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 $servers;
  43         /** @var Database[][][] Map of (connection category => server index => IDatabase[]) */
  44         private $conns;
  45         /** @var float[] Map of (server index => weight) */
  46         private $loads;
  47         /** @var array[] Map of (group => server index => weight) */
  48         private $groupLoads;
  49         /** @var bool Whether to disregard replica DB lag as a factor in replica DB selection */
  50         private $allowLagged;
  51         /** @var int Seconds to spend waiting on replica DB lag to resolve */
  52         private $waitTimeout;
  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 $readIndex;
  83         /** @var bool|DBMasterPos False if not set */
  84         private $waitForPos;
  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 $lastError = '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->servers = $params['servers'];
 143                 foreach ( $this->servers as $i => $server ) {
 144                         if ( $i == 0 ) {
 145                                 $this->servers[$i]['master'] = true;
 146                         } else {
 147                                 $this->servers[$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->waitTimeout = isset( $params['waitTimeout'] )
 157                         ? $params['waitTimeout']
 158                         : self::MAX_WAIT_DEFAULT;
 159
 160                 $this->readIndex = -1;
 161                 $this->conns = [
 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->loads = [];
 172                 $this->waitForPos = false;
 173                 $this->allowLagged = 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                         $this->loads[$i] = $server['load'];
 192                         if ( isset( $server['groupLoads'] ) ) {
 193                                 foreach ( $server['groupLoads'] as $group => $ratio ) {
 194                                         if ( !isset( $this->groupLoads[$group] ) ) {
 195                                                 $this->groupLoads[$group] = [];
 196                                         }
 197                                         $this->groupLoads[$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( $this->servers[$i]['max lag'] )
 293                                         ? $this->servers[$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->servers ) == 1 ) {
 336                         // Skip the load balancing if there's only one server
 337                         return $this->getWriterIndex();
 338                 } elseif ( $group === false && $this->readIndex >= 0 ) {
 339                         // Shortcut if the generic reader index was already cached
 340                         return $this->readIndex;
 341                 }
 342
 343                 if ( $group !== false ) {
 344                         // Use the server weight array for this load group
 345                         if ( isset( $this->groupLoads[$group] ) ) {
 346                                 $loads = $this->groupLoads[$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->loads;
 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->waitForPos && $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->readIndex <= 0 && $this->loads[$i] > 0 && $group === false ) {
 379                         // Cache the generic reader index for future ungrouped DB_REPLICA handles
 380                         $this->readIndex = $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->allowLagged || $laggedReplicaMode ) {
 412                                 $i = ArrayUtils::pickRandom( $currentLoads );
 413                         } else {
 414                                 $i = false;
 415                                 if ( $this->waitForPos && $this->waitForPos->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->waitForPos->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->waitForPos;
 475                 try {
 476                         $this->waitForPos = $pos;
 477                         // If a generic reader connection was already established, then wait now
 478                         $i = $this->readIndex;
 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->waitForPos;
 492                 try {
 493                         $this->waitForPos = $pos;
 494
 495                         $i = $this->readIndex;
 496                         if ( $i <= 0 ) {
 497                                 // Pick a generic replica DB if there isn't one yet
 498                                 $readLoads = $this->loads;
 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->waitForPos = $oldPos;
 512                 }
 513
 514                 return $ok;
 515         }
 516
 517         public function waitForAll( $pos, $timeout = null ) {
 518                 $timeout = $timeout ?: $this->waitTimeout;
 519
 520                 $oldPos = $this->waitForPos;
 521                 try {
 522                         $this->waitForPos = $pos;
 523                         $serverCount = count( $this->servers );
 524
 525                         $ok = true;
 526                         for ( $i = 1; $i < $serverCount; $i++ ) {
 527                                 if ( $this->loads[$i] > 0 ) {
 528                                         $start = microtime( true );
 529                                         $ok = $this->doWait( $i, true, $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->waitForPos = $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->waitForPos || $pos->hasReached( $this->waitForPos ) ) {
 553                         $this->waitForPos = $pos;
 554                 }
 555         }
 556
 557         /**
 558          * @param int $i
 559          * @return IDatabase|bool
 560          */
 561         public function getAnyOpenConnection( $i ) {
 562                 foreach ( $this->conns 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 "waitTimeout" given to __construct()
 579          * @return bool
 580          */
 581         protected function doWait( $index, $open = false, $timeout = null ) {
 582                 $timeout = max( 1, $timeout ?: $this->waitTimeout );
 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->waitForPos )
 592                 ) {
 593                         $this->replLogger->debug(
 594                                 __METHOD__ .
 595                                 ': replica DB {dbserver} known to be caught up (pos >= $knownReachedPos).',
 596                                 [ 'dbserver' => $server ]
 597                         );
 598                         return true;
 599                 }
 600
 601                 // Find a connection to wait on, creating one if needed and allowed
 602                 $close = false; // close the connection afterwards
 603                 $conn = $this->getAnyOpenConnection( $index );
 604                 if ( !$conn ) {
 605                         if ( !$open ) {
 606                                 $this->replLogger->debug(
 607                                         __METHOD__ . ': no connection open for {dbserver}',
 608                                         [ 'dbserver' => $server ]
 609                                 );
 610
 611                                 return false;
 612                         } else {
 613                                 $conn = $this->openConnection( $index, self::DOMAIN_ANY );
 614                                 if ( !$conn ) {
 615                                         $this->replLogger->warning(
 616                                                 __METHOD__ . ': failed to connect to {dbserver}',
 617                                                 [ 'dbserver' => $server ]
 618                                         );
 619
 620                                         return false;
 621                                 }
 622                                 // Avoid connection spam in waitForAll() when connections
 623                                 // are made just for the sake of doing this lag check.
 624                                 $close = true;
 625                         }
 626                 }
 627
 628                 $this->replLogger->info(
 629                         __METHOD__ .
 630                         ': Waiting for replica DB {dbserver} to catch up...',
 631                         [ 'dbserver' => $server ]
 632                 );
 633
 634                 $result = $conn->masterPosWait( $this->waitForPos, $timeout );
 635
 636                 if ( $result === null ) {
 637                         $this->replLogger->warning(
 638                                 __METHOD__ . ': Errored out waiting on {host} pos {pos}',
 639                                 [
 640                                         'host' => $server,
 641                                         'pos' => $this->waitForPos,
 642                                         'trace' => ( new RuntimeException() )->getTraceAsString()
 643                                 ]
 644                         );
 645                         $ok = false;
 646                 } elseif ( $result == -1 ) {
 647                         $this->replLogger->warning(
 648                                 __METHOD__ . ': Timed out waiting on {host} pos {pos}',
 649                                 [
 650                                         'host' => $server,
 651                                         'pos' => $this->waitForPos,
 652                                         'trace' => ( new RuntimeException() )->getTraceAsString()
 653                                 ]
 654                         );
 655                         $ok = false;
 656                 } else {
 657                         $this->replLogger->info( __METHOD__ . ": Done" );
 658                         $ok = true;
 659                         // Remember that the DB reached this point
 660                         $this->srvCache->set( $key, $this->waitForPos, BagOStuff::TTL_DAY );
 661                 }
 662
 663                 if ( $close ) {
 664                         $this->closeConnection( $conn );
 665                 }
 666
 667                 return $ok;
 668         }
 669
 670         public function getConnection( $i, $groups = [], $domain = false, $flags = 0 ) {
 671                 if ( $i === null || $i === false ) {
 672                         throw new InvalidArgumentException( 'Attempt to call ' . __METHOD__ .
 673                                 ' with invalid server index' );
 674                 }
 675
 676                 if ( $this->localDomain->equals( $domain ) || $domain === $this->localDomainIdAlias ) {
 677                         $domain = false; // local connection requested
 678                 }
 679
 680                 $groups = ( $groups === false || $groups === [] )
 681                         ? [ false ] // check one "group": the generic pool
 682                         : (array)$groups;
 683
 684                 $masterOnly = ( $i == self::DB_MASTER || $i == $this->getWriterIndex() );
 685                 $oldConnsOpened = $this->connsOpened; // connections open now
 686
 687                 if ( $i == self::DB_MASTER ) {
 688                         $i = $this->getWriterIndex();
 689                 } else {
 690                         # Try to find an available server in any the query groups (in order)
 691                         foreach ( $groups as $group ) {
 692                                 $groupIndex = $this->getReaderIndex( $group, $domain );
 693                                 if ( $groupIndex !== false ) {
 694                                         $i = $groupIndex;
 695                                         break;
 696                                 }
 697                         }
 698                 }
 699
 700                 # Operation-based index
 701                 if ( $i == self::DB_REPLICA ) {
 702                         $this->lastError = 'Unknown error'; // reset error string
 703                         # Try the general server pool if $groups are unavailable.
 704                         $i = ( $groups === [ false ] )
 705                                 ? false // don't bother with this if that is what was tried above
 706                                 : $this->getReaderIndex( false, $domain );
 707                         # Couldn't find a working server in getReaderIndex()?
 708                         if ( $i === false ) {
 709                                 $this->lastError = 'No working replica DB server: ' . $this->lastError;
 710                                 // Throw an exception
 711                                 $this->reportConnectionError();
 712                                 return null; // not reached
 713                         }
 714                 }
 715
 716                 # Now we have an explicit index into the servers array
 717                 $conn = $this->openConnection( $i, $domain, $flags );
 718                 if ( !$conn ) {
 719                         // Throw an exception
 720                         $this->reportConnectionError();
 721                         return null; // not reached
 722                 }
 723
 724                 # Profile any new connections that happen
 725                 if ( $this->connsOpened > $oldConnsOpened ) {
 726                         $host = $conn->getServer();
 727                         $dbname = $conn->getDBname();
 728                         $this->trxProfiler->recordConnection( $host, $dbname, $masterOnly );
 729                 }
 730
 731                 if ( $masterOnly ) {
 732                         # Make master-requested DB handles inherit any read-only mode setting
 733                         $conn->setLBInfo( 'readOnlyReason', $this->getReadOnlyReason( $domain, $conn ) );
 734                 }
 735
 736                 return $conn;
 737         }
 738
 739         public function reuseConnection( $conn ) {
 740                 $serverIndex = $conn->getLBInfo( 'serverIndex' );
 741                 $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 742                 if ( $serverIndex === null || $refCount === null ) {
 743                         /**
 744                          * This can happen in code like:
 745                          *   foreach ( $dbs as $db ) {
 746                          *     $conn = $lb->getConnection( $lb::DB_REPLICA, [], $db );
 747                          *     ...
 748                          *     $lb->reuseConnection( $conn );
 749                          *   }
 750                          * When a connection to the local DB is opened in this way, reuseConnection()
 751                          * should be ignored
 752                          */
 753                         return;
 754                 } elseif ( $conn instanceof DBConnRef ) {
 755                         // DBConnRef already handles calling reuseConnection() and only passes the live
 756                         // Database instance to this method. Any caller passing in a DBConnRef is broken.
 757                         $this->connLogger->error( __METHOD__ . ": got DBConnRef instance.\n" .
 758                                 ( new RuntimeException() )->getTraceAsString() );
 759
 760                         return;
 761                 }
 762
 763                 if ( $this->disabled ) {
 764                         return; // DBConnRef handle probably survived longer than the LoadBalancer
 765                 }
 766
 767                 if ( $conn->getLBInfo( 'autoCommitOnly' ) ) {
 768                         $connFreeKey = self::KEY_FOREIGN_FREE_NOROUND;
 769                         $connInUseKey = self::KEY_FOREIGN_INUSE_NOROUND;
 770                 } else {
 771                         $connFreeKey = self::KEY_FOREIGN_FREE;
 772                         $connInUseKey = self::KEY_FOREIGN_INUSE;
 773                 }
 774
 775                 $domain = $conn->getDomainID();
 776                 if ( !isset( $this->conns[$connInUseKey][$serverIndex][$domain] ) ) {
 777                         throw new InvalidArgumentException( __METHOD__ .
 778                                 ": connection $serverIndex/$domain not found; it may have already been freed." );
 779                 } elseif ( $this->conns[$connInUseKey][$serverIndex][$domain] !== $conn ) {
 780                         throw new InvalidArgumentException( __METHOD__ .
 781                                 ": connection $serverIndex/$domain mismatched; it may have already been freed." );
 782                 }
 783
 784                 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
 785                 if ( $refCount <= 0 ) {
 786                         $this->conns[$connFreeKey][$serverIndex][$domain] = $conn;
 787                         unset( $this->conns[$connInUseKey][$serverIndex][$domain] );
 788                         if ( !$this->conns[$connInUseKey][$serverIndex] ) {
 789                                 unset( $this->conns[$connInUseKey][$serverIndex] ); // clean up
 790                         }
 791                         $this->connLogger->debug( __METHOD__ . ": freed connection $serverIndex/$domain" );
 792                 } else {
 793                         $this->connLogger->debug( __METHOD__ .
 794                                 ": reference count for $serverIndex/$domain reduced to $refCount" );
 795                 }
 796         }
 797
 798         public function getConnectionRef( $db, $groups = [], $domain = false, $flags = 0 ) {
 799                 $domain = ( $domain !== false ) ? $domain : $this->localDomain;
 800
 801                 return new DBConnRef( $this, $this->getConnection( $db, $groups, $domain, $flags ) );
 802         }
 803
 804         public function getLazyConnectionRef( $db, $groups = [], $domain = false, $flags = 0 ) {
 805                 $domain = ( $domain !== false ) ? $domain : $this->localDomain;
 806
 807                 return new DBConnRef( $this, [ $db, $groups, $domain, $flags ] );
 808         }
 809
 810         public function getMaintenanceConnectionRef( $db, $groups = [], $domain = false, $flags = 0 ) {
 811                 $domain = ( $domain !== false ) ? $domain : $this->localDomain;
 812
 813                 return new MaintainableDBConnRef(
 814                         $this, $this->getConnection( $db, $groups, $domain, $flags ) );
 815         }
 816
 817         public function openConnection( $i, $domain = false, $flags = 0 ) {
 818                 if ( $this->localDomain->equals( $domain ) || $domain === $this->localDomainIdAlias ) {
 819                         $domain = false; // local connection requested
 820                 }
 821
 822                 if ( !$this->chronProtInitialized && $this->chronProt ) {
 823                         $this->connLogger->debug( __METHOD__ . ': calling initLB() before first connection.' );
 824                         // Load CP positions before connecting so that doWait() triggers later if needed
 825                         $this->chronProtInitialized = true;
 826                         $this->chronProt->initLB( $this );
 827                 }
 828
 829                 // Check if an auto-commit connection is being requested. If so, it will not reuse the
 830                 // main set of DB connections but rather its own pool since:
 831                 // a) those are usually set to implicitly use transaction rounds via DBO_TRX
 832                 // b) those must support the use of explicit transaction rounds via beginMasterChanges()
 833                 $autoCommit = ( ( $flags & self::CONN_TRX_AUTO ) == self::CONN_TRX_AUTO );
 834
 835                 if ( $domain !== false ) {
 836                         // Connection is to a foreign domain
 837                         $conn = $this->openForeignConnection( $i, $domain, $flags );
 838                 } else {
 839                         // Connection is to the local domain
 840                         $connKey = $autoCommit ? self::KEY_LOCAL_NOROUND : self::KEY_LOCAL;
 841                         if ( isset( $this->conns[$connKey][$i][0] ) ) {
 842                                 $conn = $this->conns[$connKey][$i][0];
 843                         } else {
 844                                 if ( !isset( $this->servers[$i] ) || !is_array( $this->servers[$i] ) ) {
 845                                         throw new InvalidArgumentException( "No server with index '$i'." );
 846                                 }
 847                                 // Open a new connection
 848                                 $server = $this->servers[$i];
 849                                 $server['serverIndex'] = $i;
 850                                 $server['autoCommitOnly'] = $autoCommit;
 851                                 if ( $this->localDomain->getDatabase() !== null ) {
 852                                         // Use the local domain table prefix if the local domain is specified
 853                                         $server['tablePrefix'] = $this->localDomain->getTablePrefix();
 854                                 }
 855                                 $conn = $this->reallyOpenConnection( $server, $this->localDomain );
 856                                 $host = $this->getServerName( $i );
 857                                 if ( $conn->isOpen() ) {
 858                                         $this->connLogger->debug( "Connected to database $i at '$host'." );
 859                                         $this->conns[$connKey][$i][0] = $conn;
 860                                 } else {
 861                                         $this->connLogger->warning( "Failed to connect to database $i at '$host'." );
 862                                         $this->errorConnection = $conn;
 863                                         $conn = false;
 864                                 }
 865                         }
 866                 }
 867
 868                 if ( $conn instanceof IDatabase && !$conn->isOpen() ) {
 869                         // Connection was made but later unrecoverably lost for some reason.
 870                         // Do not return a handle that will just throw exceptions on use,
 871                         // but let the calling code (e.g. getReaderIndex) try another server.
 872                         // See DatabaseMyslBase::ping() for how this can happen.
 873                         $this->errorConnection = $conn;
 874                         $conn = false;
 875                 }
 876
 877                 if ( $autoCommit && $conn instanceof IDatabase ) {
 878                         $conn->clearFlag( $conn::DBO_TRX ); // auto-commit mode
 879                 }
 880
 881                 return $conn;
 882         }
 883
 884         /**
 885          * Open a connection to a foreign DB, or return one if it is already open.
 886          *
 887          * Increments a reference count on the returned connection which locks the
 888          * connection to the requested domain. This reference count can be
 889          * decremented by calling reuseConnection().
 890          *
 891          * If a connection is open to the appropriate server already, but with the wrong
 892          * database, it will be switched to the right database and returned, as long as
 893          * it has been freed first with reuseConnection().
 894          *
 895          * On error, returns false, and the connection which caused the
 896          * error will be available via $this->errorConnection.
 897          *
 898          * @note If disable() was called on this LoadBalancer, this method will throw a DBAccessError.
 899          *
 900          * @param int $i Server index
 901          * @param string $domain Domain ID to open
 902          * @param int $flags Class CONN_* constant bitfield
 903          * @return Database
 904          */
 905         private function openForeignConnection( $i, $domain, $flags = 0 ) {
 906                 $domainInstance = DatabaseDomain::newFromId( $domain );
 907                 $dbName = $domainInstance->getDatabase();
 908                 $prefix = $domainInstance->getTablePrefix();
 909                 $autoCommit = ( ( $flags & self::CONN_TRX_AUTO ) == self::CONN_TRX_AUTO );
 910
 911                 if ( $autoCommit ) {
 912                         $connFreeKey = self::KEY_FOREIGN_FREE_NOROUND;
 913                         $connInUseKey = self::KEY_FOREIGN_INUSE_NOROUND;
 914                 } else {
 915                         $connFreeKey = self::KEY_FOREIGN_FREE;
 916                         $connInUseKey = self::KEY_FOREIGN_INUSE;
 917                 }
 918
 919                 if ( isset( $this->conns[$connInUseKey][$i][$domain] ) ) {
 920                         // Reuse an in-use connection for the same domain
 921                         $conn = $this->conns[$connInUseKey][$i][$domain];
 922                         $this->connLogger->debug( __METHOD__ . ": reusing connection $i/$domain" );
 923                 } elseif ( isset( $this->conns[$connFreeKey][$i][$domain] ) ) {
 924                         // Reuse a free connection for the same domain
 925                         $conn = $this->conns[$connFreeKey][$i][$domain];
 926                         unset( $this->conns[$connFreeKey][$i][$domain] );
 927                         $this->conns[$connInUseKey][$i][$domain] = $conn;
 928                         $this->connLogger->debug( __METHOD__ . ": reusing free connection $i/$domain" );
 929                 } elseif ( !empty( $this->conns[$connFreeKey][$i] ) ) {
 930                         // Reuse a free connection from another domain
 931                         $conn = reset( $this->conns[$connFreeKey][$i] );
 932                         $oldDomain = key( $this->conns[$connFreeKey][$i] );
 933                         if ( strlen( $dbName ) && !$conn->selectDB( $dbName ) ) {
 934                                 $this->lastError = "Error selecting database '$dbName' on server " .
 935                                         $conn->getServer() . " from client host {$this->host}";
 936                                 $this->errorConnection = $conn;
 937                                 $conn = false;
 938                         } else {
 939                                 $conn->tablePrefix( $prefix );
 940                                 unset( $this->conns[$connFreeKey][$i][$oldDomain] );
 941                                 // Note that if $domain is an empty string, getDomainID() might not match it
 942                                 $this->conns[$connInUseKey][$i][$conn->getDomainId()] = $conn;
 943                                 $this->connLogger->debug( __METHOD__ .
 944                                         ": reusing free connection from $oldDomain for $domain" );
 945                         }
 946                 } else {
 947                         if ( !isset( $this->servers[$i] ) || !is_array( $this->servers[$i] ) ) {
 948                                 throw new InvalidArgumentException( "No server with index '$i'." );
 949                         }
 950                         // Open a new connection
 951                         $server = $this->servers[$i];
 952                         $server['serverIndex'] = $i;
 953                         $server['foreignPoolRefCount'] = 0;
 954                         $server['foreign'] = true;
 955                         $server['autoCommitOnly'] = $autoCommit;
 956                         $conn = $this->reallyOpenConnection( $server, $domainInstance );
 957                         if ( !$conn->isOpen() ) {
 958                                 $this->connLogger->warning( __METHOD__ . ": connection error for $i/$domain" );
 959                                 $this->errorConnection = $conn;
 960                                 $conn = false;
 961                         } else {
 962                                 $conn->tablePrefix( $prefix ); // as specified
 963                                 // Note that if $domain is an empty string, getDomainID() might not match it
 964                                 $this->conns[$connInUseKey][$i][$conn->getDomainID()] = $conn;
 965                                 $this->connLogger->debug( __METHOD__ . ": opened new connection for $i/$domain" );
 966                         }
 967                 }
 968
 969                 // Increment reference count
 970                 if ( $conn instanceof IDatabase ) {
 971                         $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 972                         $conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
 973                 }
 974
 975                 return $conn;
 976         }
 977
 978         /**
 979          * Test if the specified index represents an open connection
 980          *
 981          * @param int $index Server index
 982          * @access private
 983          * @return bool
 984          */
 985         private function isOpen( $index ) {
 986                 if ( !is_int( $index ) ) {
 987                         return false;
 988                 }
 989
 990                 return (bool)$this->getAnyOpenConnection( $index );
 991         }
 992
 993         /**
 994          * Open a new network connection to a server (uncached)
 995          *
 996          * Returns a Database object whether or not the connection was successful.
 997          *
 998          * @param array $server
 999          * @param DatabaseDomain $domainOverride Use an unspecified domain to not select any database
1000          * @return Database
1001          * @throws DBAccessError
1002          * @throws InvalidArgumentException
1003          */
1004         protected function reallyOpenConnection( array $server, DatabaseDomain $domainOverride ) {
1005                 if ( $this->disabled ) {
1006                         throw new DBAccessError();
1007                 }
1008
1009                 // Handle $domainOverride being a specified or an unspecified domain
1010                 if ( $domainOverride->getDatabase() === null ) {
1011                         // Normally, an RDBMS requires a DB name specified on connection and the $server
1012                         // configuration array is assumed to already specify an appropriate DB name.
1013                         if ( $server['type'] === 'mysql' ) {
1014                                 // For MySQL, DATABASE and SCHEMA are synonyms, connections need not specify a DB,
1015                                 // and the DB name in $server might not exist due to legacy reasons (the default
1016                                 // domain used to ignore the local LB domain, even when mismatched).
1017                                 $server['dbname'] = null;
1018                         }
1019                 } else {
1020                         $server['dbname'] = $domainOverride->getDatabase();
1021                         $server['schema'] = $domainOverride->getSchema();
1022                 }
1023
1024                 // Let the handle know what the cluster master is (e.g. "db1052")
1025                 $masterName = $this->getServerName( $this->getWriterIndex() );
1026                 $server['clusterMasterHost'] = $masterName;
1027
1028                 // Log when many connection are made on requests
1029                 if ( ++$this->connsOpened >= self::CONN_HELD_WARN_THRESHOLD ) {
1030                         $this->perfLogger->warning( __METHOD__ . ": " .
1031                                 "{$this->connsOpened}+ connections made (master=$masterName)" );
1032                 }
1033
1034                 $server['srvCache'] = $this->srvCache;
1035                 // Set loggers and profilers
1036                 $server['connLogger'] = $this->connLogger;
1037                 $server['queryLogger'] = $this->queryLogger;
1038                 $server['errorLogger'] = $this->errorLogger;
1039                 $server['profiler'] = $this->profiler;
1040                 $server['trxProfiler'] = $this->trxProfiler;
1041                 // Use the same agent and PHP mode for all DB handles
1042                 $server['cliMode'] = $this->cliMode;
1043                 $server['agent'] = $this->agent;
1044                 // Use DBO_DEFAULT flags by default for LoadBalancer managed databases. Assume that the
1045                 // application calls LoadBalancer::commitMasterChanges() before the PHP script completes.
1046                 $server['flags'] = isset( $server['flags'] ) ? $server['flags'] : IDatabase::DBO_DEFAULT;
1047
1048                 // Create a live connection object
1049                 try {
1050                         $db = Database::factory( $server['type'], $server );
1051                 } catch ( DBConnectionError $e ) {
1052                         // FIXME: This is probably the ugliest thing I have ever done to
1053                         // PHP. I'm half-expecting it to segfault, just out of disgust. -- TS
1054                         $db = $e->db;
1055                 }
1056
1057                 $db->setLBInfo( $server );
1058                 $db->setLazyMasterHandle(
1059                         $this->getLazyConnectionRef( self::DB_MASTER, [], $db->getDomainID() )
1060                 );
1061                 $db->setTableAliases( $this->tableAliases );
1062
1063                 if ( $server['serverIndex'] === $this->getWriterIndex() ) {
1064                         if ( $this->trxRoundId !== false ) {
1065                                 $this->applyTransactionRoundFlags( $db );
1066                         }
1067                         foreach ( $this->trxRecurringCallbacks as $name => $callback ) {
1068                                 $db->setTransactionListener( $name, $callback );
1069                         }
1070                 }
1071
1072                 return $db;
1073         }
1074
1075         /**
1076          * @throws DBConnectionError
1077          */
1078         private function reportConnectionError() {
1079                 $conn = $this->errorConnection; // the connection which caused the error
1080                 $context = [
1081                         'method' => __METHOD__,
1082                         'last_error' => $this->lastError,
1083                 ];
1084
1085                 if ( $conn instanceof IDatabase ) {
1086                         $context['db_server'] = $conn->getServer();
1087                         $this->connLogger->warning(
1088                                 "Connection error: {last_error} ({db_server})",
1089                                 $context
1090                         );
1091
1092                         // throws DBConnectionError
1093                         $conn->reportConnectionError( "{$this->lastError} ({$context['db_server']})" );
1094                 } else {
1095                         // No last connection, probably due to all servers being too busy
1096                         $this->connLogger->error(
1097                                 "LB failure with no last connection. Connection error: {last_error}",
1098                                 $context
1099                         );
1100
1101                         // If all servers were busy, mLastError will contain something sensible
1102                         throw new DBConnectionError( null, $this->lastError );
1103                 }
1104         }
1105
1106         public function getWriterIndex() {
1107                 return 0;
1108         }
1109
1110         public function haveIndex( $i ) {
1111                 return array_key_exists( $i, $this->servers );
1112         }
1113
1114         public function isNonZeroLoad( $i ) {
1115                 return array_key_exists( $i, $this->servers ) && $this->loads[$i] != 0;
1116         }
1117
1118         public function getServerCount() {
1119                 return count( $this->servers );
1120         }
1121
1122         public function getServerName( $i ) {
1123                 if ( isset( $this->servers[$i]['hostName'] ) ) {
1124                         $name = $this->servers[$i]['hostName'];
1125                 } elseif ( isset( $this->servers[$i]['host'] ) ) {
1126                         $name = $this->servers[$i]['host'];
1127                 } else {
1128                         $name = '';
1129                 }
1130
1131                 return ( $name != '' ) ? $name : 'localhost';
1132         }
1133
1134         public function getServerType( $i ) {
1135                 return isset( $this->servers[$i]['type'] ) ? $this->servers[$i]['type'] : 'unknown';
1136         }
1137
1138         public function getMasterPos() {
1139                 # If this entire request was served from a replica DB without opening a connection to the
1140                 # master (however unlikely that may be), then we can fetch the position from the replica DB.
1141                 $masterConn = $this->getAnyOpenConnection( $this->getWriterIndex() );
1142                 if ( !$masterConn ) {
1143                         $serverCount = count( $this->servers );
1144                         for ( $i = 1; $i < $serverCount; $i++ ) {
1145                                 $conn = $this->getAnyOpenConnection( $i );
1146                                 if ( $conn ) {
1147                                         return $conn->getReplicaPos();
1148                                 }
1149                         }
1150                 } else {
1151                         return $masterConn->getMasterPos();
1152                 }
1153
1154                 return false;
1155         }
1156
1157         public function disable() {
1158                 $this->closeAll();
1159                 $this->disabled = true;
1160         }
1161
1162         public function closeAll() {
1163                 $this->forEachOpenConnection( function ( IDatabase $conn ) {
1164                         $host = $conn->getServer();
1165                         $this->connLogger->debug( "Closing connection to database '$host'." );
1166                         $conn->close();
1167                 } );
1168
1169                 $this->conns = [
1170                         self::KEY_LOCAL => [],
1171                         self::KEY_FOREIGN_INUSE => [],
1172                         self::KEY_FOREIGN_FREE => [],
1173                         self::KEY_LOCAL_NOROUND => [],
1174                         self::KEY_FOREIGN_INUSE_NOROUND => [],
1175                         self::KEY_FOREIGN_FREE_NOROUND => []
1176                 ];
1177                 $this->connsOpened = 0;
1178         }
1179
1180         public function closeConnection( IDatabase $conn ) {
1181                 $serverIndex = $conn->getLBInfo( 'serverIndex' ); // second index level of mConns
1182                 foreach ( $this->conns as $type => $connsByServer ) {
1183                         if ( !isset( $connsByServer[$serverIndex] ) ) {
1184                                 continue;
1185                         }
1186
1187                         foreach ( $connsByServer[$serverIndex] as $i => $trackedConn ) {
1188                                 if ( $conn === $trackedConn ) {
1189                                         $host = $this->getServerName( $i );
1190                                         $this->connLogger->debug( "Closing connection to database $i at '$host'." );
1191                                         unset( $this->conns[$type][$serverIndex][$i] );
1192                                         --$this->connsOpened;
1193                                         break 2;
1194                                 }
1195                         }
1196                 }
1197
1198                 $conn->close();
1199         }
1200
1201         public function commitAll( $fname = __METHOD__ ) {
1202                 $failures = [];
1203
1204                 $restore = ( $this->trxRoundId !== false );
1205                 $this->trxRoundId = false;
1206                 $this->forEachOpenConnection(
1207                         function ( IDatabase $conn ) use ( $fname, $restore, &$failures ) {
1208                                 try {
1209                                         $conn->commit( $fname, $conn::FLUSHING_ALL_PEERS );
1210                                 } catch ( DBError $e ) {
1211                                         call_user_func( $this->errorLogger, $e );
1212                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1213                                 }
1214                                 if ( $restore && $conn->getLBInfo( 'master' ) ) {
1215                                         $this->undoTransactionRoundFlags( $conn );
1216                                 }
1217                         }
1218                 );
1219
1220                 if ( $failures ) {
1221                         throw new DBExpectedError(
1222                                 null,
1223                                 "Commit failed on server(s) " . implode( "\n", array_unique( $failures ) )
1224                         );
1225                 }
1226         }
1227
1228         public function finalizeMasterChanges() {
1229                 $this->forEachOpenMasterConnection( function ( Database $conn ) {
1230                         // Any error should cause all DB transactions to be rolled back together
1231                         $conn->setTrxEndCallbackSuppression( false );
1232                         $conn->runOnTransactionPreCommitCallbacks();
1233                         // Defer post-commit callbacks until COMMIT finishes for all DBs
1234                         $conn->setTrxEndCallbackSuppression( true );
1235                 } );
1236         }
1237
1238         public function approveMasterChanges( array $options ) {
1239                 $limit = isset( $options['maxWriteDuration'] ) ? $options['maxWriteDuration'] : 0;
1240                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( $limit ) {
1241                         // If atomic sections or explicit transactions are still open, some caller must have
1242                         // caught an exception but failed to properly rollback any changes. Detect that and
1243                         // throw and error (causing rollback).
1244                         if ( $conn->explicitTrxActive() ) {
1245                                 throw new DBTransactionError(
1246                                         $conn,
1247                                         "Explicit transaction still active. A caller may have caught an error."
1248                                 );
1249                         }
1250                         // Assert that the time to replicate the transaction will be sane.
1251                         // If this fails, then all DB transactions will be rollback back together.
1252                         $time = $conn->pendingWriteQueryDuration( $conn::ESTIMATE_DB_APPLY );
1253                         if ( $limit > 0 && $time > $limit ) {
1254                                 throw new DBTransactionSizeError(
1255                                         $conn,
1256                                         "Transaction spent $time second(s) in writes, exceeding the limit of $limit.",
1257                                         [ $time, $limit ]
1258                                 );
1259                         }
1260                         // If a connection sits idle while slow queries execute on another, that connection
1261                         // may end up dropped before the commit round is reached. Ping servers to detect this.
1262                         if ( $conn->writesOrCallbacksPending() && !$conn->ping() ) {
1263                                 throw new DBTransactionError(
1264                                         $conn,
1265                                         "A connection to the {$conn->getDBname()} database was lost before commit."
1266                                 );
1267                         }
1268                 } );
1269         }
1270
1271         public function beginMasterChanges( $fname = __METHOD__ ) {
1272                 if ( $this->trxRoundId !== false ) {
1273                         throw new DBTransactionError(
1274                                 null,
1275                                 "$fname: Transaction round '{$this->trxRoundId}' already started."
1276                         );
1277                 }
1278                 $this->trxRoundId = $fname;
1279
1280                 $failures = [];
1281                 $this->forEachOpenMasterConnection(
1282                         function ( Database $conn ) use ( $fname, &$failures ) {
1283                                 $conn->setTrxEndCallbackSuppression( true );
1284                                 try {
1285                                         $conn->flushSnapshot( $fname );
1286                                 } catch ( DBError $e ) {
1287                                         call_user_func( $this->errorLogger, $e );
1288                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1289                                 }
1290                                 $conn->setTrxEndCallbackSuppression( false );
1291                                 $this->applyTransactionRoundFlags( $conn );
1292                         }
1293                 );
1294
1295                 if ( $failures ) {
1296                         throw new DBExpectedError(
1297                                 null,
1298                                 "$fname: Flush failed on server(s) " . implode( "\n", array_unique( $failures ) )
1299                         );
1300                 }
1301         }
1302
1303         public function commitMasterChanges( $fname = __METHOD__ ) {
1304                 $failures = [];
1305
1306                 /** @noinspection PhpUnusedLocalVariableInspection */
1307                 $scope = $this->getScopedPHPBehaviorForCommit(); // try to ignore client aborts
1308
1309                 $restore = ( $this->trxRoundId !== false );
1310                 $this->trxRoundId = false;
1311                 $this->forEachOpenMasterConnection(
1312                         function ( IDatabase $conn ) use ( $fname, $restore, &$failures ) {
1313                                 try {
1314                                         if ( $conn->writesOrCallbacksPending() ) {
1315                                                 $conn->commit( $fname, $conn::FLUSHING_ALL_PEERS );
1316                                         } elseif ( $restore ) {
1317                                                 $conn->flushSnapshot( $fname );
1318                                         }
1319                                 } catch ( DBError $e ) {
1320                                         call_user_func( $this->errorLogger, $e );
1321                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1322                                 }
1323                                 if ( $restore ) {
1324                                         $this->undoTransactionRoundFlags( $conn );
1325                                 }
1326                         }
1327                 );
1328
1329                 if ( $failures ) {
1330                         throw new DBExpectedError(
1331                                 null,
1332                                 "$fname: Commit failed on server(s) " . implode( "\n", array_unique( $failures ) )
1333                         );
1334                 }
1335         }
1336
1337         public function runMasterPostTrxCallbacks( $type ) {
1338                 $e = null; // first exception
1339                 $this->forEachOpenMasterConnection( function ( Database $conn ) use ( $type, &$e ) {
1340                         $conn->setTrxEndCallbackSuppression( false );
1341                         if ( $conn->writesOrCallbacksPending() ) {
1342                                 // This happens if onTransactionIdle() callbacks leave callbacks on *another* DB
1343                                 // (which finished its callbacks already). Warn and recover in this case. Let the
1344                                 // callbacks run in the final commitMasterChanges() in LBFactory::shutdown().
1345                                 $this->queryLogger->info( __METHOD__ . ": found writes/callbacks pending." );
1346                                 return;
1347                         } elseif ( $conn->trxLevel() ) {
1348                                 // This happens for single-DB setups where DB_REPLICA uses the master DB,
1349                                 // thus leaving an implicit read-only transaction open at this point. It
1350                                 // also happens if onTransactionIdle() callbacks leave implicit transactions
1351                                 // open on *other* DBs (which is slightly improper). Let these COMMIT on the
1352                                 // next call to commitMasterChanges(), possibly in LBFactory::shutdown().
1353                                 return;
1354                         }
1355                         try {
1356                                 $conn->runOnTransactionIdleCallbacks( $type );
1357                         } catch ( Exception $ex ) {
1358                                 $e = $e ?: $ex;
1359                         }
1360                         try {
1361                                 $conn->runTransactionListenerCallbacks( $type );
1362                         } catch ( Exception $ex ) {
1363                                 $e = $e ?: $ex;
1364                         }
1365                 } );
1366
1367                 return $e;
1368         }
1369
1370         public function rollbackMasterChanges( $fname = __METHOD__ ) {
1371                 $restore = ( $this->trxRoundId !== false );
1372                 $this->trxRoundId = false;
1373                 $this->forEachOpenMasterConnection(
1374                         function ( IDatabase $conn ) use ( $fname, $restore ) {
1375                                 if ( $conn->writesOrCallbacksPending() || $conn->explicitTrxActive() ) {
1376                                         $conn->rollback( $fname, $conn::FLUSHING_ALL_PEERS );
1377                                 }
1378                                 if ( $restore ) {
1379                                         $this->undoTransactionRoundFlags( $conn );
1380                                 }
1381                         }
1382                 );
1383         }
1384
1385         public function suppressTransactionEndCallbacks() {
1386                 $this->forEachOpenMasterConnection( function ( Database $conn ) {
1387                         $conn->setTrxEndCallbackSuppression( true );
1388                 } );
1389         }
1390
1391         /**
1392          * @param IDatabase $conn
1393          */
1394         private function applyTransactionRoundFlags( IDatabase $conn ) {
1395                 if ( $conn->getLBInfo( 'autoCommitOnly' ) ) {
1396                         return; // transaction rounds do not apply to these connections
1397                 }
1398
1399                 if ( $conn->getFlag( $conn::DBO_DEFAULT ) ) {
1400                         // DBO_TRX is controlled entirely by CLI mode presence with DBO_DEFAULT.
1401                         // Force DBO_TRX even in CLI mode since a commit round is expected soon.
1402                         $conn->setFlag( $conn::DBO_TRX, $conn::REMEMBER_PRIOR );
1403                         // If config has explicitly requested DBO_TRX be either on or off by not
1404                         // setting DBO_DEFAULT, then respect that. Forcing no transactions is useful
1405                         // for things like blob stores (ExternalStore) which want auto-commit mode.
1406                 }
1407         }
1408
1409         /**
1410          * @param IDatabase $conn
1411          */
1412         private function undoTransactionRoundFlags( IDatabase $conn ) {
1413                 if ( $conn->getLBInfo( 'autoCommitOnly' ) ) {
1414                         return; // transaction rounds do not apply to these connections
1415                 }
1416
1417                 if ( $conn->getFlag( $conn::DBO_DEFAULT ) ) {
1418                         $conn->restoreFlags( $conn::RESTORE_PRIOR );
1419                 }
1420         }
1421
1422         public function flushReplicaSnapshots( $fname = __METHOD__ ) {
1423                 $this->forEachOpenReplicaConnection( function ( IDatabase $conn ) {
1424                         $conn->flushSnapshot( __METHOD__ );
1425                 } );
1426         }
1427
1428         public function hasMasterConnection() {
1429                 return $this->isOpen( $this->getWriterIndex() );
1430         }
1431
1432         public function hasMasterChanges() {
1433                 $pending = 0;
1434                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$pending ) {
1435                         $pending |= $conn->writesOrCallbacksPending();
1436                 } );
1437
1438                 return (bool)$pending;
1439         }
1440
1441         public function lastMasterChangeTimestamp() {
1442                 $lastTime = false;
1443                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$lastTime ) {
1444                         $lastTime = max( $lastTime, $conn->lastDoneWrites() );
1445                 } );
1446
1447                 return $lastTime;
1448         }
1449
1450         public function hasOrMadeRecentMasterChanges( $age = null ) {
1451                 $age = ( $age === null ) ? $this->waitTimeout : $age;
1452
1453                 return ( $this->hasMasterChanges()
1454                         || $this->lastMasterChangeTimestamp() > microtime( true ) - $age );
1455         }
1456
1457         public function pendingMasterChangeCallers() {
1458                 $fnames = [];
1459                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$fnames ) {
1460                         $fnames = array_merge( $fnames, $conn->pendingWriteCallers() );
1461                 } );
1462
1463                 return $fnames;
1464         }
1465
1466         public function getLaggedReplicaMode( $domain = false ) {
1467                 // No-op if there is only one DB (also avoids recursion)
1468                 if ( !$this->laggedReplicaMode && $this->getServerCount() > 1 ) {
1469                         try {
1470                                 // See if laggedReplicaMode gets set
1471                                 $conn = $this->getConnection( self::DB_REPLICA, false, $domain );
1472                                 $this->reuseConnection( $conn );
1473                         } catch ( DBConnectionError $e ) {
1474                                 // Avoid expensive re-connect attempts and failures
1475                                 $this->allReplicasDownMode = true;
1476                                 $this->laggedReplicaMode = true;
1477                         }
1478                 }
1479
1480                 return $this->laggedReplicaMode;
1481         }
1482
1483         /**
1484          * @param bool $domain
1485          * @return bool
1486          * @deprecated 1.28; use getLaggedReplicaMode()
1487          */
1488         public function getLaggedSlaveMode( $domain = false ) {
1489                 return $this->getLaggedReplicaMode( $domain );
1490         }
1491
1492         public function laggedReplicaUsed() {
1493                 return $this->laggedReplicaMode;
1494         }
1495
1496         /**
1497          * @return bool
1498          * @since 1.27
1499          * @deprecated Since 1.28; use laggedReplicaUsed()
1500          */
1501         public function laggedSlaveUsed() {
1502                 return $this->laggedReplicaUsed();
1503         }
1504
1505         public function getReadOnlyReason( $domain = false, IDatabase $conn = null ) {
1506                 if ( $this->readOnlyReason !== false ) {
1507                         return $this->readOnlyReason;
1508                 } elseif ( $this->getLaggedReplicaMode( $domain ) ) {
1509                         if ( $this->allReplicasDownMode ) {
1510                                 return 'The database has been automatically locked ' .
1511                                         'until the replica database servers become available';
1512                         } else {
1513                                 return 'The database has been automatically locked ' .
1514                                         'while the replica database servers catch up to the master.';
1515                         }
1516                 } elseif ( $this->masterRunningReadOnly( $domain, $conn ) ) {
1517                         return 'The database master is running in read-only mode.';
1518                 }
1519
1520                 return false;
1521         }
1522
1523         /**
1524          * @param string $domain Domain ID, or false for the current domain
1525          * @param IDatabase|null $conn DB master connectionl used to avoid loops [optional]
1526          * @return bool
1527          */
1528         private function masterRunningReadOnly( $domain, IDatabase $conn = null ) {
1529                 $cache = $this->wanCache;
1530                 $masterServer = $this->getServerName( $this->getWriterIndex() );
1531
1532                 return (bool)$cache->getWithSetCallback(
1533                         $cache->makeGlobalKey( __CLASS__, 'server-read-only', $masterServer ),
1534                         self::TTL_CACHE_READONLY,
1535                         function () use ( $domain, $conn ) {
1536                                 $old = $this->trxProfiler->setSilenced( true );
1537                                 try {
1538                                         $dbw = $conn ?: $this->getConnection( self::DB_MASTER, [], $domain );
1539                                         $readOnly = (int)$dbw->serverIsReadOnly();
1540                                         if ( !$conn ) {
1541                                                 $this->reuseConnection( $dbw );
1542                                         }
1543                                 } catch ( DBError $e ) {
1544                                         $readOnly = 0;
1545                                 }
1546                                 $this->trxProfiler->setSilenced( $old );
1547                                 return $readOnly;
1548                         },
1549                         [ 'pcTTL' => $cache::TTL_PROC_LONG, 'busyValue' => 0 ]
1550                 );
1551         }
1552
1553         public function allowLagged( $mode = null ) {
1554                 if ( $mode === null ) {
1555                         return $this->allowLagged;
1556                 }
1557                 $this->allowLagged = $mode;
1558
1559                 return $this->allowLagged;
1560         }
1561
1562         public function pingAll() {
1563                 $success = true;
1564                 $this->forEachOpenConnection( function ( IDatabase $conn ) use ( &$success ) {
1565                         if ( !$conn->ping() ) {
1566                                 $success = false;
1567                         }
1568                 } );
1569
1570                 return $success;
1571         }
1572
1573         public function forEachOpenConnection( $callback, array $params = [] ) {
1574                 foreach ( $this->conns as $connsByServer ) {
1575                         foreach ( $connsByServer as $serverConns ) {
1576                                 foreach ( $serverConns as $conn ) {
1577                                         $mergedParams = array_merge( [ $conn ], $params );
1578                                         call_user_func_array( $callback, $mergedParams );
1579                                 }
1580                         }
1581                 }
1582         }
1583
1584         public function forEachOpenMasterConnection( $callback, array $params = [] ) {
1585                 $masterIndex = $this->getWriterIndex();
1586                 foreach ( $this->conns as $connsByServer ) {
1587                         if ( isset( $connsByServer[$masterIndex] ) ) {
1588                                 /** @var IDatabase $conn */
1589                                 foreach ( $connsByServer[$masterIndex] as $conn ) {
1590                                         $mergedParams = array_merge( [ $conn ], $params );
1591                                         call_user_func_array( $callback, $mergedParams );
1592                                 }
1593                         }
1594                 }
1595         }
1596
1597         public function forEachOpenReplicaConnection( $callback, array $params = [] ) {
1598                 foreach ( $this->conns as $connsByServer ) {
1599                         foreach ( $connsByServer as $i => $serverConns ) {
1600                                 if ( $i === $this->getWriterIndex() ) {
1601                                         continue; // skip master
1602                                 }
1603                                 foreach ( $serverConns as $conn ) {
1604                                         $mergedParams = array_merge( [ $conn ], $params );
1605                                         call_user_func_array( $callback, $mergedParams );
1606                                 }
1607                         }
1608                 }
1609         }
1610
1611         public function getMaxLag( $domain = false ) {
1612                 $maxLag = -1;
1613                 $host = '';
1614                 $maxIndex = 0;
1615
1616                 if ( $this->getServerCount() <= 1 ) {
1617                         return [ $host, $maxLag, $maxIndex ]; // no replication = no lag
1618                 }
1619
1620                 $lagTimes = $this->getLagTimes( $domain );
1621                 foreach ( $lagTimes as $i => $lag ) {
1622                         if ( $this->loads[$i] > 0 && $lag > $maxLag ) {
1623                                 $maxLag = $lag;
1624                                 $host = $this->servers[$i]['host'];
1625                                 $maxIndex = $i;
1626                         }
1627                 }
1628
1629                 return [ $host, $maxLag, $maxIndex ];
1630         }
1631
1632         public function getLagTimes( $domain = false ) {
1633                 if ( $this->getServerCount() <= 1 ) {
1634                         return [ $this->getWriterIndex() => 0 ]; // no replication = no lag
1635                 }
1636
1637                 $knownLagTimes = []; // map of (server index => 0 seconds)
1638                 $indexesWithLag = [];
1639                 foreach ( $this->servers as $i => $server ) {
1640                         if ( empty( $server['is static'] ) ) {
1641                                 $indexesWithLag[] = $i; // DB server might have replication lag
1642                         } else {
1643                                 $knownLagTimes[$i] = 0; // DB server is a non-replicating and read-only archive
1644                         }
1645                 }
1646
1647                 return $this->getLoadMonitor()->getLagTimes( $indexesWithLag, $domain ) + $knownLagTimes;
1648         }
1649
1650         public function safeGetLag( IDatabase $conn ) {
1651                 if ( $this->getServerCount() <= 1 ) {
1652                         return 0;
1653                 } else {
1654                         return $conn->getLag();
1655                 }
1656         }
1657
1658         /**
1659          * @param IDatabase $conn
1660          * @param DBMasterPos|bool $pos
1661          * @param int|null $timeout
1662          * @return bool
1663          */
1664         public function safeWaitForMasterPos( IDatabase $conn, $pos = false, $timeout = null ) {
1665                 $timeout = max( 1, $timeout ?: $this->waitTimeout );
1666
1667                 if ( $this->getServerCount() <= 1 || !$conn->getLBInfo( 'replica' ) ) {
1668                         return true; // server is not a replica DB
1669                 }
1670
1671                 if ( !$pos ) {
1672                         // Get the current master position, opening a connection if needed
1673                         $masterConn = $this->getAnyOpenConnection( $this->getWriterIndex() );
1674                         if ( $masterConn ) {
1675                                 $pos = $masterConn->getMasterPos();
1676                         } else {
1677                                 $masterConn = $this->openConnection( $this->getWriterIndex(), self::DOMAIN_ANY );
1678                                 $pos = $masterConn->getMasterPos();
1679                                 $this->closeConnection( $masterConn );
1680                         }
1681                 }
1682
1683                 if ( $pos instanceof DBMasterPos ) {
1684                         $result = $conn->masterPosWait( $pos, $timeout );
1685                         if ( $result == -1 || is_null( $result ) ) {
1686                                 $msg = __METHOD__ . ': Timed out waiting on {host} pos {pos}';
1687                                 $this->replLogger->warning( $msg, [
1688                                         'host' => $conn->getServer(),
1689                                         'pos' => $pos,
1690                                         'trace' => ( new RuntimeException() )->getTraceAsString()
1691                                 ] );
1692                                 $ok = false;
1693                         } else {
1694                                 $this->replLogger->info( __METHOD__ . ': Done' );
1695                                 $ok = true;
1696                         }
1697                 } else {
1698                         $ok = false; // something is misconfigured
1699                         $this->replLogger->error(
1700                                 __METHOD__ . ': could not get master pos for {host}',
1701                                 [
1702                                         'host' => $conn->getServer(),
1703                                         'trace' => ( new RuntimeException() )->getTraceAsString()
1704                                 ]
1705                         );
1706                 }
1707
1708                 return $ok;
1709         }
1710
1711         public function setTransactionListener( $name, callable $callback = null ) {
1712                 if ( $callback ) {
1713                         $this->trxRecurringCallbacks[$name] = $callback;
1714                 } else {
1715                         unset( $this->trxRecurringCallbacks[$name] );
1716                 }
1717                 $this->forEachOpenMasterConnection(
1718                         function ( IDatabase $conn ) use ( $name, $callback ) {
1719                                 $conn->setTransactionListener( $name, $callback );
1720                         }
1721                 );
1722         }
1723
1724         public function setTableAliases( array $aliases ) {
1725                 $this->tableAliases = $aliases;
1726         }
1727
1728         public function setDomainPrefix( $prefix ) {
1729                 // Find connections to explicit foreign domains still marked as in-use...
1730                 $domainsInUse = [];
1731                 $this->forEachOpenConnection( function ( IDatabase $conn ) use ( &$domainsInUse ) {
1732                         // Once reuseConnection() is called on a handle, its reference count goes from 1 to 0.
1733                         // Until then, it is still in use by the caller (explicitly or via DBConnRef scope).
1734                         if ( $conn->getLBInfo( 'foreignPoolRefCount' ) > 0 ) {
1735                                 $domainsInUse[] = $conn->getDomainID();
1736                         }
1737                 } );
1738
1739                 // Do not switch connections to explicit foreign domains unless marked as safe
1740                 if ( $domainsInUse ) {
1741                         $domains = implode( ', ', $domainsInUse );
1742                         throw new DBUnexpectedError( null,
1743                                 "Foreign domain connections are still in use ($domains)." );
1744                 }
1745
1746                 $oldDomain = $this->localDomain->getId();
1747                 $this->setLocalDomain( new DatabaseDomain(
1748                         $this->localDomain->getDatabase(),
1749                         $this->localDomain->getSchema(),
1750                         $prefix
1751                 ) );
1752
1753                 $this->forEachOpenConnection( function ( IDatabase $db ) use ( $prefix, $oldDomain ) {
1754                         if ( !$db->getLBInfo( 'foreign' ) ) {
1755                                 $db->tablePrefix( $prefix );
1756                         }
1757                 } );
1758         }
1759
1760         /**
1761          * @param DatabaseDomain $domain
1762          */
1763         private function setLocalDomain( DatabaseDomain $domain ) {
1764                 $this->localDomain = $domain;
1765                 // In case a caller assumes that the domain ID is simply <db>-<prefix>, which is almost
1766                 // always true, gracefully handle the case when they fail to account for escaping.
1767                 if ( $this->localDomain->getTablePrefix() != '' ) {
1768                         $this->localDomainIdAlias =
1769                                 $this->localDomain->getDatabase() . '-' . $this->localDomain->getTablePrefix();
1770                 } else {
1771                         $this->localDomainIdAlias = $this->localDomain->getDatabase();
1772                 }
1773         }
1774
1775         /**
1776          * Make PHP ignore user aborts/disconnects until the returned
1777          * value leaves scope. This returns null and does nothing in CLI mode.
1778          *
1779          * @return ScopedCallback|null
1780          */
1781         final protected function getScopedPHPBehaviorForCommit() {
1782                 if ( PHP_SAPI != 'cli' ) { // https://bugs.php.net/bug.php?id=47540
1783                         $old = ignore_user_abort( true ); // avoid half-finished operations
1784                         return new ScopedCallback( function () use ( $old ) {
1785                                 ignore_user_abort( $old );
1786                         } );
1787                 }
1788
1789                 return null;
1790         }
1791
1792         function __destruct() {
1793                 // Avoid connection leaks for sanity
1794                 $this->disable();
1795         }
1796 }
1797
1798 class_alias( LoadBalancer::class, 'LoadBalancer' );