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