includes/libs/rdbms/loadbalancer/LoadBalancer.php

   1 <?php
   2 /**
   3  * Database load balancing manager
   4  *
   5  * This program is free software; you can redistribute it and/or modify
   6  * it under the terms of the GNU General Public License as published by
   7  * the Free Software Foundation; either version 2 of the License, or
   8  * (at your option) any later version.
   9  *
  10  * This program is distributed in the hope that it will be useful,
  11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  13  * GNU General Public License for more details.
  14  *
  15  * You should have received a copy of the GNU General Public License along
  16  * with this program; if not, write to the Free Software Foundation, Inc.,
  17  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
  18  * http://www.gnu.org/copyleft/gpl.html
  19  *
  20  * @file
  21  * @ingroup Database
  22  */
  23 use Psr\Log\LoggerInterface;
  24 use Wikimedia\ScopedCallback;
  25
  26 /**
  27  * Database connection, tracking, load balancing, and transaction manager for a cluster
  28  *
  29  * @ingroup Database
  30  */
  31 class LoadBalancer implements ILoadBalancer {
  32         /** @var array[] Map of (server index => server config array) */
  33         private $mServers;
  34         /** @var array[] Map of (local/foreignUsed/foreignFree => server index => IDatabase array) */
  35         private $mConns;
  36         /** @var float[] Map of (server index => weight) */
  37         private $mLoads;
  38         /** @var array[] Map of (group => server index => weight) */
  39         private $mGroupLoads;
  40         /** @var bool Whether to disregard replica DB lag as a factor in replica DB selection */
  41         private $mAllowLagged;
  42         /** @var integer Seconds to spend waiting on replica DB lag to resolve */
  43         private $mWaitTimeout;
  44         /** @var array The LoadMonitor configuration */
  45         private $loadMonitorConfig;
  46         /** @var array[] $aliases Map of (table => (dbname, schema, prefix) map) */
  47         private $tableAliases = [];
  48
  49         /** @var ILoadMonitor */
  50         private $loadMonitor;
  51         /** @var BagOStuff */
  52         private $srvCache;
  53         /** @var BagOStuff */
  54         private $memCache;
  55         /** @var WANObjectCache */
  56         private $wanCache;
  57         /** @var object|string Class name or object With profileIn/profileOut methods */
  58         protected $profiler;
  59         /** @var TransactionProfiler */
  60         protected $trxProfiler;
  61         /** @var LoggerInterface */
  62         protected $replLogger;
  63         /** @var LoggerInterface */
  64         protected $connLogger;
  65         /** @var LoggerInterface */
  66         protected $queryLogger;
  67         /** @var LoggerInterface */
  68         protected $perfLogger;
  69
  70         /** @var bool|IDatabase Database connection that caused a problem */
  71         private $mErrorConnection;
  72         /** @var integer The generic (not query grouped) replica DB index (of $mServers) */
  73         private $mReadIndex;
  74         /** @var bool|DBMasterPos False if not set */
  75         private $mWaitForPos;
  76         /** @var bool Whether the generic reader fell back to a lagged replica DB */
  77         private $laggedReplicaMode = false;
  78         /** @var bool Whether the generic reader fell back to a lagged replica DB */
  79         private $allReplicasDownMode = false;
  80         /** @var string The last DB selection or connection error */
  81         private $mLastError = 'Unknown error';
  82         /** @var string|bool Reason the LB is read-only or false if not */
  83         private $readOnlyReason = false;
  84         /** @var integer Total connections opened */
  85         private $connsOpened = 0;
  86         /** @var string|bool String if a requested DBO_TRX transaction round is active */
  87         private $trxRoundId = false;
  88         /** @var array[] Map of (name => callable) */
  89         private $trxRecurringCallbacks = [];
  90         /** @var DatabaseDomain Local Domain ID and default for selectDB() calls */
  91         private $localDomain;
  92         /** @var string Alternate ID string for the domain instead of DatabaseDomain::getId() */
  93         private $localDomainIdAlias;
  94         /** @var string Current server name */
  95         private $host;
  96         /** @var bool Whether this PHP instance is for a CLI script */
  97         private $cliMode;
  98         /** @var string Agent name for query profiling */
  99         private $agent;
 100         /** @var bool[] Map of (section ID => true) for usage section IDs */
 101         private $usageSections = [];
 102
 103         /** @var callable Exception logger */
 104         private $errorLogger;
 105
 106         /** @var boolean */
 107         private $disabled = false;
 108
 109         /** @var integer Warn when this many connection are held */
 110         const CONN_HELD_WARN_THRESHOLD = 10;
 111
 112         /** @var integer Default 'max lag' when unspecified */
 113         const MAX_LAG_DEFAULT = 10;
 114         /** @var integer Seconds to cache master server read-only status */
 115         const TTL_CACHE_READONLY = 5;
 116
 117         public function __construct( array $params ) {
 118                 if ( !isset( $params['servers'] ) ) {
 119                         throw new InvalidArgumentException( __CLASS__ . ': missing servers parameter' );
 120                 }
 121                 $this->mServers = $params['servers'];
 122
 123                 $this->localDomain = isset( $params['localDomain'] )
 124                         ? DatabaseDomain::newFromId( $params['localDomain'] )
 125                         : DatabaseDomain::newUnspecified();
 126                 // In case a caller assumes that the domain ID is simply <db>-<prefix>, which is almost
 127                 // always true, gracefully handle the case when they fail to account for escaping.
 128                 if ( $this->localDomain->getTablePrefix() != '' ) {
 129                         $this->localDomainIdAlias =
 130                                 $this->localDomain->getDatabase() . '-' . $this->localDomain->getTablePrefix();
 131                 } else {
 132                         $this->localDomainIdAlias = $this->localDomain->getDatabase();
 133                 }
 134
 135                 $this->mWaitTimeout = isset( $params['waitTimeout'] ) ? $params['waitTimeout'] : 10;
 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->loadMonitorConfig = $params['loadMonitor'];
 154                 } else {
 155                         $this->loadMonitorConfig = [ 'class' => 'LoadMonitorNull' ];
 156                 }
 157
 158                 foreach ( $params['servers'] as $i => $server ) {
 159                         $this->mLoads[$i] = $server['load'];
 160                         if ( isset( $server['groupLoads'] ) ) {
 161                                 foreach ( $server['groupLoads'] as $group => $ratio ) {
 162                                         if ( !isset( $this->mGroupLoads[$group] ) ) {
 163                                                 $this->mGroupLoads[$group] = [];
 164                                         }
 165                                         $this->mGroupLoads[$group][$i] = $ratio;
 166                                 }
 167                         }
 168                 }
 169
 170                 if ( isset( $params['srvCache'] ) ) {
 171                         $this->srvCache = $params['srvCache'];
 172                 } else {
 173                         $this->srvCache = new EmptyBagOStuff();
 174                 }
 175                 if ( isset( $params['memCache'] ) ) {
 176                         $this->memCache = $params['memCache'];
 177                 } else {
 178                         $this->memCache = new EmptyBagOStuff();
 179                 }
 180                 if ( isset( $params['wanCache'] ) ) {
 181                         $this->wanCache = $params['wanCache'];
 182                 } else {
 183                         $this->wanCache = WANObjectCache::newEmpty();
 184                 }
 185                 $this->profiler = isset( $params['profiler'] ) ? $params['profiler'] : null;
 186                 if ( isset( $params['trxProfiler'] ) ) {
 187                         $this->trxProfiler = $params['trxProfiler'];
 188                 } else {
 189                         $this->trxProfiler = new TransactionProfiler();
 190                 }
 191
 192                 $this->errorLogger = isset( $params['errorLogger'] )
 193                         ? $params['errorLogger']
 194                         : function ( Exception $e ) {
 195                                 trigger_error( get_class( $e ) . ': ' . $e->getMessage(), E_USER_WARNING );
 196                         };
 197
 198                 foreach ( [ 'replLogger', 'connLogger', 'queryLogger', 'perfLogger' ] as $key ) {
 199                         $this->$key = isset( $params[$key] ) ? $params[$key] : new \Psr\Log\NullLogger();
 200                 }
 201
 202                 $this->host = isset( $params['hostname'] )
 203                         ? $params['hostname']
 204                         : ( gethostname() ?: 'unknown' );
 205                 $this->cliMode = isset( $params['cliMode'] ) ? $params['cliMode'] : PHP_SAPI === 'cli';
 206                 $this->agent = isset( $params['agent'] ) ? $params['agent'] : '';
 207         }
 208
 209         /**
 210          * Get a LoadMonitor instance
 211          *
 212          * @return ILoadMonitor
 213          */
 214         private function getLoadMonitor() {
 215                 if ( !isset( $this->loadMonitor ) ) {
 216                         $class = $this->loadMonitorConfig['class'];
 217                         $this->loadMonitor = new $class(
 218                                 $this, $this->srvCache, $this->memCache, $this->loadMonitorConfig );
 219                         $this->loadMonitor->setLogger( $this->replLogger );
 220                 }
 221
 222                 return $this->loadMonitor;
 223         }
 224
 225         /**
 226          * @param array $loads
 227          * @param bool|string $domain Domain to get non-lagged for
 228          * @param int $maxLag Restrict the maximum allowed lag to this many seconds
 229          * @return bool|int|string
 230          */
 231         private function getRandomNonLagged( array $loads, $domain = false, $maxLag = INF ) {
 232                 $lags = $this->getLagTimes( $domain );
 233
 234                 # Unset excessively lagged servers
 235                 foreach ( $lags as $i => $lag ) {
 236                         if ( $i != 0 ) {
 237                                 # How much lag this server nominally is allowed to have
 238                                 $maxServerLag = isset( $this->mServers[$i]['max lag'] )
 239                                         ? $this->mServers[$i]['max lag']
 240                                         : self::MAX_LAG_DEFAULT; // default
 241                                 # Constrain that futher by $maxLag argument
 242                                 $maxServerLag = min( $maxServerLag, $maxLag );
 243
 244                                 $host = $this->getServerName( $i );
 245                                 if ( $lag === false && !is_infinite( $maxServerLag ) ) {
 246                                         $this->replLogger->error( "Server $host (#$i) is not replicating?" );
 247                                         unset( $loads[$i] );
 248                                 } elseif ( $lag > $maxServerLag ) {
 249                                         $this->replLogger->warning( "Server $host (#$i) has >= $lag seconds of lag" );
 250                                         unset( $loads[$i] );
 251                                 }
 252                         }
 253                 }
 254
 255                 # Find out if all the replica DBs with non-zero load are lagged
 256                 $sum = 0;
 257                 foreach ( $loads as $load ) {
 258                         $sum += $load;
 259                 }
 260                 if ( $sum == 0 ) {
 261                         # No appropriate DB servers except maybe the master and some replica DBs with zero load
 262                         # Do NOT use the master
 263                         # Instead, this function will return false, triggering read-only mode,
 264                         # and a lagged replica DB will be used instead.
 265                         return false;
 266                 }
 267
 268                 if ( count( $loads ) == 0 ) {
 269                         return false;
 270                 }
 271
 272                 # Return a random representative of the remainder
 273                 return ArrayUtils::pickRandom( $loads );
 274         }
 275
 276         public function getReaderIndex( $group = false, $domain = false ) {
 277                 if ( count( $this->mServers ) == 1 ) {
 278                         # Skip the load balancing if there's only one server
 279                         return $this->getWriterIndex();
 280                 } elseif ( $group === false && $this->mReadIndex >= 0 ) {
 281                         # Shortcut if generic reader exists already
 282                         return $this->mReadIndex;
 283                 }
 284
 285                 # Find the relevant load array
 286                 if ( $group !== false ) {
 287                         if ( isset( $this->mGroupLoads[$group] ) ) {
 288                                 $nonErrorLoads = $this->mGroupLoads[$group];
 289                         } else {
 290                                 # No loads for this group, return false and the caller can use some other group
 291                                 $this->connLogger->info( __METHOD__ . ": no loads for group $group" );
 292
 293                                 return false;
 294                         }
 295                 } else {
 296                         $nonErrorLoads = $this->mLoads;
 297                 }
 298
 299                 if ( !count( $nonErrorLoads ) ) {
 300                         throw new InvalidArgumentException( "Empty server array given to LoadBalancer" );
 301                 }
 302
 303                 # Scale the configured load ratios according to the dynamic load if supported
 304                 $this->getLoadMonitor()->scaleLoads( $nonErrorLoads, $domain );
 305
 306                 $laggedReplicaMode = false;
 307
 308                 # No server found yet
 309                 $i = false;
 310                 # First try quickly looking through the available servers for a server that
 311                 # meets our criteria
 312                 $currentLoads = $nonErrorLoads;
 313                 while ( count( $currentLoads ) ) {
 314                         if ( $this->mAllowLagged || $laggedReplicaMode ) {
 315                                 $i = ArrayUtils::pickRandom( $currentLoads );
 316                         } else {
 317                                 $i = false;
 318                                 if ( $this->mWaitForPos && $this->mWaitForPos->asOfTime() ) {
 319                                         # ChronologyProtecter causes mWaitForPos to be set via sessions.
 320                                         # This triggers doWait() after connect, so it's especially good to
 321                                         # avoid lagged servers so as to avoid just blocking in that method.
 322                                         $ago = microtime( true ) - $this->mWaitForPos->asOfTime();
 323                                         # Aim for <= 1 second of waiting (being too picky can backfire)
 324                                         $i = $this->getRandomNonLagged( $currentLoads, $domain, $ago + 1 );
 325                                 }
 326                                 if ( $i === false ) {
 327                                         # Any server with less lag than it's 'max lag' param is preferable
 328                                         $i = $this->getRandomNonLagged( $currentLoads, $domain );
 329                                 }
 330                                 if ( $i === false && count( $currentLoads ) != 0 ) {
 331                                         # All replica DBs lagged. Switch to read-only mode
 332                                         $this->replLogger->error( "All replica DBs lagged. Switch to read-only mode" );
 333                                         $i = ArrayUtils::pickRandom( $currentLoads );
 334                                         $laggedReplicaMode = true;
 335                                 }
 336                         }
 337
 338                         if ( $i === false ) {
 339                                 # pickRandom() returned false
 340                                 # This is permanent and means the configuration or the load monitor
 341                                 # wants us to return false.
 342                                 $this->connLogger->debug( __METHOD__ . ": pickRandom() returned false" );
 343
 344                                 return false;
 345                         }
 346
 347                         $serverName = $this->getServerName( $i );
 348                         $this->connLogger->debug( __METHOD__ . ": Using reader #$i: $serverName..." );
 349
 350                         $conn = $this->openConnection( $i, $domain );
 351                         if ( !$conn ) {
 352                                 $this->connLogger->warning( __METHOD__ . ": Failed connecting to $i/$domain" );
 353                                 unset( $nonErrorLoads[$i] );
 354                                 unset( $currentLoads[$i] );
 355                                 $i = false;
 356                                 continue;
 357                         }
 358
 359                         // Decrement reference counter, we are finished with this connection.
 360                         // It will be incremented for the caller later.
 361                         if ( $domain !== false ) {
 362                                 $this->reuseConnection( $conn );
 363                         }
 364
 365                         # Return this server
 366                         break;
 367                 }
 368
 369                 # If all servers were down, quit now
 370                 if ( !count( $nonErrorLoads ) ) {
 371                         $this->connLogger->error( "All servers down" );
 372                 }
 373
 374                 if ( $i !== false ) {
 375                         # Replica DB connection successful.
 376                         # Wait for the session master pos for a short time.
 377                         if ( $this->mWaitForPos && $i > 0 ) {
 378                                 $this->doWait( $i );
 379                         }
 380                         if ( $this->mReadIndex <= 0 && $this->mLoads[$i] > 0 && $group === false ) {
 381                                 $this->mReadIndex = $i;
 382                                 # Record if the generic reader index is in "lagged replica DB" mode
 383                                 if ( $laggedReplicaMode ) {
 384                                         $this->laggedReplicaMode = true;
 385                                 }
 386                         }
 387                         $serverName = $this->getServerName( $i );
 388                         $this->connLogger->debug(
 389                                 __METHOD__ . ": using server $serverName for group '$group'" );
 390                 }
 391
 392                 return $i;
 393         }
 394
 395         public function waitFor( $pos ) {
 396                 $this->mWaitForPos = $pos;
 397                 $i = $this->mReadIndex;
 398
 399                 if ( $i > 0 ) {
 400                         if ( !$this->doWait( $i ) ) {
 401                                 $this->laggedReplicaMode = true;
 402                         }
 403                 }
 404         }
 405
 406         public function waitForOne( $pos, $timeout = null ) {
 407                 $this->mWaitForPos = $pos;
 408
 409                 $i = $this->mReadIndex;
 410                 if ( $i <= 0 ) {
 411                         // Pick a generic replica DB if there isn't one yet
 412                         $readLoads = $this->mLoads;
 413                         unset( $readLoads[$this->getWriterIndex()] ); // replica DBs only
 414                         $readLoads = array_filter( $readLoads ); // with non-zero load
 415                         $i = ArrayUtils::pickRandom( $readLoads );
 416                 }
 417
 418                 if ( $i > 0 ) {
 419                         $ok = $this->doWait( $i, true, $timeout );
 420                 } else {
 421                         $ok = true; // no applicable loads
 422                 }
 423
 424                 return $ok;
 425         }
 426
 427         public function waitForAll( $pos, $timeout = null ) {
 428                 $this->mWaitForPos = $pos;
 429                 $serverCount = count( $this->mServers );
 430
 431                 $ok = true;
 432                 for ( $i = 1; $i < $serverCount; $i++ ) {
 433                         if ( $this->mLoads[$i] > 0 ) {
 434                                 $ok = $this->doWait( $i, true, $timeout ) && $ok;
 435                         }
 436                 }
 437
 438                 return $ok;
 439         }
 440
 441         public function getAnyOpenConnection( $i ) {
 442                 foreach ( $this->mConns as $connsByServer ) {
 443                         if ( !empty( $connsByServer[$i] ) ) {
 444                                 return reset( $connsByServer[$i] );
 445                         }
 446                 }
 447
 448                 return false;
 449         }
 450
 451         /**
 452          * Wait for a given replica DB to catch up to the master pos stored in $this
 453          * @param int $index Server index
 454          * @param bool $open Check the server even if a new connection has to be made
 455          * @param int $timeout Max seconds to wait; default is mWaitTimeout
 456          * @return bool
 457          */
 458         protected function doWait( $index, $open = false, $timeout = null ) {
 459                 $close = false; // close the connection afterwards
 460
 461                 // Check if we already know that the DB has reached this point
 462                 $server = $this->getServerName( $index );
 463                 $key = $this->srvCache->makeGlobalKey( __CLASS__, 'last-known-pos', $server );
 464                 /** @var DBMasterPos $knownReachedPos */
 465                 $knownReachedPos = $this->srvCache->get( $key );
 466                 if ( $knownReachedPos && $knownReachedPos->hasReached( $this->mWaitForPos ) ) {
 467                         $this->replLogger->debug( __METHOD__ .
 468                                 ": replica DB $server known to be caught up (pos >= $knownReachedPos)." );
 469                         return true;
 470                 }
 471
 472                 // Find a connection to wait on, creating one if needed and allowed
 473                 $conn = $this->getAnyOpenConnection( $index );
 474                 if ( !$conn ) {
 475                         if ( !$open ) {
 476                                 $this->replLogger->debug( __METHOD__ . ": no connection open for $server" );
 477
 478                                 return false;
 479                         } else {
 480                                 $conn = $this->openConnection( $index, self::DOMAIN_ANY );
 481                                 if ( !$conn ) {
 482                                         $this->replLogger->warning( __METHOD__ . ": failed to connect to $server" );
 483
 484                                         return false;
 485                                 }
 486                                 // Avoid connection spam in waitForAll() when connections
 487                                 // are made just for the sake of doing this lag check.
 488                                 $close = true;
 489                         }
 490                 }
 491
 492                 $this->replLogger->info( __METHOD__ . ": Waiting for replica DB $server to catch up..." );
 493                 $timeout = $timeout ?: $this->mWaitTimeout;
 494                 $result = $conn->masterPosWait( $this->mWaitForPos, $timeout );
 495
 496                 if ( $result == -1 || is_null( $result ) ) {
 497                         // Timed out waiting for replica DB, use master instead
 498                         $msg = __METHOD__ . ": Timed out waiting on $server pos {$this->mWaitForPos}";
 499                         $this->replLogger->warning( "$msg" );
 500                         $ok = false;
 501                 } else {
 502                         $this->replLogger->info( __METHOD__ . ": Done" );
 503                         $ok = true;
 504                         // Remember that the DB reached this point
 505                         $this->srvCache->set( $key, $this->mWaitForPos, BagOStuff::TTL_DAY );
 506                 }
 507
 508                 if ( $close ) {
 509                         $this->closeConnection( $conn );
 510                 }
 511
 512                 return $ok;
 513         }
 514
 515         /**
 516          * @see ILoadBalancer::getConnection()
 517          *
 518          * @param int $i
 519          * @param array $groups
 520          * @param bool $domain
 521          * @return Database
 522          * @throws DBConnectionError
 523          */
 524         public function getConnection( $i, $groups = [], $domain = false ) {
 525                 if ( $i === null || $i === false ) {
 526                         throw new InvalidArgumentException( 'Attempt to call ' . __METHOD__ .
 527                                 ' with invalid server index' );
 528                 }
 529
 530                 if ( $this->localDomain->equals( $domain ) || $domain === $this->localDomainIdAlias ) {
 531                         $domain = false; // local connection requested
 532                 }
 533
 534                 $groups = ( $groups === false || $groups === [] )
 535                         ? [ false ] // check one "group": the generic pool
 536                         : (array)$groups;
 537
 538                 $masterOnly = ( $i == self::DB_MASTER || $i == $this->getWriterIndex() );
 539                 $oldConnsOpened = $this->connsOpened; // connections open now
 540
 541                 if ( $i == self::DB_MASTER ) {
 542                         $i = $this->getWriterIndex();
 543                 } else {
 544                         # Try to find an available server in any the query groups (in order)
 545                         foreach ( $groups as $group ) {
 546                                 $groupIndex = $this->getReaderIndex( $group, $domain );
 547                                 if ( $groupIndex !== false ) {
 548                                         $i = $groupIndex;
 549                                         break;
 550                                 }
 551                         }
 552                 }
 553
 554                 # Operation-based index
 555                 if ( $i == self::DB_REPLICA ) {
 556                         $this->mLastError = 'Unknown error'; // reset error string
 557                         # Try the general server pool if $groups are unavailable.
 558                         $i = ( $groups === [ false ] )
 559                                 ? false // don't bother with this if that is what was tried above
 560                                 : $this->getReaderIndex( false, $domain );
 561                         # Couldn't find a working server in getReaderIndex()?
 562                         if ( $i === false ) {
 563                                 $this->mLastError = 'No working replica DB server: ' . $this->mLastError;
 564                                 // Throw an exception
 565                                 $this->reportConnectionError();
 566                                 return null; // not reached
 567                         }
 568                 }
 569
 570                 # Now we have an explicit index into the servers array
 571                 $conn = $this->openConnection( $i, $domain );
 572                 if ( !$conn ) {
 573                         // Throw an exception
 574                         $this->reportConnectionError();
 575                         return null; // not reached
 576                 }
 577
 578                 # Profile any new connections that happen
 579                 if ( $this->connsOpened > $oldConnsOpened ) {
 580                         $host = $conn->getServer();
 581                         $dbname = $conn->getDBname();
 582                         $this->trxProfiler->recordConnection( $host, $dbname, $masterOnly );
 583                 }
 584
 585                 if ( $masterOnly ) {
 586                         # Make master-requested DB handles inherit any read-only mode setting
 587                         $conn->setLBInfo( 'readOnlyReason', $this->getReadOnlyReason( $domain, $conn ) );
 588                 }
 589
 590                 return $conn;
 591         }
 592
 593         public function reuseConnection( $conn ) {
 594                 $serverIndex = $conn->getLBInfo( 'serverIndex' );
 595                 $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 596                 if ( $serverIndex === null || $refCount === null ) {
 597                         /**
 598                          * This can happen in code like:
 599                          *   foreach ( $dbs as $db ) {
 600                          *     $conn = $lb->getConnection( $lb::DB_REPLICA, [], $db );
 601                          *     ...
 602                          *     $lb->reuseConnection( $conn );
 603                          *   }
 604                          * When a connection to the local DB is opened in this way, reuseConnection()
 605                          * should be ignored
 606                          */
 607                         return;
 608                 } elseif ( $conn instanceof DBConnRef ) {
 609                         // DBConnRef already handles calling reuseConnection() and only passes the live
 610                         // Database instance to this method. Any caller passing in a DBConnRef is broken.
 611                         $this->connLogger->error( __METHOD__ . ": got DBConnRef instance.\n" .
 612                                 ( new RuntimeException() )->getTraceAsString() );
 613
 614                         return;
 615                 }
 616
 617                 if ( $this->disabled ) {
 618                         return; // DBConnRef handle probably survived longer than the LoadBalancer
 619                 }
 620
 621                 $domain = $conn->getDomainID();
 622                 if ( !isset( $this->mConns['foreignUsed'][$serverIndex][$domain] ) ) {
 623                         throw new InvalidArgumentException( __METHOD__ .
 624                                 ": connection $serverIndex/$domain not found; it may have already been freed." );
 625                 } elseif ( $this->mConns['foreignUsed'][$serverIndex][$domain] !== $conn ) {
 626                         throw new InvalidArgumentException( __METHOD__ .
 627                                 ": connection $serverIndex/$domain mismatched; it may have already been freed." );
 628                 }
 629                 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
 630                 if ( $refCount <= 0 ) {
 631                         $this->mConns['foreignFree'][$serverIndex][$domain] = $conn;
 632                         unset( $this->mConns['foreignUsed'][$serverIndex][$domain] );
 633                         if ( !$this->mConns['foreignUsed'][$serverIndex] ) {
 634                                 unset( $this->mConns[ 'foreignUsed' ][$serverIndex] ); // clean up
 635                         }
 636                         $this->connLogger->debug( __METHOD__ . ": freed connection $serverIndex/$domain" );
 637                 } else {
 638                         $this->connLogger->debug( __METHOD__ .
 639                                 ": reference count for $serverIndex/$domain reduced to $refCount" );
 640                 }
 641         }
 642
 643         public function getConnectionRef( $db, $groups = [], $domain = false ) {
 644                 $domain = ( $domain !== false ) ? $domain : $this->localDomain;
 645
 646                 return new DBConnRef( $this, $this->getConnection( $db, $groups, $domain ) );
 647         }
 648
 649         public function getLazyConnectionRef( $db, $groups = [], $domain = false ) {
 650                 $domain = ( $domain !== false ) ? $domain : $this->localDomain;
 651
 652                 return new DBConnRef( $this, [ $db, $groups, $domain ] );
 653         }
 654
 655         /**
 656          * @see ILoadBalancer::openConnection()
 657          *
 658          * @param int $i
 659          * @param bool $domain
 660          * @return bool|Database
 661          * @throws DBAccessError
 662          */
 663         public function openConnection( $i, $domain = false ) {
 664                 if ( $this->localDomain->equals( $domain ) || $domain === $this->localDomainIdAlias ) {
 665                         $domain = false; // local connection requested
 666                 }
 667
 668                 if ( $domain !== false ) {
 669                         $conn = $this->openForeignConnection( $i, $domain );
 670                 } elseif ( isset( $this->mConns['local'][$i][0] ) ) {
 671                         $conn = $this->mConns['local'][$i][0];
 672                 } else {
 673                         if ( !isset( $this->mServers[$i] ) || !is_array( $this->mServers[$i] ) ) {
 674                                 throw new InvalidArgumentException( "No server with index '$i'." );
 675                         }
 676                         // Open a new connection
 677                         $server = $this->mServers[$i];
 678                         $server['serverIndex'] = $i;
 679                         $conn = $this->reallyOpenConnection( $server, false );
 680                         $serverName = $this->getServerName( $i );
 681                         if ( $conn->isOpen() ) {
 682                                 $this->connLogger->debug( "Connected to database $i at '$serverName'." );
 683                                 $this->mConns['local'][$i][0] = $conn;
 684                         } else {
 685                                 $this->connLogger->warning( "Failed to connect to database $i at '$serverName'." );
 686                                 $this->mErrorConnection = $conn;
 687                                 $conn = false;
 688                         }
 689                 }
 690
 691                 if ( $conn && !$conn->isOpen() ) {
 692                         // Connection was made but later unrecoverably lost for some reason.
 693                         // Do not return a handle that will just throw exceptions on use,
 694                         // but let the calling code (e.g. getReaderIndex) try another server.
 695                         // See DatabaseMyslBase::ping() for how this can happen.
 696                         $this->mErrorConnection = $conn;
 697                         $conn = false;
 698                 }
 699
 700                 return $conn;
 701         }
 702
 703         /**
 704          * Open a connection to a foreign DB, or return one if it is already open.
 705          *
 706          * Increments a reference count on the returned connection which locks the
 707          * connection to the requested domain. This reference count can be
 708          * decremented by calling reuseConnection().
 709          *
 710          * If a connection is open to the appropriate server already, but with the wrong
 711          * database, it will be switched to the right database and returned, as long as
 712          * it has been freed first with reuseConnection().
 713          *
 714          * On error, returns false, and the connection which caused the
 715          * error will be available via $this->mErrorConnection.
 716          *
 717          * @note If disable() was called on this LoadBalancer, this method will throw a DBAccessError.
 718          *
 719          * @param int $i Server index
 720          * @param string $domain Domain ID to open
 721          * @return Database
 722          */
 723         private function openForeignConnection( $i, $domain ) {
 724                 $domainInstance = DatabaseDomain::newFromId( $domain );
 725                 $dbName = $domainInstance->getDatabase();
 726                 $prefix = $domainInstance->getTablePrefix();
 727
 728                 if ( isset( $this->mConns['foreignUsed'][$i][$domain] ) ) {
 729                         // Reuse an already-used connection
 730                         $conn = $this->mConns['foreignUsed'][$i][$domain];
 731                         $this->connLogger->debug( __METHOD__ . ": reusing connection $i/$domain" );
 732                 } elseif ( isset( $this->mConns['foreignFree'][$i][$domain] ) ) {
 733                         // Reuse a free connection for the same domain
 734                         $conn = $this->mConns['foreignFree'][$i][$domain];
 735                         unset( $this->mConns['foreignFree'][$i][$domain] );
 736                         $this->mConns['foreignUsed'][$i][$domain] = $conn;
 737                         $this->connLogger->debug( __METHOD__ . ": reusing free connection $i/$domain" );
 738                 } elseif ( !empty( $this->mConns['foreignFree'][$i] ) ) {
 739                         // Reuse a connection from another domain
 740                         $conn = reset( $this->mConns['foreignFree'][$i] );
 741                         $oldDomain = key( $this->mConns['foreignFree'][$i] );
 742                         // The empty string as a DB name means "don't care".
 743                         // DatabaseMysqlBase::open() already handle this on connection.
 744                         if ( strlen( $dbName ) && !$conn->selectDB( $dbName ) ) {
 745                                 $this->mLastError = "Error selecting database '$dbName' on server " .
 746                                         $conn->getServer() . " from client host {$this->host}";
 747                                 $this->mErrorConnection = $conn;
 748                                 $conn = false;
 749                         } else {
 750                                 $conn->tablePrefix( $prefix );
 751                                 unset( $this->mConns['foreignFree'][$i][$oldDomain] );
 752                                 $this->mConns['foreignUsed'][$i][$domain] = $conn;
 753                                 $this->connLogger->debug( __METHOD__ .
 754                                         ": reusing free connection from $oldDomain for $domain" );
 755                         }
 756                 } else {
 757                         if ( !isset( $this->mServers[$i] ) || !is_array( $this->mServers[$i] ) ) {
 758                                 throw new InvalidArgumentException( "No server with index '$i'." );
 759                         }
 760                         // Open a new connection
 761                         $server = $this->mServers[$i];
 762                         $server['serverIndex'] = $i;
 763                         $server['foreignPoolRefCount'] = 0;
 764                         $server['foreign'] = true;
 765                         $conn = $this->reallyOpenConnection( $server, $dbName );
 766                         if ( !$conn->isOpen() ) {
 767                                 $this->connLogger->warning( __METHOD__ . ": connection error for $i/$domain" );
 768                                 $this->mErrorConnection = $conn;
 769                                 $conn = false;
 770                         } else {
 771                                 $conn->tablePrefix( $prefix );
 772                                 $this->mConns['foreignUsed'][$i][$domain] = $conn;
 773                                 $this->connLogger->debug( __METHOD__ . ": opened new connection for $i/$domain" );
 774                         }
 775                 }
 776
 777                 // Increment reference count
 778                 if ( $conn ) {
 779                         $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 780                         $conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
 781                 }
 782
 783                 return $conn;
 784         }
 785
 786         /**
 787          * Test if the specified index represents an open connection
 788          *
 789          * @param int $index Server index
 790          * @access private
 791          * @return bool
 792          */
 793         private function isOpen( $index ) {
 794                 if ( !is_integer( $index ) ) {
 795                         return false;
 796                 }
 797
 798                 return (bool)$this->getAnyOpenConnection( $index );
 799         }
 800
 801         /**
 802          * Really opens a connection. Uncached.
 803          * Returns a Database object whether or not the connection was successful.
 804          * @access private
 805          *
 806          * @param array $server
 807          * @param string|bool $dbNameOverride Use "" to not select any database
 808          * @return Database
 809          * @throws DBAccessError
 810          * @throws InvalidArgumentException
 811          */
 812         protected function reallyOpenConnection( array $server, $dbNameOverride = false ) {
 813                 if ( $this->disabled ) {
 814                         throw new DBAccessError();
 815                 }
 816
 817                 if ( $dbNameOverride !== false ) {
 818                         $server['dbname'] = $dbNameOverride;
 819                 }
 820
 821                 // Let the handle know what the cluster master is (e.g. "db1052")
 822                 $masterName = $this->getServerName( $this->getWriterIndex() );
 823                 $server['clusterMasterHost'] = $masterName;
 824
 825                 // Log when many connection are made on requests
 826                 if ( ++$this->connsOpened >= self::CONN_HELD_WARN_THRESHOLD ) {
 827                         $this->perfLogger->warning( __METHOD__ . ": " .
 828                                 "{$this->connsOpened}+ connections made (master=$masterName)" );
 829                 }
 830
 831                 $server['srvCache'] = $this->srvCache;
 832                 // Set loggers and profilers
 833                 $server['connLogger'] = $this->connLogger;
 834                 $server['queryLogger'] = $this->queryLogger;
 835                 $server['errorLogger'] = $this->errorLogger;
 836                 $server['profiler'] = $this->profiler;
 837                 $server['trxProfiler'] = $this->trxProfiler;
 838                 // Use the same agent and PHP mode for all DB handles
 839                 $server['cliMode'] = $this->cliMode;
 840                 $server['agent'] = $this->agent;
 841                 // Use DBO_DEFAULT flags by default for LoadBalancer managed databases. Assume that the
 842                 // application calls LoadBalancer::commitMasterChanges() before the PHP script completes.
 843                 $server['flags'] = isset( $server['flags'] ) ? $server['flags'] : IDatabase::DBO_DEFAULT;
 844
 845                 // Create a live connection object
 846                 try {
 847                         $db = Database::factory( $server['type'], $server );
 848                 } catch ( DBConnectionError $e ) {
 849                         // FIXME: This is probably the ugliest thing I have ever done to
 850                         // PHP. I'm half-expecting it to segfault, just out of disgust. -- TS
 851                         $db = $e->db;
 852                 }
 853
 854                 $db->setLBInfo( $server );
 855                 $db->setLazyMasterHandle(
 856                         $this->getLazyConnectionRef( self::DB_MASTER, [], $db->getDomainID() )
 857                 );
 858                 $db->setTableAliases( $this->tableAliases );
 859
 860                 if ( $server['serverIndex'] === $this->getWriterIndex() ) {
 861                         if ( $this->trxRoundId !== false ) {
 862                                 $this->applyTransactionRoundFlags( $db );
 863                         }
 864                         foreach ( $this->trxRecurringCallbacks as $name => $callback ) {
 865                                 $db->setTransactionListener( $name, $callback );
 866                         }
 867                 }
 868
 869                 foreach ( $this->usageSections as $id => $unused ) {
 870                         $db->declareUsageSectionStart( $id );
 871                 }
 872
 873                 return $db;
 874         }
 875
 876         /**
 877          * @throws DBConnectionError
 878          */
 879         private function reportConnectionError() {
 880                 $conn = $this->mErrorConnection; // the connection which caused the error
 881                 $context = [
 882                         'method' => __METHOD__,
 883                         'last_error' => $this->mLastError,
 884                 ];
 885
 886                 if ( !is_object( $conn ) ) {
 887                         // No last connection, probably due to all servers being too busy
 888                         $this->connLogger->error(
 889                                 "LB failure with no last connection. Connection error: {last_error}",
 890                                 $context
 891                         );
 892
 893                         // If all servers were busy, mLastError will contain something sensible
 894                         throw new DBConnectionError( null, $this->mLastError );
 895                 } else {
 896                         $context['db_server'] = $conn->getServer();
 897                         $this->connLogger->warning(
 898                                 "Connection error: {last_error} ({db_server})",
 899                                 $context
 900                         );
 901
 902                         // throws DBConnectionError
 903                         $conn->reportConnectionError( "{$this->mLastError} ({$context['db_server']})" );
 904                 }
 905         }
 906
 907         public function getWriterIndex() {
 908                 return 0;
 909         }
 910
 911         public function haveIndex( $i ) {
 912                 return array_key_exists( $i, $this->mServers );
 913         }
 914
 915         public function isNonZeroLoad( $i ) {
 916                 return array_key_exists( $i, $this->mServers ) && $this->mLoads[$i] != 0;
 917         }
 918
 919         public function getServerCount() {
 920                 return count( $this->mServers );
 921         }
 922
 923         public function getServerName( $i ) {
 924                 if ( isset( $this->mServers[$i]['hostName'] ) ) {
 925                         $name = $this->mServers[$i]['hostName'];
 926                 } elseif ( isset( $this->mServers[$i]['host'] ) ) {
 927                         $name = $this->mServers[$i]['host'];
 928                 } else {
 929                         $name = '';
 930                 }
 931
 932                 return ( $name != '' ) ? $name : 'localhost';
 933         }
 934
 935         public function getServerInfo( $i ) {
 936                 if ( isset( $this->mServers[$i] ) ) {
 937                         return $this->mServers[$i];
 938                 } else {
 939                         return false;
 940                 }
 941         }
 942
 943         public function setServerInfo( $i, array $serverInfo ) {
 944                 $this->mServers[$i] = $serverInfo;
 945         }
 946
 947         public function getMasterPos() {
 948                 # If this entire request was served from a replica DB without opening a connection to the
 949                 # master (however unlikely that may be), then we can fetch the position from the replica DB.
 950                 $masterConn = $this->getAnyOpenConnection( $this->getWriterIndex() );
 951                 if ( !$masterConn ) {
 952                         $serverCount = count( $this->mServers );
 953                         for ( $i = 1; $i < $serverCount; $i++ ) {
 954                                 $conn = $this->getAnyOpenConnection( $i );
 955                                 if ( $conn ) {
 956                                         return $conn->getReplicaPos();
 957                                 }
 958                         }
 959                 } else {
 960                         return $masterConn->getMasterPos();
 961                 }
 962
 963                 return false;
 964         }
 965
 966         public function disable() {
 967                 $this->closeAll();
 968                 $this->disabled = true;
 969         }
 970
 971         public function closeAll() {
 972                 $this->forEachOpenConnection( function ( IDatabase $conn ) {
 973                         $host = $conn->getServer();
 974                         $this->connLogger->debug( "Closing connection to database '$host'." );
 975                         $conn->close();
 976                 } );
 977
 978                 $this->mConns = [
 979                         'local' => [],
 980                         'foreignFree' => [],
 981                         'foreignUsed' => [],
 982                 ];
 983                 $this->connsOpened = 0;
 984         }
 985
 986         public function closeConnection( IDatabase $conn ) {
 987                 $serverIndex = $conn->getLBInfo( 'serverIndex' ); // second index level of mConns
 988                 foreach ( $this->mConns as $type => $connsByServer ) {
 989                         if ( !isset( $connsByServer[$serverIndex] ) ) {
 990                                 continue;
 991                         }
 992
 993                         foreach ( $connsByServer[$serverIndex] as $i => $trackedConn ) {
 994                                 if ( $conn === $trackedConn ) {
 995                                         $host = $this->getServerName( $i );
 996                                         $this->connLogger->debug( "Closing connection to database $i at '$host'." );
 997                                         unset( $this->mConns[$type][$serverIndex][$i] );
 998                                         --$this->connsOpened;
 999                                         break 2;
1000                                 }
1001                         }
1002                 }
1003
1004                 $conn->close();
1005         }
1006
1007         public function commitAll( $fname = __METHOD__ ) {
1008                 $failures = [];
1009
1010                 $restore = ( $this->trxRoundId !== false );
1011                 $this->trxRoundId = false;
1012                 $this->forEachOpenConnection(
1013                         function ( IDatabase $conn ) use ( $fname, $restore, &$failures ) {
1014                                 try {
1015                                         $conn->commit( $fname, $conn::FLUSHING_ALL_PEERS );
1016                                 } catch ( DBError $e ) {
1017                                         call_user_func( $this->errorLogger, $e );
1018                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1019                                 }
1020                                 if ( $restore && $conn->getLBInfo( 'master' ) ) {
1021                                         $this->undoTransactionRoundFlags( $conn );
1022                                 }
1023                         }
1024                 );
1025
1026                 if ( $failures ) {
1027                         throw new DBExpectedError(
1028                                 null,
1029                                 "Commit failed on server(s) " . implode( "\n", array_unique( $failures ) )
1030                         );
1031                 }
1032         }
1033
1034         public function finalizeMasterChanges() {
1035                 $this->forEachOpenMasterConnection( function ( Database $conn ) {
1036                         // Any error should cause all DB transactions to be rolled back together
1037                         $conn->setTrxEndCallbackSuppression( false );
1038                         $conn->runOnTransactionPreCommitCallbacks();
1039                         // Defer post-commit callbacks until COMMIT finishes for all DBs
1040                         $conn->setTrxEndCallbackSuppression( true );
1041                 } );
1042         }
1043
1044         public function approveMasterChanges( array $options ) {
1045                 $limit = isset( $options['maxWriteDuration'] ) ? $options['maxWriteDuration'] : 0;
1046                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( $limit ) {
1047                         // If atomic sections or explicit transactions are still open, some caller must have
1048                         // caught an exception but failed to properly rollback any changes. Detect that and
1049                         // throw and error (causing rollback).
1050                         if ( $conn->explicitTrxActive() ) {
1051                                 throw new DBTransactionError(
1052                                         $conn,
1053                                         "Explicit transaction still active. A caller may have caught an error."
1054                                 );
1055                         }
1056                         // Assert that the time to replicate the transaction will be sane.
1057                         // If this fails, then all DB transactions will be rollback back together.
1058                         $time = $conn->pendingWriteQueryDuration( $conn::ESTIMATE_DB_APPLY );
1059                         if ( $limit > 0 && $time > $limit ) {
1060                                 throw new DBTransactionSizeError(
1061                                         $conn,
1062                                         "Transaction spent $time second(s) in writes, exceeding the $limit limit.",
1063                                         [ $time, $limit ]
1064                                 );
1065                         }
1066                         // If a connection sits idle while slow queries execute on another, that connection
1067                         // may end up dropped before the commit round is reached. Ping servers to detect this.
1068                         if ( $conn->writesOrCallbacksPending() && !$conn->ping() ) {
1069                                 throw new DBTransactionError(
1070                                         $conn,
1071                                         "A connection to the {$conn->getDBname()} database was lost before commit."
1072                                 );
1073                         }
1074                 } );
1075         }
1076
1077         public function beginMasterChanges( $fname = __METHOD__ ) {
1078                 if ( $this->trxRoundId !== false ) {
1079                         throw new DBTransactionError(
1080                                 null,
1081                                 "$fname: Transaction round '{$this->trxRoundId}' already started."
1082                         );
1083                 }
1084                 $this->trxRoundId = $fname;
1085
1086                 $failures = [];
1087                 $this->forEachOpenMasterConnection(
1088                         function ( Database $conn ) use ( $fname, &$failures ) {
1089                                 $conn->setTrxEndCallbackSuppression( true );
1090                                 try {
1091                                         $conn->flushSnapshot( $fname );
1092                                 } catch ( DBError $e ) {
1093                                         call_user_func( $this->errorLogger, $e );
1094                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1095                                 }
1096                                 $conn->setTrxEndCallbackSuppression( false );
1097                                 $this->applyTransactionRoundFlags( $conn );
1098                         }
1099                 );
1100
1101                 if ( $failures ) {
1102                         throw new DBExpectedError(
1103                                 null,
1104                                 "$fname: Flush failed on server(s) " . implode( "\n", array_unique( $failures ) )
1105                         );
1106                 }
1107         }
1108
1109         public function commitMasterChanges( $fname = __METHOD__ ) {
1110                 $failures = [];
1111
1112                 /** @noinspection PhpUnusedLocalVariableInspection */
1113                 $scope = $this->getScopedPHPBehaviorForCommit(); // try to ignore client aborts
1114
1115                 $restore = ( $this->trxRoundId !== false );
1116                 $this->trxRoundId = false;
1117                 $this->forEachOpenMasterConnection(
1118                         function ( IDatabase $conn ) use ( $fname, $restore, &$failures ) {
1119                                 try {
1120                                         if ( $conn->writesOrCallbacksPending() ) {
1121                                                 $conn->commit( $fname, $conn::FLUSHING_ALL_PEERS );
1122                                         } elseif ( $restore ) {
1123                                                 $conn->flushSnapshot( $fname );
1124                                         }
1125                                 } catch ( DBError $e ) {
1126                                         call_user_func( $this->errorLogger, $e );
1127                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1128                                 }
1129                                 if ( $restore ) {
1130                                         $this->undoTransactionRoundFlags( $conn );
1131                                 }
1132                         }
1133                 );
1134
1135                 if ( $failures ) {
1136                         throw new DBExpectedError(
1137                                 null,
1138                                 "$fname: Commit failed on server(s) " . implode( "\n", array_unique( $failures ) )
1139                         );
1140                 }
1141         }
1142
1143         public function runMasterPostTrxCallbacks( $type ) {
1144                 $e = null; // first exception
1145                 $this->forEachOpenMasterConnection( function ( Database $conn ) use ( $type, &$e ) {
1146                         $conn->setTrxEndCallbackSuppression( false );
1147                         if ( $conn->writesOrCallbacksPending() ) {
1148                                 // This happens if onTransactionIdle() callbacks leave callbacks on *another* DB
1149                                 // (which finished its callbacks already). Warn and recover in this case. Let the
1150                                 // callbacks run in the final commitMasterChanges() in LBFactory::shutdown().
1151                                 $this->queryLogger->error( __METHOD__ . ": found writes/callbacks pending." );
1152                                 return;
1153                         } elseif ( $conn->trxLevel() ) {
1154                                 // This happens for single-DB setups where DB_REPLICA uses the master DB,
1155                                 // thus leaving an implicit read-only transaction open at this point. It
1156                                 // also happens if onTransactionIdle() callbacks leave implicit transactions
1157                                 // open on *other* DBs (which is slightly improper). Let these COMMIT on the
1158                                 // next call to commitMasterChanges(), possibly in LBFactory::shutdown().
1159                                 return;
1160                         }
1161                         try {
1162                                 $conn->runOnTransactionIdleCallbacks( $type );
1163                         } catch ( Exception $ex ) {
1164                                 $e = $e ?: $ex;
1165                         }
1166                         try {
1167                                 $conn->runTransactionListenerCallbacks( $type );
1168                         } catch ( Exception $ex ) {
1169                                 $e = $e ?: $ex;
1170                         }
1171                 } );
1172
1173                 return $e;
1174         }
1175
1176         public function rollbackMasterChanges( $fname = __METHOD__ ) {
1177                 $restore = ( $this->trxRoundId !== false );
1178                 $this->trxRoundId = false;
1179                 $this->forEachOpenMasterConnection(
1180                         function ( IDatabase $conn ) use ( $fname, $restore ) {
1181                                 if ( $conn->writesOrCallbacksPending() ) {
1182                                         $conn->rollback( $fname, $conn::FLUSHING_ALL_PEERS );
1183                                 }
1184                                 if ( $restore ) {
1185                                         $this->undoTransactionRoundFlags( $conn );
1186                                 }
1187                         }
1188                 );
1189         }
1190
1191         public function suppressTransactionEndCallbacks() {
1192                 $this->forEachOpenMasterConnection( function ( Database $conn ) {
1193                         $conn->setTrxEndCallbackSuppression( true );
1194                 } );
1195         }
1196
1197         /**
1198          * @param IDatabase $conn
1199          */
1200         private function applyTransactionRoundFlags( IDatabase $conn ) {
1201                 if ( $conn->getFlag( $conn::DBO_DEFAULT ) ) {
1202                         // DBO_TRX is controlled entirely by CLI mode presence with DBO_DEFAULT.
1203                         // Force DBO_TRX even in CLI mode since a commit round is expected soon.
1204                         $conn->setFlag( $conn::DBO_TRX, $conn::REMEMBER_PRIOR );
1205                         // If config has explicitly requested DBO_TRX be either on or off by not
1206                         // setting DBO_DEFAULT, then respect that. Forcing no transactions is useful
1207                         // for things like blob stores (ExternalStore) which want auto-commit mode.
1208                 }
1209         }
1210
1211         /**
1212          * @param IDatabase $conn
1213          */
1214         private function undoTransactionRoundFlags( IDatabase $conn ) {
1215                 if ( $conn->getFlag( $conn::DBO_DEFAULT ) ) {
1216                         $conn->restoreFlags( $conn::RESTORE_PRIOR );
1217                 }
1218         }
1219
1220         public function flushReplicaSnapshots( $fname = __METHOD__ ) {
1221                 $this->forEachOpenReplicaConnection( function ( IDatabase $conn ) {
1222                         $conn->flushSnapshot( __METHOD__ );
1223                 } );
1224         }
1225
1226         public function hasMasterConnection() {
1227                 return $this->isOpen( $this->getWriterIndex() );
1228         }
1229
1230         public function hasMasterChanges() {
1231                 $pending = 0;
1232                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$pending ) {
1233                         $pending |= $conn->writesOrCallbacksPending();
1234                 } );
1235
1236                 return (bool)$pending;
1237         }
1238
1239         public function lastMasterChangeTimestamp() {
1240                 $lastTime = false;
1241                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$lastTime ) {
1242                         $lastTime = max( $lastTime, $conn->lastDoneWrites() );
1243                 } );
1244
1245                 return $lastTime;
1246         }
1247
1248         public function hasOrMadeRecentMasterChanges( $age = null ) {
1249                 $age = ( $age === null ) ? $this->mWaitTimeout : $age;
1250
1251                 return ( $this->hasMasterChanges()
1252                         || $this->lastMasterChangeTimestamp() > microtime( true ) - $age );
1253         }
1254
1255         public function pendingMasterChangeCallers() {
1256                 $fnames = [];
1257                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$fnames ) {
1258                         $fnames = array_merge( $fnames, $conn->pendingWriteCallers() );
1259                 } );
1260
1261                 return $fnames;
1262         }
1263
1264         public function getLaggedReplicaMode( $domain = false ) {
1265                 // No-op if there is only one DB (also avoids recursion)
1266                 if ( !$this->laggedReplicaMode && $this->getServerCount() > 1 ) {
1267                         try {
1268                                 // See if laggedReplicaMode gets set
1269                                 $conn = $this->getConnection( self::DB_REPLICA, false, $domain );
1270                                 $this->reuseConnection( $conn );
1271                         } catch ( DBConnectionError $e ) {
1272                                 // Avoid expensive re-connect attempts and failures
1273                                 $this->allReplicasDownMode = true;
1274                                 $this->laggedReplicaMode = true;
1275                         }
1276                 }
1277
1278                 return $this->laggedReplicaMode;
1279         }
1280
1281         /**
1282          * @param bool $domain
1283          * @return bool
1284          * @deprecated 1.28; use getLaggedReplicaMode()
1285          */
1286         public function getLaggedSlaveMode( $domain = false ) {
1287                 return $this->getLaggedReplicaMode( $domain );
1288         }
1289
1290         public function laggedReplicaUsed() {
1291                 return $this->laggedReplicaMode;
1292         }
1293
1294         /**
1295          * @return bool
1296          * @since 1.27
1297          * @deprecated Since 1.28; use laggedReplicaUsed()
1298          */
1299         public function laggedSlaveUsed() {
1300                 return $this->laggedReplicaUsed();
1301         }
1302
1303         public function getReadOnlyReason( $domain = false, IDatabase $conn = null ) {
1304                 if ( $this->readOnlyReason !== false ) {
1305                         return $this->readOnlyReason;
1306                 } elseif ( $this->getLaggedReplicaMode( $domain ) ) {
1307                         if ( $this->allReplicasDownMode ) {
1308                                 return 'The database has been automatically locked ' .
1309                                         'until the replica database servers become available';
1310                         } else {
1311                                 return 'The database has been automatically locked ' .
1312                                         'while the replica database servers catch up to the master.';
1313                         }
1314                 } elseif ( $this->masterRunningReadOnly( $domain, $conn ) ) {
1315                         return 'The database master is running in read-only mode.';
1316                 }
1317
1318                 return false;
1319         }
1320
1321         /**
1322          * @param string $domain Domain ID, or false for the current domain
1323          * @param IDatabase|null DB master connectionl used to avoid loops [optional]
1324          * @return bool
1325          */
1326         private function masterRunningReadOnly( $domain, IDatabase $conn = null ) {
1327                 $cache = $this->wanCache;
1328                 $masterServer = $this->getServerName( $this->getWriterIndex() );
1329
1330                 return (bool)$cache->getWithSetCallback(
1331                         $cache->makeGlobalKey( __CLASS__, 'server-read-only', $masterServer ),
1332                         self::TTL_CACHE_READONLY,
1333                         function () use ( $domain, $conn ) {
1334                                 $old = $this->trxProfiler->setSilenced( true );
1335                                 try {
1336                                         $dbw = $conn ?: $this->getConnection( self::DB_MASTER, [], $domain );
1337                                         $readOnly = (int)$dbw->serverIsReadOnly();
1338                                         if ( !$conn ) {
1339                                                 $this->reuseConnection( $dbw );
1340                                         }
1341                                 } catch ( DBError $e ) {
1342                                         $readOnly = 0;
1343                                 }
1344                                 $this->trxProfiler->setSilenced( $old );
1345                                 return $readOnly;
1346                         },
1347                         [ 'pcTTL' => $cache::TTL_PROC_LONG, 'busyValue' => 0 ]
1348                 );
1349         }
1350
1351         public function allowLagged( $mode = null ) {
1352                 if ( $mode === null ) {
1353                         return $this->mAllowLagged;
1354                 }
1355                 $this->mAllowLagged = $mode;
1356
1357                 return $this->mAllowLagged;
1358         }
1359
1360         public function pingAll() {
1361                 $success = true;
1362                 $this->forEachOpenConnection( function ( IDatabase $conn ) use ( &$success ) {
1363                         if ( !$conn->ping() ) {
1364                                 $success = false;
1365                         }
1366                 } );
1367
1368                 return $success;
1369         }
1370
1371         public function forEachOpenConnection( $callback, array $params = [] ) {
1372                 foreach ( $this->mConns as $connsByServer ) {
1373                         foreach ( $connsByServer as $serverConns ) {
1374                                 foreach ( $serverConns as $conn ) {
1375                                         $mergedParams = array_merge( [ $conn ], $params );
1376                                         call_user_func_array( $callback, $mergedParams );
1377                                 }
1378                         }
1379                 }
1380         }
1381
1382         public function forEachOpenMasterConnection( $callback, array $params = [] ) {
1383                 $masterIndex = $this->getWriterIndex();
1384                 foreach ( $this->mConns as $connsByServer ) {
1385                         if ( isset( $connsByServer[$masterIndex] ) ) {
1386                                 /** @var IDatabase $conn */
1387                                 foreach ( $connsByServer[$masterIndex] as $conn ) {
1388                                         $mergedParams = array_merge( [ $conn ], $params );
1389                                         call_user_func_array( $callback, $mergedParams );
1390                                 }
1391                         }
1392                 }
1393         }
1394
1395         public function forEachOpenReplicaConnection( $callback, array $params = [] ) {
1396                 foreach ( $this->mConns as $connsByServer ) {
1397                         foreach ( $connsByServer as $i => $serverConns ) {
1398                                 if ( $i === $this->getWriterIndex() ) {
1399                                         continue; // skip master
1400                                 }
1401                                 foreach ( $serverConns as $conn ) {
1402                                         $mergedParams = array_merge( [ $conn ], $params );
1403                                         call_user_func_array( $callback, $mergedParams );
1404                                 }
1405                         }
1406                 }
1407         }
1408
1409         public function getMaxLag( $domain = false ) {
1410                 $maxLag = -1;
1411                 $host = '';
1412                 $maxIndex = 0;
1413
1414                 if ( $this->getServerCount() <= 1 ) {
1415                         return [ $host, $maxLag, $maxIndex ]; // no replication = no lag
1416                 }
1417
1418                 $lagTimes = $this->getLagTimes( $domain );
1419                 foreach ( $lagTimes as $i => $lag ) {
1420                         if ( $this->mLoads[$i] > 0 && $lag > $maxLag ) {
1421                                 $maxLag = $lag;
1422                                 $host = $this->mServers[$i]['host'];
1423                                 $maxIndex = $i;
1424                         }
1425                 }
1426
1427                 return [ $host, $maxLag, $maxIndex ];
1428         }
1429
1430         public function getLagTimes( $domain = false ) {
1431                 if ( $this->getServerCount() <= 1 ) {
1432                         return [ $this->getWriterIndex() => 0 ]; // no replication = no lag
1433                 }
1434
1435                 $knownLagTimes = []; // map of (server index => 0 seconds)
1436                 $indexesWithLag = [];
1437                 foreach ( $this->mServers as $i => $server ) {
1438                         if ( empty( $server['is static'] ) ) {
1439                                 $indexesWithLag[] = $i; // DB server might have replication lag
1440                         } else {
1441                                 $knownLagTimes[$i] = 0; // DB server is a non-replicating and read-only archive
1442                         }
1443                 }
1444
1445                 return $this->getLoadMonitor()->getLagTimes( $indexesWithLag, $domain ) + $knownLagTimes;
1446         }
1447
1448         public function safeGetLag( IDatabase $conn ) {
1449                 if ( $this->getServerCount() <= 1 ) {
1450                         return 0;
1451                 } else {
1452                         return $conn->getLag();
1453                 }
1454         }
1455
1456         public function safeWaitForMasterPos( IDatabase $conn, $pos = false, $timeout = 10 ) {
1457                 if ( $this->getServerCount() <= 1 || !$conn->getLBInfo( 'replica' ) ) {
1458                         return true; // server is not a replica DB
1459                 }
1460
1461                 if ( !$pos ) {
1462                         // Get the current master position, opening a connection if needed
1463                         $masterConn = $this->getAnyOpenConnection( $this->getWriterIndex() );
1464                         if ( $masterConn ) {
1465                                 $pos = $masterConn->getMasterPos();
1466                         } else {
1467                                 $masterConn = $this->openConnection( $this->getWriterIndex(), self::DOMAIN_ANY );
1468                                 $pos = $masterConn->getMasterPos();
1469                                 $this->closeConnection( $masterConn );
1470                         }
1471                 }
1472
1473                 if ( $pos instanceof DBMasterPos ) {
1474                         $result = $conn->masterPosWait( $pos, $timeout );
1475                         if ( $result == -1 || is_null( $result ) ) {
1476                                 $msg = __METHOD__ . ": Timed out waiting on {$conn->getServer()} pos {$pos}";
1477                                 $this->replLogger->warning( "$msg" );
1478                                 $ok = false;
1479                         } else {
1480                                 $this->replLogger->info( __METHOD__ . ": Done" );
1481                                 $ok = true;
1482                         }
1483                 } else {
1484                         $ok = false; // something is misconfigured
1485                         $this->replLogger->error( "Could not get master pos for {$conn->getServer()}." );
1486                 }
1487
1488                 return $ok;
1489         }
1490
1491         public function setTransactionListener( $name, callable $callback = null ) {
1492                 if ( $callback ) {
1493                         $this->trxRecurringCallbacks[$name] = $callback;
1494                 } else {
1495                         unset( $this->trxRecurringCallbacks[$name] );
1496                 }
1497                 $this->forEachOpenMasterConnection(
1498                         function ( IDatabase $conn ) use ( $name, $callback ) {
1499                                 $conn->setTransactionListener( $name, $callback );
1500                         }
1501                 );
1502         }
1503
1504         public function setTableAliases( array $aliases ) {
1505                 $this->tableAliases = $aliases;
1506         }
1507
1508         public function setDomainPrefix( $prefix ) {
1509                 if ( $this->mConns['foreignUsed'] ) {
1510                         // Do not switch connections to explicit foreign domains unless marked as free
1511                         $domains = [];
1512                         foreach ( $this->mConns['foreignUsed'] as $i => $connsByDomain ) {
1513                                 $domains = array_merge( $domains, array_keys( $connsByDomain ) );
1514                         }
1515                         $domains = implode( ', ', $domains );
1516                         throw new DBUnexpectedError( null,
1517                                 "Foreign domain connections are still in use ($domains)." );
1518                 }
1519
1520                 $this->localDomain = new DatabaseDomain(
1521                         $this->localDomain->getDatabase(),
1522                         null,
1523                         $prefix
1524                 );
1525
1526                 $this->forEachOpenConnection( function ( IDatabase $db ) use ( $prefix ) {
1527                         $db->tablePrefix( $prefix );
1528                 } );
1529         }
1530
1531         public function declareUsageSectionStart( $id = null ) {
1532                 static $nextId = 1;
1533                 if ( $id === null ) {
1534                         $id = $nextId;
1535                         ++$nextId;
1536                 }
1537                 // Handle existing connections
1538                 $this->forEachOpenConnection( function ( IDatabase $db ) use ( $id ) {
1539                         $db->declareUsageSectionStart( $id );
1540                 } );
1541                 // Remember to set this for new connections
1542                 $this->usageSections[$id] = true;
1543
1544                 return $id;
1545         }
1546
1547         public function declareUsageSectionEnd( $id ) {
1548                 $info = [ 'readQueries' => 0, 'writeQueries' => 0, 'cacheSetOptions' => null ];
1549                 $this->forEachOpenConnection( function ( IDatabase $db ) use ( $id, &$info ) {
1550                         $dbInfo = $db->declareUsageSectionEnd( $id );
1551                         $info['readQueries'] += $dbInfo['readQueries'];
1552                         $info['writeQueries'] += $dbInfo['writeQueries'];
1553                         $dbCacheOpts = $dbInfo['cacheSetOptions'];
1554                         if ( $dbCacheOpts ) {
1555                                 $info['cacheSetOptions'] = $info['cacheSetOptions']
1556                                         ? Database::mergeCacheSetOptions( $info['cacheSetOptions'], $dbCacheOpts )
1557                                         : $dbCacheOpts;
1558                         }
1559                 } );
1560                 unset( $this->usageSections[$id] );
1561
1562                 return $info;
1563         }
1564
1565         /**
1566          * Make PHP ignore user aborts/disconnects until the returned
1567          * value leaves scope. This returns null and does nothing in CLI mode.
1568          *
1569          * @return ScopedCallback|null
1570          */
1571         final protected function getScopedPHPBehaviorForCommit() {
1572                 if ( PHP_SAPI != 'cli' ) { // https://bugs.php.net/bug.php?id=47540
1573                         $old = ignore_user_abort( true ); // avoid half-finished operations
1574                         return new ScopedCallback( function () use ( $old ) {
1575                                 ignore_user_abort( $old );
1576                         } );
1577                 }
1578
1579                 return null;
1580         }
1581
1582         function __destruct() {
1583                 // Avoid connection leaks for sanity
1584                 $this->disable();
1585         }
1586 }