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 Wikimedia\Rdbms\DBError;
  27 use Wikimedia\Rdbms\DBQueryError;
  28 use Wikimedia\Rdbms\DBConnectionError;
  29 use \MediaWiki\MediaWikiServices;
  30 use \Wikimedia\WaitConditionLoop;
  31 use \Wikimedia\Rdbms\TransactionProfiler;
  32 use Wikimedia\Rdbms\LoadBalancer;
  33
  34 /**
  35  * Class to store objects in the database
  36  *
  37  * @ingroup Cache
  38  */
  39 class SqlBagOStuff extends BagOStuff {
  40         /** @var array[] (server index => server config) */
  41         protected $serverInfos;
  42         /** @var string[] (server index => tag/host name) */
  43         protected $serverTags;
  44         /** @var int */
  45         protected $numServers;
  46         /** @var int */
  47         protected $lastExpireAll = 0;
  48         /** @var int */
  49         protected $purgePeriod = 100;
  50         /** @var int */
  51         protected $shards = 1;
  52         /** @var string */
  53         protected $tableName = 'objectcache';
  54         /** @var bool */
  55         protected $replicaOnly = false;
  56         /** @var int */
  57         protected $syncTimeout = 3;
  58
  59         /** @var LoadBalancer|null */
  60         protected $separateMainLB;
  61         /** @var array */
  62         protected $conns;
  63         /** @var array UNIX timestamps */
  64         protected $connFailureTimes = [];
  65         /** @var array Exceptions */
  66         protected $connFailureErrors = [];
  67
  68         /**
  69          * Constructor. Parameters are:
  70          *   - server:      A server info structure in the format required by each
  71          *                  element in $wgDBServers.
  72          *
  73          *   - servers:     An array of server info structures describing a set of database servers
  74          *                  to distribute keys to. If this is specified, the "server" option will be
  75          *                  ignored. If string keys are used, then they will be used for consistent
  76          *                  hashing *instead* of the host name (from the server config). This is useful
  77          *                  when a cluster is replicated to another site (with different host names)
  78          *                  but each server has a corresponding replica in the other cluster.
  79          *
  80          *   - purgePeriod: The average number of object cache requests in between
  81          *                  garbage collection operations, where expired entries
  82          *                  are removed from the database. Or in other words, the
  83          *                  reciprocal of the probability of purging on any given
  84          *                  request. If this is set to zero, purging will never be
  85          *                  done.
  86          *
  87          *   - tableName:   The table name to use, default is "objectcache".
  88          *
  89          *   - shards:      The number of tables to use for data storage on each server.
  90          *                  If this is more than 1, table names will be formed in the style
  91          *                  objectcacheNNN where NNN is the shard index, between 0 and
  92          *                  shards-1. The number of digits will be the minimum number
  93          *                  required to hold the largest shard index. Data will be
  94          *                  distributed across all tables by key hash. This is for
  95          *                  MySQL bugs 61735 and 61736.
  96          *   - slaveOnly:   Whether to only use replica DBs and avoid triggering
  97          *                  garbage collection logic of expired items. This only
  98          *                  makes sense if the primary DB is used and only if get()
  99          *                  calls will be used. This is used by ReplicatedBagOStuff.
 100          *   - syncTimeout: Max seconds to wait for replica DBs to catch up for WRITE_SYNC.
 101          *
 102          * @param array $params
 103          */
 104         public function __construct( $params ) {
 105                 parent::__construct( $params );
 106
 107                 $this->attrMap[self::ATTR_EMULATION] = self::QOS_EMULATION_SQL;
 108                 $this->attrMap[self::ATTR_SYNCWRITES] = self::QOS_SYNCWRITES_NONE;
 109
 110                 if ( isset( $params['servers'] ) ) {
 111                         $this->serverInfos = [];
 112                         $this->serverTags = [];
 113                         $this->numServers = count( $params['servers'] );
 114                         $index = 0;
 115                         foreach ( $params['servers'] as $tag => $info ) {
 116                                 $this->serverInfos[$index] = $info;
 117                                 if ( is_string( $tag ) ) {
 118                                         $this->serverTags[$index] = $tag;
 119                                 } else {
 120                                         $this->serverTags[$index] = isset( $info['host'] ) ? $info['host'] : "#$index";
 121                                 }
 122                                 ++$index;
 123                         }
 124                 } elseif ( isset( $params['server'] ) ) {
 125                         $this->serverInfos = [ $params['server'] ];
 126                         $this->numServers = count( $this->serverInfos );
 127                 } else {
 128                         // Default to using the main wiki's database servers
 129                         $this->serverInfos = false;
 130                         $this->numServers = 1;
 131                         $this->attrMap[self::ATTR_SYNCWRITES] = self::QOS_SYNCWRITES_BE;
 132                 }
 133                 if ( isset( $params['purgePeriod'] ) ) {
 134                         $this->purgePeriod = intval( $params['purgePeriod'] );
 135                 }
 136                 if ( isset( $params['tableName'] ) ) {
 137                         $this->tableName = $params['tableName'];
 138                 }
 139                 if ( isset( $params['shards'] ) ) {
 140                         $this->shards = intval( $params['shards'] );
 141                 }
 142                 if ( isset( $params['syncTimeout'] ) ) {
 143                         $this->syncTimeout = $params['syncTimeout'];
 144                 }
 145                 $this->replicaOnly = !empty( $params['slaveOnly'] );
 146         }
 147
 148         /**
 149          * Get a connection to the specified database
 150          *
 151          * @param int $serverIndex
 152          * @return Database
 153          * @throws MWException
 154          */
 155         protected function getDB( $serverIndex ) {
 156                 if ( !isset( $this->conns[$serverIndex] ) ) {
 157                         if ( $serverIndex >= $this->numServers ) {
 158                                 throw new MWException( __METHOD__ . ": Invalid server index \"$serverIndex\"" );
 159                         }
 160
 161                         # Don't keep timing out trying to connect for each call if the DB is down
 162                         if ( isset( $this->connFailureErrors[$serverIndex] )
 163                                 && ( time() - $this->connFailureTimes[$serverIndex] ) < 60
 164                         ) {
 165                                 throw $this->connFailureErrors[$serverIndex];
 166                         }
 167
 168                         if ( $this->serverInfos ) {
 169                                 // Use custom database defined by server connection info
 170                                 $info = $this->serverInfos[$serverIndex];
 171                                 $type = isset( $info['type'] ) ? $info['type'] : 'mysql';
 172                                 $host = isset( $info['host'] ) ? $info['host'] : '[unknown]';
 173                                 $this->logger->debug( __CLASS__ . ": connecting to $host" );
 174                                 // Use a blank trx profiler to ignore expections as this is a cache
 175                                 $info['trxProfiler'] = new TransactionProfiler();
 176                                 $db = Database::factory( $type, $info );
 177                                 $db->clearFlag( DBO_TRX ); // auto-commit mode
 178                         } else {
 179                                 // Use the main LB database
 180                                 $lb = MediaWikiServices::getInstance()->getDBLoadBalancer();
 181                                 $index = $this->replicaOnly ? DB_REPLICA : DB_MASTER;
 182                                 if ( $lb->getServerType( $lb->getWriterIndex() ) !== 'sqlite' ) {
 183                                         // Keep a separate connection to avoid contention and deadlocks
 184                                         $db = $lb->getConnection( $index, [], false, $lb::CONN_TRX_AUTO );
 185                                         // @TODO: Use a blank trx profiler to ignore expections as this is a cache
 186                                 } else {
 187                                         // However, SQLite has the opposite behavior due to DB-level locking.
 188                                         // Stock sqlite MediaWiki installs use a separate sqlite cache DB instead.
 189                                         $db = $lb->getConnection( $index );
 190                                 }
 191                         }
 192
 193                         $this->logger->debug( sprintf( "Connection %s will be used for SqlBagOStuff", $db ) );
 194                         $this->conns[$serverIndex] = $db;
 195                 }
 196
 197                 return $this->conns[$serverIndex];
 198         }
 199
 200         /**
 201          * Get the server index and table name for a given key
 202          * @param string $key
 203          * @return array Server index and table name
 204          */
 205         protected function getTableByKey( $key ) {
 206                 if ( $this->shards > 1 ) {
 207                         $hash = hexdec( substr( md5( $key ), 0, 8 ) ) & 0x7fffffff;
 208                         $tableIndex = $hash % $this->shards;
 209                 } else {
 210                         $tableIndex = 0;
 211                 }
 212                 if ( $this->numServers > 1 ) {
 213                         $sortedServers = $this->serverTags;
 214                         ArrayUtils::consistentHashSort( $sortedServers, $key );
 215                         reset( $sortedServers );
 216                         $serverIndex = key( $sortedServers );
 217                 } else {
 218                         $serverIndex = 0;
 219                 }
 220                 return [ $serverIndex, $this->getTableNameByShard( $tableIndex ) ];
 221         }
 222
 223         /**
 224          * Get the table name for a given shard index
 225          * @param int $index
 226          * @return string
 227          */
 228         protected function getTableNameByShard( $index ) {
 229                 if ( $this->shards > 1 ) {
 230                         $decimals = strlen( $this->shards - 1 );
 231                         return $this->tableName .
 232                                 sprintf( "%0{$decimals}d", $index );
 233                 } else {
 234                         return $this->tableName;
 235                 }
 236         }
 237
 238         protected function doGet( $key, $flags = 0 ) {
 239                 $casToken = null;
 240
 241                 return $this->getWithToken( $key, $casToken, $flags );
 242         }
 243
 244         protected function getWithToken( $key, &$casToken, $flags = 0 ) {
 245                 $values = $this->getMulti( [ $key ] );
 246                 if ( array_key_exists( $key, $values ) ) {
 247                         $casToken = $values[$key];
 248                         return $values[$key];
 249                 }
 250                 return false;
 251         }
 252
 253         public function getMulti( array $keys, $flags = 0 ) {
 254                 $values = []; // array of (key => value)
 255
 256                 $keysByTable = [];
 257                 foreach ( $keys as $key ) {
 258                         list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
 259                         $keysByTable[$serverIndex][$tableName][] = $key;
 260                 }
 261
 262                 $this->garbageCollect(); // expire old entries if any
 263
 264                 $dataRows = [];
 265                 foreach ( $keysByTable as $serverIndex => $serverKeys ) {
 266                         try {
 267                                 $db = $this->getDB( $serverIndex );
 268                                 foreach ( $serverKeys as $tableName => $tableKeys ) {
 269                                         $res = $db->select( $tableName,
 270                                                 [ 'keyname', 'value', 'exptime' ],
 271                                                 [ 'keyname' => $tableKeys ],
 272                                                 __METHOD__,
 273                                                 // Approximate write-on-the-fly BagOStuff API via blocking.
 274                                                 // This approximation fails if a ROLLBACK happens (which is rare).
 275                                                 // We do not want to flush the TRX as that can break callers.
 276                                                 $db->trxLevel() ? [ 'LOCK IN SHARE MODE' ] : []
 277                                         );
 278                                         if ( $res === false ) {
 279                                                 continue;
 280                                         }
 281                                         foreach ( $res as $row ) {
 282                                                 $row->serverIndex = $serverIndex;
 283                                                 $row->tableName = $tableName;
 284                                                 $dataRows[$row->keyname] = $row;
 285                                         }
 286                                 }
 287                         } catch ( DBError $e ) {
 288                                 $this->handleReadError( $e, $serverIndex );
 289                         }
 290                 }
 291
 292                 foreach ( $keys as $key ) {
 293                         if ( isset( $dataRows[$key] ) ) { // HIT?
 294                                 $row = $dataRows[$key];
 295                                 $this->debug( "get: retrieved data; expiry time is " . $row->exptime );
 296                                 $db = null;
 297                                 try {
 298                                         $db = $this->getDB( $row->serverIndex );
 299                                         if ( $this->isExpired( $db, $row->exptime ) ) { // MISS
 300                                                 $this->debug( "get: key has expired" );
 301                                         } else { // HIT
 302                                                 $values[$key] = $this->unserialize( $db->decodeBlob( $row->value ) );
 303                                         }
 304                                 } catch ( DBQueryError $e ) {
 305                                         $this->handleWriteError( $e, $db, $row->serverIndex );
 306                                 }
 307                         } else { // MISS
 308                                 $this->debug( 'get: no matching rows' );
 309                         }
 310                 }
 311
 312                 return $values;
 313         }
 314
 315         public function setMulti( array $data, $expiry = 0 ) {
 316                 $keysByTable = [];
 317                 foreach ( $data as $key => $value ) {
 318                         list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
 319                         $keysByTable[$serverIndex][$tableName][] = $key;
 320                 }
 321
 322                 $this->garbageCollect(); // expire old entries if any
 323
 324                 $result = true;
 325                 $exptime = (int)$expiry;
 326                 foreach ( $keysByTable as $serverIndex => $serverKeys ) {
 327                         $db = null;
 328                         try {
 329                                 $db = $this->getDB( $serverIndex );
 330                         } catch ( DBError $e ) {
 331                                 $this->handleWriteError( $e, $db, $serverIndex );
 332                                 $result = false;
 333                                 continue;
 334                         }
 335
 336                         if ( $exptime < 0 ) {
 337                                 $exptime = 0;
 338                         }
 339
 340                         if ( $exptime == 0 ) {
 341                                 $encExpiry = $this->getMaxDateTime( $db );
 342                         } else {
 343                                 $exptime = $this->convertExpiry( $exptime );
 344                                 $encExpiry = $db->timestamp( $exptime );
 345                         }
 346                         foreach ( $serverKeys as $tableName => $tableKeys ) {
 347                                 $rows = [];
 348                                 foreach ( $tableKeys as $key ) {
 349                                         $rows[] = [
 350                                                 'keyname' => $key,
 351                                                 'value' => $db->encodeBlob( $this->serialize( $data[$key] ) ),
 352                                                 'exptime' => $encExpiry,
 353                                         ];
 354                                 }
 355
 356                                 try {
 357                                         $db->replace(
 358                                                 $tableName,
 359                                                 [ 'keyname' ],
 360                                                 $rows,
 361                                                 __METHOD__
 362                                         );
 363                                 } catch ( DBError $e ) {
 364                                         $this->handleWriteError( $e, $db, $serverIndex );
 365                                         $result = false;
 366                                 }
 367
 368                         }
 369
 370                 }
 371
 372                 return $result;
 373         }
 374
 375         public function set( $key, $value, $exptime = 0, $flags = 0 ) {
 376                 $ok = $this->setMulti( [ $key => $value ], $exptime );
 377                 if ( ( $flags & self::WRITE_SYNC ) == self::WRITE_SYNC ) {
 378                         $ok = $this->waitForReplication() && $ok;
 379                 }
 380
 381                 return $ok;
 382         }
 383
 384         protected function cas( $casToken, $key, $value, $exptime = 0 ) {
 385                 list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
 386                 $db = null;
 387                 try {
 388                         $db = $this->getDB( $serverIndex );
 389                         $exptime = intval( $exptime );
 390
 391                         if ( $exptime < 0 ) {
 392                                 $exptime = 0;
 393                         }
 394
 395                         if ( $exptime == 0 ) {
 396                                 $encExpiry = $this->getMaxDateTime( $db );
 397                         } else {
 398                                 $exptime = $this->convertExpiry( $exptime );
 399                                 $encExpiry = $db->timestamp( $exptime );
 400                         }
 401                         // (T26425) use a replace if the db supports it instead of
 402                         // delete/insert to avoid clashes with conflicting keynames
 403                         $db->update(
 404                                 $tableName,
 405                                 [
 406                                         'keyname' => $key,
 407                                         'value' => $db->encodeBlob( $this->serialize( $value ) ),
 408                                         'exptime' => $encExpiry
 409                                 ],
 410                                 [
 411                                         'keyname' => $key,
 412                                         'value' => $db->encodeBlob( $this->serialize( $casToken ) )
 413                                 ],
 414                                 __METHOD__
 415                         );
 416                 } catch ( DBQueryError $e ) {
 417                         $this->handleWriteError( $e, $db, $serverIndex );
 418
 419                         return false;
 420                 }
 421
 422                 return (bool)$db->affectedRows();
 423         }
 424
 425         public function delete( $key ) {
 426                 list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
 427                 $db = null;
 428                 try {
 429                         $db = $this->getDB( $serverIndex );
 430                         $db->delete(
 431                                 $tableName,
 432                                 [ 'keyname' => $key ],
 433                                 __METHOD__ );
 434                 } catch ( DBError $e ) {
 435                         $this->handleWriteError( $e, $db, $serverIndex );
 436                         return false;
 437                 }
 438
 439                 return true;
 440         }
 441
 442         public function incr( $key, $step = 1 ) {
 443                 list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
 444                 $db = null;
 445                 try {
 446                         $db = $this->getDB( $serverIndex );
 447                         $step = intval( $step );
 448                         $row = $db->selectRow(
 449                                 $tableName,
 450                                 [ 'value', 'exptime' ],
 451                                 [ 'keyname' => $key ],
 452                                 __METHOD__,
 453                                 [ 'FOR UPDATE' ] );
 454                         if ( $row === false ) {
 455                                 // Missing
 456
 457                                 return null;
 458                         }
 459                         $db->delete( $tableName, [ 'keyname' => $key ], __METHOD__ );
 460                         if ( $this->isExpired( $db, $row->exptime ) ) {
 461                                 // Expired, do not reinsert
 462
 463                                 return null;
 464                         }
 465
 466                         $oldValue = intval( $this->unserialize( $db->decodeBlob( $row->value ) ) );
 467                         $newValue = $oldValue + $step;
 468                         $db->insert( $tableName,
 469                                 [
 470                                         'keyname' => $key,
 471                                         'value' => $db->encodeBlob( $this->serialize( $newValue ) ),
 472                                         'exptime' => $row->exptime
 473                                 ], __METHOD__, 'IGNORE' );
 474
 475                         if ( $db->affectedRows() == 0 ) {
 476                                 // Race condition. See T30611
 477                                 $newValue = null;
 478                         }
 479                 } catch ( DBError $e ) {
 480                         $this->handleWriteError( $e, $db, $serverIndex );
 481                         return null;
 482                 }
 483
 484                 return $newValue;
 485         }
 486
 487         public function merge( $key, callable $callback, $exptime = 0, $attempts = 10, $flags = 0 ) {
 488                 $ok = $this->mergeViaCas( $key, $callback, $exptime, $attempts );
 489                 if ( ( $flags & self::WRITE_SYNC ) == self::WRITE_SYNC ) {
 490                         $ok = $this->waitForReplication() && $ok;
 491                 }
 492
 493                 return $ok;
 494         }
 495
 496         public function changeTTL( $key, $expiry = 0 ) {
 497                 list( $serverIndex, $tableName ) = $this->getTableByKey( $key );
 498                 $db = null;
 499                 try {
 500                         $db = $this->getDB( $serverIndex );
 501                         $db->update(
 502                                 $tableName,
 503                                 [ 'exptime' => $db->timestamp( $this->convertExpiry( $expiry ) ) ],
 504                                 [ 'keyname' => $key, 'exptime > ' . $db->addQuotes( $db->timestamp( time() ) ) ],
 505                                 __METHOD__
 506                         );
 507                         if ( $db->affectedRows() == 0 ) {
 508                                 return false;
 509                         }
 510                 } catch ( DBError $e ) {
 511                         $this->handleWriteError( $e, $db, $serverIndex );
 512                         return false;
 513                 }
 514
 515                 return true;
 516         }
 517
 518         /**
 519          * @param IDatabase $db
 520          * @param string $exptime
 521          * @return bool
 522          */
 523         protected function isExpired( $db, $exptime ) {
 524                 return $exptime != $this->getMaxDateTime( $db ) && wfTimestamp( TS_UNIX, $exptime ) < time();
 525         }
 526
 527         /**
 528          * @param IDatabase $db
 529          * @return string
 530          */
 531         protected function getMaxDateTime( $db ) {
 532                 if ( time() > 0x7fffffff ) {
 533                         return $db->timestamp( 1 << 62 );
 534                 } else {
 535                         return $db->timestamp( 0x7fffffff );
 536                 }
 537         }
 538
 539         protected function garbageCollect() {
 540                 if ( !$this->purgePeriod || $this->replicaOnly ) {
 541                         // Disabled
 542                         return;
 543                 }
 544                 // Only purge on one in every $this->purgePeriod requests.
 545                 if ( $this->purgePeriod !== 1 && mt_rand( 0, $this->purgePeriod - 1 ) ) {
 546                         return;
 547                 }
 548                 $now = time();
 549                 // Avoid repeating the delete within a few seconds
 550                 if ( $now > ( $this->lastExpireAll + 1 ) ) {
 551                         $this->lastExpireAll = $now;
 552                         $this->expireAll();
 553                 }
 554         }
 555
 556         public function expireAll() {
 557                 $this->deleteObjectsExpiringBefore( wfTimestampNow() );
 558         }
 559
 560         /**
 561          * Delete objects from the database which expire before a certain date.
 562          * @param string $timestamp
 563          * @param bool|callable $progressCallback
 564          * @return bool
 565          */
 566         public function deleteObjectsExpiringBefore( $timestamp, $progressCallback = false ) {
 567                 for ( $serverIndex = 0; $serverIndex < $this->numServers; $serverIndex++ ) {
 568                         $db = null;
 569                         try {
 570                                 $db = $this->getDB( $serverIndex );
 571                                 $dbTimestamp = $db->timestamp( $timestamp );
 572                                 $totalSeconds = false;
 573                                 $baseConds = [ 'exptime < ' . $db->addQuotes( $dbTimestamp ) ];
 574                                 for ( $i = 0; $i < $this->shards; $i++ ) {
 575                                         $maxExpTime = false;
 576                                         while ( true ) {
 577                                                 $conds = $baseConds;
 578                                                 if ( $maxExpTime !== false ) {
 579                                                         $conds[] = 'exptime >= ' . $db->addQuotes( $maxExpTime );
 580                                                 }
 581                                                 $rows = $db->select(
 582                                                         $this->getTableNameByShard( $i ),
 583                                                         [ 'keyname', 'exptime' ],
 584                                                         $conds,
 585                                                         __METHOD__,
 586                                                         [ 'LIMIT' => 100, 'ORDER BY' => 'exptime' ] );
 587                                                 if ( $rows === false || !$rows->numRows() ) {
 588                                                         break;
 589                                                 }
 590                                                 $keys = [];
 591                                                 $row = $rows->current();
 592                                                 $minExpTime = $row->exptime;
 593                                                 if ( $totalSeconds === false ) {
 594                                                         $totalSeconds = wfTimestamp( TS_UNIX, $timestamp )
 595                                                                 - wfTimestamp( TS_UNIX, $minExpTime );
 596                                                 }
 597                                                 foreach ( $rows as $row ) {
 598                                                         $keys[] = $row->keyname;
 599                                                         $maxExpTime = $row->exptime;
 600                                                 }
 601
 602                                                 $db->delete(
 603                                                         $this->getTableNameByShard( $i ),
 604                                                         [
 605                                                                 'exptime >= ' . $db->addQuotes( $minExpTime ),
 606                                                                 'exptime < ' . $db->addQuotes( $dbTimestamp ),
 607                                                                 'keyname' => $keys
 608                                                         ],
 609                                                         __METHOD__ );
 610
 611                                                 if ( $progressCallback ) {
 612                                                         if ( intval( $totalSeconds ) === 0 ) {
 613                                                                 $percent = 0;
 614                                                         } else {
 615                                                                 $remainingSeconds = wfTimestamp( TS_UNIX, $timestamp )
 616                                                                         - wfTimestamp( TS_UNIX, $maxExpTime );
 617                                                                 if ( $remainingSeconds > $totalSeconds ) {
 618                                                                         $totalSeconds = $remainingSeconds;
 619                                                                 }
 620                                                                 $processedSeconds = $totalSeconds - $remainingSeconds;
 621                                                                 $percent = ( $i + $processedSeconds / $totalSeconds )
 622                                                                         / $this->shards * 100;
 623                                                         }
 624                                                         $percent = ( $percent / $this->numServers )
 625                                                                 + ( $serverIndex / $this->numServers * 100 );
 626                                                         call_user_func( $progressCallback, $percent );
 627                                                 }
 628                                         }
 629                                 }
 630                         } catch ( DBError $e ) {
 631                                 $this->handleWriteError( $e, $db, $serverIndex );
 632                                 return false;
 633                         }
 634                 }
 635                 return true;
 636         }
 637
 638         /**
 639          * Delete content of shard tables in every server.
 640          * Return true if the operation is successful, false otherwise.
 641          * @return bool
 642          */
 643         public function deleteAll() {
 644                 for ( $serverIndex = 0; $serverIndex < $this->numServers; $serverIndex++ ) {
 645                         $db = null;
 646                         try {
 647                                 $db = $this->getDB( $serverIndex );
 648                                 for ( $i = 0; $i < $this->shards; $i++ ) {
 649                                         $db->delete( $this->getTableNameByShard( $i ), '*', __METHOD__ );
 650                                 }
 651                         } catch ( DBError $e ) {
 652                                 $this->handleWriteError( $e, $db, $serverIndex );
 653                                 return false;
 654                         }
 655                 }
 656                 return true;
 657         }
 658
 659         /**
 660          * Serialize an object and, if possible, compress the representation.
 661          * On typical message and page data, this can provide a 3X decrease
 662          * in storage requirements.
 663          *
 664          * @param mixed &$data
 665          * @return string
 666          */
 667         protected function serialize( &$data ) {
 668                 $serial = serialize( $data );
 669
 670                 if ( function_exists( 'gzdeflate' ) ) {
 671                         return gzdeflate( $serial );
 672                 } else {
 673                         return $serial;
 674                 }
 675         }
 676
 677         /**
 678          * Unserialize and, if necessary, decompress an object.
 679          * @param string $serial
 680          * @return mixed
 681          */
 682         protected function unserialize( $serial ) {
 683                 if ( function_exists( 'gzinflate' ) ) {
 684                         MediaWiki\suppressWarnings();
 685                         $decomp = gzinflate( $serial );
 686                         MediaWiki\restoreWarnings();
 687
 688                         if ( false !== $decomp ) {
 689                                 $serial = $decomp;
 690                         }
 691                 }
 692
 693                 $ret = unserialize( $serial );
 694
 695                 return $ret;
 696         }
 697
 698         /**
 699          * Handle a DBError which occurred during a read operation.
 700          *
 701          * @param DBError $exception
 702          * @param int $serverIndex
 703          */
 704         protected function handleReadError( DBError $exception, $serverIndex ) {
 705                 if ( $exception instanceof DBConnectionError ) {
 706                         $this->markServerDown( $exception, $serverIndex );
 707                 }
 708                 $this->logger->error( "DBError: {$exception->getMessage()}" );
 709                 if ( $exception instanceof DBConnectionError ) {
 710                         $this->setLastError( BagOStuff::ERR_UNREACHABLE );
 711                         $this->logger->debug( __METHOD__ . ": ignoring connection error" );
 712                 } else {
 713                         $this->setLastError( BagOStuff::ERR_UNEXPECTED );
 714                         $this->logger->debug( __METHOD__ . ": ignoring query error" );
 715                 }
 716         }
 717
 718         /**
 719          * Handle a DBQueryError which occurred during a write operation.
 720          *
 721          * @param DBError $exception
 722          * @param IDatabase|null $db DB handle or null if connection failed
 723          * @param int $serverIndex
 724          * @throws Exception
 725          */
 726         protected function handleWriteError( DBError $exception, IDatabase $db = null, $serverIndex ) {
 727                 if ( !$db ) {
 728                         $this->markServerDown( $exception, $serverIndex );
 729                 } elseif ( $db->wasReadOnlyError() ) {
 730                         if ( $db->trxLevel() && $this->usesMainDB() ) {
 731                                 // Errors like deadlocks and connection drops already cause rollback.
 732                                 // For consistency, we have no choice but to throw an error and trigger
 733                                 // complete rollback if the main DB is also being used as the cache DB.
 734                                 throw $exception;
 735                         }
 736                 }
 737
 738                 $this->logger->error( "DBError: {$exception->getMessage()}" );
 739                 if ( $exception instanceof DBConnectionError ) {
 740                         $this->setLastError( BagOStuff::ERR_UNREACHABLE );
 741                         $this->logger->debug( __METHOD__ . ": ignoring connection error" );
 742                 } else {
 743                         $this->setLastError( BagOStuff::ERR_UNEXPECTED );
 744                         $this->logger->debug( __METHOD__ . ": ignoring query error" );
 745                 }
 746         }
 747
 748         /**
 749          * Mark a server down due to a DBConnectionError exception
 750          *
 751          * @param DBError $exception
 752          * @param int $serverIndex
 753          */
 754         protected function markServerDown( DBError $exception, $serverIndex ) {
 755                 unset( $this->conns[$serverIndex] ); // bug T103435
 756
 757                 if ( isset( $this->connFailureTimes[$serverIndex] ) ) {
 758                         if ( time() - $this->connFailureTimes[$serverIndex] >= 60 ) {
 759                                 unset( $this->connFailureTimes[$serverIndex] );
 760                                 unset( $this->connFailureErrors[$serverIndex] );
 761                         } else {
 762                                 $this->logger->debug( __METHOD__ . ": Server #$serverIndex already down" );
 763                                 return;
 764                         }
 765                 }
 766                 $now = time();
 767                 $this->logger->info( __METHOD__ . ": Server #$serverIndex down until " . ( $now + 60 ) );
 768                 $this->connFailureTimes[$serverIndex] = $now;
 769                 $this->connFailureErrors[$serverIndex] = $exception;
 770         }
 771
 772         /**
 773          * Create shard tables. For use from eval.php.
 774          */
 775         public function createTables() {
 776                 for ( $serverIndex = 0; $serverIndex < $this->numServers; $serverIndex++ ) {
 777                         $db = $this->getDB( $serverIndex );
 778                         if ( $db->getType() !== 'mysql' ) {
 779                                 throw new MWException( __METHOD__ . ' is not supported on this DB server' );
 780                         }
 781
 782                         for ( $i = 0; $i < $this->shards; $i++ ) {
 783                                 $db->query(
 784                                         'CREATE TABLE ' . $db->tableName( $this->getTableNameByShard( $i ) ) .
 785                                         ' LIKE ' . $db->tableName( 'objectcache' ),
 786                                         __METHOD__ );
 787                         }
 788                 }
 789         }
 790
 791         /**
 792          * @return bool Whether the main DB is used, e.g. wfGetDB( DB_MASTER )
 793          */
 794         protected function usesMainDB() {
 795                 return !$this->serverInfos;
 796         }
 797
 798         protected function waitForReplication() {
 799                 if ( !$this->usesMainDB() ) {
 800                         // Custom DB server list; probably doesn't use replication
 801                         return true;
 802                 }
 803
 804                 $lb = MediaWikiServices::getInstance()->getDBLoadBalancer();
 805                 if ( $lb->getServerCount() <= 1 ) {
 806                         return true; // no replica DBs
 807                 }
 808
 809                 // Main LB is used; wait for any replica DBs to catch up
 810                 $masterPos = $lb->getMasterPos();
 811
 812                 $loop = new WaitConditionLoop(
 813                         function () use ( $lb, $masterPos ) {
 814                                 return $lb->waitForAll( $masterPos, 1 );
 815                         },
 816                         $this->syncTimeout,
 817                         $this->busyCallbacks
 818                 );
 819
 820                 return ( $loop->invoke() === $loop::CONDITION_REACHED );
 821         }
 822 }