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                 $this->chronProt = $this->newChronologyProtector();
  72                 $this->trxProfiler = Profiler::instance()->getTransactionProfiler();
  73                 // Use APC/memcached style caching, but avoids loops with CACHE_DB (T141804)
  74                 $sCache = ObjectCache::getLocalServerInstance();
  75                 if ( $sCache->getQoS( $sCache::ATTR_EMULATION ) > $sCache::QOS_EMULATION_SQL ) {
  76                         $this->srvCache = $sCache;
  77                 } else {
  78                         $this->srvCache = new EmptyBagOStuff();
  79                 }
  80                 $cCache = ObjectCache::getLocalClusterInstance();
  81                 if ( $cCache->getQoS( $cCache::ATTR_EMULATION ) > $cCache::QOS_EMULATION_SQL ) {
  82                         $this->memCache = $cCache;
  83                 } else {
  84                         $this->memCache = new EmptyBagOStuff();
  85                 }
  86                 $wCache = ObjectCache::getMainWANInstance();
  87                 if ( $wCache->getQoS( $wCache::ATTR_EMULATION ) > $wCache::QOS_EMULATION_SQL ) {
  88                         $this->wanCache = $wCache;
  89                 } else {
  90                         $this->wanCache = WANObjectCache::newEmpty();
  91                 }
  92                 $this->trxLogger = LoggerFactory::getInstance( 'DBTransaction' );
  93                 $this->replLogger = LoggerFactory::getInstance( 'DBReplication' );
  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                         'LBFactory_Fake' => 'LBFactoryFake',
 142                 ];
 143
 144                 $class = $config['class'];
 145
 146                 if ( isset( $bcClasses[$class] ) ) {
 147                         $class = $bcClasses[$class];
 148                         wfDeprecated(
 149                                 '$wgLBFactoryConf must be updated. See RELEASE-NOTES for details',
 150                                 '1.23'
 151                         );
 152                 }
 153
 154                 return $class;
 155         }
 156
 157         /**
 158          * Shut down, close connections and destroy the cached instance.
 159          *
 160          * @deprecated since 1.27, use LBFactory::destroy()
 161          */
 162         public static function destroyInstance() {
 163                 MediaWikiServices::getInstance()->getDBLoadBalancerFactory()->destroy();
 164         }
 165
 166         /**
 167          * Create a new load balancer object. The resulting object will be untracked,
 168          * not chronology-protected, and the caller is responsible for cleaning it up.
 169          *
 170          * @param bool|string $wiki Wiki ID, or false for the current wiki
 171          * @return LoadBalancer
 172          */
 173         abstract public function newMainLB( $wiki = false );
 174
 175         /**
 176          * Get a cached (tracked) load balancer object.
 177          *
 178          * @param bool|string $wiki Wiki ID, or false for the current wiki
 179          * @return LoadBalancer
 180          */
 181         abstract public function getMainLB( $wiki = false );
 182
 183         /**
 184          * Create a new load balancer for external storage. The resulting object will be
 185          * untracked, not chronology-protected, and the caller is responsible for
 186          * cleaning it up.
 187          *
 188          * @param string $cluster External storage cluster, or false for core
 189          * @param bool|string $wiki Wiki ID, or false for the current wiki
 190          * @return LoadBalancer
 191          */
 192         abstract protected function newExternalLB( $cluster, $wiki = false );
 193
 194         /**
 195          * Get a cached (tracked) load balancer for external storage
 196          *
 197          * @param string $cluster External storage cluster, or false for core
 198          * @param bool|string $wiki Wiki ID, or false for the current wiki
 199          * @return LoadBalancer
 200          */
 201         abstract public function getExternalLB( $cluster, $wiki = false );
 202
 203         /**
 204          * Execute a function for each tracked load balancer
 205          * The callback is called with the load balancer as the first parameter,
 206          * and $params passed as the subsequent parameters.
 207          *
 208          * @param callable $callback
 209          * @param array $params
 210          */
 211         abstract public function forEachLB( $callback, array $params = [] );
 212
 213         /**
 214          * Prepare all tracked load balancers for shutdown
 215          * @param integer $mode One of the class SHUTDOWN_* constants
 216          * @param callable|null $workCallback Work to mask ChronologyProtector writes
 217          */
 218         public function shutdown(
 219                 $mode = self::SHUTDOWN_CHRONPROT_SYNC, callable $workCallback = null
 220         ) {
 221                 if ( $mode === self::SHUTDOWN_CHRONPROT_SYNC ) {
 222                         $this->shutdownChronologyProtector( $this->chronProt, $workCallback, 'sync' );
 223                 } elseif ( $mode === self::SHUTDOWN_CHRONPROT_ASYNC ) {
 224                         $this->shutdownChronologyProtector( $this->chronProt, null, 'async' );
 225                 }
 226
 227                 $this->commitMasterChanges( __METHOD__ ); // sanity
 228         }
 229
 230         /**
 231          * Call a method of each tracked load balancer
 232          *
 233          * @param string $methodName
 234          * @param array $args
 235          */
 236         private function forEachLBCallMethod( $methodName, array $args = [] ) {
 237                 $this->forEachLB(
 238                         function ( LoadBalancer $loadBalancer, $methodName, array $args ) {
 239                                 call_user_func_array( [ $loadBalancer, $methodName ], $args );
 240                         },
 241                         [ $methodName, $args ]
 242                 );
 243         }
 244
 245         /**
 246          * Commit all replica DB transactions so as to flush any REPEATABLE-READ or SSI snapshot
 247          *
 248          * @param string $fname Caller name
 249          * @since 1.28
 250          */
 251         public function flushReplicaSnapshots( $fname = __METHOD__ ) {
 252                 $this->forEachLBCallMethod( 'flushReplicaSnapshots', [ $fname ] );
 253         }
 254
 255         /**
 256          * Commit on all connections. Done for two reasons:
 257          * 1. To commit changes to the masters.
 258          * 2. To release the snapshot on all connections, master and replica DB.
 259          * @param string $fname Caller name
 260          * @param array $options Options map:
 261          *   - maxWriteDuration: abort if more than this much time was spent in write queries
 262          */
 263         public function commitAll( $fname = __METHOD__, array $options = [] ) {
 264                 $this->commitMasterChanges( $fname, $options );
 265                 $this->forEachLBCallMethod( 'commitAll', [ $fname ] );
 266         }
 267
 268         /**
 269          * Flush any master transaction snapshots and set DBO_TRX (if DBO_DEFAULT is set)
 270          *
 271          * The DBO_TRX setting will be reverted to the default in each of these methods:
 272          *   - commitMasterChanges()
 273          *   - rollbackMasterChanges()
 274          *   - commitAll()
 275          *
 276          * This allows for custom transaction rounds from any outer transaction scope.
 277          *
 278          * @param string $fname
 279          * @throws DBTransactionError
 280          * @since 1.28
 281          */
 282         public function beginMasterChanges( $fname = __METHOD__ ) {
 283                 if ( $this->trxRoundId !== false ) {
 284                         throw new DBTransactionError(
 285                                 null,
 286                                 "$fname: transaction round '{$this->trxRoundId}' already started."
 287                         );
 288                 }
 289                 $this->trxRoundId = $fname;
 290                 // Set DBO_TRX flags on all appropriate DBs
 291                 $this->forEachLBCallMethod( 'beginMasterChanges', [ $fname ] );
 292         }
 293
 294         /**
 295          * Commit changes on all master connections
 296          * @param string $fname Caller name
 297          * @param array $options Options map:
 298          *   - maxWriteDuration: abort if more than this much time was spent in write queries
 299          * @throws Exception
 300          */
 301         public function commitMasterChanges( $fname = __METHOD__, array $options = [] ) {
 302                 if ( $this->trxRoundId !== false && $this->trxRoundId !== $fname ) {
 303                         throw new DBTransactionError(
 304                                 null,
 305                                 "$fname: transaction round '{$this->trxRoundId}' still running."
 306                         );
 307                 }
 308                 // Run pre-commit callbacks and suppress post-commit callbacks, aborting on failure
 309                 $this->forEachLBCallMethod( 'finalizeMasterChanges' );
 310                 $this->trxRoundId = false;
 311                 // Perform pre-commit checks, aborting on failure
 312                 $this->forEachLBCallMethod( 'approveMasterChanges', [ $options ] );
 313                 // Log the DBs and methods involved in multi-DB transactions
 314                 $this->logIfMultiDbTransaction();
 315                 // Actually perform the commit on all master DB connections and revert DBO_TRX
 316                 $this->forEachLBCallMethod( 'commitMasterChanges', [ $fname ] );
 317                 // Run all post-commit callbacks
 318                 /** @var Exception $e */
 319                 $e = null; // first callback exception
 320                 $this->forEachLB( function ( LoadBalancer $lb ) use ( &$e ) {
 321                         $ex = $lb->runMasterPostTrxCallbacks( IDatabase::TRIGGER_COMMIT );
 322                         $e = $e ?: $ex;
 323                 } );
 324                 // Commit any dangling DBO_TRX transactions from callbacks on one DB to another DB
 325                 $this->forEachLBCallMethod( 'commitMasterChanges', [ $fname ] );
 326                 // Throw any last post-commit callback error
 327                 if ( $e instanceof Exception ) {
 328                         throw $e;
 329                 }
 330         }
 331
 332         /**
 333          * Rollback changes on all master connections
 334          * @param string $fname Caller name
 335          * @since 1.23
 336          */
 337         public function rollbackMasterChanges( $fname = __METHOD__ ) {
 338                 $this->trxRoundId = false;
 339                 $this->forEachLBCallMethod( 'suppressTransactionEndCallbacks' );
 340                 $this->forEachLBCallMethod( 'rollbackMasterChanges', [ $fname ] );
 341                 // Run all post-rollback callbacks
 342                 $this->forEachLB( function ( LoadBalancer $lb ) {
 343                         $lb->runMasterPostTrxCallbacks( IDatabase::TRIGGER_ROLLBACK );
 344                 } );
 345         }
 346
 347         /**
 348          * Log query info if multi DB transactions are going to be committed now
 349          */
 350         private function logIfMultiDbTransaction() {
 351                 $callersByDB = [];
 352                 $this->forEachLB( function ( LoadBalancer $lb ) use ( &$callersByDB ) {
 353                         $masterName = $lb->getServerName( $lb->getWriterIndex() );
 354                         $callers = $lb->pendingMasterChangeCallers();
 355                         if ( $callers ) {
 356                                 $callersByDB[$masterName] = $callers;
 357                         }
 358                 } );
 359
 360                 if ( count( $callersByDB ) >= 2 ) {
 361                         $dbs = implode( ', ', array_keys( $callersByDB ) );
 362                         $msg = "Multi-DB transaction [{$dbs}]:\n";
 363                         foreach ( $callersByDB as $db => $callers ) {
 364                                 $msg .= "$db: " . implode( '; ', $callers ) . "\n";
 365                         }
 366                         $this->trxLogger->info( $msg );
 367                 }
 368         }
 369
 370         /**
 371          * Determine if any master connection has pending changes
 372          * @return bool
 373          * @since 1.23
 374          */
 375         public function hasMasterChanges() {
 376                 $ret = false;
 377                 $this->forEachLB( function ( LoadBalancer $lb ) use ( &$ret ) {
 378                         $ret = $ret || $lb->hasMasterChanges();
 379                 } );
 380
 381                 return $ret;
 382         }
 383
 384         /**
 385          * Detemine if any lagged replica DB connection was used
 386          * @return bool
 387          * @since 1.28
 388          */
 389         public function laggedReplicaUsed() {
 390                 $ret = false;
 391                 $this->forEachLB( function ( LoadBalancer $lb ) use ( &$ret ) {
 392                         $ret = $ret || $lb->laggedReplicaUsed();
 393                 } );
 394
 395                 return $ret;
 396         }
 397
 398         /**
 399          * @return bool
 400          * @since 1.27
 401          * @deprecated Since 1.28; use laggedReplicaUsed()
 402          */
 403         public function laggedSlaveUsed() {
 404                 return $this->laggedReplicaUsed();
 405         }
 406
 407         /**
 408          * Determine if any master connection has pending/written changes from this request
 409          * @param float $age How many seconds ago is "recent" [defaults to LB lag wait timeout]
 410          * @return bool
 411          * @since 1.27
 412          */
 413         public function hasOrMadeRecentMasterChanges( $age = null ) {
 414                 $ret = false;
 415                 $this->forEachLB( function ( LoadBalancer $lb ) use ( $age, &$ret ) {
 416                         $ret = $ret || $lb->hasOrMadeRecentMasterChanges( $age );
 417                 } );
 418                 return $ret;
 419         }
 420
 421         /**
 422          * Waits for the replica DBs to catch up to the current master position
 423          *
 424          * Use this when updating very large numbers of rows, as in maintenance scripts,
 425          * to avoid causing too much lag. Of course, this is a no-op if there are no replica DBs.
 426          *
 427          * By default this waits on all DB clusters actually used in this request.
 428          * This makes sense when lag being waiting on is caused by the code that does this check.
 429          * In that case, setting "ifWritesSince" can avoid the overhead of waiting for clusters
 430          * that were not changed since the last wait check. To forcefully wait on a specific cluster
 431          * for a given wiki, use the 'wiki' parameter. To forcefully wait on an "external" cluster,
 432          * use the "cluster" parameter.
 433          *
 434          * Never call this function after a large DB write that is *still* in a transaction.
 435          * It only makes sense to call this after the possible lag inducing changes were committed.
 436          *
 437          * @param array $opts Optional fields that include:
 438          *   - wiki : wait on the load balancer DBs that handles the given wiki
 439          *   - cluster : wait on the given external load balancer DBs
 440          *   - timeout : Max wait time. Default: ~60 seconds
 441          *   - ifWritesSince: Only wait if writes were done since this UNIX timestamp
 442          * @throws DBReplicationWaitError If a timeout or error occured waiting on a DB cluster
 443          * @since 1.27
 444          */
 445         public function waitForReplication( array $opts = [] ) {
 446                 $opts += [
 447                         'wiki' => false,
 448                         'cluster' => false,
 449                         'timeout' => 60,
 450                         'ifWritesSince' => null
 451                 ];
 452
 453                 // Figure out which clusters need to be checked
 454                 /** @var LoadBalancer[] $lbs */
 455                 $lbs = [];
 456                 if ( $opts['cluster'] !== false ) {
 457                         $lbs[] = $this->getExternalLB( $opts['cluster'] );
 458                 } elseif ( $opts['wiki'] !== false ) {
 459                         $lbs[] = $this->getMainLB( $opts['wiki'] );
 460                 } else {
 461                         $this->forEachLB( function ( LoadBalancer $lb ) use ( &$lbs ) {
 462                                 $lbs[] = $lb;
 463                         } );
 464                         if ( !$lbs ) {
 465                                 return; // nothing actually used
 466                         }
 467                 }
 468
 469                 // Get all the master positions of applicable DBs right now.
 470                 // This can be faster since waiting on one cluster reduces the
 471                 // time needed to wait on the next clusters.
 472                 $masterPositions = array_fill( 0, count( $lbs ), false );
 473                 foreach ( $lbs as $i => $lb ) {
 474                         if ( $lb->getServerCount() <= 1 ) {
 475                                 // Bug 27975 - Don't try to wait for replica DBs if there are none
 476                                 // Prevents permission error when getting master position
 477                                 continue;
 478                         } elseif ( $opts['ifWritesSince']
 479                                 && $lb->lastMasterChangeTimestamp() < $opts['ifWritesSince']
 480                         ) {
 481                                 continue; // no writes since the last wait
 482                         }
 483                         $masterPositions[$i] = $lb->getMasterPos();
 484                 }
 485
 486                 // Run any listener callbacks *after* getting the DB positions. The more
 487                 // time spent in the callbacks, the less time is spent in waitForAll().
 488                 foreach ( $this->replicationWaitCallbacks as $callback ) {
 489                         $callback();
 490                 }
 491
 492                 $failed = [];
 493                 foreach ( $lbs as $i => $lb ) {
 494                         if ( $masterPositions[$i] ) {
 495                                 // The DBMS may not support getMasterPos() or the whole
 496                                 // load balancer might be fake (e.g. $wgAllDBsAreLocalhost).
 497                                 if ( !$lb->waitForAll( $masterPositions[$i], $opts['timeout'] ) ) {
 498                                         $failed[] = $lb->getServerName( $lb->getWriterIndex() );
 499                                 }
 500                         }
 501                 }
 502
 503                 if ( $failed ) {
 504                         throw new DBReplicationWaitError(
 505                                 "Could not wait for replica DBs to catch up to " .
 506                                 implode( ', ', $failed )
 507                         );
 508                 }
 509         }
 510
 511         /**
 512          * Add a callback to be run in every call to waitForReplication() before waiting
 513          *
 514          * Callbacks must clear any transactions that they start
 515          *
 516          * @param string $name Callback name
 517          * @param callable|null $callback Use null to unset a callback
 518          * @since 1.28
 519          */
 520         public function setWaitForReplicationListener( $name, callable $callback = null ) {
 521                 if ( $callback ) {
 522                         $this->replicationWaitCallbacks[$name] = $callback;
 523                 } else {
 524                         unset( $this->replicationWaitCallbacks[$name] );
 525                 }
 526         }
 527
 528         /**
 529          * Get a token asserting that no transaction writes are active
 530          *
 531          * @param string $fname Caller name (e.g. __METHOD__)
 532          * @return mixed A value to pass to commitAndWaitForReplication()
 533          * @since 1.28
 534          */
 535         public function getEmptyTransactionTicket( $fname ) {
 536                 if ( $this->hasMasterChanges() ) {
 537                         $this->trxLogger->error( __METHOD__ . ": $fname does not have outer scope." );
 538                         return null;
 539                 }
 540
 541                 return $this->ticket;
 542         }
 543
 544         /**
 545          * Convenience method for safely running commitMasterChanges()/waitForReplication()
 546          *
 547          * This will commit and wait unless $ticket indicates it is unsafe to do so
 548          *
 549          * @param string $fname Caller name (e.g. __METHOD__)
 550          * @param mixed $ticket Result of getEmptyTransactionTicket()
 551          * @param array $opts Options to waitForReplication()
 552          * @throws DBReplicationWaitError
 553          * @since 1.28
 554          */
 555         public function commitAndWaitForReplication( $fname, $ticket, array $opts = [] ) {
 556                 if ( $ticket !== $this->ticket ) {
 557                         $logger = LoggerFactory::getInstance( 'DBPerformance' );
 558                         $logger->error( __METHOD__ . ": cannot commit; $fname does not have outer scope." );
 559                         return;
 560                 }
 561
 562                 // The transaction owner and any caller with the empty transaction ticket can commit
 563                 // so that getEmptyTransactionTicket() callers don't risk seeing DBTransactionError.
 564                 if ( $this->trxRoundId !== false && $fname !== $this->trxRoundId ) {
 565                         $this->trxLogger->info( "$fname: committing on behalf of {$this->trxRoundId}." );
 566                         $fnameEffective = $this->trxRoundId;
 567                 } else {
 568                         $fnameEffective = $fname;
 569                 }
 570
 571                 $this->commitMasterChanges( $fnameEffective );
 572                 $this->waitForReplication( $opts );
 573                 // If a nested caller committed on behalf of $fname, start another empty $fname
 574                 // transaction, leaving the caller with the same empty transaction state as before.
 575                 if ( $fnameEffective !== $fname ) {
 576                         $this->beginMasterChanges( $fnameEffective );
 577                 }
 578         }
 579
 580         /**
 581          * @param string $dbName DB master name (e.g. "db1052")
 582          * @return float|bool UNIX timestamp when client last touched the DB or false if not recent
 583          * @since 1.28
 584          */
 585         public function getChronologyProtectorTouched( $dbName ) {
 586                 return $this->chronProt->getTouched( $dbName );
 587         }
 588
 589         /**
 590          * Disable the ChronologyProtector for all load balancers
 591          *
 592          * This can be called at the start of special API entry points
 593          *
 594          * @since 1.27
 595          */
 596         public function disableChronologyProtection() {
 597                 $this->chronProt->setEnabled( false );
 598         }
 599
 600         /**
 601          * @return ChronologyProtector
 602          */
 603         protected function newChronologyProtector() {
 604                 $request = RequestContext::getMain()->getRequest();
 605                 $chronProt = new ChronologyProtector(
 606                         ObjectCache::getMainStashInstance(),
 607                         [
 608                                 'ip' => $request->getIP(),
 609                                 'agent' => $request->getHeader( 'User-Agent' ),
 610                         ],
 611                         $request->getFloat( 'cpPosTime', $request->getCookie( 'cpPosTime', '' ) )
 612                 );
 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                 ];
 674         }
 675
 676         /**
 677          * @param LoadBalancer $lb
 678          */
 679         protected function initLoadBalancer( LoadBalancer $lb ) {
 680                 if ( $this->trxRoundId !== false ) {
 681                         $lb->beginMasterChanges( $this->trxRoundId ); // set DBO_TRX
 682                 }
 683         }
 684
 685         /**
 686          * Append ?cpPosTime parameter to a URL for ChronologyProtector purposes if needed
 687          *
 688          * Note that unlike cookies, this works accross domains
 689          *
 690          * @param string $url
 691          * @param float $time UNIX timestamp just before shutdown() was called
 692          * @return string
 693          * @since 1.28
 694          */
 695         public function appendPreShutdownTimeAsQuery( $url, $time ) {
 696                 $usedCluster = 0;
 697                 $this->forEachLB( function ( LoadBalancer $lb ) use ( &$usedCluster ) {
 698                         $usedCluster |= ( $lb->getServerCount() > 1 );
 699                 } );
 700
 701                 if ( !$usedCluster ) {
 702                         return $url; // no master/replica clusters touched
 703                 }
 704
 705                 return wfAppendQuery( $url, [ 'cpPosTime' => $time ] );
 706         }
 707
 708         /**
 709          * Close all open database connections on all open load balancers.
 710          * @since 1.28
 711          */
 712         public function closeAll() {
 713                 $this->forEachLBCallMethod( 'closeAll', [] );
 714         }
 715 }