includes/libs/rdbms/loadbalancer/LoadBalancer.php

   1 <?php
   2 /**
   3  * Database load balancing manager
   4  *
   5  * This program is free software; you can redistribute it and/or modify
   6  * it under the terms of the GNU General Public License as published by
   7  * the Free Software Foundation; either version 2 of the License, or
   8  * (at your option) any later version.
   9  *
  10  * This program is distributed in the hope that it will be useful,
  11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  13  * GNU General Public License for more details.
  14  *
  15  * You should have received a copy of the GNU General Public License along
  16  * with this program; if not, write to the Free Software Foundation, Inc.,
  17  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
  18  * http://www.gnu.org/copyleft/gpl.html
  19  *
  20  * @file
  21  */
  22 namespace Wikimedia\Rdbms;
  23
  24 use Psr\Log\LoggerInterface;
  25 use Psr\Log\NullLogger;
  26 use Wikimedia\ScopedCallback;
  27 use BagOStuff;
  28 use EmptyBagOStuff;
  29 use WANObjectCache;
  30 use ArrayUtils;
  31 use UnexpectedValueException;
  32 use InvalidArgumentException;
  33 use RuntimeException;
  34 use Exception;
  35
  36 /**
  37  * Database connection, tracking, load balancing, and transaction manager for a cluster
  38  *
  39  * @ingroup Database
  40  */
  41 class LoadBalancer implements ILoadBalancer {
  42         /** @var ILoadMonitor */
  43         private $loadMonitor;
  44         /** @var callable|null Callback to run before the first connection attempt */
  45         private $chronologyCallback;
  46         /** @var BagOStuff */
  47         private $srvCache;
  48         /** @var WANObjectCache */
  49         private $wanCache;
  50         /** @var mixed Class name or object With profileIn/profileOut methods */
  51         private $profiler;
  52         /** @var TransactionProfiler */
  53         private $trxProfiler;
  54         /** @var LoggerInterface */
  55         private $replLogger;
  56         /** @var LoggerInterface */
  57         private $connLogger;
  58         /** @var LoggerInterface */
  59         private $queryLogger;
  60         /** @var LoggerInterface */
  61         private $perfLogger;
  62         /** @var callable Exception logger */
  63         private $errorLogger;
  64         /** @var callable Deprecation logger */
  65         private $deprecationLogger;
  66
  67         /** @var DatabaseDomain Local Domain ID and default for selectDB() calls */
  68         private $localDomain;
  69
  70         /** @var Database[][][] Map of (connection category => server index => IDatabase[]) */
  71         private $conns;
  72
  73         /** @var array[] Map of (server index => server config array) */
  74         private $servers;
  75         /** @var float[] Map of (server index => weight) */
  76         private $loads;
  77         /** @var array[] Map of (group => server index => weight) */
  78         private $groupLoads;
  79         /** @var bool Whether to disregard replica DB lag as a factor in replica DB selection */
  80         private $allowLagged;
  81         /** @var int Seconds to spend waiting on replica DB lag to resolve */
  82         private $waitTimeout;
  83         /** @var array The LoadMonitor configuration */
  84         private $loadMonitorConfig;
  85         /** @var string Alternate ID string for the domain instead of DatabaseDomain::getId() */
  86         private $localDomainIdAlias;
  87         /** @var int */
  88         private $maxLag = self::MAX_LAG_DEFAULT;
  89
  90         /** @var string Current server name */
  91         private $hostname;
  92         /** @var bool Whether this PHP instance is for a CLI script */
  93         private $cliMode;
  94         /** @var string Agent name for query profiling */
  95         private $agent;
  96
  97         /** @var array[] $aliases Map of (table => (dbname, schema, prefix) map) */
  98         private $tableAliases = [];
  99         /** @var string[] Map of (index alias => index) */
 100         private $indexAliases = [];
 101         /** @var array[] Map of (name => callable) */
 102         private $trxRecurringCallbacks = [];
 103
 104         /** @var Database DB connection object that caused a problem */
 105         private $errorConnection;
 106         /** @var int The generic (not query grouped) replica DB index (of $mServers) */
 107         private $readIndex;
 108         /** @var bool|DBMasterPos False if not set */
 109         private $waitForPos;
 110         /** @var bool Whether the generic reader fell back to a lagged replica DB */
 111         private $laggedReplicaMode = false;
 112         /** @var bool Whether the generic reader fell back to a lagged replica DB */
 113         private $allReplicasDownMode = false;
 114         /** @var string The last DB selection or connection error */
 115         private $lastError = 'Unknown error';
 116         /** @var string|bool Reason the LB is read-only or false if not */
 117         private $readOnlyReason = false;
 118         /** @var int Total connections opened */
 119         private $connsOpened = 0;
 120         /** @var bool */
 121         private $disabled = false;
 122         /** @var bool Whether any connection has been attempted yet */
 123         private $connectionAttempted = false;
 124
 125         /** @var string|bool String if a requested DBO_TRX transaction round is active */
 126         private $trxRoundId = false;
 127         /** @var string Stage of the current transaction round in the transaction round life-cycle */
 128         private $trxRoundStage = self::ROUND_CURSORY;
 129
 130         /** @var string|null */
 131         private $defaultGroup = null;
 132
 133         /** @var int Warn when this many connection are held */
 134         const CONN_HELD_WARN_THRESHOLD = 10;
 135
 136         /** @var int Default 'maxLag' when unspecified */
 137         const MAX_LAG_DEFAULT = 10;
 138         /** @var int Default 'waitTimeout' when unspecified */
 139         const MAX_WAIT_DEFAULT = 10;
 140         /** @var int Seconds to cache master server read-only status */
 141         const TTL_CACHE_READONLY = 5;
 142
 143         const KEY_LOCAL = 'local';
 144         const KEY_FOREIGN_FREE = 'foreignFree';
 145         const KEY_FOREIGN_INUSE = 'foreignInUse';
 146
 147         const KEY_LOCAL_NOROUND = 'localAutoCommit';
 148         const KEY_FOREIGN_FREE_NOROUND = 'foreignFreeAutoCommit';
 149         const KEY_FOREIGN_INUSE_NOROUND = 'foreignInUseAutoCommit';
 150
 151         /** @var string Transaction round, explicit or implicit, has not finished writing */
 152         const ROUND_CURSORY = 'cursory';
 153         /** @var string Transaction round writes are complete and ready for pre-commit checks */
 154         const ROUND_FINALIZED = 'finalized';
 155         /** @var string Transaction round passed final pre-commit checks */
 156         const ROUND_APPROVED = 'approved';
 157         /** @var string Transaction round was committed and post-commit callbacks must be run */
 158         const ROUND_COMMIT_CALLBACKS = 'commit-callbacks';
 159         /** @var string Transaction round was rolled back and post-rollback callbacks must be run */
 160         const ROUND_ROLLBACK_CALLBACKS = 'rollback-callbacks';
 161         /** @var string Transaction round encountered an error */
 162         const ROUND_ERROR = 'error';
 163
 164         public function __construct( array $params ) {
 165                 if ( !isset( $params['servers'] ) ) {
 166                         throw new InvalidArgumentException( __CLASS__ . ': missing servers parameter' );
 167                 }
 168                 $this->servers = $params['servers'];
 169                 foreach ( $this->servers as $i => $server ) {
 170                         if ( $i == 0 ) {
 171                                 $this->servers[$i]['master'] = true;
 172                         } else {
 173                                 $this->servers[$i]['replica'] = true;
 174                         }
 175                 }
 176
 177                 $localDomain = isset( $params['localDomain'] )
 178                         ? DatabaseDomain::newFromId( $params['localDomain'] )
 179                         : DatabaseDomain::newUnspecified();
 180                 $this->setLocalDomain( $localDomain );
 181
 182                 $this->waitTimeout = $params['waitTimeout'] ?? self::MAX_WAIT_DEFAULT;
 183
 184                 $this->readIndex = -1;
 185                 $this->conns = [
 186                         // Connection were transaction rounds may be applied
 187                         self::KEY_LOCAL => [],
 188                         self::KEY_FOREIGN_INUSE => [],
 189                         self::KEY_FOREIGN_FREE => [],
 190                         // Auto-committing counterpart connections that ignore transaction rounds
 191                         self::KEY_LOCAL_NOROUND => [],
 192                         self::KEY_FOREIGN_INUSE_NOROUND => [],
 193                         self::KEY_FOREIGN_FREE_NOROUND => []
 194                 ];
 195                 $this->loads = [];
 196                 $this->waitForPos = false;
 197                 $this->allowLagged = false;
 198
 199                 if ( isset( $params['readOnlyReason'] ) && is_string( $params['readOnlyReason'] ) ) {
 200                         $this->readOnlyReason = $params['readOnlyReason'];
 201                 }
 202
 203                 if ( isset( $params['maxLag'] ) ) {
 204                         $this->maxLag = $params['maxLag'];
 205                 }
 206
 207                 $this->loadMonitorConfig = $params['loadMonitor'] ?? [ 'class' => 'LoadMonitorNull' ];
 208                 $this->loadMonitorConfig += [ 'lagWarnThreshold' => $this->maxLag ];
 209
 210                 foreach ( $params['servers'] as $i => $server ) {
 211                         $this->loads[$i] = $server['load'];
 212                         if ( isset( $server['groupLoads'] ) ) {
 213                                 foreach ( $server['groupLoads'] as $group => $ratio ) {
 214                                         if ( !isset( $this->groupLoads[$group] ) ) {
 215                                                 $this->groupLoads[$group] = [];
 216                                         }
 217                                         $this->groupLoads[$group][$i] = $ratio;
 218                                 }
 219                         }
 220                 }
 221
 222                 $this->srvCache = $params['srvCache'] ?? new EmptyBagOStuff();
 223                 $this->wanCache = $params['wanCache'] ?? WANObjectCache::newEmpty();
 224                 $this->profiler = $params['profiler'] ?? null;
 225                 $this->trxProfiler = $params['trxProfiler'] ?? new TransactionProfiler();
 226
 227                 $this->errorLogger = $params['errorLogger'] ?? function ( Exception $e ) {
 228                         trigger_error( get_class( $e ) . ': ' . $e->getMessage(), E_USER_WARNING );
 229                 };
 230                 $this->deprecationLogger = $params['deprecationLogger'] ?? function ( $msg ) {
 231                         trigger_error( $msg, E_USER_DEPRECATED );
 232                 };
 233
 234                 foreach ( [ 'replLogger', 'connLogger', 'queryLogger', 'perfLogger' ] as $key ) {
 235                         $this->$key = $params[$key] ?? new NullLogger();
 236                 }
 237
 238                 $this->hostname = $params['hostname'] ?? ( gethostname() ?: 'unknown' );
 239                 $this->cliMode = $params['cliMode'] ?? ( PHP_SAPI === 'cli' || PHP_SAPI === 'phpdbg' );
 240                 $this->agent = $params['agent'] ?? '';
 241
 242                 if ( isset( $params['chronologyCallback'] ) ) {
 243                         $this->chronologyCallback = $params['chronologyCallback'];
 244                 }
 245
 246                 if ( isset( $params['roundStage'] ) ) {
 247                         if ( $params['roundStage'] === self::STAGE_POSTCOMMIT_CALLBACKS ) {
 248                                 $this->trxRoundStage = self::ROUND_COMMIT_CALLBACKS;
 249                         } elseif ( $params['roundStage'] === self::STAGE_POSTROLLBACK_CALLBACKS ) {
 250                                 $this->trxRoundStage = self::ROUND_ROLLBACK_CALLBACKS;
 251                         }
 252                 }
 253
 254                 $this->defaultGroup = $params['defaultGroup'] ?? null;
 255         }
 256
 257         public function getLocalDomainID() {
 258                 return $this->localDomain->getId();
 259         }
 260
 261         public function resolveDomainID( $domain ) {
 262                 return ( $domain !== false ) ? (string)$domain : $this->getLocalDomainID();
 263         }
 264
 265         /**
 266          * Get a LoadMonitor instance
 267          *
 268          * @return ILoadMonitor
 269          */
 270         private function getLoadMonitor() {
 271                 if ( !isset( $this->loadMonitor ) ) {
 272                         $compat = [
 273                                 'LoadMonitor' => LoadMonitor::class,
 274                                 'LoadMonitorNull' => LoadMonitorNull::class,
 275                                 'LoadMonitorMySQL' => LoadMonitorMySQL::class,
 276                         ];
 277
 278                         $class = $this->loadMonitorConfig['class'];
 279                         if ( isset( $compat[$class] ) ) {
 280                                 $class = $compat[$class];
 281                         }
 282
 283                         $this->loadMonitor = new $class(
 284                                 $this, $this->srvCache, $this->wanCache, $this->loadMonitorConfig );
 285                         $this->loadMonitor->setLogger( $this->replLogger );
 286                 }
 287
 288                 return $this->loadMonitor;
 289         }
 290
 291         /**
 292          * @param array $loads
 293          * @param bool|string $domain Domain to get non-lagged for
 294          * @param int $maxLag Restrict the maximum allowed lag to this many seconds
 295          * @return bool|int|string
 296          */
 297         private function getRandomNonLagged( array $loads, $domain = false, $maxLag = INF ) {
 298                 $lags = $this->getLagTimes( $domain );
 299
 300                 # Unset excessively lagged servers
 301                 foreach ( $lags as $i => $lag ) {
 302                         if ( $i != 0 ) {
 303                                 # How much lag this server nominally is allowed to have
 304                                 $maxServerLag = $this->servers[$i]['max lag'] ?? $this->maxLag; // default
 305                                 # Constrain that futher by $maxLag argument
 306                                 $maxServerLag = min( $maxServerLag, $maxLag );
 307
 308                                 $host = $this->getServerName( $i );
 309                                 if ( $lag === false && !is_infinite( $maxServerLag ) ) {
 310                                         $this->replLogger->error(
 311                                                 __METHOD__ .
 312                                                 ": server {host} is not replicating?", [ 'host' => $host ] );
 313                                         unset( $loads[$i] );
 314                                 } elseif ( $lag > $maxServerLag ) {
 315                                         $this->replLogger->info(
 316                                                 __METHOD__ .
 317                                                 ": server {host} has {lag} seconds of lag (>= {maxlag})",
 318                                                 [ 'host' => $host, 'lag' => $lag, 'maxlag' => $maxServerLag ]
 319                                         );
 320                                         unset( $loads[$i] );
 321                                 }
 322                         }
 323                 }
 324
 325                 # Find out if all the replica DBs with non-zero load are lagged
 326                 $sum = 0;
 327                 foreach ( $loads as $load ) {
 328                         $sum += $load;
 329                 }
 330                 if ( $sum == 0 ) {
 331                         # No appropriate DB servers except maybe the master and some replica DBs with zero load
 332                         # Do NOT use the master
 333                         # Instead, this function will return false, triggering read-only mode,
 334                         # and a lagged replica DB will be used instead.
 335                         return false;
 336                 }
 337
 338                 if ( count( $loads ) == 0 ) {
 339                         return false;
 340                 }
 341
 342                 # Return a random representative of the remainder
 343                 return ArrayUtils::pickRandom( $loads );
 344         }
 345
 346         public function getReaderIndex( $group = false, $domain = false ) {
 347                 if ( count( $this->servers ) == 1 ) {
 348                         // Skip the load balancing if there's only one server
 349                         return $this->getWriterIndex();
 350                 } elseif ( $group === false && $this->readIndex >= 0 ) {
 351                         // Shortcut if the generic reader index was already cached
 352                         return $this->readIndex;
 353                 }
 354
 355                 if ( $group !== false ) {
 356                         // Use the server weight array for this load group
 357                         if ( isset( $this->groupLoads[$group] ) ) {
 358                                 $loads = $this->groupLoads[$group];
 359                         } else {
 360                                 // No loads for this group, return false and the caller can use some other group
 361                                 $this->connLogger->info( __METHOD__ . ": no loads for group $group" );
 362
 363                                 return false;
 364                         }
 365                 } else {
 366                         // Use the generic load group
 367                         $loads = $this->loads;
 368                 }
 369
 370                 // Scale the configured load ratios according to each server's load and state
 371                 $this->getLoadMonitor()->scaleLoads( $loads, $domain );
 372
 373                 // Pick a server to use, accounting for weights, load, lag, and "waitForPos"
 374                 list( $i, $laggedReplicaMode ) = $this->pickReaderIndex( $loads, $domain );
 375                 if ( $i === false ) {
 376                         // Replica DB connection unsuccessful
 377                         return false;
 378                 }
 379
 380                 if ( $this->waitForPos && $i != $this->getWriterIndex() ) {
 381                         // Before any data queries are run, wait for the server to catch up to the
 382                         // specified position. This is used to improve session consistency. Note that
 383                         // when LoadBalancer::waitFor() sets "waitForPos", the waiting triggers here,
 384                         // so update laggedReplicaMode as needed for consistency.
 385                         if ( !$this->doWait( $i ) ) {
 386                                 $laggedReplicaMode = true;
 387                         }
 388                 }
 389
 390                 if ( $this->readIndex <= 0 && $this->loads[$i] > 0 && $group === false ) {
 391                         // Cache the generic reader index for future ungrouped DB_REPLICA handles
 392                         $this->readIndex = $i;
 393                         // Record if the generic reader index is in "lagged replica DB" mode
 394                         if ( $laggedReplicaMode ) {
 395                                 $this->laggedReplicaMode = true;
 396                         }
 397                 }
 398
 399                 $serverName = $this->getServerName( $i );
 400                 $this->connLogger->debug( __METHOD__ . ": using server $serverName for group '$group'" );
 401
 402                 return $i;
 403         }
 404
 405         /**
 406          * @param array $loads List of server weights
 407          * @param string|bool $domain
 408          * @return array (reader index, lagged replica mode) or false on failure
 409          */
 410         private function pickReaderIndex( array $loads, $domain = false ) {
 411                 if ( !count( $loads ) ) {
 412                         throw new InvalidArgumentException( "Empty server array given to LoadBalancer" );
 413                 }
 414
 415                 /** @var int|bool $i Index of selected server */
 416                 $i = false;
 417                 /** @var bool $laggedReplicaMode Whether server is considered lagged */
 418                 $laggedReplicaMode = false;
 419
 420                 // Quickly look through the available servers for a server that meets criteria...
 421                 $currentLoads = $loads;
 422                 while ( count( $currentLoads ) ) {
 423                         if ( $this->allowLagged || $laggedReplicaMode ) {
 424                                 $i = ArrayUtils::pickRandom( $currentLoads );
 425                         } else {
 426                                 $i = false;
 427                                 if ( $this->waitForPos && $this->waitForPos->asOfTime() ) {
 428                                         // "chronologyCallback" sets "waitForPos" for session consistency.
 429                                         // This triggers doWait() after connect, so it's especially good to
 430                                         // avoid lagged servers so as to avoid excessive delay in that method.
 431                                         $ago = microtime( true ) - $this->waitForPos->asOfTime();
 432                                         // Aim for <= 1 second of waiting (being too picky can backfire)
 433                                         $i = $this->getRandomNonLagged( $currentLoads, $domain, $ago + 1 );
 434                                 }
 435                                 if ( $i === false ) {
 436                                         // Any server with less lag than it's 'max lag' param is preferable
 437                                         $i = $this->getRandomNonLagged( $currentLoads, $domain );
 438                                 }
 439                                 if ( $i === false && count( $currentLoads ) != 0 ) {
 440                                         // All replica DBs lagged. Switch to read-only mode
 441                                         $this->replLogger->error(
 442                                                 __METHOD__ . ": all replica DBs lagged. Switch to read-only mode" );
 443                                         $i = ArrayUtils::pickRandom( $currentLoads );
 444                                         $laggedReplicaMode = true;
 445                                 }
 446                         }
 447
 448                         if ( $i === false ) {
 449                                 // pickRandom() returned false.
 450                                 // This is permanent and means the configuration or the load monitor
 451                                 // wants us to return false.
 452                                 $this->connLogger->debug( __METHOD__ . ": pickRandom() returned false" );
 453
 454                                 return [ false, false ];
 455                         }
 456
 457                         $serverName = $this->getServerName( $i );
 458                         $this->connLogger->debug( __METHOD__ . ": Using reader #$i: $serverName..." );
 459
 460                         $conn = $this->openConnection( $i, $domain );
 461                         if ( !$conn ) {
 462                                 $this->connLogger->warning( __METHOD__ . ": Failed connecting to $i/$domain" );
 463                                 unset( $currentLoads[$i] ); // avoid this server next iteration
 464                                 $i = false;
 465                                 continue;
 466                         }
 467
 468                         // Decrement reference counter, we are finished with this connection.
 469                         // It will be incremented for the caller later.
 470                         if ( $domain !== false ) {
 471                                 $this->reuseConnection( $conn );
 472                         }
 473
 474                         // Return this server
 475                         break;
 476                 }
 477
 478                 // If all servers were down, quit now
 479                 if ( !count( $currentLoads ) ) {
 480                         $this->connLogger->error( __METHOD__ . ": all servers down" );
 481                 }
 482
 483                 return [ $i, $laggedReplicaMode ];
 484         }
 485
 486         public function waitFor( $pos ) {
 487                 $oldPos = $this->waitForPos;
 488                 try {
 489                         $this->waitForPos = $pos;
 490                         // If a generic reader connection was already established, then wait now
 491                         $i = $this->readIndex;
 492                         if ( $i > 0 ) {
 493                                 if ( !$this->doWait( $i ) ) {
 494                                         $this->laggedReplicaMode = true;
 495                                 }
 496                         }
 497                 } finally {
 498                         // Restore the older position if it was higher since this is used for lag-protection
 499                         $this->setWaitForPositionIfHigher( $oldPos );
 500                 }
 501         }
 502
 503         public function waitForOne( $pos, $timeout = null ) {
 504                 $oldPos = $this->waitForPos;
 505                 try {
 506                         $this->waitForPos = $pos;
 507
 508                         $i = $this->readIndex;
 509                         if ( $i <= 0 ) {
 510                                 // Pick a generic replica DB if there isn't one yet
 511                                 $readLoads = $this->loads;
 512                                 unset( $readLoads[$this->getWriterIndex()] ); // replica DBs only
 513                                 $readLoads = array_filter( $readLoads ); // with non-zero load
 514                                 $i = ArrayUtils::pickRandom( $readLoads );
 515                         }
 516
 517                         if ( $i > 0 ) {
 518                                 $ok = $this->doWait( $i, true, $timeout );
 519                         } else {
 520                                 $ok = true; // no applicable loads
 521                         }
 522                 } finally {
 523                         # Restore the old position, as this is not used for lag-protection but for throttling
 524                         $this->waitForPos = $oldPos;
 525                 }
 526
 527                 return $ok;
 528         }
 529
 530         public function waitForAll( $pos, $timeout = null ) {
 531                 $timeout = $timeout ?: $this->waitTimeout;
 532
 533                 $oldPos = $this->waitForPos;
 534                 try {
 535                         $this->waitForPos = $pos;
 536                         $serverCount = count( $this->servers );
 537
 538                         $ok = true;
 539                         for ( $i = 1; $i < $serverCount; $i++ ) {
 540                                 if ( $this->loads[$i] > 0 ) {
 541                                         $start = microtime( true );
 542                                         $ok = $this->doWait( $i, true, $timeout ) && $ok;
 543                                         $timeout -= intval( microtime( true ) - $start );
 544                                         if ( $timeout <= 0 ) {
 545                                                 break; // timeout reached
 546                                         }
 547                                 }
 548                         }
 549                 } finally {
 550                         # Restore the old position, as this is not used for lag-protection but for throttling
 551                         $this->waitForPos = $oldPos;
 552                 }
 553
 554                 return $ok;
 555         }
 556
 557         /**
 558          * @param DBMasterPos|bool $pos
 559          */
 560         private function setWaitForPositionIfHigher( $pos ) {
 561                 if ( !$pos ) {
 562                         return;
 563                 }
 564
 565                 if ( !$this->waitForPos || $pos->hasReached( $this->waitForPos ) ) {
 566                         $this->waitForPos = $pos;
 567                 }
 568         }
 569
 570         public function getAnyOpenConnection( $i, $flags = 0 ) {
 571                 $autocommit = ( ( $flags & self::CONN_TRX_AUTOCOMMIT ) == self::CONN_TRX_AUTOCOMMIT );
 572                 foreach ( $this->conns as $connsByServer ) {
 573                         if ( !isset( $connsByServer[$i] ) ) {
 574                                 continue;
 575                         }
 576
 577                         foreach ( $connsByServer[$i] as $conn ) {
 578                                 if ( !$autocommit || $conn->getLBInfo( 'autoCommitOnly' ) ) {
 579                                         return $conn;
 580                                 }
 581                         }
 582                 }
 583
 584                 return false;
 585         }
 586
 587         /**
 588          * Wait for a given replica DB to catch up to the master pos stored in $this
 589          * @param int $index Server index
 590          * @param bool $open Check the server even if a new connection has to be made
 591          * @param int|null $timeout Max seconds to wait; default is "waitTimeout" given to __construct()
 592          * @return bool
 593          */
 594         protected function doWait( $index, $open = false, $timeout = null ) {
 595                 $timeout = max( 1, intval( $timeout ?: $this->waitTimeout ) );
 596
 597                 // Check if we already know that the DB has reached this point
 598                 $server = $this->getServerName( $index );
 599                 $key = $this->srvCache->makeGlobalKey( __CLASS__, 'last-known-pos', $server, 'v1' );
 600                 /** @var DBMasterPos $knownReachedPos */
 601                 $knownReachedPos = $this->srvCache->get( $key );
 602                 if (
 603                         $knownReachedPos instanceof DBMasterPos &&
 604                         $knownReachedPos->hasReached( $this->waitForPos )
 605                 ) {
 606                         $this->replLogger->debug(
 607                                 __METHOD__ .
 608                                 ': replica DB {dbserver} known to be caught up (pos >= $knownReachedPos).',
 609                                 [ 'dbserver' => $server ]
 610                         );
 611                         return true;
 612                 }
 613
 614                 // Find a connection to wait on, creating one if needed and allowed
 615                 $close = false; // close the connection afterwards
 616                 $conn = $this->getAnyOpenConnection( $index );
 617                 if ( !$conn ) {
 618                         if ( !$open ) {
 619                                 $this->replLogger->debug(
 620                                         __METHOD__ . ': no connection open for {dbserver}',
 621                                         [ 'dbserver' => $server ]
 622                                 );
 623
 624                                 return false;
 625                         } else {
 626                                 $conn = $this->openConnection( $index, self::DOMAIN_ANY );
 627                                 if ( !$conn ) {
 628                                         $this->replLogger->warning(
 629                                                 __METHOD__ . ': failed to connect to {dbserver}',
 630                                                 [ 'dbserver' => $server ]
 631                                         );
 632
 633                                         return false;
 634                                 }
 635                                 // Avoid connection spam in waitForAll() when connections
 636                                 // are made just for the sake of doing this lag check.
 637                                 $close = true;
 638                         }
 639                 }
 640
 641                 $this->replLogger->info(
 642                         __METHOD__ .
 643                         ': waiting for replica DB {dbserver} to catch up...',
 644                         [ 'dbserver' => $server ]
 645                 );
 646
 647                 $result = $conn->masterPosWait( $this->waitForPos, $timeout );
 648
 649                 if ( $result === null ) {
 650                         $this->replLogger->warning(
 651                                 __METHOD__ . ': Errored out waiting on {host} pos {pos}',
 652                                 [
 653                                         'host' => $server,
 654                                         'pos' => $this->waitForPos,
 655                                         'trace' => ( new RuntimeException() )->getTraceAsString()
 656                                 ]
 657                         );
 658                         $ok = false;
 659                 } elseif ( $result == -1 ) {
 660                         $this->replLogger->warning(
 661                                 __METHOD__ . ': Timed out waiting on {host} pos {pos}',
 662                                 [
 663                                         'host' => $server,
 664                                         'pos' => $this->waitForPos,
 665                                         'trace' => ( new RuntimeException() )->getTraceAsString()
 666                                 ]
 667                         );
 668                         $ok = false;
 669                 } else {
 670                         $this->replLogger->debug( __METHOD__ . ": done waiting" );
 671                         $ok = true;
 672                         // Remember that the DB reached this point
 673                         $this->srvCache->set( $key, $this->waitForPos, BagOStuff::TTL_DAY );
 674                 }
 675
 676                 if ( $close ) {
 677                         $this->closeConnection( $conn );
 678                 }
 679
 680                 return $ok;
 681         }
 682
 683         public function getConnection( $i, $groups = [], $domain = false, $flags = 0 ) {
 684                 if ( $i === null || $i === false ) {
 685                         throw new InvalidArgumentException( 'Attempt to call ' . __METHOD__ .
 686                                 ' with invalid server index' );
 687                 }
 688
 689                 if ( $this->localDomain->equals( $domain ) || $domain === $this->localDomainIdAlias ) {
 690                         $domain = false; // local connection requested
 691                 }
 692
 693                 if ( ( $flags & self::CONN_TRX_AUTOCOMMIT ) === self::CONN_TRX_AUTOCOMMIT ) {
 694                         // Assuming all servers are of the same type (or similar), which is overwhelmingly
 695                         // the case, use the master server information to get the attributes. The information
 696                         // for $i cannot be used since it might be DB_REPLICA, which might require connection
 697                         // attempts in order to be resolved into a real server index.
 698                         $attributes = $this->getServerAttributes( $this->getWriterIndex() );
 699                         if ( $attributes[Database::ATTR_DB_LEVEL_LOCKING] ) {
 700                                 // Callers sometimes want to (a) escape REPEATABLE-READ stateness without locking
 701                                 // rows (e.g. FOR UPDATE) or (b) make small commits during a larger transactions
 702                                 // to reduce lock contention. None of these apply for sqlite and using separate
 703                                 // connections just causes self-deadlocks.
 704                                 $flags &= ~self::CONN_TRX_AUTOCOMMIT;
 705                                 $this->connLogger->info( __METHOD__ .
 706                                         ': ignoring CONN_TRX_AUTOCOMMIT to avoid deadlocks.' );
 707                         }
 708                 }
 709
 710                 // Check one "group" per default: the generic pool
 711                 $defaultGroups = $this->defaultGroup ? [ $this->defaultGroup ] : [ false ];
 712
 713                 $groups = ( $groups === false || $groups === [] )
 714                         ? $defaultGroups
 715                         : (array)$groups;
 716
 717                 $masterOnly = ( $i == self::DB_MASTER || $i == $this->getWriterIndex() );
 718                 $oldConnsOpened = $this->connsOpened; // connections open now
 719
 720                 if ( $i == self::DB_MASTER ) {
 721                         $i = $this->getWriterIndex();
 722                 } elseif ( $i == self::DB_REPLICA ) {
 723                         # Try to find an available server in any the query groups (in order)
 724                         foreach ( $groups as $group ) {
 725                                 $groupIndex = $this->getReaderIndex( $group, $domain );
 726                                 if ( $groupIndex !== false ) {
 727                                         $i = $groupIndex;
 728                                         break;
 729                                 }
 730                         }
 731                 }
 732
 733                 # Operation-based index
 734                 if ( $i == self::DB_REPLICA ) {
 735                         $this->lastError = 'Unknown error'; // reset error string
 736                         # Try the general server pool if $groups are unavailable.
 737                         $i = ( $groups === [ false ] )
 738                                 ? false // don't bother with this if that is what was tried above
 739                                 : $this->getReaderIndex( false, $domain );
 740                         # Couldn't find a working server in getReaderIndex()?
 741                         if ( $i === false ) {
 742                                 $this->lastError = 'No working replica DB server: ' . $this->lastError;
 743                                 // Throw an exception
 744                                 $this->reportConnectionError();
 745                                 return null; // not reached
 746                         }
 747                 }
 748
 749                 # Now we have an explicit index into the servers array
 750                 $conn = $this->openConnection( $i, $domain, $flags );
 751                 if ( !$conn ) {
 752                         // Throw an exception
 753                         $this->reportConnectionError();
 754                         return null; // not reached
 755                 }
 756
 757                 # Profile any new connections that happen
 758                 if ( $this->connsOpened > $oldConnsOpened ) {
 759                         $host = $conn->getServer();
 760                         $dbname = $conn->getDBname();
 761                         $this->trxProfiler->recordConnection( $host, $dbname, $masterOnly );
 762                 }
 763
 764                 if ( $masterOnly ) {
 765                         # Make master-requested DB handles inherit any read-only mode setting
 766                         $conn->setLBInfo( 'readOnlyReason', $this->getReadOnlyReason( $domain, $conn ) );
 767                 }
 768
 769                 return $conn;
 770         }
 771
 772         public function reuseConnection( IDatabase $conn ) {
 773                 $serverIndex = $conn->getLBInfo( 'serverIndex' );
 774                 $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 775                 if ( $serverIndex === null || $refCount === null ) {
 776                         /**
 777                          * This can happen in code like:
 778                          *   foreach ( $dbs as $db ) {
 779                          *     $conn = $lb->getConnection( $lb::DB_REPLICA, [], $db );
 780                          *     ...
 781                          *     $lb->reuseConnection( $conn );
 782                          *   }
 783                          * When a connection to the local DB is opened in this way, reuseConnection()
 784                          * should be ignored
 785                          */
 786                         return;
 787                 } elseif ( $conn instanceof DBConnRef ) {
 788                         // DBConnRef already handles calling reuseConnection() and only passes the live
 789                         // Database instance to this method. Any caller passing in a DBConnRef is broken.
 790                         $this->connLogger->error(
 791                                 __METHOD__ . ": got DBConnRef instance.\n" .
 792                                 ( new RuntimeException() )->getTraceAsString() );
 793
 794                         return;
 795                 }
 796
 797                 if ( $this->disabled ) {
 798                         return; // DBConnRef handle probably survived longer than the LoadBalancer
 799                 }
 800
 801                 if ( $conn->getLBInfo( 'autoCommitOnly' ) ) {
 802                         $connFreeKey = self::KEY_FOREIGN_FREE_NOROUND;
 803                         $connInUseKey = self::KEY_FOREIGN_INUSE_NOROUND;
 804                 } else {
 805                         $connFreeKey = self::KEY_FOREIGN_FREE;
 806                         $connInUseKey = self::KEY_FOREIGN_INUSE;
 807                 }
 808
 809                 $domain = $conn->getDomainID();
 810                 if ( !isset( $this->conns[$connInUseKey][$serverIndex][$domain] ) ) {
 811                         throw new InvalidArgumentException( __METHOD__ .
 812                                 ": connection $serverIndex/$domain not found; it may have already been freed." );
 813                 } elseif ( $this->conns[$connInUseKey][$serverIndex][$domain] !== $conn ) {
 814                         throw new InvalidArgumentException( __METHOD__ .
 815                                 ": connection $serverIndex/$domain mismatched; it may have already been freed." );
 816                 }
 817
 818                 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
 819                 if ( $refCount <= 0 ) {
 820                         $this->conns[$connFreeKey][$serverIndex][$domain] = $conn;
 821                         unset( $this->conns[$connInUseKey][$serverIndex][$domain] );
 822                         if ( !$this->conns[$connInUseKey][$serverIndex] ) {
 823                                 unset( $this->conns[$connInUseKey][$serverIndex] ); // clean up
 824                         }
 825                         $this->connLogger->debug( __METHOD__ . ": freed connection $serverIndex/$domain" );
 826                 } else {
 827                         $this->connLogger->debug( __METHOD__ .
 828                                 ": reference count for $serverIndex/$domain reduced to $refCount" );
 829                 }
 830         }
 831
 832         public function getConnectionRef( $db, $groups = [], $domain = false, $flags = 0 ) {
 833                 $domain = $this->resolveDomainID( $domain );
 834
 835                 return new DBConnRef( $this, $this->getConnection( $db, $groups, $domain, $flags ) );
 836         }
 837
 838         public function getLazyConnectionRef( $db, $groups = [], $domain = false, $flags = 0 ) {
 839                 $domain = $this->resolveDomainID( $domain );
 840
 841                 return new DBConnRef( $this, [ $db, $groups, $domain, $flags ] );
 842         }
 843
 844         public function getMaintenanceConnectionRef( $db, $groups = [], $domain = false, $flags = 0 ) {
 845                 $domain = $this->resolveDomainID( $domain );
 846
 847                 return new MaintainableDBConnRef(
 848                         $this, $this->getConnection( $db, $groups, $domain, $flags ) );
 849         }
 850
 851         public function openConnection( $i, $domain = false, $flags = 0 ) {
 852                 if ( $this->localDomain->equals( $domain ) || $domain === $this->localDomainIdAlias ) {
 853                         $domain = false; // local connection requested
 854                 }
 855
 856                 if ( !$this->connectionAttempted && $this->chronologyCallback ) {
 857                         $this->connLogger->debug( __METHOD__ . ': calling initLB() before first connection.' );
 858                         // Load any "waitFor" positions before connecting so that doWait() is triggered
 859                         $this->connectionAttempted = true;
 860                         ( $this->chronologyCallback )( $this );
 861                 }
 862
 863                 // Check if an auto-commit connection is being requested. If so, it will not reuse the
 864                 // main set of DB connections but rather its own pool since:
 865                 // a) those are usually set to implicitly use transaction rounds via DBO_TRX
 866                 // b) those must support the use of explicit transaction rounds via beginMasterChanges()
 867                 $autoCommit = ( ( $flags & self::CONN_TRX_AUTOCOMMIT ) == self::CONN_TRX_AUTOCOMMIT );
 868
 869                 if ( $domain !== false ) {
 870                         // Connection is to a foreign domain
 871                         $conn = $this->openForeignConnection( $i, $domain, $flags );
 872                 } else {
 873                         // Connection is to the local domain
 874                         $conn = $this->openLocalConnection( $i, $flags );
 875                 }
 876
 877                 if ( $conn instanceof IDatabase && !$conn->isOpen() ) {
 878                         // Connection was made but later unrecoverably lost for some reason.
 879                         // Do not return a handle that will just throw exceptions on use,
 880                         // but let the calling code (e.g. getReaderIndex) try another server.
 881                         // See DatabaseMyslBase::ping() for how this can happen.
 882                         $this->errorConnection = $conn;
 883                         $conn = false;
 884                 }
 885
 886                 if ( $autoCommit && $conn instanceof IDatabase ) {
 887                         if ( $conn->trxLevel() ) { // sanity
 888                                 throw new DBUnexpectedError(
 889                                         $conn,
 890                                         __METHOD__ . ': CONN_TRX_AUTOCOMMIT handle has a transaction.'
 891                                 );
 892                         }
 893
 894                         $conn->clearFlag( $conn::DBO_TRX ); // auto-commit mode
 895                 }
 896
 897                 return $conn;
 898         }
 899
 900         /**
 901          * Open a connection to a local DB, or return one if it is already open.
 902          *
 903          * On error, returns false, and the connection which caused the
 904          * error will be available via $this->errorConnection.
 905          *
 906          * @note If disable() was called on this LoadBalancer, this method will throw a DBAccessError.
 907          *
 908          * @param int $i Server index
 909          * @param int $flags Class CONN_* constant bitfield
 910          * @return Database
 911          */
 912         private function openLocalConnection( $i, $flags = 0 ) {
 913                 $autoCommit = ( ( $flags & self::CONN_TRX_AUTOCOMMIT ) == self::CONN_TRX_AUTOCOMMIT );
 914
 915                 $connKey = $autoCommit ? self::KEY_LOCAL_NOROUND : self::KEY_LOCAL;
 916                 if ( isset( $this->conns[$connKey][$i][0] ) ) {
 917                         $conn = $this->conns[$connKey][$i][0];
 918                 } else {
 919                         if ( !isset( $this->servers[$i] ) || !is_array( $this->servers[$i] ) ) {
 920                                 throw new InvalidArgumentException( "No server with index '$i'." );
 921                         }
 922                         // Open a new connection
 923                         $server = $this->servers[$i];
 924                         $server['serverIndex'] = $i;
 925                         $server['autoCommitOnly'] = $autoCommit;
 926                         $conn = $this->reallyOpenConnection( $server, $this->localDomain );
 927                         $host = $this->getServerName( $i );
 928                         if ( $conn->isOpen() ) {
 929                                 $this->connLogger->debug(
 930                                         __METHOD__ . ": connected to database $i at '$host'." );
 931                                 $this->conns[$connKey][$i][0] = $conn;
 932                         } else {
 933                                 $this->connLogger->warning(
 934                                         __METHOD__ . ": failed to connect to database $i at '$host'." );
 935                                 $this->errorConnection = $conn;
 936                                 $conn = false;
 937                         }
 938                 }
 939
 940                 // Final sanity check to make sure the right domain is selected
 941                 if (
 942                         $conn instanceof IDatabase &&
 943                         !$this->localDomain->isCompatible( $conn->getDomainID() )
 944                 ) {
 945                         throw new UnexpectedValueException(
 946                                 "Got connection to '{$conn->getDomainID()}', " .
 947                                 "but expected local domain ('{$this->localDomain}')." );
 948                 }
 949
 950                 return $conn;
 951         }
 952
 953         /**
 954          * Open a connection to a foreign DB, or return one if it is already open.
 955          *
 956          * Increments a reference count on the returned connection which locks the
 957          * connection to the requested domain. This reference count can be
 958          * decremented by calling reuseConnection().
 959          *
 960          * If a connection is open to the appropriate server already, but with the wrong
 961          * database, it will be switched to the right database and returned, as long as
 962          * it has been freed first with reuseConnection().
 963          *
 964          * On error, returns false, and the connection which caused the
 965          * error will be available via $this->errorConnection.
 966          *
 967          * @note If disable() was called on this LoadBalancer, this method will throw a DBAccessError.
 968          *
 969          * @param int $i Server index
 970          * @param string $domain Domain ID to open
 971          * @param int $flags Class CONN_* constant bitfield
 972          * @return Database|bool Returns false on connection error
 973          * @throws DBError When database selection fails
 974          */
 975         private function openForeignConnection( $i, $domain, $flags = 0 ) {
 976                 $domainInstance = DatabaseDomain::newFromId( $domain );
 977                 $autoCommit = ( ( $flags & self::CONN_TRX_AUTOCOMMIT ) == self::CONN_TRX_AUTOCOMMIT );
 978
 979                 if ( $autoCommit ) {
 980                         $connFreeKey = self::KEY_FOREIGN_FREE_NOROUND;
 981                         $connInUseKey = self::KEY_FOREIGN_INUSE_NOROUND;
 982                 } else {
 983                         $connFreeKey = self::KEY_FOREIGN_FREE;
 984                         $connInUseKey = self::KEY_FOREIGN_INUSE;
 985                 }
 986
 987                 /** @var Database $conn */
 988                 $conn = null;
 989
 990                 if ( isset( $this->conns[$connInUseKey][$i][$domain] ) ) {
 991                         // Reuse an in-use connection for the same domain
 992                         $conn = $this->conns[$connInUseKey][$i][$domain];
 993                         $this->connLogger->debug( __METHOD__ . ": reusing connection $i/$domain" );
 994                 } elseif ( isset( $this->conns[$connFreeKey][$i][$domain] ) ) {
 995                         // Reuse a free connection for the same domain
 996                         $conn = $this->conns[$connFreeKey][$i][$domain];
 997                         unset( $this->conns[$connFreeKey][$i][$domain] );
 998                         $this->conns[$connInUseKey][$i][$domain] = $conn;
 999                         $this->connLogger->debug( __METHOD__ . ": reusing free connection $i/$domain" );
1000                 } elseif ( !empty( $this->conns[$connFreeKey][$i] ) ) {
1001                         // Reuse a free connection from another domain if possible
1002                         foreach ( $this->conns[$connFreeKey][$i] as $oldDomain => $conn ) {
1003                                 if ( $domainInstance->getDatabase() !== null ) {
1004                                         // Check if changing the database will require a new connection.
1005                                         // In that case, leave the connection handle alone and keep looking.
1006                                         // This prevents connections from being closed mid-transaction and can
1007                                         // also avoid overhead if the same database will later be requested.
1008                                         if (
1009                                                 $conn->databasesAreIndependent() &&
1010                                                 $conn->getDBname() !== $domainInstance->getDatabase()
1011                                         ) {
1012                                                 continue;
1013                                         }
1014                                         // Select the new database, schema, and prefix
1015                                         $conn->selectDomain( $domainInstance );
1016                                 } else {
1017                                         // Stay on the current database, but update the schema/prefix
1018                                         $conn->dbSchema( $domainInstance->getSchema() );
1019                                         $conn->tablePrefix( $domainInstance->getTablePrefix() );
1020                                 }
1021                                 unset( $this->conns[$connFreeKey][$i][$oldDomain] );
1022                                 // Note that if $domain is an empty string, getDomainID() might not match it
1023                                 $this->conns[$connInUseKey][$i][$conn->getDomainId()] = $conn;
1024                                 $this->connLogger->debug( __METHOD__ .
1025                                         ": reusing free connection from $oldDomain for $domain" );
1026                                 break;
1027                         }
1028                 }
1029
1030                 if ( !$conn ) {
1031                         if ( !isset( $this->servers[$i] ) || !is_array( $this->servers[$i] ) ) {
1032                                 throw new InvalidArgumentException( "No server with index '$i'." );
1033                         }
1034                         // Open a new connection
1035                         $server = $this->servers[$i];
1036                         $server['serverIndex'] = $i;
1037                         $server['foreignPoolRefCount'] = 0;
1038                         $server['foreign'] = true;
1039                         $server['autoCommitOnly'] = $autoCommit;
1040                         $conn = $this->reallyOpenConnection( $server, $domainInstance );
1041                         if ( !$conn->isOpen() ) {
1042                                 $this->connLogger->warning( __METHOD__ . ": connection error for $i/$domain" );
1043                                 $this->errorConnection = $conn;
1044                                 $conn = false;
1045                         } else {
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__ . ": opened new connection for $i/$domain" );
1049                         }
1050                 }
1051
1052                 if ( $conn instanceof IDatabase ) {
1053                         // Final sanity check to make sure the right domain is selected
1054                         if ( !$domainInstance->isCompatible( $conn->getDomainID() ) ) {
1055                                 throw new UnexpectedValueException(
1056                                         "Got connection to '{$conn->getDomainID()}', but expected '$domain'." );
1057                         }
1058                         // Increment reference count
1059                         $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
1060                         $conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
1061                 }
1062
1063                 return $conn;
1064         }
1065
1066         public function getServerAttributes( $i ) {
1067                 return Database::attributesFromType(
1068                         $this->getServerType( $i ),
1069                         $this->servers[$i]['driver'] ?? null
1070                 );
1071         }
1072
1073         /**
1074          * Test if the specified index represents an open connection
1075          *
1076          * @param int $index Server index
1077          * @access private
1078          * @return bool
1079          */
1080         private function isOpen( $index ) {
1081                 if ( !is_int( $index ) ) {
1082                         return false;
1083                 }
1084
1085                 return (bool)$this->getAnyOpenConnection( $index );
1086         }
1087
1088         /**
1089          * Open a new network connection to a server (uncached)
1090          *
1091          * Returns a Database object whether or not the connection was successful.
1092          *
1093          * @param array $server
1094          * @param DatabaseDomain $domain Domain the connection is for, possibly unspecified
1095          * @return Database
1096          * @throws DBAccessError
1097          * @throws InvalidArgumentException
1098          */
1099         protected function reallyOpenConnection( array $server, DatabaseDomain $domain ) {
1100                 if ( $this->disabled ) {
1101                         throw new DBAccessError();
1102                 }
1103
1104                 if ( $domain->getDatabase() === null ) {
1105                         // The database domain does not specify a DB name and some database systems require a
1106                         // valid DB specified on connection. The $server configuration array contains a default
1107                         // DB name to use for connections in such cases.
1108                         if ( $server['type'] === 'mysql' ) {
1109                                 // For MySQL, DATABASE and SCHEMA are synonyms, connections need not specify a DB,
1110                                 // and the DB name in $server might not exist due to legacy reasons (the default
1111                                 // domain used to ignore the local LB domain, even when mismatched).
1112                                 $server['dbname'] = null;
1113                         }
1114                 } else {
1115                         $server['dbname'] = $domain->getDatabase();
1116                 }
1117
1118                 if ( $domain->getSchema() !== null ) {
1119                         $server['schema'] = $domain->getSchema();
1120                 }
1121
1122                 // It is always possible to connect with any prefix, even the empty string
1123                 $server['tablePrefix'] = $domain->getTablePrefix();
1124
1125                 // Let the handle know what the cluster master is (e.g. "db1052")
1126                 $masterName = $this->getServerName( $this->getWriterIndex() );
1127                 $server['clusterMasterHost'] = $masterName;
1128
1129                 // Log when many connection are made on requests
1130                 if ( ++$this->connsOpened >= self::CONN_HELD_WARN_THRESHOLD ) {
1131                         $this->perfLogger->warning( __METHOD__ . ": " .
1132                                 "{$this->connsOpened}+ connections made (master=$masterName)" );
1133                 }
1134
1135                 $server['srvCache'] = $this->srvCache;
1136                 // Set loggers and profilers
1137                 $server['connLogger'] = $this->connLogger;
1138                 $server['queryLogger'] = $this->queryLogger;
1139                 $server['errorLogger'] = $this->errorLogger;
1140                 $server['deprecationLogger'] = $this->deprecationLogger;
1141                 $server['profiler'] = $this->profiler;
1142                 $server['trxProfiler'] = $this->trxProfiler;
1143                 // Use the same agent and PHP mode for all DB handles
1144                 $server['cliMode'] = $this->cliMode;
1145                 $server['agent'] = $this->agent;
1146                 // Use DBO_DEFAULT flags by default for LoadBalancer managed databases. Assume that the
1147                 // application calls LoadBalancer::commitMasterChanges() before the PHP script completes.
1148                 $server['flags'] = $server['flags'] ?? IDatabase::DBO_DEFAULT;
1149
1150                 // Create a live connection object
1151                 try {
1152                         $db = Database::factory( $server['type'], $server );
1153                 } catch ( DBConnectionError $e ) {
1154                         // FIXME: This is probably the ugliest thing I have ever done to
1155                         // PHP. I'm half-expecting it to segfault, just out of disgust. -- TS
1156                         $db = $e->db;
1157                 }
1158
1159                 $db->setLBInfo( $server );
1160                 $db->setLazyMasterHandle(
1161                         $this->getLazyConnectionRef( self::DB_MASTER, [], $db->getDomainID() )
1162                 );
1163                 $db->setTableAliases( $this->tableAliases );
1164                 $db->setIndexAliases( $this->indexAliases );
1165
1166                 if ( $server['serverIndex'] === $this->getWriterIndex() ) {
1167                         if ( $this->trxRoundId !== false ) {
1168                                 $this->applyTransactionRoundFlags( $db );
1169                         }
1170                         foreach ( $this->trxRecurringCallbacks as $name => $callback ) {
1171                                 $db->setTransactionListener( $name, $callback );
1172                         }
1173                 }
1174
1175                 return $db;
1176         }
1177
1178         /**
1179          * @throws DBConnectionError
1180          */
1181         private function reportConnectionError() {
1182                 $conn = $this->errorConnection; // the connection which caused the error
1183                 $context = [
1184                         'method' => __METHOD__,
1185                         'last_error' => $this->lastError,
1186                 ];
1187
1188                 if ( $conn instanceof IDatabase ) {
1189                         $context['db_server'] = $conn->getServer();
1190                         $this->connLogger->warning(
1191                                 __METHOD__ . ": connection error: {last_error} ({db_server})",
1192                                 $context
1193                         );
1194
1195                         throw new DBConnectionError( $conn, "{$this->lastError} ({$context['db_server']})" );
1196                 } else {
1197                         // No last connection, probably due to all servers being too busy
1198                         $this->connLogger->error(
1199                                 __METHOD__ .
1200                                 ": LB failure with no last connection. Connection error: {last_error}",
1201                                 $context
1202                         );
1203
1204                         // If all servers were busy, "lastError" will contain something sensible
1205                         throw new DBConnectionError( null, $this->lastError );
1206                 }
1207         }
1208
1209         public function getWriterIndex() {
1210                 return 0;
1211         }
1212
1213         public function haveIndex( $i ) {
1214                 return array_key_exists( $i, $this->servers );
1215         }
1216
1217         public function isNonZeroLoad( $i ) {
1218                 return array_key_exists( $i, $this->servers ) && $this->loads[$i] != 0;
1219         }
1220
1221         public function getServerCount() {
1222                 return count( $this->servers );
1223         }
1224
1225         public function getServerName( $i ) {
1226                 $name = $this->servers[$i]['hostName'] ?? $this->servers[$i]['host'] ?? '';
1227
1228                 return ( $name != '' ) ? $name : 'localhost';
1229         }
1230
1231         public function getServerInfo( $i ) {
1232                 return $this->servers[$i] ?? false;
1233         }
1234
1235         public function getServerType( $i ) {
1236                 return $this->servers[$i]['type'] ?? 'unknown';
1237         }
1238
1239         public function getMasterPos() {
1240                 # If this entire request was served from a replica DB without opening a connection to the
1241                 # master (however unlikely that may be), then we can fetch the position from the replica DB.
1242                 $masterConn = $this->getAnyOpenConnection( $this->getWriterIndex() );
1243                 if ( !$masterConn ) {
1244                         $serverCount = count( $this->servers );
1245                         for ( $i = 1; $i < $serverCount; $i++ ) {
1246                                 $conn = $this->getAnyOpenConnection( $i );
1247                                 if ( $conn ) {
1248                                         return $conn->getReplicaPos();
1249                                 }
1250                         }
1251                 } else {
1252                         return $masterConn->getMasterPos();
1253                 }
1254
1255                 return false;
1256         }
1257
1258         public function disable() {
1259                 $this->closeAll();
1260                 $this->disabled = true;
1261         }
1262
1263         public function closeAll() {
1264                 $fname = __METHOD__;
1265                 $this->forEachOpenConnection( function ( IDatabase $conn ) use ( $fname ) {
1266                         $host = $conn->getServer();
1267                         $this->connLogger->debug(
1268                                 $fname . ": closing connection to database '$host'." );
1269                         $conn->close();
1270                 } );
1271
1272                 $this->conns = [
1273                         self::KEY_LOCAL => [],
1274                         self::KEY_FOREIGN_INUSE => [],
1275                         self::KEY_FOREIGN_FREE => [],
1276                         self::KEY_LOCAL_NOROUND => [],
1277                         self::KEY_FOREIGN_INUSE_NOROUND => [],
1278                         self::KEY_FOREIGN_FREE_NOROUND => []
1279                 ];
1280                 $this->connsOpened = 0;
1281         }
1282
1283         public function closeConnection( IDatabase $conn ) {
1284                 if ( $conn instanceof DBConnRef ) {
1285                         // Avoid calling close() but still leaving the handle in the pool
1286                         throw new RuntimeException( __METHOD__ . ': got DBConnRef instance.' );
1287                 }
1288
1289                 $serverIndex = $conn->getLBInfo( 'serverIndex' );
1290                 foreach ( $this->conns as $type => $connsByServer ) {
1291                         if ( !isset( $connsByServer[$serverIndex] ) ) {
1292                                 continue;
1293                         }
1294
1295                         foreach ( $connsByServer[$serverIndex] as $i => $trackedConn ) {
1296                                 if ( $conn === $trackedConn ) {
1297                                         $host = $this->getServerName( $i );
1298                                         $this->connLogger->debug(
1299                                                 __METHOD__ . ": closing connection to database $i at '$host'." );
1300                                         unset( $this->conns[$type][$serverIndex][$i] );
1301                                         --$this->connsOpened;
1302                                         break 2;
1303                                 }
1304                         }
1305                 }
1306
1307                 $conn->close();
1308         }
1309
1310         public function commitAll( $fname = __METHOD__ ) {
1311                 $this->commitMasterChanges( $fname );
1312                 $this->flushMasterSnapshots( $fname );
1313                 $this->flushReplicaSnapshots( $fname );
1314         }
1315
1316         public function finalizeMasterChanges() {
1317                 $this->assertTransactionRoundStage( [ self::ROUND_CURSORY, self::ROUND_FINALIZED ] );
1318
1319                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1320                 // Loop until callbacks stop adding callbacks on other connections
1321                 $total = 0;
1322                 do {
1323                         $count = 0; // callbacks execution attempts
1324                         $this->forEachOpenMasterConnection( function ( Database $conn ) use ( &$count ) {
1325                                 // Run any pre-commit callbacks while leaving the post-commit ones suppressed.
1326                                 // Any error should cause all (peer) transactions to be rolled back together.
1327                                 $count += $conn->runOnTransactionPreCommitCallbacks();
1328                         } );
1329                         $total += $count;
1330                 } while ( $count > 0 );
1331                 // Defer post-commit callbacks until after COMMIT/ROLLBACK happens on all handles
1332                 $this->forEachOpenMasterConnection( function ( Database $conn ) {
1333                         $conn->setTrxEndCallbackSuppression( true );
1334                 } );
1335                 $this->trxRoundStage = self::ROUND_FINALIZED;
1336
1337                 return $total;
1338         }
1339
1340         public function approveMasterChanges( array $options ) {
1341                 $this->assertTransactionRoundStage( self::ROUND_FINALIZED );
1342
1343                 $limit = $options['maxWriteDuration'] ?? 0;
1344
1345                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1346                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( $limit ) {
1347                         // If atomic sections or explicit transactions are still open, some caller must have
1348                         // caught an exception but failed to properly rollback any changes. Detect that and
1349                         // throw and error (causing rollback).
1350                         $conn->assertNoOpenTransactions();
1351                         // Assert that the time to replicate the transaction will be sane.
1352                         // If this fails, then all DB transactions will be rollback back together.
1353                         $time = $conn->pendingWriteQueryDuration( $conn::ESTIMATE_DB_APPLY );
1354                         if ( $limit > 0 && $time > $limit ) {
1355                                 throw new DBTransactionSizeError(
1356                                         $conn,
1357                                         "Transaction spent $time second(s) in writes, exceeding the limit of $limit.",
1358                                         [ $time, $limit ]
1359                                 );
1360                         }
1361                         // If a connection sits idle while slow queries execute on another, that connection
1362                         // may end up dropped before the commit round is reached. Ping servers to detect this.
1363                         if ( $conn->writesOrCallbacksPending() && !$conn->ping() ) {
1364                                 throw new DBTransactionError(
1365                                         $conn,
1366                                         "A connection to the {$conn->getDBname()} database was lost before commit."
1367                                 );
1368                         }
1369                 } );
1370                 $this->trxRoundStage = self::ROUND_APPROVED;
1371         }
1372
1373         public function beginMasterChanges( $fname = __METHOD__ ) {
1374                 if ( $this->trxRoundId !== false ) {
1375                         throw new DBTransactionError(
1376                                 null,
1377                                 "$fname: Transaction round '{$this->trxRoundId}' already started."
1378                         );
1379                 }
1380                 $this->assertTransactionRoundStage( self::ROUND_CURSORY );
1381
1382                 // Clear any empty transactions (no writes/callbacks) from the implicit round
1383                 $this->flushMasterSnapshots( $fname );
1384
1385                 $this->trxRoundId = $fname;
1386                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1387                 // Mark applicable handles as participating in this explicit transaction round.
1388                 // For each of these handles, any writes and callbacks will be tied to a single
1389                 // transaction. The (peer) handles will reject begin()/commit() calls unless they
1390                 // are part of an en masse commit or an en masse rollback.
1391                 $this->forEachOpenMasterConnection( function ( Database $conn ) {
1392                         $this->applyTransactionRoundFlags( $conn );
1393                 } );
1394                 $this->trxRoundStage = self::ROUND_CURSORY;
1395         }
1396
1397         public function commitMasterChanges( $fname = __METHOD__ ) {
1398                 $this->assertTransactionRoundStage( self::ROUND_APPROVED );
1399
1400                 $failures = [];
1401
1402                 /** @noinspection PhpUnusedLocalVariableInspection */
1403                 $scope = ScopedCallback::newScopedIgnoreUserAbort(); // try to ignore client aborts
1404
1405                 $restore = ( $this->trxRoundId !== false );
1406                 $this->trxRoundId = false;
1407                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1408                 // Commit any writes and clear any snapshots as well (callbacks require AUTOCOMMIT).
1409                 // Note that callbacks should already be suppressed due to finalizeMasterChanges().
1410                 $this->forEachOpenMasterConnection(
1411                         function ( IDatabase $conn ) use ( $fname, &$failures ) {
1412                                 try {
1413                                         $conn->commit( $fname, $conn::FLUSHING_ALL_PEERS );
1414                                 } catch ( DBError $e ) {
1415                                         ( $this->errorLogger )( $e );
1416                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1417                                 }
1418                         }
1419                 );
1420                 if ( $failures ) {
1421                         throw new DBTransactionError(
1422                                 null,
1423                                 "$fname: Commit failed on server(s) " . implode( "\n", array_unique( $failures ) )
1424                         );
1425                 }
1426                 if ( $restore ) {
1427                         // Unmark handles as participating in this explicit transaction round
1428                         $this->forEachOpenMasterConnection( function ( Database $conn ) {
1429                                 $this->undoTransactionRoundFlags( $conn );
1430                         } );
1431                 }
1432                 $this->trxRoundStage = self::ROUND_COMMIT_CALLBACKS;
1433         }
1434
1435         public function runMasterTransactionIdleCallbacks() {
1436                 if ( $this->trxRoundStage === self::ROUND_COMMIT_CALLBACKS ) {
1437                         $type = IDatabase::TRIGGER_COMMIT;
1438                 } elseif ( $this->trxRoundStage === self::ROUND_ROLLBACK_CALLBACKS ) {
1439                         $type = IDatabase::TRIGGER_ROLLBACK;
1440                 } else {
1441                         throw new DBTransactionError(
1442                                 null,
1443                                 "Transaction should be in the callback stage (not '{$this->trxRoundStage}')"
1444                         );
1445                 }
1446
1447                 $oldStage = $this->trxRoundStage;
1448                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1449
1450                 // Now that the COMMIT/ROLLBACK step is over, enable post-commit callback runs
1451                 $this->forEachOpenMasterConnection( function ( Database $conn ) {
1452                         $conn->setTrxEndCallbackSuppression( false );
1453                 } );
1454
1455                 $e = null; // first exception
1456                 $fname = __METHOD__;
1457                 // Loop until callbacks stop adding callbacks on other connections
1458                 do {
1459                         // Run any pending callbacks for each connection...
1460                         $count = 0; // callback execution attempts
1461                         $this->forEachOpenMasterConnection(
1462                                 function ( Database $conn ) use ( $type, &$e, &$count ) {
1463                                         if ( $conn->trxLevel() ) {
1464                                                 return; // retry in the next iteration, after commit() is called
1465                                         }
1466                                         try {
1467                                                 $count += $conn->runOnTransactionIdleCallbacks( $type );
1468                                         } catch ( Exception $ex ) {
1469                                                 $e = $e ?: $ex;
1470                                         }
1471                                 }
1472                         );
1473                         // Clear out any active transactions left over from callbacks...
1474                         $this->forEachOpenMasterConnection( function ( Database $conn ) use ( &$e, $fname ) {
1475                                 if ( $conn->writesPending() ) {
1476                                         // A callback from another handle wrote to this one and DBO_TRX is set
1477                                         $this->queryLogger->warning( $fname . ": found writes pending." );
1478                                         $fnames = implode( ', ', $conn->pendingWriteAndCallbackCallers() );
1479                                         $this->queryLogger->warning(
1480                                                 $fname . ": found writes pending ($fnames).",
1481                                                 [
1482                                                         'db_server' => $conn->getServer(),
1483                                                         'db_name' => $conn->getDBname()
1484                                                 ]
1485                                         );
1486                                 } elseif ( $conn->trxLevel() ) {
1487                                         // A callback from another handle read from this one and DBO_TRX is set,
1488                                         // which can easily happen if there is only one DB (no replicas)
1489                                         $this->queryLogger->debug( $fname . ": found empty transaction." );
1490                                 }
1491                                 try {
1492                                         $conn->commit( $fname, $conn::FLUSHING_ALL_PEERS );
1493                                 } catch ( Exception $ex ) {
1494                                         $e = $e ?: $ex;
1495                                 }
1496                         } );
1497                 } while ( $count > 0 );
1498
1499                 $this->trxRoundStage = $oldStage;
1500
1501                 return $e;
1502         }
1503
1504         public function runMasterTransactionListenerCallbacks() {
1505                 if ( $this->trxRoundStage === self::ROUND_COMMIT_CALLBACKS ) {
1506                         $type = IDatabase::TRIGGER_COMMIT;
1507                 } elseif ( $this->trxRoundStage === self::ROUND_ROLLBACK_CALLBACKS ) {
1508                         $type = IDatabase::TRIGGER_ROLLBACK;
1509                 } else {
1510                         throw new DBTransactionError(
1511                                 null,
1512                                 "Transaction should be in the callback stage (not '{$this->trxRoundStage}')"
1513                         );
1514                 }
1515
1516                 $e = null;
1517
1518                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1519                 $this->forEachOpenMasterConnection( function ( Database $conn ) use ( $type, &$e ) {
1520                         try {
1521                                 $conn->runTransactionListenerCallbacks( $type );
1522                         } catch ( Exception $ex ) {
1523                                 $e = $e ?: $ex;
1524                         }
1525                 } );
1526                 $this->trxRoundStage = self::ROUND_CURSORY;
1527
1528                 return $e;
1529         }
1530
1531         public function rollbackMasterChanges( $fname = __METHOD__ ) {
1532                 $restore = ( $this->trxRoundId !== false );
1533                 $this->trxRoundId = false;
1534                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1535                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( $fname ) {
1536                         $conn->rollback( $fname, $conn::FLUSHING_ALL_PEERS );
1537                 } );
1538                 if ( $restore ) {
1539                         // Unmark handles as participating in this explicit transaction round
1540                         $this->forEachOpenMasterConnection( function ( Database $conn ) {
1541                                 $this->undoTransactionRoundFlags( $conn );
1542                         } );
1543                 }
1544                 $this->trxRoundStage = self::ROUND_ROLLBACK_CALLBACKS;
1545         }
1546
1547         /**
1548          * @param string|string[] $stage
1549          */
1550         private function assertTransactionRoundStage( $stage ) {
1551                 $stages = (array)$stage;
1552
1553                 if ( !in_array( $this->trxRoundStage, $stages, true ) ) {
1554                         $stageList = implode(
1555                                 '/',
1556                                 array_map( function ( $v ) {
1557                                         return "'$v'";
1558                                 }, $stages )
1559                         );
1560                         throw new DBTransactionError(
1561                                 null,
1562                                 "Transaction round stage must be $stageList (not '{$this->trxRoundStage}')"
1563                         );
1564                 }
1565         }
1566
1567         /**
1568          * Make all DB servers with DBO_DEFAULT/DBO_TRX set join the transaction round
1569          *
1570          * Some servers may have neither flag enabled, meaning that they opt out of such
1571          * transaction rounds and remain in auto-commit mode. Such behavior might be desired
1572          * when a DB server is used for something like simple key/value storage.
1573          *
1574          * @param Database $conn
1575          */
1576         private function applyTransactionRoundFlags( Database $conn ) {
1577                 if ( $conn->getLBInfo( 'autoCommitOnly' ) ) {
1578                         return; // transaction rounds do not apply to these connections
1579                 }
1580
1581                 if ( $conn->getFlag( $conn::DBO_DEFAULT ) ) {
1582                         // DBO_TRX is controlled entirely by CLI mode presence with DBO_DEFAULT.
1583                         // Force DBO_TRX even in CLI mode since a commit round is expected soon.
1584                         $conn->setFlag( $conn::DBO_TRX, $conn::REMEMBER_PRIOR );
1585                 }
1586
1587                 if ( $conn->getFlag( $conn::DBO_TRX ) ) {
1588                         $conn->setLBInfo( 'trxRoundId', $this->trxRoundId );
1589                 }
1590         }
1591
1592         /**
1593          * @param Database $conn
1594          */
1595         private function undoTransactionRoundFlags( Database $conn ) {
1596                 if ( $conn->getLBInfo( 'autoCommitOnly' ) ) {
1597                         return; // transaction rounds do not apply to these connections
1598                 }
1599
1600                 if ( $conn->getFlag( $conn::DBO_TRX ) ) {
1601                         $conn->setLBInfo( 'trxRoundId', false );
1602                 }
1603
1604                 if ( $conn->getFlag( $conn::DBO_DEFAULT ) ) {
1605                         $conn->restoreFlags( $conn::RESTORE_PRIOR );
1606                 }
1607         }
1608
1609         public function flushReplicaSnapshots( $fname = __METHOD__ ) {
1610                 $this->forEachOpenReplicaConnection( function ( IDatabase $conn ) use ( $fname ) {
1611                         $conn->flushSnapshot( $fname );
1612                 } );
1613         }
1614
1615         public function flushMasterSnapshots( $fname = __METHOD__ ) {
1616                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( $fname ) {
1617                         $conn->flushSnapshot( $fname );
1618                 } );
1619         }
1620
1621         /**
1622          * @return string
1623          * @since 1.32
1624          */
1625         public function getTransactionRoundStage() {
1626                 return $this->trxRoundStage;
1627         }
1628
1629         public function hasMasterConnection() {
1630                 return $this->isOpen( $this->getWriterIndex() );
1631         }
1632
1633         public function hasMasterChanges() {
1634                 $pending = 0;
1635                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$pending ) {
1636                         $pending |= $conn->writesOrCallbacksPending();
1637                 } );
1638
1639                 return (bool)$pending;
1640         }
1641
1642         public function lastMasterChangeTimestamp() {
1643                 $lastTime = false;
1644                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$lastTime ) {
1645                         $lastTime = max( $lastTime, $conn->lastDoneWrites() );
1646                 } );
1647
1648                 return $lastTime;
1649         }
1650
1651         public function hasOrMadeRecentMasterChanges( $age = null ) {
1652                 $age = ( $age === null ) ? $this->waitTimeout : $age;
1653
1654                 return ( $this->hasMasterChanges()
1655                         || $this->lastMasterChangeTimestamp() > microtime( true ) - $age );
1656         }
1657
1658         public function pendingMasterChangeCallers() {
1659                 $fnames = [];
1660                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$fnames ) {
1661                         $fnames = array_merge( $fnames, $conn->pendingWriteCallers() );
1662                 } );
1663
1664                 return $fnames;
1665         }
1666
1667         public function getLaggedReplicaMode( $domain = false ) {
1668                 // No-op if there is only one DB (also avoids recursion)
1669                 if ( !$this->laggedReplicaMode && $this->getServerCount() > 1 ) {
1670                         try {
1671                                 // See if laggedReplicaMode gets set
1672                                 $conn = $this->getConnection( self::DB_REPLICA, false, $domain );
1673                                 $this->reuseConnection( $conn );
1674                         } catch ( DBConnectionError $e ) {
1675                                 // Avoid expensive re-connect attempts and failures
1676                                 $this->allReplicasDownMode = true;
1677                                 $this->laggedReplicaMode = true;
1678                         }
1679                 }
1680
1681                 return $this->laggedReplicaMode;
1682         }
1683
1684         public function laggedReplicaUsed() {
1685                 return $this->laggedReplicaMode;
1686         }
1687
1688         /**
1689          * @return bool
1690          * @since 1.27
1691          * @deprecated Since 1.28; use laggedReplicaUsed()
1692          */
1693         public function laggedSlaveUsed() {
1694                 return $this->laggedReplicaUsed();
1695         }
1696
1697         public function getReadOnlyReason( $domain = false, IDatabase $conn = null ) {
1698                 if ( $this->readOnlyReason !== false ) {
1699                         return $this->readOnlyReason;
1700                 } elseif ( $this->getLaggedReplicaMode( $domain ) ) {
1701                         if ( $this->allReplicasDownMode ) {
1702                                 return 'The database has been automatically locked ' .
1703                                         'until the replica database servers become available';
1704                         } else {
1705                                 return 'The database has been automatically locked ' .
1706                                         'while the replica database servers catch up to the master.';
1707                         }
1708                 } elseif ( $this->masterRunningReadOnly( $domain, $conn ) ) {
1709                         return 'The database master is running in read-only mode.';
1710                 }
1711
1712                 return false;
1713         }
1714
1715         /**
1716          * @param string $domain Domain ID, or false for the current domain
1717          * @param IDatabase|null $conn DB master connectionl used to avoid loops [optional]
1718          * @return bool
1719          */
1720         private function masterRunningReadOnly( $domain, IDatabase $conn = null ) {
1721                 $cache = $this->wanCache;
1722                 $masterServer = $this->getServerName( $this->getWriterIndex() );
1723
1724                 return (bool)$cache->getWithSetCallback(
1725                         $cache->makeGlobalKey( __CLASS__, 'server-read-only', $masterServer ),
1726                         self::TTL_CACHE_READONLY,
1727                         function () use ( $domain, $conn ) {
1728                                 $old = $this->trxProfiler->setSilenced( true );
1729                                 try {
1730                                         $dbw = $conn ?: $this->getConnection( self::DB_MASTER, [], $domain );
1731                                         $readOnly = (int)$dbw->serverIsReadOnly();
1732                                         if ( !$conn ) {
1733                                                 $this->reuseConnection( $dbw );
1734                                         }
1735                                 } catch ( DBError $e ) {
1736                                         $readOnly = 0;
1737                                 }
1738                                 $this->trxProfiler->setSilenced( $old );
1739                                 return $readOnly;
1740                         },
1741                         [ 'pcTTL' => $cache::TTL_PROC_LONG, 'busyValue' => 0 ]
1742                 );
1743         }
1744
1745         public function allowLagged( $mode = null ) {
1746                 if ( $mode === null ) {
1747                         return $this->allowLagged;
1748                 }
1749                 $this->allowLagged = $mode;
1750
1751                 return $this->allowLagged;
1752         }
1753
1754         public function pingAll() {
1755                 $success = true;
1756                 $this->forEachOpenConnection( function ( IDatabase $conn ) use ( &$success ) {
1757                         if ( !$conn->ping() ) {
1758                                 $success = false;
1759                         }
1760                 } );
1761
1762                 return $success;
1763         }
1764
1765         public function forEachOpenConnection( $callback, array $params = [] ) {
1766                 foreach ( $this->conns as $connsByServer ) {
1767                         foreach ( $connsByServer as $serverConns ) {
1768                                 foreach ( $serverConns as $conn ) {
1769                                         $callback( $conn, ...$params );
1770                                 }
1771                         }
1772                 }
1773         }
1774
1775         public function forEachOpenMasterConnection( $callback, array $params = [] ) {
1776                 $masterIndex = $this->getWriterIndex();
1777                 foreach ( $this->conns as $connsByServer ) {
1778                         if ( isset( $connsByServer[$masterIndex] ) ) {
1779                                 /** @var IDatabase $conn */
1780                                 foreach ( $connsByServer[$masterIndex] as $conn ) {
1781                                         $callback( $conn, ...$params );
1782                                 }
1783                         }
1784                 }
1785         }
1786
1787         public function forEachOpenReplicaConnection( $callback, array $params = [] ) {
1788                 foreach ( $this->conns as $connsByServer ) {
1789                         foreach ( $connsByServer as $i => $serverConns ) {
1790                                 if ( $i === $this->getWriterIndex() ) {
1791                                         continue; // skip master
1792                                 }
1793                                 foreach ( $serverConns as $conn ) {
1794                                         $callback( $conn, ...$params );
1795                                 }
1796                         }
1797                 }
1798         }
1799
1800         public function getMaxLag( $domain = false ) {
1801                 $maxLag = -1;
1802                 $host = '';
1803                 $maxIndex = 0;
1804
1805                 if ( $this->getServerCount() <= 1 ) {
1806                         return [ $host, $maxLag, $maxIndex ]; // no replication = no lag
1807                 }
1808
1809                 $lagTimes = $this->getLagTimes( $domain );
1810                 foreach ( $lagTimes as $i => $lag ) {
1811                         if ( $this->loads[$i] > 0 && $lag > $maxLag ) {
1812                                 $maxLag = $lag;
1813                                 $host = $this->servers[$i]['host'];
1814                                 $maxIndex = $i;
1815                         }
1816                 }
1817
1818                 return [ $host, $maxLag, $maxIndex ];
1819         }
1820
1821         public function getLagTimes( $domain = false ) {
1822                 if ( $this->getServerCount() <= 1 ) {
1823                         return [ $this->getWriterIndex() => 0 ]; // no replication = no lag
1824                 }
1825
1826                 $knownLagTimes = []; // map of (server index => 0 seconds)
1827                 $indexesWithLag = [];
1828                 foreach ( $this->servers as $i => $server ) {
1829                         if ( empty( $server['is static'] ) ) {
1830                                 $indexesWithLag[] = $i; // DB server might have replication lag
1831                         } else {
1832                                 $knownLagTimes[$i] = 0; // DB server is a non-replicating and read-only archive
1833                         }
1834                 }
1835
1836                 return $this->getLoadMonitor()->getLagTimes( $indexesWithLag, $domain ) + $knownLagTimes;
1837         }
1838
1839         public function safeGetLag( IDatabase $conn ) {
1840                 if ( $this->getServerCount() <= 1 ) {
1841                         return 0;
1842                 } else {
1843                         return $conn->getLag();
1844                 }
1845         }
1846
1847         /**
1848          * @param IDatabase $conn
1849          * @param DBMasterPos|bool $pos
1850          * @param int|null $timeout
1851          * @return bool
1852          */
1853         public function safeWaitForMasterPos( IDatabase $conn, $pos = false, $timeout = null ) {
1854                 $timeout = max( 1, $timeout ?: $this->waitTimeout );
1855
1856                 if ( $this->getServerCount() <= 1 || !$conn->getLBInfo( 'replica' ) ) {
1857                         return true; // server is not a replica DB
1858                 }
1859
1860                 if ( !$pos ) {
1861                         // Get the current master position, opening a connection if needed
1862                         $masterConn = $this->getAnyOpenConnection( $this->getWriterIndex() );
1863                         if ( $masterConn ) {
1864                                 $pos = $masterConn->getMasterPos();
1865                         } else {
1866                                 $masterConn = $this->openConnection( $this->getWriterIndex(), self::DOMAIN_ANY );
1867                                 $pos = $masterConn->getMasterPos();
1868                                 $this->closeConnection( $masterConn );
1869                         }
1870                 }
1871
1872                 if ( $pos instanceof DBMasterPos ) {
1873                         $result = $conn->masterPosWait( $pos, $timeout );
1874                         if ( $result == -1 || is_null( $result ) ) {
1875                                 $msg = __METHOD__ . ': timed out waiting on {host} pos {pos}';
1876                                 $this->replLogger->warning( $msg, [
1877                                         'host' => $conn->getServer(),
1878                                         'pos' => $pos,
1879                                         'trace' => ( new RuntimeException() )->getTraceAsString()
1880                                 ] );
1881                                 $ok = false;
1882                         } else {
1883                                 $this->replLogger->debug( __METHOD__ . ': done waiting' );
1884                                 $ok = true;
1885                         }
1886                 } else {
1887                         $ok = false; // something is misconfigured
1888                         $this->replLogger->error(
1889                                 __METHOD__ . ': could not get master pos for {host}',
1890                                 [
1891                                         'host' => $conn->getServer(),
1892                                         'trace' => ( new RuntimeException() )->getTraceAsString()
1893                                 ]
1894                         );
1895                 }
1896
1897                 return $ok;
1898         }
1899
1900         public function setTransactionListener( $name, callable $callback = null ) {
1901                 if ( $callback ) {
1902                         $this->trxRecurringCallbacks[$name] = $callback;
1903                 } else {
1904                         unset( $this->trxRecurringCallbacks[$name] );
1905                 }
1906                 $this->forEachOpenMasterConnection(
1907                         function ( IDatabase $conn ) use ( $name, $callback ) {
1908                                 $conn->setTransactionListener( $name, $callback );
1909                         }
1910                 );
1911         }
1912
1913         public function setTableAliases( array $aliases ) {
1914                 $this->tableAliases = $aliases;
1915         }
1916
1917         public function setIndexAliases( array $aliases ) {
1918                 $this->indexAliases = $aliases;
1919         }
1920
1921         /**
1922          * @param string $prefix
1923          * @deprecated Since 1.33
1924          */
1925         public function setDomainPrefix( $prefix ) {
1926                 $this->setLocalDomainPrefix( $prefix );
1927         }
1928
1929         public function setLocalDomainPrefix( $prefix ) {
1930                 // Find connections to explicit foreign domains still marked as in-use...
1931                 $domainsInUse = [];
1932                 $this->forEachOpenConnection( function ( IDatabase $conn ) use ( &$domainsInUse ) {
1933                         // Once reuseConnection() is called on a handle, its reference count goes from 1 to 0.
1934                         // Until then, it is still in use by the caller (explicitly or via DBConnRef scope).
1935                         if ( $conn->getLBInfo( 'foreignPoolRefCount' ) > 0 ) {
1936                                 $domainsInUse[] = $conn->getDomainID();
1937                         }
1938                 } );
1939
1940                 // Do not switch connections to explicit foreign domains unless marked as safe
1941                 if ( $domainsInUse ) {
1942                         $domains = implode( ', ', $domainsInUse );
1943                         throw new DBUnexpectedError( null,
1944                                 "Foreign domain connections are still in use ($domains)." );
1945                 }
1946
1947                 $this->setLocalDomain( new DatabaseDomain(
1948                         $this->localDomain->getDatabase(),
1949                         $this->localDomain->getSchema(),
1950                         $prefix
1951                 ) );
1952
1953                 // Update the prefix for all local connections...
1954                 $this->forEachOpenConnection( function ( IDatabase $db ) use ( $prefix ) {
1955                         if ( !$db->getLBInfo( 'foreign' ) ) {
1956                                 $db->tablePrefix( $prefix );
1957                         }
1958                 } );
1959         }
1960
1961         public function redefineLocalDomain( $domain ) {
1962                 $this->closeAll();
1963
1964                 $this->setLocalDomain( DatabaseDomain::newFromId( $domain ) );
1965         }
1966
1967         /**
1968          * @param DatabaseDomain $domain
1969          */
1970         private function setLocalDomain( DatabaseDomain $domain ) {
1971                 $this->localDomain = $domain;
1972                 // In case a caller assumes that the domain ID is simply <db>-<prefix>, which is almost
1973                 // always true, gracefully handle the case when they fail to account for escaping.
1974                 if ( $this->localDomain->getTablePrefix() != '' ) {
1975                         $this->localDomainIdAlias =
1976                                 $this->localDomain->getDatabase() . '-' . $this->localDomain->getTablePrefix();
1977                 } else {
1978                         $this->localDomainIdAlias = $this->localDomain->getDatabase();
1979                 }
1980         }
1981
1982         function __destruct() {
1983                 // Avoid connection leaks for sanity
1984                 $this->disable();
1985         }
1986 }
1987
1988 /**
1989  * @deprecated since 1.29
1990  */
1991 class_alias( LoadBalancer::class, 'LoadBalancer' );