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 BagOStuff */
  45         protected $memCache;
  46         /** @var WANObjectCache */
  47         protected $wanCache;
  48
  49         /** @var mixed */
  50         protected $ticket;
  51         /** @var string|bool String if a requested DBO_TRX transaction round is active */
  52         protected $trxRoundId = false;
  53         /** @var string|bool Reason all LBs are read-only or false if not */
  54         protected $readOnlyReason = false;
  55         /** @var callable[] */
  56         protected $replicationWaitCallbacks = [];
  57
  58         const SHUTDOWN_NO_CHRONPROT = 0; // don't save DB positions at all
  59         const SHUTDOWN_CHRONPROT_ASYNC = 1; // save DB positions, but don't wait on remote DCs
  60         const SHUTDOWN_CHRONPROT_SYNC = 2; // save DB positions, waiting on all DCs
  61
  62         /**
  63          * Construct a factory based on a configuration array (typically from $wgLBFactoryConf)
  64          * @param array $conf
  65          * @TODO: inject objects via dependency framework
  66          */
  67         public function __construct( array $conf ) {
  68                 if ( isset( $conf['readOnlyReason'] ) && is_string( $conf['readOnlyReason'] ) ) {
  69                         $this->readOnlyReason = $conf['readOnlyReason'];
  70                 }
  71                 // Use APC/memcached style caching, but avoids loops with CACHE_DB (T141804)
  72                 $sCache = ObjectCache::getLocalServerInstance();
  73                 if ( $sCache->getQoS( $sCache::ATTR_EMULATION ) > $sCache::QOS_EMULATION_SQL ) {
  74                         $this->srvCache = $sCache;
  75                 } else {
  76                         $this->srvCache = new EmptyBagOStuff();
  77                 }
  78                 $cCache = ObjectCache::getLocalClusterInstance();
  79                 if ( $cCache->getQoS( $cCache::ATTR_EMULATION ) > $cCache::QOS_EMULATION_SQL ) {
  80                         $this->memCache = $cCache;
  81                 } else {
  82                         $this->memCache = new EmptyBagOStuff();
  83                 }
  84                 $wCache = ObjectCache::getMainWANInstance();
  85                 if ( $wCache->getQoS( $wCache::ATTR_EMULATION ) > $wCache::QOS_EMULATION_SQL ) {
  86                         $this->wanCache = $wCache;
  87                 } else {
  88                         $this->wanCache = WANObjectCache::newEmpty();
  89                 }
  90                 $this->trxProfiler = Profiler::instance()->getTransactionProfiler();
  91                 $this->trxLogger = LoggerFactory::getInstance( 'DBTransaction' );
  92                 $this->replLogger = LoggerFactory::getInstance( 'DBReplication' );
  93                 $this->chronProt = $this->newChronologyProtector();
  94                 $this->ticket = mt_rand();
  95         }
  96
  97         /**
  98          * Disables all load balancers. All connections are closed, and any attempt to
  99          * open a new connection will result in a DBAccessError.
 100          * @see LoadBalancer::disable()
 101          */
 102         public function destroy() {
 103                 $this->shutdown( self::SHUTDOWN_NO_CHRONPROT );
 104                 $this->forEachLBCallMethod( 'disable' );
 105         }
 106
 107         /**
 108          * Disables all access to the load balancer, will cause all database access
 109          * to throw a DBAccessError
 110          */
 111         public static function disableBackend() {
 112                 MediaWikiServices::disableStorageBackend();
 113         }
 114
 115         /**
 116          * Get an LBFactory instance
 117          *
 118          * @deprecated since 1.27, use MediaWikiServices::getDBLoadBalancerFactory() instead.
 119          *
 120          * @return LBFactory
 121          */
 122         public static function singleton() {
 123                 return MediaWikiServices::getInstance()->getDBLoadBalancerFactory();
 124         }
 125
 126         /**
 127          * Returns the LBFactory class to use and the load balancer configuration.
 128          *
 129          * @todo instead of this, use a ServiceContainer for managing the different implementations.
 130          *
 131          * @param array $config (e.g. $wgLBFactoryConf)
 132          * @return string Class name
 133          */
 134         public static function getLBFactoryClass( array $config ) {
 135                 // For configuration backward compatibility after removing
 136                 // underscores from class names in MediaWiki 1.23.
 137                 $bcClasses = [
 138                         'LBFactory_Simple' => 'LBFactorySimple',
 139                         'LBFactory_Single' => 'LBFactorySingle',
 140                         'LBFactory_Multi' => 'LBFactoryMulti',
 141                 ];
 142
 143                 $class = $config['class'];
 144
 145                 if ( isset( $bcClasses[$class] ) ) {
 146                         $class = $bcClasses[$class];
 147                         wfDeprecated(
 148                                 '$wgLBFactoryConf must be updated. See RELEASE-NOTES for details',
 149                                 '1.23'
 150                         );
 151                 }
 152
 153                 return $class;
 154         }
 155
 156         /**
 157          * Shut down, close connections and destroy the cached instance.
 158          *
 159          * @deprecated since 1.27, use LBFactory::destroy()
 160          */
 161         public static function destroyInstance() {
 162                 MediaWikiServices::getInstance()->getDBLoadBalancerFactory()->destroy();
 163         }
 164
 165         /**
 166          * Create a new load balancer object. The resulting object will be untracked,
 167          * not chronology-protected, and the caller is responsible for cleaning it up.
 168          *
 169          * @param bool|string $wiki Wiki ID, or false for the current wiki
 170          * @return LoadBalancer
 171          */
 172         abstract public function newMainLB( $wiki = false );
 173
 174         /**
 175          * Get a cached (tracked) load balancer object.
 176          *
 177          * @param bool|string $wiki Wiki ID, or false for the current wiki
 178          * @return LoadBalancer
 179          */
 180         abstract public function getMainLB( $wiki = false );
 181
 182         /**
 183          * Create a new load balancer for external storage. The resulting object will be
 184          * untracked, not chronology-protected, and the caller is responsible for
 185          * cleaning it up.
 186          *
 187          * @param string $cluster External storage cluster, or false for core
 188          * @param bool|string $wiki Wiki ID, or false for the current wiki
 189          * @return LoadBalancer
 190          */
 191         abstract protected function newExternalLB( $cluster, $wiki = false );
 192
 193         /**
 194          * Get a cached (tracked) load balancer for external storage
 195          *
 196          * @param string $cluster External storage cluster, or false for core
 197          * @param bool|string $wiki Wiki ID, or false for the current wiki
 198          * @return LoadBalancer
 199          */
 200         abstract public function getExternalLB( $cluster, $wiki = false );
 201
 202         /**
 203          * Execute a function for each tracked load balancer
 204          * The callback is called with the load balancer as the first parameter,
 205          * and $params passed as the subsequent parameters.
 206          *
 207          * @param callable $callback
 208          * @param array $params
 209          */
 210         abstract public function forEachLB( $callback, array $params = [] );
 211
 212         /**
 213          * Prepare all tracked load balancers for shutdown
 214          * @param integer $mode One of the class SHUTDOWN_* constants
 215          * @param callable|null $workCallback Work to mask ChronologyProtector writes
 216          */
 217         public function shutdown(
 218                 $mode = self::SHUTDOWN_CHRONPROT_SYNC, callable $workCallback = null
 219         ) {
 220                 if ( $mode === self::SHUTDOWN_CHRONPROT_SYNC ) {
 221                         $this->shutdownChronologyProtector( $this->chronProt, $workCallback, 'sync' );
 222                 } elseif ( $mode === self::SHUTDOWN_CHRONPROT_ASYNC ) {
 223                         $this->shutdownChronologyProtector( $this->chronProt, null, 'async' );
 224                 }
 225
 226                 $this->commitMasterChanges( __METHOD__ ); // sanity
 227         }
 228
 229         /**
 230          * Call a method of each tracked load balancer
 231          *
 232          * @param string $methodName
 233          * @param array $args
 234          */
 235         private function forEachLBCallMethod( $methodName, array $args = [] ) {
 236                 $this->forEachLB(
 237                         function ( LoadBalancer $loadBalancer, $methodName, array $args ) {
 238                                 call_user_func_array( [ $loadBalancer, $methodName ], $args );
 239                         },
 240                         [ $methodName, $args ]
 241                 );
 242         }
 243
 244         /**
 245          * Commit all replica DB transactions so as to flush any REPEATABLE-READ or SSI snapshot
 246          *
 247          * @param string $fname Caller name
 248          * @since 1.28
 249          */
 250         public function flushReplicaSnapshots( $fname = __METHOD__ ) {
 251                 $this->forEachLBCallMethod( 'flushReplicaSnapshots', [ $fname ] );
 252         }
 253
 254         /**
 255          * Commit on all connections. Done for two reasons:
 256          * 1. To commit changes to the masters.
 257          * 2. To release the snapshot on all connections, master and replica DB.
 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          */
 262         public function commitAll( $fname = __METHOD__, array $options = [] ) {
 263                 $this->commitMasterChanges( $fname, $options );
 264                 $this->forEachLBCallMethod( 'commitAll', [ $fname ] );
 265         }
 266
 267         /**
 268          * Flush any master transaction snapshots and set DBO_TRX (if DBO_DEFAULT is set)
 269          *
 270          * The DBO_TRX setting will be reverted to the default in each of these methods:
 271          *   - commitMasterChanges()
 272          *   - rollbackMasterChanges()
 273          *   - commitAll()
 274          *
 275          * This allows for custom transaction rounds from any outer transaction scope.
 276          *
 277          * @param string $fname
 278          * @throws DBTransactionError
 279          * @since 1.28
 280          */
 281         public function beginMasterChanges( $fname = __METHOD__ ) {
 282                 if ( $this->trxRoundId !== false ) {
 283                         throw new DBTransactionError(
 284                                 null,
 285                                 "$fname: transaction round '{$this->trxRoundId}' already started."
 286                         );
 287                 }
 288                 $this->trxRoundId = $fname;
 289                 // Set DBO_TRX flags on all appropriate DBs
 290                 $this->forEachLBCallMethod( 'beginMasterChanges', [ $fname ] );
 291         }
 292
 293         /**
 294          * Commit changes on all master connections
 295          * @param string $fname Caller name
 296          * @param array $options Options map:
 297          *   - maxWriteDuration: abort if more than this much time was spent in write queries
 298          * @throws Exception
 299          */
 300         public function commitMasterChanges( $fname = __METHOD__, array $options = [] ) {
 301                 if ( $this->trxRoundId !== false && $this->trxRoundId !== $fname ) {
 302                         throw new DBTransactionError(
 303                                 null,
 304                                 "$fname: transaction round '{$this->trxRoundId}' still running."
 305                         );
 306                 }
 307                 // Run pre-commit callbacks and suppress post-commit callbacks, aborting on failure
 308                 $this->forEachLBCallMethod( 'finalizeMasterChanges' );
 309                 $this->trxRoundId = false;
 310                 // Perform pre-commit checks, aborting on failure
 311                 $this->forEachLBCallMethod( 'approveMasterChanges', [ $options ] );
 312                 // Log the DBs and methods involved in multi-DB transactions
 313                 $this->logIfMultiDbTransaction();
 314                 // Actually perform the commit on all master DB connections and revert DBO_TRX
 315                 $this->forEachLBCallMethod( 'commitMasterChanges', [ $fname ] );
 316                 // Run all post-commit callbacks
 317                 /** @var Exception $e */
 318                 $e = null; // first callback exception
 319                 $this->forEachLB( function ( LoadBalancer $lb ) use ( &$e ) {
 320                         $ex = $lb->runMasterPostTrxCallbacks( IDatabase::TRIGGER_COMMIT );
 321                         $e = $e ?: $ex;
 322                 } );
 323                 // Commit any dangling DBO_TRX transactions from callbacks on one DB to another DB
 324                 $this->forEachLBCallMethod( 'commitMasterChanges', [ $fname ] );
 325                 // Throw any last post-commit callback error
 326                 if ( $e instanceof Exception ) {
 327                         throw $e;
 328                 }
 329         }
 330
 331         /**
 332          * Rollback changes on all master connections
 333          * @param string $fname Caller name
 334          * @since 1.23
 335          */
 336         public function rollbackMasterChanges( $fname = __METHOD__ ) {
 337                 $this->trxRoundId = false;
 338                 $this->forEachLBCallMethod( 'suppressTransactionEndCallbacks' );
 339                 $this->forEachLBCallMethod( 'rollbackMasterChanges', [ $fname ] );
 340                 // Run all post-rollback callbacks
 341                 $this->forEachLB( function ( LoadBalancer $lb ) {
 342                         $lb->runMasterPostTrxCallbacks( IDatabase::TRIGGER_ROLLBACK );
 343                 } );
 344         }
 345
 346         /**
 347          * Log query info if multi DB transactions are going to be committed now
 348          */
 349         private function logIfMultiDbTransaction() {
 350                 $callersByDB = [];
 351                 $this->forEachLB( function ( LoadBalancer $lb ) use ( &$callersByDB ) {
 352                         $masterName = $lb->getServerName( $lb->getWriterIndex() );
 353                         $callers = $lb->pendingMasterChangeCallers();
 354                         if ( $callers ) {
 355                                 $callersByDB[$masterName] = $callers;
 356                         }
 357                 } );
 358
 359                 if ( count( $callersByDB ) >= 2 ) {
 360                         $dbs = implode( ', ', array_keys( $callersByDB ) );
 361                         $msg = "Multi-DB transaction [{$dbs}]:\n";
 362                         foreach ( $callersByDB as $db => $callers ) {
 363                                 $msg .= "$db: " . implode( '; ', $callers ) . "\n";
 364                         }
 365                         $this->trxLogger->info( $msg );
 366                 }
 367         }
 368
 369         /**
 370          * Determine if any master connection has pending changes
 371          * @return bool
 372          * @since 1.23
 373          */
 374         public function hasMasterChanges() {
 375                 $ret = false;
 376                 $this->forEachLB( function ( LoadBalancer $lb ) use ( &$ret ) {
 377                         $ret = $ret || $lb->hasMasterChanges();
 378                 } );
 379
 380                 return $ret;
 381         }
 382
 383         /**
 384          * Detemine if any lagged replica DB connection was used
 385          * @return bool
 386          * @since 1.28
 387          */
 388         public function laggedReplicaUsed() {
 389                 $ret = false;
 390                 $this->forEachLB( function ( LoadBalancer $lb ) use ( &$ret ) {
 391                         $ret = $ret || $lb->laggedReplicaUsed();
 392                 } );
 393
 394                 return $ret;
 395         }
 396
 397         /**
 398          * @return bool
 399          * @since 1.27
 400          * @deprecated Since 1.28; use laggedReplicaUsed()
 401          */
 402         public function laggedSlaveUsed() {
 403                 return $this->laggedReplicaUsed();
 404         }
 405
 406         /**
 407          * Determine if any master connection has pending/written changes from this request
 408          * @param float $age How many seconds ago is "recent" [defaults to LB lag wait timeout]
 409          * @return bool
 410          * @since 1.27
 411          */
 412         public function hasOrMadeRecentMasterChanges( $age = null ) {
 413                 $ret = false;
 414                 $this->forEachLB( function ( LoadBalancer $lb ) use ( $age, &$ret ) {
 415                         $ret = $ret || $lb->hasOrMadeRecentMasterChanges( $age );
 416                 } );
 417                 return $ret;
 418         }
 419
 420         /**
 421          * Waits for the replica DBs to catch up to the current master position
 422          *
 423          * Use this when updating very large numbers of rows, as in maintenance scripts,
 424          * to avoid causing too much lag. Of course, this is a no-op if there are no replica DBs.
 425          *
 426          * By default this waits on all DB clusters actually used in this request.
 427          * This makes sense when lag being waiting on is caused by the code that does this check.
 428          * In that case, setting "ifWritesSince" can avoid the overhead of waiting for clusters
 429          * that were not changed since the last wait check. To forcefully wait on a specific cluster
 430          * for a given wiki, use the 'wiki' parameter. To forcefully wait on an "external" cluster,
 431          * use the "cluster" parameter.
 432          *
 433          * Never call this function after a large DB write that is *still* in a transaction.
 434          * It only makes sense to call this after the possible lag inducing changes were committed.
 435          *
 436          * @param array $opts Optional fields that include:
 437          *   - wiki : wait on the load balancer DBs that handles the given wiki
 438          *   - cluster : wait on the given external load balancer DBs
 439          *   - timeout : Max wait time. Default: ~60 seconds
 440          *   - ifWritesSince: Only wait if writes were done since this UNIX timestamp
 441          * @throws DBReplicationWaitError If a timeout or error occured waiting on a DB cluster
 442          * @since 1.27
 443          */
 444         public function waitForReplication( array $opts = [] ) {
 445                 $opts += [
 446                         'wiki' => false,
 447                         'cluster' => false,
 448                         'timeout' => 60,
 449                         'ifWritesSince' => null
 450                 ];
 451
 452                 // Figure out which clusters need to be checked
 453                 /** @var LoadBalancer[] $lbs */
 454                 $lbs = [];
 455                 if ( $opts['cluster'] !== false ) {
 456                         $lbs[] = $this->getExternalLB( $opts['cluster'] );
 457                 } elseif ( $opts['wiki'] !== false ) {
 458                         $lbs[] = $this->getMainLB( $opts['wiki'] );
 459                 } else {
 460                         $this->forEachLB( function ( LoadBalancer $lb ) use ( &$lbs ) {
 461                                 $lbs[] = $lb;
 462                         } );
 463                         if ( !$lbs ) {
 464                                 return; // nothing actually used
 465                         }
 466                 }
 467
 468                 // Get all the master positions of applicable DBs right now.
 469                 // This can be faster since waiting on one cluster reduces the
 470                 // time needed to wait on the next clusters.
 471                 $masterPositions = array_fill( 0, count( $lbs ), false );
 472                 foreach ( $lbs as $i => $lb ) {
 473                         if ( $lb->getServerCount() <= 1 ) {
 474                                 // Bug 27975 - Don't try to wait for replica DBs if there are none
 475                                 // Prevents permission error when getting master position
 476                                 continue;
 477                         } elseif ( $opts['ifWritesSince']
 478                                 && $lb->lastMasterChangeTimestamp() < $opts['ifWritesSince']
 479                         ) {
 480                                 continue; // no writes since the last wait
 481                         }
 482                         $masterPositions[$i] = $lb->getMasterPos();
 483                 }
 484
 485                 // Run any listener callbacks *after* getting the DB positions. The more
 486                 // time spent in the callbacks, the less time is spent in waitForAll().
 487                 foreach ( $this->replicationWaitCallbacks as $callback ) {
 488                         $callback();
 489                 }
 490
 491                 $failed = [];
 492                 foreach ( $lbs as $i => $lb ) {
 493                         if ( $masterPositions[$i] ) {
 494                                 // The DBMS may not support getMasterPos() or the whole
 495                                 // load balancer might be fake (e.g. $wgAllDBsAreLocalhost).
 496                                 if ( !$lb->waitForAll( $masterPositions[$i], $opts['timeout'] ) ) {
 497                                         $failed[] = $lb->getServerName( $lb->getWriterIndex() );
 498                                 }
 499                         }
 500                 }
 501
 502                 if ( $failed ) {
 503                         throw new DBReplicationWaitError(
 504                                 "Could not wait for replica DBs to catch up to " .
 505                                 implode( ', ', $failed )
 506                         );
 507                 }
 508         }
 509
 510         /**
 511          * Add a callback to be run in every call to waitForReplication() before waiting
 512          *
 513          * Callbacks must clear any transactions that they start
 514          *
 515          * @param string $name Callback name
 516          * @param callable|null $callback Use null to unset a callback
 517          * @since 1.28
 518          */
 519         public function setWaitForReplicationListener( $name, callable $callback = null ) {
 520                 if ( $callback ) {
 521                         $this->replicationWaitCallbacks[$name] = $callback;
 522                 } else {
 523                         unset( $this->replicationWaitCallbacks[$name] );
 524                 }
 525         }
 526
 527         /**
 528          * Get a token asserting that no transaction writes are active
 529          *
 530          * @param string $fname Caller name (e.g. __METHOD__)
 531          * @return mixed A value to pass to commitAndWaitForReplication()
 532          * @since 1.28
 533          */
 534         public function getEmptyTransactionTicket( $fname ) {
 535                 if ( $this->hasMasterChanges() ) {
 536                         $this->trxLogger->error( __METHOD__ . ": $fname does not have outer scope." );
 537                         return null;
 538                 }
 539
 540                 return $this->ticket;
 541         }
 542
 543         /**
 544          * Convenience method for safely running commitMasterChanges()/waitForReplication()
 545          *
 546          * This will commit and wait unless $ticket indicates it is unsafe to do so
 547          *
 548          * @param string $fname Caller name (e.g. __METHOD__)
 549          * @param mixed $ticket Result of getEmptyTransactionTicket()
 550          * @param array $opts Options to waitForReplication()
 551          * @throws DBReplicationWaitError
 552          * @since 1.28
 553          */
 554         public function commitAndWaitForReplication( $fname, $ticket, array $opts = [] ) {
 555                 if ( $ticket !== $this->ticket ) {
 556                         $logger = LoggerFactory::getInstance( 'DBPerformance' );
 557                         $logger->error( __METHOD__ . ": cannot commit; $fname does not have outer scope." );
 558                         return;
 559                 }
 560
 561                 // The transaction owner and any caller with the empty transaction ticket can commit
 562                 // so that getEmptyTransactionTicket() callers don't risk seeing DBTransactionError.
 563                 if ( $this->trxRoundId !== false && $fname !== $this->trxRoundId ) {
 564                         $this->trxLogger->info( "$fname: committing on behalf of {$this->trxRoundId}." );
 565                         $fnameEffective = $this->trxRoundId;
 566                 } else {
 567                         $fnameEffective = $fname;
 568                 }
 569
 570                 $this->commitMasterChanges( $fnameEffective );
 571                 $this->waitForReplication( $opts );
 572                 // If a nested caller committed on behalf of $fname, start another empty $fname
 573                 // transaction, leaving the caller with the same empty transaction state as before.
 574                 if ( $fnameEffective !== $fname ) {
 575                         $this->beginMasterChanges( $fnameEffective );
 576                 }
 577         }
 578
 579         /**
 580          * @param string $dbName DB master name (e.g. "db1052")
 581          * @return float|bool UNIX timestamp when client last touched the DB or false if not recent
 582          * @since 1.28
 583          */
 584         public function getChronologyProtectorTouched( $dbName ) {
 585                 return $this->chronProt->getTouched( $dbName );
 586         }
 587
 588         /**
 589          * Disable the ChronologyProtector for all load balancers
 590          *
 591          * This can be called at the start of special API entry points
 592          *
 593          * @since 1.27
 594          */
 595         public function disableChronologyProtection() {
 596                 $this->chronProt->setEnabled( false );
 597         }
 598
 599         /**
 600          * @return ChronologyProtector
 601          */
 602         protected function newChronologyProtector() {
 603                 $request = RequestContext::getMain()->getRequest();
 604                 $chronProt = new ChronologyProtector(
 605                         ObjectCache::getMainStashInstance(),
 606                         [
 607                                 'ip' => $request->getIP(),
 608                                 'agent' => $request->getHeader( 'User-Agent' ),
 609                         ],
 610                         $request->getFloat( 'cpPosTime', $request->getCookie( 'cpPosTime', '' ) )
 611                 );
 612                 $chronProt->setLogger( $this->replLogger );
 613                 if ( PHP_SAPI === 'cli' ) {
 614                         $chronProt->setEnabled( false );
 615                 } elseif ( $request->getHeader( 'ChronologyProtection' ) === 'false' ) {
 616                         // Request opted out of using position wait logic. This is useful for requests
 617                         // done by the job queue or background ETL that do not have a meaningful session.
 618                         $chronProt->setWaitEnabled( false );
 619                 }
 620
 621                 return $chronProt;
 622         }
 623
 624         /**
 625          * Get and record all of the staged DB positions into persistent memory storage
 626          *
 627          * @param ChronologyProtector $cp
 628          * @param callable|null $workCallback Work to do instead of waiting on syncing positions
 629          * @param string $mode One of (sync, async); whether to wait on remote datacenters
 630          */
 631         protected function shutdownChronologyProtector(
 632                 ChronologyProtector $cp, $workCallback, $mode
 633         ) {
 634                 // Record all the master positions needed
 635                 $this->forEachLB( function ( LoadBalancer $lb ) use ( $cp ) {
 636                         $cp->shutdownLB( $lb );
 637                 } );
 638                 // Write them to the persistent stash. Try to do something useful by running $work
 639                 // while ChronologyProtector waits for the stash write to replicate to all DCs.
 640                 $unsavedPositions = $cp->shutdown( $workCallback, $mode );
 641                 if ( $unsavedPositions && $workCallback ) {
 642                         // Invoke callback in case it did not cache the result yet
 643                         $workCallback(); // work now to block for less time in waitForAll()
 644                 }
 645                 // If the positions failed to write to the stash, at least wait on local datacenter
 646                 // replica DBs to catch up before responding. Even if there are several DCs, this increases
 647                 // the chance that the user will see their own changes immediately afterwards. As long
 648                 // as the sticky DC cookie applies (same domain), this is not even an issue.
 649                 $this->forEachLB( function ( LoadBalancer $lb ) use ( $unsavedPositions ) {
 650                         $masterName = $lb->getServerName( $lb->getWriterIndex() );
 651                         if ( isset( $unsavedPositions[$masterName] ) ) {
 652                                 $lb->waitForAll( $unsavedPositions[$masterName] );
 653                         }
 654                 } );
 655         }
 656
 657         /**
 658          * Base parameters to LoadBalancer::__construct()
 659          * @return array
 660          */
 661         final protected function baseLoadBalancerParams() {
 662                 return [
 663                         'localDomain' => wfWikiID(),
 664                         'readOnlyReason' => $this->readOnlyReason,
 665                         'srvCache' => $this->srvCache,
 666                         'memCache' => $this->memCache,
 667                         'wanCache' => $this->wanCache,
 668                         'trxProfiler' => $this->trxProfiler,
 669                         'queryLogger' => LoggerFactory::getInstance( 'DBQuery' ),
 670                         'connLogger' => LoggerFactory::getInstance( 'DBConnection' ),
 671                         'replLogger' => LoggerFactory::getInstance( 'DBReplication' ),
 672                         'errorLogger' => [ MWExceptionHandler::class, 'logException' ],
 673                         'hostname' => wfHostname()
 674                 ];
 675         }
 676
 677         /**
 678          * @param LoadBalancer $lb
 679          */
 680         protected function initLoadBalancer( LoadBalancer $lb ) {
 681                 if ( $this->trxRoundId !== false ) {
 682                         $lb->beginMasterChanges( $this->trxRoundId ); // set DBO_TRX
 683                 }
 684         }
 685
 686         /**
 687          * Append ?cpPosTime parameter to a URL for ChronologyProtector purposes if needed
 688          *
 689          * Note that unlike cookies, this works accross domains
 690          *
 691          * @param string $url
 692          * @param float $time UNIX timestamp just before shutdown() was called
 693          * @return string
 694          * @since 1.28
 695          */
 696         public function appendPreShutdownTimeAsQuery( $url, $time ) {
 697                 $usedCluster = 0;
 698                 $this->forEachLB( function ( LoadBalancer $lb ) use ( &$usedCluster ) {
 699                         $usedCluster |= ( $lb->getServerCount() > 1 );
 700                 } );
 701
 702                 if ( !$usedCluster ) {
 703                         return $url; // no master/replica clusters touched
 704                 }
 705
 706                 return wfAppendQuery( $url, [ 'cpPosTime' => $time ] );
 707         }
 708
 709         /**
 710          * Close all open database connections on all open load balancers.
 711          * @since 1.28
 712          */
 713         public function closeAll() {
 714                 $this->forEachLBCallMethod( 'closeAll', [] );
 715         }
 716 }