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