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