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