includes/libs/rdbms/loadbalancer/LoadBalancer.php

   1 <?php
   2 /**
   3  * Database load balancing manager
   4  *
   5  * This program is free software; you can redistribute it and/or modify
   6  * it under the terms of the GNU General Public License as published by
   7  * the Free Software Foundation; either version 2 of the License, or
   8  * (at your option) any later version.
   9  *
  10  * This program is distributed in the hope that it will be useful,
  11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  13  * GNU General Public License for more details.
  14  *
  15  * You should have received a copy of the GNU General Public License along
  16  * with this program; if not, write to the Free Software Foundation, Inc.,
  17  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
  18  * http://www.gnu.org/copyleft/gpl.html
  19  *
  20  * @file
  21  * @ingroup Database
  22  */
  23 use Psr\Log\LoggerInterface;
  24
  25 /**
  26  * Database connection, tracking, load balancing, and transaction manager for a cluster
  27  *
  28  * @ingroup Database
  29  */
  30 class LoadBalancer implements ILoadBalancer {
  31         /** @var array[] Map of (server index => server config array) */
  32         private $mServers;
  33         /** @var array[] Map of (local/foreignUsed/foreignFree => server index => IDatabase array) */
  34         private $mConns;
  35         /** @var float[] Map of (server index => weight) */
  36         private $mLoads;
  37         /** @var array[] Map of (group => server index => weight) */
  38         private $mGroupLoads;
  39         /** @var bool Whether to disregard replica DB lag as a factor in replica DB selection */
  40         private $mAllowLagged;
  41         /** @var integer Seconds to spend waiting on replica DB lag to resolve */
  42         private $mWaitTimeout;
  43         /** @var array The LoadMonitor configuration */
  44         private $loadMonitorConfig;
  45         /** @var array[] $aliases Map of (table => (dbname, schema, prefix) map) */
  46         private $tableAliases = [];
  47
  48         /** @var ILoadMonitor */
  49         private $loadMonitor;
  50         /** @var BagOStuff */
  51         private $srvCache;
  52         /** @var BagOStuff */
  53         private $memCache;
  54         /** @var WANObjectCache */
  55         private $wanCache;
  56         /** @var object|string Class name or object With profileIn/profileOut methods */
  57         protected $profiler;
  58         /** @var TransactionProfiler */
  59         protected $trxProfiler;
  60         /** @var LoggerInterface */
  61         protected $replLogger;
  62         /** @var LoggerInterface */
  63         protected $connLogger;
  64         /** @var LoggerInterface */
  65         protected $queryLogger;
  66         /** @var LoggerInterface */
  67         protected $perfLogger;
  68
  69         /** @var bool|IDatabase Database connection that caused a problem */
  70         private $mErrorConnection;
  71         /** @var integer The generic (not query grouped) replica DB index (of $mServers) */
  72         private $mReadIndex;
  73         /** @var bool|DBMasterPos False if not set */
  74         private $mWaitForPos;
  75         /** @var bool Whether the generic reader fell back to a lagged replica DB */
  76         private $laggedReplicaMode = false;
  77         /** @var bool Whether the generic reader fell back to a lagged replica DB */
  78         private $allReplicasDownMode = false;
  79         /** @var string The last DB selection or connection error */
  80         private $mLastError = 'Unknown error';
  81         /** @var string|bool Reason the LB is read-only or false if not */
  82         private $readOnlyReason = false;
  83         /** @var integer Total connections opened */
  84         private $connsOpened = 0;
  85         /** @var string|bool String if a requested DBO_TRX transaction round is active */
  86         private $trxRoundId = false;
  87         /** @var array[] Map of (name => callable) */
  88         private $trxRecurringCallbacks = [];
  89         /** @var DatabaseDomain Local Domain ID and default for selectDB() calls */
  90         private $localDomain;
  91         /** @var string Alternate ID string for the domain instead of DatabaseDomain::getId() */
  92         private $localDomainIdAlias;
  93         /** @var string Current server name */
  94         private $host;
  95         /** @var bool Whether this PHP instance is for a CLI script */
  96         protected $cliMode;
  97         /** @var string Agent name for query profiling */
  98         protected $agent;
  99
 100         /** @var callable Exception logger */
 101         private $errorLogger;
 102
 103         /** @var boolean */
 104         private $disabled = false;
 105
 106         /** @var integer Warn when this many connection are held */
 107         const CONN_HELD_WARN_THRESHOLD = 10;
 108
 109         /** @var integer Default 'max lag' when unspecified */
 110         const MAX_LAG_DEFAULT = 10;
 111         /** @var integer Seconds to cache master server read-only status */
 112         const TTL_CACHE_READONLY = 5;
 113
 114         public function __construct( array $params ) {
 115                 if ( !isset( $params['servers'] ) ) {
 116                         throw new InvalidArgumentException( __CLASS__ . ': missing servers parameter' );
 117                 }
 118                 $this->mServers = $params['servers'];
 119
 120                 $this->localDomain = isset( $params['localDomain'] )
 121                         ? DatabaseDomain::newFromId( $params['localDomain'] )
 122                         : DatabaseDomain::newUnspecified();
 123                 // In case a caller assumes that the domain ID is simply <db>-<prefix>, which is almost
 124                 // always true, gracefully handle the case when they fail to account for escaping.
 125                 if ( $this->localDomain->getTablePrefix() != '' ) {
 126                         $this->localDomainIdAlias =
 127                                 $this->localDomain->getDatabase() . '-' . $this->localDomain->getTablePrefix();
 128                 } else {
 129                         $this->localDomainIdAlias = $this->localDomain->getDatabase();
 130                 }
 131
 132                 $this->mWaitTimeout = isset( $params['waitTimeout'] ) ? $params['waitTimeout'] : 10;
 133
 134                 $this->mReadIndex = -1;
 135                 $this->mConns = [
 136                         'local'       => [],
 137                         'foreignUsed' => [],
 138                         'foreignFree' => []
 139                 ];
 140                 $this->mLoads = [];
 141                 $this->mWaitForPos = false;
 142                 $this->mErrorConnection = false;
 143                 $this->mAllowLagged = false;
 144
 145                 if ( isset( $params['readOnlyReason'] ) && is_string( $params['readOnlyReason'] ) ) {
 146                         $this->readOnlyReason = $params['readOnlyReason'];
 147                 }
 148
 149                 if ( isset( $params['loadMonitor'] ) ) {
 150                         $this->loadMonitorConfig = $params['loadMonitor'];
 151                 } else {
 152                         $this->loadMonitorConfig = [ 'class' => 'LoadMonitorNull' ];
 153                 }
 154
 155                 foreach ( $params['servers'] as $i => $server ) {
 156                         $this->mLoads[$i] = $server['load'];
 157                         if ( isset( $server['groupLoads'] ) ) {
 158                                 foreach ( $server['groupLoads'] as $group => $ratio ) {
 159                                         if ( !isset( $this->mGroupLoads[$group] ) ) {
 160                                                 $this->mGroupLoads[$group] = [];
 161                                         }
 162                                         $this->mGroupLoads[$group][$i] = $ratio;
 163                                 }
 164                         }
 165                 }
 166
 167                 if ( isset( $params['srvCache'] ) ) {
 168                         $this->srvCache = $params['srvCache'];
 169                 } else {
 170                         $this->srvCache = new EmptyBagOStuff();
 171                 }
 172                 if ( isset( $params['memCache'] ) ) {
 173                         $this->memCache = $params['memCache'];
 174                 } else {
 175                         $this->memCache = new EmptyBagOStuff();
 176                 }
 177                 if ( isset( $params['wanCache'] ) ) {
 178                         $this->wanCache = $params['wanCache'];
 179                 } else {
 180                         $this->wanCache = WANObjectCache::newEmpty();
 181                 }
 182                 $this->profiler = isset( $params['profiler'] ) ? $params['profiler'] : null;
 183                 if ( isset( $params['trxProfiler'] ) ) {
 184                         $this->trxProfiler = $params['trxProfiler'];
 185                 } else {
 186                         $this->trxProfiler = new TransactionProfiler();
 187                 }
 188
 189                 $this->errorLogger = isset( $params['errorLogger'] )
 190                         ? $params['errorLogger']
 191                         : function ( Exception $e ) {
 192                                 trigger_error( get_class( $e ) . ': ' . $e->getMessage(), E_WARNING );
 193                         };
 194
 195                 foreach ( [ 'replLogger', 'connLogger', 'queryLogger', 'perfLogger' ] as $key ) {
 196                         $this->$key = isset( $params[$key] ) ? $params[$key] : new \Psr\Log\NullLogger();
 197                 }
 198
 199                 $this->host = isset( $params['hostname'] )
 200                         ? $params['hostname']
 201                         : ( gethostname() ?: 'unknown' );
 202                 $this->cliMode = isset( $params['cliMode'] ) ? $params['cliMode'] : PHP_SAPI === 'cli';
 203                 $this->agent = isset( $params['agent'] ) ? $params['agent'] : '';
 204         }
 205
 206         /**
 207          * Get a LoadMonitor instance
 208          *
 209          * @return ILoadMonitor
 210          */
 211         private function getLoadMonitor() {
 212                 if ( !isset( $this->loadMonitor ) ) {
 213                         $class = $this->loadMonitorConfig['class'];
 214                         $this->loadMonitor = new $class(
 215                                 $this, $this->srvCache, $this->memCache, $this->loadMonitorConfig );
 216                         $this->loadMonitor->setLogger( $this->replLogger );
 217                 }
 218
 219                 return $this->loadMonitor;
 220         }
 221
 222         /**
 223          * @param array $loads
 224          * @param bool|string $domain Domain to get non-lagged for
 225          * @param int $maxLag Restrict the maximum allowed lag to this many seconds
 226          * @return bool|int|string
 227          */
 228         private function getRandomNonLagged( array $loads, $domain = false, $maxLag = INF ) {
 229                 $lags = $this->getLagTimes( $domain );
 230
 231                 # Unset excessively lagged servers
 232                 foreach ( $lags as $i => $lag ) {
 233                         if ( $i != 0 ) {
 234                                 # How much lag this server nominally is allowed to have
 235                                 $maxServerLag = isset( $this->mServers[$i]['max lag'] )
 236                                         ? $this->mServers[$i]['max lag']
 237                                         : self::MAX_LAG_DEFAULT; // default
 238                                 # Constrain that futher by $maxLag argument
 239                                 $maxServerLag = min( $maxServerLag, $maxLag );
 240
 241                                 $host = $this->getServerName( $i );
 242                                 if ( $lag === false && !is_infinite( $maxServerLag ) ) {
 243                                         $this->replLogger->error( "Server $host (#$i) is not replicating?" );
 244                                         unset( $loads[$i] );
 245                                 } elseif ( $lag > $maxServerLag ) {
 246                                         $this->replLogger->warning( "Server $host (#$i) has >= $lag seconds of lag" );
 247                                         unset( $loads[$i] );
 248                                 }
 249                         }
 250                 }
 251
 252                 # Find out if all the replica DBs with non-zero load are lagged
 253                 $sum = 0;
 254                 foreach ( $loads as $load ) {
 255                         $sum += $load;
 256                 }
 257                 if ( $sum == 0 ) {
 258                         # No appropriate DB servers except maybe the master and some replica DBs with zero load
 259                         # Do NOT use the master
 260                         # Instead, this function will return false, triggering read-only mode,
 261                         # and a lagged replica DB will be used instead.
 262                         return false;
 263                 }
 264
 265                 if ( count( $loads ) == 0 ) {
 266                         return false;
 267                 }
 268
 269                 # Return a random representative of the remainder
 270                 return ArrayUtils::pickRandom( $loads );
 271         }
 272
 273         public function getReaderIndex( $group = false, $domain = false ) {
 274                 if ( count( $this->mServers ) == 1 ) {
 275                         # Skip the load balancing if there's only one server
 276                         return $this->getWriterIndex();
 277                 } elseif ( $group === false && $this->mReadIndex >= 0 ) {
 278                         # Shortcut if generic reader exists already
 279                         return $this->mReadIndex;
 280                 }
 281
 282                 # Find the relevant load array
 283                 if ( $group !== false ) {
 284                         if ( isset( $this->mGroupLoads[$group] ) ) {
 285                                 $nonErrorLoads = $this->mGroupLoads[$group];
 286                         } else {
 287                                 # No loads for this group, return false and the caller can use some other group
 288                                 $this->connLogger->info( __METHOD__ . ": no loads for group $group" );
 289
 290                                 return false;
 291                         }
 292                 } else {
 293                         $nonErrorLoads = $this->mLoads;
 294                 }
 295
 296                 if ( !count( $nonErrorLoads ) ) {
 297                         throw new InvalidArgumentException( "Empty server array given to LoadBalancer" );
 298                 }
 299
 300                 # Scale the configured load ratios according to the dynamic load if supported
 301                 $this->getLoadMonitor()->scaleLoads( $nonErrorLoads, $domain );
 302
 303                 $laggedReplicaMode = false;
 304
 305                 # No server found yet
 306                 $i = false;
 307                 # First try quickly looking through the available servers for a server that
 308                 # meets our criteria
 309                 $currentLoads = $nonErrorLoads;
 310                 while ( count( $currentLoads ) ) {
 311                         if ( $this->mAllowLagged || $laggedReplicaMode ) {
 312                                 $i = ArrayUtils::pickRandom( $currentLoads );
 313                         } else {
 314                                 $i = false;
 315                                 if ( $this->mWaitForPos && $this->mWaitForPos->asOfTime() ) {
 316                                         # ChronologyProtecter causes mWaitForPos to be set via sessions.
 317                                         # This triggers doWait() after connect, so it's especially good to
 318                                         # avoid lagged servers so as to avoid just blocking in that method.
 319                                         $ago = microtime( true ) - $this->mWaitForPos->asOfTime();
 320                                         # Aim for <= 1 second of waiting (being too picky can backfire)
 321                                         $i = $this->getRandomNonLagged( $currentLoads, $domain, $ago + 1 );
 322                                 }
 323                                 if ( $i === false ) {
 324                                         # Any server with less lag than it's 'max lag' param is preferable
 325                                         $i = $this->getRandomNonLagged( $currentLoads, $domain );
 326                                 }
 327                                 if ( $i === false && count( $currentLoads ) != 0 ) {
 328                                         # All replica DBs lagged. Switch to read-only mode
 329                                         $this->replLogger->error( "All replica DBs lagged. Switch to read-only mode" );
 330                                         $i = ArrayUtils::pickRandom( $currentLoads );
 331                                         $laggedReplicaMode = true;
 332                                 }
 333                         }
 334
 335                         if ( $i === false ) {
 336                                 # pickRandom() returned false
 337                                 # This is permanent and means the configuration or the load monitor
 338                                 # wants us to return false.
 339                                 $this->connLogger->debug( __METHOD__ . ": pickRandom() returned false" );
 340
 341                                 return false;
 342                         }
 343
 344                         $serverName = $this->getServerName( $i );
 345                         $this->connLogger->debug( __METHOD__ . ": Using reader #$i: $serverName..." );
 346
 347                         $conn = $this->openConnection( $i, $domain );
 348                         if ( !$conn ) {
 349                                 $this->connLogger->warning( __METHOD__ . ": Failed connecting to $i/$domain" );
 350                                 unset( $nonErrorLoads[$i] );
 351                                 unset( $currentLoads[$i] );
 352                                 $i = false;
 353                                 continue;
 354                         }
 355
 356                         // Decrement reference counter, we are finished with this connection.
 357                         // It will be incremented for the caller later.
 358                         if ( $domain !== false ) {
 359                                 $this->reuseConnection( $conn );
 360                         }
 361
 362                         # Return this server
 363                         break;
 364                 }
 365
 366                 # If all servers were down, quit now
 367                 if ( !count( $nonErrorLoads ) ) {
 368                         $this->connLogger->error( "All servers down" );
 369                 }
 370
 371                 if ( $i !== false ) {
 372                         # Replica DB connection successful.
 373                         # Wait for the session master pos for a short time.
 374                         if ( $this->mWaitForPos && $i > 0 ) {
 375                                 $this->doWait( $i );
 376                         }
 377                         if ( $this->mReadIndex <= 0 && $this->mLoads[$i] > 0 && $group === false ) {
 378                                 $this->mReadIndex = $i;
 379                                 # Record if the generic reader index is in "lagged replica DB" mode
 380                                 if ( $laggedReplicaMode ) {
 381                                         $this->laggedReplicaMode = true;
 382                                 }
 383                         }
 384                         $serverName = $this->getServerName( $i );
 385                         $this->connLogger->debug(
 386                                 __METHOD__ . ": using server $serverName for group '$group'" );
 387                 }
 388
 389                 return $i;
 390         }
 391
 392         public function waitFor( $pos ) {
 393                 $this->mWaitForPos = $pos;
 394                 $i = $this->mReadIndex;
 395
 396                 if ( $i > 0 ) {
 397                         if ( !$this->doWait( $i ) ) {
 398                                 $this->laggedReplicaMode = true;
 399                         }
 400                 }
 401         }
 402
 403         public function waitForOne( $pos, $timeout = null ) {
 404                 $this->mWaitForPos = $pos;
 405
 406                 $i = $this->mReadIndex;
 407                 if ( $i <= 0 ) {
 408                         // Pick a generic replica DB if there isn't one yet
 409                         $readLoads = $this->mLoads;
 410                         unset( $readLoads[$this->getWriterIndex()] ); // replica DBs only
 411                         $readLoads = array_filter( $readLoads ); // with non-zero load
 412                         $i = ArrayUtils::pickRandom( $readLoads );
 413                 }
 414
 415                 if ( $i > 0 ) {
 416                         $ok = $this->doWait( $i, true, $timeout );
 417                 } else {
 418                         $ok = true; // no applicable loads
 419                 }
 420
 421                 return $ok;
 422         }
 423
 424         public function waitForAll( $pos, $timeout = null ) {
 425                 $this->mWaitForPos = $pos;
 426                 $serverCount = count( $this->mServers );
 427
 428                 $ok = true;
 429                 for ( $i = 1; $i < $serverCount; $i++ ) {
 430                         if ( $this->mLoads[$i] > 0 ) {
 431                                 $ok = $this->doWait( $i, true, $timeout ) && $ok;
 432                         }
 433                 }
 434
 435                 return $ok;
 436         }
 437
 438         public function getAnyOpenConnection( $i ) {
 439                 foreach ( $this->mConns as $connsByServer ) {
 440                         if ( !empty( $connsByServer[$i] ) ) {
 441                                 return reset( $connsByServer[$i] );
 442                         }
 443                 }
 444
 445                 return false;
 446         }
 447
 448         /**
 449          * Wait for a given replica DB to catch up to the master pos stored in $this
 450          * @param int $index Server index
 451          * @param bool $open Check the server even if a new connection has to be made
 452          * @param int $timeout Max seconds to wait; default is mWaitTimeout
 453          * @return bool
 454          */
 455         protected function doWait( $index, $open = false, $timeout = null ) {
 456                 $close = false; // close the connection afterwards
 457
 458                 // Check if we already know that the DB has reached this point
 459                 $server = $this->getServerName( $index );
 460                 $key = $this->srvCache->makeGlobalKey( __CLASS__, 'last-known-pos', $server );
 461                 /** @var DBMasterPos $knownReachedPos */
 462                 $knownReachedPos = $this->srvCache->get( $key );
 463                 if ( $knownReachedPos && $knownReachedPos->hasReached( $this->mWaitForPos ) ) {
 464                         $this->replLogger->debug( __METHOD__ .
 465                                 ": replica DB $server known to be caught up (pos >= $knownReachedPos)." );
 466                         return true;
 467                 }
 468
 469                 // Find a connection to wait on, creating one if needed and allowed
 470                 $conn = $this->getAnyOpenConnection( $index );
 471                 if ( !$conn ) {
 472                         if ( !$open ) {
 473                                 $this->replLogger->debug( __METHOD__ . ": no connection open for $server" );
 474
 475                                 return false;
 476                         } else {
 477                                 $conn = $this->openConnection( $index, self::DOMAIN_ANY );
 478                                 if ( !$conn ) {
 479                                         $this->replLogger->warning( __METHOD__ . ": failed to connect to $server" );
 480
 481                                         return false;
 482                                 }
 483                                 // Avoid connection spam in waitForAll() when connections
 484                                 // are made just for the sake of doing this lag check.
 485                                 $close = true;
 486                         }
 487                 }
 488
 489                 $this->replLogger->info( __METHOD__ . ": Waiting for replica DB $server to catch up..." );
 490                 $timeout = $timeout ?: $this->mWaitTimeout;
 491                 $result = $conn->masterPosWait( $this->mWaitForPos, $timeout );
 492
 493                 if ( $result == -1 || is_null( $result ) ) {
 494                         // Timed out waiting for replica DB, use master instead
 495                         $msg = __METHOD__ . ": Timed out waiting on $server pos {$this->mWaitForPos}";
 496                         $this->replLogger->warning( "$msg" );
 497                         $ok = false;
 498                 } else {
 499                         $this->replLogger->info( __METHOD__ . ": Done" );
 500                         $ok = true;
 501                         // Remember that the DB reached this point
 502                         $this->srvCache->set( $key, $this->mWaitForPos, BagOStuff::TTL_DAY );
 503                 }
 504
 505                 if ( $close ) {
 506                         $this->closeConnection( $conn );
 507                 }
 508
 509                 return $ok;
 510         }
 511
 512         /**
 513          * @see ILoadBalancer::getConnection()
 514          *
 515          * @param int $i
 516          * @param array $groups
 517          * @param bool $domain
 518          * @return Database
 519          * @throws DBConnectionError
 520          */
 521         public function getConnection( $i, $groups = [], $domain = false ) {
 522                 if ( $i === null || $i === false ) {
 523                         throw new InvalidArgumentException( 'Attempt to call ' . __METHOD__ .
 524                                 ' with invalid server index' );
 525                 }
 526
 527                 if ( $this->localDomain->equals( $domain ) || $domain === $this->localDomainIdAlias ) {
 528                         $domain = false; // local connection requested
 529                 }
 530
 531                 $groups = ( $groups === false || $groups === [] )
 532                         ? [ false ] // check one "group": the generic pool
 533                         : (array)$groups;
 534
 535                 $masterOnly = ( $i == self::DB_MASTER || $i == $this->getWriterIndex() );
 536                 $oldConnsOpened = $this->connsOpened; // connections open now
 537
 538                 if ( $i == self::DB_MASTER ) {
 539                         $i = $this->getWriterIndex();
 540                 } else {
 541                         # Try to find an available server in any the query groups (in order)
 542                         foreach ( $groups as $group ) {
 543                                 $groupIndex = $this->getReaderIndex( $group, $domain );
 544                                 if ( $groupIndex !== false ) {
 545                                         $i = $groupIndex;
 546                                         break;
 547                                 }
 548                         }
 549                 }
 550
 551                 # Operation-based index
 552                 if ( $i == self::DB_REPLICA ) {
 553                         $this->mLastError = 'Unknown error'; // reset error string
 554                         # Try the general server pool if $groups are unavailable.
 555                         $i = in_array( false, $groups, true )
 556                                 ? false // don't bother with this if that is what was tried above
 557                                 : $this->getReaderIndex( false, $domain );
 558                         # Couldn't find a working server in getReaderIndex()?
 559                         if ( $i === false ) {
 560                                 $this->mLastError = 'No working replica DB server: ' . $this->mLastError;
 561                                 // Throw an exception
 562                                 $this->reportConnectionError();
 563                                 return null; // not reached
 564                         }
 565                 }
 566
 567                 # Now we have an explicit index into the servers array
 568                 $conn = $this->openConnection( $i, $domain );
 569                 if ( !$conn ) {
 570                         // Throw an exception
 571                         $this->reportConnectionError();
 572                         return null; // not reached
 573                 }
 574
 575                 # Profile any new connections that happen
 576                 if ( $this->connsOpened > $oldConnsOpened ) {
 577                         $host = $conn->getServer();
 578                         $dbname = $conn->getDBname();
 579                         $this->trxProfiler->recordConnection( $host, $dbname, $masterOnly );
 580                 }
 581
 582                 if ( $masterOnly ) {
 583                         # Make master-requested DB handles inherit any read-only mode setting
 584                         $conn->setLBInfo( 'readOnlyReason', $this->getReadOnlyReason( $domain, $conn ) );
 585                 }
 586
 587                 return $conn;
 588         }
 589
 590         public function reuseConnection( $conn ) {
 591                 $serverIndex = $conn->getLBInfo( 'serverIndex' );
 592                 $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 593                 if ( $serverIndex === null || $refCount === null ) {
 594                         /**
 595                          * This can happen in code like:
 596                          *   foreach ( $dbs as $db ) {
 597                          *     $conn = $lb->getConnection( $lb::DB_REPLICA, [], $db );
 598                          *     ...
 599                          *     $lb->reuseConnection( $conn );
 600                          *   }
 601                          * When a connection to the local DB is opened in this way, reuseConnection()
 602                          * should be ignored
 603                          */
 604                         return;
 605                 } elseif ( $conn instanceof DBConnRef ) {
 606                         // DBConnRef already handles calling reuseConnection() and only passes the live
 607                         // Database instance to this method. Any caller passing in a DBConnRef is broken.
 608                         $this->connLogger->error( __METHOD__ . ": got DBConnRef instance.\n" .
 609                                 ( new RuntimeException() )->getTraceAsString() );
 610
 611                         return;
 612                 }
 613
 614                 if ( $this->disabled ) {
 615                         return; // DBConnRef handle probably survived longer than the LoadBalancer
 616                 }
 617
 618                 $domain = $conn->getDomainID();
 619                 if ( !isset( $this->mConns['foreignUsed'][$serverIndex][$domain] ) ) {
 620                         throw new InvalidArgumentException( __METHOD__ .
 621                                 ": connection $serverIndex/$domain not found; it may have already been freed." );
 622                 } elseif ( $this->mConns['foreignUsed'][$serverIndex][$domain] !== $conn ) {
 623                         throw new InvalidArgumentException( __METHOD__ .
 624                                 ": connection $serverIndex/$domain mismatched; it may have already been freed." );
 625                 }
 626                 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
 627                 if ( $refCount <= 0 ) {
 628                         $this->mConns['foreignFree'][$serverIndex][$domain] = $conn;
 629                         unset( $this->mConns['foreignUsed'][$serverIndex][$domain] );
 630                         if ( !$this->mConns['foreignUsed'][$serverIndex] ) {
 631                                 unset( $this->mConns[ 'foreignUsed' ][$serverIndex] ); // clean up
 632                         }
 633                         $this->connLogger->debug( __METHOD__ . ": freed connection $serverIndex/$domain" );
 634                 } else {
 635                         $this->connLogger->debug( __METHOD__ .
 636                                 ": reference count for $serverIndex/$domain reduced to $refCount" );
 637                 }
 638         }
 639
 640         public function getConnectionRef( $db, $groups = [], $domain = false ) {
 641                 $domain = ( $domain !== false ) ? $domain : $this->localDomain;
 642
 643                 return new DBConnRef( $this, $this->getConnection( $db, $groups, $domain ) );
 644         }
 645
 646         public function getLazyConnectionRef( $db, $groups = [], $domain = false ) {
 647                 $domain = ( $domain !== false ) ? $domain : $this->localDomain;
 648
 649                 return new DBConnRef( $this, [ $db, $groups, $domain ] );
 650         }
 651
 652         /**
 653          * @see ILoadBalancer::openConnection()
 654          *
 655          * @param int $i
 656          * @param bool $domain
 657          * @return bool|Database
 658          * @throws DBAccessError
 659          */
 660         public function openConnection( $i, $domain = false ) {
 661                 if ( $this->localDomain->equals( $domain ) || $domain === $this->localDomainIdAlias ) {
 662                         $domain = false; // local connection requested
 663                 }
 664
 665                 if ( $domain !== false ) {
 666                         $conn = $this->openForeignConnection( $i, $domain );
 667                 } elseif ( isset( $this->mConns['local'][$i][0] ) ) {
 668                         $conn = $this->mConns['local'][$i][0];
 669                 } else {
 670                         $server = $this->mServers[$i];
 671                         $server['serverIndex'] = $i;
 672                         $conn = $this->reallyOpenConnection( $server, false );
 673                         $serverName = $this->getServerName( $i );
 674                         if ( $conn->isOpen() ) {
 675                                 $this->connLogger->debug( "Connected to database $i at '$serverName'." );
 676                                 $this->mConns['local'][$i][0] = $conn;
 677                         } else {
 678                                 $this->connLogger->warning( "Failed to connect to database $i at '$serverName'." );
 679                                 $this->mErrorConnection = $conn;
 680                                 $conn = false;
 681                         }
 682                 }
 683
 684                 if ( $conn && !$conn->isOpen() ) {
 685                         // Connection was made but later unrecoverably lost for some reason.
 686                         // Do not return a handle that will just throw exceptions on use,
 687                         // but let the calling code (e.g. getReaderIndex) try another server.
 688                         // See DatabaseMyslBase::ping() for how this can happen.
 689                         $this->mErrorConnection = $conn;
 690                         $conn = false;
 691                 }
 692
 693                 return $conn;
 694         }
 695
 696         /**
 697          * Open a connection to a foreign DB, or return one if it is already open.
 698          *
 699          * Increments a reference count on the returned connection which locks the
 700          * connection to the requested domain. This reference count can be
 701          * decremented by calling reuseConnection().
 702          *
 703          * If a connection is open to the appropriate server already, but with the wrong
 704          * database, it will be switched to the right database and returned, as long as
 705          * it has been freed first with reuseConnection().
 706          *
 707          * On error, returns false, and the connection which caused the
 708          * error will be available via $this->mErrorConnection.
 709          *
 710          * @note If disable() was called on this LoadBalancer, this method will throw a DBAccessError.
 711          *
 712          * @param int $i Server index
 713          * @param string $domain Domain ID to open
 714          * @return Database
 715          */
 716         private function openForeignConnection( $i, $domain ) {
 717                 $domainInstance = DatabaseDomain::newFromId( $domain );
 718                 $dbName = $domainInstance->getDatabase();
 719                 $prefix = $domainInstance->getTablePrefix();
 720
 721                 if ( isset( $this->mConns['foreignUsed'][$i][$domain] ) ) {
 722                         // Reuse an already-used connection
 723                         $conn = $this->mConns['foreignUsed'][$i][$domain];
 724                         $this->connLogger->debug( __METHOD__ . ": reusing connection $i/$domain" );
 725                 } elseif ( isset( $this->mConns['foreignFree'][$i][$domain] ) ) {
 726                         // Reuse a free connection for the same domain
 727                         $conn = $this->mConns['foreignFree'][$i][$domain];
 728                         unset( $this->mConns['foreignFree'][$i][$domain] );
 729                         $this->mConns['foreignUsed'][$i][$domain] = $conn;
 730                         $this->connLogger->debug( __METHOD__ . ": reusing free connection $i/$domain" );
 731                 } elseif ( !empty( $this->mConns['foreignFree'][$i] ) ) {
 732                         // Reuse a connection from another domain
 733                         $conn = reset( $this->mConns['foreignFree'][$i] );
 734                         $oldDomain = key( $this->mConns['foreignFree'][$i] );
 735                         // The empty string as a DB name means "don't care".
 736                         // DatabaseMysqlBase::open() already handle this on connection.
 737                         if ( strlen( $dbName ) && !$conn->selectDB( $dbName ) ) {
 738                                 $this->mLastError = "Error selecting database '$dbName' on server " .
 739                                         $conn->getServer() . " from client host {$this->host}";
 740                                 $this->mErrorConnection = $conn;
 741                                 $conn = false;
 742                         } else {
 743                                 $conn->tablePrefix( $prefix );
 744                                 unset( $this->mConns['foreignFree'][$i][$oldDomain] );
 745                                 $this->mConns['foreignUsed'][$i][$domain] = $conn;
 746                                 $this->connLogger->debug( __METHOD__ .
 747                                         ": reusing free connection from $oldDomain for $domain" );
 748                         }
 749                 } else {
 750                         // Open a new connection
 751                         $server = $this->mServers[$i];
 752                         $server['serverIndex'] = $i;
 753                         $server['foreignPoolRefCount'] = 0;
 754                         $server['foreign'] = true;
 755                         $conn = $this->reallyOpenConnection( $server, $dbName );
 756                         if ( !$conn->isOpen() ) {
 757                                 $this->connLogger->warning( __METHOD__ . ": connection error for $i/$domain" );
 758                                 $this->mErrorConnection = $conn;
 759                                 $conn = false;
 760                         } else {
 761                                 $conn->tablePrefix( $prefix );
 762                                 $this->mConns['foreignUsed'][$i][$domain] = $conn;
 763                                 $this->connLogger->debug( __METHOD__ . ": opened new connection for $i/$domain" );
 764                         }
 765                 }
 766
 767                 // Increment reference count
 768                 if ( $conn ) {
 769                         $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 770                         $conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
 771                 }
 772
 773                 return $conn;
 774         }
 775
 776         /**
 777          * Test if the specified index represents an open connection
 778          *
 779          * @param int $index Server index
 780          * @access private
 781          * @return bool
 782          */
 783         private function isOpen( $index ) {
 784                 if ( !is_integer( $index ) ) {
 785                         return false;
 786                 }
 787
 788                 return (bool)$this->getAnyOpenConnection( $index );
 789         }
 790
 791         /**
 792          * Really opens a connection. Uncached.
 793          * Returns a Database object whether or not the connection was successful.
 794          * @access private
 795          *
 796          * @param array $server
 797          * @param string|bool $dbNameOverride Use "" to not select any database
 798          * @return Database
 799          * @throws DBAccessError
 800          * @throws InvalidArgumentException
 801          */
 802         protected function reallyOpenConnection( $server, $dbNameOverride = false ) {
 803                 if ( $this->disabled ) {
 804                         throw new DBAccessError();
 805                 }
 806
 807                 if ( !is_array( $server ) ) {
 808                         throw new InvalidArgumentException(
 809                                 'You must update your load-balancing configuration. ' .
 810                                 'See DefaultSettings.php entry for $wgDBservers.' );
 811                 }
 812
 813                 if ( $dbNameOverride !== false ) {
 814                         $server['dbname'] = $dbNameOverride;
 815                 }
 816
 817                 // Let the handle know what the cluster master is (e.g. "db1052")
 818                 $masterName = $this->getServerName( $this->getWriterIndex() );
 819                 $server['clusterMasterHost'] = $masterName;
 820
 821                 // Log when many connection are made on requests
 822                 if ( ++$this->connsOpened >= self::CONN_HELD_WARN_THRESHOLD ) {
 823                         $this->perfLogger->warning( __METHOD__ . ": " .
 824                                 "{$this->connsOpened}+ connections made (master=$masterName)" );
 825                 }
 826
 827                 $server['srvCache'] = $this->srvCache;
 828                 // Set loggers and profilers
 829                 $server['connLogger'] = $this->connLogger;
 830                 $server['queryLogger'] = $this->queryLogger;
 831                 $server['errorLogger'] = $this->errorLogger;
 832                 $server['profiler'] = $this->profiler;
 833                 $server['trxProfiler'] = $this->trxProfiler;
 834                 // Use the same agent and PHP mode for all DB handles
 835                 $server['cliMode'] = $this->cliMode;
 836                 $server['agent'] = $this->agent;
 837                 // Use DBO_DEFAULT flags by default for LoadBalancer managed databases. Assume that the
 838                 // application calls LoadBalancer::commitMasterChanges() before the PHP script completes.
 839                 $server['flags'] = isset( $server['flags'] ) ? $server['flags'] : IDatabase::DBO_DEFAULT;
 840
 841                 // Create a live connection object
 842                 try {
 843                         $db = Database::factory( $server['type'], $server );
 844                 } catch ( DBConnectionError $e ) {
 845                         // FIXME: This is probably the ugliest thing I have ever done to
 846                         // PHP. I'm half-expecting it to segfault, just out of disgust. -- TS
 847                         $db = $e->db;
 848                 }
 849
 850                 $db->setLBInfo( $server );
 851                 $db->setLazyMasterHandle(
 852                         $this->getLazyConnectionRef( self::DB_MASTER, [], $db->getDomainID() )
 853                 );
 854                 $db->setTableAliases( $this->tableAliases );
 855
 856                 if ( $server['serverIndex'] === $this->getWriterIndex() ) {
 857                         if ( $this->trxRoundId !== false ) {
 858                                 $this->applyTransactionRoundFlags( $db );
 859                         }
 860                         foreach ( $this->trxRecurringCallbacks as $name => $callback ) {
 861                                 $db->setTransactionListener( $name, $callback );
 862                         }
 863                 }
 864
 865                 return $db;
 866         }
 867
 868         /**
 869          * @throws DBConnectionError
 870          */
 871         private function reportConnectionError() {
 872                 $conn = $this->mErrorConnection; // the connection which caused the error
 873                 $context = [
 874                         'method' => __METHOD__,
 875                         'last_error' => $this->mLastError,
 876                 ];
 877
 878                 if ( !is_object( $conn ) ) {
 879                         // No last connection, probably due to all servers being too busy
 880                         $this->connLogger->error(
 881                                 "LB failure with no last connection. Connection error: {last_error}",
 882                                 $context
 883                         );
 884
 885                         // If all servers were busy, mLastError will contain something sensible
 886                         throw new DBConnectionError( null, $this->mLastError );
 887                 } else {
 888                         $context['db_server'] = $conn->getProperty( 'mServer' );
 889                         $this->connLogger->warning(
 890                                 "Connection error: {last_error} ({db_server})",
 891                                 $context
 892                         );
 893
 894                         // throws DBConnectionError
 895                         $conn->reportConnectionError( "{$this->mLastError} ({$context['db_server']})" );
 896                 }
 897         }
 898
 899         public function getWriterIndex() {
 900                 return 0;
 901         }
 902
 903         public function haveIndex( $i ) {
 904                 return array_key_exists( $i, $this->mServers );
 905         }
 906
 907         public function isNonZeroLoad( $i ) {
 908                 return array_key_exists( $i, $this->mServers ) && $this->mLoads[$i] != 0;
 909         }
 910
 911         public function getServerCount() {
 912                 return count( $this->mServers );
 913         }
 914
 915         public function getServerName( $i ) {
 916                 if ( isset( $this->mServers[$i]['hostName'] ) ) {
 917                         $name = $this->mServers[$i]['hostName'];
 918                 } elseif ( isset( $this->mServers[$i]['host'] ) ) {
 919                         $name = $this->mServers[$i]['host'];
 920                 } else {
 921                         $name = '';
 922                 }
 923
 924                 return ( $name != '' ) ? $name : 'localhost';
 925         }
 926
 927         public function getServerInfo( $i ) {
 928                 if ( isset( $this->mServers[$i] ) ) {
 929                         return $this->mServers[$i];
 930                 } else {
 931                         return false;
 932                 }
 933         }
 934
 935         public function setServerInfo( $i, array $serverInfo ) {
 936                 $this->mServers[$i] = $serverInfo;
 937         }
 938
 939         public function getMasterPos() {
 940                 # If this entire request was served from a replica DB without opening a connection to the
 941                 # master (however unlikely that may be), then we can fetch the position from the replica DB.
 942                 $masterConn = $this->getAnyOpenConnection( $this->getWriterIndex() );
 943                 if ( !$masterConn ) {
 944                         $serverCount = count( $this->mServers );
 945                         for ( $i = 1; $i < $serverCount; $i++ ) {
 946                                 $conn = $this->getAnyOpenConnection( $i );
 947                                 if ( $conn ) {
 948                                         return $conn->getReplicaPos();
 949                                 }
 950                         }
 951                 } else {
 952                         return $masterConn->getMasterPos();
 953                 }
 954
 955                 return false;
 956         }
 957
 958         public function disable() {
 959                 $this->closeAll();
 960                 $this->disabled = true;
 961         }
 962
 963         public function closeAll() {
 964                 $this->forEachOpenConnection( function ( IDatabase $conn ) {
 965                         $host = $conn->getServer();
 966                         $this->connLogger->debug( "Closing connection to database '$host'." );
 967                         $conn->close();
 968                 } );
 969
 970                 $this->mConns = [
 971                         'local' => [],
 972                         'foreignFree' => [],
 973                         'foreignUsed' => [],
 974                 ];
 975                 $this->connsOpened = 0;
 976         }
 977
 978         public function closeConnection( IDatabase $conn ) {
 979                 $serverIndex = $conn->getLBInfo( 'serverIndex' ); // second index level of mConns
 980                 foreach ( $this->mConns as $type => $connsByServer ) {
 981                         if ( !isset( $connsByServer[$serverIndex] ) ) {
 982                                 continue;
 983                         }
 984
 985                         foreach ( $connsByServer[$serverIndex] as $i => $trackedConn ) {
 986                                 if ( $conn === $trackedConn ) {
 987                                         $host = $this->getServerName( $i );
 988                                         $this->connLogger->debug( "Closing connection to database $i at '$host'." );
 989                                         unset( $this->mConns[$type][$serverIndex][$i] );
 990                                         --$this->connsOpened;
 991                                         break 2;
 992                                 }
 993                         }
 994                 }
 995
 996                 $conn->close();
 997         }
 998
 999         public function commitAll( $fname = __METHOD__ ) {
1000                 $failures = [];
1001
1002                 $restore = ( $this->trxRoundId !== false );
1003                 $this->trxRoundId = false;
1004                 $this->forEachOpenConnection(
1005                         function ( IDatabase $conn ) use ( $fname, $restore, &$failures ) {
1006                                 try {
1007                                         $conn->commit( $fname, $conn::FLUSHING_ALL_PEERS );
1008                                 } catch ( DBError $e ) {
1009                                         call_user_func( $this->errorLogger, $e );
1010                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1011                                 }
1012                                 if ( $restore && $conn->getLBInfo( 'master' ) ) {
1013                                         $this->undoTransactionRoundFlags( $conn );
1014                                 }
1015                         }
1016                 );
1017
1018                 if ( $failures ) {
1019                         throw new DBExpectedError(
1020                                 null,
1021                                 "Commit failed on server(s) " . implode( "\n", array_unique( $failures ) )
1022                         );
1023                 }
1024         }
1025
1026         public function finalizeMasterChanges() {
1027                 $this->forEachOpenMasterConnection( function ( Database $conn ) {
1028                         // Any error should cause all DB transactions to be rolled back together
1029                         $conn->setTrxEndCallbackSuppression( false );
1030                         $conn->runOnTransactionPreCommitCallbacks();
1031                         // Defer post-commit callbacks until COMMIT finishes for all DBs
1032                         $conn->setTrxEndCallbackSuppression( true );
1033                 } );
1034         }
1035
1036         public function approveMasterChanges( array $options ) {
1037                 $limit = isset( $options['maxWriteDuration'] ) ? $options['maxWriteDuration'] : 0;
1038                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( $limit ) {
1039                         // If atomic sections or explicit transactions are still open, some caller must have
1040                         // caught an exception but failed to properly rollback any changes. Detect that and
1041                         // throw and error (causing rollback).
1042                         if ( $conn->explicitTrxActive() ) {
1043                                 throw new DBTransactionError(
1044                                         $conn,
1045                                         "Explicit transaction still active. A caller may have caught an error."
1046                                 );
1047                         }
1048                         // Assert that the time to replicate the transaction will be sane.
1049                         // If this fails, then all DB transactions will be rollback back together.
1050                         $time = $conn->pendingWriteQueryDuration( $conn::ESTIMATE_DB_APPLY );
1051                         if ( $limit > 0 && $time > $limit ) {
1052                                 throw new DBTransactionSizeError(
1053                                         $conn,
1054                                         "Transaction spent $time second(s) in writes, exceeding the $limit limit.",
1055                                         [ $time, $limit ]
1056                                 );
1057                         }
1058                         // If a connection sits idle while slow queries execute on another, that connection
1059                         // may end up dropped before the commit round is reached. Ping servers to detect this.
1060                         if ( $conn->writesOrCallbacksPending() && !$conn->ping() ) {
1061                                 throw new DBTransactionError(
1062                                         $conn,
1063                                         "A connection to the {$conn->getDBname()} database was lost before commit."
1064                                 );
1065                         }
1066                 } );
1067         }
1068
1069         public function beginMasterChanges( $fname = __METHOD__ ) {
1070                 if ( $this->trxRoundId !== false ) {
1071                         throw new DBTransactionError(
1072                                 null,
1073                                 "$fname: Transaction round '{$this->trxRoundId}' already started."
1074                         );
1075                 }
1076                 $this->trxRoundId = $fname;
1077
1078                 $failures = [];
1079                 $this->forEachOpenMasterConnection(
1080                         function ( Database $conn ) use ( $fname, &$failures ) {
1081                                 $conn->setTrxEndCallbackSuppression( true );
1082                                 try {
1083                                         $conn->flushSnapshot( $fname );
1084                                 } catch ( DBError $e ) {
1085                                         call_user_func( $this->errorLogger, $e );
1086                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1087                                 }
1088                                 $conn->setTrxEndCallbackSuppression( false );
1089                                 $this->applyTransactionRoundFlags( $conn );
1090                         }
1091                 );
1092
1093                 if ( $failures ) {
1094                         throw new DBExpectedError(
1095                                 null,
1096                                 "$fname: Flush failed on server(s) " . implode( "\n", array_unique( $failures ) )
1097                         );
1098                 }
1099         }
1100
1101         public function commitMasterChanges( $fname = __METHOD__ ) {
1102                 $failures = [];
1103
1104                 /** @noinspection PhpUnusedLocalVariableInspection */
1105                 $scope = $this->getScopedPHPBehaviorForCommit(); // try to ignore client aborts
1106
1107                 $restore = ( $this->trxRoundId !== false );
1108                 $this->trxRoundId = false;
1109                 $this->forEachOpenMasterConnection(
1110                         function ( IDatabase $conn ) use ( $fname, $restore, &$failures ) {
1111                                 try {
1112                                         if ( $conn->writesOrCallbacksPending() ) {
1113                                                 $conn->commit( $fname, $conn::FLUSHING_ALL_PEERS );
1114                                         } elseif ( $restore ) {
1115                                                 $conn->flushSnapshot( $fname );
1116                                         }
1117                                 } catch ( DBError $e ) {
1118                                         call_user_func( $this->errorLogger, $e );
1119                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1120                                 }
1121                                 if ( $restore ) {
1122                                         $this->undoTransactionRoundFlags( $conn );
1123                                 }
1124                         }
1125                 );
1126
1127                 if ( $failures ) {
1128                         throw new DBExpectedError(
1129                                 null,
1130                                 "$fname: Commit failed on server(s) " . implode( "\n", array_unique( $failures ) )
1131                         );
1132                 }
1133         }
1134
1135         public function runMasterPostTrxCallbacks( $type ) {
1136                 $e = null; // first exception
1137                 $this->forEachOpenMasterConnection( function ( Database $conn ) use ( $type, &$e ) {
1138                         $conn->setTrxEndCallbackSuppression( false );
1139                         if ( $conn->writesOrCallbacksPending() ) {
1140                                 // This happens if onTransactionIdle() callbacks leave callbacks on *another* DB
1141                                 // (which finished its callbacks already). Warn and recover in this case. Let the
1142                                 // callbacks run in the final commitMasterChanges() in LBFactory::shutdown().
1143                                 $this->queryLogger->error( __METHOD__ . ": found writes/callbacks pending." );
1144                                 return;
1145                         } elseif ( $conn->trxLevel() ) {
1146                                 // This happens for single-DB setups where DB_REPLICA uses the master DB,
1147                                 // thus leaving an implicit read-only transaction open at this point. It
1148                                 // also happens if onTransactionIdle() callbacks leave implicit transactions
1149                                 // open on *other* DBs (which is slightly improper). Let these COMMIT on the
1150                                 // next call to commitMasterChanges(), possibly in LBFactory::shutdown().
1151                                 return;
1152                         }
1153                         try {
1154                                 $conn->runOnTransactionIdleCallbacks( $type );
1155                         } catch ( Exception $ex ) {
1156                                 $e = $e ?: $ex;
1157                         }
1158                         try {
1159                                 $conn->runTransactionListenerCallbacks( $type );
1160                         } catch ( Exception $ex ) {
1161                                 $e = $e ?: $ex;
1162                         }
1163                 } );
1164
1165                 return $e;
1166         }
1167
1168         public function rollbackMasterChanges( $fname = __METHOD__ ) {
1169                 $restore = ( $this->trxRoundId !== false );
1170                 $this->trxRoundId = false;
1171                 $this->forEachOpenMasterConnection(
1172                         function ( IDatabase $conn ) use ( $fname, $restore ) {
1173                                 if ( $conn->writesOrCallbacksPending() ) {
1174                                         $conn->rollback( $fname, $conn::FLUSHING_ALL_PEERS );
1175                                 }
1176                                 if ( $restore ) {
1177                                         $this->undoTransactionRoundFlags( $conn );
1178                                 }
1179                         }
1180                 );
1181         }
1182
1183         public function suppressTransactionEndCallbacks() {
1184                 $this->forEachOpenMasterConnection( function ( Database $conn ) {
1185                         $conn->setTrxEndCallbackSuppression( true );
1186                 } );
1187         }
1188
1189         /**
1190          * @param IDatabase $conn
1191          */
1192         private function applyTransactionRoundFlags( IDatabase $conn ) {
1193                 if ( $conn->getFlag( $conn::DBO_DEFAULT ) ) {
1194                         // DBO_TRX is controlled entirely by CLI mode presence with DBO_DEFAULT.
1195                         // Force DBO_TRX even in CLI mode since a commit round is expected soon.
1196                         $conn->setFlag( $conn::DBO_TRX, $conn::REMEMBER_PRIOR );
1197                         // If config has explicitly requested DBO_TRX be either on or off by not
1198                         // setting DBO_DEFAULT, then respect that. Forcing no transactions is useful
1199                         // for things like blob stores (ExternalStore) which want auto-commit mode.
1200                 }
1201         }
1202
1203         /**
1204          * @param IDatabase $conn
1205          */
1206         private function undoTransactionRoundFlags( IDatabase $conn ) {
1207                 if ( $conn->getFlag( $conn::DBO_DEFAULT ) ) {
1208                         $conn->restoreFlags( $conn::RESTORE_PRIOR );
1209                 }
1210         }
1211
1212         public function flushReplicaSnapshots( $fname = __METHOD__ ) {
1213                 $this->forEachOpenReplicaConnection( function ( IDatabase $conn ) {
1214                         $conn->flushSnapshot( __METHOD__ );
1215                 } );
1216         }
1217
1218         public function hasMasterConnection() {
1219                 return $this->isOpen( $this->getWriterIndex() );
1220         }
1221
1222         public function hasMasterChanges() {
1223                 $pending = 0;
1224                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$pending ) {
1225                         $pending |= $conn->writesOrCallbacksPending();
1226                 } );
1227
1228                 return (bool)$pending;
1229         }
1230
1231         public function lastMasterChangeTimestamp() {
1232                 $lastTime = false;
1233                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$lastTime ) {
1234                         $lastTime = max( $lastTime, $conn->lastDoneWrites() );
1235                 } );
1236
1237                 return $lastTime;
1238         }
1239
1240         public function hasOrMadeRecentMasterChanges( $age = null ) {
1241                 $age = ( $age === null ) ? $this->mWaitTimeout : $age;
1242
1243                 return ( $this->hasMasterChanges()
1244                         || $this->lastMasterChangeTimestamp() > microtime( true ) - $age );
1245         }
1246
1247         public function pendingMasterChangeCallers() {
1248                 $fnames = [];
1249                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$fnames ) {
1250                         $fnames = array_merge( $fnames, $conn->pendingWriteCallers() );
1251                 } );
1252
1253                 return $fnames;
1254         }
1255
1256         public function getLaggedReplicaMode( $domain = false ) {
1257                 // No-op if there is only one DB (also avoids recursion)
1258                 if ( !$this->laggedReplicaMode && $this->getServerCount() > 1 ) {
1259                         try {
1260                                 // See if laggedReplicaMode gets set
1261                                 $conn = $this->getConnection( self::DB_REPLICA, false, $domain );
1262                                 $this->reuseConnection( $conn );
1263                         } catch ( DBConnectionError $e ) {
1264                                 // Avoid expensive re-connect attempts and failures
1265                                 $this->allReplicasDownMode = true;
1266                                 $this->laggedReplicaMode = true;
1267                         }
1268                 }
1269
1270                 return $this->laggedReplicaMode;
1271         }
1272
1273         /**
1274          * @param bool $domain
1275          * @return bool
1276          * @deprecated 1.28; use getLaggedReplicaMode()
1277          */
1278         public function getLaggedSlaveMode( $domain = false ) {
1279                 return $this->getLaggedReplicaMode( $domain );
1280         }
1281
1282         public function laggedReplicaUsed() {
1283                 return $this->laggedReplicaMode;
1284         }
1285
1286         /**
1287          * @return bool
1288          * @since 1.27
1289          * @deprecated Since 1.28; use laggedReplicaUsed()
1290          */
1291         public function laggedSlaveUsed() {
1292                 return $this->laggedReplicaUsed();
1293         }
1294
1295         public function getReadOnlyReason( $domain = false, IDatabase $conn = null ) {
1296                 if ( $this->readOnlyReason !== false ) {
1297                         return $this->readOnlyReason;
1298                 } elseif ( $this->getLaggedReplicaMode( $domain ) ) {
1299                         if ( $this->allReplicasDownMode ) {
1300                                 return 'The database has been automatically locked ' .
1301                                         'until the replica database servers become available';
1302                         } else {
1303                                 return 'The database has been automatically locked ' .
1304                                         'while the replica database servers catch up to the master.';
1305                         }
1306                 } elseif ( $this->masterRunningReadOnly( $domain, $conn ) ) {
1307                         return 'The database master is running in read-only mode.';
1308                 }
1309
1310                 return false;
1311         }
1312
1313         /**
1314          * @param string $domain Domain ID, or false for the current domain
1315          * @param IDatabase|null DB master connectionl used to avoid loops [optional]
1316          * @return bool
1317          */
1318         private function masterRunningReadOnly( $domain, IDatabase $conn = null ) {
1319                 $cache = $this->wanCache;
1320                 $masterServer = $this->getServerName( $this->getWriterIndex() );
1321
1322                 return (bool)$cache->getWithSetCallback(
1323                         $cache->makeGlobalKey( __CLASS__, 'server-read-only', $masterServer ),
1324                         self::TTL_CACHE_READONLY,
1325                         function () use ( $domain, $conn ) {
1326                                 $this->trxProfiler->setSilenced( true );
1327                                 try {
1328                                         $dbw = $conn ?: $this->getConnection( self::DB_MASTER, [], $domain );
1329                                         $readOnly = (int)$dbw->serverIsReadOnly();
1330                                         if ( !$conn ) {
1331                                                 $this->reuseConnection( $dbw );
1332                                         }
1333                                 } catch ( DBError $e ) {
1334                                         $readOnly = 0;
1335                                 }
1336                                 $this->trxProfiler->setSilenced( false );
1337                                 return $readOnly;
1338                         },
1339                         [ 'pcTTL' => $cache::TTL_PROC_LONG, 'busyValue' => 0 ]
1340                 );
1341         }
1342
1343         public function allowLagged( $mode = null ) {
1344                 if ( $mode === null ) {
1345                         return $this->mAllowLagged;
1346                 }
1347                 $this->mAllowLagged = $mode;
1348
1349                 return $this->mAllowLagged;
1350         }
1351
1352         public function pingAll() {
1353                 $success = true;
1354                 $this->forEachOpenConnection( function ( IDatabase $conn ) use ( &$success ) {
1355                         if ( !$conn->ping() ) {
1356                                 $success = false;
1357                         }
1358                 } );
1359
1360                 return $success;
1361         }
1362
1363         public function forEachOpenConnection( $callback, array $params = [] ) {
1364                 foreach ( $this->mConns as $connsByServer ) {
1365                         foreach ( $connsByServer as $serverConns ) {
1366                                 foreach ( $serverConns as $conn ) {
1367                                         $mergedParams = array_merge( [ $conn ], $params );
1368                                         call_user_func_array( $callback, $mergedParams );
1369                                 }
1370                         }
1371                 }
1372         }
1373
1374         public function forEachOpenMasterConnection( $callback, array $params = [] ) {
1375                 $masterIndex = $this->getWriterIndex();
1376                 foreach ( $this->mConns as $connsByServer ) {
1377                         if ( isset( $connsByServer[$masterIndex] ) ) {
1378                                 /** @var IDatabase $conn */
1379                                 foreach ( $connsByServer[$masterIndex] as $conn ) {
1380                                         $mergedParams = array_merge( [ $conn ], $params );
1381                                         call_user_func_array( $callback, $mergedParams );
1382                                 }
1383                         }
1384                 }
1385         }
1386
1387         public function forEachOpenReplicaConnection( $callback, array $params = [] ) {
1388                 foreach ( $this->mConns as $connsByServer ) {
1389                         foreach ( $connsByServer as $i => $serverConns ) {
1390                                 if ( $i === $this->getWriterIndex() ) {
1391                                         continue; // skip master
1392                                 }
1393                                 foreach ( $serverConns as $conn ) {
1394                                         $mergedParams = array_merge( [ $conn ], $params );
1395                                         call_user_func_array( $callback, $mergedParams );
1396                                 }
1397                         }
1398                 }
1399         }
1400
1401         public function getMaxLag( $domain = false ) {
1402                 $maxLag = -1;
1403                 $host = '';
1404                 $maxIndex = 0;
1405
1406                 if ( $this->getServerCount() <= 1 ) {
1407                         return [ $host, $maxLag, $maxIndex ]; // no replication = no lag
1408                 }
1409
1410                 $lagTimes = $this->getLagTimes( $domain );
1411                 foreach ( $lagTimes as $i => $lag ) {
1412                         if ( $this->mLoads[$i] > 0 && $lag > $maxLag ) {
1413                                 $maxLag = $lag;
1414                                 $host = $this->mServers[$i]['host'];
1415                                 $maxIndex = $i;
1416                         }
1417                 }
1418
1419                 return [ $host, $maxLag, $maxIndex ];
1420         }
1421
1422         public function getLagTimes( $domain = false ) {
1423                 if ( $this->getServerCount() <= 1 ) {
1424                         return [ $this->getWriterIndex() => 0 ]; // no replication = no lag
1425                 }
1426
1427                 $knownLagTimes = []; // map of (server index => 0 seconds)
1428                 $indexesWithLag = [];
1429                 foreach ( $this->mServers as $i => $server ) {
1430                         if ( empty( $server['is static'] ) ) {
1431                                 $indexesWithLag[] = $i; // DB server might have replication lag
1432                         } else {
1433                                 $knownLagTimes[$i] = 0; // DB server is a non-replicating and read-only archive
1434                         }
1435                 }
1436
1437                 return $this->getLoadMonitor()->getLagTimes( $indexesWithLag, $domain ) + $knownLagTimes;
1438         }
1439
1440         public function safeGetLag( IDatabase $conn ) {
1441                 if ( $this->getServerCount() <= 1 ) {
1442                         return 0;
1443                 } else {
1444                         return $conn->getLag();
1445                 }
1446         }
1447
1448         public function safeWaitForMasterPos( IDatabase $conn, $pos = false, $timeout = 10 ) {
1449                 if ( $this->getServerCount() <= 1 || !$conn->getLBInfo( 'replica' ) ) {
1450                         return true; // server is not a replica DB
1451                 }
1452
1453                 if ( !$pos ) {
1454                         // Get the current master position, opening a connection if needed
1455                         $masterConn = $this->getAnyOpenConnection( $this->getWriterIndex() );
1456                         if ( $masterConn ) {
1457                                 $pos = $masterConn->getMasterPos();
1458                         } else {
1459                                 $masterConn = $this->openConnection( $this->getWriterIndex(), self::DOMAIN_ANY );
1460                                 $pos = $masterConn->getMasterPos();
1461                                 $this->closeConnection( $masterConn );
1462                         }
1463                 }
1464
1465                 if ( $pos instanceof DBMasterPos ) {
1466                         $result = $conn->masterPosWait( $pos, $timeout );
1467                         if ( $result == -1 || is_null( $result ) ) {
1468                                 $msg = __METHOD__ . ": Timed out waiting on {$conn->getServer()} pos {$pos}";
1469                                 $this->replLogger->warning( "$msg" );
1470                                 $ok = false;
1471                         } else {
1472                                 $this->replLogger->info( __METHOD__ . ": Done" );
1473                                 $ok = true;
1474                         }
1475                 } else {
1476                         $ok = false; // something is misconfigured
1477                         $this->replLogger->error( "Could not get master pos for {$conn->getServer()}." );
1478                 }
1479
1480                 return $ok;
1481         }
1482
1483         public function setTransactionListener( $name, callable $callback = null ) {
1484                 if ( $callback ) {
1485                         $this->trxRecurringCallbacks[$name] = $callback;
1486                 } else {
1487                         unset( $this->trxRecurringCallbacks[$name] );
1488                 }
1489                 $this->forEachOpenMasterConnection(
1490                         function ( IDatabase $conn ) use ( $name, $callback ) {
1491                                 $conn->setTransactionListener( $name, $callback );
1492                         }
1493                 );
1494         }
1495
1496         public function setTableAliases( array $aliases ) {
1497                 $this->tableAliases = $aliases;
1498         }
1499
1500         public function setDomainPrefix( $prefix ) {
1501                 if ( $this->mConns['foreignUsed'] ) {
1502                         // Do not switch connections to explicit foreign domains unless marked as free
1503                         $domains = [];
1504                         foreach ( $this->mConns['foreignUsed'] as $i => $connsByDomain ) {
1505                                 $domains = array_merge( $domains, array_keys( $connsByDomain ) );
1506                         }
1507                         $domains = implode( ', ', $domains );
1508                         throw new DBUnexpectedError( null,
1509                                 "Foreign domain connections are still in use ($domains)." );
1510                 }
1511
1512                 $this->localDomain = new DatabaseDomain(
1513                         $this->localDomain->getDatabase(),
1514                         null,
1515                         $prefix
1516                 );
1517
1518                 $this->forEachOpenConnection( function ( IDatabase $db ) use ( $prefix ) {
1519                         $db->tablePrefix( $prefix );
1520                 } );
1521         }
1522
1523         /**
1524          * Make PHP ignore user aborts/disconnects until the returned
1525          * value leaves scope. This returns null and does nothing in CLI mode.
1526          *
1527          * @return ScopedCallback|null
1528          */
1529         final protected function getScopedPHPBehaviorForCommit() {
1530                 if ( PHP_SAPI != 'cli' ) { // http://bugs.php.net/bug.php?id=47540
1531                         $old = ignore_user_abort( true ); // avoid half-finished operations
1532                         return new ScopedCallback( function () use ( $old ) {
1533                                 ignore_user_abort( $old );
1534                         } );
1535                 }
1536
1537                 return null;
1538         }
1539
1540         function __destruct() {
1541                 // Avoid connection leaks for sanity
1542                 $this->disable();
1543         }
1544 }