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 connections opened */
 121         private $connsOpened = 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::newConnsArray();
 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 newConnsArray() {
 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->connsOpened;
 838
 839                 // Choose a server if $i is DB_MASTER/DB_REPLICA (might trigger new connections)
 840                 $serverIndex = $this->getConnectionIndex( $i, $groups, $domain );
 841                 // Get an open connection to that server (might trigger a new connection)
 842                 $conn = $this->localDomain->equals( $domain )
 843                         ? $this->getLocalConnection( $serverIndex, $flags )
 844                         : $this->getForeignConnection( $serverIndex, $domain, $flags );
 845                 // Throw an error or bail out if the connection attempt failed
 846                 if ( !( $conn instanceof IDatabase ) ) {
 847                         if ( ( $flags & self::CONN_SILENCE_ERRORS ) != self::CONN_SILENCE_ERRORS ) {
 848                                 $this->reportConnectionError();
 849                         }
 850
 851                         return false;
 852                 }
 853
 854                 // Profile any new connections caused by this method
 855                 if ( $this->connsOpened > $priorConnectionsMade ) {
 856                         $host = $conn->getServer();
 857                         $dbname = $conn->getDBname();
 858                         $this->trxProfiler->recordConnection( $host, $dbname, $masterOnly );
 859                 }
 860
 861                 if ( !$conn->isOpen() ) {
 862                         // Connection was made but later unrecoverably lost for some reason.
 863                         // Do not return a handle that will just throw exceptions on use,
 864                         // but let the calling code (e.g. getReaderIndex) try another server.
 865                         $this->errorConnection = $conn;
 866                         return false;
 867                 }
 868
 869                 $this->enforceConnectionFlags( $conn, $flags );
 870                 if ( $serverIndex === $this->getWriterIndex() ) {
 871                         // If the load balancer is read-only, perhaps due to replication lag, then master
 872                         // DB handles will reflect that. Note that Database::assertIsWritableMaster() takes
 873                         // care of replica DB handles whereas getReadOnlyReason() would cause infinite loops.
 874                         $conn->setLBInfo( 'readOnlyReason', $this->getReadOnlyReason( $domain, $conn ) );
 875                 }
 876
 877                 return $conn;
 878         }
 879
 880         public function reuseConnection( IDatabase $conn ) {
 881                 $serverIndex = $conn->getLBInfo( 'serverIndex' );
 882                 $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 883                 if ( $serverIndex === null || $refCount === null ) {
 884                         /**
 885                          * This can happen in code like:
 886                          *   foreach ( $dbs as $db ) {
 887                          *     $conn = $lb->getConnection( $lb::DB_REPLICA, [], $db );
 888                          *     ...
 889                          *     $lb->reuseConnection( $conn );
 890                          *   }
 891                          * When a connection to the local DB is opened in this way, reuseConnection()
 892                          * should be ignored
 893                          */
 894                         return;
 895                 } elseif ( $conn instanceof DBConnRef ) {
 896                         // DBConnRef already handles calling reuseConnection() and only passes the live
 897                         // Database instance to this method. Any caller passing in a DBConnRef is broken.
 898                         $this->connLogger->error(
 899                                 __METHOD__ . ": got DBConnRef instance.\n" .
 900                                 ( new RuntimeException() )->getTraceAsString() );
 901
 902                         return;
 903                 }
 904
 905                 if ( $this->disabled ) {
 906                         return; // DBConnRef handle probably survived longer than the LoadBalancer
 907                 }
 908
 909                 if ( $conn->getLBInfo( 'autoCommitOnly' ) ) {
 910                         $connFreeKey = self::KEY_FOREIGN_FREE_NOROUND;
 911                         $connInUseKey = self::KEY_FOREIGN_INUSE_NOROUND;
 912                 } else {
 913                         $connFreeKey = self::KEY_FOREIGN_FREE;
 914                         $connInUseKey = self::KEY_FOREIGN_INUSE;
 915                 }
 916
 917                 $domain = $conn->getDomainID();
 918                 if ( !isset( $this->conns[$connInUseKey][$serverIndex][$domain] ) ) {
 919                         throw new InvalidArgumentException(
 920                                 "Connection $serverIndex/$domain not found; it may have already been freed" );
 921                 } elseif ( $this->conns[$connInUseKey][$serverIndex][$domain] !== $conn ) {
 922                         throw new InvalidArgumentException(
 923                                 "Connection $serverIndex/$domain mismatched; it may have already been freed" );
 924                 }
 925
 926                 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
 927                 if ( $refCount <= 0 ) {
 928                         $this->conns[$connFreeKey][$serverIndex][$domain] = $conn;
 929                         unset( $this->conns[$connInUseKey][$serverIndex][$domain] );
 930                         if ( !$this->conns[$connInUseKey][$serverIndex] ) {
 931                                 unset( $this->conns[$connInUseKey][$serverIndex] ); // clean up
 932                         }
 933                         $this->connLogger->debug( __METHOD__ . ": freed connection $serverIndex/$domain" );
 934                 } else {
 935                         $this->connLogger->debug( __METHOD__ .
 936                                 ": reference count for $serverIndex/$domain reduced to $refCount" );
 937                 }
 938         }
 939
 940         public function getConnectionRef( $i, $groups = [], $domain = false, $flags = 0 ) {
 941                 $domain = $this->resolveDomainID( $domain );
 942                 $role = $this->getRoleFromIndex( $i );
 943
 944                 return new DBConnRef( $this, $this->getConnection( $i, $groups, $domain, $flags ), $role );
 945         }
 946
 947         public function getLazyConnectionRef( $i, $groups = [], $domain = false, $flags = 0 ) {
 948                 $domain = $this->resolveDomainID( $domain );
 949                 $role = $this->getRoleFromIndex( $i );
 950
 951                 return new DBConnRef( $this, [ $i, $groups, $domain, $flags ], $role );
 952         }
 953
 954         public function getMaintenanceConnectionRef( $i, $groups = [], $domain = false, $flags = 0 ) {
 955                 $domain = $this->resolveDomainID( $domain );
 956                 $role = $this->getRoleFromIndex( $i );
 957
 958                 return new MaintainableDBConnRef(
 959                         $this, $this->getConnection( $i, $groups, $domain, $flags ), $role );
 960         }
 961
 962         /**
 963          * @param int $i Server index or DB_MASTER/DB_REPLICA
 964          * @return int One of DB_MASTER/DB_REPLICA
 965          */
 966         private function getRoleFromIndex( $i ) {
 967                 return ( $i === self::DB_MASTER || $i === $this->getWriterIndex() )
 968                         ? self::DB_MASTER
 969                         : self::DB_REPLICA;
 970         }
 971
 972         /**
 973          * @param int $i
 974          * @param bool $domain
 975          * @param int $flags
 976          * @return Database|bool Live database handle or false on failure
 977          * @deprecated Since 1.34 Use getConnection() instead
 978          */
 979         public function openConnection( $i, $domain = false, $flags = 0 ) {
 980                 return $this->getConnection( $i, [], $domain, $flags | self::CONN_SILENCE_ERRORS );
 981         }
 982
 983         /**
 984          * Open a connection to a local DB, or return one if it is already open.
 985          *
 986          * On error, returns false, and the connection which caused the
 987          * error will be available via $this->errorConnection.
 988          *
 989          * @note If disable() was called on this LoadBalancer, this method will throw a DBAccessError.
 990          *
 991          * @param int $i Server index
 992          * @param int $flags Class CONN_* constant bitfield
 993          * @return Database
 994          */
 995         private function getLocalConnection( $i, $flags = 0 ) {
 996                 // Connection handles required to be in auto-commit mode use a separate connection
 997                 // pool since the main pool is effected by implicit and explicit transaction rounds
 998                 $autoCommit = ( ( $flags & self::CONN_TRX_AUTOCOMMIT ) == self::CONN_TRX_AUTOCOMMIT );
 999
1000                 $connKey = $autoCommit ? self::KEY_LOCAL_NOROUND : self::KEY_LOCAL;
1001                 if ( isset( $this->conns[$connKey][$i][0] ) ) {
1002                         $conn = $this->conns[$connKey][$i][0];
1003                 } else {
1004                         if ( !isset( $this->servers[$i] ) || !is_array( $this->servers[$i] ) ) {
1005                                 throw new InvalidArgumentException( "No server with index '$i'" );
1006                         }
1007                         // Open a new connection
1008                         $server = $this->servers[$i];
1009                         $server['serverIndex'] = $i;
1010                         $server['autoCommitOnly'] = $autoCommit;
1011                         $conn = $this->reallyOpenConnection( $server, $this->localDomain );
1012                         $host = $this->getServerName( $i );
1013                         if ( $conn->isOpen() ) {
1014                                 $this->connLogger->debug(
1015                                         __METHOD__ . ": connected to database $i at '$host'." );
1016                                 $this->conns[$connKey][$i][0] = $conn;
1017                         } else {
1018                                 $this->connLogger->warning(
1019                                         __METHOD__ . ": failed to connect to database $i at '$host'." );
1020                                 $this->errorConnection = $conn;
1021                                 $conn = false;
1022                         }
1023                 }
1024
1025                 // Final sanity check to make sure the right domain is selected
1026                 if (
1027                         $conn instanceof IDatabase &&
1028                         !$this->localDomain->isCompatible( $conn->getDomainID() )
1029                 ) {
1030                         throw new UnexpectedValueException(
1031                                 "Got connection to '{$conn->getDomainID()}', " .
1032                                 "but expected local domain ('{$this->localDomain}')" );
1033                 }
1034
1035                 return $conn;
1036         }
1037
1038         /**
1039          * Open a connection to a foreign DB, or return one if it is already open.
1040          *
1041          * Increments a reference count on the returned connection which locks the
1042          * connection to the requested domain. This reference count can be
1043          * decremented by calling reuseConnection().
1044          *
1045          * If a connection is open to the appropriate server already, but with the wrong
1046          * database, it will be switched to the right database and returned, as long as
1047          * it has been freed first with reuseConnection().
1048          *
1049          * On error, returns false, and the connection which caused the
1050          * error will be available via $this->errorConnection.
1051          *
1052          * @note If disable() was called on this LoadBalancer, this method will throw a DBAccessError.
1053          *
1054          * @param int $i Server index
1055          * @param string $domain Domain ID to open
1056          * @param int $flags Class CONN_* constant bitfield
1057          * @return Database|bool Returns false on connection error
1058          * @throws DBError When database selection fails
1059          */
1060         private function getForeignConnection( $i, $domain, $flags = 0 ) {
1061                 $domainInstance = DatabaseDomain::newFromId( $domain );
1062                 // Connection handles required to be in auto-commit mode use a separate connection
1063                 // pool since the main pool is effected by implicit and explicit transaction rounds
1064                 $autoCommit = ( ( $flags & self::CONN_TRX_AUTOCOMMIT ) == self::CONN_TRX_AUTOCOMMIT );
1065
1066                 if ( $autoCommit ) {
1067                         $connFreeKey = self::KEY_FOREIGN_FREE_NOROUND;
1068                         $connInUseKey = self::KEY_FOREIGN_INUSE_NOROUND;
1069                 } else {
1070                         $connFreeKey = self::KEY_FOREIGN_FREE;
1071                         $connInUseKey = self::KEY_FOREIGN_INUSE;
1072                 }
1073
1074                 /** @var Database $conn */
1075                 $conn = null;
1076
1077                 if ( isset( $this->conns[$connInUseKey][$i][$domain] ) ) {
1078                         // Reuse an in-use connection for the same domain
1079                         $conn = $this->conns[$connInUseKey][$i][$domain];
1080                         $this->connLogger->debug( __METHOD__ . ": reusing connection $i/$domain" );
1081                 } elseif ( isset( $this->conns[$connFreeKey][$i][$domain] ) ) {
1082                         // Reuse a free connection for the same domain
1083                         $conn = $this->conns[$connFreeKey][$i][$domain];
1084                         unset( $this->conns[$connFreeKey][$i][$domain] );
1085                         $this->conns[$connInUseKey][$i][$domain] = $conn;
1086                         $this->connLogger->debug( __METHOD__ . ": reusing free connection $i/$domain" );
1087                 } elseif ( !empty( $this->conns[$connFreeKey][$i] ) ) {
1088                         // Reuse a free connection from another domain if possible
1089                         foreach ( $this->conns[$connFreeKey][$i] as $oldDomain => $conn ) {
1090                                 if ( $domainInstance->getDatabase() !== null ) {
1091                                         // Check if changing the database will require a new connection.
1092                                         // In that case, leave the connection handle alone and keep looking.
1093                                         // This prevents connections from being closed mid-transaction and can
1094                                         // also avoid overhead if the same database will later be requested.
1095                                         if (
1096                                                 $conn->databasesAreIndependent() &&
1097                                                 $conn->getDBname() !== $domainInstance->getDatabase()
1098                                         ) {
1099                                                 continue;
1100                                         }
1101                                         // Select the new database, schema, and prefix
1102                                         $conn->selectDomain( $domainInstance );
1103                                 } else {
1104                                         // Stay on the current database, but update the schema/prefix
1105                                         $conn->dbSchema( $domainInstance->getSchema() );
1106                                         $conn->tablePrefix( $domainInstance->getTablePrefix() );
1107                                 }
1108                                 unset( $this->conns[$connFreeKey][$i][$oldDomain] );
1109                                 // Note that if $domain is an empty string, getDomainID() might not match it
1110                                 $this->conns[$connInUseKey][$i][$conn->getDomainID()] = $conn;
1111                                 $this->connLogger->debug( __METHOD__ .
1112                                         ": reusing free connection from $oldDomain for $domain" );
1113                                 break;
1114                         }
1115                 }
1116
1117                 if ( !$conn ) {
1118                         if ( !isset( $this->servers[$i] ) || !is_array( $this->servers[$i] ) ) {
1119                                 throw new InvalidArgumentException( "No server with index '$i'" );
1120                         }
1121                         // Open a new connection
1122                         $server = $this->servers[$i];
1123                         $server['serverIndex'] = $i;
1124                         $server['foreignPoolRefCount'] = 0;
1125                         $server['foreign'] = true;
1126                         $server['autoCommitOnly'] = $autoCommit;
1127                         $conn = $this->reallyOpenConnection( $server, $domainInstance );
1128                         if ( !$conn->isOpen() ) {
1129                                 $this->connLogger->warning( __METHOD__ . ": connection error for $i/$domain" );
1130                                 $this->errorConnection = $conn;
1131                                 $conn = false;
1132                         } else {
1133                                 // Note that if $domain is an empty string, getDomainID() might not match it
1134                                 $this->conns[$connInUseKey][$i][$conn->getDomainID()] = $conn;
1135                                 $this->connLogger->debug( __METHOD__ . ": opened new connection for $i/$domain" );
1136                         }
1137                 }
1138
1139                 if ( $conn instanceof IDatabase ) {
1140                         // Final sanity check to make sure the right domain is selected
1141                         if ( !$domainInstance->isCompatible( $conn->getDomainID() ) ) {
1142                                 throw new UnexpectedValueException(
1143                                         "Got connection to '{$conn->getDomainID()}', but expected '$domain'" );
1144                         }
1145                         // Increment reference count
1146                         $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
1147                         $conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
1148                 }
1149
1150                 return $conn;
1151         }
1152
1153         public function getServerAttributes( $i ) {
1154                 return Database::attributesFromType(
1155                         $this->getServerType( $i ),
1156                         $this->servers[$i]['driver'] ?? null
1157                 );
1158         }
1159
1160         /**
1161          * Test if the specified index represents an open connection
1162          *
1163          * @param int $index Server index
1164          * @private
1165          * @return bool
1166          */
1167         private function isOpen( $index ) {
1168                 if ( !is_int( $index ) ) {
1169                         return false;
1170                 }
1171
1172                 return (bool)$this->getAnyOpenConnection( $index );
1173         }
1174
1175         /**
1176          * Open a new network connection to a server (uncached)
1177          *
1178          * Returns a Database object whether or not the connection was successful.
1179          *
1180          * @param array $server
1181          * @param DatabaseDomain $domain Domain the connection is for, possibly unspecified
1182          * @return Database
1183          * @throws DBAccessError
1184          * @throws InvalidArgumentException
1185          */
1186         protected function reallyOpenConnection( array $server, DatabaseDomain $domain ) {
1187                 if ( $this->disabled ) {
1188                         throw new DBAccessError();
1189                 }
1190
1191                 if ( $domain->getDatabase() === null ) {
1192                         // The database domain does not specify a DB name and some database systems require a
1193                         // valid DB specified on connection. The $server configuration array contains a default
1194                         // DB name to use for connections in such cases.
1195                         if ( $server['type'] === 'mysql' ) {
1196                                 // For MySQL, DATABASE and SCHEMA are synonyms, connections need not specify a DB,
1197                                 // and the DB name in $server might not exist due to legacy reasons (the default
1198                                 // domain used to ignore the local LB domain, even when mismatched).
1199                                 $server['dbname'] = null;
1200                         }
1201                 } else {
1202                         $server['dbname'] = $domain->getDatabase();
1203                 }
1204
1205                 if ( $domain->getSchema() !== null ) {
1206                         $server['schema'] = $domain->getSchema();
1207                 }
1208
1209                 // It is always possible to connect with any prefix, even the empty string
1210                 $server['tablePrefix'] = $domain->getTablePrefix();
1211
1212                 // Let the handle know what the cluster master is (e.g. "db1052")
1213                 $masterName = $this->getServerName( $this->getWriterIndex() );
1214                 $server['clusterMasterHost'] = $masterName;
1215
1216                 // Log when many connection are made on requests
1217                 if ( ++$this->connsOpened >= self::CONN_HELD_WARN_THRESHOLD ) {
1218                         $this->perfLogger->warning( __METHOD__ . ": " .
1219                                 "{$this->connsOpened}+ connections made (master=$masterName)" );
1220                 }
1221
1222                 $server['srvCache'] = $this->srvCache;
1223                 // Set loggers and profilers
1224                 $server['connLogger'] = $this->connLogger;
1225                 $server['queryLogger'] = $this->queryLogger;
1226                 $server['errorLogger'] = $this->errorLogger;
1227                 $server['deprecationLogger'] = $this->deprecationLogger;
1228                 $server['profiler'] = $this->profiler;
1229                 $server['trxProfiler'] = $this->trxProfiler;
1230                 // Use the same agent and PHP mode for all DB handles
1231                 $server['cliMode'] = $this->cliMode;
1232                 $server['agent'] = $this->agent;
1233                 // Use DBO_DEFAULT flags by default for LoadBalancer managed databases. Assume that the
1234                 // application calls LoadBalancer::commitMasterChanges() before the PHP script completes.
1235                 $server['flags'] = $server['flags'] ?? IDatabase::DBO_DEFAULT;
1236
1237                 // Create a live connection object
1238                 try {
1239                         $db = Database::factory( $server['type'], $server );
1240                 } catch ( DBConnectionError $e ) {
1241                         // FIXME: This is probably the ugliest thing I have ever done to
1242                         // PHP. I'm half-expecting it to segfault, just out of disgust. -- TS
1243                         $db = $e->db;
1244                 }
1245
1246                 $db->setLBInfo( $server );
1247                 $db->setLazyMasterHandle(
1248                         $this->getLazyConnectionRef( self::DB_MASTER, [], $db->getDomainID() )
1249                 );
1250                 $db->setTableAliases( $this->tableAliases );
1251                 $db->setIndexAliases( $this->indexAliases );
1252
1253                 if ( $server['serverIndex'] === $this->getWriterIndex() ) {
1254                         if ( $this->trxRoundId !== false ) {
1255                                 $this->applyTransactionRoundFlags( $db );
1256                         }
1257                         foreach ( $this->trxRecurringCallbacks as $name => $callback ) {
1258                                 $db->setTransactionListener( $name, $callback );
1259                         }
1260                 }
1261
1262                 $this->lazyLoadReplicationPositions(); // session consistency
1263
1264                 return $db;
1265         }
1266
1267         /**
1268          * Make sure that any "waitForPos" positions are loaded and available to doWait()
1269          */
1270         private function lazyLoadReplicationPositions() {
1271                 if ( !$this->connectionAttempted && $this->chronologyCallback ) {
1272                         $this->connectionAttempted = true;
1273                         ( $this->chronologyCallback )( $this ); // generally calls waitFor()
1274                         $this->connLogger->debug( __METHOD__ . ': executed chronology callback.' );
1275                 }
1276         }
1277
1278         /**
1279          * @throws DBConnectionError
1280          */
1281         private function reportConnectionError() {
1282                 $conn = $this->errorConnection; // the connection which caused the error
1283                 $context = [
1284                         'method' => __METHOD__,
1285                         'last_error' => $this->lastError,
1286                 ];
1287
1288                 if ( $conn instanceof IDatabase ) {
1289                         $context['db_server'] = $conn->getServer();
1290                         $this->connLogger->warning(
1291                                 __METHOD__ . ": connection error: {last_error} ({db_server})",
1292                                 $context
1293                         );
1294
1295                         throw new DBConnectionError( $conn, "{$this->lastError} ({$context['db_server']})" );
1296                 } else {
1297                         // No last connection, probably due to all servers being too busy
1298                         $this->connLogger->error(
1299                                 __METHOD__ .
1300                                 ": LB failure with no last connection. Connection error: {last_error}",
1301                                 $context
1302                         );
1303
1304                         // If all servers were busy, "lastError" will contain something sensible
1305                         throw new DBConnectionError( null, $this->lastError );
1306                 }
1307         }
1308
1309         public function getWriterIndex() {
1310                 return 0;
1311         }
1312
1313         public function haveIndex( $i ) {
1314                 return array_key_exists( $i, $this->servers );
1315         }
1316
1317         public function isNonZeroLoad( $i ) {
1318                 return array_key_exists( $i, $this->servers ) && $this->genericLoads[$i] != 0;
1319         }
1320
1321         public function getServerCount() {
1322                 return count( $this->servers );
1323         }
1324
1325         public function hasReplicaServers() {
1326                 return ( $this->getServerCount() > 1 );
1327         }
1328
1329         public function hasStreamingReplicaServers() {
1330                 foreach ( $this->servers as $i => $server ) {
1331                         if ( $i !== $this->getWriterIndex() && empty( $server['is static'] ) ) {
1332                                 return true;
1333                         }
1334                 }
1335
1336                 return false;
1337         }
1338
1339         public function getServerName( $i ) {
1340                 $name = $this->servers[$i]['hostName'] ?? $this->servers[$i]['host'] ?? '';
1341
1342                 return ( $name != '' ) ? $name : 'localhost';
1343         }
1344
1345         public function getServerInfo( $i ) {
1346                 return $this->servers[$i] ?? false;
1347         }
1348
1349         public function getServerType( $i ) {
1350                 return $this->servers[$i]['type'] ?? 'unknown';
1351         }
1352
1353         public function getMasterPos() {
1354                 # If this entire request was served from a replica DB without opening a connection to the
1355                 # master (however unlikely that may be), then we can fetch the position from the replica DB.
1356                 $masterConn = $this->getAnyOpenConnection( $this->getWriterIndex() );
1357                 if ( !$masterConn ) {
1358                         $serverCount = $this->getServerCount();
1359                         for ( $i = 1; $i < $serverCount; $i++ ) {
1360                                 $conn = $this->getAnyOpenConnection( $i );
1361                                 if ( $conn ) {
1362                                         return $conn->getReplicaPos();
1363                                 }
1364                         }
1365                 } else {
1366                         return $masterConn->getMasterPos();
1367                 }
1368
1369                 return false;
1370         }
1371
1372         public function disable() {
1373                 $this->closeAll();
1374                 $this->disabled = true;
1375         }
1376
1377         public function closeAll() {
1378                 $fname = __METHOD__;
1379                 $this->forEachOpenConnection( function ( IDatabase $conn ) use ( $fname ) {
1380                         $host = $conn->getServer();
1381                         $this->connLogger->debug(
1382                                 $fname . ": closing connection to database '$host'." );
1383                         $conn->close();
1384                 } );
1385
1386                 $this->conns = self::newConnsArray();
1387                 $this->connsOpened = 0;
1388         }
1389
1390         public function closeConnection( IDatabase $conn ) {
1391                 if ( $conn instanceof DBConnRef ) {
1392                         // Avoid calling close() but still leaving the handle in the pool
1393                         throw new RuntimeException( 'Cannot close DBConnRef instance; it must be shareable' );
1394                 }
1395
1396                 $serverIndex = $conn->getLBInfo( 'serverIndex' );
1397                 foreach ( $this->conns as $type => $connsByServer ) {
1398                         if ( !isset( $connsByServer[$serverIndex] ) ) {
1399                                 continue;
1400                         }
1401
1402                         foreach ( $connsByServer[$serverIndex] as $i => $trackedConn ) {
1403                                 if ( $conn === $trackedConn ) {
1404                                         $host = $this->getServerName( $i );
1405                                         $this->connLogger->debug(
1406                                                 __METHOD__ . ": closing connection to database $i at '$host'." );
1407                                         unset( $this->conns[$type][$serverIndex][$i] );
1408                                         --$this->connsOpened;
1409                                         break 2;
1410                                 }
1411                         }
1412                 }
1413
1414                 $conn->close();
1415         }
1416
1417         public function commitAll( $fname = __METHOD__, $owner = null ) {
1418                 $this->commitMasterChanges( $fname, $owner );
1419                 $this->flushMasterSnapshots( $fname );
1420                 $this->flushReplicaSnapshots( $fname );
1421         }
1422
1423         public function finalizeMasterChanges( $fname = __METHOD__, $owner = null ) {
1424                 $this->assertOwnership( $fname, $owner );
1425                 $this->assertTransactionRoundStage( [ self::ROUND_CURSORY, self::ROUND_FINALIZED ] );
1426
1427                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1428                 // Loop until callbacks stop adding callbacks on other connections
1429                 $total = 0;
1430                 do {
1431                         $count = 0; // callbacks execution attempts
1432                         $this->forEachOpenMasterConnection( function ( Database $conn ) use ( &$count ) {
1433                                 // Run any pre-commit callbacks while leaving the post-commit ones suppressed.
1434                                 // Any error should cause all (peer) transactions to be rolled back together.
1435                                 $count += $conn->runOnTransactionPreCommitCallbacks();
1436                         } );
1437                         $total += $count;
1438                 } while ( $count > 0 );
1439                 // Defer post-commit callbacks until after COMMIT/ROLLBACK happens on all handles
1440                 $this->forEachOpenMasterConnection( function ( Database $conn ) {
1441                         $conn->setTrxEndCallbackSuppression( true );
1442                 } );
1443                 $this->trxRoundStage = self::ROUND_FINALIZED;
1444
1445                 return $total;
1446         }
1447
1448         public function approveMasterChanges( array $options, $fname = __METHOD__, $owner = null ) {
1449                 $this->assertOwnership( $fname, $owner );
1450                 $this->assertTransactionRoundStage( self::ROUND_FINALIZED );
1451
1452                 $limit = $options['maxWriteDuration'] ?? 0;
1453
1454                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1455                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( $limit ) {
1456                         // If atomic sections or explicit transactions are still open, some caller must have
1457                         // caught an exception but failed to properly rollback any changes. Detect that and
1458                         // throw and error (causing rollback).
1459                         $conn->assertNoOpenTransactions();
1460                         // Assert that the time to replicate the transaction will be sane.
1461                         // If this fails, then all DB transactions will be rollback back together.
1462                         $time = $conn->pendingWriteQueryDuration( $conn::ESTIMATE_DB_APPLY );
1463                         if ( $limit > 0 && $time > $limit ) {
1464                                 throw new DBTransactionSizeError(
1465                                         $conn,
1466                                         "Transaction spent $time second(s) in writes, exceeding the limit of $limit",
1467                                         [ $time, $limit ]
1468                                 );
1469                         }
1470                         // If a connection sits idle while slow queries execute on another, that connection
1471                         // may end up dropped before the commit round is reached. Ping servers to detect this.
1472                         if ( $conn->writesOrCallbacksPending() && !$conn->ping() ) {
1473                                 throw new DBTransactionError(
1474                                         $conn,
1475                                         "A connection to the {$conn->getDBname()} database was lost before commit"
1476                                 );
1477                         }
1478                 } );
1479                 $this->trxRoundStage = self::ROUND_APPROVED;
1480         }
1481
1482         public function beginMasterChanges( $fname = __METHOD__, $owner = null ) {
1483                 $this->assertOwnership( $fname, $owner );
1484                 if ( $this->trxRoundId !== false ) {
1485                         throw new DBTransactionError(
1486                                 null,
1487                                 "$fname: Transaction round '{$this->trxRoundId}' already started"
1488                         );
1489                 }
1490                 $this->assertTransactionRoundStage( self::ROUND_CURSORY );
1491
1492                 // Clear any empty transactions (no writes/callbacks) from the implicit round
1493                 $this->flushMasterSnapshots( $fname );
1494
1495                 $this->trxRoundId = $fname;
1496                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1497                 // Mark applicable handles as participating in this explicit transaction round.
1498                 // For each of these handles, any writes and callbacks will be tied to a single
1499                 // transaction. The (peer) handles will reject begin()/commit() calls unless they
1500                 // are part of an en masse commit or an en masse rollback.
1501                 $this->forEachOpenMasterConnection( function ( Database $conn ) {
1502                         $this->applyTransactionRoundFlags( $conn );
1503                 } );
1504                 $this->trxRoundStage = self::ROUND_CURSORY;
1505         }
1506
1507         public function commitMasterChanges( $fname = __METHOD__, $owner = null ) {
1508                 $this->assertOwnership( $fname, $owner );
1509                 $this->assertTransactionRoundStage( self::ROUND_APPROVED );
1510
1511                 $failures = [];
1512
1513                 /** @noinspection PhpUnusedLocalVariableInspection */
1514                 $scope = ScopedCallback::newScopedIgnoreUserAbort(); // try to ignore client aborts
1515
1516                 $restore = ( $this->trxRoundId !== false );
1517                 $this->trxRoundId = false;
1518                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1519                 // Commit any writes and clear any snapshots as well (callbacks require AUTOCOMMIT).
1520                 // Note that callbacks should already be suppressed due to finalizeMasterChanges().
1521                 $this->forEachOpenMasterConnection(
1522                         function ( IDatabase $conn ) use ( $fname, &$failures ) {
1523                                 try {
1524                                         $conn->commit( $fname, $conn::FLUSHING_ALL_PEERS );
1525                                 } catch ( DBError $e ) {
1526                                         ( $this->errorLogger )( $e );
1527                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1528                                 }
1529                         }
1530                 );
1531                 if ( $failures ) {
1532                         throw new DBTransactionError(
1533                                 null,
1534                                 "$fname: Commit failed on server(s) " . implode( "\n", array_unique( $failures ) )
1535                         );
1536                 }
1537                 if ( $restore ) {
1538                         // Unmark handles as participating in this explicit transaction round
1539                         $this->forEachOpenMasterConnection( function ( Database $conn ) {
1540                                 $this->undoTransactionRoundFlags( $conn );
1541                         } );
1542                 }
1543                 $this->trxRoundStage = self::ROUND_COMMIT_CALLBACKS;
1544         }
1545
1546         public function runMasterTransactionIdleCallbacks( $fname = __METHOD__, $owner = null ) {
1547                 $this->assertOwnership( $fname, $owner );
1548                 if ( $this->trxRoundStage === self::ROUND_COMMIT_CALLBACKS ) {
1549                         $type = IDatabase::TRIGGER_COMMIT;
1550                 } elseif ( $this->trxRoundStage === self::ROUND_ROLLBACK_CALLBACKS ) {
1551                         $type = IDatabase::TRIGGER_ROLLBACK;
1552                 } else {
1553                         throw new DBTransactionError(
1554                                 null,
1555                                 "Transaction should be in the callback stage (not '{$this->trxRoundStage}')"
1556                         );
1557                 }
1558
1559                 $oldStage = $this->trxRoundStage;
1560                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1561
1562                 // Now that the COMMIT/ROLLBACK step is over, enable post-commit callback runs
1563                 $this->forEachOpenMasterConnection( function ( Database $conn ) {
1564                         $conn->setTrxEndCallbackSuppression( false );
1565                 } );
1566
1567                 $e = null; // first exception
1568                 $fname = __METHOD__;
1569                 // Loop until callbacks stop adding callbacks on other connections
1570                 do {
1571                         // Run any pending callbacks for each connection...
1572                         $count = 0; // callback execution attempts
1573                         $this->forEachOpenMasterConnection(
1574                                 function ( Database $conn ) use ( $type, &$e, &$count ) {
1575                                         if ( $conn->trxLevel() ) {
1576                                                 return; // retry in the next iteration, after commit() is called
1577                                         }
1578                                         try {
1579                                                 $count += $conn->runOnTransactionIdleCallbacks( $type );
1580                                         } catch ( Exception $ex ) {
1581                                                 $e = $e ?: $ex;
1582                                         }
1583                                 }
1584                         );
1585                         // Clear out any active transactions left over from callbacks...
1586                         $this->forEachOpenMasterConnection( function ( Database $conn ) use ( &$e, $fname ) {
1587                                 if ( $conn->writesPending() ) {
1588                                         // A callback from another handle wrote to this one and DBO_TRX is set
1589                                         $this->queryLogger->warning( $fname . ": found writes pending." );
1590                                         $fnames = implode( ', ', $conn->pendingWriteAndCallbackCallers() );
1591                                         $this->queryLogger->warning(
1592                                                 $fname . ": found writes pending ($fnames).",
1593                                                 [
1594                                                         'db_server' => $conn->getServer(),
1595                                                         'db_name' => $conn->getDBname()
1596                                                 ]
1597                                         );
1598                                 } elseif ( $conn->trxLevel() ) {
1599                                         // A callback from another handle read from this one and DBO_TRX is set,
1600                                         // which can easily happen if there is only one DB (no replicas)
1601                                         $this->queryLogger->debug( $fname . ": found empty transaction." );
1602                                 }
1603                                 try {
1604                                         $conn->commit( $fname, $conn::FLUSHING_ALL_PEERS );
1605                                 } catch ( Exception $ex ) {
1606                                         $e = $e ?: $ex;
1607                                 }
1608                         } );
1609                 } while ( $count > 0 );
1610
1611                 $this->trxRoundStage = $oldStage;
1612
1613                 return $e;
1614         }
1615
1616         public function runMasterTransactionListenerCallbacks( $fname = __METHOD__, $owner = null ) {
1617                 $this->assertOwnership( $fname, $owner );
1618                 if ( $this->trxRoundStage === self::ROUND_COMMIT_CALLBACKS ) {
1619                         $type = IDatabase::TRIGGER_COMMIT;
1620                 } elseif ( $this->trxRoundStage === self::ROUND_ROLLBACK_CALLBACKS ) {
1621                         $type = IDatabase::TRIGGER_ROLLBACK;
1622                 } else {
1623                         throw new DBTransactionError(
1624                                 null,
1625                                 "Transaction should be in the callback stage (not '{$this->trxRoundStage}')"
1626                         );
1627                 }
1628
1629                 $e = null;
1630
1631                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1632                 $this->forEachOpenMasterConnection( function ( Database $conn ) use ( $type, &$e ) {
1633                         try {
1634                                 $conn->runTransactionListenerCallbacks( $type );
1635                         } catch ( Exception $ex ) {
1636                                 $e = $e ?: $ex;
1637                         }
1638                 } );
1639                 $this->trxRoundStage = self::ROUND_CURSORY;
1640
1641                 return $e;
1642         }
1643
1644         public function rollbackMasterChanges( $fname = __METHOD__, $owner = null ) {
1645                 $this->assertOwnership( $fname, $owner );
1646
1647                 $restore = ( $this->trxRoundId !== false );
1648                 $this->trxRoundId = false;
1649                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1650                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( $fname ) {
1651                         $conn->rollback( $fname, $conn::FLUSHING_ALL_PEERS );
1652                 } );
1653                 if ( $restore ) {
1654                         // Unmark handles as participating in this explicit transaction round
1655                         $this->forEachOpenMasterConnection( function ( Database $conn ) {
1656                                 $this->undoTransactionRoundFlags( $conn );
1657                         } );
1658                 }
1659                 $this->trxRoundStage = self::ROUND_ROLLBACK_CALLBACKS;
1660         }
1661
1662         /**
1663          * @param string|string[] $stage
1664          * @throws DBTransactionError
1665          */
1666         private function assertTransactionRoundStage( $stage ) {
1667                 $stages = (array)$stage;
1668
1669                 if ( !in_array( $this->trxRoundStage, $stages, true ) ) {
1670                         $stageList = implode(
1671                                 '/',
1672                                 array_map( function ( $v ) {
1673                                         return "'$v'";
1674                                 }, $stages )
1675                         );
1676                         throw new DBTransactionError(
1677                                 null,
1678                                 "Transaction round stage must be $stageList (not '{$this->trxRoundStage}')"
1679                         );
1680                 }
1681         }
1682
1683         /**
1684          * @param string $fname
1685          * @param int|null $owner Owner ID of the caller
1686          * @throws DBTransactionError
1687          */
1688         private function assertOwnership( $fname, $owner ) {
1689                 if ( $this->ownerId !== null && $owner !== $this->ownerId ) {
1690                         throw new DBTransactionError(
1691                                 null,
1692                                 "$fname: LoadBalancer is owned by LBFactory #{$this->ownerId} (got '$owner')."
1693                         );
1694                 }
1695         }
1696
1697         /**
1698          * Make all DB servers with DBO_DEFAULT/DBO_TRX set join the transaction round
1699          *
1700          * Some servers may have neither flag enabled, meaning that they opt out of such
1701          * transaction rounds and remain in auto-commit mode. Such behavior might be desired
1702          * when a DB server is used for something like simple key/value storage.
1703          *
1704          * @param Database $conn
1705          */
1706         private function applyTransactionRoundFlags( Database $conn ) {
1707                 if ( $conn->getLBInfo( 'autoCommitOnly' ) ) {
1708                         return; // transaction rounds do not apply to these connections
1709                 }
1710
1711                 if ( $conn->getFlag( $conn::DBO_DEFAULT ) ) {
1712                         // DBO_TRX is controlled entirely by CLI mode presence with DBO_DEFAULT.
1713                         // Force DBO_TRX even in CLI mode since a commit round is expected soon.
1714                         $conn->setFlag( $conn::DBO_TRX, $conn::REMEMBER_PRIOR );
1715                 }
1716
1717                 if ( $conn->getFlag( $conn::DBO_TRX ) ) {
1718                         $conn->setLBInfo( 'trxRoundId', $this->trxRoundId );
1719                 }
1720         }
1721
1722         /**
1723          * @param Database $conn
1724          */
1725         private function undoTransactionRoundFlags( Database $conn ) {
1726                 if ( $conn->getLBInfo( 'autoCommitOnly' ) ) {
1727                         return; // transaction rounds do not apply to these connections
1728                 }
1729
1730                 if ( $conn->getFlag( $conn::DBO_TRX ) ) {
1731                         $conn->setLBInfo( 'trxRoundId', false );
1732                 }
1733
1734                 if ( $conn->getFlag( $conn::DBO_DEFAULT ) ) {
1735                         $conn->restoreFlags( $conn::RESTORE_PRIOR );
1736                 }
1737         }
1738
1739         public function flushReplicaSnapshots( $fname = __METHOD__ ) {
1740                 $this->forEachOpenReplicaConnection( function ( IDatabase $conn ) use ( $fname ) {
1741                         $conn->flushSnapshot( $fname );
1742                 } );
1743         }
1744
1745         public function flushMasterSnapshots( $fname = __METHOD__ ) {
1746                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( $fname ) {
1747                         $conn->flushSnapshot( $fname );
1748                 } );
1749         }
1750
1751         /**
1752          * @return string
1753          * @since 1.32
1754          */
1755         public function getTransactionRoundStage() {
1756                 return $this->trxRoundStage;
1757         }
1758
1759         public function hasMasterConnection() {
1760                 return $this->isOpen( $this->getWriterIndex() );
1761         }
1762
1763         public function hasMasterChanges() {
1764                 $pending = 0;
1765                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$pending ) {
1766                         $pending |= $conn->writesOrCallbacksPending();
1767                 } );
1768
1769                 return (bool)$pending;
1770         }
1771
1772         public function lastMasterChangeTimestamp() {
1773                 $lastTime = false;
1774                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$lastTime ) {
1775                         $lastTime = max( $lastTime, $conn->lastDoneWrites() );
1776                 } );
1777
1778                 return $lastTime;
1779         }
1780
1781         public function hasOrMadeRecentMasterChanges( $age = null ) {
1782                 $age = ( $age === null ) ? $this->waitTimeout : $age;
1783
1784                 return ( $this->hasMasterChanges()
1785                         || $this->lastMasterChangeTimestamp() > microtime( true ) - $age );
1786         }
1787
1788         public function pendingMasterChangeCallers() {
1789                 $fnames = [];
1790                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$fnames ) {
1791                         $fnames = array_merge( $fnames, $conn->pendingWriteCallers() );
1792                 } );
1793
1794                 return $fnames;
1795         }
1796
1797         public function getLaggedReplicaMode( $domain = false ) {
1798                 if (
1799                         // Avoid recursion if there is only one DB
1800                         $this->hasStreamingReplicaServers() &&
1801                         // Avoid recursion if the (non-zero load) master DB was picked for generic reads
1802                         $this->genericReadIndex !== $this->getWriterIndex() &&
1803                         // Stay in lagged replica mode during the load balancer instance lifetime
1804                         !$this->laggedReplicaMode
1805                 ) {
1806                         try {
1807                                 // Calling this method will set "laggedReplicaMode" as needed
1808                                 $this->getReaderIndex( false, $domain );
1809                         } catch ( DBConnectionError $e ) {
1810                                 // Avoid expensive re-connect attempts and failures
1811                                 $this->allReplicasDownMode = true;
1812                                 $this->laggedReplicaMode = true;
1813                         }
1814                 }
1815
1816                 return $this->laggedReplicaMode;
1817         }
1818
1819         public function laggedReplicaUsed() {
1820                 return $this->laggedReplicaMode;
1821         }
1822
1823         /**
1824          * @return bool
1825          * @since 1.27
1826          * @deprecated Since 1.28; use laggedReplicaUsed()
1827          */
1828         public function laggedSlaveUsed() {
1829                 return $this->laggedReplicaUsed();
1830         }
1831
1832         public function getReadOnlyReason( $domain = false, IDatabase $conn = null ) {
1833                 if ( $this->readOnlyReason !== false ) {
1834                         return $this->readOnlyReason;
1835                 } elseif ( $this->getLaggedReplicaMode( $domain ) ) {
1836                         if ( $this->allReplicasDownMode ) {
1837                                 return 'The database has been automatically locked ' .
1838                                         'until the replica database servers become available';
1839                         } else {
1840                                 return 'The database has been automatically locked ' .
1841                                         'while the replica database servers catch up to the master.';
1842                         }
1843                 } elseif ( $this->masterRunningReadOnly( $domain, $conn ) ) {
1844                         return 'The database master is running in read-only mode.';
1845                 }
1846
1847                 return false;
1848         }
1849
1850         /**
1851          * @param string $domain Domain ID, or false for the current domain
1852          * @param IDatabase|null $conn DB master connectionl used to avoid loops [optional]
1853          * @return bool
1854          */
1855         private function masterRunningReadOnly( $domain, IDatabase $conn = null ) {
1856                 $cache = $this->wanCache;
1857                 $masterServer = $this->getServerName( $this->getWriterIndex() );
1858
1859                 return (bool)$cache->getWithSetCallback(
1860                         $cache->makeGlobalKey( __CLASS__, 'server-read-only', $masterServer ),
1861                         self::TTL_CACHE_READONLY,
1862                         function () use ( $domain, $conn ) {
1863                                 $old = $this->trxProfiler->setSilenced( true );
1864                                 try {
1865                                         $dbw = $conn ?: $this->getConnection( self::DB_MASTER, [], $domain );
1866                                         $readOnly = (int)$dbw->serverIsReadOnly();
1867                                         if ( !$conn ) {
1868                                                 $this->reuseConnection( $dbw );
1869                                         }
1870                                 } catch ( DBError $e ) {
1871                                         $readOnly = 0;
1872                                 }
1873                                 $this->trxProfiler->setSilenced( $old );
1874                                 return $readOnly;
1875                         },
1876                         [ 'pcTTL' => $cache::TTL_PROC_LONG, 'busyValue' => 0 ]
1877                 );
1878         }
1879
1880         public function allowLagged( $mode = null ) {
1881                 if ( $mode === null ) {
1882                         return $this->allowLagged;
1883                 }
1884                 $this->allowLagged = $mode;
1885
1886                 return $this->allowLagged;
1887         }
1888
1889         public function pingAll() {
1890                 $success = true;
1891                 $this->forEachOpenConnection( function ( IDatabase $conn ) use ( &$success ) {
1892                         if ( !$conn->ping() ) {
1893                                 $success = false;
1894                         }
1895                 } );
1896
1897                 return $success;
1898         }
1899
1900         public function forEachOpenConnection( $callback, array $params = [] ) {
1901                 foreach ( $this->conns as $connsByServer ) {
1902                         foreach ( $connsByServer as $serverConns ) {
1903                                 foreach ( $serverConns as $conn ) {
1904                                         $callback( $conn, ...$params );
1905                                 }
1906                         }
1907                 }
1908         }
1909
1910         public function forEachOpenMasterConnection( $callback, array $params = [] ) {
1911                 $masterIndex = $this->getWriterIndex();
1912                 foreach ( $this->conns as $connsByServer ) {
1913                         if ( isset( $connsByServer[$masterIndex] ) ) {
1914                                 /** @var IDatabase $conn */
1915                                 foreach ( $connsByServer[$masterIndex] as $conn ) {
1916                                         $callback( $conn, ...$params );
1917                                 }
1918                         }
1919                 }
1920         }
1921
1922         public function forEachOpenReplicaConnection( $callback, array $params = [] ) {
1923                 foreach ( $this->conns as $connsByServer ) {
1924                         foreach ( $connsByServer as $i => $serverConns ) {
1925                                 if ( $i === $this->getWriterIndex() ) {
1926                                         continue; // skip master
1927                                 }
1928                                 foreach ( $serverConns as $conn ) {
1929                                         $callback( $conn, ...$params );
1930                                 }
1931                         }
1932                 }
1933         }
1934
1935         public function getMaxLag( $domain = false ) {
1936                 $host = '';
1937                 $maxLag = -1;
1938                 $maxIndex = 0;
1939
1940                 if ( $this->hasReplicaServers() ) {
1941                         $lagTimes = $this->getLagTimes( $domain );
1942                         foreach ( $lagTimes as $i => $lag ) {
1943                                 if ( $this->genericLoads[$i] > 0 && $lag > $maxLag ) {
1944                                         $maxLag = $lag;
1945                                         $host = $this->servers[$i]['host'];
1946                                         $maxIndex = $i;
1947                                 }
1948                         }
1949                 }
1950
1951                 return [ $host, $maxLag, $maxIndex ];
1952         }
1953
1954         public function getLagTimes( $domain = false ) {
1955                 if ( !$this->hasReplicaServers() ) {
1956                         return [ $this->getWriterIndex() => 0 ]; // no replication = no lag
1957                 }
1958
1959                 $knownLagTimes = []; // map of (server index => 0 seconds)
1960                 $indexesWithLag = [];
1961                 foreach ( $this->servers as $i => $server ) {
1962                         if ( empty( $server['is static'] ) ) {
1963                                 $indexesWithLag[] = $i; // DB server might have replication lag
1964                         } else {
1965                                 $knownLagTimes[$i] = 0; // DB server is a non-replicating and read-only archive
1966                         }
1967                 }
1968
1969                 return $this->getLoadMonitor()->getLagTimes( $indexesWithLag, $domain ) + $knownLagTimes;
1970         }
1971
1972         /**
1973          * Get the lag in seconds for a given connection, or zero if this load
1974          * balancer does not have replication enabled.
1975          *
1976          * This should be used in preference to Database::getLag() in cases where
1977          * replication may not be in use, since there is no way to determine if
1978          * replication is in use at the connection level without running
1979          * potentially restricted queries such as SHOW SLAVE STATUS. Using this
1980          * function instead of Database::getLag() avoids a fatal error in this
1981          * case on many installations.
1982          *
1983          * @param IDatabase $conn
1984          * @return int|bool Returns false on error
1985          * @deprecated Since 1.34 Use IDatabase::getLag() instead
1986          */
1987         public function safeGetLag( IDatabase $conn ) {
1988                 if ( $conn->getLBInfo( 'is static' ) ) {
1989                         return 0; // static dataset
1990                 } elseif ( $conn->getLBInfo( 'serverIndex' ) == $this->getWriterIndex() ) {
1991                         return 0; // this is the master
1992                 }
1993
1994                 return $conn->getLag();
1995         }
1996
1997         public function safeWaitForMasterPos( IDatabase $conn, $pos = false, $timeout = null ) {
1998                 $timeout = max( 1, $timeout ?: $this->waitTimeout );
1999
2000                 if ( $this->getServerCount() <= 1 || !$conn->getLBInfo( 'replica' ) ) {
2001                         return true; // server is not a replica DB
2002                 }
2003
2004                 if ( !$pos ) {
2005                         // Get the current master position, opening a connection if needed
2006                         $index = $this->getWriterIndex();
2007                         $masterConn = $this->getAnyOpenConnection( $index );
2008                         if ( $masterConn ) {
2009                                 $pos = $masterConn->getMasterPos();
2010                         } else {
2011                                 $flags = self::CONN_SILENCE_ERRORS;
2012                                 $masterConn = $this->getConnection( $index, [], self::DOMAIN_ANY, $flags );
2013                                 if ( !$masterConn ) {
2014                                         throw new DBReplicationWaitError(
2015                                                 null,
2016                                                 "Could not obtain a master database connection to get the position"
2017                                         );
2018                                 }
2019                                 $pos = $masterConn->getMasterPos();
2020                                 $this->closeConnection( $masterConn );
2021                         }
2022                 }
2023
2024                 if ( $pos instanceof DBMasterPos ) {
2025                         $start = microtime( true );
2026                         $result = $conn->masterPosWait( $pos, $timeout );
2027                         $seconds = max( microtime( true ) - $start, 0 );
2028                         if ( $result == -1 || is_null( $result ) ) {
2029                                 $msg = __METHOD__ . ': timed out waiting on {host} pos {pos} [{seconds}s]';
2030                                 $this->replLogger->warning( $msg, [
2031                                         'host' => $conn->getServer(),
2032                                         'pos' => $pos,
2033                                         'seconds' => round( $seconds, 6 ),
2034                                         'trace' => ( new RuntimeException() )->getTraceAsString()
2035                                 ] );
2036                                 $ok = false;
2037                         } else {
2038                                 $this->replLogger->debug( __METHOD__ . ': done waiting' );
2039                                 $ok = true;
2040                         }
2041                 } else {
2042                         $ok = false; // something is misconfigured
2043                         $this->replLogger->error(
2044                                 __METHOD__ . ': could not get master pos for {host}',
2045                                 [
2046                                         'host' => $conn->getServer(),
2047                                         'trace' => ( new RuntimeException() )->getTraceAsString()
2048                                 ]
2049                         );
2050                 }
2051
2052                 return $ok;
2053         }
2054
2055         public function setTransactionListener( $name, callable $callback = null ) {
2056                 if ( $callback ) {
2057                         $this->trxRecurringCallbacks[$name] = $callback;
2058                 } else {
2059                         unset( $this->trxRecurringCallbacks[$name] );
2060                 }
2061                 $this->forEachOpenMasterConnection(
2062                         function ( IDatabase $conn ) use ( $name, $callback ) {
2063                                 $conn->setTransactionListener( $name, $callback );
2064                         }
2065                 );
2066         }
2067
2068         public function setTableAliases( array $aliases ) {
2069                 $this->tableAliases = $aliases;
2070         }
2071
2072         public function setIndexAliases( array $aliases ) {
2073                 $this->indexAliases = $aliases;
2074         }
2075
2076         /**
2077          * @param string $prefix
2078          * @deprecated Since 1.33
2079          */
2080         public function setDomainPrefix( $prefix ) {
2081                 $this->setLocalDomainPrefix( $prefix );
2082         }
2083
2084         public function setLocalDomainPrefix( $prefix ) {
2085                 // Find connections to explicit foreign domains still marked as in-use...
2086                 $domainsInUse = [];
2087                 $this->forEachOpenConnection( function ( IDatabase $conn ) use ( &$domainsInUse ) {
2088                         // Once reuseConnection() is called on a handle, its reference count goes from 1 to 0.
2089                         // Until then, it is still in use by the caller (explicitly or via DBConnRef scope).
2090                         if ( $conn->getLBInfo( 'foreignPoolRefCount' ) > 0 ) {
2091                                 $domainsInUse[] = $conn->getDomainID();
2092                         }
2093                 } );
2094
2095                 // Do not switch connections to explicit foreign domains unless marked as safe
2096                 if ( $domainsInUse ) {
2097                         $domains = implode( ', ', $domainsInUse );
2098                         throw new DBUnexpectedError( null,
2099                                 "Foreign domain connections are still in use ($domains)" );
2100                 }
2101
2102                 $this->setLocalDomain( new DatabaseDomain(
2103                         $this->localDomain->getDatabase(),
2104                         $this->localDomain->getSchema(),
2105                         $prefix
2106                 ) );
2107
2108                 // Update the prefix for all local connections...
2109                 $this->forEachOpenConnection( function ( IDatabase $db ) use ( $prefix ) {
2110                         if ( !$db->getLBInfo( 'foreign' ) ) {
2111                                 $db->tablePrefix( $prefix );
2112                         }
2113                 } );
2114         }
2115
2116         public function redefineLocalDomain( $domain ) {
2117                 $this->closeAll();
2118
2119                 $this->setLocalDomain( DatabaseDomain::newFromId( $domain ) );
2120         }
2121
2122         /**
2123          * @param DatabaseDomain $domain
2124          */
2125         private function setLocalDomain( DatabaseDomain $domain ) {
2126                 $this->localDomain = $domain;
2127                 // In case a caller assumes that the domain ID is simply <db>-<prefix>, which is almost
2128                 // always true, gracefully handle the case when they fail to account for escaping.
2129                 if ( $this->localDomain->getTablePrefix() != '' ) {
2130                         $this->localDomainIdAlias =
2131                                 $this->localDomain->getDatabase() . '-' . $this->localDomain->getTablePrefix();
2132                 } else {
2133                         $this->localDomainIdAlias = $this->localDomain->getDatabase();
2134                 }
2135         }
2136
2137         function __destruct() {
2138                 // Avoid connection leaks for sanity
2139                 $this->disable();
2140         }
2141 }
2142
2143 /**
2144  * @deprecated since 1.29
2145  */
2146 class_alias( LoadBalancer::class, 'LoadBalancer' );