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