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 Psr\Log\LoggerInterface;
  25 use MediaWiki\MediaWikiServices;
  26 use MediaWiki\Services\DestructibleService;
  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 LoggerInterface */
  41         protected $replLogger;
  42         /** @var BagOStuff */
  43         protected $srvCache;
  44         /** @var WANObjectCache */
  45         protected $wanCache;
  46
  47         /** @var mixed */
  48         protected $ticket;
  49         /** @var string|bool String if a requested DBO_TRX transaction round is active */
  50         protected $trxRoundId = false;
  51         /** @var string|bool Reason all LBs are read-only or false if not */
  52         protected $readOnlyReason = false;
  53         /** @var callable[] */
  54         protected $replicationWaitCallbacks = [];
  55
  56         const SHUTDOWN_NO_CHRONPROT = 0; // don't save DB positions at all
  57         const SHUTDOWN_CHRONPROT_ASYNC = 1; // save DB positions, but don't wait on remote DCs
  58         const SHUTDOWN_CHRONPROT_SYNC = 2; // save DB positions, waiting on all DCs
  59
  60         /**
  61          * Construct a factory based on a configuration array (typically from $wgLBFactoryConf)
  62          * @param array $conf
  63          * @TODO: inject objects via dependency framework
  64          */
  65         public function __construct( array $conf ) {
  66                 if ( isset( $conf['readOnlyReason'] ) && is_string( $conf['readOnlyReason'] ) ) {
  67                         $this->readOnlyReason = $conf['readOnlyReason'];
  68                 }
  69                 $this->chronProt = $this->newChronologyProtector();
  70                 $this->trxProfiler = Profiler::instance()->getTransactionProfiler();
  71                 // Use APC/memcached style caching, but avoids loops with CACHE_DB (T141804)
  72                 $cache = ObjectCache::getLocalServerInstance();
  73                 if ( $cache->getQoS( $cache::ATTR_EMULATION ) > $cache::QOS_EMULATION_SQL ) {
  74                         $this->srvCache = $cache;
  75                 } else {
  76                         $this->srvCache = new EmptyBagOStuff();
  77                 }
  78                 $wCache = ObjectCache::getMainWANInstance();
  79                 if ( $wCache->getQoS( $wCache::ATTR_EMULATION ) > $wCache::QOS_EMULATION_SQL ) {
  80                         $this->wanCache = $wCache;
  81                 } else {
  82                         $this->wanCache = WANObjectCache::newEmpty();
  83                 }
  84                 $this->trxLogger = LoggerFactory::getInstance( 'DBTransaction' );
  85                 $this->replLogger = LoggerFactory::getInstance( 'DBReplication' );
  86                 $this->ticket = mt_rand();
  87         }
  88
  89         /**
  90          * Disables all load balancers. All connections are closed, and any attempt to
  91          * open a new connection will result in a DBAccessError.
  92          * @see LoadBalancer::disable()
  93          */
  94         public function destroy() {
  95                 $this->shutdown( self::SHUTDOWN_NO_CHRONPROT );
  96                 $this->forEachLBCallMethod( 'disable' );
  97         }
  98
  99         /**
 100          * Disables all access to the load balancer, will cause all database access
 101          * to throw a DBAccessError
 102          */
 103         public static function disableBackend() {
 104                 MediaWikiServices::disableStorageBackend();
 105         }
 106
 107         /**
 108          * Get an LBFactory instance
 109          *
 110          * @deprecated since 1.27, use MediaWikiServices::getDBLoadBalancerFactory() instead.
 111          *
 112          * @return LBFactory
 113          */
 114         public static function singleton() {
 115                 return MediaWikiServices::getInstance()->getDBLoadBalancerFactory();
 116         }
 117
 118         /**
 119          * Returns the LBFactory class to use and the load balancer configuration.
 120          *
 121          * @todo instead of this, use a ServiceContainer for managing the different implementations.
 122          *
 123          * @param array $config (e.g. $wgLBFactoryConf)
 124          * @return string Class name
 125          */
 126         public static function getLBFactoryClass( array $config ) {
 127                 // For configuration backward compatibility after removing
 128                 // underscores from class names in MediaWiki 1.23.
 129                 $bcClasses = [
 130                         'LBFactory_Simple' => 'LBFactorySimple',
 131                         'LBFactory_Single' => 'LBFactorySingle',
 132                         'LBFactory_Multi' => 'LBFactoryMulti',
 133                         'LBFactory_Fake' => 'LBFactoryFake',
 134                 ];
 135
 136                 $class = $config['class'];
 137
 138                 if ( isset( $bcClasses[$class] ) ) {
 139                         $class = $bcClasses[$class];
 140                         wfDeprecated(
 141                                 '$wgLBFactoryConf must be updated. See RELEASE-NOTES for details',
 142                                 '1.23'
 143                         );
 144                 }
 145
 146                 return $class;
 147         }
 148
 149         /**
 150          * Shut down, close connections and destroy the cached instance.
 151          *
 152          * @deprecated since 1.27, use LBFactory::destroy()
 153          */
 154         public static function destroyInstance() {
 155                 MediaWikiServices::getInstance()->getDBLoadBalancerFactory()->destroy();
 156         }
 157
 158         /**
 159          * Create a new load balancer object. The resulting object will be untracked,
 160          * not chronology-protected, and the caller is responsible for cleaning it up.
 161          *
 162          * @param bool|string $wiki Wiki ID, or false for the current wiki
 163          * @return LoadBalancer
 164          */
 165         abstract public function newMainLB( $wiki = false );
 166
 167         /**
 168          * Get a cached (tracked) load balancer object.
 169          *
 170          * @param bool|string $wiki Wiki ID, or false for the current wiki
 171          * @return LoadBalancer
 172          */
 173         abstract public function getMainLB( $wiki = false );
 174
 175         /**
 176          * Create a new load balancer for external storage. The resulting object will be
 177          * untracked, not chronology-protected, and the caller is responsible for
 178          * cleaning it up.
 179          *
 180          * @param string $cluster External storage cluster, or false for core
 181          * @param bool|string $wiki Wiki ID, or false for the current wiki
 182          * @return LoadBalancer
 183          */
 184         abstract protected function newExternalLB( $cluster, $wiki = false );
 185
 186         /**
 187          * Get a cached (tracked) load balancer for external storage
 188          *
 189          * @param string $cluster External storage cluster, or false for core
 190          * @param bool|string $wiki Wiki ID, or false for the current wiki
 191          * @return LoadBalancer
 192          */
 193         abstract public function getExternalLB( $cluster, $wiki = false );
 194
 195         /**
 196          * Execute a function for each tracked load balancer
 197          * The callback is called with the load balancer as the first parameter,
 198          * and $params passed as the subsequent parameters.
 199          *
 200          * @param callable $callback
 201          * @param array $params
 202          */
 203         abstract public function forEachLB( $callback, array $params = [] );
 204
 205         /**
 206          * Prepare all tracked load balancers for shutdown
 207          * @param integer $mode One of the class SHUTDOWN_* constants
 208          * @param callable|null $workCallback Work to mask ChronologyProtector writes
 209          */
 210         public function shutdown(
 211                 $mode = self::SHUTDOWN_CHRONPROT_SYNC, callable $workCallback = null
 212         ) {
 213                 if ( $mode === self::SHUTDOWN_CHRONPROT_SYNC ) {
 214                         $this->shutdownChronologyProtector( $this->chronProt, $workCallback, 'sync' );
 215                 } elseif ( $mode === self::SHUTDOWN_CHRONPROT_ASYNC ) {
 216                         $this->shutdownChronologyProtector( $this->chronProt, null, 'async' );
 217                 }
 218
 219                 $this->commitMasterChanges( __METHOD__ ); // sanity
 220         }
 221
 222         /**
 223          * Call a method of each tracked load balancer
 224          *
 225          * @param string $methodName
 226          * @param array $args
 227          */
 228         private function forEachLBCallMethod( $methodName, array $args = [] ) {
 229                 $this->forEachLB(
 230                         function ( LoadBalancer $loadBalancer, $methodName, array $args ) {
 231                                 call_user_func_array( [ $loadBalancer, $methodName ], $args );
 232                         },
 233                         [ $methodName, $args ]
 234                 );
 235         }
 236
 237         /**
 238          * Commit all replica DB transactions so as to flush any REPEATABLE-READ or SSI snapshot
 239          *
 240          * @param string $fname Caller name
 241          * @since 1.28
 242          */
 243         public function flushReplicaSnapshots( $fname = __METHOD__ ) {
 244                 $this->forEachLBCallMethod( 'flushReplicaSnapshots', [ $fname ] );
 245         }
 246
 247         /**
 248          * Commit on all connections. Done for two reasons:
 249          * 1. To commit changes to the masters.
 250          * 2. To release the snapshot on all connections, master and replica DB.
 251          * @param string $fname Caller name
 252          * @param array $options Options map:
 253          *   - maxWriteDuration: abort if more than this much time was spent in write queries
 254          */
 255         public function commitAll( $fname = __METHOD__, array $options = [] ) {
 256                 $this->commitMasterChanges( $fname, $options );
 257                 $this->forEachLBCallMethod( 'commitAll', [ $fname ] );
 258         }
 259
 260         /**
 261          * Flush any master transaction snapshots and set DBO_TRX (if DBO_DEFAULT is set)
 262          *
 263          * The DBO_TRX setting will be reverted to the default in each of these methods:
 264          *   - commitMasterChanges()
 265          *   - rollbackMasterChanges()
 266          *   - commitAll()
 267          *
 268          * This allows for custom transaction rounds from any outer transaction scope.
 269          *
 270          * @param string $fname
 271          * @throws DBTransactionError
 272          * @since 1.28
 273          */
 274         public function beginMasterChanges( $fname = __METHOD__ ) {
 275                 if ( $this->trxRoundId !== false ) {
 276                         throw new DBTransactionError(
 277                                 null,
 278                                 "$fname: transaction round '{$this->trxRoundId}' already started."
 279                         );
 280                 }
 281                 $this->trxRoundId = $fname;
 282                 // Set DBO_TRX flags on all appropriate DBs
 283                 $this->forEachLBCallMethod( 'beginMasterChanges', [ $fname ] );
 284         }
 285
 286         /**
 287          * Commit changes on all master connections
 288          * @param string $fname Caller name
 289          * @param array $options Options map:
 290          *   - maxWriteDuration: abort if more than this much time was spent in write queries
 291          * @throws Exception
 292          */
 293         public function commitMasterChanges( $fname = __METHOD__, array $options = [] ) {
 294                 if ( $this->trxRoundId !== false && $this->trxRoundId !== $fname ) {
 295                         throw new DBTransactionError(
 296                                 null,
 297                                 "$fname: transaction round '{$this->trxRoundId}' still running."
 298                         );
 299                 }
 300                 // Run pre-commit callbacks and suppress post-commit callbacks, aborting on failure
 301                 $this->forEachLBCallMethod( 'finalizeMasterChanges' );
 302                 $this->trxRoundId = false;
 303                 // Perform pre-commit checks, aborting on failure
 304                 $this->forEachLBCallMethod( 'approveMasterChanges', [ $options ] );
 305                 // Log the DBs and methods involved in multi-DB transactions
 306                 $this->logIfMultiDbTransaction();
 307                 // Actually perform the commit on all master DB connections and revert DBO_TRX
 308                 $this->forEachLBCallMethod( 'commitMasterChanges', [ $fname ] );
 309                 // Run all post-commit callbacks
 310                 /** @var Exception $e */
 311                 $e = null; // first callback exception
 312                 $this->forEachLB( function ( LoadBalancer $lb ) use ( &$e ) {
 313                         $ex = $lb->runMasterPostTrxCallbacks( IDatabase::TRIGGER_COMMIT );
 314                         $e = $e ?: $ex;
 315                 } );
 316                 // Commit any dangling DBO_TRX transactions from callbacks on one DB to another DB
 317                 $this->forEachLBCallMethod( 'commitMasterChanges', [ $fname ] );
 318                 // Throw any last post-commit callback error
 319                 if ( $e instanceof Exception ) {
 320                         throw $e;
 321                 }
 322         }
 323
 324         /**
 325          * Rollback changes on all master connections
 326          * @param string $fname Caller name
 327          * @since 1.23
 328          */
 329         public function rollbackMasterChanges( $fname = __METHOD__ ) {
 330                 $this->trxRoundId = false;
 331                 $this->forEachLBCallMethod( 'suppressTransactionEndCallbacks' );
 332                 $this->forEachLBCallMethod( 'rollbackMasterChanges', [ $fname ] );
 333                 // Run all post-rollback callbacks
 334                 $this->forEachLB( function ( LoadBalancer $lb ) {
 335                         $lb->runMasterPostTrxCallbacks( IDatabase::TRIGGER_ROLLBACK );
 336                 } );
 337         }
 338
 339         /**
 340          * Log query info if multi DB transactions are going to be committed now
 341          */
 342         private function logIfMultiDbTransaction() {
 343                 $callersByDB = [];
 344                 $this->forEachLB( function ( LoadBalancer $lb ) use ( &$callersByDB ) {
 345                         $masterName = $lb->getServerName( $lb->getWriterIndex() );
 346                         $callers = $lb->pendingMasterChangeCallers();
 347                         if ( $callers ) {
 348                                 $callersByDB[$masterName] = $callers;
 349                         }
 350                 } );
 351
 352                 if ( count( $callersByDB ) >= 2 ) {
 353                         $dbs = implode( ', ', array_keys( $callersByDB ) );
 354                         $msg = "Multi-DB transaction [{$dbs}]:\n";
 355                         foreach ( $callersByDB as $db => $callers ) {
 356                                 $msg .= "$db: " . implode( '; ', $callers ) . "\n";
 357                         }
 358                         $this->trxLogger->info( $msg );
 359                 }
 360         }
 361
 362         /**
 363          * Determine if any master connection has pending changes
 364          * @return bool
 365          * @since 1.23
 366          */
 367         public function hasMasterChanges() {
 368                 $ret = false;
 369                 $this->forEachLB( function ( LoadBalancer $lb ) use ( &$ret ) {
 370                         $ret = $ret || $lb->hasMasterChanges();
 371                 } );
 372
 373                 return $ret;
 374         }
 375
 376         /**
 377          * Detemine if any lagged replica DB connection was used
 378          * @return bool
 379          * @since 1.28
 380          */
 381         public function laggedReplicaUsed() {
 382                 $ret = false;
 383                 $this->forEachLB( function ( LoadBalancer $lb ) use ( &$ret ) {
 384                         $ret = $ret || $lb->laggedReplicaUsed();
 385                 } );
 386
 387                 return $ret;
 388         }
 389
 390         /**
 391          * @return bool
 392          * @since 1.27
 393          * @deprecated Since 1.28; use laggedReplicaUsed()
 394          */
 395         public function laggedSlaveUsed() {
 396                 return $this->laggedReplicaUsed();
 397         }
 398
 399         /**
 400          * Determine if any master connection has pending/written changes from this request
 401          * @param float $age How many seconds ago is "recent" [defaults to LB lag wait timeout]
 402          * @return bool
 403          * @since 1.27
 404          */
 405         public function hasOrMadeRecentMasterChanges( $age = null ) {
 406                 $ret = false;
 407                 $this->forEachLB( function ( LoadBalancer $lb ) use ( $age, &$ret ) {
 408                         $ret = $ret || $lb->hasOrMadeRecentMasterChanges( $age );
 409                 } );
 410                 return $ret;
 411         }
 412
 413         /**
 414          * Waits for the replica DBs to catch up to the current master position
 415          *
 416          * Use this when updating very large numbers of rows, as in maintenance scripts,
 417          * to avoid causing too much lag. Of course, this is a no-op if there are no replica DBs.
 418          *
 419          * By default this waits on all DB clusters actually used in this request.
 420          * This makes sense when lag being waiting on is caused by the code that does this check.
 421          * In that case, setting "ifWritesSince" can avoid the overhead of waiting for clusters
 422          * that were not changed since the last wait check. To forcefully wait on a specific cluster
 423          * for a given wiki, use the 'wiki' parameter. To forcefully wait on an "external" cluster,
 424          * use the "cluster" parameter.
 425          *
 426          * Never call this function after a large DB write that is *still* in a transaction.
 427          * It only makes sense to call this after the possible lag inducing changes were committed.
 428          *
 429          * @param array $opts Optional fields that include:
 430          *   - wiki : wait on the load balancer DBs that handles the given wiki
 431          *   - cluster : wait on the given external load balancer DBs
 432          *   - timeout : Max wait time. Default: ~60 seconds
 433          *   - ifWritesSince: Only wait if writes were done since this UNIX timestamp
 434          * @throws DBReplicationWaitError If a timeout or error occured waiting on a DB cluster
 435          * @since 1.27
 436          */
 437         public function waitForReplication( array $opts = [] ) {
 438                 $opts += [
 439                         'wiki' => false,
 440                         'cluster' => false,
 441                         'timeout' => 60,
 442                         'ifWritesSince' => null
 443                 ];
 444
 445                 // Figure out which clusters need to be checked
 446                 /** @var LoadBalancer[] $lbs */
 447                 $lbs = [];
 448                 if ( $opts['cluster'] !== false ) {
 449                         $lbs[] = $this->getExternalLB( $opts['cluster'] );
 450                 } elseif ( $opts['wiki'] !== false ) {
 451                         $lbs[] = $this->getMainLB( $opts['wiki'] );
 452                 } else {
 453                         $this->forEachLB( function ( LoadBalancer $lb ) use ( &$lbs ) {
 454                                 $lbs[] = $lb;
 455                         } );
 456                         if ( !$lbs ) {
 457                                 return; // nothing actually used
 458                         }
 459                 }
 460
 461                 // Get all the master positions of applicable DBs right now.
 462                 // This can be faster since waiting on one cluster reduces the
 463                 // time needed to wait on the next clusters.
 464                 $masterPositions = array_fill( 0, count( $lbs ), false );
 465                 foreach ( $lbs as $i => $lb ) {
 466                         if ( $lb->getServerCount() <= 1 ) {
 467                                 // Bug 27975 - Don't try to wait for replica DBs if there are none
 468                                 // Prevents permission error when getting master position
 469                                 continue;
 470                         } elseif ( $opts['ifWritesSince']
 471                                 && $lb->lastMasterChangeTimestamp() < $opts['ifWritesSince']
 472                         ) {
 473                                 continue; // no writes since the last wait
 474                         }
 475                         $masterPositions[$i] = $lb->getMasterPos();
 476                 }
 477
 478                 // Run any listener callbacks *after* getting the DB positions. The more
 479                 // time spent in the callbacks, the less time is spent in waitForAll().
 480                 foreach ( $this->replicationWaitCallbacks as $callback ) {
 481                         $callback();
 482                 }
 483
 484                 $failed = [];
 485                 foreach ( $lbs as $i => $lb ) {
 486                         if ( $masterPositions[$i] ) {
 487                                 // The DBMS may not support getMasterPos() or the whole
 488                                 // load balancer might be fake (e.g. $wgAllDBsAreLocalhost).
 489                                 if ( !$lb->waitForAll( $masterPositions[$i], $opts['timeout'] ) ) {
 490                                         $failed[] = $lb->getServerName( $lb->getWriterIndex() );
 491                                 }
 492                         }
 493                 }
 494
 495                 if ( $failed ) {
 496                         throw new DBReplicationWaitError(
 497                                 "Could not wait for replica DBs to catch up to " .
 498                                 implode( ', ', $failed )
 499                         );
 500                 }
 501         }
 502
 503         /**
 504          * Add a callback to be run in every call to waitForReplication() before waiting
 505          *
 506          * Callbacks must clear any transactions that they start
 507          *
 508          * @param string $name Callback name
 509          * @param callable|null $callback Use null to unset a callback
 510          * @since 1.28
 511          */
 512         public function setWaitForReplicationListener( $name, callable $callback = null ) {
 513                 if ( $callback ) {
 514                         $this->replicationWaitCallbacks[$name] = $callback;
 515                 } else {
 516                         unset( $this->replicationWaitCallbacks[$name] );
 517                 }
 518         }
 519
 520         /**
 521          * Get a token asserting that no transaction writes are active
 522          *
 523          * @param string $fname Caller name (e.g. __METHOD__)
 524          * @return mixed A value to pass to commitAndWaitForReplication()
 525          * @since 1.28
 526          */
 527         public function getEmptyTransactionTicket( $fname ) {
 528                 if ( $this->hasMasterChanges() ) {
 529                         $this->trxLogger->error( __METHOD__ . ": $fname does not have outer scope." );
 530                         return null;
 531                 }
 532
 533                 return $this->ticket;
 534         }
 535
 536         /**
 537          * Convenience method for safely running commitMasterChanges()/waitForReplication()
 538          *
 539          * This will commit and wait unless $ticket indicates it is unsafe to do so
 540          *
 541          * @param string $fname Caller name (e.g. __METHOD__)
 542          * @param mixed $ticket Result of getEmptyTransactionTicket()
 543          * @param array $opts Options to waitForReplication()
 544          * @throws DBReplicationWaitError
 545          * @since 1.28
 546          */
 547         public function commitAndWaitForReplication( $fname, $ticket, array $opts = [] ) {
 548                 if ( $ticket !== $this->ticket ) {
 549                         $logger = LoggerFactory::getInstance( 'DBPerformance' );
 550                         $logger->error( __METHOD__ . ": cannot commit; $fname does not have outer scope." );
 551                         return;
 552                 }
 553
 554                 // The transaction owner and any caller with the empty transaction ticket can commit
 555                 // so that getEmptyTransactionTicket() callers don't risk seeing DBTransactionError.
 556                 if ( $this->trxRoundId !== false && $fname !== $this->trxRoundId ) {
 557                         $this->trxLogger->info( "$fname: committing on behalf of {$this->trxRoundId}." );
 558                         $fnameEffective = $this->trxRoundId;
 559                 } else {
 560                         $fnameEffective = $fname;
 561                 }
 562
 563                 $this->commitMasterChanges( $fnameEffective );
 564                 $this->waitForReplication( $opts );
 565                 // If a nested caller committed on behalf of $fname, start another empty $fname
 566                 // transaction, leaving the caller with the same empty transaction state as before.
 567                 if ( $fnameEffective !== $fname ) {
 568                         $this->beginMasterChanges( $fnameEffective );
 569                 }
 570         }
 571
 572         /**
 573          * @param string $dbName DB master name (e.g. "db1052")
 574          * @return float|bool UNIX timestamp when client last touched the DB or false if not recent
 575          * @since 1.28
 576          */
 577         public function getChronologyProtectorTouched( $dbName ) {
 578                 return $this->chronProt->getTouched( $dbName );
 579         }
 580
 581         /**
 582          * Disable the ChronologyProtector for all load balancers
 583          *
 584          * This can be called at the start of special API entry points
 585          *
 586          * @since 1.27
 587          */
 588         public function disableChronologyProtection() {
 589                 $this->chronProt->setEnabled( false );
 590         }
 591
 592         /**
 593          * @return ChronologyProtector
 594          */
 595         protected function newChronologyProtector() {
 596                 $request = RequestContext::getMain()->getRequest();
 597                 $chronProt = new ChronologyProtector(
 598                         ObjectCache::getMainStashInstance(),
 599                         [
 600                                 'ip' => $request->getIP(),
 601                                 'agent' => $request->getHeader( 'User-Agent' ),
 602                         ],
 603                         $request->getFloat( 'cpPosTime', null )
 604                 );
 605                 if ( PHP_SAPI === 'cli' ) {
 606                         $chronProt->setEnabled( false );
 607                 } elseif ( $request->getHeader( 'ChronologyProtection' ) === 'false' ) {
 608                         // Request opted out of using position wait logic. This is useful for requests
 609                         // done by the job queue or background ETL that do not have a meaningful session.
 610                         $chronProt->setWaitEnabled( false );
 611                 }
 612
 613                 return $chronProt;
 614         }
 615
 616         /**
 617          * Get and record all of the staged DB positions into persistent memory storage
 618          *
 619          * @param ChronologyProtector $cp
 620          * @param callable|null $workCallback Work to do instead of waiting on syncing positions
 621          * @param string $mode One of (sync, async); whether to wait on remote datacenters
 622          */
 623         protected function shutdownChronologyProtector(
 624                 ChronologyProtector $cp, $workCallback, $mode
 625         ) {
 626                 // Record all the master positions needed
 627                 $this->forEachLB( function ( LoadBalancer $lb ) use ( $cp ) {
 628                         $cp->shutdownLB( $lb );
 629                 } );
 630                 // Write them to the persistent stash. Try to do something useful by running $work
 631                 // while ChronologyProtector waits for the stash write to replicate to all DCs.
 632                 $unsavedPositions = $cp->shutdown( $workCallback, $mode );
 633                 if ( $unsavedPositions && $workCallback ) {
 634                         // Invoke callback in case it did not cache the result yet
 635                         $workCallback(); // work now to block for less time in waitForAll()
 636                 }
 637                 // If the positions failed to write to the stash, at least wait on local datacenter
 638                 // replica DBs to catch up before responding. Even if there are several DCs, this increases
 639                 // the chance that the user will see their own changes immediately afterwards. As long
 640                 // as the sticky DC cookie applies (same domain), this is not even an issue.
 641                 $this->forEachLB( function ( LoadBalancer $lb ) use ( $unsavedPositions ) {
 642                         $masterName = $lb->getServerName( $lb->getWriterIndex() );
 643                         if ( isset( $unsavedPositions[$masterName] ) ) {
 644                                 $lb->waitForAll( $unsavedPositions[$masterName] );
 645                         }
 646                 } );
 647         }
 648
 649         /**
 650          * Base parameters to LoadBalancer::__construct()
 651          * @return array
 652          */
 653         final protected function baseLoadBalancerParams() {
 654                 return [
 655                         'localDomain' => wfWikiID(),
 656                         'readOnlyReason' => $this->readOnlyReason,
 657                         'srvCache' => $this->srvCache,
 658                         'wanCache' => $this->wanCache,
 659                         'trxProfiler' => $this->trxProfiler,
 660                         'queryLogger' => LoggerFactory::getInstance( 'DBQuery' ),
 661                         'connLogger' => LoggerFactory::getInstance( 'DBConnection' ),
 662                         'replLogger' => LoggerFactory::getInstance( 'DBReplication' ),
 663                         'errorLogger' => [ MWExceptionHandler::class, 'logException' ]
 664                 ];
 665         }
 666
 667         /**
 668          * @param LoadBalancer $lb
 669          */
 670         protected function initLoadBalancer( LoadBalancer $lb ) {
 671                 if ( $this->trxRoundId !== false ) {
 672                         $lb->beginMasterChanges( $this->trxRoundId ); // set DBO_TRX
 673                 }
 674         }
 675
 676         /**
 677          * Append ?cpPosTime parameter to a URL for ChronologyProtector purposes if needed
 678          *
 679          * Note that unlike cookies, this works accross domains
 680          *
 681          * @param string $url
 682          * @param float $time UNIX timestamp just before shutdown() was called
 683          * @return string
 684          * @since 1.28
 685          */
 686         public function appendPreShutdownTimeAsQuery( $url, $time ) {
 687                 $usedCluster = 0;
 688                 $this->forEachLB( function ( LoadBalancer $lb ) use ( &$usedCluster ) {
 689                         $usedCluster |= ( $lb->getServerCount() > 1 );
 690                 } );
 691
 692                 if ( !$usedCluster ) {
 693                         return $url; // no master/replica clusters touched
 694                 }
 695
 696                 return wfAppendQuery( $url, [ 'cpPosTime' => $time ] );
 697         }
 698
 699         /**
 700          * Close all open database connections on all open load balancers.
 701          * @since 1.28
 702          */
 703         public function closeAll() {
 704                 $this->forEachLBCallMethod( 'closeAll', [] );
 705         }
 706 }