message and page data, this can provide a 3X decrease
 671          * in storage requirements.
 672          *
 673          * @param mixed $data
 674          * @return string
 675          */
 676         protected function serialize( &$data ) {
 677                 $serial = serialize( $data );
 678
 679                 if ( function_exists( 'gzdeflate' ) ) {
 680                         return gzdeflate( $serial );
 681                 } else {
 682                         return $serial;
 683                 }
 684         }
 685
 686         /**
 687          * Unserialize and, if necessary, decompress an object.
 688          * @param string $serial
 689          * @return mixed
 690          */
 691         protected function unserialize( $serial ) {
 692                 if ( function_exists( 'gzinflate' ) ) {
 693                         MediaWiki\suppressWarnings();
 694                         $decomp = gzinflate( $serial );
 695                         MediaWiki\restoreWarnings();
 696
 697                         if ( false !== $decomp ) {
 698                                 $serial = $decomp;
 699                         }
 700                 }
 701
 702                 $ret = unserialize( $serial );
 703
 704                 return $ret;
 705         }
 706
 707         /**
 708          * Handle a DBError which occurred during a read operation.
 709          *
 710          * @param DBError $exception
 711          * @param int $serverIndex
 712          */
 713         protected function handleReadError( DBError $exception, $serverIndex ) {
 714                 if ( $exception instanceof DBConnectionError ) {
 715                         $this->markServerDown( $exception, $serverIndex );
 716                 }
 717                 $this->logger->error( "DBError: {$exception->getMessage()}" );
 718                 if ( $exception instanceof DBConnectionError ) {
 719                         $this->setLastError( BagOStuff::ERR_UNREACHABLE );
 720                         $this->logger->debug( __METHOD__ . ": ignoring connection error" );
 721                 } else {
 722                         $this->setLastError( BagOStuff::ERR_UNEXPECTED );
 723                         $this->logger->debug( __METHOD__ . ": ignoring query error" );
 724                 }
 725         }
 726
 727         /**
 728          * Handle a DBQueryError which occurred during a write operation.
 729          *
 730          * @param DBError $exception
 731          * @param IDatabase|null $db DB handle or null if connection failed
 732          * @param int $serverIndex
 733          * @throws Exception
 734          */
 735         protected function handleWriteError( DBError $exception, IDatabase $db = null, $serverIndex ) {
 736                 if ( !$db ) {
 737                         $this->markServerDown( $exception, $serverIndex );
 738                 } elseif ( $db->wasReadOnlyError() ) {
 739                         if ( $db->trxLevel() && $this->usesMainDB() ) {
 740                                 // Errors like deadlocks and connection drops already cause rollback.
 741                                 // For consistency, we have no choice but to throw an error and trigger
 742                                 // complete rollback if the main DB is also being used as the cache DB.
 743                                 throw $exception;
 744                         }
 745                 }
 746
 747                 $this->logger->error( "DBError: {$exception->getMessage()}" );
 748                 if ( $exception instanceof DBConnectionError ) {
 749                         $this->setLastError( BagOStuff::ERR_UNREACHABLE );
 750                         $this->logger->debug( __METHOD__ . ": ignoring connection error" );
 751                 } else {
 752                         $this->setLastError( BagOStuff::ERR_UNEXPECTED );
 753                         $this->logger->debug( __METHOD__ . ": ignoring query error" );
 754                 }
 755         }
 756
 757         /**
 758          * Mark a server down due to a DBConnectionError exception
 759          *
 760          * @param DBError $exception
 761          * @param int $serverIndex
 762          */
 763         protected function markServerDown( DBError $exception, $serverIndex ) {
 764                 unset( $this->conns[$serverIndex] ); // bug T103435
 765
 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 ' . $db->tableName( 'objectcache' ),
 795                                         __METHOD__ );
 796                         }
 797                 }
 798         }
 799
 800         /**
 801          * @return bool Whether the main DB is used, e.g. wfGetDB( DB_MASTER )
 802          */
 803         protected function usesMainDB() {
 804                 return !$this->serverInfos;
 805         }
 806
 807         protected function waitForReplication() {
 808                 if ( !$this->usesMainDB() ) {
 809                         // Custom DB server list; probably doesn't use replication
 810                         return true;
 811                 }
 812
 813                 $lb = $this->getSeparateMainLB()
 814                         ?: MediaWikiServices::getInstance()->getDBLoadBalancer();
 815
 816                 if ( $lb->getServerCount() <= 1 ) {
 817                         return true; // no replica DBs
 818                 }
 819
 820                 // Main LB is used; wait for any replica DBs to catch up
 821                 $masterPos = $lb->getMasterPos();
 822
 823                 $loop = new WaitConditionLoop(
 824                         function () use ( $lb, $masterPos ) {
 825                                 return $lb->waitForAll( $masterPos, 1 );
 826                         },
 827                         $this->syncTimeout,
 828                         $this->busyCallbacks
 829                 );
 830
 831                 return ( $loop->invoke() === $loop::CONDITION_REACHED );
 832         }
 833 }