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                 } elseif ( $conn instanceof DBConnRef ) {
 601                         // DBConnRef already handles calling reuseConnection() and only passes the live
 602                         // Database instance to this method. Any caller passing in a DBConnRef is broken.
 603                         $this->connLogger->error( __METHOD__ . ": got DBConnRef instance.\n" .
 604                                 ( new RuntimeException() )->getTraceAsString() );
 605
 606                         return;
 607                 }
 608
 609                 $domain = $conn->getDomainID();
 610                 if ( $this->mConns['foreignUsed'][$serverIndex][$domain] !== $conn ) {
 611                         throw new InvalidArgumentException( __METHOD__ .
 612                                 ": connection not found, has the connection been freed already?" );
 613                 }
 614                 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
 615                 if ( $refCount <= 0 ) {
 616                         $this->mConns['foreignFree'][$serverIndex][$domain] = $conn;
 617                         unset( $this->mConns['foreignUsed'][$serverIndex][$domain] );
 618                         if ( !$this->mConns['foreignUsed'][$serverIndex] ) {
 619                                 unset( $this->mConns[ 'foreignUsed' ][$serverIndex] ); // clean up
 620                         }
 621                         $this->connLogger->debug( __METHOD__ . ": freed connection $serverIndex/$domain" );
 622                 } else {
 623                         $this->connLogger->debug( __METHOD__ .
 624                                 ": reference count for $serverIndex/$domain reduced to $refCount" );
 625                 }
 626         }
 627
 628         public function getConnectionRef( $db, $groups = [], $domain = false ) {
 629                 $domain = ( $domain !== false ) ? $domain : $this->localDomain;
 630
 631                 return new DBConnRef( $this, $this->getConnection( $db, $groups, $domain ) );
 632         }
 633
 634         public function getLazyConnectionRef( $db, $groups = [], $domain = false ) {
 635                 $domain = ( $domain !== false ) ? $domain : $this->localDomain;
 636
 637                 return new DBConnRef( $this, [ $db, $groups, $domain ] );
 638         }
 639
 640         public function openConnection( $i, $domain = false ) {
 641                 if ( $this->localDomain->equals( $domain ) || $domain === $this->localDomainIdAlias ) {
 642                         $domain = false; // local connection requested
 643                 }
 644
 645                 if ( $domain !== false ) {
 646                         $conn = $this->openForeignConnection( $i, $domain );
 647                 } elseif ( isset( $this->mConns['local'][$i][0] ) ) {
 648                         $conn = $this->mConns['local'][$i][0];
 649                 } else {
 650                         $server = $this->mServers[$i];
 651                         $server['serverIndex'] = $i;
 652                         $conn = $this->reallyOpenConnection( $server, false );
 653                         $serverName = $this->getServerName( $i );
 654                         if ( $conn->isOpen() ) {
 655                                 $this->connLogger->debug( "Connected to database $i at '$serverName'." );
 656                                 $this->mConns['local'][$i][0] = $conn;
 657                         } else {
 658                                 $this->connLogger->warning( "Failed to connect to database $i at '$serverName'." );
 659                                 $this->mErrorConnection = $conn;
 660                                 $conn = false;
 661                         }
 662                 }
 663
 664                 if ( $conn && !$conn->isOpen() ) {
 665                         // Connection was made but later unrecoverably lost for some reason.
 666                         // Do not return a handle that will just throw exceptions on use,
 667                         // but let the calling code (e.g. getReaderIndex) try another server.
 668                         // See DatabaseMyslBase::ping() for how this can happen.
 669                         $this->mErrorConnection = $conn;
 670                         $conn = false;
 671                 }
 672
 673                 return $conn;
 674         }
 675
 676         /**
 677          * Open a connection to a foreign DB, or return one if it is already open.
 678          *
 679          * Increments a reference count on the returned connection which locks the
 680          * connection to the requested domain. This reference count can be
 681          * decremented by calling reuseConnection().
 682          *
 683          * If a connection is open to the appropriate server already, but with the wrong
 684          * database, it will be switched to the right database and returned, as long as
 685          * it has been freed first with reuseConnection().
 686          *
 687          * On error, returns false, and the connection which caused the
 688          * error will be available via $this->mErrorConnection.
 689          *
 690          * @note If disable() was called on this LoadBalancer, this method will throw a DBAccessError.
 691          *
 692          * @param int $i Server index
 693          * @param string $domain Domain ID to open
 694          * @return IDatabase
 695          */
 696         private function openForeignConnection( $i, $domain ) {
 697                 $domainInstance = DatabaseDomain::newFromId( $domain );
 698                 $dbName = $domainInstance->getDatabase();
 699                 $prefix = $domainInstance->getTablePrefix();
 700
 701                 if ( isset( $this->mConns['foreignUsed'][$i][$domain] ) ) {
 702                         // Reuse an already-used connection
 703                         $conn = $this->mConns['foreignUsed'][$i][$domain];
 704                         $this->connLogger->debug( __METHOD__ . ": reusing connection $i/$domain" );
 705                 } elseif ( isset( $this->mConns['foreignFree'][$i][$domain] ) ) {
 706                         // Reuse a free connection for the same domain
 707                         $conn = $this->mConns['foreignFree'][$i][$domain];
 708                         unset( $this->mConns['foreignFree'][$i][$domain] );
 709                         $this->mConns['foreignUsed'][$i][$domain] = $conn;
 710                         $this->connLogger->debug( __METHOD__ . ": reusing free connection $i/$domain" );
 711                 } elseif ( !empty( $this->mConns['foreignFree'][$i] ) ) {
 712                         // Reuse a connection from another domain
 713                         $conn = reset( $this->mConns['foreignFree'][$i] );
 714                         $oldDomain = key( $this->mConns['foreignFree'][$i] );
 715                         // The empty string as a DB name means "don't care".
 716                         // DatabaseMysqlBase::open() already handle this on connection.
 717                         if ( strlen( $dbName ) && !$conn->selectDB( $dbName ) ) {
 718                                 $this->mLastError = "Error selecting database '$dbName' on server " .
 719                                         $conn->getServer() . " from client host {$this->host}";
 720                                 $this->mErrorConnection = $conn;
 721                                 $conn = false;
 722                         } else {
 723                                 $conn->tablePrefix( $prefix );
 724                                 unset( $this->mConns['foreignFree'][$i][$oldDomain] );
 725                                 $this->mConns['foreignUsed'][$i][$domain] = $conn;
 726                                 $this->connLogger->debug( __METHOD__ .
 727                                         ": reusing free connection from $oldDomain for $domain" );
 728                         }
 729                 } else {
 730                         // Open a new connection
 731                         $server = $this->mServers[$i];
 732                         $server['serverIndex'] = $i;
 733                         $server['foreignPoolRefCount'] = 0;
 734                         $server['foreign'] = true;
 735                         $conn = $this->reallyOpenConnection( $server, $dbName );
 736                         if ( !$conn->isOpen() ) {
 737                                 $this->connLogger->warning( __METHOD__ . ": connection error for $i/$domain" );
 738                                 $this->mErrorConnection = $conn;
 739                                 $conn = false;
 740                         } else {
 741                                 $conn->tablePrefix( $prefix );
 742                                 $this->mConns['foreignUsed'][$i][$domain] = $conn;
 743                                 $this->connLogger->debug( __METHOD__ . ": opened new connection for $i/$domain" );
 744                         }
 745                 }
 746
 747                 // Increment reference count
 748                 if ( $conn ) {
 749                         $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 750                         $conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
 751                 }
 752
 753                 return $conn;
 754         }
 755
 756         /**
 757          * Test if the specified index represents an open connection
 758          *
 759          * @param int $index Server index
 760          * @access private
 761          * @return bool
 762          */
 763         private function isOpen( $index ) {
 764                 if ( !is_integer( $index ) ) {
 765                         return false;
 766                 }
 767
 768                 return (bool)$this->getAnyOpenConnection( $index );
 769         }
 770
 771         /**
 772          * Really opens a connection. Uncached.
 773          * Returns a Database object whether or not the connection was successful.
 774          * @access private
 775          *
 776          * @param array $server
 777          * @param string|bool $dbNameOverride Use "" to not select any database
 778          * @return IDatabase
 779          * @throws DBAccessError
 780          * @throws InvalidArgumentException
 781          */
 782         protected function reallyOpenConnection( $server, $dbNameOverride = false ) {
 783                 if ( $this->disabled ) {
 784                         throw new DBAccessError();
 785                 }
 786
 787                 if ( !is_array( $server ) ) {
 788                         throw new InvalidArgumentException(
 789                                 'You must update your load-balancing configuration. ' .
 790                                 'See DefaultSettings.php entry for $wgDBservers.' );
 791                 }
 792
 793                 if ( $dbNameOverride !== false ) {
 794                         $server['dbname'] = $dbNameOverride;
 795                 }
 796
 797                 // Let the handle know what the cluster master is (e.g. "db1052")
 798                 $masterName = $this->getServerName( $this->getWriterIndex() );
 799                 $server['clusterMasterHost'] = $masterName;
 800
 801                 // Log when many connection are made on requests
 802                 if ( ++$this->connsOpened >= self::CONN_HELD_WARN_THRESHOLD ) {
 803                         $this->perfLogger->warning( __METHOD__ . ": " .
 804                                 "{$this->connsOpened}+ connections made (master=$masterName)" );
 805                 }
 806
 807                 $server['srvCache'] = $this->srvCache;
 808                 // Set loggers and profilers
 809                 $server['connLogger'] = $this->connLogger;
 810                 $server['queryLogger'] = $this->queryLogger;
 811                 $server['errorLogger'] = $this->errorLogger;
 812                 $server['profiler'] = $this->profiler;
 813                 $server['trxProfiler'] = $this->trxProfiler;
 814                 // Use the same agent and PHP mode for all DB handles
 815                 $server['cliMode'] = $this->cliMode;
 816                 $server['agent'] = $this->agent;
 817                 // Use DBO_DEFAULT flags by default for LoadBalancer managed databases. Assume that the
 818                 // application calls LoadBalancer::commitMasterChanges() before the PHP script completes.
 819                 $server['flags'] = isset( $server['flags'] ) ? $server['flags'] : DBO_DEFAULT;
 820
 821                 // Create a live connection object
 822                 try {
 823                         $db = Database::factory( $server['type'], $server );
 824                 } catch ( DBConnectionError $e ) {
 825                         // FIXME: This is probably the ugliest thing I have ever done to
 826                         // PHP. I'm half-expecting it to segfault, just out of disgust. -- TS
 827                         $db = $e->db;
 828                 }
 829
 830                 $db->setLBInfo( $server );
 831                 $db->setLazyMasterHandle(
 832                         $this->getLazyConnectionRef( DB_MASTER, [], $db->getDomainID() )
 833                 );
 834                 $db->setTableAliases( $this->tableAliases );
 835
 836                 if ( $server['serverIndex'] === $this->getWriterIndex() ) {
 837                         if ( $this->trxRoundId !== false ) {
 838                                 $this->applyTransactionRoundFlags( $db );
 839                         }
 840                         foreach ( $this->trxRecurringCallbacks as $name => $callback ) {
 841                                 $db->setTransactionListener( $name, $callback );
 842                         }
 843                 }
 844
 845                 return $db;
 846         }
 847
 848         /**
 849          * @throws DBConnectionError
 850          * @return bool
 851          */
 852         private function reportConnectionError() {
 853                 $conn = $this->mErrorConnection; // The connection which caused the error
 854                 $context = [
 855                         'method' => __METHOD__,
 856                         'last_error' => $this->mLastError,
 857                 ];
 858
 859                 if ( !is_object( $conn ) ) {
 860                         // No last connection, probably due to all servers being too busy
 861                         $this->connLogger->error(
 862                                 "LB failure with no last connection. Connection error: {last_error}",
 863                                 $context
 864                         );
 865
 866                         // If all servers were busy, mLastError will contain something sensible
 867                         throw new DBConnectionError( null, $this->mLastError );
 868                 } else {
 869                         $context['db_server'] = $conn->getProperty( 'mServer' );
 870                         $this->connLogger->warning(
 871                                 "Connection error: {last_error} ({db_server})",
 872                                 $context
 873                         );
 874
 875                         // throws DBConnectionError
 876                         $conn->reportConnectionError( "{$this->mLastError} ({$context['db_server']})" );
 877                 }
 878
 879                 return false; /* not reached */
 880         }
 881
 882         public function getWriterIndex() {
 883                 return 0;
 884         }
 885
 886         public function haveIndex( $i ) {
 887                 return array_key_exists( $i, $this->mServers );
 888         }
 889
 890         public function isNonZeroLoad( $i ) {
 891                 return array_key_exists( $i, $this->mServers ) && $this->mLoads[$i] != 0;
 892         }
 893
 894         public function getServerCount() {
 895                 return count( $this->mServers );
 896         }
 897
 898         public function getServerName( $i ) {
 899                 if ( isset( $this->mServers[$i]['hostName'] ) ) {
 900                         $name = $this->mServers[$i]['hostName'];
 901                 } elseif ( isset( $this->mServers[$i]['host'] ) ) {
 902                         $name = $this->mServers[$i]['host'];
 903                 } else {
 904                         $name = '';
 905                 }
 906
 907                 return ( $name != '' ) ? $name : 'localhost';
 908         }
 909
 910         public function getServerInfo( $i ) {
 911                 if ( isset( $this->mServers[$i] ) ) {
 912                         return $this->mServers[$i];
 913                 } else {
 914                         return false;
 915                 }
 916         }
 917
 918         public function setServerInfo( $i, array $serverInfo ) {
 919                 $this->mServers[$i] = $serverInfo;
 920         }
 921
 922         public function getMasterPos() {
 923                 # If this entire request was served from a replica DB without opening a connection to the
 924                 # master (however unlikely that may be), then we can fetch the position from the replica DB.
 925                 $masterConn = $this->getAnyOpenConnection( $this->getWriterIndex() );
 926                 if ( !$masterConn ) {
 927                         $serverCount = count( $this->mServers );
 928                         for ( $i = 1; $i < $serverCount; $i++ ) {
 929                                 $conn = $this->getAnyOpenConnection( $i );
 930                                 if ( $conn ) {
 931                                         return $conn->getSlavePos();
 932                                 }
 933                         }
 934                 } else {
 935                         return $masterConn->getMasterPos();
 936                 }
 937
 938                 return false;
 939         }
 940
 941         public function disable() {
 942                 $this->closeAll();
 943                 $this->disabled = true;
 944         }
 945
 946         public function closeAll() {
 947                 $this->forEachOpenConnection( function ( IDatabase $conn ) {
 948                         $host = $conn->getServer();
 949                         $this->connLogger->debug( "Closing connection to database '$host'." );
 950                         $conn->close();
 951                 } );
 952
 953                 $this->mConns = [
 954                         'local' => [],
 955                         'foreignFree' => [],
 956                         'foreignUsed' => [],
 957                 ];
 958                 $this->connsOpened = 0;
 959         }
 960
 961         public function closeConnection( IDatabase $conn ) {
 962                 $serverIndex = $conn->getLBInfo( 'serverIndex' ); // second index level of mConns
 963                 foreach ( $this->mConns as $type => $connsByServer ) {
 964                         if ( !isset( $connsByServer[$serverIndex] ) ) {
 965                                 continue;
 966                         }
 967
 968                         foreach ( $connsByServer[$serverIndex] as $i => $trackedConn ) {
 969                                 if ( $conn === $trackedConn ) {
 970                                         $host = $this->getServerName( $i );
 971                                         $this->connLogger->debug( "Closing connection to database $i at '$host'." );
 972                                         unset( $this->mConns[$type][$serverIndex][$i] );
 973                                         --$this->connsOpened;
 974                                         break 2;
 975                                 }
 976                         }
 977                 }
 978
 979                 $conn->close();
 980         }
 981
 982         public function commitAll( $fname = __METHOD__ ) {
 983                 $failures = [];
 984
 985                 $restore = ( $this->trxRoundId !== false );
 986                 $this->trxRoundId = false;
 987                 $this->forEachOpenConnection(
 988                         function ( IDatabase $conn ) use ( $fname, $restore, &$failures ) {
 989                                 try {
 990                                         $conn->commit( $fname, $conn::FLUSHING_ALL_PEERS );
 991                                 } catch ( DBError $e ) {
 992                                         call_user_func( $this->errorLogger, $e );
 993                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
 994                                 }
 995                                 if ( $restore && $conn->getLBInfo( 'master' ) ) {
 996                                         $this->undoTransactionRoundFlags( $conn );
 997                                 }
 998                         }
 999                 );
1000
1001                 if ( $failures ) {
1002                         throw new DBExpectedError(
1003                                 null,
1004                                 "Commit failed on server(s) " . implode( "\n", array_unique( $failures ) )
1005                         );
1006                 }
1007         }
1008
1009         public function finalizeMasterChanges() {
1010                 $this->forEachOpenMasterConnection( function ( DatabaseBase $conn ) {
1011                         // Any error should cause all DB transactions to be rolled back together
1012                         $conn->setTrxEndCallbackSuppression( false );
1013                         $conn->runOnTransactionPreCommitCallbacks();
1014                         // Defer post-commit callbacks until COMMIT finishes for all DBs
1015                         $conn->setTrxEndCallbackSuppression( true );
1016                 } );
1017         }
1018
1019         public function approveMasterChanges( array $options ) {
1020                 $limit = isset( $options['maxWriteDuration'] ) ? $options['maxWriteDuration'] : 0;
1021                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( $limit ) {
1022                         // If atomic sections or explicit transactions are still open, some caller must have
1023                         // caught an exception but failed to properly rollback any changes. Detect that and
1024                         // throw and error (causing rollback).
1025                         if ( $conn->explicitTrxActive() ) {
1026                                 throw new DBTransactionError(
1027                                         $conn,
1028                                         "Explicit transaction still active. A caller may have caught an error."
1029                                 );
1030                         }
1031                         // Assert that the time to replicate the transaction will be sane.
1032                         // If this fails, then all DB transactions will be rollback back together.
1033                         $time = $conn->pendingWriteQueryDuration( $conn::ESTIMATE_DB_APPLY );
1034                         if ( $limit > 0 && $time > $limit ) {
1035                                 throw new DBTransactionSizeError(
1036                                         $conn,
1037                                         "Transaction spent $time second(s) in writes, exceeding the $limit limit.",
1038                                         [ $time, $limit ]
1039                                 );
1040                         }
1041                         // If a connection sits idle while slow queries execute on another, that connection
1042                         // may end up dropped before the commit round is reached. Ping servers to detect this.
1043                         if ( $conn->writesOrCallbacksPending() && !$conn->ping() ) {
1044                                 throw new DBTransactionError(
1045                                         $conn,
1046                                         "A connection to the {$conn->getDBname()} database was lost before commit."
1047                                 );
1048                         }
1049                 } );
1050         }
1051
1052         public function beginMasterChanges( $fname = __METHOD__ ) {
1053                 if ( $this->trxRoundId !== false ) {
1054                         throw new DBTransactionError(
1055                                 null,
1056                                 "$fname: Transaction round '{$this->trxRoundId}' already started."
1057                         );
1058                 }
1059                 $this->trxRoundId = $fname;
1060
1061                 $failures = [];
1062                 $this->forEachOpenMasterConnection(
1063                         function ( DatabaseBase $conn ) use ( $fname, &$failures ) {
1064                                 $conn->setTrxEndCallbackSuppression( true );
1065                                 try {
1066                                         $conn->flushSnapshot( $fname );
1067                                 } catch ( DBError $e ) {
1068                                         call_user_func( $this->errorLogger, $e );
1069                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1070                                 }
1071                                 $conn->setTrxEndCallbackSuppression( false );
1072                                 $this->applyTransactionRoundFlags( $conn );
1073                         }
1074                 );
1075
1076                 if ( $failures ) {
1077                         throw new DBExpectedError(
1078                                 null,
1079                                 "$fname: Flush failed on server(s) " . implode( "\n", array_unique( $failures ) )
1080                         );
1081                 }
1082         }
1083
1084         public function commitMasterChanges( $fname = __METHOD__ ) {
1085                 $failures = [];
1086
1087                 $restore = ( $this->trxRoundId !== false );
1088                 $this->trxRoundId = false;
1089                 $this->forEachOpenMasterConnection(
1090                         function ( IDatabase $conn ) use ( $fname, $restore, &$failures ) {
1091                                 try {
1092                                         if ( $conn->writesOrCallbacksPending() ) {
1093                                                 $conn->commit( $fname, $conn::FLUSHING_ALL_PEERS );
1094                                         } elseif ( $restore ) {
1095                                                 $conn->flushSnapshot( $fname );
1096                                         }
1097                                 } catch ( DBError $e ) {
1098                                         call_user_func( $this->errorLogger, $e );
1099                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1100                                 }
1101                                 if ( $restore ) {
1102                                         $this->undoTransactionRoundFlags( $conn );
1103                                 }
1104                         }
1105                 );
1106
1107                 if ( $failures ) {
1108                         throw new DBExpectedError(
1109                                 null,
1110                                 "$fname: Commit failed on server(s) " . implode( "\n", array_unique( $failures ) )
1111                         );
1112                 }
1113         }
1114
1115         public function runMasterPostTrxCallbacks( $type ) {
1116                 $e = null; // first exception
1117                 $this->forEachOpenMasterConnection( function ( DatabaseBase $conn ) use ( $type, &$e ) {
1118                         $conn->setTrxEndCallbackSuppression( false );
1119                         if ( $conn->writesOrCallbacksPending() ) {
1120                                 // This happens if onTransactionIdle() callbacks leave callbacks on *another* DB
1121                                 // (which finished its callbacks already). Warn and recover in this case. Let the
1122                                 // callbacks run in the final commitMasterChanges() in LBFactory::shutdown().
1123                                 $this->queryLogger->error( __METHOD__ . ": found writes/callbacks pending." );
1124                                 return;
1125                         } elseif ( $conn->trxLevel() ) {
1126                                 // This happens for single-DB setups where DB_REPLICA uses the master DB,
1127                                 // thus leaving an implicit read-only transaction open at this point. It
1128                                 // also happens if onTransactionIdle() callbacks leave implicit transactions
1129                                 // open on *other* DBs (which is slightly improper). Let these COMMIT on the
1130                                 // next call to commitMasterChanges(), possibly in LBFactory::shutdown().
1131                                 return;
1132                         }
1133                         try {
1134                                 $conn->runOnTransactionIdleCallbacks( $type );
1135                         } catch ( Exception $ex ) {
1136                                 $e = $e ?: $ex;
1137                         }
1138                         try {
1139                                 $conn->runTransactionListenerCallbacks( $type );
1140                         } catch ( Exception $ex ) {
1141                                 $e = $e ?: $ex;
1142                         }
1143                 } );
1144
1145                 return $e;
1146         }
1147
1148         public function rollbackMasterChanges( $fname = __METHOD__ ) {
1149                 $restore = ( $this->trxRoundId !== false );
1150                 $this->trxRoundId = false;
1151                 $this->forEachOpenMasterConnection(
1152                         function ( IDatabase $conn ) use ( $fname, $restore ) {
1153                                 if ( $conn->writesOrCallbacksPending() ) {
1154                                         $conn->rollback( $fname, $conn::FLUSHING_ALL_PEERS );
1155                                 }
1156                                 if ( $restore ) {
1157                                         $this->undoTransactionRoundFlags( $conn );
1158                                 }
1159                         }
1160                 );
1161         }
1162
1163         public function suppressTransactionEndCallbacks() {
1164                 $this->forEachOpenMasterConnection( function ( DatabaseBase $conn ) {
1165                         $conn->setTrxEndCallbackSuppression( true );
1166                 } );
1167         }
1168
1169         /**
1170          * @param IDatabase $conn
1171          */
1172         private function applyTransactionRoundFlags( IDatabase $conn ) {
1173                 if ( $conn->getFlag( DBO_DEFAULT ) ) {
1174                         // DBO_TRX is controlled entirely by CLI mode presence with DBO_DEFAULT.
1175                         // Force DBO_TRX even in CLI mode since a commit round is expected soon.
1176                         $conn->setFlag( DBO_TRX, $conn::REMEMBER_PRIOR );
1177                         // If config has explicitly requested DBO_TRX be either on or off by not
1178                         // setting DBO_DEFAULT, then respect that. Forcing no transactions is useful
1179                         // for things like blob stores (ExternalStore) which want auto-commit mode.
1180                 }
1181         }
1182
1183         /**
1184          * @param IDatabase $conn
1185          */
1186         private function undoTransactionRoundFlags( IDatabase $conn ) {
1187                 if ( $conn->getFlag( DBO_DEFAULT ) ) {
1188                         $conn->restoreFlags( $conn::RESTORE_PRIOR );
1189                 }
1190         }
1191
1192         public function flushReplicaSnapshots( $fname = __METHOD__ ) {
1193                 $this->forEachOpenReplicaConnection( function ( IDatabase $conn ) {
1194                         $conn->flushSnapshot( __METHOD__ );
1195                 } );
1196         }
1197
1198         public function hasMasterConnection() {
1199                 return $this->isOpen( $this->getWriterIndex() );
1200         }
1201
1202         public function hasMasterChanges() {
1203                 $pending = 0;
1204                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$pending ) {
1205                         $pending |= $conn->writesOrCallbacksPending();
1206                 } );
1207
1208                 return (bool)$pending;
1209         }
1210
1211         public function lastMasterChangeTimestamp() {
1212                 $lastTime = false;
1213                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$lastTime ) {
1214                         $lastTime = max( $lastTime, $conn->lastDoneWrites() );
1215                 } );
1216
1217                 return $lastTime;
1218         }
1219
1220         public function hasOrMadeRecentMasterChanges( $age = null ) {
1221                 $age = ( $age === null ) ? $this->mWaitTimeout : $age;
1222
1223                 return ( $this->hasMasterChanges()
1224                         || $this->lastMasterChangeTimestamp() > microtime( true ) - $age );
1225         }
1226
1227         public function pendingMasterChangeCallers() {
1228                 $fnames = [];
1229                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$fnames ) {
1230                         $fnames = array_merge( $fnames, $conn->pendingWriteCallers() );
1231                 } );
1232
1233                 return $fnames;
1234         }
1235
1236         public function getLaggedReplicaMode( $domain = false ) {
1237                 // No-op if there is only one DB (also avoids recursion)
1238                 if ( !$this->laggedReplicaMode && $this->getServerCount() > 1 ) {
1239                         try {
1240                                 // See if laggedReplicaMode gets set
1241                                 $conn = $this->getConnection( DB_REPLICA, false, $domain );
1242                                 $this->reuseConnection( $conn );
1243                         } catch ( DBConnectionError $e ) {
1244                                 // Avoid expensive re-connect attempts and failures
1245                                 $this->allReplicasDownMode = true;
1246                                 $this->laggedReplicaMode = true;
1247                         }
1248                 }
1249
1250                 return $this->laggedReplicaMode;
1251         }
1252
1253         /**
1254          * @param bool $domain
1255          * @return bool
1256          * @deprecated 1.28; use getLaggedReplicaMode()
1257          */
1258         public function getLaggedSlaveMode( $domain = false ) {
1259                 return $this->getLaggedReplicaMode( $domain );
1260         }
1261
1262         public function laggedReplicaUsed() {
1263                 return $this->laggedReplicaMode;
1264         }
1265
1266         /**
1267          * @return bool
1268          * @since 1.27
1269          * @deprecated Since 1.28; use laggedReplicaUsed()
1270          */
1271         public function laggedSlaveUsed() {
1272                 return $this->laggedReplicaUsed();
1273         }
1274
1275         public function getReadOnlyReason( $domain = false, IDatabase $conn = null ) {
1276                 if ( $this->readOnlyReason !== false ) {
1277                         return $this->readOnlyReason;
1278                 } elseif ( $this->getLaggedReplicaMode( $domain ) ) {
1279                         if ( $this->allReplicasDownMode ) {
1280                                 return 'The database has been automatically locked ' .
1281                                         'until the replica database servers become available';
1282                         } else {
1283                                 return 'The database has been automatically locked ' .
1284                                         'while the replica database servers catch up to the master.';
1285                         }
1286                 } elseif ( $this->masterRunningReadOnly( $domain, $conn ) ) {
1287                         return 'The database master is running in read-only mode.';
1288                 }
1289
1290                 return false;
1291         }
1292
1293         /**
1294          * @param string $domain Domain ID, or false for the current domain
1295          * @param IDatabase|null DB master connectionl used to avoid loops [optional]
1296          * @return bool
1297          */
1298         private function masterRunningReadOnly( $domain, IDatabase $conn = null ) {
1299                 $cache = $this->wanCache;
1300                 $masterServer = $this->getServerName( $this->getWriterIndex() );
1301
1302                 return (bool)$cache->getWithSetCallback(
1303                         $cache->makeGlobalKey( __CLASS__, 'server-read-only', $masterServer ),
1304                         self::TTL_CACHE_READONLY,
1305                         function () use ( $domain, $conn ) {
1306                                 $this->trxProfiler->setSilenced( true );
1307                                 try {
1308                                         $dbw = $conn ?: $this->getConnection( DB_MASTER, [], $domain );
1309                                         $readOnly = (int)$dbw->serverIsReadOnly();
1310                                         if ( !$conn ) {
1311                                                 $this->reuseConnection( $dbw );
1312                                         }
1313                                 } catch ( DBError $e ) {
1314                                         $readOnly = 0;
1315                                 }
1316                                 $this->trxProfiler->setSilenced( false );
1317                                 return $readOnly;
1318                         },
1319                         [ 'pcTTL' => $cache::TTL_PROC_LONG, 'busyValue' => 0 ]
1320                 );
1321         }
1322
1323         public function allowLagged( $mode = null ) {
1324                 if ( $mode === null ) {
1325                         return $this->mAllowLagged;
1326                 }
1327                 $this->mAllowLagged = $mode;
1328
1329                 return $this->mAllowLagged;
1330         }
1331
1332         public function pingAll() {
1333                 $success = true;
1334                 $this->forEachOpenConnection( function ( IDatabase $conn ) use ( &$success ) {
1335                         if ( !$conn->ping() ) {
1336                                 $success = false;
1337                         }
1338                 } );
1339
1340                 return $success;
1341         }
1342
1343         public function forEachOpenConnection( $callback, array $params = [] ) {
1344                 foreach ( $this->mConns as $connsByServer ) {
1345                         foreach ( $connsByServer as $serverConns ) {
1346                                 foreach ( $serverConns as $conn ) {
1347                                         $mergedParams = array_merge( [ $conn ], $params );
1348                                         call_user_func_array( $callback, $mergedParams );
1349                                 }
1350                         }
1351                 }
1352         }
1353
1354         public function forEachOpenMasterConnection( $callback, array $params = [] ) {
1355                 $masterIndex = $this->getWriterIndex();
1356                 foreach ( $this->mConns as $connsByServer ) {
1357                         if ( isset( $connsByServer[$masterIndex] ) ) {
1358                                 /** @var IDatabase $conn */
1359                                 foreach ( $connsByServer[$masterIndex] as $conn ) {
1360                                         $mergedParams = array_merge( [ $conn ], $params );
1361                                         call_user_func_array( $callback, $mergedParams );
1362                                 }
1363                         }
1364                 }
1365         }
1366
1367         public function forEachOpenReplicaConnection( $callback, array $params = [] ) {
1368                 foreach ( $this->mConns as $connsByServer ) {
1369                         foreach ( $connsByServer as $i => $serverConns ) {
1370                                 if ( $i === $this->getWriterIndex() ) {
1371                                         continue; // skip master
1372                                 }
1373                                 foreach ( $serverConns as $conn ) {
1374                                         $mergedParams = array_merge( [ $conn ], $params );
1375                                         call_user_func_array( $callback, $mergedParams );
1376                                 }
1377                         }
1378                 }
1379         }
1380
1381         public function getMaxLag( $domain = false ) {
1382                 $maxLag = -1;
1383                 $host = '';
1384                 $maxIndex = 0;
1385
1386                 if ( $this->getServerCount() <= 1 ) {
1387                         return [ $host, $maxLag, $maxIndex ]; // no replication = no lag
1388                 }
1389
1390                 $lagTimes = $this->getLagTimes( $domain );
1391                 foreach ( $lagTimes as $i => $lag ) {
1392                         if ( $this->mLoads[$i] > 0 && $lag > $maxLag ) {
1393                                 $maxLag = $lag;
1394                                 $host = $this->mServers[$i]['host'];
1395                                 $maxIndex = $i;
1396                         }
1397                 }
1398
1399                 return [ $host, $maxLag, $maxIndex ];
1400         }
1401
1402         public function getLagTimes( $domain = false ) {
1403                 if ( $this->getServerCount() <= 1 ) {
1404                         return [ $this->getWriterIndex() => 0 ]; // no replication = no lag
1405                 }
1406
1407                 $knownLagTimes = []; // map of (server index => 0 seconds)
1408                 $indexesWithLag = [];
1409                 foreach ( $this->mServers as $i => $server ) {
1410                         if ( empty( $server['is static'] ) ) {
1411                                 $indexesWithLag[] = $i; // DB server might have replication lag
1412                         } else {
1413                                 $knownLagTimes[$i] = 0; // DB server is a non-replicating and read-only archive
1414                         }
1415                 }
1416
1417                 return $this->getLoadMonitor()->getLagTimes( $indexesWithLag, $domain ) + $knownLagTimes;
1418         }
1419
1420         public function safeGetLag( IDatabase $conn ) {
1421                 if ( $this->getServerCount() <= 1 ) {
1422                         return 0;
1423                 } else {
1424                         return $conn->getLag();
1425                 }
1426         }
1427
1428         public function safeWaitForMasterPos( IDatabase $conn, $pos = false, $timeout = 10 ) {
1429                 if ( $this->getServerCount() <= 1 || !$conn->getLBInfo( 'replica' ) ) {
1430                         return true; // server is not a replica DB
1431                 }
1432
1433                 if ( !$pos ) {
1434                         // Get the current master position
1435                         $dbw = $this->getConnection( DB_MASTER );
1436                         $pos = $dbw->getMasterPos();
1437                         $this->reuseConnection( $dbw );
1438                 }
1439
1440                 if ( $pos instanceof DBMasterPos ) {
1441                         $result = $conn->masterPosWait( $pos, $timeout );
1442                         if ( $result == -1 || is_null( $result ) ) {
1443                                 $msg = __METHOD__ . ": Timed out waiting on {$conn->getServer()} pos {$pos}";
1444                                 $this->replLogger->warning( "$msg" );
1445                                 $ok = false;
1446                         } else {
1447                                 $this->replLogger->info( __METHOD__ . ": Done" );
1448                                 $ok = true;
1449                         }
1450                 } else {
1451                         $ok = false; // something is misconfigured
1452                         $this->replLogger->error( "Could not get master pos for {$conn->getServer()}." );
1453                 }
1454
1455                 return $ok;
1456         }
1457
1458         public function clearLagTimeCache() {
1459                 $this->getLoadMonitor()->clearCaches();
1460         }
1461
1462         public function setTransactionListener( $name, callable $callback = null ) {
1463                 if ( $callback ) {
1464                         $this->trxRecurringCallbacks[$name] = $callback;
1465                 } else {
1466                         unset( $this->trxRecurringCallbacks[$name] );
1467                 }
1468                 $this->forEachOpenMasterConnection(
1469                         function ( IDatabase $conn ) use ( $name, $callback ) {
1470                                 $conn->setTransactionListener( $name, $callback );
1471                         }
1472                 );
1473         }
1474
1475         public function setTableAliases( array $aliases ) {
1476                 $this->tableAliases = $aliases;
1477         }
1478
1479         public function setDomainPrefix( $prefix ) {
1480                 if ( $this->mConns['foreignUsed'] ) {
1481                         // Do not switch connections to explicit foreign domains unless marked as free
1482                         $domains = [];
1483                         foreach ( $this->mConns['foreignUsed'] as $i => $connsByDomain ) {
1484                                 $domains = array_merge( $domains, array_keys( $connsByDomain ) );
1485                         }
1486                         $domains = implode( ', ', $domains );
1487                         throw new DBUnexpectedError( null,
1488                                 "Foreign domain connections are still in use ($domains)." );
1489                 }
1490
1491                 $this->localDomain = new DatabaseDomain(
1492                         $this->localDomain->getDatabase(),
1493                         null,
1494                         $prefix
1495                 );
1496
1497                 $this->forEachOpenConnection( function ( IDatabase $db ) use ( $prefix ) {
1498                         $db->tablePrefix( $prefix );
1499                 } );
1500         }
1501
1502         function __destruct() {
1503                 // Avoid connection leaks for sanity
1504                 $this->closeAll();
1505         }
1506 }