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 use \Wikimedia\Rdbms\TransactionProfiler;
  27
  28 /**
  29  * Class to store objects in the database
  30  *
  31  * @ingroup Cache
  32  */
  33 class SqlBagOStuff extends BagOStuff {
  34         /** @var array[] (server index => server config) */
  35         protected $serverInfos;
  36         /** @var string[] (server index => tag/host name) */
  37         protected $serverTags;
  38         /** @var int */
  39         protected $numServers;
  40         /** @var int */
  41         protected $lastExpireAll = 0;
  42         /** @var int */
  43         protected $purgePeriod = 100;
  44         /** @var int */
  45         protected $shards = 1;
  46         /** @var string */
  47         protected $tableName = 'objectcache';
  48         /** @var bool */
  49         protected $replicaOnly = false;
  50         /** @var int */
  51         protected $syncTimeout = 3;
  52
  53         /** @var LoadBalancer|null */
  54         protected $separateMainLB;
  55         /** @var array */
  56         protected $conns;
  57         /** @var array UNIX timestamps */
  58         protected $connFailureTimes = [];
  59         /** @var array Exceptions */
  60         protected $connFailureErrors = [];
  61
  62         /**
  63          * Constructor. Parameters are:
  64          *   - server:      A server info structure in the format required by each
  65          *                  element in $wgDBServers.
  66          *
  67          *   - servers:     An array of server info structures describing a set of database servers
  68          *                  to distribute keys to. If this is specified, the "server" option will be
  69          *                  ignored. If string keys are used, then they will be used for consistent
  70          *                  hashing *instead* of the host name (from the server config). This is useful
  71          *                  when a cluster is replicated to another site (with different host names)
  72          *                  but each server has a corresponding replica in the other cluster.
  73          *
  74          *   - purgePeriod: The average number of object cache requests in between
  75          *                  garbage collection operations, where expired entries
  76          *                  are removed from the database. Or in other words, the
  77          *                  reciprocal of the probability of purging on any given
  78          *                  request. If this is set to zero, purging will never be
  79          *                  done.
  80          *
  81          *   - tableName:   The table name to use, default is "objectcache".
  82          *
  83          *   - shards:      The number of tables to use for data storage on each server.
  84          *                  If this is more than 1, table names will be formed in the style
  85          *                  objectcacheNNN where NNN is the shard index, between 0 and
  86          *                  shards-1. The number of digits will be the minimum number
  87          *                  required to hold the largest shard index. Data will be
  88          *                  distributed across all tables by key hash. This is for
  89          *                  MySQL bugs 61735 and 61736.
  90          *   - slaveOnly:   Whether to only use replica DBs and avoid triggering
  91          *                  garbage collection logic of expired items. This only
  92          *                  makes sense if the primary DB is used and only if get()
  93          *                  calls will be used. This is used by ReplicatedBagOStuff.
  94          *   - syncTimeout: Max seconds to wait for replica DBs to catch up for WRITE_SYNC.
  95          *
  96          * @param array $params
  97          */
  98         public function __construct( $params ) {
  99                 parent::__construct( $params );
 100
 101                 $this->attrMap[self::ATTR_EMULATION] = self::QOS_EMULATION_SQL;
 102                 $this->attrMap[self::ATTR_SYNCWRITES] = self::QOS_SYNCWRITES_NONE;
 103
 104                 if ( isset( $params['servers'] ) ) {
 105                         $this->serverInfos = [];
 106                         $this->serverTags = [];
 107                         $this->numServers = count( $params['servers'] );
 108                         $index = 0;
 109                         foreach ( $params['servers'] as $tag => $info ) {
 110                                 $this->serverInfos[$index] = $info;
 111                                 if ( is_string( $tag ) ) {
 112                                         $this->serverTags[$index] = $tag;
 113                                 } else {
 114                                         $this->serverTags[$index] = isset( $info['host'] ) ? $info['host'] : "#$index";
 115                                 }
 116                                 ++$index;
 117                         }
 118                 } elseif ( isset( $params['server'] ) ) {
 119                         $this->serverInfos = [ $params['server'] ];
 120                         $this->numServers = count( $this->serverInfos );
 121                 } else {
 122                         // Default to using the main wiki's database servers
 123                         $this->serverInfos = false;
 124                         $this->numServers = 1;
 125                         $this->attrMap[self::ATTR_SYNCWRITES] = self::QOS_SYNCWRITES_BE;
 126                 }
 127                 if ( isset( $params['purgePeriod'] ) ) {
 128                         $this->purgePeriod = intval( $params['purgePeriod'] );
 129                 }
 130                 if ( isset( $params['tableName'] ) ) {
 131                         $this->tableName = $params['tableName'];
 132                 }
 133                 if ( isset( $params['shards'] ) ) {
 134                         $this->shards = intval( $params['shards'] );
 135                 }
 136                 if ( isset( $params['syncTimeout'] ) ) {
 137                         $this->syncTimeout = $params['syncTimeout'];
 138                 }
 139                 $this->replicaOnly = !empty( $params['slaveOnly'] );
 140         }
 141
 142         protected function getSeparateMainLB() {
 143                 global $wgDBtype;
 144
 145                 if ( $wgDBtype === 'mysql' && $this->usesMainDB() ) {
 146                         if ( !$this->separateMainLB ) {
 147                                 // We must keep a separate connection to MySQL in order to avoid deadlocks
 148                                 $lbFactory = MediaWikiServices::getInstance()->getDBLoadBalancerFactory();
 149                                 $this->separateMainLB = $lbFactory->newMainLB();
 150                         }
 151                         return $this->separateMainLB;
 152                 } else {
 153                         // However, SQLite has an opposite behavior. And PostgreSQL needs to know
 154                         // if we are in transaction or not (@TODO: find some PostgreSQL work-around).
 155                         return null;
 156                 }
 157         }
 158
 159         /**
 160          * Get a connection to the specified database
 161          *
 162          * @param int $serverIndex
 163          * @return IDatabase
 164          * @throws MWException
 165          */
 166         protected function getDB( $serverIndex ) {
 167                 if ( !isset( $this->conns[$serverIndex] ) ) {
 168                         if ( $serverIndex >= $this->numServers ) {
 169                                 throw new MWException( __METHOD__ . ": Invalid server index \"$serverIndex\"" );
 170                         }
 171
 172                         # Don't keep timing out trying to connect for each call if the DB is down
 173                         if ( isset( $this->connFailureErrors[$serverIndex] )
 174                                 && ( time() - $this->connFailureTimes[$serverIndex] ) < 60
 175                         ) {
 176                                 throw $this->connFailureErrors[$serverIndex];
 177                         }
 178
 179                         # If server connection info was given, use that
 180                         if ( $this->serverInfos ) {
 181                                 $info = $this->serverInfos[$serverIndex];
 182                                 $type = isset( $info['type'] ) ? $info['type'] : 'mysql';
 183                                 $host = isset( $info['host'] ) ? $info['host'] : '[unknown]';
 184                                 $this->logger->debug( __CLASS__ . ": connecting to $host" );
 185                                 // Use a blank trx profiler to ignore expections as this is a cache
 186                                 $info['trxProfiler'] = new TransactionProfiler();
 187                                 $db = Database::factory( $type, $info );
 188                                 $db->clearFlag( DBO_TRX );
 189                         } else {
 190                                 $index = $this->replicaOnly ? DB_REPLICA : DB_MASTER;
 191                                 if ( $this->getSeparateMainLB() ) {
 192                                         $db = $this->getSeparateMainLB()->getConnection( $index );
 193                                         $db->clearFlag( DBO_TRX ); // auto-commit mode
 194                                 } else {
 195                                         $db = wfGetDB( $index );
 196                                         // Can't mess with transaction rounds (DBO_TRX) :(
 197                                 }
 198                         }
 199                         $this->logger->debug( sprintf( "Connection %s will be used for SqlBagOStuff", $db ) );
 200                         $this->conns[$serverIndex] = $db;
 201                 }
 202
 203                 return $this->conns[$serverIndex];
 204         }
 205
 206         /**
 207          * Get the server index and table name for a given key
 208          * @param string $key
 209          * @return array Server index and table name
 210          */
 211         protected function getTableByKey( $key ) {
 212                 if ( $this->shards > 1 ) {
 213                         $hash = hexdec( substr( md5( $key ), 0, 8 ) ) & 0x7fffffff;
 214                         $tableIndex = $hash % $this->shards;
 215                 } else {
 216                         $tableIndex = 0;
 217                 }
 218                 if ( $this->numServers > 1 ) {
 219                         $sortedServers = $this->serverTags;
 220                         ArrayUtils::consistentHashSort( $sortedServers, $key );
 221                         reset( $sortedServers );
 222                         $serverIndex = key( $sortedServers );
 223                 } else {
 224                         $serverIndex = 0;
 225                 }
 226                 return [ $serverIndex, $this->getTableNameByShard( $tableIndex ) ];
 227         }
 228
 229         /**
 230          * Get the table name for a given shard index
 231          * @param int $index
 232          * @return string
 233          */
 234         protected function getTableNameByShard( $index ) {
 235                 if ( $this->shards > 1 ) {
 236                         $decimals = strlen( $this->shards - 1 );
 237                         return $this->tableName .
 238                                 sprintf( "%0{$decimals}d", $index );
 239                 } else {
 240                         return $this->tableName;
 241                 }
 242         }
 243
 244         protected function doGet( $key, $flags = 0 ) {
 245                 $casToken = null;
 246
 247                 return $this->getWithToken( $key, $casToken, $flags );
 248         }
 249
 250         protected function getWithToken( $key, &$casToken, $flags = 0 ) {
 251                 $values = $this->getMulti( [ $key ] );
 252                 if ( array_key_exists( $key, $values ) ) {
 253                         $casToken = $values[$key];
 254                         return $values[$key];
 255                 }
 256                 return false;
 257         }
 258
 259         public function getMulti( array $keys, $flags = 0 ) {
 260                 $values = []; // array of (key => value)
 261
 262                 $keysByTable = [];
 263                 foreach ( $keys as $key ) {
 264                         list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
 265                         $keysByTable[$serverIndex][$tableName][] = $key;
 266                 }
 267
 268                 $this->garbageCollect(); // expire old entries if any
 269
 270                 $dataRows = [];
 271                 foreach ( $keysByTable as $serverIndex => $serverKeys ) {
 272                         try {
 273                                 $db = $this->getDB( $serverIndex );
 274                                 foreach ( $serverKeys as $tableName => $tableKeys ) {
 275                                         $res = $db->select( $tableName,
 276                                                 [ 'keyname', 'value', 'exptime' ],
 277                                                 [ 'keyname' => $tableKeys ],
 278                                                 __METHOD__,
 279                                                 // Approximate write-on-the-fly BagOStuff API via blocking.
 280                                                 // This approximation fails if a ROLLBACK happens (which is rare).
 281                                                 // We do not want to flush the TRX as that can break callers.
 282                                                 $db->trxLevel() ? [ 'LOCK IN SHARE MODE' ] : []
 283                                         );
 284                                         if ( $res === false ) {
 285                                                 continue;
 286                                         }
 287                                         foreach ( $res as $row ) {
 288                                                 $row->serverIndex = $serverIndex;
 289                                                 $row->tableName = $tableName;
 290                                                 $dataRows[$row->keyname] = $row;
 291                                         }
 292                                 }
 293                         } catch ( DBError $e ) {
 294                                 $this->handleReadError( $e, $serverIndex );
 295                         }
 296                 }
 297
 298                 foreach ( $keys as $key ) {
 299                         if ( isset( $dataRows[$key] ) ) { // HIT?
 300                                 $row = $dataRows[$key];
 301                                 $this->debug( "get: retrieved data; expiry time is " . $row->exptime );
 302                                 $db = null;
 303                                 try {
 304                                         $db = $this->getDB( $row->serverIndex );
 305                                         if ( $this->isExpired( $db, $row->exptime ) ) { // MISS
 306                                                 $this->debug( "get: key has expired" );
 307                                         } else { // HIT
 308                                                 $values[$key] = $this->unserialize( $db->decodeBlob( $row->value ) );
 309                                         }
 310                                 } catch ( DBQueryError $e ) {
 311                                         $this->handleWriteError( $e, $db, $row->serverIndex );
 312                                 }
 313                         } else { // MISS
 314                                 $this->debug( 'get: no matching rows' );
 315                         }
 316                 }
 317
 318                 return $values;
 319         }
 320
 321         public function setMulti( array $data, $expiry = 0 ) {
 322                 $keysByTable = [];
 323                 foreach ( $data as $key => $value ) {
 324                         list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
 325                         $keysByTable[$serverIndex][$tableName][] = $key;
 326                 }
 327
 328                 $this->garbageCollect(); // expire old entries if any
 329
 330                 $result = true;
 331                 $exptime = (int)$expiry;
 332                 foreach ( $keysByTable as $serverIndex => $serverKeys ) {
 333                         $db = null;
 334                         try {
 335                                 $db = $this->getDB( $serverIndex );
 336                         } catch ( DBError $e ) {
 337                                 $this->handleWriteError( $e, $db, $serverIndex );
 338                                 $result = false;
 339                                 continue;
 340                         }
 341
 342                         if ( $exptime < 0 ) {
 343                                 $exptime = 0;
 344                         }
 345
 346                         if ( $exptime == 0 ) {
 347                                 $encExpiry = $this->getMaxDateTime( $db );
 348                         } else {
 349                                 $exptime = $this->convertExpiry( $exptime );
 350                                 $encExpiry = $db->timestamp( $exptime );
 351                         }
 352                         foreach ( $serverKeys as $tableName => $tableKeys ) {
 353                                 $rows = [];
 354                                 foreach ( $tableKeys as $key ) {
 355                                         $rows[] = [
 356                                                 'keyname' => $key,
 357                                                 'value' => $db->encodeBlob( $this->serialize( $data[$key] ) ),
 358                                                 'exptime' => $encExpiry,
 359                                         ];
 360                                 }
 361
 362                                 try {
 363                                         $db->replace(
 364                                                 $tableName,
 365                                                 [ 'keyname' ],
 366                                                 $rows,
 367                                                 __METHOD__
 368                                         );
 369                                 } catch ( DBError $e ) {
 370                                         $this->handleWriteError( $e, $db, $serverIndex );
 371                                         $result = false;
 372                                 }
 373
 374                         }
 375
 376                 }
 377
 378                 return $result;
 379         }
 380
 381         public function set( $key, $value, $exptime = 0, $flags = 0 ) {
 382                 $ok = $this->setMulti( [ $key => $value ], $exptime );
 383                 if ( ( $flags & self::WRITE_SYNC ) == self::WRITE_SYNC ) {
 384                         $ok = $this->waitForReplication() && $ok;
 385                 }
 386
 387                 return $ok;
 388         }
 389
 390         protected function cas( $casToken, $key, $value, $exptime = 0 ) {
 391                 list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
 392                 $db = null;
 393                 try {
 394                         $db = $this->getDB( $serverIndex );
 395                         $exptime = intval( $exptime );
 396
 397                         if ( $exptime < 0 ) {
 398                                 $exptime = 0;
 399                         }
 400
 401                         if ( $exptime == 0 ) {
 402                                 $encExpiry = $this->getMaxDateTime( $db );
 403                         } else {
 404                                 $exptime = $this->convertExpiry( $exptime );
 405                                 $encExpiry = $db->timestamp( $exptime );
 406                         }
 407                         // (bug 24425) use a replace if the db supports it instead of
 408                         // delete/insert to avoid clashes with conflicting keynames
 409                         $db->update(
 410                                 $tableName,
 411                                 [
 412                                         'keyname' => $key,
 413                                         'value' => $db->encodeBlob( $this->serialize( $value ) ),
 414                                         'exptime' => $encExpiry
 415                                 ],
 416                                 [
 417                                         'keyname' => $key,
 418                                         'value' => $db->encodeBlob( $this->serialize( $casToken ) )
 419                                 ],
 420                                 __METHOD__
 421                         );
 422                 } catch ( DBQueryError $e ) {
 423                         $this->handleWriteError( $e, $db, $serverIndex );
 424
 425                         return false;
 426                 }
 427
 428                 return (bool)$db->affectedRows();
 429         }
 430
 431         public function delete( $key ) {
 432                 list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
 433                 $db = null;
 434                 try {
 435                         $db = $this->getDB( $serverIndex );
 436                         $db->delete(
 437                                 $tableName,
 438                                 [ 'keyname' => $key ],
 439                                 __METHOD__ );
 440                 } catch ( DBError $e ) {
 441                         $this->handleWriteError( $e, $db, $serverIndex );
 442                         return false;
 443                 }
 444
 445                 return true;
 446         }
 447
 448         public function incr( $key, $step = 1 ) {
 449                 list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
 450                 $db = null;
 451                 try {
 452                         $db = $this->getDB( $serverIndex );
 453                         $step = intval( $step );
 454                         $row = $db->selectRow(
 455                                 $tableName,
 456                                 [ 'value', 'exptime' ],
 457                                 [ 'keyname' => $key ],
 458                                 __METHOD__,
 459                                 [ 'FOR UPDATE' ] );
 460                         if ( $row === false ) {
 461                                 // Missing
 462
 463                                 return null;
 464                         }
 465                         $db->delete( $tableName, [ 'keyname' => $key ], __METHOD__ );
 466                         if ( $this->isExpired( $db, $row->exptime ) ) {
 467                                 // Expired, do not reinsert
 468
 469                                 return null;
 470                         }
 471
 472                         $oldValue = intval( $this->unserialize( $db->decodeBlob( $row->value ) ) );
 473                         $newValue = $oldValue + $step;
 474                         $db->insert( $tableName,
 475                                 [
 476                                         'keyname' => $key,
 477                                         'value' => $db->encodeBlob( $this->serialize( $newValue ) ),
 478                                         'exptime' => $row->exptime
 479                                 ], __METHOD__, 'IGNORE' );
 480
 481                         if ( $db->affectedRows() == 0 ) {
 482                                 // Race condition. See bug 28611
 483                                 $newValue = null;
 484                         }
 485                 } catch ( DBError $e ) {
 486                         $this->handleWriteError( $e, $db, $serverIndex );
 487                         return null;
 488                 }
 489
 490                 return $newValue;
 491         }
 492
 493         public function merge( $key, callable $callback, $exptime = 0, $attempts = 10, $flags = 0 ) {
 494                 $ok = $this->mergeViaCas( $key, $callback, $exptime, $attempts );
 495                 if ( ( $flags & self::WRITE_SYNC ) == self::WRITE_SYNC ) {
 496                         $ok = $this->waitForReplication() && $ok;
 497                 }
 498
 499                 return $ok;
 500         }
 501
 502         public function changeTTL( $key, $expiry = 0 ) {
 503                 list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
 504                 $db = null;
 505                 try {
 506                         $db = $this->getDB( $serverIndex );
 507                         $db->update(
 508                                 $tableName,
 509                                 [ 'exptime' => $db->timestamp( $this->convertExpiry( $expiry ) ) ],
 510                                 [ 'keyname' => $key, 'exptime > ' . $db->addQuotes( $db->timestamp( time() ) ) ],
 511                                 __METHOD__
 512                         );
 513                         if ( $db->affectedRows() == 0 ) {
 514                                 return false;
 515                         }
 516                 } catch ( DBError $e ) {
 517                         $this->handleWriteError( $e, $db, $serverIndex );
 518                         return false;
 519                 }
 520
 521                 return true;
 522         }
 523
 524         /**
 525          * @param IDatabase $db
 526          * @param string $exptime
 527          * @return bool
 528          */
 529         protected function isExpired( $db, $exptime ) {
 530                 return $exptime != $this->getMaxDateTime( $db ) && wfTimestamp( TS_UNIX, $exptime ) < time();
 531         }
 532
 533         /**
 534          * @param IDatabase $db
 535          * @return string
 536          */
 537         protected function getMaxDateTime( $db ) {
 538                 if ( time() > 0x7fffffff ) {
 539                         return $db->timestamp( 1 << 62 );
 540                 } else {
 541                         return $db->timestamp( 0x7fffffff );
 542                 }
 543         }
 544
 545         protected function garbageCollect() {
 546                 if ( !$this->purgePeriod || $this->replicaOnly ) {
 547                         // Disabled
 548                         return;
 549                 }
 550                 // Only purge on one in every $this->purgePeriod requests.
 551                 if ( $this->purgePeriod !== 1 && mt_rand( 0, $this->purgePeriod - 1 ) ) {
 552                         return;
 553                 }
 554                 $now = time();
 555                 // Avoid repeating the delete within a few seconds
 556                 if ( $now > ( $this->lastExpireAll + 1 ) ) {
 557                         $this->lastExpireAll = $now;
 558                         $this->expireAll();
 559                 }
 560         }
 561
 562         public function expireAll() {
 563                 $this->deleteObjectsExpiringBefore( wfTimestampNow() );
 564         }
 565
 566         /**
 567          * Delete objects from the database which expire before a certain date.
 568          * @param string $timestamp
 569          * @param bool|callable $progressCallback
 570          * @return bool
 571          */
 572         public function deleteObjectsExpiringBefore( $timestamp, $progressCallback = false ) {
 573                 for ( $serverIndex = 0; $serverIndex < $this->numServers; $serverIndex++ ) {
 574                         $db = null;
 575                         try {
 576                                 $db = $this->getDB( $serverIndex );
 577                                 $dbTimestamp = $db->timestamp( $timestamp );
 578                                 $totalSeconds = false;
 579                                 $baseConds = [ 'exptime < ' . $db->addQuotes( $dbTimestamp ) ];
 580                                 for ( $i = 0; $i < $this->shards; $i++ ) {
 581                                         $maxExpTime = false;
 582                                         while ( true ) {
 583                                                 $conds = $baseConds;
 584                                                 if ( $maxExpTime !== false ) {
 585                                                         $conds[] = 'exptime > ' . $db->addQuotes( $maxExpTime );
 586                                                 }
 587                                                 $rows = $db->select(
 588                                                         $this->getTableNameByShard( $i ),
 589                                                         [ 'keyname', 'exptime' ],
 590                                                         $conds,
 591                                                         __METHOD__,
 592                                                         [ 'LIMIT' => 100, 'ORDER BY' => 'exptime' ] );
 593                                                 if ( $rows === false || !$rows->numRows() ) {
 594                                                         break;
 595                                                 }
 596                                                 $keys = [];
 597                                                 $row = $rows->current();
 598                                                 $minExpTime = $row->exptime;
 599                                                 if ( $totalSeconds === false ) {
 600                                                         $totalSeconds = wfTimestamp( TS_UNIX, $timestamp )
 601                                                                 - wfTimestamp( TS_UNIX, $minExpTime );
 602                                                 }
 603                                                 foreach ( $rows as $row ) {
 604                                                         $keys[] = $row->keyname;
 605                                                         $maxExpTime = $row->exptime;
 606                                                 }
 607
 608                                                 $db->delete(
 609                                                         $this->getTableNameByShard( $i ),
 610                                                         [
 611                                                                 'exptime >= ' . $db->addQuotes( $minExpTime ),
 612                                                                 'exptime < ' . $db->addQuotes( $dbTimestamp ),
 613                                                                 'keyname' => $keys
 614                                                         ],
 615                                                         __METHOD__ );
 616
 617                                                 if ( $progressCallback ) {
 618                                                         if ( intval( $totalSeconds ) === 0 ) {
 619                                                                 $percent = 0;
 620                                                         } else {
 621                                                                 $remainingSeconds = wfTimestamp( TS_UNIX, $timestamp )
 622                                                                         - wfTimestamp( TS_UNIX, $maxExpTime );
 623                                                                 if ( $remainingSeconds > $totalSeconds ) {
 624                                                                         $totalSeconds = $remainingSeconds;
 625                                                                 }
 626                                                                 $processedSeconds = $totalSeconds - $remainingSeconds;
 627                                                                 $percent = ( $i + $processedSeconds / $totalSeconds )
 628                                                                         / $this->shards * 100;
 629                                                         }
 630                                                         $percent = ( $percent / $this->numServers )
 631                                                                 + ( $serverIndex / $this->numServers * 100 );
 632                                                         call_user_func( $progressCallback, $percent );
 633                                                 }
 634                                         }
 635                                 }
 636                         } catch ( DBError $e ) {
 637                                 $this->handleWriteError( $e, $db, $serverIndex );
 638                                 return false;
 639                         }
 640                 }
 641                 return true;
 642         }
 643
 644         /**
 645          * Delete content of shard tables in every server.
 646          * Return true if the operation is successful, false otherwise.
 647          * @return bool
 648          */
 649         public function deleteAll() {
 650                 for ( $serverIndex = 0; $serverIndex < $this->numServers; $serverIndex++ ) {
 651                         $db = null;
 652                         try {
 653                                 $db = $this->getDB( $serverIndex );
 654                                 for ( $i = 0; $i < $this->shards; $i++ ) {
 655                                         $db->delete( $this->getTableNameByShard( $i ), '*', __METHOD__ );
 656                                 }
 657                         } catch ( DBError $e ) {
 658                                 $this->handleWriteError( $e, $db, $serverIndex );
 659                                 return false;
 660                         }
 661                 }
 662                 return true;
 663         }
 664
 665         /**
 666          * Serialize an object and, if possible, compress the representation.
 667          * On typical message and page data, this can provide a 3X decrease
 668          * in storage requirements.
 669          *
 670          * @param mixed $data
 671          * @return string
 672          */
 673         protected function serialize( &$data ) {
 674                 $serial = serialize( $data );
 675
 676                 if ( function_exists( 'gzdeflate' ) ) {
 677                         return gzdeflate( $serial );
 678                 } else {
 679                         return $serial;
 680                 }
 681         }
 682
 683         /**
 684          * Unserialize and, if necessary, decompress an object.
 685          * @param string $serial
 686          * @return mixed
 687          */
 688         protected function unserialize( $serial ) {
 689                 if ( function_exists( 'gzinflate' ) ) {
 690                         MediaWiki\suppressWarnings();
 691                         $decomp = gzinflate( $serial );
 692                         MediaWiki\restoreWarnings();
 693
 694                         if ( false !== $decomp ) {
 695                                 $serial = $decomp;
 696                         }
 697                 }
 698
 699                 $ret = unserialize( $serial );
 700
 701                 return $ret;
 702         }
 703
 704         /**
 705          * Handle a DBError which occurred during a read operation.
 706          *
 707          * @param DBError $exception
 708          * @param int $serverIndex
 709          */
 710         protected function handleReadError( DBError $exception, $serverIndex ) {
 711                 if ( $exception instanceof DBConnectionError ) {
 712                         $this->markServerDown( $exception, $serverIndex );
 713                 }
 714                 $this->logger->error( "DBError: {$exception->getMessage()}" );
 715                 if ( $exception instanceof DBConnectionError ) {
 716                         $this->setLastError( BagOStuff::ERR_UNREACHABLE );
 717                         $this->logger->debug( __METHOD__ . ": ignoring connection error" );
 718                 } else {
 719                         $this->setLastError( BagOStuff::ERR_UNEXPECTED );
 720                         $this->logger->debug( __METHOD__ . ": ignoring query error" );
 721                 }
 722         }
 723
 724         /**
 725          * Handle a DBQueryError which occurred during a write operation.
 726          *
 727          * @param DBError $exception
 728          * @param IDatabase|null $db DB handle or null if connection failed
 729          * @param int $serverIndex
 730          * @throws Exception
 731          */
 732         protected function handleWriteError( DBError $exception, IDatabase $db = null, $serverIndex ) {
 733                 if ( !$db ) {
 734                         $this->markServerDown( $exception, $serverIndex );
 735                 } elseif ( $db->wasReadOnlyError() ) {
 736                         if ( $db->trxLevel() && $this->usesMainDB() ) {
 737                                 // Errors like deadlocks and connection drops already cause rollback.
 738                                 // For consistency, we have no choice but to throw an error and trigger
 739                                 // complete rollback if the main DB is also being used as the cache DB.
 740                                 throw $exception;
 741                         }
 742                 }
 743
 744                 $this->logger->error( "DBError: {$exception->getMessage()}" );
 745                 if ( $exception instanceof DBConnectionError ) {
 746                         $this->setLastError( BagOStuff::ERR_UNREACHABLE );
 747                         $this->logger->debug( __METHOD__ . ": ignoring connection error" );
 748                 } else {
 749                         $this->setLastError( BagOStuff::ERR_UNEXPECTED );
 750                         $this->logger->debug( __METHOD__ . ": ignoring query error" );
 751                 }
 752         }
 753
 754         /**
 755          * Mark a server down due to a DBConnectionError exception
 756          *
 757          * @param DBError $exception
 758          * @param int $serverIndex
 759          */
 760         protected function markServerDown( DBError $exception, $serverIndex ) {
 761                 unset( $this->conns[$serverIndex] ); // bug T103435
 762
 763                 if ( isset( $this->connFailureTimes[$serverIndex] ) ) {
 764                         if ( time() - $this->connFailureTimes[$serverIndex] >= 60 ) {
 765                                 unset( $this->connFailureTimes[$serverIndex] );
 766                                 unset( $this->connFailureErrors[$serverIndex] );
 767                         } else {
 768                                 $this->logger->debug( __METHOD__ . ": Server #$serverIndex already down" );
 769                                 return;
 770                         }
 771                 }
 772                 $now = time();
 773                 $this->logger->info( __METHOD__ . ": Server #$serverIndex down until " . ( $now + 60 ) );
 774                 $this->connFailureTimes[$serverIndex] = $now;
 775                 $this->connFailureErrors[$serverIndex] = $exception;
 776         }
 777
 778         /**
 779          * Create shard tables. For use from eval.php.
 780          */
 781         public function createTables() {
 782                 for ( $serverIndex = 0; $serverIndex < $this->numServers; $serverIndex++ ) {
 783                         $db = $this->getDB( $serverIndex );
 784                         if ( $db->getType() !== 'mysql' ) {
 785                                 throw new MWException( __METHOD__ . ' is not supported on this DB server' );
 786                         }
 787
 788                         for ( $i = 0; $i < $this->shards; $i++ ) {
 789                                 $db->query(
 790                                         'CREATE TABLE ' . $db->tableName( $this->getTableNameByShard( $i ) ) .
 791                                         ' LIKE ' . $db->tableName( 'objectcache' ),
 792                                         __METHOD__ );
 793                         }
 794                 }
 795         }
 796
 797         /**
 798          * @return bool Whether the main DB is used, e.g. wfGetDB( DB_MASTER )
 799          */
 800         protected function usesMainDB() {
 801                 return !$this->serverInfos;
 802         }
 803
 804         protected function waitForReplication() {
 805                 if ( !$this->usesMainDB() ) {
 806                         // Custom DB server list; probably doesn't use replication
 807                         return true;
 808                 }
 809
 810                 $lb = $this->getSeparateMainLB()
 811                         ?: MediaWikiServices::getInstance()->getDBLoadBalancer();
 812
 813                 if ( $lb->getServerCount() <= 1 ) {
 814                         return true; // no replica DBs
 815                 }
 816
 817                 // Main LB is used; wait for any replica DBs to catch up
 818                 $masterPos = $lb->getMasterPos();
 819
 820                 $loop = new WaitConditionLoop(
 821                         function () use ( $lb, $masterPos ) {
 822                                 return $lb->waitForAll( $masterPos, 1 );
 823                         },
 824                         $this->syncTimeout,
 825                         $this->busyCallbacks
 826                 );
 827
 828                 return ( $loop->invoke() === $loop::CONDITION_REACHED );
 829         }
 830 }