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 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'] ) ) {
 170                         throw new InvalidArgumentException( __CLASS__ . ': missing "servers" parameter' );
 171                 }
 172                 $this->servers = $params['servers'];
 173                 foreach ( $this->servers as $i => $server ) {
 174                         if ( $i == 0 ) {
 175                                 $this->servers[$i]['master'] = true;
 176                         } else {
 177                                 $this->servers[$i]['replica'] = true;
 178                         }
 179                 }
 180
 181                 $localDomain = isset( $params['localDomain'] )
 182                         ? DatabaseDomain::newFromId( $params['localDomain'] )
 183                         : DatabaseDomain::newUnspecified();
 184                 $this->setLocalDomain( $localDomain );
 185
 186                 $this->waitTimeout = $params['waitTimeout'] ?? self::MAX_WAIT_DEFAULT;
 187
 188                 $this->conns = [
 189                         // Connection were transaction rounds may be applied
 190                         self::KEY_LOCAL => [],
 191                         self::KEY_FOREIGN_INUSE => [],
 192                         self::KEY_FOREIGN_FREE => [],
 193                         // Auto-committing counterpart connections that ignore transaction rounds
 194                         self::KEY_LOCAL_NOROUND => [],
 195                         self::KEY_FOREIGN_INUSE_NOROUND => [],
 196                         self::KEY_FOREIGN_FREE_NOROUND => []
 197                 ];
 198                 $this->genericLoads = [];
 199                 $this->waitForPos = false;
 200                 $this->allowLagged = false;
 201
 202                 if ( isset( $params['readOnlyReason'] ) && is_string( $params['readOnlyReason'] ) ) {
 203                         $this->readOnlyReason = $params['readOnlyReason'];
 204                 }
 205
 206                 $this->maxLag = $params['maxLag'] ?? self::MAX_LAG_DEFAULT;
 207
 208                 $this->loadMonitorConfig = $params['loadMonitor'] ?? [ 'class' => 'LoadMonitorNull' ];
 209                 $this->loadMonitorConfig += [ 'lagWarnThreshold' => $this->maxLag ];
 210
 211                 foreach ( $params['servers'] as $i => $server ) {
 212                         $this->genericLoads[$i] = $server['load'];
 213                         if ( isset( $server['groupLoads'] ) ) {
 214                                 foreach ( $server['groupLoads'] as $group => $ratio ) {
 215                                         if ( !isset( $this->groupLoads[$group] ) ) {
 216                                                 $this->groupLoads[$group] = [];
 217                                         }
 218                                         $this->groupLoads[$group][$i] = $ratio;
 219                                 }
 220                         }
 221                 }
 222
 223                 $this->srvCache = $params['srvCache'] ?? new EmptyBagOStuff();
 224                 $this->wanCache = $params['wanCache'] ?? WANObjectCache::newEmpty();
 225                 $this->profiler = $params['profiler'] ?? null;
 226                 $this->trxProfiler = $params['trxProfiler'] ?? new TransactionProfiler();
 227
 228                 $this->errorLogger = $params['errorLogger'] ?? function ( Exception $e ) {
 229                         trigger_error( get_class( $e ) . ': ' . $e->getMessage(), E_USER_WARNING );
 230                 };
 231                 $this->deprecationLogger = $params['deprecationLogger'] ?? function ( $msg ) {
 232                         trigger_error( $msg, E_USER_DEPRECATED );
 233                 };
 234
 235                 foreach ( [ 'replLogger', 'connLogger', 'queryLogger', 'perfLogger' ] as $key ) {
 236                         $this->$key = $params[$key] ?? new NullLogger();
 237                 }
 238
 239                 $this->hostname = $params['hostname'] ?? ( gethostname() ?: 'unknown' );
 240                 $this->cliMode = $params['cliMode'] ?? ( PHP_SAPI === 'cli' || PHP_SAPI === 'phpdbg' );
 241                 $this->agent = $params['agent'] ?? '';
 242
 243                 if ( isset( $params['chronologyCallback'] ) ) {
 244                         $this->chronologyCallback = $params['chronologyCallback'];
 245                 }
 246
 247                 if ( isset( $params['roundStage'] ) ) {
 248                         if ( $params['roundStage'] === self::STAGE_POSTCOMMIT_CALLBACKS ) {
 249                                 $this->trxRoundStage = self::ROUND_COMMIT_CALLBACKS;
 250                         } elseif ( $params['roundStage'] === self::STAGE_POSTROLLBACK_CALLBACKS ) {
 251                                 $this->trxRoundStage = self::ROUND_ROLLBACK_CALLBACKS;
 252                         }
 253                 }
 254
 255                 $this->defaultGroup = $params['defaultGroup'] ?? null;
 256                 $this->ownerId = $params['ownerId'] ?? null;
 257         }
 258
 259         public function getLocalDomainID() {
 260                 return $this->localDomain->getId();
 261         }
 262
 263         public function resolveDomainID( $domain ) {
 264                 if ( $domain === $this->localDomainIdAlias || $domain === false ) {
 265                         // Local connection requested via some backwards-compatibility domain alias
 266                         return $this->getLocalDomainID();
 267                 }
 268
 269                 return (string)$domain;
 270         }
 271
 272         /**
 273          * Get a LoadMonitor instance
 274          *
 275          * @return ILoadMonitor
 276          */
 277         private function getLoadMonitor() {
 278                 if ( !isset( $this->loadMonitor ) ) {
 279                         $compat = [
 280                                 'LoadMonitor' => LoadMonitor::class,
 281                                 'LoadMonitorNull' => LoadMonitorNull::class,
 282                                 'LoadMonitorMySQL' => LoadMonitorMySQL::class,
 283                         ];
 284
 285                         $class = $this->loadMonitorConfig['class'];
 286                         if ( isset( $compat[$class] ) ) {
 287                                 $class = $compat[$class];
 288                         }
 289
 290                         $this->loadMonitor = new $class(
 291                                 $this, $this->srvCache, $this->wanCache, $this->loadMonitorConfig );
 292                         $this->loadMonitor->setLogger( $this->replLogger );
 293                 }
 294
 295                 return $this->loadMonitor;
 296         }
 297
 298         /**
 299          * @param array $loads
 300          * @param bool|string $domain Domain to get non-lagged for
 301          * @param int $maxLag Restrict the maximum allowed lag to this many seconds
 302          * @return bool|int|string
 303          */
 304         private function getRandomNonLagged( array $loads, $domain = false, $maxLag = INF ) {
 305                 $lags = $this->getLagTimes( $domain );
 306
 307                 # Unset excessively lagged servers
 308                 foreach ( $lags as $i => $lag ) {
 309                         if ( $i != 0 ) {
 310                                 # How much lag this server nominally is allowed to have
 311                                 $maxServerLag = $this->servers[$i]['max lag'] ?? $this->maxLag; // default
 312                                 # Constrain that futher by $maxLag argument
 313                                 $maxServerLag = min( $maxServerLag, $maxLag );
 314
 315                                 $host = $this->getServerName( $i );
 316                                 if ( $lag === false && !is_infinite( $maxServerLag ) ) {
 317                                         $this->replLogger->debug(
 318                                                 __METHOD__ .
 319                                                 ": server {host} is not replicating?", [ 'host' => $host ] );
 320                                         unset( $loads[$i] );
 321                                 } elseif ( $lag > $maxServerLag ) {
 322                                         $this->replLogger->debug(
 323                                                 __METHOD__ .
 324                                                 ": server {host} has {lag} seconds of lag (>= {maxlag})",
 325                                                 [ 'host' => $host, 'lag' => $lag, 'maxlag' => $maxServerLag ]
 326                                         );
 327                                         unset( $loads[$i] );
 328                                 }
 329                         }
 330                 }
 331
 332                 # Find out if all the replica DBs with non-zero load are lagged
 333                 $sum = 0;
 334                 foreach ( $loads as $load ) {
 335                         $sum += $load;
 336                 }
 337                 if ( $sum == 0 ) {
 338                         # No appropriate DB servers except maybe the master and some replica DBs with zero load
 339                         # Do NOT use the master
 340                         # Instead, this function will return false, triggering read-only mode,
 341                         # and a lagged replica DB will be used instead.
 342                         return false;
 343                 }
 344
 345                 if ( count( $loads ) == 0 ) {
 346                         return false;
 347                 }
 348
 349                 # Return a random representative of the remainder
 350                 return ArrayUtils::pickRandom( $loads );
 351         }
 352
 353         /**
 354          * @param int $i
 355          * @param array $groups
 356          * @param string|bool $domain
 357          * @return int
 358          */
 359         private function getConnectionIndex( $i, $groups, $domain ) {
 360                 // Check one "group" per default: the generic pool
 361                 $defaultGroups = $this->defaultGroup ? [ $this->defaultGroup ] : [ false ];
 362
 363                 $groups = ( $groups === false || $groups === [] )
 364                         ? $defaultGroups
 365                         : (array)$groups;
 366
 367                 if ( $i == self::DB_MASTER ) {
 368                         $i = $this->getWriterIndex();
 369                 } elseif ( $i == self::DB_REPLICA ) {
 370                         # Try to find an available server in any the query groups (in order)
 371                         foreach ( $groups as $group ) {
 372                                 $groupIndex = $this->getReaderIndex( $group, $domain );
 373                                 if ( $groupIndex !== false ) {
 374                                         $i = $groupIndex;
 375                                         break;
 376                                 }
 377                         }
 378                 }
 379
 380                 # Operation-based index
 381                 if ( $i == self::DB_REPLICA ) {
 382                         $this->lastError = 'Unknown error'; // reset error string
 383                         # Try the general server pool if $groups are unavailable.
 384                         $i = ( $groups === [ false ] )
 385                                 ? false // don't bother with this if that is what was tried above
 386                                 : $this->getReaderIndex( false, $domain );
 387                         # Couldn't find a working server in getReaderIndex()?
 388                         if ( $i === false ) {
 389                                 $this->lastError = 'No working replica DB server: ' . $this->lastError;
 390                                 // Throw an exception
 391                                 $this->reportConnectionError();
 392                                 return null; // not reached
 393                         }
 394                 }
 395
 396                 return $i;
 397         }
 398
 399         public function getReaderIndex( $group = false, $domain = false ) {
 400                 if ( count( $this->servers ) == 1 ) {
 401                         // Skip the load balancing if there's only one server
 402                         return $this->getWriterIndex();
 403                 }
 404
 405                 $index = $this->getExistingReaderIndex( $group );
 406                 if ( $index >= 0 ) {
 407                         // A reader index was already selected and "waitForPos" was handled
 408                         return $index;
 409                 }
 410
 411                 if ( $group !== false ) {
 412                         // Use the server weight array for this load group
 413                         if ( isset( $this->groupLoads[$group] ) ) {
 414                                 $loads = $this->groupLoads[$group];
 415                         } else {
 416                                 // No loads for this group, return false and the caller can use some other group
 417                                 $this->connLogger->info( __METHOD__ . ": no loads for group $group" );
 418
 419                                 return false;
 420                         }
 421                 } else {
 422                         // Use the generic load group
 423                         $loads = $this->genericLoads;
 424                 }
 425
 426                 // Scale the configured load ratios according to each server's load and state
 427                 $this->getLoadMonitor()->scaleLoads( $loads, $domain );
 428
 429                 // Pick a server to use, accounting for weights, load, lag, and "waitForPos"
 430                 list( $i, $laggedReplicaMode ) = $this->pickReaderIndex( $loads, $domain );
 431                 if ( $i === false ) {
 432                         // DB connection unsuccessful
 433                         return false;
 434                 }
 435
 436                 // If data seen by queries is expected to reflect the transactions committed as of
 437                 // or after a given replication position then wait for the DB to apply those changes
 438                 if ( $this->waitForPos && $i != $this->getWriterIndex() && !$this->doWait( $i ) ) {
 439                         // Data will be outdated compared to what was expected
 440                         $laggedReplicaMode = true;
 441                 }
 442
 443                 // Cache the reader index for future DB_REPLICA handles
 444                 $this->setExistingReaderIndex( $group, $i );
 445                 // Record whether the generic reader index is in "lagged replica DB" mode
 446                 if ( $group === false && $laggedReplicaMode ) {
 447                         $this->laggedReplicaMode = true;
 448                 }
 449
 450                 $serverName = $this->getServerName( $i );
 451                 $this->connLogger->debug( __METHOD__ . ": using server $serverName for group '$group'" );
 452
 453                 return $i;
 454         }
 455
 456         /**
 457          * Get the server index chosen by the load balancer for use with the given query group
 458          *
 459          * @param string|bool $group Query group; use false for the generic group
 460          * @return int Server index or -1 if none was chosen
 461          */
 462         protected function getExistingReaderIndex( $group ) {
 463                 if ( $group === false ) {
 464                         $index = $this->genericReadIndex;
 465                 } else {
 466                         $index = $this->readIndexByGroup[$group] ?? -1;
 467                 }
 468
 469                 return $index;
 470         }
 471
 472         /**
 473          * Set the server index chosen by the load balancer for use with the given query group
 474          *
 475          * @param string|bool $group Query group; use false for the generic group
 476          * @param int $index The index of a specific server
 477          */
 478         private function setExistingReaderIndex( $group, $index ) {
 479                 if ( $index < 0 ) {
 480                         throw new UnexpectedValueException( "Cannot set a negative read server index" );
 481                 }
 482
 483                 if ( $group === false ) {
 484                         $this->genericReadIndex = $index;
 485                 } else {
 486                         $this->readIndexByGroup[$group] = $index;
 487                 }
 488         }
 489
 490         /**
 491          * @param array $loads List of server weights
 492          * @param string|bool $domain
 493          * @return array (reader index, lagged replica mode) or false on failure
 494          */
 495         private function pickReaderIndex( array $loads, $domain = false ) {
 496                 if ( $loads === [] ) {
 497                         throw new InvalidArgumentException( "Server configuration array is empty" );
 498                 }
 499
 500                 /** @var int|bool $i Index of selected server */
 501                 $i = false;
 502                 /** @var bool $laggedReplicaMode Whether server is considered lagged */
 503                 $laggedReplicaMode = false;
 504
 505                 // Quickly look through the available servers for a server that meets criteria...
 506                 $currentLoads = $loads;
 507                 while ( count( $currentLoads ) ) {
 508                         if ( $this->allowLagged || $laggedReplicaMode ) {
 509                                 $i = ArrayUtils::pickRandom( $currentLoads );
 510                         } else {
 511                                 $i = false;
 512                                 if ( $this->waitForPos && $this->waitForPos->asOfTime() ) {
 513                                         // "chronologyCallback" sets "waitForPos" for session consistency.
 514                                         // This triggers doWait() after connect, so it's especially good to
 515                                         // avoid lagged servers so as to avoid excessive delay in that method.
 516                                         $ago = microtime( true ) - $this->waitForPos->asOfTime();
 517                                         // Aim for <= 1 second of waiting (being too picky can backfire)
 518                                         $i = $this->getRandomNonLagged( $currentLoads, $domain, $ago + 1 );
 519                                 }
 520                                 if ( $i === false ) {
 521                                         // Any server with less lag than it's 'max lag' param is preferable
 522                                         $i = $this->getRandomNonLagged( $currentLoads, $domain );
 523                                 }
 524                                 if ( $i === false && count( $currentLoads ) != 0 ) {
 525                                         // All replica DBs lagged. Switch to read-only mode
 526                                         $this->replLogger->error(
 527                                                 __METHOD__ . ": all replica DBs lagged. Switch to read-only mode" );
 528                                         $i = ArrayUtils::pickRandom( $currentLoads );
 529                                         $laggedReplicaMode = true;
 530                                 }
 531                         }
 532
 533                         if ( $i === false ) {
 534                                 // pickRandom() returned false.
 535                                 // This is permanent and means the configuration or the load monitor
 536                                 // wants us to return false.
 537                                 $this->connLogger->debug( __METHOD__ . ": pickRandom() returned false" );
 538
 539                                 return [ false, false ];
 540                         }
 541
 542                         $serverName = $this->getServerName( $i );
 543                         $this->connLogger->debug( __METHOD__ . ": Using reader #$i: $serverName..." );
 544
 545                         $conn = $this->openConnection( $i, $domain );
 546                         if ( !$conn ) {
 547                                 $this->connLogger->warning( __METHOD__ . ": Failed connecting to $i/$domain" );
 548                                 unset( $currentLoads[$i] ); // avoid this server next iteration
 549                                 $i = false;
 550                                 continue;
 551                         }
 552
 553                         // Decrement reference counter, we are finished with this connection.
 554                         // It will be incremented for the caller later.
 555                         if ( $domain !== false ) {
 556                                 $this->reuseConnection( $conn );
 557                         }
 558
 559                         // Return this server
 560                         break;
 561                 }
 562
 563                 // If all servers were down, quit now
 564                 if ( $currentLoads === [] ) {
 565                         $this->connLogger->error( __METHOD__ . ": all servers down" );
 566                 }
 567
 568                 return [ $i, $laggedReplicaMode ];
 569         }
 570
 571         public function waitFor( $pos ) {
 572                 $oldPos = $this->waitForPos;
 573                 try {
 574                         $this->waitForPos = $pos;
 575                         // If a generic reader connection was already established, then wait now
 576                         if ( $this->genericReadIndex > 0 && !$this->doWait( $this->genericReadIndex ) ) {
 577                                 $this->laggedReplicaMode = true;
 578                         }
 579                         // Otherwise, wait until a connection is established in getReaderIndex()
 580                 } finally {
 581                         // Restore the older position if it was higher since this is used for lag-protection
 582                         $this->setWaitForPositionIfHigher( $oldPos );
 583                 }
 584         }
 585
 586         public function waitForOne( $pos, $timeout = null ) {
 587                 $oldPos = $this->waitForPos;
 588                 try {
 589                         $this->waitForPos = $pos;
 590
 591                         $i = $this->genericReadIndex;
 592                         if ( $i <= 0 ) {
 593                                 // Pick a generic replica DB if there isn't one yet
 594                                 $readLoads = $this->genericLoads;
 595                                 unset( $readLoads[$this->getWriterIndex()] ); // replica DBs only
 596                                 $readLoads = array_filter( $readLoads ); // with non-zero load
 597                                 $i = ArrayUtils::pickRandom( $readLoads );
 598                         }
 599
 600                         if ( $i > 0 ) {
 601                                 $ok = $this->doWait( $i, true, $timeout );
 602                         } else {
 603                                 $ok = true; // no applicable loads
 604                         }
 605                 } finally {
 606                         # Restore the old position, as this is not used for lag-protection but for throttling
 607                         $this->waitForPos = $oldPos;
 608                 }
 609
 610                 return $ok;
 611         }
 612
 613         public function waitForAll( $pos, $timeout = null ) {
 614                 $timeout = $timeout ?: $this->waitTimeout;
 615
 616                 $oldPos = $this->waitForPos;
 617                 try {
 618                         $this->waitForPos = $pos;
 619                         $serverCount = count( $this->servers );
 620
 621                         $ok = true;
 622                         for ( $i = 1; $i < $serverCount; $i++ ) {
 623                                 if ( $this->genericLoads[$i] > 0 ) {
 624                                         $start = microtime( true );
 625                                         $ok = $this->doWait( $i, true, $timeout ) && $ok;
 626                                         $timeout -= intval( microtime( true ) - $start );
 627                                         if ( $timeout <= 0 ) {
 628                                                 break; // timeout reached
 629                                         }
 630                                 }
 631                         }
 632                 } finally {
 633                         # Restore the old position, as this is not used for lag-protection but for throttling
 634                         $this->waitForPos = $oldPos;
 635                 }
 636
 637                 return $ok;
 638         }
 639
 640         /**
 641          * @param DBMasterPos|bool $pos
 642          */
 643         private function setWaitForPositionIfHigher( $pos ) {
 644                 if ( !$pos ) {
 645                         return;
 646                 }
 647
 648                 if ( !$this->waitForPos || $pos->hasReached( $this->waitForPos ) ) {
 649                         $this->waitForPos = $pos;
 650                 }
 651         }
 652
 653         public function getAnyOpenConnection( $i, $flags = 0 ) {
 654                 $i = ( $i === self::DB_MASTER ) ? $this->getWriterIndex() : $i;
 655                 $autocommit = ( ( $flags & self::CONN_TRX_AUTOCOMMIT ) == self::CONN_TRX_AUTOCOMMIT );
 656
 657                 foreach ( $this->conns as $connsByServer ) {
 658                         if ( $i === self::DB_REPLICA ) {
 659                                 $indexes = array_keys( $connsByServer );
 660                         } else {
 661                                 $indexes = isset( $connsByServer[$i] ) ? [ $i ] : [];
 662                         }
 663
 664                         foreach ( $indexes as $index ) {
 665                                 foreach ( $connsByServer[$index] as $conn ) {
 666                                         if ( !$conn->isOpen() ) {
 667                                                 continue; // some sort of error occured?
 668                                         }
 669                                         if ( !$autocommit || $conn->getLBInfo( 'autoCommitOnly' ) ) {
 670                                                 return $conn;
 671                                         }
 672                                 }
 673                         }
 674                 }
 675
 676                 return false;
 677         }
 678
 679         /**
 680          * Wait for a given replica DB to catch up to the master pos stored in $this
 681          * @param int $index Server index
 682          * @param bool $open Check the server even if a new connection has to be made
 683          * @param int|null $timeout Max seconds to wait; default is "waitTimeout" given to __construct()
 684          * @return bool
 685          */
 686         protected function doWait( $index, $open = false, $timeout = null ) {
 687                 $timeout = max( 1, intval( $timeout ?: $this->waitTimeout ) );
 688
 689                 // Check if we already know that the DB has reached this point
 690                 $server = $this->getServerName( $index );
 691                 $key = $this->srvCache->makeGlobalKey( __CLASS__, 'last-known-pos', $server, 'v1' );
 692                 /** @var DBMasterPos $knownReachedPos */
 693                 $knownReachedPos = $this->srvCache->get( $key );
 694                 if (
 695                         $knownReachedPos instanceof DBMasterPos &&
 696                         $knownReachedPos->hasReached( $this->waitForPos )
 697                 ) {
 698                         $this->replLogger->debug(
 699                                 __METHOD__ .
 700                                 ': replica DB {dbserver} known to be caught up (pos >= $knownReachedPos).',
 701                                 [ 'dbserver' => $server ]
 702                         );
 703                         return true;
 704                 }
 705
 706                 // Find a connection to wait on, creating one if needed and allowed
 707                 $close = false; // close the connection afterwards
 708                 $conn = $this->getAnyOpenConnection( $index );
 709                 if ( !$conn ) {
 710                         if ( !$open ) {
 711                                 $this->replLogger->debug(
 712                                         __METHOD__ . ': no connection open for {dbserver}',
 713                                         [ 'dbserver' => $server ]
 714                                 );
 715
 716                                 return false;
 717                         } else {
 718                                 $conn = $this->openConnection( $index, self::DOMAIN_ANY );
 719                                 if ( !$conn ) {
 720                                         $this->replLogger->warning(
 721                                                 __METHOD__ . ': failed to connect to {dbserver}',
 722                                                 [ 'dbserver' => $server ]
 723                                         );
 724
 725                                         return false;
 726                                 }
 727                                 // Avoid connection spam in waitForAll() when connections
 728                                 // are made just for the sake of doing this lag check.
 729                                 $close = true;
 730                         }
 731                 }
 732
 733                 $this->replLogger->info(
 734                         __METHOD__ .
 735                         ': waiting for replica DB {dbserver} to catch up...',
 736                         [ 'dbserver' => $server ]
 737                 );
 738
 739                 $result = $conn->masterPosWait( $this->waitForPos, $timeout );
 740
 741                 if ( $result === null ) {
 742                         $this->replLogger->warning(
 743                                 __METHOD__ . ': Errored out waiting on {host} pos {pos}',
 744                                 [
 745                                         'host' => $server,
 746                                         'pos' => $this->waitForPos,
 747                                         'trace' => ( new RuntimeException() )->getTraceAsString()
 748                                 ]
 749                         );
 750                         $ok = false;
 751                 } elseif ( $result == -1 ) {
 752                         $this->replLogger->warning(
 753                                 __METHOD__ . ': Timed out waiting on {host} pos {pos}',
 754                                 [
 755                                         'host' => $server,
 756                                         'pos' => $this->waitForPos,
 757                                         'trace' => ( new RuntimeException() )->getTraceAsString()
 758                                 ]
 759                         );
 760                         $ok = false;
 761                 } else {
 762                         $this->replLogger->debug( __METHOD__ . ": done waiting" );
 763                         $ok = true;
 764                         // Remember that the DB reached this point
 765                         $this->srvCache->set( $key, $this->waitForPos, BagOStuff::TTL_DAY );
 766                 }
 767
 768                 if ( $close ) {
 769                         $this->closeConnection( $conn );
 770                 }
 771
 772                 return $ok;
 773         }
 774
 775         public function getConnection( $i, $groups = [], $domain = false, $flags = 0 ) {
 776                 if ( $i === null || $i === false ) {
 777                         throw new InvalidArgumentException( "Cannot connect without a server index" );
 778                 }
 779
 780                 $domain = $this->resolveDomainID( $domain );
 781                 $masterOnly = ( $i == self::DB_MASTER || $i == $this->getWriterIndex() );
 782
 783                 if ( ( $flags & self::CONN_TRX_AUTOCOMMIT ) === self::CONN_TRX_AUTOCOMMIT ) {
 784                         // Assuming all servers are of the same type (or similar), which is overwhelmingly
 785                         // the case, use the master server information to get the attributes. The information
 786                         // for $i cannot be used since it might be DB_REPLICA, which might require connection
 787                         // attempts in order to be resolved into a real server index.
 788                         $attributes = $this->getServerAttributes( $this->getWriterIndex() );
 789                         if ( $attributes[Database::ATTR_DB_LEVEL_LOCKING] ) {
 790                                 // Callers sometimes want to (a) escape REPEATABLE-READ stateness without locking
 791                                 // rows (e.g. FOR UPDATE) or (b) make small commits during a larger transactions
 792                                 // to reduce lock contention. None of these apply for sqlite and using separate
 793                                 // connections just causes self-deadlocks.
 794                                 $flags &= ~self::CONN_TRX_AUTOCOMMIT;
 795                                 $this->connLogger->info( __METHOD__ .
 796                                         ': ignoring CONN_TRX_AUTOCOMMIT to avoid deadlocks.' );
 797                         }
 798                 }
 799
 800                 // Number of connections made before getting the server index and handle
 801                 $priorConnectionsMade = $this->connsOpened;
 802                 // Decide which server to use (might trigger new connections)
 803                 $serverIndex = $this->getConnectionIndex( $i, $groups, $domain );
 804                 // Get an open connection to that server (might trigger a new connection)
 805                 $conn = $this->openConnection( $serverIndex, $domain, $flags );
 806                 if ( !$conn ) {
 807                         $this->reportConnectionError();
 808                         return null; // unreachable due to exception
 809                 }
 810
 811                 // Profile any new connections caused by this method
 812                 if ( $this->connsOpened > $priorConnectionsMade ) {
 813                         $host = $conn->getServer();
 814                         $dbname = $conn->getDBname();
 815                         $this->trxProfiler->recordConnection( $host, $dbname, $masterOnly );
 816                 }
 817
 818                 if ( $serverIndex == $this->getWriterIndex() ) {
 819                         // If the load balancer is read-only, perhaps due to replication lag, then master
 820                         // DB handles will reflect that. Note that Database::assertIsWritableMaster() takes
 821                         // care of replica DB handles whereas getReadOnlyReason() would cause infinite loops.
 822                         $conn->setLBInfo( 'readOnlyReason', $this->getReadOnlyReason( $domain, $conn ) );
 823                 }
 824
 825                 return $conn;
 826         }
 827
 828         public function reuseConnection( IDatabase $conn ) {
 829                 $serverIndex = $conn->getLBInfo( 'serverIndex' );
 830                 $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 831                 if ( $serverIndex === null || $refCount === null ) {
 832                         /**
 833                          * This can happen in code like:
 834                          *   foreach ( $dbs as $db ) {
 835                          *     $conn = $lb->getConnection( $lb::DB_REPLICA, [], $db );
 836                          *     ...
 837                          *     $lb->reuseConnection( $conn );
 838                          *   }
 839                          * When a connection to the local DB is opened in this way, reuseConnection()
 840                          * should be ignored
 841                          */
 842                         return;
 843                 } elseif ( $conn instanceof DBConnRef ) {
 844                         // DBConnRef already handles calling reuseConnection() and only passes the live
 845                         // Database instance to this method. Any caller passing in a DBConnRef is broken.
 846                         $this->connLogger->error(
 847                                 __METHOD__ . ": got DBConnRef instance.\n" .
 848                                 ( new RuntimeException() )->getTraceAsString() );
 849
 850                         return;
 851                 }
 852
 853                 if ( $this->disabled ) {
 854                         return; // DBConnRef handle probably survived longer than the LoadBalancer
 855                 }
 856
 857                 if ( $conn->getLBInfo( 'autoCommitOnly' ) ) {
 858                         $connFreeKey = self::KEY_FOREIGN_FREE_NOROUND;
 859                         $connInUseKey = self::KEY_FOREIGN_INUSE_NOROUND;
 860                 } else {
 861                         $connFreeKey = self::KEY_FOREIGN_FREE;
 862                         $connInUseKey = self::KEY_FOREIGN_INUSE;
 863                 }
 864
 865                 $domain = $conn->getDomainID();
 866                 if ( !isset( $this->conns[$connInUseKey][$serverIndex][$domain] ) ) {
 867                         throw new InvalidArgumentException(
 868                                 "Connection $serverIndex/$domain not found; it may have already been freed" );
 869                 } elseif ( $this->conns[$connInUseKey][$serverIndex][$domain] !== $conn ) {
 870                         throw new InvalidArgumentException(
 871                                 "Connection $serverIndex/$domain mismatched; it may have already been freed" );
 872                 }
 873
 874                 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
 875                 if ( $refCount <= 0 ) {
 876                         $this->conns[$connFreeKey][$serverIndex][$domain] = $conn;
 877                         unset( $this->conns[$connInUseKey][$serverIndex][$domain] );
 878                         if ( !$this->conns[$connInUseKey][$serverIndex] ) {
 879                                 unset( $this->conns[$connInUseKey][$serverIndex] ); // clean up
 880                         }
 881                         $this->connLogger->debug( __METHOD__ . ": freed connection $serverIndex/$domain" );
 882                 } else {
 883                         $this->connLogger->debug( __METHOD__ .
 884                                 ": reference count for $serverIndex/$domain reduced to $refCount" );
 885                 }
 886         }
 887
 888         public function getConnectionRef( $i, $groups = [], $domain = false, $flags = 0 ) {
 889                 $domain = $this->resolveDomainID( $domain );
 890                 $role = $this->getRoleFromIndex( $i );
 891
 892                 return new DBConnRef( $this, $this->getConnection( $i, $groups, $domain, $flags ), $role );
 893         }
 894
 895         public function getLazyConnectionRef( $i, $groups = [], $domain = false, $flags = 0 ) {
 896                 $domain = $this->resolveDomainID( $domain );
 897                 $role = $this->getRoleFromIndex( $i );
 898
 899                 return new DBConnRef( $this, [ $i, $groups, $domain, $flags ], $role );
 900         }
 901
 902         public function getMaintenanceConnectionRef( $i, $groups = [], $domain = false, $flags = 0 ) {
 903                 $domain = $this->resolveDomainID( $domain );
 904                 $role = $this->getRoleFromIndex( $i );
 905
 906                 return new MaintainableDBConnRef(
 907                         $this, $this->getConnection( $i, $groups, $domain, $flags ), $role );
 908         }
 909
 910         /**
 911          * @param int $i Server index or DB_MASTER/DB_REPLICA
 912          * @return int One of DB_MASTER/DB_REPLICA
 913          */
 914         private function getRoleFromIndex( $i ) {
 915                 return ( $i === self::DB_MASTER || $i === $this->getWriterIndex() )
 916                         ? self::DB_MASTER
 917                         : self::DB_REPLICA;
 918         }
 919
 920         public function openConnection( $i, $domain = false, $flags = 0 ) {
 921                 $domain = $this->resolveDomainID( $domain );
 922
 923                 if ( !$this->connectionAttempted && $this->chronologyCallback ) {
 924                         // Load any "waitFor" positions before connecting so that doWait() is triggered
 925                         $this->connLogger->debug( __METHOD__ . ': calling initLB() before first connection.' );
 926                         $this->connectionAttempted = true;
 927                         ( $this->chronologyCallback )( $this );
 928                 }
 929
 930                 $conn = $this->localDomain->equals( $domain )
 931                         ? $this->openLocalConnection( $i, $flags )
 932                         : $this->openForeignConnection( $i, $domain, $flags );
 933
 934                 if ( $conn instanceof IDatabase && !$conn->isOpen() ) {
 935                         // Connection was made but later unrecoverably lost for some reason.
 936                         // Do not return a handle that will just throw exceptions on use,
 937                         // but let the calling code (e.g. getReaderIndex) try another server.
 938                         $this->errorConnection = $conn;
 939                         $conn = false;
 940                 }
 941
 942                 if (
 943                         $conn instanceof IDatabase &&
 944                         ( ( $flags & self::CONN_TRX_AUTOCOMMIT ) == self::CONN_TRX_AUTOCOMMIT )
 945                 ) {
 946                         if ( $conn->trxLevel() ) { // sanity
 947                                 throw new DBUnexpectedError(
 948                                         $conn,
 949                                         'Handle requested with CONN_TRX_AUTOCOMMIT yet it has a transaction'
 950                                 );
 951                         }
 952
 953                         $conn->clearFlag( $conn::DBO_TRX ); // auto-commit mode
 954                 }
 955
 956                 return $conn;
 957         }
 958
 959         /**
 960          * Open a connection to a local DB, or return one if it is already open.
 961          *
 962          * On error, returns false, and the connection which caused the
 963          * error will be available via $this->errorConnection.
 964          *
 965          * @note If disable() was called on this LoadBalancer, this method will throw a DBAccessError.
 966          *
 967          * @param int $i Server index
 968          * @param int $flags Class CONN_* constant bitfield
 969          * @return Database
 970          */
 971         private function openLocalConnection( $i, $flags = 0 ) {
 972                 // Connection handles required to be in auto-commit mode use a separate connection
 973                 // pool since the main pool is effected by implicit and explicit transaction rounds
 974                 $autoCommit = ( ( $flags & self::CONN_TRX_AUTOCOMMIT ) == self::CONN_TRX_AUTOCOMMIT );
 975
 976                 $connKey = $autoCommit ? self::KEY_LOCAL_NOROUND : self::KEY_LOCAL;
 977                 if ( isset( $this->conns[$connKey][$i][0] ) ) {
 978                         $conn = $this->conns[$connKey][$i][0];
 979                 } else {
 980                         if ( !isset( $this->servers[$i] ) || !is_array( $this->servers[$i] ) ) {
 981                                 throw new InvalidArgumentException( "No server with index '$i'" );
 982                         }
 983                         // Open a new connection
 984                         $server = $this->servers[$i];
 985                         $server['serverIndex'] = $i;
 986                         $server['autoCommitOnly'] = $autoCommit;
 987                         $conn = $this->reallyOpenConnection( $server, $this->localDomain );
 988                         $host = $this->getServerName( $i );
 989                         if ( $conn->isOpen() ) {
 990                                 $this->connLogger->debug(
 991                                         __METHOD__ . ": connected to database $i at '$host'." );
 992                                 $this->conns[$connKey][$i][0] = $conn;
 993                         } else {
 994                                 $this->connLogger->warning(
 995                                         __METHOD__ . ": failed to connect to database $i at '$host'." );
 996                                 $this->errorConnection = $conn;
 997                                 $conn = false;
 998                         }
 999                 }
1000
1001                 // Final sanity check to make sure the right domain is selected
1002                 if (
1003                         $conn instanceof IDatabase &&
1004                         !$this->localDomain->isCompatible( $conn->getDomainID() )
1005                 ) {
1006                         throw new UnexpectedValueException(
1007                                 "Got connection to '{$conn->getDomainID()}', " .
1008                                 "but expected local domain ('{$this->localDomain}')" );
1009                 }
1010
1011                 return $conn;
1012         }
1013
1014         /**
1015          * Open a connection to a foreign DB, or return one if it is already open.
1016          *
1017          * Increments a reference count on the returned connection which locks the
1018          * connection to the requested domain. This reference count can be
1019          * decremented by calling reuseConnection().
1020          *
1021          * If a connection is open to the appropriate server already, but with the wrong
1022          * database, it will be switched to the right database and returned, as long as
1023          * it has been freed first with reuseConnection().
1024          *
1025          * On error, returns false, and the connection which caused the
1026          * error will be available via $this->errorConnection.
1027          *
1028          * @note If disable() was called on this LoadBalancer, this method will throw a DBAccessError.
1029          *
1030          * @param int $i Server index
1031          * @param string $domain Domain ID to open
1032          * @param int $flags Class CONN_* constant bitfield
1033          * @return Database|bool Returns false on connection error
1034          * @throws DBError When database selection fails
1035          */
1036         private function openForeignConnection( $i, $domain, $flags = 0 ) {
1037                 $domainInstance = DatabaseDomain::newFromId( $domain );
1038                 // Connection handles required to be in auto-commit mode use a separate connection
1039                 // pool since the main pool is effected by implicit and explicit transaction rounds
1040                 $autoCommit = ( ( $flags & self::CONN_TRX_AUTOCOMMIT ) == self::CONN_TRX_AUTOCOMMIT );
1041
1042                 if ( $autoCommit ) {
1043                         $connFreeKey = self::KEY_FOREIGN_FREE_NOROUND;
1044                         $connInUseKey = self::KEY_FOREIGN_INUSE_NOROUND;
1045                 } else {
1046                         $connFreeKey = self::KEY_FOREIGN_FREE;
1047                         $connInUseKey = self::KEY_FOREIGN_INUSE;
1048                 }
1049
1050                 /** @var Database $conn */
1051                 $conn = null;
1052
1053                 if ( isset( $this->conns[$connInUseKey][$i][$domain] ) ) {
1054                         // Reuse an in-use connection for the same domain
1055                         $conn = $this->conns[$connInUseKey][$i][$domain];
1056                         $this->connLogger->debug( __METHOD__ . ": reusing connection $i/$domain" );
1057                 } elseif ( isset( $this->conns[$connFreeKey][$i][$domain] ) ) {
1058                         // Reuse a free connection for the same domain
1059                         $conn = $this->conns[$connFreeKey][$i][$domain];
1060                         unset( $this->conns[$connFreeKey][$i][$domain] );
1061                         $this->conns[$connInUseKey][$i][$domain] = $conn;
1062                         $this->connLogger->debug( __METHOD__ . ": reusing free connection $i/$domain" );
1063                 } elseif ( !empty( $this->conns[$connFreeKey][$i] ) ) {
1064                         // Reuse a free connection from another domain if possible
1065                         foreach ( $this->conns[$connFreeKey][$i] as $oldDomain => $conn ) {
1066                                 if ( $domainInstance->getDatabase() !== null ) {
1067                                         // Check if changing the database will require a new connection.
1068                                         // In that case, leave the connection handle alone and keep looking.
1069                                         // This prevents connections from being closed mid-transaction and can
1070                                         // also avoid overhead if the same database will later be requested.
1071                                         if (
1072                                                 $conn->databasesAreIndependent() &&
1073                                                 $conn->getDBname() !== $domainInstance->getDatabase()
1074                                         ) {
1075                                                 continue;
1076                                         }
1077                                         // Select the new database, schema, and prefix
1078                                         $conn->selectDomain( $domainInstance );
1079                                 } else {
1080                                         // Stay on the current database, but update the schema/prefix
1081                                         $conn->dbSchema( $domainInstance->getSchema() );
1082                                         $conn->tablePrefix( $domainInstance->getTablePrefix() );
1083                                 }
1084                                 unset( $this->conns[$connFreeKey][$i][$oldDomain] );
1085                                 // Note that if $domain is an empty string, getDomainID() might not match it
1086                                 $this->conns[$connInUseKey][$i][$conn->getDomainID()] = $conn;
1087                                 $this->connLogger->debug( __METHOD__ .
1088                                         ": reusing free connection from $oldDomain for $domain" );
1089                                 break;
1090                         }
1091                 }
1092
1093                 if ( !$conn ) {
1094                         if ( !isset( $this->servers[$i] ) || !is_array( $this->servers[$i] ) ) {
1095                                 throw new InvalidArgumentException( "No server with index '$i'" );
1096                         }
1097                         // Open a new connection
1098                         $server = $this->servers[$i];
1099                         $server['serverIndex'] = $i;
1100                         $server['foreignPoolRefCount'] = 0;
1101                         $server['foreign'] = true;
1102                         $server['autoCommitOnly'] = $autoCommit;
1103                         $conn = $this->reallyOpenConnection( $server, $domainInstance );
1104                         if ( !$conn->isOpen() ) {
1105                                 $this->connLogger->warning( __METHOD__ . ": connection error for $i/$domain" );
1106                                 $this->errorConnection = $conn;
1107                                 $conn = false;
1108                         } else {
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__ . ": opened new connection for $i/$domain" );
1112                         }
1113                 }
1114
1115                 if ( $conn instanceof IDatabase ) {
1116                         // Final sanity check to make sure the right domain is selected
1117                         if ( !$domainInstance->isCompatible( $conn->getDomainID() ) ) {
1118                                 throw new UnexpectedValueException(
1119                                         "Got connection to '{$conn->getDomainID()}', but expected '$domain'" );
1120                         }
1121                         // Increment reference count
1122                         $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
1123                         $conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
1124                 }
1125
1126                 return $conn;
1127         }
1128
1129         public function getServerAttributes( $i ) {
1130                 return Database::attributesFromType(
1131                         $this->getServerType( $i ),
1132                         $this->servers[$i]['driver'] ?? null
1133                 );
1134         }
1135
1136         /**
1137          * Test if the specified index represents an open connection
1138          *
1139          * @param int $index Server index
1140          * @private
1141          * @return bool
1142          */
1143         private function isOpen( $index ) {
1144                 if ( !is_int( $index ) ) {
1145                         return false;
1146                 }
1147
1148                 return (bool)$this->getAnyOpenConnection( $index );
1149         }
1150
1151         /**
1152          * Open a new network connection to a server (uncached)
1153          *
1154          * Returns a Database object whether or not the connection was successful.
1155          *
1156          * @param array $server
1157          * @param DatabaseDomain $domain Domain the connection is for, possibly unspecified
1158          * @return Database
1159          * @throws DBAccessError
1160          * @throws InvalidArgumentException
1161          */
1162         protected function reallyOpenConnection( array $server, DatabaseDomain $domain ) {
1163                 if ( $this->disabled ) {
1164                         throw new DBAccessError();
1165                 }
1166
1167                 if ( $domain->getDatabase() === null ) {
1168                         // The database domain does not specify a DB name and some database systems require a
1169                         // valid DB specified on connection. The $server configuration array contains a default
1170                         // DB name to use for connections in such cases.
1171                         if ( $server['type'] === 'mysql' ) {
1172                                 // For MySQL, DATABASE and SCHEMA are synonyms, connections need not specify a DB,
1173                                 // and the DB name in $server might not exist due to legacy reasons (the default
1174                                 // domain used to ignore the local LB domain, even when mismatched).
1175                                 $server['dbname'] = null;
1176                         }
1177                 } else {
1178                         $server['dbname'] = $domain->getDatabase();
1179                 }
1180
1181                 if ( $domain->getSchema() !== null ) {
1182                         $server['schema'] = $domain->getSchema();
1183                 }
1184
1185                 // It is always possible to connect with any prefix, even the empty string
1186                 $server['tablePrefix'] = $domain->getTablePrefix();
1187
1188                 // Let the handle know what the cluster master is (e.g. "db1052")
1189                 $masterName = $this->getServerName( $this->getWriterIndex() );
1190                 $server['clusterMasterHost'] = $masterName;
1191
1192                 // Log when many connection are made on requests
1193                 if ( ++$this->connsOpened >= self::CONN_HELD_WARN_THRESHOLD ) {
1194                         $this->perfLogger->warning( __METHOD__ . ": " .
1195                                 "{$this->connsOpened}+ connections made (master=$masterName)" );
1196                 }
1197
1198                 $server['srvCache'] = $this->srvCache;
1199                 // Set loggers and profilers
1200                 $server['connLogger'] = $this->connLogger;
1201                 $server['queryLogger'] = $this->queryLogger;
1202                 $server['errorLogger'] = $this->errorLogger;
1203                 $server['deprecationLogger'] = $this->deprecationLogger;
1204                 $server['profiler'] = $this->profiler;
1205                 $server['trxProfiler'] = $this->trxProfiler;
1206                 // Use the same agent and PHP mode for all DB handles
1207                 $server['cliMode'] = $this->cliMode;
1208                 $server['agent'] = $this->agent;
1209                 // Use DBO_DEFAULT flags by default for LoadBalancer managed databases. Assume that the
1210                 // application calls LoadBalancer::commitMasterChanges() before the PHP script completes.
1211                 $server['flags'] = $server['flags'] ?? IDatabase::DBO_DEFAULT;
1212
1213                 // Create a live connection object
1214                 try {
1215                         $db = Database::factory( $server['type'], $server );
1216                 } catch ( DBConnectionError $e ) {
1217                         // FIXME: This is probably the ugliest thing I have ever done to
1218                         // PHP. I'm half-expecting it to segfault, just out of disgust. -- TS
1219                         $db = $e->db;
1220                 }
1221
1222                 $db->setLBInfo( $server );
1223                 $db->setLazyMasterHandle(
1224                         $this->getLazyConnectionRef( self::DB_MASTER, [], $db->getDomainID() )
1225                 );
1226                 $db->setTableAliases( $this->tableAliases );
1227                 $db->setIndexAliases( $this->indexAliases );
1228
1229                 if ( $server['serverIndex'] === $this->getWriterIndex() ) {
1230                         if ( $this->trxRoundId !== false ) {
1231                                 $this->applyTransactionRoundFlags( $db );
1232                         }
1233                         foreach ( $this->trxRecurringCallbacks as $name => $callback ) {
1234                                 $db->setTransactionListener( $name, $callback );
1235                         }
1236                 }
1237
1238                 return $db;
1239         }
1240
1241         /**
1242          * @throws DBConnectionError
1243          */
1244         private function reportConnectionError() {
1245                 $conn = $this->errorConnection; // the connection which caused the error
1246                 $context = [
1247                         'method' => __METHOD__,
1248                         'last_error' => $this->lastError,
1249                 ];
1250
1251                 if ( $conn instanceof IDatabase ) {
1252                         $context['db_server'] = $conn->getServer();
1253                         $this->connLogger->warning(
1254                                 __METHOD__ . ": connection error: {last_error} ({db_server})",
1255                                 $context
1256                         );
1257
1258                         throw new DBConnectionError( $conn, "{$this->lastError} ({$context['db_server']})" );
1259                 } else {
1260                         // No last connection, probably due to all servers being too busy
1261                         $this->connLogger->error(
1262                                 __METHOD__ .
1263                                 ": LB failure with no last connection. Connection error: {last_error}",
1264                                 $context
1265                         );
1266
1267                         // If all servers were busy, "lastError" will contain something sensible
1268                         throw new DBConnectionError( null, $this->lastError );
1269                 }
1270         }
1271
1272         public function getWriterIndex() {
1273                 return 0;
1274         }
1275
1276         public function haveIndex( $i ) {
1277                 return array_key_exists( $i, $this->servers );
1278         }
1279
1280         public function isNonZeroLoad( $i ) {
1281                 return array_key_exists( $i, $this->servers ) && $this->genericLoads[$i] != 0;
1282         }
1283
1284         public function getServerCount() {
1285                 return count( $this->servers );
1286         }
1287
1288         public function getServerName( $i ) {
1289                 $name = $this->servers[$i]['hostName'] ?? $this->servers[$i]['host'] ?? '';
1290
1291                 return ( $name != '' ) ? $name : 'localhost';
1292         }
1293
1294         public function getServerInfo( $i ) {
1295                 return $this->servers[$i] ?? false;
1296         }
1297
1298         public function getServerType( $i ) {
1299                 return $this->servers[$i]['type'] ?? 'unknown';
1300         }
1301
1302         public function getMasterPos() {
1303                 # If this entire request was served from a replica DB without opening a connection to the
1304                 # master (however unlikely that may be), then we can fetch the position from the replica DB.
1305                 $masterConn = $this->getAnyOpenConnection( $this->getWriterIndex() );
1306                 if ( !$masterConn ) {
1307                         $serverCount = count( $this->servers );
1308                         for ( $i = 1; $i < $serverCount; $i++ ) {
1309                                 $conn = $this->getAnyOpenConnection( $i );
1310                                 if ( $conn ) {
1311                                         return $conn->getReplicaPos();
1312                                 }
1313                         }
1314                 } else {
1315                         return $masterConn->getMasterPos();
1316                 }
1317
1318                 return false;
1319         }
1320
1321         public function disable() {
1322                 $this->closeAll();
1323                 $this->disabled = true;
1324         }
1325
1326         public function closeAll() {
1327                 $fname = __METHOD__;
1328                 $this->forEachOpenConnection( function ( IDatabase $conn ) use ( $fname ) {
1329                         $host = $conn->getServer();
1330                         $this->connLogger->debug(
1331                                 $fname . ": closing connection to database '$host'." );
1332                         $conn->close();
1333                 } );
1334
1335                 $this->conns = [
1336                         self::KEY_LOCAL => [],
1337                         self::KEY_FOREIGN_INUSE => [],
1338                         self::KEY_FOREIGN_FREE => [],
1339                         self::KEY_LOCAL_NOROUND => [],
1340                         self::KEY_FOREIGN_INUSE_NOROUND => [],
1341                         self::KEY_FOREIGN_FREE_NOROUND => []
1342                 ];
1343                 $this->connsOpened = 0;
1344         }
1345
1346         public function closeConnection( IDatabase $conn ) {
1347                 if ( $conn instanceof DBConnRef ) {
1348                         // Avoid calling close() but still leaving the handle in the pool
1349                         throw new RuntimeException( 'Cannot close DBConnRef instance; it must be shareable' );
1350                 }
1351
1352                 $serverIndex = $conn->getLBInfo( 'serverIndex' );
1353                 foreach ( $this->conns as $type => $connsByServer ) {
1354                         if ( !isset( $connsByServer[$serverIndex] ) ) {
1355                                 continue;
1356                         }
1357
1358                         foreach ( $connsByServer[$serverIndex] as $i => $trackedConn ) {
1359                                 if ( $conn === $trackedConn ) {
1360                                         $host = $this->getServerName( $i );
1361                                         $this->connLogger->debug(
1362                                                 __METHOD__ . ": closing connection to database $i at '$host'." );
1363                                         unset( $this->conns[$type][$serverIndex][$i] );
1364                                         --$this->connsOpened;
1365                                         break 2;
1366                                 }
1367                         }
1368                 }
1369
1370                 $conn->close();
1371         }
1372
1373         public function commitAll( $fname = __METHOD__, $owner = null ) {
1374                 $this->commitMasterChanges( $fname, $owner );
1375                 $this->flushMasterSnapshots( $fname );
1376                 $this->flushReplicaSnapshots( $fname );
1377         }
1378
1379         public function finalizeMasterChanges( $fname = __METHOD__, $owner = null ) {
1380                 $this->assertOwnership( $fname, $owner );
1381                 $this->assertTransactionRoundStage( [ self::ROUND_CURSORY, self::ROUND_FINALIZED ] );
1382
1383                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1384                 // Loop until callbacks stop adding callbacks on other connections
1385                 $total = 0;
1386                 do {
1387                         $count = 0; // callbacks execution attempts
1388                         $this->forEachOpenMasterConnection( function ( Database $conn ) use ( &$count ) {
1389                                 // Run any pre-commit callbacks while leaving the post-commit ones suppressed.
1390                                 // Any error should cause all (peer) transactions to be rolled back together.
1391                                 $count += $conn->runOnTransactionPreCommitCallbacks();
1392                         } );
1393                         $total += $count;
1394                 } while ( $count > 0 );
1395                 // Defer post-commit callbacks until after COMMIT/ROLLBACK happens on all handles
1396                 $this->forEachOpenMasterConnection( function ( Database $conn ) {
1397                         $conn->setTrxEndCallbackSuppression( true );
1398                 } );
1399                 $this->trxRoundStage = self::ROUND_FINALIZED;
1400
1401                 return $total;
1402         }
1403
1404         public function approveMasterChanges( array $options, $fname = __METHOD__, $owner = null ) {
1405                 $this->assertOwnership( $fname, $owner );
1406                 $this->assertTransactionRoundStage( self::ROUND_FINALIZED );
1407
1408                 $limit = $options['maxWriteDuration'] ?? 0;
1409
1410                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1411                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( $limit ) {
1412                         // If atomic sections or explicit transactions are still open, some caller must have
1413                         // caught an exception but failed to properly rollback any changes. Detect that and
1414                         // throw and error (causing rollback).
1415                         $conn->assertNoOpenTransactions();
1416                         // Assert that the time to replicate the transaction will be sane.
1417                         // If this fails, then all DB transactions will be rollback back together.
1418                         $time = $conn->pendingWriteQueryDuration( $conn::ESTIMATE_DB_APPLY );
1419                         if ( $limit > 0 && $time > $limit ) {
1420                                 throw new DBTransactionSizeError(
1421                                         $conn,
1422                                         "Transaction spent $time second(s) in writes, exceeding the limit of $limit",
1423                                         [ $time, $limit ]
1424                                 );
1425                         }
1426                         // If a connection sits idle while slow queries execute on another, that connection
1427                         // may end up dropped before the commit round is reached. Ping servers to detect this.
1428                         if ( $conn->writesOrCallbacksPending() && !$conn->ping() ) {
1429                                 throw new DBTransactionError(
1430                                         $conn,
1431                                         "A connection to the {$conn->getDBname()} database was lost before commit"
1432                                 );
1433                         }
1434                 } );
1435                 $this->trxRoundStage = self::ROUND_APPROVED;
1436         }
1437
1438         public function beginMasterChanges( $fname = __METHOD__, $owner = null ) {
1439                 $this->assertOwnership( $fname, $owner );
1440                 if ( $this->trxRoundId !== false ) {
1441                         throw new DBTransactionError(
1442                                 null,
1443                                 "$fname: Transaction round '{$this->trxRoundId}' already started"
1444                         );
1445                 }
1446                 $this->assertTransactionRoundStage( self::ROUND_CURSORY );
1447
1448                 // Clear any empty transactions (no writes/callbacks) from the implicit round
1449                 $this->flushMasterSnapshots( $fname );
1450
1451                 $this->trxRoundId = $fname;
1452                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1453                 // Mark applicable handles as participating in this explicit transaction round.
1454                 // For each of these handles, any writes and callbacks will be tied to a single
1455                 // transaction. The (peer) handles will reject begin()/commit() calls unless they
1456                 // are part of an en masse commit or an en masse rollback.
1457                 $this->forEachOpenMasterConnection( function ( Database $conn ) {
1458                         $this->applyTransactionRoundFlags( $conn );
1459                 } );
1460                 $this->trxRoundStage = self::ROUND_CURSORY;
1461         }
1462
1463         public function commitMasterChanges( $fname = __METHOD__, $owner = null ) {
1464                 $this->assertOwnership( $fname, $owner );
1465                 $this->assertTransactionRoundStage( self::ROUND_APPROVED );
1466
1467                 $failures = [];
1468
1469                 /** @noinspection PhpUnusedLocalVariableInspection */
1470                 $scope = ScopedCallback::newScopedIgnoreUserAbort(); // try to ignore client aborts
1471
1472                 $restore = ( $this->trxRoundId !== false );
1473                 $this->trxRoundId = false;
1474                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1475                 // Commit any writes and clear any snapshots as well (callbacks require AUTOCOMMIT).
1476                 // Note that callbacks should already be suppressed due to finalizeMasterChanges().
1477                 $this->forEachOpenMasterConnection(
1478                         function ( IDatabase $conn ) use ( $fname, &$failures ) {
1479                                 try {
1480                                         $conn->commit( $fname, $conn::FLUSHING_ALL_PEERS );
1481                                 } catch ( DBError $e ) {
1482                                         ( $this->errorLogger )( $e );
1483                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1484                                 }
1485                         }
1486                 );
1487                 if ( $failures ) {
1488                         throw new DBTransactionError(
1489                                 null,
1490                                 "$fname: Commit failed on server(s) " . implode( "\n", array_unique( $failures ) )
1491                         );
1492                 }
1493                 if ( $restore ) {
1494                         // Unmark handles as participating in this explicit transaction round
1495                         $this->forEachOpenMasterConnection( function ( Database $conn ) {
1496                                 $this->undoTransactionRoundFlags( $conn );
1497                         } );
1498                 }
1499                 $this->trxRoundStage = self::ROUND_COMMIT_CALLBACKS;
1500         }
1501
1502         public function runMasterTransactionIdleCallbacks( $fname = __METHOD__, $owner = null ) {
1503                 $this->assertOwnership( $fname, $owner );
1504                 if ( $this->trxRoundStage === self::ROUND_COMMIT_CALLBACKS ) {
1505                         $type = IDatabase::TRIGGER_COMMIT;
1506                 } elseif ( $this->trxRoundStage === self::ROUND_ROLLBACK_CALLBACKS ) {
1507                         $type = IDatabase::TRIGGER_ROLLBACK;
1508                 } else {
1509                         throw new DBTransactionError(
1510                                 null,
1511                                 "Transaction should be in the callback stage (not '{$this->trxRoundStage}')"
1512                         );
1513                 }
1514
1515                 $oldStage = $this->trxRoundStage;
1516                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1517
1518                 // Now that the COMMIT/ROLLBACK step is over, enable post-commit callback runs
1519                 $this->forEachOpenMasterConnection( function ( Database $conn ) {
1520                         $conn->setTrxEndCallbackSuppression( false );
1521                 } );
1522
1523                 $e = null; // first exception
1524                 $fname = __METHOD__;
1525                 // Loop until callbacks stop adding callbacks on other connections
1526                 do {
1527                         // Run any pending callbacks for each connection...
1528                         $count = 0; // callback execution attempts
1529                         $this->forEachOpenMasterConnection(
1530                                 function ( Database $conn ) use ( $type, &$e, &$count ) {
1531                                         if ( $conn->trxLevel() ) {
1532                                                 return; // retry in the next iteration, after commit() is called
1533                                         }
1534                                         try {
1535                                                 $count += $conn->runOnTransactionIdleCallbacks( $type );
1536                                         } catch ( Exception $ex ) {
1537                                                 $e = $e ?: $ex;
1538                                         }
1539                                 }
1540                         );
1541                         // Clear out any active transactions left over from callbacks...
1542                         $this->forEachOpenMasterConnection( function ( Database $conn ) use ( &$e, $fname ) {
1543                                 if ( $conn->writesPending() ) {
1544                                         // A callback from another handle wrote to this one and DBO_TRX is set
1545                                         $this->queryLogger->warning( $fname . ": found writes pending." );
1546                                         $fnames = implode( ', ', $conn->pendingWriteAndCallbackCallers() );
1547                                         $this->queryLogger->warning(
1548                                                 $fname . ": found writes pending ($fnames).",
1549                                                 [
1550                                                         'db_server' => $conn->getServer(),
1551                                                         'db_name' => $conn->getDBname()
1552                                                 ]
1553                                         );
1554                                 } elseif ( $conn->trxLevel() ) {
1555                                         // A callback from another handle read from this one and DBO_TRX is set,
1556                                         // which can easily happen if there is only one DB (no replicas)
1557                                         $this->queryLogger->debug( $fname . ": found empty transaction." );
1558                                 }
1559                                 try {
1560                                         $conn->commit( $fname, $conn::FLUSHING_ALL_PEERS );
1561                                 } catch ( Exception $ex ) {
1562                                         $e = $e ?: $ex;
1563                                 }
1564                         } );
1565                 } while ( $count > 0 );
1566
1567                 $this->trxRoundStage = $oldStage;
1568
1569                 return $e;
1570         }
1571
1572         public function runMasterTransactionListenerCallbacks( $fname = __METHOD__, $owner = null ) {
1573                 $this->assertOwnership( $fname, $owner );
1574                 if ( $this->trxRoundStage === self::ROUND_COMMIT_CALLBACKS ) {
1575                         $type = IDatabase::TRIGGER_COMMIT;
1576                 } elseif ( $this->trxRoundStage === self::ROUND_ROLLBACK_CALLBACKS ) {
1577                         $type = IDatabase::TRIGGER_ROLLBACK;
1578                 } else {
1579                         throw new DBTransactionError(
1580                                 null,
1581                                 "Transaction should be in the callback stage (not '{$this->trxRoundStage}')"
1582                         );
1583                 }
1584
1585                 $e = null;
1586
1587                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1588                 $this->forEachOpenMasterConnection( function ( Database $conn ) use ( $type, &$e ) {
1589                         try {
1590                                 $conn->runTransactionListenerCallbacks( $type );
1591                         } catch ( Exception $ex ) {
1592                                 $e = $e ?: $ex;
1593                         }
1594                 } );
1595                 $this->trxRoundStage = self::ROUND_CURSORY;
1596
1597                 return $e;
1598         }
1599
1600         public function rollbackMasterChanges( $fname = __METHOD__, $owner = null ) {
1601                 $this->assertOwnership( $fname, $owner );
1602
1603                 $restore = ( $this->trxRoundId !== false );
1604                 $this->trxRoundId = false;
1605                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1606                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( $fname ) {
1607                         $conn->rollback( $fname, $conn::FLUSHING_ALL_PEERS );
1608                 } );
1609                 if ( $restore ) {
1610                         // Unmark handles as participating in this explicit transaction round
1611                         $this->forEachOpenMasterConnection( function ( Database $conn ) {
1612                                 $this->undoTransactionRoundFlags( $conn );
1613                         } );
1614                 }
1615                 $this->trxRoundStage = self::ROUND_ROLLBACK_CALLBACKS;
1616         }
1617
1618         /**
1619          * @param string|string[] $stage
1620          * @throws DBTransactionError
1621          */
1622         private function assertTransactionRoundStage( $stage ) {
1623                 $stages = (array)$stage;
1624
1625                 if ( !in_array( $this->trxRoundStage, $stages, true ) ) {
1626                         $stageList = implode(
1627                                 '/',
1628                                 array_map( function ( $v ) {
1629                                         return "'$v'";
1630                                 }, $stages )
1631                         );
1632                         throw new DBTransactionError(
1633                                 null,
1634                                 "Transaction round stage must be $stageList (not '{$this->trxRoundStage}')"
1635                         );
1636                 }
1637         }
1638
1639         /**
1640          * @param string $fname
1641          * @param int|null $owner Owner ID of the caller
1642          * @throws DBTransactionError
1643          */
1644         private function assertOwnership( $fname, $owner ) {
1645                 if ( $this->ownerId !== null && $owner !== $this->ownerId ) {
1646                         throw new DBTransactionError(
1647                                 null,
1648                                 "$fname: LoadBalancer is owned by LBFactory #{$this->ownerId} (got '$owner')."
1649                         );
1650                 }
1651         }
1652
1653         /**
1654          * Make all DB servers with DBO_DEFAULT/DBO_TRX set join the transaction round
1655          *
1656          * Some servers may have neither flag enabled, meaning that they opt out of such
1657          * transaction rounds and remain in auto-commit mode. Such behavior might be desired
1658          * when a DB server is used for something like simple key/value storage.
1659          *
1660          * @param Database $conn
1661          */
1662         private function applyTransactionRoundFlags( Database $conn ) {
1663                 if ( $conn->getLBInfo( 'autoCommitOnly' ) ) {
1664                         return; // transaction rounds do not apply to these connections
1665                 }
1666
1667                 if ( $conn->getFlag( $conn::DBO_DEFAULT ) ) {
1668                         // DBO_TRX is controlled entirely by CLI mode presence with DBO_DEFAULT.
1669                         // Force DBO_TRX even in CLI mode since a commit round is expected soon.
1670                         $conn->setFlag( $conn::DBO_TRX, $conn::REMEMBER_PRIOR );
1671                 }
1672
1673                 if ( $conn->getFlag( $conn::DBO_TRX ) ) {
1674                         $conn->setLBInfo( 'trxRoundId', $this->trxRoundId );
1675                 }
1676         }
1677
1678         /**
1679          * @param Database $conn
1680          */
1681         private function undoTransactionRoundFlags( Database $conn ) {
1682                 if ( $conn->getLBInfo( 'autoCommitOnly' ) ) {
1683                         return; // transaction rounds do not apply to these connections
1684                 }
1685
1686                 if ( $conn->getFlag( $conn::DBO_TRX ) ) {
1687                         $conn->setLBInfo( 'trxRoundId', false );
1688                 }
1689
1690                 if ( $conn->getFlag( $conn::DBO_DEFAULT ) ) {
1691                         $conn->restoreFlags( $conn::RESTORE_PRIOR );
1692                 }
1693         }
1694
1695         public function flushReplicaSnapshots( $fname = __METHOD__ ) {
1696                 $this->forEachOpenReplicaConnection( function ( IDatabase $conn ) use ( $fname ) {
1697                         $conn->flushSnapshot( $fname );
1698                 } );
1699         }
1700
1701         public function flushMasterSnapshots( $fname = __METHOD__ ) {
1702                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( $fname ) {
1703                         $conn->flushSnapshot( $fname );
1704                 } );
1705         }
1706
1707         /**
1708          * @return string
1709          * @since 1.32
1710          */
1711         public function getTransactionRoundStage() {
1712                 return $this->trxRoundStage;
1713         }
1714
1715         public function hasMasterConnection() {
1716                 return $this->isOpen( $this->getWriterIndex() );
1717         }
1718
1719         public function hasMasterChanges() {
1720                 $pending = 0;
1721                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$pending ) {
1722                         $pending |= $conn->writesOrCallbacksPending();
1723                 } );
1724
1725                 return (bool)$pending;
1726         }
1727
1728         public function lastMasterChangeTimestamp() {
1729                 $lastTime = false;
1730                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$lastTime ) {
1731                         $lastTime = max( $lastTime, $conn->lastDoneWrites() );
1732                 } );
1733
1734                 return $lastTime;
1735         }
1736
1737         public function hasOrMadeRecentMasterChanges( $age = null ) {
1738                 $age = ( $age === null ) ? $this->waitTimeout : $age;
1739
1740                 return ( $this->hasMasterChanges()
1741                         || $this->lastMasterChangeTimestamp() > microtime( true ) - $age );
1742         }
1743
1744         public function pendingMasterChangeCallers() {
1745                 $fnames = [];
1746                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$fnames ) {
1747                         $fnames = array_merge( $fnames, $conn->pendingWriteCallers() );
1748                 } );
1749
1750                 return $fnames;
1751         }
1752
1753         public function getLaggedReplicaMode( $domain = false ) {
1754                 if (
1755                         // Avoid recursion if there is only one DB
1756                         $this->getServerCount() > 1 &&
1757                         // Avoid recursion if the (non-zero load) master DB was picked for generic reads
1758                         $this->genericReadIndex !== $this->getWriterIndex() &&
1759                         // Stay in lagged replica mode during the load balancer instance lifetime
1760                         !$this->laggedReplicaMode
1761                 ) {
1762                         try {
1763                                 // Calling this method will set "laggedReplicaMode" as needed
1764                                 $this->getReaderIndex( false, $domain );
1765                         } catch ( DBConnectionError $e ) {
1766                                 // Avoid expensive re-connect attempts and failures
1767                                 $this->allReplicasDownMode = true;
1768                                 $this->laggedReplicaMode = true;
1769                         }
1770                 }
1771
1772                 return $this->laggedReplicaMode;
1773         }
1774
1775         public function laggedReplicaUsed() {
1776                 return $this->laggedReplicaMode;
1777         }
1778
1779         /**
1780          * @return bool
1781          * @since 1.27
1782          * @deprecated Since 1.28; use laggedReplicaUsed()
1783          */
1784         public function laggedSlaveUsed() {
1785                 return $this->laggedReplicaUsed();
1786         }
1787
1788         public function getReadOnlyReason( $domain = false, IDatabase $conn = null ) {
1789                 if ( $this->readOnlyReason !== false ) {
1790                         return $this->readOnlyReason;
1791                 } elseif ( $this->getLaggedReplicaMode( $domain ) ) {
1792                         if ( $this->allReplicasDownMode ) {
1793                                 return 'The database has been automatically locked ' .
1794                                         'until the replica database servers become available';
1795                         } else {
1796                                 return 'The database has been automatically locked ' .
1797                                         'while the replica database servers catch up to the master.';
1798                         }
1799                 } elseif ( $this->masterRunningReadOnly( $domain, $conn ) ) {
1800                         return 'The database master is running in read-only mode.';
1801                 }
1802
1803                 return false;
1804         }
1805
1806         /**
1807          * @param string $domain Domain ID, or false for the current domain
1808          * @param IDatabase|null $conn DB master connectionl used to avoid loops [optional]
1809          * @return bool
1810          */
1811         private function masterRunningReadOnly( $domain, IDatabase $conn = null ) {
1812                 $cache = $this->wanCache;
1813                 $masterServer = $this->getServerName( $this->getWriterIndex() );
1814
1815                 return (bool)$cache->getWithSetCallback(
1816                         $cache->makeGlobalKey( __CLASS__, 'server-read-only', $masterServer ),
1817                         self::TTL_CACHE_READONLY,
1818                         function () use ( $domain, $conn ) {
1819                                 $old = $this->trxProfiler->setSilenced( true );
1820                                 try {
1821                                         $dbw = $conn ?: $this->getConnection( self::DB_MASTER, [], $domain );
1822                                         $readOnly = (int)$dbw->serverIsReadOnly();
1823                                         if ( !$conn ) {
1824                                                 $this->reuseConnection( $dbw );
1825                                         }
1826                                 } catch ( DBError $e ) {
1827                                         $readOnly = 0;
1828                                 }
1829                                 $this->trxProfiler->setSilenced( $old );
1830                                 return $readOnly;
1831                         },
1832                         [ 'pcTTL' => $cache::TTL_PROC_LONG, 'busyValue' => 0 ]
1833                 );
1834         }
1835
1836         public function allowLagged( $mode = null ) {
1837                 if ( $mode === null ) {
1838                         return $this->allowLagged;
1839                 }
1840                 $this->allowLagged = $mode;
1841
1842                 return $this->allowLagged;
1843         }
1844
1845         public function pingAll() {
1846                 $success = true;
1847                 $this->forEachOpenConnection( function ( IDatabase $conn ) use ( &$success ) {
1848                         if ( !$conn->ping() ) {
1849                                 $success = false;
1850                         }
1851                 } );
1852
1853                 return $success;
1854         }
1855
1856         public function forEachOpenConnection( $callback, array $params = [] ) {
1857                 foreach ( $this->conns as $connsByServer ) {
1858                         foreach ( $connsByServer as $serverConns ) {
1859                                 foreach ( $serverConns as $conn ) {
1860                                         $callback( $conn, ...$params );
1861                                 }
1862                         }
1863                 }
1864         }
1865
1866         public function forEachOpenMasterConnection( $callback, array $params = [] ) {
1867                 $masterIndex = $this->getWriterIndex();
1868                 foreach ( $this->conns as $connsByServer ) {
1869                         if ( isset( $connsByServer[$masterIndex] ) ) {
1870                                 /** @var IDatabase $conn */
1871                                 foreach ( $connsByServer[$masterIndex] as $conn ) {
1872                                         $callback( $conn, ...$params );
1873                                 }
1874                         }
1875                 }
1876         }
1877
1878         public function forEachOpenReplicaConnection( $callback, array $params = [] ) {
1879                 foreach ( $this->conns as $connsByServer ) {
1880                         foreach ( $connsByServer as $i => $serverConns ) {
1881                                 if ( $i === $this->getWriterIndex() ) {
1882                                         continue; // skip master
1883                                 }
1884                                 foreach ( $serverConns as $conn ) {
1885                                         $callback( $conn, ...$params );
1886                                 }
1887                         }
1888                 }
1889         }
1890
1891         public function getMaxLag( $domain = false ) {
1892                 $maxLag = -1;
1893                 $host = '';
1894                 $maxIndex = 0;
1895
1896                 if ( $this->getServerCount() <= 1 ) {
1897                         return [ $host, $maxLag, $maxIndex ]; // no replication = no lag
1898                 }
1899
1900                 $lagTimes = $this->getLagTimes( $domain );
1901                 foreach ( $lagTimes as $i => $lag ) {
1902                         if ( $this->genericLoads[$i] > 0 && $lag > $maxLag ) {
1903                                 $maxLag = $lag;
1904                                 $host = $this->servers[$i]['host'];
1905                                 $maxIndex = $i;
1906                         }
1907                 }
1908
1909                 return [ $host, $maxLag, $maxIndex ];
1910         }
1911
1912         public function getLagTimes( $domain = false ) {
1913                 if ( $this->getServerCount() <= 1 ) {
1914                         return [ $this->getWriterIndex() => 0 ]; // no replication = no lag
1915                 }
1916
1917                 $knownLagTimes = []; // map of (server index => 0 seconds)
1918                 $indexesWithLag = [];
1919                 foreach ( $this->servers as $i => $server ) {
1920                         if ( empty( $server['is static'] ) ) {
1921                                 $indexesWithLag[] = $i; // DB server might have replication lag
1922                         } else {
1923                                 $knownLagTimes[$i] = 0; // DB server is a non-replicating and read-only archive
1924                         }
1925                 }
1926
1927                 return $this->getLoadMonitor()->getLagTimes( $indexesWithLag, $domain ) + $knownLagTimes;
1928         }
1929
1930         public function safeGetLag( IDatabase $conn ) {
1931                 if ( $this->getServerCount() <= 1 ) {
1932                         return 0;
1933                 } else {
1934                         return $conn->getLag();
1935                 }
1936         }
1937
1938         public function safeWaitForMasterPos( IDatabase $conn, $pos = false, $timeout = null ) {
1939                 $timeout = max( 1, $timeout ?: $this->waitTimeout );
1940
1941                 if ( $this->getServerCount() <= 1 || !$conn->getLBInfo( 'replica' ) ) {
1942                         return true; // server is not a replica DB
1943                 }
1944
1945                 if ( !$pos ) {
1946                         // Get the current master position, opening a connection if needed
1947                         $masterConn = $this->getAnyOpenConnection( $this->getWriterIndex() );
1948                         if ( $masterConn ) {
1949                                 $pos = $masterConn->getMasterPos();
1950                         } else {
1951                                 $masterConn = $this->openConnection( $this->getWriterIndex(), self::DOMAIN_ANY );
1952                                 if ( !$masterConn ) {
1953                                         throw new DBReplicationWaitError(
1954                                                 null,
1955                                                 "Could not obtain a master database connection to get the position"
1956                                         );
1957                                 }
1958                                 $pos = $masterConn->getMasterPos();
1959                                 $this->closeConnection( $masterConn );
1960                         }
1961                 }
1962
1963                 if ( $pos instanceof DBMasterPos ) {
1964                         $start = microtime( true );
1965                         $result = $conn->masterPosWait( $pos, $timeout );
1966                         $seconds = max( microtime( true ) - $start, 0 );
1967                         if ( $result == -1 || is_null( $result ) ) {
1968                                 $msg = __METHOD__ . ': timed out waiting on {host} pos {pos} [{seconds}s]';
1969                                 $this->replLogger->warning( $msg, [
1970                                         'host' => $conn->getServer(),
1971                                         'pos' => $pos,
1972                                         'seconds' => round( $seconds, 6 ),
1973                                         'trace' => ( new RuntimeException() )->getTraceAsString()
1974                                 ] );
1975                                 $ok = false;
1976                         } else {
1977                                 $this->replLogger->debug( __METHOD__ . ': done waiting' );
1978                                 $ok = true;
1979                         }
1980                 } else {
1981                         $ok = false; // something is misconfigured
1982                         $this->replLogger->error(
1983                                 __METHOD__ . ': could not get master pos for {host}',
1984                                 [
1985                                         'host' => $conn->getServer(),
1986                                         'trace' => ( new RuntimeException() )->getTraceAsString()
1987                                 ]
1988                         );
1989                 }
1990
1991                 return $ok;
1992         }
1993
1994         public function setTransactionListener( $name, callable $callback = null ) {
1995                 if ( $callback ) {
1996                         $this->trxRecurringCallbacks[$name] = $callback;
1997                 } else {
1998                         unset( $this->trxRecurringCallbacks[$name] );
1999                 }
2000                 $this->forEachOpenMasterConnection(
2001                         function ( IDatabase $conn ) use ( $name, $callback ) {
2002                                 $conn->setTransactionListener( $name, $callback );
2003                         }
2004                 );
2005         }
2006
2007         public function setTableAliases( array $aliases ) {
2008                 $this->tableAliases = $aliases;
2009         }
2010
2011         public function setIndexAliases( array $aliases ) {
2012                 $this->indexAliases = $aliases;
2013         }
2014
2015         /**
2016          * @param string $prefix
2017          * @deprecated Since 1.33
2018          */
2019         public function setDomainPrefix( $prefix ) {
2020                 $this->setLocalDomainPrefix( $prefix );
2021         }
2022
2023         public function setLocalDomainPrefix( $prefix ) {
2024                 // Find connections to explicit foreign domains still marked as in-use...
2025                 $domainsInUse = [];
2026                 $this->forEachOpenConnection( function ( IDatabase $conn ) use ( &$domainsInUse ) {
2027                         // Once reuseConnection() is called on a handle, its reference count goes from 1 to 0.
2028                         // Until then, it is still in use by the caller (explicitly or via DBConnRef scope).
2029                         if ( $conn->getLBInfo( 'foreignPoolRefCount' ) > 0 ) {
2030                                 $domainsInUse[] = $conn->getDomainID();
2031                         }
2032                 } );
2033
2034                 // Do not switch connections to explicit foreign domains unless marked as safe
2035                 if ( $domainsInUse ) {
2036                         $domains = implode( ', ', $domainsInUse );
2037                         throw new DBUnexpectedError( null,
2038                                 "Foreign domain connections are still in use ($domains)" );
2039                 }
2040
2041                 $this->setLocalDomain( new DatabaseDomain(
2042                         $this->localDomain->getDatabase(),
2043                         $this->localDomain->getSchema(),
2044                         $prefix
2045                 ) );
2046
2047                 // Update the prefix for all local connections...
2048                 $this->forEachOpenConnection( function ( IDatabase $db ) use ( $prefix ) {
2049                         if ( !$db->getLBInfo( 'foreign' ) ) {
2050                                 $db->tablePrefix( $prefix );
2051                         }
2052                 } );
2053         }
2054
2055         public function redefineLocalDomain( $domain ) {
2056                 $this->closeAll();
2057
2058                 $this->setLocalDomain( DatabaseDomain::newFromId( $domain ) );
2059         }
2060
2061         /**
2062          * @param DatabaseDomain $domain
2063          */
2064         private function setLocalDomain( DatabaseDomain $domain ) {
2065                 $this->localDomain = $domain;
2066                 // In case a caller assumes that the domain ID is simply <db>-<prefix>, which is almost
2067                 // always true, gracefully handle the case when they fail to account for escaping.
2068                 if ( $this->localDomain->getTablePrefix() != '' ) {
2069                         $this->localDomainIdAlias =
2070                                 $this->localDomain->getDatabase() . '-' . $this->localDomain->getTablePrefix();
2071                 } else {
2072                         $this->localDomainIdAlias = $this->localDomain->getDatabase();
2073                 }
2074         }
2075
2076         function __destruct() {
2077                 // Avoid connection leaks for sanity
2078                 $this->disable();
2079         }
2080 }
2081
2082 /**
2083  * @deprecated since 1.29
2084  */
2085 class_alias( LoadBalancer::class, 'LoadBalancer' );