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 load balancing, tracking, and transaction management object
  27  *
  28  * @ingroup Database
  29  */
  30 class LoadBalancer implements ILoadBalancer {
  31         /** @var array[] Map of (server index => server config array) */
  32         private $mServers;
  33         /** @var array[] Map of (local/foreignUsed/foreignFree => server index => IDatabase array) */
  34         private $mConns;
  35         /** @var array Map of (server index => weight) */
  36         private $mLoads;
  37         /** @var array[] Map of (group => server index => weight) */
  38         private $mGroupLoads;
  39         /** @var bool Whether to disregard replica DB lag as a factor in replica DB selection */
  40         private $mAllowLagged;
  41         /** @var integer Seconds to spend waiting on replica DB lag to resolve */
  42         private $mWaitTimeout;
  43         /** @var string The LoadMonitor subclass name */
  44         private $mLoadMonitorClass;
  45         /** @var array[] $aliases Map of (table => (dbname, schema, prefix) map) */
  46         private $tableAliases = [];
  47
  48         /** @var LoadMonitor */
  49         private $mLoadMonitor;
  50         /** @var BagOStuff */
  51         private $srvCache;
  52         /** @var BagOStuff */
  53         private $memCache;
  54         /** @var WANObjectCache */
  55         private $wanCache;
  56         /** @var TransactionProfiler */
  57         protected $trxProfiler;
  58         /** @var LoggerInterface */
  59         protected $replLogger;
  60         /** @var LoggerInterface */
  61         protected $connLogger;
  62         /** @var LoggerInterface */
  63         protected $queryLogger;
  64         /** @var LoggerInterface */
  65         protected $perfLogger;
  66
  67         /** @var bool|IDatabase Database connection that caused a problem */
  68         private $mErrorConnection;
  69         /** @var integer The generic (not query grouped) replica DB index (of $mServers) */
  70         private $mReadIndex;
  71         /** @var bool|DBMasterPos False if not set */
  72         private $mWaitForPos;
  73         /** @var bool Whether the generic reader fell back to a lagged replica DB */
  74         private $laggedReplicaMode = false;
  75         /** @var bool Whether the generic reader fell back to a lagged replica DB */
  76         private $allReplicasDownMode = false;
  77         /** @var string The last DB selection or connection error */
  78         private $mLastError = 'Unknown error';
  79         /** @var string|bool Reason the LB is read-only or false if not */
  80         private $readOnlyReason = false;
  81         /** @var integer Total connections opened */
  82         private $connsOpened = 0;
  83         /** @var string|bool String if a requested DBO_TRX transaction round is active */
  84         private $trxRoundId = false;
  85         /** @var array[] Map of (name => callable) */
  86         private $trxRecurringCallbacks = [];
  87         /** @var string Local Domain ID and default for selectDB() calls */
  88         private $localDomain;
  89         /** @var string Current server name */
  90         private $host;
  91
  92         /** @var callable Exception logger */
  93         private $errorLogger;
  94
  95         /** @var boolean */
  96         private $disabled = false;
  97
  98         /** @var integer Warn when this many connection are held */
  99         const CONN_HELD_WARN_THRESHOLD = 10;
 100         /** @var integer Default 'max lag' when unspecified */
 101         const MAX_LAG_DEFAULT = 10;
 102         /** @var integer Max time to wait for a replica DB to catch up (e.g. ChronologyProtector) */
 103         const POS_WAIT_TIMEOUT = 10;
 104         /** @var integer Seconds to cache master server read-only status */
 105         const TTL_CACHE_READONLY = 5;
 106
 107         public function __construct( array $params ) {
 108                 if ( !isset( $params['servers'] ) ) {
 109                         throw new InvalidArgumentException( __CLASS__ . ': missing servers parameter' );
 110                 }
 111                 $this->mServers = $params['servers'];
 112                 $this->mWaitTimeout = isset( $params['waitTimeout'] )
 113                         ? $params['waitTimeout']
 114                         : self::POS_WAIT_TIMEOUT;
 115                 $this->localDomain = isset( $params['localDomain'] ) ? $params['localDomain'] : '';
 116
 117                 $this->mReadIndex = -1;
 118                 $this->mConns = [
 119                         'local' => [],
 120                         'foreignUsed' => [],
 121                         'foreignFree' => [] ];
 122                 $this->mLoads = [];
 123                 $this->mWaitForPos = false;
 124                 $this->mErrorConnection = false;
 125                 $this->mAllowLagged = false;
 126
 127                 if ( isset( $params['readOnlyReason'] ) && is_string( $params['readOnlyReason'] ) ) {
 128                         $this->readOnlyReason = $params['readOnlyReason'];
 129                 }
 130
 131                 if ( isset( $params['loadMonitor'] ) ) {
 132                         $this->mLoadMonitorClass = $params['loadMonitor'];
 133                 } else {
 134                         $master = reset( $params['servers'] );
 135                         if ( isset( $master['type'] ) && $master['type'] === 'mysql' ) {
 136                                 $this->mLoadMonitorClass = 'LoadMonitorMySQL';
 137                         } else {
 138                                 $this->mLoadMonitorClass = 'LoadMonitorNull';
 139                         }
 140                 }
 141
 142                 foreach ( $params['servers'] as $i => $server ) {
 143                         $this->mLoads[$i] = $server['load'];
 144                         if ( isset( $server['groupLoads'] ) ) {
 145                                 foreach ( $server['groupLoads'] as $group => $ratio ) {
 146                                         if ( !isset( $this->mGroupLoads[$group] ) ) {
 147                                                 $this->mGroupLoads[$group] = [];
 148                                         }
 149                                         $this->mGroupLoads[$group][$i] = $ratio;
 150                                 }
 151                         }
 152                 }
 153
 154                 if ( isset( $params['srvCache'] ) ) {
 155                         $this->srvCache = $params['srvCache'];
 156                 } else {
 157                         $this->srvCache = new EmptyBagOStuff();
 158                 }
 159                 if ( isset( $params['memCache'] ) ) {
 160                         $this->memCache = $params['memCache'];
 161                 } else {
 162                         $this->memCache = new EmptyBagOStuff();
 163                 }
 164                 if ( isset( $params['wanCache'] ) ) {
 165                         $this->wanCache = $params['wanCache'];
 166                 } else {
 167                         $this->wanCache = WANObjectCache::newEmpty();
 168                 }
 169                 if ( isset( $params['trxProfiler'] ) ) {
 170                         $this->trxProfiler = $params['trxProfiler'];
 171                 } else {
 172                         $this->trxProfiler = new TransactionProfiler();
 173                 }
 174
 175                 $this->errorLogger = isset( $params['errorLogger'] )
 176                         ? $params['errorLogger']
 177                         : function ( Exception $e ) {
 178                                 trigger_error( E_WARNING, $e->getMessage() );
 179                         };
 180
 181                 foreach ( [ 'replLogger', 'connLogger', 'queryLogger', 'perfLogger' ] as $key ) {
 182                         $this->$key = isset( $params[$key] ) ? $params[$key] : new \Psr\Log\NullLogger();
 183                 }
 184
 185                 $this->host = isset( $params['hostname'] )
 186                         ? $params['hostname']
 187                         : ( gethostname() ?: 'unknown' );
 188         }
 189
 190         /**
 191          * Get a LoadMonitor instance
 192          *
 193          * @return LoadMonitor
 194          */
 195         private function getLoadMonitor() {
 196                 if ( !isset( $this->mLoadMonitor ) ) {
 197                         $class = $this->mLoadMonitorClass;
 198                         $this->mLoadMonitor = new $class( $this, $this->srvCache, $this->memCache );
 199                         $this->mLoadMonitor->setLogger( $this->replLogger );
 200                 }
 201
 202                 return $this->mLoadMonitor;
 203         }
 204
 205         /**
 206          * @param array $loads
 207          * @param bool|string $domain Domain to get non-lagged for
 208          * @param int $maxLag Restrict the maximum allowed lag to this many seconds
 209          * @return bool|int|string
 210          */
 211         private function getRandomNonLagged( array $loads, $domain = false, $maxLag = INF ) {
 212                 $lags = $this->getLagTimes( $domain );
 213
 214                 # Unset excessively lagged servers
 215                 foreach ( $lags as $i => $lag ) {
 216                         if ( $i != 0 ) {
 217                                 # How much lag this server nominally is allowed to have
 218                                 $maxServerLag = isset( $this->mServers[$i]['max lag'] )
 219                                         ? $this->mServers[$i]['max lag']
 220                                         : self::MAX_LAG_DEFAULT; // default
 221                                 # Constrain that futher by $maxLag argument
 222                                 $maxServerLag = min( $maxServerLag, $maxLag );
 223
 224                                 $host = $this->getServerName( $i );
 225                                 if ( $lag === false && !is_infinite( $maxServerLag ) ) {
 226                                         $this->replLogger->error( "Server $host (#$i) is not replicating?" );
 227                                         unset( $loads[$i] );
 228                                 } elseif ( $lag > $maxServerLag ) {
 229                                         $this->replLogger->warning( "Server $host (#$i) has >= $lag seconds of lag" );
 230                                         unset( $loads[$i] );
 231                                 }
 232                         }
 233                 }
 234
 235                 # Find out if all the replica DBs with non-zero load are lagged
 236                 $sum = 0;
 237                 foreach ( $loads as $load ) {
 238                         $sum += $load;
 239                 }
 240                 if ( $sum == 0 ) {
 241                         # No appropriate DB servers except maybe the master and some replica DBs with zero load
 242                         # Do NOT use the master
 243                         # Instead, this function will return false, triggering read-only mode,
 244                         # and a lagged replica DB will be used instead.
 245                         return false;
 246                 }
 247
 248                 if ( count( $loads ) == 0 ) {
 249                         return false;
 250                 }
 251
 252                 # Return a random representative of the remainder
 253                 return ArrayUtils::pickRandom( $loads );
 254         }
 255
 256         public function getReaderIndex( $group = false, $domain = false ) {
 257                 if ( count( $this->mServers ) == 1 ) {
 258                         # Skip the load balancing if there's only one server
 259                         return $this->getWriterIndex();
 260                 } elseif ( $group === false && $this->mReadIndex >= 0 ) {
 261                         # Shortcut if generic reader exists already
 262                         return $this->mReadIndex;
 263                 }
 264
 265                 # Find the relevant load array
 266                 if ( $group !== false ) {
 267                         if ( isset( $this->mGroupLoads[$group] ) ) {
 268                                 $nonErrorLoads = $this->mGroupLoads[$group];
 269                         } else {
 270                                 # No loads for this group, return false and the caller can use some other group
 271                                 $this->connLogger->info( __METHOD__ . ": no loads for group $group" );
 272
 273                                 return false;
 274                         }
 275                 } else {
 276                         $nonErrorLoads = $this->mLoads;
 277                 }
 278
 279                 if ( !count( $nonErrorLoads ) ) {
 280                         throw new InvalidArgumentException( "Empty server array given to LoadBalancer" );
 281                 }
 282
 283                 # Scale the configured load ratios according to the dynamic load if supported
 284                 $this->getLoadMonitor()->scaleLoads( $nonErrorLoads, $group, $domain );
 285
 286                 $laggedReplicaMode = false;
 287
 288                 # No server found yet
 289                 $i = false;
 290                 # First try quickly looking through the available servers for a server that
 291                 # meets our criteria
 292                 $currentLoads = $nonErrorLoads;
 293                 while ( count( $currentLoads ) ) {
 294                         if ( $this->mAllowLagged || $laggedReplicaMode ) {
 295                                 $i = ArrayUtils::pickRandom( $currentLoads );
 296                         } else {
 297                                 $i = false;
 298                                 if ( $this->mWaitForPos && $this->mWaitForPos->asOfTime() ) {
 299                                         # ChronologyProtecter causes mWaitForPos to be set via sessions.
 300                                         # This triggers doWait() after connect, so it's especially good to
 301                                         # avoid lagged servers so as to avoid just blocking in that method.
 302                                         $ago = microtime( true ) - $this->mWaitForPos->asOfTime();
 303                                         # Aim for <= 1 second of waiting (being too picky can backfire)
 304                                         $i = $this->getRandomNonLagged( $currentLoads, $domain, $ago + 1 );
 305                                 }
 306                                 if ( $i === false ) {
 307                                         # Any server with less lag than it's 'max lag' param is preferable
 308                                         $i = $this->getRandomNonLagged( $currentLoads, $domain );
 309                                 }
 310                                 if ( $i === false && count( $currentLoads ) != 0 ) {
 311                                         # All replica DBs lagged. Switch to read-only mode
 312                                         $this->replLogger->error( "All replica DBs lagged. Switch to read-only mode" );
 313                                         $i = ArrayUtils::pickRandom( $currentLoads );
 314                                         $laggedReplicaMode = true;
 315                                 }
 316                         }
 317
 318                         if ( $i === false ) {
 319                                 # pickRandom() returned false
 320                                 # This is permanent and means the configuration or the load monitor
 321                                 # wants us to return false.
 322                                 $this->connLogger->debug( __METHOD__ . ": pickRandom() returned false" );
 323
 324                                 return false;
 325                         }
 326
 327                         $serverName = $this->getServerName( $i );
 328                         $this->connLogger->debug( __METHOD__ . ": Using reader #$i: $serverName..." );
 329
 330                         $conn = $this->openConnection( $i, $domain );
 331                         if ( !$conn ) {
 332                                 $this->connLogger->warning( __METHOD__ . ": Failed connecting to $i/$domain" );
 333                                 unset( $nonErrorLoads[$i] );
 334                                 unset( $currentLoads[$i] );
 335                                 $i = false;
 336                                 continue;
 337                         }
 338
 339                         // Decrement reference counter, we are finished with this connection.
 340                         // It will be incremented for the caller later.
 341                         if ( $domain !== false ) {
 342                                 $this->reuseConnection( $conn );
 343                         }
 344
 345                         # Return this server
 346                         break;
 347                 }
 348
 349                 # If all servers were down, quit now
 350                 if ( !count( $nonErrorLoads ) ) {
 351                         $this->connLogger->error( "All servers down" );
 352                 }
 353
 354                 if ( $i !== false ) {
 355                         # Replica DB connection successful.
 356                         # Wait for the session master pos for a short time.
 357                         if ( $this->mWaitForPos && $i > 0 ) {
 358                                 $this->doWait( $i );
 359                         }
 360                         if ( $this->mReadIndex <= 0 && $this->mLoads[$i] > 0 && $group === false ) {
 361                                 $this->mReadIndex = $i;
 362                                 # Record if the generic reader index is in "lagged replica DB" mode
 363                                 if ( $laggedReplicaMode ) {
 364                                         $this->laggedReplicaMode = true;
 365                                 }
 366                         }
 367                         $serverName = $this->getServerName( $i );
 368                         $this->connLogger->debug(
 369                                 __METHOD__ . ": using server $serverName for group '$group'" );
 370                 }
 371
 372                 return $i;
 373         }
 374
 375         public function waitFor( $pos ) {
 376                 $this->mWaitForPos = $pos;
 377                 $i = $this->mReadIndex;
 378
 379                 if ( $i > 0 ) {
 380                         if ( !$this->doWait( $i ) ) {
 381                                 $this->laggedReplicaMode = true;
 382                         }
 383                 }
 384         }
 385
 386         /**
 387          * Set the master wait position and wait for a "generic" replica DB to catch up to it
 388          *
 389          * This can be used a faster proxy for waitForAll()
 390          *
 391          * @param DBMasterPos $pos
 392          * @param int $timeout Max seconds to wait; default is mWaitTimeout
 393          * @return bool Success (able to connect and no timeouts reached)
 394          * @since 1.26
 395          */
 396         public function waitForOne( $pos, $timeout = null ) {
 397                 $this->mWaitForPos = $pos;
 398
 399                 $i = $this->mReadIndex;
 400                 if ( $i <= 0 ) {
 401                         // Pick a generic replica DB if there isn't one yet
 402                         $readLoads = $this->mLoads;
 403                         unset( $readLoads[$this->getWriterIndex()] ); // replica DBs only
 404                         $readLoads = array_filter( $readLoads ); // with non-zero load
 405                         $i = ArrayUtils::pickRandom( $readLoads );
 406                 }
 407
 408                 if ( $i > 0 ) {
 409                         $ok = $this->doWait( $i, true, $timeout );
 410                 } else {
 411                         $ok = true; // no applicable loads
 412                 }
 413
 414                 return $ok;
 415         }
 416
 417         public function waitForAll( $pos, $timeout = null ) {
 418                 $this->mWaitForPos = $pos;
 419                 $serverCount = count( $this->mServers );
 420
 421                 $ok = true;
 422                 for ( $i = 1; $i < $serverCount; $i++ ) {
 423                         if ( $this->mLoads[$i] > 0 ) {
 424                                 $ok = $this->doWait( $i, true, $timeout ) && $ok;
 425                         }
 426                 }
 427
 428                 return $ok;
 429         }
 430
 431         public function getAnyOpenConnection( $i ) {
 432                 foreach ( $this->mConns as $connsByServer ) {
 433                         if ( !empty( $connsByServer[$i] ) ) {
 434                                 return reset( $connsByServer[$i] );
 435                         }
 436                 }
 437
 438                 return false;
 439         }
 440
 441         /**
 442          * Wait for a given replica DB to catch up to the master pos stored in $this
 443          * @param int $index Server index
 444          * @param bool $open Check the server even if a new connection has to be made
 445          * @param int $timeout Max seconds to wait; default is mWaitTimeout
 446          * @return bool
 447          */
 448         protected function doWait( $index, $open = false, $timeout = null ) {
 449                 $close = false; // close the connection afterwards
 450
 451                 // Check if we already know that the DB has reached this point
 452                 $server = $this->getServerName( $index );
 453                 $key = $this->srvCache->makeGlobalKey( __CLASS__, 'last-known-pos', $server );
 454                 /** @var DBMasterPos $knownReachedPos */
 455                 $knownReachedPos = $this->srvCache->get( $key );
 456                 if ( $knownReachedPos && $knownReachedPos->hasReached( $this->mWaitForPos ) ) {
 457                         $this->replLogger->debug( __METHOD__ .
 458                                 ": replica DB $server known to be caught up (pos >= $knownReachedPos)." );
 459                         return true;
 460                 }
 461
 462                 // Find a connection to wait on, creating one if needed and allowed
 463                 $conn = $this->getAnyOpenConnection( $index );
 464                 if ( !$conn ) {
 465                         if ( !$open ) {
 466                                 $this->replLogger->debug( __METHOD__ . ": no connection open for $server" );
 467
 468                                 return false;
 469                         } else {
 470                                 $conn = $this->openConnection( $index, '' );
 471                                 if ( !$conn ) {
 472                                         $this->replLogger->warning( __METHOD__ . ": failed to connect to $server" );
 473
 474                                         return false;
 475                                 }
 476                                 // Avoid connection spam in waitForAll() when connections
 477                                 // are made just for the sake of doing this lag check.
 478                                 $close = true;
 479                         }
 480                 }
 481
 482                 $this->replLogger->info( __METHOD__ . ": Waiting for replica DB $server to catch up..." );
 483                 $timeout = $timeout ?: $this->mWaitTimeout;
 484                 $result = $conn->masterPosWait( $this->mWaitForPos, $timeout );
 485
 486                 if ( $result == -1 || is_null( $result ) ) {
 487                         // Timed out waiting for replica DB, use master instead
 488                         $msg = __METHOD__ . ": Timed out waiting on $server pos {$this->mWaitForPos}";
 489                         $this->replLogger->warning( "$msg" );
 490                         $ok = false;
 491                 } else {
 492                         $this->replLogger->info( __METHOD__ . ": Done" );
 493                         $ok = true;
 494                         // Remember that the DB reached this point
 495                         $this->srvCache->set( $key, $this->mWaitForPos, BagOStuff::TTL_DAY );
 496                 }
 497
 498                 if ( $close ) {
 499                         $this->closeConnection( $conn );
 500                 }
 501
 502                 return $ok;
 503         }
 504
 505         public function getConnection( $i, $groups = [], $domain = false ) {
 506                 if ( $i === null || $i === false ) {
 507                         throw new InvalidArgumentException( 'Attempt to call ' . __METHOD__ .
 508                                 ' with invalid server index' );
 509                 }
 510
 511                 if ( $domain === $this->localDomain ) {
 512                         $domain = false;
 513                 }
 514
 515                 $groups = ( $groups === false || $groups === [] )
 516                         ? [ false ] // check one "group": the generic pool
 517                         : (array)$groups;
 518
 519                 $masterOnly = ( $i == DB_MASTER || $i == $this->getWriterIndex() );
 520                 $oldConnsOpened = $this->connsOpened; // connections open now
 521
 522                 if ( $i == DB_MASTER ) {
 523                         $i = $this->getWriterIndex();
 524                 } else {
 525                         # Try to find an available server in any the query groups (in order)
 526                         foreach ( $groups as $group ) {
 527                                 $groupIndex = $this->getReaderIndex( $group, $domain );
 528                                 if ( $groupIndex !== false ) {
 529                                         $i = $groupIndex;
 530                                         break;
 531                                 }
 532                         }
 533                 }
 534
 535                 # Operation-based index
 536                 if ( $i == DB_REPLICA ) {
 537                         $this->mLastError = 'Unknown error'; // reset error string
 538                         # Try the general server pool if $groups are unavailable.
 539                         $i = in_array( false, $groups, true )
 540                                 ? false // don't bother with this if that is what was tried above
 541                                 : $this->getReaderIndex( false, $domain );
 542                         # Couldn't find a working server in getReaderIndex()?
 543                         if ( $i === false ) {
 544                                 $this->mLastError = 'No working replica DB server: ' . $this->mLastError;
 545
 546                                 return $this->reportConnectionError();
 547                         }
 548                 }
 549
 550                 # Now we have an explicit index into the servers array
 551                 $conn = $this->openConnection( $i, $domain );
 552                 if ( !$conn ) {
 553                         return $this->reportConnectionError();
 554                 }
 555
 556                 # Profile any new connections that happen
 557                 if ( $this->connsOpened > $oldConnsOpened ) {
 558                         $host = $conn->getServer();
 559                         $dbname = $conn->getDBname();
 560                         $this->trxProfiler->recordConnection( $host, $dbname, $masterOnly );
 561                 }
 562
 563                 if ( $masterOnly ) {
 564                         # Make master-requested DB handles inherit any read-only mode setting
 565                         $conn->setLBInfo( 'readOnlyReason', $this->getReadOnlyReason( $domain, $conn ) );
 566                 }
 567
 568                 return $conn;
 569         }
 570
 571         public function reuseConnection( $conn ) {
 572                 $serverIndex = $conn->getLBInfo( 'serverIndex' );
 573                 $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 574                 if ( $serverIndex === null || $refCount === null ) {
 575                         /**
 576                          * This can happen in code like:
 577                          *   foreach ( $dbs as $db ) {
 578                          *     $conn = $lb->getConnection( DB_REPLICA, [], $db );
 579                          *     ...
 580                          *     $lb->reuseConnection( $conn );
 581                          *   }
 582                          * When a connection to the local DB is opened in this way, reuseConnection()
 583                          * should be ignored
 584                          */
 585                         return;
 586                 }
 587
 588                 $dbName = $conn->getDBname();
 589                 $prefix = $conn->tablePrefix();
 590                 if ( strval( $prefix ) !== '' ) {
 591                         $domain = "$dbName-$prefix";
 592                 } else {
 593                         $domain = $dbName;
 594                 }
 595                 if ( $this->mConns['foreignUsed'][$serverIndex][$domain] !== $conn ) {
 596                         throw new InvalidArgumentException( __METHOD__ . ": connection not found, has " .
 597                                 "the connection been freed already?" );
 598                 }
 599                 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
 600                 if ( $refCount <= 0 ) {
 601                         $this->mConns['foreignFree'][$serverIndex][$domain] = $conn;
 602                         unset( $this->mConns['foreignUsed'][$serverIndex][$domain] );
 603                         $this->connLogger->debug( __METHOD__ . ": freed connection $serverIndex/$domain" );
 604                 } else {
 605                         $this->connLogger->debug( __METHOD__ .
 606                                 ": reference count for $serverIndex/$domain reduced to $refCount" );
 607                 }
 608         }
 609
 610         /**
 611          * Get a database connection handle reference
 612          *
 613          * The handle's methods wrap simply wrap those of a IDatabase handle
 614          *
 615          * @see LoadBalancer::getConnection() for parameter information
 616          *
 617          * @param int $db
 618          * @param array|string|bool $groups Query group(s), or false for the generic reader
 619          * @param string|bool $domain Domain ID, or false for the current domain
 620          * @return DBConnRef
 621          * @since 1.22
 622          */
 623         public function getConnectionRef( $db, $groups = [], $domain = false ) {
 624                 return new DBConnRef( $this, $this->getConnection( $db, $groups, $domain ) );
 625         }
 626
 627         /**
 628          * Get a database connection handle reference without connecting yet
 629          *
 630          * The handle's methods wrap simply wrap those of a IDatabase handle
 631          *
 632          * @see LoadBalancer::getConnection() for parameter information
 633          *
 634          * @param int $db
 635          * @param array|string|bool $groups Query group(s), or false for the generic reader
 636          * @param string|bool $domain Domain ID, or false for the current domain
 637          * @return DBConnRef
 638          * @since 1.22
 639          */
 640         public function getLazyConnectionRef( $db, $groups = [], $domain = false ) {
 641                 $domain = ( $domain !== false ) ? $domain : $this->localDomain;
 642
 643                 return new DBConnRef( $this, [ $db, $groups, $domain ] );
 644         }
 645
 646         public function openConnection( $i, $domain = false ) {
 647                 if ( $domain !== false ) {
 648                         $conn = $this->openForeignConnection( $i, $domain );
 649                 } elseif ( isset( $this->mConns['local'][$i][0] ) ) {
 650                         $conn = $this->mConns['local'][$i][0];
 651                 } else {
 652                         $server = $this->mServers[$i];
 653                         $server['serverIndex'] = $i;
 654                         $conn = $this->reallyOpenConnection( $server, false );
 655                         $serverName = $this->getServerName( $i );
 656                         if ( $conn->isOpen() ) {
 657                                 $this->connLogger->debug( "Connected to database $i at '$serverName'." );
 658                                 $this->mConns['local'][$i][0] = $conn;
 659                         } else {
 660                                 $this->connLogger->warning( "Failed to connect to database $i at '$serverName'." );
 661                                 $this->mErrorConnection = $conn;
 662                                 $conn = false;
 663                         }
 664                 }
 665
 666                 if ( $conn && !$conn->isOpen() ) {
 667                         // Connection was made but later unrecoverably lost for some reason.
 668                         // Do not return a handle that will just throw exceptions on use,
 669                         // but let the calling code (e.g. getReaderIndex) try another server.
 670                         // See DatabaseMyslBase::ping() for how this can happen.
 671                         $this->mErrorConnection = $conn;
 672                         $conn = false;
 673                 }
 674
 675                 return $conn;
 676         }
 677
 678         /**
 679          * Open a connection to a foreign DB, or return one if it is already open.
 680          *
 681          * Increments a reference count on the returned connection which locks the
 682          * connection to the requested domain. This reference count can be
 683          * decremented by calling reuseConnection().
 684          *
 685          * If a connection is open to the appropriate server already, but with the wrong
 686          * database, it will be switched to the right database and returned, as long as
 687          * it has been freed first with reuseConnection().
 688          *
 689          * On error, returns false, and the connection which caused the
 690          * error will be available via $this->mErrorConnection.
 691          *
 692          * @note If disable() was called on this LoadBalancer, this method will throw a DBAccessError.
 693          *
 694          * @param int $i Server index
 695          * @param string $domain Domain ID to open
 696          * @return IDatabase
 697          */
 698         private function openForeignConnection( $i, $domain ) {
 699                 list( $dbName, $prefix ) = explode( '-', $domain, 2 ) + [ '', '' ];
 700
 701                 if ( isset( $this->mConns['foreignUsed'][$i][$domain] ) ) {
 702                         // Reuse an already-used connection
 703                         $conn = $this->mConns['foreignUsed'][$i][$domain];
 704                         $this->connLogger->debug( __METHOD__ . ": reusing connection $i/$domain" );
 705                 } elseif ( isset( $this->mConns['foreignFree'][$i][$domain] ) ) {
 706                         // Reuse a free connection for the same domain
 707                         $conn = $this->mConns['foreignFree'][$i][$domain];
 708                         unset( $this->mConns['foreignFree'][$i][$domain] );
 709                         $this->mConns['foreignUsed'][$i][$domain] = $conn;
 710                         $this->connLogger->debug( __METHOD__ . ": reusing free connection $i/$domain" );
 711                 } elseif ( !empty( $this->mConns['foreignFree'][$i] ) ) {
 712                         // Reuse a connection from another domain
 713                         $conn = reset( $this->mConns['foreignFree'][$i] );
 714                         $oldDomain = key( $this->mConns['foreignFree'][$i] );
 715
 716                         // The empty string as a DB name means "don't care".
 717                         // DatabaseMysqlBase::open() already handle this on connection.
 718                         if ( $dbName !== '' && !$conn->selectDB( $dbName ) ) {
 719                                 $this->mLastError = "Error selecting database $dbName on server " .
 720                                         $conn->getServer() . " from client host {$this->host}";
 721                                 $this->mErrorConnection = $conn;
 722                                 $conn = false;
 723                         } else {
 724                                 $conn->tablePrefix( $prefix );
 725                                 unset( $this->mConns['foreignFree'][$i][$oldDomain] );
 726                                 $this->mConns['foreignUsed'][$i][$domain] = $conn;
 727                                 $this->connLogger->debug( __METHOD__ .
 728                                         ": reusing free connection from $oldDomain for $domain" );
 729                         }
 730                 } else {
 731                         // Open a new connection
 732                         $server = $this->mServers[$i];
 733                         $server['serverIndex'] = $i;
 734                         $server['foreignPoolRefCount'] = 0;
 735                         $server['foreign'] = true;
 736                         $conn = $this->reallyOpenConnection( $server, $dbName );
 737                         if ( !$conn->isOpen() ) {
 738                                 $this->connLogger->warning( __METHOD__ . ": connection error for $i/$domain" );
 739                                 $this->mErrorConnection = $conn;
 740                                 $conn = false;
 741                         } else {
 742                                 $conn->tablePrefix( $prefix );
 743                                 $this->mConns['foreignUsed'][$i][$domain] = $conn;
 744                                 $this->connLogger->debug( __METHOD__ . ": opened new connection for $i/$domain" );
 745                         }
 746                 }
 747
 748                 // Increment reference count
 749                 if ( $conn ) {
 750                         $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 751                         $conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
 752                 }
 753
 754                 return $conn;
 755         }
 756
 757         /**
 758          * Test if the specified index represents an open connection
 759          *
 760          * @param int $index Server index
 761          * @access private
 762          * @return bool
 763          */
 764         private function isOpen( $index ) {
 765                 if ( !is_integer( $index ) ) {
 766                         return false;
 767                 }
 768
 769                 return (bool)$this->getAnyOpenConnection( $index );
 770         }
 771
 772         /**
 773          * Really opens a connection. Uncached.
 774          * Returns a Database object whether or not the connection was successful.
 775          * @access private
 776          *
 777          * @param array $server
 778          * @param bool $dbNameOverride
 779          * @return IDatabase
 780          * @throws DBAccessError
 781          * @throws InvalidArgumentException
 782          */
 783         protected function reallyOpenConnection( $server, $dbNameOverride = false ) {
 784                 if ( $this->disabled ) {
 785                         throw new DBAccessError();
 786                 }
 787
 788                 if ( !is_array( $server ) ) {
 789                         throw new InvalidArgumentException(
 790                                 'You must update your load-balancing configuration. ' .
 791                                 'See DefaultSettings.php entry for $wgDBservers.' );
 792                 }
 793
 794                 if ( $dbNameOverride !== false ) {
 795                         $server['dbname'] = $dbNameOverride;
 796                 }
 797
 798                 // Let the handle know what the cluster master is (e.g. "db1052")
 799                 $masterName = $this->getServerName( $this->getWriterIndex() );
 800                 $server['clusterMasterHost'] = $masterName;
 801
 802                 // Log when many connection are made on requests
 803                 if ( ++$this->connsOpened >= self::CONN_HELD_WARN_THRESHOLD ) {
 804                         $this->perfLogger->warning( __METHOD__ . ": " .
 805                                 "{$this->connsOpened}+ connections made (master=$masterName)" );
 806                 }
 807
 808                 $server['srvCache'] = $this->srvCache;
 809                 // Set loggers
 810                 $server['connLogger'] = $this->connLogger;
 811                 $server['queryLogger'] = $this->queryLogger;
 812                 $server['trxProfiler'] = $this->trxProfiler;
 813
 814                 // Create a live connection object
 815                 try {
 816                         $db = DatabaseBase::factory( $server['type'], $server );
 817                 } catch ( DBConnectionError $e ) {
 818                         // FIXME: This is probably the ugliest thing I have ever done to
 819                         // PHP. I'm half-expecting it to segfault, just out of disgust. -- TS
 820                         $db = $e->db;
 821                 }
 822
 823                 $db->setLBInfo( $server );
 824                 $db->setLazyMasterHandle(
 825                         $this->getLazyConnectionRef( DB_MASTER, [], $db->getWikiID() )
 826                 );
 827                 $db->setTableAliases( $this->tableAliases );
 828
 829                 if ( $server['serverIndex'] === $this->getWriterIndex() ) {
 830                         if ( $this->trxRoundId !== false ) {
 831                                 $this->applyTransactionRoundFlags( $db );
 832                         }
 833                         foreach ( $this->trxRecurringCallbacks as $name => $callback ) {
 834                                 $db->setTransactionListener( $name, $callback );
 835                         }
 836                 }
 837
 838                 return $db;
 839         }
 840
 841         /**
 842          * @throws DBConnectionError
 843          * @return bool
 844          */
 845         private function reportConnectionError() {
 846                 $conn = $this->mErrorConnection; // The connection which caused the error
 847                 $context = [
 848                         'method' => __METHOD__,
 849                         'last_error' => $this->mLastError,
 850                 ];
 851
 852                 if ( !is_object( $conn ) ) {
 853                         // No last connection, probably due to all servers being too busy
 854                         $this->connLogger->error(
 855                                 "LB failure with no last connection. Connection error: {last_error}",
 856                                 $context
 857                         );
 858
 859                         // If all servers were busy, mLastError will contain something sensible
 860                         throw new DBConnectionError( null, $this->mLastError );
 861                 } else {
 862                         $context['db_server'] = $conn->getProperty( 'mServer' );
 863                         $this->connLogger->warning(
 864                                 "Connection error: {last_error} ({db_server})",
 865                                 $context
 866                         );
 867
 868                         // throws DBConnectionError
 869                         $conn->reportConnectionError( "{$this->mLastError} ({$context['db_server']})" );
 870                 }
 871
 872                 return false; /* not reached */
 873         }
 874
 875         public function getWriterIndex() {
 876                 return 0;
 877         }
 878
 879         public function haveIndex( $i ) {
 880                 return array_key_exists( $i, $this->mServers );
 881         }
 882
 883         public function isNonZeroLoad( $i ) {
 884                 return array_key_exists( $i, $this->mServers ) && $this->mLoads[$i] != 0;
 885         }
 886
 887         public function getServerCount() {
 888                 return count( $this->mServers );
 889         }
 890
 891         public function getServerName( $i ) {
 892                 if ( isset( $this->mServers[$i]['hostName'] ) ) {
 893                         $name = $this->mServers[$i]['hostName'];
 894                 } elseif ( isset( $this->mServers[$i]['host'] ) ) {
 895                         $name = $this->mServers[$i]['host'];
 896                 } else {
 897                         $name = '';
 898                 }
 899
 900                 return ( $name != '' ) ? $name : 'localhost';
 901         }
 902
 903         public function getServerInfo( $i ) {
 904                 if ( isset( $this->mServers[$i] ) ) {
 905                         return $this->mServers[$i];
 906                 } else {
 907                         return false;
 908                 }
 909         }
 910
 911         public function setServerInfo( $i, array $serverInfo ) {
 912                 $this->mServers[$i] = $serverInfo;
 913         }
 914
 915         public function getMasterPos() {
 916                 # If this entire request was served from a replica DB without opening a connection to the
 917                 # master (however unlikely that may be), then we can fetch the position from the replica DB.
 918                 $masterConn = $this->getAnyOpenConnection( $this->getWriterIndex() );
 919                 if ( !$masterConn ) {
 920                         $serverCount = count( $this->mServers );
 921                         for ( $i = 1; $i < $serverCount; $i++ ) {
 922                                 $conn = $this->getAnyOpenConnection( $i );
 923                                 if ( $conn ) {
 924                                         return $conn->getSlavePos();
 925                                 }
 926                         }
 927                 } else {
 928                         return $masterConn->getMasterPos();
 929                 }
 930
 931                 return false;
 932         }
 933
 934         /**
 935          * Disable this load balancer. All connections are closed, and any attempt to
 936          * open a new connection will result in a DBAccessError.
 937          *
 938          * @since 1.27
 939          */
 940         public function disable() {
 941                 $this->closeAll();
 942                 $this->disabled = true;
 943         }
 944
 945         public function closeAll() {
 946                 $this->forEachOpenConnection( function ( IDatabase $conn ) {
 947                         $conn->close();
 948                 } );
 949
 950                 $this->mConns = [
 951                         'local' => [],
 952                         'foreignFree' => [],
 953                         'foreignUsed' => [],
 954                 ];
 955                 $this->connsOpened = 0;
 956         }
 957
 958         public function closeConnection( IDatabase $conn ) {
 959                 $serverIndex = $conn->getLBInfo( 'serverIndex' ); // second index level of mConns
 960                 foreach ( $this->mConns as $type => $connsByServer ) {
 961                         if ( !isset( $connsByServer[$serverIndex] ) ) {
 962                                 continue;
 963                         }
 964
 965                         foreach ( $connsByServer[$serverIndex] as $i => $trackedConn ) {
 966                                 if ( $conn === $trackedConn ) {
 967                                         unset( $this->mConns[$type][$serverIndex][$i] );
 968                                         --$this->connsOpened;
 969                                         break 2;
 970                                 }
 971                         }
 972                 }
 973
 974                 $conn->close();
 975         }
 976
 977         public function commitAll( $fname = __METHOD__ ) {
 978                 $failures = [];
 979
 980                 $restore = ( $this->trxRoundId !== false );
 981                 $this->trxRoundId = false;
 982                 $this->forEachOpenConnection(
 983                         function ( IDatabase $conn ) use ( $fname, $restore, &$failures ) {
 984                                 try {
 985                                         $conn->commit( $fname, $conn::FLUSHING_ALL_PEERS );
 986                                 } catch ( DBError $e ) {
 987                                         call_user_func( $this->errorLogger, $e );
 988                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
 989                                 }
 990                                 if ( $restore && $conn->getLBInfo( 'master' ) ) {
 991                                         $this->undoTransactionRoundFlags( $conn );
 992                                 }
 993                         }
 994                 );
 995
 996                 if ( $failures ) {
 997                         throw new DBExpectedError(
 998                                 null,
 999                                 "Commit failed on server(s) " . implode( "\n", array_unique( $failures ) )
1000                         );
1001                 }
1002         }
1003
1004         /**
1005          * Perform all pre-commit callbacks that remain part of the atomic transactions
1006          * and disable any post-commit callbacks until runMasterPostTrxCallbacks()
1007          * @since 1.28
1008          */
1009         public function finalizeMasterChanges() {
1010                 $this->forEachOpenMasterConnection( function ( DatabaseBase $conn ) {
1011                         // Any error should cause all DB transactions to be rolled back together
1012                         $conn->setTrxEndCallbackSuppression( false );
1013                         $conn->runOnTransactionPreCommitCallbacks();
1014                         // Defer post-commit callbacks until COMMIT finishes for all DBs
1015                         $conn->setTrxEndCallbackSuppression( true );
1016                 } );
1017         }
1018
1019         /**
1020          * Perform all pre-commit checks for things like replication safety
1021          * @param array $options Includes:
1022          *   - maxWriteDuration : max write query duration time in seconds
1023          * @throws DBTransactionError
1024          * @since 1.28
1025          */
1026         public function approveMasterChanges( array $options ) {
1027                 $limit = isset( $options['maxWriteDuration'] ) ? $options['maxWriteDuration'] : 0;
1028                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( $limit ) {
1029                         // If atomic sections or explicit transactions are still open, some caller must have
1030                         // caught an exception but failed to properly rollback any changes. Detect that and
1031                         // throw and error (causing rollback).
1032                         if ( $conn->explicitTrxActive() ) {
1033                                 throw new DBTransactionError(
1034                                         $conn,
1035                                         "Explicit transaction still active. A caller may have caught an error."
1036                                 );
1037                         }
1038                         // Assert that the time to replicate the transaction will be sane.
1039                         // If this fails, then all DB transactions will be rollback back together.
1040                         $time = $conn->pendingWriteQueryDuration( $conn::ESTIMATE_DB_APPLY );
1041                         if ( $limit > 0 && $time > $limit ) {
1042                                 throw new DBTransactionSizeError(
1043                                         $conn,
1044                                         "Transaction spent $time second(s) in writes, exceeding the $limit limit.",
1045                                         [ $time, $limit ]
1046                                 );
1047                         }
1048                         // If a connection sits idle while slow queries execute on another, that connection
1049                         // may end up dropped before the commit round is reached. Ping servers to detect this.
1050                         if ( $conn->writesOrCallbacksPending() && !$conn->ping() ) {
1051                                 throw new DBTransactionError(
1052                                         $conn,
1053                                         "A connection to the {$conn->getDBname()} database was lost before commit."
1054                                 );
1055                         }
1056                 } );
1057         }
1058
1059         /**
1060          * Flush any master transaction snapshots and set DBO_TRX (if DBO_DEFAULT is set)
1061          *
1062          * The DBO_TRX setting will be reverted to the default in each of these methods:
1063          *   - commitMasterChanges()
1064          *   - rollbackMasterChanges()
1065          *   - commitAll()
1066          * This allows for custom transaction rounds from any outer transaction scope.
1067          *
1068          * @param string $fname
1069          * @throws DBExpectedError
1070          * @since 1.28
1071          */
1072         public function beginMasterChanges( $fname = __METHOD__ ) {
1073                 if ( $this->trxRoundId !== false ) {
1074                         throw new DBTransactionError(
1075                                 null,
1076                                 "$fname: Transaction round '{$this->trxRoundId}' already started."
1077                         );
1078                 }
1079                 $this->trxRoundId = $fname;
1080
1081                 $failures = [];
1082                 $this->forEachOpenMasterConnection(
1083                         function ( DatabaseBase $conn ) use ( $fname, &$failures ) {
1084                                 $conn->setTrxEndCallbackSuppression( true );
1085                                 try {
1086                                         $conn->flushSnapshot( $fname );
1087                                 } catch ( DBError $e ) {
1088                                         call_user_func( $this->errorLogger, $e );
1089                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1090                                 }
1091                                 $conn->setTrxEndCallbackSuppression( false );
1092                                 $this->applyTransactionRoundFlags( $conn );
1093                         }
1094                 );
1095
1096                 if ( $failures ) {
1097                         throw new DBExpectedError(
1098                                 null,
1099                                 "$fname: Flush failed on server(s) " . implode( "\n", array_unique( $failures ) )
1100                         );
1101                 }
1102         }
1103
1104         public function commitMasterChanges( $fname = __METHOD__ ) {
1105                 $failures = [];
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         /**
1136          * Issue all pending post-COMMIT/ROLLBACK callbacks
1137          * @param integer $type IDatabase::TRIGGER_* constant
1138          * @return Exception|null The first exception or null if there were none
1139          * @since 1.28
1140          */
1141         public function runMasterPostTrxCallbacks( $type ) {
1142                 $e = null; // first exception
1143                 $this->forEachOpenMasterConnection( function ( DatabaseBase $conn ) use ( $type, &$e ) {
1144                         $conn->setTrxEndCallbackSuppression( false );
1145                         if ( $conn->writesOrCallbacksPending() ) {
1146                                 // This happens if onTransactionIdle() callbacks leave callbacks on *another* DB
1147                                 // (which finished its callbacks already). Warn and recover in this case. Let the
1148                                 // callbacks run in the final commitMasterChanges() in LBFactory::shutdown().
1149                                 $this->queryLogger->error( __METHOD__ . ": found writes/callbacks pending." );
1150                                 return;
1151                         } elseif ( $conn->trxLevel() ) {
1152                                 // This happens for single-DB setups where DB_REPLICA uses the master DB,
1153                                 // thus leaving an implicit read-only transaction open at this point. It
1154                                 // also happens if onTransactionIdle() callbacks leave implicit transactions
1155                                 // open on *other* DBs (which is slightly improper). Let these COMMIT on the
1156                                 // next call to commitMasterChanges(), possibly in LBFactory::shutdown().
1157                                 return;
1158                         }
1159                         try {
1160                                 $conn->runOnTransactionIdleCallbacks( $type );
1161                         } catch ( Exception $ex ) {
1162                                 $e = $e ?: $ex;
1163                         }
1164                         try {
1165                                 $conn->runTransactionListenerCallbacks( $type );
1166                         } catch ( Exception $ex ) {
1167                                 $e = $e ?: $ex;
1168                         }
1169                 } );
1170
1171                 return $e;
1172         }
1173
1174         /**
1175          * Issue ROLLBACK only on master, only if queries were done on connection
1176          * @param string $fname Caller name
1177          * @throws DBExpectedError
1178          * @since 1.23
1179          */
1180         public function rollbackMasterChanges( $fname = __METHOD__ ) {
1181                 $restore = ( $this->trxRoundId !== false );
1182                 $this->trxRoundId = false;
1183                 $this->forEachOpenMasterConnection(
1184                         function ( IDatabase $conn ) use ( $fname, $restore ) {
1185                                 if ( $conn->writesOrCallbacksPending() ) {
1186                                         $conn->rollback( $fname, $conn::FLUSHING_ALL_PEERS );
1187                                 }
1188                                 if ( $restore ) {
1189                                         $this->undoTransactionRoundFlags( $conn );
1190                                 }
1191                         }
1192                 );
1193         }
1194
1195         /**
1196          * Suppress all pending post-COMMIT/ROLLBACK callbacks
1197          * @return Exception|null The first exception or null if there were none
1198          * @since 1.28
1199          */
1200         public function suppressTransactionEndCallbacks() {
1201                 $this->forEachOpenMasterConnection( function ( DatabaseBase $conn ) {
1202                         $conn->setTrxEndCallbackSuppression( true );
1203                 } );
1204         }
1205
1206         /**
1207          * @param IDatabase $conn
1208          */
1209         private function applyTransactionRoundFlags( IDatabase $conn ) {
1210                 if ( $conn->getFlag( DBO_DEFAULT ) ) {
1211                         // DBO_TRX is controlled entirely by CLI mode presence with DBO_DEFAULT.
1212                         // Force DBO_TRX even in CLI mode since a commit round is expected soon.
1213                         $conn->setFlag( DBO_TRX, $conn::REMEMBER_PRIOR );
1214                         // If config has explicitly requested DBO_TRX be either on or off by not
1215                         // setting DBO_DEFAULT, then respect that. Forcing no transactions is useful
1216                         // for things like blob stores (ExternalStore) which want auto-commit mode.
1217                 }
1218         }
1219
1220         /**
1221          * @param IDatabase $conn
1222          */
1223         private function undoTransactionRoundFlags( IDatabase $conn ) {
1224                 if ( $conn->getFlag( DBO_DEFAULT ) ) {
1225                         $conn->restoreFlags( $conn::RESTORE_PRIOR );
1226                 }
1227         }
1228
1229         /**
1230          * Commit all replica DB transactions so as to flush any REPEATABLE-READ or SSI snapshot
1231          *
1232          * @param string $fname Caller name
1233          * @since 1.28
1234          */
1235         public function flushReplicaSnapshots( $fname = __METHOD__ ) {
1236                 $this->forEachOpenReplicaConnection( function ( IDatabase $conn ) {
1237                         $conn->flushSnapshot( __METHOD__ );
1238                 } );
1239         }
1240
1241         /**
1242          * @return bool Whether a master connection is already open
1243          * @since 1.24
1244          */
1245         public function hasMasterConnection() {
1246                 return $this->isOpen( $this->getWriterIndex() );
1247         }
1248
1249         /**
1250          * Determine if there are pending changes in a transaction by this thread
1251          * @since 1.23
1252          * @return bool
1253          */
1254         public function hasMasterChanges() {
1255                 $pending = 0;
1256                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$pending ) {
1257                         $pending |= $conn->writesOrCallbacksPending();
1258                 } );
1259
1260                 return (bool)$pending;
1261         }
1262
1263         /**
1264          * Get the timestamp of the latest write query done by this thread
1265          * @since 1.25
1266          * @return float|bool UNIX timestamp or false
1267          */
1268         public function lastMasterChangeTimestamp() {
1269                 $lastTime = false;
1270                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$lastTime ) {
1271                         $lastTime = max( $lastTime, $conn->lastDoneWrites() );
1272                 } );
1273
1274                 return $lastTime;
1275         }
1276
1277         /**
1278          * Check if this load balancer object had any recent or still
1279          * pending writes issued against it by this PHP thread
1280          *
1281          * @param float $age How many seconds ago is "recent" [defaults to mWaitTimeout]
1282          * @return bool
1283          * @since 1.25
1284          */
1285         public function hasOrMadeRecentMasterChanges( $age = null ) {
1286                 $age = ( $age === null ) ? $this->mWaitTimeout : $age;
1287
1288                 return ( $this->hasMasterChanges()
1289                         || $this->lastMasterChangeTimestamp() > microtime( true ) - $age );
1290         }
1291
1292         /**
1293          * Get the list of callers that have pending master changes
1294          *
1295          * @return string[] List of method names
1296          * @since 1.27
1297          */
1298         public function pendingMasterChangeCallers() {
1299                 $fnames = [];
1300                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$fnames ) {
1301                         $fnames = array_merge( $fnames, $conn->pendingWriteCallers() );
1302                 } );
1303
1304                 return $fnames;
1305         }
1306
1307         public function getLaggedReplicaMode( $domain = false ) {
1308                 // No-op if there is only one DB (also avoids recursion)
1309                 if ( !$this->laggedReplicaMode && $this->getServerCount() > 1 ) {
1310                         try {
1311                                 // See if laggedReplicaMode gets set
1312                                 $conn = $this->getConnection( DB_REPLICA, false, $domain );
1313                                 $this->reuseConnection( $conn );
1314                         } catch ( DBConnectionError $e ) {
1315                                 // Avoid expensive re-connect attempts and failures
1316                                 $this->allReplicasDownMode = true;
1317                                 $this->laggedReplicaMode = true;
1318                         }
1319                 }
1320
1321                 return $this->laggedReplicaMode;
1322         }
1323
1324         /**
1325          * @param bool $domain
1326          * @return bool
1327          * @deprecated 1.28; use getLaggedReplicaMode()
1328          */
1329         public function getLaggedSlaveMode( $domain = false ) {
1330                 return $this->getLaggedReplicaMode( $domain );
1331         }
1332
1333         /**
1334          * @note This method will never cause a new DB connection
1335          * @return bool Whether any generic connection used for reads was highly "lagged"
1336          * @since 1.28
1337          */
1338         public function laggedReplicaUsed() {
1339                 return $this->laggedReplicaMode;
1340         }
1341
1342         /**
1343          * @return bool
1344          * @since 1.27
1345          * @deprecated Since 1.28; use laggedReplicaUsed()
1346          */
1347         public function laggedSlaveUsed() {
1348                 return $this->laggedReplicaUsed();
1349         }
1350
1351         /**
1352          * @note This method may trigger a DB connection if not yet done
1353          * @param string|bool $domain Domain ID, or false for the current domain
1354          * @param IDatabase|null DB master connection; used to avoid loops [optional]
1355          * @return string|bool Reason the master is read-only or false if it is not
1356          * @since 1.27
1357          */
1358         public function getReadOnlyReason( $domain = false, IDatabase $conn = null ) {
1359                 if ( $this->readOnlyReason !== false ) {
1360                         return $this->readOnlyReason;
1361                 } elseif ( $this->getLaggedReplicaMode( $domain ) ) {
1362                         if ( $this->allReplicasDownMode ) {
1363                                 return 'The database has been automatically locked ' .
1364                                         'until the replica database servers become available';
1365                         } else {
1366                                 return 'The database has been automatically locked ' .
1367                                         'while the replica database servers catch up to the master.';
1368                         }
1369                 } elseif ( $this->masterRunningReadOnly( $domain, $conn ) ) {
1370                         return 'The database master is running in read-only mode.';
1371                 }
1372
1373                 return false;
1374         }
1375
1376         /**
1377          * @param string $domain Domain ID, or false for the current domain
1378          * @param IDatabase|null DB master connectionl used to avoid loops [optional]
1379          * @return bool
1380          */
1381         private function masterRunningReadOnly( $domain, IDatabase $conn = null ) {
1382                 $cache = $this->wanCache;
1383                 $masterServer = $this->getServerName( $this->getWriterIndex() );
1384
1385                 return (bool)$cache->getWithSetCallback(
1386                         $cache->makeGlobalKey( __CLASS__, 'server-read-only', $masterServer ),
1387                         self::TTL_CACHE_READONLY,
1388                         function () use ( $domain, $conn ) {
1389                                 $this->trxProfiler->setSilenced( true );
1390                                 try {
1391                                         $dbw = $conn ?: $this->getConnection( DB_MASTER, [], $domain );
1392                                         $readOnly = (int)$dbw->serverIsReadOnly();
1393                                 } catch ( DBError $e ) {
1394                                         $readOnly = 0;
1395                                 }
1396                                 $this->trxProfiler->setSilenced( false );
1397                                 return $readOnly;
1398                         },
1399                         [ 'pcTTL' => $cache::TTL_PROC_LONG, 'busyValue' => 0 ]
1400                 );
1401         }
1402
1403         public function allowLagged( $mode = null ) {
1404                 if ( $mode === null ) {
1405                         return $this->mAllowLagged;
1406                 }
1407                 $this->mAllowLagged = $mode;
1408
1409                 return $this->mAllowLagged;
1410         }
1411
1412         public function pingAll() {
1413                 $success = true;
1414                 $this->forEachOpenConnection( function ( IDatabase $conn ) use ( &$success ) {
1415                         if ( !$conn->ping() ) {
1416                                 $success = false;
1417                         }
1418                 } );
1419
1420                 return $success;
1421         }
1422
1423         public function forEachOpenConnection( $callback, array $params = [] ) {
1424                 foreach ( $this->mConns as $connsByServer ) {
1425                         foreach ( $connsByServer as $serverConns ) {
1426                                 foreach ( $serverConns as $conn ) {
1427                                         $mergedParams = array_merge( [ $conn ], $params );
1428                                         call_user_func_array( $callback, $mergedParams );
1429                                 }
1430                         }
1431                 }
1432         }
1433
1434         /**
1435          * Call a function with each open connection object to a master
1436          * @param callable $callback
1437          * @param array $params
1438          * @since 1.28
1439          */
1440         public function forEachOpenMasterConnection( $callback, array $params = [] ) {
1441                 $masterIndex = $this->getWriterIndex();
1442                 foreach ( $this->mConns as $connsByServer ) {
1443                         if ( isset( $connsByServer[$masterIndex] ) ) {
1444                                 /** @var IDatabase $conn */
1445                                 foreach ( $connsByServer[$masterIndex] as $conn ) {
1446                                         $mergedParams = array_merge( [ $conn ], $params );
1447                                         call_user_func_array( $callback, $mergedParams );
1448                                 }
1449                         }
1450                 }
1451         }
1452
1453         /**
1454          * Call a function with each open replica DB connection object
1455          * @param callable $callback
1456          * @param array $params
1457          * @since 1.28
1458          */
1459         public function forEachOpenReplicaConnection( $callback, array $params = [] ) {
1460                 foreach ( $this->mConns as $connsByServer ) {
1461                         foreach ( $connsByServer as $i => $serverConns ) {
1462                                 if ( $i === $this->getWriterIndex() ) {
1463                                         continue; // skip master
1464                                 }
1465                                 foreach ( $serverConns as $conn ) {
1466                                         $mergedParams = array_merge( [ $conn ], $params );
1467                                         call_user_func_array( $callback, $mergedParams );
1468                                 }
1469                         }
1470                 }
1471         }
1472
1473         public function getMaxLag( $domain = false ) {
1474                 $maxLag = -1;
1475                 $host = '';
1476                 $maxIndex = 0;
1477
1478                 if ( $this->getServerCount() <= 1 ) {
1479                         return [ $host, $maxLag, $maxIndex ]; // no replication = no lag
1480                 }
1481
1482                 $lagTimes = $this->getLagTimes( $domain );
1483                 foreach ( $lagTimes as $i => $lag ) {
1484                         if ( $this->mLoads[$i] > 0 && $lag > $maxLag ) {
1485                                 $maxLag = $lag;
1486                                 $host = $this->mServers[$i]['host'];
1487                                 $maxIndex = $i;
1488                         }
1489                 }
1490
1491                 return [ $host, $maxLag, $maxIndex ];
1492         }
1493
1494         public function getLagTimes( $domain = false ) {
1495                 if ( $this->getServerCount() <= 1 ) {
1496                         return [ 0 => 0 ]; // no replication = no lag
1497                 }
1498
1499                 # Send the request to the load monitor
1500                 return $this->getLoadMonitor()->getLagTimes( array_keys( $this->mServers ), $domain );
1501         }
1502
1503         public function safeGetLag( IDatabase $conn ) {
1504                 if ( $this->getServerCount() == 1 ) {
1505                         return 0;
1506                 } else {
1507                         return $conn->getLag();
1508                 }
1509         }
1510
1511         /**
1512          * Wait for a replica DB to reach a specified master position
1513          *
1514          * This will connect to the master to get an accurate position if $pos is not given
1515          *
1516          * @param IDatabase $conn Replica DB
1517          * @param DBMasterPos|bool $pos Master position; default: current position
1518          * @param integer $timeout Timeout in seconds
1519          * @return bool Success
1520          * @since 1.27
1521          */
1522         public function safeWaitForMasterPos( IDatabase $conn, $pos = false, $timeout = 10 ) {
1523                 if ( $this->getServerCount() == 1 || !$conn->getLBInfo( 'replica' ) ) {
1524                         return true; // server is not a replica DB
1525                 }
1526
1527                 $pos = $pos ?: $this->getConnection( DB_MASTER )->getMasterPos();
1528                 if ( !( $pos instanceof DBMasterPos ) ) {
1529                         return false; // something is misconfigured
1530                 }
1531
1532                 $result = $conn->masterPosWait( $pos, $timeout );
1533                 if ( $result == -1 || is_null( $result ) ) {
1534                         $msg = __METHOD__ . ": Timed out waiting on {$conn->getServer()} pos {$pos}";
1535                         $this->replLogger->warning( "$msg" );
1536                         $ok = false;
1537                 } else {
1538                         $this->replLogger->info( __METHOD__ . ": Done" );
1539                         $ok = true;
1540                 }
1541
1542                 return $ok;
1543         }
1544
1545         /**
1546          * Clear the cache for slag lag delay times
1547          *
1548          * This is only used for testing
1549          * @since 1.26
1550          */
1551         public function clearLagTimeCache() {
1552                 $this->getLoadMonitor()->clearCaches();
1553         }
1554
1555         /**
1556          * Set a callback via IDatabase::setTransactionListener() on
1557          * all current and future master connections of this load balancer
1558          *
1559          * @param string $name Callback name
1560          * @param callable|null $callback
1561          * @since 1.28
1562          */
1563         public function setTransactionListener( $name, callable $callback = null ) {
1564                 if ( $callback ) {
1565                         $this->trxRecurringCallbacks[$name] = $callback;
1566                 } else {
1567                         unset( $this->trxRecurringCallbacks[$name] );
1568                 }
1569                 $this->forEachOpenMasterConnection(
1570                         function ( IDatabase $conn ) use ( $name, $callback ) {
1571                                 $conn->setTransactionListener( $name, $callback );
1572                         }
1573                 );
1574         }
1575
1576         /**
1577          * Make certain table names use their own database, schema, and table prefix
1578          * when passed into SQL queries pre-escaped and without a qualified database name
1579          *
1580          * For example, "user" can be converted to "myschema.mydbname.user" for convenience.
1581          * Appearances like `user`, somedb.user, somedb.someschema.user will used literally.
1582          *
1583          * Calling this twice will completely clear any old table aliases. Also, note that
1584          * callers are responsible for making sure the schemas and databases actually exist.
1585          *
1586          * @param array[] $aliases Map of (table => (dbname, schema, prefix) map)
1587          * @since 1.28
1588          */
1589         public function setTableAliases( array $aliases ) {
1590                 $this->tableAliases = $aliases;
1591         }
1592
1593         /**
1594          * Set a new table prefix for the existing local domain ID for testing
1595          *
1596          * @param string $prefix
1597          * @since 1.28
1598          */
1599         public function setDomainPrefix( $prefix ) {
1600                 list( $dbName, ) = explode( '-', $this->localDomain, 2 );
1601
1602                 $this->localDomain = "{$dbName}-{$prefix}";
1603         }
1604 }