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 array[] Map of (server index => server config array) */
  42         private $servers;
  43         /** @var Database[][][] Map of (connection category => server index => IDatabase[]) */
  44         private $conns;
  45         /** @var float[] Map of (server index => weight) */
  46         private $loads;
  47         /** @var array[] Map of (group => server index => weight) */
  48         private $groupLoads;
  49         /** @var bool Whether to disregard replica DB lag as a factor in replica DB selection */
  50         private $allowLagged;
  51         /** @var int Seconds to spend waiting on replica DB lag to resolve */
  52         private $waitTimeout;
  53         /** @var array The LoadMonitor configuration */
  54         private $loadMonitorConfig;
  55         /** @var array[] $aliases Map of (table => (dbname, schema, prefix) map) */
  56         private $tableAliases = [];
  57         /** @var string[] Map of (index alias => index) */
  58         private $indexAliases = [];
  59
  60         /** @var ILoadMonitor */
  61         private $loadMonitor;
  62         /** @var callable|null Callback to run before the first connection attempt */
  63         private $chronologyCallback;
  64         /** @var BagOStuff */
  65         private $srvCache;
  66         /** @var WANObjectCache */
  67         private $wanCache;
  68         /** @var object|string Class name or object With profileIn/profileOut methods */
  69         protected $profiler;
  70         /** @var TransactionProfiler */
  71         protected $trxProfiler;
  72         /** @var LoggerInterface */
  73         protected $replLogger;
  74         /** @var LoggerInterface */
  75         protected $connLogger;
  76         /** @var LoggerInterface */
  77         protected $queryLogger;
  78         /** @var LoggerInterface */
  79         protected $perfLogger;
  80
  81         /** @var Database DB connection object that caused a problem */
  82         private $errorConnection;
  83         /** @var int The generic (not query grouped) replica DB index (of $mServers) */
  84         private $readIndex;
  85         /** @var bool|DBMasterPos False if not set */
  86         private $waitForPos;
  87         /** @var bool Whether the generic reader fell back to a lagged replica DB */
  88         private $laggedReplicaMode = false;
  89         /** @var bool Whether the generic reader fell back to a lagged replica DB */
  90         private $allReplicasDownMode = false;
  91         /** @var string The last DB selection or connection error */
  92         private $lastError = 'Unknown error';
  93         /** @var string|bool Reason the LB is read-only or false if not */
  94         private $readOnlyReason = false;
  95         /** @var int Total connections opened */
  96         private $connsOpened = 0;
  97         /** @var string|bool String if a requested DBO_TRX transaction round is active */
  98         private $trxRoundId = false;
  99         /** @var array[] Map of (name => callable) */
 100         private $trxRecurringCallbacks = [];
 101         /** @var DatabaseDomain Local Domain ID and default for selectDB() calls */
 102         private $localDomain;
 103         /** @var string Alternate ID string for the domain instead of DatabaseDomain::getId() */
 104         private $localDomainIdAlias;
 105         /** @var string Current server name */
 106         private $host;
 107         /** @var bool Whether this PHP instance is for a CLI script */
 108         protected $cliMode;
 109         /** @var string Agent name for query profiling */
 110         protected $agent;
 111
 112         /** @var callable Exception logger */
 113         private $errorLogger;
 114         /** @var callable Deprecation logger */
 115         private $deprecationLogger;
 116
 117         /** @var bool */
 118         private $disabled = false;
 119         /** @var bool Whether any connection has been attempted yet */
 120         private $connectionAttempted = false;
 121         /** @var int */
 122         private $maxLag = self::MAX_LAG_DEFAULT;
 123
 124         /** @var int Warn when this many connection are held */
 125         const CONN_HELD_WARN_THRESHOLD = 10;
 126
 127         /** @var int Default 'maxLag' when unspecified */
 128         const MAX_LAG_DEFAULT = 10;
 129         /** @var int Default 'waitTimeout' when unspecified */
 130         const MAX_WAIT_DEFAULT = 10;
 131         /** @var int Seconds to cache master server read-only status */
 132         const TTL_CACHE_READONLY = 5;
 133
 134         const KEY_LOCAL = 'local';
 135         const KEY_FOREIGN_FREE = 'foreignFree';
 136         const KEY_FOREIGN_INUSE = 'foreignInUse';
 137
 138         const KEY_LOCAL_NOROUND = 'localAutoCommit';
 139         const KEY_FOREIGN_FREE_NOROUND = 'foreignFreeAutoCommit';
 140         const KEY_FOREIGN_INUSE_NOROUND = 'foreignInUseAutoCommit';
 141
 142         public function __construct( array $params ) {
 143                 if ( !isset( $params['servers'] ) ) {
 144                         throw new InvalidArgumentException( __CLASS__ . ': missing servers parameter' );
 145                 }
 146                 $this->servers = $params['servers'];
 147                 foreach ( $this->servers as $i => $server ) {
 148                         if ( $i == 0 ) {
 149                                 $this->servers[$i]['master'] = true;
 150                         } else {
 151                                 $this->servers[$i]['replica'] = true;
 152                         }
 153                 }
 154
 155                 $localDomain = isset( $params['localDomain'] )
 156                         ? DatabaseDomain::newFromId( $params['localDomain'] )
 157                         : DatabaseDomain::newUnspecified();
 158                 $this->setLocalDomain( $localDomain );
 159
 160                 $this->waitTimeout = isset( $params['waitTimeout'] )
 161                         ? $params['waitTimeout']
 162                         : self::MAX_WAIT_DEFAULT;
 163
 164                 $this->readIndex = -1;
 165                 $this->conns = [
 166                         // Connection were transaction rounds may be applied
 167                         self::KEY_LOCAL => [],
 168                         self::KEY_FOREIGN_INUSE => [],
 169                         self::KEY_FOREIGN_FREE => [],
 170                         // Auto-committing counterpart connections that ignore transaction rounds
 171                         self::KEY_LOCAL_NOROUND => [],
 172                         self::KEY_FOREIGN_INUSE_NOROUND => [],
 173                         self::KEY_FOREIGN_FREE_NOROUND => []
 174                 ];
 175                 $this->loads = [];
 176                 $this->waitForPos = false;
 177                 $this->allowLagged = false;
 178
 179                 if ( isset( $params['readOnlyReason'] ) && is_string( $params['readOnlyReason'] ) ) {
 180                         $this->readOnlyReason = $params['readOnlyReason'];
 181                 }
 182
 183                 if ( isset( $params['maxLag'] ) ) {
 184                         $this->maxLag = $params['maxLag'];
 185                 }
 186
 187                 if ( isset( $params['loadMonitor'] ) ) {
 188                         $this->loadMonitorConfig = $params['loadMonitor'];
 189                 } else {
 190                         $this->loadMonitorConfig = [ 'class' => 'LoadMonitorNull' ];
 191                 }
 192                 $this->loadMonitorConfig += [ 'lagWarnThreshold' => $this->maxLag ];
 193
 194                 foreach ( $params['servers'] as $i => $server ) {
 195                         $this->loads[$i] = $server['load'];
 196                         if ( isset( $server['groupLoads'] ) ) {
 197                                 foreach ( $server['groupLoads'] as $group => $ratio ) {
 198                                         if ( !isset( $this->groupLoads[$group] ) ) {
 199                                                 $this->groupLoads[$group] = [];
 200                                         }
 201                                         $this->groupLoads[$group][$i] = $ratio;
 202                                 }
 203                         }
 204                 }
 205
 206                 if ( isset( $params['srvCache'] ) ) {
 207                         $this->srvCache = $params['srvCache'];
 208                 } else {
 209                         $this->srvCache = new EmptyBagOStuff();
 210                 }
 211                 if ( isset( $params['wanCache'] ) ) {
 212                         $this->wanCache = $params['wanCache'];
 213                 } else {
 214                         $this->wanCache = WANObjectCache::newEmpty();
 215                 }
 216                 $this->profiler = isset( $params['profiler'] ) ? $params['profiler'] : null;
 217                 if ( isset( $params['trxProfiler'] ) ) {
 218                         $this->trxProfiler = $params['trxProfiler'];
 219                 } else {
 220                         $this->trxProfiler = new TransactionProfiler();
 221                 }
 222
 223                 $this->errorLogger = isset( $params['errorLogger'] )
 224                         ? $params['errorLogger']
 225                         : function ( Exception $e ) {
 226                                 trigger_error( get_class( $e ) . ': ' . $e->getMessage(), E_USER_WARNING );
 227                         };
 228                 $this->deprecationLogger = isset( $params['deprecationLogger'] )
 229                         ? $params['deprecationLogger']
 230                         : function ( $msg ) {
 231                                 trigger_error( $msg, E_USER_DEPRECATED );
 232                         };
 233
 234                 foreach ( [ 'replLogger', 'connLogger', 'queryLogger', 'perfLogger' ] as $key ) {
 235                         $this->$key = isset( $params[$key] ) ? $params[$key] : new NullLogger();
 236                 }
 237
 238                 $this->host = isset( $params['hostname'] )
 239                         ? $params['hostname']
 240                         : ( gethostname() ?: 'unknown' );
 241                 $this->cliMode = isset( $params['cliMode'] )
 242                         ? $params['cliMode']
 243                         : ( PHP_SAPI === 'cli' || PHP_SAPI === 'phpdbg' );
 244                 $this->agent = isset( $params['agent'] ) ? $params['agent'] : '';
 245
 246                 if ( isset( $params['chronologyCallback'] ) ) {
 247                         $this->chronologyCallback = $params['chronologyCallback'];
 248                 }
 249         }
 250
 251         /**
 252          * Get the local (and default) database domain ID of connection handles
 253          *
 254          * @see DatabaseDomain
 255          * @return string Database domain ID; this specifies DB name, schema, and table prefix
 256          * @since 1.31
 257          */
 258         public function getLocalDomainID() {
 259                 return $this->localDomain->getId();
 260         }
 261
 262         /**
 263          * Get a LoadMonitor instance
 264          *
 265          * @return ILoadMonitor
 266          */
 267         private function getLoadMonitor() {
 268                 if ( !isset( $this->loadMonitor ) ) {
 269                         $compat = [
 270                                 'LoadMonitor' => LoadMonitor::class,
 271                                 'LoadMonitorNull' => LoadMonitorNull::class,
 272                                 'LoadMonitorMySQL' => LoadMonitorMySQL::class,
 273                         ];
 274
 275                         $class = $this->loadMonitorConfig['class'];
 276                         if ( isset( $compat[$class] ) ) {
 277                                 $class = $compat[$class];
 278                         }
 279
 280                         $this->loadMonitor = new $class(
 281                                 $this, $this->srvCache, $this->wanCache, $this->loadMonitorConfig );
 282                         $this->loadMonitor->setLogger( $this->replLogger );
 283                 }
 284
 285                 return $this->loadMonitor;
 286         }
 287
 288         /**
 289          * @param array $loads
 290          * @param bool|string $domain Domain to get non-lagged for
 291          * @param int $maxLag Restrict the maximum allowed lag to this many seconds
 292          * @return bool|int|string
 293          */
 294         private function getRandomNonLagged( array $loads, $domain = false, $maxLag = INF ) {
 295                 $lags = $this->getLagTimes( $domain );
 296
 297                 # Unset excessively lagged servers
 298                 foreach ( $lags as $i => $lag ) {
 299                         if ( $i != 0 ) {
 300                                 # How much lag this server nominally is allowed to have
 301                                 $maxServerLag = isset( $this->servers[$i]['max lag'] )
 302                                         ? $this->servers[$i]['max lag']
 303                                         : $this->maxLag; // default
 304                                 # Constrain that futher by $maxLag argument
 305                                 $maxServerLag = min( $maxServerLag, $maxLag );
 306
 307                                 $host = $this->getServerName( $i );
 308                                 if ( $lag === false && !is_infinite( $maxServerLag ) ) {
 309                                         $this->replLogger->error(
 310                                                 __METHOD__ .
 311                                                 ": server {host} is not replicating?", [ 'host' => $host ] );
 312                                         unset( $loads[$i] );
 313                                 } elseif ( $lag > $maxServerLag ) {
 314                                         $this->replLogger->info(
 315                                                 __METHOD__ .
 316                                                 ": server {host} has {lag} seconds of lag (>= {maxlag})",
 317                                                 [ 'host' => $host, 'lag' => $lag, 'maxlag' => $maxServerLag ]
 318                                         );
 319                                         unset( $loads[$i] );
 320                                 }
 321                         }
 322                 }
 323
 324                 # Find out if all the replica DBs with non-zero load are lagged
 325                 $sum = 0;
 326                 foreach ( $loads as $load ) {
 327                         $sum += $load;
 328                 }
 329                 if ( $sum == 0 ) {
 330                         # No appropriate DB servers except maybe the master and some replica DBs with zero load
 331                         # Do NOT use the master
 332                         # Instead, this function will return false, triggering read-only mode,
 333                         # and a lagged replica DB will be used instead.
 334                         return false;
 335                 }
 336
 337                 if ( count( $loads ) == 0 ) {
 338                         return false;
 339                 }
 340
 341                 # Return a random representative of the remainder
 342                 return ArrayUtils::pickRandom( $loads );
 343         }
 344
 345         public function getReaderIndex( $group = false, $domain = false ) {
 346                 if ( count( $this->servers ) == 1 ) {
 347                         // Skip the load balancing if there's only one server
 348                         return $this->getWriterIndex();
 349                 } elseif ( $group === false && $this->readIndex >= 0 ) {
 350                         // Shortcut if the generic reader index was already cached
 351                         return $this->readIndex;
 352                 }
 353
 354                 if ( $group !== false ) {
 355                         // Use the server weight array for this load group
 356                         if ( isset( $this->groupLoads[$group] ) ) {
 357                                 $loads = $this->groupLoads[$group];
 358                         } else {
 359                                 // No loads for this group, return false and the caller can use some other group
 360                                 $this->connLogger->info( __METHOD__ . ": no loads for group $group" );
 361
 362                                 return false;
 363                         }
 364                 } else {
 365                         // Use the generic load group
 366                         $loads = $this->loads;
 367                 }
 368
 369                 // Scale the configured load ratios according to each server's load and state
 370                 $this->getLoadMonitor()->scaleLoads( $loads, $domain );
 371
 372                 // Pick a server to use, accounting for weights, load, lag, and "waitForPos"
 373                 list( $i, $laggedReplicaMode ) = $this->pickReaderIndex( $loads, $domain );
 374                 if ( $i === false ) {
 375                         // Replica DB connection unsuccessful
 376                         return false;
 377                 }
 378
 379                 if ( $this->waitForPos && $i != $this->getWriterIndex() ) {
 380                         // Before any data queries are run, wait for the server to catch up to the
 381                         // specified position. This is used to improve session consistency. Note that
 382                         // when LoadBalancer::waitFor() sets "waitForPos", the waiting triggers here,
 383                         // so update laggedReplicaMode as needed for consistency.
 384                         if ( !$this->doWait( $i ) ) {
 385                                 $laggedReplicaMode = true;
 386                         }
 387                 }
 388
 389                 if ( $this->readIndex <= 0 && $this->loads[$i] > 0 && $group === false ) {
 390                         // Cache the generic reader index for future ungrouped DB_REPLICA handles
 391                         $this->readIndex = $i;
 392                         // Record if the generic reader index is in "lagged replica DB" mode
 393                         if ( $laggedReplicaMode ) {
 394                                 $this->laggedReplicaMode = true;
 395                         }
 396                 }
 397
 398                 $serverName = $this->getServerName( $i );
 399                 $this->connLogger->debug( __METHOD__ . ": using server $serverName for group '$group'" );
 400
 401                 return $i;
 402         }
 403
 404         /**
 405          * @param array $loads List of server weights
 406          * @param string|bool $domain
 407          * @return array (reader index, lagged replica mode) or false on failure
 408          */
 409         private function pickReaderIndex( array $loads, $domain = false ) {
 410                 if ( !count( $loads ) ) {
 411                         throw new InvalidArgumentException( "Empty server array given to LoadBalancer" );
 412                 }
 413
 414                 /** @var int|bool $i Index of selected server */
 415                 $i = false;
 416                 /** @var bool $laggedReplicaMode Whether server is considered lagged */
 417                 $laggedReplicaMode = false;
 418
 419                 // Quickly look through the available servers for a server that meets criteria...
 420                 $currentLoads = $loads;
 421                 while ( count( $currentLoads ) ) {
 422                         if ( $this->allowLagged || $laggedReplicaMode ) {
 423                                 $i = ArrayUtils::pickRandom( $currentLoads );
 424                         } else {
 425                                 $i = false;
 426                                 if ( $this->waitForPos && $this->waitForPos->asOfTime() ) {
 427                                         // "chronologyCallback" sets "waitForPos" for session consistency.
 428                                         // This triggers doWait() after connect, so it's especially good to
 429                                         // avoid lagged servers so as to avoid excessive delay in that method.
 430                                         $ago = microtime( true ) - $this->waitForPos->asOfTime();
 431                                         // Aim for <= 1 second of waiting (being too picky can backfire)
 432                                         $i = $this->getRandomNonLagged( $currentLoads, $domain, $ago + 1 );
 433                                 }
 434                                 if ( $i === false ) {
 435                                         // Any server with less lag than it's 'max lag' param is preferable
 436                                         $i = $this->getRandomNonLagged( $currentLoads, $domain );
 437                                 }
 438                                 if ( $i === false && count( $currentLoads ) != 0 ) {
 439                                         // All replica DBs lagged. Switch to read-only mode
 440                                         $this->replLogger->error(
 441                                                 __METHOD__ . ": all replica DBs lagged. Switch to read-only mode" );
 442                                         $i = ArrayUtils::pickRandom( $currentLoads );
 443                                         $laggedReplicaMode = true;
 444                                 }
 445                         }
 446
 447                         if ( $i === false ) {
 448                                 // pickRandom() returned false.
 449                                 // This is permanent and means the configuration or the load monitor
 450                                 // wants us to return false.
 451                                 $this->connLogger->debug( __METHOD__ . ": pickRandom() returned false" );
 452
 453                                 return [ false, false ];
 454                         }
 455
 456                         $serverName = $this->getServerName( $i );
 457                         $this->connLogger->debug( __METHOD__ . ": Using reader #$i: $serverName..." );
 458
 459                         $conn = $this->openConnection( $i, $domain );
 460                         if ( !$conn ) {
 461                                 $this->connLogger->warning( __METHOD__ . ": Failed connecting to $i/$domain" );
 462                                 unset( $currentLoads[$i] ); // avoid this server next iteration
 463                                 $i = false;
 464                                 continue;
 465                         }
 466
 467                         // Decrement reference counter, we are finished with this connection.
 468                         // It will be incremented for the caller later.
 469                         if ( $domain !== false ) {
 470                                 $this->reuseConnection( $conn );
 471                         }
 472
 473                         // Return this server
 474                         break;
 475                 }
 476
 477                 // If all servers were down, quit now
 478                 if ( !count( $currentLoads ) ) {
 479                         $this->connLogger->error( __METHOD__ . ": all servers down" );
 480                 }
 481
 482                 return [ $i, $laggedReplicaMode ];
 483         }
 484
 485         public function waitFor( $pos ) {
 486                 $oldPos = $this->waitForPos;
 487                 try {
 488                         $this->waitForPos = $pos;
 489                         // If a generic reader connection was already established, then wait now
 490                         $i = $this->readIndex;
 491                         if ( $i > 0 ) {
 492                                 if ( !$this->doWait( $i ) ) {
 493                                         $this->laggedReplicaMode = true;
 494                                 }
 495                         }
 496                 } finally {
 497                         // Restore the older position if it was higher since this is used for lag-protection
 498                         $this->setWaitForPositionIfHigher( $oldPos );
 499                 }
 500         }
 501
 502         public function waitForOne( $pos, $timeout = null ) {
 503                 $oldPos = $this->waitForPos;
 504                 try {
 505                         $this->waitForPos = $pos;
 506
 507                         $i = $this->readIndex;
 508                         if ( $i <= 0 ) {
 509                                 // Pick a generic replica DB if there isn't one yet
 510                                 $readLoads = $this->loads;
 511                                 unset( $readLoads[$this->getWriterIndex()] ); // replica DBs only
 512                                 $readLoads = array_filter( $readLoads ); // with non-zero load
 513                                 $i = ArrayUtils::pickRandom( $readLoads );
 514                         }
 515
 516                         if ( $i > 0 ) {
 517                                 $ok = $this->doWait( $i, true, $timeout );
 518                         } else {
 519                                 $ok = true; // no applicable loads
 520                         }
 521                 } finally {
 522                         # Restore the old position, as this is not used for lag-protection but for throttling
 523                         $this->waitForPos = $oldPos;
 524                 }
 525
 526                 return $ok;
 527         }
 528
 529         public function waitForAll( $pos, $timeout = null ) {
 530                 $timeout = $timeout ?: $this->waitTimeout;
 531
 532                 $oldPos = $this->waitForPos;
 533                 try {
 534                         $this->waitForPos = $pos;
 535                         $serverCount = count( $this->servers );
 536
 537                         $ok = true;
 538                         for ( $i = 1; $i < $serverCount; $i++ ) {
 539                                 if ( $this->loads[$i] > 0 ) {
 540                                         $start = microtime( true );
 541                                         $ok = $this->doWait( $i, true, $timeout ) && $ok;
 542                                         $timeout -= intval( microtime( true ) - $start );
 543                                         if ( $timeout <= 0 ) {
 544                                                 break; // timeout reached
 545                                         }
 546                                 }
 547                         }
 548                 } finally {
 549                         # Restore the old position, as this is not used for lag-protection but for throttling
 550                         $this->waitForPos = $oldPos;
 551                 }
 552
 553                 return $ok;
 554         }
 555
 556         /**
 557          * @param DBMasterPos|bool $pos
 558          */
 559         private function setWaitForPositionIfHigher( $pos ) {
 560                 if ( !$pos ) {
 561                         return;
 562                 }
 563
 564                 if ( !$this->waitForPos || $pos->hasReached( $this->waitForPos ) ) {
 565                         $this->waitForPos = $pos;
 566                 }
 567         }
 568
 569         public function getAnyOpenConnection( $i, $flags = 0 ) {
 570                 $autocommit = ( ( $flags & self::CONN_TRX_AUTOCOMMIT ) == self::CONN_TRX_AUTOCOMMIT );
 571                 foreach ( $this->conns as $connsByServer ) {
 572                         if ( !isset( $connsByServer[$i] ) ) {
 573                                 continue;
 574                         }
 575
 576                         foreach ( $connsByServer[$i] as $conn ) {
 577                                 if ( !$autocommit || $conn->getLBInfo( 'autoCommitOnly' ) ) {
 578                                         return $conn;
 579                                 }
 580                         }
 581                 }
 582
 583                 return false;
 584         }
 585
 586         /**
 587          * Wait for a given replica DB to catch up to the master pos stored in $this
 588          * @param int $index Server index
 589          * @param bool $open Check the server even if a new connection has to be made
 590          * @param int $timeout Max seconds to wait; default is "waitTimeout" given to __construct()
 591          * @return bool
 592          */
 593         protected function doWait( $index, $open = false, $timeout = null ) {
 594                 $timeout = max( 1, intval( $timeout ?: $this->waitTimeout ) );
 595
 596                 // Check if we already know that the DB has reached this point
 597                 $server = $this->getServerName( $index );
 598                 $key = $this->srvCache->makeGlobalKey( __CLASS__, 'last-known-pos', $server, 'v1' );
 599                 /** @var DBMasterPos $knownReachedPos */
 600                 $knownReachedPos = $this->srvCache->get( $key );
 601                 if (
 602                         $knownReachedPos instanceof DBMasterPos &&
 603                         $knownReachedPos->hasReached( $this->waitForPos )
 604                 ) {
 605                         $this->replLogger->debug(
 606                                 __METHOD__ .
 607                                 ': replica DB {dbserver} known to be caught up (pos >= $knownReachedPos).',
 608                                 [ 'dbserver' => $server ]
 609                         );
 610                         return true;
 611                 }
 612
 613                 // Find a connection to wait on, creating one if needed and allowed
 614                 $close = false; // close the connection afterwards
 615                 $conn = $this->getAnyOpenConnection( $index );
 616                 if ( !$conn ) {
 617                         if ( !$open ) {
 618                                 $this->replLogger->debug(
 619                                         __METHOD__ . ': no connection open for {dbserver}',
 620                                         [ 'dbserver' => $server ]
 621                                 );
 622
 623                                 return false;
 624                         } else {
 625                                 $conn = $this->openConnection( $index, self::DOMAIN_ANY );
 626                                 if ( !$conn ) {
 627                                         $this->replLogger->warning(
 628                                                 __METHOD__ . ': failed to connect to {dbserver}',
 629                                                 [ 'dbserver' => $server ]
 630                                         );
 631
 632                                         return false;
 633                                 }
 634                                 // Avoid connection spam in waitForAll() when connections
 635                                 // are made just for the sake of doing this lag check.
 636                                 $close = true;
 637                         }
 638                 }
 639
 640                 $this->replLogger->info(
 641                         __METHOD__ .
 642                         ': waiting for replica DB {dbserver} to catch up...',
 643                         [ 'dbserver' => $server ]
 644                 );
 645
 646                 $result = $conn->masterPosWait( $this->waitForPos, $timeout );
 647
 648                 if ( $result === null ) {
 649                         $this->replLogger->warning(
 650                                 __METHOD__ . ': Errored out waiting on {host} pos {pos}',
 651                                 [
 652                                         'host' => $server,
 653                                         'pos' => $this->waitForPos,
 654                                         'trace' => ( new RuntimeException() )->getTraceAsString()
 655                                 ]
 656                         );
 657                         $ok = false;
 658                 } elseif ( $result == -1 ) {
 659                         $this->replLogger->warning(
 660                                 __METHOD__ . ': Timed out waiting on {host} pos {pos}',
 661                                 [
 662                                         'host' => $server,
 663                                         'pos' => $this->waitForPos,
 664                                         'trace' => ( new RuntimeException() )->getTraceAsString()
 665                                 ]
 666                         );
 667                         $ok = false;
 668                 } else {
 669                         $this->replLogger->debug( __METHOD__ . ": done waiting" );
 670                         $ok = true;
 671                         // Remember that the DB reached this point
 672                         $this->srvCache->set( $key, $this->waitForPos, BagOStuff::TTL_DAY );
 673                 }
 674
 675                 if ( $close ) {
 676                         $this->closeConnection( $conn );
 677                 }
 678
 679                 return $ok;
 680         }
 681
 682         public function getConnection( $i, $groups = [], $domain = false, $flags = 0 ) {
 683                 if ( $i === null || $i === false ) {
 684                         throw new InvalidArgumentException( 'Attempt to call ' . __METHOD__ .
 685                                 ' with invalid server index' );
 686                 }
 687
 688                 if ( $this->localDomain->equals( $domain ) || $domain === $this->localDomainIdAlias ) {
 689                         $domain = false; // local connection requested
 690                 }
 691
 692                 if ( ( $flags & self::CONN_TRX_AUTOCOMMIT ) === self::CONN_TRX_AUTOCOMMIT ) {
 693                         // Assuming all servers are of the same type (or similar), which is overwhelmingly
 694                         // the case, use the master server information to get the attributes. The information
 695                         // for $i cannot be used since it might be DB_REPLICA, which might require connection
 696                         // attempts in order to be resolved into a real server index.
 697                         $attributes = $this->getServerAttributes( $this->getWriterIndex() );
 698                         if ( $attributes[Database::ATTR_DB_LEVEL_LOCKING] ) {
 699                                 // Callers sometimes want to (a) escape REPEATABLE-READ stateness without locking
 700                                 // rows (e.g. FOR UPDATE) or (b) make small commits during a larger transactions
 701                                 // to reduce lock contention. None of these apply for sqlite and using separate
 702                                 // connections just causes self-deadlocks.
 703                                 $flags &= ~self::CONN_TRX_AUTOCOMMIT;
 704                                 $this->connLogger->info( __METHOD__ .
 705                                         ': ignoring CONN_TRX_AUTOCOMMIT to avoid deadlocks.' );
 706                         }
 707                 }
 708
 709                 $groups = ( $groups === false || $groups === [] )
 710                         ? [ false ] // check one "group": the generic pool
 711                         : (array)$groups;
 712
 713                 $masterOnly = ( $i == self::DB_MASTER || $i == $this->getWriterIndex() );
 714                 $oldConnsOpened = $this->connsOpened; // connections open now
 715
 716                 if ( $i == self::DB_MASTER ) {
 717                         $i = $this->getWriterIndex();
 718                 } elseif ( $i == self::DB_REPLICA ) {
 719                         # Try to find an available server in any the query groups (in order)
 720                         foreach ( $groups as $group ) {
 721                                 $groupIndex = $this->getReaderIndex( $group, $domain );
 722                                 if ( $groupIndex !== false ) {
 723                                         $i = $groupIndex;
 724                                         break;
 725                                 }
 726                         }
 727                 }
 728
 729                 # Operation-based index
 730                 if ( $i == self::DB_REPLICA ) {
 731                         $this->lastError = 'Unknown error'; // reset error string
 732                         # Try the general server pool if $groups are unavailable.
 733                         $i = ( $groups === [ false ] )
 734                                 ? false // don't bother with this if that is what was tried above
 735                                 : $this->getReaderIndex( false, $domain );
 736                         # Couldn't find a working server in getReaderIndex()?
 737                         if ( $i === false ) {
 738                                 $this->lastError = 'No working replica DB server: ' . $this->lastError;
 739                                 // Throw an exception
 740                                 $this->reportConnectionError();
 741                                 return null; // not reached
 742                         }
 743                 }
 744
 745                 # Now we have an explicit index into the servers array
 746                 $conn = $this->openConnection( $i, $domain, $flags );
 747                 if ( !$conn ) {
 748                         // Throw an exception
 749                         $this->reportConnectionError();
 750                         return null; // not reached
 751                 }
 752
 753                 # Profile any new connections that happen
 754                 if ( $this->connsOpened > $oldConnsOpened ) {
 755                         $host = $conn->getServer();
 756                         $dbname = $conn->getDBname();
 757                         $this->trxProfiler->recordConnection( $host, $dbname, $masterOnly );
 758                 }
 759
 760                 if ( $masterOnly ) {
 761                         # Make master-requested DB handles inherit any read-only mode setting
 762                         $conn->setLBInfo( 'readOnlyReason', $this->getReadOnlyReason( $domain, $conn ) );
 763                 }
 764
 765                 return $conn;
 766         }
 767
 768         public function reuseConnection( IDatabase $conn ) {
 769                 $serverIndex = $conn->getLBInfo( 'serverIndex' );
 770                 $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 771                 if ( $serverIndex === null || $refCount === null ) {
 772                         /**
 773                          * This can happen in code like:
 774                          *   foreach ( $dbs as $db ) {
 775                          *     $conn = $lb->getConnection( $lb::DB_REPLICA, [], $db );
 776                          *     ...
 777                          *     $lb->reuseConnection( $conn );
 778                          *   }
 779                          * When a connection to the local DB is opened in this way, reuseConnection()
 780                          * should be ignored
 781                          */
 782                         return;
 783                 } elseif ( $conn instanceof DBConnRef ) {
 784                         // DBConnRef already handles calling reuseConnection() and only passes the live
 785                         // Database instance to this method. Any caller passing in a DBConnRef is broken.
 786                         $this->connLogger->error(
 787                                 __METHOD__ . ": got DBConnRef instance.\n" .
 788                                 ( new RuntimeException() )->getTraceAsString() );
 789
 790                         return;
 791                 }
 792
 793                 if ( $this->disabled ) {
 794                         return; // DBConnRef handle probably survived longer than the LoadBalancer
 795                 }
 796
 797                 if ( $conn->getLBInfo( 'autoCommitOnly' ) ) {
 798                         $connFreeKey = self::KEY_FOREIGN_FREE_NOROUND;
 799                         $connInUseKey = self::KEY_FOREIGN_INUSE_NOROUND;
 800                 } else {
 801                         $connFreeKey = self::KEY_FOREIGN_FREE;
 802                         $connInUseKey = self::KEY_FOREIGN_INUSE;
 803                 }
 804
 805                 $domain = $conn->getDomainID();
 806                 if ( !isset( $this->conns[$connInUseKey][$serverIndex][$domain] ) ) {
 807                         throw new InvalidArgumentException( __METHOD__ .
 808                                 ": connection $serverIndex/$domain not found; it may have already been freed." );
 809                 } elseif ( $this->conns[$connInUseKey][$serverIndex][$domain] !== $conn ) {
 810                         throw new InvalidArgumentException( __METHOD__ .
 811                                 ": connection $serverIndex/$domain mismatched; it may have already been freed." );
 812                 }
 813
 814                 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
 815                 if ( $refCount <= 0 ) {
 816                         $this->conns[$connFreeKey][$serverIndex][$domain] = $conn;
 817                         unset( $this->conns[$connInUseKey][$serverIndex][$domain] );
 818                         if ( !$this->conns[$connInUseKey][$serverIndex] ) {
 819                                 unset( $this->conns[$connInUseKey][$serverIndex] ); // clean up
 820                         }
 821                         $this->connLogger->debug( __METHOD__ . ": freed connection $serverIndex/$domain" );
 822                 } else {
 823                         $this->connLogger->debug( __METHOD__ .
 824                                 ": reference count for $serverIndex/$domain reduced to $refCount" );
 825                 }
 826         }
 827
 828         public function getConnectionRef( $db, $groups = [], $domain = false, $flags = 0 ) {
 829                 $domain = ( $domain !== false ) ? $domain : $this->localDomain;
 830
 831                 return new DBConnRef( $this, $this->getConnection( $db, $groups, $domain, $flags ) );
 832         }
 833
 834         public function getLazyConnectionRef( $db, $groups = [], $domain = false, $flags = 0 ) {
 835                 $domain = ( $domain !== false ) ? $domain : $this->localDomain;
 836
 837                 return new DBConnRef( $this, [ $db, $groups, $domain, $flags ] );
 838         }
 839
 840         public function getMaintenanceConnectionRef( $db, $groups = [], $domain = false, $flags = 0 ) {
 841                 $domain = ( $domain !== false ) ? $domain : $this->localDomain;
 842
 843                 return new MaintainableDBConnRef(
 844                         $this, $this->getConnection( $db, $groups, $domain, $flags ) );
 845         }
 846
 847         public function openConnection( $i, $domain = false, $flags = 0 ) {
 848                 if ( $this->localDomain->equals( $domain ) || $domain === $this->localDomainIdAlias ) {
 849                         $domain = false; // local connection requested
 850                 }
 851
 852                 if ( !$this->connectionAttempted && $this->chronologyCallback ) {
 853                         $this->connLogger->debug( __METHOD__ . ': calling initLB() before first connection.' );
 854                         // Load any "waitFor" positions before connecting so that doWait() is triggered
 855                         $this->connectionAttempted = true;
 856                         call_user_func( $this->chronologyCallback, $this );
 857                 }
 858
 859                 // Check if an auto-commit connection is being requested. If so, it will not reuse the
 860                 // main set of DB connections but rather its own pool since:
 861                 // a) those are usually set to implicitly use transaction rounds via DBO_TRX
 862                 // b) those must support the use of explicit transaction rounds via beginMasterChanges()
 863                 $autoCommit = ( ( $flags & self::CONN_TRX_AUTOCOMMIT ) == self::CONN_TRX_AUTOCOMMIT );
 864
 865                 if ( $domain !== false ) {
 866                         // Connection is to a foreign domain
 867                         $conn = $this->openForeignConnection( $i, $domain, $flags );
 868                 } else {
 869                         // Connection is to the local domain
 870                         $connKey = $autoCommit ? self::KEY_LOCAL_NOROUND : self::KEY_LOCAL;
 871                         if ( isset( $this->conns[$connKey][$i][0] ) ) {
 872                                 $conn = $this->conns[$connKey][$i][0];
 873                         } else {
 874                                 if ( !isset( $this->servers[$i] ) || !is_array( $this->servers[$i] ) ) {
 875                                         throw new InvalidArgumentException( "No server with index '$i'." );
 876                                 }
 877                                 // Open a new connection
 878                                 $server = $this->servers[$i];
 879                                 $server['serverIndex'] = $i;
 880                                 $server['autoCommitOnly'] = $autoCommit;
 881                                 if ( $this->localDomain->getDatabase() !== null ) {
 882                                         // Use the local domain table prefix if the local domain is specified
 883                                         $server['tablePrefix'] = $this->localDomain->getTablePrefix();
 884                                 }
 885                                 $conn = $this->reallyOpenConnection( $server, $this->localDomain );
 886                                 $host = $this->getServerName( $i );
 887                                 if ( $conn->isOpen() ) {
 888                                         $this->connLogger->debug(
 889                                                 __METHOD__ . ": connected to database $i at '$host'." );
 890                                         $this->conns[$connKey][$i][0] = $conn;
 891                                 } else {
 892                                         $this->connLogger->warning(
 893                                                 __METHOD__ . ": failed to connect to database $i at '$host'." );
 894                                         $this->errorConnection = $conn;
 895                                         $conn = false;
 896                                 }
 897                         }
 898                 }
 899
 900                 if ( $conn instanceof IDatabase && !$conn->isOpen() ) {
 901                         // Connection was made but later unrecoverably lost for some reason.
 902                         // Do not return a handle that will just throw exceptions on use,
 903                         // but let the calling code (e.g. getReaderIndex) try another server.
 904                         // See DatabaseMyslBase::ping() for how this can happen.
 905                         $this->errorConnection = $conn;
 906                         $conn = false;
 907                 }
 908
 909                 if ( $autoCommit && $conn instanceof IDatabase ) {
 910                         $conn->clearFlag( $conn::DBO_TRX ); // auto-commit mode
 911                 }
 912
 913                 return $conn;
 914         }
 915
 916         /**
 917          * Open a connection to a foreign DB, or return one if it is already open.
 918          *
 919          * Increments a reference count on the returned connection which locks the
 920          * connection to the requested domain. This reference count can be
 921          * decremented by calling reuseConnection().
 922          *
 923          * If a connection is open to the appropriate server already, but with the wrong
 924          * database, it will be switched to the right database and returned, as long as
 925          * it has been freed first with reuseConnection().
 926          *
 927          * On error, returns false, and the connection which caused the
 928          * error will be available via $this->errorConnection.
 929          *
 930          * @note If disable() was called on this LoadBalancer, this method will throw a DBAccessError.
 931          *
 932          * @param int $i Server index
 933          * @param string $domain Domain ID to open
 934          * @param int $flags Class CONN_* constant bitfield
 935          * @return Database
 936          */
 937         private function openForeignConnection( $i, $domain, $flags = 0 ) {
 938                 $domainInstance = DatabaseDomain::newFromId( $domain );
 939                 $dbName = $domainInstance->getDatabase();
 940                 $prefix = $domainInstance->getTablePrefix();
 941                 $autoCommit = ( ( $flags & self::CONN_TRX_AUTOCOMMIT ) == self::CONN_TRX_AUTOCOMMIT );
 942
 943                 if ( $autoCommit ) {
 944                         $connFreeKey = self::KEY_FOREIGN_FREE_NOROUND;
 945                         $connInUseKey = self::KEY_FOREIGN_INUSE_NOROUND;
 946                 } else {
 947                         $connFreeKey = self::KEY_FOREIGN_FREE;
 948                         $connInUseKey = self::KEY_FOREIGN_INUSE;
 949                 }
 950
 951                 if ( isset( $this->conns[$connInUseKey][$i][$domain] ) ) {
 952                         // Reuse an in-use connection for the same domain
 953                         $conn = $this->conns[$connInUseKey][$i][$domain];
 954                         $this->connLogger->debug( __METHOD__ . ": reusing connection $i/$domain" );
 955                 } elseif ( isset( $this->conns[$connFreeKey][$i][$domain] ) ) {
 956                         // Reuse a free connection for the same domain
 957                         $conn = $this->conns[$connFreeKey][$i][$domain];
 958                         unset( $this->conns[$connFreeKey][$i][$domain] );
 959                         $this->conns[$connInUseKey][$i][$domain] = $conn;
 960                         $this->connLogger->debug( __METHOD__ . ": reusing free connection $i/$domain" );
 961                 } elseif ( !empty( $this->conns[$connFreeKey][$i] ) ) {
 962                         // Reuse a free connection from another domain
 963                         $conn = reset( $this->conns[$connFreeKey][$i] );
 964                         $oldDomain = key( $this->conns[$connFreeKey][$i] );
 965                         if ( strlen( $dbName ) && !$conn->selectDB( $dbName ) ) {
 966                                 $this->lastError = "Error selecting database '$dbName' on server " .
 967                                         $conn->getServer() . " from client host {$this->host}";
 968                                 $this->errorConnection = $conn;
 969                                 $conn = false;
 970                         } else {
 971                                 $conn->tablePrefix( $prefix );
 972                                 unset( $this->conns[$connFreeKey][$i][$oldDomain] );
 973                                 // Note that if $domain is an empty string, getDomainID() might not match it
 974                                 $this->conns[$connInUseKey][$i][$conn->getDomainId()] = $conn;
 975                                 $this->connLogger->debug( __METHOD__ .
 976                                         ": reusing free connection from $oldDomain for $domain" );
 977                         }
 978                 } else {
 979                         if ( !isset( $this->servers[$i] ) || !is_array( $this->servers[$i] ) ) {
 980                                 throw new InvalidArgumentException( "No server with index '$i'." );
 981                         }
 982                         // Open a new connection
 983                         $server = $this->servers[$i];
 984                         $server['serverIndex'] = $i;
 985                         $server['foreignPoolRefCount'] = 0;
 986                         $server['foreign'] = true;
 987                         $server['autoCommitOnly'] = $autoCommit;
 988                         $conn = $this->reallyOpenConnection( $server, $domainInstance );
 989                         if ( !$conn->isOpen() ) {
 990                                 $this->connLogger->warning( __METHOD__ . ": connection error for $i/$domain" );
 991                                 $this->errorConnection = $conn;
 992                                 $conn = false;
 993                         } else {
 994                                 $conn->tablePrefix( $prefix ); // as specified
 995                                 // Note that if $domain is an empty string, getDomainID() might not match it
 996                                 $this->conns[$connInUseKey][$i][$conn->getDomainID()] = $conn;
 997                                 $this->connLogger->debug( __METHOD__ . ": opened new connection for $i/$domain" );
 998                         }
 999                 }
1000
1001                 // Increment reference count
1002                 if ( $conn instanceof IDatabase ) {
1003                         $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
1004                         $conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
1005                 }
1006
1007                 return $conn;
1008         }
1009
1010         public function getServerAttributes( $i ) {
1011                 return Database::attributesFromType(
1012                         $this->getServerType( $i ),
1013                         isset( $this->servers[$i]['driver'] ) ? $this->servers[$i]['driver'] : null
1014                 );
1015         }
1016
1017         /**
1018          * Test if the specified index represents an open connection
1019          *
1020          * @param int $index Server index
1021          * @access private
1022          * @return bool
1023          */
1024         private function isOpen( $index ) {
1025                 if ( !is_int( $index ) ) {
1026                         return false;
1027                 }
1028
1029                 return (bool)$this->getAnyOpenConnection( $index );
1030         }
1031
1032         /**
1033          * Open a new network connection to a server (uncached)
1034          *
1035          * Returns a Database object whether or not the connection was successful.
1036          *
1037          * @param array $server
1038          * @param DatabaseDomain $domainOverride Use an unspecified domain to not select any database
1039          * @return Database
1040          * @throws DBAccessError
1041          * @throws InvalidArgumentException
1042          */
1043         protected function reallyOpenConnection( array $server, DatabaseDomain $domainOverride ) {
1044                 if ( $this->disabled ) {
1045                         throw new DBAccessError();
1046                 }
1047
1048                 // Handle $domainOverride being a specified or an unspecified domain
1049                 if ( $domainOverride->getDatabase() === null ) {
1050                         // Normally, an RDBMS requires a DB name specified on connection and the $server
1051                         // configuration array is assumed to already specify an appropriate DB name.
1052                         if ( $server['type'] === 'mysql' ) {
1053                                 // For MySQL, DATABASE and SCHEMA are synonyms, connections need not specify a DB,
1054                                 // and the DB name in $server might not exist due to legacy reasons (the default
1055                                 // domain used to ignore the local LB domain, even when mismatched).
1056                                 $server['dbname'] = null;
1057                         }
1058                 } else {
1059                         $server['dbname'] = $domainOverride->getDatabase();
1060                         $server['schema'] = $domainOverride->getSchema();
1061                 }
1062
1063                 // Let the handle know what the cluster master is (e.g. "db1052")
1064                 $masterName = $this->getServerName( $this->getWriterIndex() );
1065                 $server['clusterMasterHost'] = $masterName;
1066
1067                 // Log when many connection are made on requests
1068                 if ( ++$this->connsOpened >= self::CONN_HELD_WARN_THRESHOLD ) {
1069                         $this->perfLogger->warning( __METHOD__ . ": " .
1070                                 "{$this->connsOpened}+ connections made (master=$masterName)" );
1071                 }
1072
1073                 $server['srvCache'] = $this->srvCache;
1074                 // Set loggers and profilers
1075                 $server['connLogger'] = $this->connLogger;
1076                 $server['queryLogger'] = $this->queryLogger;
1077                 $server['errorLogger'] = $this->errorLogger;
1078                 $server['deprecationLogger'] = $this->deprecationLogger;
1079                 $server['profiler'] = $this->profiler;
1080                 $server['trxProfiler'] = $this->trxProfiler;
1081                 // Use the same agent and PHP mode for all DB handles
1082                 $server['cliMode'] = $this->cliMode;
1083                 $server['agent'] = $this->agent;
1084                 // Use DBO_DEFAULT flags by default for LoadBalancer managed databases. Assume that the
1085                 // application calls LoadBalancer::commitMasterChanges() before the PHP script completes.
1086                 $server['flags'] = isset( $server['flags'] ) ? $server['flags'] : IDatabase::DBO_DEFAULT;
1087
1088                 // Create a live connection object
1089                 try {
1090                         $db = Database::factory( $server['type'], $server );
1091                 } catch ( DBConnectionError $e ) {
1092                         // FIXME: This is probably the ugliest thing I have ever done to
1093                         // PHP. I'm half-expecting it to segfault, just out of disgust. -- TS
1094                         $db = $e->db;
1095                 }
1096
1097                 $db->setLBInfo( $server );
1098                 $db->setLazyMasterHandle(
1099                         $this->getLazyConnectionRef( self::DB_MASTER, [], $db->getDomainID() )
1100                 );
1101                 $db->setTableAliases( $this->tableAliases );
1102                 $db->setIndexAliases( $this->indexAliases );
1103
1104                 if ( $server['serverIndex'] === $this->getWriterIndex() ) {
1105                         if ( $this->trxRoundId !== false ) {
1106                                 $this->applyTransactionRoundFlags( $db );
1107                         }
1108                         foreach ( $this->trxRecurringCallbacks as $name => $callback ) {
1109                                 $db->setTransactionListener( $name, $callback );
1110                         }
1111                 }
1112
1113                 return $db;
1114         }
1115
1116         /**
1117          * @throws DBConnectionError
1118          */
1119         private function reportConnectionError() {
1120                 $conn = $this->errorConnection; // the connection which caused the error
1121                 $context = [
1122                         'method' => __METHOD__,
1123                         'last_error' => $this->lastError,
1124                 ];
1125
1126                 if ( $conn instanceof IDatabase ) {
1127                         $context['db_server'] = $conn->getServer();
1128                         $this->connLogger->warning(
1129                                 __METHOD__ . ": connection error: {last_error} ({db_server})",
1130                                 $context
1131                         );
1132
1133                         // throws DBConnectionError
1134                         $conn->reportConnectionError( "{$this->lastError} ({$context['db_server']})" );
1135                 } else {
1136                         // No last connection, probably due to all servers being too busy
1137                         $this->connLogger->error(
1138                                 __METHOD__ .
1139                                 ": LB failure with no last connection. Connection error: {last_error}",
1140                                 $context
1141                         );
1142
1143                         // If all servers were busy, "lastError" will contain something sensible
1144                         throw new DBConnectionError( null, $this->lastError );
1145                 }
1146         }
1147
1148         public function getWriterIndex() {
1149                 return 0;
1150         }
1151
1152         public function haveIndex( $i ) {
1153                 return array_key_exists( $i, $this->servers );
1154         }
1155
1156         public function isNonZeroLoad( $i ) {
1157                 return array_key_exists( $i, $this->servers ) && $this->loads[$i] != 0;
1158         }
1159
1160         public function getServerCount() {
1161                 return count( $this->servers );
1162         }
1163
1164         public function getServerName( $i ) {
1165                 if ( isset( $this->servers[$i]['hostName'] ) ) {
1166                         $name = $this->servers[$i]['hostName'];
1167                 } elseif ( isset( $this->servers[$i]['host'] ) ) {
1168                         $name = $this->servers[$i]['host'];
1169                 } else {
1170                         $name = '';
1171                 }
1172
1173                 return ( $name != '' ) ? $name : 'localhost';
1174         }
1175
1176         public function getServerInfo( $i ) {
1177                 if ( isset( $this->servers[$i] ) ) {
1178                         return $this->servers[$i];
1179                 } else {
1180                         return false;
1181                 }
1182         }
1183
1184         public function getServerType( $i ) {
1185                 return isset( $this->servers[$i]['type'] ) ? $this->servers[$i]['type'] : 'unknown';
1186         }
1187
1188         public function getMasterPos() {
1189                 # If this entire request was served from a replica DB without opening a connection to the
1190                 # master (however unlikely that may be), then we can fetch the position from the replica DB.
1191                 $masterConn = $this->getAnyOpenConnection( $this->getWriterIndex() );
1192                 if ( !$masterConn ) {
1193                         $serverCount = count( $this->servers );
1194                         for ( $i = 1; $i < $serverCount; $i++ ) {
1195                                 $conn = $this->getAnyOpenConnection( $i );
1196                                 if ( $conn ) {
1197                                         return $conn->getReplicaPos();
1198                                 }
1199                         }
1200                 } else {
1201                         return $masterConn->getMasterPos();
1202                 }
1203
1204                 return false;
1205         }
1206
1207         public function disable() {
1208                 $this->closeAll();
1209                 $this->disabled = true;
1210         }
1211
1212         public function closeAll() {
1213                 $this->forEachOpenConnection( function ( IDatabase $conn ) {
1214                         $host = $conn->getServer();
1215                         $this->connLogger->debug(
1216                                 __METHOD__ . ": closing connection to database '$host'." );
1217                         $conn->close();
1218                 } );
1219
1220                 $this->conns = [
1221                         self::KEY_LOCAL => [],
1222                         self::KEY_FOREIGN_INUSE => [],
1223                         self::KEY_FOREIGN_FREE => [],
1224                         self::KEY_LOCAL_NOROUND => [],
1225                         self::KEY_FOREIGN_INUSE_NOROUND => [],
1226                         self::KEY_FOREIGN_FREE_NOROUND => []
1227                 ];
1228                 $this->connsOpened = 0;
1229         }
1230
1231         public function closeConnection( IDatabase $conn ) {
1232                 $serverIndex = $conn->getLBInfo( 'serverIndex' );
1233                 foreach ( $this->conns as $type => $connsByServer ) {
1234                         if ( !isset( $connsByServer[$serverIndex] ) ) {
1235                                 continue;
1236                         }
1237
1238                         foreach ( $connsByServer[$serverIndex] as $i => $trackedConn ) {
1239                                 if ( $conn === $trackedConn ) {
1240                                         $host = $this->getServerName( $i );
1241                                         $this->connLogger->debug(
1242                                                 __METHOD__ . ": closing connection to database $i at '$host'." );
1243                                         unset( $this->conns[$type][$serverIndex][$i] );
1244                                         --$this->connsOpened;
1245                                         break 2;
1246                                 }
1247                         }
1248                 }
1249
1250                 $conn->close();
1251         }
1252
1253         public function commitAll( $fname = __METHOD__ ) {
1254                 $failures = [];
1255
1256                 $restore = ( $this->trxRoundId !== false );
1257                 $this->trxRoundId = false;
1258                 $this->forEachOpenConnection(
1259                         function ( IDatabase $conn ) use ( $fname, $restore, &$failures ) {
1260                                 try {
1261                                         $conn->commit( $fname, $conn::FLUSHING_ALL_PEERS );
1262                                 } catch ( DBError $e ) {
1263                                         call_user_func( $this->errorLogger, $e );
1264                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1265                                 }
1266                                 if ( $restore && $conn->getLBInfo( 'master' ) ) {
1267                                         $this->undoTransactionRoundFlags( $conn );
1268                                 }
1269                         }
1270                 );
1271
1272                 if ( $failures ) {
1273                         throw new DBExpectedError(
1274                                 null,
1275                                 "Commit failed on server(s) " . implode( "\n", array_unique( $failures ) )
1276                         );
1277                 }
1278         }
1279
1280         public function finalizeMasterChanges() {
1281                 $this->forEachOpenMasterConnection( function ( Database $conn ) {
1282                         // Any error should cause all DB transactions to be rolled back together
1283                         $conn->setTrxEndCallbackSuppression( false );
1284                         $conn->runOnTransactionPreCommitCallbacks();
1285                         // Defer post-commit callbacks until COMMIT finishes for all DBs
1286                         $conn->setTrxEndCallbackSuppression( true );
1287                 } );
1288         }
1289
1290         public function approveMasterChanges( array $options ) {
1291                 $limit = isset( $options['maxWriteDuration'] ) ? $options['maxWriteDuration'] : 0;
1292                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( $limit ) {
1293                         // If atomic sections or explicit transactions are still open, some caller must have
1294                         // caught an exception but failed to properly rollback any changes. Detect that and
1295                         // throw and error (causing rollback).
1296                         if ( $conn->explicitTrxActive() ) {
1297                                 throw new DBTransactionError(
1298                                         $conn,
1299                                         "Explicit transaction still active. A caller may have caught an error."
1300                                 );
1301                         }
1302                         // Assert that the time to replicate the transaction will be sane.
1303                         // If this fails, then all DB transactions will be rollback back together.
1304                         $time = $conn->pendingWriteQueryDuration( $conn::ESTIMATE_DB_APPLY );
1305                         if ( $limit > 0 && $time > $limit ) {
1306                                 throw new DBTransactionSizeError(
1307                                         $conn,
1308                                         "Transaction spent $time second(s) in writes, exceeding the limit of $limit.",
1309                                         [ $time, $limit ]
1310                                 );
1311                         }
1312                         // If a connection sits idle while slow queries execute on another, that connection
1313                         // may end up dropped before the commit round is reached. Ping servers to detect this.
1314                         if ( $conn->writesOrCallbacksPending() && !$conn->ping() ) {
1315                                 throw new DBTransactionError(
1316                                         $conn,
1317                                         "A connection to the {$conn->getDBname()} database was lost before commit."
1318                                 );
1319                         }
1320                 } );
1321         }
1322
1323         public function beginMasterChanges( $fname = __METHOD__ ) {
1324                 if ( $this->trxRoundId !== false ) {
1325                         throw new DBTransactionError(
1326                                 null,
1327                                 "$fname: Transaction round '{$this->trxRoundId}' already started."
1328                         );
1329                 }
1330                 $this->trxRoundId = $fname;
1331
1332                 $failures = [];
1333                 $this->forEachOpenMasterConnection(
1334                         function ( Database $conn ) use ( $fname, &$failures ) {
1335                                 $conn->setTrxEndCallbackSuppression( true );
1336                                 try {
1337                                         $conn->flushSnapshot( $fname );
1338                                 } catch ( DBError $e ) {
1339                                         call_user_func( $this->errorLogger, $e );
1340                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1341                                 }
1342                                 $conn->setTrxEndCallbackSuppression( false );
1343                                 $this->applyTransactionRoundFlags( $conn );
1344                         }
1345                 );
1346
1347                 if ( $failures ) {
1348                         throw new DBExpectedError(
1349                                 null,
1350                                 "$fname: Flush failed on server(s) " . implode( "\n", array_unique( $failures ) )
1351                         );
1352                 }
1353         }
1354
1355         public function commitMasterChanges( $fname = __METHOD__ ) {
1356                 $failures = [];
1357
1358                 /** @noinspection PhpUnusedLocalVariableInspection */
1359                 $scope = $this->getScopedPHPBehaviorForCommit(); // try to ignore client aborts
1360
1361                 $restore = ( $this->trxRoundId !== false );
1362                 $this->trxRoundId = false;
1363                 $this->forEachOpenMasterConnection(
1364                         function ( IDatabase $conn ) use ( $fname, $restore, &$failures ) {
1365                                 try {
1366                                         if ( $conn->writesOrCallbacksPending() ) {
1367                                                 $conn->commit( $fname, $conn::FLUSHING_ALL_PEERS );
1368                                         } elseif ( $restore ) {
1369                                                 $conn->flushSnapshot( $fname );
1370                                         }
1371                                 } catch ( DBError $e ) {
1372                                         call_user_func( $this->errorLogger, $e );
1373                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1374                                 }
1375                                 if ( $restore ) {
1376                                         $this->undoTransactionRoundFlags( $conn );
1377                                 }
1378                         }
1379                 );
1380
1381                 if ( $failures ) {
1382                         throw new DBExpectedError(
1383                                 null,
1384                                 "$fname: Commit failed on server(s) " . implode( "\n", array_unique( $failures ) )
1385                         );
1386                 }
1387         }
1388
1389         public function runMasterPostTrxCallbacks( $type ) {
1390                 $e = null; // first exception
1391                 $this->forEachOpenMasterConnection( function ( Database $conn ) use ( $type, &$e ) {
1392                         $conn->setTrxEndCallbackSuppression( false );
1393                         // Callbacks run in AUTO-COMMIT mode, so make sure no transactions are pending...
1394                         if ( $conn->writesPending() ) {
1395                                 // This happens if onTransactionIdle() callbacks write to *other* handles
1396                                 // (which already finished their callbacks). Let any callbacks run in the final
1397                                 // commitMasterChanges() in LBFactory::shutdown(), when the transaction is gone.
1398                                 $this->queryLogger->warning( __METHOD__ . ": found writes pending." );
1399                                 return;
1400                         } elseif ( $conn->trxLevel() ) {
1401                                 // This happens for single-DB setups where DB_REPLICA uses the master DB,
1402                                 // thus leaving an implicit read-only transaction open at this point. It
1403                                 // also happens if onTransactionIdle() callbacks leave implicit transactions
1404                                 // open on *other* DBs (which is slightly improper). Let these COMMIT on the
1405                                 // next call to commitMasterChanges(), possibly in LBFactory::shutdown().
1406                                 return;
1407                         }
1408                         try {
1409                                 $conn->runOnTransactionIdleCallbacks( $type );
1410                         } catch ( Exception $ex ) {
1411                                 $e = $e ?: $ex;
1412                         }
1413                         try {
1414                                 $conn->runTransactionListenerCallbacks( $type );
1415                         } catch ( Exception $ex ) {
1416                                 $e = $e ?: $ex;
1417                         }
1418                 } );
1419
1420                 return $e;
1421         }
1422
1423         public function rollbackMasterChanges( $fname = __METHOD__ ) {
1424                 $restore = ( $this->trxRoundId !== false );
1425                 $this->trxRoundId = false;
1426                 $this->forEachOpenMasterConnection(
1427                         function ( IDatabase $conn ) use ( $fname, $restore ) {
1428                                 $conn->rollback( $fname, $conn::FLUSHING_ALL_PEERS );
1429                                 if ( $restore ) {
1430                                         $this->undoTransactionRoundFlags( $conn );
1431                                 }
1432                         }
1433                 );
1434         }
1435
1436         public function suppressTransactionEndCallbacks() {
1437                 $this->forEachOpenMasterConnection( function ( Database $conn ) {
1438                         $conn->setTrxEndCallbackSuppression( true );
1439                 } );
1440         }
1441
1442         /**
1443          * Make all DB servers with DBO_DEFAULT/DBO_TRX set join the transaction round
1444          *
1445          * Some servers may have neither flag enabled, meaning that they opt out of such
1446          * transaction rounds and remain in auto-commit mode. Such behavior might be desired
1447          * when a DB server is used for something like simple key/value storage.
1448          *
1449          * @param IDatabase $conn
1450          */
1451         private function applyTransactionRoundFlags( IDatabase $conn ) {
1452                 if ( $conn->getLBInfo( 'autoCommitOnly' ) ) {
1453                         return; // transaction rounds do not apply to these connections
1454                 }
1455
1456                 if ( $conn->getFlag( $conn::DBO_DEFAULT ) ) {
1457                         // DBO_TRX is controlled entirely by CLI mode presence with DBO_DEFAULT.
1458                         // Force DBO_TRX even in CLI mode since a commit round is expected soon.
1459                         $conn->setFlag( $conn::DBO_TRX, $conn::REMEMBER_PRIOR );
1460                 }
1461
1462                 if ( $conn->getFlag( $conn::DBO_TRX ) ) {
1463                         $conn->setLBInfo( 'trxRoundId', $this->trxRoundId );
1464                 }
1465         }
1466
1467         /**
1468          * @param IDatabase $conn
1469          */
1470         private function undoTransactionRoundFlags( IDatabase $conn ) {
1471                 if ( $conn->getLBInfo( 'autoCommitOnly' ) ) {
1472                         return; // transaction rounds do not apply to these connections
1473                 }
1474
1475                 if ( $conn->getFlag( $conn::DBO_TRX ) ) {
1476                         $conn->setLBInfo( 'trxRoundId', false );
1477                 }
1478
1479                 if ( $conn->getFlag( $conn::DBO_DEFAULT ) ) {
1480                         $conn->restoreFlags( $conn::RESTORE_PRIOR );
1481                 }
1482         }
1483
1484         public function flushReplicaSnapshots( $fname = __METHOD__ ) {
1485                 $this->forEachOpenReplicaConnection( function ( IDatabase $conn ) {
1486                         $conn->flushSnapshot( __METHOD__ );
1487                 } );
1488         }
1489
1490         public function hasMasterConnection() {
1491                 return $this->isOpen( $this->getWriterIndex() );
1492         }
1493
1494         public function hasMasterChanges() {
1495                 $pending = 0;
1496                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$pending ) {
1497                         $pending |= $conn->writesOrCallbacksPending();
1498                 } );
1499
1500                 return (bool)$pending;
1501         }
1502
1503         public function lastMasterChangeTimestamp() {
1504                 $lastTime = false;
1505                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$lastTime ) {
1506                         $lastTime = max( $lastTime, $conn->lastDoneWrites() );
1507                 } );
1508
1509                 return $lastTime;
1510         }
1511
1512         public function hasOrMadeRecentMasterChanges( $age = null ) {
1513                 $age = ( $age === null ) ? $this->waitTimeout : $age;
1514
1515                 return ( $this->hasMasterChanges()
1516                         || $this->lastMasterChangeTimestamp() > microtime( true ) - $age );
1517         }
1518
1519         public function pendingMasterChangeCallers() {
1520                 $fnames = [];
1521                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$fnames ) {
1522                         $fnames = array_merge( $fnames, $conn->pendingWriteCallers() );
1523                 } );
1524
1525                 return $fnames;
1526         }
1527
1528         public function getLaggedReplicaMode( $domain = false ) {
1529                 // No-op if there is only one DB (also avoids recursion)
1530                 if ( !$this->laggedReplicaMode && $this->getServerCount() > 1 ) {
1531                         try {
1532                                 // See if laggedReplicaMode gets set
1533                                 $conn = $this->getConnection( self::DB_REPLICA, false, $domain );
1534                                 $this->reuseConnection( $conn );
1535                         } catch ( DBConnectionError $e ) {
1536                                 // Avoid expensive re-connect attempts and failures
1537                                 $this->allReplicasDownMode = true;
1538                                 $this->laggedReplicaMode = true;
1539                         }
1540                 }
1541
1542                 return $this->laggedReplicaMode;
1543         }
1544
1545         /**
1546          * @param bool $domain
1547          * @return bool
1548          * @deprecated 1.28; use getLaggedReplicaMode()
1549          */
1550         public function getLaggedSlaveMode( $domain = false ) {
1551                 return $this->getLaggedReplicaMode( $domain );
1552         }
1553
1554         public function laggedReplicaUsed() {
1555                 return $this->laggedReplicaMode;
1556         }
1557
1558         /**
1559          * @return bool
1560          * @since 1.27
1561          * @deprecated Since 1.28; use laggedReplicaUsed()
1562          */
1563         public function laggedSlaveUsed() {
1564                 return $this->laggedReplicaUsed();
1565         }
1566
1567         public function getReadOnlyReason( $domain = false, IDatabase $conn = null ) {
1568                 if ( $this->readOnlyReason !== false ) {
1569                         return $this->readOnlyReason;
1570                 } elseif ( $this->getLaggedReplicaMode( $domain ) ) {
1571                         if ( $this->allReplicasDownMode ) {
1572                                 return 'The database has been automatically locked ' .
1573                                         'until the replica database servers become available';
1574                         } else {
1575                                 return 'The database has been automatically locked ' .
1576                                         'while the replica database servers catch up to the master.';
1577                         }
1578                 } elseif ( $this->masterRunningReadOnly( $domain, $conn ) ) {
1579                         return 'The database master is running in read-only mode.';
1580                 }
1581
1582                 return false;
1583         }
1584
1585         /**
1586          * @param string $domain Domain ID, or false for the current domain
1587          * @param IDatabase|null $conn DB master connectionl used to avoid loops [optional]
1588          * @return bool
1589          */
1590         private function masterRunningReadOnly( $domain, IDatabase $conn = null ) {
1591                 $cache = $this->wanCache;
1592                 $masterServer = $this->getServerName( $this->getWriterIndex() );
1593
1594                 return (bool)$cache->getWithSetCallback(
1595                         $cache->makeGlobalKey( __CLASS__, 'server-read-only', $masterServer ),
1596                         self::TTL_CACHE_READONLY,
1597                         function () use ( $domain, $conn ) {
1598                                 $old = $this->trxProfiler->setSilenced( true );
1599                                 try {
1600                                         $dbw = $conn ?: $this->getConnection( self::DB_MASTER, [], $domain );
1601                                         $readOnly = (int)$dbw->serverIsReadOnly();
1602                                         if ( !$conn ) {
1603                                                 $this->reuseConnection( $dbw );
1604                                         }
1605                                 } catch ( DBError $e ) {
1606                                         $readOnly = 0;
1607                                 }
1608                                 $this->trxProfiler->setSilenced( $old );
1609                                 return $readOnly;
1610                         },
1611                         [ 'pcTTL' => $cache::TTL_PROC_LONG, 'busyValue' => 0 ]
1612                 );
1613         }
1614
1615         public function allowLagged( $mode = null ) {
1616                 if ( $mode === null ) {
1617                         return $this->allowLagged;
1618                 }
1619                 $this->allowLagged = $mode;
1620
1621                 return $this->allowLagged;
1622         }
1623
1624         public function pingAll() {
1625                 $success = true;
1626                 $this->forEachOpenConnection( function ( IDatabase $conn ) use ( &$success ) {
1627                         if ( !$conn->ping() ) {
1628                                 $success = false;
1629                         }
1630                 } );
1631
1632                 return $success;
1633         }
1634
1635         public function forEachOpenConnection( $callback, array $params = [] ) {
1636                 foreach ( $this->conns as $connsByServer ) {
1637                         foreach ( $connsByServer as $serverConns ) {
1638                                 foreach ( $serverConns as $conn ) {
1639                                         $mergedParams = array_merge( [ $conn ], $params );
1640                                         call_user_func_array( $callback, $mergedParams );
1641                                 }
1642                         }
1643                 }
1644         }
1645
1646         public function forEachOpenMasterConnection( $callback, array $params = [] ) {
1647                 $masterIndex = $this->getWriterIndex();
1648                 foreach ( $this->conns as $connsByServer ) {
1649                         if ( isset( $connsByServer[$masterIndex] ) ) {
1650                                 /** @var IDatabase $conn */
1651                                 foreach ( $connsByServer[$masterIndex] as $conn ) {
1652                                         $mergedParams = array_merge( [ $conn ], $params );
1653                                         call_user_func_array( $callback, $mergedParams );
1654                                 }
1655                         }
1656                 }
1657         }
1658
1659         public function forEachOpenReplicaConnection( $callback, array $params = [] ) {
1660                 foreach ( $this->conns as $connsByServer ) {
1661                         foreach ( $connsByServer as $i => $serverConns ) {
1662                                 if ( $i === $this->getWriterIndex() ) {
1663                                         continue; // skip master
1664                                 }
1665                                 foreach ( $serverConns as $conn ) {
1666                                         $mergedParams = array_merge( [ $conn ], $params );
1667                                         call_user_func_array( $callback, $mergedParams );
1668                                 }
1669                         }
1670                 }
1671         }
1672
1673         public function getMaxLag( $domain = false ) {
1674                 $maxLag = -1;
1675                 $host = '';
1676                 $maxIndex = 0;
1677
1678                 if ( $this->getServerCount() <= 1 ) {
1679                         return [ $host, $maxLag, $maxIndex ]; // no replication = no lag
1680                 }
1681
1682                 $lagTimes = $this->getLagTimes( $domain );
1683                 foreach ( $lagTimes as $i => $lag ) {
1684                         if ( $this->loads[$i] > 0 && $lag > $maxLag ) {
1685                                 $maxLag = $lag;
1686                                 $host = $this->servers[$i]['host'];
1687                                 $maxIndex = $i;
1688                         }
1689                 }
1690
1691                 return [ $host, $maxLag, $maxIndex ];
1692         }
1693
1694         public function getLagTimes( $domain = false ) {
1695                 if ( $this->getServerCount() <= 1 ) {
1696                         return [ $this->getWriterIndex() => 0 ]; // no replication = no lag
1697                 }
1698
1699                 $knownLagTimes = []; // map of (server index => 0 seconds)
1700                 $indexesWithLag = [];
1701                 foreach ( $this->servers as $i => $server ) {
1702                         if ( empty( $server['is static'] ) ) {
1703                                 $indexesWithLag[] = $i; // DB server might have replication lag
1704                         } else {
1705                                 $knownLagTimes[$i] = 0; // DB server is a non-replicating and read-only archive
1706                         }
1707                 }
1708
1709                 return $this->getLoadMonitor()->getLagTimes( $indexesWithLag, $domain ) + $knownLagTimes;
1710         }
1711
1712         public function safeGetLag( IDatabase $conn ) {
1713                 if ( $this->getServerCount() <= 1 ) {
1714                         return 0;
1715                 } else {
1716                         return $conn->getLag();
1717                 }
1718         }
1719
1720         /**
1721          * @param IDatabase $conn
1722          * @param DBMasterPos|bool $pos
1723          * @param int|null $timeout
1724          * @return bool
1725          */
1726         public function safeWaitForMasterPos( IDatabase $conn, $pos = false, $timeout = null ) {
1727                 $timeout = max( 1, $timeout ?: $this->waitTimeout );
1728
1729                 if ( $this->getServerCount() <= 1 || !$conn->getLBInfo( 'replica' ) ) {
1730                         return true; // server is not a replica DB
1731                 }
1732
1733                 if ( !$pos ) {
1734                         // Get the current master position, opening a connection if needed
1735                         $masterConn = $this->getAnyOpenConnection( $this->getWriterIndex() );
1736                         if ( $masterConn ) {
1737                                 $pos = $masterConn->getMasterPos();
1738                         } else {
1739                                 $masterConn = $this->openConnection( $this->getWriterIndex(), self::DOMAIN_ANY );
1740                                 $pos = $masterConn->getMasterPos();
1741                                 $this->closeConnection( $masterConn );
1742                         }
1743                 }
1744
1745                 if ( $pos instanceof DBMasterPos ) {
1746                         $result = $conn->masterPosWait( $pos, $timeout );
1747                         if ( $result == -1 || is_null( $result ) ) {
1748                                 $msg = __METHOD__ . ': timed out waiting on {host} pos {pos}';
1749                                 $this->replLogger->warning( $msg, [
1750                                         'host' => $conn->getServer(),
1751                                         'pos' => $pos,
1752                                         'trace' => ( new RuntimeException() )->getTraceAsString()
1753                                 ] );
1754                                 $ok = false;
1755                         } else {
1756                                 $this->replLogger->debug( __METHOD__ . ': done waiting' );
1757                                 $ok = true;
1758                         }
1759                 } else {
1760                         $ok = false; // something is misconfigured
1761                         $this->replLogger->error(
1762                                 __METHOD__ . ': could not get master pos for {host}',
1763                                 [
1764                                         'host' => $conn->getServer(),
1765                                         'trace' => ( new RuntimeException() )->getTraceAsString()
1766                                 ]
1767                         );
1768                 }
1769
1770                 return $ok;
1771         }
1772
1773         public function setTransactionListener( $name, callable $callback = null ) {
1774                 if ( $callback ) {
1775                         $this->trxRecurringCallbacks[$name] = $callback;
1776                 } else {
1777                         unset( $this->trxRecurringCallbacks[$name] );
1778                 }
1779                 $this->forEachOpenMasterConnection(
1780                         function ( IDatabase $conn ) use ( $name, $callback ) {
1781                                 $conn->setTransactionListener( $name, $callback );
1782                         }
1783                 );
1784         }
1785
1786         public function setTableAliases( array $aliases ) {
1787                 $this->tableAliases = $aliases;
1788         }
1789
1790         public function setIndexAliases( array $aliases ) {
1791                 $this->indexAliases = $aliases;
1792         }
1793
1794         public function setDomainPrefix( $prefix ) {
1795                 // Find connections to explicit foreign domains still marked as in-use...
1796                 $domainsInUse = [];
1797                 $this->forEachOpenConnection( function ( IDatabase $conn ) use ( &$domainsInUse ) {
1798                         // Once reuseConnection() is called on a handle, its reference count goes from 1 to 0.
1799                         // Until then, it is still in use by the caller (explicitly or via DBConnRef scope).
1800                         if ( $conn->getLBInfo( 'foreignPoolRefCount' ) > 0 ) {
1801                                 $domainsInUse[] = $conn->getDomainID();
1802                         }
1803                 } );
1804
1805                 // Do not switch connections to explicit foreign domains unless marked as safe
1806                 if ( $domainsInUse ) {
1807                         $domains = implode( ', ', $domainsInUse );
1808                         throw new DBUnexpectedError( null,
1809                                 "Foreign domain connections are still in use ($domains)." );
1810                 }
1811
1812                 $oldDomain = $this->localDomain->getId();
1813                 $this->setLocalDomain( new DatabaseDomain(
1814                         $this->localDomain->getDatabase(),
1815                         $this->localDomain->getSchema(),
1816                         $prefix
1817                 ) );
1818
1819                 $this->forEachOpenConnection( function ( IDatabase $db ) use ( $prefix, $oldDomain ) {
1820                         if ( !$db->getLBInfo( 'foreign' ) ) {
1821                                 $db->tablePrefix( $prefix );
1822                         }
1823                 } );
1824         }
1825
1826         /**
1827          * @param DatabaseDomain $domain
1828          */
1829         private function setLocalDomain( DatabaseDomain $domain ) {
1830                 $this->localDomain = $domain;
1831                 // In case a caller assumes that the domain ID is simply <db>-<prefix>, which is almost
1832                 // always true, gracefully handle the case when they fail to account for escaping.
1833                 if ( $this->localDomain->getTablePrefix() != '' ) {
1834                         $this->localDomainIdAlias =
1835                                 $this->localDomain->getDatabase() . '-' . $this->localDomain->getTablePrefix();
1836                 } else {
1837                         $this->localDomainIdAlias = $this->localDomain->getDatabase();
1838                 }
1839         }
1840
1841         /**
1842          * Make PHP ignore user aborts/disconnects until the returned
1843          * value leaves scope. This returns null and does nothing in CLI mode.
1844          *
1845          * @return ScopedCallback|null
1846          */
1847         final protected function getScopedPHPBehaviorForCommit() {
1848                 if ( PHP_SAPI != 'cli' ) { // https://bugs.php.net/bug.php?id=47540
1849                         $old = ignore_user_abort( true ); // avoid half-finished operations
1850                         return new ScopedCallback( function () use ( $old ) {
1851                                 ignore_user_abort( $old );
1852                         } );
1853                 }
1854
1855                 return null;
1856         }
1857
1858         function __destruct() {
1859                 // Avoid connection leaks for sanity
1860                 $this->disable();
1861         }
1862 }
1863
1864 class_alias( LoadBalancer::class, 'LoadBalancer' );