includes/libs/rdbms/loadbalancer/LoadBalancer.php

   1 <?php
   2 /**
   3  * Database load balancing manager
   4  *
   5  * This program is free software; you can redistribute it and/or modify
   6  * it under the terms of the GNU General Public License as published by
   7  * the Free Software Foundation; either version 2 of the License, or
   8  * (at your option) any later version.
   9  *
  10  * This program is distributed in the hope that it will be useful,
  11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  13  * GNU General Public License for more details.
  14  *
  15  * You should have received a copy of the GNU General Public License along
  16  * with this program; if not, write to the Free Software Foundation, Inc.,
  17  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
  18  * http://www.gnu.org/copyleft/gpl.html
  19  *
  20  * @file
  21  * @ingroup Database
  22  */
  23 use Psr\Log\LoggerInterface;
  24 use Wikimedia\ScopedCallback;
  25 use Wikimedia\Rdbms\TransactionProfiler;
  26
  27 /**
  28  * Database connection, tracking, load balancing, and transaction manager for a cluster
  29  *
  30  * @ingroup Database
  31  */
  32 class LoadBalancer implements ILoadBalancer {
  33         /** @var array[] Map of (server index => server config array) */
  34         private $mServers;
  35         /** @var IDatabase[][][] Map of local/foreignUsed/foreignFree => server index => IDatabase array */
  36         private $mConns;
  37         /** @var float[] Map of (server index => weight) */
  38         private $mLoads;
  39         /** @var array[] Map of (group => server index => weight) */
  40         private $mGroupLoads;
  41         /** @var bool Whether to disregard replica DB lag as a factor in replica DB selection */
  42         private $mAllowLagged;
  43         /** @var integer Seconds to spend waiting on replica DB lag to resolve */
  44         private $mWaitTimeout;
  45         /** @var array The LoadMonitor configuration */
  46         private $loadMonitorConfig;
  47         /** @var array[] $aliases Map of (table => (dbname, schema, prefix) map) */
  48         private $tableAliases = [];
  49
  50         /** @var ILoadMonitor */
  51         private $loadMonitor;
  52         /** @var BagOStuff */
  53         private $srvCache;
  54         /** @var BagOStuff */
  55         private $memCache;
  56         /** @var WANObjectCache */
  57         private $wanCache;
  58         /** @var object|string Class name or object With profileIn/profileOut methods */
  59         protected $profiler;
  60         /** @var TransactionProfiler */
  61         protected $trxProfiler;
  62         /** @var LoggerInterface */
  63         protected $replLogger;
  64         /** @var LoggerInterface */
  65         protected $connLogger;
  66         /** @var LoggerInterface */
  67         protected $queryLogger;
  68         /** @var LoggerInterface */
  69         protected $perfLogger;
  70
  71         /** @var bool|IDatabase Database connection that caused a problem */
  72         private $mErrorConnection;
  73         /** @var integer The generic (not query grouped) replica DB index (of $mServers) */
  74         private $mReadIndex;
  75         /** @var bool|DBMasterPos False if not set */
  76         private $mWaitForPos;
  77         /** @var bool Whether the generic reader fell back to a lagged replica DB */
  78         private $laggedReplicaMode = false;
  79         /** @var bool Whether the generic reader fell back to a lagged replica DB */
  80         private $allReplicasDownMode = false;
  81         /** @var string The last DB selection or connection error */
  82         private $mLastError = 'Unknown error';
  83         /** @var string|bool Reason the LB is read-only or false if not */
  84         private $readOnlyReason = false;
  85         /** @var integer Total connections opened */
  86         private $connsOpened = 0;
  87         /** @var string|bool String if a requested DBO_TRX transaction round is active */
  88         private $trxRoundId = false;
  89         /** @var array[] Map of (name => callable) */
  90         private $trxRecurringCallbacks = [];
  91         /** @var DatabaseDomain Local Domain ID and default for selectDB() calls */
  92         private $localDomain;
  93         /** @var string Alternate ID string for the domain instead of DatabaseDomain::getId() */
  94         private $localDomainIdAlias;
  95         /** @var string Current server name */
  96         private $host;
  97         /** @var bool Whether this PHP instance is for a CLI script */
  98         protected $cliMode;
  99         /** @var string Agent name for query profiling */
 100         protected $agent;
 101
 102         /** @var callable Exception logger */
 103         private $errorLogger;
 104
 105         /** @var boolean */
 106         private $disabled = false;
 107
 108         /** @var integer Warn when this many connection are held */
 109         const CONN_HELD_WARN_THRESHOLD = 10;
 110
 111         /** @var integer Default 'max lag' when unspecified */
 112         const MAX_LAG_DEFAULT = 10;
 113         /** @var integer Seconds to cache master server read-only status */
 114         const TTL_CACHE_READONLY = 5;
 115
 116         public function __construct( array $params ) {
 117                 if ( !isset( $params['servers'] ) ) {
 118                         throw new InvalidArgumentException( __CLASS__ . ': missing servers parameter' );
 119                 }
 120                 $this->mServers = $params['servers'];
 121
 122                 $this->localDomain = isset( $params['localDomain'] )
 123                         ? DatabaseDomain::newFromId( $params['localDomain'] )
 124                         : DatabaseDomain::newUnspecified();
 125                 // In case a caller assumes that the domain ID is simply <db>-<prefix>, which is almost
 126                 // always true, gracefully handle the case when they fail to account for escaping.
 127                 if ( $this->localDomain->getTablePrefix() != '' ) {
 128                         $this->localDomainIdAlias =
 129                                 $this->localDomain->getDatabase() . '-' . $this->localDomain->getTablePrefix();
 130                 } else {
 131                         $this->localDomainIdAlias = $this->localDomain->getDatabase();
 132                 }
 133
 134                 $this->mWaitTimeout = isset( $params['waitTimeout'] ) ? $params['waitTimeout'] : 10;
 135
 136                 $this->mReadIndex = -1;
 137                 $this->mConns = [
 138                         'local'       => [],
 139                         'foreignUsed' => [],
 140                         'foreignFree' => []
 141                 ];
 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->loadMonitorConfig = $params['loadMonitor'];
 153                 } else {
 154                         $this->loadMonitorConfig = [ 'class' => 'LoadMonitorNull' ];
 155                 }
 156
 157                 foreach ( $params['servers'] as $i => $server ) {
 158                         $this->mLoads[$i] = $server['load'];
 159                         if ( isset( $server['groupLoads'] ) ) {
 160                                 foreach ( $server['groupLoads'] as $group => $ratio ) {
 161                                         if ( !isset( $this->mGroupLoads[$group] ) ) {
 162                                                 $this->mGroupLoads[$group] = [];
 163                                         }
 164                                         $this->mGroupLoads[$group][$i] = $ratio;
 165                                 }
 166                         }
 167                 }
 168
 169                 if ( isset( $params['srvCache'] ) ) {
 170                         $this->srvCache = $params['srvCache'];
 171                 } else {
 172                         $this->srvCache = new EmptyBagOStuff();
 173                 }
 174                 if ( isset( $params['memCache'] ) ) {
 175                         $this->memCache = $params['memCache'];
 176                 } else {
 177                         $this->memCache = new EmptyBagOStuff();
 178                 }
 179                 if ( isset( $params['wanCache'] ) ) {
 180                         $this->wanCache = $params['wanCache'];
 181                 } else {
 182                         $this->wanCache = WANObjectCache::newEmpty();
 183                 }
 184                 $this->profiler = isset( $params['profiler'] ) ? $params['profiler'] : null;
 185                 if ( isset( $params['trxProfiler'] ) ) {
 186                         $this->trxProfiler = $params['trxProfiler'];
 187                 } else {
 188                         $this->trxProfiler = new TransactionProfiler();
 189                 }
 190
 191                 $this->errorLogger = isset( $params['errorLogger'] )
 192                         ? $params['errorLogger']
 193                         : function ( Exception $e ) {
 194                                 trigger_error( get_class( $e ) . ': ' . $e->getMessage(), E_USER_WARNING );
 195                         };
 196
 197                 foreach ( [ 'replLogger', 'connLogger', 'queryLogger', 'perfLogger' ] as $key ) {
 198                         $this->$key = isset( $params[$key] ) ? $params[$key] : new \Psr\Log\NullLogger();
 199                 }
 200
 201                 $this->host = isset( $params['hostname'] )
 202                         ? $params['hostname']
 203                         : ( gethostname() ?: 'unknown' );
 204                 $this->cliMode = isset( $params['cliMode'] ) ? $params['cliMode'] : PHP_SAPI === 'cli';
 205                 $this->agent = isset( $params['agent'] ) ? $params['agent'] : '';
 206         }
 207
 208         /**
 209          * Get a LoadMonitor instance
 210          *
 211          * @return ILoadMonitor
 212          */
 213         private function getLoadMonitor() {
 214                 if ( !isset( $this->loadMonitor ) ) {
 215                         $class = $this->loadMonitorConfig['class'];
 216                         $this->loadMonitor = new $class(
 217                                 $this, $this->srvCache, $this->memCache, $this->loadMonitorConfig );
 218                         $this->loadMonitor->setLogger( $this->replLogger );
 219                 }
 220
 221                 return $this->loadMonitor;
 222         }
 223
 224         /**
 225          * @param array $loads
 226          * @param bool|string $domain Domain to get non-lagged for
 227          * @param int $maxLag Restrict the maximum allowed lag to this many seconds
 228          * @return bool|int|string
 229          */
 230         private function getRandomNonLagged( array $loads, $domain = false, $maxLag = INF ) {
 231                 $lags = $this->getLagTimes( $domain );
 232
 233                 # Unset excessively lagged servers
 234                 foreach ( $lags as $i => $lag ) {
 235                         if ( $i != 0 ) {
 236                                 # How much lag this server nominally is allowed to have
 237                                 $maxServerLag = isset( $this->mServers[$i]['max lag'] )
 238                                         ? $this->mServers[$i]['max lag']
 239                                         : self::MAX_LAG_DEFAULT; // default
 240                                 # Constrain that futher by $maxLag argument
 241                                 $maxServerLag = min( $maxServerLag, $maxLag );
 242
 243                                 $host = $this->getServerName( $i );
 244                                 if ( $lag === false && !is_infinite( $maxServerLag ) ) {
 245                                         $this->replLogger->error(
 246                                                 "Server {host} (#$i) is not replicating?", [ 'host' => $host ] );
 247                                         unset( $loads[$i] );
 248                                 } elseif ( $lag > $maxServerLag ) {
 249                                         $this->replLogger->warning(
 250                                                 "Server {host} (#$i) has {lag} seconds of lag (>= {maxlag})",
 251                                                 [ 'host' => $host, 'lag' => $lag, 'maxlag' => $maxServerLag ]
 252                                         );
 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, $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         /**
 399          * @param DBMasterPos|false $pos
 400          */
 401         public function waitFor( $pos ) {
 402                 $this->mWaitForPos = $pos;
 403                 $i = $this->mReadIndex;
 404
 405                 if ( $i > 0 ) {
 406                         if ( !$this->doWait( $i ) ) {
 407                                 $this->laggedReplicaMode = true;
 408                         }
 409                 }
 410         }
 411
 412         public function waitForOne( $pos, $timeout = null ) {
 413                 $this->mWaitForPos = $pos;
 414
 415                 $i = $this->mReadIndex;
 416                 if ( $i <= 0 ) {
 417                         // Pick a generic replica DB if there isn't one yet
 418                         $readLoads = $this->mLoads;
 419                         unset( $readLoads[$this->getWriterIndex()] ); // replica DBs only
 420                         $readLoads = array_filter( $readLoads ); // with non-zero load
 421                         $i = ArrayUtils::pickRandom( $readLoads );
 422                 }
 423
 424                 if ( $i > 0 ) {
 425                         $ok = $this->doWait( $i, true, $timeout );
 426                 } else {
 427                         $ok = true; // no applicable loads
 428                 }
 429
 430                 return $ok;
 431         }
 432
 433         public function waitForAll( $pos, $timeout = null ) {
 434                 $this->mWaitForPos = $pos;
 435                 $serverCount = count( $this->mServers );
 436
 437                 $ok = true;
 438                 for ( $i = 1; $i < $serverCount; $i++ ) {
 439                         if ( $this->mLoads[$i] > 0 ) {
 440                                 $ok = $this->doWait( $i, true, $timeout ) && $ok;
 441                         }
 442                 }
 443
 444                 return $ok;
 445         }
 446
 447         /**
 448          * @param int $i
 449          * @return IDatabase|bool
 450          */
 451         public function getAnyOpenConnection( $i ) {
 452                 foreach ( $this->mConns as $connsByServer ) {
 453                         if ( !empty( $connsByServer[$i] ) ) {
 454                                 /** @var $serverConns IDatabase[] */
 455                                 $serverConns = $connsByServer[$i];
 456
 457                                 return reset( $serverConns );
 458                         }
 459                 }
 460
 461                 return false;
 462         }
 463
 464         /**
 465          * Wait for a given replica DB to catch up to the master pos stored in $this
 466          * @param int $index Server index
 467          * @param bool $open Check the server even if a new connection has to be made
 468          * @param int $timeout Max seconds to wait; default is mWaitTimeout
 469          * @return bool
 470          */
 471         protected function doWait( $index, $open = false, $timeout = null ) {
 472                 $close = false; // close the connection afterwards
 473
 474                 // Check if we already know that the DB has reached this point
 475                 $server = $this->getServerName( $index );
 476                 $key = $this->srvCache->makeGlobalKey( __CLASS__, 'last-known-pos', $server );
 477                 /** @var DBMasterPos $knownReachedPos */
 478                 $knownReachedPos = $this->srvCache->get( $key );
 479                 if ( $knownReachedPos && $knownReachedPos->hasReached( $this->mWaitForPos ) ) {
 480                         $this->replLogger->debug( __METHOD__ .
 481                                 ": replica DB $server known to be caught up (pos >= $knownReachedPos)." );
 482                         return true;
 483                 }
 484
 485                 // Find a connection to wait on, creating one if needed and allowed
 486                 $conn = $this->getAnyOpenConnection( $index );
 487                 if ( !$conn ) {
 488                         if ( !$open ) {
 489                                 $this->replLogger->debug( __METHOD__ . ": no connection open for $server" );
 490
 491                                 return false;
 492                         } else {
 493                                 $conn = $this->openConnection( $index, self::DOMAIN_ANY );
 494                                 if ( !$conn ) {
 495                                         $this->replLogger->warning( __METHOD__ . ": failed to connect to $server" );
 496
 497                                         return false;
 498                                 }
 499                                 // Avoid connection spam in waitForAll() when connections
 500                                 // are made just for the sake of doing this lag check.
 501                                 $close = true;
 502                         }
 503                 }
 504
 505                 $this->replLogger->info( __METHOD__ . ": Waiting for replica DB $server to catch up..." );
 506                 $timeout = $timeout ?: $this->mWaitTimeout;
 507                 $result = $conn->masterPosWait( $this->mWaitForPos, $timeout );
 508
 509                 if ( $result == -1 || is_null( $result ) ) {
 510                         // Timed out waiting for replica DB, use master instead
 511                         $this->replLogger->warning(
 512                                 __METHOD__ . ": Timed out waiting on {host} pos {$this->mWaitForPos}",
 513                                 [ 'host' => $server ]
 514                         );
 515                         $ok = false;
 516                 } else {
 517                         $this->replLogger->info( __METHOD__ . ": Done" );
 518                         $ok = true;
 519                         // Remember that the DB reached this point
 520                         $this->srvCache->set( $key, $this->mWaitForPos, BagOStuff::TTL_DAY );
 521                 }
 522
 523                 if ( $close ) {
 524                         $this->closeConnection( $conn );
 525                 }
 526
 527                 return $ok;
 528         }
 529
 530         /**
 531          * @see ILoadBalancer::getConnection()
 532          *
 533          * @param int $i
 534          * @param array $groups
 535          * @param bool $domain
 536          * @return Database
 537          * @throws DBConnectionError
 538          */
 539         public function getConnection( $i, $groups = [], $domain = false ) {
 540                 if ( $i === null || $i === false ) {
 541                         throw new InvalidArgumentException( 'Attempt to call ' . __METHOD__ .
 542                                 ' with invalid server index' );
 543                 }
 544
 545                 if ( $this->localDomain->equals( $domain ) || $domain === $this->localDomainIdAlias ) {
 546                         $domain = false; // local connection requested
 547                 }
 548
 549                 $groups = ( $groups === false || $groups === [] )
 550                         ? [ false ] // check one "group": the generic pool
 551                         : (array)$groups;
 552
 553                 $masterOnly = ( $i == self::DB_MASTER || $i == $this->getWriterIndex() );
 554                 $oldConnsOpened = $this->connsOpened; // connections open now
 555
 556                 if ( $i == self::DB_MASTER ) {
 557                         $i = $this->getWriterIndex();
 558                 } else {
 559                         # Try to find an available server in any the query groups (in order)
 560                         foreach ( $groups as $group ) {
 561                                 $groupIndex = $this->getReaderIndex( $group, $domain );
 562                                 if ( $groupIndex !== false ) {
 563                                         $i = $groupIndex;
 564                                         break;
 565                                 }
 566                         }
 567                 }
 568
 569                 # Operation-based index
 570                 if ( $i == self::DB_REPLICA ) {
 571                         $this->mLastError = 'Unknown error'; // reset error string
 572                         # Try the general server pool if $groups are unavailable.
 573                         $i = ( $groups === [ false ] )
 574                                 ? false // don't bother with this if that is what was tried above
 575                                 : $this->getReaderIndex( false, $domain );
 576                         # Couldn't find a working server in getReaderIndex()?
 577                         if ( $i === false ) {
 578                                 $this->mLastError = 'No working replica DB server: ' . $this->mLastError;
 579                                 // Throw an exception
 580                                 $this->reportConnectionError();
 581                                 return null; // not reached
 582                         }
 583                 }
 584
 585                 # Now we have an explicit index into the servers array
 586                 $conn = $this->openConnection( $i, $domain );
 587                 if ( !$conn ) {
 588                         // Throw an exception
 589                         $this->reportConnectionError();
 590                         return null; // not reached
 591                 }
 592
 593                 # Profile any new connections that happen
 594                 if ( $this->connsOpened > $oldConnsOpened ) {
 595                         $host = $conn->getServer();
 596                         $dbname = $conn->getDBname();
 597                         $this->trxProfiler->recordConnection( $host, $dbname, $masterOnly );
 598                 }
 599
 600                 if ( $masterOnly ) {
 601                         # Make master-requested DB handles inherit any read-only mode setting
 602                         $conn->setLBInfo( 'readOnlyReason', $this->getReadOnlyReason( $domain, $conn ) );
 603                 }
 604
 605                 return $conn;
 606         }
 607
 608         public function reuseConnection( $conn ) {
 609                 $serverIndex = $conn->getLBInfo( 'serverIndex' );
 610                 $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 611                 if ( $serverIndex === null || $refCount === null ) {
 612                         /**
 613                          * This can happen in code like:
 614                          *   foreach ( $dbs as $db ) {
 615                          *     $conn = $lb->getConnection( $lb::DB_REPLICA, [], $db );
 616                          *     ...
 617                          *     $lb->reuseConnection( $conn );
 618                          *   }
 619                          * When a connection to the local DB is opened in this way, reuseConnection()
 620                          * should be ignored
 621                          */
 622                         return;
 623                 } elseif ( $conn instanceof DBConnRef ) {
 624                         // DBConnRef already handles calling reuseConnection() and only passes the live
 625                         // Database instance to this method. Any caller passing in a DBConnRef is broken.
 626                         $this->connLogger->error( __METHOD__ . ": got DBConnRef instance.\n" .
 627                                 ( new RuntimeException() )->getTraceAsString() );
 628
 629                         return;
 630                 }
 631
 632                 if ( $this->disabled ) {
 633                         return; // DBConnRef handle probably survived longer than the LoadBalancer
 634                 }
 635
 636                 $domain = $conn->getDomainID();
 637                 if ( !isset( $this->mConns['foreignUsed'][$serverIndex][$domain] ) ) {
 638                         throw new InvalidArgumentException( __METHOD__ .
 639                                 ": connection $serverIndex/$domain not found; it may have already been freed." );
 640                 } elseif ( $this->mConns['foreignUsed'][$serverIndex][$domain] !== $conn ) {
 641                         throw new InvalidArgumentException( __METHOD__ .
 642                                 ": connection $serverIndex/$domain mismatched; it may have already been freed." );
 643                 }
 644                 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
 645                 if ( $refCount <= 0 ) {
 646                         $this->mConns['foreignFree'][$serverIndex][$domain] = $conn;
 647                         unset( $this->mConns['foreignUsed'][$serverIndex][$domain] );
 648                         if ( !$this->mConns['foreignUsed'][$serverIndex] ) {
 649                                 unset( $this->mConns[ 'foreignUsed' ][$serverIndex] ); // clean up
 650                         }
 651                         $this->connLogger->debug( __METHOD__ . ": freed connection $serverIndex/$domain" );
 652                 } else {
 653                         $this->connLogger->debug( __METHOD__ .
 654                                 ": reference count for $serverIndex/$domain reduced to $refCount" );
 655                 }
 656         }
 657
 658         public function getConnectionRef( $db, $groups = [], $domain = false ) {
 659                 $domain = ( $domain !== false ) ? $domain : $this->localDomain;
 660
 661                 return new DBConnRef( $this, $this->getConnection( $db, $groups, $domain ) );
 662         }
 663
 664         public function getLazyConnectionRef( $db, $groups = [], $domain = false ) {
 665                 $domain = ( $domain !== false ) ? $domain : $this->localDomain;
 666
 667                 return new DBConnRef( $this, [ $db, $groups, $domain ] );
 668         }
 669
 670         public function getMaintenanceConnectionRef( $db, $groups = [], $domain = false ) {
 671                 $domain = ( $domain !== false ) ? $domain : $this->localDomain;
 672
 673                 return new MaintainableDBConnRef( $this, $this->getConnection( $db, $groups, $domain ) );
 674         }
 675
 676         /**
 677          * @see ILoadBalancer::openConnection()
 678          *
 679          * @param int $i
 680          * @param bool $domain
 681          * @return bool|Database
 682          * @throws DBAccessError
 683          */
 684         public function openConnection( $i, $domain = false ) {
 685                 if ( $this->localDomain->equals( $domain ) || $domain === $this->localDomainIdAlias ) {
 686                         $domain = false; // local connection requested
 687                 }
 688
 689                 if ( $domain !== false ) {
 690                         $conn = $this->openForeignConnection( $i, $domain );
 691                 } elseif ( isset( $this->mConns['local'][$i][0] ) ) {
 692                         $conn = $this->mConns['local'][$i][0];
 693                 } else {
 694                         if ( !isset( $this->mServers[$i] ) || !is_array( $this->mServers[$i] ) ) {
 695                                 throw new InvalidArgumentException( "No server with index '$i'." );
 696                         }
 697                         // Open a new connection
 698                         $server = $this->mServers[$i];
 699                         $server['serverIndex'] = $i;
 700                         $conn = $this->reallyOpenConnection( $server, false );
 701                         $serverName = $this->getServerName( $i );
 702                         if ( $conn->isOpen() ) {
 703                                 $this->connLogger->debug( "Connected to database $i at '$serverName'." );
 704                                 $this->mConns['local'][$i][0] = $conn;
 705                         } else {
 706                                 $this->connLogger->warning( "Failed to connect to database $i at '$serverName'." );
 707                                 $this->mErrorConnection = $conn;
 708                                 $conn = false;
 709                         }
 710                 }
 711
 712                 if ( $conn && !$conn->isOpen() ) {
 713                         // Connection was made but later unrecoverably lost for some reason.
 714                         // Do not return a handle that will just throw exceptions on use,
 715                         // but let the calling code (e.g. getReaderIndex) try another server.
 716                         // See DatabaseMyslBase::ping() for how this can happen.
 717                         $this->mErrorConnection = $conn;
 718                         $conn = false;
 719                 }
 720
 721                 return $conn;
 722         }
 723
 724         /**
 725          * Open a connection to a foreign DB, or return one if it is already open.
 726          *
 727          * Increments a reference count on the returned connection which locks the
 728          * connection to the requested domain. This reference count can be
 729          * decremented by calling reuseConnection().
 730          *
 731          * If a connection is open to the appropriate server already, but with the wrong
 732          * database, it will be switched to the right database and returned, as long as
 733          * it has been freed first with reuseConnection().
 734          *
 735          * On error, returns false, and the connection which caused the
 736          * error will be available via $this->mErrorConnection.
 737          *
 738          * @note If disable() was called on this LoadBalancer, this method will throw a DBAccessError.
 739          *
 740          * @param int $i Server index
 741          * @param string $domain Domain ID to open
 742          * @return Database
 743          */
 744         private function openForeignConnection( $i, $domain ) {
 745                 $domainInstance = DatabaseDomain::newFromId( $domain );
 746                 $dbName = $domainInstance->getDatabase();
 747                 $prefix = $domainInstance->getTablePrefix();
 748
 749                 if ( isset( $this->mConns['foreignUsed'][$i][$domain] ) ) {
 750                         // Reuse an already-used connection
 751                         $conn = $this->mConns['foreignUsed'][$i][$domain];
 752                         $this->connLogger->debug( __METHOD__ . ": reusing connection $i/$domain" );
 753                 } elseif ( isset( $this->mConns['foreignFree'][$i][$domain] ) ) {
 754                         // Reuse a free connection for the same domain
 755                         $conn = $this->mConns['foreignFree'][$i][$domain];
 756                         unset( $this->mConns['foreignFree'][$i][$domain] );
 757                         $this->mConns['foreignUsed'][$i][$domain] = $conn;
 758                         $this->connLogger->debug( __METHOD__ . ": reusing free connection $i/$domain" );
 759                 } elseif ( !empty( $this->mConns['foreignFree'][$i] ) ) {
 760                         // Reuse a connection from another domain
 761                         $conn = reset( $this->mConns['foreignFree'][$i] );
 762                         $oldDomain = key( $this->mConns['foreignFree'][$i] );
 763                         // The empty string as a DB name means "don't care".
 764                         // DatabaseMysqlBase::open() already handle this on connection.
 765                         if ( strlen( $dbName ) && !$conn->selectDB( $dbName ) ) {
 766                                 $this->mLastError = "Error selecting database '$dbName' on server " .
 767                                         $conn->getServer() . " from client host {$this->host}";
 768                                 $this->mErrorConnection = $conn;
 769                                 $conn = false;
 770                         } else {
 771                                 $conn->tablePrefix( $prefix );
 772                                 unset( $this->mConns['foreignFree'][$i][$oldDomain] );
 773                                 $this->mConns['foreignUsed'][$i][$domain] = $conn;
 774                                 $this->connLogger->debug( __METHOD__ .
 775                                         ": reusing free connection from $oldDomain for $domain" );
 776                         }
 777                 } else {
 778                         if ( !isset( $this->mServers[$i] ) || !is_array( $this->mServers[$i] ) ) {
 779                                 throw new InvalidArgumentException( "No server with index '$i'." );
 780                         }
 781                         // Open a new connection
 782                         $server = $this->mServers[$i];
 783                         $server['serverIndex'] = $i;
 784                         $server['foreignPoolRefCount'] = 0;
 785                         $server['foreign'] = true;
 786                         $conn = $this->reallyOpenConnection( $server, $dbName );
 787                         if ( !$conn->isOpen() ) {
 788                                 $this->connLogger->warning( __METHOD__ . ": connection error for $i/$domain" );
 789                                 $this->mErrorConnection = $conn;
 790                                 $conn = false;
 791                         } else {
 792                                 $conn->tablePrefix( $prefix );
 793                                 $this->mConns['foreignUsed'][$i][$domain] = $conn;
 794                                 $this->connLogger->debug( __METHOD__ . ": opened new connection for $i/$domain" );
 795                         }
 796                 }
 797
 798                 // Increment reference count
 799                 if ( $conn ) {
 800                         $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 801                         $conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
 802                 }
 803
 804                 return $conn;
 805         }
 806
 807         /**
 808          * Test if the specified index represents an open connection
 809          *
 810          * @param int $index Server index
 811          * @access private
 812          * @return bool
 813          */
 814         private function isOpen( $index ) {
 815                 if ( !is_integer( $index ) ) {
 816                         return false;
 817                 }
 818
 819                 return (bool)$this->getAnyOpenConnection( $index );
 820         }
 821
 822         /**
 823          * Really opens a connection. Uncached.
 824          * Returns a Database object whether or not the connection was successful.
 825          * @access private
 826          *
 827          * @param array $server
 828          * @param string|bool $dbNameOverride Use "" to not select any database
 829          * @return Database
 830          * @throws DBAccessError
 831          * @throws InvalidArgumentException
 832          */
 833         protected function reallyOpenConnection( array $server, $dbNameOverride = false ) {
 834                 if ( $this->disabled ) {
 835                         throw new DBAccessError();
 836                 }
 837
 838                 if ( $dbNameOverride !== false ) {
 839                         $server['dbname'] = $dbNameOverride;
 840                 }
 841
 842                 // Let the handle know what the cluster master is (e.g. "db1052")
 843                 $masterName = $this->getServerName( $this->getWriterIndex() );
 844                 $server['clusterMasterHost'] = $masterName;
 845
 846                 // Log when many connection are made on requests
 847                 if ( ++$this->connsOpened >= self::CONN_HELD_WARN_THRESHOLD ) {
 848                         $this->perfLogger->warning( __METHOD__ . ": " .
 849                                 "{$this->connsOpened}+ connections made (master=$masterName)" );
 850                 }
 851
 852                 $server['srvCache'] = $this->srvCache;
 853                 // Set loggers and profilers
 854                 $server['connLogger'] = $this->connLogger;
 855                 $server['queryLogger'] = $this->queryLogger;
 856                 $server['errorLogger'] = $this->errorLogger;
 857                 $server['profiler'] = $this->profiler;
 858                 $server['trxProfiler'] = $this->trxProfiler;
 859                 // Use the same agent and PHP mode for all DB handles
 860                 $server['cliMode'] = $this->cliMode;
 861                 $server['agent'] = $this->agent;
 862                 // Use DBO_DEFAULT flags by default for LoadBalancer managed databases. Assume that the
 863                 // application calls LoadBalancer::commitMasterChanges() before the PHP script completes.
 864                 $server['flags'] = isset( $server['flags'] ) ? $server['flags'] : IDatabase::DBO_DEFAULT;
 865
 866                 // Create a live connection object
 867                 try {
 868                         $db = Database::factory( $server['type'], $server );
 869                 } catch ( DBConnectionError $e ) {
 870                         // FIXME: This is probably the ugliest thing I have ever done to
 871                         // PHP. I'm half-expecting it to segfault, just out of disgust. -- TS
 872                         $db = $e->db;
 873                 }
 874
 875                 $db->setLBInfo( $server );
 876                 $db->setLazyMasterHandle(
 877                         $this->getLazyConnectionRef( self::DB_MASTER, [], $db->getDomainID() )
 878                 );
 879                 $db->setTableAliases( $this->tableAliases );
 880
 881                 if ( $server['serverIndex'] === $this->getWriterIndex() ) {
 882                         if ( $this->trxRoundId !== false ) {
 883                                 $this->applyTransactionRoundFlags( $db );
 884                         }
 885                         foreach ( $this->trxRecurringCallbacks as $name => $callback ) {
 886                                 $db->setTransactionListener( $name, $callback );
 887                         }
 888                 }
 889
 890                 return $db;
 891         }
 892
 893         /**
 894          * @throws DBConnectionError
 895          */
 896         private function reportConnectionError() {
 897                 $conn = $this->mErrorConnection; // the connection which caused the error
 898                 $context = [
 899                         'method' => __METHOD__,
 900                         'last_error' => $this->mLastError,
 901                 ];
 902
 903                 if ( !is_object( $conn ) ) {
 904                         // No last connection, probably due to all servers being too busy
 905                         $this->connLogger->error(
 906                                 "LB failure with no last connection. Connection error: {last_error}",
 907                                 $context
 908                         );
 909
 910                         // If all servers were busy, mLastError will contain something sensible
 911                         throw new DBConnectionError( null, $this->mLastError );
 912                 } else {
 913                         $context['db_server'] = $conn->getServer();
 914                         $this->connLogger->warning(
 915                                 "Connection error: {last_error} ({db_server})",
 916                                 $context
 917                         );
 918
 919                         // throws DBConnectionError
 920                         $conn->reportConnectionError( "{$this->mLastError} ({$context['db_server']})" );
 921                 }
 922         }
 923
 924         public function getWriterIndex() {
 925                 return 0;
 926         }
 927
 928         public function haveIndex( $i ) {
 929                 return array_key_exists( $i, $this->mServers );
 930         }
 931
 932         public function isNonZeroLoad( $i ) {
 933                 return array_key_exists( $i, $this->mServers ) && $this->mLoads[$i] != 0;
 934         }
 935
 936         public function getServerCount() {
 937                 return count( $this->mServers );
 938         }
 939
 940         public function getServerName( $i ) {
 941                 if ( isset( $this->mServers[$i]['hostName'] ) ) {
 942                         $name = $this->mServers[$i]['hostName'];
 943                 } elseif ( isset( $this->mServers[$i]['host'] ) ) {
 944                         $name = $this->mServers[$i]['host'];
 945                 } else {
 946                         $name = '';
 947                 }
 948
 949                 return ( $name != '' ) ? $name : 'localhost';
 950         }
 951
 952         public function getServerInfo( $i ) {
 953                 if ( isset( $this->mServers[$i] ) ) {
 954                         return $this->mServers[$i];
 955                 } else {
 956                         return false;
 957                 }
 958         }
 959
 960         public function setServerInfo( $i, array $serverInfo ) {
 961                 $this->mServers[$i] = $serverInfo;
 962         }
 963
 964         public function getMasterPos() {
 965                 # If this entire request was served from a replica DB without opening a connection to the
 966                 # master (however unlikely that may be), then we can fetch the position from the replica DB.
 967                 $masterConn = $this->getAnyOpenConnection( $this->getWriterIndex() );
 968                 if ( !$masterConn ) {
 969                         $serverCount = count( $this->mServers );
 970                         for ( $i = 1; $i < $serverCount; $i++ ) {
 971                                 $conn = $this->getAnyOpenConnection( $i );
 972                                 if ( $conn ) {
 973                                         return $conn->getReplicaPos();
 974                                 }
 975                         }
 976                 } else {
 977                         return $masterConn->getMasterPos();
 978                 }
 979
 980                 return false;
 981         }
 982
 983         public function disable() {
 984                 $this->closeAll();
 985                 $this->disabled = true;
 986         }
 987
 988         public function closeAll() {
 989                 $this->forEachOpenConnection( function ( IDatabase $conn ) {
 990                         $host = $conn->getServer();
 991                         $this->connLogger->debug( "Closing connection to database '$host'." );
 992                         $conn->close();
 993                 } );
 994
 995                 $this->mConns = [
 996                         'local' => [],
 997                         'foreignFree' => [],
 998                         'foreignUsed' => [],
 999                 ];
1000                 $this->connsOpened = 0;
1001         }
1002
1003         public function closeConnection( IDatabase $conn ) {
1004                 $serverIndex = $conn->getLBInfo( 'serverIndex' ); // second index level of mConns
1005                 foreach ( $this->mConns as $type => $connsByServer ) {
1006                         if ( !isset( $connsByServer[$serverIndex] ) ) {
1007                                 continue;
1008                         }
1009
1010                         foreach ( $connsByServer[$serverIndex] as $i => $trackedConn ) {
1011                                 if ( $conn === $trackedConn ) {
1012                                         $host = $this->getServerName( $i );
1013                                         $this->connLogger->debug( "Closing connection to database $i at '$host'." );
1014                                         unset( $this->mConns[$type][$serverIndex][$i] );
1015                                         --$this->connsOpened;
1016                                         break 2;
1017                                 }
1018                         }
1019                 }
1020
1021                 $conn->close();
1022         }
1023
1024         public function commitAll( $fname = __METHOD__ ) {
1025                 $failures = [];
1026
1027                 $restore = ( $this->trxRoundId !== false );
1028                 $this->trxRoundId = false;
1029                 $this->forEachOpenConnection(
1030                         function ( IDatabase $conn ) use ( $fname, $restore, &$failures ) {
1031                                 try {
1032                                         $conn->commit( $fname, $conn::FLUSHING_ALL_PEERS );
1033                                 } catch ( DBError $e ) {
1034                                         call_user_func( $this->errorLogger, $e );
1035                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1036                                 }
1037                                 if ( $restore && $conn->getLBInfo( 'master' ) ) {
1038                                         $this->undoTransactionRoundFlags( $conn );
1039                                 }
1040                         }
1041                 );
1042
1043                 if ( $failures ) {
1044                         throw new DBExpectedError(
1045                                 null,
1046                                 "Commit failed on server(s) " . implode( "\n", array_unique( $failures ) )
1047                         );
1048                 }
1049         }
1050
1051         public function finalizeMasterChanges() {
1052                 $this->forEachOpenMasterConnection( function ( Database $conn ) {
1053                         // Any error should cause all DB transactions to be rolled back together
1054                         $conn->setTrxEndCallbackSuppression( false );
1055                         $conn->runOnTransactionPreCommitCallbacks();
1056                         // Defer post-commit callbacks until COMMIT finishes for all DBs
1057                         $conn->setTrxEndCallbackSuppression( true );
1058                 } );
1059         }
1060
1061         public function approveMasterChanges( array $options ) {
1062                 $limit = isset( $options['maxWriteDuration'] ) ? $options['maxWriteDuration'] : 0;
1063                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( $limit ) {
1064                         // If atomic sections or explicit transactions are still open, some caller must have
1065                         // caught an exception but failed to properly rollback any changes. Detect that and
1066                         // throw and error (causing rollback).
1067                         if ( $conn->explicitTrxActive() ) {
1068                                 throw new DBTransactionError(
1069                                         $conn,
1070                                         "Explicit transaction still active. A caller may have caught an error."
1071                                 );
1072                         }
1073                         // Assert that the time to replicate the transaction will be sane.
1074                         // If this fails, then all DB transactions will be rollback back together.
1075                         $time = $conn->pendingWriteQueryDuration( $conn::ESTIMATE_DB_APPLY );
1076                         if ( $limit > 0 && $time > $limit ) {
1077                                 throw new DBTransactionSizeError(
1078                                         $conn,
1079                                         "Transaction spent $time second(s) in writes, exceeding the $limit limit.",
1080                                         [ $time, $limit ]
1081                                 );
1082                         }
1083                         // If a connection sits idle while slow queries execute on another, that connection
1084                         // may end up dropped before the commit round is reached. Ping servers to detect this.
1085                         if ( $conn->writesOrCallbacksPending() && !$conn->ping() ) {
1086                                 throw new DBTransactionError(
1087                                         $conn,
1088                                         "A connection to the {$conn->getDBname()} database was lost before commit."
1089                                 );
1090                         }
1091                 } );
1092         }
1093
1094         public function beginMasterChanges( $fname = __METHOD__ ) {
1095                 if ( $this->trxRoundId !== false ) {
1096                         throw new DBTransactionError(
1097                                 null,
1098                                 "$fname: Transaction round '{$this->trxRoundId}' already started."
1099                         );
1100                 }
1101                 $this->trxRoundId = $fname;
1102
1103                 $failures = [];
1104                 $this->forEachOpenMasterConnection(
1105                         function ( Database $conn ) use ( $fname, &$failures ) {
1106                                 $conn->setTrxEndCallbackSuppression( true );
1107                                 try {
1108                                         $conn->flushSnapshot( $fname );
1109                                 } catch ( DBError $e ) {
1110                                         call_user_func( $this->errorLogger, $e );
1111                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1112                                 }
1113                                 $conn->setTrxEndCallbackSuppression( false );
1114                                 $this->applyTransactionRoundFlags( $conn );
1115                         }
1116                 );
1117
1118                 if ( $failures ) {
1119                         throw new DBExpectedError(
1120                                 null,
1121                                 "$fname: Flush failed on server(s) " . implode( "\n", array_unique( $failures ) )
1122                         );
1123                 }
1124         }
1125
1126         public function commitMasterChanges( $fname = __METHOD__ ) {
1127                 $failures = [];
1128
1129                 /** @noinspection PhpUnusedLocalVariableInspection */
1130                 $scope = $this->getScopedPHPBehaviorForCommit(); // try to ignore client aborts
1131
1132                 $restore = ( $this->trxRoundId !== false );
1133                 $this->trxRoundId = false;
1134                 $this->forEachOpenMasterConnection(
1135                         function ( IDatabase $conn ) use ( $fname, $restore, &$failures ) {
1136                                 try {
1137                                         if ( $conn->writesOrCallbacksPending() ) {
1138                                                 $conn->commit( $fname, $conn::FLUSHING_ALL_PEERS );
1139                                         } elseif ( $restore ) {
1140                                                 $conn->flushSnapshot( $fname );
1141                                         }
1142                                 } catch ( DBError $e ) {
1143                                         call_user_func( $this->errorLogger, $e );
1144                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1145                                 }
1146                                 if ( $restore ) {
1147                                         $this->undoTransactionRoundFlags( $conn );
1148                                 }
1149                         }
1150                 );
1151
1152                 if ( $failures ) {
1153                         throw new DBExpectedError(
1154                                 null,
1155                                 "$fname: Commit failed on server(s) " . implode( "\n", array_unique( $failures ) )
1156                         );
1157                 }
1158         }
1159
1160         public function runMasterPostTrxCallbacks( $type ) {
1161                 $e = null; // first exception
1162                 $this->forEachOpenMasterConnection( function ( Database $conn ) use ( $type, &$e ) {
1163                         $conn->setTrxEndCallbackSuppression( false );
1164                         if ( $conn->writesOrCallbacksPending() ) {
1165                                 // This happens if onTransactionIdle() callbacks leave callbacks on *another* DB
1166                                 // (which finished its callbacks already). Warn and recover in this case. Let the
1167                                 // callbacks run in the final commitMasterChanges() in LBFactory::shutdown().
1168                                 $this->queryLogger->error( __METHOD__ . ": found writes/callbacks pending." );
1169                                 return;
1170                         } elseif ( $conn->trxLevel() ) {
1171                                 // This happens for single-DB setups where DB_REPLICA uses the master DB,
1172                                 // thus leaving an implicit read-only transaction open at this point. It
1173                                 // also happens if onTransactionIdle() callbacks leave implicit transactions
1174                                 // open on *other* DBs (which is slightly improper). Let these COMMIT on the
1175                                 // next call to commitMasterChanges(), possibly in LBFactory::shutdown().
1176                                 return;
1177                         }
1178                         try {
1179                                 $conn->runOnTransactionIdleCallbacks( $type );
1180                         } catch ( Exception $ex ) {
1181                                 $e = $e ?: $ex;
1182                         }
1183                         try {
1184                                 $conn->runTransactionListenerCallbacks( $type );
1185                         } catch ( Exception $ex ) {
1186                                 $e = $e ?: $ex;
1187                         }
1188                 } );
1189
1190                 return $e;
1191         }
1192
1193         public function rollbackMasterChanges( $fname = __METHOD__ ) {
1194                 $restore = ( $this->trxRoundId !== false );
1195                 $this->trxRoundId = false;
1196                 $this->forEachOpenMasterConnection(
1197                         function ( IDatabase $conn ) use ( $fname, $restore ) {
1198                                 if ( $conn->writesOrCallbacksPending() ) {
1199                                         $conn->rollback( $fname, $conn::FLUSHING_ALL_PEERS );
1200                                 }
1201                                 if ( $restore ) {
1202                                         $this->undoTransactionRoundFlags( $conn );
1203                                 }
1204                         }
1205                 );
1206         }
1207
1208         public function suppressTransactionEndCallbacks() {
1209                 $this->forEachOpenMasterConnection( function ( Database $conn ) {
1210                         $conn->setTrxEndCallbackSuppression( true );
1211                 } );
1212         }
1213
1214         /**
1215          * @param IDatabase $conn
1216          */
1217         private function applyTransactionRoundFlags( IDatabase $conn ) {
1218                 if ( $conn->getFlag( $conn::DBO_DEFAULT ) ) {
1219                         // DBO_TRX is controlled entirely by CLI mode presence with DBO_DEFAULT.
1220                         // Force DBO_TRX even in CLI mode since a commit round is expected soon.
1221                         $conn->setFlag( $conn::DBO_TRX, $conn::REMEMBER_PRIOR );
1222                         // If config has explicitly requested DBO_TRX be either on or off by not
1223                         // setting DBO_DEFAULT, then respect that. Forcing no transactions is useful
1224                         // for things like blob stores (ExternalStore) which want auto-commit mode.
1225                 }
1226         }
1227
1228         /**
1229          * @param IDatabase $conn
1230          */
1231         private function undoTransactionRoundFlags( IDatabase $conn ) {
1232                 if ( $conn->getFlag( $conn::DBO_DEFAULT ) ) {
1233                         $conn->restoreFlags( $conn::RESTORE_PRIOR );
1234                 }
1235         }
1236
1237         public function flushReplicaSnapshots( $fname = __METHOD__ ) {
1238                 $this->forEachOpenReplicaConnection( function ( IDatabase $conn ) {
1239                         $conn->flushSnapshot( __METHOD__ );
1240                 } );
1241         }
1242
1243         public function hasMasterConnection() {
1244                 return $this->isOpen( $this->getWriterIndex() );
1245         }
1246
1247         public function hasMasterChanges() {
1248                 $pending = 0;
1249                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$pending ) {
1250                         $pending |= $conn->writesOrCallbacksPending();
1251                 } );
1252
1253                 return (bool)$pending;
1254         }
1255
1256         public function lastMasterChangeTimestamp() {
1257                 $lastTime = false;
1258                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$lastTime ) {
1259                         $lastTime = max( $lastTime, $conn->lastDoneWrites() );
1260                 } );
1261
1262                 return $lastTime;
1263         }
1264
1265         public function hasOrMadeRecentMasterChanges( $age = null ) {
1266                 $age = ( $age === null ) ? $this->mWaitTimeout : $age;
1267
1268                 return ( $this->hasMasterChanges()
1269                         || $this->lastMasterChangeTimestamp() > microtime( true ) - $age );
1270         }
1271
1272         public function pendingMasterChangeCallers() {
1273                 $fnames = [];
1274                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$fnames ) {
1275                         $fnames = array_merge( $fnames, $conn->pendingWriteCallers() );
1276                 } );
1277
1278                 return $fnames;
1279         }
1280
1281         public function getLaggedReplicaMode( $domain = false ) {
1282                 // No-op if there is only one DB (also avoids recursion)
1283                 if ( !$this->laggedReplicaMode && $this->getServerCount() > 1 ) {
1284                         try {
1285                                 // See if laggedReplicaMode gets set
1286                                 $conn = $this->getConnection( self::DB_REPLICA, false, $domain );
1287                                 $this->reuseConnection( $conn );
1288                         } catch ( DBConnectionError $e ) {
1289                                 // Avoid expensive re-connect attempts and failures
1290                                 $this->allReplicasDownMode = true;
1291                                 $this->laggedReplicaMode = true;
1292                         }
1293                 }
1294
1295                 return $this->laggedReplicaMode;
1296         }
1297
1298         /**
1299          * @param bool $domain
1300          * @return bool
1301          * @deprecated 1.28; use getLaggedReplicaMode()
1302          */
1303         public function getLaggedSlaveMode( $domain = false ) {
1304                 return $this->getLaggedReplicaMode( $domain );
1305         }
1306
1307         public function laggedReplicaUsed() {
1308                 return $this->laggedReplicaMode;
1309         }
1310
1311         /**
1312          * @return bool
1313          * @since 1.27
1314          * @deprecated Since 1.28; use laggedReplicaUsed()
1315          */
1316         public function laggedSlaveUsed() {
1317                 return $this->laggedReplicaUsed();
1318         }
1319
1320         public function getReadOnlyReason( $domain = false, IDatabase $conn = null ) {
1321                 if ( $this->readOnlyReason !== false ) {
1322                         return $this->readOnlyReason;
1323                 } elseif ( $this->getLaggedReplicaMode( $domain ) ) {
1324                         if ( $this->allReplicasDownMode ) {
1325                                 return 'The database has been automatically locked ' .
1326                                         'until the replica database servers become available';
1327                         } else {
1328                                 return 'The database has been automatically locked ' .
1329                                         'while the replica database servers catch up to the master.';
1330                         }
1331                 } elseif ( $this->masterRunningReadOnly( $domain, $conn ) ) {
1332                         return 'The database master is running in read-only mode.';
1333                 }
1334
1335                 return false;
1336         }
1337
1338         /**
1339          * @param string $domain Domain ID, or false for the current domain
1340          * @param IDatabase|null DB master connectionl used to avoid loops [optional]
1341          * @return bool
1342          */
1343         private function masterRunningReadOnly( $domain, IDatabase $conn = null ) {
1344                 $cache = $this->wanCache;
1345                 $masterServer = $this->getServerName( $this->getWriterIndex() );
1346
1347                 return (bool)$cache->getWithSetCallback(
1348                         $cache->makeGlobalKey( __CLASS__, 'server-read-only', $masterServer ),
1349                         self::TTL_CACHE_READONLY,
1350                         function () use ( $domain, $conn ) {
1351                                 $old = $this->trxProfiler->setSilenced( true );
1352                                 try {
1353                                         $dbw = $conn ?: $this->getConnection( self::DB_MASTER, [], $domain );
1354                                         $readOnly = (int)$dbw->serverIsReadOnly();
1355                                         if ( !$conn ) {
1356                                                 $this->reuseConnection( $dbw );
1357                                         }
1358                                 } catch ( DBError $e ) {
1359                                         $readOnly = 0;
1360                                 }
1361                                 $this->trxProfiler->setSilenced( $old );
1362                                 return $readOnly;
1363                         },
1364                         [ 'pcTTL' => $cache::TTL_PROC_LONG, 'busyValue' => 0 ]
1365                 );
1366         }
1367
1368         public function allowLagged( $mode = null ) {
1369                 if ( $mode === null ) {
1370                         return $this->mAllowLagged;
1371                 }
1372                 $this->mAllowLagged = $mode;
1373
1374                 return $this->mAllowLagged;
1375         }
1376
1377         public function pingAll() {
1378                 $success = true;
1379                 $this->forEachOpenConnection( function ( IDatabase $conn ) use ( &$success ) {
1380                         if ( !$conn->ping() ) {
1381                                 $success = false;
1382                         }
1383                 } );
1384
1385                 return $success;
1386         }
1387
1388         public function forEachOpenConnection( $callback, array $params = [] ) {
1389                 foreach ( $this->mConns as $connsByServer ) {
1390                         foreach ( $connsByServer as $serverConns ) {
1391                                 foreach ( $serverConns as $conn ) {
1392                                         $mergedParams = array_merge( [ $conn ], $params );
1393                                         call_user_func_array( $callback, $mergedParams );
1394                                 }
1395                         }
1396                 }
1397         }
1398
1399         public function forEachOpenMasterConnection( $callback, array $params = [] ) {
1400                 $masterIndex = $this->getWriterIndex();
1401                 foreach ( $this->mConns as $connsByServer ) {
1402                         if ( isset( $connsByServer[$masterIndex] ) ) {
1403                                 /** @var IDatabase $conn */
1404                                 foreach ( $connsByServer[$masterIndex] as $conn ) {
1405                                         $mergedParams = array_merge( [ $conn ], $params );
1406                                         call_user_func_array( $callback, $mergedParams );
1407                                 }
1408                         }
1409                 }
1410         }
1411
1412         public function forEachOpenReplicaConnection( $callback, array $params = [] ) {
1413                 foreach ( $this->mConns as $connsByServer ) {
1414                         foreach ( $connsByServer as $i => $serverConns ) {
1415                                 if ( $i === $this->getWriterIndex() ) {
1416                                         continue; // skip master
1417                                 }
1418                                 foreach ( $serverConns as $conn ) {
1419                                         $mergedParams = array_merge( [ $conn ], $params );
1420                                         call_user_func_array( $callback, $mergedParams );
1421                                 }
1422                         }
1423                 }
1424         }
1425
1426         public function getMaxLag( $domain = false ) {
1427                 $maxLag = -1;
1428                 $host = '';
1429                 $maxIndex = 0;
1430
1431                 if ( $this->getServerCount() <= 1 ) {
1432                         return [ $host, $maxLag, $maxIndex ]; // no replication = no lag
1433                 }
1434
1435                 $lagTimes = $this->getLagTimes( $domain );
1436                 foreach ( $lagTimes as $i => $lag ) {
1437                         if ( $this->mLoads[$i] > 0 && $lag > $maxLag ) {
1438                                 $maxLag = $lag;
1439                                 $host = $this->mServers[$i]['host'];
1440                                 $maxIndex = $i;
1441                         }
1442                 }
1443
1444                 return [ $host, $maxLag, $maxIndex ];
1445         }
1446
1447         public function getLagTimes( $domain = false ) {
1448                 if ( $this->getServerCount() <= 1 ) {
1449                         return [ $this->getWriterIndex() => 0 ]; // no replication = no lag
1450                 }
1451
1452                 $knownLagTimes = []; // map of (server index => 0 seconds)
1453                 $indexesWithLag = [];
1454                 foreach ( $this->mServers as $i => $server ) {
1455                         if ( empty( $server['is static'] ) ) {
1456                                 $indexesWithLag[] = $i; // DB server might have replication lag
1457                         } else {
1458                                 $knownLagTimes[$i] = 0; // DB server is a non-replicating and read-only archive
1459                         }
1460                 }
1461
1462                 return $this->getLoadMonitor()->getLagTimes( $indexesWithLag, $domain ) + $knownLagTimes;
1463         }
1464
1465         public function safeGetLag( IDatabase $conn ) {
1466                 if ( $this->getServerCount() <= 1 ) {
1467                         return 0;
1468                 } else {
1469                         return $conn->getLag();
1470                 }
1471         }
1472
1473         /**
1474          * @param IDatabase $conn
1475          * @param DBMasterPos|false $pos
1476          * @param int $timeout
1477          */
1478         public function safeWaitForMasterPos( IDatabase $conn, $pos = false, $timeout = 10 ) {
1479                 if ( $this->getServerCount() <= 1 || !$conn->getLBInfo( 'replica' ) ) {
1480                         return true; // server is not a replica DB
1481                 }
1482
1483                 if ( !$pos ) {
1484                         // Get the current master position, opening a connection if needed
1485                         $masterConn = $this->getAnyOpenConnection( $this->getWriterIndex() );
1486                         if ( $masterConn ) {
1487                                 $pos = $masterConn->getMasterPos();
1488                         } else {
1489                                 $masterConn = $this->openConnection( $this->getWriterIndex(), self::DOMAIN_ANY );
1490                                 $pos = $masterConn->getMasterPos();
1491                                 $this->closeConnection( $masterConn );
1492                         }
1493                 }
1494
1495                 if ( $pos instanceof DBMasterPos ) {
1496                         $result = $conn->masterPosWait( $pos, $timeout );
1497                         if ( $result == -1 || is_null( $result ) ) {
1498                                 $msg = __METHOD__ . ": Timed out waiting on {$conn->getServer()} pos {$pos}";
1499                                 $this->replLogger->warning( "$msg" );
1500                                 $ok = false;
1501                         } else {
1502                                 $this->replLogger->info( __METHOD__ . ": Done" );
1503                                 $ok = true;
1504                         }
1505                 } else {
1506                         $ok = false; // something is misconfigured
1507                         $this->replLogger->error( "Could not get master pos for {$conn->getServer()}." );
1508                 }
1509
1510                 return $ok;
1511         }
1512
1513         public function setTransactionListener( $name, callable $callback = null ) {
1514                 if ( $callback ) {
1515                         $this->trxRecurringCallbacks[$name] = $callback;
1516                 } else {
1517                         unset( $this->trxRecurringCallbacks[$name] );
1518                 }
1519                 $this->forEachOpenMasterConnection(
1520                         function ( IDatabase $conn ) use ( $name, $callback ) {
1521                                 $conn->setTransactionListener( $name, $callback );
1522                         }
1523                 );
1524         }
1525
1526         public function setTableAliases( array $aliases ) {
1527                 $this->tableAliases = $aliases;
1528         }
1529
1530         public function setDomainPrefix( $prefix ) {
1531                 if ( $this->mConns['foreignUsed'] ) {
1532                         // Do not switch connections to explicit foreign domains unless marked as free
1533                         $domains = [];
1534                         foreach ( $this->mConns['foreignUsed'] as $i => $connsByDomain ) {
1535                                 $domains = array_merge( $domains, array_keys( $connsByDomain ) );
1536                         }
1537                         $domains = implode( ', ', $domains );
1538                         throw new DBUnexpectedError( null,
1539                                 "Foreign domain connections are still in use ($domains)." );
1540                 }
1541
1542                 $this->localDomain = new DatabaseDomain(
1543                         $this->localDomain->getDatabase(),
1544                         null,
1545                         $prefix
1546                 );
1547
1548                 $this->forEachOpenConnection( function ( IDatabase $db ) use ( $prefix ) {
1549                         $db->tablePrefix( $prefix );
1550                 } );
1551         }
1552
1553         /**
1554          * Make PHP ignore user aborts/disconnects until the returned
1555          * value leaves scope. This returns null and does nothing in CLI mode.
1556          *
1557          * @return ScopedCallback|null
1558          */
1559         final protected function getScopedPHPBehaviorForCommit() {
1560                 if ( PHP_SAPI != 'cli' ) { // https://bugs.php.net/bug.php?id=47540
1561                         $old = ignore_user_abort( true ); // avoid half-finished operations
1562                         return new ScopedCallback( function () use ( $old ) {
1563                                 ignore_user_abort( $old );
1564                         } );
1565                 }
1566
1567                 return null;
1568         }
1569
1570         function __destruct() {
1571                 // Avoid connection leaks for sanity
1572                 $this->disable();
1573         }
1574 }