includes/libs/rdbms/loadbalancer/LoadBalancer.php

   1 <?php
   2 /**
   3  * Database load balancing manager
   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  */
  22 namespace Wikimedia\Rdbms;
  23
  24 use Psr\Log\LoggerInterface;
  25 use Psr\Log\NullLogger;
  26 use Wikimedia\ScopedCallback;
  27 use BagOStuff;
  28 use EmptyBagOStuff;
  29 use WANObjectCache;
  30 use ArrayUtils;
  31 use InvalidArgumentException;
  32 use RuntimeException;
  33 use Exception;
  34
  35 /**
  36  * Database connection, tracking, load balancing, and transaction manager for a cluster
  37  *
  38  * @ingroup Database
  39  */
  40 class LoadBalancer implements ILoadBalancer {
  41         /** @var array[] Map of (server index => server config array) */
  42         private $mServers;
  43         /** @var Database[][][] Map of (connection category => server index => IDatabase[]) */
  44         private $mConns;
  45         /** @var float[] Map of (server index => weight) */
  46         private $mLoads;
  47         /** @var array[] Map of (group => server index => weight) */
  48         private $mGroupLoads;
  49         /** @var bool Whether to disregard replica DB lag as a factor in replica DB selection */
  50         private $mAllowLagged;
  51         /** @var int Seconds to spend waiting on replica DB lag to resolve */
  52         private $mWaitTimeout;
  53         /** @var array The LoadMonitor configuration */
  54         private $loadMonitorConfig;
  55         /** @var array[] $aliases Map of (table => (dbname, schema, prefix) map) */
  56         private $tableAliases = [];
  57
  58         /** @var ILoadMonitor */
  59         private $loadMonitor;
  60         /** @var ChronologyProtector|null */
  61         private $chronProt;
  62         /** @var BagOStuff */
  63         private $srvCache;
  64         /** @var WANObjectCache */
  65         private $wanCache;
  66         /** @var object|string Class name or object With profileIn/profileOut methods */
  67         protected $profiler;
  68         /** @var TransactionProfiler */
  69         protected $trxProfiler;
  70         /** @var LoggerInterface */
  71         protected $replLogger;
  72         /** @var LoggerInterface */
  73         protected $connLogger;
  74         /** @var LoggerInterface */
  75         protected $queryLogger;
  76         /** @var LoggerInterface */
  77         protected $perfLogger;
  78
  79         /** @var Database DB connection object that caused a problem */
  80         private $errorConnection;
  81         /** @var int The generic (not query grouped) replica DB index (of $mServers) */
  82         private $mReadIndex;
  83         /** @var bool|DBMasterPos False if not set */
  84         private $mWaitForPos;
  85         /** @var bool Whether the generic reader fell back to a lagged replica DB */
  86         private $laggedReplicaMode = false;
  87         /** @var bool Whether the generic reader fell back to a lagged replica DB */
  88         private $allReplicasDownMode = false;
  89         /** @var string The last DB selection or connection error */
  90         private $mLastError = 'Unknown error';
  91         /** @var string|bool Reason the LB is read-only or false if not */
  92         private $readOnlyReason = false;
  93         /** @var int Total connections opened */
  94         private $connsOpened = 0;
  95         /** @var string|bool String if a requested DBO_TRX transaction round is active */
  96         private $trxRoundId = false;
  97         /** @var array[] Map of (name => callable) */
  98         private $trxRecurringCallbacks = [];
  99         /** @var DatabaseDomain Local Domain ID and default for selectDB() calls */
 100         private $localDomain;
 101         /** @var string Alternate ID string for the domain instead of DatabaseDomain::getId() */
 102         private $localDomainIdAlias;
 103         /** @var string Current server name */
 104         private $host;
 105         /** @var bool Whether this PHP instance is for a CLI script */
 106         protected $cliMode;
 107         /** @var string Agent name for query profiling */
 108         protected $agent;
 109
 110         /** @var callable Exception logger */
 111         private $errorLogger;
 112
 113         /** @var bool */
 114         private $disabled = false;
 115         /** @var bool */
 116         private $chronProtInitialized = false;
 117         /** @var int */
 118         private $maxLag = self::MAX_LAG_DEFAULT;
 119
 120         /** @var int Warn when this many connection are held */
 121         const CONN_HELD_WARN_THRESHOLD = 10;
 122
 123         /** @var int Default 'maxLag' when unspecified */
 124         const MAX_LAG_DEFAULT = 10;
 125         /** @var int Default 'waitTimeout' when unspecified */
 126         const MAX_WAIT_DEFAULT = 10;
 127         /** @var int Seconds to cache master server read-only status */
 128         const TTL_CACHE_READONLY = 5;
 129
 130         const KEY_LOCAL = 'local';
 131         const KEY_FOREIGN_FREE = 'foreignFree';
 132         const KEY_FOREIGN_INUSE = 'foreignInUse';
 133
 134         const KEY_LOCAL_NOROUND = 'localAutoCommit';
 135         const KEY_FOREIGN_FREE_NOROUND = 'foreignFreeAutoCommit';
 136         const KEY_FOREIGN_INUSE_NOROUND = 'foreignInUseAutoCommit';
 137
 138         public function __construct( array $params ) {
 139                 if ( !isset( $params['servers'] ) ) {
 140                         throw new InvalidArgumentException( __CLASS__ . ': missing servers parameter' );
 141                 }
 142                 $this->mServers = $params['servers'];
 143                 foreach ( $this->mServers as $i => $server ) {
 144                         if ( $i == 0 ) {
 145                                 $this->mServers[$i]['master'] = true;
 146                         } else {
 147                                 $this->mServers[$i]['replica'] = true;
 148                         }
 149                 }
 150
 151                 $localDomain = isset( $params['localDomain'] )
 152                         ? DatabaseDomain::newFromId( $params['localDomain'] )
 153                         : DatabaseDomain::newUnspecified();
 154                 $this->setLocalDomain( $localDomain );
 155
 156                 $this->mWaitTimeout = isset( $params['waitTimeout'] )
 157                         ? $params['waitTimeout']
 158                         : self::MAX_WAIT_DEFAULT;
 159
 160                 $this->mReadIndex = -1;
 161                 $this->mConns = [
 162                         // Connection were transaction rounds may be applied
 163                         self::KEY_LOCAL => [],
 164                         self::KEY_FOREIGN_INUSE => [],
 165                         self::KEY_FOREIGN_FREE => [],
 166                         // Auto-committing counterpart connections that ignore transaction rounds
 167                         self::KEY_LOCAL_NOROUND => [],
 168                         self::KEY_FOREIGN_INUSE_NOROUND => [],
 169                         self::KEY_FOREIGN_FREE_NOROUND => []
 170                 ];
 171                 $this->mLoads = [];
 172                 $this->mWaitForPos = false;
 173                 $this->mAllowLagged = false;
 174
 175                 if ( isset( $params['readOnlyReason'] ) && is_string( $params['readOnlyReason'] ) ) {
 176                         $this->readOnlyReason = $params['readOnlyReason'];
 177                 }
 178
 179                 if ( isset( $params['maxLag'] ) ) {
 180                         $this->maxLag = $params['maxLag'];
 181                 }
 182
 183                 if ( isset( $params['loadMonitor'] ) ) {
 184                         $this->loadMonitorConfig = $params['loadMonitor'];
 185                 } else {
 186                         $this->loadMonitorConfig = [ 'class' => 'LoadMonitorNull' ];
 187                 }
 188                 $this->loadMonitorConfig += [ 'lagWarnThreshold' => $this->maxLag ];
 189
 190                 foreach ( $params['servers'] as $i => $server ) {
 191                         $this->mLoads[$i] = $server['load'];
 192                         if ( isset( $server['groupLoads'] ) ) {
 193                                 foreach ( $server['groupLoads'] as $group => $ratio ) {
 194                                         if ( !isset( $this->mGroupLoads[$group] ) ) {
 195                                                 $this->mGroupLoads[$group] = [];
 196                                         }
 197                                         $this->mGroupLoads[$group][$i] = $ratio;
 198                                 }
 199                         }
 200                 }
 201
 202                 if ( isset( $params['srvCache'] ) ) {
 203                         $this->srvCache = $params['srvCache'];
 204                 } else {
 205                         $this->srvCache = new EmptyBagOStuff();
 206                 }
 207                 if ( isset( $params['wanCache'] ) ) {
 208                         $this->wanCache = $params['wanCache'];
 209                 } else {
 210                         $this->wanCache = WANObjectCache::newEmpty();
 211                 }
 212                 $this->profiler = isset( $params['profiler'] ) ? $params['profiler'] : null;
 213                 if ( isset( $params['trxProfiler'] ) ) {
 214                         $this->trxProfiler = $params['trxProfiler'];
 215                 } else {
 216                         $this->trxProfiler = new TransactionProfiler();
 217                 }
 218
 219                 $this->errorLogger = isset( $params['errorLogger'] )
 220                         ? $params['errorLogger']
 221                         : function ( Exception $e ) {
 222                                 trigger_error( get_class( $e ) . ': ' . $e->getMessage(), E_USER_WARNING );
 223                         };
 224
 225                 foreach ( [ 'replLogger', 'connLogger', 'queryLogger', 'perfLogger' ] as $key ) {
 226                         $this->$key = isset( $params[$key] ) ? $params[$key] : new NullLogger();
 227                 }
 228
 229                 $this->host = isset( $params['hostname'] )
 230                         ? $params['hostname']
 231                         : ( gethostname() ?: 'unknown' );
 232                 $this->cliMode = isset( $params['cliMode'] )
 233                         ? $params['cliMode']
 234                         : ( PHP_SAPI === 'cli' || PHP_SAPI === 'phpdbg' );
 235                 $this->agent = isset( $params['agent'] ) ? $params['agent'] : '';
 236
 237                 if ( isset( $params['chronologyProtector'] ) ) {
 238                         $this->chronProt = $params['chronologyProtector'];
 239                 }
 240         }
 241
 242         /**
 243          * Get the local (and default) database domain ID of connection handles
 244          *
 245          * @see DatabaseDomain
 246          * @return string Database domain ID; this specifies DB name, schema, and table prefix
 247          * @since 1.31
 248          */
 249         public function getLocalDomainID() {
 250                 return $this->localDomain->getId();
 251         }
 252
 253         /**
 254          * Get a LoadMonitor instance
 255          *
 256          * @return ILoadMonitor
 257          */
 258         private function getLoadMonitor() {
 259                 if ( !isset( $this->loadMonitor ) ) {
 260                         $compat = [
 261                                 'LoadMonitor' => LoadMonitor::class,
 262                                 'LoadMonitorNull' => LoadMonitorNull::class,
 263                                 'LoadMonitorMySQL' => LoadMonitorMySQL::class,
 264                         ];
 265
 266                         $class = $this->loadMonitorConfig['class'];
 267                         if ( isset( $compat[$class] ) ) {
 268                                 $class = $compat[$class];
 269                         }
 270
 271                         $this->loadMonitor = new $class(
 272                                 $this, $this->srvCache, $this->wanCache, $this->loadMonitorConfig );
 273                         $this->loadMonitor->setLogger( $this->replLogger );
 274                 }
 275
 276                 return $this->loadMonitor;
 277         }
 278
 279         /**
 280          * @param array $loads
 281          * @param bool|string $domain Domain to get non-lagged for
 282          * @param int $maxLag Restrict the maximum allowed lag to this many seconds
 283          * @return bool|int|string
 284          */
 285         private function getRandomNonLagged( array $loads, $domain = false, $maxLag = INF ) {
 286                 $lags = $this->getLagTimes( $domain );
 287
 288                 # Unset excessively lagged servers
 289                 foreach ( $lags as $i => $lag ) {
 290                         if ( $i != 0 ) {
 291                                 # How much lag this server nominally is allowed to have
 292                                 $maxServerLag = isset( $this->mServers[$i]['max lag'] )
 293                                         ? $this->mServers[$i]['max lag']
 294                                         : $this->maxLag; // default
 295                                 # Constrain that futher by $maxLag argument
 296                                 $maxServerLag = min( $maxServerLag, $maxLag );
 297
 298                                 $host = $this->getServerName( $i );
 299                                 if ( $lag === false && !is_infinite( $maxServerLag ) ) {
 300                                         $this->replLogger->error(
 301                                                 "Server {host} is not replicating?", [ 'host' => $host ] );
 302                                         unset( $loads[$i] );
 303                                 } elseif ( $lag > $maxServerLag ) {
 304                                         $this->replLogger->info(
 305                                                 "Server {host} has {lag} seconds of lag (>= {maxlag})",
 306                                                 [ 'host' => $host, 'lag' => $lag, 'maxlag' => $maxServerLag ]
 307                                         );
 308                                         unset( $loads[$i] );
 309                                 }
 310                         }
 311                 }
 312
 313                 # Find out if all the replica DBs with non-zero load are lagged
 314                 $sum = 0;
 315                 foreach ( $loads as $load ) {
 316                         $sum += $load;
 317                 }
 318                 if ( $sum == 0 ) {
 319                         # No appropriate DB servers except maybe the master and some replica DBs with zero load
 320                         # Do NOT use the master
 321                         # Instead, this function will return false, triggering read-only mode,
 322                         # and a lagged replica DB will be used instead.
 323                         return false;
 324                 }
 325
 326                 if ( count( $loads ) == 0 ) {
 327                         return false;
 328                 }
 329
 330                 # Return a random representative of the remainder
 331                 return ArrayUtils::pickRandom( $loads );
 332         }
 333
 334         public function getReaderIndex( $group = false, $domain = false ) {
 335                 if ( count( $this->mServers ) == 1 ) {
 336                         // Skip the load balancing if there's only one server
 337                         return $this->getWriterIndex();
 338                 } elseif ( $group === false && $this->mReadIndex >= 0 ) {
 339                         // Shortcut if the generic reader index was already cached
 340                         return $this->mReadIndex;
 341                 }
 342
 343                 if ( $group !== false ) {
 344                         // Use the server weight array for this load group
 345                         if ( isset( $this->mGroupLoads[$group] ) ) {
 346                                 $loads = $this->mGroupLoads[$group];
 347                         } else {
 348                                 // No loads for this group, return false and the caller can use some other group
 349                                 $this->connLogger->info( __METHOD__ . ": no loads for group $group" );
 350
 351                                 return false;
 352                         }
 353                 } else {
 354                         // Use the generic load group
 355                         $loads = $this->mLoads;
 356                 }
 357
 358                 // Scale the configured load ratios according to each server's load and state
 359                 $this->getLoadMonitor()->scaleLoads( $loads, $domain );
 360
 361                 // Pick a server to use, accounting for weights, load, lag, and mWaitForPos
 362                 list( $i, $laggedReplicaMode ) = $this->pickReaderIndex( $loads, $domain );
 363                 if ( $i === false ) {
 364                         // Replica DB connection unsuccessful
 365                         return false;
 366                 }
 367
 368                 if ( $this->mWaitForPos && $i != $this->getWriterIndex() ) {
 369                         // Before any data queries are run, wait for the server to catch up to the
 370                         // specified position. This is used to improve session consistency. Note that
 371                         // when LoadBalancer::waitFor() sets mWaitForPos, the waiting triggers here,
 372                         // so update laggedReplicaMode as needed for consistency.
 373                         if ( !$this->doWait( $i ) ) {
 374                                 $laggedReplicaMode = true;
 375                         }
 376                 }
 377
 378                 if ( $this->mReadIndex <= 0 && $this->mLoads[$i] > 0 && $group === false ) {
 379                         // Cache the generic reader index for future ungrouped DB_REPLICA handles
 380                         $this->mReadIndex = $i;
 381                         // Record if the generic reader index is in "lagged replica DB" mode
 382                         if ( $laggedReplicaMode ) {
 383                                 $this->laggedReplicaMode = true;
 384                         }
 385                 }
 386
 387                 $serverName = $this->getServerName( $i );
 388                 $this->connLogger->debug( __METHOD__ . ": using server $serverName for group '$group'" );
 389
 390                 return $i;
 391         }
 392
 393         /**
 394          * @param array $loads List of server weights
 395          * @param string|bool $domain
 396          * @return array (reader index, lagged replica mode) or false on failure
 397          */
 398         private function pickReaderIndex( array $loads, $domain = false ) {
 399                 if ( !count( $loads ) ) {
 400                         throw new InvalidArgumentException( "Empty server array given to LoadBalancer" );
 401                 }
 402
 403                 /** @var int|bool $i Index of selected server */
 404                 $i = false;
 405                 /** @var bool $laggedReplicaMode Whether server is considered lagged */
 406                 $laggedReplicaMode = false;
 407
 408                 // Quickly look through the available servers for a server that meets criteria...
 409                 $currentLoads = $loads;
 410                 while ( count( $currentLoads ) ) {
 411                         if ( $this->mAllowLagged || $laggedReplicaMode ) {
 412                                 $i = ArrayUtils::pickRandom( $currentLoads );
 413                         } else {
 414                                 $i = false;
 415                                 if ( $this->mWaitForPos && $this->mWaitForPos->asOfTime() ) {
 416                                         // ChronologyProtecter sets mWaitForPos for session consistency.
 417                                         // This triggers doWait() after connect, so it's especially good to
 418                                         // avoid lagged servers so as to avoid excessive delay in that method.
 419                                         $ago = microtime( true ) - $this->mWaitForPos->asOfTime();
 420                                         // Aim for <= 1 second of waiting (being too picky can backfire)
 421                                         $i = $this->getRandomNonLagged( $currentLoads, $domain, $ago + 1 );
 422                                 }
 423                                 if ( $i === false ) {
 424                                         // Any server with less lag than it's 'max lag' param is preferable
 425                                         $i = $this->getRandomNonLagged( $currentLoads, $domain );
 426                                 }
 427                                 if ( $i === false && count( $currentLoads ) != 0 ) {
 428                                         // All replica DBs lagged. Switch to read-only mode
 429                                         $this->replLogger->error( "All replica DBs lagged. Switch to read-only mode" );
 430                                         $i = ArrayUtils::pickRandom( $currentLoads );
 431                                         $laggedReplicaMode = true;
 432                                 }
 433                         }
 434
 435                         if ( $i === false ) {
 436                                 // pickRandom() returned false.
 437                                 // This is permanent and means the configuration or the load monitor
 438                                 // wants us to return false.
 439                                 $this->connLogger->debug( __METHOD__ . ": pickRandom() returned false" );
 440
 441                                 return [ false, false ];
 442                         }
 443
 444                         $serverName = $this->getServerName( $i );
 445                         $this->connLogger->debug( __METHOD__ . ": Using reader #$i: $serverName..." );
 446
 447                         $conn = $this->openConnection( $i, $domain );
 448                         if ( !$conn ) {
 449                                 $this->connLogger->warning( __METHOD__ . ": Failed connecting to $i/$domain" );
 450                                 unset( $currentLoads[$i] ); // avoid this server next iteration
 451                                 $i = false;
 452                                 continue;
 453                         }
 454
 455                         // Decrement reference counter, we are finished with this connection.
 456                         // It will be incremented for the caller later.
 457                         if ( $domain !== false ) {
 458                                 $this->reuseConnection( $conn );
 459                         }
 460
 461                         // Return this server
 462                         break;
 463                 }
 464
 465                 // If all servers were down, quit now
 466                 if ( !count( $currentLoads ) ) {
 467                         $this->connLogger->error( "All servers down" );
 468                 }
 469
 470                 return [ $i, $laggedReplicaMode ];
 471         }
 472
 473         public function waitFor( $pos ) {
 474                 $oldPos = $this->mWaitForPos;
 475                 try {
 476                         $this->mWaitForPos = $pos;
 477                         // If a generic reader connection was already established, then wait now
 478                         $i = $this->mReadIndex;
 479                         if ( $i > 0 ) {
 480                                 if ( !$this->doWait( $i ) ) {
 481                                         $this->laggedReplicaMode = true;
 482                                 }
 483                         }
 484                 } finally {
 485                         // Restore the older position if it was higher since this is used for lag-protection
 486                         $this->setWaitForPositionIfHigher( $oldPos );
 487                 }
 488         }
 489
 490         public function waitForOne( $pos, $timeout = null ) {
 491                 $oldPos = $this->mWaitForPos;
 492                 try {
 493                         $this->mWaitForPos = $pos;
 494
 495                         $i = $this->mReadIndex;
 496                         if ( $i <= 0 ) {
 497                                 // Pick a generic replica DB if there isn't one yet
 498                                 $readLoads = $this->mLoads;
 499                                 unset( $readLoads[$this->getWriterIndex()] ); // replica DBs only
 500                                 $readLoads = array_filter( $readLoads ); // with non-zero load
 501                                 $i = ArrayUtils::pickRandom( $readLoads );
 502                         }
 503
 504                         if ( $i > 0 ) {
 505                                 $ok = $this->doWait( $i, true, $timeout );
 506                         } else {
 507                                 $ok = true; // no applicable loads
 508                         }
 509                 } finally {
 510                         # Restore the old position, as this is not used for lag-protection but for throttling
 511                         $this->mWaitForPos = $oldPos;
 512                 }
 513
 514                 return $ok;
 515         }
 516
 517         public function waitForAll( $pos, $timeout = null ) {
 518                 $timeout = $timeout ?: $this->mWaitTimeout;
 519
 520                 $oldPos = $this->mWaitForPos;
 521                 try {
 522                         $this->mWaitForPos = $pos;
 523                         $serverCount = count( $this->mServers );
 524
 525                         $ok = true;
 526                         for ( $i = 1; $i < $serverCount; $i++ ) {
 527                                 if ( $this->mLoads[$i] > 0 ) {
 528                                         $start = microtime( true );
 529                                         $ok = $this->doWait( $i, true, max( 1, (int)$timeout ) ) && $ok;
 530                                         $timeout -= ( microtime( true ) - $start );
 531                                         if ( $timeout <= 0 ) {
 532                                                 break; // timeout reached
 533                                         }
 534                                 }
 535                         }
 536                 } finally {
 537                         # Restore the old position, as this is not used for lag-protection but for throttling
 538                         $this->mWaitForPos = $oldPos;
 539                 }
 540
 541                 return $ok;
 542         }
 543
 544         /**
 545          * @param DBMasterPos|bool $pos
 546          */
 547         private function setWaitForPositionIfHigher( $pos ) {
 548                 if ( !$pos ) {
 549                         return;
 550                 }
 551
 552                 if ( !$this->mWaitForPos || $pos->hasReached( $this->mWaitForPos ) ) {
 553                         $this->mWaitForPos = $pos;
 554                 }
 555         }
 556
 557         /**
 558          * @param int $i
 559          * @return IDatabase|bool
 560          */
 561         public function getAnyOpenConnection( $i ) {
 562                 foreach ( $this->mConns as $connsByServer ) {
 563                         if ( !empty( $connsByServer[$i] ) ) {
 564                                 /** @var IDatabase[] $serverConns */
 565                                 $serverConns = $connsByServer[$i];
 566
 567                                 return reset( $serverConns );
 568                         }
 569                 }
 570
 571                 return false;
 572         }
 573
 574         /**
 575          * Wait for a given replica DB to catch up to the master pos stored in $this
 576          * @param int $index Server index
 577          * @param bool $open Check the server even if a new connection has to be made
 578          * @param int $timeout Max seconds to wait; default is mWaitTimeout
 579          * @return bool
 580          */
 581         protected function doWait( $index, $open = false, $timeout = null ) {
 582                 $close = false; // close the connection afterwards
 583
 584                 // Check if we already know that the DB has reached this point
 585                 $server = $this->getServerName( $index );
 586                 $key = $this->srvCache->makeGlobalKey( __CLASS__, 'last-known-pos', $server, 'v1' );
 587                 /** @var DBMasterPos $knownReachedPos */
 588                 $knownReachedPos = $this->srvCache->get( $key );
 589                 if (
 590                         $knownReachedPos instanceof DBMasterPos &&
 591                         $knownReachedPos->hasReached( $this->mWaitForPos )
 592                 ) {
 593                         $this->replLogger->debug( __METHOD__ .
 594                                 ': replica DB {dbserver} known to be caught up (pos >= $knownReachedPos).',
 595                                 [ 'dbserver' => $server ] );
 596                         return true;
 597                 }
 598
 599                 // Find a connection to wait on, creating one if needed and allowed
 600                 $conn = $this->getAnyOpenConnection( $index );
 601                 if ( !$conn ) {
 602                         if ( !$open ) {
 603                                 $this->replLogger->debug( __METHOD__ . ': no connection open for {dbserver}',
 604                                         [ 'dbserver' => $server ] );
 605
 606                                 return false;
 607                         } else {
 608                                 $conn = $this->openConnection( $index, self::DOMAIN_ANY );
 609                                 if ( !$conn ) {
 610                                         $this->replLogger->warning( __METHOD__ . ': failed to connect to {dbserver}',
 611                                                 [ 'dbserver' => $server ] );
 612
 613                                         return false;
 614                                 }
 615                                 // Avoid connection spam in waitForAll() when connections
 616                                 // are made just for the sake of doing this lag check.
 617                                 $close = true;
 618                         }
 619                 }
 620
 621                 $this->replLogger->info( __METHOD__ . ': Waiting for replica DB {dbserver} to catch up...',
 622                         [ 'dbserver' => $server ] );
 623                 $timeout = $timeout ?: $this->mWaitTimeout;
 624                 $result = $conn->masterPosWait( $this->mWaitForPos, $timeout );
 625
 626                 if ( $result == -1 || is_null( $result ) ) {
 627                         // Timed out waiting for replica DB, use master instead
 628                         $this->replLogger->warning(
 629                                 __METHOD__ . ': Timed out waiting on {host} pos {pos}',
 630                                 [ 'host' => $server, 'pos' => $this->mWaitForPos ]
 631                         );
 632                         $ok = false;
 633                 } else {
 634                         $this->replLogger->info( __METHOD__ . ": Done" );
 635                         $ok = true;
 636                         // Remember that the DB reached this point
 637                         $this->srvCache->set( $key, $this->mWaitForPos, BagOStuff::TTL_DAY );
 638                 }
 639
 640                 if ( $close ) {
 641                         $this->closeConnection( $conn );
 642                 }
 643
 644                 return $ok;
 645         }
 646
 647         public function getConnection( $i, $groups = [], $domain = false, $flags = 0 ) {
 648                 if ( $i === null || $i === false ) {
 649                         throw new InvalidArgumentException( 'Attempt to call ' . __METHOD__ .
 650                                 ' with invalid server index' );
 651                 }
 652
 653                 if ( $this->localDomain->equals( $domain ) || $domain === $this->localDomainIdAlias ) {
 654                         $domain = false; // local connection requested
 655                 }
 656
 657                 $groups = ( $groups === false || $groups === [] )
 658                         ? [ false ] // check one "group": the generic pool
 659                         : (array)$groups;
 660
 661                 $masterOnly = ( $i == self::DB_MASTER || $i == $this->getWriterIndex() );
 662                 $oldConnsOpened = $this->connsOpened; // connections open now
 663
 664                 if ( $i == self::DB_MASTER ) {
 665                         $i = $this->getWriterIndex();
 666                 } else {
 667                         # Try to find an available server in any the query groups (in order)
 668                         foreach ( $groups as $group ) {
 669                                 $groupIndex = $this->getReaderIndex( $group, $domain );
 670                                 if ( $groupIndex !== false ) {
 671                                         $i = $groupIndex;
 672                                         break;
 673                                 }
 674                         }
 675                 }
 676
 677                 # Operation-based index
 678                 if ( $i == self::DB_REPLICA ) {
 679                         $this->mLastError = 'Unknown error'; // reset error string
 680                         # Try the general server pool if $groups are unavailable.
 681                         $i = ( $groups === [ false ] )
 682                                 ? false // don't bother with this if that is what was tried above
 683                                 : $this->getReaderIndex( false, $domain );
 684                         # Couldn't find a working server in getReaderIndex()?
 685                         if ( $i === false ) {
 686                                 $this->mLastError = 'No working replica DB server: ' . $this->mLastError;
 687                                 // Throw an exception
 688                                 $this->reportConnectionError();
 689                                 return null; // not reached
 690                         }
 691                 }
 692
 693                 # Now we have an explicit index into the servers array
 694                 $conn = $this->openConnection( $i, $domain, $flags );
 695                 if ( !$conn ) {
 696                         // Throw an exception
 697                         $this->reportConnectionError();
 698                         return null; // not reached
 699                 }
 700
 701                 # Profile any new connections that happen
 702                 if ( $this->connsOpened > $oldConnsOpened ) {
 703                         $host = $conn->getServer();
 704                         $dbname = $conn->getDBname();
 705                         $this->trxProfiler->recordConnection( $host, $dbname, $masterOnly );
 706                 }
 707
 708                 if ( $masterOnly ) {
 709                         # Make master-requested DB handles inherit any read-only mode setting
 710                         $conn->setLBInfo( 'readOnlyReason', $this->getReadOnlyReason( $domain, $conn ) );
 711                 }
 712
 713                 return $conn;
 714         }
 715
 716         public function reuseConnection( $conn ) {
 717                 $serverIndex = $conn->getLBInfo( 'serverIndex' );
 718                 $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 719                 if ( $serverIndex === null || $refCount === null ) {
 720                         /**
 721                          * This can happen in code like:
 722                          *   foreach ( $dbs as $db ) {
 723                          *     $conn = $lb->getConnection( $lb::DB_REPLICA, [], $db );
 724                          *     ...
 725                          *     $lb->reuseConnection( $conn );
 726                          *   }
 727                          * When a connection to the local DB is opened in this way, reuseConnection()
 728                          * should be ignored
 729                          */
 730                         return;
 731                 } elseif ( $conn instanceof DBConnRef ) {
 732                         // DBConnRef already handles calling reuseConnection() and only passes the live
 733                         // Database instance to this method. Any caller passing in a DBConnRef is broken.
 734                         $this->connLogger->error( __METHOD__ . ": got DBConnRef instance.\n" .
 735                                 ( new RuntimeException() )->getTraceAsString() );
 736
 737                         return;
 738                 }
 739
 740                 if ( $this->disabled ) {
 741                         return; // DBConnRef handle probably survived longer than the LoadBalancer
 742                 }
 743
 744                 if ( $conn->getLBInfo( 'autoCommitOnly' ) ) {
 745                         $connFreeKey = self::KEY_FOREIGN_FREE_NOROUND;
 746                         $connInUseKey = self::KEY_FOREIGN_INUSE_NOROUND;
 747                 } else {
 748                         $connFreeKey = self::KEY_FOREIGN_FREE;
 749                         $connInUseKey = self::KEY_FOREIGN_INUSE;
 750                 }
 751
 752                 $domain = $conn->getDomainID();
 753                 if ( !isset( $this->mConns[$connInUseKey][$serverIndex][$domain] ) ) {
 754                         throw new InvalidArgumentException( __METHOD__ .
 755                                 ": connection $serverIndex/$domain not found; it may have already been freed." );
 756                 } elseif ( $this->mConns[$connInUseKey][$serverIndex][$domain] !== $conn ) {
 757                         throw new InvalidArgumentException( __METHOD__ .
 758                                 ": connection $serverIndex/$domain mismatched; it may have already been freed." );
 759                 }
 760
 761                 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
 762                 if ( $refCount <= 0 ) {
 763                         $this->mConns[$connFreeKey][$serverIndex][$domain] = $conn;
 764                         unset( $this->mConns[$connInUseKey][$serverIndex][$domain] );
 765                         if ( !$this->mConns[$connInUseKey][$serverIndex] ) {
 766                                 unset( $this->mConns[$connInUseKey][$serverIndex] ); // clean up
 767                         }
 768                         $this->connLogger->debug( __METHOD__ . ": freed connection $serverIndex/$domain" );
 769                 } else {
 770                         $this->connLogger->debug( __METHOD__ .
 771                                 ": reference count for $serverIndex/$domain reduced to $refCount" );
 772                 }
 773         }
 774
 775         public function getConnectionRef( $db, $groups = [], $domain = false, $flags = 0 ) {
 776                 $domain = ( $domain !== false ) ? $domain : $this->localDomain;
 777
 778                 return new DBConnRef( $this, $this->getConnection( $db, $groups, $domain, $flags ) );
 779         }
 780
 781         public function getLazyConnectionRef( $db, $groups = [], $domain = false, $flags = 0 ) {
 782                 $domain = ( $domain !== false ) ? $domain : $this->localDomain;
 783
 784                 return new DBConnRef( $this, [ $db, $groups, $domain, $flags ] );
 785         }
 786
 787         public function getMaintenanceConnectionRef( $db, $groups = [], $domain = false, $flags = 0 ) {
 788                 $domain = ( $domain !== false ) ? $domain : $this->localDomain;
 789
 790                 return new MaintainableDBConnRef(
 791                         $this, $this->getConnection( $db, $groups, $domain, $flags ) );
 792         }
 793
 794         public function openConnection( $i, $domain = false, $flags = 0 ) {
 795                 if ( $this->localDomain->equals( $domain ) || $domain === $this->localDomainIdAlias ) {
 796                         $domain = false; // local connection requested
 797                 }
 798
 799                 if ( !$this->chronProtInitialized && $this->chronProt ) {
 800                         $this->connLogger->debug( __METHOD__ . ': calling initLB() before first connection.' );
 801                         // Load CP positions before connecting so that doWait() triggers later if needed
 802                         $this->chronProtInitialized = true;
 803                         $this->chronProt->initLB( $this );
 804                 }
 805
 806                 // Check if an auto-commit connection is being requested. If so, it will not reuse the
 807                 // main set of DB connections but rather its own pool since:
 808                 // a) those are usually set to implicitly use transaction rounds via DBO_TRX
 809                 // b) those must support the use of explicit transaction rounds via beginMasterChanges()
 810                 $autoCommit = ( ( $flags & self::CONN_TRX_AUTO ) == self::CONN_TRX_AUTO );
 811
 812                 if ( $domain !== false ) {
 813                         // Connection is to a foreign domain
 814                         $conn = $this->openForeignConnection( $i, $domain, $flags );
 815                 } else {
 816                         // Connection is to the local domain
 817                         $connKey = $autoCommit ? self::KEY_LOCAL_NOROUND : self::KEY_LOCAL;
 818                         if ( isset( $this->mConns[$connKey][$i][0] ) ) {
 819                                 $conn = $this->mConns[$connKey][$i][0];
 820                         } else {
 821                                 if ( !isset( $this->mServers[$i] ) || !is_array( $this->mServers[$i] ) ) {
 822                                         throw new InvalidArgumentException( "No server with index '$i'." );
 823                                 }
 824                                 // Open a new connection
 825                                 $server = $this->mServers[$i];
 826                                 $server['serverIndex'] = $i;
 827                                 $server['autoCommitOnly'] = $autoCommit;
 828                                 if ( $this->localDomain->getDatabase() !== null ) {
 829                                         // Use the local domain table prefix if the local domain is specified
 830                                         $server['tablePrefix'] = $this->localDomain->getTablePrefix();
 831                                 }
 832                                 $conn = $this->reallyOpenConnection( $server, $this->localDomain );
 833                                 $host = $this->getServerName( $i );
 834                                 if ( $conn->isOpen() ) {
 835                                         $this->connLogger->debug( "Connected to database $i at '$host'." );
 836                                         $this->mConns[$connKey][$i][0] = $conn;
 837                                 } else {
 838                                         $this->connLogger->warning( "Failed to connect to database $i at '$host'." );
 839                                         $this->errorConnection = $conn;
 840                                         $conn = false;
 841                                 }
 842                         }
 843                 }
 844
 845                 if ( $conn instanceof IDatabase && !$conn->isOpen() ) {
 846                         // Connection was made but later unrecoverably lost for some reason.
 847                         // Do not return a handle that will just throw exceptions on use,
 848                         // but let the calling code (e.g. getReaderIndex) try another server.
 849                         // See DatabaseMyslBase::ping() for how this can happen.
 850                         $this->errorConnection = $conn;
 851                         $conn = false;
 852                 }
 853
 854                 if ( $autoCommit && $conn instanceof IDatabase ) {
 855                         $conn->clearFlag( $conn::DBO_TRX ); // auto-commit mode
 856                 }
 857
 858                 return $conn;
 859         }
 860
 861         /**
 862          * Open a connection to a foreign DB, or return one if it is already open.
 863          *
 864          * Increments a reference count on the returned connection which locks the
 865          * connection to the requested domain. This reference count can be
 866          * decremented by calling reuseConnection().
 867          *
 868          * If a connection is open to the appropriate server already, but with the wrong
 869          * database, it will be switched to the right database and returned, as long as
 870          * it has been freed first with reuseConnection().
 871          *
 872          * On error, returns false, and the connection which caused the
 873          * error will be available via $this->errorConnection.
 874          *
 875          * @note If disable() was called on this LoadBalancer, this method will throw a DBAccessError.
 876          *
 877          * @param int $i Server index
 878          * @param string $domain Domain ID to open
 879          * @param int $flags Class CONN_* constant bitfield
 880          * @return Database
 881          */
 882         private function openForeignConnection( $i, $domain, $flags = 0 ) {
 883                 $domainInstance = DatabaseDomain::newFromId( $domain );
 884                 $dbName = $domainInstance->getDatabase();
 885                 $prefix = $domainInstance->getTablePrefix();
 886                 $autoCommit = ( ( $flags & self::CONN_TRX_AUTO ) == self::CONN_TRX_AUTO );
 887
 888                 if ( $autoCommit ) {
 889                         $connFreeKey = self::KEY_FOREIGN_FREE_NOROUND;
 890                         $connInUseKey = self::KEY_FOREIGN_INUSE_NOROUND;
 891                 } else {
 892                         $connFreeKey = self::KEY_FOREIGN_FREE;
 893                         $connInUseKey = self::KEY_FOREIGN_INUSE;
 894                 }
 895
 896                 if ( isset( $this->mConns[$connInUseKey][$i][$domain] ) ) {
 897                         // Reuse an in-use connection for the same domain
 898                         $conn = $this->mConns[$connInUseKey][$i][$domain];
 899                         $this->connLogger->debug( __METHOD__ . ": reusing connection $i/$domain" );
 900                 } elseif ( isset( $this->mConns[$connFreeKey][$i][$domain] ) ) {
 901                         // Reuse a free connection for the same domain
 902                         $conn = $this->mConns[$connFreeKey][$i][$domain];
 903                         unset( $this->mConns[$connFreeKey][$i][$domain] );
 904                         $this->mConns[$connInUseKey][$i][$domain] = $conn;
 905                         $this->connLogger->debug( __METHOD__ . ": reusing free connection $i/$domain" );
 906                 } elseif ( !empty( $this->mConns[$connFreeKey][$i] ) ) {
 907                         // Reuse a free connection from another domain
 908                         $conn = reset( $this->mConns[$connFreeKey][$i] );
 909                         $oldDomain = key( $this->mConns[$connFreeKey][$i] );
 910                         if ( strlen( $dbName ) && !$conn->selectDB( $dbName ) ) {
 911                                 $this->mLastError = "Error selecting database '$dbName' on server " .
 912                                         $conn->getServer() . " from client host {$this->host}";
 913                                 $this->errorConnection = $conn;
 914                                 $conn = false;
 915                         } else {
 916                                 $conn->tablePrefix( $prefix );
 917                                 unset( $this->mConns[$connFreeKey][$i][$oldDomain] );
 918                                 // Note that if $domain is an empty string, getDomainID() might not match it
 919                                 $this->mConns[$connInUseKey][$i][$conn->getDomainId()] = $conn;
 920                                 $this->connLogger->debug( __METHOD__ .
 921                                         ": reusing free connection from $oldDomain for $domain" );
 922                         }
 923                 } else {
 924                         if ( !isset( $this->mServers[$i] ) || !is_array( $this->mServers[$i] ) ) {
 925                                 throw new InvalidArgumentException( "No server with index '$i'." );
 926                         }
 927                         // Open a new connection
 928                         $server = $this->mServers[$i];
 929                         $server['serverIndex'] = $i;
 930                         $server['foreignPoolRefCount'] = 0;
 931                         $server['foreign'] = true;
 932                         $server['autoCommitOnly'] = $autoCommit;
 933                         $conn = $this->reallyOpenConnection( $server, $domainInstance );
 934                         if ( !$conn->isOpen() ) {
 935                                 $this->connLogger->warning( __METHOD__ . ": connection error for $i/$domain" );
 936                                 $this->errorConnection = $conn;
 937                                 $conn = false;
 938                         } else {
 939                                 $conn->tablePrefix( $prefix ); // as specified
 940                                 // Note that if $domain is an empty string, getDomainID() might not match it
 941                                 $this->mConns[$connInUseKey][$i][$conn->getDomainID()] = $conn;
 942                                 $this->connLogger->debug( __METHOD__ . ": opened new connection for $i/$domain" );
 943                         }
 944                 }
 945
 946                 // Increment reference count
 947                 if ( $conn instanceof IDatabase ) {
 948                         $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 949                         $conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
 950                 }
 951
 952                 return $conn;
 953         }
 954
 955         /**
 956          * Test if the specified index represents an open connection
 957          *
 958          * @param int $index Server index
 959          * @access private
 960          * @return bool
 961          */
 962         private function isOpen( $index ) {
 963                 if ( !is_int( $index ) ) {
 964                         return false;
 965                 }
 966
 967                 return (bool)$this->getAnyOpenConnection( $index );
 968         }
 969
 970         /**
 971          * Open a new network connection to a server (uncached)
 972          *
 973          * Returns a Database object whether or not the connection was successful.
 974          *
 975          * @param array $server
 976          * @param DatabaseDomain $domainOverride Use an unspecified domain to not select any database
 977          * @return Database
 978          * @throws DBAccessError
 979          * @throws InvalidArgumentException
 980          */
 981         protected function reallyOpenConnection( array $server, DatabaseDomain $domainOverride ) {
 982                 if ( $this->disabled ) {
 983                         throw new DBAccessError();
 984                 }
 985
 986                 if ( $domainOverride->getDatabase() !== null ) {
 987                         $server['dbname'] = $domainOverride->getDatabase();
 988                         $server['schema'] = $domainOverride->getSchema();
 989                 }
 990
 991                 // Let the handle know what the cluster master is (e.g. "db1052")
 992                 $masterName = $this->getServerName( $this->getWriterIndex() );
 993                 $server['clusterMasterHost'] = $masterName;
 994
 995                 // Log when many connection are made on requests
 996                 if ( ++$this->connsOpened >= self::CONN_HELD_WARN_THRESHOLD ) {
 997                         $this->perfLogger->warning( __METHOD__ . ": " .
 998                                 "{$this->connsOpened}+ connections made (master=$masterName)" );
 999                 }
1000
1001                 $server['srvCache'] = $this->srvCache;
1002                 // Set loggers and profilers
1003                 $server['connLogger'] = $this->connLogger;
1004                 $server['queryLogger'] = $this->queryLogger;
1005                 $server['errorLogger'] = $this->errorLogger;
1006                 $server['profiler'] = $this->profiler;
1007                 $server['trxProfiler'] = $this->trxProfiler;
1008                 // Use the same agent and PHP mode for all DB handles
1009                 $server['cliMode'] = $this->cliMode;
1010                 $server['agent'] = $this->agent;
1011                 // Use DBO_DEFAULT flags by default for LoadBalancer managed databases. Assume that the
1012                 // application calls LoadBalancer::commitMasterChanges() before the PHP script completes.
1013                 $server['flags'] = isset( $server['flags'] ) ? $server['flags'] : IDatabase::DBO_DEFAULT;
1014
1015                 // Create a live connection object
1016                 try {
1017                         $db = Database::factory( $server['type'], $server );
1018                 } catch ( DBConnectionError $e ) {
1019                         // FIXME: This is probably the ugliest thing I have ever done to
1020                         // PHP. I'm half-expecting it to segfault, just out of disgust. -- TS
1021                         $db = $e->db;
1022                 }
1023
1024                 $db->setLBInfo( $server );
1025                 $db->setLazyMasterHandle(
1026                         $this->getLazyConnectionRef( self::DB_MASTER, [], $db->getDomainID() )
1027                 );
1028                 $db->setTableAliases( $this->tableAliases );
1029
1030                 if ( $server['serverIndex'] === $this->getWriterIndex() ) {
1031                         if ( $this->trxRoundId !== false ) {
1032                                 $this->applyTransactionRoundFlags( $db );
1033                         }
1034                         foreach ( $this->trxRecurringCallbacks as $name => $callback ) {
1035                                 $db->setTransactionListener( $name, $callback );
1036                         }
1037                 }
1038
1039                 return $db;
1040         }
1041
1042         /**
1043          * @throws DBConnectionError
1044          */
1045         private function reportConnectionError() {
1046                 $conn = $this->errorConnection; // the connection which caused the error
1047                 $context = [
1048                         'method' => __METHOD__,
1049                         'last_error' => $this->mLastError,
1050                 ];
1051
1052                 if ( $conn instanceof IDatabase ) {
1053                         $context['db_server'] = $conn->getServer();
1054                         $this->connLogger->warning(
1055                                 "Connection error: {last_error} ({db_server})",
1056                                 $context
1057                         );
1058
1059                         // throws DBConnectionError
1060                         $conn->reportConnectionError( "{$this->mLastError} ({$context['db_server']})" );
1061                 } else {
1062                         // No last connection, probably due to all servers being too busy
1063                         $this->connLogger->error(
1064                                 "LB failure with no last connection. Connection error: {last_error}",
1065                                 $context
1066                         );
1067
1068                         // If all servers were busy, mLastError will contain something sensible
1069                         throw new DBConnectionError( null, $this->mLastError );
1070                 }
1071         }
1072
1073         public function getWriterIndex() {
1074                 return 0;
1075         }
1076
1077         public function haveIndex( $i ) {
1078                 return array_key_exists( $i, $this->mServers );
1079         }
1080
1081         public function isNonZeroLoad( $i ) {
1082                 return array_key_exists( $i, $this->mServers ) && $this->mLoads[$i] != 0;
1083         }
1084
1085         public function getServerCount() {
1086                 return count( $this->mServers );
1087         }
1088
1089         public function getServerName( $i ) {
1090                 if ( isset( $this->mServers[$i]['hostName'] ) ) {
1091                         $name = $this->mServers[$i]['hostName'];
1092                 } elseif ( isset( $this->mServers[$i]['host'] ) ) {
1093                         $name = $this->mServers[$i]['host'];
1094                 } else {
1095                         $name = '';
1096                 }
1097
1098                 return ( $name != '' ) ? $name : 'localhost';
1099         }
1100
1101         public function getServerType( $i ) {
1102                 return isset( $this->mServers[$i]['type'] ) ? $this->mServers[$i]['type'] : 'unknown';
1103         }
1104
1105         public function getMasterPos() {
1106                 # If this entire request was served from a replica DB without opening a connection to the
1107                 # master (however unlikely that may be), then we can fetch the position from the replica DB.
1108                 $masterConn = $this->getAnyOpenConnection( $this->getWriterIndex() );
1109                 if ( !$masterConn ) {
1110                         $serverCount = count( $this->mServers );
1111                         for ( $i = 1; $i < $serverCount; $i++ ) {
1112                                 $conn = $this->getAnyOpenConnection( $i );
1113                                 if ( $conn ) {
1114                                         return $conn->getReplicaPos();
1115                                 }
1116                         }
1117                 } else {
1118                         return $masterConn->getMasterPos();
1119                 }
1120
1121                 return false;
1122         }
1123
1124         public function disable() {
1125                 $this->closeAll();
1126                 $this->disabled = true;
1127         }
1128
1129         public function closeAll() {
1130                 $this->forEachOpenConnection( function ( IDatabase $conn ) {
1131                         $host = $conn->getServer();
1132                         $this->connLogger->debug( "Closing connection to database '$host'." );
1133                         $conn->close();
1134                 } );
1135
1136                 $this->mConns = [
1137                         self::KEY_LOCAL => [],
1138                         self::KEY_FOREIGN_INUSE => [],
1139                         self::KEY_FOREIGN_FREE => [],
1140                         self::KEY_LOCAL_NOROUND => [],
1141                         self::KEY_FOREIGN_INUSE_NOROUND => [],
1142                         self::KEY_FOREIGN_FREE_NOROUND => []
1143                 ];
1144                 $this->connsOpened = 0;
1145         }
1146
1147         public function closeConnection( IDatabase $conn ) {
1148                 $serverIndex = $conn->getLBInfo( 'serverIndex' ); // second index level of mConns
1149                 foreach ( $this->mConns as $type => $connsByServer ) {
1150                         if ( !isset( $connsByServer[$serverIndex] ) ) {
1151                                 continue;
1152                         }
1153
1154                         foreach ( $connsByServer[$serverIndex] as $i => $trackedConn ) {
1155                                 if ( $conn === $trackedConn ) {
1156                                         $host = $this->getServerName( $i );
1157                                         $this->connLogger->debug( "Closing connection to database $i at '$host'." );
1158                                         unset( $this->mConns[$type][$serverIndex][$i] );
1159                                         --$this->connsOpened;
1160                                         break 2;
1161                                 }
1162                         }
1163                 }
1164
1165                 $conn->close();
1166         }
1167
1168         public function commitAll( $fname = __METHOD__ ) {
1169                 $failures = [];
1170
1171                 $restore = ( $this->trxRoundId !== false );
1172                 $this->trxRoundId = false;
1173                 $this->forEachOpenConnection(
1174                         function ( IDatabase $conn ) use ( $fname, $restore, &$failures ) {
1175                                 try {
1176                                         $conn->commit( $fname, $conn::FLUSHING_ALL_PEERS );
1177                                 } catch ( DBError $e ) {
1178                                         call_user_func( $this->errorLogger, $e );
1179                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1180                                 }
1181                                 if ( $restore && $conn->getLBInfo( 'master' ) ) {
1182                                         $this->undoTransactionRoundFlags( $conn );
1183                                 }
1184                         }
1185                 );
1186
1187                 if ( $failures ) {
1188                         throw new DBExpectedError(
1189                                 null,
1190                                 "Commit failed on server(s) " . implode( "\n", array_unique( $failures ) )
1191                         );
1192                 }
1193         }
1194
1195         public function finalizeMasterChanges() {
1196                 $this->forEachOpenMasterConnection( function ( Database $conn ) {
1197                         // Any error should cause all DB transactions to be rolled back together
1198                         $conn->setTrxEndCallbackSuppression( false );
1199                         $conn->runOnTransactionPreCommitCallbacks();
1200                         // Defer post-commit callbacks until COMMIT finishes for all DBs
1201                         $conn->setTrxEndCallbackSuppression( true );
1202                 } );
1203         }
1204
1205         public function approveMasterChanges( array $options ) {
1206                 $limit = isset( $options['maxWriteDuration'] ) ? $options['maxWriteDuration'] : 0;
1207                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( $limit ) {
1208                         // If atomic sections or explicit transactions are still open, some caller must have
1209                         // caught an exception but failed to properly rollback any changes. Detect that and
1210                         // throw and error (causing rollback).
1211                         if ( $conn->explicitTrxActive() ) {
1212                                 throw new DBTransactionError(
1213                                         $conn,
1214                                         "Explicit transaction still active. A caller may have caught an error."
1215                                 );
1216                         }
1217                         // Assert that the time to replicate the transaction will be sane.
1218                         // If this fails, then all DB transactions will be rollback back together.
1219                         $time = $conn->pendingWriteQueryDuration( $conn::ESTIMATE_DB_APPLY );
1220                         if ( $limit > 0 && $time > $limit ) {
1221                                 throw new DBTransactionSizeError(
1222                                         $conn,
1223                                         "Transaction spent $time second(s) in writes, exceeding the limit of $limit.",
1224                                         [ $time, $limit ]
1225                                 );
1226                         }
1227                         // If a connection sits idle while slow queries execute on another, that connection
1228                         // may end up dropped before the commit round is reached. Ping servers to detect this.
1229                         if ( $conn->writesOrCallbacksPending() && !$conn->ping() ) {
1230                                 throw new DBTransactionError(
1231                                         $conn,
1232                                         "A connection to the {$conn->getDBname()} database was lost before commit."
1233                                 );
1234                         }
1235                 } );
1236         }
1237
1238         public function beginMasterChanges( $fname = __METHOD__ ) {
1239                 if ( $this->trxRoundId !== false ) {
1240                         throw new DBTransactionError(
1241                                 null,
1242                                 "$fname: Transaction round '{$this->trxRoundId}' already started."
1243                         );
1244                 }
1245                 $this->trxRoundId = $fname;
1246
1247                 $failures = [];
1248                 $this->forEachOpenMasterConnection(
1249                         function ( Database $conn ) use ( $fname, &$failures ) {
1250                                 $conn->setTrxEndCallbackSuppression( true );
1251                                 try {
1252                                         $conn->flushSnapshot( $fname );
1253                                 } catch ( DBError $e ) {
1254                                         call_user_func( $this->errorLogger, $e );
1255                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1256                                 }
1257                                 $conn->setTrxEndCallbackSuppression( false );
1258                                 $this->applyTransactionRoundFlags( $conn );
1259                         }
1260                 );
1261
1262                 if ( $failures ) {
1263                         throw new DBExpectedError(
1264                                 null,
1265                                 "$fname: Flush failed on server(s) " . implode( "\n", array_unique( $failures ) )
1266                         );
1267                 }
1268         }
1269
1270         public function commitMasterChanges( $fname = __METHOD__ ) {
1271                 $failures = [];
1272
1273                 /** @noinspection PhpUnusedLocalVariableInspection */
1274                 $scope = $this->getScopedPHPBehaviorForCommit(); // try to ignore client aborts
1275
1276                 $restore = ( $this->trxRoundId !== false );
1277                 $this->trxRoundId = false;
1278                 $this->forEachOpenMasterConnection(
1279                         function ( IDatabase $conn ) use ( $fname, $restore, &$failures ) {
1280                                 try {
1281                                         if ( $conn->writesOrCallbacksPending() ) {
1282                                                 $conn->commit( $fname, $conn::FLUSHING_ALL_PEERS );
1283                                         } elseif ( $restore ) {
1284                                                 $conn->flushSnapshot( $fname );
1285                                         }
1286                                 } catch ( DBError $e ) {
1287                                         call_user_func( $this->errorLogger, $e );
1288                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1289                                 }
1290                                 if ( $restore ) {
1291                                         $this->undoTransactionRoundFlags( $conn );
1292                                 }
1293                         }
1294                 );
1295
1296                 if ( $failures ) {
1297                         throw new DBExpectedError(
1298                                 null,
1299                                 "$fname: Commit failed on server(s) " . implode( "\n", array_unique( $failures ) )
1300                         );
1301                 }
1302         }
1303
1304         public function runMasterPostTrxCallbacks( $type ) {
1305                 $e = null; // first exception
1306                 $this->forEachOpenMasterConnection( function ( Database $conn ) use ( $type, &$e ) {
1307                         $conn->setTrxEndCallbackSuppression( false );
1308                         if ( $conn->writesOrCallbacksPending() ) {
1309                                 // This happens if onTransactionIdle() callbacks leave callbacks on *another* DB
1310                                 // (which finished its callbacks already). Warn and recover in this case. Let the
1311                                 // callbacks run in the final commitMasterChanges() in LBFactory::shutdown().
1312                                 $this->queryLogger->info( __METHOD__ . ": found writes/callbacks pending." );
1313                                 return;
1314                         } elseif ( $conn->trxLevel() ) {
1315                                 // This happens for single-DB setups where DB_REPLICA uses the master DB,
1316                                 // thus leaving an implicit read-only transaction open at this point. It
1317                                 // also happens if onTransactionIdle() callbacks leave implicit transactions
1318                                 // open on *other* DBs (which is slightly improper). Let these COMMIT on the
1319                                 // next call to commitMasterChanges(), possibly in LBFactory::shutdown().
1320                                 return;
1321                         }
1322                         try {
1323                                 $conn->runOnTransactionIdleCallbacks( $type );
1324                         } catch ( Exception $ex ) {
1325                                 $e = $e ?: $ex;
1326                         }
1327                         try {
1328                                 $conn->runTransactionListenerCallbacks( $type );
1329                         } catch ( Exception $ex ) {
1330                                 $e = $e ?: $ex;
1331                         }
1332                 } );
1333
1334                 return $e;
1335         }
1336
1337         public function rollbackMasterChanges( $fname = __METHOD__ ) {
1338                 $restore = ( $this->trxRoundId !== false );
1339                 $this->trxRoundId = false;
1340                 $this->forEachOpenMasterConnection(
1341                         function ( IDatabase $conn ) use ( $fname, $restore ) {
1342                                 if ( $conn->writesOrCallbacksPending() ) {
1343                                         $conn->rollback( $fname, $conn::FLUSHING_ALL_PEERS );
1344                                 }
1345                                 if ( $restore ) {
1346                                         $this->undoTransactionRoundFlags( $conn );
1347                                 }
1348                         }
1349                 );
1350         }
1351
1352         public function suppressTransactionEndCallbacks() {
1353                 $this->forEachOpenMasterConnection( function ( Database $conn ) {
1354                         $conn->setTrxEndCallbackSuppression( true );
1355                 } );
1356         }
1357
1358         /**
1359          * @param IDatabase $conn
1360          */
1361         private function applyTransactionRoundFlags( IDatabase $conn ) {
1362                 if ( $conn->getLBInfo( 'autoCommitOnly' ) ) {
1363                         return; // transaction rounds do not apply to these connections
1364                 }
1365
1366                 if ( $conn->getFlag( $conn::DBO_DEFAULT ) ) {
1367                         // DBO_TRX is controlled entirely by CLI mode presence with DBO_DEFAULT.
1368                         // Force DBO_TRX even in CLI mode since a commit round is expected soon.
1369                         $conn->setFlag( $conn::DBO_TRX, $conn::REMEMBER_PRIOR );
1370                         // If config has explicitly requested DBO_TRX be either on or off by not
1371                         // setting DBO_DEFAULT, then respect that. Forcing no transactions is useful
1372                         // for things like blob stores (ExternalStore) which want auto-commit mode.
1373                 }
1374         }
1375
1376         /**
1377          * @param IDatabase $conn
1378          */
1379         private function undoTransactionRoundFlags( IDatabase $conn ) {
1380                 if ( $conn->getLBInfo( 'autoCommitOnly' ) ) {
1381                         return; // transaction rounds do not apply to these connections
1382                 }
1383
1384                 if ( $conn->getFlag( $conn::DBO_DEFAULT ) ) {
1385                         $conn->restoreFlags( $conn::RESTORE_PRIOR );
1386                 }
1387         }
1388
1389         public function flushReplicaSnapshots( $fname = __METHOD__ ) {
1390                 $this->forEachOpenReplicaConnection( function ( IDatabase $conn ) {
1391                         $conn->flushSnapshot( __METHOD__ );
1392                 } );
1393         }
1394
1395         public function hasMasterConnection() {
1396                 return $this->isOpen( $this->getWriterIndex() );
1397         }
1398
1399         public function hasMasterChanges() {
1400                 $pending = 0;
1401                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$pending ) {
1402                         $pending |= $conn->writesOrCallbacksPending();
1403                 } );
1404
1405                 return (bool)$pending;
1406         }
1407
1408         public function lastMasterChangeTimestamp() {
1409                 $lastTime = false;
1410                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$lastTime ) {
1411                         $lastTime = max( $lastTime, $conn->lastDoneWrites() );
1412                 } );
1413
1414                 return $lastTime;
1415         }
1416
1417         public function hasOrMadeRecentMasterChanges( $age = null ) {
1418                 $age = ( $age === null ) ? $this->mWaitTimeout : $age;
1419
1420                 return ( $this->hasMasterChanges()
1421                         || $this->lastMasterChangeTimestamp() > microtime( true ) - $age );
1422         }
1423
1424         public function pendingMasterChangeCallers() {
1425                 $fnames = [];
1426                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$fnames ) {
1427                         $fnames = array_merge( $fnames, $conn->pendingWriteCallers() );
1428                 } );
1429
1430                 return $fnames;
1431         }
1432
1433         public function getLaggedReplicaMode( $domain = false ) {
1434                 // No-op if there is only one DB (also avoids recursion)
1435                 if ( !$this->laggedReplicaMode && $this->getServerCount() > 1 ) {
1436                         try {
1437                                 // See if laggedReplicaMode gets set
1438                                 $conn = $this->getConnection( self::DB_REPLICA, false, $domain );
1439                                 $this->reuseConnection( $conn );
1440                         } catch ( DBConnectionError $e ) {
1441                                 // Avoid expensive re-connect attempts and failures
1442                                 $this->allReplicasDownMode = true;
1443                                 $this->laggedReplicaMode = true;
1444                         }
1445                 }
1446
1447                 return $this->laggedReplicaMode;
1448         }
1449
1450         /**
1451          * @param bool $domain
1452          * @return bool
1453          * @deprecated 1.28; use getLaggedReplicaMode()
1454          */
1455         public function getLaggedSlaveMode( $domain = false ) {
1456                 return $this->getLaggedReplicaMode( $domain );
1457         }
1458
1459         public function laggedReplicaUsed() {
1460                 return $this->laggedReplicaMode;
1461         }
1462
1463         /**
1464          * @return bool
1465          * @since 1.27
1466          * @deprecated Since 1.28; use laggedReplicaUsed()
1467          */
1468         public function laggedSlaveUsed() {
1469                 return $this->laggedReplicaUsed();
1470         }
1471
1472         public function getReadOnlyReason( $domain = false, IDatabase $conn = null ) {
1473                 if ( $this->readOnlyReason !== false ) {
1474                         return $this->readOnlyReason;
1475                 } elseif ( $this->getLaggedReplicaMode( $domain ) ) {
1476                         if ( $this->allReplicasDownMode ) {
1477                                 return 'The database has been automatically locked ' .
1478                                         'until the replica database servers become available';
1479                         } else {
1480                                 return 'The database has been automatically locked ' .
1481                                         'while the replica database servers catch up to the master.';
1482                         }
1483                 } elseif ( $this->masterRunningReadOnly( $domain, $conn ) ) {
1484                         return 'The database master is running in read-only mode.';
1485                 }
1486
1487                 return false;
1488         }
1489
1490         /**
1491          * @param string $domain Domain ID, or false for the current domain
1492          * @param IDatabase|null $conn DB master connectionl used to avoid loops [optional]
1493          * @return bool
1494          */
1495         private function masterRunningReadOnly( $domain, IDatabase $conn = null ) {
1496                 $cache = $this->wanCache;
1497                 $masterServer = $this->getServerName( $this->getWriterIndex() );
1498
1499                 return (bool)$cache->getWithSetCallback(
1500                         $cache->makeGlobalKey( __CLASS__, 'server-read-only', $masterServer ),
1501                         self::TTL_CACHE_READONLY,
1502                         function () use ( $domain, $conn ) {
1503                                 $old = $this->trxProfiler->setSilenced( true );
1504                                 try {
1505                                         $dbw = $conn ?: $this->getConnection( self::DB_MASTER, [], $domain );
1506                                         $readOnly = (int)$dbw->serverIsReadOnly();
1507                                         if ( !$conn ) {
1508                                                 $this->reuseConnection( $dbw );
1509                                         }
1510                                 } catch ( DBError $e ) {
1511                                         $readOnly = 0;
1512                                 }
1513                                 $this->trxProfiler->setSilenced( $old );
1514                                 return $readOnly;
1515                         },
1516                         [ 'pcTTL' => $cache::TTL_PROC_LONG, 'busyValue' => 0 ]
1517                 );
1518         }
1519
1520         public function allowLagged( $mode = null ) {
1521                 if ( $mode === null ) {
1522                         return $this->mAllowLagged;
1523                 }
1524                 $this->mAllowLagged = $mode;
1525
1526                 return $this->mAllowLagged;
1527         }
1528
1529         public function pingAll() {
1530                 $success = true;
1531                 $this->forEachOpenConnection( function ( IDatabase $conn ) use ( &$success ) {
1532                         if ( !$conn->ping() ) {
1533                                 $success = false;
1534                         }
1535                 } );
1536
1537                 return $success;
1538         }
1539
1540         public function forEachOpenConnection( $callback, array $params = [] ) {
1541                 foreach ( $this->mConns as $connsByServer ) {
1542                         foreach ( $connsByServer as $serverConns ) {
1543                                 foreach ( $serverConns as $conn ) {
1544                                         $mergedParams = array_merge( [ $conn ], $params );
1545                                         call_user_func_array( $callback, $mergedParams );
1546                                 }
1547                         }
1548                 }
1549         }
1550
1551         public function forEachOpenMasterConnection( $callback, array $params = [] ) {
1552                 $masterIndex = $this->getWriterIndex();
1553                 foreach ( $this->mConns as $connsByServer ) {
1554                         if ( isset( $connsByServer[$masterIndex] ) ) {
1555                                 /** @var IDatabase $conn */
1556                                 foreach ( $connsByServer[$masterIndex] as $conn ) {
1557                                         $mergedParams = array_merge( [ $conn ], $params );
1558                                         call_user_func_array( $callback, $mergedParams );
1559                                 }
1560                         }
1561                 }
1562         }
1563
1564         public function forEachOpenReplicaConnection( $callback, array $params = [] ) {
1565                 foreach ( $this->mConns as $connsByServer ) {
1566                         foreach ( $connsByServer as $i => $serverConns ) {
1567                                 if ( $i === $this->getWriterIndex() ) {
1568                                         continue; // skip master
1569                                 }
1570                                 foreach ( $serverConns as $conn ) {
1571                                         $mergedParams = array_merge( [ $conn ], $params );
1572                                         call_user_func_array( $callback, $mergedParams );
1573                                 }
1574                         }
1575                 }
1576         }
1577
1578         public function getMaxLag( $domain = false ) {
1579                 $maxLag = -1;
1580                 $host = '';
1581                 $maxIndex = 0;
1582
1583                 if ( $this->getServerCount() <= 1 ) {
1584                         return [ $host, $maxLag, $maxIndex ]; // no replication = no lag
1585                 }
1586
1587                 $lagTimes = $this->getLagTimes( $domain );
1588                 foreach ( $lagTimes as $i => $lag ) {
1589                         if ( $this->mLoads[$i] > 0 && $lag > $maxLag ) {
1590                                 $maxLag = $lag;
1591                                 $host = $this->mServers[$i]['host'];
1592                                 $maxIndex = $i;
1593                         }
1594                 }
1595
1596                 return [ $host, $maxLag, $maxIndex ];
1597         }
1598
1599         public function getLagTimes( $domain = false ) {
1600                 if ( $this->getServerCount() <= 1 ) {
1601                         return [ $this->getWriterIndex() => 0 ]; // no replication = no lag
1602                 }
1603
1604                 $knownLagTimes = []; // map of (server index => 0 seconds)
1605                 $indexesWithLag = [];
1606                 foreach ( $this->mServers as $i => $server ) {
1607                         if ( empty( $server['is static'] ) ) {
1608                                 $indexesWithLag[] = $i; // DB server might have replication lag
1609                         } else {
1610                                 $knownLagTimes[$i] = 0; // DB server is a non-replicating and read-only archive
1611                         }
1612                 }
1613
1614                 return $this->getLoadMonitor()->getLagTimes( $indexesWithLag, $domain ) + $knownLagTimes;
1615         }
1616
1617         public function safeGetLag( IDatabase $conn ) {
1618                 if ( $this->getServerCount() <= 1 ) {
1619                         return 0;
1620                 } else {
1621                         return $conn->getLag();
1622                 }
1623         }
1624
1625         /**
1626          * @param IDatabase $conn
1627          * @param DBMasterPos|bool $pos
1628          * @param int $timeout
1629          * @return bool
1630          */
1631         public function safeWaitForMasterPos( IDatabase $conn, $pos = false, $timeout = 10 ) {
1632                 if ( $this->getServerCount() <= 1 || !$conn->getLBInfo( 'replica' ) ) {
1633                         return true; // server is not a replica DB
1634                 }
1635
1636                 if ( !$pos ) {
1637                         // Get the current master position, opening a connection if needed
1638                         $masterConn = $this->getAnyOpenConnection( $this->getWriterIndex() );
1639                         if ( $masterConn ) {
1640                                 $pos = $masterConn->getMasterPos();
1641                         } else {
1642                                 $masterConn = $this->openConnection( $this->getWriterIndex(), self::DOMAIN_ANY );
1643                                 $pos = $masterConn->getMasterPos();
1644                                 $this->closeConnection( $masterConn );
1645                         }
1646                 }
1647
1648                 if ( $pos instanceof DBMasterPos ) {
1649                         $result = $conn->masterPosWait( $pos, $timeout );
1650                         if ( $result == -1 || is_null( $result ) ) {
1651                                 $msg = __METHOD__ . ': Timed out waiting on {host} pos {pos}';
1652                                 $this->replLogger->warning( $msg,
1653                                         [ 'host' => $conn->getServer(), 'pos' => $pos ] );
1654                                 $ok = false;
1655                         } else {
1656                                 $this->replLogger->info( __METHOD__ . ': Done' );
1657                                 $ok = true;
1658                         }
1659                 } else {
1660                         $ok = false; // something is misconfigured
1661                         $this->replLogger->error( 'Could not get master pos for {host}',
1662                                 [ 'host' => $conn->getServer() ] );
1663                 }
1664
1665                 return $ok;
1666         }
1667
1668         public function setTransactionListener( $name, callable $callback = null ) {
1669                 if ( $callback ) {
1670                         $this->trxRecurringCallbacks[$name] = $callback;
1671                 } else {
1672                         unset( $this->trxRecurringCallbacks[$name] );
1673                 }
1674                 $this->forEachOpenMasterConnection(
1675                         function ( IDatabase $conn ) use ( $name, $callback ) {
1676                                 $conn->setTransactionListener( $name, $callback );
1677                         }
1678                 );
1679         }
1680
1681         public function setTableAliases( array $aliases ) {
1682                 $this->tableAliases = $aliases;
1683         }
1684
1685         public function setDomainPrefix( $prefix ) {
1686                 // Find connections to explicit foreign domains still marked as in-use...
1687                 $domainsInUse = [];
1688                 $this->forEachOpenConnection( function ( IDatabase $conn ) use ( &$domainsInUse ) {
1689                         // Once reuseConnection() is called on a handle, its reference count goes from 1 to 0.
1690                         // Until then, it is still in use by the caller (explicitly or via DBConnRef scope).
1691                         if ( $conn->getLBInfo( 'foreignPoolRefCount' ) > 0 ) {
1692                                 $domainsInUse[] = $conn->getDomainID();
1693                         }
1694                 } );
1695
1696                 // Do not switch connections to explicit foreign domains unless marked as safe
1697                 if ( $domainsInUse ) {
1698                         $domains = implode( ', ', $domainsInUse );
1699                         throw new DBUnexpectedError( null,
1700                                 "Foreign domain connections are still in use ($domains)." );
1701                 }
1702
1703                 $oldDomain = $this->localDomain->getId();
1704                 $this->setLocalDomain( new DatabaseDomain(
1705                         $this->localDomain->getDatabase(),
1706                         $this->localDomain->getSchema(),
1707                         $prefix
1708                 ) );
1709
1710                 $this->forEachOpenConnection( function ( IDatabase $db ) use ( $prefix, $oldDomain ) {
1711                         if ( !$db->getLBInfo( 'foreign' ) ) {
1712                                 $db->tablePrefix( $prefix );
1713                         }
1714                 } );
1715         }
1716
1717         /**
1718          * @param DatabaseDomain $domain
1719          */
1720         private function setLocalDomain( DatabaseDomain $domain ) {
1721                 $this->localDomain = $domain;
1722                 // In case a caller assumes that the domain ID is simply <db>-<prefix>, which is almost
1723                 // always true, gracefully handle the case when they fail to account for escaping.
1724                 if ( $this->localDomain->getTablePrefix() != '' ) {
1725                         $this->localDomainIdAlias =
1726                                 $this->localDomain->getDatabase() . '-' . $this->localDomain->getTablePrefix();
1727                 } else {
1728                         $this->localDomainIdAlias = $this->localDomain->getDatabase();
1729                 }
1730         }
1731
1732         /**
1733          * Make PHP ignore user aborts/disconnects until the returned
1734          * value leaves scope. This returns null and does nothing in CLI mode.
1735          *
1736          * @return ScopedCallback|null
1737          */
1738         final protected function getScopedPHPBehaviorForCommit() {
1739                 if ( PHP_SAPI != 'cli' ) { // https://bugs.php.net/bug.php?id=47540
1740                         $old = ignore_user_abort( true ); // avoid half-finished operations
1741                         return new ScopedCallback( function () use ( $old ) {
1742                                 ignore_user_abort( $old );
1743                         } );
1744                 }
1745
1746                 return null;
1747         }
1748
1749         function __destruct() {
1750                 // Avoid connection leaks for sanity
1751                 $this->disable();
1752         }
1753 }
1754
1755 class_alias( LoadBalancer::class, 'LoadBalancer' );