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 bool|DBMasterPos False if not set */
 109         private $waitForPos;
 110         /** @var bool Whether the generic reader fell back to a lagged replica DB */
 111         private $laggedReplicaMode = false;
 112         /** @var bool Whether the generic reader fell back to a lagged replica DB */
 113         private $allReplicasDownMode = false;
 114         /** @var string The last DB selection or connection error */
 115         private $lastError = 'Unknown error';
 116         /** @var string|bool Reason the LB is read-only or false if not */
 117         private $readOnlyReason = false;
 118         /** @var int Total connections opened */
 119         private $connsOpened = 0;
 120         /** @var bool */
 121         private $disabled = false;
 122         /** @var bool Whether any connection has been attempted yet */
 123         private $connectionAttempted = false;
 124
 125         /** @var int|null An integer ID of the managing LBFactory instance or null */
 126         private $ownerId;
 127         /** @var string|bool String if a requested DBO_TRX transaction round is active */
 128         private $trxRoundId = false;
 129         /** @var string Stage of the current transaction round in the transaction round life-cycle */
 130         private $trxRoundStage = self::ROUND_CURSORY;
 131
 132         /** @var string|null */
 133         private $defaultGroup = null;
 134
 135         /** @var int Warn when this many connection are held */
 136         const CONN_HELD_WARN_THRESHOLD = 10;
 137
 138         /** @var int Default 'maxLag' when unspecified */
 139         const MAX_LAG_DEFAULT = 6;
 140         /** @var int Default 'waitTimeout' when unspecified */
 141         const MAX_WAIT_DEFAULT = 10;
 142         /** @var int Seconds to cache master server read-only status */
 143         const TTL_CACHE_READONLY = 5;
 144
 145         const KEY_LOCAL = 'local';
 146         const KEY_FOREIGN_FREE = 'foreignFree';
 147         const KEY_FOREIGN_INUSE = 'foreignInUse';
 148
 149         const KEY_LOCAL_NOROUND = 'localAutoCommit';
 150         const KEY_FOREIGN_FREE_NOROUND = 'foreignFreeAutoCommit';
 151         const KEY_FOREIGN_INUSE_NOROUND = 'foreignInUseAutoCommit';
 152
 153         /** @var string Transaction round, explicit or implicit, has not finished writing */
 154         const ROUND_CURSORY = 'cursory';
 155         /** @var string Transaction round writes are complete and ready for pre-commit checks */
 156         const ROUND_FINALIZED = 'finalized';
 157         /** @var string Transaction round passed final pre-commit checks */
 158         const ROUND_APPROVED = 'approved';
 159         /** @var string Transaction round was committed and post-commit callbacks must be run */
 160         const ROUND_COMMIT_CALLBACKS = 'commit-callbacks';
 161         /** @var string Transaction round was rolled back and post-rollback callbacks must be run */
 162         const ROUND_ROLLBACK_CALLBACKS = 'rollback-callbacks';
 163         /** @var string Transaction round encountered an error */
 164         const ROUND_ERROR = 'error';
 165
 166         public function __construct( array $params ) {
 167                 if ( !isset( $params['servers'] ) ) {
 168                         throw new InvalidArgumentException( __CLASS__ . ': missing "servers" parameter' );
 169                 }
 170                 $this->servers = $params['servers'];
 171                 foreach ( $this->servers as $i => $server ) {
 172                         if ( $i == 0 ) {
 173                                 $this->servers[$i]['master'] = true;
 174                         } else {
 175                                 $this->servers[$i]['replica'] = true;
 176                         }
 177                 }
 178
 179                 $localDomain = isset( $params['localDomain'] )
 180                         ? DatabaseDomain::newFromId( $params['localDomain'] )
 181                         : DatabaseDomain::newUnspecified();
 182                 $this->setLocalDomain( $localDomain );
 183
 184                 $this->waitTimeout = $params['waitTimeout'] ?? self::MAX_WAIT_DEFAULT;
 185
 186                 $this->conns = [
 187                         // Connection were transaction rounds may be applied
 188                         self::KEY_LOCAL => [],
 189                         self::KEY_FOREIGN_INUSE => [],
 190                         self::KEY_FOREIGN_FREE => [],
 191                         // Auto-committing counterpart connections that ignore transaction rounds
 192                         self::KEY_LOCAL_NOROUND => [],
 193                         self::KEY_FOREIGN_INUSE_NOROUND => [],
 194                         self::KEY_FOREIGN_FREE_NOROUND => []
 195                 ];
 196                 $this->genericLoads = [];
 197                 $this->waitForPos = false;
 198                 $this->allowLagged = false;
 199
 200                 if ( isset( $params['readOnlyReason'] ) && is_string( $params['readOnlyReason'] ) ) {
 201                         $this->readOnlyReason = $params['readOnlyReason'];
 202                 }
 203
 204                 $this->maxLag = $params['maxLag'] ?? self::MAX_LAG_DEFAULT;
 205
 206                 $this->loadMonitorConfig = $params['loadMonitor'] ?? [ 'class' => 'LoadMonitorNull' ];
 207                 $this->loadMonitorConfig += [ 'lagWarnThreshold' => $this->maxLag ];
 208
 209                 foreach ( $params['servers'] as $i => $server ) {
 210                         $this->genericLoads[$i] = $server['load'];
 211                         if ( isset( $server['groupLoads'] ) ) {
 212                                 foreach ( $server['groupLoads'] as $group => $ratio ) {
 213                                         if ( !isset( $this->groupLoads[$group] ) ) {
 214                                                 $this->groupLoads[$group] = [];
 215                                         }
 216                                         $this->groupLoads[$group][$i] = $ratio;
 217                                 }
 218                         }
 219                 }
 220
 221                 $this->srvCache = $params['srvCache'] ?? new EmptyBagOStuff();
 222                 $this->wanCache = $params['wanCache'] ?? WANObjectCache::newEmpty();
 223                 $this->profiler = $params['profiler'] ?? null;
 224                 $this->trxProfiler = $params['trxProfiler'] ?? new TransactionProfiler();
 225
 226                 $this->errorLogger = $params['errorLogger'] ?? function ( Exception $e ) {
 227                         trigger_error( get_class( $e ) . ': ' . $e->getMessage(), E_USER_WARNING );
 228                 };
 229                 $this->deprecationLogger = $params['deprecationLogger'] ?? function ( $msg ) {
 230                         trigger_error( $msg, E_USER_DEPRECATED );
 231                 };
 232
 233                 foreach ( [ 'replLogger', 'connLogger', 'queryLogger', 'perfLogger' ] as $key ) {
 234                         $this->$key = $params[$key] ?? new NullLogger();
 235                 }
 236
 237                 $this->hostname = $params['hostname'] ?? ( gethostname() ?: 'unknown' );
 238                 $this->cliMode = $params['cliMode'] ?? ( PHP_SAPI === 'cli' || PHP_SAPI === 'phpdbg' );
 239                 $this->agent = $params['agent'] ?? '';
 240
 241                 if ( isset( $params['chronologyCallback'] ) ) {
 242                         $this->chronologyCallback = $params['chronologyCallback'];
 243                 }
 244
 245                 if ( isset( $params['roundStage'] ) ) {
 246                         if ( $params['roundStage'] === self::STAGE_POSTCOMMIT_CALLBACKS ) {
 247                                 $this->trxRoundStage = self::ROUND_COMMIT_CALLBACKS;
 248                         } elseif ( $params['roundStage'] === self::STAGE_POSTROLLBACK_CALLBACKS ) {
 249                                 $this->trxRoundStage = self::ROUND_ROLLBACK_CALLBACKS;
 250                         }
 251                 }
 252
 253                 $this->defaultGroup = $params['defaultGroup'] ?? null;
 254                 $this->ownerId = $params['ownerId'] ?? null;
 255         }
 256
 257         public function getLocalDomainID() {
 258                 return $this->localDomain->getId();
 259         }
 260
 261         public function resolveDomainID( $domain ) {
 262                 if ( $domain === $this->localDomainIdAlias || $domain === false ) {
 263                         // Local connection requested via some backwards-compatibility domain alias
 264                         return $this->getLocalDomainID();
 265                 }
 266
 267                 return (string)$domain;
 268         }
 269
 270         /**
 271          * Get a LoadMonitor instance
 272          *
 273          * @return ILoadMonitor
 274          */
 275         private function getLoadMonitor() {
 276                 if ( !isset( $this->loadMonitor ) ) {
 277                         $compat = [
 278                                 'LoadMonitor' => LoadMonitor::class,
 279                                 'LoadMonitorNull' => LoadMonitorNull::class,
 280                                 'LoadMonitorMySQL' => LoadMonitorMySQL::class,
 281                         ];
 282
 283                         $class = $this->loadMonitorConfig['class'];
 284                         if ( isset( $compat[$class] ) ) {
 285                                 $class = $compat[$class];
 286                         }
 287
 288                         $this->loadMonitor = new $class(
 289                                 $this, $this->srvCache, $this->wanCache, $this->loadMonitorConfig );
 290                         $this->loadMonitor->setLogger( $this->replLogger );
 291                 }
 292
 293                 return $this->loadMonitor;
 294         }
 295
 296         /**
 297          * @param array $loads
 298          * @param bool|string $domain Domain to get non-lagged for
 299          * @param int $maxLag Restrict the maximum allowed lag to this many seconds
 300          * @return bool|int|string
 301          */
 302         private function getRandomNonLagged( array $loads, $domain = false, $maxLag = INF ) {
 303                 $lags = $this->getLagTimes( $domain );
 304
 305                 # Unset excessively lagged servers
 306                 foreach ( $lags as $i => $lag ) {
 307                         if ( $i != 0 ) {
 308                                 # How much lag this server nominally is allowed to have
 309                                 $maxServerLag = $this->servers[$i]['max lag'] ?? $this->maxLag; // default
 310                                 # Constrain that futher by $maxLag argument
 311                                 $maxServerLag = min( $maxServerLag, $maxLag );
 312
 313                                 $host = $this->getServerName( $i );
 314                                 if ( $lag === false && !is_infinite( $maxServerLag ) ) {
 315                                         $this->replLogger->debug(
 316                                                 __METHOD__ .
 317                                                 ": server {host} is not replicating?", [ 'host' => $host ] );
 318                                         unset( $loads[$i] );
 319                                 } elseif ( $lag > $maxServerLag ) {
 320                                         $this->replLogger->debug(
 321                                                 __METHOD__ .
 322                                                 ": server {host} has {lag} seconds of lag (>= {maxlag})",
 323                                                 [ 'host' => $host, 'lag' => $lag, 'maxlag' => $maxServerLag ]
 324                                         );
 325                                         unset( $loads[$i] );
 326                                 }
 327                         }
 328                 }
 329
 330                 # Find out if all the replica DBs with non-zero load are lagged
 331                 $sum = 0;
 332                 foreach ( $loads as $load ) {
 333                         $sum += $load;
 334                 }
 335                 if ( $sum == 0 ) {
 336                         # No appropriate DB servers except maybe the master and some replica DBs with zero load
 337                         # Do NOT use the master
 338                         # Instead, this function will return false, triggering read-only mode,
 339                         # and a lagged replica DB will be used instead.
 340                         return false;
 341                 }
 342
 343                 if ( count( $loads ) == 0 ) {
 344                         return false;
 345                 }
 346
 347                 # Return a random representative of the remainder
 348                 return ArrayUtils::pickRandom( $loads );
 349         }
 350
 351         /**
 352          * @param int $i
 353          * @param array $groups
 354          * @param string|bool $domain
 355          * @return int
 356          */
 357         private function getConnectionIndex( $i, $groups, $domain ) {
 358                 // Check one "group" per default: the generic pool
 359                 $defaultGroups = $this->defaultGroup ? [ $this->defaultGroup ] : [ false ];
 360
 361                 $groups = ( $groups === false || $groups === [] )
 362                         ? $defaultGroups
 363                         : (array)$groups;
 364
 365                 if ( $i == self::DB_MASTER ) {
 366                         $i = $this->getWriterIndex();
 367                 } elseif ( $i == self::DB_REPLICA ) {
 368                         # Try to find an available server in any the query groups (in order)
 369                         foreach ( $groups as $group ) {
 370                                 $groupIndex = $this->getReaderIndex( $group, $domain );
 371                                 if ( $groupIndex !== false ) {
 372                                         $i = $groupIndex;
 373                                         break;
 374                                 }
 375                         }
 376                 }
 377
 378                 # Operation-based index
 379                 if ( $i == self::DB_REPLICA ) {
 380                         $this->lastError = 'Unknown error'; // reset error string
 381                         # Try the general server pool if $groups are unavailable.
 382                         $i = ( $groups === [ false ] )
 383                                 ? false // don't bother with this if that is what was tried above
 384                                 : $this->getReaderIndex( false, $domain );
 385                         # Couldn't find a working server in getReaderIndex()?
 386                         if ( $i === false ) {
 387                                 $this->lastError = 'No working replica DB server: ' . $this->lastError;
 388                                 // Throw an exception
 389                                 $this->reportConnectionError();
 390                                 return null; // not reached
 391                         }
 392                 }
 393
 394                 return $i;
 395         }
 396
 397         public function getReaderIndex( $group = false, $domain = false ) {
 398                 if ( count( $this->servers ) == 1 ) {
 399                         // Skip the load balancing if there's only one server
 400                         return $this->getWriterIndex();
 401                 } elseif ( $group === false && $this->genericReadIndex >= 0 ) {
 402                         // A generic reader index was already selected and "waitForPos" was handled
 403                         return $this->genericReadIndex;
 404                 }
 405
 406                 if ( $group !== false ) {
 407                         // Use the server weight array for this load group
 408                         if ( isset( $this->groupLoads[$group] ) ) {
 409                                 $loads = $this->groupLoads[$group];
 410                         } else {
 411                                 // No loads for this group, return false and the caller can use some other group
 412                                 $this->connLogger->info( __METHOD__ . ": no loads for group $group" );
 413
 414                                 return false;
 415                         }
 416                 } else {
 417                         // Use the generic load group
 418                         $loads = $this->genericLoads;
 419                 }
 420
 421                 // Scale the configured load ratios according to each server's load and state
 422                 $this->getLoadMonitor()->scaleLoads( $loads, $domain );
 423
 424                 // Pick a server to use, accounting for weights, load, lag, and "waitForPos"
 425                 list( $i, $laggedReplicaMode ) = $this->pickReaderIndex( $loads, $domain );
 426                 if ( $i === false ) {
 427                         // DB connection unsuccessful
 428                         return false;
 429                 }
 430
 431                 // If data seen by queries is expected to reflect the transactions committed as of
 432                 // or after a given replication position then wait for the DB to apply those changes
 433                 if ( $this->waitForPos && $i != $this->getWriterIndex() && !$this->doWait( $i ) ) {
 434                         // Data will be outdated compared to what was expected
 435                         $laggedReplicaMode = true;
 436                 }
 437
 438                 if ( $this->genericReadIndex < 0 && $this->genericLoads[$i] > 0 && $group === false ) {
 439                         // Cache the generic (ungrouped) reader index for future DB_REPLICA handles
 440                         $this->genericReadIndex = $i;
 441                         // Record if the generic reader index is in "lagged replica DB" mode
 442                         $this->laggedReplicaMode = ( $laggedReplicaMode || $this->laggedReplicaMode );
 443                 }
 444
 445                 $serverName = $this->getServerName( $i );
 446                 $this->connLogger->debug( __METHOD__ . ": using server $serverName for group '$group'" );
 447
 448                 return $i;
 449         }
 450
 451         /**
 452          * @param array $loads List of server weights
 453          * @param string|bool $domain
 454          * @return array (reader index, lagged replica mode) or false on failure
 455          */
 456         private function pickReaderIndex( array $loads, $domain = false ) {
 457                 if ( $loads === [] ) {
 458                         throw new InvalidArgumentException( "Server configuration array is empty" );
 459                 }
 460
 461                 /** @var int|bool $i Index of selected server */
 462                 $i = false;
 463                 /** @var bool $laggedReplicaMode Whether server is considered lagged */
 464                 $laggedReplicaMode = false;
 465
 466                 // Quickly look through the available servers for a server that meets criteria...
 467                 $currentLoads = $loads;
 468                 while ( count( $currentLoads ) ) {
 469                         if ( $this->allowLagged || $laggedReplicaMode ) {
 470                                 $i = ArrayUtils::pickRandom( $currentLoads );
 471                         } else {
 472                                 $i = false;
 473                                 if ( $this->waitForPos && $this->waitForPos->asOfTime() ) {
 474                                         // "chronologyCallback" sets "waitForPos" for session consistency.
 475                                         // This triggers doWait() after connect, so it's especially good to
 476                                         // avoid lagged servers so as to avoid excessive delay in that method.
 477                                         $ago = microtime( true ) - $this->waitForPos->asOfTime();
 478                                         // Aim for <= 1 second of waiting (being too picky can backfire)
 479                                         $i = $this->getRandomNonLagged( $currentLoads, $domain, $ago + 1 );
 480                                 }
 481                                 if ( $i === false ) {
 482                                         // Any server with less lag than it's 'max lag' param is preferable
 483                                         $i = $this->getRandomNonLagged( $currentLoads, $domain );
 484                                 }
 485                                 if ( $i === false && count( $currentLoads ) != 0 ) {
 486                                         // All replica DBs lagged. Switch to read-only mode
 487                                         $this->replLogger->error(
 488                                                 __METHOD__ . ": all replica DBs lagged. Switch to read-only mode" );
 489                                         $i = ArrayUtils::pickRandom( $currentLoads );
 490                                         $laggedReplicaMode = true;
 491                                 }
 492                         }
 493
 494                         if ( $i === false ) {
 495                                 // pickRandom() returned false.
 496                                 // This is permanent and means the configuration or the load monitor
 497                                 // wants us to return false.
 498                                 $this->connLogger->debug( __METHOD__ . ": pickRandom() returned false" );
 499
 500                                 return [ false, false ];
 501                         }
 502
 503                         $serverName = $this->getServerName( $i );
 504                         $this->connLogger->debug( __METHOD__ . ": Using reader #$i: $serverName..." );
 505
 506                         $conn = $this->openConnection( $i, $domain );
 507                         if ( !$conn ) {
 508                                 $this->connLogger->warning( __METHOD__ . ": Failed connecting to $i/$domain" );
 509                                 unset( $currentLoads[$i] ); // avoid this server next iteration
 510                                 $i = false;
 511                                 continue;
 512                         }
 513
 514                         // Decrement reference counter, we are finished with this connection.
 515                         // It will be incremented for the caller later.
 516                         if ( $domain !== false ) {
 517                                 $this->reuseConnection( $conn );
 518                         }
 519
 520                         // Return this server
 521                         break;
 522                 }
 523
 524                 // If all servers were down, quit now
 525                 if ( $currentLoads === [] ) {
 526                         $this->connLogger->error( __METHOD__ . ": all servers down" );
 527                 }
 528
 529                 return [ $i, $laggedReplicaMode ];
 530         }
 531
 532         public function waitFor( $pos ) {
 533                 $oldPos = $this->waitForPos;
 534                 try {
 535                         $this->waitForPos = $pos;
 536                         // If a generic reader connection was already established, then wait now
 537                         if ( $this->genericReadIndex > 0 && !$this->doWait( $this->genericReadIndex ) ) {
 538                                 $this->laggedReplicaMode = true;
 539                         }
 540                         // Otherwise, wait until a connection is established in getReaderIndex()
 541                 } finally {
 542                         // Restore the older position if it was higher since this is used for lag-protection
 543                         $this->setWaitForPositionIfHigher( $oldPos );
 544                 }
 545         }
 546
 547         public function waitForOne( $pos, $timeout = null ) {
 548                 $oldPos = $this->waitForPos;
 549                 try {
 550                         $this->waitForPos = $pos;
 551
 552                         $i = $this->genericReadIndex;
 553                         if ( $i <= 0 ) {
 554                                 // Pick a generic replica DB if there isn't one yet
 555                                 $readLoads = $this->genericLoads;
 556                                 unset( $readLoads[$this->getWriterIndex()] ); // replica DBs only
 557                                 $readLoads = array_filter( $readLoads ); // with non-zero load
 558                                 $i = ArrayUtils::pickRandom( $readLoads );
 559                         }
 560
 561                         if ( $i > 0 ) {
 562                                 $ok = $this->doWait( $i, true, $timeout );
 563                         } else {
 564                                 $ok = true; // no applicable loads
 565                         }
 566                 } finally {
 567                         # Restore the old position, as this is not used for lag-protection but for throttling
 568                         $this->waitForPos = $oldPos;
 569                 }
 570
 571                 return $ok;
 572         }
 573
 574         public function waitForAll( $pos, $timeout = null ) {
 575                 $timeout = $timeout ?: $this->waitTimeout;
 576
 577                 $oldPos = $this->waitForPos;
 578                 try {
 579                         $this->waitForPos = $pos;
 580                         $serverCount = count( $this->servers );
 581
 582                         $ok = true;
 583                         for ( $i = 1; $i < $serverCount; $i++ ) {
 584                                 if ( $this->genericLoads[$i] > 0 ) {
 585                                         $start = microtime( true );
 586                                         $ok = $this->doWait( $i, true, $timeout ) && $ok;
 587                                         $timeout -= intval( microtime( true ) - $start );
 588                                         if ( $timeout <= 0 ) {
 589                                                 break; // timeout reached
 590                                         }
 591                                 }
 592                         }
 593                 } finally {
 594                         # Restore the old position, as this is not used for lag-protection but for throttling
 595                         $this->waitForPos = $oldPos;
 596                 }
 597
 598                 return $ok;
 599         }
 600
 601         /**
 602          * @param DBMasterPos|bool $pos
 603          */
 604         private function setWaitForPositionIfHigher( $pos ) {
 605                 if ( !$pos ) {
 606                         return;
 607                 }
 608
 609                 if ( !$this->waitForPos || $pos->hasReached( $this->waitForPos ) ) {
 610                         $this->waitForPos = $pos;
 611                 }
 612         }
 613
 614         public function getAnyOpenConnection( $i, $flags = 0 ) {
 615                 $i = ( $i === self::DB_MASTER ) ? $this->getWriterIndex() : $i;
 616                 $autocommit = ( ( $flags & self::CONN_TRX_AUTOCOMMIT ) == self::CONN_TRX_AUTOCOMMIT );
 617
 618                 foreach ( $this->conns as $connsByServer ) {
 619                         if ( $i === self::DB_REPLICA ) {
 620                                 $indexes = array_keys( $connsByServer );
 621                         } else {
 622                                 $indexes = isset( $connsByServer[$i] ) ? [ $i ] : [];
 623                         }
 624
 625                         foreach ( $indexes as $index ) {
 626                                 foreach ( $connsByServer[$index] as $conn ) {
 627                                         if ( !$conn->isOpen() ) {
 628                                                 continue; // some sort of error occured?
 629                                         }
 630                                         if ( !$autocommit || $conn->getLBInfo( 'autoCommitOnly' ) ) {
 631                                                 return $conn;
 632                                         }
 633                                 }
 634                         }
 635                 }
 636
 637                 return false;
 638         }
 639
 640         /**
 641          * Wait for a given replica DB to catch up to the master pos stored in $this
 642          * @param int $index Server index
 643          * @param bool $open Check the server even if a new connection has to be made
 644          * @param int|null $timeout Max seconds to wait; default is "waitTimeout" given to __construct()
 645          * @return bool
 646          */
 647         protected function doWait( $index, $open = false, $timeout = null ) {
 648                 $timeout = max( 1, intval( $timeout ?: $this->waitTimeout ) );
 649
 650                 // Check if we already know that the DB has reached this point
 651                 $server = $this->getServerName( $index );
 652                 $key = $this->srvCache->makeGlobalKey( __CLASS__, 'last-known-pos', $server, 'v1' );
 653                 /** @var DBMasterPos $knownReachedPos */
 654                 $knownReachedPos = $this->srvCache->get( $key );
 655                 if (
 656                         $knownReachedPos instanceof DBMasterPos &&
 657                         $knownReachedPos->hasReached( $this->waitForPos )
 658                 ) {
 659                         $this->replLogger->debug(
 660                                 __METHOD__ .
 661                                 ': replica DB {dbserver} known to be caught up (pos >= $knownReachedPos).',
 662                                 [ 'dbserver' => $server ]
 663                         );
 664                         return true;
 665                 }
 666
 667                 // Find a connection to wait on, creating one if needed and allowed
 668                 $close = false; // close the connection afterwards
 669                 $conn = $this->getAnyOpenConnection( $index );
 670                 if ( !$conn ) {
 671                         if ( !$open ) {
 672                                 $this->replLogger->debug(
 673                                         __METHOD__ . ': no connection open for {dbserver}',
 674                                         [ 'dbserver' => $server ]
 675                                 );
 676
 677                                 return false;
 678                         } else {
 679                                 $conn = $this->openConnection( $index, self::DOMAIN_ANY );
 680                                 if ( !$conn ) {
 681                                         $this->replLogger->warning(
 682                                                 __METHOD__ . ': failed to connect to {dbserver}',
 683                                                 [ 'dbserver' => $server ]
 684                                         );
 685
 686                                         return false;
 687                                 }
 688                                 // Avoid connection spam in waitForAll() when connections
 689                                 // are made just for the sake of doing this lag check.
 690                                 $close = true;
 691                         }
 692                 }
 693
 694                 $this->replLogger->info(
 695                         __METHOD__ .
 696                         ': waiting for replica DB {dbserver} to catch up...',
 697                         [ 'dbserver' => $server ]
 698                 );
 699
 700                 $result = $conn->masterPosWait( $this->waitForPos, $timeout );
 701
 702                 if ( $result === null ) {
 703                         $this->replLogger->warning(
 704                                 __METHOD__ . ': Errored out waiting on {host} pos {pos}',
 705                                 [
 706                                         'host' => $server,
 707                                         'pos' => $this->waitForPos,
 708                                         'trace' => ( new RuntimeException() )->getTraceAsString()
 709                                 ]
 710                         );
 711                         $ok = false;
 712                 } elseif ( $result == -1 ) {
 713                         $this->replLogger->warning(
 714                                 __METHOD__ . ': Timed out waiting on {host} pos {pos}',
 715                                 [
 716                                         'host' => $server,
 717                                         'pos' => $this->waitForPos,
 718                                         'trace' => ( new RuntimeException() )->getTraceAsString()
 719                                 ]
 720                         );
 721                         $ok = false;
 722                 } else {
 723                         $this->replLogger->debug( __METHOD__ . ": done waiting" );
 724                         $ok = true;
 725                         // Remember that the DB reached this point
 726                         $this->srvCache->set( $key, $this->waitForPos, BagOStuff::TTL_DAY );
 727                 }
 728
 729                 if ( $close ) {
 730                         $this->closeConnection( $conn );
 731                 }
 732
 733                 return $ok;
 734         }
 735
 736         public function getConnection( $i, $groups = [], $domain = false, $flags = 0 ) {
 737                 if ( $i === null || $i === false ) {
 738                         throw new InvalidArgumentException( "Cannot connect without a server index" );
 739                 }
 740
 741                 $domain = $this->resolveDomainID( $domain );
 742                 $masterOnly = ( $i == self::DB_MASTER || $i == $this->getWriterIndex() );
 743
 744                 if ( ( $flags & self::CONN_TRX_AUTOCOMMIT ) === self::CONN_TRX_AUTOCOMMIT ) {
 745                         // Assuming all servers are of the same type (or similar), which is overwhelmingly
 746                         // the case, use the master server information to get the attributes. The information
 747                         // for $i cannot be used since it might be DB_REPLICA, which might require connection
 748                         // attempts in order to be resolved into a real server index.
 749                         $attributes = $this->getServerAttributes( $this->getWriterIndex() );
 750                         if ( $attributes[Database::ATTR_DB_LEVEL_LOCKING] ) {
 751                                 // Callers sometimes want to (a) escape REPEATABLE-READ stateness without locking
 752                                 // rows (e.g. FOR UPDATE) or (b) make small commits during a larger transactions
 753                                 // to reduce lock contention. None of these apply for sqlite and using separate
 754                                 // connections just causes self-deadlocks.
 755                                 $flags &= ~self::CONN_TRX_AUTOCOMMIT;
 756                                 $this->connLogger->info( __METHOD__ .
 757                                         ': ignoring CONN_TRX_AUTOCOMMIT to avoid deadlocks.' );
 758                         }
 759                 }
 760
 761                 // Number of connections made before getting the server index and handle
 762                 $priorConnectionsMade = $this->connsOpened;
 763                 // Decide which server to use (might trigger new connections)
 764                 $serverIndex = $this->getConnectionIndex( $i, $groups, $domain );
 765                 // Get an open connection to that server (might trigger a new connection)
 766                 $conn = $this->openConnection( $serverIndex, $domain, $flags );
 767                 if ( !$conn ) {
 768                         $this->reportConnectionError();
 769                         return null; // unreachable due to exception
 770                 }
 771
 772                 // Profile any new connections caused by this method
 773                 if ( $this->connsOpened > $priorConnectionsMade ) {
 774                         $host = $conn->getServer();
 775                         $dbname = $conn->getDBname();
 776                         $this->trxProfiler->recordConnection( $host, $dbname, $masterOnly );
 777                 }
 778
 779                 if ( $serverIndex == $this->getWriterIndex() ) {
 780                         // If the load balancer is read-only, perhaps due to replication lag, then master
 781                         // DB handles will reflect that. Note that Database::assertIsWritableMaster() takes
 782                         // care of replica DB handles whereas getReadOnlyReason() would cause infinite loops.
 783                         $conn->setLBInfo( 'readOnlyReason', $this->getReadOnlyReason( $domain, $conn ) );
 784                 }
 785
 786                 return $conn;
 787         }
 788
 789         public function reuseConnection( IDatabase $conn ) {
 790                 $serverIndex = $conn->getLBInfo( 'serverIndex' );
 791                 $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 792                 if ( $serverIndex === null || $refCount === null ) {
 793                         /**
 794                          * This can happen in code like:
 795                          *   foreach ( $dbs as $db ) {
 796                          *     $conn = $lb->getConnection( $lb::DB_REPLICA, [], $db );
 797                          *     ...
 798                          *     $lb->reuseConnection( $conn );
 799                          *   }
 800                          * When a connection to the local DB is opened in this way, reuseConnection()
 801                          * should be ignored
 802                          */
 803                         return;
 804                 } elseif ( $conn instanceof DBConnRef ) {
 805                         // DBConnRef already handles calling reuseConnection() and only passes the live
 806                         // Database instance to this method. Any caller passing in a DBConnRef is broken.
 807                         $this->connLogger->error(
 808                                 __METHOD__ . ": got DBConnRef instance.\n" .
 809                                 ( new RuntimeException() )->getTraceAsString() );
 810
 811                         return;
 812                 }
 813
 814                 if ( $this->disabled ) {
 815                         return; // DBConnRef handle probably survived longer than the LoadBalancer
 816                 }
 817
 818                 if ( $conn->getLBInfo( 'autoCommitOnly' ) ) {
 819                         $connFreeKey = self::KEY_FOREIGN_FREE_NOROUND;
 820                         $connInUseKey = self::KEY_FOREIGN_INUSE_NOROUND;
 821                 } else {
 822                         $connFreeKey = self::KEY_FOREIGN_FREE;
 823                         $connInUseKey = self::KEY_FOREIGN_INUSE;
 824                 }
 825
 826                 $domain = $conn->getDomainID();
 827                 if ( !isset( $this->conns[$connInUseKey][$serverIndex][$domain] ) ) {
 828                         throw new InvalidArgumentException(
 829                                 "Connection $serverIndex/$domain not found; it may have already been freed" );
 830                 } elseif ( $this->conns[$connInUseKey][$serverIndex][$domain] !== $conn ) {
 831                         throw new InvalidArgumentException(
 832                                 "Connection $serverIndex/$domain mismatched; it may have already been freed" );
 833                 }
 834
 835                 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
 836                 if ( $refCount <= 0 ) {
 837                         $this->conns[$connFreeKey][$serverIndex][$domain] = $conn;
 838                         unset( $this->conns[$connInUseKey][$serverIndex][$domain] );
 839                         if ( !$this->conns[$connInUseKey][$serverIndex] ) {
 840                                 unset( $this->conns[$connInUseKey][$serverIndex] ); // clean up
 841                         }
 842                         $this->connLogger->debug( __METHOD__ . ": freed connection $serverIndex/$domain" );
 843                 } else {
 844                         $this->connLogger->debug( __METHOD__ .
 845                                 ": reference count for $serverIndex/$domain reduced to $refCount" );
 846                 }
 847         }
 848
 849         public function getConnectionRef( $i, $groups = [], $domain = false, $flags = 0 ) {
 850                 $domain = $this->resolveDomainID( $domain );
 851                 $role = $this->getRoleFromIndex( $i );
 852
 853                 return new DBConnRef( $this, $this->getConnection( $i, $groups, $domain, $flags ), $role );
 854         }
 855
 856         public function getLazyConnectionRef( $i, $groups = [], $domain = false, $flags = 0 ) {
 857                 $domain = $this->resolveDomainID( $domain );
 858                 $role = $this->getRoleFromIndex( $i );
 859
 860                 return new DBConnRef( $this, [ $i, $groups, $domain, $flags ], $role );
 861         }
 862
 863         public function getMaintenanceConnectionRef( $i, $groups = [], $domain = false, $flags = 0 ) {
 864                 $domain = $this->resolveDomainID( $domain );
 865                 $role = $this->getRoleFromIndex( $i );
 866
 867                 return new MaintainableDBConnRef(
 868                         $this, $this->getConnection( $i, $groups, $domain, $flags ), $role );
 869         }
 870
 871         /**
 872          * @param int $i Server index or DB_MASTER/DB_REPLICA
 873          * @return int One of DB_MASTER/DB_REPLICA
 874          */
 875         private function getRoleFromIndex( $i ) {
 876                 return ( $i === self::DB_MASTER || $i === $this->getWriterIndex() )
 877                         ? self::DB_MASTER
 878                         : self::DB_REPLICA;
 879         }
 880
 881         public function openConnection( $i, $domain = false, $flags = 0 ) {
 882                 $domain = $this->resolveDomainID( $domain );
 883
 884                 if ( !$this->connectionAttempted && $this->chronologyCallback ) {
 885                         // Load any "waitFor" positions before connecting so that doWait() is triggered
 886                         $this->connLogger->debug( __METHOD__ . ': calling initLB() before first connection.' );
 887                         $this->connectionAttempted = true;
 888                         ( $this->chronologyCallback )( $this );
 889                 }
 890
 891                 $conn = $this->localDomain->equals( $domain )
 892                         ? $this->openLocalConnection( $i, $flags )
 893                         : $this->openForeignConnection( $i, $domain, $flags );
 894
 895                 if ( $conn instanceof IDatabase && !$conn->isOpen() ) {
 896                         // Connection was made but later unrecoverably lost for some reason.
 897                         // Do not return a handle that will just throw exceptions on use,
 898                         // but let the calling code (e.g. getReaderIndex) try another server.
 899                         $this->errorConnection = $conn;
 900                         $conn = false;
 901                 }
 902
 903                 if (
 904                         $conn instanceof IDatabase &&
 905                         ( ( $flags & self::CONN_TRX_AUTOCOMMIT ) == self::CONN_TRX_AUTOCOMMIT )
 906                 ) {
 907                         if ( $conn->trxLevel() ) { // sanity
 908                                 throw new DBUnexpectedError(
 909                                         $conn,
 910                                         'Handle requested with CONN_TRX_AUTOCOMMIT yet it has a transaction'
 911                                 );
 912                         }
 913
 914                         $conn->clearFlag( $conn::DBO_TRX ); // auto-commit mode
 915                 }
 916
 917                 return $conn;
 918         }
 919
 920         /**
 921          * Open a connection to a local DB, or return one if it is already open.
 922          *
 923          * On error, returns false, and the connection which caused the
 924          * error will be available via $this->errorConnection.
 925          *
 926          * @note If disable() was called on this LoadBalancer, this method will throw a DBAccessError.
 927          *
 928          * @param int $i Server index
 929          * @param int $flags Class CONN_* constant bitfield
 930          * @return Database
 931          */
 932         private function openLocalConnection( $i, $flags = 0 ) {
 933                 // Connection handles required to be in auto-commit mode use a separate connection
 934                 // pool since the main pool is effected by implicit and explicit transaction rounds
 935                 $autoCommit = ( ( $flags & self::CONN_TRX_AUTOCOMMIT ) == self::CONN_TRX_AUTOCOMMIT );
 936
 937                 $connKey = $autoCommit ? self::KEY_LOCAL_NOROUND : self::KEY_LOCAL;
 938                 if ( isset( $this->conns[$connKey][$i][0] ) ) {
 939                         $conn = $this->conns[$connKey][$i][0];
 940                 } else {
 941                         if ( !isset( $this->servers[$i] ) || !is_array( $this->servers[$i] ) ) {
 942                                 throw new InvalidArgumentException( "No server with index '$i'" );
 943                         }
 944                         // Open a new connection
 945                         $server = $this->servers[$i];
 946                         $server['serverIndex'] = $i;
 947                         $server['autoCommitOnly'] = $autoCommit;
 948                         $conn = $this->reallyOpenConnection( $server, $this->localDomain );
 949                         $host = $this->getServerName( $i );
 950                         if ( $conn->isOpen() ) {
 951                                 $this->connLogger->debug(
 952                                         __METHOD__ . ": connected to database $i at '$host'." );
 953                                 $this->conns[$connKey][$i][0] = $conn;
 954                         } else {
 955                                 $this->connLogger->warning(
 956                                         __METHOD__ . ": failed to connect to database $i at '$host'." );
 957                                 $this->errorConnection = $conn;
 958                                 $conn = false;
 959                         }
 960                 }
 961
 962                 // Final sanity check to make sure the right domain is selected
 963                 if (
 964                         $conn instanceof IDatabase &&
 965                         !$this->localDomain->isCompatible( $conn->getDomainID() )
 966                 ) {
 967                         throw new UnexpectedValueException(
 968                                 "Got connection to '{$conn->getDomainID()}', " .
 969                                 "but expected local domain ('{$this->localDomain}')" );
 970                 }
 971
 972                 return $conn;
 973         }
 974
 975         /**
 976          * Open a connection to a foreign DB, or return one if it is already open.
 977          *
 978          * Increments a reference count on the returned connection which locks the
 979          * connection to the requested domain. This reference count can be
 980          * decremented by calling reuseConnection().
 981          *
 982          * If a connection is open to the appropriate server already, but with the wrong
 983          * database, it will be switched to the right database and returned, as long as
 984          * it has been freed first with reuseConnection().
 985          *
 986          * On error, returns false, and the connection which caused the
 987          * error will be available via $this->errorConnection.
 988          *
 989          * @note If disable() was called on this LoadBalancer, this method will throw a DBAccessError.
 990          *
 991          * @param int $i Server index
 992          * @param string $domain Domain ID to open
 993          * @param int $flags Class CONN_* constant bitfield
 994          * @return Database|bool Returns false on connection error
 995          * @throws DBError When database selection fails
 996          */
 997         private function openForeignConnection( $i, $domain, $flags = 0 ) {
 998                 $domainInstance = DatabaseDomain::newFromId( $domain );
 999                 // Connection handles required to be in auto-commit mode use a separate connection
1000                 // pool since the main pool is effected by implicit and explicit transaction rounds
1001                 $autoCommit = ( ( $flags & self::CONN_TRX_AUTOCOMMIT ) == self::CONN_TRX_AUTOCOMMIT );
1002
1003                 if ( $autoCommit ) {
1004                         $connFreeKey = self::KEY_FOREIGN_FREE_NOROUND;
1005                         $connInUseKey = self::KEY_FOREIGN_INUSE_NOROUND;
1006                 } else {
1007                         $connFreeKey = self::KEY_FOREIGN_FREE;
1008                         $connInUseKey = self::KEY_FOREIGN_INUSE;
1009                 }
1010
1011                 /** @var Database $conn */
1012                 $conn = null;
1013
1014                 if ( isset( $this->conns[$connInUseKey][$i][$domain] ) ) {
1015                         // Reuse an in-use connection for the same domain
1016                         $conn = $this->conns[$connInUseKey][$i][$domain];
1017                         $this->connLogger->debug( __METHOD__ . ": reusing connection $i/$domain" );
1018                 } elseif ( isset( $this->conns[$connFreeKey][$i][$domain] ) ) {
1019                         // Reuse a free connection for the same domain
1020                         $conn = $this->conns[$connFreeKey][$i][$domain];
1021                         unset( $this->conns[$connFreeKey][$i][$domain] );
1022                         $this->conns[$connInUseKey][$i][$domain] = $conn;
1023                         $this->connLogger->debug( __METHOD__ . ": reusing free connection $i/$domain" );
1024                 } elseif ( !empty( $this->conns[$connFreeKey][$i] ) ) {
1025                         // Reuse a free connection from another domain if possible
1026                         foreach ( $this->conns[$connFreeKey][$i] as $oldDomain => $conn ) {
1027                                 if ( $domainInstance->getDatabase() !== null ) {
1028                                         // Check if changing the database will require a new connection.
1029                                         // In that case, leave the connection handle alone and keep looking.
1030                                         // This prevents connections from being closed mid-transaction and can
1031                                         // also avoid overhead if the same database will later be requested.
1032                                         if (
1033                                                 $conn->databasesAreIndependent() &&
1034                                                 $conn->getDBname() !== $domainInstance->getDatabase()
1035                                         ) {
1036                                                 continue;
1037                                         }
1038                                         // Select the new database, schema, and prefix
1039                                         $conn->selectDomain( $domainInstance );
1040                                 } else {
1041                                         // Stay on the current database, but update the schema/prefix
1042                                         $conn->dbSchema( $domainInstance->getSchema() );
1043                                         $conn->tablePrefix( $domainInstance->getTablePrefix() );
1044                                 }
1045                                 unset( $this->conns[$connFreeKey][$i][$oldDomain] );
1046                                 // Note that if $domain is an empty string, getDomainID() might not match it
1047                                 $this->conns[$connInUseKey][$i][$conn->getDomainID()] = $conn;
1048                                 $this->connLogger->debug( __METHOD__ .
1049                                         ": reusing free connection from $oldDomain for $domain" );
1050                                 break;
1051                         }
1052                 }
1053
1054                 if ( !$conn ) {
1055                         if ( !isset( $this->servers[$i] ) || !is_array( $this->servers[$i] ) ) {
1056                                 throw new InvalidArgumentException( "No server with index '$i'" );
1057                         }
1058                         // Open a new connection
1059                         $server = $this->servers[$i];
1060                         $server['serverIndex'] = $i;
1061                         $server['foreignPoolRefCount'] = 0;
1062                         $server['foreign'] = true;
1063                         $server['autoCommitOnly'] = $autoCommit;
1064                         $conn = $this->reallyOpenConnection( $server, $domainInstance );
1065                         if ( !$conn->isOpen() ) {
1066                                 $this->connLogger->warning( __METHOD__ . ": connection error for $i/$domain" );
1067                                 $this->errorConnection = $conn;
1068                                 $conn = false;
1069                         } else {
1070                                 // Note that if $domain is an empty string, getDomainID() might not match it
1071                                 $this->conns[$connInUseKey][$i][$conn->getDomainID()] = $conn;
1072                                 $this->connLogger->debug( __METHOD__ . ": opened new connection for $i/$domain" );
1073                         }
1074                 }
1075
1076                 if ( $conn instanceof IDatabase ) {
1077                         // Final sanity check to make sure the right domain is selected
1078                         if ( !$domainInstance->isCompatible( $conn->getDomainID() ) ) {
1079                                 throw new UnexpectedValueException(
1080                                         "Got connection to '{$conn->getDomainID()}', but expected '$domain'" );
1081                         }
1082                         // Increment reference count
1083                         $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
1084                         $conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
1085                 }
1086
1087                 return $conn;
1088         }
1089
1090         public function getServerAttributes( $i ) {
1091                 return Database::attributesFromType(
1092                         $this->getServerType( $i ),
1093                         $this->servers[$i]['driver'] ?? null
1094                 );
1095         }
1096
1097         /**
1098          * Test if the specified index represents an open connection
1099          *
1100          * @param int $index Server index
1101          * @private
1102          * @return bool
1103          */
1104         private function isOpen( $index ) {
1105                 if ( !is_int( $index ) ) {
1106                         return false;
1107                 }
1108
1109                 return (bool)$this->getAnyOpenConnection( $index );
1110         }
1111
1112         /**
1113          * Open a new network connection to a server (uncached)
1114          *
1115          * Returns a Database object whether or not the connection was successful.
1116          *
1117          * @param array $server
1118          * @param DatabaseDomain $domain Domain the connection is for, possibly unspecified
1119          * @return Database
1120          * @throws DBAccessError
1121          * @throws InvalidArgumentException
1122          */
1123         protected function reallyOpenConnection( array $server, DatabaseDomain $domain ) {
1124                 if ( $this->disabled ) {
1125                         throw new DBAccessError();
1126                 }
1127
1128                 if ( $domain->getDatabase() === null ) {
1129                         // The database domain does not specify a DB name and some database systems require a
1130                         // valid DB specified on connection. The $server configuration array contains a default
1131                         // DB name to use for connections in such cases.
1132                         if ( $server['type'] === 'mysql' ) {
1133                                 // For MySQL, DATABASE and SCHEMA are synonyms, connections need not specify a DB,
1134                                 // and the DB name in $server might not exist due to legacy reasons (the default
1135                                 // domain used to ignore the local LB domain, even when mismatched).
1136                                 $server['dbname'] = null;
1137                         }
1138                 } else {
1139                         $server['dbname'] = $domain->getDatabase();
1140                 }
1141
1142                 if ( $domain->getSchema() !== null ) {
1143                         $server['schema'] = $domain->getSchema();
1144                 }
1145
1146                 // It is always possible to connect with any prefix, even the empty string
1147                 $server['tablePrefix'] = $domain->getTablePrefix();
1148
1149                 // Let the handle know what the cluster master is (e.g. "db1052")
1150                 $masterName = $this->getServerName( $this->getWriterIndex() );
1151                 $server['clusterMasterHost'] = $masterName;
1152
1153                 // Log when many connection are made on requests
1154                 if ( ++$this->connsOpened >= self::CONN_HELD_WARN_THRESHOLD ) {
1155                         $this->perfLogger->warning( __METHOD__ . ": " .
1156                                 "{$this->connsOpened}+ connections made (master=$masterName)" );
1157                 }
1158
1159                 $server['srvCache'] = $this->srvCache;
1160                 // Set loggers and profilers
1161                 $server['connLogger'] = $this->connLogger;
1162                 $server['queryLogger'] = $this->queryLogger;
1163                 $server['errorLogger'] = $this->errorLogger;
1164                 $server['deprecationLogger'] = $this->deprecationLogger;
1165                 $server['profiler'] = $this->profiler;
1166                 $server['trxProfiler'] = $this->trxProfiler;
1167                 // Use the same agent and PHP mode for all DB handles
1168                 $server['cliMode'] = $this->cliMode;
1169                 $server['agent'] = $this->agent;
1170                 // Use DBO_DEFAULT flags by default for LoadBalancer managed databases. Assume that the
1171                 // application calls LoadBalancer::commitMasterChanges() before the PHP script completes.
1172                 $server['flags'] = $server['flags'] ?? IDatabase::DBO_DEFAULT;
1173
1174                 // Create a live connection object
1175                 try {
1176                         $db = Database::factory( $server['type'], $server );
1177                 } catch ( DBConnectionError $e ) {
1178                         // FIXME: This is probably the ugliest thing I have ever done to
1179                         // PHP. I'm half-expecting it to segfault, just out of disgust. -- TS
1180                         $db = $e->db;
1181                 }
1182
1183                 $db->setLBInfo( $server );
1184                 $db->setLazyMasterHandle(
1185                         $this->getLazyConnectionRef( self::DB_MASTER, [], $db->getDomainID() )
1186                 );
1187                 $db->setTableAliases( $this->tableAliases );
1188                 $db->setIndexAliases( $this->indexAliases );
1189
1190                 if ( $server['serverIndex'] === $this->getWriterIndex() ) {
1191                         if ( $this->trxRoundId !== false ) {
1192                                 $this->applyTransactionRoundFlags( $db );
1193                         }
1194                         foreach ( $this->trxRecurringCallbacks as $name => $callback ) {
1195                                 $db->setTransactionListener( $name, $callback );
1196                         }
1197                 }
1198
1199                 return $db;
1200         }
1201
1202         /**
1203          * @throws DBConnectionError
1204          */
1205         private function reportConnectionError() {
1206                 $conn = $this->errorConnection; // the connection which caused the error
1207                 $context = [
1208                         'method' => __METHOD__,
1209                         'last_error' => $this->lastError,
1210                 ];
1211
1212                 if ( $conn instanceof IDatabase ) {
1213                         $context['db_server'] = $conn->getServer();
1214                         $this->connLogger->warning(
1215                                 __METHOD__ . ": connection error: {last_error} ({db_server})",
1216                                 $context
1217                         );
1218
1219                         throw new DBConnectionError( $conn, "{$this->lastError} ({$context['db_server']})" );
1220                 } else {
1221                         // No last connection, probably due to all servers being too busy
1222                         $this->connLogger->error(
1223                                 __METHOD__ .
1224                                 ": LB failure with no last connection. Connection error: {last_error}",
1225                                 $context
1226                         );
1227
1228                         // If all servers were busy, "lastError" will contain something sensible
1229                         throw new DBConnectionError( null, $this->lastError );
1230                 }
1231         }
1232
1233         public function getWriterIndex() {
1234                 return 0;
1235         }
1236
1237         public function haveIndex( $i ) {
1238                 return array_key_exists( $i, $this->servers );
1239         }
1240
1241         public function isNonZeroLoad( $i ) {
1242                 return array_key_exists( $i, $this->servers ) && $this->genericLoads[$i] != 0;
1243         }
1244
1245         public function getServerCount() {
1246                 return count( $this->servers );
1247         }
1248
1249         public function getServerName( $i ) {
1250                 $name = $this->servers[$i]['hostName'] ?? $this->servers[$i]['host'] ?? '';
1251
1252                 return ( $name != '' ) ? $name : 'localhost';
1253         }
1254
1255         public function getServerInfo( $i ) {
1256                 return $this->servers[$i] ?? false;
1257         }
1258
1259         public function getServerType( $i ) {
1260                 return $this->servers[$i]['type'] ?? 'unknown';
1261         }
1262
1263         public function getMasterPos() {
1264                 # If this entire request was served from a replica DB without opening a connection to the
1265                 # master (however unlikely that may be), then we can fetch the position from the replica DB.
1266                 $masterConn = $this->getAnyOpenConnection( $this->getWriterIndex() );
1267                 if ( !$masterConn ) {
1268                         $serverCount = count( $this->servers );
1269                         for ( $i = 1; $i < $serverCount; $i++ ) {
1270                                 $conn = $this->getAnyOpenConnection( $i );
1271                                 if ( $conn ) {
1272                                         return $conn->getReplicaPos();
1273                                 }
1274                         }
1275                 } else {
1276                         return $masterConn->getMasterPos();
1277                 }
1278
1279                 return false;
1280         }
1281
1282         public function disable() {
1283                 $this->closeAll();
1284                 $this->disabled = true;
1285         }
1286
1287         public function closeAll() {
1288                 $fname = __METHOD__;
1289                 $this->forEachOpenConnection( function ( IDatabase $conn ) use ( $fname ) {
1290                         $host = $conn->getServer();
1291                         $this->connLogger->debug(
1292                                 $fname . ": closing connection to database '$host'." );
1293                         $conn->close();
1294                 } );
1295
1296                 $this->conns = [
1297                         self::KEY_LOCAL => [],
1298                         self::KEY_FOREIGN_INUSE => [],
1299                         self::KEY_FOREIGN_FREE => [],
1300                         self::KEY_LOCAL_NOROUND => [],
1301                         self::KEY_FOREIGN_INUSE_NOROUND => [],
1302                         self::KEY_FOREIGN_FREE_NOROUND => []
1303                 ];
1304                 $this->connsOpened = 0;
1305         }
1306
1307         public function closeConnection( IDatabase $conn ) {
1308                 if ( $conn instanceof DBConnRef ) {
1309                         // Avoid calling close() but still leaving the handle in the pool
1310                         throw new RuntimeException( 'Cannot close DBConnRef instance; it must be shareable' );
1311                 }
1312
1313                 $serverIndex = $conn->getLBInfo( 'serverIndex' );
1314                 foreach ( $this->conns as $type => $connsByServer ) {
1315                         if ( !isset( $connsByServer[$serverIndex] ) ) {
1316                                 continue;
1317                         }
1318
1319                         foreach ( $connsByServer[$serverIndex] as $i => $trackedConn ) {
1320                                 if ( $conn === $trackedConn ) {
1321                                         $host = $this->getServerName( $i );
1322                                         $this->connLogger->debug(
1323                                                 __METHOD__ . ": closing connection to database $i at '$host'." );
1324                                         unset( $this->conns[$type][$serverIndex][$i] );
1325                                         --$this->connsOpened;
1326                                         break 2;
1327                                 }
1328                         }
1329                 }
1330
1331                 $conn->close();
1332         }
1333
1334         public function commitAll( $fname = __METHOD__, $owner = null ) {
1335                 $this->commitMasterChanges( $fname, $owner );
1336                 $this->flushMasterSnapshots( $fname );
1337                 $this->flushReplicaSnapshots( $fname );
1338         }
1339
1340         public function finalizeMasterChanges( $fname = __METHOD__, $owner = null ) {
1341                 $this->assertOwnership( $fname, $owner );
1342                 $this->assertTransactionRoundStage( [ self::ROUND_CURSORY, self::ROUND_FINALIZED ] );
1343
1344                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1345                 // Loop until callbacks stop adding callbacks on other connections
1346                 $total = 0;
1347                 do {
1348                         $count = 0; // callbacks execution attempts
1349                         $this->forEachOpenMasterConnection( function ( Database $conn ) use ( &$count ) {
1350                                 // Run any pre-commit callbacks while leaving the post-commit ones suppressed.
1351                                 // Any error should cause all (peer) transactions to be rolled back together.
1352                                 $count += $conn->runOnTransactionPreCommitCallbacks();
1353                         } );
1354                         $total += $count;
1355                 } while ( $count > 0 );
1356                 // Defer post-commit callbacks until after COMMIT/ROLLBACK happens on all handles
1357                 $this->forEachOpenMasterConnection( function ( Database $conn ) {
1358                         $conn->setTrxEndCallbackSuppression( true );
1359                 } );
1360                 $this->trxRoundStage = self::ROUND_FINALIZED;
1361
1362                 return $total;
1363         }
1364
1365         public function approveMasterChanges( array $options, $fname = __METHOD__, $owner = null ) {
1366                 $this->assertOwnership( $fname, $owner );
1367                 $this->assertTransactionRoundStage( self::ROUND_FINALIZED );
1368
1369                 $limit = $options['maxWriteDuration'] ?? 0;
1370
1371                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1372                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( $limit ) {
1373                         // If atomic sections or explicit transactions are still open, some caller must have
1374                         // caught an exception but failed to properly rollback any changes. Detect that and
1375                         // throw and error (causing rollback).
1376                         $conn->assertNoOpenTransactions();
1377                         // Assert that the time to replicate the transaction will be sane.
1378                         // If this fails, then all DB transactions will be rollback back together.
1379                         $time = $conn->pendingWriteQueryDuration( $conn::ESTIMATE_DB_APPLY );
1380                         if ( $limit > 0 && $time > $limit ) {
1381                                 throw new DBTransactionSizeError(
1382                                         $conn,
1383                                         "Transaction spent $time second(s) in writes, exceeding the limit of $limit",
1384                                         [ $time, $limit ]
1385                                 );
1386                         }
1387                         // If a connection sits idle while slow queries execute on another, that connection
1388                         // may end up dropped before the commit round is reached. Ping servers to detect this.
1389                         if ( $conn->writesOrCallbacksPending() && !$conn->ping() ) {
1390                                 throw new DBTransactionError(
1391                                         $conn,
1392                                         "A connection to the {$conn->getDBname()} database was lost before commit"
1393                                 );
1394                         }
1395                 } );
1396                 $this->trxRoundStage = self::ROUND_APPROVED;
1397         }
1398
1399         public function beginMasterChanges( $fname = __METHOD__, $owner = null ) {
1400                 $this->assertOwnership( $fname, $owner );
1401                 if ( $this->trxRoundId !== false ) {
1402                         throw new DBTransactionError(
1403                                 null,
1404                                 "$fname: Transaction round '{$this->trxRoundId}' already started"
1405                         );
1406                 }
1407                 $this->assertTransactionRoundStage( self::ROUND_CURSORY );
1408
1409                 // Clear any empty transactions (no writes/callbacks) from the implicit round
1410                 $this->flushMasterSnapshots( $fname );
1411
1412                 $this->trxRoundId = $fname;
1413                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1414                 // Mark applicable handles as participating in this explicit transaction round.
1415                 // For each of these handles, any writes and callbacks will be tied to a single
1416                 // transaction. The (peer) handles will reject begin()/commit() calls unless they
1417                 // are part of an en masse commit or an en masse rollback.
1418                 $this->forEachOpenMasterConnection( function ( Database $conn ) {
1419                         $this->applyTransactionRoundFlags( $conn );
1420                 } );
1421                 $this->trxRoundStage = self::ROUND_CURSORY;
1422         }
1423
1424         public function commitMasterChanges( $fname = __METHOD__, $owner = null ) {
1425                 $this->assertOwnership( $fname, $owner );
1426                 $this->assertTransactionRoundStage( self::ROUND_APPROVED );
1427
1428                 $failures = [];
1429
1430                 /** @noinspection PhpUnusedLocalVariableInspection */
1431                 $scope = ScopedCallback::newScopedIgnoreUserAbort(); // try to ignore client aborts
1432
1433                 $restore = ( $this->trxRoundId !== false );
1434                 $this->trxRoundId = false;
1435                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1436                 // Commit any writes and clear any snapshots as well (callbacks require AUTOCOMMIT).
1437                 // Note that callbacks should already be suppressed due to finalizeMasterChanges().
1438                 $this->forEachOpenMasterConnection(
1439                         function ( IDatabase $conn ) use ( $fname, &$failures ) {
1440                                 try {
1441                                         $conn->commit( $fname, $conn::FLUSHING_ALL_PEERS );
1442                                 } catch ( DBError $e ) {
1443                                         ( $this->errorLogger )( $e );
1444                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1445                                 }
1446                         }
1447                 );
1448                 if ( $failures ) {
1449                         throw new DBTransactionError(
1450                                 null,
1451                                 "$fname: Commit failed on server(s) " . implode( "\n", array_unique( $failures ) )
1452                         );
1453                 }
1454                 if ( $restore ) {
1455                         // Unmark handles as participating in this explicit transaction round
1456                         $this->forEachOpenMasterConnection( function ( Database $conn ) {
1457                                 $this->undoTransactionRoundFlags( $conn );
1458                         } );
1459                 }
1460                 $this->trxRoundStage = self::ROUND_COMMIT_CALLBACKS;
1461         }
1462
1463         public function runMasterTransactionIdleCallbacks( $fname = __METHOD__, $owner = null ) {
1464                 $this->assertOwnership( $fname, $owner );
1465                 if ( $this->trxRoundStage === self::ROUND_COMMIT_CALLBACKS ) {
1466                         $type = IDatabase::TRIGGER_COMMIT;
1467                 } elseif ( $this->trxRoundStage === self::ROUND_ROLLBACK_CALLBACKS ) {
1468                         $type = IDatabase::TRIGGER_ROLLBACK;
1469                 } else {
1470                         throw new DBTransactionError(
1471                                 null,
1472                                 "Transaction should be in the callback stage (not '{$this->trxRoundStage}')"
1473                         );
1474                 }
1475
1476                 $oldStage = $this->trxRoundStage;
1477                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1478
1479                 // Now that the COMMIT/ROLLBACK step is over, enable post-commit callback runs
1480                 $this->forEachOpenMasterConnection( function ( Database $conn ) {
1481                         $conn->setTrxEndCallbackSuppression( false );
1482                 } );
1483
1484                 $e = null; // first exception
1485                 $fname = __METHOD__;
1486                 // Loop until callbacks stop adding callbacks on other connections
1487                 do {
1488                         // Run any pending callbacks for each connection...
1489                         $count = 0; // callback execution attempts
1490                         $this->forEachOpenMasterConnection(
1491                                 function ( Database $conn ) use ( $type, &$e, &$count ) {
1492                                         if ( $conn->trxLevel() ) {
1493                                                 return; // retry in the next iteration, after commit() is called
1494                                         }
1495                                         try {
1496                                                 $count += $conn->runOnTransactionIdleCallbacks( $type );
1497                                         } catch ( Exception $ex ) {
1498                                                 $e = $e ?: $ex;
1499                                         }
1500                                 }
1501                         );
1502                         // Clear out any active transactions left over from callbacks...
1503                         $this->forEachOpenMasterConnection( function ( Database $conn ) use ( &$e, $fname ) {
1504                                 if ( $conn->writesPending() ) {
1505                                         // A callback from another handle wrote to this one and DBO_TRX is set
1506                                         $this->queryLogger->warning( $fname . ": found writes pending." );
1507                                         $fnames = implode( ', ', $conn->pendingWriteAndCallbackCallers() );
1508                                         $this->queryLogger->warning(
1509                                                 $fname . ": found writes pending ($fnames).",
1510                                                 [
1511                                                         'db_server' => $conn->getServer(),
1512                                                         'db_name' => $conn->getDBname()
1513                                                 ]
1514                                         );
1515                                 } elseif ( $conn->trxLevel() ) {
1516                                         // A callback from another handle read from this one and DBO_TRX is set,
1517                                         // which can easily happen if there is only one DB (no replicas)
1518                                         $this->queryLogger->debug( $fname . ": found empty transaction." );
1519                                 }
1520                                 try {
1521                                         $conn->commit( $fname, $conn::FLUSHING_ALL_PEERS );
1522                                 } catch ( Exception $ex ) {
1523                                         $e = $e ?: $ex;
1524                                 }
1525                         } );
1526                 } while ( $count > 0 );
1527
1528                 $this->trxRoundStage = $oldStage;
1529
1530                 return $e;
1531         }
1532
1533         public function runMasterTransactionListenerCallbacks( $fname = __METHOD__, $owner = null ) {
1534                 $this->assertOwnership( $fname, $owner );
1535                 if ( $this->trxRoundStage === self::ROUND_COMMIT_CALLBACKS ) {
1536                         $type = IDatabase::TRIGGER_COMMIT;
1537                 } elseif ( $this->trxRoundStage === self::ROUND_ROLLBACK_CALLBACKS ) {
1538                         $type = IDatabase::TRIGGER_ROLLBACK;
1539                 } else {
1540                         throw new DBTransactionError(
1541                                 null,
1542                                 "Transaction should be in the callback stage (not '{$this->trxRoundStage}')"
1543                         );
1544                 }
1545
1546                 $e = null;
1547
1548                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1549                 $this->forEachOpenMasterConnection( function ( Database $conn ) use ( $type, &$e ) {
1550                         try {
1551                                 $conn->runTransactionListenerCallbacks( $type );
1552                         } catch ( Exception $ex ) {
1553                                 $e = $e ?: $ex;
1554                         }
1555                 } );
1556                 $this->trxRoundStage = self::ROUND_CURSORY;
1557
1558                 return $e;
1559         }
1560
1561         public function rollbackMasterChanges( $fname = __METHOD__, $owner = null ) {
1562                 $this->assertOwnership( $fname, $owner );
1563
1564                 $restore = ( $this->trxRoundId !== false );
1565                 $this->trxRoundId = false;
1566                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1567                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( $fname ) {
1568                         $conn->rollback( $fname, $conn::FLUSHING_ALL_PEERS );
1569                 } );
1570                 if ( $restore ) {
1571                         // Unmark handles as participating in this explicit transaction round
1572                         $this->forEachOpenMasterConnection( function ( Database $conn ) {
1573                                 $this->undoTransactionRoundFlags( $conn );
1574                         } );
1575                 }
1576                 $this->trxRoundStage = self::ROUND_ROLLBACK_CALLBACKS;
1577         }
1578
1579         /**
1580          * @param string|string[] $stage
1581          * @throws DBTransactionError
1582          */
1583         private function assertTransactionRoundStage( $stage ) {
1584                 $stages = (array)$stage;
1585
1586                 if ( !in_array( $this->trxRoundStage, $stages, true ) ) {
1587                         $stageList = implode(
1588                                 '/',
1589                                 array_map( function ( $v ) {
1590                                         return "'$v'";
1591                                 }, $stages )
1592                         );
1593                         throw new DBTransactionError(
1594                                 null,
1595                                 "Transaction round stage must be $stageList (not '{$this->trxRoundStage}')"
1596                         );
1597                 }
1598         }
1599
1600         /**
1601          * @param string $fname
1602          * @param int|null $owner Owner ID of the caller
1603          * @throws DBTransactionError
1604          */
1605         private function assertOwnership( $fname, $owner ) {
1606                 if ( $this->ownerId !== null && $owner !== $this->ownerId ) {
1607                         throw new DBTransactionError(
1608                                 null,
1609                                 "$fname: LoadBalancer is owned by LBFactory #{$this->ownerId} (got '$owner')."
1610                         );
1611                 }
1612         }
1613
1614         /**
1615          * Make all DB servers with DBO_DEFAULT/DBO_TRX set join the transaction round
1616          *
1617          * Some servers may have neither flag enabled, meaning that they opt out of such
1618          * transaction rounds and remain in auto-commit mode. Such behavior might be desired
1619          * when a DB server is used for something like simple key/value storage.
1620          *
1621          * @param Database $conn
1622          */
1623         private function applyTransactionRoundFlags( Database $conn ) {
1624                 if ( $conn->getLBInfo( 'autoCommitOnly' ) ) {
1625                         return; // transaction rounds do not apply to these connections
1626                 }
1627
1628                 if ( $conn->getFlag( $conn::DBO_DEFAULT ) ) {
1629                         // DBO_TRX is controlled entirely by CLI mode presence with DBO_DEFAULT.
1630                         // Force DBO_TRX even in CLI mode since a commit round is expected soon.
1631                         $conn->setFlag( $conn::DBO_TRX, $conn::REMEMBER_PRIOR );
1632                 }
1633
1634                 if ( $conn->getFlag( $conn::DBO_TRX ) ) {
1635                         $conn->setLBInfo( 'trxRoundId', $this->trxRoundId );
1636                 }
1637         }
1638
1639         /**
1640          * @param Database $conn
1641          */
1642         private function undoTransactionRoundFlags( Database $conn ) {
1643                 if ( $conn->getLBInfo( 'autoCommitOnly' ) ) {
1644                         return; // transaction rounds do not apply to these connections
1645                 }
1646
1647                 if ( $conn->getFlag( $conn::DBO_TRX ) ) {
1648                         $conn->setLBInfo( 'trxRoundId', false );
1649                 }
1650
1651                 if ( $conn->getFlag( $conn::DBO_DEFAULT ) ) {
1652                         $conn->restoreFlags( $conn::RESTORE_PRIOR );
1653                 }
1654         }
1655
1656         public function flushReplicaSnapshots( $fname = __METHOD__ ) {
1657                 $this->forEachOpenReplicaConnection( function ( IDatabase $conn ) use ( $fname ) {
1658                         $conn->flushSnapshot( $fname );
1659                 } );
1660         }
1661
1662         public function flushMasterSnapshots( $fname = __METHOD__ ) {
1663                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( $fname ) {
1664                         $conn->flushSnapshot( $fname );
1665                 } );
1666         }
1667
1668         /**
1669          * @return string
1670          * @since 1.32
1671          */
1672         public function getTransactionRoundStage() {
1673                 return $this->trxRoundStage;
1674         }
1675
1676         public function hasMasterConnection() {
1677                 return $this->isOpen( $this->getWriterIndex() );
1678         }
1679
1680         public function hasMasterChanges() {
1681                 $pending = 0;
1682                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$pending ) {
1683                         $pending |= $conn->writesOrCallbacksPending();
1684                 } );
1685
1686                 return (bool)$pending;
1687         }
1688
1689         public function lastMasterChangeTimestamp() {
1690                 $lastTime = false;
1691                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$lastTime ) {
1692                         $lastTime = max( $lastTime, $conn->lastDoneWrites() );
1693                 } );
1694
1695                 return $lastTime;
1696         }
1697
1698         public function hasOrMadeRecentMasterChanges( $age = null ) {
1699                 $age = ( $age === null ) ? $this->waitTimeout : $age;
1700
1701                 return ( $this->hasMasterChanges()
1702                         || $this->lastMasterChangeTimestamp() > microtime( true ) - $age );
1703         }
1704
1705         public function pendingMasterChangeCallers() {
1706                 $fnames = [];
1707                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$fnames ) {
1708                         $fnames = array_merge( $fnames, $conn->pendingWriteCallers() );
1709                 } );
1710
1711                 return $fnames;
1712         }
1713
1714         public function getLaggedReplicaMode( $domain = false ) {
1715                 if (
1716                         // Avoid recursion if there is only one DB
1717                         $this->getServerCount() > 1 &&
1718                         // Avoid recursion if the (non-zero load) master DB was picked for generic reads
1719                         $this->genericReadIndex !== $this->getWriterIndex() &&
1720                         // Stay in lagged replica mode during the load balancer instance lifetime
1721                         !$this->laggedReplicaMode
1722                 ) {
1723                         try {
1724                                 // Calling this method will set "laggedReplicaMode" as needed
1725                                 $this->getReaderIndex( false, $domain );
1726                         } catch ( DBConnectionError $e ) {
1727                                 // Avoid expensive re-connect attempts and failures
1728                                 $this->allReplicasDownMode = true;
1729                                 $this->laggedReplicaMode = true;
1730                         }
1731                 }
1732
1733                 return $this->laggedReplicaMode;
1734         }
1735
1736         public function laggedReplicaUsed() {
1737                 return $this->laggedReplicaMode;
1738         }
1739
1740         /**
1741          * @return bool
1742          * @since 1.27
1743          * @deprecated Since 1.28; use laggedReplicaUsed()
1744          */
1745         public function laggedSlaveUsed() {
1746                 return $this->laggedReplicaUsed();
1747         }
1748
1749         public function getReadOnlyReason( $domain = false, IDatabase $conn = null ) {
1750                 if ( $this->readOnlyReason !== false ) {
1751                         return $this->readOnlyReason;
1752                 } elseif ( $this->getLaggedReplicaMode( $domain ) ) {
1753                         if ( $this->allReplicasDownMode ) {
1754                                 return 'The database has been automatically locked ' .
1755                                         'until the replica database servers become available';
1756                         } else {
1757                                 return 'The database has been automatically locked ' .
1758                                         'while the replica database servers catch up to the master.';
1759                         }
1760                 } elseif ( $this->masterRunningReadOnly( $domain, $conn ) ) {
1761                         return 'The database master is running in read-only mode.';
1762                 }
1763
1764                 return false;
1765         }
1766
1767         /**
1768          * @param string $domain Domain ID, or false for the current domain
1769          * @param IDatabase|null $conn DB master connectionl used to avoid loops [optional]
1770          * @return bool
1771          */
1772         private function masterRunningReadOnly( $domain, IDatabase $conn = null ) {
1773                 $cache = $this->wanCache;
1774                 $masterServer = $this->getServerName( $this->getWriterIndex() );
1775
1776                 return (bool)$cache->getWithSetCallback(
1777                         $cache->makeGlobalKey( __CLASS__, 'server-read-only', $masterServer ),
1778                         self::TTL_CACHE_READONLY,
1779                         function () use ( $domain, $conn ) {
1780                                 $old = $this->trxProfiler->setSilenced( true );
1781                                 try {
1782                                         $dbw = $conn ?: $this->getConnection( self::DB_MASTER, [], $domain );
1783                                         $readOnly = (int)$dbw->serverIsReadOnly();
1784                                         if ( !$conn ) {
1785                                                 $this->reuseConnection( $dbw );
1786                                         }
1787                                 } catch ( DBError $e ) {
1788                                         $readOnly = 0;
1789                                 }
1790                                 $this->trxProfiler->setSilenced( $old );
1791                                 return $readOnly;
1792                         },
1793                         [ 'pcTTL' => $cache::TTL_PROC_LONG, 'busyValue' => 0 ]
1794                 );
1795         }
1796
1797         public function allowLagged( $mode = null ) {
1798                 if ( $mode === null ) {
1799                         return $this->allowLagged;
1800                 }
1801                 $this->allowLagged = $mode;
1802
1803                 return $this->allowLagged;
1804         }
1805
1806         public function pingAll() {
1807                 $success = true;
1808                 $this->forEachOpenConnection( function ( IDatabase $conn ) use ( &$success ) {
1809                         if ( !$conn->ping() ) {
1810                                 $success = false;
1811                         }
1812                 } );
1813
1814                 return $success;
1815         }
1816
1817         public function forEachOpenConnection( $callback, array $params = [] ) {
1818                 foreach ( $this->conns as $connsByServer ) {
1819                         foreach ( $connsByServer as $serverConns ) {
1820                                 foreach ( $serverConns as $conn ) {
1821                                         $callback( $conn, ...$params );
1822                                 }
1823                         }
1824                 }
1825         }
1826
1827         public function forEachOpenMasterConnection( $callback, array $params = [] ) {
1828                 $masterIndex = $this->getWriterIndex();
1829                 foreach ( $this->conns as $connsByServer ) {
1830                         if ( isset( $connsByServer[$masterIndex] ) ) {
1831                                 /** @var IDatabase $conn */
1832                                 foreach ( $connsByServer[$masterIndex] as $conn ) {
1833                                         $callback( $conn, ...$params );
1834                                 }
1835                         }
1836                 }
1837         }
1838
1839         public function forEachOpenReplicaConnection( $callback, array $params = [] ) {
1840                 foreach ( $this->conns as $connsByServer ) {
1841                         foreach ( $connsByServer as $i => $serverConns ) {
1842                                 if ( $i === $this->getWriterIndex() ) {
1843                                         continue; // skip master
1844                                 }
1845                                 foreach ( $serverConns as $conn ) {
1846                                         $callback( $conn, ...$params );
1847                                 }
1848                         }
1849                 }
1850         }
1851
1852         public function getMaxLag( $domain = false ) {
1853                 $maxLag = -1;
1854                 $host = '';
1855                 $maxIndex = 0;
1856
1857                 if ( $this->getServerCount() <= 1 ) {
1858                         return [ $host, $maxLag, $maxIndex ]; // no replication = no lag
1859                 }
1860
1861                 $lagTimes = $this->getLagTimes( $domain );
1862                 foreach ( $lagTimes as $i => $lag ) {
1863                         if ( $this->genericLoads[$i] > 0 && $lag > $maxLag ) {
1864                                 $maxLag = $lag;
1865                                 $host = $this->servers[$i]['host'];
1866                                 $maxIndex = $i;
1867                         }
1868                 }
1869
1870                 return [ $host, $maxLag, $maxIndex ];
1871         }
1872
1873         public function getLagTimes( $domain = false ) {
1874                 if ( $this->getServerCount() <= 1 ) {
1875                         return [ $this->getWriterIndex() => 0 ]; // no replication = no lag
1876                 }
1877
1878                 $knownLagTimes = []; // map of (server index => 0 seconds)
1879                 $indexesWithLag = [];
1880                 foreach ( $this->servers as $i => $server ) {
1881                         if ( empty( $server['is static'] ) ) {
1882                                 $indexesWithLag[] = $i; // DB server might have replication lag
1883                         } else {
1884                                 $knownLagTimes[$i] = 0; // DB server is a non-replicating and read-only archive
1885                         }
1886                 }
1887
1888                 return $this->getLoadMonitor()->getLagTimes( $indexesWithLag, $domain ) + $knownLagTimes;
1889         }
1890
1891         public function safeGetLag( IDatabase $conn ) {
1892                 if ( $this->getServerCount() <= 1 ) {
1893                         return 0;
1894                 } else {
1895                         return $conn->getLag();
1896                 }
1897         }
1898
1899         public function safeWaitForMasterPos( IDatabase $conn, $pos = false, $timeout = null ) {
1900                 $timeout = max( 1, $timeout ?: $this->waitTimeout );
1901
1902                 if ( $this->getServerCount() <= 1 || !$conn->getLBInfo( 'replica' ) ) {
1903                         return true; // server is not a replica DB
1904                 }
1905
1906                 if ( !$pos ) {
1907                         // Get the current master position, opening a connection if needed
1908                         $masterConn = $this->getAnyOpenConnection( $this->getWriterIndex() );
1909                         if ( $masterConn ) {
1910                                 $pos = $masterConn->getMasterPos();
1911                         } else {
1912                                 $masterConn = $this->openConnection( $this->getWriterIndex(), self::DOMAIN_ANY );
1913                                 if ( !$masterConn ) {
1914                                         throw new DBReplicationWaitError(
1915                                                 null,
1916                                                 "Could not obtain a master database connection to get the position"
1917                                         );
1918                                 }
1919                                 $pos = $masterConn->getMasterPos();
1920                                 $this->closeConnection( $masterConn );
1921                         }
1922                 }
1923
1924                 if ( $pos instanceof DBMasterPos ) {
1925                         $result = $conn->masterPosWait( $pos, $timeout );
1926                         if ( $result == -1 || is_null( $result ) ) {
1927                                 $msg = __METHOD__ . ': timed out waiting on {host} pos {pos}';
1928                                 $this->replLogger->warning( $msg, [
1929                                         'host' => $conn->getServer(),
1930                                         'pos' => $pos,
1931                                         'trace' => ( new RuntimeException() )->getTraceAsString()
1932                                 ] );
1933                                 $ok = false;
1934                         } else {
1935                                 $this->replLogger->debug( __METHOD__ . ': done waiting' );
1936                                 $ok = true;
1937                         }
1938                 } else {
1939                         $ok = false; // something is misconfigured
1940                         $this->replLogger->error(
1941                                 __METHOD__ . ': could not get master pos for {host}',
1942                                 [
1943                                         'host' => $conn->getServer(),
1944                                         'trace' => ( new RuntimeException() )->getTraceAsString()
1945                                 ]
1946                         );
1947                 }
1948
1949                 return $ok;
1950         }
1951
1952         public function setTransactionListener( $name, callable $callback = null ) {
1953                 if ( $callback ) {
1954                         $this->trxRecurringCallbacks[$name] = $callback;
1955                 } else {
1956                         unset( $this->trxRecurringCallbacks[$name] );
1957                 }
1958                 $this->forEachOpenMasterConnection(
1959                         function ( IDatabase $conn ) use ( $name, $callback ) {
1960                                 $conn->setTransactionListener( $name, $callback );
1961                         }
1962                 );
1963         }
1964
1965         public function setTableAliases( array $aliases ) {
1966                 $this->tableAliases = $aliases;
1967         }
1968
1969         public function setIndexAliases( array $aliases ) {
1970                 $this->indexAliases = $aliases;
1971         }
1972
1973         /**
1974          * @param string $prefix
1975          * @deprecated Since 1.33
1976          */
1977         public function setDomainPrefix( $prefix ) {
1978                 $this->setLocalDomainPrefix( $prefix );
1979         }
1980
1981         public function setLocalDomainPrefix( $prefix ) {
1982                 // Find connections to explicit foreign domains still marked as in-use...
1983                 $domainsInUse = [];
1984                 $this->forEachOpenConnection( function ( IDatabase $conn ) use ( &$domainsInUse ) {
1985                         // Once reuseConnection() is called on a handle, its reference count goes from 1 to 0.
1986                         // Until then, it is still in use by the caller (explicitly or via DBConnRef scope).
1987                         if ( $conn->getLBInfo( 'foreignPoolRefCount' ) > 0 ) {
1988                                 $domainsInUse[] = $conn->getDomainID();
1989                         }
1990                 } );
1991
1992                 // Do not switch connections to explicit foreign domains unless marked as safe
1993                 if ( $domainsInUse ) {
1994                         $domains = implode( ', ', $domainsInUse );
1995                         throw new DBUnexpectedError( null,
1996                                 "Foreign domain connections are still in use ($domains)" );
1997                 }
1998
1999                 $this->setLocalDomain( new DatabaseDomain(
2000                         $this->localDomain->getDatabase(),
2001                         $this->localDomain->getSchema(),
2002                         $prefix
2003                 ) );
2004
2005                 // Update the prefix for all local connections...
2006                 $this->forEachOpenConnection( function ( IDatabase $db ) use ( $prefix ) {
2007                         if ( !$db->getLBInfo( 'foreign' ) ) {
2008                                 $db->tablePrefix( $prefix );
2009                         }
2010                 } );
2011         }
2012
2013         public function redefineLocalDomain( $domain ) {
2014                 $this->closeAll();
2015
2016                 $this->setLocalDomain( DatabaseDomain::newFromId( $domain ) );
2017         }
2018
2019         /**
2020          * @param DatabaseDomain $domain
2021          */
2022         private function setLocalDomain( DatabaseDomain $domain ) {
2023                 $this->localDomain = $domain;
2024                 // In case a caller assumes that the domain ID is simply <db>-<prefix>, which is almost
2025                 // always true, gracefully handle the case when they fail to account for escaping.
2026                 if ( $this->localDomain->getTablePrefix() != '' ) {
2027                         $this->localDomainIdAlias =
2028                                 $this->localDomain->getDatabase() . '-' . $this->localDomain->getTablePrefix();
2029                 } else {
2030                         $this->localDomainIdAlias = $this->localDomain->getDatabase();
2031                 }
2032         }
2033
2034         function __destruct() {
2035                 // Avoid connection leaks for sanity
2036                 $this->disable();
2037         }
2038 }
2039
2040 /**
2041  * @deprecated since 1.29
2042  */
2043 class_alias( LoadBalancer::class, 'LoadBalancer' );