includes/libs/rdbms/loadbalancer/LoadBalancer.php

   1 <?php
   2 /**
   3  * Database load balancing manager
   4  *
   5  * This program is free software; you can redistribute it and/or modify
   6  * it under the terms of the GNU General Public License as published by
   7  * the Free Software Foundation; either version 2 of the License, or
   8  * (at your option) any later version.
   9  *
  10  * This program is distributed in the hope that it will be useful,
  11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  13  * GNU General Public License for more details.
  14  *
  15  * You should have received a copy of the GNU General Public License along
  16  * with this program; if not, write to the Free Software Foundation, Inc.,
  17  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
  18  * http://www.gnu.org/copyleft/gpl.html
  19  *
  20  * @file
  21  */
  22 namespace Wikimedia\Rdbms;
  23
  24 use Psr\Log\LoggerInterface;
  25 use Psr\Log\NullLogger;
  26 use Wikimedia\ScopedCallback;
  27 use BagOStuff;
  28 use EmptyBagOStuff;
  29 use WANObjectCache;
  30 use ArrayUtils;
  31 use UnexpectedValueException;
  32 use InvalidArgumentException;
  33 use RuntimeException;
  34 use Exception;
  35
  36 /**
  37  * Database connection, tracking, load balancing, and transaction manager for a cluster
  38  *
  39  * @ingroup Database
  40  */
  41 class LoadBalancer implements ILoadBalancer {
  42         /** @var ILoadMonitor */
  43         private $loadMonitor;
  44         /** @var callable|null Callback to run before the first connection attempt */
  45         private $chronologyCallback;
  46         /** @var BagOStuff */
  47         private $srvCache;
  48         /** @var WANObjectCache */
  49         private $wanCache;
  50         /** @var mixed Class name or object With profileIn/profileOut methods */
  51         private $profiler;
  52         /** @var TransactionProfiler */
  53         private $trxProfiler;
  54         /** @var LoggerInterface */
  55         private $replLogger;
  56         /** @var LoggerInterface */
  57         private $connLogger;
  58         /** @var LoggerInterface */
  59         private $queryLogger;
  60         /** @var LoggerInterface */
  61         private $perfLogger;
  62         /** @var callable Exception logger */
  63         private $errorLogger;
  64         /** @var callable Deprecation logger */
  65         private $deprecationLogger;
  66
  67         /** @var DatabaseDomain Local Domain ID and default for selectDB() calls */
  68         private $localDomain;
  69
  70         /** @var Database[][][] Map of (connection category => server index => IDatabase[]) */
  71         private $conns;
  72
  73         /** @var array[] Map of (server index => server config array) */
  74         private $servers;
  75         /** @var float[] Map of (server index => weight) */
  76         private $loads;
  77         /** @var array[] Map of (group => server index => weight) */
  78         private $groupLoads;
  79         /** @var bool Whether to disregard replica DB lag as a factor in replica DB selection */
  80         private $allowLagged;
  81         /** @var int Seconds to spend waiting on replica DB lag to resolve */
  82         private $waitTimeout;
  83         /** @var array The LoadMonitor configuration */
  84         private $loadMonitorConfig;
  85         /** @var string Alternate ID string for the domain instead of DatabaseDomain::getId() */
  86         private $localDomainIdAlias;
  87         /** @var int */
  88         private $maxLag = self::MAX_LAG_DEFAULT;
  89
  90         /** @var string Current server name */
  91         private $hostname;
  92         /** @var bool Whether this PHP instance is for a CLI script */
  93         private $cliMode;
  94         /** @var string Agent name for query profiling */
  95         private $agent;
  96
  97         /** @var array[] $aliases Map of (table => (dbname, schema, prefix) map) */
  98         private $tableAliases = [];
  99         /** @var string[] Map of (index alias => index) */
 100         private $indexAliases = [];
 101         /** @var array[] Map of (name => callable) */
 102         private $trxRecurringCallbacks = [];
 103
 104         /** @var Database DB connection object that caused a problem */
 105         private $errorConnection;
 106         /** @var int The generic (not query grouped) replica DB index (of $mServers) */
 107         private $readIndex;
 108         /** @var bool|DBMasterPos False if not set */
 109         private $waitForPos;
 110         /** @var bool Whether the generic reader fell back to a lagged replica DB */
 111         private $laggedReplicaMode = false;
 112         /** @var bool Whether the generic reader fell back to a lagged replica DB */
 113         private $allReplicasDownMode = false;
 114         /** @var string The last DB selection or connection error */
 115         private $lastError = 'Unknown error';
 116         /** @var string|bool Reason the LB is read-only or false if not */
 117         private $readOnlyReason = false;
 118         /** @var int Total connections opened */
 119         private $connsOpened = 0;
 120         /** @var bool */
 121         private $disabled = false;
 122         /** @var bool Whether any connection has been attempted yet */
 123         private $connectionAttempted = false;
 124
 125         /** @var string|bool String if a requested DBO_TRX transaction round is active */
 126         private $trxRoundId = false;
 127         /** @var string Stage of the current transaction round in the transaction round life-cycle */
 128         private $trxRoundStage = self::ROUND_CURSORY;
 129
 130         /** @var string|null */
 131         private $defaultGroup = null;
 132
 133         /** @var int Warn when this many connection are held */
 134         const CONN_HELD_WARN_THRESHOLD = 10;
 135
 136         /** @var int Default 'maxLag' when unspecified */
 137         const MAX_LAG_DEFAULT = 10;
 138         /** @var int Default 'waitTimeout' when unspecified */
 139         const MAX_WAIT_DEFAULT = 10;
 140         /** @var int Seconds to cache master server read-only status */
 141         const TTL_CACHE_READONLY = 5;
 142
 143         const KEY_LOCAL = 'local';
 144         const KEY_FOREIGN_FREE = 'foreignFree';
 145         const KEY_FOREIGN_INUSE = 'foreignInUse';
 146
 147         const KEY_LOCAL_NOROUND = 'localAutoCommit';
 148         const KEY_FOREIGN_FREE_NOROUND = 'foreignFreeAutoCommit';
 149         const KEY_FOREIGN_INUSE_NOROUND = 'foreignInUseAutoCommit';
 150
 151         /** @var string Transaction round, explicit or implicit, has not finished writing */
 152         const ROUND_CURSORY = 'cursory';
 153         /** @var string Transaction round writes are complete and ready for pre-commit checks */
 154         const ROUND_FINALIZED = 'finalized';
 155         /** @var string Transaction round passed final pre-commit checks */
 156         const ROUND_APPROVED = 'approved';
 157         /** @var string Transaction round was committed and post-commit callbacks must be run */
 158         const ROUND_COMMIT_CALLBACKS = 'commit-callbacks';
 159         /** @var string Transaction round was rolled back and post-rollback callbacks must be run */
 160         const ROUND_ROLLBACK_CALLBACKS = 'rollback-callbacks';
 161         /** @var string Transaction round encountered an error */
 162         const ROUND_ERROR = 'error';
 163
 164         public function __construct( array $params ) {
 165                 if ( !isset( $params['servers'] ) ) {
 166                         throw new InvalidArgumentException( __CLASS__ . ': missing servers parameter' );
 167                 }
 168                 $this->servers = $params['servers'];
 169                 foreach ( $this->servers as $i => $server ) {
 170                         if ( $i == 0 ) {
 171                                 $this->servers[$i]['master'] = true;
 172                         } else {
 173                                 $this->servers[$i]['replica'] = true;
 174                         }
 175                 }
 176
 177                 $localDomain = isset( $params['localDomain'] )
 178                         ? DatabaseDomain::newFromId( $params['localDomain'] )
 179                         : DatabaseDomain::newUnspecified();
 180                 $this->setLocalDomain( $localDomain );
 181
 182                 $this->waitTimeout = $params['waitTimeout'] ?? self::MAX_WAIT_DEFAULT;
 183
 184                 $this->readIndex = -1;
 185                 $this->conns = [
 186                         // Connection were transaction rounds may be applied
 187                         self::KEY_LOCAL => [],
 188                         self::KEY_FOREIGN_INUSE => [],
 189                         self::KEY_FOREIGN_FREE => [],
 190                         // Auto-committing counterpart connections that ignore transaction rounds
 191                         self::KEY_LOCAL_NOROUND => [],
 192                         self::KEY_FOREIGN_INUSE_NOROUND => [],
 193                         self::KEY_FOREIGN_FREE_NOROUND => []
 194                 ];
 195                 $this->loads = [];
 196                 $this->waitForPos = false;
 197                 $this->allowLagged = false;
 198
 199                 if ( isset( $params['readOnlyReason'] ) && is_string( $params['readOnlyReason'] ) ) {
 200                         $this->readOnlyReason = $params['readOnlyReason'];
 201                 }
 202
 203                 if ( isset( $params['maxLag'] ) ) {
 204                         $this->maxLag = $params['maxLag'];
 205                 }
 206
 207                 if ( isset( $params['loadMonitor'] ) ) {
 208                         $this->loadMonitorConfig = $params['loadMonitor'];
 209                 } else {
 210                         $this->loadMonitorConfig = [ 'class' => 'LoadMonitorNull' ];
 211                 }
 212                 $this->loadMonitorConfig += [ 'lagWarnThreshold' => $this->maxLag ];
 213
 214                 foreach ( $params['servers'] as $i => $server ) {
 215                         $this->loads[$i] = $server['load'];
 216                         if ( isset( $server['groupLoads'] ) ) {
 217                                 foreach ( $server['groupLoads'] as $group => $ratio ) {
 218                                         if ( !isset( $this->groupLoads[$group] ) ) {
 219                                                 $this->groupLoads[$group] = [];
 220                                         }
 221                                         $this->groupLoads[$group][$i] = $ratio;
 222                                 }
 223                         }
 224                 }
 225
 226                 if ( isset( $params['srvCache'] ) ) {
 227                         $this->srvCache = $params['srvCache'];
 228                 } else {
 229                         $this->srvCache = new EmptyBagOStuff();
 230                 }
 231                 if ( isset( $params['wanCache'] ) ) {
 232                         $this->wanCache = $params['wanCache'];
 233                 } else {
 234                         $this->wanCache = WANObjectCache::newEmpty();
 235                 }
 236                 $this->profiler = $params['profiler'] ?? null;
 237                 if ( isset( $params['trxProfiler'] ) ) {
 238                         $this->trxProfiler = $params['trxProfiler'];
 239                 } else {
 240                         $this->trxProfiler = new TransactionProfiler();
 241                 }
 242
 243                 $this->errorLogger = $params['errorLogger'] ?? function ( Exception $e ) {
 244                         trigger_error( get_class( $e ) . ': ' . $e->getMessage(), E_USER_WARNING );
 245                 };
 246                 $this->deprecationLogger = $params['deprecationLogger'] ?? function ( $msg ) {
 247                         trigger_error( $msg, E_USER_DEPRECATED );
 248                 };
 249
 250                 foreach ( [ 'replLogger', 'connLogger', 'queryLogger', 'perfLogger' ] as $key ) {
 251                         $this->$key = $params[$key] ?? new NullLogger();
 252                 }
 253
 254                 $this->hostname = $params['hostname'] ?? ( gethostname() ?: 'unknown' );
 255                 $this->cliMode = $params['cliMode'] ?? ( PHP_SAPI === 'cli' || PHP_SAPI === 'phpdbg' );
 256                 $this->agent = $params['agent'] ?? '';
 257
 258                 if ( isset( $params['chronologyCallback'] ) ) {
 259                         $this->chronologyCallback = $params['chronologyCallback'];
 260                 }
 261
 262                 if ( isset( $params['roundStage'] ) ) {
 263                         if ( $params['roundStage'] === self::STAGE_POSTCOMMIT_CALLBACKS ) {
 264                                 $this->trxRoundStage = self::ROUND_COMMIT_CALLBACKS;
 265                         } elseif ( $params['roundStage'] === self::STAGE_POSTROLLBACK_CALLBACKS ) {
 266                                 $this->trxRoundStage = self::ROUND_ROLLBACK_CALLBACKS;
 267                         }
 268                 }
 269
 270                 $this->defaultGroup = $params['defaultGroup'] ?? null;
 271         }
 272
 273         public function getLocalDomainID() {
 274                 return $this->localDomain->getId();
 275         }
 276
 277         public function resolveDomainID( $domain ) {
 278                 return ( $domain !== false ) ? (string)$domain : $this->getLocalDomainID();
 279         }
 280
 281         /**
 282          * Get a LoadMonitor instance
 283          *
 284          * @return ILoadMonitor
 285          */
 286         private function getLoadMonitor() {
 287                 if ( !isset( $this->loadMonitor ) ) {
 288                         $compat = [
 289                                 'LoadMonitor' => LoadMonitor::class,
 290                                 'LoadMonitorNull' => LoadMonitorNull::class,
 291                                 'LoadMonitorMySQL' => LoadMonitorMySQL::class,
 292                         ];
 293
 294                         $class = $this->loadMonitorConfig['class'];
 295                         if ( isset( $compat[$class] ) ) {
 296                                 $class = $compat[$class];
 297                         }
 298
 299                         $this->loadMonitor = new $class(
 300                                 $this, $this->srvCache, $this->wanCache, $this->loadMonitorConfig );
 301                         $this->loadMonitor->setLogger( $this->replLogger );
 302                 }
 303
 304                 return $this->loadMonitor;
 305         }
 306
 307         /**
 308          * @param array $loads
 309          * @param bool|string $domain Domain to get non-lagged for
 310          * @param int $maxLag Restrict the maximum allowed lag to this many seconds
 311          * @return bool|int|string
 312          */
 313         private function getRandomNonLagged( array $loads, $domain = false, $maxLag = INF ) {
 314                 $lags = $this->getLagTimes( $domain );
 315
 316                 # Unset excessively lagged servers
 317                 foreach ( $lags as $i => $lag ) {
 318                         if ( $i != 0 ) {
 319                                 # How much lag this server nominally is allowed to have
 320                                 $maxServerLag = $this->servers[$i]['max lag'] ?? $this->maxLag; // default
 321                                 # Constrain that futher by $maxLag argument
 322                                 $maxServerLag = min( $maxServerLag, $maxLag );
 323
 324                                 $host = $this->getServerName( $i );
 325                                 if ( $lag === false && !is_infinite( $maxServerLag ) ) {
 326                                         $this->replLogger->error(
 327                                                 __METHOD__ .
 328                                                 ": server {host} is not replicating?", [ 'host' => $host ] );
 329                                         unset( $loads[$i] );
 330                                 } elseif ( $lag > $maxServerLag ) {
 331                                         $this->replLogger->info(
 332                                                 __METHOD__ .
 333                                                 ": server {host} has {lag} seconds of lag (>= {maxlag})",
 334                                                 [ 'host' => $host, 'lag' => $lag, 'maxlag' => $maxServerLag ]
 335                                         );
 336                                         unset( $loads[$i] );
 337                                 }
 338                         }
 339                 }
 340
 341                 # Find out if all the replica DBs with non-zero load are lagged
 342                 $sum = 0;
 343                 foreach ( $loads as $load ) {
 344                         $sum += $load;
 345                 }
 346                 if ( $sum == 0 ) {
 347                         # No appropriate DB servers except maybe the master and some replica DBs with zero load
 348                         # Do NOT use the master
 349                         # Instead, this function will return false, triggering read-only mode,
 350                         # and a lagged replica DB will be used instead.
 351                         return false;
 352                 }
 353
 354                 if ( count( $loads ) == 0 ) {
 355                         return false;
 356                 }
 357
 358                 # Return a random representative of the remainder
 359                 return ArrayUtils::pickRandom( $loads );
 360         }
 361
 362         public function getReaderIndex( $group = false, $domain = false ) {
 363                 if ( count( $this->servers ) == 1 ) {
 364                         // Skip the load balancing if there's only one server
 365                         return $this->getWriterIndex();
 366                 } elseif ( $group === false && $this->readIndex >= 0 ) {
 367                         // Shortcut if the generic reader index was already cached
 368                         return $this->readIndex;
 369                 }
 370
 371                 if ( $group !== false ) {
 372                         // Use the server weight array for this load group
 373                         if ( isset( $this->groupLoads[$group] ) ) {
 374                                 $loads = $this->groupLoads[$group];
 375                         } else {
 376                                 // No loads for this group, return false and the caller can use some other group
 377                                 $this->connLogger->info( __METHOD__ . ": no loads for group $group" );
 378
 379                                 return false;
 380                         }
 381                 } else {
 382                         // Use the generic load group
 383                         $loads = $this->loads;
 384                 }
 385
 386                 // Scale the configured load ratios according to each server's load and state
 387                 $this->getLoadMonitor()->scaleLoads( $loads, $domain );
 388
 389                 // Pick a server to use, accounting for weights, load, lag, and "waitForPos"
 390                 list( $i, $laggedReplicaMode ) = $this->pickReaderIndex( $loads, $domain );
 391                 if ( $i === false ) {
 392                         // Replica DB connection unsuccessful
 393                         return false;
 394                 }
 395
 396                 if ( $this->waitForPos && $i != $this->getWriterIndex() ) {
 397                         // Before any data queries are run, wait for the server to catch up to the
 398                         // specified position. This is used to improve session consistency. Note that
 399                         // when LoadBalancer::waitFor() sets "waitForPos", the waiting triggers here,
 400                         // so update laggedReplicaMode as needed for consistency.
 401                         if ( !$this->doWait( $i ) ) {
 402                                 $laggedReplicaMode = true;
 403                         }
 404                 }
 405
 406                 if ( $this->readIndex <= 0 && $this->loads[$i] > 0 && $group === false ) {
 407                         // Cache the generic reader index for future ungrouped DB_REPLICA handles
 408                         $this->readIndex = $i;
 409                         // Record if the generic reader index is in "lagged replica DB" mode
 410                         if ( $laggedReplicaMode ) {
 411                                 $this->laggedReplicaMode = true;
 412                         }
 413                 }
 414
 415                 $serverName = $this->getServerName( $i );
 416                 $this->connLogger->debug( __METHOD__ . ": using server $serverName for group '$group'" );
 417
 418                 return $i;
 419         }
 420
 421         /**
 422          * @param array $loads List of server weights
 423          * @param string|bool $domain
 424          * @return array (reader index, lagged replica mode) or false on failure
 425          */
 426         private function pickReaderIndex( array $loads, $domain = false ) {
 427                 if ( !count( $loads ) ) {
 428                         throw new InvalidArgumentException( "Empty server array given to LoadBalancer" );
 429                 }
 430
 431                 /** @var int|bool $i Index of selected server */
 432                 $i = false;
 433                 /** @var bool $laggedReplicaMode Whether server is considered lagged */
 434                 $laggedReplicaMode = false;
 435
 436                 // Quickly look through the available servers for a server that meets criteria...
 437                 $currentLoads = $loads;
 438                 while ( count( $currentLoads ) ) {
 439                         if ( $this->allowLagged || $laggedReplicaMode ) {
 440                                 $i = ArrayUtils::pickRandom( $currentLoads );
 441                         } else {
 442                                 $i = false;
 443                                 if ( $this->waitForPos && $this->waitForPos->asOfTime() ) {
 444                                         // "chronologyCallback" sets "waitForPos" for session consistency.
 445                                         // This triggers doWait() after connect, so it's especially good to
 446                                         // avoid lagged servers so as to avoid excessive delay in that method.
 447                                         $ago = microtime( true ) - $this->waitForPos->asOfTime();
 448                                         // Aim for <= 1 second of waiting (being too picky can backfire)
 449                                         $i = $this->getRandomNonLagged( $currentLoads, $domain, $ago + 1 );
 450                                 }
 451                                 if ( $i === false ) {
 452                                         // Any server with less lag than it's 'max lag' param is preferable
 453                                         $i = $this->getRandomNonLagged( $currentLoads, $domain );
 454                                 }
 455                                 if ( $i === false && count( $currentLoads ) != 0 ) {
 456                                         // All replica DBs lagged. Switch to read-only mode
 457                                         $this->replLogger->error(
 458                                                 __METHOD__ . ": all replica DBs lagged. Switch to read-only mode" );
 459                                         $i = ArrayUtils::pickRandom( $currentLoads );
 460                                         $laggedReplicaMode = true;
 461                                 }
 462                         }
 463
 464                         if ( $i === false ) {
 465                                 // pickRandom() returned false.
 466                                 // This is permanent and means the configuration or the load monitor
 467                                 // wants us to return false.
 468                                 $this->connLogger->debug( __METHOD__ . ": pickRandom() returned false" );
 469
 470                                 return [ false, false ];
 471                         }
 472
 473                         $serverName = $this->getServerName( $i );
 474                         $this->connLogger->debug( __METHOD__ . ": Using reader #$i: $serverName..." );
 475
 476                         $conn = $this->openConnection( $i, $domain );
 477                         if ( !$conn ) {
 478                                 $this->connLogger->warning( __METHOD__ . ": Failed connecting to $i/$domain" );
 479                                 unset( $currentLoads[$i] ); // avoid this server next iteration
 480                                 $i = false;
 481                                 continue;
 482                         }
 483
 484                         // Decrement reference counter, we are finished with this connection.
 485                         // It will be incremented for the caller later.
 486                         if ( $domain !== false ) {
 487                                 $this->reuseConnection( $conn );
 488                         }
 489
 490                         // Return this server
 491                         break;
 492                 }
 493
 494                 // If all servers were down, quit now
 495                 if ( !count( $currentLoads ) ) {
 496                         $this->connLogger->error( __METHOD__ . ": all servers down" );
 497                 }
 498
 499                 return [ $i, $laggedReplicaMode ];
 500         }
 501
 502         public function waitFor( $pos ) {
 503                 $oldPos = $this->waitForPos;
 504                 try {
 505                         $this->waitForPos = $pos;
 506                         // If a generic reader connection was already established, then wait now
 507                         $i = $this->readIndex;
 508                         if ( $i > 0 ) {
 509                                 if ( !$this->doWait( $i ) ) {
 510                                         $this->laggedReplicaMode = true;
 511                                 }
 512                         }
 513                 } finally {
 514                         // Restore the older position if it was higher since this is used for lag-protection
 515                         $this->setWaitForPositionIfHigher( $oldPos );
 516                 }
 517         }
 518
 519         public function waitForOne( $pos, $timeout = null ) {
 520                 $oldPos = $this->waitForPos;
 521                 try {
 522                         $this->waitForPos = $pos;
 523
 524                         $i = $this->readIndex;
 525                         if ( $i <= 0 ) {
 526                                 // Pick a generic replica DB if there isn't one yet
 527                                 $readLoads = $this->loads;
 528                                 unset( $readLoads[$this->getWriterIndex()] ); // replica DBs only
 529                                 $readLoads = array_filter( $readLoads ); // with non-zero load
 530                                 $i = ArrayUtils::pickRandom( $readLoads );
 531                         }
 532
 533                         if ( $i > 0 ) {
 534                                 $ok = $this->doWait( $i, true, $timeout );
 535                         } else {
 536                                 $ok = true; // no applicable loads
 537                         }
 538                 } finally {
 539                         # Restore the old position, as this is not used for lag-protection but for throttling
 540                         $this->waitForPos = $oldPos;
 541                 }
 542
 543                 return $ok;
 544         }
 545
 546         public function waitForAll( $pos, $timeout = null ) {
 547                 $timeout = $timeout ?: $this->waitTimeout;
 548
 549                 $oldPos = $this->waitForPos;
 550                 try {
 551                         $this->waitForPos = $pos;
 552                         $serverCount = count( $this->servers );
 553
 554                         $ok = true;
 555                         for ( $i = 1; $i < $serverCount; $i++ ) {
 556                                 if ( $this->loads[$i] > 0 ) {
 557                                         $start = microtime( true );
 558                                         $ok = $this->doWait( $i, true, $timeout ) && $ok;
 559                                         $timeout -= intval( microtime( true ) - $start );
 560                                         if ( $timeout <= 0 ) {
 561                                                 break; // timeout reached
 562                                         }
 563                                 }
 564                         }
 565                 } finally {
 566                         # Restore the old position, as this is not used for lag-protection but for throttling
 567                         $this->waitForPos = $oldPos;
 568                 }
 569
 570                 return $ok;
 571         }
 572
 573         /**
 574          * @param DBMasterPos|bool $pos
 575          */
 576         private function setWaitForPositionIfHigher( $pos ) {
 577                 if ( !$pos ) {
 578                         return;
 579                 }
 580
 581                 if ( !$this->waitForPos || $pos->hasReached( $this->waitForPos ) ) {
 582                         $this->waitForPos = $pos;
 583                 }
 584         }
 585
 586         public function getAnyOpenConnection( $i, $flags = 0 ) {
 587                 $autocommit = ( ( $flags & self::CONN_TRX_AUTOCOMMIT ) == self::CONN_TRX_AUTOCOMMIT );
 588                 foreach ( $this->conns as $connsByServer ) {
 589                         if ( !isset( $connsByServer[$i] ) ) {
 590                                 continue;
 591                         }
 592
 593                         foreach ( $connsByServer[$i] as $conn ) {
 594                                 if ( !$autocommit || $conn->getLBInfo( 'autoCommitOnly' ) ) {
 595                                         return $conn;
 596                                 }
 597                         }
 598                 }
 599
 600                 return false;
 601         }
 602
 603         /**
 604          * Wait for a given replica DB to catch up to the master pos stored in $this
 605          * @param int $index Server index
 606          * @param bool $open Check the server even if a new connection has to be made
 607          * @param int|null $timeout Max seconds to wait; default is "waitTimeout" given to __construct()
 608          * @return bool
 609          */
 610         protected function doWait( $index, $open = false, $timeout = null ) {
 611                 $timeout = max( 1, intval( $timeout ?: $this->waitTimeout ) );
 612
 613                 // Check if we already know that the DB has reached this point
 614                 $server = $this->getServerName( $index );
 615                 $key = $this->srvCache->makeGlobalKey( __CLASS__, 'last-known-pos', $server, 'v1' );
 616                 /** @var DBMasterPos $knownReachedPos */
 617                 $knownReachedPos = $this->srvCache->get( $key );
 618                 if (
 619                         $knownReachedPos instanceof DBMasterPos &&
 620                         $knownReachedPos->hasReached( $this->waitForPos )
 621                 ) {
 622                         $this->replLogger->debug(
 623                                 __METHOD__ .
 624                                 ': replica DB {dbserver} known to be caught up (pos >= $knownReachedPos).',
 625                                 [ 'dbserver' => $server ]
 626                         );
 627                         return true;
 628                 }
 629
 630                 // Find a connection to wait on, creating one if needed and allowed
 631                 $close = false; // close the connection afterwards
 632                 $conn = $this->getAnyOpenConnection( $index );
 633                 if ( !$conn ) {
 634                         if ( !$open ) {
 635                                 $this->replLogger->debug(
 636                                         __METHOD__ . ': no connection open for {dbserver}',
 637                                         [ 'dbserver' => $server ]
 638                                 );
 639
 640                                 return false;
 641                         } else {
 642                                 $conn = $this->openConnection( $index, self::DOMAIN_ANY );
 643                                 if ( !$conn ) {
 644                                         $this->replLogger->warning(
 645                                                 __METHOD__ . ': failed to connect to {dbserver}',
 646                                                 [ 'dbserver' => $server ]
 647                                         );
 648
 649                                         return false;
 650                                 }
 651                                 // Avoid connection spam in waitForAll() when connections
 652                                 // are made just for the sake of doing this lag check.
 653                                 $close = true;
 654                         }
 655                 }
 656
 657                 $this->replLogger->info(
 658                         __METHOD__ .
 659                         ': waiting for replica DB {dbserver} to catch up...',
 660                         [ 'dbserver' => $server ]
 661                 );
 662
 663                 $result = $conn->masterPosWait( $this->waitForPos, $timeout );
 664
 665                 if ( $result === null ) {
 666                         $this->replLogger->warning(
 667                                 __METHOD__ . ': Errored out waiting on {host} pos {pos}',
 668                                 [
 669                                         'host' => $server,
 670                                         'pos' => $this->waitForPos,
 671                                         'trace' => ( new RuntimeException() )->getTraceAsString()
 672                                 ]
 673                         );
 674                         $ok = false;
 675                 } elseif ( $result == -1 ) {
 676                         $this->replLogger->warning(
 677                                 __METHOD__ . ': Timed out waiting on {host} pos {pos}',
 678                                 [
 679                                         'host' => $server,
 680                                         'pos' => $this->waitForPos,
 681                                         'trace' => ( new RuntimeException() )->getTraceAsString()
 682                                 ]
 683                         );
 684                         $ok = false;
 685                 } else {
 686                         $this->replLogger->debug( __METHOD__ . ": done waiting" );
 687                         $ok = true;
 688                         // Remember that the DB reached this point
 689                         $this->srvCache->set( $key, $this->waitForPos, BagOStuff::TTL_DAY );
 690                 }
 691
 692                 if ( $close ) {
 693                         $this->closeConnection( $conn );
 694                 }
 695
 696                 return $ok;
 697         }
 698
 699         public function getConnection( $i, $groups = [], $domain = false, $flags = 0 ) {
 700                 if ( $i === null || $i === false ) {
 701                         throw new InvalidArgumentException( 'Attempt to call ' . __METHOD__ .
 702                                 ' with invalid server index' );
 703                 }
 704
 705                 if ( $this->localDomain->equals( $domain ) || $domain === $this->localDomainIdAlias ) {
 706                         $domain = false; // local connection requested
 707                 }
 708
 709                 if ( ( $flags & self::CONN_TRX_AUTOCOMMIT ) === self::CONN_TRX_AUTOCOMMIT ) {
 710                         // Assuming all servers are of the same type (or similar), which is overwhelmingly
 711                         // the case, use the master server information to get the attributes. The information
 712                         // for $i cannot be used since it might be DB_REPLICA, which might require connection
 713                         // attempts in order to be resolved into a real server index.
 714                         $attributes = $this->getServerAttributes( $this->getWriterIndex() );
 715                         if ( $attributes[Database::ATTR_DB_LEVEL_LOCKING] ) {
 716                                 // Callers sometimes want to (a) escape REPEATABLE-READ stateness without locking
 717                                 // rows (e.g. FOR UPDATE) or (b) make small commits during a larger transactions
 718                                 // to reduce lock contention. None of these apply for sqlite and using separate
 719                                 // connections just causes self-deadlocks.
 720                                 $flags &= ~self::CONN_TRX_AUTOCOMMIT;
 721                                 $this->connLogger->info( __METHOD__ .
 722                                         ': ignoring CONN_TRX_AUTOCOMMIT to avoid deadlocks.' );
 723                         }
 724                 }
 725
 726                 // Check one "group" per default: the generic pool
 727                 $defaultGroups = $this->defaultGroup ? [ $this->defaultGroup ] : [ false ];
 728
 729                 $groups = ( $groups === false || $groups === [] )
 730                         ? $defaultGroups
 731                         : (array)$groups;
 732
 733                 $masterOnly = ( $i == self::DB_MASTER || $i == $this->getWriterIndex() );
 734                 $oldConnsOpened = $this->connsOpened; // connections open now
 735
 736                 if ( $i == self::DB_MASTER ) {
 737                         $i = $this->getWriterIndex();
 738                 } elseif ( $i == self::DB_REPLICA ) {
 739                         # Try to find an available server in any the query groups (in order)
 740                         foreach ( $groups as $group ) {
 741                                 $groupIndex = $this->getReaderIndex( $group, $domain );
 742                                 if ( $groupIndex !== false ) {
 743                                         $i = $groupIndex;
 744                                         break;
 745                                 }
 746                         }
 747                 }
 748
 749                 # Operation-based index
 750                 if ( $i == self::DB_REPLICA ) {
 751                         $this->lastError = 'Unknown error'; // reset error string
 752                         # Try the general server pool if $groups are unavailable.
 753                         $i = ( $groups === [ false ] )
 754                                 ? false // don't bother with this if that is what was tried above
 755                                 : $this->getReaderIndex( false, $domain );
 756                         # Couldn't find a working server in getReaderIndex()?
 757                         if ( $i === false ) {
 758                                 $this->lastError = 'No working replica DB server: ' . $this->lastError;
 759                                 // Throw an exception
 760                                 $this->reportConnectionError();
 761                                 return null; // not reached
 762                         }
 763                 }
 764
 765                 # Now we have an explicit index into the servers array
 766                 $conn = $this->openConnection( $i, $domain, $flags );
 767                 if ( !$conn ) {
 768                         // Throw an exception
 769                         $this->reportConnectionError();
 770                         return null; // not reached
 771                 }
 772
 773                 # Profile any new connections that happen
 774                 if ( $this->connsOpened > $oldConnsOpened ) {
 775                         $host = $conn->getServer();
 776                         $dbname = $conn->getDBname();
 777                         $this->trxProfiler->recordConnection( $host, $dbname, $masterOnly );
 778                 }
 779
 780                 if ( $masterOnly ) {
 781                         # Make master-requested DB handles inherit any read-only mode setting
 782                         $conn->setLBInfo( 'readOnlyReason', $this->getReadOnlyReason( $domain, $conn ) );
 783                 }
 784
 785                 return $conn;
 786         }
 787
 788         public function reuseConnection( IDatabase $conn ) {
 789                 $serverIndex = $conn->getLBInfo( 'serverIndex' );
 790                 $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 791                 if ( $serverIndex === null || $refCount === null ) {
 792                         /**
 793                          * This can happen in code like:
 794                          *   foreach ( $dbs as $db ) {
 795                          *     $conn = $lb->getConnection( $lb::DB_REPLICA, [], $db );
 796                          *     ...
 797                          *     $lb->reuseConnection( $conn );
 798                          *   }
 799                          * When a connection to the local DB is opened in this way, reuseConnection()
 800                          * should be ignored
 801                          */
 802                         return;
 803                 } elseif ( $conn instanceof DBConnRef ) {
 804                         // DBConnRef already handles calling reuseConnection() and only passes the live
 805                         // Database instance to this method. Any caller passing in a DBConnRef is broken.
 806                         $this->connLogger->error(
 807                                 __METHOD__ . ": got DBConnRef instance.\n" .
 808                                 ( new RuntimeException() )->getTraceAsString() );
 809
 810                         return;
 811                 }
 812
 813                 if ( $this->disabled ) {
 814                         return; // DBConnRef handle probably survived longer than the LoadBalancer
 815                 }
 816
 817                 if ( $conn->getLBInfo( 'autoCommitOnly' ) ) {
 818                         $connFreeKey = self::KEY_FOREIGN_FREE_NOROUND;
 819                         $connInUseKey = self::KEY_FOREIGN_INUSE_NOROUND;
 820                 } else {
 821                         $connFreeKey = self::KEY_FOREIGN_FREE;
 822                         $connInUseKey = self::KEY_FOREIGN_INUSE;
 823                 }
 824
 825                 $domain = $conn->getDomainID();
 826                 if ( !isset( $this->conns[$connInUseKey][$serverIndex][$domain] ) ) {
 827                         throw new InvalidArgumentException( __METHOD__ .
 828                                 ": connection $serverIndex/$domain not found; it may have already been freed." );
 829                 } elseif ( $this->conns[$connInUseKey][$serverIndex][$domain] !== $conn ) {
 830                         throw new InvalidArgumentException( __METHOD__ .
 831                                 ": connection $serverIndex/$domain mismatched; it may have already been freed." );
 832                 }
 833
 834                 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
 835                 if ( $refCount <= 0 ) {
 836                         $this->conns[$connFreeKey][$serverIndex][$domain] = $conn;
 837                         unset( $this->conns[$connInUseKey][$serverIndex][$domain] );
 838                         if ( !$this->conns[$connInUseKey][$serverIndex] ) {
 839                                 unset( $this->conns[$connInUseKey][$serverIndex] ); // clean up
 840                         }
 841                         $this->connLogger->debug( __METHOD__ . ": freed connection $serverIndex/$domain" );
 842                 } else {
 843                         $this->connLogger->debug( __METHOD__ .
 844                                 ": reference count for $serverIndex/$domain reduced to $refCount" );
 845                 }
 846         }
 847
 848         public function getConnectionRef( $db, $groups = [], $domain = false, $flags = 0 ) {
 849                 $domain = $this->resolveDomainID( $domain );
 850
 851                 return new DBConnRef( $this, $this->getConnection( $db, $groups, $domain, $flags ) );
 852         }
 853
 854         public function getLazyConnectionRef( $db, $groups = [], $domain = false, $flags = 0 ) {
 855                 $domain = $this->resolveDomainID( $domain );
 856
 857                 return new DBConnRef( $this, [ $db, $groups, $domain, $flags ] );
 858         }
 859
 860         public function getMaintenanceConnectionRef( $db, $groups = [], $domain = false, $flags = 0 ) {
 861                 $domain = $this->resolveDomainID( $domain );
 862
 863                 return new MaintainableDBConnRef(
 864                         $this, $this->getConnection( $db, $groups, $domain, $flags ) );
 865         }
 866
 867         public function openConnection( $i, $domain = false, $flags = 0 ) {
 868                 if ( $this->localDomain->equals( $domain ) || $domain === $this->localDomainIdAlias ) {
 869                         $domain = false; // local connection requested
 870                 }
 871
 872                 if ( !$this->connectionAttempted && $this->chronologyCallback ) {
 873                         $this->connLogger->debug( __METHOD__ . ': calling initLB() before first connection.' );
 874                         // Load any "waitFor" positions before connecting so that doWait() is triggered
 875                         $this->connectionAttempted = true;
 876                         ( $this->chronologyCallback )( $this );
 877                 }
 878
 879                 // Check if an auto-commit connection is being requested. If so, it will not reuse the
 880                 // main set of DB connections but rather its own pool since:
 881                 // a) those are usually set to implicitly use transaction rounds via DBO_TRX
 882                 // b) those must support the use of explicit transaction rounds via beginMasterChanges()
 883                 $autoCommit = ( ( $flags & self::CONN_TRX_AUTOCOMMIT ) == self::CONN_TRX_AUTOCOMMIT );
 884
 885                 if ( $domain !== false ) {
 886                         // Connection is to a foreign domain
 887                         $conn = $this->openForeignConnection( $i, $domain, $flags );
 888                 } else {
 889                         // Connection is to the local domain
 890                         $conn = $this->openLocalConnection( $i, $flags );
 891                 }
 892
 893                 if ( $conn instanceof IDatabase && !$conn->isOpen() ) {
 894                         // Connection was made but later unrecoverably lost for some reason.
 895                         // Do not return a handle that will just throw exceptions on use,
 896                         // but let the calling code (e.g. getReaderIndex) try another server.
 897                         // See DatabaseMyslBase::ping() for how this can happen.
 898                         $this->errorConnection = $conn;
 899                         $conn = false;
 900                 }
 901
 902                 if ( $autoCommit && $conn instanceof IDatabase ) {
 903                         if ( $conn->trxLevel() ) { // sanity
 904                                 throw new DBUnexpectedError(
 905                                         $conn,
 906                                         __METHOD__ . ': CONN_TRX_AUTOCOMMIT handle has a transaction.'
 907                                 );
 908                         }
 909
 910                         $conn->clearFlag( $conn::DBO_TRX ); // auto-commit mode
 911                 }
 912
 913                 return $conn;
 914         }
 915
 916         /**
 917          * Open a connection to a local DB, or return one if it is already open.
 918          *
 919          * On error, returns false, and the connection which caused the
 920          * error will be available via $this->errorConnection.
 921          *
 922          * @note If disable() was called on this LoadBalancer, this method will throw a DBAccessError.
 923          *
 924          * @param int $i Server index
 925          * @param int $flags Class CONN_* constant bitfield
 926          * @return Database
 927          */
 928         private function openLocalConnection( $i, $flags = 0 ) {
 929                 $autoCommit = ( ( $flags & self::CONN_TRX_AUTOCOMMIT ) == self::CONN_TRX_AUTOCOMMIT );
 930
 931                 $connKey = $autoCommit ? self::KEY_LOCAL_NOROUND : self::KEY_LOCAL;
 932                 if ( isset( $this->conns[$connKey][$i][0] ) ) {
 933                         $conn = $this->conns[$connKey][$i][0];
 934                 } else {
 935                         if ( !isset( $this->servers[$i] ) || !is_array( $this->servers[$i] ) ) {
 936                                 throw new InvalidArgumentException( "No server with index '$i'." );
 937                         }
 938                         // Open a new connection
 939                         $server = $this->servers[$i];
 940                         $server['serverIndex'] = $i;
 941                         $server['autoCommitOnly'] = $autoCommit;
 942                         $conn = $this->reallyOpenConnection( $server, $this->localDomain );
 943                         $host = $this->getServerName( $i );
 944                         if ( $conn->isOpen() ) {
 945                                 $this->connLogger->debug(
 946                                         __METHOD__ . ": connected to database $i at '$host'." );
 947                                 $this->conns[$connKey][$i][0] = $conn;
 948                         } else {
 949                                 $this->connLogger->warning(
 950                                         __METHOD__ . ": failed to connect to database $i at '$host'." );
 951                                 $this->errorConnection = $conn;
 952                                 $conn = false;
 953                         }
 954                 }
 955
 956                 // Final sanity check to make sure the right domain is selected
 957                 if (
 958                         $conn instanceof IDatabase &&
 959                         !$this->localDomain->isCompatible( $conn->getDomainID() )
 960                 ) {
 961                         throw new UnexpectedValueException(
 962                                 "Got connection to '{$conn->getDomainID()}', " .
 963                                 "but expected local domain ('{$this->localDomain}')." );
 964                 }
 965
 966                 return $conn;
 967         }
 968
 969         /**
 970          * Open a connection to a foreign DB, or return one if it is already open.
 971          *
 972          * Increments a reference count on the returned connection which locks the
 973          * connection to the requested domain. This reference count can be
 974          * decremented by calling reuseConnection().
 975          *
 976          * If a connection is open to the appropriate server already, but with the wrong
 977          * database, it will be switched to the right database and returned, as long as
 978          * it has been freed first with reuseConnection().
 979          *
 980          * On error, returns false, and the connection which caused the
 981          * error will be available via $this->errorConnection.
 982          *
 983          * @note If disable() was called on this LoadBalancer, this method will throw a DBAccessError.
 984          *
 985          * @param int $i Server index
 986          * @param string $domain Domain ID to open
 987          * @param int $flags Class CONN_* constant bitfield
 988          * @return Database|bool Returns false on connection error
 989          * @throws DBError When database selection fails
 990          */
 991         private function openForeignConnection( $i, $domain, $flags = 0 ) {
 992                 $domainInstance = DatabaseDomain::newFromId( $domain );
 993                 $autoCommit = ( ( $flags & self::CONN_TRX_AUTOCOMMIT ) == self::CONN_TRX_AUTOCOMMIT );
 994
 995                 if ( $autoCommit ) {
 996                         $connFreeKey = self::KEY_FOREIGN_FREE_NOROUND;
 997                         $connInUseKey = self::KEY_FOREIGN_INUSE_NOROUND;
 998                 } else {
 999                         $connFreeKey = self::KEY_FOREIGN_FREE;
1000                         $connInUseKey = self::KEY_FOREIGN_INUSE;
1001                 }
1002
1003                 /** @var Database $conn */
1004                 if ( isset( $this->conns[$connInUseKey][$i][$domain] ) ) {
1005                         // Reuse an in-use connection for the same domain
1006                         $conn = $this->conns[$connInUseKey][$i][$domain];
1007                         $this->connLogger->debug( __METHOD__ . ": reusing connection $i/$domain" );
1008                 } elseif ( isset( $this->conns[$connFreeKey][$i][$domain] ) ) {
1009                         // Reuse a free connection for the same domain
1010                         $conn = $this->conns[$connFreeKey][$i][$domain];
1011                         unset( $this->conns[$connFreeKey][$i][$domain] );
1012                         $this->conns[$connInUseKey][$i][$domain] = $conn;
1013                         $this->connLogger->debug( __METHOD__ . ": reusing free connection $i/$domain" );
1014                 } elseif ( !empty( $this->conns[$connFreeKey][$i] ) ) {
1015                         // Reuse a free connection from another domain
1016                         $conn = reset( $this->conns[$connFreeKey][$i] );
1017                         $oldDomain = key( $this->conns[$connFreeKey][$i] );
1018                         if ( $domainInstance->getDatabase() !== null ) {
1019                                 $conn->selectDomain( $domainInstance );
1020                         } else {
1021                                 // Stay on the current database, but update the schema/prefix
1022                                 $conn->dbSchema( $domainInstance->getSchema() );
1023                                 $conn->tablePrefix( $domainInstance->getTablePrefix() );
1024                         }
1025                         unset( $this->conns[$connFreeKey][$i][$oldDomain] );
1026                         // Note that if $domain is an empty string, getDomainID() might not match it
1027                         $this->conns[$connInUseKey][$i][$conn->getDomainId()] = $conn;
1028                         $this->connLogger->debug( __METHOD__ .
1029                                 ": reusing free connection from $oldDomain for $domain" );
1030                 } else {
1031                         if ( !isset( $this->servers[$i] ) || !is_array( $this->servers[$i] ) ) {
1032                                 throw new InvalidArgumentException( "No server with index '$i'." );
1033                         }
1034                         // Open a new connection
1035                         $server = $this->servers[$i];
1036                         $server['serverIndex'] = $i;
1037                         $server['foreignPoolRefCount'] = 0;
1038                         $server['foreign'] = true;
1039                         $server['autoCommitOnly'] = $autoCommit;
1040                         $conn = $this->reallyOpenConnection( $server, $domainInstance );
1041                         if ( !$conn->isOpen() ) {
1042                                 $this->connLogger->warning( __METHOD__ . ": connection error for $i/$domain" );
1043                                 $this->errorConnection = $conn;
1044                                 $conn = false;
1045                         } else {
1046                                 // Note that if $domain is an empty string, getDomainID() might not match it
1047                                 $this->conns[$connInUseKey][$i][$conn->getDomainID()] = $conn;
1048                                 $this->connLogger->debug( __METHOD__ . ": opened new connection for $i/$domain" );
1049                         }
1050                 }
1051
1052                 if ( $conn instanceof IDatabase ) {
1053                         // Final sanity check to make sure the right domain is selected
1054                         if ( !$domainInstance->isCompatible( $conn->getDomainID() ) ) {
1055                                 throw new UnexpectedValueException(
1056                                         "Got connection to '{$conn->getDomainID()}', but expected '$domain'." );
1057                         }
1058                         // Increment reference count
1059                         $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
1060                         $conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
1061                 }
1062
1063                 return $conn;
1064         }
1065
1066         public function getServerAttributes( $i ) {
1067                 return Database::attributesFromType(
1068                         $this->getServerType( $i ),
1069                         $this->servers[$i]['driver'] ?? null
1070                 );
1071         }
1072
1073         /**
1074          * Test if the specified index represents an open connection
1075          *
1076          * @param int $index Server index
1077          * @access private
1078          * @return bool
1079          */
1080         private function isOpen( $index ) {
1081                 if ( !is_int( $index ) ) {
1082                         return false;
1083                 }
1084
1085                 return (bool)$this->getAnyOpenConnection( $index );
1086         }
1087
1088         /**
1089          * Open a new network connection to a server (uncached)
1090          *
1091          * Returns a Database object whether or not the connection was successful.
1092          *
1093          * @param array $server
1094          * @param DatabaseDomain $domain Domain the connection is for, possibly unspecified
1095          * @return Database
1096          * @throws DBAccessError
1097          * @throws InvalidArgumentException
1098          */
1099         protected function reallyOpenConnection( array $server, DatabaseDomain $domain ) {
1100                 if ( $this->disabled ) {
1101                         throw new DBAccessError();
1102                 }
1103
1104                 if ( $domain->getDatabase() === null ) {
1105                         // The database domain does not specify a DB name and some database systems require a
1106                         // valid DB specified on connection. The $server configuration array contains a default
1107                         // DB name to use for connections in such cases.
1108                         if ( $server['type'] === 'mysql' ) {
1109                                 // For MySQL, DATABASE and SCHEMA are synonyms, connections need not specify a DB,
1110                                 // and the DB name in $server might not exist due to legacy reasons (the default
1111                                 // domain used to ignore the local LB domain, even when mismatched).
1112                                 $server['dbname'] = null;
1113                         }
1114                 } else {
1115                         $server['dbname'] = $domain->getDatabase();
1116                 }
1117
1118                 if ( $domain->getSchema() !== null ) {
1119                         $server['schema'] = $domain->getSchema();
1120                 }
1121
1122                 // It is always possible to connect with any prefix, even the empty string
1123                 $server['tablePrefix'] = $domain->getTablePrefix();
1124
1125                 // Let the handle know what the cluster master is (e.g. "db1052")
1126                 $masterName = $this->getServerName( $this->getWriterIndex() );
1127                 $server['clusterMasterHost'] = $masterName;
1128
1129                 // Log when many connection are made on requests
1130                 if ( ++$this->connsOpened >= self::CONN_HELD_WARN_THRESHOLD ) {
1131                         $this->perfLogger->warning( __METHOD__ . ": " .
1132                                 "{$this->connsOpened}+ connections made (master=$masterName)" );
1133                 }
1134
1135                 $server['srvCache'] = $this->srvCache;
1136                 // Set loggers and profilers
1137                 $server['connLogger'] = $this->connLogger;
1138                 $server['queryLogger'] = $this->queryLogger;
1139                 $server['errorLogger'] = $this->errorLogger;
1140                 $server['deprecationLogger'] = $this->deprecationLogger;
1141                 $server['profiler'] = $this->profiler;
1142                 $server['trxProfiler'] = $this->trxProfiler;
1143                 // Use the same agent and PHP mode for all DB handles
1144                 $server['cliMode'] = $this->cliMode;
1145                 $server['agent'] = $this->agent;
1146                 // Use DBO_DEFAULT flags by default for LoadBalancer managed databases. Assume that the
1147                 // application calls LoadBalancer::commitMasterChanges() before the PHP script completes.
1148                 $server['flags'] = $server['flags'] ?? IDatabase::DBO_DEFAULT;
1149
1150                 // Create a live connection object
1151                 try {
1152                         $db = Database::factory( $server['type'], $server );
1153                 } catch ( DBConnectionError $e ) {
1154                         // FIXME: This is probably the ugliest thing I have ever done to
1155                         // PHP. I'm half-expecting it to segfault, just out of disgust. -- TS
1156                         $db = $e->db;
1157                 }
1158
1159                 $db->setLBInfo( $server );
1160                 $db->setLazyMasterHandle(
1161                         $this->getLazyConnectionRef( self::DB_MASTER, [], $db->getDomainID() )
1162                 );
1163                 $db->setTableAliases( $this->tableAliases );
1164                 $db->setIndexAliases( $this->indexAliases );
1165
1166                 if ( $server['serverIndex'] === $this->getWriterIndex() ) {
1167                         if ( $this->trxRoundId !== false ) {
1168                                 $this->applyTransactionRoundFlags( $db );
1169                         }
1170                         foreach ( $this->trxRecurringCallbacks as $name => $callback ) {
1171                                 $db->setTransactionListener( $name, $callback );
1172                         }
1173                 }
1174
1175                 return $db;
1176         }
1177
1178         /**
1179          * @throws DBConnectionError
1180          */
1181         private function reportConnectionError() {
1182                 $conn = $this->errorConnection; // the connection which caused the error
1183                 $context = [
1184                         'method' => __METHOD__,
1185                         'last_error' => $this->lastError,
1186                 ];
1187
1188                 if ( $conn instanceof IDatabase ) {
1189                         $context['db_server'] = $conn->getServer();
1190                         $this->connLogger->warning(
1191                                 __METHOD__ . ": connection error: {last_error} ({db_server})",
1192                                 $context
1193                         );
1194
1195                         throw new DBConnectionError( $conn, "{$this->lastError} ({$context['db_server']})" );
1196                 } else {
1197                         // No last connection, probably due to all servers being too busy
1198                         $this->connLogger->error(
1199                                 __METHOD__ .
1200                                 ": LB failure with no last connection. Connection error: {last_error}",
1201                                 $context
1202                         );
1203
1204                         // If all servers were busy, "lastError" will contain something sensible
1205                         throw new DBConnectionError( null, $this->lastError );
1206                 }
1207         }
1208
1209         public function getWriterIndex() {
1210                 return 0;
1211         }
1212
1213         public function haveIndex( $i ) {
1214                 return array_key_exists( $i, $this->servers );
1215         }
1216
1217         public function isNonZeroLoad( $i ) {
1218                 return array_key_exists( $i, $this->servers ) && $this->loads[$i] != 0;
1219         }
1220
1221         public function getServerCount() {
1222                 return count( $this->servers );
1223         }
1224
1225         public function getServerName( $i ) {
1226                 if ( isset( $this->servers[$i]['hostName'] ) ) {
1227                         $name = $this->servers[$i]['hostName'];
1228                 } elseif ( isset( $this->servers[$i]['host'] ) ) {
1229                         $name = $this->servers[$i]['host'];
1230                 } else {
1231                         $name = '';
1232                 }
1233
1234                 return ( $name != '' ) ? $name : 'localhost';
1235         }
1236
1237         public function getServerInfo( $i ) {
1238                 if ( isset( $this->servers[$i] ) ) {
1239                         return $this->servers[$i];
1240                 } else {
1241                         return false;
1242                 }
1243         }
1244
1245         public function getServerType( $i ) {
1246                 return $this->servers[$i]['type'] ?? 'unknown';
1247         }
1248
1249         public function getMasterPos() {
1250                 # If this entire request was served from a replica DB without opening a connection to the
1251                 # master (however unlikely that may be), then we can fetch the position from the replica DB.
1252                 $masterConn = $this->getAnyOpenConnection( $this->getWriterIndex() );
1253                 if ( !$masterConn ) {
1254                         $serverCount = count( $this->servers );
1255                         for ( $i = 1; $i < $serverCount; $i++ ) {
1256                                 $conn = $this->getAnyOpenConnection( $i );
1257                                 if ( $conn ) {
1258                                         return $conn->getReplicaPos();
1259                                 }
1260                         }
1261                 } else {
1262                         return $masterConn->getMasterPos();
1263                 }
1264
1265                 return false;
1266         }
1267
1268         public function disable() {
1269                 $this->closeAll();
1270                 $this->disabled = true;
1271         }
1272
1273         public function closeAll() {
1274                 $fname = __METHOD__;
1275                 $this->forEachOpenConnection( function ( IDatabase $conn ) use ( $fname ) {
1276                         $host = $conn->getServer();
1277                         $this->connLogger->debug(
1278                                 $fname . ": closing connection to database '$host'." );
1279                         $conn->close();
1280                 } );
1281
1282                 $this->conns = [
1283                         self::KEY_LOCAL => [],
1284                         self::KEY_FOREIGN_INUSE => [],
1285                         self::KEY_FOREIGN_FREE => [],
1286                         self::KEY_LOCAL_NOROUND => [],
1287                         self::KEY_FOREIGN_INUSE_NOROUND => [],
1288                         self::KEY_FOREIGN_FREE_NOROUND => []
1289                 ];
1290                 $this->connsOpened = 0;
1291         }
1292
1293         public function closeConnection( IDatabase $conn ) {
1294                 $serverIndex = $conn->getLBInfo( 'serverIndex' );
1295                 foreach ( $this->conns as $type => $connsByServer ) {
1296                         if ( !isset( $connsByServer[$serverIndex] ) ) {
1297                                 continue;
1298                         }
1299
1300                         foreach ( $connsByServer[$serverIndex] as $i => $trackedConn ) {
1301                                 if ( $conn === $trackedConn ) {
1302                                         $host = $this->getServerName( $i );
1303                                         $this->connLogger->debug(
1304                                                 __METHOD__ . ": closing connection to database $i at '$host'." );
1305                                         unset( $this->conns[$type][$serverIndex][$i] );
1306                                         --$this->connsOpened;
1307                                         break 2;
1308                                 }
1309                         }
1310                 }
1311
1312                 $conn->close();
1313         }
1314
1315         public function commitAll( $fname = __METHOD__ ) {
1316                 $this->commitMasterChanges( $fname );
1317                 $this->flushMasterSnapshots( $fname );
1318                 $this->flushReplicaSnapshots( $fname );
1319         }
1320
1321         public function finalizeMasterChanges() {
1322                 $this->assertTransactionRoundStage( [ self::ROUND_CURSORY, self::ROUND_FINALIZED ] );
1323
1324                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1325                 // Loop until callbacks stop adding callbacks on other connections
1326                 $total = 0;
1327                 do {
1328                         $count = 0; // callbacks execution attempts
1329                         $this->forEachOpenMasterConnection( function ( Database $conn ) use ( &$count ) {
1330                                 // Run any pre-commit callbacks while leaving the post-commit ones suppressed.
1331                                 // Any error should cause all (peer) transactions to be rolled back together.
1332                                 $count += $conn->runOnTransactionPreCommitCallbacks();
1333                         } );
1334                         $total += $count;
1335                 } while ( $count > 0 );
1336                 // Defer post-commit callbacks until after COMMIT/ROLLBACK happens on all handles
1337                 $this->forEachOpenMasterConnection( function ( Database $conn ) {
1338                         $conn->setTrxEndCallbackSuppression( true );
1339                 } );
1340                 $this->trxRoundStage = self::ROUND_FINALIZED;
1341
1342                 return $total;
1343         }
1344
1345         public function approveMasterChanges( array $options ) {
1346                 $this->assertTransactionRoundStage( self::ROUND_FINALIZED );
1347
1348                 $limit = $options['maxWriteDuration'] ?? 0;
1349
1350                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1351                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( $limit ) {
1352                         // If atomic sections or explicit transactions are still open, some caller must have
1353                         // caught an exception but failed to properly rollback any changes. Detect that and
1354                         // throw and error (causing rollback).
1355                         $conn->assertNoOpenTransactions();
1356                         // Assert that the time to replicate the transaction will be sane.
1357                         // If this fails, then all DB transactions will be rollback back together.
1358                         $time = $conn->pendingWriteQueryDuration( $conn::ESTIMATE_DB_APPLY );
1359                         if ( $limit > 0 && $time > $limit ) {
1360                                 throw new DBTransactionSizeError(
1361                                         $conn,
1362                                         "Transaction spent $time second(s) in writes, exceeding the limit of $limit.",
1363                                         [ $time, $limit ]
1364                                 );
1365                         }
1366                         // If a connection sits idle while slow queries execute on another, that connection
1367                         // may end up dropped before the commit round is reached. Ping servers to detect this.
1368                         if ( $conn->writesOrCallbacksPending() && !$conn->ping() ) {
1369                                 throw new DBTransactionError(
1370                                         $conn,
1371                                         "A connection to the {$conn->getDBname()} database was lost before commit."
1372                                 );
1373                         }
1374                 } );
1375                 $this->trxRoundStage = self::ROUND_APPROVED;
1376         }
1377
1378         public function beginMasterChanges( $fname = __METHOD__ ) {
1379                 if ( $this->trxRoundId !== false ) {
1380                         throw new DBTransactionError(
1381                                 null,
1382                                 "$fname: Transaction round '{$this->trxRoundId}' already started."
1383                         );
1384                 }
1385                 $this->assertTransactionRoundStage( self::ROUND_CURSORY );
1386
1387                 // Clear any empty transactions (no writes/callbacks) from the implicit round
1388                 $this->flushMasterSnapshots( $fname );
1389
1390                 $this->trxRoundId = $fname;
1391                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1392                 // Mark applicable handles as participating in this explicit transaction round.
1393                 // For each of these handles, any writes and callbacks will be tied to a single
1394                 // transaction. The (peer) handles will reject begin()/commit() calls unless they
1395                 // are part of an en masse commit or an en masse rollback.
1396                 $this->forEachOpenMasterConnection( function ( Database $conn ) {
1397                         $this->applyTransactionRoundFlags( $conn );
1398                 } );
1399                 $this->trxRoundStage = self::ROUND_CURSORY;
1400         }
1401
1402         public function commitMasterChanges( $fname = __METHOD__ ) {
1403                 $this->assertTransactionRoundStage( self::ROUND_APPROVED );
1404
1405                 $failures = [];
1406
1407                 /** @noinspection PhpUnusedLocalVariableInspection */
1408                 $scope = $this->getScopedPHPBehaviorForCommit(); // try to ignore client aborts
1409
1410                 $restore = ( $this->trxRoundId !== false );
1411                 $this->trxRoundId = false;
1412                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1413                 // Commit any writes and clear any snapshots as well (callbacks require AUTOCOMMIT).
1414                 // Note that callbacks should already be suppressed due to finalizeMasterChanges().
1415                 $this->forEachOpenMasterConnection(
1416                         function ( IDatabase $conn ) use ( $fname, &$failures ) {
1417                                 try {
1418                                         $conn->commit( $fname, $conn::FLUSHING_ALL_PEERS );
1419                                 } catch ( DBError $e ) {
1420                                         ( $this->errorLogger )( $e );
1421                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1422                                 }
1423                         }
1424                 );
1425                 if ( $failures ) {
1426                         throw new DBTransactionError(
1427                                 null,
1428                                 "$fname: Commit failed on server(s) " . implode( "\n", array_unique( $failures ) )
1429                         );
1430                 }
1431                 if ( $restore ) {
1432                         // Unmark handles as participating in this explicit transaction round
1433                         $this->forEachOpenMasterConnection( function ( Database $conn ) {
1434                                 $this->undoTransactionRoundFlags( $conn );
1435                         } );
1436                 }
1437                 $this->trxRoundStage = self::ROUND_COMMIT_CALLBACKS;
1438         }
1439
1440         public function runMasterTransactionIdleCallbacks() {
1441                 if ( $this->trxRoundStage === self::ROUND_COMMIT_CALLBACKS ) {
1442                         $type = IDatabase::TRIGGER_COMMIT;
1443                 } elseif ( $this->trxRoundStage === self::ROUND_ROLLBACK_CALLBACKS ) {
1444                         $type = IDatabase::TRIGGER_ROLLBACK;
1445                 } else {
1446                         throw new DBTransactionError(
1447                                 null,
1448                                 "Transaction should be in the callback stage (not '{$this->trxRoundStage}')"
1449                         );
1450                 }
1451
1452                 $oldStage = $this->trxRoundStage;
1453                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1454
1455                 // Now that the COMMIT/ROLLBACK step is over, enable post-commit callback runs
1456                 $this->forEachOpenMasterConnection( function ( Database $conn ) {
1457                         $conn->setTrxEndCallbackSuppression( false );
1458                 } );
1459
1460                 $e = null; // first exception
1461                 $fname = __METHOD__;
1462                 // Loop until callbacks stop adding callbacks on other connections
1463                 do {
1464                         // Run any pending callbacks for each connection...
1465                         $count = 0; // callback execution attempts
1466                         $this->forEachOpenMasterConnection(
1467                                 function ( Database $conn ) use ( $type, &$e, &$count ) {
1468                                         if ( $conn->trxLevel() ) {
1469                                                 return; // retry in the next iteration, after commit() is called
1470                                         }
1471                                         try {
1472                                                 $count += $conn->runOnTransactionIdleCallbacks( $type );
1473                                         } catch ( Exception $ex ) {
1474                                                 $e = $e ?: $ex;
1475                                         }
1476                                 }
1477                         );
1478                         // Clear out any active transactions left over from callbacks...
1479                         $this->forEachOpenMasterConnection( function ( Database $conn ) use ( &$e, $fname ) {
1480                                 if ( $conn->writesPending() ) {
1481                                         // A callback from another handle wrote to this one and DBO_TRX is set
1482                                         $this->queryLogger->warning( $fname . ": found writes pending." );
1483                                         $fnames = implode( ', ', $conn->pendingWriteAndCallbackCallers() );
1484                                         $this->queryLogger->warning(
1485                                                 $fname . ": found writes pending ($fnames).",
1486                                                 [
1487                                                         'db_server' => $conn->getServer(),
1488                                                         'db_name' => $conn->getDBname()
1489                                                 ]
1490                                         );
1491                                 } elseif ( $conn->trxLevel() ) {
1492                                         // A callback from another handle read from this one and DBO_TRX is set,
1493                                         // which can easily happen if there is only one DB (no replicas)
1494                                         $this->queryLogger->debug( $fname . ": found empty transaction." );
1495                                 }
1496                                 try {
1497                                         $conn->commit( $fname, $conn::FLUSHING_ALL_PEERS );
1498                                 } catch ( Exception $ex ) {
1499                                         $e = $e ?: $ex;
1500                                 }
1501                         } );
1502                 } while ( $count > 0 );
1503
1504                 $this->trxRoundStage = $oldStage;
1505
1506                 return $e;
1507         }
1508
1509         public function runMasterTransactionListenerCallbacks() {
1510                 if ( $this->trxRoundStage === self::ROUND_COMMIT_CALLBACKS ) {
1511                         $type = IDatabase::TRIGGER_COMMIT;
1512                 } elseif ( $this->trxRoundStage === self::ROUND_ROLLBACK_CALLBACKS ) {
1513                         $type = IDatabase::TRIGGER_ROLLBACK;
1514                 } else {
1515                         throw new DBTransactionError(
1516                                 null,
1517                                 "Transaction should be in the callback stage (not '{$this->trxRoundStage}')"
1518                         );
1519                 }
1520
1521                 $e = null;
1522
1523                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1524                 $this->forEachOpenMasterConnection( function ( Database $conn ) use ( $type, &$e ) {
1525                         try {
1526                                 $conn->runTransactionListenerCallbacks( $type );
1527                         } catch ( Exception $ex ) {
1528                                 $e = $e ?: $ex;
1529                         }
1530                 } );
1531                 $this->trxRoundStage = self::ROUND_CURSORY;
1532
1533                 return $e;
1534         }
1535
1536         public function rollbackMasterChanges( $fname = __METHOD__ ) {
1537                 $restore = ( $this->trxRoundId !== false );
1538                 $this->trxRoundId = false;
1539                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1540                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( $fname ) {
1541                         $conn->rollback( $fname, $conn::FLUSHING_ALL_PEERS );
1542                 } );
1543                 if ( $restore ) {
1544                         // Unmark handles as participating in this explicit transaction round
1545                         $this->forEachOpenMasterConnection( function ( Database $conn ) {
1546                                 $this->undoTransactionRoundFlags( $conn );
1547                         } );
1548                 }
1549                 $this->trxRoundStage = self::ROUND_ROLLBACK_CALLBACKS;
1550         }
1551
1552         /**
1553          * @param string|string[] $stage
1554          */
1555         private function assertTransactionRoundStage( $stage ) {
1556                 $stages = (array)$stage;
1557
1558                 if ( !in_array( $this->trxRoundStage, $stages, true ) ) {
1559                         $stageList = implode(
1560                                 '/',
1561                                 array_map( function ( $v ) {
1562                                         return "'$v'";
1563                                 }, $stages )
1564                         );
1565                         throw new DBTransactionError(
1566                                 null,
1567                                 "Transaction round stage must be $stageList (not '{$this->trxRoundStage}')"
1568                         );
1569                 }
1570         }
1571
1572         /**
1573          * Make all DB servers with DBO_DEFAULT/DBO_TRX set join the transaction round
1574          *
1575          * Some servers may have neither flag enabled, meaning that they opt out of such
1576          * transaction rounds and remain in auto-commit mode. Such behavior might be desired
1577          * when a DB server is used for something like simple key/value storage.
1578          *
1579          * @param Database $conn
1580          */
1581         private function applyTransactionRoundFlags( Database $conn ) {
1582                 if ( $conn->getLBInfo( 'autoCommitOnly' ) ) {
1583                         return; // transaction rounds do not apply to these connections
1584                 }
1585
1586                 if ( $conn->getFlag( $conn::DBO_DEFAULT ) ) {
1587                         // DBO_TRX is controlled entirely by CLI mode presence with DBO_DEFAULT.
1588                         // Force DBO_TRX even in CLI mode since a commit round is expected soon.
1589                         $conn->setFlag( $conn::DBO_TRX, $conn::REMEMBER_PRIOR );
1590                 }
1591
1592                 if ( $conn->getFlag( $conn::DBO_TRX ) ) {
1593                         $conn->setLBInfo( 'trxRoundId', $this->trxRoundId );
1594                 }
1595         }
1596
1597         /**
1598          * @param Database $conn
1599          */
1600         private function undoTransactionRoundFlags( Database $conn ) {
1601                 if ( $conn->getLBInfo( 'autoCommitOnly' ) ) {
1602                         return; // transaction rounds do not apply to these connections
1603                 }
1604
1605                 if ( $conn->getFlag( $conn::DBO_TRX ) ) {
1606                         $conn->setLBInfo( 'trxRoundId', false );
1607                 }
1608
1609                 if ( $conn->getFlag( $conn::DBO_DEFAULT ) ) {
1610                         $conn->restoreFlags( $conn::RESTORE_PRIOR );
1611                 }
1612         }
1613
1614         public function flushReplicaSnapshots( $fname = __METHOD__ ) {
1615                 $this->forEachOpenReplicaConnection( function ( IDatabase $conn ) use ( $fname ) {
1616                         $conn->flushSnapshot( $fname );
1617                 } );
1618         }
1619
1620         public function flushMasterSnapshots( $fname = __METHOD__ ) {
1621                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( $fname ) {
1622                         $conn->flushSnapshot( $fname );
1623                 } );
1624         }
1625
1626         /**
1627          * @return string
1628          * @since 1.32
1629          */
1630         public function getTransactionRoundStage() {
1631                 return $this->trxRoundStage;
1632         }
1633
1634         public function hasMasterConnection() {
1635                 return $this->isOpen( $this->getWriterIndex() );
1636         }
1637
1638         public function hasMasterChanges() {
1639                 $pending = 0;
1640                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$pending ) {
1641                         $pending |= $conn->writesOrCallbacksPending();
1642                 } );
1643
1644                 return (bool)$pending;
1645         }
1646
1647         public function lastMasterChangeTimestamp() {
1648                 $lastTime = false;
1649                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$lastTime ) {
1650                         $lastTime = max( $lastTime, $conn->lastDoneWrites() );
1651                 } );
1652
1653                 return $lastTime;
1654         }
1655
1656         public function hasOrMadeRecentMasterChanges( $age = null ) {
1657                 $age = ( $age === null ) ? $this->waitTimeout : $age;
1658
1659                 return ( $this->hasMasterChanges()
1660                         || $this->lastMasterChangeTimestamp() > microtime( true ) - $age );
1661         }
1662
1663         public function pendingMasterChangeCallers() {
1664                 $fnames = [];
1665                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$fnames ) {
1666                         $fnames = array_merge( $fnames, $conn->pendingWriteCallers() );
1667                 } );
1668
1669                 return $fnames;
1670         }
1671
1672         public function getLaggedReplicaMode( $domain = false ) {
1673                 // No-op if there is only one DB (also avoids recursion)
1674                 if ( !$this->laggedReplicaMode && $this->getServerCount() > 1 ) {
1675                         try {
1676                                 // See if laggedReplicaMode gets set
1677                                 $conn = $this->getConnection( self::DB_REPLICA, false, $domain );
1678                                 $this->reuseConnection( $conn );
1679                         } catch ( DBConnectionError $e ) {
1680                                 // Avoid expensive re-connect attempts and failures
1681                                 $this->allReplicasDownMode = true;
1682                                 $this->laggedReplicaMode = true;
1683                         }
1684                 }
1685
1686                 return $this->laggedReplicaMode;
1687         }
1688
1689         public function laggedReplicaUsed() {
1690                 return $this->laggedReplicaMode;
1691         }
1692
1693         /**
1694          * @return bool
1695          * @since 1.27
1696          * @deprecated Since 1.28; use laggedReplicaUsed()
1697          */
1698         public function laggedSlaveUsed() {
1699                 return $this->laggedReplicaUsed();
1700         }
1701
1702         public function getReadOnlyReason( $domain = false, IDatabase $conn = null ) {
1703                 if ( $this->readOnlyReason !== false ) {
1704                         return $this->readOnlyReason;
1705                 } elseif ( $this->getLaggedReplicaMode( $domain ) ) {
1706                         if ( $this->allReplicasDownMode ) {
1707                                 return 'The database has been automatically locked ' .
1708                                         'until the replica database servers become available';
1709                         } else {
1710                                 return 'The database has been automatically locked ' .
1711                                         'while the replica database servers catch up to the master.';
1712                         }
1713                 } elseif ( $this->masterRunningReadOnly( $domain, $conn ) ) {
1714                         return 'The database master is running in read-only mode.';
1715                 }
1716
1717                 return false;
1718         }
1719
1720         /**
1721          * @param string $domain Domain ID, or false for the current domain
1722          * @param IDatabase|null $conn DB master connectionl used to avoid loops [optional]
1723          * @return bool
1724          */
1725         private function masterRunningReadOnly( $domain, IDatabase $conn = null ) {
1726                 $cache = $this->wanCache;
1727                 $masterServer = $this->getServerName( $this->getWriterIndex() );
1728
1729                 return (bool)$cache->getWithSetCallback(
1730                         $cache->makeGlobalKey( __CLASS__, 'server-read-only', $masterServer ),
1731                         self::TTL_CACHE_READONLY,
1732                         function () use ( $domain, $conn ) {
1733                                 $old = $this->trxProfiler->setSilenced( true );
1734                                 try {
1735                                         $dbw = $conn ?: $this->getConnection( self::DB_MASTER, [], $domain );
1736                                         $readOnly = (int)$dbw->serverIsReadOnly();
1737                                         if ( !$conn ) {
1738                                                 $this->reuseConnection( $dbw );
1739                                         }
1740                                 } catch ( DBError $e ) {
1741                                         $readOnly = 0;
1742                                 }
1743                                 $this->trxProfiler->setSilenced( $old );
1744                                 return $readOnly;
1745                         },
1746                         [ 'pcTTL' => $cache::TTL_PROC_LONG, 'busyValue' => 0 ]
1747                 );
1748         }
1749
1750         public function allowLagged( $mode = null ) {
1751                 if ( $mode === null ) {
1752                         return $this->allowLagged;
1753                 }
1754                 $this->allowLagged = $mode;
1755
1756                 return $this->allowLagged;
1757         }
1758
1759         public function pingAll() {
1760                 $success = true;
1761                 $this->forEachOpenConnection( function ( IDatabase $conn ) use ( &$success ) {
1762                         if ( !$conn->ping() ) {
1763                                 $success = false;
1764                         }
1765                 } );
1766
1767                 return $success;
1768         }
1769
1770         public function forEachOpenConnection( $callback, array $params = [] ) {
1771                 foreach ( $this->conns as $connsByServer ) {
1772                         foreach ( $connsByServer as $serverConns ) {
1773                                 foreach ( $serverConns as $conn ) {
1774                                         $callback( $conn, ...$params );
1775                                 }
1776                         }
1777                 }
1778         }
1779
1780         public function forEachOpenMasterConnection( $callback, array $params = [] ) {
1781                 $masterIndex = $this->getWriterIndex();
1782                 foreach ( $this->conns as $connsByServer ) {
1783                         if ( isset( $connsByServer[$masterIndex] ) ) {
1784                                 /** @var IDatabase $conn */
1785                                 foreach ( $connsByServer[$masterIndex] as $conn ) {
1786                                         $callback( $conn, ...$params );
1787                                 }
1788                         }
1789                 }
1790         }
1791
1792         public function forEachOpenReplicaConnection( $callback, array $params = [] ) {
1793                 foreach ( $this->conns as $connsByServer ) {
1794                         foreach ( $connsByServer as $i => $serverConns ) {
1795                                 if ( $i === $this->getWriterIndex() ) {
1796                                         continue; // skip master
1797                                 }
1798                                 foreach ( $serverConns as $conn ) {
1799                                         $callback( $conn, ...$params );
1800                                 }
1801                         }
1802                 }
1803         }
1804
1805         public function getMaxLag( $domain = false ) {
1806                 $maxLag = -1;
1807                 $host = '';
1808                 $maxIndex = 0;
1809
1810                 if ( $this->getServerCount() <= 1 ) {
1811                         return [ $host, $maxLag, $maxIndex ]; // no replication = no lag
1812                 }
1813
1814                 $lagTimes = $this->getLagTimes( $domain );
1815                 foreach ( $lagTimes as $i => $lag ) {
1816                         if ( $this->loads[$i] > 0 && $lag > $maxLag ) {
1817                                 $maxLag = $lag;
1818                                 $host = $this->servers[$i]['host'];
1819                                 $maxIndex = $i;
1820                         }
1821                 }
1822
1823                 return [ $host, $maxLag, $maxIndex ];
1824         }
1825
1826         public function getLagTimes( $domain = false ) {
1827                 if ( $this->getServerCount() <= 1 ) {
1828                         return [ $this->getWriterIndex() => 0 ]; // no replication = no lag
1829                 }
1830
1831                 $knownLagTimes = []; // map of (server index => 0 seconds)
1832                 $indexesWithLag = [];
1833                 foreach ( $this->servers as $i => $server ) {
1834                         if ( empty( $server['is static'] ) ) {
1835                                 $indexesWithLag[] = $i; // DB server might have replication lag
1836                         } else {
1837                                 $knownLagTimes[$i] = 0; // DB server is a non-replicating and read-only archive
1838                         }
1839                 }
1840
1841                 return $this->getLoadMonitor()->getLagTimes( $indexesWithLag, $domain ) + $knownLagTimes;
1842         }
1843
1844         public function safeGetLag( IDatabase $conn ) {
1845                 if ( $this->getServerCount() <= 1 ) {
1846                         return 0;
1847                 } else {
1848                         return $conn->getLag();
1849                 }
1850         }
1851
1852         /**
1853          * @param IDatabase $conn
1854          * @param DBMasterPos|bool $pos
1855          * @param int|null $timeout
1856          * @return bool
1857          */
1858         public function safeWaitForMasterPos( IDatabase $conn, $pos = false, $timeout = null ) {
1859                 $timeout = max( 1, $timeout ?: $this->waitTimeout );
1860
1861                 if ( $this->getServerCount() <= 1 || !$conn->getLBInfo( 'replica' ) ) {
1862                         return true; // server is not a replica DB
1863                 }
1864
1865                 if ( !$pos ) {
1866                         // Get the current master position, opening a connection if needed
1867                         $masterConn = $this->getAnyOpenConnection( $this->getWriterIndex() );
1868                         if ( $masterConn ) {
1869                                 $pos = $masterConn->getMasterPos();
1870                         } else {
1871                                 $masterConn = $this->openConnection( $this->getWriterIndex(), self::DOMAIN_ANY );
1872                                 $pos = $masterConn->getMasterPos();
1873                                 $this->closeConnection( $masterConn );
1874                         }
1875                 }
1876
1877                 if ( $pos instanceof DBMasterPos ) {
1878                         $result = $conn->masterPosWait( $pos, $timeout );
1879                         if ( $result == -1 || is_null( $result ) ) {
1880                                 $msg = __METHOD__ . ': timed out waiting on {host} pos {pos}';
1881                                 $this->replLogger->warning( $msg, [
1882                                         'host' => $conn->getServer(),
1883                                         'pos' => $pos,
1884                                         'trace' => ( new RuntimeException() )->getTraceAsString()
1885                                 ] );
1886                                 $ok = false;
1887                         } else {
1888                                 $this->replLogger->debug( __METHOD__ . ': done waiting' );
1889                                 $ok = true;
1890                         }
1891                 } else {
1892                         $ok = false; // something is misconfigured
1893                         $this->replLogger->error(
1894                                 __METHOD__ . ': could not get master pos for {host}',
1895                                 [
1896                                         'host' => $conn->getServer(),
1897                                         'trace' => ( new RuntimeException() )->getTraceAsString()
1898                                 ]
1899                         );
1900                 }
1901
1902                 return $ok;
1903         }
1904
1905         public function setTransactionListener( $name, callable $callback = null ) {
1906                 if ( $callback ) {
1907                         $this->trxRecurringCallbacks[$name] = $callback;
1908                 } else {
1909                         unset( $this->trxRecurringCallbacks[$name] );
1910                 }
1911                 $this->forEachOpenMasterConnection(
1912                         function ( IDatabase $conn ) use ( $name, $callback ) {
1913                                 $conn->setTransactionListener( $name, $callback );
1914                         }
1915                 );
1916         }
1917
1918         public function setTableAliases( array $aliases ) {
1919                 $this->tableAliases = $aliases;
1920         }
1921
1922         public function setIndexAliases( array $aliases ) {
1923                 $this->indexAliases = $aliases;
1924         }
1925
1926         public function setDomainPrefix( $prefix ) {
1927                 // Find connections to explicit foreign domains still marked as in-use...
1928                 $domainsInUse = [];
1929                 $this->forEachOpenConnection( function ( IDatabase $conn ) use ( &$domainsInUse ) {
1930                         // Once reuseConnection() is called on a handle, its reference count goes from 1 to 0.
1931                         // Until then, it is still in use by the caller (explicitly or via DBConnRef scope).
1932                         if ( $conn->getLBInfo( 'foreignPoolRefCount' ) > 0 ) {
1933                                 $domainsInUse[] = $conn->getDomainID();
1934                         }
1935                 } );
1936
1937                 // Do not switch connections to explicit foreign domains unless marked as safe
1938                 if ( $domainsInUse ) {
1939                         $domains = implode( ', ', $domainsInUse );
1940                         throw new DBUnexpectedError( null,
1941                                 "Foreign domain connections are still in use ($domains)." );
1942                 }
1943
1944                 $this->setLocalDomain( new DatabaseDomain(
1945                         $this->localDomain->getDatabase(),
1946                         $this->localDomain->getSchema(),
1947                         $prefix
1948                 ) );
1949
1950                 // Update the prefix for all local connections...
1951                 $this->forEachOpenConnection( function ( IDatabase $db ) use ( $prefix ) {
1952                         if ( !$db->getLBInfo( 'foreign' ) ) {
1953                                 $db->tablePrefix( $prefix );
1954                         }
1955                 } );
1956         }
1957
1958         /**
1959          * @param DatabaseDomain $domain
1960          */
1961         private function setLocalDomain( DatabaseDomain $domain ) {
1962                 $this->localDomain = $domain;
1963                 // In case a caller assumes that the domain ID is simply <db>-<prefix>, which is almost
1964                 // always true, gracefully handle the case when they fail to account for escaping.
1965                 if ( $this->localDomain->getTablePrefix() != '' ) {
1966                         $this->localDomainIdAlias =
1967                                 $this->localDomain->getDatabase() . '-' . $this->localDomain->getTablePrefix();
1968                 } else {
1969                         $this->localDomainIdAlias = $this->localDomain->getDatabase();
1970                 }
1971         }
1972
1973         /**
1974          * Make PHP ignore user aborts/disconnects until the returned
1975          * value leaves scope. This returns null and does nothing in CLI mode.
1976          *
1977          * @return ScopedCallback|null
1978          */
1979         final protected function getScopedPHPBehaviorForCommit() {
1980                 if ( PHP_SAPI != 'cli' ) { // https://bugs.php.net/bug.php?id=47540
1981                         $old = ignore_user_abort( true ); // avoid half-finished operations
1982                         return new ScopedCallback( function () use ( $old ) {
1983                                 ignore_user_abort( $old );
1984                         } );
1985                 }
1986
1987                 return null;
1988         }
1989
1990         function __destruct() {
1991                 // Avoid connection leaks for sanity
1992                 $this->disable();
1993         }
1994 }
1995
1996 /**
1997  * @deprecated since 1.29
1998  */
1999 class_alias( LoadBalancer::class, 'LoadBalancer' );