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 DB 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 $genericLoads;
  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 local DB 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 */
 107         private $genericReadIndex = -1;
 108         /** @var int[] The group replica DB indexes keyed by group */
 109         private $readIndexByGroup = [];
 110         /** @var bool|DBMasterPos Replication sync position or false if not set */
 111         private $waitForPos;
 112         /** @var bool Whether the generic reader fell back to a lagged replica DB */
 113         private $laggedReplicaMode = false;
 114         /** @var bool Whether the generic reader fell back to a lagged replica DB */
 115         private $allReplicasDownMode = false;
 116         /** @var string The last DB selection or connection error */
 117         private $lastError = 'Unknown error';
 118         /** @var string|bool Reason the LB is read-only or false if not */
 119         private $readOnlyReason = false;
 120         /** @var int Total number of new connections ever made with this instance */
 121         private $connectionCounter = 0;
 122         /** @var bool */
 123         private $disabled = false;
 124         /** @var bool Whether any connection has been attempted yet */
 125         private $connectionAttempted = false;
 126
 127         /** @var int|null An integer ID of the managing LBFactory instance or null */
 128         private $ownerId;
 129         /** @var string|bool String if a requested DBO_TRX transaction round is active */
 130         private $trxRoundId = false;
 131         /** @var string Stage of the current transaction round in the transaction round life-cycle */
 132         private $trxRoundStage = self::ROUND_CURSORY;
 133
 134         /** @var string|null */
 135         private $defaultGroup = null;
 136
 137         /** @var int Warn when this many connection are held */
 138         const CONN_HELD_WARN_THRESHOLD = 10;
 139
 140         /** @var int Default 'maxLag' when unspecified */
 141         const MAX_LAG_DEFAULT = 6;
 142         /** @var int Default 'waitTimeout' when unspecified */
 143         const MAX_WAIT_DEFAULT = 10;
 144         /** @var int Seconds to cache master server read-only status */
 145         const TTL_CACHE_READONLY = 5;
 146
 147         const KEY_LOCAL = 'local';
 148         const KEY_FOREIGN_FREE = 'foreignFree';
 149         const KEY_FOREIGN_INUSE = 'foreignInUse';
 150
 151         const KEY_LOCAL_NOROUND = 'localAutoCommit';
 152         const KEY_FOREIGN_FREE_NOROUND = 'foreignFreeAutoCommit';
 153         const KEY_FOREIGN_INUSE_NOROUND = 'foreignInUseAutoCommit';
 154
 155         /** @var string Transaction round, explicit or implicit, has not finished writing */
 156         const ROUND_CURSORY = 'cursory';
 157         /** @var string Transaction round writes are complete and ready for pre-commit checks */
 158         const ROUND_FINALIZED = 'finalized';
 159         /** @var string Transaction round passed final pre-commit checks */
 160         const ROUND_APPROVED = 'approved';
 161         /** @var string Transaction round was committed and post-commit callbacks must be run */
 162         const ROUND_COMMIT_CALLBACKS = 'commit-callbacks';
 163         /** @var string Transaction round was rolled back and post-rollback callbacks must be run */
 164         const ROUND_ROLLBACK_CALLBACKS = 'rollback-callbacks';
 165         /** @var string Transaction round encountered an error */
 166         const ROUND_ERROR = 'error';
 167
 168         public function __construct( array $params ) {
 169                 if ( !isset( $params['servers'] ) || !count( $params['servers'] ) ) {
 170                         throw new InvalidArgumentException( 'Missing or empty "servers" parameter' );
 171                 }
 172
 173                 $listKey = -1;
 174                 $this->servers = [];
 175                 $this->genericLoads = [];
 176                 foreach ( $params['servers'] as $i => $server ) {
 177                         if ( ++$listKey !== $i ) {
 178                                 throw new UnexpectedValueException( 'List expected for "servers" parameter' );
 179                         }
 180                         if ( $i == 0 ) {
 181                                 $server['master'] = true;
 182                         } else {
 183                                 $server['replica'] = true;
 184                         }
 185                         $this->servers[$i] = $server;
 186
 187                         $this->genericLoads[$i] = $server['load'];
 188                         if ( isset( $server['groupLoads'] ) ) {
 189                                 foreach ( $server['groupLoads'] as $group => $ratio ) {
 190                                         $this->groupLoads[$group][$i] = $ratio;
 191                                 }
 192                         }
 193                 }
 194
 195                 $localDomain = isset( $params['localDomain'] )
 196                         ? DatabaseDomain::newFromId( $params['localDomain'] )
 197                         : DatabaseDomain::newUnspecified();
 198                 $this->setLocalDomain( $localDomain );
 199
 200                 $this->waitTimeout = $params['waitTimeout'] ?? self::MAX_WAIT_DEFAULT;
 201
 202                 $this->conns = self::newTrackedConnectionsArray();
 203                 $this->waitForPos = false;
 204                 $this->allowLagged = false;
 205
 206                 if ( isset( $params['readOnlyReason'] ) && is_string( $params['readOnlyReason'] ) ) {
 207                         $this->readOnlyReason = $params['readOnlyReason'];
 208                 }
 209
 210                 $this->maxLag = $params['maxLag'] ?? self::MAX_LAG_DEFAULT;
 211
 212                 $this->loadMonitorConfig = $params['loadMonitor'] ?? [ 'class' => 'LoadMonitorNull' ];
 213                 $this->loadMonitorConfig += [ 'lagWarnThreshold' => $this->maxLag ];
 214
 215                 $this->srvCache = $params['srvCache'] ?? new EmptyBagOStuff();
 216                 $this->wanCache = $params['wanCache'] ?? WANObjectCache::newEmpty();
 217                 $this->profiler = $params['profiler'] ?? null;
 218                 $this->trxProfiler = $params['trxProfiler'] ?? new TransactionProfiler();
 219
 220                 $this->errorLogger = $params['errorLogger'] ?? function ( Exception $e ) {
 221                         trigger_error( get_class( $e ) . ': ' . $e->getMessage(), E_USER_WARNING );
 222                 };
 223                 $this->deprecationLogger = $params['deprecationLogger'] ?? function ( $msg ) {
 224                         trigger_error( $msg, E_USER_DEPRECATED );
 225                 };
 226
 227                 foreach ( [ 'replLogger', 'connLogger', 'queryLogger', 'perfLogger' ] as $key ) {
 228                         $this->$key = $params[$key] ?? new NullLogger();
 229                 }
 230
 231                 $this->hostname = $params['hostname'] ?? ( gethostname() ?: 'unknown' );
 232                 $this->cliMode = $params['cliMode'] ?? ( PHP_SAPI === 'cli' || PHP_SAPI === 'phpdbg' );
 233                 $this->agent = $params['agent'] ?? '';
 234
 235                 if ( isset( $params['chronologyCallback'] ) ) {
 236                         $this->chronologyCallback = $params['chronologyCallback'];
 237                 }
 238
 239                 if ( isset( $params['roundStage'] ) ) {
 240                         if ( $params['roundStage'] === self::STAGE_POSTCOMMIT_CALLBACKS ) {
 241                                 $this->trxRoundStage = self::ROUND_COMMIT_CALLBACKS;
 242                         } elseif ( $params['roundStage'] === self::STAGE_POSTROLLBACK_CALLBACKS ) {
 243                                 $this->trxRoundStage = self::ROUND_ROLLBACK_CALLBACKS;
 244                         }
 245                 }
 246
 247                 $this->defaultGroup = $params['defaultGroup'] ?? null;
 248                 $this->ownerId = $params['ownerId'] ?? null;
 249         }
 250
 251         private static function newTrackedConnectionsArray() {
 252                 return [
 253                         // Connection were transaction rounds may be applied
 254                         self::KEY_LOCAL => [],
 255                         self::KEY_FOREIGN_INUSE => [],
 256                         self::KEY_FOREIGN_FREE => [],
 257                         // Auto-committing counterpart connections that ignore transaction rounds
 258                         self::KEY_LOCAL_NOROUND => [],
 259                         self::KEY_FOREIGN_INUSE_NOROUND => [],
 260                         self::KEY_FOREIGN_FREE_NOROUND => []
 261                 ];
 262         }
 263
 264         public function getLocalDomainID() {
 265                 return $this->localDomain->getId();
 266         }
 267
 268         public function resolveDomainID( $domain ) {
 269                 if ( $domain === $this->localDomainIdAlias || $domain === false ) {
 270                         // Local connection requested via some backwards-compatibility domain alias
 271                         return $this->getLocalDomainID();
 272                 }
 273
 274                 return (string)$domain;
 275         }
 276
 277         /**
 278          * @param int $flags
 279          * @return bool
 280          */
 281         private function sanitizeConnectionFlags( $flags ) {
 282                 if ( ( $flags & self::CONN_TRX_AUTOCOMMIT ) === self::CONN_TRX_AUTOCOMMIT ) {
 283                         // Assuming all servers are of the same type (or similar), which is overwhelmingly
 284                         // the case, use the master server information to get the attributes. The information
 285                         // for $i cannot be used since it might be DB_REPLICA, which might require connection
 286                         // attempts in order to be resolved into a real server index.
 287                         $attributes = $this->getServerAttributes( $this->getWriterIndex() );
 288                         if ( $attributes[Database::ATTR_DB_LEVEL_LOCKING] ) {
 289                                 // Callers sometimes want to (a) escape REPEATABLE-READ stateness without locking
 290                                 // rows (e.g. FOR UPDATE) or (b) make small commits during a larger transactions
 291                                 // to reduce lock contention. None of these apply for sqlite and using separate
 292                                 // connections just causes self-deadlocks.
 293                                 $flags &= ~self::CONN_TRX_AUTOCOMMIT;
 294                                 $this->connLogger->info( __METHOD__ .
 295                                         ': ignoring CONN_TRX_AUTOCOMMIT to avoid deadlocks.' );
 296                         }
 297                 }
 298
 299                 return $flags;
 300         }
 301
 302         /**
 303          * @param IDatabase $conn
 304          * @param int $flags
 305          * @throws DBUnexpectedError
 306          */
 307         private function enforceConnectionFlags( IDatabase $conn, $flags ) {
 308                 if ( ( $flags & self::CONN_TRX_AUTOCOMMIT ) == self::CONN_TRX_AUTOCOMMIT ) {
 309                         if ( $conn->trxLevel() ) { // sanity
 310                                 throw new DBUnexpectedError(
 311                                         $conn,
 312                                         'Handle requested with CONN_TRX_AUTOCOMMIT yet it has a transaction'
 313                                 );
 314                         }
 315
 316                         $conn->clearFlag( $conn::DBO_TRX ); // auto-commit mode
 317                 }
 318         }
 319
 320                 /**
 321          * Get a LoadMonitor instance
 322          *
 323          * @return ILoadMonitor
 324          */
 325         private function getLoadMonitor() {
 326                 if ( !isset( $this->loadMonitor ) ) {
 327                         $compat = [
 328                                 'LoadMonitor' => LoadMonitor::class,
 329                                 'LoadMonitorNull' => LoadMonitorNull::class,
 330                                 'LoadMonitorMySQL' => LoadMonitorMySQL::class,
 331                         ];
 332
 333                         $class = $this->loadMonitorConfig['class'];
 334                         if ( isset( $compat[$class] ) ) {
 335                                 $class = $compat[$class];
 336                         }
 337
 338                         $this->loadMonitor = new $class(
 339                                 $this, $this->srvCache, $this->wanCache, $this->loadMonitorConfig );
 340                         $this->loadMonitor->setLogger( $this->replLogger );
 341                 }
 342
 343                 return $this->loadMonitor;
 344         }
 345
 346         /**
 347          * @param array $loads
 348          * @param bool|string $domain Domain to get non-lagged for
 349          * @param int $maxLag Restrict the maximum allowed lag to this many seconds
 350          * @return bool|int|string
 351          */
 352         private function getRandomNonLagged( array $loads, $domain = false, $maxLag = INF ) {
 353                 $lags = $this->getLagTimes( $domain );
 354
 355                 # Unset excessively lagged servers
 356                 foreach ( $lags as $i => $lag ) {
 357                         if ( $i !== $this->getWriterIndex() ) {
 358                                 # How much lag this server nominally is allowed to have
 359                                 $maxServerLag = $this->servers[$i]['max lag'] ?? $this->maxLag; // default
 360                                 # Constrain that futher by $maxLag argument
 361                                 $maxServerLag = min( $maxServerLag, $maxLag );
 362
 363                                 $host = $this->getServerName( $i );
 364                                 if ( $lag === false && !is_infinite( $maxServerLag ) ) {
 365                                         $this->replLogger->debug(
 366                                                 __METHOD__ .
 367                                                 ": server {host} is not replicating?", [ 'host' => $host ] );
 368                                         unset( $loads[$i] );
 369                                 } elseif ( $lag > $maxServerLag ) {
 370                                         $this->replLogger->debug(
 371                                                 __METHOD__ .
 372                                                 ": server {host} has {lag} seconds of lag (>= {maxlag})",
 373                                                 [ 'host' => $host, 'lag' => $lag, 'maxlag' => $maxServerLag ]
 374                                         );
 375                                         unset( $loads[$i] );
 376                                 }
 377                         }
 378                 }
 379
 380                 # Find out if all the replica DBs with non-zero load are lagged
 381                 $sum = 0;
 382                 foreach ( $loads as $load ) {
 383                         $sum += $load;
 384                 }
 385                 if ( $sum == 0 ) {
 386                         # No appropriate DB servers except maybe the master and some replica DBs with zero load
 387                         # Do NOT use the master
 388                         # Instead, this function will return false, triggering read-only mode,
 389                         # and a lagged replica DB will be used instead.
 390                         return false;
 391                 }
 392
 393                 if ( count( $loads ) == 0 ) {
 394                         return false;
 395                 }
 396
 397                 # Return a random representative of the remainder
 398                 return ArrayUtils::pickRandom( $loads );
 399         }
 400
 401         /**
 402          * @param int $i
 403          * @param array $groups
 404          * @param string|bool $domain
 405          * @return int The index of a specific server (replica DBs are checked for connectivity)
 406          */
 407         private function getConnectionIndex( $i, $groups, $domain ) {
 408                 // Check one "group" per default: the generic pool
 409                 $defaultGroups = $this->defaultGroup ? [ $this->defaultGroup ] : [ false ];
 410
 411                 $groups = ( $groups === false || $groups === [] )
 412                         ? $defaultGroups
 413                         : (array)$groups;
 414
 415                 if ( $i === self::DB_MASTER ) {
 416                         $i = $this->getWriterIndex();
 417                 } elseif ( $i === self::DB_REPLICA ) {
 418                         # Try to find an available server in any the query groups (in order)
 419                         foreach ( $groups as $group ) {
 420                                 $groupIndex = $this->getReaderIndex( $group, $domain );
 421                                 if ( $groupIndex !== false ) {
 422                                         $i = $groupIndex;
 423                                         break;
 424                                 }
 425                         }
 426                 }
 427
 428                 # Operation-based index
 429                 if ( $i === self::DB_REPLICA ) {
 430                         $this->lastError = 'Unknown error'; // reset error string
 431                         # Try the general server pool if $groups are unavailable.
 432                         $i = ( $groups === [ false ] )
 433                                 ? false // don't bother with this if that is what was tried above
 434                                 : $this->getReaderIndex( false, $domain );
 435                         # Couldn't find a working server in getReaderIndex()?
 436                         if ( $i === false ) {
 437                                 $this->lastError = 'No working replica DB server: ' . $this->lastError;
 438                                 // Throw an exception
 439                                 $this->reportConnectionError();
 440                                 return null; // unreachable due to exception
 441                         }
 442                 }
 443
 444                 return $i;
 445         }
 446
 447         public function getReaderIndex( $group = false, $domain = false ) {
 448                 if ( $this->getServerCount() == 1 ) {
 449                         // Skip the load balancing if there's only one server
 450                         return $this->getWriterIndex();
 451                 }
 452
 453                 $index = $this->getExistingReaderIndex( $group );
 454                 if ( $index >= 0 ) {
 455                         // A reader index was already selected and "waitForPos" was handled
 456                         return $index;
 457                 }
 458
 459                 if ( $group !== false ) {
 460                         // Use the server weight array for this load group
 461                         if ( isset( $this->groupLoads[$group] ) ) {
 462                                 $loads = $this->groupLoads[$group];
 463                         } else {
 464                                 // No loads for this group, return false and the caller can use some other group
 465                                 $this->connLogger->info( __METHOD__ . ": no loads for group $group" );
 466
 467                                 return false;
 468                         }
 469                 } else {
 470                         // Use the generic load group
 471                         $loads = $this->genericLoads;
 472                 }
 473
 474                 // Scale the configured load ratios according to each server's load and state
 475                 $this->getLoadMonitor()->scaleLoads( $loads, $domain );
 476
 477                 // Pick a server to use, accounting for weights, load, lag, and "waitForPos"
 478                 $this->lazyLoadReplicationPositions(); // optimizes server candidate selection
 479                 list( $i, $laggedReplicaMode ) = $this->pickReaderIndex( $loads, $domain );
 480                 if ( $i === false ) {
 481                         // DB connection unsuccessful
 482                         return false;
 483                 }
 484
 485                 // If data seen by queries is expected to reflect the transactions committed as of
 486                 // or after a given replication position then wait for the DB to apply those changes
 487                 if ( $this->waitForPos && $i !== $this->getWriterIndex() && !$this->doWait( $i ) ) {
 488                         // Data will be outdated compared to what was expected
 489                         $laggedReplicaMode = true;
 490                 }
 491
 492                 // Cache the reader index for future DB_REPLICA handles
 493                 $this->setExistingReaderIndex( $group, $i );
 494                 // Record whether the generic reader index is in "lagged replica DB" mode
 495                 if ( $group === false && $laggedReplicaMode ) {
 496                         $this->laggedReplicaMode = true;
 497                 }
 498
 499                 $serverName = $this->getServerName( $i );
 500                 $this->connLogger->debug( __METHOD__ . ": using server $serverName for group '$group'" );
 501
 502                 return $i;
 503         }
 504
 505         /**
 506          * Get the server index chosen by the load balancer for use with the given query group
 507          *
 508          * @param string|bool $group Query group; use false for the generic group
 509          * @return int Server index or -1 if none was chosen
 510          */
 511         protected function getExistingReaderIndex( $group ) {
 512                 if ( $group === false ) {
 513                         $index = $this->genericReadIndex;
 514                 } else {
 515                         $index = $this->readIndexByGroup[$group] ?? -1;
 516                 }
 517
 518                 return $index;
 519         }
 520
 521         /**
 522          * Set the server index chosen by the load balancer for use with the given query group
 523          *
 524          * @param string|bool $group Query group; use false for the generic group
 525          * @param int $index The index of a specific server
 526          */
 527         private function setExistingReaderIndex( $group, $index ) {
 528                 if ( $index < 0 ) {
 529                         throw new UnexpectedValueException( "Cannot set a negative read server index" );
 530                 }
 531
 532                 if ( $group === false ) {
 533                         $this->genericReadIndex = $index;
 534                 } else {
 535                         $this->readIndexByGroup[$group] = $index;
 536                 }
 537         }
 538
 539         /**
 540          * @param array $loads List of server weights
 541          * @param string|bool $domain
 542          * @return array (reader index, lagged replica mode) or false on failure
 543          */
 544         private function pickReaderIndex( array $loads, $domain = false ) {
 545                 if ( $loads === [] ) {
 546                         throw new InvalidArgumentException( "Server configuration array is empty" );
 547                 }
 548
 549                 /** @var int|bool $i Index of selected server */
 550                 $i = false;
 551                 /** @var bool $laggedReplicaMode Whether server is considered lagged */
 552                 $laggedReplicaMode = false;
 553
 554                 // Quickly look through the available servers for a server that meets criteria...
 555                 $currentLoads = $loads;
 556                 while ( count( $currentLoads ) ) {
 557                         if ( $this->allowLagged || $laggedReplicaMode ) {
 558                                 $i = ArrayUtils::pickRandom( $currentLoads );
 559                         } else {
 560                                 $i = false;
 561                                 if ( $this->waitForPos && $this->waitForPos->asOfTime() ) {
 562                                         $this->replLogger->debug( __METHOD__ . ": replication positions detected" );
 563                                         // "chronologyCallback" sets "waitForPos" for session consistency.
 564                                         // This triggers doWait() after connect, so it's especially good to
 565                                         // avoid lagged servers so as to avoid excessive delay in that method.
 566                                         $ago = microtime( true ) - $this->waitForPos->asOfTime();
 567                                         // Aim for <= 1 second of waiting (being too picky can backfire)
 568                                         $i = $this->getRandomNonLagged( $currentLoads, $domain, $ago + 1 );
 569                                 }
 570                                 if ( $i === false ) {
 571                                         // Any server with less lag than it's 'max lag' param is preferable
 572                                         $i = $this->getRandomNonLagged( $currentLoads, $domain );
 573                                 }
 574                                 if ( $i === false && count( $currentLoads ) ) {
 575                                         // All replica DBs lagged. Switch to read-only mode
 576                                         $this->replLogger->error(
 577                                                 __METHOD__ . ": all replica DBs lagged. Switch to read-only mode" );
 578                                         $i = ArrayUtils::pickRandom( $currentLoads );
 579                                         $laggedReplicaMode = true;
 580                                 }
 581                         }
 582
 583                         if ( $i === false ) {
 584                                 // pickRandom() returned false.
 585                                 // This is permanent and means the configuration or the load monitor
 586                                 // wants us to return false.
 587                                 $this->connLogger->debug( __METHOD__ . ": pickRandom() returned false" );
 588
 589                                 return [ false, false ];
 590                         }
 591
 592                         $serverName = $this->getServerName( $i );
 593                         $this->connLogger->debug( __METHOD__ . ": Using reader #$i: $serverName..." );
 594
 595                         $conn = $this->getConnection( $i, [], $domain, self::CONN_SILENCE_ERRORS );
 596                         if ( !$conn ) {
 597                                 $this->connLogger->warning( __METHOD__ . ": Failed connecting to $i/$domain" );
 598                                 unset( $currentLoads[$i] ); // avoid this server next iteration
 599                                 $i = false;
 600                                 continue;
 601                         }
 602
 603                         // Decrement reference counter, we are finished with this connection.
 604                         // It will be incremented for the caller later.
 605                         if ( $domain !== false ) {
 606                                 $this->reuseConnection( $conn );
 607                         }
 608
 609                         // Return this server
 610                         break;
 611                 }
 612
 613                 // If all servers were down, quit now
 614                 if ( $currentLoads === [] ) {
 615                         $this->connLogger->error( __METHOD__ . ": all servers down" );
 616                 }
 617
 618                 return [ $i, $laggedReplicaMode ];
 619         }
 620
 621         public function waitFor( $pos ) {
 622                 $oldPos = $this->waitForPos;
 623                 try {
 624                         $this->waitForPos = $pos;
 625                         // If a generic reader connection was already established, then wait now
 626                         if ( $this->genericReadIndex > 0 && !$this->doWait( $this->genericReadIndex ) ) {
 627                                 $this->laggedReplicaMode = true;
 628                         }
 629                         // Otherwise, wait until a connection is established in getReaderIndex()
 630                 } finally {
 631                         // Restore the older position if it was higher since this is used for lag-protection
 632                         $this->setWaitForPositionIfHigher( $oldPos );
 633                 }
 634         }
 635
 636         public function waitForOne( $pos, $timeout = null ) {
 637                 $oldPos = $this->waitForPos;
 638                 try {
 639                         $this->waitForPos = $pos;
 640
 641                         $i = $this->genericReadIndex;
 642                         if ( $i <= 0 ) {
 643                                 // Pick a generic replica DB if there isn't one yet
 644                                 $readLoads = $this->genericLoads;
 645                                 unset( $readLoads[$this->getWriterIndex()] ); // replica DBs only
 646                                 $readLoads = array_filter( $readLoads ); // with non-zero load
 647                                 $i = ArrayUtils::pickRandom( $readLoads );
 648                         }
 649
 650                         if ( $i > 0 ) {
 651                                 $ok = $this->doWait( $i, true, $timeout );
 652                         } else {
 653                                 $ok = true; // no applicable loads
 654                         }
 655                 } finally {
 656                         # Restore the old position, as this is not used for lag-protection but for throttling
 657                         $this->waitForPos = $oldPos;
 658                 }
 659
 660                 return $ok;
 661         }
 662
 663         public function waitForAll( $pos, $timeout = null ) {
 664                 $timeout = $timeout ?: $this->waitTimeout;
 665
 666                 $oldPos = $this->waitForPos;
 667                 try {
 668                         $this->waitForPos = $pos;
 669                         $serverCount = $this->getServerCount();
 670
 671                         $ok = true;
 672                         for ( $i = 1; $i < $serverCount; $i++ ) {
 673                                 if ( $this->genericLoads[$i] > 0 ) {
 674                                         $start = microtime( true );
 675                                         $ok = $this->doWait( $i, true, $timeout ) && $ok;
 676                                         $timeout -= intval( microtime( true ) - $start );
 677                                         if ( $timeout <= 0 ) {
 678                                                 break; // timeout reached
 679                                         }
 680                                 }
 681                         }
 682                 } finally {
 683                         # Restore the old position, as this is not used for lag-protection but for throttling
 684                         $this->waitForPos = $oldPos;
 685                 }
 686
 687                 return $ok;
 688         }
 689
 690         /**
 691          * @param DBMasterPos|bool $pos
 692          */
 693         private function setWaitForPositionIfHigher( $pos ) {
 694                 if ( !$pos ) {
 695                         return;
 696                 }
 697
 698                 if ( !$this->waitForPos || $pos->hasReached( $this->waitForPos ) ) {
 699                         $this->waitForPos = $pos;
 700                 }
 701         }
 702
 703         public function getAnyOpenConnection( $i, $flags = 0 ) {
 704                 $i = ( $i === self::DB_MASTER ) ? $this->getWriterIndex() : $i;
 705                 $autocommit = ( ( $flags & self::CONN_TRX_AUTOCOMMIT ) == self::CONN_TRX_AUTOCOMMIT );
 706
 707                 foreach ( $this->conns as $connsByServer ) {
 708                         if ( $i === self::DB_REPLICA ) {
 709                                 $indexes = array_keys( $connsByServer );
 710                         } else {
 711                                 $indexes = isset( $connsByServer[$i] ) ? [ $i ] : [];
 712                         }
 713
 714                         foreach ( $indexes as $index ) {
 715                                 foreach ( $connsByServer[$index] as $conn ) {
 716                                         if ( !$conn->isOpen() ) {
 717                                                 continue; // some sort of error occured?
 718                                         }
 719                                         if ( !$autocommit || $conn->getLBInfo( 'autoCommitOnly' ) ) {
 720                                                 return $conn;
 721                                         }
 722                                 }
 723                         }
 724                 }
 725
 726                 return false;
 727         }
 728
 729         /**
 730          * Wait for a given replica DB to catch up to the master pos stored in "waitForPos"
 731          * @param int $index Server index
 732          * @param bool $open Check the server even if a new connection has to be made
 733          * @param int|null $timeout Max seconds to wait; default is "waitTimeout"
 734          * @return bool
 735          */
 736         protected function doWait( $index, $open = false, $timeout = null ) {
 737                 $timeout = max( 1, intval( $timeout ?: $this->waitTimeout ) );
 738
 739                 // Check if we already know that the DB has reached this point
 740                 $server = $this->getServerName( $index );
 741                 $key = $this->srvCache->makeGlobalKey( __CLASS__, 'last-known-pos', $server, 'v1' );
 742                 /** @var DBMasterPos $knownReachedPos */
 743                 $knownReachedPos = $this->srvCache->get( $key );
 744                 if (
 745                         $knownReachedPos instanceof DBMasterPos &&
 746                         $knownReachedPos->hasReached( $this->waitForPos )
 747                 ) {
 748                         $this->replLogger->debug(
 749                                 __METHOD__ .
 750                                 ': replica DB {dbserver} known to be caught up (pos >= $knownReachedPos).',
 751                                 [ 'dbserver' => $server ]
 752                         );
 753                         return true;
 754                 }
 755
 756                 // Find a connection to wait on, creating one if needed and allowed
 757                 $close = false; // close the connection afterwards
 758                 $conn = $this->getAnyOpenConnection( $index );
 759                 if ( !$conn ) {
 760                         if ( !$open ) {
 761                                 $this->replLogger->debug(
 762                                         __METHOD__ . ': no connection open for {dbserver}',
 763                                         [ 'dbserver' => $server ]
 764                                 );
 765
 766                                 return false;
 767                         }
 768                         // Open a temporary new connection in order to wait for replication
 769                         $conn = $this->getConnection( $index, [], self::DOMAIN_ANY, self::CONN_SILENCE_ERRORS );
 770                         if ( !$conn ) {
 771                                 $this->replLogger->warning(
 772                                         __METHOD__ . ': failed to connect to {dbserver}',
 773                                         [ 'dbserver' => $server ]
 774                                 );
 775
 776                                 return false;
 777                         }
 778                         // Avoid connection spam in waitForAll() when connections
 779                         // are made just for the sake of doing this lag check.
 780                         $close = true;
 781                 }
 782
 783                 $this->replLogger->info(
 784                         __METHOD__ .
 785                         ': waiting for replica DB {dbserver} to catch up...',
 786                         [ 'dbserver' => $server ]
 787                 );
 788
 789                 $result = $conn->masterPosWait( $this->waitForPos, $timeout );
 790
 791                 if ( $result === null ) {
 792                         $this->replLogger->warning(
 793                                 __METHOD__ . ': Errored out waiting on {host} pos {pos}',
 794                                 [
 795                                         'host' => $server,
 796                                         'pos' => $this->waitForPos,
 797                                         'trace' => ( new RuntimeException() )->getTraceAsString()
 798                                 ]
 799                         );
 800                         $ok = false;
 801                 } elseif ( $result == -1 ) {
 802                         $this->replLogger->warning(
 803                                 __METHOD__ . ': Timed out waiting on {host} pos {pos}',
 804                                 [
 805                                         'host' => $server,
 806                                         'pos' => $this->waitForPos,
 807                                         'trace' => ( new RuntimeException() )->getTraceAsString()
 808                                 ]
 809                         );
 810                         $ok = false;
 811                 } else {
 812                         $this->replLogger->debug( __METHOD__ . ": done waiting" );
 813                         $ok = true;
 814                         // Remember that the DB reached this point
 815                         $this->srvCache->set( $key, $this->waitForPos, BagOStuff::TTL_DAY );
 816                 }
 817
 818                 if ( $close ) {
 819                         $this->closeConnection( $conn );
 820                 }
 821
 822                 return $ok;
 823         }
 824
 825         public function getConnection( $i, $groups = [], $domain = false, $flags = 0 ) {
 826                 if ( !is_int( $i ) ) {
 827                         throw new InvalidArgumentException( "Cannot connect without a server index" );
 828                 } elseif ( $groups && $i > 0 ) {
 829                         throw new InvalidArgumentException( "Got query groups with server index #$i" );
 830                 }
 831
 832                 $domain = $this->resolveDomainID( $domain );
 833                 $flags = $this->sanitizeConnectionFlags( $flags );
 834                 $masterOnly = ( $i === self::DB_MASTER || $i === $this->getWriterIndex() );
 835
 836                 // Number of connections made before getting the server index and handle
 837                 $priorConnectionsMade = $this->connectionCounter;
 838                 // Choose a server if $i is DB_MASTER/DB_REPLICA (might trigger new connections)
 839                 $serverIndex = $this->getConnectionIndex( $i, $groups, $domain );
 840                 // Get an open connection to that server (might trigger a new connection)
 841                 $conn = $this->localDomain->equals( $domain )
 842                         ? $this->getLocalConnection( $serverIndex, $flags )
 843                         : $this->getForeignConnection( $serverIndex, $domain, $flags );
 844                 // Throw an error or bail out if the connection attempt failed
 845                 if ( !( $conn instanceof IDatabase ) ) {
 846                         if ( ( $flags & self::CONN_SILENCE_ERRORS ) != self::CONN_SILENCE_ERRORS ) {
 847                                 $this->reportConnectionError();
 848                         }
 849
 850                         return false;
 851                 }
 852
 853                 // Profile any new connections caused by this method
 854                 if ( $this->connectionCounter > $priorConnectionsMade ) {
 855                         $host = $conn->getServer();
 856                         $dbname = $conn->getDBname();
 857                         $this->trxProfiler->recordConnection( $host, $dbname, $masterOnly );
 858                 }
 859
 860                 if ( !$conn->isOpen() ) {
 861                         // Connection was made but later unrecoverably lost for some reason.
 862                         // Do not return a handle that will just throw exceptions on use,
 863                         // but let the calling code (e.g. getReaderIndex) try another server.
 864                         $this->errorConnection = $conn;
 865                         return false;
 866                 }
 867
 868                 $this->enforceConnectionFlags( $conn, $flags );
 869                 if ( $serverIndex === $this->getWriterIndex() ) {
 870                         // If the load balancer is read-only, perhaps due to replication lag, then master
 871                         // DB handles will reflect that. Note that Database::assertIsWritableMaster() takes
 872                         // care of replica DB handles whereas getReadOnlyReason() would cause infinite loops.
 873                         $conn->setLBInfo( 'readOnlyReason', $this->getReadOnlyReason( $domain, $conn ) );
 874                 }
 875
 876                 return $conn;
 877         }
 878
 879         public function reuseConnection( IDatabase $conn ) {
 880                 $serverIndex = $conn->getLBInfo( 'serverIndex' );
 881                 $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 882                 if ( $serverIndex === null || $refCount === null ) {
 883                         /**
 884                          * This can happen in code like:
 885                          *   foreach ( $dbs as $db ) {
 886                          *     $conn = $lb->getConnection( $lb::DB_REPLICA, [], $db );
 887                          *     ...
 888                          *     $lb->reuseConnection( $conn );
 889                          *   }
 890                          * When a connection to the local DB is opened in this way, reuseConnection()
 891                          * should be ignored
 892                          */
 893                         return;
 894                 } elseif ( $conn instanceof DBConnRef ) {
 895                         // DBConnRef already handles calling reuseConnection() and only passes the live
 896                         // Database instance to this method. Any caller passing in a DBConnRef is broken.
 897                         $this->connLogger->error(
 898                                 __METHOD__ . ": got DBConnRef instance.\n" .
 899                                 ( new RuntimeException() )->getTraceAsString() );
 900
 901                         return;
 902                 }
 903
 904                 if ( $this->disabled ) {
 905                         return; // DBConnRef handle probably survived longer than the LoadBalancer
 906                 }
 907
 908                 if ( $conn->getLBInfo( 'autoCommitOnly' ) ) {
 909                         $connFreeKey = self::KEY_FOREIGN_FREE_NOROUND;
 910                         $connInUseKey = self::KEY_FOREIGN_INUSE_NOROUND;
 911                 } else {
 912                         $connFreeKey = self::KEY_FOREIGN_FREE;
 913                         $connInUseKey = self::KEY_FOREIGN_INUSE;
 914                 }
 915
 916                 $domain = $conn->getDomainID();
 917                 if ( !isset( $this->conns[$connInUseKey][$serverIndex][$domain] ) ) {
 918                         throw new InvalidArgumentException(
 919                                 "Connection $serverIndex/$domain not found; it may have already been freed" );
 920                 } elseif ( $this->conns[$connInUseKey][$serverIndex][$domain] !== $conn ) {
 921                         throw new InvalidArgumentException(
 922                                 "Connection $serverIndex/$domain mismatched; it may have already been freed" );
 923                 }
 924
 925                 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
 926                 if ( $refCount <= 0 ) {
 927                         $this->conns[$connFreeKey][$serverIndex][$domain] = $conn;
 928                         unset( $this->conns[$connInUseKey][$serverIndex][$domain] );
 929                         if ( !$this->conns[$connInUseKey][$serverIndex] ) {
 930                                 unset( $this->conns[$connInUseKey][$serverIndex] ); // clean up
 931                         }
 932                         $this->connLogger->debug( __METHOD__ . ": freed connection $serverIndex/$domain" );
 933                 } else {
 934                         $this->connLogger->debug( __METHOD__ .
 935                                 ": reference count for $serverIndex/$domain reduced to $refCount" );
 936                 }
 937         }
 938
 939         public function getConnectionRef( $i, $groups = [], $domain = false, $flags = 0 ) {
 940                 $domain = $this->resolveDomainID( $domain );
 941                 $role = $this->getRoleFromIndex( $i );
 942
 943                 return new DBConnRef( $this, $this->getConnection( $i, $groups, $domain, $flags ), $role );
 944         }
 945
 946         public function getLazyConnectionRef( $i, $groups = [], $domain = false, $flags = 0 ) {
 947                 $domain = $this->resolveDomainID( $domain );
 948                 $role = $this->getRoleFromIndex( $i );
 949
 950                 return new DBConnRef( $this, [ $i, $groups, $domain, $flags ], $role );
 951         }
 952
 953         public function getMaintenanceConnectionRef( $i, $groups = [], $domain = false, $flags = 0 ) {
 954                 $domain = $this->resolveDomainID( $domain );
 955                 $role = $this->getRoleFromIndex( $i );
 956
 957                 return new MaintainableDBConnRef(
 958                         $this, $this->getConnection( $i, $groups, $domain, $flags ), $role );
 959         }
 960
 961         /**
 962          * @param int $i Server index or DB_MASTER/DB_REPLICA
 963          * @return int One of DB_MASTER/DB_REPLICA
 964          */
 965         private function getRoleFromIndex( $i ) {
 966                 return ( $i === self::DB_MASTER || $i === $this->getWriterIndex() )
 967                         ? self::DB_MASTER
 968                         : self::DB_REPLICA;
 969         }
 970
 971         /**
 972          * @param int $i
 973          * @param bool $domain
 974          * @param int $flags
 975          * @return Database|bool Live database handle or false on failure
 976          * @deprecated Since 1.34 Use getConnection() instead
 977          */
 978         public function openConnection( $i, $domain = false, $flags = 0 ) {
 979                 return $this->getConnection( $i, [], $domain, $flags | self::CONN_SILENCE_ERRORS );
 980         }
 981
 982         /**
 983          * Open a connection to a local DB, or return one if it is already open.
 984          *
 985          * On error, returns false, and the connection which caused the
 986          * error will be available via $this->errorConnection.
 987          *
 988          * @note If disable() was called on this LoadBalancer, this method will throw a DBAccessError.
 989          *
 990          * @param int $i Server index
 991          * @param int $flags Class CONN_* constant bitfield
 992          * @return Database
 993          */
 994         private function getLocalConnection( $i, $flags = 0 ) {
 995                 // Connection handles required to be in auto-commit mode use a separate connection
 996                 // pool since the main pool is effected by implicit and explicit transaction rounds
 997                 $autoCommit = ( ( $flags & self::CONN_TRX_AUTOCOMMIT ) == self::CONN_TRX_AUTOCOMMIT );
 998
 999                 $connKey = $autoCommit ? self::KEY_LOCAL_NOROUND : self::KEY_LOCAL;
1000                 if ( isset( $this->conns[$connKey][$i][0] ) ) {
1001                         $conn = $this->conns[$connKey][$i][0];
1002                 } else {
1003                         // Open a new connection
1004                         $server = $this->getServerInfoStrict( $i );
1005                         $server['serverIndex'] = $i;
1006                         $server['autoCommitOnly'] = $autoCommit;
1007                         $conn = $this->reallyOpenConnection( $server, $this->localDomain );
1008                         $host = $this->getServerName( $i );
1009                         if ( $conn->isOpen() ) {
1010                                 $this->connLogger->debug(
1011                                         __METHOD__ . ": connected to database $i at '$host'." );
1012                                 $this->conns[$connKey][$i][0] = $conn;
1013                         } else {
1014                                 $this->connLogger->warning(
1015                                         __METHOD__ . ": failed to connect to database $i at '$host'." );
1016                                 $this->errorConnection = $conn;
1017                                 $conn = false;
1018                         }
1019                 }
1020
1021                 // Final sanity check to make sure the right domain is selected
1022                 if (
1023                         $conn instanceof IDatabase &&
1024                         !$this->localDomain->isCompatible( $conn->getDomainID() )
1025                 ) {
1026                         throw new UnexpectedValueException(
1027                                 "Got connection to '{$conn->getDomainID()}', " .
1028                                 "but expected local domain ('{$this->localDomain}')" );
1029                 }
1030
1031                 return $conn;
1032         }
1033
1034         /**
1035          * Open a connection to a foreign DB, or return one if it is already open.
1036          *
1037          * Increments a reference count on the returned connection which locks the
1038          * connection to the requested domain. This reference count can be
1039          * decremented by calling reuseConnection().
1040          *
1041          * If a connection is open to the appropriate server already, but with the wrong
1042          * database, it will be switched to the right database and returned, as long as
1043          * it has been freed first with reuseConnection().
1044          *
1045          * On error, returns false, and the connection which caused the
1046          * error will be available via $this->errorConnection.
1047          *
1048          * @note If disable() was called on this LoadBalancer, this method will throw a DBAccessError.
1049          *
1050          * @param int $i Server index
1051          * @param string $domain Domain ID to open
1052          * @param int $flags Class CONN_* constant bitfield
1053          * @return Database|bool Returns false on connection error
1054          * @throws DBError When database selection fails
1055          */
1056         private function getForeignConnection( $i, $domain, $flags = 0 ) {
1057                 $domainInstance = DatabaseDomain::newFromId( $domain );
1058                 // Connection handles required to be in auto-commit mode use a separate connection
1059                 // pool since the main pool is effected by implicit and explicit transaction rounds
1060                 $autoCommit = ( ( $flags & self::CONN_TRX_AUTOCOMMIT ) == self::CONN_TRX_AUTOCOMMIT );
1061
1062                 if ( $autoCommit ) {
1063                         $connFreeKey = self::KEY_FOREIGN_FREE_NOROUND;
1064                         $connInUseKey = self::KEY_FOREIGN_INUSE_NOROUND;
1065                 } else {
1066                         $connFreeKey = self::KEY_FOREIGN_FREE;
1067                         $connInUseKey = self::KEY_FOREIGN_INUSE;
1068                 }
1069
1070                 /** @var Database $conn */
1071                 $conn = null;
1072
1073                 if ( isset( $this->conns[$connInUseKey][$i][$domain] ) ) {
1074                         // Reuse an in-use connection for the same domain
1075                         $conn = $this->conns[$connInUseKey][$i][$domain];
1076                         $this->connLogger->debug( __METHOD__ . ": reusing connection $i/$domain" );
1077                 } elseif ( isset( $this->conns[$connFreeKey][$i][$domain] ) ) {
1078                         // Reuse a free connection for the same domain
1079                         $conn = $this->conns[$connFreeKey][$i][$domain];
1080                         unset( $this->conns[$connFreeKey][$i][$domain] );
1081                         $this->conns[$connInUseKey][$i][$domain] = $conn;
1082                         $this->connLogger->debug( __METHOD__ . ": reusing free connection $i/$domain" );
1083                 } elseif ( !empty( $this->conns[$connFreeKey][$i] ) ) {
1084                         // Reuse a free connection from another domain if possible
1085                         foreach ( $this->conns[$connFreeKey][$i] as $oldDomain => $conn ) {
1086                                 if ( $domainInstance->getDatabase() !== null ) {
1087                                         // Check if changing the database will require a new connection.
1088                                         // In that case, leave the connection handle alone and keep looking.
1089                                         // This prevents connections from being closed mid-transaction and can
1090                                         // also avoid overhead if the same database will later be requested.
1091                                         if (
1092                                                 $conn->databasesAreIndependent() &&
1093                                                 $conn->getDBname() !== $domainInstance->getDatabase()
1094                                         ) {
1095                                                 continue;
1096                                         }
1097                                         // Select the new database, schema, and prefix
1098                                         $conn->selectDomain( $domainInstance );
1099                                 } else {
1100                                         // Stay on the current database, but update the schema/prefix
1101                                         $conn->dbSchema( $domainInstance->getSchema() );
1102                                         $conn->tablePrefix( $domainInstance->getTablePrefix() );
1103                                 }
1104                                 unset( $this->conns[$connFreeKey][$i][$oldDomain] );
1105                                 // Note that if $domain is an empty string, getDomainID() might not match it
1106                                 $this->conns[$connInUseKey][$i][$conn->getDomainID()] = $conn;
1107                                 $this->connLogger->debug( __METHOD__ .
1108                                         ": reusing free connection from $oldDomain for $domain" );
1109                                 break;
1110                         }
1111                 }
1112
1113                 if ( !$conn ) {
1114                         // Open a new connection
1115                         $server = $this->getServerInfoStrict( $i );
1116                         $server['serverIndex'] = $i;
1117                         $server['foreignPoolRefCount'] = 0;
1118                         $server['foreign'] = true;
1119                         $server['autoCommitOnly'] = $autoCommit;
1120                         $conn = $this->reallyOpenConnection( $server, $domainInstance );
1121                         if ( !$conn->isOpen() ) {
1122                                 $this->connLogger->warning( __METHOD__ . ": connection error for $i/$domain" );
1123                                 $this->errorConnection = $conn;
1124                                 $conn = false;
1125                         } else {
1126                                 // Note that if $domain is an empty string, getDomainID() might not match it
1127                                 $this->conns[$connInUseKey][$i][$conn->getDomainID()] = $conn;
1128                                 $this->connLogger->debug( __METHOD__ . ": opened new connection for $i/$domain" );
1129                         }
1130                 }
1131
1132                 if ( $conn instanceof IDatabase ) {
1133                         // Final sanity check to make sure the right domain is selected
1134                         if ( !$domainInstance->isCompatible( $conn->getDomainID() ) ) {
1135                                 throw new UnexpectedValueException(
1136                                         "Got connection to '{$conn->getDomainID()}', but expected '$domain'" );
1137                         }
1138                         // Increment reference count
1139                         $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
1140                         $conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
1141                 }
1142
1143                 return $conn;
1144         }
1145
1146         public function getServerAttributes( $i ) {
1147                 return Database::attributesFromType(
1148                         $this->getServerType( $i ),
1149                         $this->servers[$i]['driver'] ?? null
1150                 );
1151         }
1152
1153         /**
1154          * Test if the specified index represents an open connection
1155          *
1156          * @param int $index Server index
1157          * @private
1158          * @return bool
1159          */
1160         private function isOpen( $index ) {
1161                 if ( !is_int( $index ) ) {
1162                         return false;
1163                 }
1164
1165                 return (bool)$this->getAnyOpenConnection( $index );
1166         }
1167
1168         /**
1169          * Open a new network connection to a server (uncached)
1170          *
1171          * Returns a Database object whether or not the connection was successful.
1172          *
1173          * @param array $server
1174          * @param DatabaseDomain $domain Domain the connection is for, possibly unspecified
1175          * @return Database
1176          * @throws DBAccessError
1177          * @throws InvalidArgumentException
1178          */
1179         protected function reallyOpenConnection( array $server, DatabaseDomain $domain ) {
1180                 if ( $this->disabled ) {
1181                         throw new DBAccessError();
1182                 }
1183
1184                 if ( $domain->getDatabase() === null ) {
1185                         // The database domain does not specify a DB name and some database systems require a
1186                         // valid DB specified on connection. The $server configuration array contains a default
1187                         // DB name to use for connections in such cases.
1188                         if ( $server['type'] === 'mysql' ) {
1189                                 // For MySQL, DATABASE and SCHEMA are synonyms, connections need not specify a DB,
1190                                 // and the DB name in $server might not exist due to legacy reasons (the default
1191                                 // domain used to ignore the local LB domain, even when mismatched).
1192                                 $server['dbname'] = null;
1193                         }
1194                 } else {
1195                         $server['dbname'] = $domain->getDatabase();
1196                 }
1197
1198                 if ( $domain->getSchema() !== null ) {
1199                         $server['schema'] = $domain->getSchema();
1200                 }
1201
1202                 // It is always possible to connect with any prefix, even the empty string
1203                 $server['tablePrefix'] = $domain->getTablePrefix();
1204
1205                 // Let the handle know what the cluster master is (e.g. "db1052")
1206                 $masterName = $this->getServerName( $this->getWriterIndex() );
1207                 $server['clusterMasterHost'] = $masterName;
1208
1209                 $server['srvCache'] = $this->srvCache;
1210                 // Set loggers and profilers
1211                 $server['connLogger'] = $this->connLogger;
1212                 $server['queryLogger'] = $this->queryLogger;
1213                 $server['errorLogger'] = $this->errorLogger;
1214                 $server['deprecationLogger'] = $this->deprecationLogger;
1215                 $server['profiler'] = $this->profiler;
1216                 $server['trxProfiler'] = $this->trxProfiler;
1217                 // Use the same agent and PHP mode for all DB handles
1218                 $server['cliMode'] = $this->cliMode;
1219                 $server['agent'] = $this->agent;
1220                 // Use DBO_DEFAULT flags by default for LoadBalancer managed databases. Assume that the
1221                 // application calls LoadBalancer::commitMasterChanges() before the PHP script completes.
1222                 $server['flags'] = $server['flags'] ?? IDatabase::DBO_DEFAULT;
1223
1224                 // Create a live connection object
1225                 try {
1226                         $db = Database::factory( $server['type'], $server );
1227                         // Log when many connection are made on requests
1228                         ++$this->connectionCounter;
1229                         $currentConnCount = $this->getCurrentConnectionCount();
1230                         if ( $currentConnCount >= self::CONN_HELD_WARN_THRESHOLD ) {
1231                                 $this->perfLogger->warning(
1232                                         __METHOD__ . ": {connections}+ connections made (master={masterdb})",
1233                                         [ 'connections' => $currentConnCount, 'masterdb' => $masterName ]
1234                                 );
1235                         }
1236                 } catch ( DBConnectionError $e ) {
1237                         // FIXME: This is probably the ugliest thing I have ever done to
1238                         // PHP. I'm half-expecting it to segfault, just out of disgust. -- TS
1239                         $db = $e->db;
1240                 }
1241
1242                 $db->setLBInfo( $server );
1243                 $db->setLazyMasterHandle(
1244                         $this->getLazyConnectionRef( self::DB_MASTER, [], $db->getDomainID() )
1245                 );
1246                 $db->setTableAliases( $this->tableAliases );
1247                 $db->setIndexAliases( $this->indexAliases );
1248
1249                 if ( $server['serverIndex'] === $this->getWriterIndex() ) {
1250                         if ( $this->trxRoundId !== false ) {
1251                                 $this->applyTransactionRoundFlags( $db );
1252                         }
1253                         foreach ( $this->trxRecurringCallbacks as $name => $callback ) {
1254                                 $db->setTransactionListener( $name, $callback );
1255                         }
1256                 }
1257
1258                 $this->lazyLoadReplicationPositions(); // session consistency
1259
1260                 return $db;
1261         }
1262
1263         /**
1264          * Make sure that any "waitForPos" positions are loaded and available to doWait()
1265          */
1266         private function lazyLoadReplicationPositions() {
1267                 if ( !$this->connectionAttempted && $this->chronologyCallback ) {
1268                         $this->connectionAttempted = true;
1269                         ( $this->chronologyCallback )( $this ); // generally calls waitFor()
1270                         $this->connLogger->debug( __METHOD__ . ': executed chronology callback.' );
1271                 }
1272         }
1273
1274         /**
1275          * @throws DBConnectionError
1276          */
1277         private function reportConnectionError() {
1278                 $conn = $this->errorConnection; // the connection which caused the error
1279                 $context = [
1280                         'method' => __METHOD__,
1281                         'last_error' => $this->lastError,
1282                 ];
1283
1284                 if ( $conn instanceof IDatabase ) {
1285                         $context['db_server'] = $conn->getServer();
1286                         $this->connLogger->warning(
1287                                 __METHOD__ . ": connection error: {last_error} ({db_server})",
1288                                 $context
1289                         );
1290
1291                         throw new DBConnectionError( $conn, "{$this->lastError} ({$context['db_server']})" );
1292                 } else {
1293                         // No last connection, probably due to all servers being too busy
1294                         $this->connLogger->error(
1295                                 __METHOD__ .
1296                                 ": LB failure with no last connection. Connection error: {last_error}",
1297                                 $context
1298                         );
1299
1300                         // If all servers were busy, "lastError" will contain something sensible
1301                         throw new DBConnectionError( null, $this->lastError );
1302                 }
1303         }
1304
1305         public function getWriterIndex() {
1306                 return 0;
1307         }
1308
1309         /**
1310          * Returns true if the specified index is a valid server index
1311          *
1312          * @param int $i
1313          * @return bool
1314          * @deprecated Since 1.34
1315          */
1316         public function haveIndex( $i ) {
1317                 return array_key_exists( $i, $this->servers );
1318         }
1319
1320         /**
1321          * Returns true if the specified index is valid and has non-zero load
1322          *
1323          * @param int $i
1324          * @return bool
1325          * @deprecated Since 1.34
1326          */
1327         public function isNonZeroLoad( $i ) {
1328                 return array_key_exists( $i, $this->servers ) && $this->genericLoads[$i] != 0;
1329         }
1330
1331         public function getServerCount() {
1332                 return count( $this->servers );
1333         }
1334
1335         public function hasReplicaServers() {
1336                 return ( $this->getServerCount() > 1 );
1337         }
1338
1339         public function hasStreamingReplicaServers() {
1340                 foreach ( $this->servers as $i => $server ) {
1341                         if ( $i !== $this->getWriterIndex() && empty( $server['is static'] ) ) {
1342                                 return true;
1343                         }
1344                 }
1345
1346                 return false;
1347         }
1348
1349         public function getServerName( $i ) {
1350                 $name = $this->servers[$i]['hostName'] ?? ( $this->servers[$i]['host'] ?? '' );
1351
1352                 return ( $name != '' ) ? $name : 'localhost';
1353         }
1354
1355         public function getServerInfo( $i ) {
1356                 return $this->servers[$i] ?? false;
1357         }
1358
1359         public function getServerType( $i ) {
1360                 return $this->servers[$i]['type'] ?? 'unknown';
1361         }
1362
1363         public function getMasterPos() {
1364                 # If this entire request was served from a replica DB without opening a connection to the
1365                 # master (however unlikely that may be), then we can fetch the position from the replica DB.
1366                 $masterConn = $this->getAnyOpenConnection( $this->getWriterIndex() );
1367                 if ( !$masterConn ) {
1368                         $serverCount = $this->getServerCount();
1369                         for ( $i = 1; $i < $serverCount; $i++ ) {
1370                                 $conn = $this->getAnyOpenConnection( $i );
1371                                 if ( $conn ) {
1372                                         return $conn->getReplicaPos();
1373                                 }
1374                         }
1375                 } else {
1376                         return $masterConn->getMasterPos();
1377                 }
1378
1379                 return false;
1380         }
1381
1382         public function disable() {
1383                 $this->closeAll();
1384                 $this->disabled = true;
1385         }
1386
1387         public function closeAll() {
1388                 $fname = __METHOD__;
1389                 $this->forEachOpenConnection( function ( IDatabase $conn ) use ( $fname ) {
1390                         $host = $conn->getServer();
1391                         $this->connLogger->debug(
1392                                 $fname . ": closing connection to database '$host'." );
1393                         $conn->close();
1394                 } );
1395
1396                 $this->conns = self::newTrackedConnectionsArray();
1397         }
1398
1399         public function closeConnection( IDatabase $conn ) {
1400                 if ( $conn instanceof DBConnRef ) {
1401                         // Avoid calling close() but still leaving the handle in the pool
1402                         throw new RuntimeException( 'Cannot close DBConnRef instance; it must be shareable' );
1403                 }
1404
1405                 $serverIndex = $conn->getLBInfo( 'serverIndex' );
1406                 foreach ( $this->conns as $type => $connsByServer ) {
1407                         if ( !isset( $connsByServer[$serverIndex] ) ) {
1408                                 continue;
1409                         }
1410
1411                         foreach ( $connsByServer[$serverIndex] as $i => $trackedConn ) {
1412                                 if ( $conn === $trackedConn ) {
1413                                         $host = $this->getServerName( $i );
1414                                         $this->connLogger->debug(
1415                                                 __METHOD__ . ": closing connection to database $i at '$host'." );
1416                                         unset( $this->conns[$type][$serverIndex][$i] );
1417                                         break 2;
1418                                 }
1419                         }
1420                 }
1421
1422                 $conn->close();
1423         }
1424
1425         public function commitAll( $fname = __METHOD__, $owner = null ) {
1426                 $this->commitMasterChanges( $fname, $owner );
1427                 $this->flushMasterSnapshots( $fname );
1428                 $this->flushReplicaSnapshots( $fname );
1429         }
1430
1431         public function finalizeMasterChanges( $fname = __METHOD__, $owner = null ) {
1432                 $this->assertOwnership( $fname, $owner );
1433                 $this->assertTransactionRoundStage( [ self::ROUND_CURSORY, self::ROUND_FINALIZED ] );
1434
1435                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1436                 // Loop until callbacks stop adding callbacks on other connections
1437                 $total = 0;
1438                 do {
1439                         $count = 0; // callbacks execution attempts
1440                         $this->forEachOpenMasterConnection( function ( Database $conn ) use ( &$count ) {
1441                                 // Run any pre-commit callbacks while leaving the post-commit ones suppressed.
1442                                 // Any error should cause all (peer) transactions to be rolled back together.
1443                                 $count += $conn->runOnTransactionPreCommitCallbacks();
1444                         } );
1445                         $total += $count;
1446                 } while ( $count > 0 );
1447                 // Defer post-commit callbacks until after COMMIT/ROLLBACK happens on all handles
1448                 $this->forEachOpenMasterConnection( function ( Database $conn ) {
1449                         $conn->setTrxEndCallbackSuppression( true );
1450                 } );
1451                 $this->trxRoundStage = self::ROUND_FINALIZED;
1452
1453                 return $total;
1454         }
1455
1456         public function approveMasterChanges( array $options, $fname = __METHOD__, $owner = null ) {
1457                 $this->assertOwnership( $fname, $owner );
1458                 $this->assertTransactionRoundStage( self::ROUND_FINALIZED );
1459
1460                 $limit = $options['maxWriteDuration'] ?? 0;
1461
1462                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1463                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( $limit ) {
1464                         // If atomic sections or explicit transactions are still open, some caller must have
1465                         // caught an exception but failed to properly rollback any changes. Detect that and
1466                         // throw and error (causing rollback).
1467                         $conn->assertNoOpenTransactions();
1468                         // Assert that the time to replicate the transaction will be sane.
1469                         // If this fails, then all DB transactions will be rollback back together.
1470                         $time = $conn->pendingWriteQueryDuration( $conn::ESTIMATE_DB_APPLY );
1471                         if ( $limit > 0 && $time > $limit ) {
1472                                 throw new DBTransactionSizeError(
1473                                         $conn,
1474                                         "Transaction spent $time second(s) in writes, exceeding the limit of $limit",
1475                                         [ $time, $limit ]
1476                                 );
1477                         }
1478                         // If a connection sits idle while slow queries execute on another, that connection
1479                         // may end up dropped before the commit round is reached. Ping servers to detect this.
1480                         if ( $conn->writesOrCallbacksPending() && !$conn->ping() ) {
1481                                 throw new DBTransactionError(
1482                                         $conn,
1483                                         "A connection to the {$conn->getDBname()} database was lost before commit"
1484                                 );
1485                         }
1486                 } );
1487                 $this->trxRoundStage = self::ROUND_APPROVED;
1488         }
1489
1490         public function beginMasterChanges( $fname = __METHOD__, $owner = null ) {
1491                 $this->assertOwnership( $fname, $owner );
1492                 if ( $this->trxRoundId !== false ) {
1493                         throw new DBTransactionError(
1494                                 null,
1495                                 "$fname: Transaction round '{$this->trxRoundId}' already started"
1496                         );
1497                 }
1498                 $this->assertTransactionRoundStage( self::ROUND_CURSORY );
1499
1500                 // Clear any empty transactions (no writes/callbacks) from the implicit round
1501                 $this->flushMasterSnapshots( $fname );
1502
1503                 $this->trxRoundId = $fname;
1504                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1505                 // Mark applicable handles as participating in this explicit transaction round.
1506                 // For each of these handles, any writes and callbacks will be tied to a single
1507                 // transaction. The (peer) handles will reject begin()/commit() calls unless they
1508                 // are part of an en masse commit or an en masse rollback.
1509                 $this->forEachOpenMasterConnection( function ( Database $conn ) {
1510                         $this->applyTransactionRoundFlags( $conn );
1511                 } );
1512                 $this->trxRoundStage = self::ROUND_CURSORY;
1513         }
1514
1515         public function commitMasterChanges( $fname = __METHOD__, $owner = null ) {
1516                 $this->assertOwnership( $fname, $owner );
1517                 $this->assertTransactionRoundStage( self::ROUND_APPROVED );
1518
1519                 $failures = [];
1520
1521                 /** @noinspection PhpUnusedLocalVariableInspection */
1522                 $scope = ScopedCallback::newScopedIgnoreUserAbort(); // try to ignore client aborts
1523
1524                 $restore = ( $this->trxRoundId !== false );
1525                 $this->trxRoundId = false;
1526                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1527                 // Commit any writes and clear any snapshots as well (callbacks require AUTOCOMMIT).
1528                 // Note that callbacks should already be suppressed due to finalizeMasterChanges().
1529                 $this->forEachOpenMasterConnection(
1530                         function ( IDatabase $conn ) use ( $fname, &$failures ) {
1531                                 try {
1532                                         $conn->commit( $fname, $conn::FLUSHING_ALL_PEERS );
1533                                 } catch ( DBError $e ) {
1534                                         ( $this->errorLogger )( $e );
1535                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1536                                 }
1537                         }
1538                 );
1539                 if ( $failures ) {
1540                         throw new DBTransactionError(
1541                                 null,
1542                                 "$fname: Commit failed on server(s) " . implode( "\n", array_unique( $failures ) )
1543                         );
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_COMMIT_CALLBACKS;
1552         }
1553
1554         public function runMasterTransactionIdleCallbacks( $fname = __METHOD__, $owner = null ) {
1555                 $this->assertOwnership( $fname, $owner );
1556                 if ( $this->trxRoundStage === self::ROUND_COMMIT_CALLBACKS ) {
1557                         $type = IDatabase::TRIGGER_COMMIT;
1558                 } elseif ( $this->trxRoundStage === self::ROUND_ROLLBACK_CALLBACKS ) {
1559                         $type = IDatabase::TRIGGER_ROLLBACK;
1560                 } else {
1561                         throw new DBTransactionError(
1562                                 null,
1563                                 "Transaction should be in the callback stage (not '{$this->trxRoundStage}')"
1564                         );
1565                 }
1566
1567                 $oldStage = $this->trxRoundStage;
1568                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1569
1570                 // Now that the COMMIT/ROLLBACK step is over, enable post-commit callback runs
1571                 $this->forEachOpenMasterConnection( function ( Database $conn ) {
1572                         $conn->setTrxEndCallbackSuppression( false );
1573                 } );
1574
1575                 $e = null; // first exception
1576                 $fname = __METHOD__;
1577                 // Loop until callbacks stop adding callbacks on other connections
1578                 do {
1579                         // Run any pending callbacks for each connection...
1580                         $count = 0; // callback execution attempts
1581                         $this->forEachOpenMasterConnection(
1582                                 function ( Database $conn ) use ( $type, &$e, &$count ) {
1583                                         if ( $conn->trxLevel() ) {
1584                                                 return; // retry in the next iteration, after commit() is called
1585                                         }
1586                                         try {
1587                                                 $count += $conn->runOnTransactionIdleCallbacks( $type );
1588                                         } catch ( Exception $ex ) {
1589                                                 $e = $e ?: $ex;
1590                                         }
1591                                 }
1592                         );
1593                         // Clear out any active transactions left over from callbacks...
1594                         $this->forEachOpenMasterConnection( function ( Database $conn ) use ( &$e, $fname ) {
1595                                 if ( $conn->writesPending() ) {
1596                                         // A callback from another handle wrote to this one and DBO_TRX is set
1597                                         $this->queryLogger->warning( $fname . ": found writes pending." );
1598                                         $fnames = implode( ', ', $conn->pendingWriteAndCallbackCallers() );
1599                                         $this->queryLogger->warning(
1600                                                 $fname . ": found writes pending ($fnames).",
1601                                                 [
1602                                                         'db_server' => $conn->getServer(),
1603                                                         'db_name' => $conn->getDBname()
1604                                                 ]
1605                                         );
1606                                 } elseif ( $conn->trxLevel() ) {
1607                                         // A callback from another handle read from this one and DBO_TRX is set,
1608                                         // which can easily happen if there is only one DB (no replicas)
1609                                         $this->queryLogger->debug( $fname . ": found empty transaction." );
1610                                 }
1611                                 try {
1612                                         $conn->commit( $fname, $conn::FLUSHING_ALL_PEERS );
1613                                 } catch ( Exception $ex ) {
1614                                         $e = $e ?: $ex;
1615                                 }
1616                         } );
1617                 } while ( $count > 0 );
1618
1619                 $this->trxRoundStage = $oldStage;
1620
1621                 return $e;
1622         }
1623
1624         public function runMasterTransactionListenerCallbacks( $fname = __METHOD__, $owner = null ) {
1625                 $this->assertOwnership( $fname, $owner );
1626                 if ( $this->trxRoundStage === self::ROUND_COMMIT_CALLBACKS ) {
1627                         $type = IDatabase::TRIGGER_COMMIT;
1628                 } elseif ( $this->trxRoundStage === self::ROUND_ROLLBACK_CALLBACKS ) {
1629                         $type = IDatabase::TRIGGER_ROLLBACK;
1630                 } else {
1631                         throw new DBTransactionError(
1632                                 null,
1633                                 "Transaction should be in the callback stage (not '{$this->trxRoundStage}')"
1634                         );
1635                 }
1636
1637                 $e = null;
1638
1639                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1640                 $this->forEachOpenMasterConnection( function ( Database $conn ) use ( $type, &$e ) {
1641                         try {
1642                                 $conn->runTransactionListenerCallbacks( $type );
1643                         } catch ( Exception $ex ) {
1644                                 $e = $e ?: $ex;
1645                         }
1646                 } );
1647                 $this->trxRoundStage = self::ROUND_CURSORY;
1648
1649                 return $e;
1650         }
1651
1652         public function rollbackMasterChanges( $fname = __METHOD__, $owner = null ) {
1653                 $this->assertOwnership( $fname, $owner );
1654
1655                 $restore = ( $this->trxRoundId !== false );
1656                 $this->trxRoundId = false;
1657                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1658                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( $fname ) {
1659                         $conn->rollback( $fname, $conn::FLUSHING_ALL_PEERS );
1660                 } );
1661                 if ( $restore ) {
1662                         // Unmark handles as participating in this explicit transaction round
1663                         $this->forEachOpenMasterConnection( function ( Database $conn ) {
1664                                 $this->undoTransactionRoundFlags( $conn );
1665                         } );
1666                 }
1667                 $this->trxRoundStage = self::ROUND_ROLLBACK_CALLBACKS;
1668         }
1669
1670         /**
1671          * @param string|string[] $stage
1672          * @throws DBTransactionError
1673          */
1674         private function assertTransactionRoundStage( $stage ) {
1675                 $stages = (array)$stage;
1676
1677                 if ( !in_array( $this->trxRoundStage, $stages, true ) ) {
1678                         $stageList = implode(
1679                                 '/',
1680                                 array_map( function ( $v ) {
1681                                         return "'$v'";
1682                                 }, $stages )
1683                         );
1684                         throw new DBTransactionError(
1685                                 null,
1686                                 "Transaction round stage must be $stageList (not '{$this->trxRoundStage}')"
1687                         );
1688                 }
1689         }
1690
1691         /**
1692          * @param string $fname
1693          * @param int|null $owner Owner ID of the caller
1694          * @throws DBTransactionError
1695          */
1696         private function assertOwnership( $fname, $owner ) {
1697                 if ( $this->ownerId !== null && $owner !== $this->ownerId ) {
1698                         throw new DBTransactionError(
1699                                 null,
1700                                 "$fname: LoadBalancer is owned by LBFactory #{$this->ownerId} (got '$owner')."
1701                         );
1702                 }
1703         }
1704
1705         /**
1706          * Make all DB servers with DBO_DEFAULT/DBO_TRX set join the transaction round
1707          *
1708          * Some servers may have neither flag enabled, meaning that they opt out of such
1709          * transaction rounds and remain in auto-commit mode. Such behavior might be desired
1710          * when a DB server is used for something like simple key/value storage.
1711          *
1712          * @param Database $conn
1713          */
1714         private function applyTransactionRoundFlags( Database $conn ) {
1715                 if ( $conn->getLBInfo( 'autoCommitOnly' ) ) {
1716                         return; // transaction rounds do not apply to these connections
1717                 }
1718
1719                 if ( $conn->getFlag( $conn::DBO_DEFAULT ) ) {
1720                         // DBO_TRX is controlled entirely by CLI mode presence with DBO_DEFAULT.
1721                         // Force DBO_TRX even in CLI mode since a commit round is expected soon.
1722                         $conn->setFlag( $conn::DBO_TRX, $conn::REMEMBER_PRIOR );
1723                 }
1724
1725                 if ( $conn->getFlag( $conn::DBO_TRX ) ) {
1726                         $conn->setLBInfo( 'trxRoundId', $this->trxRoundId );
1727                 }
1728         }
1729
1730         /**
1731          * @param Database $conn
1732          */
1733         private function undoTransactionRoundFlags( Database $conn ) {
1734                 if ( $conn->getLBInfo( 'autoCommitOnly' ) ) {
1735                         return; // transaction rounds do not apply to these connections
1736                 }
1737
1738                 if ( $conn->getFlag( $conn::DBO_TRX ) ) {
1739                         $conn->setLBInfo( 'trxRoundId', false );
1740                 }
1741
1742                 if ( $conn->getFlag( $conn::DBO_DEFAULT ) ) {
1743                         $conn->restoreFlags( $conn::RESTORE_PRIOR );
1744                 }
1745         }
1746
1747         public function flushReplicaSnapshots( $fname = __METHOD__ ) {
1748                 $this->forEachOpenReplicaConnection( function ( IDatabase $conn ) use ( $fname ) {
1749                         $conn->flushSnapshot( $fname );
1750                 } );
1751         }
1752
1753         public function flushMasterSnapshots( $fname = __METHOD__ ) {
1754                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( $fname ) {
1755                         $conn->flushSnapshot( $fname );
1756                 } );
1757         }
1758
1759         /**
1760          * @return string
1761          * @since 1.32
1762          */
1763         public function getTransactionRoundStage() {
1764                 return $this->trxRoundStage;
1765         }
1766
1767         public function hasMasterConnection() {
1768                 return $this->isOpen( $this->getWriterIndex() );
1769         }
1770
1771         public function hasMasterChanges() {
1772                 $pending = 0;
1773                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$pending ) {
1774                         $pending |= $conn->writesOrCallbacksPending();
1775                 } );
1776
1777                 return (bool)$pending;
1778         }
1779
1780         public function lastMasterChangeTimestamp() {
1781                 $lastTime = false;
1782                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$lastTime ) {
1783                         $lastTime = max( $lastTime, $conn->lastDoneWrites() );
1784                 } );
1785
1786                 return $lastTime;
1787         }
1788
1789         public function hasOrMadeRecentMasterChanges( $age = null ) {
1790                 $age = ( $age === null ) ? $this->waitTimeout : $age;
1791
1792                 return ( $this->hasMasterChanges()
1793                         || $this->lastMasterChangeTimestamp() > microtime( true ) - $age );
1794         }
1795
1796         public function pendingMasterChangeCallers() {
1797                 $fnames = [];
1798                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$fnames ) {
1799                         $fnames = array_merge( $fnames, $conn->pendingWriteCallers() );
1800                 } );
1801
1802                 return $fnames;
1803         }
1804
1805         public function getLaggedReplicaMode( $domain = false ) {
1806                 if (
1807                         // Avoid recursion if there is only one DB
1808                         $this->hasStreamingReplicaServers() &&
1809                         // Avoid recursion if the (non-zero load) master DB was picked for generic reads
1810                         $this->genericReadIndex !== $this->getWriterIndex() &&
1811                         // Stay in lagged replica mode during the load balancer instance lifetime
1812                         !$this->laggedReplicaMode
1813                 ) {
1814                         try {
1815                                 // Calling this method will set "laggedReplicaMode" as needed
1816                                 $this->getReaderIndex( false, $domain );
1817                         } catch ( DBConnectionError $e ) {
1818                                 // Avoid expensive re-connect attempts and failures
1819                                 $this->allReplicasDownMode = true;
1820                                 $this->laggedReplicaMode = true;
1821                         }
1822                 }
1823
1824                 return $this->laggedReplicaMode;
1825         }
1826
1827         public function laggedReplicaUsed() {
1828                 return $this->laggedReplicaMode;
1829         }
1830
1831         /**
1832          * @return bool
1833          * @since 1.27
1834          * @deprecated Since 1.28; use laggedReplicaUsed()
1835          */
1836         public function laggedSlaveUsed() {
1837                 return $this->laggedReplicaUsed();
1838         }
1839
1840         public function getReadOnlyReason( $domain = false, IDatabase $conn = null ) {
1841                 if ( $this->readOnlyReason !== false ) {
1842                         return $this->readOnlyReason;
1843                 } elseif ( $this->getLaggedReplicaMode( $domain ) ) {
1844                         if ( $this->allReplicasDownMode ) {
1845                                 return 'The database has been automatically locked ' .
1846                                         'until the replica database servers become available';
1847                         } else {
1848                                 return 'The database has been automatically locked ' .
1849                                         'while the replica database servers catch up to the master.';
1850                         }
1851                 } elseif ( $this->masterRunningReadOnly( $domain, $conn ) ) {
1852                         return 'The database master is running in read-only mode.';
1853                 }
1854
1855                 return false;
1856         }
1857
1858         /**
1859          * @param string $domain Domain ID, or false for the current domain
1860          * @param IDatabase|null $conn DB master connectionl used to avoid loops [optional]
1861          * @return bool
1862          */
1863         private function masterRunningReadOnly( $domain, IDatabase $conn = null ) {
1864                 $cache = $this->wanCache;
1865                 $masterServer = $this->getServerName( $this->getWriterIndex() );
1866
1867                 return (bool)$cache->getWithSetCallback(
1868                         $cache->makeGlobalKey( __CLASS__, 'server-read-only', $masterServer ),
1869                         self::TTL_CACHE_READONLY,
1870                         function () use ( $domain, $conn ) {
1871                                 $old = $this->trxProfiler->setSilenced( true );
1872                                 try {
1873                                         $dbw = $conn ?: $this->getConnection( self::DB_MASTER, [], $domain );
1874                                         $readOnly = (int)$dbw->serverIsReadOnly();
1875                                         if ( !$conn ) {
1876                                                 $this->reuseConnection( $dbw );
1877                                         }
1878                                 } catch ( DBError $e ) {
1879                                         $readOnly = 0;
1880                                 }
1881                                 $this->trxProfiler->setSilenced( $old );
1882                                 return $readOnly;
1883                         },
1884                         [ 'pcTTL' => $cache::TTL_PROC_LONG, 'busyValue' => 0 ]
1885                 );
1886         }
1887
1888         public function allowLagged( $mode = null ) {
1889                 if ( $mode === null ) {
1890                         return $this->allowLagged;
1891                 }
1892                 $this->allowLagged = $mode;
1893
1894                 return $this->allowLagged;
1895         }
1896
1897         public function pingAll() {
1898                 $success = true;
1899                 $this->forEachOpenConnection( function ( IDatabase $conn ) use ( &$success ) {
1900                         if ( !$conn->ping() ) {
1901                                 $success = false;
1902                         }
1903                 } );
1904
1905                 return $success;
1906         }
1907
1908         public function forEachOpenConnection( $callback, array $params = [] ) {
1909                 foreach ( $this->conns as $connsByServer ) {
1910                         foreach ( $connsByServer as $serverConns ) {
1911                                 foreach ( $serverConns as $conn ) {
1912                                         $callback( $conn, ...$params );
1913                                 }
1914                         }
1915                 }
1916         }
1917
1918         public function forEachOpenMasterConnection( $callback, array $params = [] ) {
1919                 $masterIndex = $this->getWriterIndex();
1920                 foreach ( $this->conns as $connsByServer ) {
1921                         if ( isset( $connsByServer[$masterIndex] ) ) {
1922                                 /** @var IDatabase $conn */
1923                                 foreach ( $connsByServer[$masterIndex] as $conn ) {
1924                                         $callback( $conn, ...$params );
1925                                 }
1926                         }
1927                 }
1928         }
1929
1930         public function forEachOpenReplicaConnection( $callback, array $params = [] ) {
1931                 foreach ( $this->conns as $connsByServer ) {
1932                         foreach ( $connsByServer as $i => $serverConns ) {
1933                                 if ( $i === $this->getWriterIndex() ) {
1934                                         continue; // skip master
1935                                 }
1936                                 foreach ( $serverConns as $conn ) {
1937                                         $callback( $conn, ...$params );
1938                                 }
1939                         }
1940                 }
1941         }
1942
1943         /**
1944          * @return int
1945          */
1946         private function getCurrentConnectionCount() {
1947                 $count = 0;
1948                 foreach ( $this->conns as $connsByServer ) {
1949                         foreach ( $connsByServer as $serverConns ) {
1950                                 $count += count( $serverConns );
1951                         }
1952                 }
1953
1954                 return $count;
1955         }
1956
1957         public function getMaxLag( $domain = false ) {
1958                 $host = '';
1959                 $maxLag = -1;
1960                 $maxIndex = 0;
1961
1962                 if ( $this->hasReplicaServers() ) {
1963                         $lagTimes = $this->getLagTimes( $domain );
1964                         foreach ( $lagTimes as $i => $lag ) {
1965                                 if ( $this->genericLoads[$i] > 0 && $lag > $maxLag ) {
1966                                         $maxLag = $lag;
1967                                         $host = $this->getServerInfoStrict( $i, 'host' );
1968                                         $maxIndex = $i;
1969                                 }
1970                         }
1971                 }
1972
1973                 return [ $host, $maxLag, $maxIndex ];
1974         }
1975
1976         public function getLagTimes( $domain = false ) {
1977                 if ( !$this->hasReplicaServers() ) {
1978                         return [ $this->getWriterIndex() => 0 ]; // no replication = no lag
1979                 }
1980
1981                 $knownLagTimes = []; // map of (server index => 0 seconds)
1982                 $indexesWithLag = [];
1983                 foreach ( $this->servers as $i => $server ) {
1984                         if ( empty( $server['is static'] ) ) {
1985                                 $indexesWithLag[] = $i; // DB server might have replication lag
1986                         } else {
1987                                 $knownLagTimes[$i] = 0; // DB server is a non-replicating and read-only archive
1988                         }
1989                 }
1990
1991                 return $this->getLoadMonitor()->getLagTimes( $indexesWithLag, $domain ) + $knownLagTimes;
1992         }
1993
1994         /**
1995          * Get the lag in seconds for a given connection, or zero if this load
1996          * balancer does not have replication enabled.
1997          *
1998          * This should be used in preference to Database::getLag() in cases where
1999          * replication may not be in use, since there is no way to determine if
2000          * replication is in use at the connection level without running
2001          * potentially restricted queries such as SHOW SLAVE STATUS. Using this
2002          * function instead of Database::getLag() avoids a fatal error in this
2003          * case on many installations.
2004          *
2005          * @param IDatabase $conn
2006          * @return int|bool Returns false on error
2007          * @deprecated Since 1.34 Use IDatabase::getLag() instead
2008          */
2009         public function safeGetLag( IDatabase $conn ) {
2010                 if ( $conn->getLBInfo( 'is static' ) ) {
2011                         return 0; // static dataset
2012                 } elseif ( $conn->getLBInfo( 'serverIndex' ) == $this->getWriterIndex() ) {
2013                         return 0; // this is the master
2014                 }
2015
2016                 return $conn->getLag();
2017         }
2018
2019         public function waitForMasterPos( IDatabase $conn, $pos = false, $timeout = null ) {
2020                 $timeout = max( 1, $timeout ?: $this->waitTimeout );
2021
2022                 if ( $this->getServerCount() <= 1 || !$conn->getLBInfo( 'replica' ) ) {
2023                         return true; // server is not a replica DB
2024                 }
2025
2026                 if ( !$pos ) {
2027                         // Get the current master position, opening a connection if needed
2028                         $index = $this->getWriterIndex();
2029                         $masterConn = $this->getAnyOpenConnection( $index );
2030                         if ( $masterConn ) {
2031                                 $pos = $masterConn->getMasterPos();
2032                         } else {
2033                                 $flags = self::CONN_SILENCE_ERRORS;
2034                                 $masterConn = $this->getConnection( $index, [], self::DOMAIN_ANY, $flags );
2035                                 if ( !$masterConn ) {
2036                                         throw new DBReplicationWaitError(
2037                                                 null,
2038                                                 "Could not obtain a master database connection to get the position"
2039                                         );
2040                                 }
2041                                 $pos = $masterConn->getMasterPos();
2042                                 $this->closeConnection( $masterConn );
2043                         }
2044                 }
2045
2046                 if ( $pos instanceof DBMasterPos ) {
2047                         $start = microtime( true );
2048                         $result = $conn->masterPosWait( $pos, $timeout );
2049                         $seconds = max( microtime( true ) - $start, 0 );
2050                         if ( $result == -1 || is_null( $result ) ) {
2051                                 $msg = __METHOD__ . ': timed out waiting on {host} pos {pos} [{seconds}s]';
2052                                 $this->replLogger->warning( $msg, [
2053                                         'host' => $conn->getServer(),
2054                                         'pos' => $pos,
2055                                         'seconds' => round( $seconds, 6 ),
2056                                         'trace' => ( new RuntimeException() )->getTraceAsString()
2057                                 ] );
2058                                 $ok = false;
2059                         } else {
2060                                 $this->replLogger->debug( __METHOD__ . ': done waiting' );
2061                                 $ok = true;
2062                         }
2063                 } else {
2064                         $ok = false; // something is misconfigured
2065                         $this->replLogger->error(
2066                                 __METHOD__ . ': could not get master pos for {host}',
2067                                 [
2068                                         'host' => $conn->getServer(),
2069                                         'trace' => ( new RuntimeException() )->getTraceAsString()
2070                                 ]
2071                         );
2072                 }
2073
2074                 return $ok;
2075         }
2076
2077         /**
2078          * Wait for a replica DB to reach a specified master position
2079          *
2080          * This will connect to the master to get an accurate position if $pos is not given
2081          *
2082          * @param IDatabase $conn Replica DB
2083          * @param DBMasterPos|bool $pos Master position; default: current position
2084          * @param int $timeout Timeout in seconds [optional]
2085          * @return bool Success
2086          * @since 1.28
2087          * @deprecated Since 1.34 Use waitForMasterPos() instead
2088          */
2089         public function safeWaitForMasterPos( IDatabase $conn, $pos = false, $timeout = null ) {
2090                 return $this->waitForMasterPos( $conn, $pos, $timeout );
2091         }
2092
2093         public function setTransactionListener( $name, callable $callback = null ) {
2094                 if ( $callback ) {
2095                         $this->trxRecurringCallbacks[$name] = $callback;
2096                 } else {
2097                         unset( $this->trxRecurringCallbacks[$name] );
2098                 }
2099                 $this->forEachOpenMasterConnection(
2100                         function ( IDatabase $conn ) use ( $name, $callback ) {
2101                                 $conn->setTransactionListener( $name, $callback );
2102                         }
2103                 );
2104         }
2105
2106         public function setTableAliases( array $aliases ) {
2107                 $this->tableAliases = $aliases;
2108         }
2109
2110         public function setIndexAliases( array $aliases ) {
2111                 $this->indexAliases = $aliases;
2112         }
2113
2114         /**
2115          * @param string $prefix
2116          * @deprecated Since 1.33
2117          */
2118         public function setDomainPrefix( $prefix ) {
2119                 $this->setLocalDomainPrefix( $prefix );
2120         }
2121
2122         public function setLocalDomainPrefix( $prefix ) {
2123                 // Find connections to explicit foreign domains still marked as in-use...
2124                 $domainsInUse = [];
2125                 $this->forEachOpenConnection( function ( IDatabase $conn ) use ( &$domainsInUse ) {
2126                         // Once reuseConnection() is called on a handle, its reference count goes from 1 to 0.
2127                         // Until then, it is still in use by the caller (explicitly or via DBConnRef scope).
2128                         if ( $conn->getLBInfo( 'foreignPoolRefCount' ) > 0 ) {
2129                                 $domainsInUse[] = $conn->getDomainID();
2130                         }
2131                 } );
2132
2133                 // Do not switch connections to explicit foreign domains unless marked as safe
2134                 if ( $domainsInUse ) {
2135                         $domains = implode( ', ', $domainsInUse );
2136                         throw new DBUnexpectedError( null,
2137                                 "Foreign domain connections are still in use ($domains)" );
2138                 }
2139
2140                 $this->setLocalDomain( new DatabaseDomain(
2141                         $this->localDomain->getDatabase(),
2142                         $this->localDomain->getSchema(),
2143                         $prefix
2144                 ) );
2145
2146                 // Update the prefix for all local connections...
2147                 $this->forEachOpenConnection( function ( IDatabase $db ) use ( $prefix ) {
2148                         if ( !$db->getLBInfo( 'foreign' ) ) {
2149                                 $db->tablePrefix( $prefix );
2150                         }
2151                 } );
2152         }
2153
2154         public function redefineLocalDomain( $domain ) {
2155                 $this->closeAll();
2156
2157                 $this->setLocalDomain( DatabaseDomain::newFromId( $domain ) );
2158         }
2159
2160         /**
2161          * @param DatabaseDomain $domain
2162          */
2163         private function setLocalDomain( DatabaseDomain $domain ) {
2164                 $this->localDomain = $domain;
2165                 // In case a caller assumes that the domain ID is simply <db>-<prefix>, which is almost
2166                 // always true, gracefully handle the case when they fail to account for escaping.
2167                 if ( $this->localDomain->getTablePrefix() != '' ) {
2168                         $this->localDomainIdAlias =
2169                                 $this->localDomain->getDatabase() . '-' . $this->localDomain->getTablePrefix();
2170                 } else {
2171                         $this->localDomainIdAlias = $this->localDomain->getDatabase();
2172                 }
2173         }
2174
2175         /**
2176          * @param int $i Server index
2177          * @param string|null $field Server index field [optional]
2178          * @return array|mixed
2179          * @throws InvalidArgumentException
2180          */
2181         private function getServerInfoStrict( $i, $field = null ) {
2182                 if ( !isset( $this->servers[$i] ) || !is_array( $this->servers[$i] ) ) {
2183                         throw new InvalidArgumentException( "No server with index '$i'" );
2184                 }
2185
2186                 if ( $field !== null ) {
2187                         if ( !array_key_exists( $field, $this->servers[$i] ) ) {
2188                                 throw new InvalidArgumentException( "No field '$field' in server index '$i'" );
2189                         }
2190
2191                         return $this->servers[$i][$field];
2192                 }
2193
2194                 return $this->servers[$i];
2195         }
2196
2197         function __destruct() {
2198                 // Avoid connection leaks for sanity
2199                 $this->disable();
2200         }
2201 }
2202
2203 /**
2204  * @deprecated since 1.29
2205  */
2206 class_alias( LoadBalancer::class, 'LoadBalancer' );