includes/db/loadbalancer/LBFactory.php

   1 <?php
   2 /**
   3  * Generator of database load balancing objects.
   4  *
   5  * This program is free software; you can redistribute it and/or modify
   6  * it under the terms of the GNU General Public License as published by
   7  * the Free Software Foundation; either version 2 of the License, or
   8  * (at your option) any later version.
   9  *
  10  * This program is distributed in the hope that it will be useful,
  11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  13  * GNU General Public License for more details.
  14  *
  15  * You should have received a copy of the GNU General Public License along
  16  * with this program; if not, write to the Free Software Foundation, Inc.,
  17  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
  18  * http://www.gnu.org/copyleft/gpl.html
  19  *
  20  * @file
  21  * @ingroup Database
  22  */
  23
  24 use MediaWiki\MediaWikiServices;
  25 use MediaWiki\Services\DestructibleService;
  26 use Psr\Log\LoggerInterface;
  27 use MediaWiki\Logger\LoggerFactory;
  28
  29 /**
  30  * An interface for generating database load balancers
  31  * @ingroup Database
  32  */
  33 abstract class LBFactory implements DestructibleService {
  34         /** @var ChronologyProtector */
  35         protected $chronProt;
  36         /** @var TransactionProfiler */
  37         protected $trxProfiler;
  38         /** @var LoggerInterface */
  39         protected $trxLogger;
  40         /** @var BagOStuff */
  41         protected $srvCache;
  42         /** @var WANObjectCache */
  43         protected $wanCache;
  44
  45         /** @var mixed */
  46         protected $ticket;
  47         /** @var string|bool String if a requested DBO_TRX transaction round is active */
  48         protected $trxRoundId = false;
  49         /** @var string|bool Reason all LBs are read-only or false if not */
  50         protected $readOnlyReason = false;
  51         /** @var callable[] */
  52         protected $replicationWaitCallbacks = [];
  53
  54         const SHUTDOWN_NO_CHRONPROT = 0; // don't save DB positions at all
  55         const SHUTDOWN_CHRONPROT_ASYNC = 1; // save DB positions, but don't wait on remote DCs
  56         const SHUTDOWN_CHRONPROT_SYNC = 2; // save DB positions, waiting on all DCs
  57
  58         /**
  59          * Construct a factory based on a configuration array (typically from $wgLBFactoryConf)
  60          * @param array $conf
  61          * @TODO: inject objects via dependency framework
  62          */
  63         public function __construct( array $conf ) {
  64                 if ( isset( $conf['readOnlyReason'] ) && is_string( $conf['readOnlyReason'] ) ) {
  65                         $this->readOnlyReason = $conf['readOnlyReason'];
  66                 }
  67                 $this->chronProt = $this->newChronologyProtector();
  68                 $this->trxProfiler = Profiler::instance()->getTransactionProfiler();
  69                 // Use APC/memcached style caching, but avoids loops with CACHE_DB (T141804)
  70                 $cache = ObjectCache::getLocalServerInstance();
  71                 if ( $cache->getQoS( $cache::ATTR_EMULATION ) > $cache::QOS_EMULATION_SQL ) {
  72                         $this->srvCache = $cache;
  73                 } else {
  74                         $this->srvCache = new EmptyBagOStuff();
  75                 }
  76                 $wCache = ObjectCache::getMainWANInstance();
  77                 if ( $wCache->getQoS( $wCache::ATTR_EMULATION ) > $wCache::QOS_EMULATION_SQL ) {
  78                         $this->wanCache = $wCache;
  79                 } else {
  80                         $this->wanCache = WANObjectCache::newEmpty();
  81                 }
  82                 $this->trxLogger = LoggerFactory::getInstance( 'DBTransaction' );
  83                 $this->ticket = mt_rand();
  84         }
  85
  86         /**
  87          * Disables all load balancers. All connections are closed, and any attempt to
  88          * open a new connection will result in a DBAccessError.
  89          * @see LoadBalancer::disable()
  90          */
  91         public function destroy() {
  92                 $this->shutdown( self::SHUTDOWN_NO_CHRONPROT );
  93                 $this->forEachLBCallMethod( 'disable' );
  94         }
  95
  96         /**
  97          * Disables all access to the load balancer, will cause all database access
  98          * to throw a DBAccessError
  99          */
 100         public static function disableBackend() {
 101                 MediaWikiServices::disableStorageBackend();
 102         }
 103
 104         /**
 105          * Get an LBFactory instance
 106          *
 107          * @deprecated since 1.27, use MediaWikiServices::getDBLoadBalancerFactory() instead.
 108          *
 109          * @return LBFactory
 110          */
 111         public static function singleton() {
 112                 return MediaWikiServices::getInstance()->getDBLoadBalancerFactory();
 113         }
 114
 115         /**
 116          * Returns the LBFactory class to use and the load balancer configuration.
 117          *
 118          * @todo instead of this, use a ServiceContainer for managing the different implementations.
 119          *
 120          * @param array $config (e.g. $wgLBFactoryConf)
 121          * @return string Class name
 122          */
 123         public static function getLBFactoryClass( array $config ) {
 124                 // For configuration backward compatibility after removing
 125                 // underscores from class names in MediaWiki 1.23.
 126                 $bcClasses = [
 127                         'LBFactory_Simple' => 'LBFactorySimple',
 128                         'LBFactory_Single' => 'LBFactorySingle',
 129                         'LBFactory_Multi' => 'LBFactoryMulti',
 130                         'LBFactory_Fake' => 'LBFactoryFake',
 131                 ];
 132
 133                 $class = $config['class'];
 134
 135                 if ( isset( $bcClasses[$class] ) ) {
 136                         $class = $bcClasses[$class];
 137                         wfDeprecated(
 138                                 '$wgLBFactoryConf must be updated. See RELEASE-NOTES for details',
 139                                 '1.23'
 140                         );
 141                 }
 142
 143                 return $class;
 144         }
 145
 146         /**
 147          * Shut down, close connections and destroy the cached instance.
 148          *
 149          * @deprecated since 1.27, use LBFactory::destroy()
 150          */
 151         public static function destroyInstance() {
 152                 self::singleton()->destroy();
 153         }
 154
 155         /**
 156          * Create a new load balancer object. The resulting object will be untracked,
 157          * not chronology-protected, and the caller is responsible for cleaning it up.
 158          *
 159          * @param bool|string $wiki Wiki ID, or false for the current wiki
 160          * @return LoadBalancer
 161          */
 162         abstract public function newMainLB( $wiki = false );
 163
 164         /**
 165          * Get a cached (tracked) load balancer object.
 166          *
 167          * @param bool|string $wiki Wiki ID, or false for the current wiki
 168          * @return LoadBalancer
 169          */
 170         abstract public function getMainLB( $wiki = false );
 171
 172         /**
 173          * Create a new load balancer for external storage. The resulting object will be
 174          * untracked, not chronology-protected, and the caller is responsible for
 175          * cleaning it up.
 176          *
 177          * @param string $cluster External storage cluster, or false for core
 178          * @param bool|string $wiki Wiki ID, or false for the current wiki
 179          * @return LoadBalancer
 180          */
 181         abstract protected function newExternalLB( $cluster, $wiki = false );
 182
 183         /**
 184          * Get a cached (tracked) load balancer for external storage
 185          *
 186          * @param string $cluster External storage cluster, or false for core
 187          * @param bool|string $wiki Wiki ID, or false for the current wiki
 188          * @return LoadBalancer
 189          */
 190         abstract public function getExternalLB( $cluster, $wiki = false );
 191
 192         /**
 193          * Execute a function for each tracked load balancer
 194          * The callback is called with the load balancer as the first parameter,
 195          * and $params passed as the subsequent parameters.
 196          *
 197          * @param callable $callback
 198          * @param array $params
 199          */
 200         abstract public function forEachLB( $callback, array $params = [] );
 201
 202         /**
 203          * Prepare all tracked load balancers for shutdown
 204          * @param integer $mode One of the class SHUTDOWN_* constants
 205          * @param callable|null $workCallback Work to mask ChronologyProtector writes
 206          */
 207         public function shutdown(
 208                 $mode = self::SHUTDOWN_CHRONPROT_SYNC, callable $workCallback = null
 209         ) {
 210                 if ( $mode === self::SHUTDOWN_CHRONPROT_SYNC ) {
 211                         $this->shutdownChronologyProtector( $this->chronProt, $workCallback, 'sync' );
 212                 } elseif ( $mode === self::SHUTDOWN_CHRONPROT_ASYNC ) {
 213                         $this->shutdownChronologyProtector( $this->chronProt, null, 'async' );
 214                 }
 215
 216                 $this->commitMasterChanges( __METHOD__ ); // sanity
 217         }
 218
 219         /**
 220          * Call a method of each tracked load balancer
 221          *
 222          * @param string $methodName
 223          * @param array $args
 224          */
 225         private function forEachLBCallMethod( $methodName, array $args = [] ) {
 226                 $this->forEachLB(
 227                         function ( LoadBalancer $loadBalancer, $methodName, array $args ) {
 228                                 call_user_func_array( [ $loadBalancer, $methodName ], $args );
 229                         },
 230                         [ $methodName, $args ]
 231                 );
 232         }
 233
 234         /**
 235          * Commit all replica DB transactions so as to flush any REPEATABLE-READ or SSI snapshot
 236          *
 237          * @param string $fname Caller name
 238          * @since 1.28
 239          */
 240         public function flushReplicaSnapshots( $fname = __METHOD__ ) {
 241                 $this->forEachLBCallMethod( 'flushReplicaSnapshots', [ $fname ] );
 242         }
 243
 244         /**
 245          * Commit on all connections. Done for two reasons:
 246          * 1. To commit changes to the masters.
 247          * 2. To release the snapshot on all connections, master and replica DB.
 248          * @param string $fname Caller name
 249          * @param array $options Options map:
 250          *   - maxWriteDuration: abort if more than this much time was spent in write queries
 251          */
 252         public function commitAll( $fname = __METHOD__, array $options = [] ) {
 253                 $this->commitMasterChanges( $fname, $options );
 254                 $this->forEachLBCallMethod( 'commitAll', [ $fname ] );
 255         }
 256
 257         /**
 258          * Flush any master transaction snapshots and set DBO_TRX (if DBO_DEFAULT is set)
 259          *
 260          * The DBO_TRX setting will be reverted to the default in each of these methods:
 261          *   - commitMasterChanges()
 262          *   - rollbackMasterChanges()
 263          *   - commitAll()
 264          *
 265          * This allows for custom transaction rounds from any outer transaction scope.
 266          *
 267          * @param string $fname
 268          * @throws DBTransactionError
 269          * @since 1.28
 270          */
 271         public function beginMasterChanges( $fname = __METHOD__ ) {
 272                 if ( $this->trxRoundId !== false ) {
 273                         throw new DBTransactionError(
 274                                 null,
 275                                 "$fname: transaction round '{$this->trxRoundId}' already started."
 276                         );
 277                 }
 278                 $this->trxRoundId = $fname;
 279                 // Set DBO_TRX flags on all appropriate DBs
 280                 $this->forEachLBCallMethod( 'beginMasterChanges', [ $fname ] );
 281         }
 282
 283         /**
 284          * Commit changes on all master connections
 285          * @param string $fname Caller name
 286          * @param array $options Options map:
 287          *   - maxWriteDuration: abort if more than this much time was spent in write queries
 288          * @throws Exception
 289          */
 290         public function commitMasterChanges( $fname = __METHOD__, array $options = [] ) {
 291                 if ( $this->trxRoundId !== false && $this->trxRoundId !== $fname ) {
 292                         throw new DBTransactionError(
 293                                 null,
 294                                 "$fname: transaction round '{$this->trxRoundId}' still running."
 295                         );
 296                 }
 297                 // Run pre-commit callbacks and suppress post-commit callbacks, aborting on failure
 298                 $this->forEachLBCallMethod( 'finalizeMasterChanges' );
 299                 $this->trxRoundId = false;
 300                 // Perform pre-commit checks, aborting on failure
 301                 $this->forEachLBCallMethod( 'approveMasterChanges', [ $options ] );
 302                 // Log the DBs and methods involved in multi-DB transactions
 303                 $this->logIfMultiDbTransaction();
 304                 // Actually perform the commit on all master DB connections and revert DBO_TRX
 305                 $this->forEachLBCallMethod( 'commitMasterChanges', [ $fname ] );
 306                 // Run all post-commit callbacks
 307                 /** @var Exception $e */
 308                 $e = null; // first callback exception
 309                 $this->forEachLB( function ( LoadBalancer $lb ) use ( &$e ) {
 310                         $ex = $lb->runMasterPostTrxCallbacks( IDatabase::TRIGGER_COMMIT );
 311                         $e = $e ?: $ex;
 312                 } );
 313                 // Commit any dangling DBO_TRX transactions from callbacks on one DB to another DB
 314                 $this->forEachLBCallMethod( 'commitMasterChanges', [ $fname ] );
 315                 // Throw any last post-commit callback error
 316                 if ( $e instanceof Exception ) {
 317                         throw $e;
 318                 }
 319         }
 320
 321         /**
 322          * Rollback changes on all master connections
 323          * @param string $fname Caller name
 324          * @since 1.23
 325          */
 326         public function rollbackMasterChanges( $fname = __METHOD__ ) {
 327                 $this->trxRoundId = false;
 328                 $this->forEachLBCallMethod( 'suppressTransactionEndCallbacks' );
 329                 $this->forEachLBCallMethod( 'rollbackMasterChanges', [ $fname ] );
 330                 // Run all post-rollback callbacks
 331                 $this->forEachLB( function ( LoadBalancer $lb ) {
 332                         $lb->runMasterPostTrxCallbacks( IDatabase::TRIGGER_ROLLBACK );
 333                 } );
 334         }
 335
 336         /**
 337          * Log query info if multi DB transactions are going to be committed now
 338          */
 339         private function logIfMultiDbTransaction() {
 340                 $callersByDB = [];
 341                 $this->forEachLB( function ( LoadBalancer $lb ) use ( &$callersByDB ) {
 342                         $masterName = $lb->getServerName( $lb->getWriterIndex() );
 343                         $callers = $lb->pendingMasterChangeCallers();
 344                         if ( $callers ) {
 345                                 $callersByDB[$masterName] = $callers;
 346                         }
 347                 } );
 348
 349                 if ( count( $callersByDB ) >= 2 ) {
 350                         $dbs = implode( ', ', array_keys( $callersByDB ) );
 351                         $msg = "Multi-DB transaction [{$dbs}]:\n";
 352                         foreach ( $callersByDB as $db => $callers ) {
 353                                 $msg .= "$db: " . implode( '; ', $callers ) . "\n";
 354                         }
 355                         $this->trxLogger->info( $msg );
 356                 }
 357         }
 358
 359         /**
 360          * Determine if any master connection has pending changes
 361          * @return bool
 362          * @since 1.23
 363          */
 364         public function hasMasterChanges() {
 365                 $ret = false;
 366                 $this->forEachLB( function ( LoadBalancer $lb ) use ( &$ret ) {
 367                         $ret = $ret || $lb->hasMasterChanges();
 368                 } );
 369
 370                 return $ret;
 371         }
 372
 373         /**
 374          * Detemine if any lagged replica DB connection was used
 375          * @return bool
 376          * @since 1.28
 377          */
 378         public function laggedReplicaUsed() {
 379                 $ret = false;
 380                 $this->forEachLB( function ( LoadBalancer $lb ) use ( &$ret ) {
 381                         $ret = $ret || $lb->laggedReplicaUsed();
 382                 } );
 383
 384                 return $ret;
 385         }
 386
 387         /**
 388          * @return bool
 389          * @since 1.27
 390          * @deprecated Since 1.28; use laggedReplicaUsed()
 391          */
 392         public function laggedSlaveUsed() {
 393                 return $this->laggedReplicaUsed();
 394         }
 395
 396         /**
 397          * Determine if any master connection has pending/written changes from this request
 398          * @param float $age How many seconds ago is "recent" [defaults to LB lag wait timeout]
 399          * @return bool
 400          * @since 1.27
 401          */
 402         public function hasOrMadeRecentMasterChanges( $age = null ) {
 403                 $ret = false;
 404                 $this->forEachLB( function ( LoadBalancer $lb ) use ( $age, &$ret ) {
 405                         $ret = $ret || $lb->hasOrMadeRecentMasterChanges( $age );
 406                 } );
 407                 return $ret;
 408         }
 409
 410         /**
 411          * Waits for the replica DBs to catch up to the current master position
 412          *
 413          * Use this when updating very large numbers of rows, as in maintenance scripts,
 414          * to avoid causing too much lag. Of course, this is a no-op if there are no replica DBs.
 415          *
 416          * By default this waits on all DB clusters actually used in this request.
 417          * This makes sense when lag being waiting on is caused by the code that does this check.
 418          * In that case, setting "ifWritesSince" can avoid the overhead of waiting for clusters
 419          * that were not changed since the last wait check. To forcefully wait on a specific cluster
 420          * for a given wiki, use the 'wiki' parameter. To forcefully wait on an "external" cluster,
 421          * use the "cluster" parameter.
 422          *
 423          * Never call this function after a large DB write that is *still* in a transaction.
 424          * It only makes sense to call this after the possible lag inducing changes were committed.
 425          *
 426          * @param array $opts Optional fields that include:
 427          *   - wiki : wait on the load balancer DBs that handles the given wiki
 428          *   - cluster : wait on the given external load balancer DBs
 429          *   - timeout : Max wait time. Default: ~60 seconds
 430          *   - ifWritesSince: Only wait if writes were done since this UNIX timestamp
 431          * @throws DBReplicationWaitError If a timeout or error occured waiting on a DB cluster
 432          * @since 1.27
 433          */
 434         public function waitForReplication( array $opts = [] ) {
 435                 $opts += [
 436                         'wiki' => false,
 437                         'cluster' => false,
 438                         'timeout' => 60,
 439                         'ifWritesSince' => null
 440                 ];
 441
 442                 foreach ( $this->replicationWaitCallbacks as $callback ) {
 443                         $callback();
 444                 }
 445
 446                 // Figure out which clusters need to be checked
 447                 /** @var LoadBalancer[] $lbs */
 448                 $lbs = [];
 449                 if ( $opts['cluster'] !== false ) {
 450                         $lbs[] = $this->getExternalLB( $opts['cluster'] );
 451                 } elseif ( $opts['wiki'] !== false ) {
 452                         $lbs[] = $this->getMainLB( $opts['wiki'] );
 453                 } else {
 454                         $this->forEachLB( function ( LoadBalancer $lb ) use ( &$lbs ) {
 455                                 $lbs[] = $lb;
 456                         } );
 457                         if ( !$lbs ) {
 458                                 return; // nothing actually used
 459                         }
 460                 }
 461
 462                 // Get all the master positions of applicable DBs right now.
 463                 // This can be faster since waiting on one cluster reduces the
 464                 // time needed to wait on the next clusters.
 465                 $masterPositions = array_fill( 0, count( $lbs ), false );
 466                 foreach ( $lbs as $i => $lb ) {
 467                         if ( $lb->getServerCount() <= 1 ) {
 468                                 // Bug 27975 - Don't try to wait for replica DBs if there are none
 469                                 // Prevents permission error when getting master position
 470                                 continue;
 471                         } elseif ( $opts['ifWritesSince']
 472                                 && $lb->lastMasterChangeTimestamp() < $opts['ifWritesSince']
 473                         ) {
 474                                 continue; // no writes since the last wait
 475                         }
 476                         $masterPositions[$i] = $lb->getMasterPos();
 477                 }
 478
 479                 $failed = [];
 480                 foreach ( $lbs as $i => $lb ) {
 481                         if ( $masterPositions[$i] ) {
 482                                 // The DBMS may not support getMasterPos() or the whole
 483                                 // load balancer might be fake (e.g. $wgAllDBsAreLocalhost).
 484                                 if ( !$lb->waitForAll( $masterPositions[$i], $opts['timeout'] ) ) {
 485                                         $failed[] = $lb->getServerName( $lb->getWriterIndex() );
 486                                 }
 487                         }
 488                 }
 489
 490                 if ( $failed ) {
 491                         throw new DBReplicationWaitError(
 492                                 "Could not wait for replica DBs to catch up to " .
 493                                 implode( ', ', $failed )
 494                         );
 495                 }
 496         }
 497
 498         /**
 499          * Add a callback to be run in every call to waitForReplication() before waiting
 500          *
 501          * Callbacks must clear any transactions that they start
 502          *
 503          * @param string $name Callback name
 504          * @param callable|null $callback Use null to unset a callback
 505          * @since 1.28
 506          */
 507         public function setWaitForReplicationListener( $name, callable $callback = null ) {
 508                 if ( $callback ) {
 509                         $this->replicationWaitCallbacks[$name] = $callback;
 510                 } else {
 511                         unset( $this->replicationWaitCallbacks[$name] );
 512                 }
 513         }
 514
 515         /**
 516          * Get a token asserting that no transaction writes are active
 517          *
 518          * @param string $fname Caller name (e.g. __METHOD__)
 519          * @return mixed A value to pass to commitAndWaitForReplication()
 520          * @since 1.28
 521          */
 522         public function getEmptyTransactionTicket( $fname ) {
 523                 if ( $this->hasMasterChanges() ) {
 524                         $this->trxLogger->error( __METHOD__ . ": $fname does not have outer scope." );
 525                         return null;
 526                 }
 527
 528                 return $this->ticket;
 529         }
 530
 531         /**
 532          * Convenience method for safely running commitMasterChanges()/waitForReplication()
 533          *
 534          * This will commit and wait unless $ticket indicates it is unsafe to do so
 535          *
 536          * @param string $fname Caller name (e.g. __METHOD__)
 537          * @param mixed $ticket Result of getEmptyTransactionTicket()
 538          * @param array $opts Options to waitForReplication()
 539          * @throws DBReplicationWaitError
 540          * @since 1.28
 541          */
 542         public function commitAndWaitForReplication( $fname, $ticket, array $opts = [] ) {
 543                 if ( $ticket !== $this->ticket ) {
 544                         $logger = LoggerFactory::getInstance( 'DBPerformance' );
 545                         $logger->error( __METHOD__ . ": cannot commit; $fname does not have outer scope." );
 546                         return;
 547                 }
 548
 549                 // The transaction owner and any caller with the empty transaction ticket can commit
 550                 // so that getEmptyTransactionTicket() callers don't risk seeing DBTransactionError.
 551                 if ( $this->trxRoundId !== false && $fname !== $this->trxRoundId ) {
 552                         $this->trxLogger->info( "$fname: committing on behalf of {$this->trxRoundId}." );
 553                         $fnameEffective = $this->trxRoundId;
 554                 } else {
 555                         $fnameEffective = $fname;
 556                 }
 557
 558                 $this->commitMasterChanges( $fnameEffective );
 559                 $this->waitForReplication( $opts );
 560                 // If a nested caller committed on behalf of $fname, start another empty $fname
 561                 // transaction, leaving the caller with the same empty transaction state as before.
 562                 if ( $fnameEffective !== $fname ) {
 563                         $this->beginMasterChanges( $fnameEffective );
 564                 }
 565         }
 566
 567         /**
 568          * @param string $dbName DB master name (e.g. "db1052")
 569          * @return float|bool UNIX timestamp when client last touched the DB or false if not recent
 570          * @since 1.28
 571          */
 572         public function getChronologyProtectorTouched( $dbName ) {
 573                 return $this->chronProt->getTouched( $dbName );
 574         }
 575
 576         /**
 577          * Disable the ChronologyProtector for all load balancers
 578          *
 579          * This can be called at the start of special API entry points
 580          *
 581          * @since 1.27
 582          */
 583         public function disableChronologyProtection() {
 584                 $this->chronProt->setEnabled( false );
 585         }
 586
 587         /**
 588          * @return ChronologyProtector
 589          */
 590         protected function newChronologyProtector() {
 591                 $request = RequestContext::getMain()->getRequest();
 592                 $chronProt = new ChronologyProtector(
 593                         ObjectCache::getMainStashInstance(),
 594                         [
 595                                 'ip' => $request->getIP(),
 596                                 'agent' => $request->getHeader( 'User-Agent' ),
 597                         ],
 598                         $request->getFloat( 'cpPosTime', null )
 599                 );
 600                 if ( PHP_SAPI === 'cli' ) {
 601                         $chronProt->setEnabled( false );
 602                 } elseif ( $request->getHeader( 'ChronologyProtection' ) === 'false' ) {
 603                         // Request opted out of using position wait logic. This is useful for requests
 604                         // done by the job queue or background ETL that do not have a meaningful session.
 605                         $chronProt->setWaitEnabled( false );
 606                 }
 607
 608                 return $chronProt;
 609         }
 610
 611         /**
 612          * Get and record all of the staged DB positions into persistent memory storage
 613          *
 614          * @param ChronologyProtector $cp
 615          * @param callable|null $workCallback Work to do instead of waiting on syncing positions
 616          * @param string $mode One of (sync, async); whether to wait on remote datacenters
 617          */
 618         protected function shutdownChronologyProtector(
 619                 ChronologyProtector $cp, $workCallback, $mode
 620         ) {
 621                 // Record all the master positions needed
 622                 $this->forEachLB( function ( LoadBalancer $lb ) use ( $cp ) {
 623                         $cp->shutdownLB( $lb );
 624                 } );
 625                 // Write them to the persistent stash. Try to do something useful by running $work
 626                 // while ChronologyProtector waits for the stash write to replicate to all DCs.
 627                 $unsavedPositions = $cp->shutdown( $workCallback, $mode );
 628                 if ( $unsavedPositions && $workCallback ) {
 629                         // Invoke callback in case it did not cache the result yet
 630                         $workCallback(); // work now to block for less time in waitForAll()
 631                 }
 632                 // If the positions failed to write to the stash, at least wait on local datacenter
 633                 // replica DBs to catch up before responding. Even if there are several DCs, this increases
 634                 // the chance that the user will see their own changes immediately afterwards. As long
 635                 // as the sticky DC cookie applies (same domain), this is not even an issue.
 636                 $this->forEachLB( function ( LoadBalancer $lb ) use ( $unsavedPositions ) {
 637                         $masterName = $lb->getServerName( $lb->getWriterIndex() );
 638                         if ( isset( $unsavedPositions[$masterName] ) ) {
 639                                 $lb->waitForAll( $unsavedPositions[$masterName] );
 640                         }
 641                 } );
 642         }
 643
 644         /**
 645          * @param LoadBalancer $lb
 646          */
 647         protected function initLoadBalancer( LoadBalancer $lb ) {
 648                 if ( $this->trxRoundId !== false ) {
 649                         $lb->beginMasterChanges( $this->trxRoundId ); // set DBO_TRX
 650                 }
 651         }
 652
 653         /**
 654          * Append ?cpPosTime parameter to a URL for ChronologyProtector purposes if needed
 655          *
 656          * Note that unlike cookies, this works accross domains
 657          *
 658          * @param string $url
 659          * @param float $time UNIX timestamp just before shutdown() was called
 660          * @return string
 661          * @since 1.28
 662          */
 663         public function appendPreShutdownTimeAsQuery( $url, $time ) {
 664                 $usedCluster = 0;
 665                 $this->forEachLB( function ( LoadBalancer $lb ) use ( &$usedCluster ) {
 666                         $usedCluster |= ( $lb->getServerCount() > 1 );
 667                 } );
 668
 669                 if ( !$usedCluster ) {
 670                         return $url; // no master/replica clusters touched
 671                 }
 672
 673                 return wfAppendQuery( $url, [ 'cpPosTime' => $time ] );
 674         }
 675
 676         /**
 677          * Close all open database connections on all open load balancers.
 678          * @since 1.28
 679          */
 680         public function closeAll() {
 681                 $this->forEachLBCallMethod( 'closeAll', [] );
 682         }
 683 }