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 ChronologyProtector|null */
  63         private $chronProt;
  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 */
 120         private $chronProtInitialized = 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['chronologyProtector'] ) ) {
 247                         $this->chronProt = $params['chronologyProtector'];
 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 mWaitForPos
 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 != $this->getWriterIndex() ) {
 380                         // Before any data queries are run, wait for the server to catch up to the
 381                         // specified position. This is used to improve session consistency. Note that
 382                         // when LoadBalancer::waitFor() sets mWaitForPos, the waiting triggers here,
 383                         // so update laggedReplicaMode as needed for consistency.
 384                         if ( !$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                                         // ChronologyProtecter sets mWaitForPos 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         /**
 570          * @param int $i
 571          * @return IDatabase|bool
 572          */
 573         public function getAnyOpenConnection( $i ) {
 574                 foreach ( $this->conns as $connsByServer ) {
 575                         if ( !empty( $connsByServer[$i] ) ) {
 576                                 /** @var IDatabase[] $serverConns */
 577                                 $serverConns = $connsByServer[$i];
 578
 579                                 return reset( $serverConns );
 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, $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_AUTO ) === self::CONN_TRX_AUTO ) {
 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_AUTO;
 704                                 $this->connLogger->info( __METHOD__ . ': ignoring CONN_TRX_AUTO to avoid deadlocks.' );
 705                         }
 706                 }
 707
 708                 $groups = ( $groups === false || $groups === [] )
 709                         ? [ false ] // check one "group": the generic pool
 710                         : (array)$groups;
 711
 712                 $masterOnly = ( $i == self::DB_MASTER || $i == $this->getWriterIndex() );
 713                 $oldConnsOpened = $this->connsOpened; // connections open now
 714
 715                 if ( $i == self::DB_MASTER ) {
 716                         $i = $this->getWriterIndex();
 717                 } else {
 718                         # Try to find an available server in any the query groups (in order)
 719                         foreach ( $groups as $group ) {
 720                                 $groupIndex = $this->getReaderIndex( $group, $domain );
 721                                 if ( $groupIndex !== false ) {
 722                                         $i = $groupIndex;
 723                                         break;
 724                                 }
 725                         }
 726                 }
 727
 728                 # Operation-based index
 729                 if ( $i == self::DB_REPLICA ) {
 730                         $this->lastError = 'Unknown error'; // reset error string
 731                         # Try the general server pool if $groups are unavailable.
 732                         $i = ( $groups === [ false ] )
 733                                 ? false // don't bother with this if that is what was tried above
 734                                 : $this->getReaderIndex( false, $domain );
 735                         # Couldn't find a working server in getReaderIndex()?
 736                         if ( $i === false ) {
 737                                 $this->lastError = 'No working replica DB server: ' . $this->lastError;
 738                                 // Throw an exception
 739                                 $this->reportConnectionError();
 740                                 return null; // not reached
 741                         }
 742                 }
 743
 744                 # Now we have an explicit index into the servers array
 745                 $conn = $this->openConnection( $i, $domain, $flags );
 746                 if ( !$conn ) {
 747                         // Throw an exception
 748                         $this->reportConnectionError();
 749                         return null; // not reached
 750                 }
 751
 752                 # Profile any new connections that happen
 753                 if ( $this->connsOpened > $oldConnsOpened ) {
 754                         $host = $conn->getServer();
 755                         $dbname = $conn->getDBname();
 756                         $this->trxProfiler->recordConnection( $host, $dbname, $masterOnly );
 757                 }
 758
 759                 if ( $masterOnly ) {
 760                         # Make master-requested DB handles inherit any read-only mode setting
 761                         $conn->setLBInfo( 'readOnlyReason', $this->getReadOnlyReason( $domain, $conn ) );
 762                 }
 763
 764                 return $conn;
 765         }
 766
 767         public function reuseConnection( IDatabase $conn ) {
 768                 $serverIndex = $conn->getLBInfo( 'serverIndex' );
 769                 $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 770                 if ( $serverIndex === null || $refCount === null ) {
 771                         /**
 772                          * This can happen in code like:
 773                          *   foreach ( $dbs as $db ) {
 774                          *     $conn = $lb->getConnection( $lb::DB_REPLICA, [], $db );
 775                          *     ...
 776                          *     $lb->reuseConnection( $conn );
 777                          *   }
 778                          * When a connection to the local DB is opened in this way, reuseConnection()
 779                          * should be ignored
 780                          */
 781                         return;
 782                 } elseif ( $conn instanceof DBConnRef ) {
 783                         // DBConnRef already handles calling reuseConnection() and only passes the live
 784                         // Database instance to this method. Any caller passing in a DBConnRef is broken.
 785                         $this->connLogger->error(
 786                                 __METHOD__ . ": got DBConnRef instance.\n" .
 787                                 ( new RuntimeException() )->getTraceAsString() );
 788
 789                         return;
 790                 }
 791
 792                 if ( $this->disabled ) {
 793                         return; // DBConnRef handle probably survived longer than the LoadBalancer
 794                 }
 795
 796                 if ( $conn->getLBInfo( 'autoCommitOnly' ) ) {
 797                         $connFreeKey = self::KEY_FOREIGN_FREE_NOROUND;
 798                         $connInUseKey = self::KEY_FOREIGN_INUSE_NOROUND;
 799                 } else {
 800                         $connFreeKey = self::KEY_FOREIGN_FREE;
 801                         $connInUseKey = self::KEY_FOREIGN_INUSE;
 802                 }
 803
 804                 $domain = $conn->getDomainID();
 805                 if ( !isset( $this->conns[$connInUseKey][$serverIndex][$domain] ) ) {
 806                         throw new InvalidArgumentException( __METHOD__ .
 807                                 ": connection $serverIndex/$domain not found; it may have already been freed." );
 808                 } elseif ( $this->conns[$connInUseKey][$serverIndex][$domain] !== $conn ) {
 809                         throw new InvalidArgumentException( __METHOD__ .
 810                                 ": connection $serverIndex/$domain mismatched; it may have already been freed." );
 811                 }
 812
 813                 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
 814                 if ( $refCount <= 0 ) {
 815                         $this->conns[$connFreeKey][$serverIndex][$domain] = $conn;
 816                         unset( $this->conns[$connInUseKey][$serverIndex][$domain] );
 817                         if ( !$this->conns[$connInUseKey][$serverIndex] ) {
 818                                 unset( $this->conns[$connInUseKey][$serverIndex] ); // clean up
 819                         }
 820                         $this->connLogger->debug( __METHOD__ . ": freed connection $serverIndex/$domain" );
 821                 } else {
 822                         $this->connLogger->debug( __METHOD__ .
 823                                 ": reference count for $serverIndex/$domain reduced to $refCount" );
 824                 }
 825         }
 826
 827         public function getConnectionRef( $db, $groups = [], $domain = false, $flags = 0 ) {
 828                 $domain = ( $domain !== false ) ? $domain : $this->localDomain;
 829
 830                 return new DBConnRef( $this, $this->getConnection( $db, $groups, $domain, $flags ) );
 831         }
 832
 833         public function getLazyConnectionRef( $db, $groups = [], $domain = false, $flags = 0 ) {
 834                 $domain = ( $domain !== false ) ? $domain : $this->localDomain;
 835
 836                 return new DBConnRef( $this, [ $db, $groups, $domain, $flags ] );
 837         }
 838
 839         public function getMaintenanceConnectionRef( $db, $groups = [], $domain = false, $flags = 0 ) {
 840                 $domain = ( $domain !== false ) ? $domain : $this->localDomain;
 841
 842                 return new MaintainableDBConnRef(
 843                         $this, $this->getConnection( $db, $groups, $domain, $flags ) );
 844         }
 845
 846         public function openConnection( $i, $domain = false, $flags = 0 ) {
 847                 if ( $this->localDomain->equals( $domain ) || $domain === $this->localDomainIdAlias ) {
 848                         $domain = false; // local connection requested
 849                 }
 850
 851                 if ( !$this->chronProtInitialized && $this->chronProt ) {
 852                         $this->connLogger->debug( __METHOD__ . ': calling initLB() before first connection.' );
 853                         // Load CP positions before connecting so that doWait() triggers later if needed
 854                         $this->chronProtInitialized = true;
 855                         $this->chronProt->initLB( $this );
 856                 }
 857
 858                 // Check if an auto-commit connection is being requested. If so, it will not reuse the
 859                 // main set of DB connections but rather its own pool since:
 860                 // a) those are usually set to implicitly use transaction rounds via DBO_TRX
 861                 // b) those must support the use of explicit transaction rounds via beginMasterChanges()
 862                 $autoCommit = ( ( $flags & self::CONN_TRX_AUTO ) == self::CONN_TRX_AUTO );
 863
 864                 if ( $domain !== false ) {
 865                         // Connection is to a foreign domain
 866                         $conn = $this->openForeignConnection( $i, $domain, $flags );
 867                 } else {
 868                         // Connection is to the local domain
 869                         $connKey = $autoCommit ? self::KEY_LOCAL_NOROUND : self::KEY_LOCAL;
 870                         if ( isset( $this->conns[$connKey][$i][0] ) ) {
 871                                 $conn = $this->conns[$connKey][$i][0];
 872                         } else {
 873                                 if ( !isset( $this->servers[$i] ) || !is_array( $this->servers[$i] ) ) {
 874                                         throw new InvalidArgumentException( "No server with index '$i'." );
 875                                 }
 876                                 // Open a new connection
 877                                 $server = $this->servers[$i];
 878                                 $server['serverIndex'] = $i;
 879                                 $server['autoCommitOnly'] = $autoCommit;
 880                                 if ( $this->localDomain->getDatabase() !== null ) {
 881                                         // Use the local domain table prefix if the local domain is specified
 882                                         $server['tablePrefix'] = $this->localDomain->getTablePrefix();
 883                                 }
 884                                 $conn = $this->reallyOpenConnection( $server, $this->localDomain );
 885                                 $host = $this->getServerName( $i );
 886                                 if ( $conn->isOpen() ) {
 887                                         $this->connLogger->debug(
 888                                                 __METHOD__ . ": connected to database $i at '$host'." );
 889                                         $this->conns[$connKey][$i][0] = $conn;
 890                                 } else {
 891                                         $this->connLogger->warning(
 892                                                 __METHOD__ . ": failed to connect to database $i at '$host'." );
 893                                         $this->errorConnection = $conn;
 894                                         $conn = false;
 895                                 }
 896                         }
 897                 }
 898
 899                 if ( $conn instanceof IDatabase && !$conn->isOpen() ) {
 900                         // Connection was made but later unrecoverably lost for some reason.
 901                         // Do not return a handle that will just throw exceptions on use,
 902                         // but let the calling code (e.g. getReaderIndex) try another server.
 903                         // See DatabaseMyslBase::ping() for how this can happen.
 904                         $this->errorConnection = $conn;
 905                         $conn = false;
 906                 }
 907
 908                 if ( $autoCommit && $conn instanceof IDatabase ) {
 909                         $conn->clearFlag( $conn::DBO_TRX ); // auto-commit mode
 910                 }
 911
 912                 return $conn;
 913         }
 914
 915         /**
 916          * Open a connection to a foreign DB, or return one if it is already open.
 917          *
 918          * Increments a reference count on the returned connection which locks the
 919          * connection to the requested domain. This reference count can be
 920          * decremented by calling reuseConnection().
 921          *
 922          * If a connection is open to the appropriate server already, but with the wrong
 923          * database, it will be switched to the right database and returned, as long as
 924          * it has been freed first with reuseConnection().
 925          *
 926          * On error, returns false, and the connection which caused the
 927          * error will be available via $this->errorConnection.
 928          *
 929          * @note If disable() was called on this LoadBalancer, this method will throw a DBAccessError.
 930          *
 931          * @param int $i Server index
 932          * @param string $domain Domain ID to open
 933          * @param int $flags Class CONN_* constant bitfield
 934          * @return Database
 935          */
 936         private function openForeignConnection( $i, $domain, $flags = 0 ) {
 937                 $domainInstance = DatabaseDomain::newFromId( $domain );
 938                 $dbName = $domainInstance->getDatabase();
 939                 $prefix = $domainInstance->getTablePrefix();
 940                 $autoCommit = ( ( $flags & self::CONN_TRX_AUTO ) == self::CONN_TRX_AUTO );
 941
 942                 if ( $autoCommit ) {
 943                         $connFreeKey = self::KEY_FOREIGN_FREE_NOROUND;
 944                         $connInUseKey = self::KEY_FOREIGN_INUSE_NOROUND;
 945                 } else {
 946                         $connFreeKey = self::KEY_FOREIGN_FREE;
 947                         $connInUseKey = self::KEY_FOREIGN_INUSE;
 948                 }
 949
 950                 if ( isset( $this->conns[$connInUseKey][$i][$domain] ) ) {
 951                         // Reuse an in-use connection for the same domain
 952                         $conn = $this->conns[$connInUseKey][$i][$domain];
 953                         $this->connLogger->debug( __METHOD__ . ": reusing connection $i/$domain" );
 954                 } elseif ( isset( $this->conns[$connFreeKey][$i][$domain] ) ) {
 955                         // Reuse a free connection for the same domain
 956                         $conn = $this->conns[$connFreeKey][$i][$domain];
 957                         unset( $this->conns[$connFreeKey][$i][$domain] );
 958                         $this->conns[$connInUseKey][$i][$domain] = $conn;
 959                         $this->connLogger->debug( __METHOD__ . ": reusing free connection $i/$domain" );
 960                 } elseif ( !empty( $this->conns[$connFreeKey][$i] ) ) {
 961                         // Reuse a free connection from another domain
 962                         $conn = reset( $this->conns[$connFreeKey][$i] );
 963                         $oldDomain = key( $this->conns[$connFreeKey][$i] );
 964                         if ( strlen( $dbName ) && !$conn->selectDB( $dbName ) ) {
 965                                 $this->lastError = "Error selecting database '$dbName' on server " .
 966                                         $conn->getServer() . " from client host {$this->host}";
 967                                 $this->errorConnection = $conn;
 968                                 $conn = false;
 969                         } else {
 970                                 $conn->tablePrefix( $prefix );
 971                                 unset( $this->conns[$connFreeKey][$i][$oldDomain] );
 972                                 // Note that if $domain is an empty string, getDomainID() might not match it
 973                                 $this->conns[$connInUseKey][$i][$conn->getDomainId()] = $conn;
 974                                 $this->connLogger->debug( __METHOD__ .
 975                                         ": reusing free connection from $oldDomain for $domain" );
 976                         }
 977                 } else {
 978                         if ( !isset( $this->servers[$i] ) || !is_array( $this->servers[$i] ) ) {
 979                                 throw new InvalidArgumentException( "No server with index '$i'." );
 980                         }
 981                         // Open a new connection
 982                         $server = $this->servers[$i];
 983                         $server['serverIndex'] = $i;
 984                         $server['foreignPoolRefCount'] = 0;
 985                         $server['foreign'] = true;
 986                         $server['autoCommitOnly'] = $autoCommit;
 987                         $conn = $this->reallyOpenConnection( $server, $domainInstance );
 988                         if ( !$conn->isOpen() ) {
 989                                 $this->connLogger->warning( __METHOD__ . ": connection error for $i/$domain" );
 990                                 $this->errorConnection = $conn;
 991                                 $conn = false;
 992                         } else {
 993                                 $conn->tablePrefix( $prefix ); // as specified
 994                                 // Note that if $domain is an empty string, getDomainID() might not match it
 995                                 $this->conns[$connInUseKey][$i][$conn->getDomainID()] = $conn;
 996                                 $this->connLogger->debug( __METHOD__ . ": opened new connection for $i/$domain" );
 997                         }
 998                 }
 999
1000                 // Increment reference count
1001                 if ( $conn instanceof IDatabase ) {
1002                         $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
1003                         $conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
1004                 }
1005
1006                 return $conn;
1007         }
1008
1009         public function getServerAttributes( $i ) {
1010                 return Database::attributesFromType(
1011                         $this->getServerType( $i ),
1012                         isset( $this->servers[$i]['driver'] ) ? $this->servers[$i]['driver'] : null
1013                 );
1014         }
1015
1016         /**
1017          * Test if the specified index represents an open connection
1018          *
1019          * @param int $index Server index
1020          * @access private
1021          * @return bool
1022          */
1023         private function isOpen( $index ) {
1024                 if ( !is_int( $index ) ) {
1025                         return false;
1026                 }
1027
1028                 return (bool)$this->getAnyOpenConnection( $index );
1029         }
1030
1031         /**
1032          * Open a new network connection to a server (uncached)
1033          *
1034          * Returns a Database object whether or not the connection was successful.
1035          *
1036          * @param array $server
1037          * @param DatabaseDomain $domainOverride Use an unspecified domain to not select any database
1038          * @return Database
1039          * @throws DBAccessError
1040          * @throws InvalidArgumentException
1041          */
1042         protected function reallyOpenConnection( array $server, DatabaseDomain $domainOverride ) {
1043                 if ( $this->disabled ) {
1044                         throw new DBAccessError();
1045                 }
1046
1047                 // Handle $domainOverride being a specified or an unspecified domain
1048                 if ( $domainOverride->getDatabase() === null ) {
1049                         // Normally, an RDBMS requires a DB name specified on connection and the $server
1050                         // configuration array is assumed to already specify an appropriate DB name.
1051                         if ( $server['type'] === 'mysql' ) {
1052                                 // For MySQL, DATABASE and SCHEMA are synonyms, connections need not specify a DB,
1053                                 // and the DB name in $server might not exist due to legacy reasons (the default
1054                                 // domain used to ignore the local LB domain, even when mismatched).
1055                                 $server['dbname'] = null;
1056                         }
1057                 } else {
1058                         $server['dbname'] = $domainOverride->getDatabase();
1059                         $server['schema'] = $domainOverride->getSchema();
1060                 }
1061
1062                 // Let the handle know what the cluster master is (e.g. "db1052")
1063                 $masterName = $this->getServerName( $this->getWriterIndex() );
1064                 $server['clusterMasterHost'] = $masterName;
1065
1066                 // Log when many connection are made on requests
1067                 if ( ++$this->connsOpened >= self::CONN_HELD_WARN_THRESHOLD ) {
1068                         $this->perfLogger->warning( __METHOD__ . ": " .
1069                                 "{$this->connsOpened}+ connections made (master=$masterName)" );
1070                 }
1071
1072                 $server['srvCache'] = $this->srvCache;
1073                 // Set loggers and profilers
1074                 $server['connLogger'] = $this->connLogger;
1075                 $server['queryLogger'] = $this->queryLogger;
1076                 $server['errorLogger'] = $this->errorLogger;
1077                 $server['deprecationLogger'] = $this->deprecationLogger;
1078                 $server['profiler'] = $this->profiler;
1079                 $server['trxProfiler'] = $this->trxProfiler;
1080                 // Use the same agent and PHP mode for all DB handles
1081                 $server['cliMode'] = $this->cliMode;
1082                 $server['agent'] = $this->agent;
1083                 // Use DBO_DEFAULT flags by default for LoadBalancer managed databases. Assume that the
1084                 // application calls LoadBalancer::commitMasterChanges() before the PHP script completes.
1085                 $server['flags'] = isset( $server['flags'] ) ? $server['flags'] : IDatabase::DBO_DEFAULT;
1086
1087                 // Create a live connection object
1088                 try {
1089                         $db = Database::factory( $server['type'], $server );
1090                 } catch ( DBConnectionError $e ) {
1091                         // FIXME: This is probably the ugliest thing I have ever done to
1092                         // PHP. I'm half-expecting it to segfault, just out of disgust. -- TS
1093                         $db = $e->db;
1094                 }
1095
1096                 $db->setLBInfo( $server );
1097                 $db->setLazyMasterHandle(
1098                         $this->getLazyConnectionRef( self::DB_MASTER, [], $db->getDomainID() )
1099                 );
1100                 $db->setTableAliases( $this->tableAliases );
1101                 $db->setIndexAliases( $this->indexAliases );
1102
1103                 if ( $server['serverIndex'] === $this->getWriterIndex() ) {
1104                         if ( $this->trxRoundId !== false ) {
1105                                 $this->applyTransactionRoundFlags( $db );
1106                         }
1107                         foreach ( $this->trxRecurringCallbacks as $name => $callback ) {
1108                                 $db->setTransactionListener( $name, $callback );
1109                         }
1110                 }
1111
1112                 return $db;
1113         }
1114
1115         /**
1116          * @throws DBConnectionError
1117          */
1118         private function reportConnectionError() {
1119                 $conn = $this->errorConnection; // the connection which caused the error
1120                 $context = [
1121                         'method' => __METHOD__,
1122                         'last_error' => $this->lastError,
1123                 ];
1124
1125                 if ( $conn instanceof IDatabase ) {
1126                         $context['db_server'] = $conn->getServer();
1127                         $this->connLogger->warning(
1128                                 __METHOD__ . ": connection error: {last_error} ({db_server})",
1129                                 $context
1130                         );
1131
1132                         // throws DBConnectionError
1133                         $conn->reportConnectionError( "{$this->lastError} ({$context['db_server']})" );
1134                 } else {
1135                         // No last connection, probably due to all servers being too busy
1136                         $this->connLogger->error(
1137                                 __METHOD__ .
1138                                 ": LB failure with no last connection. Connection error: {last_error}",
1139                                 $context
1140                         );
1141
1142                         // If all servers were busy, mLastError will contain something sensible
1143                         throw new DBConnectionError( null, $this->lastError );
1144                 }
1145         }
1146
1147         public function getWriterIndex() {
1148                 return 0;
1149         }
1150
1151         public function haveIndex( $i ) {
1152                 return array_key_exists( $i, $this->servers );
1153         }
1154
1155         public function isNonZeroLoad( $i ) {
1156                 return array_key_exists( $i, $this->servers ) && $this->loads[$i] != 0;
1157         }
1158
1159         public function getServerCount() {
1160                 return count( $this->servers );
1161         }
1162
1163         public function getServerName( $i ) {
1164                 if ( isset( $this->servers[$i]['hostName'] ) ) {
1165                         $name = $this->servers[$i]['hostName'];
1166                 } elseif ( isset( $this->servers[$i]['host'] ) ) {
1167                         $name = $this->servers[$i]['host'];
1168                 } else {
1169                         $name = '';
1170                 }
1171
1172                 return ( $name != '' ) ? $name : 'localhost';
1173         }
1174
1175         public function getServerType( $i ) {
1176                 return isset( $this->servers[$i]['type'] ) ? $this->servers[$i]['type'] : 'unknown';
1177         }
1178
1179         public function getMasterPos() {
1180                 # If this entire request was served from a replica DB without opening a connection to the
1181                 # master (however unlikely that may be), then we can fetch the position from the replica DB.
1182                 $masterConn = $this->getAnyOpenConnection( $this->getWriterIndex() );
1183                 if ( !$masterConn ) {
1184                         $serverCount = count( $this->servers );
1185                         for ( $i = 1; $i < $serverCount; $i++ ) {
1186                                 $conn = $this->getAnyOpenConnection( $i );
1187                                 if ( $conn ) {
1188                                         return $conn->getReplicaPos();
1189                                 }
1190                         }
1191                 } else {
1192                         return $masterConn->getMasterPos();
1193                 }
1194
1195                 return false;
1196         }
1197
1198         public function disable() {
1199                 $this->closeAll();
1200                 $this->disabled = true;
1201         }
1202
1203         public function closeAll() {
1204                 $this->forEachOpenConnection( function ( IDatabase $conn ) {
1205                         $host = $conn->getServer();
1206                         $this->connLogger->debug(
1207                                 __METHOD__ . ": closing connection to database '$host'." );
1208                         $conn->close();
1209                 } );
1210
1211                 $this->conns = [
1212                         self::KEY_LOCAL => [],
1213                         self::KEY_FOREIGN_INUSE => [],
1214                         self::KEY_FOREIGN_FREE => [],
1215                         self::KEY_LOCAL_NOROUND => [],
1216                         self::KEY_FOREIGN_INUSE_NOROUND => [],
1217                         self::KEY_FOREIGN_FREE_NOROUND => []
1218                 ];
1219                 $this->connsOpened = 0;
1220         }
1221
1222         public function closeConnection( IDatabase $conn ) {
1223                 $serverIndex = $conn->getLBInfo( 'serverIndex' ); // second index level of mConns
1224                 foreach ( $this->conns as $type => $connsByServer ) {
1225                         if ( !isset( $connsByServer[$serverIndex] ) ) {
1226                                 continue;
1227                         }
1228
1229                         foreach ( $connsByServer[$serverIndex] as $i => $trackedConn ) {
1230                                 if ( $conn === $trackedConn ) {
1231                                         $host = $this->getServerName( $i );
1232                                         $this->connLogger->debug(
1233                                                 __METHOD__ . ": closing connection to database $i at '$host'." );
1234                                         unset( $this->conns[$type][$serverIndex][$i] );
1235                                         --$this->connsOpened;
1236                                         break 2;
1237                                 }
1238                         }
1239                 }
1240
1241                 $conn->close();
1242         }
1243
1244         public function commitAll( $fname = __METHOD__ ) {
1245                 $failures = [];
1246
1247                 $restore = ( $this->trxRoundId !== false );
1248                 $this->trxRoundId = false;
1249                 $this->forEachOpenConnection(
1250                         function ( IDatabase $conn ) use ( $fname, $restore, &$failures ) {
1251                                 try {
1252                                         $conn->commit( $fname, $conn::FLUSHING_ALL_PEERS );
1253                                 } catch ( DBError $e ) {
1254                                         call_user_func( $this->errorLogger, $e );
1255                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1256                                 }
1257                                 if ( $restore && $conn->getLBInfo( 'master' ) ) {
1258                                         $this->undoTransactionRoundFlags( $conn );
1259                                 }
1260                         }
1261                 );
1262
1263                 if ( $failures ) {
1264                         throw new DBExpectedError(
1265                                 null,
1266                                 "Commit failed on server(s) " . implode( "\n", array_unique( $failures ) )
1267                         );
1268                 }
1269         }
1270
1271         public function finalizeMasterChanges() {
1272                 $this->forEachOpenMasterConnection( function ( Database $conn ) {
1273                         // Any error should cause all DB transactions to be rolled back together
1274                         $conn->setTrxEndCallbackSuppression( false );
1275                         $conn->runOnTransactionPreCommitCallbacks();
1276                         // Defer post-commit callbacks until COMMIT finishes for all DBs
1277                         $conn->setTrxEndCallbackSuppression( true );
1278                 } );
1279         }
1280
1281         public function approveMasterChanges( array $options ) {
1282                 $limit = isset( $options['maxWriteDuration'] ) ? $options['maxWriteDuration'] : 0;
1283                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( $limit ) {
1284                         // If atomic sections or explicit transactions are still open, some caller must have
1285                         // caught an exception but failed to properly rollback any changes. Detect that and
1286                         // throw and error (causing rollback).
1287                         if ( $conn->explicitTrxActive() ) {
1288                                 throw new DBTransactionError(
1289                                         $conn,
1290                                         "Explicit transaction still active. A caller may have caught an error."
1291                                 );
1292                         }
1293                         // Assert that the time to replicate the transaction will be sane.
1294                         // If this fails, then all DB transactions will be rollback back together.
1295                         $time = $conn->pendingWriteQueryDuration( $conn::ESTIMATE_DB_APPLY );
1296                         if ( $limit > 0 && $time > $limit ) {
1297                                 throw new DBTransactionSizeError(
1298                                         $conn,
1299                                         "Transaction spent $time second(s) in writes, exceeding the limit of $limit.",
1300                                         [ $time, $limit ]
1301                                 );
1302                         }
1303                         // If a connection sits idle while slow queries execute on another, that connection
1304                         // may end up dropped before the commit round is reached. Ping servers to detect this.
1305                         if ( $conn->writesOrCallbacksPending() && !$conn->ping() ) {
1306                                 throw new DBTransactionError(
1307                                         $conn,
1308                                         "A connection to the {$conn->getDBname()} database was lost before commit."
1309                                 );
1310                         }
1311                 } );
1312         }
1313
1314         public function beginMasterChanges( $fname = __METHOD__ ) {
1315                 if ( $this->trxRoundId !== false ) {
1316                         throw new DBTransactionError(
1317                                 null,
1318                                 "$fname: Transaction round '{$this->trxRoundId}' already started."
1319                         );
1320                 }
1321                 $this->trxRoundId = $fname;
1322
1323                 $failures = [];
1324                 $this->forEachOpenMasterConnection(
1325                         function ( Database $conn ) use ( $fname, &$failures ) {
1326                                 $conn->setTrxEndCallbackSuppression( true );
1327                                 try {
1328                                         $conn->flushSnapshot( $fname );
1329                                 } catch ( DBError $e ) {
1330                                         call_user_func( $this->errorLogger, $e );
1331                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1332                                 }
1333                                 $conn->setTrxEndCallbackSuppression( false );
1334                                 $this->applyTransactionRoundFlags( $conn );
1335                         }
1336                 );
1337
1338                 if ( $failures ) {
1339                         throw new DBExpectedError(
1340                                 null,
1341                                 "$fname: Flush failed on server(s) " . implode( "\n", array_unique( $failures ) )
1342                         );
1343                 }
1344         }
1345
1346         public function commitMasterChanges( $fname = __METHOD__ ) {
1347                 $failures = [];
1348
1349                 /** @noinspection PhpUnusedLocalVariableInspection */
1350                 $scope = $this->getScopedPHPBehaviorForCommit(); // try to ignore client aborts
1351
1352                 $restore = ( $this->trxRoundId !== false );
1353                 $this->trxRoundId = false;
1354                 $this->forEachOpenMasterConnection(
1355                         function ( IDatabase $conn ) use ( $fname, $restore, &$failures ) {
1356                                 try {
1357                                         if ( $conn->writesOrCallbacksPending() ) {
1358                                                 $conn->commit( $fname, $conn::FLUSHING_ALL_PEERS );
1359                                         } elseif ( $restore ) {
1360                                                 $conn->flushSnapshot( $fname );
1361                                         }
1362                                 } catch ( DBError $e ) {
1363                                         call_user_func( $this->errorLogger, $e );
1364                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1365                                 }
1366                                 if ( $restore ) {
1367                                         $this->undoTransactionRoundFlags( $conn );
1368                                 }
1369                         }
1370                 );
1371
1372                 if ( $failures ) {
1373                         throw new DBExpectedError(
1374                                 null,
1375                                 "$fname: Commit failed on server(s) " . implode( "\n", array_unique( $failures ) )
1376                         );
1377                 }
1378         }
1379
1380         public function runMasterPostTrxCallbacks( $type ) {
1381                 $e = null; // first exception
1382                 $this->forEachOpenMasterConnection( function ( Database $conn ) use ( $type, &$e ) {
1383                         $conn->setTrxEndCallbackSuppression( false );
1384                         // Callbacks run in AUTO-COMMIT mode, so make sure no transactions are pending...
1385                         if ( $conn->writesPending() ) {
1386                                 // This happens if onTransactionIdle() callbacks write to *other* handles
1387                                 // (which already finished their callbacks). Let any callbacks run in the final
1388                                 // commitMasterChanges() in LBFactory::shutdown(), when the transaction is gone.
1389                                 $this->queryLogger->warning( __METHOD__ . ": found writes pending." );
1390                                 return;
1391                         } elseif ( $conn->trxLevel() ) {
1392                                 // This happens for single-DB setups where DB_REPLICA uses the master DB,
1393                                 // thus leaving an implicit read-only transaction open at this point. It
1394                                 // also happens if onTransactionIdle() callbacks leave implicit transactions
1395                                 // open on *other* DBs (which is slightly improper). Let these COMMIT on the
1396                                 // next call to commitMasterChanges(), possibly in LBFactory::shutdown().
1397                                 return;
1398                         }
1399                         try {
1400                                 $conn->runOnTransactionIdleCallbacks( $type );
1401                         } catch ( Exception $ex ) {
1402                                 $e = $e ?: $ex;
1403                         }
1404                         try {
1405                                 $conn->runTransactionListenerCallbacks( $type );
1406                         } catch ( Exception $ex ) {
1407                                 $e = $e ?: $ex;
1408                         }
1409                 } );
1410
1411                 return $e;
1412         }
1413
1414         public function rollbackMasterChanges( $fname = __METHOD__ ) {
1415                 $restore = ( $this->trxRoundId !== false );
1416                 $this->trxRoundId = false;
1417                 $this->forEachOpenMasterConnection(
1418                         function ( IDatabase $conn ) use ( $fname, $restore ) {
1419                                 $conn->rollback( $fname, $conn::FLUSHING_ALL_PEERS );
1420                                 if ( $restore ) {
1421                                         $this->undoTransactionRoundFlags( $conn );
1422                                 }
1423                         }
1424                 );
1425         }
1426
1427         public function suppressTransactionEndCallbacks() {
1428                 $this->forEachOpenMasterConnection( function ( Database $conn ) {
1429                         $conn->setTrxEndCallbackSuppression( true );
1430                 } );
1431         }
1432
1433         /**
1434          * Make all DB servers with DBO_DEFAULT/DBO_TRX set join the transaction round
1435          *
1436          * Some servers may have neither flag enabled, meaning that they opt out of such
1437          * transaction rounds and remain in auto-commit mode. Such behavior might be desired
1438          * when a DB server is used for something like simple key/value storage.
1439          *
1440          * @param IDatabase $conn
1441          */
1442         private function applyTransactionRoundFlags( IDatabase $conn ) {
1443                 if ( $conn->getLBInfo( 'autoCommitOnly' ) ) {
1444                         return; // transaction rounds do not apply to these connections
1445                 }
1446
1447                 if ( $conn->getFlag( $conn::DBO_DEFAULT ) ) {
1448                         // DBO_TRX is controlled entirely by CLI mode presence with DBO_DEFAULT.
1449                         // Force DBO_TRX even in CLI mode since a commit round is expected soon.
1450                         $conn->setFlag( $conn::DBO_TRX, $conn::REMEMBER_PRIOR );
1451                 }
1452
1453                 if ( $conn->getFlag( $conn::DBO_TRX ) ) {
1454                         $conn->setLBInfo( 'trxRoundId', $this->trxRoundId );
1455                 }
1456         }
1457
1458         /**
1459          * @param IDatabase $conn
1460          */
1461         private function undoTransactionRoundFlags( IDatabase $conn ) {
1462                 if ( $conn->getLBInfo( 'autoCommitOnly' ) ) {
1463                         return; // transaction rounds do not apply to these connections
1464                 }
1465
1466                 if ( $conn->getFlag( $conn::DBO_TRX ) ) {
1467                         $conn->setLBInfo( 'trxRoundId', false );
1468                 }
1469
1470                 if ( $conn->getFlag( $conn::DBO_DEFAULT ) ) {
1471                         $conn->restoreFlags( $conn::RESTORE_PRIOR );
1472                 }
1473         }
1474
1475         public function flushReplicaSnapshots( $fname = __METHOD__ ) {
1476                 $this->forEachOpenReplicaConnection( function ( IDatabase $conn ) {
1477                         $conn->flushSnapshot( __METHOD__ );
1478                 } );
1479         }
1480
1481         public function hasMasterConnection() {
1482                 return $this->isOpen( $this->getWriterIndex() );
1483         }
1484
1485         public function hasMasterChanges() {
1486                 $pending = 0;
1487                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$pending ) {
1488                         $pending |= $conn->writesOrCallbacksPending();
1489                 } );
1490
1491                 return (bool)$pending;
1492         }
1493
1494         public function lastMasterChangeTimestamp() {
1495                 $lastTime = false;
1496                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$lastTime ) {
1497                         $lastTime = max( $lastTime, $conn->lastDoneWrites() );
1498                 } );
1499
1500                 return $lastTime;
1501         }
1502
1503         public function hasOrMadeRecentMasterChanges( $age = null ) {
1504                 $age = ( $age === null ) ? $this->waitTimeout : $age;
1505
1506                 return ( $this->hasMasterChanges()
1507                         || $this->lastMasterChangeTimestamp() > microtime( true ) - $age );
1508         }
1509
1510         public function pendingMasterChangeCallers() {
1511                 $fnames = [];
1512                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$fnames ) {
1513                         $fnames = array_merge( $fnames, $conn->pendingWriteCallers() );
1514                 } );
1515
1516                 return $fnames;
1517         }
1518
1519         public function getLaggedReplicaMode( $domain = false ) {
1520                 // No-op if there is only one DB (also avoids recursion)
1521                 if ( !$this->laggedReplicaMode && $this->getServerCount() > 1 ) {
1522                         try {
1523                                 // See if laggedReplicaMode gets set
1524                                 $conn = $this->getConnection( self::DB_REPLICA, false, $domain );
1525                                 $this->reuseConnection( $conn );
1526                         } catch ( DBConnectionError $e ) {
1527                                 // Avoid expensive re-connect attempts and failures
1528                                 $this->allReplicasDownMode = true;
1529                                 $this->laggedReplicaMode = true;
1530                         }
1531                 }
1532
1533                 return $this->laggedReplicaMode;
1534         }
1535
1536         /**
1537          * @param bool $domain
1538          * @return bool
1539          * @deprecated 1.28; use getLaggedReplicaMode()
1540          */
1541         public function getLaggedSlaveMode( $domain = false ) {
1542                 return $this->getLaggedReplicaMode( $domain );
1543         }
1544
1545         public function laggedReplicaUsed() {
1546                 return $this->laggedReplicaMode;
1547         }
1548
1549         /**
1550          * @return bool
1551          * @since 1.27
1552          * @deprecated Since 1.28; use laggedReplicaUsed()
1553          */
1554         public function laggedSlaveUsed() {
1555                 return $this->laggedReplicaUsed();
1556         }
1557
1558         public function getReadOnlyReason( $domain = false, IDatabase $conn = null ) {
1559                 if ( $this->readOnlyReason !== false ) {
1560                         return $this->readOnlyReason;
1561                 } elseif ( $this->getLaggedReplicaMode( $domain ) ) {
1562                         if ( $this->allReplicasDownMode ) {
1563                                 return 'The database has been automatically locked ' .
1564                                         'until the replica database servers become available';
1565                         } else {
1566                                 return 'The database has been automatically locked ' .
1567                                         'while the replica database servers catch up to the master.';
1568                         }
1569                 } elseif ( $this->masterRunningReadOnly( $domain, $conn ) ) {
1570                         return 'The database master is running in read-only mode.';
1571                 }
1572
1573                 return false;
1574         }
1575
1576         /**
1577          * @param string $domain Domain ID, or false for the current domain
1578          * @param IDatabase|null $conn DB master connectionl used to avoid loops [optional]
1579          * @return bool
1580          */
1581         private function masterRunningReadOnly( $domain, IDatabase $conn = null ) {
1582                 $cache = $this->wanCache;
1583                 $masterServer = $this->getServerName( $this->getWriterIndex() );
1584
1585                 return (bool)$cache->getWithSetCallback(
1586                         $cache->makeGlobalKey( __CLASS__, 'server-read-only', $masterServer ),
1587                         self::TTL_CACHE_READONLY,
1588                         function () use ( $domain, $conn ) {
1589                                 $old = $this->trxProfiler->setSilenced( true );
1590                                 try {
1591                                         $dbw = $conn ?: $this->getConnection( self::DB_MASTER, [], $domain );
1592                                         $readOnly = (int)$dbw->serverIsReadOnly();
1593                                         if ( !$conn ) {
1594                                                 $this->reuseConnection( $dbw );
1595                                         }
1596                                 } catch ( DBError $e ) {
1597                                         $readOnly = 0;
1598                                 }
1599                                 $this->trxProfiler->setSilenced( $old );
1600                                 return $readOnly;
1601                         },
1602                         [ 'pcTTL' => $cache::TTL_PROC_LONG, 'busyValue' => 0 ]
1603                 );
1604         }
1605
1606         public function allowLagged( $mode = null ) {
1607                 if ( $mode === null ) {
1608                         return $this->allowLagged;
1609                 }
1610                 $this->allowLagged = $mode;
1611
1612                 return $this->allowLagged;
1613         }
1614
1615         public function pingAll() {
1616                 $success = true;
1617                 $this->forEachOpenConnection( function ( IDatabase $conn ) use ( &$success ) {
1618                         if ( !$conn->ping() ) {
1619                                 $success = false;
1620                         }
1621                 } );
1622
1623                 return $success;
1624         }
1625
1626         public function forEachOpenConnection( $callback, array $params = [] ) {
1627                 foreach ( $this->conns as $connsByServer ) {
1628                         foreach ( $connsByServer as $serverConns ) {
1629                                 foreach ( $serverConns as $conn ) {
1630                                         $mergedParams = array_merge( [ $conn ], $params );
1631                                         call_user_func_array( $callback, $mergedParams );
1632                                 }
1633                         }
1634                 }
1635         }
1636
1637         public function forEachOpenMasterConnection( $callback, array $params = [] ) {
1638                 $masterIndex = $this->getWriterIndex();
1639                 foreach ( $this->conns as $connsByServer ) {
1640                         if ( isset( $connsByServer[$masterIndex] ) ) {
1641                                 /** @var IDatabase $conn */
1642                                 foreach ( $connsByServer[$masterIndex] as $conn ) {
1643                                         $mergedParams = array_merge( [ $conn ], $params );
1644                                         call_user_func_array( $callback, $mergedParams );
1645                                 }
1646                         }
1647                 }
1648         }
1649
1650         public function forEachOpenReplicaConnection( $callback, array $params = [] ) {
1651                 foreach ( $this->conns as $connsByServer ) {
1652                         foreach ( $connsByServer as $i => $serverConns ) {
1653                                 if ( $i === $this->getWriterIndex() ) {
1654                                         continue; // skip master
1655                                 }
1656                                 foreach ( $serverConns as $conn ) {
1657                                         $mergedParams = array_merge( [ $conn ], $params );
1658                                         call_user_func_array( $callback, $mergedParams );
1659                                 }
1660                         }
1661                 }
1662         }
1663
1664         public function getMaxLag( $domain = false ) {
1665                 $maxLag = -1;
1666                 $host = '';
1667                 $maxIndex = 0;
1668
1669                 if ( $this->getServerCount() <= 1 ) {
1670                         return [ $host, $maxLag, $maxIndex ]; // no replication = no lag
1671                 }
1672
1673                 $lagTimes = $this->getLagTimes( $domain );
1674                 foreach ( $lagTimes as $i => $lag ) {
1675                         if ( $this->loads[$i] > 0 && $lag > $maxLag ) {
1676                                 $maxLag = $lag;
1677                                 $host = $this->servers[$i]['host'];
1678                                 $maxIndex = $i;
1679                         }
1680                 }
1681
1682                 return [ $host, $maxLag, $maxIndex ];
1683         }
1684
1685         public function getLagTimes( $domain = false ) {
1686                 if ( $this->getServerCount() <= 1 ) {
1687                         return [ $this->getWriterIndex() => 0 ]; // no replication = no lag
1688                 }
1689
1690                 $knownLagTimes = []; // map of (server index => 0 seconds)
1691                 $indexesWithLag = [];
1692                 foreach ( $this->servers as $i => $server ) {
1693                         if ( empty( $server['is static'] ) ) {
1694                                 $indexesWithLag[] = $i; // DB server might have replication lag
1695                         } else {
1696                                 $knownLagTimes[$i] = 0; // DB server is a non-replicating and read-only archive
1697                         }
1698                 }
1699
1700                 return $this->getLoadMonitor()->getLagTimes( $indexesWithLag, $domain ) + $knownLagTimes;
1701         }
1702
1703         public function safeGetLag( IDatabase $conn ) {
1704                 if ( $this->getServerCount() <= 1 ) {
1705                         return 0;
1706                 } else {
1707                         return $conn->getLag();
1708                 }
1709         }
1710
1711         /**
1712          * @param IDatabase $conn
1713          * @param DBMasterPos|bool $pos
1714          * @param int|null $timeout
1715          * @return bool
1716          */
1717         public function safeWaitForMasterPos( IDatabase $conn, $pos = false, $timeout = null ) {
1718                 $timeout = max( 1, $timeout ?: $this->waitTimeout );
1719
1720                 if ( $this->getServerCount() <= 1 || !$conn->getLBInfo( 'replica' ) ) {
1721                         return true; // server is not a replica DB
1722                 }
1723
1724                 if ( !$pos ) {
1725                         // Get the current master position, opening a connection if needed
1726                         $masterConn = $this->getAnyOpenConnection( $this->getWriterIndex() );
1727                         if ( $masterConn ) {
1728                                 $pos = $masterConn->getMasterPos();
1729                         } else {
1730                                 $masterConn = $this->openConnection( $this->getWriterIndex(), self::DOMAIN_ANY );
1731                                 $pos = $masterConn->getMasterPos();
1732                                 $this->closeConnection( $masterConn );
1733                         }
1734                 }
1735
1736                 if ( $pos instanceof DBMasterPos ) {
1737                         $result = $conn->masterPosWait( $pos, $timeout );
1738                         if ( $result == -1 || is_null( $result ) ) {
1739                                 $msg = __METHOD__ . ': timed out waiting on {host} pos {pos}';
1740                                 $this->replLogger->warning( $msg, [
1741                                         'host' => $conn->getServer(),
1742                                         'pos' => $pos,
1743                                         'trace' => ( new RuntimeException() )->getTraceAsString()
1744                                 ] );
1745                                 $ok = false;
1746                         } else {
1747                                 $this->replLogger->debug( __METHOD__ . ': done waiting' );
1748                                 $ok = true;
1749                         }
1750                 } else {
1751                         $ok = false; // something is misconfigured
1752                         $this->replLogger->error(
1753                                 __METHOD__ . ': could not get master pos for {host}',
1754                                 [
1755                                         'host' => $conn->getServer(),
1756                                         'trace' => ( new RuntimeException() )->getTraceAsString()
1757                                 ]
1758                         );
1759                 }
1760
1761                 return $ok;
1762         }
1763
1764         public function setTransactionListener( $name, callable $callback = null ) {
1765                 if ( $callback ) {
1766                         $this->trxRecurringCallbacks[$name] = $callback;
1767                 } else {
1768                         unset( $this->trxRecurringCallbacks[$name] );
1769                 }
1770                 $this->forEachOpenMasterConnection(
1771                         function ( IDatabase $conn ) use ( $name, $callback ) {
1772                                 $conn->setTransactionListener( $name, $callback );
1773                         }
1774                 );
1775         }
1776
1777         public function setTableAliases( array $aliases ) {
1778                 $this->tableAliases = $aliases;
1779         }
1780
1781         public function setIndexAliases( array $aliases ) {
1782                 $this->indexAliases = $aliases;
1783         }
1784
1785         public function setDomainPrefix( $prefix ) {
1786                 // Find connections to explicit foreign domains still marked as in-use...
1787                 $domainsInUse = [];
1788                 $this->forEachOpenConnection( function ( IDatabase $conn ) use ( &$domainsInUse ) {
1789                         // Once reuseConnection() is called on a handle, its reference count goes from 1 to 0.
1790                         // Until then, it is still in use by the caller (explicitly or via DBConnRef scope).
1791                         if ( $conn->getLBInfo( 'foreignPoolRefCount' ) > 0 ) {
1792                                 $domainsInUse[] = $conn->getDomainID();
1793                         }
1794                 } );
1795
1796                 // Do not switch connections to explicit foreign domains unless marked as safe
1797                 if ( $domainsInUse ) {
1798                         $domains = implode( ', ', $domainsInUse );
1799                         throw new DBUnexpectedError( null,
1800                                 "Foreign domain connections are still in use ($domains)." );
1801                 }
1802
1803                 $oldDomain = $this->localDomain->getId();
1804                 $this->setLocalDomain( new DatabaseDomain(
1805                         $this->localDomain->getDatabase(),
1806                         $this->localDomain->getSchema(),
1807                         $prefix
1808                 ) );
1809
1810                 $this->forEachOpenConnection( function ( IDatabase $db ) use ( $prefix, $oldDomain ) {
1811                         if ( !$db->getLBInfo( 'foreign' ) ) {
1812                                 $db->tablePrefix( $prefix );
1813                         }
1814                 } );
1815         }
1816
1817         /**
1818          * @param DatabaseDomain $domain
1819          */
1820         private function setLocalDomain( DatabaseDomain $domain ) {
1821                 $this->localDomain = $domain;
1822                 // In case a caller assumes that the domain ID is simply <db>-<prefix>, which is almost
1823                 // always true, gracefully handle the case when they fail to account for escaping.
1824                 if ( $this->localDomain->getTablePrefix() != '' ) {
1825                         $this->localDomainIdAlias =
1826                                 $this->localDomain->getDatabase() . '-' . $this->localDomain->getTablePrefix();
1827                 } else {
1828                         $this->localDomainIdAlias = $this->localDomain->getDatabase();
1829                 }
1830         }
1831
1832         /**
1833          * Make PHP ignore user aborts/disconnects until the returned
1834          * value leaves scope. This returns null and does nothing in CLI mode.
1835          *
1836          * @return ScopedCallback|null
1837          */
1838         final protected function getScopedPHPBehaviorForCommit() {
1839                 if ( PHP_SAPI != 'cli' ) { // https://bugs.php.net/bug.php?id=47540
1840                         $old = ignore_user_abort( true ); // avoid half-finished operations
1841                         return new ScopedCallback( function () use ( $old ) {
1842                                 ignore_user_abort( $old );
1843                         } );
1844                 }
1845
1846                 return null;
1847         }
1848
1849         function __destruct() {
1850                 // Avoid connection leaks for sanity
1851                 $this->disable();
1852         }
1853 }
1854
1855 class_alias( LoadBalancer::class, 'LoadBalancer' );