includes/db/loadbalancer/LBFactory.php

   1 <?php
   2 /**
   3  * Generator of database load balancing objects.
   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 Database
  22  */
  23
  24 use MediaWiki\MediaWikiServices;
  25 use MediaWiki\Services\DestructibleService;
  26 use Psr\Log\LoggerInterface;
  27 use MediaWiki\Logger\LoggerFactory;
  28
  29 /**
  30  * An interface for generating database load balancers
  31  * @ingroup Database
  32  */
  33 abstract class LBFactory implements DestructibleService {
  34         /** @var ChronologyProtector */
  35         protected $chronProt;
  36         /** @var TransactionProfiler */
  37         protected $trxProfiler;
  38         /** @var LoggerInterface */
  39         protected $trxLogger;
  40         /** @var BagOStuff */
  41         protected $srvCache;
  42         /** @var WANObjectCache */
  43         protected $wanCache;
  44
  45         /** @var mixed */
  46         protected $ticket;
  47         /** @var string|bool String if a requested DBO_TRX transaction round is active */
  48         protected $trxRoundId = false;
  49         /** @var string|bool Reason all LBs are read-only or false if not */
  50         protected $readOnlyReason = false;
  51         /** @var callable[] */
  52         protected $replicationWaitCallbacks = [];
  53
  54         const SHUTDOWN_NO_CHRONPROT = 1; // don't save ChronologyProtector positions (for async code)
  55
  56         /**
  57          * Construct a factory based on a configuration array (typically from $wgLBFactoryConf)
  58          * @param array $conf
  59          * @TODO: inject objects via dependency framework
  60          */
  61         public function __construct( array $conf ) {
  62                 if ( isset( $conf['readOnlyReason'] ) && is_string( $conf['readOnlyReason'] ) ) {
  63                         $this->readOnlyReason = $conf['readOnlyReason'];
  64                 }
  65                 $this->chronProt = $this->newChronologyProtector();
  66                 $this->trxProfiler = Profiler::instance()->getTransactionProfiler();
  67                 // Use APC/memcached style caching, but avoids loops with CACHE_DB (T141804)
  68                 $cache = ObjectCache::getLocalServerInstance();
  69                 if ( $cache->getQoS( $cache::ATTR_EMULATION ) > $cache::QOS_EMULATION_SQL ) {
  70                         $this->srvCache = $cache;
  71                 } else {
  72                         $this->srvCache = new EmptyBagOStuff();
  73                 }
  74                 $wCache = ObjectCache::getMainWANInstance();
  75                 if ( $wCache->getQoS( $wCache::ATTR_EMULATION ) > $wCache::QOS_EMULATION_SQL ) {
  76                         $this->wanCache = $wCache;
  77                 } else {
  78                         $this->wanCache = WANObjectCache::newEmpty();
  79                 }
  80                 $this->trxLogger = LoggerFactory::getInstance( 'DBTransaction' );
  81                 $this->ticket = mt_rand();
  82         }
  83
  84         /**
  85          * Disables all load balancers. All connections are closed, and any attempt to
  86          * open a new connection will result in a DBAccessError.
  87          * @see LoadBalancer::disable()
  88          */
  89         public function destroy() {
  90                 $this->shutdown();
  91                 $this->forEachLBCallMethod( 'disable' );
  92         }
  93
  94         /**
  95          * Disables all access to the load balancer, will cause all database access
  96          * to throw a DBAccessError
  97          */
  98         public static function disableBackend() {
  99                 MediaWikiServices::disableStorageBackend();
 100         }
 101
 102         /**
 103          * Get an LBFactory instance
 104          *
 105          * @deprecated since 1.27, use MediaWikiServices::getDBLoadBalancerFactory() instead.
 106          *
 107          * @return LBFactory
 108          */
 109         public static function singleton() {
 110                 return MediaWikiServices::getInstance()->getDBLoadBalancerFactory();
 111         }
 112
 113         /**
 114          * Returns the LBFactory class to use and the load balancer configuration.
 115          *
 116          * @todo instead of this, use a ServiceContainer for managing the different implementations.
 117          *
 118          * @param array $config (e.g. $wgLBFactoryConf)
 119          * @return string Class name
 120          */
 121         public static function getLBFactoryClass( array $config ) {
 122                 // For configuration backward compatibility after removing
 123                 // underscores from class names in MediaWiki 1.23.
 124                 $bcClasses = [
 125                         'LBFactory_Simple' => 'LBFactorySimple',
 126                         'LBFactory_Single' => 'LBFactorySingle',
 127                         'LBFactory_Multi' => 'LBFactoryMulti',
 128                         'LBFactory_Fake' => 'LBFactoryFake',
 129                 ];
 130
 131                 $class = $config['class'];
 132
 133                 if ( isset( $bcClasses[$class] ) ) {
 134                         $class = $bcClasses[$class];
 135                         wfDeprecated(
 136                                 '$wgLBFactoryConf must be updated. See RELEASE-NOTES for details',
 137                                 '1.23'
 138                         );
 139                 }
 140
 141                 return $class;
 142         }
 143
 144         /**
 145          * Shut down, close connections and destroy the cached instance.
 146          *
 147          * @deprecated since 1.27, use LBFactory::destroy()
 148          */
 149         public static function destroyInstance() {
 150                 self::singleton()->destroy();
 151         }
 152
 153         /**
 154          * Create a new load balancer object. The resulting object will be untracked,
 155          * not chronology-protected, and the caller is responsible for cleaning it up.
 156          *
 157          * @param bool|string $wiki Wiki ID, or false for the current wiki
 158          * @return LoadBalancer
 159          */
 160         abstract public function newMainLB( $wiki = false );
 161
 162         /**
 163          * Get a cached (tracked) load balancer object.
 164          *
 165          * @param bool|string $wiki Wiki ID, or false for the current wiki
 166          * @return LoadBalancer
 167          */
 168         abstract public function getMainLB( $wiki = false );
 169
 170         /**
 171          * Create a new load balancer for external storage. The resulting object will be
 172          * untracked, not chronology-protected, and the caller is responsible for
 173          * cleaning it up.
 174          *
 175          * @param string $cluster External storage cluster, or false for core
 176          * @param bool|string $wiki Wiki ID, or false for the current wiki
 177          * @return LoadBalancer
 178          */
 179         abstract protected function newExternalLB( $cluster, $wiki = false );
 180
 181         /**
 182          * Get a cached (tracked) load balancer for external storage
 183          *
 184          * @param string $cluster External storage cluster, or false for core
 185          * @param bool|string $wiki Wiki ID, or false for the current wiki
 186          * @return LoadBalancer
 187          */
 188         abstract public function getExternalLB( $cluster, $wiki = false );
 189
 190         /**
 191          * Execute a function for each tracked load balancer
 192          * The callback is called with the load balancer as the first parameter,
 193          * and $params passed as the subsequent parameters.
 194          *
 195          * @param callable $callback
 196          * @param array $params
 197          */
 198         abstract public function forEachLB( $callback, array $params = [] );
 199
 200         /**
 201          * Prepare all tracked load balancers for shutdown
 202          * @param integer $flags Supports SHUTDOWN_* flags
 203          */
 204         public function shutdown( $flags = 0 ) {
 205                 if ( !( $flags & self::SHUTDOWN_NO_CHRONPROT ) ) {
 206                         $this->shutdownChronologyProtector( $this->chronProt );
 207                 }
 208                 $this->commitMasterChanges( __METHOD__ ); // sanity
 209         }
 210
 211         /**
 212          * Call a method of each tracked load balancer
 213          *
 214          * @param string $methodName
 215          * @param array $args
 216          */
 217         private function forEachLBCallMethod( $methodName, array $args = [] ) {
 218                 $this->forEachLB(
 219                         function ( LoadBalancer $loadBalancer, $methodName, array $args ) {
 220                                 call_user_func_array( [ $loadBalancer, $methodName ], $args );
 221                         },
 222                         [ $methodName, $args ]
 223                 );
 224         }
 225
 226         /**
 227          * Commit all replica DB transactions so as to flush any REPEATABLE-READ or SSI snapshot
 228          *
 229          * @param string $fname Caller name
 230          * @since 1.28
 231          */
 232         public function flushReplicaSnapshots( $fname = __METHOD__ ) {
 233                 $this->forEachLBCallMethod( 'flushReplicaSnapshots', [ $fname ] );
 234         }
 235
 236         /**
 237          * Commit on all connections. Done for two reasons:
 238          * 1. To commit changes to the masters.
 239          * 2. To release the snapshot on all connections, master and replica DB.
 240          * @param string $fname Caller name
 241          * @param array $options Options map:
 242          *   - maxWriteDuration: abort if more than this much time was spent in write queries
 243          */
 244         public function commitAll( $fname = __METHOD__, array $options = [] ) {
 245                 $this->commitMasterChanges( $fname, $options );
 246                 $this->forEachLBCallMethod( 'commitAll', [ $fname ] );
 247         }
 248
 249         /**
 250          * Flush any master transaction snapshots and set DBO_TRX (if DBO_DEFAULT is set)
 251          *
 252          * The DBO_TRX setting will be reverted to the default in each of these methods:
 253          *   - commitMasterChanges()
 254          *   - rollbackMasterChanges()
 255          *   - commitAll()
 256          *
 257          * This allows for custom transaction rounds from any outer transaction scope.
 258          *
 259          * @param string $fname
 260          * @throws DBTransactionError
 261          * @since 1.28
 262          */
 263         public function beginMasterChanges( $fname = __METHOD__ ) {
 264                 if ( $this->trxRoundId !== false ) {
 265                         throw new DBTransactionError(
 266                                 null,
 267                                 "$fname: transaction round '{$this->trxRoundId}' already started."
 268                         );
 269                 }
 270                 $this->trxRoundId = $fname;
 271                 // Set DBO_TRX flags on all appropriate DBs
 272                 $this->forEachLBCallMethod( 'beginMasterChanges', [ $fname ] );
 273         }
 274
 275         /**
 276          * Commit changes on all master connections
 277          * @param string $fname Caller name
 278          * @param array $options Options map:
 279          *   - maxWriteDuration: abort if more than this much time was spent in write queries
 280          * @throws Exception
 281          */
 282         public function commitMasterChanges( $fname = __METHOD__, array $options = [] ) {
 283                 if ( $this->trxRoundId !== false && $this->trxRoundId !== $fname ) {
 284                         throw new DBTransactionError(
 285                                 null,
 286                                 "$fname: transaction round '{$this->trxRoundId}' still running."
 287                         );
 288                 }
 289                 // Run pre-commit callbacks and suppress post-commit callbacks, aborting on failure
 290                 $this->forEachLBCallMethod( 'finalizeMasterChanges' );
 291                 $this->trxRoundId = false;
 292                 // Perform pre-commit checks, aborting on failure
 293                 $this->forEachLBCallMethod( 'approveMasterChanges', [ $options ] );
 294                 // Log the DBs and methods involved in multi-DB transactions
 295                 $this->logIfMultiDbTransaction();
 296                 // Actually perform the commit on all master DB connections and revert DBO_TRX
 297                 $this->forEachLBCallMethod( 'commitMasterChanges', [ $fname ] );
 298                 // Run all post-commit callbacks
 299                 /** @var Exception $e */
 300                 $e = null; // first callback exception
 301                 $this->forEachLB( function ( LoadBalancer $lb ) use ( &$e ) {
 302                         $ex = $lb->runMasterPostTrxCallbacks( IDatabase::TRIGGER_COMMIT );
 303                         $e = $e ?: $ex;
 304                 } );
 305                 // Commit any dangling DBO_TRX transactions from callbacks on one DB to another DB
 306                 $this->forEachLBCallMethod( 'commitMasterChanges', [ $fname ] );
 307                 // Throw any last post-commit callback error
 308                 if ( $e instanceof Exception ) {
 309                         throw $e;
 310                 }
 311         }
 312
 313         /**
 314          * Rollback changes on all master connections
 315          * @param string $fname Caller name
 316          * @since 1.23
 317          */
 318         public function rollbackMasterChanges( $fname = __METHOD__ ) {
 319                 $this->trxRoundId = false;
 320                 $this->forEachLBCallMethod( 'suppressTransactionEndCallbacks' );
 321                 $this->forEachLBCallMethod( 'rollbackMasterChanges', [ $fname ] );
 322                 // Run all post-rollback callbacks
 323                 $this->forEachLB( function ( LoadBalancer $lb ) {
 324                         $lb->runMasterPostTrxCallbacks( IDatabase::TRIGGER_ROLLBACK );
 325                 } );
 326         }
 327
 328         /**
 329          * Log query info if multi DB transactions are going to be committed now
 330          */
 331         private function logIfMultiDbTransaction() {
 332                 $callersByDB = [];
 333                 $this->forEachLB( function ( LoadBalancer $lb ) use ( &$callersByDB ) {
 334                         $masterName = $lb->getServerName( $lb->getWriterIndex() );
 335                         $callers = $lb->pendingMasterChangeCallers();
 336                         if ( $callers ) {
 337                                 $callersByDB[$masterName] = $callers;
 338                         }
 339                 } );
 340
 341                 if ( count( $callersByDB ) >= 2 ) {
 342                         $dbs = implode( ', ', array_keys( $callersByDB ) );
 343                         $msg = "Multi-DB transaction [{$dbs}]:\n";
 344                         foreach ( $callersByDB as $db => $callers ) {
 345                                 $msg .= "$db: " . implode( '; ', $callers ) . "\n";
 346                         }
 347                         $this->trxLogger->info( $msg );
 348                 }
 349         }
 350
 351         /**
 352          * Determine if any master connection has pending changes
 353          * @return bool
 354          * @since 1.23
 355          */
 356         public function hasMasterChanges() {
 357                 $ret = false;
 358                 $this->forEachLB( function ( LoadBalancer $lb ) use ( &$ret ) {
 359                         $ret = $ret || $lb->hasMasterChanges();
 360                 } );
 361
 362                 return $ret;
 363         }
 364
 365         /**
 366          * Detemine if any lagged replica DB connection was used
 367          * @return bool
 368          * @since 1.28
 369          */
 370         public function laggedReplicaUsed() {
 371                 $ret = false;
 372                 $this->forEachLB( function ( LoadBalancer $lb ) use ( &$ret ) {
 373                         $ret = $ret || $lb->laggedReplicaUsed();
 374                 } );
 375
 376                 return $ret;
 377         }
 378
 379         /**
 380          * @return bool
 381          * @since 1.27
 382          * @deprecated Since 1.28; use laggedReplicaUsed()
 383          */
 384         public function laggedSlaveUsed() {
 385                 return $this->laggedReplicaUsed();
 386         }
 387
 388         /**
 389          * Determine if any master connection has pending/written changes from this request
 390          * @return bool
 391          * @since 1.27
 392          */
 393         public function hasOrMadeRecentMasterChanges() {
 394                 $ret = false;
 395                 $this->forEachLB( function ( LoadBalancer $lb ) use ( &$ret ) {
 396                         $ret = $ret || $lb->hasOrMadeRecentMasterChanges();
 397                 } );
 398                 return $ret;
 399         }
 400
 401         /**
 402          * Waits for the replica DBs to catch up to the current master position
 403          *
 404          * Use this when updating very large numbers of rows, as in maintenance scripts,
 405          * to avoid causing too much lag. Of course, this is a no-op if there are no replica DBs.
 406          *
 407          * By default this waits on all DB clusters actually used in this request.
 408          * This makes sense when lag being waiting on is caused by the code that does this check.
 409          * In that case, setting "ifWritesSince" can avoid the overhead of waiting for clusters
 410          * that were not changed since the last wait check. To forcefully wait on a specific cluster
 411          * for a given wiki, use the 'wiki' parameter. To forcefully wait on an "external" cluster,
 412          * use the "cluster" parameter.
 413          *
 414          * Never call this function after a large DB write that is *still* in a transaction.
 415          * It only makes sense to call this after the possible lag inducing changes were committed.
 416          *
 417          * @param array $opts Optional fields that include:
 418          *   - wiki : wait on the load balancer DBs that handles the given wiki
 419          *   - cluster : wait on the given external load balancer DBs
 420          *   - timeout : Max wait time. Default: ~60 seconds
 421          *   - ifWritesSince: Only wait if writes were done since this UNIX timestamp
 422          * @throws DBReplicationWaitError If a timeout or error occured waiting on a DB cluster
 423          * @since 1.27
 424          */
 425         public function waitForReplication( array $opts = [] ) {
 426                 $opts += [
 427                         'wiki' => false,
 428                         'cluster' => false,
 429                         'timeout' => 60,
 430                         'ifWritesSince' => null
 431                 ];
 432
 433                 foreach ( $this->replicationWaitCallbacks as $callback ) {
 434                         $callback();
 435                 }
 436
 437                 // Figure out which clusters need to be checked
 438                 /** @var LoadBalancer[] $lbs */
 439                 $lbs = [];
 440                 if ( $opts['cluster'] !== false ) {
 441                         $lbs[] = $this->getExternalLB( $opts['cluster'] );
 442                 } elseif ( $opts['wiki'] !== false ) {
 443                         $lbs[] = $this->getMainLB( $opts['wiki'] );
 444                 } else {
 445                         $this->forEachLB( function ( LoadBalancer $lb ) use ( &$lbs ) {
 446                                 $lbs[] = $lb;
 447                         } );
 448                         if ( !$lbs ) {
 449                                 return; // nothing actually used
 450                         }
 451                 }
 452
 453                 // Get all the master positions of applicable DBs right now.
 454                 // This can be faster since waiting on one cluster reduces the
 455                 // time needed to wait on the next clusters.
 456                 $masterPositions = array_fill( 0, count( $lbs ), false );
 457                 foreach ( $lbs as $i => $lb ) {
 458                         if ( $lb->getServerCount() <= 1 ) {
 459                                 // Bug 27975 - Don't try to wait for replica DBs if there are none
 460                                 // Prevents permission error when getting master position
 461                                 continue;
 462                         } elseif ( $opts['ifWritesSince']
 463                                 && $lb->lastMasterChangeTimestamp() < $opts['ifWritesSince']
 464                         ) {
 465                                 continue; // no writes since the last wait
 466                         }
 467                         $masterPositions[$i] = $lb->getMasterPos();
 468                 }
 469
 470                 $failed = [];
 471                 foreach ( $lbs as $i => $lb ) {
 472                         if ( $masterPositions[$i] ) {
 473                                 // The DBMS may not support getMasterPos() or the whole
 474                                 // load balancer might be fake (e.g. $wgAllDBsAreLocalhost).
 475                                 if ( !$lb->waitForAll( $masterPositions[$i], $opts['timeout'] ) ) {
 476                                         $failed[] = $lb->getServerName( $lb->getWriterIndex() );
 477                                 }
 478                         }
 479                 }
 480
 481                 if ( $failed ) {
 482                         throw new DBReplicationWaitError(
 483                                 "Could not wait for replica DBs to catch up to " .
 484                                 implode( ', ', $failed )
 485                         );
 486                 }
 487         }
 488
 489         /**
 490          * Add a callback to be run in every call to waitForReplication() before waiting
 491          *
 492          * Callbacks must clear any transactions that they start
 493          *
 494          * @param string $name Callback name
 495          * @param callable|null $callback Use null to unset a callback
 496          * @since 1.28
 497          */
 498         public function setWaitForReplicationListener( $name, callable $callback = null ) {
 499                 if ( $callback ) {
 500                         $this->replicationWaitCallbacks[$name] = $callback;
 501                 } else {
 502                         unset( $this->replicationWaitCallbacks[$name] );
 503                 }
 504         }
 505
 506         /**
 507          * Get a token asserting that no transaction writes are active
 508          *
 509          * @param string $fname Caller name (e.g. __METHOD__)
 510          * @return mixed A value to pass to commitAndWaitForReplication()
 511          * @since 1.28
 512          */
 513         public function getEmptyTransactionTicket( $fname ) {
 514                 if ( $this->hasMasterChanges() ) {
 515                         $this->trxLogger->error( __METHOD__ . ": $fname does not have outer scope." );
 516                         return null;
 517                 }
 518
 519                 return $this->ticket;
 520         }
 521
 522         /**
 523          * Convenience method for safely running commitMasterChanges()/waitForReplication()
 524          *
 525          * This will commit and wait unless $ticket indicates it is unsafe to do so
 526          *
 527          * @param string $fname Caller name (e.g. __METHOD__)
 528          * @param mixed $ticket Result of getEmptyTransactionTicket()
 529          * @param array $opts Options to waitForReplication()
 530          * @throws DBReplicationWaitError
 531          * @since 1.28
 532          */
 533         public function commitAndWaitForReplication( $fname, $ticket, array $opts = [] ) {
 534                 if ( $ticket !== $this->ticket ) {
 535                         $logger = LoggerFactory::getInstance( 'DBPerformance' );
 536                         $logger->error( __METHOD__ . ": cannot commit; $fname does not have outer scope." );
 537                         return;
 538                 }
 539
 540                 // The transaction owner and any caller with the empty transaction ticket can commit
 541                 // so that getEmptyTransactionTicket() callers don't risk seeing DBTransactionError.
 542                 if ( $this->trxRoundId !== false && $fname !== $this->trxRoundId ) {
 543                         $this->trxLogger->info( "$fname: committing on behalf of {$this->trxRoundId}." );
 544                         $fnameEffective = $this->trxRoundId;
 545                 } else {
 546                         $fnameEffective = $fname;
 547                 }
 548
 549                 $this->commitMasterChanges( $fnameEffective );
 550                 $this->waitForReplication( $opts );
 551                 // If a nested caller committed on behalf of $fname, start another empty $fname
 552                 // transaction, leaving the caller with the same empty transaction state as before.
 553                 if ( $fnameEffective !== $fname ) {
 554                         $this->beginMasterChanges( $fnameEffective );
 555                 }
 556         }
 557
 558         /**
 559          * Disable the ChronologyProtector for all load balancers
 560          *
 561          * This can be called at the start of special API entry points
 562          *
 563          * @since 1.27
 564          */
 565         public function disableChronologyProtection() {
 566                 $this->chronProt->setEnabled( false );
 567         }
 568
 569         /**
 570          * @return ChronologyProtector
 571          */
 572         protected function newChronologyProtector() {
 573                 $request = RequestContext::getMain()->getRequest();
 574                 $chronProt = new ChronologyProtector(
 575                         ObjectCache::getMainStashInstance(),
 576                         [
 577                                 'ip' => $request->getIP(),
 578                                 'agent' => $request->getHeader( 'User-Agent' )
 579                         ]
 580                 );
 581                 if ( PHP_SAPI === 'cli' ) {
 582                         $chronProt->setEnabled( false );
 583                 } elseif ( $request->getHeader( 'ChronologyProtection' ) === 'false' ) {
 584                         // Request opted out of using position wait logic. This is useful for requests
 585                         // done by the job queue or background ETL that do not have a meaningful session.
 586                         $chronProt->setWaitEnabled( false );
 587                 }
 588
 589                 return $chronProt;
 590         }
 591
 592         /**
 593          * @param ChronologyProtector $cp
 594          */
 595         protected function shutdownChronologyProtector( ChronologyProtector $cp ) {
 596                 // Get all the master positions needed
 597                 $this->forEachLB( function ( LoadBalancer $lb ) use ( $cp ) {
 598                         $cp->shutdownLB( $lb );
 599                 } );
 600                 // Write them to the stash
 601                 $unsavedPositions = $cp->shutdown();
 602                 // If the positions failed to write to the stash, at least wait on local datacenter
 603                 // replica DBs to catch up before responding. Even if there are several DCs, this increases
 604                 // the chance that the user will see their own changes immediately afterwards. As long
 605                 // as the sticky DC cookie applies (same domain), this is not even an issue.
 606                 $this->forEachLB( function ( LoadBalancer $lb ) use ( $unsavedPositions ) {
 607                         $masterName = $lb->getServerName( $lb->getWriterIndex() );
 608                         if ( isset( $unsavedPositions[$masterName] ) ) {
 609                                 $lb->waitForAll( $unsavedPositions[$masterName] );
 610                         }
 611                 } );
 612         }
 613
 614         /**
 615          * @param LoadBalancer $lb
 616          */
 617         protected function initLoadBalancer( LoadBalancer $lb ) {
 618                 if ( $this->trxRoundId !== false ) {
 619                         $lb->beginMasterChanges( $this->trxRoundId ); // set DBO_TRX
 620                 }
 621         }
 622
 623         /**
 624          * Close all open database connections on all open load balancers.
 625          * @since 1.28
 626          */
 627         public function closeAll() {
 628                 $this->forEachLBCallMethod( 'closeAll', [] );
 629         }
 630
 631 }