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 LogicException;
  32 use UnexpectedValueException;
  33 use InvalidArgumentException;
  34 use RuntimeException;
  35 use Exception;
  36
  37 /**
  38  * Database connection, tracking, load balancing, and transaction manager for a cluster
  39  *
  40  * @ingroup Database
  41  */
  42 class LoadBalancer implements ILoadBalancer {
  43         /** @var ILoadMonitor */
  44         private $loadMonitor;
  45         /** @var callable|null Callback to run before the first connection attempt */
  46         private $chronologyCallback;
  47         /** @var BagOStuff */
  48         private $srvCache;
  49         /** @var WANObjectCache */
  50         private $wanCache;
  51         /** @var mixed Class name or object With profileIn/profileOut methods */
  52         private $profiler;
  53         /** @var TransactionProfiler */
  54         private $trxProfiler;
  55         /** @var LoggerInterface */
  56         private $replLogger;
  57         /** @var LoggerInterface */
  58         private $connLogger;
  59         /** @var LoggerInterface */
  60         private $queryLogger;
  61         /** @var LoggerInterface */
  62         private $perfLogger;
  63         /** @var callable Exception logger */
  64         private $errorLogger;
  65         /** @var callable Deprecation logger */
  66         private $deprecationLogger;
  67
  68         /** @var DatabaseDomain Local DB domain ID and default for selectDB() calls */
  69         private $localDomain;
  70
  71         /** @var Database[][][] Map of (connection category => server index => IDatabase[]) */
  72         private $conns;
  73
  74         /** @var array[] Map of (server index => server config array) */
  75         private $servers;
  76         /** @var array[] Map of (group => server index => weight) */
  77         private $groupLoads;
  78         /** @var bool Whether to disregard replica DB lag as a factor in replica DB selection */
  79         private $allowLagged;
  80         /** @var int Seconds to spend waiting on replica DB lag to resolve */
  81         private $waitTimeout;
  82         /** @var array The LoadMonitor configuration */
  83         private $loadMonitorConfig;
  84         /** @var string Alternate local DB domain instead of DatabaseDomain::getId() */
  85         private $localDomainIdAlias;
  86         /** @var int Amount of replication lag, in seconds, that is considered "high" */
  87         private $maxLag;
  88         /** @var string|null Default query group to use with getConnection() */
  89         private $defaultGroup;
  90
  91         /** @var string Current server name */
  92         private $hostname;
  93         /** @var bool Whether this PHP instance is for a CLI script */
  94         private $cliMode;
  95         /** @var string Agent name for query profiling */
  96         private $agent;
  97
  98         /** @var array[] $aliases Map of (table => (dbname, schema, prefix) map) */
  99         private $tableAliases = [];
 100         /** @var string[] Map of (index alias => index) */
 101         private $indexAliases = [];
 102         /** @var array[] Map of (name => callable) */
 103         private $trxRecurringCallbacks = [];
 104         /** @var bool[] Map of (domain => whether to use "temp tables only" mode) */
 105         private $tempTablesOnlyMode = [];
 106
 107         /** @var Database Connection handle that caused a problem */
 108         private $errorConnection;
 109         /** @var int[] The group replica server indexes keyed by group */
 110         private $readIndexByGroup = [];
 111         /** @var bool|DBMasterPos Replication sync position or false if not set */
 112         private $waitForPos;
 113         /** @var bool Whether the generic reader fell back to a lagged replica DB */
 114         private $laggedReplicaMode = false;
 115         /** @var string The last DB selection or connection error */
 116         private $lastError = 'Unknown error';
 117         /** @var string|bool Reason this instance is read-only or false if not */
 118         private $readOnlyReason = false;
 119         /** @var int Total number of new connections ever made with this instance */
 120         private $connectionCounter = 0;
 121         /** @var bool */
 122         private $disabled = false;
 123         /** @var bool Whether any connection has been attempted yet */
 124         private $connectionAttempted = false;
 125
 126         /** @var int|null Integer ID of the managing LBFactory instance or null if none */
 127         private $ownerId;
 128         /** @var string|bool Explicit DBO_TRX transaction round active or false if none */
 129         private $trxRoundId = false;
 130         /** @var string Stage of the current transaction round in the transaction round life-cycle */
 131         private $trxRoundStage = self::ROUND_CURSORY;
 132
 133         /** @var int Warn when this many connection are held */
 134         const CONN_HELD_WARN_THRESHOLD = 10;
 135
 136         /** @var int Default 'maxLag' when unspecified */
 137         const MAX_LAG_DEFAULT = 6;
 138         /** @var int Default 'waitTimeout' when unspecified */
 139         const MAX_WAIT_DEFAULT = 10;
 140         /** @var int Seconds to cache master DB server read-only status */
 141         const TTL_CACHE_READONLY = 5;
 142
 143         const KEY_LOCAL = 'local';
 144         const KEY_FOREIGN_FREE = 'foreignFree';
 145         const KEY_FOREIGN_INUSE = 'foreignInUse';
 146
 147         const KEY_LOCAL_NOROUND = 'localAutoCommit';
 148         const KEY_FOREIGN_FREE_NOROUND = 'foreignFreeAutoCommit';
 149         const KEY_FOREIGN_INUSE_NOROUND = 'foreignInUseAutoCommit';
 150
 151         /** @var string Transaction round, explicit or implicit, has not finished writing */
 152         const ROUND_CURSORY = 'cursory';
 153         /** @var string Transaction round writes are complete and ready for pre-commit checks */
 154         const ROUND_FINALIZED = 'finalized';
 155         /** @var string Transaction round passed final pre-commit checks */
 156         const ROUND_APPROVED = 'approved';
 157         /** @var string Transaction round was committed and post-commit callbacks must be run */
 158         const ROUND_COMMIT_CALLBACKS = 'commit-callbacks';
 159         /** @var string Transaction round was rolled back and post-rollback callbacks must be run */
 160         const ROUND_ROLLBACK_CALLBACKS = 'rollback-callbacks';
 161         /** @var string Transaction round encountered an error */
 162         const ROUND_ERROR = 'error';
 163
 164         public function __construct( array $params ) {
 165                 if ( !isset( $params['servers'] ) || !count( $params['servers'] ) ) {
 166                         throw new InvalidArgumentException( 'Missing or empty "servers" parameter' );
 167                 }
 168
 169                 $listKey = -1;
 170                 $this->servers = [];
 171                 $this->groupLoads = [ self::GROUP_GENERIC => [] ];
 172                 foreach ( $params['servers'] as $i => $server ) {
 173                         if ( ++$listKey !== $i ) {
 174                                 throw new UnexpectedValueException( 'List expected for "servers" parameter' );
 175                         }
 176                         if ( $i == 0 ) {
 177                                 $server['master'] = true;
 178                         } else {
 179                                 $server['replica'] = true;
 180                         }
 181                         $this->servers[$i] = $server;
 182                         foreach ( ( $server['groupLoads'] ?? [] ) as $group => $ratio ) {
 183                                 $this->groupLoads[$group][$i] = $ratio;
 184                         }
 185                         $this->groupLoads[self::GROUP_GENERIC][$i] = $server['load'];
 186                 }
 187
 188                 $localDomain = isset( $params['localDomain'] )
 189                         ? DatabaseDomain::newFromId( $params['localDomain'] )
 190                         : DatabaseDomain::newUnspecified();
 191                 $this->setLocalDomain( $localDomain );
 192
 193                 $this->waitTimeout = $params['waitTimeout'] ?? self::MAX_WAIT_DEFAULT;
 194
 195                 $this->conns = self::newTrackedConnectionsArray();
 196                 $this->waitForPos = false;
 197                 $this->allowLagged = false;
 198
 199                 if ( isset( $params['readOnlyReason'] ) && is_string( $params['readOnlyReason'] ) ) {
 200                         $this->readOnlyReason = $params['readOnlyReason'];
 201                 }
 202
 203                 $this->maxLag = $params['maxLag'] ?? self::MAX_LAG_DEFAULT;
 204
 205                 $this->loadMonitorConfig = $params['loadMonitor'] ?? [ 'class' => 'LoadMonitorNull' ];
 206                 $this->loadMonitorConfig += [ 'lagWarnThreshold' => $this->maxLag ];
 207
 208                 $this->srvCache = $params['srvCache'] ?? new EmptyBagOStuff();
 209                 $this->wanCache = $params['wanCache'] ?? WANObjectCache::newEmpty();
 210                 $this->profiler = $params['profiler'] ?? null;
 211                 $this->trxProfiler = $params['trxProfiler'] ?? new TransactionProfiler();
 212
 213                 $this->errorLogger = $params['errorLogger'] ?? function ( Exception $e ) {
 214                         trigger_error( get_class( $e ) . ': ' . $e->getMessage(), E_USER_WARNING );
 215                 };
 216                 $this->deprecationLogger = $params['deprecationLogger'] ?? function ( $msg ) {
 217                         trigger_error( $msg, E_USER_DEPRECATED );
 218                 };
 219
 220                 foreach ( [ 'replLogger', 'connLogger', 'queryLogger', 'perfLogger' ] as $key ) {
 221                         $this->$key = $params[$key] ?? new NullLogger();
 222                 }
 223
 224                 $this->hostname = $params['hostname'] ?? ( gethostname() ?: 'unknown' );
 225                 $this->cliMode = $params['cliMode'] ?? ( PHP_SAPI === 'cli' || PHP_SAPI === 'phpdbg' );
 226                 $this->agent = $params['agent'] ?? '';
 227
 228                 if ( isset( $params['chronologyCallback'] ) ) {
 229                         $this->chronologyCallback = $params['chronologyCallback'];
 230                 }
 231
 232                 if ( isset( $params['roundStage'] ) ) {
 233                         if ( $params['roundStage'] === self::STAGE_POSTCOMMIT_CALLBACKS ) {
 234                                 $this->trxRoundStage = self::ROUND_COMMIT_CALLBACKS;
 235                         } elseif ( $params['roundStage'] === self::STAGE_POSTROLLBACK_CALLBACKS ) {
 236                                 $this->trxRoundStage = self::ROUND_ROLLBACK_CALLBACKS;
 237                         }
 238                 }
 239
 240                 $group = $params['defaultGroup'] ?? self::GROUP_GENERIC;
 241                 $this->defaultGroup = isset( $this->groupLoads[$group] ) ? $group : self::GROUP_GENERIC;
 242
 243                 $this->ownerId = $params['ownerId'] ?? null;
 244         }
 245
 246         private static function newTrackedConnectionsArray() {
 247                 return [
 248                         // Connection were transaction rounds may be applied
 249                         self::KEY_LOCAL => [],
 250                         self::KEY_FOREIGN_INUSE => [],
 251                         self::KEY_FOREIGN_FREE => [],
 252                         // Auto-committing counterpart connections that ignore transaction rounds
 253                         self::KEY_LOCAL_NOROUND => [],
 254                         self::KEY_FOREIGN_INUSE_NOROUND => [],
 255                         self::KEY_FOREIGN_FREE_NOROUND => []
 256                 ];
 257         }
 258
 259         public function getLocalDomainID() {
 260                 return $this->localDomain->getId();
 261         }
 262
 263         public function resolveDomainID( $domain ) {
 264                 if ( $domain === $this->localDomainIdAlias || $domain === false ) {
 265                         // Local connection requested via some backwards-compatibility domain alias
 266                         return $this->getLocalDomainID();
 267                 }
 268
 269                 return (string)$domain;
 270         }
 271
 272         /**
 273          * Resolve $groups into a list of query groups defining as having database servers
 274          *
 275          * @param string[]|string|bool $groups Query group(s) in preference order, [], or false
 276          * @param int $i Specific server index or DB_MASTER/DB_REPLICA
 277          * @return string[] Non-empty group list in preference order with the default group appended
 278          */
 279         private function resolveGroups( $groups, $i ) {
 280                 // If a specific replica server was specified, then $groups makes no sense
 281                 if ( $i > 0 && $groups !== [] && $groups !== false ) {
 282                         $list = implode( ', ', (array)$groups );
 283                         throw new LogicException( "Query group(s) ($list) given with server index (#$i)" );
 284                 }
 285
 286                 if ( $groups === [] || $groups === false || $groups === $this->defaultGroup ) {
 287                         $resolvedGroups = [ $this->defaultGroup ]; // common case
 288                 } elseif ( is_string( $groups ) && isset( $this->groupLoads[$groups] ) ) {
 289                         $resolvedGroups = [ $groups, $this->defaultGroup ];
 290                 } elseif ( is_array( $groups ) ) {
 291                         $resolvedGroups = array_keys( array_flip( $groups ) + [ self::GROUP_GENERIC => 1 ] );
 292                 } else {
 293                         $resolvedGroups = [ $this->defaultGroup ];
 294                 }
 295
 296                 return $resolvedGroups;
 297         }
 298
 299         /**
 300          * @param int $flags Bitfield of class CONN_* constants
 301          * @param int $i Specific server index or DB_MASTER/DB_REPLICA
 302          * @param string $domain Database domain
 303          * @return int Sanitized bitfield
 304          */
 305         private function sanitizeConnectionFlags( $flags, $i, $domain ) {
 306                 // Whether an outside caller is explicitly requesting the master database server
 307                 if ( $i === self::DB_MASTER || $i === $this->getWriterIndex() ) {
 308                         $flags |= self::CONN_INTENT_WRITABLE;
 309                 }
 310
 311                 if ( ( $flags & self::CONN_TRX_AUTOCOMMIT ) == self::CONN_TRX_AUTOCOMMIT ) {
 312                         // Callers use CONN_TRX_AUTOCOMMIT to bypass REPEATABLE-READ staleness without
 313                         // resorting to row locks (e.g. FOR UPDATE) or to make small out-of-band commits
 314                         // during larger transactions. This is useful for avoiding lock contention.
 315
 316                         // Master DB server attributes (should match those of the replica DB servers)
 317                         $attributes = $this->getServerAttributes( $this->getWriterIndex() );
 318                         if ( $attributes[Database::ATTR_DB_LEVEL_LOCKING] ) {
 319                                 // The RDBMS does not support concurrent writes (e.g. SQLite), so attempts
 320                                 // to use separate connections would just cause self-deadlocks. Note that
 321                                 // REPEATABLE-READ staleness is not an issue since DB-level locking means
 322                                 // that transactions are Strict Serializable anyway.
 323                                 $flags &= ~self::CONN_TRX_AUTOCOMMIT;
 324                                 $type = $this->getServerType( $this->getWriterIndex() );
 325                                 $this->connLogger->info( __METHOD__ . ": CONN_TRX_AUTOCOMMIT disallowed ($type)" );
 326                         } elseif ( isset( $this->tempTablesOnlyMode[$domain] ) ) {
 327                                 // T202116: integration tests are active and queries should be all be using
 328                                 // temporary clone tables (via prefix). Such tables are not visible accross
 329                                 // different connections nor can there be REPEATABLE-READ snapshot staleness,
 330                                 // so use the same connection for everything.
 331                                 $flags &= ~self::CONN_TRX_AUTOCOMMIT;
 332                         }
 333                 }
 334
 335                 return $flags;
 336         }
 337
 338         /**
 339          * @param IDatabase $conn
 340          * @param int $flags
 341          * @throws DBUnexpectedError
 342          */
 343         private function enforceConnectionFlags( IDatabase $conn, $flags ) {
 344                 if ( ( $flags & self::CONN_TRX_AUTOCOMMIT ) == self::CONN_TRX_AUTOCOMMIT ) {
 345                         if ( $conn->trxLevel() ) { // sanity
 346                                 throw new DBUnexpectedError(
 347                                         $conn,
 348                                         'Handle requested with CONN_TRX_AUTOCOMMIT yet it has a transaction'
 349                                 );
 350                         }
 351
 352                         $conn->clearFlag( $conn::DBO_TRX ); // auto-commit mode
 353                 }
 354         }
 355
 356         /**
 357          * Get a LoadMonitor instance
 358          *
 359          * @return ILoadMonitor
 360          */
 361         private function getLoadMonitor() {
 362                 if ( !isset( $this->loadMonitor ) ) {
 363                         $compat = [
 364                                 'LoadMonitor' => LoadMonitor::class,
 365                                 'LoadMonitorNull' => LoadMonitorNull::class,
 366                                 'LoadMonitorMySQL' => LoadMonitorMySQL::class,
 367                         ];
 368
 369                         $class = $this->loadMonitorConfig['class'];
 370                         if ( isset( $compat[$class] ) ) {
 371                                 $class = $compat[$class];
 372                         }
 373
 374                         $this->loadMonitor = new $class(
 375                                 $this, $this->srvCache, $this->wanCache, $this->loadMonitorConfig );
 376                         $this->loadMonitor->setLogger( $this->replLogger );
 377                 }
 378
 379                 return $this->loadMonitor;
 380         }
 381
 382         /**
 383          * @param array $loads
 384          * @param bool|string $domain Domain to get non-lagged for
 385          * @param int $maxLag Restrict the maximum allowed lag to this many seconds
 386          * @return bool|int|string
 387          */
 388         private function getRandomNonLagged( array $loads, $domain = false, $maxLag = INF ) {
 389                 $lags = $this->getLagTimes( $domain );
 390
 391                 # Unset excessively lagged servers
 392                 foreach ( $lags as $i => $lag ) {
 393                         if ( $i !== $this->getWriterIndex() ) {
 394                                 # How much lag this server nominally is allowed to have
 395                                 $maxServerLag = $this->servers[$i]['max lag'] ?? $this->maxLag; // default
 396                                 # Constrain that futher by $maxLag argument
 397                                 $maxServerLag = min( $maxServerLag, $maxLag );
 398
 399                                 $host = $this->getServerName( $i );
 400                                 if ( $lag === false && !is_infinite( $maxServerLag ) ) {
 401                                         $this->replLogger->debug(
 402                                                 __METHOD__ .
 403                                                 ": server {host} is not replicating?", [ 'host' => $host ] );
 404                                         unset( $loads[$i] );
 405                                 } elseif ( $lag > $maxServerLag ) {
 406                                         $this->replLogger->debug(
 407                                                 __METHOD__ .
 408                                                 ": server {host} has {lag} seconds of lag (>= {maxlag})",
 409                                                 [ 'host' => $host, 'lag' => $lag, 'maxlag' => $maxServerLag ]
 410                                         );
 411                                         unset( $loads[$i] );
 412                                 }
 413                         }
 414                 }
 415
 416                 # Find out if all the replica DBs with non-zero load are lagged
 417                 $sum = 0;
 418                 foreach ( $loads as $load ) {
 419                         $sum += $load;
 420                 }
 421                 if ( $sum == 0 ) {
 422                         # No appropriate DB servers except maybe the master and some replica DBs with zero load
 423                         # Do NOT use the master
 424                         # Instead, this function will return false, triggering read-only mode,
 425                         # and a lagged replica DB will be used instead.
 426                         return false;
 427                 }
 428
 429                 if ( count( $loads ) == 0 ) {
 430                         return false;
 431                 }
 432
 433                 # Return a random representative of the remainder
 434                 return ArrayUtils::pickRandom( $loads );
 435         }
 436
 437         /**
 438          * Get the server index to use for a specified server index and query group list
 439          *
 440          * @param int $i Specific server index or DB_MASTER/DB_REPLICA
 441          * @param string[] $groups Non-empty query group list in preference order
 442          * @param string|bool $domain
 443          * @return int A specific server index (replica DBs are checked for connectivity)
 444          */
 445         private function getConnectionIndex( $i, array $groups, $domain ) {
 446                 if ( $i === self::DB_MASTER ) {
 447                         $i = $this->getWriterIndex();
 448                 } elseif ( $i === self::DB_REPLICA ) {
 449                         foreach ( $groups as $group ) {
 450                                 $groupIndex = $this->getReaderIndex( $group, $domain );
 451                                 if ( $groupIndex !== false ) {
 452                                         $i = $groupIndex; // group connection succeeded
 453                                         break;
 454                                 }
 455                         }
 456                 } elseif ( !isset( $this->servers[$i] ) ) {
 457                         throw new UnexpectedValueException( "Invalid server index index #$i" );
 458                 }
 459
 460                 if ( $i === self::DB_REPLICA ) {
 461                         $this->lastError = 'Unknown error'; // set here in case of worse failure
 462                         $this->lastError = 'No working replica DB server: ' . $this->lastError;
 463                         $this->reportConnectionError();
 464                         return null; // unreachable due to exception
 465                 }
 466
 467                 return $i;
 468         }
 469
 470         public function getReaderIndex( $group = false, $domain = false ) {
 471                 if ( $this->getServerCount() == 1 ) {
 472                         // Skip the load balancing if there's only one server
 473                         return $this->getWriterIndex();
 474                 }
 475
 476                 $group = is_string( $group ) ? $group : self::GROUP_GENERIC;
 477
 478                 $index = $this->getExistingReaderIndex( $group );
 479                 if ( $index >= 0 ) {
 480                         // A reader index was already selected and "waitForPos" was handled
 481                         return $index;
 482                 }
 483
 484                 // Use the server weight array for this load group
 485                 if ( isset( $this->groupLoads[$group] ) ) {
 486                         $loads = $this->groupLoads[$group];
 487                 } else {
 488                         $this->connLogger->info( __METHOD__ . ": no loads for group $group" );
 489
 490                         return false;
 491                 }
 492
 493                 // Scale the configured load ratios according to each server's load and state
 494                 $this->getLoadMonitor()->scaleLoads( $loads, $domain );
 495
 496                 // Pick a server to use, accounting for weights, load, lag, and "waitForPos"
 497                 $this->lazyLoadReplicationPositions(); // optimizes server candidate selection
 498                 list( $i, $laggedReplicaMode ) = $this->pickReaderIndex( $loads, $domain );
 499                 if ( $i === false ) {
 500                         // DB connection unsuccessful
 501                         return false;
 502                 }
 503
 504                 // If data seen by queries is expected to reflect the transactions committed as of
 505                 // or after a given replication position then wait for the DB to apply those changes
 506                 if ( $this->waitForPos && $i !== $this->getWriterIndex() && !$this->doWait( $i ) ) {
 507                         // Data will be outdated compared to what was expected
 508                         $laggedReplicaMode = true;
 509                 }
 510
 511                 // Cache the reader index for future DB_REPLICA handles
 512                 $this->setExistingReaderIndex( $group, $i );
 513                 // Record whether the generic reader index is in "lagged replica DB" mode
 514                 if ( $group === self::GROUP_GENERIC && $laggedReplicaMode ) {
 515                         $this->laggedReplicaMode = true;
 516                 }
 517
 518                 $serverName = $this->getServerName( $i );
 519                 $this->connLogger->debug( __METHOD__ . ": using server $serverName for group '$group'" );
 520
 521                 return $i;
 522         }
 523
 524         /**
 525          * Get the server index chosen by the load balancer for use with the given query group
 526          *
 527          * @param string $group Query group; use false for the generic group
 528          * @return int Server index or -1 if none was chosen
 529          */
 530         protected function getExistingReaderIndex( $group ) {
 531                 return $this->readIndexByGroup[$group] ?? -1;
 532         }
 533
 534         /**
 535          * Set the server index chosen by the load balancer for use with the given query group
 536          *
 537          * @param string $group Query group; use false for the generic group
 538          * @param int $index The index of a specific server
 539          */
 540         private function setExistingReaderIndex( $group, $index ) {
 541                 if ( $index < 0 ) {
 542                         throw new UnexpectedValueException( "Cannot set a negative read server index" );
 543                 }
 544                 $this->readIndexByGroup[$group] = $index;
 545         }
 546
 547         /**
 548          * @param array $loads List of server weights
 549          * @param string|bool $domain
 550          * @return array (reader index, lagged replica mode) or (false, false) on failure
 551          */
 552         private function pickReaderIndex( array $loads, $domain = false ) {
 553                 if ( $loads === [] ) {
 554                         throw new InvalidArgumentException( "Server configuration array is empty" );
 555                 }
 556
 557                 /** @var int|bool $i Index of selected server */
 558                 $i = false;
 559                 /** @var bool $laggedReplicaMode Whether server is considered lagged */
 560                 $laggedReplicaMode = false;
 561
 562                 // Quickly look through the available servers for a server that meets criteria...
 563                 $currentLoads = $loads;
 564                 while ( count( $currentLoads ) ) {
 565                         if ( $this->allowLagged || $laggedReplicaMode ) {
 566                                 $i = ArrayUtils::pickRandom( $currentLoads );
 567                         } else {
 568                                 $i = false;
 569                                 if ( $this->waitForPos && $this->waitForPos->asOfTime() ) {
 570                                         $this->replLogger->debug( __METHOD__ . ": replication positions detected" );
 571                                         // "chronologyCallback" sets "waitForPos" for session consistency.
 572                                         // This triggers doWait() after connect, so it's especially good to
 573                                         // avoid lagged servers so as to avoid excessive delay in that method.
 574                                         $ago = microtime( true ) - $this->waitForPos->asOfTime();
 575                                         // Aim for <= 1 second of waiting (being too picky can backfire)
 576                                         $i = $this->getRandomNonLagged( $currentLoads, $domain, $ago + 1 );
 577                                 }
 578                                 if ( $i === false ) {
 579                                         // Any server with less lag than it's 'max lag' param is preferable
 580                                         $i = $this->getRandomNonLagged( $currentLoads, $domain );
 581                                 }
 582                                 if ( $i === false && count( $currentLoads ) ) {
 583                                         // All replica DBs lagged. Switch to read-only mode
 584                                         $this->replLogger->error(
 585                                                 __METHOD__ . ": all replica DBs lagged. Switch to read-only mode" );
 586                                         $i = ArrayUtils::pickRandom( $currentLoads );
 587                                         $laggedReplicaMode = true;
 588                                 }
 589                         }
 590
 591                         if ( $i === false ) {
 592                                 // pickRandom() returned false.
 593                                 // This is permanent and means the configuration or the load monitor
 594                                 // wants us to return false.
 595                                 $this->connLogger->debug( __METHOD__ . ": pickRandom() returned false" );
 596
 597                                 return [ false, false ];
 598                         }
 599
 600                         $serverName = $this->getServerName( $i );
 601                         $this->connLogger->debug( __METHOD__ . ": Using reader #$i: $serverName..." );
 602
 603                         // Get a connection to this server without triggering other server connections
 604                         $conn = $this->getServerConnection( $i, $domain, self::CONN_SILENCE_ERRORS );
 605                         if ( !$conn ) {
 606                                 $this->connLogger->warning( __METHOD__ . ": Failed connecting to $i/$domain" );
 607                                 unset( $currentLoads[$i] ); // avoid this server next iteration
 608                                 $i = false;
 609                                 continue;
 610                         }
 611
 612                         // Decrement reference counter, we are finished with this connection.
 613                         // It will be incremented for the caller later.
 614                         if ( $domain !== false ) {
 615                                 $this->reuseConnection( $conn );
 616                         }
 617
 618                         // Return this server
 619                         break;
 620                 }
 621
 622                 // If all servers were down, quit now
 623                 if ( $currentLoads === [] ) {
 624                         $this->connLogger->error( __METHOD__ . ": all servers down" );
 625                 }
 626
 627                 return [ $i, $laggedReplicaMode ];
 628         }
 629
 630         public function waitFor( $pos ) {
 631                 $oldPos = $this->waitForPos;
 632                 try {
 633                         $this->waitForPos = $pos;
 634                         // If a generic reader connection was already established, then wait now
 635                         $i = $this->getExistingReaderIndex( self::GROUP_GENERIC );
 636                         if ( $i > 0 && !$this->doWait( $i ) ) {
 637                                 $this->laggedReplicaMode = true;
 638                         }
 639                         // Otherwise, wait until a connection is established in getReaderIndex()
 640                 } finally {
 641                         // Restore the older position if it was higher since this is used for lag-protection
 642                         $this->setWaitForPositionIfHigher( $oldPos );
 643                 }
 644         }
 645
 646         public function waitForOne( $pos, $timeout = null ) {
 647                 $oldPos = $this->waitForPos;
 648                 try {
 649                         $this->waitForPos = $pos;
 650
 651                         $i = $this->getExistingReaderIndex( self::GROUP_GENERIC );
 652                         if ( $i <= 0 ) {
 653                                 // Pick a generic replica DB if there isn't one yet
 654                                 $readLoads = $this->groupLoads[self::GROUP_GENERIC];
 655                                 unset( $readLoads[$this->getWriterIndex()] ); // replica DBs only
 656                                 $readLoads = array_filter( $readLoads ); // with non-zero load
 657                                 $i = ArrayUtils::pickRandom( $readLoads );
 658                         }
 659
 660                         if ( $i > 0 ) {
 661                                 $ok = $this->doWait( $i, true, $timeout );
 662                         } else {
 663                                 $ok = true; // no applicable loads
 664                         }
 665                 } finally {
 666                         // Restore the old position; this is used for throttling, not lag-protection
 667                         $this->waitForPos = $oldPos;
 668                 }
 669
 670                 return $ok;
 671         }
 672
 673         public function waitForAll( $pos, $timeout = null ) {
 674                 $timeout = $timeout ?: $this->waitTimeout;
 675
 676                 $oldPos = $this->waitForPos;
 677                 try {
 678                         $this->waitForPos = $pos;
 679                         $serverCount = $this->getServerCount();
 680
 681                         $ok = true;
 682                         for ( $i = 1; $i < $serverCount; $i++ ) {
 683                                 if ( $this->serverHasLoadInAnyGroup( $i ) ) {
 684                                         $start = microtime( true );
 685                                         $ok = $this->doWait( $i, true, $timeout ) && $ok;
 686                                         $timeout -= intval( microtime( true ) - $start );
 687                                         if ( $timeout <= 0 ) {
 688                                                 break; // timeout reached
 689                                         }
 690                                 }
 691                         }
 692                 } finally {
 693                         // Restore the old position; this is used for throttling, not lag-protection
 694                         $this->waitForPos = $oldPos;
 695                 }
 696
 697                 return $ok;
 698         }
 699
 700         /**
 701          * @param int $i Specific server index
 702          * @return bool
 703          */
 704         private function serverHasLoadInAnyGroup( $i ) {
 705                 foreach ( $this->groupLoads as $loadsByIndex ) {
 706                         if ( ( $loadsByIndex[$i] ?? 0 ) > 0 ) {
 707                                 return true;
 708                         }
 709                 }
 710
 711                 return false;
 712         }
 713
 714         /**
 715          * @param DBMasterPos|bool $pos
 716          */
 717         private function setWaitForPositionIfHigher( $pos ) {
 718                 if ( !$pos ) {
 719                         return;
 720                 }
 721
 722                 if ( !$this->waitForPos || $pos->hasReached( $this->waitForPos ) ) {
 723                         $this->waitForPos = $pos;
 724                 }
 725         }
 726
 727         public function getAnyOpenConnection( $i, $flags = 0 ) {
 728                 $i = ( $i === self::DB_MASTER ) ? $this->getWriterIndex() : $i;
 729                 // Connection handles required to be in auto-commit mode use a separate connection
 730                 // pool since the main pool is effected by implicit and explicit transaction rounds
 731                 $autocommit = ( ( $flags & self::CONN_TRX_AUTOCOMMIT ) == self::CONN_TRX_AUTOCOMMIT );
 732
 733                 $conn = false;
 734                 foreach ( $this->conns as $connsByServer ) {
 735                         // Get the connection array server indexes to inspect
 736                         if ( $i === self::DB_REPLICA ) {
 737                                 $indexes = array_keys( $connsByServer );
 738                         } else {
 739                                 $indexes = isset( $connsByServer[$i] ) ? [ $i ] : [];
 740                         }
 741
 742                         foreach ( $indexes as $index ) {
 743                                 $conn = $this->pickAnyOpenConnection( $connsByServer[$index], $autocommit );
 744                                 if ( $conn ) {
 745                                         break;
 746                                 }
 747                         }
 748                 }
 749
 750                 if ( $conn ) {
 751                         $this->enforceConnectionFlags( $conn, $flags );
 752                 }
 753
 754                 return $conn;
 755         }
 756
 757         /**
 758          * @param IDatabase[] $candidateConns
 759          * @param bool $autocommit Whether to only look for auto-commit connections
 760          * @return IDatabase|false An appropriate open connection or false if none found
 761          */
 762         private function pickAnyOpenConnection( $candidateConns, $autocommit ) {
 763                 $conn = false;
 764
 765                 foreach ( $candidateConns as $candidateConn ) {
 766                         if ( !$candidateConn->isOpen() ) {
 767                                 continue; // some sort of error occured?
 768                         } elseif (
 769                                 $autocommit &&
 770                                 (
 771                                         // Connection is transaction round aware
 772                                         !$candidateConn->getLBInfo( 'autoCommitOnly' ) ||
 773                                         // Some sort of error left a transaction open?
 774                                         $candidateConn->trxLevel()
 775                                 )
 776                         ) {
 777                                 continue; // some sort of error left a transaction open?
 778                         }
 779
 780                         $conn = $candidateConn;
 781                 }
 782
 783                 return $conn;
 784         }
 785
 786         /**
 787          * Wait for a given replica DB to catch up to the master pos stored in "waitForPos"
 788          * @param int $index Specific server index
 789          * @param bool $open Check the server even if a new connection has to be made
 790          * @param int|null $timeout Max seconds to wait; default is "waitTimeout"
 791          * @return bool
 792          */
 793         protected function doWait( $index, $open = false, $timeout = null ) {
 794                 $timeout = max( 1, intval( $timeout ?: $this->waitTimeout ) );
 795
 796                 // Check if we already know that the DB has reached this point
 797                 $server = $this->getServerName( $index );
 798                 $key = $this->srvCache->makeGlobalKey( __CLASS__, 'last-known-pos', $server, 'v1' );
 799                 /** @var DBMasterPos $knownReachedPos */
 800                 $knownReachedPos = $this->srvCache->get( $key );
 801                 if (
 802                         $knownReachedPos instanceof DBMasterPos &&
 803                         $knownReachedPos->hasReached( $this->waitForPos )
 804                 ) {
 805                         $this->replLogger->debug(
 806                                 __METHOD__ .
 807                                 ': replica DB {dbserver} known to be caught up (pos >= $knownReachedPos).',
 808                                 [ 'dbserver' => $server ]
 809                         );
 810                         return true;
 811                 }
 812
 813                 // Find a connection to wait on, creating one if needed and allowed
 814                 $close = false; // close the connection afterwards
 815                 $flags = self::CONN_SILENCE_ERRORS;
 816                 $conn = $this->getAnyOpenConnection( $index, $flags );
 817                 if ( !$conn ) {
 818                         if ( !$open ) {
 819                                 $this->replLogger->debug(
 820                                         __METHOD__ . ': no connection open for {dbserver}',
 821                                         [ 'dbserver' => $server ]
 822                                 );
 823
 824                                 return false;
 825                         }
 826                         // Get a connection to this server without triggering other server connections
 827                         $conn = $this->getServerConnection( $index, self::DOMAIN_ANY, $flags );
 828                         if ( !$conn ) {
 829                                 $this->replLogger->warning(
 830                                         __METHOD__ . ': failed to connect to {dbserver}',
 831                                         [ 'dbserver' => $server ]
 832                                 );
 833
 834                                 return false;
 835                         }
 836                         // Avoid connection spam in waitForAll() when connections
 837                         // are made just for the sake of doing this lag check.
 838                         $close = true;
 839                 }
 840
 841                 $this->replLogger->info(
 842                         __METHOD__ .
 843                         ': waiting for replica DB {dbserver} to catch up...',
 844                         [ 'dbserver' => $server ]
 845                 );
 846
 847                 $result = $conn->masterPosWait( $this->waitForPos, $timeout );
 848
 849                 if ( $result === null ) {
 850                         $this->replLogger->warning(
 851                                 __METHOD__ . ': Errored out waiting on {host} pos {pos}',
 852                                 [
 853                                         'host' => $server,
 854                                         'pos' => $this->waitForPos,
 855                                         'trace' => ( new RuntimeException() )->getTraceAsString()
 856                                 ]
 857                         );
 858                         $ok = false;
 859                 } elseif ( $result == -1 ) {
 860                         $this->replLogger->warning(
 861                                 __METHOD__ . ': Timed out waiting on {host} pos {pos}',
 862                                 [
 863                                         'host' => $server,
 864                                         'pos' => $this->waitForPos,
 865                                         'trace' => ( new RuntimeException() )->getTraceAsString()
 866                                 ]
 867                         );
 868                         $ok = false;
 869                 } else {
 870                         $this->replLogger->debug( __METHOD__ . ": done waiting" );
 871                         $ok = true;
 872                         // Remember that the DB reached this point
 873                         $this->srvCache->set( $key, $this->waitForPos, BagOStuff::TTL_DAY );
 874                 }
 875
 876                 if ( $close ) {
 877                         $this->closeConnection( $conn );
 878                 }
 879
 880                 return $ok;
 881         }
 882
 883         public function getConnection( $i, $groups = [], $domain = false, $flags = 0 ) {
 884                 $domain = $this->resolveDomainID( $domain );
 885                 $groups = $this->resolveGroups( $groups, $i );
 886                 $flags = $this->sanitizeConnectionFlags( $flags, $i, $domain );
 887                 // If given DB_MASTER/DB_REPLICA, resolve it to a specific server index. Resolving
 888                 // DB_REPLICA might trigger getServerConnection() calls due to the getReaderIndex()
 889                 // connectivity checks or LoadMonitor::scaleLoads() server state cache regeneration.
 890                 // The use of getServerConnection() instead of getConnection() avoids infinite loops.
 891                 $serverIndex = $this->getConnectionIndex( $i, $groups, $domain );
 892                 // Get an open connection to that server (might trigger a new connection)
 893                 $conn = $this->getServerConnection( $serverIndex, $domain, $flags );
 894                 // Set master DB handles as read-only if there is high replication lag
 895                 if (
 896                         $serverIndex === $this->getWriterIndex() &&
 897                         $this->getLaggedReplicaMode( $domain ) &&
 898                         !is_string( $conn->getLBInfo( 'readOnlyReason' ) )
 899                 ) {
 900                         $reason = ( $this->getExistingReaderIndex( self::GROUP_GENERIC ) >= 0 )
 901                                 ? 'The database is read-only until replication lag decreases.'
 902                                 : 'The database is read-only until replica database servers becomes reachable.';
 903                         $conn->setLBInfo( 'readOnlyReason', $reason );
 904                 }
 905
 906                 return $conn;
 907         }
 908
 909         /**
 910          * @param int $i Specific server index
 911          * @param string $domain Resolved DB domain
 912          * @param int $flags Bitfield of class CONN_* constants
 913          * @return IDatabase|bool
 914          * @throws InvalidArgumentException When the server index is invalid
 915          */
 916         public function getServerConnection( $i, $domain, $flags = 0 ) {
 917                 // Number of connections made before getting the server index and handle
 918                 $priorConnectionsMade = $this->connectionCounter;
 919                 // Get an open connection to this server (might trigger a new connection)
 920                 $conn = $this->localDomain->equals( $domain )
 921                         ? $this->getLocalConnection( $i, $flags )
 922                         : $this->getForeignConnection( $i, $domain, $flags );
 923                 // Throw an error or otherwise bail out if the connection attempt failed
 924                 if ( !( $conn instanceof IDatabase ) ) {
 925                         if ( ( $flags & self::CONN_SILENCE_ERRORS ) != self::CONN_SILENCE_ERRORS ) {
 926                                 $this->reportConnectionError();
 927                         }
 928
 929                         return false;
 930                 }
 931
 932                 // Profile any new connections caused by this method
 933                 if ( $this->connectionCounter > $priorConnectionsMade ) {
 934                         $this->trxProfiler->recordConnection(
 935                                 $conn->getServer(),
 936                                 $conn->getDBname(),
 937                                 ( ( $flags & self::CONN_INTENT_WRITABLE ) == self::CONN_INTENT_WRITABLE )
 938                         );
 939                 }
 940
 941                 if ( !$conn->isOpen() ) {
 942                         $this->errorConnection = $conn;
 943                         // Connection was made but later unrecoverably lost for some reason.
 944                         // Do not return a handle that will just throw exceptions on use, but
 945                         // let the calling code, e.g. getReaderIndex(), try another server.
 946                         return false;
 947                 }
 948
 949                 // Make sure that flags like CONN_TRX_AUTOCOMMIT are respected by this handle
 950                 $this->enforceConnectionFlags( $conn, $flags );
 951                 // Set master DB handles as read-only if the load balancer is configured as read-only
 952                 // or the master database server is running in server-side read-only mode. Note that
 953                 // replica DB handles are always read-only via Database::assertIsWritableMaster().
 954                 // Read-only mode due to replication lag is *avoided* here to avoid recursion.
 955                 if ( $i === $this->getWriterIndex() ) {
 956                         if ( $this->readOnlyReason !== false ) {
 957                                 $readOnlyReason = $this->readOnlyReason;
 958                         } elseif ( $this->isMasterConnectionReadOnly( $conn, $flags ) ) {
 959                                 $readOnlyReason = 'The master database server is running in read-only mode.';
 960                         } else {
 961                                 $readOnlyReason = false;
 962                         }
 963                         $conn->setLBInfo( 'readOnlyReason', $readOnlyReason );
 964                 }
 965
 966                 return $conn;
 967         }
 968
 969         public function reuseConnection( IDatabase $conn ) {
 970                 $serverIndex = $conn->getLBInfo( 'serverIndex' );
 971                 $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 972                 if ( $serverIndex === null || $refCount === null ) {
 973                         return; // non-foreign connection; no domain-use tracking to update
 974                 } elseif ( $conn instanceof DBConnRef ) {
 975                         // DBConnRef already handles calling reuseConnection() and only passes the live
 976                         // Database instance to this method. Any caller passing in a DBConnRef is broken.
 977                         $this->connLogger->error(
 978                                 __METHOD__ . ": got DBConnRef instance.\n" .
 979                                 ( new LogicException() )->getTraceAsString() );
 980
 981                         return;
 982                 }
 983
 984                 if ( $this->disabled ) {
 985                         return; // DBConnRef handle probably survived longer than the LoadBalancer
 986                 }
 987
 988                 if ( $conn->getLBInfo( 'autoCommitOnly' ) ) {
 989                         $connFreeKey = self::KEY_FOREIGN_FREE_NOROUND;
 990                         $connInUseKey = self::KEY_FOREIGN_INUSE_NOROUND;
 991                 } else {
 992                         $connFreeKey = self::KEY_FOREIGN_FREE;
 993                         $connInUseKey = self::KEY_FOREIGN_INUSE;
 994                 }
 995
 996                 $domain = $conn->getDomainID();
 997                 if ( !isset( $this->conns[$connInUseKey][$serverIndex][$domain] ) ) {
 998                         throw new InvalidArgumentException(
 999                                 "Connection $serverIndex/$domain not found; it may have already been freed" );
1000                 } elseif ( $this->conns[$connInUseKey][$serverIndex][$domain] !== $conn ) {
1001                         throw new InvalidArgumentException(
1002                                 "Connection $serverIndex/$domain mismatched; it may have already been freed" );
1003                 }
1004
1005                 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
1006                 if ( $refCount <= 0 ) {
1007                         $this->conns[$connFreeKey][$serverIndex][$domain] = $conn;
1008                         unset( $this->conns[$connInUseKey][$serverIndex][$domain] );
1009                         if ( !$this->conns[$connInUseKey][$serverIndex] ) {
1010                                 unset( $this->conns[$connInUseKey][$serverIndex] ); // clean up
1011                         }
1012                         $this->connLogger->debug( __METHOD__ . ": freed connection $serverIndex/$domain" );
1013                 } else {
1014                         $this->connLogger->debug( __METHOD__ .
1015                                 ": reference count for $serverIndex/$domain reduced to $refCount" );
1016                 }
1017         }
1018
1019         public function getConnectionRef( $i, $groups = [], $domain = false, $flags = 0 ) {
1020                 $domain = $this->resolveDomainID( $domain );
1021                 $role = $this->getRoleFromIndex( $i );
1022
1023                 return new DBConnRef( $this, $this->getConnection( $i, $groups, $domain, $flags ), $role );
1024         }
1025
1026         public function getLazyConnectionRef( $i, $groups = [], $domain = false, $flags = 0 ) {
1027                 $domain = $this->resolveDomainID( $domain );
1028                 $role = $this->getRoleFromIndex( $i );
1029
1030                 return new DBConnRef( $this, [ $i, $groups, $domain, $flags ], $role );
1031         }
1032
1033         public function getMaintenanceConnectionRef( $i, $groups = [], $domain = false, $flags = 0 ) {
1034                 $domain = $this->resolveDomainID( $domain );
1035                 $role = $this->getRoleFromIndex( $i );
1036
1037                 return new MaintainableDBConnRef(
1038                         $this, $this->getConnection( $i, $groups, $domain, $flags ), $role );
1039         }
1040
1041         /**
1042          * @param int $i Server index or DB_MASTER/DB_REPLICA
1043          * @return int One of DB_MASTER/DB_REPLICA
1044          */
1045         private function getRoleFromIndex( $i ) {
1046                 return ( $i === self::DB_MASTER || $i === $this->getWriterIndex() )
1047                         ? self::DB_MASTER
1048                         : self::DB_REPLICA;
1049         }
1050
1051         /**
1052          * @param int $i
1053          * @param string|bool $domain
1054          * @param int $flags
1055          * @return Database|bool Live database handle or false on failure
1056          * @deprecated Since 1.34 Use getConnection() instead
1057          */
1058         public function openConnection( $i, $domain = false, $flags = 0 ) {
1059                 return $this->getConnection( $i, [], $domain, $flags | self::CONN_SILENCE_ERRORS );
1060         }
1061
1062         /**
1063          * Open a connection to a local DB, or return one if it is already open.
1064          *
1065          * On error, returns false, and the connection which caused the
1066          * error will be available via $this->errorConnection.
1067          *
1068          * @note If disable() was called on this LoadBalancer, this method will throw a DBAccessError.
1069          *
1070          * @param int $i Server index
1071          * @param int $flags Class CONN_* constant bitfield
1072          * @return Database
1073          * @throws InvalidArgumentException When the server index is invalid
1074          * @throws UnexpectedValueException When the DB domain of the connection is corrupted
1075          */
1076         private function getLocalConnection( $i, $flags = 0 ) {
1077                 // Connection handles required to be in auto-commit mode use a separate connection
1078                 // pool since the main pool is effected by implicit and explicit transaction rounds
1079                 $autoCommit = ( ( $flags & self::CONN_TRX_AUTOCOMMIT ) == self::CONN_TRX_AUTOCOMMIT );
1080
1081                 $connKey = $autoCommit ? self::KEY_LOCAL_NOROUND : self::KEY_LOCAL;
1082                 if ( isset( $this->conns[$connKey][$i][0] ) ) {
1083                         $conn = $this->conns[$connKey][$i][0];
1084                 } else {
1085                         // Open a new connection
1086                         $server = $this->getServerInfoStrict( $i );
1087                         $server['serverIndex'] = $i;
1088                         $server['autoCommitOnly'] = $autoCommit;
1089                         $conn = $this->reallyOpenConnection( $server, $this->localDomain );
1090                         $host = $this->getServerName( $i );
1091                         if ( $conn->isOpen() ) {
1092                                 $this->connLogger->debug(
1093                                         __METHOD__ . ": connected to database $i at '$host'." );
1094                                 $this->conns[$connKey][$i][0] = $conn;
1095                         } else {
1096                                 $this->connLogger->warning(
1097                                         __METHOD__ . ": failed to connect to database $i at '$host'." );
1098                                 $this->errorConnection = $conn;
1099                                 $conn = false;
1100                         }
1101                 }
1102
1103                 // Final sanity check to make sure the right domain is selected
1104                 if (
1105                         $conn instanceof IDatabase &&
1106                         !$this->localDomain->isCompatible( $conn->getDomainID() )
1107                 ) {
1108                         throw new UnexpectedValueException(
1109                                 "Got connection to '{$conn->getDomainID()}', " .
1110                                 "but expected local domain ('{$this->localDomain}')" );
1111                 }
1112
1113                 return $conn;
1114         }
1115
1116         /**
1117          * Open a connection to a foreign DB, or return one if it is already open.
1118          *
1119          * Increments a reference count on the returned connection which locks the
1120          * connection to the requested domain. This reference count can be
1121          * decremented by calling reuseConnection().
1122          *
1123          * If a connection is open to the appropriate server already, but with the wrong
1124          * database, it will be switched to the right database and returned, as long as
1125          * it has been freed first with reuseConnection().
1126          *
1127          * On error, returns false, and the connection which caused the
1128          * error will be available via $this->errorConnection.
1129          *
1130          * @note If disable() was called on this LoadBalancer, this method will throw a DBAccessError.
1131          *
1132          * @param int $i Server index
1133          * @param string $domain Domain ID to open
1134          * @param int $flags Class CONN_* constant bitfield
1135          * @return Database|bool Returns false on connection error
1136          * @throws DBError When database selection fails
1137          * @throws InvalidArgumentException When the server index is invalid
1138          * @throws UnexpectedValueException When the DB domain of the connection is corrupted
1139          */
1140         private function getForeignConnection( $i, $domain, $flags = 0 ) {
1141                 $domainInstance = DatabaseDomain::newFromId( $domain );
1142                 // Connection handles required to be in auto-commit mode use a separate connection
1143                 // pool since the main pool is effected by implicit and explicit transaction rounds
1144                 $autoCommit = ( ( $flags & self::CONN_TRX_AUTOCOMMIT ) == self::CONN_TRX_AUTOCOMMIT );
1145
1146                 if ( $autoCommit ) {
1147                         $connFreeKey = self::KEY_FOREIGN_FREE_NOROUND;
1148                         $connInUseKey = self::KEY_FOREIGN_INUSE_NOROUND;
1149                 } else {
1150                         $connFreeKey = self::KEY_FOREIGN_FREE;
1151                         $connInUseKey = self::KEY_FOREIGN_INUSE;
1152                 }
1153
1154                 /** @var Database $conn */
1155                 $conn = null;
1156
1157                 if ( isset( $this->conns[$connInUseKey][$i][$domain] ) ) {
1158                         // Reuse an in-use connection for the same domain
1159                         $conn = $this->conns[$connInUseKey][$i][$domain];
1160                         $this->connLogger->debug( __METHOD__ . ": reusing connection $i/$domain" );
1161                 } elseif ( isset( $this->conns[$connFreeKey][$i][$domain] ) ) {
1162                         // Reuse a free connection for the same domain
1163                         $conn = $this->conns[$connFreeKey][$i][$domain];
1164                         unset( $this->conns[$connFreeKey][$i][$domain] );
1165                         $this->conns[$connInUseKey][$i][$domain] = $conn;
1166                         $this->connLogger->debug( __METHOD__ . ": reusing free connection $i/$domain" );
1167                 } elseif ( !empty( $this->conns[$connFreeKey][$i] ) ) {
1168                         // Reuse a free connection from another domain if possible
1169                         foreach ( $this->conns[$connFreeKey][$i] as $oldDomain => $conn ) {
1170                                 if ( $domainInstance->getDatabase() !== null ) {
1171                                         // Check if changing the database will require a new connection.
1172                                         // In that case, leave the connection handle alone and keep looking.
1173                                         // This prevents connections from being closed mid-transaction and can
1174                                         // also avoid overhead if the same database will later be requested.
1175                                         if (
1176                                                 $conn->databasesAreIndependent() &&
1177                                                 $conn->getDBname() !== $domainInstance->getDatabase()
1178                                         ) {
1179                                                 continue;
1180                                         }
1181                                         // Select the new database, schema, and prefix
1182                                         $conn->selectDomain( $domainInstance );
1183                                 } else {
1184                                         // Stay on the current database, but update the schema/prefix
1185                                         $conn->dbSchema( $domainInstance->getSchema() );
1186                                         $conn->tablePrefix( $domainInstance->getTablePrefix() );
1187                                 }
1188                                 unset( $this->conns[$connFreeKey][$i][$oldDomain] );
1189                                 // Note that if $domain is an empty string, getDomainID() might not match it
1190                                 $this->conns[$connInUseKey][$i][$conn->getDomainID()] = $conn;
1191                                 $this->connLogger->debug( __METHOD__ .
1192                                         ": reusing free connection from $oldDomain for $domain" );
1193                                 break;
1194                         }
1195                 }
1196
1197                 if ( !$conn ) {
1198                         // Open a new connection
1199                         $server = $this->getServerInfoStrict( $i );
1200                         $server['serverIndex'] = $i;
1201                         $server['foreignPoolRefCount'] = 0;
1202                         $server['foreign'] = true;
1203                         $server['autoCommitOnly'] = $autoCommit;
1204                         $conn = $this->reallyOpenConnection( $server, $domainInstance );
1205                         if ( !$conn->isOpen() ) {
1206                                 $this->connLogger->warning( __METHOD__ . ": connection error for $i/$domain" );
1207                                 $this->errorConnection = $conn;
1208                                 $conn = false;
1209                         } else {
1210                                 // Note that if $domain is an empty string, getDomainID() might not match it
1211                                 $this->conns[$connInUseKey][$i][$conn->getDomainID()] = $conn;
1212                                 $this->connLogger->debug( __METHOD__ . ": opened new connection for $i/$domain" );
1213                         }
1214                 }
1215
1216                 if ( $conn instanceof IDatabase ) {
1217                         // Final sanity check to make sure the right domain is selected
1218                         if ( !$domainInstance->isCompatible( $conn->getDomainID() ) ) {
1219                                 throw new UnexpectedValueException(
1220                                         "Got connection to '{$conn->getDomainID()}', but expected '$domain'" );
1221                         }
1222                         // Increment reference count
1223                         $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
1224                         $conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
1225                 }
1226
1227                 return $conn;
1228         }
1229
1230         public function getServerAttributes( $i ) {
1231                 return Database::attributesFromType(
1232                         $this->getServerType( $i ),
1233                         $this->servers[$i]['driver'] ?? null
1234                 );
1235         }
1236
1237         /**
1238          * Test if the specified index represents an open connection
1239          *
1240          * @param int $index Server index
1241          * @return bool
1242          */
1243         private function isOpen( $index ) {
1244                 return (bool)$this->getAnyOpenConnection( $index );
1245         }
1246
1247         /**
1248          * Open a new network connection to a server (uncached)
1249          *
1250          * Returns a Database object whether or not the connection was successful.
1251          *
1252          * @param array $server
1253          * @param DatabaseDomain $domain Domain the connection is for, possibly unspecified
1254          * @return Database
1255          * @throws DBAccessError
1256          * @throws InvalidArgumentException
1257          */
1258         protected function reallyOpenConnection( array $server, DatabaseDomain $domain ) {
1259                 if ( $this->disabled ) {
1260                         throw new DBAccessError();
1261                 }
1262
1263                 if ( $domain->getDatabase() === null ) {
1264                         // The database domain does not specify a DB name and some database systems require a
1265                         // valid DB specified on connection. The $server configuration array contains a default
1266                         // DB name to use for connections in such cases.
1267                         if ( $server['type'] === 'mysql' ) {
1268                                 // For MySQL, DATABASE and SCHEMA are synonyms, connections need not specify a DB,
1269                                 // and the DB name in $server might not exist due to legacy reasons (the default
1270                                 // domain used to ignore the local LB domain, even when mismatched).
1271                                 $server['dbname'] = null;
1272                         }
1273                 } else {
1274                         $server['dbname'] = $domain->getDatabase();
1275                 }
1276
1277                 if ( $domain->getSchema() !== null ) {
1278                         $server['schema'] = $domain->getSchema();
1279                 }
1280
1281                 // It is always possible to connect with any prefix, even the empty string
1282                 $server['tablePrefix'] = $domain->getTablePrefix();
1283
1284                 // Let the handle know what the cluster master is (e.g. "db1052")
1285                 $masterName = $this->getServerName( $this->getWriterIndex() );
1286                 $server['clusterMasterHost'] = $masterName;
1287
1288                 $server['srvCache'] = $this->srvCache;
1289                 // Set loggers and profilers
1290                 $server['connLogger'] = $this->connLogger;
1291                 $server['queryLogger'] = $this->queryLogger;
1292                 $server['errorLogger'] = $this->errorLogger;
1293                 $server['deprecationLogger'] = $this->deprecationLogger;
1294                 $server['profiler'] = $this->profiler;
1295                 $server['trxProfiler'] = $this->trxProfiler;
1296                 // Use the same agent and PHP mode for all DB handles
1297                 $server['cliMode'] = $this->cliMode;
1298                 $server['agent'] = $this->agent;
1299                 // Use DBO_DEFAULT flags by default for LoadBalancer managed databases. Assume that the
1300                 // application calls LoadBalancer::commitMasterChanges() before the PHP script completes.
1301                 $server['flags'] = $server['flags'] ?? IDatabase::DBO_DEFAULT;
1302
1303                 // Create a live connection object
1304                 try {
1305                         $conn = Database::factory( $server['type'], $server );
1306                         // Log when many connection are made on requests
1307                         ++$this->connectionCounter;
1308                         $currentConnCount = $this->getCurrentConnectionCount();
1309                         if ( $currentConnCount >= self::CONN_HELD_WARN_THRESHOLD ) {
1310                                 $this->perfLogger->warning(
1311                                         __METHOD__ . ": {connections}+ connections made (master={masterdb})",
1312                                         [ 'connections' => $currentConnCount, 'masterdb' => $masterName ]
1313                                 );
1314                         }
1315                 } catch ( DBConnectionError $e ) {
1316                         // FIXME: This is probably the ugliest thing I have ever done to
1317                         // PHP. I'm half-expecting it to segfault, just out of disgust. -- TS
1318                         $conn = $e->db;
1319                 }
1320
1321                 $conn->setLBInfo( $server );
1322                 $conn->setLazyMasterHandle(
1323                         $this->getLazyConnectionRef( self::DB_MASTER, [], $conn->getDomainID() )
1324                 );
1325                 $conn->setTableAliases( $this->tableAliases );
1326                 $conn->setIndexAliases( $this->indexAliases );
1327
1328                 if ( $server['serverIndex'] === $this->getWriterIndex() ) {
1329                         if ( $this->trxRoundId !== false ) {
1330                                 $this->applyTransactionRoundFlags( $conn );
1331                         }
1332                         foreach ( $this->trxRecurringCallbacks as $name => $callback ) {
1333                                 $conn->setTransactionListener( $name, $callback );
1334                         }
1335                 }
1336
1337                 $this->lazyLoadReplicationPositions(); // session consistency
1338
1339                 return $conn;
1340         }
1341
1342         /**
1343          * Make sure that any "waitForPos" positions are loaded and available to doWait()
1344          */
1345         private function lazyLoadReplicationPositions() {
1346                 if ( !$this->connectionAttempted && $this->chronologyCallback ) {
1347                         $this->connectionAttempted = true;
1348                         ( $this->chronologyCallback )( $this ); // generally calls waitFor()
1349                         $this->connLogger->debug( __METHOD__ . ': executed chronology callback.' );
1350                 }
1351         }
1352
1353         /**
1354          * @throws DBConnectionError
1355          */
1356         private function reportConnectionError() {
1357                 $conn = $this->errorConnection; // the connection which caused the error
1358                 $context = [
1359                         'method' => __METHOD__,
1360                         'last_error' => $this->lastError,
1361                 ];
1362
1363                 if ( $conn instanceof IDatabase ) {
1364                         $context['db_server'] = $conn->getServer();
1365                         $this->connLogger->warning(
1366                                 __METHOD__ . ": connection error: {last_error} ({db_server})",
1367                                 $context
1368                         );
1369
1370                         throw new DBConnectionError( $conn, "{$this->lastError} ({$context['db_server']})" );
1371                 } else {
1372                         // No last connection, probably due to all servers being too busy
1373                         $this->connLogger->error(
1374                                 __METHOD__ .
1375                                 ": LB failure with no last connection. Connection error: {last_error}",
1376                                 $context
1377                         );
1378
1379                         // If all servers were busy, "lastError" will contain something sensible
1380                         throw new DBConnectionError( null, $this->lastError );
1381                 }
1382         }
1383
1384         public function getWriterIndex() {
1385                 return 0;
1386         }
1387
1388         /**
1389          * Returns true if the specified index is a valid server index
1390          *
1391          * @param int $i
1392          * @return bool
1393          * @deprecated Since 1.34
1394          */
1395         public function haveIndex( $i ) {
1396                 return array_key_exists( $i, $this->servers );
1397         }
1398
1399         /**
1400          * Returns true if the specified index is valid and has non-zero load
1401          *
1402          * @param int $i
1403          * @return bool
1404          * @deprecated Since 1.34
1405          */
1406         public function isNonZeroLoad( $i ) {
1407                 return ( isset( $this->servers[$i] ) && $this->groupLoads[self::GROUP_GENERIC][$i] > 0 );
1408         }
1409
1410         public function getServerCount() {
1411                 return count( $this->servers );
1412         }
1413
1414         public function hasReplicaServers() {
1415                 return ( $this->getServerCount() > 1 );
1416         }
1417
1418         public function hasStreamingReplicaServers() {
1419                 foreach ( $this->servers as $i => $server ) {
1420                         if ( $i !== $this->getWriterIndex() && empty( $server['is static'] ) ) {
1421                                 return true;
1422                         }
1423                 }
1424
1425                 return false;
1426         }
1427
1428         public function getServerName( $i ) {
1429                 $name = $this->servers[$i]['hostName'] ?? ( $this->servers[$i]['host'] ?? '' );
1430
1431                 return ( $name != '' ) ? $name : 'localhost';
1432         }
1433
1434         public function getServerInfo( $i ) {
1435                 return $this->servers[$i] ?? false;
1436         }
1437
1438         public function getServerType( $i ) {
1439                 return $this->servers[$i]['type'] ?? 'unknown';
1440         }
1441
1442         public function getMasterPos() {
1443                 $index = $this->getWriterIndex();
1444
1445                 $conn = $this->getAnyOpenConnection( $index );
1446                 if ( $conn ) {
1447                         return $conn->getMasterPos();
1448                 }
1449
1450                 $conn = $this->getConnection( $index, self::CONN_SILENCE_ERRORS );
1451                 if ( !$conn ) {
1452                         $this->reportConnectionError();
1453                         return null; // unreachable due to exception
1454                 }
1455
1456                 try {
1457                         $pos = $conn->getMasterPos();
1458                 } finally {
1459                         $this->closeConnection( $conn );
1460                 }
1461
1462                 return $pos;
1463         }
1464
1465         public function getReplicaResumePos() {
1466                 // Get the position of any existing master server connection
1467                 $masterConn = $this->getAnyOpenConnection( $this->getWriterIndex() );
1468                 if ( $masterConn ) {
1469                         return $masterConn->getMasterPos();
1470                 }
1471
1472                 // Get the highest position of any existing replica server connection
1473                 $highestPos = false;
1474                 $serverCount = $this->getServerCount();
1475                 for ( $i = 1; $i < $serverCount; $i++ ) {
1476                         if ( !empty( $this->servers[$i]['is static'] ) ) {
1477                                 continue; // server does not use replication
1478                         }
1479
1480                         $conn = $this->getAnyOpenConnection( $i );
1481                         $pos = $conn ? $conn->getReplicaPos() : false;
1482                         if ( !$pos ) {
1483                                 continue; // no open connection or could not get position
1484                         }
1485
1486                         $highestPos = $highestPos ?: $pos;
1487                         if ( $pos->hasReached( $highestPos ) ) {
1488                                 $highestPos = $pos;
1489                         }
1490                 }
1491
1492                 return $highestPos;
1493         }
1494
1495         public function disable() {
1496                 $this->closeAll();
1497                 $this->disabled = true;
1498         }
1499
1500         public function closeAll() {
1501                 if ( $this->ownerId === null ) {
1502                         /** @noinspection PhpUnusedLocalVariableInspection */
1503                         $scope = ScopedCallback::newScopedIgnoreUserAbort();
1504                 }
1505
1506                 $fname = __METHOD__;
1507                 $this->forEachOpenConnection( function ( IDatabase $conn ) use ( $fname ) {
1508                         $host = $conn->getServer();
1509                         $this->connLogger->debug(
1510                                 $fname . ": closing connection to database '$host'." );
1511                         $conn->close();
1512                 } );
1513
1514                 $this->conns = self::newTrackedConnectionsArray();
1515         }
1516
1517         public function closeConnection( IDatabase $conn ) {
1518                 if ( $conn instanceof DBConnRef ) {
1519                         // Avoid calling close() but still leaving the handle in the pool
1520                         throw new RuntimeException( 'Cannot close DBConnRef instance; it must be shareable' );
1521                 }
1522
1523                 $serverIndex = $conn->getLBInfo( 'serverIndex' );
1524                 foreach ( $this->conns as $type => $connsByServer ) {
1525                         if ( !isset( $connsByServer[$serverIndex] ) ) {
1526                                 continue;
1527                         }
1528
1529                         foreach ( $connsByServer[$serverIndex] as $i => $trackedConn ) {
1530                                 if ( $conn === $trackedConn ) {
1531                                         $host = $this->getServerName( $i );
1532                                         $this->connLogger->debug(
1533                                                 __METHOD__ . ": closing connection to database $i at '$host'." );
1534                                         unset( $this->conns[$type][$serverIndex][$i] );
1535                                         break 2;
1536                                 }
1537                         }
1538                 }
1539
1540                 $conn->close();
1541         }
1542
1543         public function commitAll( $fname = __METHOD__, $owner = null ) {
1544                 $this->commitMasterChanges( $fname, $owner );
1545                 $this->flushMasterSnapshots( $fname );
1546                 $this->flushReplicaSnapshots( $fname );
1547         }
1548
1549         public function finalizeMasterChanges( $fname = __METHOD__, $owner = null ) {
1550                 $this->assertOwnership( $fname, $owner );
1551                 $this->assertTransactionRoundStage( [ self::ROUND_CURSORY, self::ROUND_FINALIZED ] );
1552                 if ( $this->ownerId === null ) {
1553                         /** @noinspection PhpUnusedLocalVariableInspection */
1554                         $scope = ScopedCallback::newScopedIgnoreUserAbort();
1555                 }
1556
1557                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1558                 // Loop until callbacks stop adding callbacks on other connections
1559                 $total = 0;
1560                 do {
1561                         $count = 0; // callbacks execution attempts
1562                         $this->forEachOpenMasterConnection( function ( Database $conn ) use ( &$count ) {
1563                                 // Run any pre-commit callbacks while leaving the post-commit ones suppressed.
1564                                 // Any error should cause all (peer) transactions to be rolled back together.
1565                                 $count += $conn->runOnTransactionPreCommitCallbacks();
1566                         } );
1567                         $total += $count;
1568                 } while ( $count > 0 );
1569                 // Defer post-commit callbacks until after COMMIT/ROLLBACK happens on all handles
1570                 $this->forEachOpenMasterConnection( function ( Database $conn ) {
1571                         $conn->setTrxEndCallbackSuppression( true );
1572                 } );
1573                 $this->trxRoundStage = self::ROUND_FINALIZED;
1574
1575                 return $total;
1576         }
1577
1578         public function approveMasterChanges( array $options, $fname = __METHOD__, $owner = null ) {
1579                 $this->assertOwnership( $fname, $owner );
1580                 $this->assertTransactionRoundStage( self::ROUND_FINALIZED );
1581                 if ( $this->ownerId === null ) {
1582                         /** @noinspection PhpUnusedLocalVariableInspection */
1583                         $scope = ScopedCallback::newScopedIgnoreUserAbort();
1584                 }
1585
1586                 $limit = $options['maxWriteDuration'] ?? 0;
1587
1588                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1589                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( $limit ) {
1590                         // If atomic sections or explicit transactions are still open, some caller must have
1591                         // caught an exception but failed to properly rollback any changes. Detect that and
1592                         // throw and error (causing rollback).
1593                         $conn->assertNoOpenTransactions();
1594                         // Assert that the time to replicate the transaction will be sane.
1595                         // If this fails, then all DB transactions will be rollback back together.
1596                         $time = $conn->pendingWriteQueryDuration( $conn::ESTIMATE_DB_APPLY );
1597                         if ( $limit > 0 && $time > $limit ) {
1598                                 throw new DBTransactionSizeError(
1599                                         $conn,
1600                                         "Transaction spent $time second(s) in writes, exceeding the limit of $limit",
1601                                         [ $time, $limit ]
1602                                 );
1603                         }
1604                         // If a connection sits idle while slow queries execute on another, that connection
1605                         // may end up dropped before the commit round is reached. Ping servers to detect this.
1606                         if ( $conn->writesOrCallbacksPending() && !$conn->ping() ) {
1607                                 throw new DBTransactionError(
1608                                         $conn,
1609                                         "A connection to the {$conn->getDBname()} database was lost before commit"
1610                                 );
1611                         }
1612                 } );
1613                 $this->trxRoundStage = self::ROUND_APPROVED;
1614         }
1615
1616         public function beginMasterChanges( $fname = __METHOD__, $owner = null ) {
1617                 $this->assertOwnership( $fname, $owner );
1618                 if ( $this->trxRoundId !== false ) {
1619                         throw new DBTransactionError(
1620                                 null,
1621                                 "$fname: Transaction round '{$this->trxRoundId}' already started"
1622                         );
1623                 }
1624                 $this->assertTransactionRoundStage( self::ROUND_CURSORY );
1625                 if ( $this->ownerId === null ) {
1626                         /** @noinspection PhpUnusedLocalVariableInspection */
1627                         $scope = ScopedCallback::newScopedIgnoreUserAbort();
1628                 }
1629
1630                 // Clear any empty transactions (no writes/callbacks) from the implicit round
1631                 $this->flushMasterSnapshots( $fname );
1632
1633                 $this->trxRoundId = $fname;
1634                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1635                 // Mark applicable handles as participating in this explicit transaction round.
1636                 // For each of these handles, any writes and callbacks will be tied to a single
1637                 // transaction. The (peer) handles will reject begin()/commit() calls unless they
1638                 // are part of an en masse commit or an en masse rollback.
1639                 $this->forEachOpenMasterConnection( function ( Database $conn ) {
1640                         $this->applyTransactionRoundFlags( $conn );
1641                 } );
1642                 $this->trxRoundStage = self::ROUND_CURSORY;
1643         }
1644
1645         public function commitMasterChanges( $fname = __METHOD__, $owner = null ) {
1646                 $this->assertOwnership( $fname, $owner );
1647                 $this->assertTransactionRoundStage( self::ROUND_APPROVED );
1648                 if ( $this->ownerId === null ) {
1649                         /** @noinspection PhpUnusedLocalVariableInspection */
1650                         $scope = ScopedCallback::newScopedIgnoreUserAbort();
1651                 }
1652
1653                 $failures = [];
1654
1655                 $restore = ( $this->trxRoundId !== false );
1656                 $this->trxRoundId = false;
1657                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1658                 // Commit any writes and clear any snapshots as well (callbacks require AUTOCOMMIT).
1659                 // Note that callbacks should already be suppressed due to finalizeMasterChanges().
1660                 $this->forEachOpenMasterConnection(
1661                         function ( IDatabase $conn ) use ( $fname, &$failures ) {
1662                                 try {
1663                                         $conn->commit( $fname, $conn::FLUSHING_ALL_PEERS );
1664                                 } catch ( DBError $e ) {
1665                                         ( $this->errorLogger )( $e );
1666                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1667                                 }
1668                         }
1669                 );
1670                 if ( $failures ) {
1671                         throw new DBTransactionError(
1672                                 null,
1673                                 "$fname: Commit failed on server(s) " . implode( "\n", array_unique( $failures ) )
1674                         );
1675                 }
1676                 if ( $restore ) {
1677                         // Unmark handles as participating in this explicit transaction round
1678                         $this->forEachOpenMasterConnection( function ( Database $conn ) {
1679                                 $this->undoTransactionRoundFlags( $conn );
1680                         } );
1681                 }
1682                 $this->trxRoundStage = self::ROUND_COMMIT_CALLBACKS;
1683         }
1684
1685         public function runMasterTransactionIdleCallbacks( $fname = __METHOD__, $owner = null ) {
1686                 $this->assertOwnership( $fname, $owner );
1687                 if ( $this->trxRoundStage === self::ROUND_COMMIT_CALLBACKS ) {
1688                         $type = IDatabase::TRIGGER_COMMIT;
1689                 } elseif ( $this->trxRoundStage === self::ROUND_ROLLBACK_CALLBACKS ) {
1690                         $type = IDatabase::TRIGGER_ROLLBACK;
1691                 } else {
1692                         throw new DBTransactionError(
1693                                 null,
1694                                 "Transaction should be in the callback stage (not '{$this->trxRoundStage}')"
1695                         );
1696                 }
1697                 if ( $this->ownerId === null ) {
1698                         /** @noinspection PhpUnusedLocalVariableInspection */
1699                         $scope = ScopedCallback::newScopedIgnoreUserAbort();
1700                 }
1701
1702                 $oldStage = $this->trxRoundStage;
1703                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1704
1705                 // Now that the COMMIT/ROLLBACK step is over, enable post-commit callback runs
1706                 $this->forEachOpenMasterConnection( function ( Database $conn ) {
1707                         $conn->setTrxEndCallbackSuppression( false );
1708                 } );
1709
1710                 $e = null; // first exception
1711                 $fname = __METHOD__;
1712                 // Loop until callbacks stop adding callbacks on other connections
1713                 do {
1714                         // Run any pending callbacks for each connection...
1715                         $count = 0; // callback execution attempts
1716                         $this->forEachOpenMasterConnection(
1717                                 function ( Database $conn ) use ( $type, &$e, &$count ) {
1718                                         if ( $conn->trxLevel() ) {
1719                                                 return; // retry in the next iteration, after commit() is called
1720                                         }
1721                                         try {
1722                                                 $count += $conn->runOnTransactionIdleCallbacks( $type );
1723                                         } catch ( Exception $ex ) {
1724                                                 $e = $e ?: $ex;
1725                                         }
1726                                 }
1727                         );
1728                         // Clear out any active transactions left over from callbacks...
1729                         $this->forEachOpenMasterConnection( function ( Database $conn ) use ( &$e, $fname ) {
1730                                 if ( $conn->writesPending() ) {
1731                                         // A callback from another handle wrote to this one and DBO_TRX is set
1732                                         $this->queryLogger->warning( $fname . ": found writes pending." );
1733                                         $fnames = implode( ', ', $conn->pendingWriteAndCallbackCallers() );
1734                                         $this->queryLogger->warning(
1735                                                 $fname . ": found writes pending ($fnames).",
1736                                                 [
1737                                                         'db_server' => $conn->getServer(),
1738                                                         'db_name' => $conn->getDBname()
1739                                                 ]
1740                                         );
1741                                 } elseif ( $conn->trxLevel() ) {
1742                                         // A callback from another handle read from this one and DBO_TRX is set,
1743                                         // which can easily happen if there is only one DB (no replicas)
1744                                         $this->queryLogger->debug( $fname . ": found empty transaction." );
1745                                 }
1746                                 try {
1747                                         $conn->commit( $fname, $conn::FLUSHING_ALL_PEERS );
1748                                 } catch ( Exception $ex ) {
1749                                         $e = $e ?: $ex;
1750                                 }
1751                         } );
1752                 } while ( $count > 0 );
1753
1754                 $this->trxRoundStage = $oldStage;
1755
1756                 return $e;
1757         }
1758
1759         public function runMasterTransactionListenerCallbacks( $fname = __METHOD__, $owner = null ) {
1760                 $this->assertOwnership( $fname, $owner );
1761                 if ( $this->trxRoundStage === self::ROUND_COMMIT_CALLBACKS ) {
1762                         $type = IDatabase::TRIGGER_COMMIT;
1763                 } elseif ( $this->trxRoundStage === self::ROUND_ROLLBACK_CALLBACKS ) {
1764                         $type = IDatabase::TRIGGER_ROLLBACK;
1765                 } else {
1766                         throw new DBTransactionError(
1767                                 null,
1768                                 "Transaction should be in the callback stage (not '{$this->trxRoundStage}')"
1769                         );
1770                 }
1771                 if ( $this->ownerId === null ) {
1772                         /** @noinspection PhpUnusedLocalVariableInspection */
1773                         $scope = ScopedCallback::newScopedIgnoreUserAbort();
1774                 }
1775
1776                 $e = null;
1777
1778                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1779                 $this->forEachOpenMasterConnection( function ( Database $conn ) use ( $type, &$e ) {
1780                         try {
1781                                 $conn->runTransactionListenerCallbacks( $type );
1782                         } catch ( Exception $ex ) {
1783                                 $e = $e ?: $ex;
1784                         }
1785                 } );
1786                 $this->trxRoundStage = self::ROUND_CURSORY;
1787
1788                 return $e;
1789         }
1790
1791         public function rollbackMasterChanges( $fname = __METHOD__, $owner = null ) {
1792                 $this->assertOwnership( $fname, $owner );
1793                 if ( $this->ownerId === null ) {
1794                         /** @noinspection PhpUnusedLocalVariableInspection */
1795                         $scope = ScopedCallback::newScopedIgnoreUserAbort();
1796                 }
1797
1798                 $restore = ( $this->trxRoundId !== false );
1799                 $this->trxRoundId = false;
1800                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1801                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( $fname ) {
1802                         $conn->rollback( $fname, $conn::FLUSHING_ALL_PEERS );
1803                 } );
1804                 if ( $restore ) {
1805                         // Unmark handles as participating in this explicit transaction round
1806                         $this->forEachOpenMasterConnection( function ( Database $conn ) {
1807                                 $this->undoTransactionRoundFlags( $conn );
1808                         } );
1809                 }
1810                 $this->trxRoundStage = self::ROUND_ROLLBACK_CALLBACKS;
1811         }
1812
1813         /**
1814          * @param string|string[] $stage
1815          * @throws DBTransactionError
1816          */
1817         private function assertTransactionRoundStage( $stage ) {
1818                 $stages = (array)$stage;
1819
1820                 if ( !in_array( $this->trxRoundStage, $stages, true ) ) {
1821                         $stageList = implode(
1822                                 '/',
1823                                 array_map( function ( $v ) {
1824                                         return "'$v'";
1825                                 }, $stages )
1826                         );
1827                         throw new DBTransactionError(
1828                                 null,
1829                                 "Transaction round stage must be $stageList (not '{$this->trxRoundStage}')"
1830                         );
1831                 }
1832         }
1833
1834         /**
1835          * @param string $fname
1836          * @param int|null $owner Owner ID of the caller
1837          * @throws DBTransactionError
1838          */
1839         private function assertOwnership( $fname, $owner ) {
1840                 if ( $this->ownerId !== null && $owner !== $this->ownerId ) {
1841                         throw new DBTransactionError(
1842                                 null,
1843                                 "$fname: LoadBalancer is owned by LBFactory #{$this->ownerId} (got '$owner')."
1844                         );
1845                 }
1846         }
1847
1848         /**
1849          * Make all DB servers with DBO_DEFAULT/DBO_TRX set join the transaction round
1850          *
1851          * Some servers may have neither flag enabled, meaning that they opt out of such
1852          * transaction rounds and remain in auto-commit mode. Such behavior might be desired
1853          * when a DB server is used for something like simple key/value storage.
1854          *
1855          * @param Database $conn
1856          */
1857         private function applyTransactionRoundFlags( Database $conn ) {
1858                 if ( $conn->getLBInfo( 'autoCommitOnly' ) ) {
1859                         return; // transaction rounds do not apply to these connections
1860                 }
1861
1862                 if ( $conn->getFlag( $conn::DBO_DEFAULT ) ) {
1863                         // DBO_TRX is controlled entirely by CLI mode presence with DBO_DEFAULT.
1864                         // Force DBO_TRX even in CLI mode since a commit round is expected soon.
1865                         $conn->setFlag( $conn::DBO_TRX, $conn::REMEMBER_PRIOR );
1866                 }
1867
1868                 if ( $conn->getFlag( $conn::DBO_TRX ) ) {
1869                         $conn->setLBInfo( 'trxRoundId', $this->trxRoundId );
1870                 }
1871         }
1872
1873         /**
1874          * @param Database $conn
1875          */
1876         private function undoTransactionRoundFlags( Database $conn ) {
1877                 if ( $conn->getLBInfo( 'autoCommitOnly' ) ) {
1878                         return; // transaction rounds do not apply to these connections
1879                 }
1880
1881                 if ( $conn->getFlag( $conn::DBO_TRX ) ) {
1882                         $conn->setLBInfo( 'trxRoundId', null ); // remove the round ID
1883                 }
1884
1885                 if ( $conn->getFlag( $conn::DBO_DEFAULT ) ) {
1886                         $conn->restoreFlags( $conn::RESTORE_PRIOR );
1887                 }
1888         }
1889
1890         public function flushReplicaSnapshots( $fname = __METHOD__ ) {
1891                 $this->forEachOpenReplicaConnection( function ( IDatabase $conn ) use ( $fname ) {
1892                         $conn->flushSnapshot( $fname );
1893                 } );
1894         }
1895
1896         public function flushMasterSnapshots( $fname = __METHOD__ ) {
1897                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( $fname ) {
1898                         $conn->flushSnapshot( $fname );
1899                 } );
1900         }
1901
1902         /**
1903          * @return string
1904          * @since 1.32
1905          */
1906         public function getTransactionRoundStage() {
1907                 return $this->trxRoundStage;
1908         }
1909
1910         public function hasMasterConnection() {
1911                 return $this->isOpen( $this->getWriterIndex() );
1912         }
1913
1914         public function hasMasterChanges() {
1915                 $pending = 0;
1916                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$pending ) {
1917                         $pending |= $conn->writesOrCallbacksPending();
1918                 } );
1919
1920                 return (bool)$pending;
1921         }
1922
1923         public function lastMasterChangeTimestamp() {
1924                 $lastTime = false;
1925                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$lastTime ) {
1926                         $lastTime = max( $lastTime, $conn->lastDoneWrites() );
1927                 } );
1928
1929                 return $lastTime;
1930         }
1931
1932         public function hasOrMadeRecentMasterChanges( $age = null ) {
1933                 $age = ( $age === null ) ? $this->waitTimeout : $age;
1934
1935                 return ( $this->hasMasterChanges()
1936                         || $this->lastMasterChangeTimestamp() > microtime( true ) - $age );
1937         }
1938
1939         public function pendingMasterChangeCallers() {
1940                 $fnames = [];
1941                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$fnames ) {
1942                         $fnames = array_merge( $fnames, $conn->pendingWriteCallers() );
1943                 } );
1944
1945                 return $fnames;
1946         }
1947
1948         public function getLaggedReplicaMode( $domain = false ) {
1949                 if ( $this->laggedReplicaMode ) {
1950                         return true; // stay in lagged replica mode
1951                 }
1952
1953                 if ( $this->hasStreamingReplicaServers() ) {
1954                         // This will set "laggedReplicaMode" as needed
1955                         $this->getReaderIndex( self::GROUP_GENERIC, $domain );
1956                 }
1957
1958                 return $this->laggedReplicaMode;
1959         }
1960
1961         public function laggedReplicaUsed() {
1962                 return $this->laggedReplicaMode;
1963         }
1964
1965         public function getReadOnlyReason( $domain = false ) {
1966                 $domainInstance = DatabaseDomain::newFromId( $this->resolveDomainID( $domain ) );
1967
1968                 if ( $this->readOnlyReason !== false ) {
1969                         return $this->readOnlyReason;
1970                 } elseif ( $this->isMasterRunningReadOnly( $domainInstance ) ) {
1971                         return 'The master database server is running in read-only mode.';
1972                 } elseif ( $this->getLaggedReplicaMode( $domain ) ) {
1973                         return ( $this->getExistingReaderIndex( self::GROUP_GENERIC ) >= 0 )
1974                                 ? 'The database is read-only until replication lag decreases.'
1975                                 : 'The database is read-only until a replica database server becomes reachable.';
1976                 }
1977
1978                 return false;
1979         }
1980
1981         /**
1982          * @param IDatabase $conn Master connection
1983          * @param int $flags Bitfield of class CONN_* constants
1984          * @return bool Whether the entire server or currently selected DB/schema is read-only
1985          */
1986         private function isMasterConnectionReadOnly( IDatabase $conn, $flags = 0 ) {
1987                 // Note that table prefixes are not related to server-side read-only mode
1988                 $key = $this->srvCache->makeGlobalKey(
1989                         'rdbms-server-readonly',
1990                         $conn->getServer(),
1991                         $conn->getDBname(),
1992                         $conn->dbSchema()
1993                 );
1994
1995                 if ( ( $flags & self::CONN_REFRESH_READ_ONLY ) == self::CONN_REFRESH_READ_ONLY ) {
1996                         try {
1997                                 $readOnly = (int)$conn->serverIsReadOnly();
1998                         } catch ( DBError $e ) {
1999                                 $readOnly = 0;
2000                         }
2001                         $this->srvCache->set( $key, $readOnly, BagOStuff::TTL_PROC_SHORT );
2002                 } else {
2003                         $readOnly = $this->srvCache->getWithSetCallback(
2004                                 $key,
2005                                 BagOStuff::TTL_PROC_SHORT,
2006                                 function () use ( $conn ) {
2007                                         try {
2008                                                 return (int)$conn->serverIsReadOnly();
2009                                         } catch ( DBError $e ) {
2010                                                 return 0;
2011                                         }
2012                                 }
2013                         );
2014                 }
2015
2016                 return (bool)$readOnly;
2017         }
2018
2019         /**
2020          * @param DatabaseDomain $domain
2021          * @return bool Whether the entire master server or the local domain DB is read-only
2022          */
2023         private function isMasterRunningReadOnly( DatabaseDomain $domain ) {
2024                 // Context will often be HTTP GET/HEAD; heavily cache the results
2025                 return (bool)$this->wanCache->getWithSetCallback(
2026                         // Note that table prefixes are not related to server-side read-only mode
2027                         $this->wanCache->makeGlobalKey(
2028                                 'rdbms-server-readonly',
2029                                 $this->getMasterServerName(),
2030                                 $domain->getDatabase(),
2031                                 $domain->getSchema()
2032                         ),
2033                         self::TTL_CACHE_READONLY,
2034                         function () use ( $domain ) {
2035                                 $old = $this->trxProfiler->setSilenced( true );
2036                                 try {
2037                                         $index = $this->getWriterIndex();
2038                                         // Reset the cache for isMasterConnectionReadOnly()
2039                                         $flags = self::CONN_REFRESH_READ_ONLY;
2040                                         $conn = $this->getServerConnection( $index, $domain->getId(), $flags );
2041                                         // Reuse the process cache set above
2042                                         $readOnly = (int)$this->isMasterConnectionReadOnly( $conn );
2043                                         $this->reuseConnection( $conn );
2044                                 } catch ( DBError $e ) {
2045                                         $readOnly = 0;
2046                                 }
2047                                 $this->trxProfiler->setSilenced( $old );
2048
2049                                 return $readOnly;
2050                         },
2051                         [ 'pcTTL' => WANObjectCache::TTL_PROC_LONG, 'lockTSE' => 10, 'busyValue' => 0 ]
2052                 );
2053         }
2054
2055         public function allowLagged( $mode = null ) {
2056                 if ( $mode === null ) {
2057                         return $this->allowLagged;
2058                 }
2059                 $this->allowLagged = $mode;
2060
2061                 return $this->allowLagged;
2062         }
2063
2064         public function pingAll() {
2065                 $success = true;
2066                 $this->forEachOpenConnection( function ( IDatabase $conn ) use ( &$success ) {
2067                         if ( !$conn->ping() ) {
2068                                 $success = false;
2069                         }
2070                 } );
2071
2072                 return $success;
2073         }
2074
2075         public function forEachOpenConnection( $callback, array $params = [] ) {
2076                 foreach ( $this->conns as $connsByServer ) {
2077                         foreach ( $connsByServer as $serverConns ) {
2078                                 foreach ( $serverConns as $conn ) {
2079                                         $callback( $conn, ...$params );
2080                                 }
2081                         }
2082                 }
2083         }
2084
2085         public function forEachOpenMasterConnection( $callback, array $params = [] ) {
2086                 $masterIndex = $this->getWriterIndex();
2087                 foreach ( $this->conns as $connsByServer ) {
2088                         if ( isset( $connsByServer[$masterIndex] ) ) {
2089                                 /** @var IDatabase $conn */
2090                                 foreach ( $connsByServer[$masterIndex] as $conn ) {
2091                                         $callback( $conn, ...$params );
2092                                 }
2093                         }
2094                 }
2095         }
2096
2097         public function forEachOpenReplicaConnection( $callback, array $params = [] ) {
2098                 foreach ( $this->conns as $connsByServer ) {
2099                         foreach ( $connsByServer as $i => $serverConns ) {
2100                                 if ( $i === $this->getWriterIndex() ) {
2101                                         continue; // skip master
2102                                 }
2103                                 foreach ( $serverConns as $conn ) {
2104                                         $callback( $conn, ...$params );
2105                                 }
2106                         }
2107                 }
2108         }
2109
2110         /**
2111          * @return int
2112          */
2113         private function getCurrentConnectionCount() {
2114                 $count = 0;
2115                 foreach ( $this->conns as $connsByServer ) {
2116                         foreach ( $connsByServer as $serverConns ) {
2117                                 $count += count( $serverConns );
2118                         }
2119                 }
2120
2121                 return $count;
2122         }
2123
2124         public function getMaxLag( $domain = false ) {
2125                 $host = '';
2126                 $maxLag = -1;
2127                 $maxIndex = 0;
2128
2129                 if ( $this->hasReplicaServers() ) {
2130                         $lagTimes = $this->getLagTimes( $domain );
2131                         foreach ( $lagTimes as $i => $lag ) {
2132                                 if ( $this->groupLoads[self::GROUP_GENERIC][$i] > 0 && $lag > $maxLag ) {
2133                                         $maxLag = $lag;
2134                                         $host = $this->getServerInfoStrict( $i, 'host' );
2135                                         $maxIndex = $i;
2136                                 }
2137                         }
2138                 }
2139
2140                 return [ $host, $maxLag, $maxIndex ];
2141         }
2142
2143         public function getLagTimes( $domain = false ) {
2144                 if ( !$this->hasReplicaServers() ) {
2145                         return [ $this->getWriterIndex() => 0 ]; // no replication = no lag
2146                 }
2147
2148                 $knownLagTimes = []; // map of (server index => 0 seconds)
2149                 $indexesWithLag = [];
2150                 foreach ( $this->servers as $i => $server ) {
2151                         if ( empty( $server['is static'] ) ) {
2152                                 $indexesWithLag[] = $i; // DB server might have replication lag
2153                         } else {
2154                                 $knownLagTimes[$i] = 0; // DB server is a non-replicating and read-only archive
2155                         }
2156                 }
2157
2158                 return $this->getLoadMonitor()->getLagTimes( $indexesWithLag, $domain ) + $knownLagTimes;
2159         }
2160
2161         /**
2162          * Get the lag in seconds for a given connection, or zero if this load
2163          * balancer does not have replication enabled.
2164          *
2165          * This should be used in preference to Database::getLag() in cases where
2166          * replication may not be in use, since there is no way to determine if
2167          * replication is in use at the connection level without running
2168          * potentially restricted queries such as SHOW SLAVE STATUS. Using this
2169          * function instead of Database::getLag() avoids a fatal error in this
2170          * case on many installations.
2171          *
2172          * @param IDatabase $conn
2173          * @return int|bool Returns false on error
2174          * @deprecated Since 1.34 Use IDatabase::getLag() instead
2175          */
2176         public function safeGetLag( IDatabase $conn ) {
2177                 if ( $conn->getLBInfo( 'is static' ) ) {
2178                         return 0; // static dataset
2179                 } elseif ( $conn->getLBInfo( 'serverIndex' ) == $this->getWriterIndex() ) {
2180                         return 0; // this is the master
2181                 }
2182
2183                 return $conn->getLag();
2184         }
2185
2186         public function waitForMasterPos( IDatabase $conn, $pos = false, $timeout = null ) {
2187                 $timeout = max( 1, $timeout ?: $this->waitTimeout );
2188
2189                 if ( $this->getServerCount() <= 1 || !$conn->getLBInfo( 'replica' ) ) {
2190                         return true; // server is not a replica DB
2191                 }
2192
2193                 if ( !$pos ) {
2194                         // Get the current master position, opening a connection if needed
2195                         $index = $this->getWriterIndex();
2196                         $flags = self::CONN_SILENCE_ERRORS;
2197                         $masterConn = $this->getAnyOpenConnection( $index, $flags );
2198                         if ( $masterConn ) {
2199                                 $pos = $masterConn->getMasterPos();
2200                         } else {
2201                                 $masterConn = $this->getServerConnection( $index, self::DOMAIN_ANY, $flags );
2202                                 if ( !$masterConn ) {
2203                                         throw new DBReplicationWaitError(
2204                                                 null,
2205                                                 "Could not obtain a master database connection to get the position"
2206                                         );
2207                                 }
2208                                 $pos = $masterConn->getMasterPos();
2209                                 $this->closeConnection( $masterConn );
2210                         }
2211                 }
2212
2213                 if ( $pos instanceof DBMasterPos ) {
2214                         $start = microtime( true );
2215                         $result = $conn->masterPosWait( $pos, $timeout );
2216                         $seconds = max( microtime( true ) - $start, 0 );
2217                         if ( $result == -1 || is_null( $result ) ) {
2218                                 $msg = __METHOD__ . ': timed out waiting on {host} pos {pos} [{seconds}s]';
2219                                 $this->replLogger->warning( $msg, [
2220                                         'host' => $conn->getServer(),
2221                                         'pos' => $pos,
2222                                         'seconds' => round( $seconds, 6 ),
2223                                         'trace' => ( new RuntimeException() )->getTraceAsString()
2224                                 ] );
2225                                 $ok = false;
2226                         } else {
2227                                 $this->replLogger->debug( __METHOD__ . ': done waiting' );
2228                                 $ok = true;
2229                         }
2230                 } else {
2231                         $ok = false; // something is misconfigured
2232                         $this->replLogger->error(
2233                                 __METHOD__ . ': could not get master pos for {host}',
2234                                 [
2235                                         'host' => $conn->getServer(),
2236                                         'trace' => ( new RuntimeException() )->getTraceAsString()
2237                                 ]
2238                         );
2239                 }
2240
2241                 return $ok;
2242         }
2243
2244         /**
2245          * Wait for a replica DB to reach a specified master position
2246          *
2247          * This will connect to the master to get an accurate position if $pos is not given
2248          *
2249          * @param IDatabase $conn Replica DB
2250          * @param DBMasterPos|bool $pos Master position; default: current position
2251          * @param int $timeout Timeout in seconds [optional]
2252          * @return bool Success
2253          * @since 1.28
2254          * @deprecated Since 1.34 Use waitForMasterPos() instead
2255          */
2256         public function safeWaitForMasterPos( IDatabase $conn, $pos = false, $timeout = null ) {
2257                 return $this->waitForMasterPos( $conn, $pos, $timeout );
2258         }
2259
2260         public function setTransactionListener( $name, callable $callback = null ) {
2261                 if ( $callback ) {
2262                         $this->trxRecurringCallbacks[$name] = $callback;
2263                 } else {
2264                         unset( $this->trxRecurringCallbacks[$name] );
2265                 }
2266                 $this->forEachOpenMasterConnection(
2267                         function ( IDatabase $conn ) use ( $name, $callback ) {
2268                                 $conn->setTransactionListener( $name, $callback );
2269                         }
2270                 );
2271         }
2272
2273         public function setTableAliases( array $aliases ) {
2274                 $this->tableAliases = $aliases;
2275         }
2276
2277         public function setIndexAliases( array $aliases ) {
2278                 $this->indexAliases = $aliases;
2279         }
2280
2281         public function setLocalDomainPrefix( $prefix ) {
2282                 // Find connections to explicit foreign domains still marked as in-use...
2283                 $domainsInUse = [];
2284                 $this->forEachOpenConnection( function ( IDatabase $conn ) use ( &$domainsInUse ) {
2285                         // Once reuseConnection() is called on a handle, its reference count goes from 1 to 0.
2286                         // Until then, it is still in use by the caller (explicitly or via DBConnRef scope).
2287                         if ( $conn->getLBInfo( 'foreignPoolRefCount' ) > 0 ) {
2288                                 $domainsInUse[] = $conn->getDomainID();
2289                         }
2290                 } );
2291
2292                 // Do not switch connections to explicit foreign domains unless marked as safe
2293                 if ( $domainsInUse ) {
2294                         $domains = implode( ', ', $domainsInUse );
2295                         throw new DBUnexpectedError( null,
2296                                 "Foreign domain connections are still in use ($domains)" );
2297                 }
2298
2299                 $this->setLocalDomain( new DatabaseDomain(
2300                         $this->localDomain->getDatabase(),
2301                         $this->localDomain->getSchema(),
2302                         $prefix
2303                 ) );
2304
2305                 // Update the prefix for all local connections...
2306                 $this->forEachOpenConnection( function ( IDatabase $conn ) use ( $prefix ) {
2307                         if ( !$conn->getLBInfo( 'foreign' ) ) {
2308                                 $conn->tablePrefix( $prefix );
2309                         }
2310                 } );
2311         }
2312
2313         public function redefineLocalDomain( $domain ) {
2314                 $this->closeAll();
2315
2316                 $this->setLocalDomain( DatabaseDomain::newFromId( $domain ) );
2317         }
2318
2319         public function setTempTablesOnlyMode( $value, $domain ) {
2320                 $old = $this->tempTablesOnlyMode[$domain] ?? false;
2321                 if ( $value ) {
2322                         $this->tempTablesOnlyMode[$domain] = true;
2323                 } else {
2324                         unset( $this->tempTablesOnlyMode[$domain] );
2325                 }
2326
2327                 return $old;
2328         }
2329
2330         /**
2331          * @param DatabaseDomain $domain
2332          */
2333         private function setLocalDomain( DatabaseDomain $domain ) {
2334                 $this->localDomain = $domain;
2335                 // In case a caller assumes that the domain ID is simply <db>-<prefix>, which is almost
2336                 // always true, gracefully handle the case when they fail to account for escaping.
2337                 if ( $this->localDomain->getTablePrefix() != '' ) {
2338                         $this->localDomainIdAlias =
2339                                 $this->localDomain->getDatabase() . '-' . $this->localDomain->getTablePrefix();
2340                 } else {
2341                         $this->localDomainIdAlias = $this->localDomain->getDatabase();
2342                 }
2343         }
2344
2345         /**
2346          * @param int $i Server index
2347          * @param string|null $field Server index field [optional]
2348          * @return array|mixed
2349          * @throws InvalidArgumentException
2350          */
2351         private function getServerInfoStrict( $i, $field = null ) {
2352                 if ( !isset( $this->servers[$i] ) || !is_array( $this->servers[$i] ) ) {
2353                         throw new InvalidArgumentException( "No server with index '$i'" );
2354                 }
2355
2356                 if ( $field !== null ) {
2357                         if ( !array_key_exists( $field, $this->servers[$i] ) ) {
2358                                 throw new InvalidArgumentException( "No field '$field' in server index '$i'" );
2359                         }
2360
2361                         return $this->servers[$i][$field];
2362                 }
2363
2364                 return $this->servers[$i];
2365         }
2366
2367         /**
2368          * @return string
2369          */
2370         private function getMasterServerName() {
2371                 return $this->getServerName( $this->getWriterIndex() );
2372         }
2373
2374         function __destruct() {
2375                 // Avoid connection leaks for sanity
2376                 $this->disable();
2377         }
2378 }
2379
2380 /**
2381  * @deprecated since 1.29
2382  */
2383 class_alias( LoadBalancer::class, 'LoadBalancer' );