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