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 UnexpectedValueException;
  32 use InvalidArgumentException;
  33 use RuntimeException;
  34 use Exception;
  35
  36 /**
  37  * Database connection, tracking, load balancing, and transaction manager for a cluster
  38  *
  39  * @ingroup Database
  40  */
  41 class LoadBalancer implements ILoadBalancer {
  42         /** @var ILoadMonitor */
  43         private $loadMonitor;
  44         /** @var callable|null Callback to run before the first connection attempt */
  45         private $chronologyCallback;
  46         /** @var BagOStuff */
  47         private $srvCache;
  48         /** @var WANObjectCache */
  49         private $wanCache;
  50         /** @var mixed Class name or object With profileIn/profileOut methods */
  51         private $profiler;
  52         /** @var TransactionProfiler */
  53         private $trxProfiler;
  54         /** @var LoggerInterface */
  55         private $replLogger;
  56         /** @var LoggerInterface */
  57         private $connLogger;
  58         /** @var LoggerInterface */
  59         private $queryLogger;
  60         /** @var LoggerInterface */
  61         private $perfLogger;
  62         /** @var callable Exception logger */
  63         private $errorLogger;
  64         /** @var callable Deprecation logger */
  65         private $deprecationLogger;
  66
  67         /** @var DatabaseDomain Local Domain ID and default for selectDB() calls */
  68         private $localDomain;
  69
  70         /** @var Database[][][] Map of (connection category => server index => IDatabase[]) */
  71         private $conns;
  72
  73         /** @var array[] Map of (server index => server config array) */
  74         private $servers;
  75         /** @var float[] Map of (server index => weight) */
  76         private $loads;
  77         /** @var array[] Map of (group => server index => weight) */
  78         private $groupLoads;
  79         /** @var bool Whether to disregard replica DB lag as a factor in replica DB selection */
  80         private $allowLagged;
  81         /** @var int Seconds to spend waiting on replica DB lag to resolve */
  82         private $waitTimeout;
  83         /** @var array The LoadMonitor configuration */
  84         private $loadMonitorConfig;
  85         /** @var string Alternate ID string for the domain instead of DatabaseDomain::getId() */
  86         private $localDomainIdAlias;
  87         /** @var int */
  88         private $maxLag;
  89
  90         /** @var string Current server name */
  91         private $hostname;
  92         /** @var bool Whether this PHP instance is for a CLI script */
  93         private $cliMode;
  94         /** @var string Agent name for query profiling */
  95         private $agent;
  96
  97         /** @var array[] $aliases Map of (table => (dbname, schema, prefix) map) */
  98         private $tableAliases = [];
  99         /** @var string[] Map of (index alias => index) */
 100         private $indexAliases = [];
 101         /** @var array[] Map of (name => callable) */
 102         private $trxRecurringCallbacks = [];
 103
 104         /** @var Database DB connection object that caused a problem */
 105         private $errorConnection;
 106         /** @var int The generic (not query grouped) replica DB index (of $mServers) */
 107         private $readIndex;
 108         /** @var bool|DBMasterPos False if not set */
 109         private $waitForPos;
 110         /** @var bool Whether the generic reader fell back to a lagged replica DB */
 111         private $laggedReplicaMode = false;
 112         /** @var bool Whether the generic reader fell back to a lagged replica DB */
 113         private $allReplicasDownMode = false;
 114         /** @var string The last DB selection or connection error */
 115         private $lastError = 'Unknown error';
 116         /** @var string|bool Reason the LB is read-only or false if not */
 117         private $readOnlyReason = false;
 118         /** @var int Total connections opened */
 119         private $connsOpened = 0;
 120         /** @var bool */
 121         private $disabled = false;
 122         /** @var bool Whether any connection has been attempted yet */
 123         private $connectionAttempted = false;
 124
 125         /** @var string|bool String if a requested DBO_TRX transaction round is active */
 126         private $trxRoundId = false;
 127         /** @var string Stage of the current transaction round in the transaction round life-cycle */
 128         private $trxRoundStage = self::ROUND_CURSORY;
 129
 130         /** @var string|null */
 131         private $defaultGroup = null;
 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 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'] ) ) {
 166                         throw new InvalidArgumentException( __CLASS__ . ': missing servers parameter' );
 167                 }
 168                 $this->servers = $params['servers'];
 169                 foreach ( $this->servers as $i => $server ) {
 170                         if ( $i == 0 ) {
 171                                 $this->servers[$i]['master'] = true;
 172                         } else {
 173                                 $this->servers[$i]['replica'] = true;
 174                         }
 175                 }
 176
 177                 $localDomain = isset( $params['localDomain'] )
 178                         ? DatabaseDomain::newFromId( $params['localDomain'] )
 179                         : DatabaseDomain::newUnspecified();
 180                 $this->setLocalDomain( $localDomain );
 181
 182                 $this->waitTimeout = $params['waitTimeout'] ?? self::MAX_WAIT_DEFAULT;
 183
 184                 $this->readIndex = -1;
 185                 $this->conns = [
 186                         // Connection were transaction rounds may be applied
 187                         self::KEY_LOCAL => [],
 188                         self::KEY_FOREIGN_INUSE => [],
 189                         self::KEY_FOREIGN_FREE => [],
 190                         // Auto-committing counterpart connections that ignore transaction rounds
 191                         self::KEY_LOCAL_NOROUND => [],
 192                         self::KEY_FOREIGN_INUSE_NOROUND => [],
 193                         self::KEY_FOREIGN_FREE_NOROUND => []
 194                 ];
 195                 $this->loads = [];
 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                 foreach ( $params['servers'] as $i => $server ) {
 209                         $this->loads[$i] = $server['load'];
 210                         if ( isset( $server['groupLoads'] ) ) {
 211                                 foreach ( $server['groupLoads'] as $group => $ratio ) {
 212                                         if ( !isset( $this->groupLoads[$group] ) ) {
 213                                                 $this->groupLoads[$group] = [];
 214                                         }
 215                                         $this->groupLoads[$group][$i] = $ratio;
 216                                 }
 217                         }
 218                 }
 219
 220                 $this->srvCache = $params['srvCache'] ?? new EmptyBagOStuff();
 221                 $this->wanCache = $params['wanCache'] ?? WANObjectCache::newEmpty();
 222                 $this->profiler = $params['profiler'] ?? null;
 223                 $this->trxProfiler = $params['trxProfiler'] ?? new TransactionProfiler();
 224
 225                 $this->errorLogger = $params['errorLogger'] ?? function ( Exception $e ) {
 226                         trigger_error( get_class( $e ) . ': ' . $e->getMessage(), E_USER_WARNING );
 227                 };
 228                 $this->deprecationLogger = $params['deprecationLogger'] ?? function ( $msg ) {
 229                         trigger_error( $msg, E_USER_DEPRECATED );
 230                 };
 231
 232                 foreach ( [ 'replLogger', 'connLogger', 'queryLogger', 'perfLogger' ] as $key ) {
 233                         $this->$key = $params[$key] ?? new NullLogger();
 234                 }
 235
 236                 $this->hostname = $params['hostname'] ?? ( gethostname() ?: 'unknown' );
 237                 $this->cliMode = $params['cliMode'] ?? ( PHP_SAPI === 'cli' || PHP_SAPI === 'phpdbg' );
 238                 $this->agent = $params['agent'] ?? '';
 239
 240                 if ( isset( $params['chronologyCallback'] ) ) {
 241                         $this->chronologyCallback = $params['chronologyCallback'];
 242                 }
 243
 244                 if ( isset( $params['roundStage'] ) ) {
 245                         if ( $params['roundStage'] === self::STAGE_POSTCOMMIT_CALLBACKS ) {
 246                                 $this->trxRoundStage = self::ROUND_COMMIT_CALLBACKS;
 247                         } elseif ( $params['roundStage'] === self::STAGE_POSTROLLBACK_CALLBACKS ) {
 248                                 $this->trxRoundStage = self::ROUND_ROLLBACK_CALLBACKS;
 249                         }
 250                 }
 251
 252                 $this->defaultGroup = $params['defaultGroup'] ?? null;
 253         }
 254
 255         public function getLocalDomainID() {
 256                 return $this->localDomain->getId();
 257         }
 258
 259         public function resolveDomainID( $domain ) {
 260                 return ( $domain !== false ) ? (string)$domain : $this->getLocalDomainID();
 261         }
 262
 263         /**
 264          * Get a LoadMonitor instance
 265          *
 266          * @return ILoadMonitor
 267          */
 268         private function getLoadMonitor() {
 269                 if ( !isset( $this->loadMonitor ) ) {
 270                         $compat = [
 271                                 'LoadMonitor' => LoadMonitor::class,
 272                                 'LoadMonitorNull' => LoadMonitorNull::class,
 273                                 'LoadMonitorMySQL' => LoadMonitorMySQL::class,
 274                         ];
 275
 276                         $class = $this->loadMonitorConfig['class'];
 277                         if ( isset( $compat[$class] ) ) {
 278                                 $class = $compat[$class];
 279                         }
 280
 281                         $this->loadMonitor = new $class(
 282                                 $this, $this->srvCache, $this->wanCache, $this->loadMonitorConfig );
 283                         $this->loadMonitor->setLogger( $this->replLogger );
 284                 }
 285
 286                 return $this->loadMonitor;
 287         }
 288
 289         /**
 290          * @param array $loads
 291          * @param bool|string $domain Domain to get non-lagged for
 292          * @param int $maxLag Restrict the maximum allowed lag to this many seconds
 293          * @return bool|int|string
 294          */
 295         private function getRandomNonLagged( array $loads, $domain = false, $maxLag = INF ) {
 296                 $lags = $this->getLagTimes( $domain );
 297
 298                 # Unset excessively lagged servers
 299                 foreach ( $lags as $i => $lag ) {
 300                         if ( $i != 0 ) {
 301                                 # How much lag this server nominally is allowed to have
 302                                 $maxServerLag = $this->servers[$i]['max lag'] ?? $this->maxLag; // default
 303                                 # Constrain that futher by $maxLag argument
 304                                 $maxServerLag = min( $maxServerLag, $maxLag );
 305
 306                                 $host = $this->getServerName( $i );
 307                                 if ( $lag === false && !is_infinite( $maxServerLag ) ) {
 308                                         $this->replLogger->debug(
 309                                                 __METHOD__ .
 310                                                 ": server {host} is not replicating?", [ 'host' => $host ] );
 311                                         unset( $loads[$i] );
 312                                 } elseif ( $lag > $maxServerLag ) {
 313                                         $this->replLogger->debug(
 314                                                 __METHOD__ .
 315                                                 ": server {host} has {lag} seconds of lag (>= {maxlag})",
 316                                                 [ 'host' => $host, 'lag' => $lag, 'maxlag' => $maxServerLag ]
 317                                         );
 318                                         unset( $loads[$i] );
 319                                 }
 320                         }
 321                 }
 322
 323                 # Find out if all the replica DBs with non-zero load are lagged
 324                 $sum = 0;
 325                 foreach ( $loads as $load ) {
 326                         $sum += $load;
 327                 }
 328                 if ( $sum == 0 ) {
 329                         # No appropriate DB servers except maybe the master and some replica DBs with zero load
 330                         # Do NOT use the master
 331                         # Instead, this function will return false, triggering read-only mode,
 332                         # and a lagged replica DB will be used instead.
 333                         return false;
 334                 }
 335
 336                 if ( count( $loads ) == 0 ) {
 337                         return false;
 338                 }
 339
 340                 # Return a random representative of the remainder
 341                 return ArrayUtils::pickRandom( $loads );
 342         }
 343
 344         public function getReaderIndex( $group = false, $domain = false ) {
 345                 if ( count( $this->servers ) == 1 ) {
 346                         // Skip the load balancing if there's only one server
 347                         return $this->getWriterIndex();
 348                 } elseif ( $group === false && $this->readIndex >= 0 ) {
 349                         // Shortcut if the generic reader index was already cached
 350                         return $this->readIndex;
 351                 }
 352
 353                 if ( $group !== false ) {
 354                         // Use the server weight array for this load group
 355                         if ( isset( $this->groupLoads[$group] ) ) {
 356                                 $loads = $this->groupLoads[$group];
 357                         } else {
 358                                 // No loads for this group, return false and the caller can use some other group
 359                                 $this->connLogger->info( __METHOD__ . ": no loads for group $group" );
 360
 361                                 return false;
 362                         }
 363                 } else {
 364                         // Use the generic load group
 365                         $loads = $this->loads;
 366                 }
 367
 368                 // Scale the configured load ratios according to each server's load and state
 369                 $this->getLoadMonitor()->scaleLoads( $loads, $domain );
 370
 371                 // Pick a server to use, accounting for weights, load, lag, and "waitForPos"
 372                 list( $i, $laggedReplicaMode ) = $this->pickReaderIndex( $loads, $domain );
 373                 if ( $i === false ) {
 374                         // Replica DB connection unsuccessful
 375                         return false;
 376                 }
 377
 378                 if ( $this->waitForPos && $i != $this->getWriterIndex() ) {
 379                         // Before any data queries are run, wait for the server to catch up to the
 380                         // specified position. This is used to improve session consistency. Note that
 381                         // when LoadBalancer::waitFor() sets "waitForPos", the waiting triggers here,
 382                         // so update laggedReplicaMode as needed for consistency.
 383                         if ( !$this->doWait( $i ) ) {
 384                                 $laggedReplicaMode = true;
 385                         }
 386                 }
 387
 388                 if ( $this->readIndex <= 0 && $this->loads[$i] > 0 && $group === false ) {
 389                         // Cache the generic reader index for future ungrouped DB_REPLICA handles
 390                         $this->readIndex = $i;
 391                         // Record if the generic reader index is in "lagged replica DB" mode
 392                         if ( $laggedReplicaMode ) {
 393                                 $this->laggedReplicaMode = true;
 394                         }
 395                 }
 396
 397                 $serverName = $this->getServerName( $i );
 398                 $this->connLogger->debug( __METHOD__ . ": using server $serverName for group '$group'" );
 399
 400                 return $i;
 401         }
 402
 403         /**
 404          * @param array $loads List of server weights
 405          * @param string|bool $domain
 406          * @return array (reader index, lagged replica mode) or false on failure
 407          */
 408         private function pickReaderIndex( array $loads, $domain = false ) {
 409                 if ( $loads === [] ) {
 410                         throw new InvalidArgumentException( "Empty server array given to LoadBalancer" );
 411                 }
 412
 413                 /** @var int|bool $i Index of selected server */
 414                 $i = false;
 415                 /** @var bool $laggedReplicaMode Whether server is considered lagged */
 416                 $laggedReplicaMode = false;
 417
 418                 // Quickly look through the available servers for a server that meets criteria...
 419                 $currentLoads = $loads;
 420                 while ( count( $currentLoads ) ) {
 421                         if ( $this->allowLagged || $laggedReplicaMode ) {
 422                                 $i = ArrayUtils::pickRandom( $currentLoads );
 423                         } else {
 424                                 $i = false;
 425                                 if ( $this->waitForPos && $this->waitForPos->asOfTime() ) {
 426                                         // "chronologyCallback" sets "waitForPos" for session consistency.
 427                                         // This triggers doWait() after connect, so it's especially good to
 428                                         // avoid lagged servers so as to avoid excessive delay in that method.
 429                                         $ago = microtime( true ) - $this->waitForPos->asOfTime();
 430                                         // Aim for <= 1 second of waiting (being too picky can backfire)
 431                                         $i = $this->getRandomNonLagged( $currentLoads, $domain, $ago + 1 );
 432                                 }
 433                                 if ( $i === false ) {
 434                                         // Any server with less lag than it's 'max lag' param is preferable
 435                                         $i = $this->getRandomNonLagged( $currentLoads, $domain );
 436                                 }
 437                                 if ( $i === false && count( $currentLoads ) != 0 ) {
 438                                         // All replica DBs lagged. Switch to read-only mode
 439                                         $this->replLogger->error(
 440                                                 __METHOD__ . ": all replica DBs lagged. Switch to read-only mode" );
 441                                         $i = ArrayUtils::pickRandom( $currentLoads );
 442                                         $laggedReplicaMode = true;
 443                                 }
 444                         }
 445
 446                         if ( $i === false ) {
 447                                 // pickRandom() returned false.
 448                                 // This is permanent and means the configuration or the load monitor
 449                                 // wants us to return false.
 450                                 $this->connLogger->debug( __METHOD__ . ": pickRandom() returned false" );
 451
 452                                 return [ false, false ];
 453                         }
 454
 455                         $serverName = $this->getServerName( $i );
 456                         $this->connLogger->debug( __METHOD__ . ": Using reader #$i: $serverName..." );
 457
 458                         $conn = $this->openConnection( $i, $domain );
 459                         if ( !$conn ) {
 460                                 $this->connLogger->warning( __METHOD__ . ": Failed connecting to $i/$domain" );
 461                                 unset( $currentLoads[$i] ); // avoid this server next iteration
 462                                 $i = false;
 463                                 continue;
 464                         }
 465
 466                         // Decrement reference counter, we are finished with this connection.
 467                         // It will be incremented for the caller later.
 468                         if ( $domain !== false ) {
 469                                 $this->reuseConnection( $conn );
 470                         }
 471
 472                         // Return this server
 473                         break;
 474                 }
 475
 476                 // If all servers were down, quit now
 477                 if ( $currentLoads === [] ) {
 478                         $this->connLogger->error( __METHOD__ . ": all servers down" );
 479                 }
 480
 481                 return [ $i, $laggedReplicaMode ];
 482         }
 483
 484         public function waitFor( $pos ) {
 485                 $oldPos = $this->waitForPos;
 486                 try {
 487                         $this->waitForPos = $pos;
 488                         // If a generic reader connection was already established, then wait now
 489                         $i = $this->readIndex;
 490                         if ( ( $i > 0 ) && !$this->doWait( $i ) ) {
 491                                 $this->laggedReplicaMode = true;
 492                         }
 493                 } finally {
 494                         // Restore the older position if it was higher since this is used for lag-protection
 495                         $this->setWaitForPositionIfHigher( $oldPos );
 496                 }
 497         }
 498
 499         public function waitForOne( $pos, $timeout = null ) {
 500                 $oldPos = $this->waitForPos;
 501                 try {
 502                         $this->waitForPos = $pos;
 503
 504                         $i = $this->readIndex;
 505                         if ( $i <= 0 ) {
 506                                 // Pick a generic replica DB if there isn't one yet
 507                                 $readLoads = $this->loads;
 508                                 unset( $readLoads[$this->getWriterIndex()] ); // replica DBs only
 509                                 $readLoads = array_filter( $readLoads ); // with non-zero load
 510                                 $i = ArrayUtils::pickRandom( $readLoads );
 511                         }
 512
 513                         if ( $i > 0 ) {
 514                                 $ok = $this->doWait( $i, true, $timeout );
 515                         } else {
 516                                 $ok = true; // no applicable loads
 517                         }
 518                 } finally {
 519                         # Restore the old position, as this is not used for lag-protection but for throttling
 520                         $this->waitForPos = $oldPos;
 521                 }
 522
 523                 return $ok;
 524         }
 525
 526         public function waitForAll( $pos, $timeout = null ) {
 527                 $timeout = $timeout ?: $this->waitTimeout;
 528
 529                 $oldPos = $this->waitForPos;
 530                 try {
 531                         $this->waitForPos = $pos;
 532                         $serverCount = count( $this->servers );
 533
 534                         $ok = true;
 535                         for ( $i = 1; $i < $serverCount; $i++ ) {
 536                                 if ( $this->loads[$i] > 0 ) {
 537                                         $start = microtime( true );
 538                                         $ok = $this->doWait( $i, true, $timeout ) && $ok;
 539                                         $timeout -= intval( microtime( true ) - $start );
 540                                         if ( $timeout <= 0 ) {
 541                                                 break; // timeout reached
 542                                         }
 543                                 }
 544                         }
 545                 } finally {
 546                         # Restore the old position, as this is not used for lag-protection but for throttling
 547                         $this->waitForPos = $oldPos;
 548                 }
 549
 550                 return $ok;
 551         }
 552
 553         /**
 554          * @param DBMasterPos|bool $pos
 555          */
 556         private function setWaitForPositionIfHigher( $pos ) {
 557                 if ( !$pos ) {
 558                         return;
 559                 }
 560
 561                 if ( !$this->waitForPos || $pos->hasReached( $this->waitForPos ) ) {
 562                         $this->waitForPos = $pos;
 563                 }
 564         }
 565
 566         public function getAnyOpenConnection( $i, $flags = 0 ) {
 567                 $i = ( $i === self::DB_MASTER ) ? $this->getWriterIndex() : $i;
 568                 $autocommit = ( ( $flags & self::CONN_TRX_AUTOCOMMIT ) == self::CONN_TRX_AUTOCOMMIT );
 569
 570                 foreach ( $this->conns as $connsByServer ) {
 571                         if ( $i === self::DB_REPLICA ) {
 572                                 $indexes = array_keys( $connsByServer );
 573                         } else {
 574                                 $indexes = isset( $connsByServer[$i] ) ? [ $i ] : [];
 575                         }
 576
 577                         foreach ( $indexes as $index ) {
 578                                 foreach ( $connsByServer[$index] as $conn ) {
 579                                         if ( !$conn->isOpen() ) {
 580                                                 continue; // some sort of error occured?
 581                                         }
 582                                         if ( !$autocommit || $conn->getLBInfo( 'autoCommitOnly' ) ) {
 583                                                 return $conn;
 584                                         }
 585                                 }
 586                         }
 587                 }
 588
 589                 return false;
 590         }
 591
 592         /**
 593          * Wait for a given replica DB to catch up to the master pos stored in $this
 594          * @param int $index Server index
 595          * @param bool $open Check the server even if a new connection has to be made
 596          * @param int|null $timeout Max seconds to wait; default is "waitTimeout" given to __construct()
 597          * @return bool
 598          */
 599         protected function doWait( $index, $open = false, $timeout = null ) {
 600                 $timeout = max( 1, intval( $timeout ?: $this->waitTimeout ) );
 601
 602                 // Check if we already know that the DB has reached this point
 603                 $server = $this->getServerName( $index );
 604                 $key = $this->srvCache->makeGlobalKey( __CLASS__, 'last-known-pos', $server, 'v1' );
 605                 /** @var DBMasterPos $knownReachedPos */
 606                 $knownReachedPos = $this->srvCache->get( $key );
 607                 if (
 608                         $knownReachedPos instanceof DBMasterPos &&
 609                         $knownReachedPos->hasReached( $this->waitForPos )
 610                 ) {
 611                         $this->replLogger->debug(
 612                                 __METHOD__ .
 613                                 ': replica DB {dbserver} known to be caught up (pos >= $knownReachedPos).',
 614                                 [ 'dbserver' => $server ]
 615                         );
 616                         return true;
 617                 }
 618
 619                 // Find a connection to wait on, creating one if needed and allowed
 620                 $close = false; // close the connection afterwards
 621                 $conn = $this->getAnyOpenConnection( $index );
 622                 if ( !$conn ) {
 623                         if ( !$open ) {
 624                                 $this->replLogger->debug(
 625                                         __METHOD__ . ': no connection open for {dbserver}',
 626                                         [ 'dbserver' => $server ]
 627                                 );
 628
 629                                 return false;
 630                         } else {
 631                                 $conn = $this->openConnection( $index, self::DOMAIN_ANY );
 632                                 if ( !$conn ) {
 633                                         $this->replLogger->warning(
 634                                                 __METHOD__ . ': failed to connect to {dbserver}',
 635                                                 [ 'dbserver' => $server ]
 636                                         );
 637
 638                                         return false;
 639                                 }
 640                                 // Avoid connection spam in waitForAll() when connections
 641                                 // are made just for the sake of doing this lag check.
 642                                 $close = true;
 643                         }
 644                 }
 645
 646                 $this->replLogger->info(
 647                         __METHOD__ .
 648                         ': waiting for replica DB {dbserver} to catch up...',
 649                         [ 'dbserver' => $server ]
 650                 );
 651
 652                 $result = $conn->masterPosWait( $this->waitForPos, $timeout );
 653
 654                 if ( $result === null ) {
 655                         $this->replLogger->warning(
 656                                 __METHOD__ . ': Errored out waiting on {host} pos {pos}',
 657                                 [
 658                                         'host' => $server,
 659                                         'pos' => $this->waitForPos,
 660                                         'trace' => ( new RuntimeException() )->getTraceAsString()
 661                                 ]
 662                         );
 663                         $ok = false;
 664                 } elseif ( $result == -1 ) {
 665                         $this->replLogger->warning(
 666                                 __METHOD__ . ': Timed out waiting on {host} pos {pos}',
 667                                 [
 668                                         'host' => $server,
 669                                         'pos' => $this->waitForPos,
 670                                         'trace' => ( new RuntimeException() )->getTraceAsString()
 671                                 ]
 672                         );
 673                         $ok = false;
 674                 } else {
 675                         $this->replLogger->debug( __METHOD__ . ": done waiting" );
 676                         $ok = true;
 677                         // Remember that the DB reached this point
 678                         $this->srvCache->set( $key, $this->waitForPos, BagOStuff::TTL_DAY );
 679                 }
 680
 681                 if ( $close ) {
 682                         $this->closeConnection( $conn );
 683                 }
 684
 685                 return $ok;
 686         }
 687
 688         public function getConnection( $i, $groups = [], $domain = false, $flags = 0 ) {
 689                 if ( $i === null || $i === false ) {
 690                         throw new InvalidArgumentException( 'Attempt to call ' . __METHOD__ .
 691                                 ' with invalid server index' );
 692                 }
 693
 694                 if ( $this->localDomain->equals( $domain ) || $domain === $this->localDomainIdAlias ) {
 695                         $domain = false; // local connection requested
 696                 }
 697
 698                 if ( ( $flags & self::CONN_TRX_AUTOCOMMIT ) === self::CONN_TRX_AUTOCOMMIT ) {
 699                         // Assuming all servers are of the same type (or similar), which is overwhelmingly
 700                         // the case, use the master server information to get the attributes. The information
 701                         // for $i cannot be used since it might be DB_REPLICA, which might require connection
 702                         // attempts in order to be resolved into a real server index.
 703                         $attributes = $this->getServerAttributes( $this->getWriterIndex() );
 704                         if ( $attributes[Database::ATTR_DB_LEVEL_LOCKING] ) {
 705                                 // Callers sometimes want to (a) escape REPEATABLE-READ stateness without locking
 706                                 // rows (e.g. FOR UPDATE) or (b) make small commits during a larger transactions
 707                                 // to reduce lock contention. None of these apply for sqlite and using separate
 708                                 // connections just causes self-deadlocks.
 709                                 $flags &= ~self::CONN_TRX_AUTOCOMMIT;
 710                                 $this->connLogger->info( __METHOD__ .
 711                                         ': ignoring CONN_TRX_AUTOCOMMIT to avoid deadlocks.' );
 712                         }
 713                 }
 714
 715                 // Check one "group" per default: the generic pool
 716                 $defaultGroups = $this->defaultGroup ? [ $this->defaultGroup ] : [ false ];
 717
 718                 $groups = ( $groups === false || $groups === [] )
 719                         ? $defaultGroups
 720                         : (array)$groups;
 721
 722                 $masterOnly = ( $i == self::DB_MASTER || $i == $this->getWriterIndex() );
 723                 $oldConnsOpened = $this->connsOpened; // connections open now
 724
 725                 if ( $i == self::DB_MASTER ) {
 726                         $i = $this->getWriterIndex();
 727                 } elseif ( $i == self::DB_REPLICA ) {
 728                         # Try to find an available server in any the query groups (in order)
 729                         foreach ( $groups as $group ) {
 730                                 $groupIndex = $this->getReaderIndex( $group, $domain );
 731                                 if ( $groupIndex !== false ) {
 732                                         $i = $groupIndex;
 733                                         break;
 734                                 }
 735                         }
 736                 }
 737
 738                 # Operation-based index
 739                 if ( $i == self::DB_REPLICA ) {
 740                         $this->lastError = 'Unknown error'; // reset error string
 741                         # Try the general server pool if $groups are unavailable.
 742                         $i = ( $groups === [ false ] )
 743                                 ? false // don't bother with this if that is what was tried above
 744                                 : $this->getReaderIndex( false, $domain );
 745                         # Couldn't find a working server in getReaderIndex()?
 746                         if ( $i === false ) {
 747                                 $this->lastError = 'No working replica DB server: ' . $this->lastError;
 748                                 // Throw an exception
 749                                 $this->reportConnectionError();
 750                                 return null; // not reached
 751                         }
 752                 }
 753
 754                 # Now we have an explicit index into the servers array
 755                 $conn = $this->openConnection( $i, $domain, $flags );
 756                 if ( !$conn ) {
 757                         // Throw an exception
 758                         $this->reportConnectionError();
 759                         return null; // not reached
 760                 }
 761
 762                 # Profile any new connections that happen
 763                 if ( $this->connsOpened > $oldConnsOpened ) {
 764                         $host = $conn->getServer();
 765                         $dbname = $conn->getDBname();
 766                         $this->trxProfiler->recordConnection( $host, $dbname, $masterOnly );
 767                 }
 768
 769                 if ( $masterOnly ) {
 770                         # Make master-requested DB handles inherit any read-only mode setting
 771                         $conn->setLBInfo( 'readOnlyReason', $this->getReadOnlyReason( $domain, $conn ) );
 772                 }
 773
 774                 return $conn;
 775         }
 776
 777         public function reuseConnection( IDatabase $conn ) {
 778                 $serverIndex = $conn->getLBInfo( 'serverIndex' );
 779                 $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 780                 if ( $serverIndex === null || $refCount === null ) {
 781                         /**
 782                          * This can happen in code like:
 783                          *   foreach ( $dbs as $db ) {
 784                          *     $conn = $lb->getConnection( $lb::DB_REPLICA, [], $db );
 785                          *     ...
 786                          *     $lb->reuseConnection( $conn );
 787                          *   }
 788                          * When a connection to the local DB is opened in this way, reuseConnection()
 789                          * should be ignored
 790                          */
 791                         return;
 792                 } elseif ( $conn instanceof DBConnRef ) {
 793                         // DBConnRef already handles calling reuseConnection() and only passes the live
 794                         // Database instance to this method. Any caller passing in a DBConnRef is broken.
 795                         $this->connLogger->error(
 796                                 __METHOD__ . ": got DBConnRef instance.\n" .
 797                                 ( new RuntimeException() )->getTraceAsString() );
 798
 799                         return;
 800                 }
 801
 802                 if ( $this->disabled ) {
 803                         return; // DBConnRef handle probably survived longer than the LoadBalancer
 804                 }
 805
 806                 if ( $conn->getLBInfo( 'autoCommitOnly' ) ) {
 807                         $connFreeKey = self::KEY_FOREIGN_FREE_NOROUND;
 808                         $connInUseKey = self::KEY_FOREIGN_INUSE_NOROUND;
 809                 } else {
 810                         $connFreeKey = self::KEY_FOREIGN_FREE;
 811                         $connInUseKey = self::KEY_FOREIGN_INUSE;
 812                 }
 813
 814                 $domain = $conn->getDomainID();
 815                 if ( !isset( $this->conns[$connInUseKey][$serverIndex][$domain] ) ) {
 816                         throw new InvalidArgumentException( __METHOD__ .
 817                                 ": connection $serverIndex/$domain not found; it may have already been freed." );
 818                 } elseif ( $this->conns[$connInUseKey][$serverIndex][$domain] !== $conn ) {
 819                         throw new InvalidArgumentException( __METHOD__ .
 820                                 ": connection $serverIndex/$domain mismatched; it may have already been freed." );
 821                 }
 822
 823                 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
 824                 if ( $refCount <= 0 ) {
 825                         $this->conns[$connFreeKey][$serverIndex][$domain] = $conn;
 826                         unset( $this->conns[$connInUseKey][$serverIndex][$domain] );
 827                         if ( !$this->conns[$connInUseKey][$serverIndex] ) {
 828                                 unset( $this->conns[$connInUseKey][$serverIndex] ); // clean up
 829                         }
 830                         $this->connLogger->debug( __METHOD__ . ": freed connection $serverIndex/$domain" );
 831                 } else {
 832                         $this->connLogger->debug( __METHOD__ .
 833                                 ": reference count for $serverIndex/$domain reduced to $refCount" );
 834                 }
 835         }
 836
 837         public function getConnectionRef( $i, $groups = [], $domain = false, $flags = 0 ) {
 838                 $domain = $this->resolveDomainID( $domain );
 839                 $role = $this->getRoleFromIndex( $i );
 840
 841                 return new DBConnRef( $this, $this->getConnection( $i, $groups, $domain, $flags ), $role );
 842         }
 843
 844         public function getLazyConnectionRef( $i, $groups = [], $domain = false, $flags = 0 ) {
 845                 $domain = $this->resolveDomainID( $domain );
 846                 $role = $this->getRoleFromIndex( $i );
 847
 848                 return new DBConnRef( $this, [ $i, $groups, $domain, $flags ], $role );
 849         }
 850
 851         public function getMaintenanceConnectionRef( $i, $groups = [], $domain = false, $flags = 0 ) {
 852                 $domain = $this->resolveDomainID( $domain );
 853                 $role = $this->getRoleFromIndex( $i );
 854
 855                 return new MaintainableDBConnRef(
 856                         $this, $this->getConnection( $i, $groups, $domain, $flags ), $role );
 857         }
 858
 859         /**
 860          * @param int $i Server index or DB_MASTER/DB_REPLICA
 861          * @return int One of DB_MASTER/DB_REPLICA
 862          */
 863         private function getRoleFromIndex( $i ) {
 864                 return ( $i === self::DB_MASTER || $i === $this->getWriterIndex() )
 865                         ? self::DB_MASTER
 866                         : self::DB_REPLICA;
 867         }
 868
 869         public function openConnection( $i, $domain = false, $flags = 0 ) {
 870                 if ( $this->localDomain->equals( $domain ) || $domain === $this->localDomainIdAlias ) {
 871                         $domain = false; // local connection requested
 872                 }
 873
 874                 if ( !$this->connectionAttempted && $this->chronologyCallback ) {
 875                         $this->connLogger->debug( __METHOD__ . ': calling initLB() before first connection.' );
 876                         // Load any "waitFor" positions before connecting so that doWait() is triggered
 877                         $this->connectionAttempted = true;
 878                         ( $this->chronologyCallback )( $this );
 879                 }
 880
 881                 // Check if an auto-commit connection is being requested. If so, it will not reuse the
 882                 // main set of DB connections but rather its own pool since:
 883                 // a) those are usually set to implicitly use transaction rounds via DBO_TRX
 884                 // b) those must support the use of explicit transaction rounds via beginMasterChanges()
 885                 $autoCommit = ( ( $flags & self::CONN_TRX_AUTOCOMMIT ) == self::CONN_TRX_AUTOCOMMIT );
 886
 887                 if ( $domain !== false ) {
 888                         // Connection is to a foreign domain
 889                         $conn = $this->openForeignConnection( $i, $domain, $flags );
 890                 } else {
 891                         // Connection is to the local domain
 892                         $conn = $this->openLocalConnection( $i, $flags );
 893                 }
 894
 895                 if ( $conn instanceof IDatabase && !$conn->isOpen() ) {
 896                         // Connection was made but later unrecoverably lost for some reason.
 897                         // Do not return a handle that will just throw exceptions on use,
 898                         // but let the calling code (e.g. getReaderIndex) try another server.
 899                         // See DatabaseMyslBase::ping() for how this can happen.
 900                         $this->errorConnection = $conn;
 901                         $conn = false;
 902                 }
 903
 904                 if ( $autoCommit && $conn instanceof IDatabase ) {
 905                         if ( $conn->trxLevel() ) { // sanity
 906                                 throw new DBUnexpectedError(
 907                                         $conn,
 908                                         __METHOD__ . ': CONN_TRX_AUTOCOMMIT handle has a transaction.'
 909                                 );
 910                         }
 911
 912                         $conn->clearFlag( $conn::DBO_TRX ); // auto-commit mode
 913                 }
 914
 915                 return $conn;
 916         }
 917
 918         /**
 919          * Open a connection to a local DB, or return one if it is already open.
 920          *
 921          * On error, returns false, and the connection which caused the
 922          * error will be available via $this->errorConnection.
 923          *
 924          * @note If disable() was called on this LoadBalancer, this method will throw a DBAccessError.
 925          *
 926          * @param int $i Server index
 927          * @param int $flags Class CONN_* constant bitfield
 928          * @return Database
 929          */
 930         private function openLocalConnection( $i, $flags = 0 ) {
 931                 $autoCommit = ( ( $flags & self::CONN_TRX_AUTOCOMMIT ) == self::CONN_TRX_AUTOCOMMIT );
 932
 933                 $connKey = $autoCommit ? self::KEY_LOCAL_NOROUND : self::KEY_LOCAL;
 934                 if ( isset( $this->conns[$connKey][$i][0] ) ) {
 935                         $conn = $this->conns[$connKey][$i][0];
 936                 } else {
 937                         if ( !isset( $this->servers[$i] ) || !is_array( $this->servers[$i] ) ) {
 938                                 throw new InvalidArgumentException( "No server with index '$i'." );
 939                         }
 940                         // Open a new connection
 941                         $server = $this->servers[$i];
 942                         $server['serverIndex'] = $i;
 943                         $server['autoCommitOnly'] = $autoCommit;
 944                         $conn = $this->reallyOpenConnection( $server, $this->localDomain );
 945                         $host = $this->getServerName( $i );
 946                         if ( $conn->isOpen() ) {
 947                                 $this->connLogger->debug(
 948                                         __METHOD__ . ": connected to database $i at '$host'." );
 949                                 $this->conns[$connKey][$i][0] = $conn;
 950                         } else {
 951                                 $this->connLogger->warning(
 952                                         __METHOD__ . ": failed to connect to database $i at '$host'." );
 953                                 $this->errorConnection = $conn;
 954                                 $conn = false;
 955                         }
 956                 }
 957
 958                 // Final sanity check to make sure the right domain is selected
 959                 if (
 960                         $conn instanceof IDatabase &&
 961                         !$this->localDomain->isCompatible( $conn->getDomainID() )
 962                 ) {
 963                         throw new UnexpectedValueException(
 964                                 "Got connection to '{$conn->getDomainID()}', " .
 965                                 "but expected local domain ('{$this->localDomain}')." );
 966                 }
 967
 968                 return $conn;
 969         }
 970
 971         /**
 972          * Open a connection to a foreign DB, or return one if it is already open.
 973          *
 974          * Increments a reference count on the returned connection which locks the
 975          * connection to the requested domain. This reference count can be
 976          * decremented by calling reuseConnection().
 977          *
 978          * If a connection is open to the appropriate server already, but with the wrong
 979          * database, it will be switched to the right database and returned, as long as
 980          * it has been freed first with reuseConnection().
 981          *
 982          * On error, returns false, and the connection which caused the
 983          * error will be available via $this->errorConnection.
 984          *
 985          * @note If disable() was called on this LoadBalancer, this method will throw a DBAccessError.
 986          *
 987          * @param int $i Server index
 988          * @param string $domain Domain ID to open
 989          * @param int $flags Class CONN_* constant bitfield
 990          * @return Database|bool Returns false on connection error
 991          * @throws DBError When database selection fails
 992          */
 993         private function openForeignConnection( $i, $domain, $flags = 0 ) {
 994                 $domainInstance = DatabaseDomain::newFromId( $domain );
 995                 $autoCommit = ( ( $flags & self::CONN_TRX_AUTOCOMMIT ) == self::CONN_TRX_AUTOCOMMIT );
 996
 997                 if ( $autoCommit ) {
 998                         $connFreeKey = self::KEY_FOREIGN_FREE_NOROUND;
 999                         $connInUseKey = self::KEY_FOREIGN_INUSE_NOROUND;
1000                 } else {
1001                         $connFreeKey = self::KEY_FOREIGN_FREE;
1002                         $connInUseKey = self::KEY_FOREIGN_INUSE;
1003                 }
1004
1005                 /** @var Database $conn */
1006                 $conn = null;
1007
1008                 if ( isset( $this->conns[$connInUseKey][$i][$domain] ) ) {
1009                         // Reuse an in-use connection for the same domain
1010                         $conn = $this->conns[$connInUseKey][$i][$domain];
1011                         $this->connLogger->debug( __METHOD__ . ": reusing connection $i/$domain" );
1012                 } elseif ( isset( $this->conns[$connFreeKey][$i][$domain] ) ) {
1013                         // Reuse a free connection for the same domain
1014                         $conn = $this->conns[$connFreeKey][$i][$domain];
1015                         unset( $this->conns[$connFreeKey][$i][$domain] );
1016                         $this->conns[$connInUseKey][$i][$domain] = $conn;
1017                         $this->connLogger->debug( __METHOD__ . ": reusing free connection $i/$domain" );
1018                 } elseif ( !empty( $this->conns[$connFreeKey][$i] ) ) {
1019                         // Reuse a free connection from another domain if possible
1020                         foreach ( $this->conns[$connFreeKey][$i] as $oldDomain => $conn ) {
1021                                 if ( $domainInstance->getDatabase() !== null ) {
1022                                         // Check if changing the database will require a new connection.
1023                                         // In that case, leave the connection handle alone and keep looking.
1024                                         // This prevents connections from being closed mid-transaction and can
1025                                         // also avoid overhead if the same database will later be requested.
1026                                         if (
1027                                                 $conn->databasesAreIndependent() &&
1028                                                 $conn->getDBname() !== $domainInstance->getDatabase()
1029                                         ) {
1030                                                 continue;
1031                                         }
1032                                         // Select the new database, schema, and prefix
1033                                         $conn->selectDomain( $domainInstance );
1034                                 } else {
1035                                         // Stay on the current database, but update the schema/prefix
1036                                         $conn->dbSchema( $domainInstance->getSchema() );
1037                                         $conn->tablePrefix( $domainInstance->getTablePrefix() );
1038                                 }
1039                                 unset( $this->conns[$connFreeKey][$i][$oldDomain] );
1040                                 // Note that if $domain is an empty string, getDomainID() might not match it
1041                                 $this->conns[$connInUseKey][$i][$conn->getDomainID()] = $conn;
1042                                 $this->connLogger->debug( __METHOD__ .
1043                                         ": reusing free connection from $oldDomain for $domain" );
1044                                 break;
1045                         }
1046                 }
1047
1048                 if ( !$conn ) {
1049                         if ( !isset( $this->servers[$i] ) || !is_array( $this->servers[$i] ) ) {
1050                                 throw new InvalidArgumentException( "No server with index '$i'." );
1051                         }
1052                         // Open a new connection
1053                         $server = $this->servers[$i];
1054                         $server['serverIndex'] = $i;
1055                         $server['foreignPoolRefCount'] = 0;
1056                         $server['foreign'] = true;
1057                         $server['autoCommitOnly'] = $autoCommit;
1058                         $conn = $this->reallyOpenConnection( $server, $domainInstance );
1059                         if ( !$conn->isOpen() ) {
1060                                 $this->connLogger->warning( __METHOD__ . ": connection error for $i/$domain" );
1061                                 $this->errorConnection = $conn;
1062                                 $conn = false;
1063                         } else {
1064                                 // Note that if $domain is an empty string, getDomainID() might not match it
1065                                 $this->conns[$connInUseKey][$i][$conn->getDomainID()] = $conn;
1066                                 $this->connLogger->debug( __METHOD__ . ": opened new connection for $i/$domain" );
1067                         }
1068                 }
1069
1070                 if ( $conn instanceof IDatabase ) {
1071                         // Final sanity check to make sure the right domain is selected
1072                         if ( !$domainInstance->isCompatible( $conn->getDomainID() ) ) {
1073                                 throw new UnexpectedValueException(
1074                                         "Got connection to '{$conn->getDomainID()}', but expected '$domain'." );
1075                         }
1076                         // Increment reference count
1077                         $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
1078                         $conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
1079                 }
1080
1081                 return $conn;
1082         }
1083
1084         public function getServerAttributes( $i ) {
1085                 return Database::attributesFromType(
1086                         $this->getServerType( $i ),
1087                         $this->servers[$i]['driver'] ?? null
1088                 );
1089         }
1090
1091         /**
1092          * Test if the specified index represents an open connection
1093          *
1094          * @param int $index Server index
1095          * @private
1096          * @return bool
1097          */
1098         private function isOpen( $index ) {
1099                 if ( !is_int( $index ) ) {
1100                         return false;
1101                 }
1102
1103                 return (bool)$this->getAnyOpenConnection( $index );
1104         }
1105
1106         /**
1107          * Open a new network connection to a server (uncached)
1108          *
1109          * Returns a Database object whether or not the connection was successful.
1110          *
1111          * @param array $server
1112          * @param DatabaseDomain $domain Domain the connection is for, possibly unspecified
1113          * @return Database
1114          * @throws DBAccessError
1115          * @throws InvalidArgumentException
1116          */
1117         protected function reallyOpenConnection( array $server, DatabaseDomain $domain ) {
1118                 if ( $this->disabled ) {
1119                         throw new DBAccessError();
1120                 }
1121
1122                 if ( $domain->getDatabase() === null ) {
1123                         // The database domain does not specify a DB name and some database systems require a
1124                         // valid DB specified on connection. The $server configuration array contains a default
1125                         // DB name to use for connections in such cases.
1126                         if ( $server['type'] === 'mysql' ) {
1127                                 // For MySQL, DATABASE and SCHEMA are synonyms, connections need not specify a DB,
1128                                 // and the DB name in $server might not exist due to legacy reasons (the default
1129                                 // domain used to ignore the local LB domain, even when mismatched).
1130                                 $server['dbname'] = null;
1131                         }
1132                 } else {
1133                         $server['dbname'] = $domain->getDatabase();
1134                 }
1135
1136                 if ( $domain->getSchema() !== null ) {
1137                         $server['schema'] = $domain->getSchema();
1138                 }
1139
1140                 // It is always possible to connect with any prefix, even the empty string
1141                 $server['tablePrefix'] = $domain->getTablePrefix();
1142
1143                 // Let the handle know what the cluster master is (e.g. "db1052")
1144                 $masterName = $this->getServerName( $this->getWriterIndex() );
1145                 $server['clusterMasterHost'] = $masterName;
1146
1147                 // Log when many connection are made on requests
1148                 if ( ++$this->connsOpened >= self::CONN_HELD_WARN_THRESHOLD ) {
1149                         $this->perfLogger->warning( __METHOD__ . ": " .
1150                                 "{$this->connsOpened}+ connections made (master=$masterName)" );
1151                 }
1152
1153                 $server['srvCache'] = $this->srvCache;
1154                 // Set loggers and profilers
1155                 $server['connLogger'] = $this->connLogger;
1156                 $server['queryLogger'] = $this->queryLogger;
1157                 $server['errorLogger'] = $this->errorLogger;
1158                 $server['deprecationLogger'] = $this->deprecationLogger;
1159                 $server['profiler'] = $this->profiler;
1160                 $server['trxProfiler'] = $this->trxProfiler;
1161                 // Use the same agent and PHP mode for all DB handles
1162                 $server['cliMode'] = $this->cliMode;
1163                 $server['agent'] = $this->agent;
1164                 // Use DBO_DEFAULT flags by default for LoadBalancer managed databases. Assume that the
1165                 // application calls LoadBalancer::commitMasterChanges() before the PHP script completes.
1166                 $server['flags'] = $server['flags'] ?? IDatabase::DBO_DEFAULT;
1167
1168                 // Create a live connection object
1169                 try {
1170                         $db = Database::factory( $server['type'], $server );
1171                 } catch ( DBConnectionError $e ) {
1172                         // FIXME: This is probably the ugliest thing I have ever done to
1173                         // PHP. I'm half-expecting it to segfault, just out of disgust. -- TS
1174                         $db = $e->db;
1175                 }
1176
1177                 $db->setLBInfo( $server );
1178                 $db->setLazyMasterHandle(
1179                         $this->getLazyConnectionRef( self::DB_MASTER, [], $db->getDomainID() )
1180                 );
1181                 $db->setTableAliases( $this->tableAliases );
1182                 $db->setIndexAliases( $this->indexAliases );
1183
1184                 if ( $server['serverIndex'] === $this->getWriterIndex() ) {
1185                         if ( $this->trxRoundId !== false ) {
1186                                 $this->applyTransactionRoundFlags( $db );
1187                         }
1188                         foreach ( $this->trxRecurringCallbacks as $name => $callback ) {
1189                                 $db->setTransactionListener( $name, $callback );
1190                         }
1191                 }
1192
1193                 return $db;
1194         }
1195
1196         /**
1197          * @throws DBConnectionError
1198          */
1199         private function reportConnectionError() {
1200                 $conn = $this->errorConnection; // the connection which caused the error
1201                 $context = [
1202                         'method' => __METHOD__,
1203                         'last_error' => $this->lastError,
1204                 ];
1205
1206                 if ( $conn instanceof IDatabase ) {
1207                         $context['db_server'] = $conn->getServer();
1208                         $this->connLogger->warning(
1209                                 __METHOD__ . ": connection error: {last_error} ({db_server})",
1210                                 $context
1211                         );
1212
1213                         throw new DBConnectionError( $conn, "{$this->lastError} ({$context['db_server']})" );
1214                 } else {
1215                         // No last connection, probably due to all servers being too busy
1216                         $this->connLogger->error(
1217                                 __METHOD__ .
1218                                 ": LB failure with no last connection. Connection error: {last_error}",
1219                                 $context
1220                         );
1221
1222                         // If all servers were busy, "lastError" will contain something sensible
1223                         throw new DBConnectionError( null, $this->lastError );
1224                 }
1225         }
1226
1227         public function getWriterIndex() {
1228                 return 0;
1229         }
1230
1231         public function haveIndex( $i ) {
1232                 return array_key_exists( $i, $this->servers );
1233         }
1234
1235         public function isNonZeroLoad( $i ) {
1236                 return array_key_exists( $i, $this->servers ) && $this->loads[$i] != 0;
1237         }
1238
1239         public function getServerCount() {
1240                 return count( $this->servers );
1241         }
1242
1243         public function getServerName( $i ) {
1244                 $name = $this->servers[$i]['hostName'] ?? $this->servers[$i]['host'] ?? '';
1245
1246                 return ( $name != '' ) ? $name : 'localhost';
1247         }
1248
1249         public function getServerInfo( $i ) {
1250                 return $this->servers[$i] ?? false;
1251         }
1252
1253         public function getServerType( $i ) {
1254                 return $this->servers[$i]['type'] ?? 'unknown';
1255         }
1256
1257         public function getMasterPos() {
1258                 # If this entire request was served from a replica DB without opening a connection to the
1259                 # master (however unlikely that may be), then we can fetch the position from the replica DB.
1260                 $masterConn = $this->getAnyOpenConnection( $this->getWriterIndex() );
1261                 if ( !$masterConn ) {
1262                         $serverCount = count( $this->servers );
1263                         for ( $i = 1; $i < $serverCount; $i++ ) {
1264                                 $conn = $this->getAnyOpenConnection( $i );
1265                                 if ( $conn ) {
1266                                         return $conn->getReplicaPos();
1267                                 }
1268                         }
1269                 } else {
1270                         return $masterConn->getMasterPos();
1271                 }
1272
1273                 return false;
1274         }
1275
1276         public function disable() {
1277                 $this->closeAll();
1278                 $this->disabled = true;
1279         }
1280
1281         public function closeAll() {
1282                 $fname = __METHOD__;
1283                 $this->forEachOpenConnection( function ( IDatabase $conn ) use ( $fname ) {
1284                         $host = $conn->getServer();
1285                         $this->connLogger->debug(
1286                                 $fname . ": closing connection to database '$host'." );
1287                         $conn->close();
1288                 } );
1289
1290                 $this->conns = [
1291                         self::KEY_LOCAL => [],
1292                         self::KEY_FOREIGN_INUSE => [],
1293                         self::KEY_FOREIGN_FREE => [],
1294                         self::KEY_LOCAL_NOROUND => [],
1295                         self::KEY_FOREIGN_INUSE_NOROUND => [],
1296                         self::KEY_FOREIGN_FREE_NOROUND => []
1297                 ];
1298                 $this->connsOpened = 0;
1299         }
1300
1301         public function closeConnection( IDatabase $conn ) {
1302                 if ( $conn instanceof DBConnRef ) {
1303                         // Avoid calling close() but still leaving the handle in the pool
1304                         throw new RuntimeException( __METHOD__ . ': got DBConnRef instance.' );
1305                 }
1306
1307                 $serverIndex = $conn->getLBInfo( 'serverIndex' );
1308                 foreach ( $this->conns as $type => $connsByServer ) {
1309                         if ( !isset( $connsByServer[$serverIndex] ) ) {
1310                                 continue;
1311                         }
1312
1313                         foreach ( $connsByServer[$serverIndex] as $i => $trackedConn ) {
1314                                 if ( $conn === $trackedConn ) {
1315                                         $host = $this->getServerName( $i );
1316                                         $this->connLogger->debug(
1317                                                 __METHOD__ . ": closing connection to database $i at '$host'." );
1318                                         unset( $this->conns[$type][$serverIndex][$i] );
1319                                         --$this->connsOpened;
1320                                         break 2;
1321                                 }
1322                         }
1323                 }
1324
1325                 $conn->close();
1326         }
1327
1328         public function commitAll( $fname = __METHOD__ ) {
1329                 $this->commitMasterChanges( $fname );
1330                 $this->flushMasterSnapshots( $fname );
1331                 $this->flushReplicaSnapshots( $fname );
1332         }
1333
1334         public function finalizeMasterChanges() {
1335                 $this->assertTransactionRoundStage( [ self::ROUND_CURSORY, self::ROUND_FINALIZED ] );
1336
1337                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1338                 // Loop until callbacks stop adding callbacks on other connections
1339                 $total = 0;
1340                 do {
1341                         $count = 0; // callbacks execution attempts
1342                         $this->forEachOpenMasterConnection( function ( Database $conn ) use ( &$count ) {
1343                                 // Run any pre-commit callbacks while leaving the post-commit ones suppressed.
1344                                 // Any error should cause all (peer) transactions to be rolled back together.
1345                                 $count += $conn->runOnTransactionPreCommitCallbacks();
1346                         } );
1347                         $total += $count;
1348                 } while ( $count > 0 );
1349                 // Defer post-commit callbacks until after COMMIT/ROLLBACK happens on all handles
1350                 $this->forEachOpenMasterConnection( function ( Database $conn ) {
1351                         $conn->setTrxEndCallbackSuppression( true );
1352                 } );
1353                 $this->trxRoundStage = self::ROUND_FINALIZED;
1354
1355                 return $total;
1356         }
1357
1358         public function approveMasterChanges( array $options ) {
1359                 $this->assertTransactionRoundStage( self::ROUND_FINALIZED );
1360
1361                 $limit = $options['maxWriteDuration'] ?? 0;
1362
1363                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1364                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( $limit ) {
1365                         // If atomic sections or explicit transactions are still open, some caller must have
1366                         // caught an exception but failed to properly rollback any changes. Detect that and
1367                         // throw and error (causing rollback).
1368                         $conn->assertNoOpenTransactions();
1369                         // Assert that the time to replicate the transaction will be sane.
1370                         // If this fails, then all DB transactions will be rollback back together.
1371                         $time = $conn->pendingWriteQueryDuration( $conn::ESTIMATE_DB_APPLY );
1372                         if ( $limit > 0 && $time > $limit ) {
1373                                 throw new DBTransactionSizeError(
1374                                         $conn,
1375                                         "Transaction spent $time second(s) in writes, exceeding the limit of $limit.",
1376                                         [ $time, $limit ]
1377                                 );
1378                         }
1379                         // If a connection sits idle while slow queries execute on another, that connection
1380                         // may end up dropped before the commit round is reached. Ping servers to detect this.
1381                         if ( $conn->writesOrCallbacksPending() && !$conn->ping() ) {
1382                                 throw new DBTransactionError(
1383                                         $conn,
1384                                         "A connection to the {$conn->getDBname()} database was lost before commit."
1385                                 );
1386                         }
1387                 } );
1388                 $this->trxRoundStage = self::ROUND_APPROVED;
1389         }
1390
1391         public function beginMasterChanges( $fname = __METHOD__ ) {
1392                 if ( $this->trxRoundId !== false ) {
1393                         throw new DBTransactionError(
1394                                 null,
1395                                 "$fname: Transaction round '{$this->trxRoundId}' already started."
1396                         );
1397                 }
1398                 $this->assertTransactionRoundStage( self::ROUND_CURSORY );
1399
1400                 // Clear any empty transactions (no writes/callbacks) from the implicit round
1401                 $this->flushMasterSnapshots( $fname );
1402
1403                 $this->trxRoundId = $fname;
1404                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1405                 // Mark applicable handles as participating in this explicit transaction round.
1406                 // For each of these handles, any writes and callbacks will be tied to a single
1407                 // transaction. The (peer) handles will reject begin()/commit() calls unless they
1408                 // are part of an en masse commit or an en masse rollback.
1409                 $this->forEachOpenMasterConnection( function ( Database $conn ) {
1410                         $this->applyTransactionRoundFlags( $conn );
1411                 } );
1412                 $this->trxRoundStage = self::ROUND_CURSORY;
1413         }
1414
1415         public function commitMasterChanges( $fname = __METHOD__ ) {
1416                 $this->assertTransactionRoundStage( self::ROUND_APPROVED );
1417
1418                 $failures = [];
1419
1420                 /** @noinspection PhpUnusedLocalVariableInspection */
1421                 $scope = ScopedCallback::newScopedIgnoreUserAbort(); // try to ignore client aborts
1422
1423                 $restore = ( $this->trxRoundId !== false );
1424                 $this->trxRoundId = false;
1425                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1426                 // Commit any writes and clear any snapshots as well (callbacks require AUTOCOMMIT).
1427                 // Note that callbacks should already be suppressed due to finalizeMasterChanges().
1428                 $this->forEachOpenMasterConnection(
1429                         function ( IDatabase $conn ) use ( $fname, &$failures ) {
1430                                 try {
1431                                         $conn->commit( $fname, $conn::FLUSHING_ALL_PEERS );
1432                                 } catch ( DBError $e ) {
1433                                         ( $this->errorLogger )( $e );
1434                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1435                                 }
1436                         }
1437                 );
1438                 if ( $failures ) {
1439                         throw new DBTransactionError(
1440                                 null,
1441                                 "$fname: Commit failed on server(s) " . implode( "\n", array_unique( $failures ) )
1442                         );
1443                 }
1444                 if ( $restore ) {
1445                         // Unmark handles as participating in this explicit transaction round
1446                         $this->forEachOpenMasterConnection( function ( Database $conn ) {
1447                                 $this->undoTransactionRoundFlags( $conn );
1448                         } );
1449                 }
1450                 $this->trxRoundStage = self::ROUND_COMMIT_CALLBACKS;
1451         }
1452
1453         public function runMasterTransactionIdleCallbacks() {
1454                 if ( $this->trxRoundStage === self::ROUND_COMMIT_CALLBACKS ) {
1455                         $type = IDatabase::TRIGGER_COMMIT;
1456                 } elseif ( $this->trxRoundStage === self::ROUND_ROLLBACK_CALLBACKS ) {
1457                         $type = IDatabase::TRIGGER_ROLLBACK;
1458                 } else {
1459                         throw new DBTransactionError(
1460                                 null,
1461                                 "Transaction should be in the callback stage (not '{$this->trxRoundStage}')"
1462                         );
1463                 }
1464
1465                 $oldStage = $this->trxRoundStage;
1466                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1467
1468                 // Now that the COMMIT/ROLLBACK step is over, enable post-commit callback runs
1469                 $this->forEachOpenMasterConnection( function ( Database $conn ) {
1470                         $conn->setTrxEndCallbackSuppression( false );
1471                 } );
1472
1473                 $e = null; // first exception
1474                 $fname = __METHOD__;
1475                 // Loop until callbacks stop adding callbacks on other connections
1476                 do {
1477                         // Run any pending callbacks for each connection...
1478                         $count = 0; // callback execution attempts
1479                         $this->forEachOpenMasterConnection(
1480                                 function ( Database $conn ) use ( $type, &$e, &$count ) {
1481                                         if ( $conn->trxLevel() ) {
1482                                                 return; // retry in the next iteration, after commit() is called
1483                                         }
1484                                         try {
1485                                                 $count += $conn->runOnTransactionIdleCallbacks( $type );
1486                                         } catch ( Exception $ex ) {
1487                                                 $e = $e ?: $ex;
1488                                         }
1489                                 }
1490                         );
1491                         // Clear out any active transactions left over from callbacks...
1492                         $this->forEachOpenMasterConnection( function ( Database $conn ) use ( &$e, $fname ) {
1493                                 if ( $conn->writesPending() ) {
1494                                         // A callback from another handle wrote to this one and DBO_TRX is set
1495                                         $this->queryLogger->warning( $fname . ": found writes pending." );
1496                                         $fnames = implode( ', ', $conn->pendingWriteAndCallbackCallers() );
1497                                         $this->queryLogger->warning(
1498                                                 $fname . ": found writes pending ($fnames).",
1499                                                 [
1500                                                         'db_server' => $conn->getServer(),
1501                                                         'db_name' => $conn->getDBname()
1502                                                 ]
1503                                         );
1504                                 } elseif ( $conn->trxLevel() ) {
1505                                         // A callback from another handle read from this one and DBO_TRX is set,
1506                                         // which can easily happen if there is only one DB (no replicas)
1507                                         $this->queryLogger->debug( $fname . ": found empty transaction." );
1508                                 }
1509                                 try {
1510                                         $conn->commit( $fname, $conn::FLUSHING_ALL_PEERS );
1511                                 } catch ( Exception $ex ) {
1512                                         $e = $e ?: $ex;
1513                                 }
1514                         } );
1515                 } while ( $count > 0 );
1516
1517                 $this->trxRoundStage = $oldStage;
1518
1519                 return $e;
1520         }
1521
1522         public function runMasterTransactionListenerCallbacks() {
1523                 if ( $this->trxRoundStage === self::ROUND_COMMIT_CALLBACKS ) {
1524                         $type = IDatabase::TRIGGER_COMMIT;
1525                 } elseif ( $this->trxRoundStage === self::ROUND_ROLLBACK_CALLBACKS ) {
1526                         $type = IDatabase::TRIGGER_ROLLBACK;
1527                 } else {
1528                         throw new DBTransactionError(
1529                                 null,
1530                                 "Transaction should be in the callback stage (not '{$this->trxRoundStage}')"
1531                         );
1532                 }
1533
1534                 $e = null;
1535
1536                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1537                 $this->forEachOpenMasterConnection( function ( Database $conn ) use ( $type, &$e ) {
1538                         try {
1539                                 $conn->runTransactionListenerCallbacks( $type );
1540                         } catch ( Exception $ex ) {
1541                                 $e = $e ?: $ex;
1542                         }
1543                 } );
1544                 $this->trxRoundStage = self::ROUND_CURSORY;
1545
1546                 return $e;
1547         }
1548
1549         public function rollbackMasterChanges( $fname = __METHOD__ ) {
1550                 $restore = ( $this->trxRoundId !== false );
1551                 $this->trxRoundId = false;
1552                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1553                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( $fname ) {
1554                         $conn->rollback( $fname, $conn::FLUSHING_ALL_PEERS );
1555                 } );
1556                 if ( $restore ) {
1557                         // Unmark handles as participating in this explicit transaction round
1558                         $this->forEachOpenMasterConnection( function ( Database $conn ) {
1559                                 $this->undoTransactionRoundFlags( $conn );
1560                         } );
1561                 }
1562                 $this->trxRoundStage = self::ROUND_ROLLBACK_CALLBACKS;
1563         }
1564
1565         /**
1566          * @param string|string[] $stage
1567          */
1568         private function assertTransactionRoundStage( $stage ) {
1569                 $stages = (array)$stage;
1570
1571                 if ( !in_array( $this->trxRoundStage, $stages, true ) ) {
1572                         $stageList = implode(
1573                                 '/',
1574                                 array_map( function ( $v ) {
1575                                         return "'$v'";
1576                                 }, $stages )
1577                         );
1578                         throw new DBTransactionError(
1579                                 null,
1580                                 "Transaction round stage must be $stageList (not '{$this->trxRoundStage}')"
1581                         );
1582                 }
1583         }
1584
1585         /**
1586          * Make all DB servers with DBO_DEFAULT/DBO_TRX set join the transaction round
1587          *
1588          * Some servers may have neither flag enabled, meaning that they opt out of such
1589          * transaction rounds and remain in auto-commit mode. Such behavior might be desired
1590          * when a DB server is used for something like simple key/value storage.
1591          *
1592          * @param Database $conn
1593          */
1594         private function applyTransactionRoundFlags( Database $conn ) {
1595                 if ( $conn->getLBInfo( 'autoCommitOnly' ) ) {
1596                         return; // transaction rounds do not apply to these connections
1597                 }
1598
1599                 if ( $conn->getFlag( $conn::DBO_DEFAULT ) ) {
1600                         // DBO_TRX is controlled entirely by CLI mode presence with DBO_DEFAULT.
1601                         // Force DBO_TRX even in CLI mode since a commit round is expected soon.
1602                         $conn->setFlag( $conn::DBO_TRX, $conn::REMEMBER_PRIOR );
1603                 }
1604
1605                 if ( $conn->getFlag( $conn::DBO_TRX ) ) {
1606                         $conn->setLBInfo( 'trxRoundId', $this->trxRoundId );
1607                 }
1608         }
1609
1610         /**
1611          * @param Database $conn
1612          */
1613         private function undoTransactionRoundFlags( Database $conn ) {
1614                 if ( $conn->getLBInfo( 'autoCommitOnly' ) ) {
1615                         return; // transaction rounds do not apply to these connections
1616                 }
1617
1618                 if ( $conn->getFlag( $conn::DBO_TRX ) ) {
1619                         $conn->setLBInfo( 'trxRoundId', false );
1620                 }
1621
1622                 if ( $conn->getFlag( $conn::DBO_DEFAULT ) ) {
1623                         $conn->restoreFlags( $conn::RESTORE_PRIOR );
1624                 }
1625         }
1626
1627         public function flushReplicaSnapshots( $fname = __METHOD__ ) {
1628                 $this->forEachOpenReplicaConnection( function ( IDatabase $conn ) use ( $fname ) {
1629                         $conn->flushSnapshot( $fname );
1630                 } );
1631         }
1632
1633         public function flushMasterSnapshots( $fname = __METHOD__ ) {
1634                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( $fname ) {
1635                         $conn->flushSnapshot( $fname );
1636                 } );
1637         }
1638
1639         /**
1640          * @return string
1641          * @since 1.32
1642          */
1643         public function getTransactionRoundStage() {
1644                 return $this->trxRoundStage;
1645         }
1646
1647         public function hasMasterConnection() {
1648                 return $this->isOpen( $this->getWriterIndex() );
1649         }
1650
1651         public function hasMasterChanges() {
1652                 $pending = 0;
1653                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$pending ) {
1654                         $pending |= $conn->writesOrCallbacksPending();
1655                 } );
1656
1657                 return (bool)$pending;
1658         }
1659
1660         public function lastMasterChangeTimestamp() {
1661                 $lastTime = false;
1662                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$lastTime ) {
1663                         $lastTime = max( $lastTime, $conn->lastDoneWrites() );
1664                 } );
1665
1666                 return $lastTime;
1667         }
1668
1669         public function hasOrMadeRecentMasterChanges( $age = null ) {
1670                 $age = ( $age === null ) ? $this->waitTimeout : $age;
1671
1672                 return ( $this->hasMasterChanges()
1673                         || $this->lastMasterChangeTimestamp() > microtime( true ) - $age );
1674         }
1675
1676         public function pendingMasterChangeCallers() {
1677                 $fnames = [];
1678                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$fnames ) {
1679                         $fnames = array_merge( $fnames, $conn->pendingWriteCallers() );
1680                 } );
1681
1682                 return $fnames;
1683         }
1684
1685         public function getLaggedReplicaMode( $domain = false ) {
1686                 // No-op if there is only one DB (also avoids recursion)
1687                 if ( !$this->laggedReplicaMode && $this->getServerCount() > 1 ) {
1688                         try {
1689                                 // See if laggedReplicaMode gets set
1690                                 $conn = $this->getConnection( self::DB_REPLICA, false, $domain );
1691                                 $this->reuseConnection( $conn );
1692                         } catch ( DBConnectionError $e ) {
1693                                 // Avoid expensive re-connect attempts and failures
1694                                 $this->allReplicasDownMode = true;
1695                                 $this->laggedReplicaMode = true;
1696                         }
1697                 }
1698
1699                 return $this->laggedReplicaMode;
1700         }
1701
1702         public function laggedReplicaUsed() {
1703                 return $this->laggedReplicaMode;
1704         }
1705
1706         /**
1707          * @return bool
1708          * @since 1.27
1709          * @deprecated Since 1.28; use laggedReplicaUsed()
1710          */
1711         public function laggedSlaveUsed() {
1712                 return $this->laggedReplicaUsed();
1713         }
1714
1715         public function getReadOnlyReason( $domain = false, IDatabase $conn = null ) {
1716                 if ( $this->readOnlyReason !== false ) {
1717                         return $this->readOnlyReason;
1718                 } elseif ( $this->getLaggedReplicaMode( $domain ) ) {
1719                         if ( $this->allReplicasDownMode ) {
1720                                 return 'The database has been automatically locked ' .
1721                                         'until the replica database servers become available';
1722                         } else {
1723                                 return 'The database has been automatically locked ' .
1724                                         'while the replica database servers catch up to the master.';
1725                         }
1726                 } elseif ( $this->masterRunningReadOnly( $domain, $conn ) ) {
1727                         return 'The database master is running in read-only mode.';
1728                 }
1729
1730                 return false;
1731         }
1732
1733         /**
1734          * @param string $domain Domain ID, or false for the current domain
1735          * @param IDatabase|null $conn DB master connectionl used to avoid loops [optional]
1736          * @return bool
1737          */
1738         private function masterRunningReadOnly( $domain, IDatabase $conn = null ) {
1739                 $cache = $this->wanCache;
1740                 $masterServer = $this->getServerName( $this->getWriterIndex() );
1741
1742                 return (bool)$cache->getWithSetCallback(
1743                         $cache->makeGlobalKey( __CLASS__, 'server-read-only', $masterServer ),
1744                         self::TTL_CACHE_READONLY,
1745                         function () use ( $domain, $conn ) {
1746                                 $old = $this->trxProfiler->setSilenced( true );
1747                                 try {
1748                                         $dbw = $conn ?: $this->getConnection( self::DB_MASTER, [], $domain );
1749                                         $readOnly = (int)$dbw->serverIsReadOnly();
1750                                         if ( !$conn ) {
1751                                                 $this->reuseConnection( $dbw );
1752                                         }
1753                                 } catch ( DBError $e ) {
1754                                         $readOnly = 0;
1755                                 }
1756                                 $this->trxProfiler->setSilenced( $old );
1757                                 return $readOnly;
1758                         },
1759                         [ 'pcTTL' => $cache::TTL_PROC_LONG, 'busyValue' => 0 ]
1760                 );
1761         }
1762
1763         public function allowLagged( $mode = null ) {
1764                 if ( $mode === null ) {
1765                         return $this->allowLagged;
1766                 }
1767                 $this->allowLagged = $mode;
1768
1769                 return $this->allowLagged;
1770         }
1771
1772         public function pingAll() {
1773                 $success = true;
1774                 $this->forEachOpenConnection( function ( IDatabase $conn ) use ( &$success ) {
1775                         if ( !$conn->ping() ) {
1776                                 $success = false;
1777                         }
1778                 } );
1779
1780                 return $success;
1781         }
1782
1783         public function forEachOpenConnection( $callback, array $params = [] ) {
1784                 foreach ( $this->conns as $connsByServer ) {
1785                         foreach ( $connsByServer as $serverConns ) {
1786                                 foreach ( $serverConns as $conn ) {
1787                                         $callback( $conn, ...$params );
1788                                 }
1789                         }
1790                 }
1791         }
1792
1793         public function forEachOpenMasterConnection( $callback, array $params = [] ) {
1794                 $masterIndex = $this->getWriterIndex();
1795                 foreach ( $this->conns as $connsByServer ) {
1796                         if ( isset( $connsByServer[$masterIndex] ) ) {
1797                                 /** @var IDatabase $conn */
1798                                 foreach ( $connsByServer[$masterIndex] as $conn ) {
1799                                         $callback( $conn, ...$params );
1800                                 }
1801                         }
1802                 }
1803         }
1804
1805         public function forEachOpenReplicaConnection( $callback, array $params = [] ) {
1806                 foreach ( $this->conns as $connsByServer ) {
1807                         foreach ( $connsByServer as $i => $serverConns ) {
1808                                 if ( $i === $this->getWriterIndex() ) {
1809                                         continue; // skip master
1810                                 }
1811                                 foreach ( $serverConns as $conn ) {
1812                                         $callback( $conn, ...$params );
1813                                 }
1814                         }
1815                 }
1816         }
1817
1818         public function getMaxLag( $domain = false ) {
1819                 $maxLag = -1;
1820                 $host = '';
1821                 $maxIndex = 0;
1822
1823                 if ( $this->getServerCount() <= 1 ) {
1824                         return [ $host, $maxLag, $maxIndex ]; // no replication = no lag
1825                 }
1826
1827                 $lagTimes = $this->getLagTimes( $domain );
1828                 foreach ( $lagTimes as $i => $lag ) {
1829                         if ( $this->loads[$i] > 0 && $lag > $maxLag ) {
1830                                 $maxLag = $lag;
1831                                 $host = $this->servers[$i]['host'];
1832                                 $maxIndex = $i;
1833                         }
1834                 }
1835
1836                 return [ $host, $maxLag, $maxIndex ];
1837         }
1838
1839         public function getLagTimes( $domain = false ) {
1840                 if ( $this->getServerCount() <= 1 ) {
1841                         return [ $this->getWriterIndex() => 0 ]; // no replication = no lag
1842                 }
1843
1844                 $knownLagTimes = []; // map of (server index => 0 seconds)
1845                 $indexesWithLag = [];
1846                 foreach ( $this->servers as $i => $server ) {
1847                         if ( empty( $server['is static'] ) ) {
1848                                 $indexesWithLag[] = $i; // DB server might have replication lag
1849                         } else {
1850                                 $knownLagTimes[$i] = 0; // DB server is a non-replicating and read-only archive
1851                         }
1852                 }
1853
1854                 return $this->getLoadMonitor()->getLagTimes( $indexesWithLag, $domain ) + $knownLagTimes;
1855         }
1856
1857         public function safeGetLag( IDatabase $conn ) {
1858                 if ( $this->getServerCount() <= 1 ) {
1859                         return 0;
1860                 } else {
1861                         return $conn->getLag();
1862                 }
1863         }
1864
1865         public function safeWaitForMasterPos( IDatabase $conn, $pos = false, $timeout = null ) {
1866                 $timeout = max( 1, $timeout ?: $this->waitTimeout );
1867
1868                 if ( $this->getServerCount() <= 1 || !$conn->getLBInfo( 'replica' ) ) {
1869                         return true; // server is not a replica DB
1870                 }
1871
1872                 if ( !$pos ) {
1873                         // Get the current master position, opening a connection if needed
1874                         $masterConn = $this->getAnyOpenConnection( $this->getWriterIndex() );
1875                         if ( $masterConn ) {
1876                                 $pos = $masterConn->getMasterPos();
1877                         } else {
1878                                 $masterConn = $this->openConnection( $this->getWriterIndex(), self::DOMAIN_ANY );
1879                                 if ( !$masterConn ) {
1880                                         throw new DBReplicationWaitError(
1881                                                 null,
1882                                                 "Could not obtain a master database connection to get the position"
1883                                         );
1884                                 }
1885                                 $pos = $masterConn->getMasterPos();
1886                                 $this->closeConnection( $masterConn );
1887                         }
1888                 }
1889
1890                 if ( $pos instanceof DBMasterPos ) {
1891                         $result = $conn->masterPosWait( $pos, $timeout );
1892                         if ( $result == -1 || is_null( $result ) ) {
1893                                 $msg = __METHOD__ . ': timed out waiting on {host} pos {pos}';
1894                                 $this->replLogger->warning( $msg, [
1895                                         'host' => $conn->getServer(),
1896                                         'pos' => $pos,
1897                                         'trace' => ( new RuntimeException() )->getTraceAsString()
1898                                 ] );
1899                                 $ok = false;
1900                         } else {
1901                                 $this->replLogger->debug( __METHOD__ . ': done waiting' );
1902                                 $ok = true;
1903                         }
1904                 } else {
1905                         $ok = false; // something is misconfigured
1906                         $this->replLogger->error(
1907                                 __METHOD__ . ': could not get master pos for {host}',
1908                                 [
1909                                         'host' => $conn->getServer(),
1910                                         'trace' => ( new RuntimeException() )->getTraceAsString()
1911                                 ]
1912                         );
1913                 }
1914
1915                 return $ok;
1916         }
1917
1918         public function setTransactionListener( $name, callable $callback = null ) {
1919                 if ( $callback ) {
1920                         $this->trxRecurringCallbacks[$name] = $callback;
1921                 } else {
1922                         unset( $this->trxRecurringCallbacks[$name] );
1923                 }
1924                 $this->forEachOpenMasterConnection(
1925                         function ( IDatabase $conn ) use ( $name, $callback ) {
1926                                 $conn->setTransactionListener( $name, $callback );
1927                         }
1928                 );
1929         }
1930
1931         public function setTableAliases( array $aliases ) {
1932                 $this->tableAliases = $aliases;
1933         }
1934
1935         public function setIndexAliases( array $aliases ) {
1936                 $this->indexAliases = $aliases;
1937         }
1938
1939         /**
1940          * @param string $prefix
1941          * @deprecated Since 1.33
1942          */
1943         public function setDomainPrefix( $prefix ) {
1944                 $this->setLocalDomainPrefix( $prefix );
1945         }
1946
1947         public function setLocalDomainPrefix( $prefix ) {
1948                 // Find connections to explicit foreign domains still marked as in-use...
1949                 $domainsInUse = [];
1950                 $this->forEachOpenConnection( function ( IDatabase $conn ) use ( &$domainsInUse ) {
1951                         // Once reuseConnection() is called on a handle, its reference count goes from 1 to 0.
1952                         // Until then, it is still in use by the caller (explicitly or via DBConnRef scope).
1953                         if ( $conn->getLBInfo( 'foreignPoolRefCount' ) > 0 ) {
1954                                 $domainsInUse[] = $conn->getDomainID();
1955                         }
1956                 } );
1957
1958                 // Do not switch connections to explicit foreign domains unless marked as safe
1959                 if ( $domainsInUse ) {
1960                         $domains = implode( ', ', $domainsInUse );
1961                         throw new DBUnexpectedError( null,
1962                                 "Foreign domain connections are still in use ($domains)." );
1963                 }
1964
1965                 $this->setLocalDomain( new DatabaseDomain(
1966                         $this->localDomain->getDatabase(),
1967                         $this->localDomain->getSchema(),
1968                         $prefix
1969                 ) );
1970
1971                 // Update the prefix for all local connections...
1972                 $this->forEachOpenConnection( function ( IDatabase $db ) use ( $prefix ) {
1973                         if ( !$db->getLBInfo( 'foreign' ) ) {
1974                                 $db->tablePrefix( $prefix );
1975                         }
1976                 } );
1977         }
1978
1979         public function redefineLocalDomain( $domain ) {
1980                 $this->closeAll();
1981
1982                 $this->setLocalDomain( DatabaseDomain::newFromId( $domain ) );
1983         }
1984
1985         /**
1986          * @param DatabaseDomain $domain
1987          */
1988         private function setLocalDomain( DatabaseDomain $domain ) {
1989                 $this->localDomain = $domain;
1990                 // In case a caller assumes that the domain ID is simply <db>-<prefix>, which is almost
1991                 // always true, gracefully handle the case when they fail to account for escaping.
1992                 if ( $this->localDomain->getTablePrefix() != '' ) {
1993                         $this->localDomainIdAlias =
1994                                 $this->localDomain->getDatabase() . '-' . $this->localDomain->getTablePrefix();
1995                 } else {
1996                         $this->localDomainIdAlias = $this->localDomain->getDatabase();
1997                 }
1998         }
1999
2000         function __destruct() {
2001                 // Avoid connection leaks for sanity
2002                 $this->disable();
2003         }
2004 }
2005
2006 /**
2007  * @deprecated since 1.29
2008  */
2009 class_alias( LoadBalancer::class, 'LoadBalancer' );