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  * @ingroup Database
  22  */
  23 namespace Wikimedia\Rdbms;
  24
  25 use Psr\Log\LoggerInterface;
  26 use Psr\Log\NullLogger;
  27 use Wikimedia\ScopedCallback;
  28 use Database;
  29 use DBConnRef;
  30 use MaintainableDBConnRef;
  31 use BagOStuff;
  32 use EmptyBagOStuff;
  33 use WANObjectCache;
  34 use ArrayUtils;
  35 use DBError;
  36 use DBAccessError;
  37 use DBExpectedError;
  38 use DBUnexpectedError;
  39 use DBTransactionError;
  40 use DBTransactionSizeError;
  41 use DBConnectionError;
  42 use InvalidArgumentException;
  43 use RuntimeException;
  44 use Exception;
  45
  46 /**
  47  * Database connection, tracking, load balancing, and transaction manager for a cluster
  48  *
  49  * @ingroup Database
  50  */
  51 class LoadBalancer implements ILoadBalancer {
  52         /** @var array[] Map of (server index => server config array) */
  53         private $mServers;
  54         /** @var \Database[][][] Map of local/foreignUsed/foreignFree => server index => IDatabase array */
  55         private $mConns;
  56         /** @var float[] Map of (server index => weight) */
  57         private $mLoads;
  58         /** @var array[] Map of (group => server index => weight) */
  59         private $mGroupLoads;
  60         /** @var bool Whether to disregard replica DB lag as a factor in replica DB selection */
  61         private $mAllowLagged;
  62         /** @var integer Seconds to spend waiting on replica DB lag to resolve */
  63         private $mWaitTimeout;
  64         /** @var array The LoadMonitor configuration */
  65         private $loadMonitorConfig;
  66         /** @var array[] $aliases Map of (table => (dbname, schema, prefix) map) */
  67         private $tableAliases = [];
  68
  69         /** @var ILoadMonitor */
  70         private $loadMonitor;
  71         /** @var BagOStuff */
  72         private $srvCache;
  73         /** @var BagOStuff */
  74         private $memCache;
  75         /** @var WANObjectCache */
  76         private $wanCache;
  77         /** @var object|string Class name or object With profileIn/profileOut methods */
  78         protected $profiler;
  79         /** @var TransactionProfiler */
  80         protected $trxProfiler;
  81         /** @var LoggerInterface */
  82         protected $replLogger;
  83         /** @var LoggerInterface */
  84         protected $connLogger;
  85         /** @var LoggerInterface */
  86         protected $queryLogger;
  87         /** @var LoggerInterface */
  88         protected $perfLogger;
  89
  90         /** @var \Database Database connection that caused a problem */
  91         private $errorConnection;
  92         /** @var integer The generic (not query grouped) replica DB index (of $mServers) */
  93         private $mReadIndex;
  94         /** @var bool|DBMasterPos False if not set */
  95         private $mWaitForPos;
  96         /** @var bool Whether the generic reader fell back to a lagged replica DB */
  97         private $laggedReplicaMode = false;
  98         /** @var bool Whether the generic reader fell back to a lagged replica DB */
  99         private $allReplicasDownMode = false;
 100         /** @var string The last DB selection or connection error */
 101         private $mLastError = 'Unknown error';
 102         /** @var string|bool Reason the LB is read-only or false if not */
 103         private $readOnlyReason = false;
 104         /** @var integer Total connections opened */
 105         private $connsOpened = 0;
 106         /** @var string|bool String if a requested DBO_TRX transaction round is active */
 107         private $trxRoundId = false;
 108         /** @var array[] Map of (name => callable) */
 109         private $trxRecurringCallbacks = [];
 110         /** @var DatabaseDomain Local Domain ID and default for selectDB() calls */
 111         private $localDomain;
 112         /** @var string Alternate ID string for the domain instead of DatabaseDomain::getId() */
 113         private $localDomainIdAlias;
 114         /** @var string Current server name */
 115         private $host;
 116         /** @var bool Whether this PHP instance is for a CLI script */
 117         protected $cliMode;
 118         /** @var string Agent name for query profiling */
 119         protected $agent;
 120
 121         /** @var callable Exception logger */
 122         private $errorLogger;
 123
 124         /** @var boolean */
 125         private $disabled = false;
 126
 127         /** @var integer Warn when this many connection are held */
 128         const CONN_HELD_WARN_THRESHOLD = 10;
 129
 130         /** @var integer Default 'max lag' when unspecified */
 131         const MAX_LAG_DEFAULT = 10;
 132         /** @var integer Seconds to cache master server read-only status */
 133         const TTL_CACHE_READONLY = 5;
 134
 135         public function __construct( array $params ) {
 136                 if ( !isset( $params['servers'] ) ) {
 137                         throw new InvalidArgumentException( __CLASS__ . ': missing servers parameter' );
 138                 }
 139                 $this->mServers = $params['servers'];
 140
 141                 $this->localDomain = isset( $params['localDomain'] )
 142                         ? DatabaseDomain::newFromId( $params['localDomain'] )
 143                         : DatabaseDomain::newUnspecified();
 144                 // In case a caller assumes that the domain ID is simply <db>-<prefix>, which is almost
 145                 // always true, gracefully handle the case when they fail to account for escaping.
 146                 if ( $this->localDomain->getTablePrefix() != '' ) {
 147                         $this->localDomainIdAlias =
 148                                 $this->localDomain->getDatabase() . '-' . $this->localDomain->getTablePrefix();
 149                 } else {
 150                         $this->localDomainIdAlias = $this->localDomain->getDatabase();
 151                 }
 152
 153                 $this->mWaitTimeout = isset( $params['waitTimeout'] ) ? $params['waitTimeout'] : 10;
 154
 155                 $this->mReadIndex = -1;
 156                 $this->mConns = [
 157                         'local'       => [],
 158                         'foreignUsed' => [],
 159                         'foreignFree' => []
 160                 ];
 161                 $this->mLoads = [];
 162                 $this->mWaitForPos = false;
 163                 $this->mAllowLagged = false;
 164
 165                 if ( isset( $params['readOnlyReason'] ) && is_string( $params['readOnlyReason'] ) ) {
 166                         $this->readOnlyReason = $params['readOnlyReason'];
 167                 }
 168
 169                 if ( isset( $params['loadMonitor'] ) ) {
 170                         $this->loadMonitorConfig = $params['loadMonitor'];
 171                 } else {
 172                         $this->loadMonitorConfig = [ 'class' => 'LoadMonitorNull' ];
 173                 }
 174
 175                 foreach ( $params['servers'] as $i => $server ) {
 176                         $this->mLoads[$i] = $server['load'];
 177                         if ( isset( $server['groupLoads'] ) ) {
 178                                 foreach ( $server['groupLoads'] as $group => $ratio ) {
 179                                         if ( !isset( $this->mGroupLoads[$group] ) ) {
 180                                                 $this->mGroupLoads[$group] = [];
 181                                         }
 182                                         $this->mGroupLoads[$group][$i] = $ratio;
 183                                 }
 184                         }
 185                 }
 186
 187                 if ( isset( $params['srvCache'] ) ) {
 188                         $this->srvCache = $params['srvCache'];
 189                 } else {
 190                         $this->srvCache = new EmptyBagOStuff();
 191                 }
 192                 if ( isset( $params['memCache'] ) ) {
 193                         $this->memCache = $params['memCache'];
 194                 } else {
 195                         $this->memCache = new EmptyBagOStuff();
 196                 }
 197                 if ( isset( $params['wanCache'] ) ) {
 198                         $this->wanCache = $params['wanCache'];
 199                 } else {
 200                         $this->wanCache = WANObjectCache::newEmpty();
 201                 }
 202                 $this->profiler = isset( $params['profiler'] ) ? $params['profiler'] : null;
 203                 if ( isset( $params['trxProfiler'] ) ) {
 204                         $this->trxProfiler = $params['trxProfiler'];
 205                 } else {
 206                         $this->trxProfiler = new TransactionProfiler();
 207                 }
 208
 209                 $this->errorLogger = isset( $params['errorLogger'] )
 210                         ? $params['errorLogger']
 211                         : function ( Exception $e ) {
 212                                 trigger_error( get_class( $e ) . ': ' . $e->getMessage(), E_USER_WARNING );
 213                         };
 214
 215                 foreach ( [ 'replLogger', 'connLogger', 'queryLogger', 'perfLogger' ] as $key ) {
 216                         $this->$key = isset( $params[$key] ) ? $params[$key] : new NullLogger();
 217                 }
 218
 219                 $this->host = isset( $params['hostname'] )
 220                         ? $params['hostname']
 221                         : ( gethostname() ?: 'unknown' );
 222                 $this->cliMode = isset( $params['cliMode'] ) ? $params['cliMode'] : PHP_SAPI === 'cli';
 223                 $this->agent = isset( $params['agent'] ) ? $params['agent'] : '';
 224         }
 225
 226         /**
 227          * Get a LoadMonitor instance
 228          *
 229          * @return ILoadMonitor
 230          */
 231         private function getLoadMonitor() {
 232                 if ( !isset( $this->loadMonitor ) ) {
 233                         $compat = [
 234                                 'LoadMonitor' => LoadMonitor::class,
 235                                 'LoadMonitorNull' => LoadMonitorNull::class,
 236                                 'LoadMonitorMySQL' => LoadMonitorMySQL::class,
 237                         ];
 238
 239                         $class = $this->loadMonitorConfig['class'];
 240                         if ( isset( $compat[$class] ) ) {
 241                                 $class = $compat[$class];
 242                         }
 243
 244                         $this->loadMonitor = new $class(
 245                                 $this, $this->srvCache, $this->memCache, $this->loadMonitorConfig );
 246                         $this->loadMonitor->setLogger( $this->replLogger );
 247                 }
 248
 249                 return $this->loadMonitor;
 250         }
 251
 252         /**
 253          * @param array $loads
 254          * @param bool|string $domain Domain to get non-lagged for
 255          * @param int $maxLag Restrict the maximum allowed lag to this many seconds
 256          * @return bool|int|string
 257          */
 258         private function getRandomNonLagged( array $loads, $domain = false, $maxLag = INF ) {
 259                 $lags = $this->getLagTimes( $domain );
 260
 261                 # Unset excessively lagged servers
 262                 foreach ( $lags as $i => $lag ) {
 263                         if ( $i != 0 ) {
 264                                 # How much lag this server nominally is allowed to have
 265                                 $maxServerLag = isset( $this->mServers[$i]['max lag'] )
 266                                         ? $this->mServers[$i]['max lag']
 267                                         : self::MAX_LAG_DEFAULT; // default
 268                                 # Constrain that futher by $maxLag argument
 269                                 $maxServerLag = min( $maxServerLag, $maxLag );
 270
 271                                 $host = $this->getServerName( $i );
 272                                 if ( $lag === false && !is_infinite( $maxServerLag ) ) {
 273                                         $this->replLogger->error(
 274                                                 "Server {host} (#$i) is not replicating?", [ 'host' => $host ] );
 275                                         unset( $loads[$i] );
 276                                 } elseif ( $lag > $maxServerLag ) {
 277                                         $this->replLogger->warning(
 278                                                 "Server {host} (#$i) has {lag} seconds of lag (>= {maxlag})",
 279                                                 [ 'host' => $host, 'lag' => $lag, 'maxlag' => $maxServerLag ]
 280                                         );
 281                                         unset( $loads[$i] );
 282                                 }
 283                         }
 284                 }
 285
 286                 # Find out if all the replica DBs with non-zero load are lagged
 287                 $sum = 0;
 288                 foreach ( $loads as $load ) {
 289                         $sum += $load;
 290                 }
 291                 if ( $sum == 0 ) {
 292                         # No appropriate DB servers except maybe the master and some replica DBs with zero load
 293                         # Do NOT use the master
 294                         # Instead, this function will return false, triggering read-only mode,
 295                         # and a lagged replica DB will be used instead.
 296                         return false;
 297                 }
 298
 299                 if ( count( $loads ) == 0 ) {
 300                         return false;
 301                 }
 302
 303                 # Return a random representative of the remainder
 304                 return ArrayUtils::pickRandom( $loads );
 305         }
 306
 307         public function getReaderIndex( $group = false, $domain = false ) {
 308                 if ( count( $this->mServers ) == 1 ) {
 309                         # Skip the load balancing if there's only one server
 310                         return $this->getWriterIndex();
 311                 } elseif ( $group === false && $this->mReadIndex >= 0 ) {
 312                         # Shortcut if generic reader exists already
 313                         return $this->mReadIndex;
 314                 }
 315
 316                 # Find the relevant load array
 317                 if ( $group !== false ) {
 318                         if ( isset( $this->mGroupLoads[$group] ) ) {
 319                                 $nonErrorLoads = $this->mGroupLoads[$group];
 320                         } else {
 321                                 # No loads for this group, return false and the caller can use some other group
 322                                 $this->connLogger->info( __METHOD__ . ": no loads for group $group" );
 323
 324                                 return false;
 325                         }
 326                 } else {
 327                         $nonErrorLoads = $this->mLoads;
 328                 }
 329
 330                 if ( !count( $nonErrorLoads ) ) {
 331                         throw new InvalidArgumentException( "Empty server array given to LoadBalancer" );
 332                 }
 333
 334                 # Scale the configured load ratios according to the dynamic load if supported
 335                 $this->getLoadMonitor()->scaleLoads( $nonErrorLoads, $domain );
 336
 337                 $laggedReplicaMode = false;
 338
 339                 # No server found yet
 340                 $i = false;
 341                 # First try quickly looking through the available servers for a server that
 342                 # meets our criteria
 343                 $currentLoads = $nonErrorLoads;
 344                 while ( count( $currentLoads ) ) {
 345                         if ( $this->mAllowLagged || $laggedReplicaMode ) {
 346                                 $i = ArrayUtils::pickRandom( $currentLoads );
 347                         } else {
 348                                 $i = false;
 349                                 if ( $this->mWaitForPos && $this->mWaitForPos->asOfTime() ) {
 350                                         # ChronologyProtecter causes mWaitForPos to be set via sessions.
 351                                         # This triggers doWait() after connect, so it's especially good to
 352                                         # avoid lagged servers so as to avoid just blocking in that method.
 353                                         $ago = microtime( true ) - $this->mWaitForPos->asOfTime();
 354                                         # Aim for <= 1 second of waiting (being too picky can backfire)
 355                                         $i = $this->getRandomNonLagged( $currentLoads, $domain, $ago + 1 );
 356                                 }
 357                                 if ( $i === false ) {
 358                                         # Any server with less lag than it's 'max lag' param is preferable
 359                                         $i = $this->getRandomNonLagged( $currentLoads, $domain );
 360                                 }
 361                                 if ( $i === false && count( $currentLoads ) != 0 ) {
 362                                         # All replica DBs lagged. Switch to read-only mode
 363                                         $this->replLogger->error( "All replica DBs lagged. Switch to read-only mode" );
 364                                         $i = ArrayUtils::pickRandom( $currentLoads );
 365                                         $laggedReplicaMode = true;
 366                                 }
 367                         }
 368
 369                         if ( $i === false ) {
 370                                 # pickRandom() returned false
 371                                 # This is permanent and means the configuration or the load monitor
 372                                 # wants us to return false.
 373                                 $this->connLogger->debug( __METHOD__ . ": pickRandom() returned false" );
 374
 375                                 return false;
 376                         }
 377
 378                         $serverName = $this->getServerName( $i );
 379                         $this->connLogger->debug( __METHOD__ . ": Using reader #$i: $serverName..." );
 380
 381                         $conn = $this->openConnection( $i, $domain );
 382                         if ( !$conn ) {
 383                                 $this->connLogger->warning( __METHOD__ . ": Failed connecting to $i/$domain" );
 384                                 unset( $nonErrorLoads[$i] );
 385                                 unset( $currentLoads[$i] );
 386                                 $i = false;
 387                                 continue;
 388                         }
 389
 390                         // Decrement reference counter, we are finished with this connection.
 391                         // It will be incremented for the caller later.
 392                         if ( $domain !== false ) {
 393                                 $this->reuseConnection( $conn );
 394                         }
 395
 396                         # Return this server
 397                         break;
 398                 }
 399
 400                 # If all servers were down, quit now
 401                 if ( !count( $nonErrorLoads ) ) {
 402                         $this->connLogger->error( "All servers down" );
 403                 }
 404
 405                 if ( $i !== false ) {
 406                         # Replica DB connection successful.
 407                         # Wait for the session master pos for a short time.
 408                         if ( $this->mWaitForPos && $i > 0 ) {
 409                                 $this->doWait( $i );
 410                         }
 411                         if ( $this->mReadIndex <= 0 && $this->mLoads[$i] > 0 && $group === false ) {
 412                                 $this->mReadIndex = $i;
 413                                 # Record if the generic reader index is in "lagged replica DB" mode
 414                                 if ( $laggedReplicaMode ) {
 415                                         $this->laggedReplicaMode = true;
 416                                 }
 417                         }
 418                         $serverName = $this->getServerName( $i );
 419                         $this->connLogger->debug(
 420                                 __METHOD__ . ": using server $serverName for group '$group'" );
 421                 }
 422
 423                 return $i;
 424         }
 425
 426         /**
 427          * @param DBMasterPos|false $pos
 428          */
 429         public function waitFor( $pos ) {
 430                 $this->mWaitForPos = $pos;
 431                 $i = $this->mReadIndex;
 432
 433                 if ( $i > 0 ) {
 434                         if ( !$this->doWait( $i ) ) {
 435                                 $this->laggedReplicaMode = true;
 436                         }
 437                 }
 438         }
 439
 440         public function waitForOne( $pos, $timeout = null ) {
 441                 $this->mWaitForPos = $pos;
 442
 443                 $i = $this->mReadIndex;
 444                 if ( $i <= 0 ) {
 445                         // Pick a generic replica DB if there isn't one yet
 446                         $readLoads = $this->mLoads;
 447                         unset( $readLoads[$this->getWriterIndex()] ); // replica DBs only
 448                         $readLoads = array_filter( $readLoads ); // with non-zero load
 449                         $i = ArrayUtils::pickRandom( $readLoads );
 450                 }
 451
 452                 if ( $i > 0 ) {
 453                         $ok = $this->doWait( $i, true, $timeout );
 454                 } else {
 455                         $ok = true; // no applicable loads
 456                 }
 457
 458                 return $ok;
 459         }
 460
 461         public function waitForAll( $pos, $timeout = null ) {
 462                 $this->mWaitForPos = $pos;
 463                 $serverCount = count( $this->mServers );
 464
 465                 $ok = true;
 466                 for ( $i = 1; $i < $serverCount; $i++ ) {
 467                         if ( $this->mLoads[$i] > 0 ) {
 468                                 $ok = $this->doWait( $i, true, $timeout ) && $ok;
 469                         }
 470                 }
 471
 472                 return $ok;
 473         }
 474
 475         /**
 476          * @param int $i
 477          * @return IDatabase|bool
 478          */
 479         public function getAnyOpenConnection( $i ) {
 480                 foreach ( $this->mConns as $connsByServer ) {
 481                         if ( !empty( $connsByServer[$i] ) ) {
 482                                 /** @var $serverConns IDatabase[] */
 483                                 $serverConns = $connsByServer[$i];
 484
 485                                 return reset( $serverConns );
 486                         }
 487                 }
 488
 489                 return false;
 490         }
 491
 492         /**
 493          * Wait for a given replica DB to catch up to the master pos stored in $this
 494          * @param int $index Server index
 495          * @param bool $open Check the server even if a new connection has to be made
 496          * @param int $timeout Max seconds to wait; default is mWaitTimeout
 497          * @return bool
 498          */
 499         protected function doWait( $index, $open = false, $timeout = null ) {
 500                 $close = false; // close the connection afterwards
 501
 502                 // Check if we already know that the DB has reached this point
 503                 $server = $this->getServerName( $index );
 504                 $key = $this->srvCache->makeGlobalKey( __CLASS__, 'last-known-pos', $server, 'v1' );
 505                 /** @var DBMasterPos $knownReachedPos */
 506                 $knownReachedPos = $this->srvCache->get( $key );
 507                 if (
 508                         $knownReachedPos instanceof DBMasterPos &&
 509                         $knownReachedPos->hasReached( $this->mWaitForPos )
 510                 ) {
 511                         $this->replLogger->debug( __METHOD__ .
 512                                 ": replica DB $server known to be caught up (pos >= $knownReachedPos)." );
 513                         return true;
 514                 }
 515
 516                 // Find a connection to wait on, creating one if needed and allowed
 517                 $conn = $this->getAnyOpenConnection( $index );
 518                 if ( !$conn ) {
 519                         if ( !$open ) {
 520                                 $this->replLogger->debug( __METHOD__ . ": no connection open for $server" );
 521
 522                                 return false;
 523                         } else {
 524                                 $conn = $this->openConnection( $index, self::DOMAIN_ANY );
 525                                 if ( !$conn ) {
 526                                         $this->replLogger->warning( __METHOD__ . ": failed to connect to $server" );
 527
 528                                         return false;
 529                                 }
 530                                 // Avoid connection spam in waitForAll() when connections
 531                                 // are made just for the sake of doing this lag check.
 532                                 $close = true;
 533                         }
 534                 }
 535
 536                 $this->replLogger->info( __METHOD__ . ": Waiting for replica DB $server to catch up..." );
 537                 $timeout = $timeout ?: $this->mWaitTimeout;
 538                 $result = $conn->masterPosWait( $this->mWaitForPos, $timeout );
 539
 540                 if ( $result == -1 || is_null( $result ) ) {
 541                         // Timed out waiting for replica DB, use master instead
 542                         $this->replLogger->warning(
 543                                 __METHOD__ . ": Timed out waiting on {host} pos {$this->mWaitForPos}",
 544                                 [ 'host' => $server ]
 545                         );
 546                         $ok = false;
 547                 } else {
 548                         $this->replLogger->info( __METHOD__ . ": Done" );
 549                         $ok = true;
 550                         // Remember that the DB reached this point
 551                         $this->srvCache->set( $key, $this->mWaitForPos, BagOStuff::TTL_DAY );
 552                 }
 553
 554                 if ( $close ) {
 555                         $this->closeConnection( $conn );
 556                 }
 557
 558                 return $ok;
 559         }
 560
 561         /**
 562          * @see ILoadBalancer::getConnection()
 563          *
 564          * @param int $i
 565          * @param array $groups
 566          * @param bool $domain
 567          * @return Database
 568          * @throws DBConnectionError
 569          */
 570         public function getConnection( $i, $groups = [], $domain = false ) {
 571                 if ( $i === null || $i === false ) {
 572                         throw new InvalidArgumentException( 'Attempt to call ' . __METHOD__ .
 573                                 ' with invalid server index' );
 574                 }
 575
 576                 if ( $this->localDomain->equals( $domain ) || $domain === $this->localDomainIdAlias ) {
 577                         $domain = false; // local connection requested
 578                 }
 579
 580                 $groups = ( $groups === false || $groups === [] )
 581                         ? [ false ] // check one "group": the generic pool
 582                         : (array)$groups;
 583
 584                 $masterOnly = ( $i == self::DB_MASTER || $i == $this->getWriterIndex() );
 585                 $oldConnsOpened = $this->connsOpened; // connections open now
 586
 587                 if ( $i == self::DB_MASTER ) {
 588                         $i = $this->getWriterIndex();
 589                 } else {
 590                         # Try to find an available server in any the query groups (in order)
 591                         foreach ( $groups as $group ) {
 592                                 $groupIndex = $this->getReaderIndex( $group, $domain );
 593                                 if ( $groupIndex !== false ) {
 594                                         $i = $groupIndex;
 595                                         break;
 596                                 }
 597                         }
 598                 }
 599
 600                 # Operation-based index
 601                 if ( $i == self::DB_REPLICA ) {
 602                         $this->mLastError = 'Unknown error'; // reset error string
 603                         # Try the general server pool if $groups are unavailable.
 604                         $i = ( $groups === [ false ] )
 605                                 ? false // don't bother with this if that is what was tried above
 606                                 : $this->getReaderIndex( false, $domain );
 607                         # Couldn't find a working server in getReaderIndex()?
 608                         if ( $i === false ) {
 609                                 $this->mLastError = 'No working replica DB server: ' . $this->mLastError;
 610                                 // Throw an exception
 611                                 $this->reportConnectionError();
 612                                 return null; // not reached
 613                         }
 614                 }
 615
 616                 # Now we have an explicit index into the servers array
 617                 $conn = $this->openConnection( $i, $domain );
 618                 if ( !$conn ) {
 619                         // Throw an exception
 620                         $this->reportConnectionError();
 621                         return null; // not reached
 622                 }
 623
 624                 # Profile any new connections that happen
 625                 if ( $this->connsOpened > $oldConnsOpened ) {
 626                         $host = $conn->getServer();
 627                         $dbname = $conn->getDBname();
 628                         $this->trxProfiler->recordConnection( $host, $dbname, $masterOnly );
 629                 }
 630
 631                 if ( $masterOnly ) {
 632                         # Make master-requested DB handles inherit any read-only mode setting
 633                         $conn->setLBInfo( 'readOnlyReason', $this->getReadOnlyReason( $domain, $conn ) );
 634                 }
 635
 636                 return $conn;
 637         }
 638
 639         public function reuseConnection( $conn ) {
 640                 $serverIndex = $conn->getLBInfo( 'serverIndex' );
 641                 $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 642                 if ( $serverIndex === null || $refCount === null ) {
 643                         /**
 644                          * This can happen in code like:
 645                          *   foreach ( $dbs as $db ) {
 646                          *     $conn = $lb->getConnection( $lb::DB_REPLICA, [], $db );
 647                          *     ...
 648                          *     $lb->reuseConnection( $conn );
 649                          *   }
 650                          * When a connection to the local DB is opened in this way, reuseConnection()
 651                          * should be ignored
 652                          */
 653                         return;
 654                 } elseif ( $conn instanceof DBConnRef ) {
 655                         // DBConnRef already handles calling reuseConnection() and only passes the live
 656                         // Database instance to this method. Any caller passing in a DBConnRef is broken.
 657                         $this->connLogger->error( __METHOD__ . ": got DBConnRef instance.\n" .
 658                                 ( new RuntimeException() )->getTraceAsString() );
 659
 660                         return;
 661                 }
 662
 663                 if ( $this->disabled ) {
 664                         return; // DBConnRef handle probably survived longer than the LoadBalancer
 665                 }
 666
 667                 $domain = $conn->getDomainID();
 668                 if ( !isset( $this->mConns['foreignUsed'][$serverIndex][$domain] ) ) {
 669                         throw new InvalidArgumentException( __METHOD__ .
 670                                 ": connection $serverIndex/$domain not found; it may have already been freed." );
 671                 } elseif ( $this->mConns['foreignUsed'][$serverIndex][$domain] !== $conn ) {
 672                         throw new InvalidArgumentException( __METHOD__ .
 673                                 ": connection $serverIndex/$domain mismatched; it may have already been freed." );
 674                 }
 675                 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
 676                 if ( $refCount <= 0 ) {
 677                         $this->mConns['foreignFree'][$serverIndex][$domain] = $conn;
 678                         unset( $this->mConns['foreignUsed'][$serverIndex][$domain] );
 679                         if ( !$this->mConns['foreignUsed'][$serverIndex] ) {
 680                                 unset( $this->mConns[ 'foreignUsed' ][$serverIndex] ); // clean up
 681                         }
 682                         $this->connLogger->debug( __METHOD__ . ": freed connection $serverIndex/$domain" );
 683                 } else {
 684                         $this->connLogger->debug( __METHOD__ .
 685                                 ": reference count for $serverIndex/$domain reduced to $refCount" );
 686                 }
 687         }
 688
 689         public function getConnectionRef( $db, $groups = [], $domain = false ) {
 690                 $domain = ( $domain !== false ) ? $domain : $this->localDomain;
 691
 692                 return new DBConnRef( $this, $this->getConnection( $db, $groups, $domain ) );
 693         }
 694
 695         public function getLazyConnectionRef( $db, $groups = [], $domain = false ) {
 696                 $domain = ( $domain !== false ) ? $domain : $this->localDomain;
 697
 698                 return new DBConnRef( $this, [ $db, $groups, $domain ] );
 699         }
 700
 701         public function getMaintenanceConnectionRef( $db, $groups = [], $domain = false ) {
 702                 $domain = ( $domain !== false ) ? $domain : $this->localDomain;
 703
 704                 return new MaintainableDBConnRef( $this, $this->getConnection( $db, $groups, $domain ) );
 705         }
 706
 707         /**
 708          * @see ILoadBalancer::openConnection()
 709          *
 710          * @param int $i
 711          * @param bool $domain
 712          * @return bool|Database
 713          * @throws DBAccessError
 714          */
 715         public function openConnection( $i, $domain = false ) {
 716                 if ( $this->localDomain->equals( $domain ) || $domain === $this->localDomainIdAlias ) {
 717                         $domain = false; // local connection requested
 718                 }
 719
 720                 if ( $domain !== false ) {
 721                         $conn = $this->openForeignConnection( $i, $domain );
 722                 } elseif ( isset( $this->mConns['local'][$i][0] ) ) {
 723                         $conn = $this->mConns['local'][$i][0];
 724                 } else {
 725                         if ( !isset( $this->mServers[$i] ) || !is_array( $this->mServers[$i] ) ) {
 726                                 throw new InvalidArgumentException( "No server with index '$i'." );
 727                         }
 728                         // Open a new connection
 729                         $server = $this->mServers[$i];
 730                         $server['serverIndex'] = $i;
 731                         $conn = $this->reallyOpenConnection( $server, false );
 732                         $serverName = $this->getServerName( $i );
 733                         if ( $conn->isOpen() ) {
 734                                 $this->connLogger->debug( "Connected to database $i at '$serverName'." );
 735                                 $this->mConns['local'][$i][0] = $conn;
 736                         } else {
 737                                 $this->connLogger->warning( "Failed to connect to database $i at '$serverName'." );
 738                                 $this->errorConnection = $conn;
 739                                 $conn = false;
 740                         }
 741                 }
 742
 743                 if ( $conn instanceof IDatabase && !$conn->isOpen() ) {
 744                         // Connection was made but later unrecoverably lost for some reason.
 745                         // Do not return a handle that will just throw exceptions on use,
 746                         // but let the calling code (e.g. getReaderIndex) try another server.
 747                         // See DatabaseMyslBase::ping() for how this can happen.
 748                         $this->errorConnection = $conn;
 749                         $conn = false;
 750                 }
 751
 752                 return $conn;
 753         }
 754
 755         /**
 756          * Open a connection to a foreign DB, or return one if it is already open.
 757          *
 758          * Increments a reference count on the returned connection which locks the
 759          * connection to the requested domain. This reference count can be
 760          * decremented by calling reuseConnection().
 761          *
 762          * If a connection is open to the appropriate server already, but with the wrong
 763          * database, it will be switched to the right database and returned, as long as
 764          * it has been freed first with reuseConnection().
 765          *
 766          * On error, returns false, and the connection which caused the
 767          * error will be available via $this->errorConnection.
 768          *
 769          * @note If disable() was called on this LoadBalancer, this method will throw a DBAccessError.
 770          *
 771          * @param int $i Server index
 772          * @param string $domain Domain ID to open
 773          * @return Database
 774          */
 775         private function openForeignConnection( $i, $domain ) {
 776                 $domainInstance = DatabaseDomain::newFromId( $domain );
 777                 $dbName = $domainInstance->getDatabase();
 778                 $prefix = $domainInstance->getTablePrefix();
 779
 780                 if ( isset( $this->mConns['foreignUsed'][$i][$domain] ) ) {
 781                         // Reuse an already-used connection
 782                         $conn = $this->mConns['foreignUsed'][$i][$domain];
 783                         $this->connLogger->debug( __METHOD__ . ": reusing connection $i/$domain" );
 784                 } elseif ( isset( $this->mConns['foreignFree'][$i][$domain] ) ) {
 785                         // Reuse a free connection for the same domain
 786                         $conn = $this->mConns['foreignFree'][$i][$domain];
 787                         unset( $this->mConns['foreignFree'][$i][$domain] );
 788                         $this->mConns['foreignUsed'][$i][$domain] = $conn;
 789                         $this->connLogger->debug( __METHOD__ . ": reusing free connection $i/$domain" );
 790                 } elseif ( !empty( $this->mConns['foreignFree'][$i] ) ) {
 791                         // Reuse a connection from another domain
 792                         $conn = reset( $this->mConns['foreignFree'][$i] );
 793                         $oldDomain = key( $this->mConns['foreignFree'][$i] );
 794                         // The empty string as a DB name means "don't care".
 795                         // DatabaseMysqlBase::open() already handle this on connection.
 796                         if ( strlen( $dbName ) && !$conn->selectDB( $dbName ) ) {
 797                                 $this->mLastError = "Error selecting database '$dbName' on server " .
 798                                         $conn->getServer() . " from client host {$this->host}";
 799                                 $this->errorConnection = $conn;
 800                                 $conn = false;
 801                         } else {
 802                                 $conn->tablePrefix( $prefix );
 803                                 unset( $this->mConns['foreignFree'][$i][$oldDomain] );
 804                                 $this->mConns['foreignUsed'][$i][$domain] = $conn;
 805                                 $this->connLogger->debug( __METHOD__ .
 806                                         ": reusing free connection from $oldDomain for $domain" );
 807                         }
 808                 } else {
 809                         if ( !isset( $this->mServers[$i] ) || !is_array( $this->mServers[$i] ) ) {
 810                                 throw new InvalidArgumentException( "No server with index '$i'." );
 811                         }
 812                         // Open a new connection
 813                         $server = $this->mServers[$i];
 814                         $server['serverIndex'] = $i;
 815                         $server['foreignPoolRefCount'] = 0;
 816                         $server['foreign'] = true;
 817                         $conn = $this->reallyOpenConnection( $server, $dbName );
 818                         if ( !$conn->isOpen() ) {
 819                                 $this->connLogger->warning( __METHOD__ . ": connection error for $i/$domain" );
 820                                 $this->errorConnection = $conn;
 821                                 $conn = false;
 822                         } else {
 823                                 $conn->tablePrefix( $prefix );
 824                                 $this->mConns['foreignUsed'][$i][$domain] = $conn;
 825                                 $this->connLogger->debug( __METHOD__ . ": opened new connection for $i/$domain" );
 826                         }
 827                 }
 828
 829                 // Increment reference count
 830                 if ( $conn instanceof IDatabase ) {
 831                         $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 832                         $conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
 833                 }
 834
 835                 return $conn;
 836         }
 837
 838         /**
 839          * Test if the specified index represents an open connection
 840          *
 841          * @param int $index Server index
 842          * @access private
 843          * @return bool
 844          */
 845         private function isOpen( $index ) {
 846                 if ( !is_integer( $index ) ) {
 847                         return false;
 848                 }
 849
 850                 return (bool)$this->getAnyOpenConnection( $index );
 851         }
 852
 853         /**
 854          * Really opens a connection. Uncached.
 855          * Returns a Database object whether or not the connection was successful.
 856          * @access private
 857          *
 858          * @param array $server
 859          * @param string|bool $dbNameOverride Use "" to not select any database
 860          * @return Database
 861          * @throws DBAccessError
 862          * @throws InvalidArgumentException
 863          */
 864         protected function reallyOpenConnection( array $server, $dbNameOverride = false ) {
 865                 if ( $this->disabled ) {
 866                         throw new DBAccessError();
 867                 }
 868
 869                 if ( $dbNameOverride !== false ) {
 870                         $server['dbname'] = $dbNameOverride;
 871                 }
 872
 873                 // Let the handle know what the cluster master is (e.g. "db1052")
 874                 $masterName = $this->getServerName( $this->getWriterIndex() );
 875                 $server['clusterMasterHost'] = $masterName;
 876
 877                 // Log when many connection are made on requests
 878                 if ( ++$this->connsOpened >= self::CONN_HELD_WARN_THRESHOLD ) {
 879                         $this->perfLogger->warning( __METHOD__ . ": " .
 880                                 "{$this->connsOpened}+ connections made (master=$masterName)" );
 881                 }
 882
 883                 $server['srvCache'] = $this->srvCache;
 884                 // Set loggers and profilers
 885                 $server['connLogger'] = $this->connLogger;
 886                 $server['queryLogger'] = $this->queryLogger;
 887                 $server['errorLogger'] = $this->errorLogger;
 888                 $server['profiler'] = $this->profiler;
 889                 $server['trxProfiler'] = $this->trxProfiler;
 890                 // Use the same agent and PHP mode for all DB handles
 891                 $server['cliMode'] = $this->cliMode;
 892                 $server['agent'] = $this->agent;
 893                 // Use DBO_DEFAULT flags by default for LoadBalancer managed databases. Assume that the
 894                 // application calls LoadBalancer::commitMasterChanges() before the PHP script completes.
 895                 $server['flags'] = isset( $server['flags'] ) ? $server['flags'] : IDatabase::DBO_DEFAULT;
 896
 897                 // Create a live connection object
 898                 try {
 899                         $db = Database::factory( $server['type'], $server );
 900                 } catch ( DBConnectionError $e ) {
 901                         // FIXME: This is probably the ugliest thing I have ever done to
 902                         // PHP. I'm half-expecting it to segfault, just out of disgust. -- TS
 903                         $db = $e->db;
 904                 }
 905
 906                 $db->setLBInfo( $server );
 907                 $db->setLazyMasterHandle(
 908                         $this->getLazyConnectionRef( self::DB_MASTER, [], $db->getDomainID() )
 909                 );
 910                 $db->setTableAliases( $this->tableAliases );
 911
 912                 if ( $server['serverIndex'] === $this->getWriterIndex() ) {
 913                         if ( $this->trxRoundId !== false ) {
 914                                 $this->applyTransactionRoundFlags( $db );
 915                         }
 916                         foreach ( $this->trxRecurringCallbacks as $name => $callback ) {
 917                                 $db->setTransactionListener( $name, $callback );
 918                         }
 919                 }
 920
 921                 return $db;
 922         }
 923
 924         /**
 925          * @throws DBConnectionError
 926          */
 927         private function reportConnectionError() {
 928                 $conn = $this->errorConnection; // the connection which caused the error
 929                 $context = [
 930                         'method' => __METHOD__,
 931                         'last_error' => $this->mLastError,
 932                 ];
 933
 934                 if ( $conn instanceof IDatabase ) {
 935                         $context['db_server'] = $conn->getServer();
 936                         $this->connLogger->warning(
 937                                 "Connection error: {last_error} ({db_server})",
 938                                 $context
 939                         );
 940
 941                         // throws DBConnectionError
 942                         $conn->reportConnectionError( "{$this->mLastError} ({$context['db_server']})" );
 943                 } else {
 944                         // No last connection, probably due to all servers being too busy
 945                         $this->connLogger->error(
 946                                 "LB failure with no last connection. Connection error: {last_error}",
 947                                 $context
 948                         );
 949
 950                         // If all servers were busy, mLastError will contain something sensible
 951                         throw new DBConnectionError( null, $this->mLastError );
 952                 }
 953         }
 954
 955         public function getWriterIndex() {
 956                 return 0;
 957         }
 958
 959         public function haveIndex( $i ) {
 960                 return array_key_exists( $i, $this->mServers );
 961         }
 962
 963         public function isNonZeroLoad( $i ) {
 964                 return array_key_exists( $i, $this->mServers ) && $this->mLoads[$i] != 0;
 965         }
 966
 967         public function getServerCount() {
 968                 return count( $this->mServers );
 969         }
 970
 971         public function getServerName( $i ) {
 972                 if ( isset( $this->mServers[$i]['hostName'] ) ) {
 973                         $name = $this->mServers[$i]['hostName'];
 974                 } elseif ( isset( $this->mServers[$i]['host'] ) ) {
 975                         $name = $this->mServers[$i]['host'];
 976                 } else {
 977                         $name = '';
 978                 }
 979
 980                 return ( $name != '' ) ? $name : 'localhost';
 981         }
 982
 983         public function getServerInfo( $i ) {
 984                 if ( isset( $this->mServers[$i] ) ) {
 985                         return $this->mServers[$i];
 986                 } else {
 987                         return false;
 988                 }
 989         }
 990
 991         public function setServerInfo( $i, array $serverInfo ) {
 992                 $this->mServers[$i] = $serverInfo;
 993         }
 994
 995         public function getMasterPos() {
 996                 # If this entire request was served from a replica DB without opening a connection to the
 997                 # master (however unlikely that may be), then we can fetch the position from the replica DB.
 998                 $masterConn = $this->getAnyOpenConnection( $this->getWriterIndex() );
 999                 if ( !$masterConn ) {
1000                         $serverCount = count( $this->mServers );
1001                         for ( $i = 1; $i < $serverCount; $i++ ) {
1002                                 $conn = $this->getAnyOpenConnection( $i );
1003                                 if ( $conn ) {
1004                                         return $conn->getReplicaPos();
1005                                 }
1006                         }
1007                 } else {
1008                         return $masterConn->getMasterPos();
1009                 }
1010
1011                 return false;
1012         }
1013
1014         public function disable() {
1015                 $this->closeAll();
1016                 $this->disabled = true;
1017         }
1018
1019         public function closeAll() {
1020                 $this->forEachOpenConnection( function ( IDatabase $conn ) {
1021                         $host = $conn->getServer();
1022                         $this->connLogger->debug( "Closing connection to database '$host'." );
1023                         $conn->close();
1024                 } );
1025
1026                 $this->mConns = [
1027                         'local' => [],
1028                         'foreignFree' => [],
1029                         'foreignUsed' => [],
1030                 ];
1031                 $this->connsOpened = 0;
1032         }
1033
1034         public function closeConnection( IDatabase $conn ) {
1035                 $serverIndex = $conn->getLBInfo( 'serverIndex' ); // second index level of mConns
1036                 foreach ( $this->mConns as $type => $connsByServer ) {
1037                         if ( !isset( $connsByServer[$serverIndex] ) ) {
1038                                 continue;
1039                         }
1040
1041                         foreach ( $connsByServer[$serverIndex] as $i => $trackedConn ) {
1042                                 if ( $conn === $trackedConn ) {
1043                                         $host = $this->getServerName( $i );
1044                                         $this->connLogger->debug( "Closing connection to database $i at '$host'." );
1045                                         unset( $this->mConns[$type][$serverIndex][$i] );
1046                                         --$this->connsOpened;
1047                                         break 2;
1048                                 }
1049                         }
1050                 }
1051
1052                 $conn->close();
1053         }
1054
1055         public function commitAll( $fname = __METHOD__ ) {
1056                 $failures = [];
1057
1058                 $restore = ( $this->trxRoundId !== false );
1059                 $this->trxRoundId = false;
1060                 $this->forEachOpenConnection(
1061                         function ( IDatabase $conn ) use ( $fname, $restore, &$failures ) {
1062                                 try {
1063                                         $conn->commit( $fname, $conn::FLUSHING_ALL_PEERS );
1064                                 } catch ( DBError $e ) {
1065                                         call_user_func( $this->errorLogger, $e );
1066                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1067                                 }
1068                                 if ( $restore && $conn->getLBInfo( 'master' ) ) {
1069                                         $this->undoTransactionRoundFlags( $conn );
1070                                 }
1071                         }
1072                 );
1073
1074                 if ( $failures ) {
1075                         throw new DBExpectedError(
1076                                 null,
1077                                 "Commit failed on server(s) " . implode( "\n", array_unique( $failures ) )
1078                         );
1079                 }
1080         }
1081
1082         public function finalizeMasterChanges() {
1083                 $this->forEachOpenMasterConnection( function ( Database $conn ) {
1084                         // Any error should cause all DB transactions to be rolled back together
1085                         $conn->setTrxEndCallbackSuppression( false );
1086                         $conn->runOnTransactionPreCommitCallbacks();
1087                         // Defer post-commit callbacks until COMMIT finishes for all DBs
1088                         $conn->setTrxEndCallbackSuppression( true );
1089                 } );
1090         }
1091
1092         public function approveMasterChanges( array $options ) {
1093                 $limit = isset( $options['maxWriteDuration'] ) ? $options['maxWriteDuration'] : 0;
1094                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( $limit ) {
1095                         // If atomic sections or explicit transactions are still open, some caller must have
1096                         // caught an exception but failed to properly rollback any changes. Detect that and
1097                         // throw and error (causing rollback).
1098                         if ( $conn->explicitTrxActive() ) {
1099                                 throw new DBTransactionError(
1100                                         $conn,
1101                                         "Explicit transaction still active. A caller may have caught an error."
1102                                 );
1103                         }
1104                         // Assert that the time to replicate the transaction will be sane.
1105                         // If this fails, then all DB transactions will be rollback back together.
1106                         $time = $conn->pendingWriteQueryDuration( $conn::ESTIMATE_DB_APPLY );
1107                         if ( $limit > 0 && $time > $limit ) {
1108                                 throw new DBTransactionSizeError(
1109                                         $conn,
1110                                         "Transaction spent $time second(s) in writes, exceeding the $limit limit.",
1111                                         [ $time, $limit ]
1112                                 );
1113                         }
1114                         // If a connection sits idle while slow queries execute on another, that connection
1115                         // may end up dropped before the commit round is reached. Ping servers to detect this.
1116                         if ( $conn->writesOrCallbacksPending() && !$conn->ping() ) {
1117                                 throw new DBTransactionError(
1118                                         $conn,
1119                                         "A connection to the {$conn->getDBname()} database was lost before commit."
1120                                 );
1121                         }
1122                 } );
1123         }
1124
1125         public function beginMasterChanges( $fname = __METHOD__ ) {
1126                 if ( $this->trxRoundId !== false ) {
1127                         throw new DBTransactionError(
1128                                 null,
1129                                 "$fname: Transaction round '{$this->trxRoundId}' already started."
1130                         );
1131                 }
1132                 $this->trxRoundId = $fname;
1133
1134                 $failures = [];
1135                 $this->forEachOpenMasterConnection(
1136                         function ( Database $conn ) use ( $fname, &$failures ) {
1137                                 $conn->setTrxEndCallbackSuppression( true );
1138                                 try {
1139                                         $conn->flushSnapshot( $fname );
1140                                 } catch ( DBError $e ) {
1141                                         call_user_func( $this->errorLogger, $e );
1142                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1143                                 }
1144                                 $conn->setTrxEndCallbackSuppression( false );
1145                                 $this->applyTransactionRoundFlags( $conn );
1146                         }
1147                 );
1148
1149                 if ( $failures ) {
1150                         throw new DBExpectedError(
1151                                 null,
1152                                 "$fname: Flush failed on server(s) " . implode( "\n", array_unique( $failures ) )
1153                         );
1154                 }
1155         }
1156
1157         public function commitMasterChanges( $fname = __METHOD__ ) {
1158                 $failures = [];
1159
1160                 /** @noinspection PhpUnusedLocalVariableInspection */
1161                 $scope = $this->getScopedPHPBehaviorForCommit(); // try to ignore client aborts
1162
1163                 $restore = ( $this->trxRoundId !== false );
1164                 $this->trxRoundId = false;
1165                 $this->forEachOpenMasterConnection(
1166                         function ( IDatabase $conn ) use ( $fname, $restore, &$failures ) {
1167                                 try {
1168                                         if ( $conn->writesOrCallbacksPending() ) {
1169                                                 $conn->commit( $fname, $conn::FLUSHING_ALL_PEERS );
1170                                         } elseif ( $restore ) {
1171                                                 $conn->flushSnapshot( $fname );
1172                                         }
1173                                 } catch ( DBError $e ) {
1174                                         call_user_func( $this->errorLogger, $e );
1175                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1176                                 }
1177                                 if ( $restore ) {
1178                                         $this->undoTransactionRoundFlags( $conn );
1179                                 }
1180                         }
1181                 );
1182
1183                 if ( $failures ) {
1184                         throw new DBExpectedError(
1185                                 null,
1186                                 "$fname: Commit failed on server(s) " . implode( "\n", array_unique( $failures ) )
1187                         );
1188                 }
1189         }
1190
1191         public function runMasterPostTrxCallbacks( $type ) {
1192                 $e = null; // first exception
1193                 $this->forEachOpenMasterConnection( function ( Database $conn ) use ( $type, &$e ) {
1194                         $conn->setTrxEndCallbackSuppression( false );
1195                         if ( $conn->writesOrCallbacksPending() ) {
1196                                 // This happens if onTransactionIdle() callbacks leave callbacks on *another* DB
1197                                 // (which finished its callbacks already). Warn and recover in this case. Let the
1198                                 // callbacks run in the final commitMasterChanges() in LBFactory::shutdown().
1199                                 $this->queryLogger->error( __METHOD__ . ": found writes/callbacks pending." );
1200                                 return;
1201                         } elseif ( $conn->trxLevel() ) {
1202                                 // This happens for single-DB setups where DB_REPLICA uses the master DB,
1203                                 // thus leaving an implicit read-only transaction open at this point. It
1204                                 // also happens if onTransactionIdle() callbacks leave implicit transactions
1205                                 // open on *other* DBs (which is slightly improper). Let these COMMIT on the
1206                                 // next call to commitMasterChanges(), possibly in LBFactory::shutdown().
1207                                 return;
1208                         }
1209                         try {
1210                                 $conn->runOnTransactionIdleCallbacks( $type );
1211                         } catch ( Exception $ex ) {
1212                                 $e = $e ?: $ex;
1213                         }
1214                         try {
1215                                 $conn->runTransactionListenerCallbacks( $type );
1216                         } catch ( Exception $ex ) {
1217                                 $e = $e ?: $ex;
1218                         }
1219                 } );
1220
1221                 return $e;
1222         }
1223
1224         public function rollbackMasterChanges( $fname = __METHOD__ ) {
1225                 $restore = ( $this->trxRoundId !== false );
1226                 $this->trxRoundId = false;
1227                 $this->forEachOpenMasterConnection(
1228                         function ( IDatabase $conn ) use ( $fname, $restore ) {
1229                                 if ( $conn->writesOrCallbacksPending() ) {
1230                                         $conn->rollback( $fname, $conn::FLUSHING_ALL_PEERS );
1231                                 }
1232                                 if ( $restore ) {
1233                                         $this->undoTransactionRoundFlags( $conn );
1234                                 }
1235                         }
1236                 );
1237         }
1238
1239         public function suppressTransactionEndCallbacks() {
1240                 $this->forEachOpenMasterConnection( function ( Database $conn ) {
1241                         $conn->setTrxEndCallbackSuppression( true );
1242                 } );
1243         }
1244
1245         /**
1246          * @param IDatabase $conn
1247          */
1248         private function applyTransactionRoundFlags( IDatabase $conn ) {
1249                 if ( $conn->getFlag( $conn::DBO_DEFAULT ) ) {
1250                         // DBO_TRX is controlled entirely by CLI mode presence with DBO_DEFAULT.
1251                         // Force DBO_TRX even in CLI mode since a commit round is expected soon.
1252                         $conn->setFlag( $conn::DBO_TRX, $conn::REMEMBER_PRIOR );
1253                         // If config has explicitly requested DBO_TRX be either on or off by not
1254                         // setting DBO_DEFAULT, then respect that. Forcing no transactions is useful
1255                         // for things like blob stores (ExternalStore) which want auto-commit mode.
1256                 }
1257         }
1258
1259         /**
1260          * @param IDatabase $conn
1261          */
1262         private function undoTransactionRoundFlags( IDatabase $conn ) {
1263                 if ( $conn->getFlag( $conn::DBO_DEFAULT ) ) {
1264                         $conn->restoreFlags( $conn::RESTORE_PRIOR );
1265                 }
1266         }
1267
1268         public function flushReplicaSnapshots( $fname = __METHOD__ ) {
1269                 $this->forEachOpenReplicaConnection( function ( IDatabase $conn ) {
1270                         $conn->flushSnapshot( __METHOD__ );
1271                 } );
1272         }
1273
1274         public function hasMasterConnection() {
1275                 return $this->isOpen( $this->getWriterIndex() );
1276         }
1277
1278         public function hasMasterChanges() {
1279                 $pending = 0;
1280                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$pending ) {
1281                         $pending |= $conn->writesOrCallbacksPending();
1282                 } );
1283
1284                 return (bool)$pending;
1285         }
1286
1287         public function lastMasterChangeTimestamp() {
1288                 $lastTime = false;
1289                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$lastTime ) {
1290                         $lastTime = max( $lastTime, $conn->lastDoneWrites() );
1291                 } );
1292
1293                 return $lastTime;
1294         }
1295
1296         public function hasOrMadeRecentMasterChanges( $age = null ) {
1297                 $age = ( $age === null ) ? $this->mWaitTimeout : $age;
1298
1299                 return ( $this->hasMasterChanges()
1300                         || $this->lastMasterChangeTimestamp() > microtime( true ) - $age );
1301         }
1302
1303         public function pendingMasterChangeCallers() {
1304                 $fnames = [];
1305                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$fnames ) {
1306                         $fnames = array_merge( $fnames, $conn->pendingWriteCallers() );
1307                 } );
1308
1309                 return $fnames;
1310         }
1311
1312         public function getLaggedReplicaMode( $domain = false ) {
1313                 // No-op if there is only one DB (also avoids recursion)
1314                 if ( !$this->laggedReplicaMode && $this->getServerCount() > 1 ) {
1315                         try {
1316                                 // See if laggedReplicaMode gets set
1317                                 $conn = $this->getConnection( self::DB_REPLICA, false, $domain );
1318                                 $this->reuseConnection( $conn );
1319                         } catch ( DBConnectionError $e ) {
1320                                 // Avoid expensive re-connect attempts and failures
1321                                 $this->allReplicasDownMode = true;
1322                                 $this->laggedReplicaMode = true;
1323                         }
1324                 }
1325
1326                 return $this->laggedReplicaMode;
1327         }
1328
1329         /**
1330          * @param bool $domain
1331          * @return bool
1332          * @deprecated 1.28; use getLaggedReplicaMode()
1333          */
1334         public function getLaggedSlaveMode( $domain = false ) {
1335                 return $this->getLaggedReplicaMode( $domain );
1336         }
1337
1338         public function laggedReplicaUsed() {
1339                 return $this->laggedReplicaMode;
1340         }
1341
1342         /**
1343          * @return bool
1344          * @since 1.27
1345          * @deprecated Since 1.28; use laggedReplicaUsed()
1346          */
1347         public function laggedSlaveUsed() {
1348                 return $this->laggedReplicaUsed();
1349         }
1350
1351         public function getReadOnlyReason( $domain = false, IDatabase $conn = null ) {
1352                 if ( $this->readOnlyReason !== false ) {
1353                         return $this->readOnlyReason;
1354                 } elseif ( $this->getLaggedReplicaMode( $domain ) ) {
1355                         if ( $this->allReplicasDownMode ) {
1356                                 return 'The database has been automatically locked ' .
1357                                         'until the replica database servers become available';
1358                         } else {
1359                                 return 'The database has been automatically locked ' .
1360                                         'while the replica database servers catch up to the master.';
1361                         }
1362                 } elseif ( $this->masterRunningReadOnly( $domain, $conn ) ) {
1363                         return 'The database master is running in read-only mode.';
1364                 }
1365
1366                 return false;
1367         }
1368
1369         /**
1370          * @param string $domain Domain ID, or false for the current domain
1371          * @param IDatabase|null $conn DB master connectionl used to avoid loops [optional]
1372          * @return bool
1373          */
1374         private function masterRunningReadOnly( $domain, IDatabase $conn = null ) {
1375                 $cache = $this->wanCache;
1376                 $masterServer = $this->getServerName( $this->getWriterIndex() );
1377
1378                 return (bool)$cache->getWithSetCallback(
1379                         $cache->makeGlobalKey( __CLASS__, 'server-read-only', $masterServer ),
1380                         self::TTL_CACHE_READONLY,
1381                         function () use ( $domain, $conn ) {
1382                                 $old = $this->trxProfiler->setSilenced( true );
1383                                 try {
1384                                         $dbw = $conn ?: $this->getConnection( self::DB_MASTER, [], $domain );
1385                                         $readOnly = (int)$dbw->serverIsReadOnly();
1386                                         if ( !$conn ) {
1387                                                 $this->reuseConnection( $dbw );
1388                                         }
1389                                 } catch ( DBError $e ) {
1390                                         $readOnly = 0;
1391                                 }
1392                                 $this->trxProfiler->setSilenced( $old );
1393                                 return $readOnly;
1394                         },
1395                         [ 'pcTTL' => $cache::TTL_PROC_LONG, 'busyValue' => 0 ]
1396                 );
1397         }
1398
1399         public function allowLagged( $mode = null ) {
1400                 if ( $mode === null ) {
1401                         return $this->mAllowLagged;
1402                 }
1403                 $this->mAllowLagged = $mode;
1404
1405                 return $this->mAllowLagged;
1406         }
1407
1408         public function pingAll() {
1409                 $success = true;
1410                 $this->forEachOpenConnection( function ( IDatabase $conn ) use ( &$success ) {
1411                         if ( !$conn->ping() ) {
1412                                 $success = false;
1413                         }
1414                 } );
1415
1416                 return $success;
1417         }
1418
1419         public function forEachOpenConnection( $callback, array $params = [] ) {
1420                 foreach ( $this->mConns as $connsByServer ) {
1421                         foreach ( $connsByServer as $serverConns ) {
1422                                 foreach ( $serverConns as $conn ) {
1423                                         $mergedParams = array_merge( [ $conn ], $params );
1424                                         call_user_func_array( $callback, $mergedParams );
1425                                 }
1426                         }
1427                 }
1428         }
1429
1430         public function forEachOpenMasterConnection( $callback, array $params = [] ) {
1431                 $masterIndex = $this->getWriterIndex();
1432                 foreach ( $this->mConns as $connsByServer ) {
1433                         if ( isset( $connsByServer[$masterIndex] ) ) {
1434                                 /** @var IDatabase $conn */
1435                                 foreach ( $connsByServer[$masterIndex] as $conn ) {
1436                                         $mergedParams = array_merge( [ $conn ], $params );
1437                                         call_user_func_array( $callback, $mergedParams );
1438                                 }
1439                         }
1440                 }
1441         }
1442
1443         public function forEachOpenReplicaConnection( $callback, array $params = [] ) {
1444                 foreach ( $this->mConns as $connsByServer ) {
1445                         foreach ( $connsByServer as $i => $serverConns ) {
1446                                 if ( $i === $this->getWriterIndex() ) {
1447                                         continue; // skip master
1448                                 }
1449                                 foreach ( $serverConns as $conn ) {
1450                                         $mergedParams = array_merge( [ $conn ], $params );
1451                                         call_user_func_array( $callback, $mergedParams );
1452                                 }
1453                         }
1454                 }
1455         }
1456
1457         public function getMaxLag( $domain = false ) {
1458                 $maxLag = -1;
1459                 $host = '';
1460                 $maxIndex = 0;
1461
1462                 if ( $this->getServerCount() <= 1 ) {
1463                         return [ $host, $maxLag, $maxIndex ]; // no replication = no lag
1464                 }
1465
1466                 $lagTimes = $this->getLagTimes( $domain );
1467                 foreach ( $lagTimes as $i => $lag ) {
1468                         if ( $this->mLoads[$i] > 0 && $lag > $maxLag ) {
1469                                 $maxLag = $lag;
1470                                 $host = $this->mServers[$i]['host'];
1471                                 $maxIndex = $i;
1472                         }
1473                 }
1474
1475                 return [ $host, $maxLag, $maxIndex ];
1476         }
1477
1478         public function getLagTimes( $domain = false ) {
1479                 if ( $this->getServerCount() <= 1 ) {
1480                         return [ $this->getWriterIndex() => 0 ]; // no replication = no lag
1481                 }
1482
1483                 $knownLagTimes = []; // map of (server index => 0 seconds)
1484                 $indexesWithLag = [];
1485                 foreach ( $this->mServers as $i => $server ) {
1486                         if ( empty( $server['is static'] ) ) {
1487                                 $indexesWithLag[] = $i; // DB server might have replication lag
1488                         } else {
1489                                 $knownLagTimes[$i] = 0; // DB server is a non-replicating and read-only archive
1490                         }
1491                 }
1492
1493                 return $this->getLoadMonitor()->getLagTimes( $indexesWithLag, $domain ) + $knownLagTimes;
1494         }
1495
1496         public function safeGetLag( IDatabase $conn ) {
1497                 if ( $this->getServerCount() <= 1 ) {
1498                         return 0;
1499                 } else {
1500                         return $conn->getLag();
1501                 }
1502         }
1503
1504         /**
1505          * @param IDatabase $conn
1506          * @param DBMasterPos|bool $pos
1507          * @param int $timeout
1508          * @return bool
1509          */
1510         public function safeWaitForMasterPos( IDatabase $conn, $pos = false, $timeout = 10 ) {
1511                 if ( $this->getServerCount() <= 1 || !$conn->getLBInfo( 'replica' ) ) {
1512                         return true; // server is not a replica DB
1513                 }
1514
1515                 if ( !$pos ) {
1516                         // Get the current master position, opening a connection if needed
1517                         $masterConn = $this->getAnyOpenConnection( $this->getWriterIndex() );
1518                         if ( $masterConn ) {
1519                                 $pos = $masterConn->getMasterPos();
1520                         } else {
1521                                 $masterConn = $this->openConnection( $this->getWriterIndex(), self::DOMAIN_ANY );
1522                                 $pos = $masterConn->getMasterPos();
1523                                 $this->closeConnection( $masterConn );
1524                         }
1525                 }
1526
1527                 if ( $pos instanceof DBMasterPos ) {
1528                         $result = $conn->masterPosWait( $pos, $timeout );
1529                         if ( $result == -1 || is_null( $result ) ) {
1530                                 $msg = __METHOD__ . ": Timed out waiting on {$conn->getServer()} pos {$pos}";
1531                                 $this->replLogger->warning( "$msg" );
1532                                 $ok = false;
1533                         } else {
1534                                 $this->replLogger->info( __METHOD__ . ": Done" );
1535                                 $ok = true;
1536                         }
1537                 } else {
1538                         $ok = false; // something is misconfigured
1539                         $this->replLogger->error( "Could not get master pos for {$conn->getServer()}." );
1540                 }
1541
1542                 return $ok;
1543         }
1544
1545         public function setTransactionListener( $name, callable $callback = null ) {
1546                 if ( $callback ) {
1547                         $this->trxRecurringCallbacks[$name] = $callback;
1548                 } else {
1549                         unset( $this->trxRecurringCallbacks[$name] );
1550                 }
1551                 $this->forEachOpenMasterConnection(
1552                         function ( IDatabase $conn ) use ( $name, $callback ) {
1553                                 $conn->setTransactionListener( $name, $callback );
1554                         }
1555                 );
1556         }
1557
1558         public function setTableAliases( array $aliases ) {
1559                 $this->tableAliases = $aliases;
1560         }
1561
1562         public function setDomainPrefix( $prefix ) {
1563                 if ( $this->mConns['foreignUsed'] ) {
1564                         // Do not switch connections to explicit foreign domains unless marked as free
1565                         $domains = [];
1566                         foreach ( $this->mConns['foreignUsed'] as $i => $connsByDomain ) {
1567                                 $domains = array_merge( $domains, array_keys( $connsByDomain ) );
1568                         }
1569                         $domains = implode( ', ', $domains );
1570                         throw new DBUnexpectedError( null,
1571                                 "Foreign domain connections are still in use ($domains)." );
1572                 }
1573
1574                 $this->localDomain = new DatabaseDomain(
1575                         $this->localDomain->getDatabase(),
1576                         null,
1577                         $prefix
1578                 );
1579
1580                 $this->forEachOpenConnection( function ( IDatabase $db ) use ( $prefix ) {
1581                         $db->tablePrefix( $prefix );
1582                 } );
1583         }
1584
1585         /**
1586          * Make PHP ignore user aborts/disconnects until the returned
1587          * value leaves scope. This returns null and does nothing in CLI mode.
1588          *
1589          * @return ScopedCallback|null
1590          */
1591         final protected function getScopedPHPBehaviorForCommit() {
1592                 if ( PHP_SAPI != 'cli' ) { // https://bugs.php.net/bug.php?id=47540
1593                         $old = ignore_user_abort( true ); // avoid half-finished operations
1594                         return new ScopedCallback( function () use ( $old ) {
1595                                 ignore_user_abort( $old );
1596                         } );
1597                 }
1598
1599                 return null;
1600         }
1601
1602         function __destruct() {
1603                 // Avoid connection leaks for sanity
1604                 $this->disable();
1605         }
1606 }
1607
1608 class_alias( LoadBalancer::class, 'LoadBalancer' );