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