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