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