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