includes/libs/rdbms/lbfactory/LBFactory.php

   1 <?php
   2 /**
   3  * Generator and manager 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 Psr\Log\LoggerInterface;
  25
  26 /**
  27  * An interface for generating database load balancers
  28  * @ingroup Database
  29  */
  30 abstract class LBFactory {
  31         /** @var ChronologyProtector */
  32         protected $chronProt;
  33         /** @var object|string Class name or object With profileIn/profileOut methods */
  34         protected $profiler;
  35         /** @var TransactionProfiler */
  36         protected $trxProfiler;
  37         /** @var LoggerInterface */
  38         protected $replLogger;
  39         /** @var LoggerInterface */
  40         protected $connLogger;
  41         /** @var LoggerInterface */
  42         protected $queryLogger;
  43         /** @var LoggerInterface */
  44         protected $perfLogger;
  45         /** @var callable Error logger */
  46         protected $errorLogger;
  47         /** @var BagOStuff */
  48         protected $srvCache;
  49         /** @var BagOStuff */
  50         protected $memCache;
  51         /** @var WANObjectCache */
  52         protected $wanCache;
  53
  54         /** @var DatabaseDomain Local domain */
  55         protected $localDomain;
  56         /** @var string Local hostname of the app server */
  57         protected $hostname;
  58         /** @var mixed */
  59         protected $ticket;
  60         /** @var string|bool String if a requested DBO_TRX transaction round is active */
  61         protected $trxRoundId = false;
  62         /** @var string|bool Reason all LBs are read-only or false if not */
  63         protected $readOnlyReason = false;
  64         /** @var callable[] */
  65         protected $replicationWaitCallbacks = [];
  66
  67         /** @var bool Whether this PHP instance is for a CLI script */
  68         protected $cliMode;
  69         /** @var string Agent name for query profiling */
  70         protected $agent;
  71
  72         const SHUTDOWN_NO_CHRONPROT = 0; // don't save DB positions at all
  73         const SHUTDOWN_CHRONPROT_ASYNC = 1; // save DB positions, but don't wait on remote DCs
  74         const SHUTDOWN_CHRONPROT_SYNC = 2; // save DB positions, waiting on all DCs
  75
  76         private static $loggerFields =
  77                 [ 'replLogger', 'connLogger', 'queryLogger', 'perfLogger' ];
  78
  79         /**
  80          * @TODO: document base params here
  81          * @param array $conf
  82          */
  83         public function __construct( array $conf ) {
  84                 $this->localDomain = isset( $conf['localDomain'] )
  85                         ? DatabaseDomain::newFromId( $conf['localDomain'] )
  86                         : DatabaseDomain::newUnspecified();
  87
  88                 if ( isset( $conf['readOnlyReason'] ) && is_string( $conf['readOnlyReason'] ) ) {
  89                         $this->readOnlyReason = $conf['readOnlyReason'];
  90                 }
  91
  92                 $this->srvCache = isset( $conf['srvCache'] ) ? $conf['srvCache'] : new EmptyBagOStuff();
  93                 $this->memCache = isset( $conf['memCache'] ) ? $conf['memCache'] : new EmptyBagOStuff();
  94                 $this->wanCache = isset( $conf['wanCache'] )
  95                         ? $conf['wanCache']
  96                         : WANObjectCache::newEmpty();
  97
  98                 foreach ( self::$loggerFields as $key ) {
  99                         $this->$key = isset( $conf[$key] ) ? $conf[$key] : new \Psr\Log\NullLogger();
 100                 }
 101                 $this->errorLogger = isset( $conf['errorLogger'] )
 102                         ? $conf['errorLogger']
 103                         : function ( Exception $e ) {
 104                                 trigger_error( E_WARNING, get_class( $e ) . ': ' . $e->getMessage() );
 105                         };
 106                 $this->hostname = isset( $conf['hostname'] )
 107                         ? $conf['hostname']
 108                         : gethostname();
 109
 110                 $this->chronProt = isset( $conf['chronProt'] )
 111                         ? $conf['chronProt']
 112                         : $this->newChronologyProtector();
 113
 114                 $this->profiler = isset( $params['profiler'] ) ? $params['profiler'] : null;
 115                 $this->trxProfiler = isset( $conf['trxProfiler'] )
 116                         ? $conf['trxProfiler']
 117                         : new TransactionProfiler();
 118
 119                 $this->ticket = mt_rand();
 120                 $this->cliMode = isset( $params['cliMode'] ) ? $params['cliMode'] : PHP_SAPI === 'cli';
 121                 $this->agent = isset( $params['agent'] ) ? $params['agent'] : '';
 122         }
 123
 124         /**
 125          * Disables all load balancers. All connections are closed, and any attempt to
 126          * open a new connection will result in a DBAccessError.
 127          * @see LoadBalancer::disable()
 128          */
 129         public function destroy() {
 130                 $this->shutdown( self::SHUTDOWN_NO_CHRONPROT );
 131                 $this->forEachLBCallMethod( 'disable' );
 132         }
 133
 134         /**
 135          * Create a new load balancer object. The resulting object will be untracked,
 136          * not chronology-protected, and the caller is responsible for cleaning it up.
 137          *
 138          * @param bool|string $domain Wiki ID, or false for the current wiki
 139          * @return ILoadBalancer
 140          */
 141         abstract public function newMainLB( $domain = false );
 142
 143         /**
 144          * Get a cached (tracked) load balancer object.
 145          *
 146          * @param bool|string $domain Wiki ID, or false for the current wiki
 147          * @return ILoadBalancer
 148          */
 149         abstract public function getMainLB( $domain = false );
 150
 151         /**
 152          * Create a new load balancer for external storage. The resulting object will be
 153          * untracked, not chronology-protected, and the caller is responsible for
 154          * cleaning it up.
 155          *
 156          * @param string $cluster External storage cluster, or false for core
 157          * @param bool|string $domain Wiki ID, or false for the current wiki
 158          * @return ILoadBalancer
 159          */
 160         abstract protected function newExternalLB( $cluster, $domain = false );
 161
 162         /**
 163          * Get a cached (tracked) load balancer for external storage
 164          *
 165          * @param string $cluster External storage cluster, or false for core
 166          * @param bool|string $domain Wiki ID, or false for the current wiki
 167          * @return ILoadBalancer
 168          */
 169         abstract public function getExternalLB( $cluster, $domain = false );
 170
 171         /**
 172          * Execute a function for each tracked load balancer
 173          * The callback is called with the load balancer as the first parameter,
 174          * and $params passed as the subsequent parameters.
 175          *
 176          * @param callable $callback
 177          * @param array $params
 178          */
 179         abstract public function forEachLB( $callback, array $params = [] );
 180
 181         /**
 182          * Prepare all tracked load balancers for shutdown
 183          * @param integer $mode One of the class SHUTDOWN_* constants
 184          * @param callable|null $workCallback Work to mask ChronologyProtector writes
 185          */
 186         public function shutdown(
 187                 $mode = self::SHUTDOWN_CHRONPROT_SYNC, callable $workCallback = null
 188         ) {
 189                 if ( $mode === self::SHUTDOWN_CHRONPROT_SYNC ) {
 190                         $this->shutdownChronologyProtector( $this->chronProt, $workCallback, 'sync' );
 191                 } elseif ( $mode === self::SHUTDOWN_CHRONPROT_ASYNC ) {
 192                         $this->shutdownChronologyProtector( $this->chronProt, null, 'async' );
 193                 }
 194
 195                 $this->commitMasterChanges( __METHOD__ ); // sanity
 196         }
 197
 198         /**
 199          * Call a method of each tracked load balancer
 200          *
 201          * @param string $methodName
 202          * @param array $args
 203          */
 204         protected function forEachLBCallMethod( $methodName, array $args = [] ) {
 205                 $this->forEachLB(
 206                         function ( ILoadBalancer $loadBalancer, $methodName, array $args ) {
 207                                 call_user_func_array( [ $loadBalancer, $methodName ], $args );
 208                         },
 209                         [ $methodName, $args ]
 210                 );
 211         }
 212
 213         /**
 214          * Commit all replica DB transactions so as to flush any REPEATABLE-READ or SSI snapshot
 215          *
 216          * @param string $fname Caller name
 217          * @since 1.28
 218          */
 219         public function flushReplicaSnapshots( $fname = __METHOD__ ) {
 220                 $this->forEachLBCallMethod( 'flushReplicaSnapshots', [ $fname ] );
 221         }
 222
 223         /**
 224          * Commit on all connections. Done for two reasons:
 225          * 1. To commit changes to the masters.
 226          * 2. To release the snapshot on all connections, master and replica DB.
 227          * @param string $fname Caller name
 228          * @param array $options Options map:
 229          *   - maxWriteDuration: abort if more than this much time was spent in write queries
 230          */
 231         public function commitAll( $fname = __METHOD__, array $options = [] ) {
 232                 $this->commitMasterChanges( $fname, $options );
 233                 $this->forEachLBCallMethod( 'commitAll', [ $fname ] );
 234         }
 235
 236         /**
 237          * Flush any master transaction snapshots and set DBO_TRX (if DBO_DEFAULT is set)
 238          *
 239          * The DBO_TRX setting will be reverted to the default in each of these methods:
 240          *   - commitMasterChanges()
 241          *   - rollbackMasterChanges()
 242          *   - commitAll()
 243          *
 244          * This allows for custom transaction rounds from any outer transaction scope.
 245          *
 246          * @param string $fname
 247          * @throws DBTransactionError
 248          * @since 1.28
 249          */
 250         public function beginMasterChanges( $fname = __METHOD__ ) {
 251                 if ( $this->trxRoundId !== false ) {
 252                         throw new DBTransactionError(
 253                                 null,
 254                                 "$fname: transaction round '{$this->trxRoundId}' already started."
 255                         );
 256                 }
 257                 $this->trxRoundId = $fname;
 258                 // Set DBO_TRX flags on all appropriate DBs
 259                 $this->forEachLBCallMethod( 'beginMasterChanges', [ $fname ] );
 260         }
 261
 262         /**
 263          * Commit changes on all master connections
 264          * @param string $fname Caller name
 265          * @param array $options Options map:
 266          *   - maxWriteDuration: abort if more than this much time was spent in write queries
 267          * @throws Exception
 268          */
 269         public function commitMasterChanges( $fname = __METHOD__, array $options = [] ) {
 270                 if ( $this->trxRoundId !== false && $this->trxRoundId !== $fname ) {
 271                         throw new DBTransactionError(
 272                                 null,
 273                                 "$fname: transaction round '{$this->trxRoundId}' still running."
 274                         );
 275                 }
 276                 // Run pre-commit callbacks and suppress post-commit callbacks, aborting on failure
 277                 $this->forEachLBCallMethod( 'finalizeMasterChanges' );
 278                 $this->trxRoundId = false;
 279                 // Perform pre-commit checks, aborting on failure
 280                 $this->forEachLBCallMethod( 'approveMasterChanges', [ $options ] );
 281                 // Log the DBs and methods involved in multi-DB transactions
 282                 $this->logIfMultiDbTransaction();
 283                 // Actually perform the commit on all master DB connections and revert DBO_TRX
 284                 $this->forEachLBCallMethod( 'commitMasterChanges', [ $fname ] );
 285                 // Run all post-commit callbacks
 286                 /** @var Exception $e */
 287                 $e = null; // first callback exception
 288                 $this->forEachLB( function ( ILoadBalancer $lb ) use ( &$e ) {
 289                         $ex = $lb->runMasterPostTrxCallbacks( IDatabase::TRIGGER_COMMIT );
 290                         $e = $e ?: $ex;
 291                 } );
 292                 // Commit any dangling DBO_TRX transactions from callbacks on one DB to another DB
 293                 $this->forEachLBCallMethod( 'commitMasterChanges', [ $fname ] );
 294                 // Throw any last post-commit callback error
 295                 if ( $e instanceof Exception ) {
 296                         throw $e;
 297                 }
 298         }
 299
 300         /**
 301          * Rollback changes on all master connections
 302          * @param string $fname Caller name
 303          * @since 1.23
 304          */
 305         public function rollbackMasterChanges( $fname = __METHOD__ ) {
 306                 $this->trxRoundId = false;
 307                 $this->forEachLBCallMethod( 'suppressTransactionEndCallbacks' );
 308                 $this->forEachLBCallMethod( 'rollbackMasterChanges', [ $fname ] );
 309                 // Run all post-rollback callbacks
 310                 $this->forEachLB( function ( ILoadBalancer $lb ) {
 311                         $lb->runMasterPostTrxCallbacks( IDatabase::TRIGGER_ROLLBACK );
 312                 } );
 313         }
 314
 315         /**
 316          * Log query info if multi DB transactions are going to be committed now
 317          */
 318         private function logIfMultiDbTransaction() {
 319                 $callersByDB = [];
 320                 $this->forEachLB( function ( ILoadBalancer $lb ) use ( &$callersByDB ) {
 321                         $masterName = $lb->getServerName( $lb->getWriterIndex() );
 322                         $callers = $lb->pendingMasterChangeCallers();
 323                         if ( $callers ) {
 324                                 $callersByDB[$masterName] = $callers;
 325                         }
 326                 } );
 327
 328                 if ( count( $callersByDB ) >= 2 ) {
 329                         $dbs = implode( ', ', array_keys( $callersByDB ) );
 330                         $msg = "Multi-DB transaction [{$dbs}]:\n";
 331                         foreach ( $callersByDB as $db => $callers ) {
 332                                 $msg .= "$db: " . implode( '; ', $callers ) . "\n";
 333                         }
 334                         $this->queryLogger->info( $msg );
 335                 }
 336         }
 337
 338         /**
 339          * Determine if any master connection has pending changes
 340          * @return bool
 341          * @since 1.23
 342          */
 343         public function hasMasterChanges() {
 344                 $ret = false;
 345                 $this->forEachLB( function ( ILoadBalancer $lb ) use ( &$ret ) {
 346                         $ret = $ret || $lb->hasMasterChanges();
 347                 } );
 348
 349                 return $ret;
 350         }
 351
 352         /**
 353          * Detemine if any lagged replica DB connection was used
 354          * @return bool
 355          * @since 1.28
 356          */
 357         public function laggedReplicaUsed() {
 358                 $ret = false;
 359                 $this->forEachLB( function ( ILoadBalancer $lb ) use ( &$ret ) {
 360                         $ret = $ret || $lb->laggedReplicaUsed();
 361                 } );
 362
 363                 return $ret;
 364         }
 365
 366         /**
 367          * Determine if any master connection has pending/written changes from this request
 368          * @param float $age How many seconds ago is "recent" [defaults to LB lag wait timeout]
 369          * @return bool
 370          * @since 1.27
 371          */
 372         public function hasOrMadeRecentMasterChanges( $age = null ) {
 373                 $ret = false;
 374                 $this->forEachLB( function ( ILoadBalancer $lb ) use ( $age, &$ret ) {
 375                         $ret = $ret || $lb->hasOrMadeRecentMasterChanges( $age );
 376                 } );
 377                 return $ret;
 378         }
 379
 380         /**
 381          * Waits for the replica DBs to catch up to the current master position
 382          *
 383          * Use this when updating very large numbers of rows, as in maintenance scripts,
 384          * to avoid causing too much lag. Of course, this is a no-op if there are no replica DBs.
 385          *
 386          * By default this waits on all DB clusters actually used in this request.
 387          * This makes sense when lag being waiting on is caused by the code that does this check.
 388          * In that case, setting "ifWritesSince" can avoid the overhead of waiting for clusters
 389          * that were not changed since the last wait check. To forcefully wait on a specific cluster
 390          * for a given wiki, use the 'wiki' parameter. To forcefully wait on an "external" cluster,
 391          * use the "cluster" parameter.
 392          *
 393          * Never call this function after a large DB write that is *still* in a transaction.
 394          * It only makes sense to call this after the possible lag inducing changes were committed.
 395          *
 396          * @param array $opts Optional fields that include:
 397          *   - wiki : wait on the load balancer DBs that handles the given wiki
 398          *   - cluster : wait on the given external load balancer DBs
 399          *   - timeout : Max wait time. Default: ~60 seconds
 400          *   - ifWritesSince: Only wait if writes were done since this UNIX timestamp
 401          * @throws DBReplicationWaitError If a timeout or error occured waiting on a DB cluster
 402          * @since 1.27
 403          */
 404         public function waitForReplication( array $opts = [] ) {
 405                 $opts += [
 406                         'wiki' => false,
 407                         'cluster' => false,
 408                         'timeout' => 60,
 409                         'ifWritesSince' => null
 410                 ];
 411
 412                 // Figure out which clusters need to be checked
 413                 /** @var ILoadBalancer[] $lbs */
 414                 $lbs = [];
 415                 if ( $opts['cluster'] !== false ) {
 416                         $lbs[] = $this->getExternalLB( $opts['cluster'] );
 417                 } elseif ( $opts['wiki'] !== false ) {
 418                         $lbs[] = $this->getMainLB( $opts['wiki'] );
 419                 } else {
 420                         $this->forEachLB( function ( ILoadBalancer $lb ) use ( &$lbs ) {
 421                                 $lbs[] = $lb;
 422                         } );
 423                         if ( !$lbs ) {
 424                                 return; // nothing actually used
 425                         }
 426                 }
 427
 428                 // Get all the master positions of applicable DBs right now.
 429                 // This can be faster since waiting on one cluster reduces the
 430                 // time needed to wait on the next clusters.
 431                 $masterPositions = array_fill( 0, count( $lbs ), false );
 432                 foreach ( $lbs as $i => $lb ) {
 433                         if ( $lb->getServerCount() <= 1 ) {
 434                                 // Bug 27975 - Don't try to wait for replica DBs if there are none
 435                                 // Prevents permission error when getting master position
 436                                 continue;
 437                         } elseif ( $opts['ifWritesSince']
 438                                 && $lb->lastMasterChangeTimestamp() < $opts['ifWritesSince']
 439                         ) {
 440                                 continue; // no writes since the last wait
 441                         }
 442                         $masterPositions[$i] = $lb->getMasterPos();
 443                 }
 444
 445                 // Run any listener callbacks *after* getting the DB positions. The more
 446                 // time spent in the callbacks, the less time is spent in waitForAll().
 447                 foreach ( $this->replicationWaitCallbacks as $callback ) {
 448                         $callback();
 449                 }
 450
 451                 $failed = [];
 452                 foreach ( $lbs as $i => $lb ) {
 453                         if ( $masterPositions[$i] ) {
 454                                 // The DBMS may not support getMasterPos()
 455                                 if ( !$lb->waitForAll( $masterPositions[$i], $opts['timeout'] ) ) {
 456                                         $failed[] = $lb->getServerName( $lb->getWriterIndex() );
 457                                 }
 458                         }
 459                 }
 460
 461                 if ( $failed ) {
 462                         throw new DBReplicationWaitError(
 463                                 "Could not wait for replica DBs to catch up to " .
 464                                 implode( ', ', $failed )
 465                         );
 466                 }
 467         }
 468
 469         /**
 470          * Add a callback to be run in every call to waitForReplication() before waiting
 471          *
 472          * Callbacks must clear any transactions that they start
 473          *
 474          * @param string $name Callback name
 475          * @param callable|null $callback Use null to unset a callback
 476          * @since 1.28
 477          */
 478         public function setWaitForReplicationListener( $name, callable $callback = null ) {
 479                 if ( $callback ) {
 480                         $this->replicationWaitCallbacks[$name] = $callback;
 481                 } else {
 482                         unset( $this->replicationWaitCallbacks[$name] );
 483                 }
 484         }
 485
 486         /**
 487          * Get a token asserting that no transaction writes are active
 488          *
 489          * @param string $fname Caller name (e.g. __METHOD__)
 490          * @return mixed A value to pass to commitAndWaitForReplication()
 491          * @since 1.28
 492          */
 493         public function getEmptyTransactionTicket( $fname ) {
 494                 if ( $this->hasMasterChanges() ) {
 495                         $this->queryLogger->error( __METHOD__ . ": $fname does not have outer scope." );
 496                         return null;
 497                 }
 498
 499                 return $this->ticket;
 500         }
 501
 502         /**
 503          * Convenience method for safely running commitMasterChanges()/waitForReplication()
 504          *
 505          * This will commit and wait unless $ticket indicates it is unsafe to do so
 506          *
 507          * @param string $fname Caller name (e.g. __METHOD__)
 508          * @param mixed $ticket Result of getEmptyTransactionTicket()
 509          * @param array $opts Options to waitForReplication()
 510          * @throws DBReplicationWaitError
 511          * @since 1.28
 512          */
 513         public function commitAndWaitForReplication( $fname, $ticket, array $opts = [] ) {
 514                 if ( $ticket !== $this->ticket ) {
 515                         $this->perfLogger->error( __METHOD__ . ": $fname does not have outer scope." );
 516                         return;
 517                 }
 518
 519                 // The transaction owner and any caller with the empty transaction ticket can commit
 520                 // so that getEmptyTransactionTicket() callers don't risk seeing DBTransactionError.
 521                 if ( $this->trxRoundId !== false && $fname !== $this->trxRoundId ) {
 522                         $this->queryLogger->info( "$fname: committing on behalf of {$this->trxRoundId}." );
 523                         $fnameEffective = $this->trxRoundId;
 524                 } else {
 525                         $fnameEffective = $fname;
 526                 }
 527
 528                 $this->commitMasterChanges( $fnameEffective );
 529                 $this->waitForReplication( $opts );
 530                 // If a nested caller committed on behalf of $fname, start another empty $fname
 531                 // transaction, leaving the caller with the same empty transaction state as before.
 532                 if ( $fnameEffective !== $fname ) {
 533                         $this->beginMasterChanges( $fnameEffective );
 534                 }
 535         }
 536
 537         /**
 538          * @param string $dbName DB master name (e.g. "db1052")
 539          * @return float|bool UNIX timestamp when client last touched the DB or false if not recent
 540          * @since 1.28
 541          */
 542         public function getChronologyProtectorTouched( $dbName ) {
 543                 return $this->chronProt->getTouched( $dbName );
 544         }
 545
 546         /**
 547          * Disable the ChronologyProtector for all load balancers
 548          *
 549          * This can be called at the start of special API entry points
 550          *
 551          * @since 1.27
 552          */
 553         public function disableChronologyProtection() {
 554                 $this->chronProt->setEnabled( false );
 555         }
 556
 557         /**
 558          * @return ChronologyProtector
 559          */
 560         protected function newChronologyProtector() {
 561                 $chronProt = new ChronologyProtector(
 562                         $this->memCache,
 563                         [
 564                                 'ip' => isset( $_SERVER[ 'REMOTE_ADDR' ] ) ? $_SERVER[ 'REMOTE_ADDR' ] : '',
 565                                 'agent' => isset( $_SERVER['HTTP_USER_AGENT'] ) ? $_SERVER['HTTP_USER_AGENT'] : ''
 566                         ],
 567                         isset( $_GET['cpPosTime'] ) ? $_GET['cpPosTime'] : null
 568                 );
 569                 $chronProt->setLogger( $this->replLogger );
 570                 if ( $this->cliMode ) {
 571                         $chronProt->setEnabled( false );
 572                 }
 573
 574                 return $chronProt;
 575         }
 576
 577         /**
 578          * Get and record all of the staged DB positions into persistent memory storage
 579          *
 580          * @param ChronologyProtector $cp
 581          * @param callable|null $workCallback Work to do instead of waiting on syncing positions
 582          * @param string $mode One of (sync, async); whether to wait on remote datacenters
 583          */
 584         protected function shutdownChronologyProtector(
 585                 ChronologyProtector $cp, $workCallback, $mode
 586         ) {
 587                 // Record all the master positions needed
 588                 $this->forEachLB( function ( ILoadBalancer $lb ) use ( $cp ) {
 589                         $cp->shutdownLB( $lb );
 590                 } );
 591                 // Write them to the persistent stash. Try to do something useful by running $work
 592                 // while ChronologyProtector waits for the stash write to replicate to all DCs.
 593                 $unsavedPositions = $cp->shutdown( $workCallback, $mode );
 594                 if ( $unsavedPositions && $workCallback ) {
 595                         // Invoke callback in case it did not cache the result yet
 596                         $workCallback(); // work now to block for less time in waitForAll()
 597                 }
 598                 // If the positions failed to write to the stash, at least wait on local datacenter
 599                 // replica DBs to catch up before responding. Even if there are several DCs, this increases
 600                 // the chance that the user will see their own changes immediately afterwards. As long
 601                 // as the sticky DC cookie applies (same domain), this is not even an issue.
 602                 $this->forEachLB( function ( ILoadBalancer $lb ) use ( $unsavedPositions ) {
 603                         $masterName = $lb->getServerName( $lb->getWriterIndex() );
 604                         if ( isset( $unsavedPositions[$masterName] ) ) {
 605                                 $lb->waitForAll( $unsavedPositions[$masterName] );
 606                         }
 607                 } );
 608         }
 609
 610         /**
 611          * Base parameters to LoadBalancer::__construct()
 612          * @return array
 613          */
 614         final protected function baseLoadBalancerParams() {
 615                 return [
 616                         'localDomain' => $this->localDomain,
 617                         'readOnlyReason' => $this->readOnlyReason,
 618                         'srvCache' => $this->srvCache,
 619                         'wanCache' => $this->wanCache,
 620                         'profiler' => $this->profiler,
 621                         'trxProfiler' => $this->trxProfiler,
 622                         'queryLogger' => $this->queryLogger,
 623                         'connLogger' => $this->connLogger,
 624                         'replLogger' => $this->replLogger,
 625                         'errorLogger' => $this->errorLogger,
 626                         'hostname' => $this->hostname,
 627                         'cliMode' => $this->cliMode,
 628                         'agent' => $this->agent
 629                 ];
 630         }
 631
 632         /**
 633          * @param ILoadBalancer $lb
 634          */
 635         protected function initLoadBalancer( ILoadBalancer $lb ) {
 636                 if ( $this->trxRoundId !== false ) {
 637                         $lb->beginMasterChanges( $this->trxRoundId ); // set DBO_TRX
 638                 }
 639         }
 640
 641         /**
 642          * Set a new table prefix for the existing local domain ID for testing
 643          *
 644          * @param string $prefix
 645          * @since 1.28
 646          */
 647         public function setDomainPrefix( $prefix ) {
 648                 $this->localDomain = new DatabaseDomain(
 649                         $this->localDomain->getDatabase(),
 650                         null,
 651                         $prefix
 652                 );
 653
 654                 $this->forEachLB( function( LoadBalancer $lb ) use ( $prefix ) {
 655                         $lb->setDomainPrefix( $prefix );
 656                 } );
 657         }
 658
 659         /**
 660          * Close all open database connections on all open load balancers.
 661          * @since 1.28
 662          */
 663         public function closeAll() {
 664                 $this->forEachLBCallMethod( 'closeAll', [] );
 665         }
 666
 667         /**
 668          * @param string $agent Agent name for query profiling
 669          * @since 1.28
 670          */
 671         public function setAgentName( $agent ) {
 672                 $this->agent = $agent;
 673         }
 674 }