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 Psr\Log\NullLogger;
  25 use Wikimedia\ScopedCallback;
  26 use Wikimedia\Rdbms\TransactionProfiler;
  27 use Wikimedia\Rdbms\ILoadMonitor;
  28 use Wikimedia\Rdbms\DatabaseDomain;
  29 use Wikimedia\Rdbms\ILoadBalancer;
  30 use Wikimedia\Rdbms\DBMasterPos;
  31
  32 /**
  33  * Database connection, tracking, load balancing, and transaction manager for a cluster
  34  *
  35  * @ingroup Database
  36  */
  37 class LoadBalancer implements ILoadBalancer {
  38         /** @var array[] Map of (server index => server config array) */
  39         private $mServers;
  40         /** @var IDatabase[][][] Map of local/foreignUsed/foreignFree => server index => IDatabase array */
  41         private $mConns;
  42         /** @var float[] Map of (server index => weight) */
  43         private $mLoads;
  44         /** @var array[] Map of (group => server index => weight) */
  45         private $mGroupLoads;
  46         /** @var bool Whether to disregard replica DB lag as a factor in replica DB selection */
  47         private $mAllowLagged;
  48         /** @var integer Seconds to spend waiting on replica DB lag to resolve */
  49         private $mWaitTimeout;
  50         /** @var array The LoadMonitor configuration */
  51         private $loadMonitorConfig;
  52         /** @var array[] $aliases Map of (table => (dbname, schema, prefix) map) */
  53         private $tableAliases = [];
  54
  55         /** @var ILoadMonitor */
  56         private $loadMonitor;
  57         /** @var BagOStuff */
  58         private $srvCache;
  59         /** @var BagOStuff */
  60         private $memCache;
  61         /** @var WANObjectCache */
  62         private $wanCache;
  63         /** @var object|string Class name or object With profileIn/profileOut methods */
  64         protected $profiler;
  65         /** @var TransactionProfiler */
  66         protected $trxProfiler;
  67         /** @var LoggerInterface */
  68         protected $replLogger;
  69         /** @var LoggerInterface */
  70         protected $connLogger;
  71         /** @var LoggerInterface */
  72         protected $queryLogger;
  73         /** @var LoggerInterface */
  74         protected $perfLogger;
  75
  76         /** @var bool|IDatabase Database connection that caused a problem */
  77         private $mErrorConnection;
  78         /** @var integer The generic (not query grouped) replica DB index (of $mServers) */
  79         private $mReadIndex;
  80         /** @var bool|DBMasterPos False if not set */
  81         private $mWaitForPos;
  82         /** @var bool Whether the generic reader fell back to a lagged replica DB */
  83         private $laggedReplicaMode = false;
  84         /** @var bool Whether the generic reader fell back to a lagged replica DB */
  85         private $allReplicasDownMode = false;
  86         /** @var string The last DB selection or connection error */
  87         private $mLastError = 'Unknown error';
  88         /** @var string|bool Reason the LB is read-only or false if not */
  89         private $readOnlyReason = false;
  90         /** @var integer Total connections opened */
  91         private $connsOpened = 0;
  92         /** @var string|bool String if a requested DBO_TRX transaction round is active */
  93         private $trxRoundId = false;
  94         /** @var array[] Map of (name => callable) */
  95         private $trxRecurringCallbacks = [];
  96         /** @var DatabaseDomain Local Domain ID and default for selectDB() calls */
  97         private $localDomain;
  98         /** @var string Alternate ID string for the domain instead of DatabaseDomain::getId() */
  99         private $localDomainIdAlias;
 100         /** @var string Current server name */
 101         private $host;
 102         /** @var bool Whether this PHP instance is for a CLI script */
 103         protected $cliMode;
 104         /** @var string Agent name for query profiling */
 105         protected $agent;
 106
 107         /** @var callable Exception logger */
 108         private $errorLogger;
 109
 110         /** @var boolean */
 111         private $disabled = false;
 112
 113         /** @var integer Warn when this many connection are held */
 114         const CONN_HELD_WARN_THRESHOLD = 10;
 115
 116         /** @var integer Default 'max lag' when unspecified */
 117         const MAX_LAG_DEFAULT = 10;
 118         /** @var integer Seconds to cache master server read-only status */
 119         const TTL_CACHE_READONLY = 5;
 120
 121         public function __construct( array $params ) {
 122                 if ( !isset( $params['servers'] ) ) {
 123                         throw new InvalidArgumentException( __CLASS__ . ': missing servers parameter' );
 124                 }
 125                 $this->mServers = $params['servers'];
 126
 127                 $this->localDomain = isset( $params['localDomain'] )
 128                         ? DatabaseDomain::newFromId( $params['localDomain'] )
 129                         : DatabaseDomain::newUnspecified();
 130                 // In case a caller assumes that the domain ID is simply <db>-<prefix>, which is almost
 131                 // always true, gracefully handle the case when they fail to account for escaping.
 132                 if ( $this->localDomain->getTablePrefix() != '' ) {
 133                         $this->localDomainIdAlias =
 134                                 $this->localDomain->getDatabase() . '-' . $this->localDomain->getTablePrefix();
 135                 } else {
 136                         $this->localDomainIdAlias = $this->localDomain->getDatabase();
 137                 }
 138
 139                 $this->mWaitTimeout = isset( $params['waitTimeout'] ) ? $params['waitTimeout'] : 10;
 140
 141                 $this->mReadIndex = -1;
 142                 $this->mConns = [
 143                         'local'       => [],
 144                         'foreignUsed' => [],
 145                         'foreignFree' => []
 146                 ];
 147                 $this->mLoads = [];
 148                 $this->mWaitForPos = false;
 149                 $this->mErrorConnection = false;
 150                 $this->mAllowLagged = false;
 151
 152                 if ( isset( $params['readOnlyReason'] ) && is_string( $params['readOnlyReason'] ) ) {
 153                         $this->readOnlyReason = $params['readOnlyReason'];
 154                 }
 155
 156                 if ( isset( $params['loadMonitor'] ) ) {
 157                         $this->loadMonitorConfig = $params['loadMonitor'];
 158                 } else {
 159                         $this->loadMonitorConfig = [ 'class' => 'LoadMonitorNull' ];
 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_USER_WARNING );
 200                         };
 201
 202                 foreach ( [ 'replLogger', 'connLogger', 'queryLogger', 'perfLogger' ] as $key ) {
 203                         $this->$key = isset( $params[$key] ) ? $params[$key] : new 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->loadMonitor ) ) {
 220                         $compat = [
 221                                 'LoadMonitor' => Wikimedia\Rdbms\LoadMonitor::class,
 222                                 'LoadMonitorNull' => Wikimedia\Rdbms\LoadMonitorNull::class,
 223                                 'LoadMonitorMySQL' => Wikimedia\Rdbms\LoadMonitorMySQL::class,
 224                         ];
 225
 226                         $class = $this->loadMonitorConfig['class'];
 227                         if ( isset( $compat[$class] ) ) {
 228                                 $class = $compat[$class];
 229                         }
 230
 231                         $this->loadMonitor = new $class(
 232                                 $this, $this->srvCache, $this->memCache, $this->loadMonitorConfig );
 233                         $this->loadMonitor->setLogger( $this->replLogger );
 234                 }
 235
 236                 return $this->loadMonitor;
 237         }
 238
 239         /**
 240          * @param array $loads
 241          * @param bool|string $domain Domain to get non-lagged for
 242          * @param int $maxLag Restrict the maximum allowed lag to this many seconds
 243          * @return bool|int|string
 244          */
 245         private function getRandomNonLagged( array $loads, $domain = false, $maxLag = INF ) {
 246                 $lags = $this->getLagTimes( $domain );
 247
 248                 # Unset excessively lagged servers
 249                 foreach ( $lags as $i => $lag ) {
 250                         if ( $i != 0 ) {
 251                                 # How much lag this server nominally is allowed to have
 252                                 $maxServerLag = isset( $this->mServers[$i]['max lag'] )
 253                                         ? $this->mServers[$i]['max lag']
 254                                         : self::MAX_LAG_DEFAULT; // default
 255                                 # Constrain that futher by $maxLag argument
 256                                 $maxServerLag = min( $maxServerLag, $maxLag );
 257
 258                                 $host = $this->getServerName( $i );
 259                                 if ( $lag === false && !is_infinite( $maxServerLag ) ) {
 260                                         $this->replLogger->error(
 261                                                 "Server {host} (#$i) is not replicating?", [ 'host' => $host ] );
 262                                         unset( $loads[$i] );
 263                                 } elseif ( $lag > $maxServerLag ) {
 264                                         $this->replLogger->warning(
 265                                                 "Server {host} (#$i) has {lag} seconds of lag (>= {maxlag})",
 266                                                 [ 'host' => $host, 'lag' => $lag, 'maxlag' => $maxServerLag ]
 267                                         );
 268                                         unset( $loads[$i] );
 269                                 }
 270                         }
 271                 }
 272
 273                 # Find out if all the replica DBs with non-zero load are lagged
 274                 $sum = 0;
 275                 foreach ( $loads as $load ) {
 276                         $sum += $load;
 277                 }
 278                 if ( $sum == 0 ) {
 279                         # No appropriate DB servers except maybe the master and some replica DBs with zero load
 280                         # Do NOT use the master
 281                         # Instead, this function will return false, triggering read-only mode,
 282                         # and a lagged replica DB will be used instead.
 283                         return false;
 284                 }
 285
 286                 if ( count( $loads ) == 0 ) {
 287                         return false;
 288                 }
 289
 290                 # Return a random representative of the remainder
 291                 return ArrayUtils::pickRandom( $loads );
 292         }
 293
 294         public function getReaderIndex( $group = false, $domain = false ) {
 295                 if ( count( $this->mServers ) == 1 ) {
 296                         # Skip the load balancing if there's only one server
 297                         return $this->getWriterIndex();
 298                 } elseif ( $group === false && $this->mReadIndex >= 0 ) {
 299                         # Shortcut if generic reader exists already
 300                         return $this->mReadIndex;
 301                 }
 302
 303                 # Find the relevant load array
 304                 if ( $group !== false ) {
 305                         if ( isset( $this->mGroupLoads[$group] ) ) {
 306                                 $nonErrorLoads = $this->mGroupLoads[$group];
 307                         } else {
 308                                 # No loads for this group, return false and the caller can use some other group
 309                                 $this->connLogger->info( __METHOD__ . ": no loads for group $group" );
 310
 311                                 return false;
 312                         }
 313                 } else {
 314                         $nonErrorLoads = $this->mLoads;
 315                 }
 316
 317                 if ( !count( $nonErrorLoads ) ) {
 318                         throw new InvalidArgumentException( "Empty server array given to LoadBalancer" );
 319                 }
 320
 321                 # Scale the configured load ratios according to the dynamic load if supported
 322                 $this->getLoadMonitor()->scaleLoads( $nonErrorLoads, $domain );
 323
 324                 $laggedReplicaMode = false;
 325
 326                 # No server found yet
 327                 $i = false;
 328                 # First try quickly looking through the available servers for a server that
 329                 # meets our criteria
 330                 $currentLoads = $nonErrorLoads;
 331                 while ( count( $currentLoads ) ) {
 332                         if ( $this->mAllowLagged || $laggedReplicaMode ) {
 333                                 $i = ArrayUtils::pickRandom( $currentLoads );
 334                         } else {
 335                                 $i = false;
 336                                 if ( $this->mWaitForPos && $this->mWaitForPos->asOfTime() ) {
 337                                         # ChronologyProtecter causes mWaitForPos to be set via sessions.
 338                                         # This triggers doWait() after connect, so it's especially good to
 339                                         # avoid lagged servers so as to avoid just blocking in that method.
 340                                         $ago = microtime( true ) - $this->mWaitForPos->asOfTime();
 341                                         # Aim for <= 1 second of waiting (being too picky can backfire)
 342                                         $i = $this->getRandomNonLagged( $currentLoads, $domain, $ago + 1 );
 343                                 }
 344                                 if ( $i === false ) {
 345                                         # Any server with less lag than it's 'max lag' param is preferable
 346                                         $i = $this->getRandomNonLagged( $currentLoads, $domain );
 347                                 }
 348                                 if ( $i === false && count( $currentLoads ) != 0 ) {
 349                                         # All replica DBs lagged. Switch to read-only mode
 350                                         $this->replLogger->error( "All replica DBs lagged. Switch to read-only mode" );
 351                                         $i = ArrayUtils::pickRandom( $currentLoads );
 352                                         $laggedReplicaMode = true;
 353                                 }
 354                         }
 355
 356                         if ( $i === false ) {
 357                                 # pickRandom() returned false
 358                                 # This is permanent and means the configuration or the load monitor
 359                                 # wants us to return false.
 360                                 $this->connLogger->debug( __METHOD__ . ": pickRandom() returned false" );
 361
 362                                 return false;
 363                         }
 364
 365                         $serverName = $this->getServerName( $i );
 366                         $this->connLogger->debug( __METHOD__ . ": Using reader #$i: $serverName..." );
 367
 368                         $conn = $this->openConnection( $i, $domain );
 369                         if ( !$conn ) {
 370                                 $this->connLogger->warning( __METHOD__ . ": Failed connecting to $i/$domain" );
 371                                 unset( $nonErrorLoads[$i] );
 372                                 unset( $currentLoads[$i] );
 373                                 $i = false;
 374                                 continue;
 375                         }
 376
 377                         // Decrement reference counter, we are finished with this connection.
 378                         // It will be incremented for the caller later.
 379                         if ( $domain !== false ) {
 380                                 $this->reuseConnection( $conn );
 381                         }
 382
 383                         # Return this server
 384                         break;
 385                 }
 386
 387                 # If all servers were down, quit now
 388                 if ( !count( $nonErrorLoads ) ) {
 389                         $this->connLogger->error( "All servers down" );
 390                 }
 391
 392                 if ( $i !== false ) {
 393                         # Replica DB connection successful.
 394                         # Wait for the session master pos for a short time.
 395                         if ( $this->mWaitForPos && $i > 0 ) {
 396                                 $this->doWait( $i );
 397                         }
 398                         if ( $this->mReadIndex <= 0 && $this->mLoads[$i] > 0 && $group === false ) {
 399                                 $this->mReadIndex = $i;
 400                                 # Record if the generic reader index is in "lagged replica DB" mode
 401                                 if ( $laggedReplicaMode ) {
 402                                         $this->laggedReplicaMode = true;
 403                                 }
 404                         }
 405                         $serverName = $this->getServerName( $i );
 406                         $this->connLogger->debug(
 407                                 __METHOD__ . ": using server $serverName for group '$group'" );
 408                 }
 409
 410                 return $i;
 411         }
 412
 413         /**
 414          * @param DBMasterPos|false $pos
 415          */
 416         public function waitFor( $pos ) {
 417                 $this->mWaitForPos = $pos;
 418                 $i = $this->mReadIndex;
 419
 420                 if ( $i > 0 ) {
 421                         if ( !$this->doWait( $i ) ) {
 422                                 $this->laggedReplicaMode = true;
 423                         }
 424                 }
 425         }
 426
 427         public function waitForOne( $pos, $timeout = null ) {
 428                 $this->mWaitForPos = $pos;
 429
 430                 $i = $this->mReadIndex;
 431                 if ( $i <= 0 ) {
 432                         // Pick a generic replica DB if there isn't one yet
 433                         $readLoads = $this->mLoads;
 434                         unset( $readLoads[$this->getWriterIndex()] ); // replica DBs only
 435                         $readLoads = array_filter( $readLoads ); // with non-zero load
 436                         $i = ArrayUtils::pickRandom( $readLoads );
 437                 }
 438
 439                 if ( $i > 0 ) {
 440                         $ok = $this->doWait( $i, true, $timeout );
 441                 } else {
 442                         $ok = true; // no applicable loads
 443                 }
 444
 445                 return $ok;
 446         }
 447
 448         public function waitForAll( $pos, $timeout = null ) {
 449                 $this->mWaitForPos = $pos;
 450                 $serverCount = count( $this->mServers );
 451
 452                 $ok = true;
 453                 for ( $i = 1; $i < $serverCount; $i++ ) {
 454                         if ( $this->mLoads[$i] > 0 ) {
 455                                 $ok = $this->doWait( $i, true, $timeout ) && $ok;
 456                         }
 457                 }
 458
 459                 return $ok;
 460         }
 461
 462         /**
 463          * @param int $i
 464          * @return IDatabase|bool
 465          */
 466         public function getAnyOpenConnection( $i ) {
 467                 foreach ( $this->mConns as $connsByServer ) {
 468                         if ( !empty( $connsByServer[$i] ) ) {
 469                                 /** @var $serverConns IDatabase[] */
 470                                 $serverConns = $connsByServer[$i];
 471
 472                                 return reset( $serverConns );
 473                         }
 474                 }
 475
 476                 return false;
 477         }
 478
 479         /**
 480          * Wait for a given replica DB to catch up to the master pos stored in $this
 481          * @param int $index Server index
 482          * @param bool $open Check the server even if a new connection has to be made
 483          * @param int $timeout Max seconds to wait; default is mWaitTimeout
 484          * @return bool
 485          */
 486         protected function doWait( $index, $open = false, $timeout = null ) {
 487                 $close = false; // close the connection afterwards
 488
 489                 // Check if we already know that the DB has reached this point
 490                 $server = $this->getServerName( $index );
 491                 $key = $this->srvCache->makeGlobalKey( __CLASS__, 'last-known-pos', $server );
 492                 /** @var DBMasterPos $knownReachedPos */
 493                 $knownReachedPos = $this->srvCache->get( $key );
 494                 if ( $knownReachedPos && $knownReachedPos->hasReached( $this->mWaitForPos ) ) {
 495                         $this->replLogger->debug( __METHOD__ .
 496                                 ": replica DB $server known to be caught up (pos >= $knownReachedPos)." );
 497                         return true;
 498                 }
 499
 500                 // Find a connection to wait on, creating one if needed and allowed
 501                 $conn = $this->getAnyOpenConnection( $index );
 502                 if ( !$conn ) {
 503                         if ( !$open ) {
 504                                 $this->replLogger->debug( __METHOD__ . ": no connection open for $server" );
 505
 506                                 return false;
 507                         } else {
 508                                 $conn = $this->openConnection( $index, self::DOMAIN_ANY );
 509                                 if ( !$conn ) {
 510                                         $this->replLogger->warning( __METHOD__ . ": failed to connect to $server" );
 511
 512                                         return false;
 513                                 }
 514                                 // Avoid connection spam in waitForAll() when connections
 515                                 // are made just for the sake of doing this lag check.
 516                                 $close = true;
 517                         }
 518                 }
 519
 520                 $this->replLogger->info( __METHOD__ . ": Waiting for replica DB $server to catch up..." );
 521                 $timeout = $timeout ?: $this->mWaitTimeout;
 522                 $result = $conn->masterPosWait( $this->mWaitForPos, $timeout );
 523
 524                 if ( $result == -1 || is_null( $result ) ) {
 525                         // Timed out waiting for replica DB, use master instead
 526                         $this->replLogger->warning(
 527                                 __METHOD__ . ": Timed out waiting on {host} pos {$this->mWaitForPos}",
 528                                 [ 'host' => $server ]
 529                         );
 530                         $ok = false;
 531                 } else {
 532                         $this->replLogger->info( __METHOD__ . ": Done" );
 533                         $ok = true;
 534                         // Remember that the DB reached this point
 535                         $this->srvCache->set( $key, $this->mWaitForPos, BagOStuff::TTL_DAY );
 536                 }
 537
 538                 if ( $close ) {
 539                         $this->closeConnection( $conn );
 540                 }
 541
 542                 return $ok;
 543         }
 544
 545         /**
 546          * @see ILoadBalancer::getConnection()
 547          *
 548          * @param int $i
 549          * @param array $groups
 550          * @param bool $domain
 551          * @return Database
 552          * @throws DBConnectionError
 553          */
 554         public function getConnection( $i, $groups = [], $domain = false ) {
 555                 if ( $i === null || $i === false ) {
 556                         throw new InvalidArgumentException( 'Attempt to call ' . __METHOD__ .
 557                                 ' with invalid server index' );
 558                 }
 559
 560                 if ( $this->localDomain->equals( $domain ) || $domain === $this->localDomainIdAlias ) {
 561                         $domain = false; // local connection requested
 562                 }
 563
 564                 $groups = ( $groups === false || $groups === [] )
 565                         ? [ false ] // check one "group": the generic pool
 566                         : (array)$groups;
 567
 568                 $masterOnly = ( $i == self::DB_MASTER || $i == $this->getWriterIndex() );
 569                 $oldConnsOpened = $this->connsOpened; // connections open now
 570
 571                 if ( $i == self::DB_MASTER ) {
 572                         $i = $this->getWriterIndex();
 573                 } else {
 574                         # Try to find an available server in any the query groups (in order)
 575                         foreach ( $groups as $group ) {
 576                                 $groupIndex = $this->getReaderIndex( $group, $domain );
 577                                 if ( $groupIndex !== false ) {
 578                                         $i = $groupIndex;
 579                                         break;
 580                                 }
 581                         }
 582                 }
 583
 584                 # Operation-based index
 585                 if ( $i == self::DB_REPLICA ) {
 586                         $this->mLastError = 'Unknown error'; // reset error string
 587                         # Try the general server pool if $groups are unavailable.
 588                         $i = ( $groups === [ false ] )
 589                                 ? false // don't bother with this if that is what was tried above
 590                                 : $this->getReaderIndex( false, $domain );
 591                         # Couldn't find a working server in getReaderIndex()?
 592                         if ( $i === false ) {
 593                                 $this->mLastError = 'No working replica DB server: ' . $this->mLastError;
 594                                 // Throw an exception
 595                                 $this->reportConnectionError();
 596                                 return null; // not reached
 597                         }
 598                 }
 599
 600                 # Now we have an explicit index into the servers array
 601                 $conn = $this->openConnection( $i, $domain );
 602                 if ( !$conn ) {
 603                         // Throw an exception
 604                         $this->reportConnectionError();
 605                         return null; // not reached
 606                 }
 607
 608                 # Profile any new connections that happen
 609                 if ( $this->connsOpened > $oldConnsOpened ) {
 610                         $host = $conn->getServer();
 611                         $dbname = $conn->getDBname();
 612                         $this->trxProfiler->recordConnection( $host, $dbname, $masterOnly );
 613                 }
 614
 615                 if ( $masterOnly ) {
 616                         # Make master-requested DB handles inherit any read-only mode setting
 617                         $conn->setLBInfo( 'readOnlyReason', $this->getReadOnlyReason( $domain, $conn ) );
 618                 }
 619
 620                 return $conn;
 621         }
 622
 623         public function reuseConnection( $conn ) {
 624                 $serverIndex = $conn->getLBInfo( 'serverIndex' );
 625                 $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 626                 if ( $serverIndex === null || $refCount === null ) {
 627                         /**
 628                          * This can happen in code like:
 629                          *   foreach ( $dbs as $db ) {
 630                          *     $conn = $lb->getConnection( $lb::DB_REPLICA, [], $db );
 631                          *     ...
 632                          *     $lb->reuseConnection( $conn );
 633                          *   }
 634                          * When a connection to the local DB is opened in this way, reuseConnection()
 635                          * should be ignored
 636                          */
 637                         return;
 638                 } elseif ( $conn instanceof DBConnRef ) {
 639                         // DBConnRef already handles calling reuseConnection() and only passes the live
 640                         // Database instance to this method. Any caller passing in a DBConnRef is broken.
 641                         $this->connLogger->error( __METHOD__ . ": got DBConnRef instance.\n" .
 642                                 ( new RuntimeException() )->getTraceAsString() );
 643
 644                         return;
 645                 }
 646
 647                 if ( $this->disabled ) {
 648                         return; // DBConnRef handle probably survived longer than the LoadBalancer
 649                 }
 650
 651                 $domain = $conn->getDomainID();
 652                 if ( !isset( $this->mConns['foreignUsed'][$serverIndex][$domain] ) ) {
 653                         throw new InvalidArgumentException( __METHOD__ .
 654                                 ": connection $serverIndex/$domain not found; it may have already been freed." );
 655                 } elseif ( $this->mConns['foreignUsed'][$serverIndex][$domain] !== $conn ) {
 656                         throw new InvalidArgumentException( __METHOD__ .
 657                                 ": connection $serverIndex/$domain mismatched; it may have already been freed." );
 658                 }
 659                 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
 660                 if ( $refCount <= 0 ) {
 661                         $this->mConns['foreignFree'][$serverIndex][$domain] = $conn;
 662                         unset( $this->mConns['foreignUsed'][$serverIndex][$domain] );
 663                         if ( !$this->mConns['foreignUsed'][$serverIndex] ) {
 664                                 unset( $this->mConns[ 'foreignUsed' ][$serverIndex] ); // clean up
 665                         }
 666                         $this->connLogger->debug( __METHOD__ . ": freed connection $serverIndex/$domain" );
 667                 } else {
 668                         $this->connLogger->debug( __METHOD__ .
 669                                 ": reference count for $serverIndex/$domain reduced to $refCount" );
 670                 }
 671         }
 672
 673         public function getConnectionRef( $db, $groups = [], $domain = false ) {
 674                 $domain = ( $domain !== false ) ? $domain : $this->localDomain;
 675
 676                 return new DBConnRef( $this, $this->getConnection( $db, $groups, $domain ) );
 677         }
 678
 679         public function getLazyConnectionRef( $db, $groups = [], $domain = false ) {
 680                 $domain = ( $domain !== false ) ? $domain : $this->localDomain;
 681
 682                 return new DBConnRef( $this, [ $db, $groups, $domain ] );
 683         }
 684
 685         public function getMaintenanceConnectionRef( $db, $groups = [], $domain = false ) {
 686                 $domain = ( $domain !== false ) ? $domain : $this->localDomain;
 687
 688                 return new MaintainableDBConnRef( $this, $this->getConnection( $db, $groups, $domain ) );
 689         }
 690
 691         /**
 692          * @see ILoadBalancer::openConnection()
 693          *
 694          * @param int $i
 695          * @param bool $domain
 696          * @return bool|Database
 697          * @throws DBAccessError
 698          */
 699         public function openConnection( $i, $domain = false ) {
 700                 if ( $this->localDomain->equals( $domain ) || $domain === $this->localDomainIdAlias ) {
 701                         $domain = false; // local connection requested
 702                 }
 703
 704                 if ( $domain !== false ) {
 705                         $conn = $this->openForeignConnection( $i, $domain );
 706                 } elseif ( isset( $this->mConns['local'][$i][0] ) ) {
 707                         $conn = $this->mConns['local'][$i][0];
 708                 } else {
 709                         if ( !isset( $this->mServers[$i] ) || !is_array( $this->mServers[$i] ) ) {
 710                                 throw new InvalidArgumentException( "No server with index '$i'." );
 711                         }
 712                         // Open a new connection
 713                         $server = $this->mServers[$i];
 714                         $server['serverIndex'] = $i;
 715                         $conn = $this->reallyOpenConnection( $server, false );
 716                         $serverName = $this->getServerName( $i );
 717                         if ( $conn->isOpen() ) {
 718                                 $this->connLogger->debug( "Connected to database $i at '$serverName'." );
 719                                 $this->mConns['local'][$i][0] = $conn;
 720                         } else {
 721                                 $this->connLogger->warning( "Failed to connect to database $i at '$serverName'." );
 722                                 $this->mErrorConnection = $conn;
 723                                 $conn = false;
 724                         }
 725                 }
 726
 727                 if ( $conn && !$conn->isOpen() ) {
 728                         // Connection was made but later unrecoverably lost for some reason.
 729                         // Do not return a handle that will just throw exceptions on use,
 730                         // but let the calling code (e.g. getReaderIndex) try another server.
 731                         // See DatabaseMyslBase::ping() for how this can happen.
 732                         $this->mErrorConnection = $conn;
 733                         $conn = false;
 734                 }
 735
 736                 return $conn;
 737         }
 738
 739         /**
 740          * Open a connection to a foreign DB, or return one if it is already open.
 741          *
 742          * Increments a reference count on the returned connection which locks the
 743          * connection to the requested domain. This reference count can be
 744          * decremented by calling reuseConnection().
 745          *
 746          * If a connection is open to the appropriate server already, but with the wrong
 747          * database, it will be switched to the right database and returned, as long as
 748          * it has been freed first with reuseConnection().
 749          *
 750          * On error, returns false, and the connection which caused the
 751          * error will be available via $this->mErrorConnection.
 752          *
 753          * @note If disable() was called on this LoadBalancer, this method will throw a DBAccessError.
 754          *
 755          * @param int $i Server index
 756          * @param string $domain Domain ID to open
 757          * @return Database
 758          */
 759         private function openForeignConnection( $i, $domain ) {
 760                 $domainInstance = DatabaseDomain::newFromId( $domain );
 761                 $dbName = $domainInstance->getDatabase();
 762                 $prefix = $domainInstance->getTablePrefix();
 763
 764                 if ( isset( $this->mConns['foreignUsed'][$i][$domain] ) ) {
 765                         // Reuse an already-used connection
 766                         $conn = $this->mConns['foreignUsed'][$i][$domain];
 767                         $this->connLogger->debug( __METHOD__ . ": reusing connection $i/$domain" );
 768                 } elseif ( isset( $this->mConns['foreignFree'][$i][$domain] ) ) {
 769                         // Reuse a free connection for the same domain
 770                         $conn = $this->mConns['foreignFree'][$i][$domain];
 771                         unset( $this->mConns['foreignFree'][$i][$domain] );
 772                         $this->mConns['foreignUsed'][$i][$domain] = $conn;
 773                         $this->connLogger->debug( __METHOD__ . ": reusing free connection $i/$domain" );
 774                 } elseif ( !empty( $this->mConns['foreignFree'][$i] ) ) {
 775                         // Reuse a connection from another domain
 776                         $conn = reset( $this->mConns['foreignFree'][$i] );
 777                         $oldDomain = key( $this->mConns['foreignFree'][$i] );
 778                         // The empty string as a DB name means "don't care".
 779                         // DatabaseMysqlBase::open() already handle this on connection.
 780                         if ( strlen( $dbName ) && !$conn->selectDB( $dbName ) ) {
 781                                 $this->mLastError = "Error selecting database '$dbName' on server " .
 782                                         $conn->getServer() . " from client host {$this->host}";
 783                                 $this->mErrorConnection = $conn;
 784                                 $conn = false;
 785                         } else {
 786                                 $conn->tablePrefix( $prefix );
 787                                 unset( $this->mConns['foreignFree'][$i][$oldDomain] );
 788                                 $this->mConns['foreignUsed'][$i][$domain] = $conn;
 789                                 $this->connLogger->debug( __METHOD__ .
 790                                         ": reusing free connection from $oldDomain for $domain" );
 791                         }
 792                 } else {
 793                         if ( !isset( $this->mServers[$i] ) || !is_array( $this->mServers[$i] ) ) {
 794                                 throw new InvalidArgumentException( "No server with index '$i'." );
 795                         }
 796                         // Open a new connection
 797                         $server = $this->mServers[$i];
 798                         $server['serverIndex'] = $i;
 799                         $server['foreignPoolRefCount'] = 0;
 800                         $server['foreign'] = true;
 801                         $conn = $this->reallyOpenConnection( $server, $dbName );
 802                         if ( !$conn->isOpen() ) {
 803                                 $this->connLogger->warning( __METHOD__ . ": connection error for $i/$domain" );
 804                                 $this->mErrorConnection = $conn;
 805                                 $conn = false;
 806                         } else {
 807                                 $conn->tablePrefix( $prefix );
 808                                 $this->mConns['foreignUsed'][$i][$domain] = $conn;
 809                                 $this->connLogger->debug( __METHOD__ . ": opened new connection for $i/$domain" );
 810                         }
 811                 }
 812
 813                 // Increment reference count
 814                 if ( $conn ) {
 815                         $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 816                         $conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
 817                 }
 818
 819                 return $conn;
 820         }
 821
 822         /**
 823          * Test if the specified index represents an open connection
 824          *
 825          * @param int $index Server index
 826          * @access private
 827          * @return bool
 828          */
 829         private function isOpen( $index ) {
 830                 if ( !is_integer( $index ) ) {
 831                         return false;
 832                 }
 833
 834                 return (bool)$this->getAnyOpenConnection( $index );
 835         }
 836
 837         /**
 838          * Really opens a connection. Uncached.
 839          * Returns a Database object whether or not the connection was successful.
 840          * @access private
 841          *
 842          * @param array $server
 843          * @param string|bool $dbNameOverride Use "" to not select any database
 844          * @return Database
 845          * @throws DBAccessError
 846          * @throws InvalidArgumentException
 847          */
 848         protected function reallyOpenConnection( array $server, $dbNameOverride = false ) {
 849                 if ( $this->disabled ) {
 850                         throw new DBAccessError();
 851                 }
 852
 853                 if ( $dbNameOverride !== false ) {
 854                         $server['dbname'] = $dbNameOverride;
 855                 }
 856
 857                 // Let the handle know what the cluster master is (e.g. "db1052")
 858                 $masterName = $this->getServerName( $this->getWriterIndex() );
 859                 $server['clusterMasterHost'] = $masterName;
 860
 861                 // Log when many connection are made on requests
 862                 if ( ++$this->connsOpened >= self::CONN_HELD_WARN_THRESHOLD ) {
 863                         $this->perfLogger->warning( __METHOD__ . ": " .
 864                                 "{$this->connsOpened}+ connections made (master=$masterName)" );
 865                 }
 866
 867                 $server['srvCache'] = $this->srvCache;
 868                 // Set loggers and profilers
 869                 $server['connLogger'] = $this->connLogger;
 870                 $server['queryLogger'] = $this->queryLogger;
 871                 $server['errorLogger'] = $this->errorLogger;
 872                 $server['profiler'] = $this->profiler;
 873                 $server['trxProfiler'] = $this->trxProfiler;
 874                 // Use the same agent and PHP mode for all DB handles
 875                 $server['cliMode'] = $this->cliMode;
 876                 $server['agent'] = $this->agent;
 877                 // Use DBO_DEFAULT flags by default for LoadBalancer managed databases. Assume that the
 878                 // application calls LoadBalancer::commitMasterChanges() before the PHP script completes.
 879                 $server['flags'] = isset( $server['flags'] ) ? $server['flags'] : IDatabase::DBO_DEFAULT;
 880
 881                 // Create a live connection object
 882                 try {
 883                         $db = Database::factory( $server['type'], $server );
 884                 } catch ( DBConnectionError $e ) {
 885                         // FIXME: This is probably the ugliest thing I have ever done to
 886                         // PHP. I'm half-expecting it to segfault, just out of disgust. -- TS
 887                         $db = $e->db;
 888                 }
 889
 890                 $db->setLBInfo( $server );
 891                 $db->setLazyMasterHandle(
 892                         $this->getLazyConnectionRef( self::DB_MASTER, [], $db->getDomainID() )
 893                 );
 894                 $db->setTableAliases( $this->tableAliases );
 895
 896                 if ( $server['serverIndex'] === $this->getWriterIndex() ) {
 897                         if ( $this->trxRoundId !== false ) {
 898                                 $this->applyTransactionRoundFlags( $db );
 899                         }
 900                         foreach ( $this->trxRecurringCallbacks as $name => $callback ) {
 901                                 $db->setTransactionListener( $name, $callback );
 902                         }
 903                 }
 904
 905                 return $db;
 906         }
 907
 908         /**
 909          * @throws DBConnectionError
 910          */
 911         private function reportConnectionError() {
 912                 $conn = $this->mErrorConnection; // the connection which caused the error
 913                 $context = [
 914                         'method' => __METHOD__,
 915                         'last_error' => $this->mLastError,
 916                 ];
 917
 918                 if ( !is_object( $conn ) ) {
 919                         // No last connection, probably due to all servers being too busy
 920                         $this->connLogger->error(
 921                                 "LB failure with no last connection. Connection error: {last_error}",
 922                                 $context
 923                         );
 924
 925                         // If all servers were busy, mLastError will contain something sensible
 926                         throw new DBConnectionError( null, $this->mLastError );
 927                 } else {
 928                         $context['db_server'] = $conn->getServer();
 929                         $this->connLogger->warning(
 930                                 "Connection error: {last_error} ({db_server})",
 931                                 $context
 932                         );
 933
 934                         // throws DBConnectionError
 935                         $conn->reportConnectionError( "{$this->mLastError} ({$context['db_server']})" );
 936                 }
 937         }
 938
 939         public function getWriterIndex() {
 940                 return 0;
 941         }
 942
 943         public function haveIndex( $i ) {
 944                 return array_key_exists( $i, $this->mServers );
 945         }
 946
 947         public function isNonZeroLoad( $i ) {
 948                 return array_key_exists( $i, $this->mServers ) && $this->mLoads[$i] != 0;
 949         }
 950
 951         public function getServerCount() {
 952                 return count( $this->mServers );
 953         }
 954
 955         public function getServerName( $i ) {
 956                 if ( isset( $this->mServers[$i]['hostName'] ) ) {
 957                         $name = $this->mServers[$i]['hostName'];
 958                 } elseif ( isset( $this->mServers[$i]['host'] ) ) {
 959                         $name = $this->mServers[$i]['host'];
 960                 } else {
 961                         $name = '';
 962                 }
 963
 964                 return ( $name != '' ) ? $name : 'localhost';
 965         }
 966
 967         public function getServerInfo( $i ) {
 968                 if ( isset( $this->mServers[$i] ) ) {
 969                         return $this->mServers[$i];
 970                 } else {
 971                         return false;
 972                 }
 973         }
 974
 975         public function setServerInfo( $i, array $serverInfo ) {
 976                 $this->mServers[$i] = $serverInfo;
 977         }
 978
 979         public function getMasterPos() {
 980                 # If this entire request was served from a replica DB without opening a connection to the
 981                 # master (however unlikely that may be), then we can fetch the position from the replica DB.
 982                 $masterConn = $this->getAnyOpenConnection( $this->getWriterIndex() );
 983                 if ( !$masterConn ) {
 984                         $serverCount = count( $this->mServers );
 985                         for ( $i = 1; $i < $serverCount; $i++ ) {
 986                                 $conn = $this->getAnyOpenConnection( $i );
 987                                 if ( $conn ) {
 988                                         return $conn->getReplicaPos();
 989                                 }
 990                         }
 991                 } else {
 992                         return $masterConn->getMasterPos();
 993                 }
 994
 995                 return false;
 996         }
 997
 998         public function disable() {
 999                 $this->closeAll();
1000                 $this->disabled = true;
1001         }
1002
1003         public function closeAll() {
1004                 $this->forEachOpenConnection( function ( IDatabase $conn ) {
1005                         $host = $conn->getServer();
1006                         $this->connLogger->debug( "Closing connection to database '$host'." );
1007                         $conn->close();
1008                 } );
1009
1010                 $this->mConns = [
1011                         'local' => [],
1012                         'foreignFree' => [],
1013                         'foreignUsed' => [],
1014                 ];
1015                 $this->connsOpened = 0;
1016         }
1017
1018         public function closeConnection( IDatabase $conn ) {
1019                 $serverIndex = $conn->getLBInfo( 'serverIndex' ); // second index level of mConns
1020                 foreach ( $this->mConns as $type => $connsByServer ) {
1021                         if ( !isset( $connsByServer[$serverIndex] ) ) {
1022                                 continue;
1023                         }
1024
1025                         foreach ( $connsByServer[$serverIndex] as $i => $trackedConn ) {
1026                                 if ( $conn === $trackedConn ) {
1027                                         $host = $this->getServerName( $i );
1028                                         $this->connLogger->debug( "Closing connection to database $i at '$host'." );
1029                                         unset( $this->mConns[$type][$serverIndex][$i] );
1030                                         --$this->connsOpened;
1031                                         break 2;
1032                                 }
1033                         }
1034                 }
1035
1036                 $conn->close();
1037         }
1038
1039         public function commitAll( $fname = __METHOD__ ) {
1040                 $failures = [];
1041
1042                 $restore = ( $this->trxRoundId !== false );
1043                 $this->trxRoundId = false;
1044                 $this->forEachOpenConnection(
1045                         function ( IDatabase $conn ) use ( $fname, $restore, &$failures ) {
1046                                 try {
1047                                         $conn->commit( $fname, $conn::FLUSHING_ALL_PEERS );
1048                                 } catch ( DBError $e ) {
1049                                         call_user_func( $this->errorLogger, $e );
1050                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1051                                 }
1052                                 if ( $restore && $conn->getLBInfo( 'master' ) ) {
1053                                         $this->undoTransactionRoundFlags( $conn );
1054                                 }
1055                         }
1056                 );
1057
1058                 if ( $failures ) {
1059                         throw new DBExpectedError(
1060                                 null,
1061                                 "Commit failed on server(s) " . implode( "\n", array_unique( $failures ) )
1062                         );
1063                 }
1064         }
1065
1066         public function finalizeMasterChanges() {
1067                 $this->forEachOpenMasterConnection( function ( Database $conn ) {
1068                         // Any error should cause all DB transactions to be rolled back together
1069                         $conn->setTrxEndCallbackSuppression( false );
1070                         $conn->runOnTransactionPreCommitCallbacks();
1071                         // Defer post-commit callbacks until COMMIT finishes for all DBs
1072                         $conn->setTrxEndCallbackSuppression( true );
1073                 } );
1074         }
1075
1076         public function approveMasterChanges( array $options ) {
1077                 $limit = isset( $options['maxWriteDuration'] ) ? $options['maxWriteDuration'] : 0;
1078                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( $limit ) {
1079                         // If atomic sections or explicit transactions are still open, some caller must have
1080                         // caught an exception but failed to properly rollback any changes. Detect that and
1081                         // throw and error (causing rollback).
1082                         if ( $conn->explicitTrxActive() ) {
1083                                 throw new DBTransactionError(
1084                                         $conn,
1085                                         "Explicit transaction still active. A caller may have caught an error."
1086                                 );
1087                         }
1088                         // Assert that the time to replicate the transaction will be sane.
1089                         // If this fails, then all DB transactions will be rollback back together.
1090                         $time = $conn->pendingWriteQueryDuration( $conn::ESTIMATE_DB_APPLY );
1091                         if ( $limit > 0 && $time > $limit ) {
1092                                 throw new DBTransactionSizeError(
1093                                         $conn,
1094                                         "Transaction spent $time second(s) in writes, exceeding the $limit limit.",
1095                                         [ $time, $limit ]
1096                                 );
1097                         }
1098                         // If a connection sits idle while slow queries execute on another, that connection
1099                         // may end up dropped before the commit round is reached. Ping servers to detect this.
1100                         if ( $conn->writesOrCallbacksPending() && !$conn->ping() ) {
1101                                 throw new DBTransactionError(
1102                                         $conn,
1103                                         "A connection to the {$conn->getDBname()} database was lost before commit."
1104                                 );
1105                         }
1106                 } );
1107         }
1108
1109         public function beginMasterChanges( $fname = __METHOD__ ) {
1110                 if ( $this->trxRoundId !== false ) {
1111                         throw new DBTransactionError(
1112                                 null,
1113                                 "$fname: Transaction round '{$this->trxRoundId}' already started."
1114                         );
1115                 }
1116                 $this->trxRoundId = $fname;
1117
1118                 $failures = [];
1119                 $this->forEachOpenMasterConnection(
1120                         function ( Database $conn ) use ( $fname, &$failures ) {
1121                                 $conn->setTrxEndCallbackSuppression( true );
1122                                 try {
1123                                         $conn->flushSnapshot( $fname );
1124                                 } catch ( DBError $e ) {
1125                                         call_user_func( $this->errorLogger, $e );
1126                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1127                                 }
1128                                 $conn->setTrxEndCallbackSuppression( false );
1129                                 $this->applyTransactionRoundFlags( $conn );
1130                         }
1131                 );
1132
1133                 if ( $failures ) {
1134                         throw new DBExpectedError(
1135                                 null,
1136                                 "$fname: Flush failed on server(s) " . implode( "\n", array_unique( $failures ) )
1137                         );
1138                 }
1139         }
1140
1141         public function commitMasterChanges( $fname = __METHOD__ ) {
1142                 $failures = [];
1143
1144                 /** @noinspection PhpUnusedLocalVariableInspection */
1145                 $scope = $this->getScopedPHPBehaviorForCommit(); // try to ignore client aborts
1146
1147                 $restore = ( $this->trxRoundId !== false );
1148                 $this->trxRoundId = false;
1149                 $this->forEachOpenMasterConnection(
1150                         function ( IDatabase $conn ) use ( $fname, $restore, &$failures ) {
1151                                 try {
1152                                         if ( $conn->writesOrCallbacksPending() ) {
1153                                                 $conn->commit( $fname, $conn::FLUSHING_ALL_PEERS );
1154                                         } elseif ( $restore ) {
1155                                                 $conn->flushSnapshot( $fname );
1156                                         }
1157                                 } catch ( DBError $e ) {
1158                                         call_user_func( $this->errorLogger, $e );
1159                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1160                                 }
1161                                 if ( $restore ) {
1162                                         $this->undoTransactionRoundFlags( $conn );
1163                                 }
1164                         }
1165                 );
1166
1167                 if ( $failures ) {
1168                         throw new DBExpectedError(
1169                                 null,
1170                                 "$fname: Commit failed on server(s) " . implode( "\n", array_unique( $failures ) )
1171                         );
1172                 }
1173         }
1174
1175         public function runMasterPostTrxCallbacks( $type ) {
1176                 $e = null; // first exception
1177                 $this->forEachOpenMasterConnection( function ( Database $conn ) use ( $type, &$e ) {
1178                         $conn->setTrxEndCallbackSuppression( false );
1179                         if ( $conn->writesOrCallbacksPending() ) {
1180                                 // This happens if onTransactionIdle() callbacks leave callbacks on *another* DB
1181                                 // (which finished its callbacks already). Warn and recover in this case. Let the
1182                                 // callbacks run in the final commitMasterChanges() in LBFactory::shutdown().
1183                                 $this->queryLogger->error( __METHOD__ . ": found writes/callbacks pending." );
1184                                 return;
1185                         } elseif ( $conn->trxLevel() ) {
1186                                 // This happens for single-DB setups where DB_REPLICA uses the master DB,
1187                                 // thus leaving an implicit read-only transaction open at this point. It
1188                                 // also happens if onTransactionIdle() callbacks leave implicit transactions
1189                                 // open on *other* DBs (which is slightly improper). Let these COMMIT on the
1190                                 // next call to commitMasterChanges(), possibly in LBFactory::shutdown().
1191                                 return;
1192                         }
1193                         try {
1194                                 $conn->runOnTransactionIdleCallbacks( $type );
1195                         } catch ( Exception $ex ) {
1196                                 $e = $e ?: $ex;
1197                         }
1198                         try {
1199                                 $conn->runTransactionListenerCallbacks( $type );
1200                         } catch ( Exception $ex ) {
1201                                 $e = $e ?: $ex;
1202                         }
1203                 } );
1204
1205                 return $e;
1206         }
1207
1208         public function rollbackMasterChanges( $fname = __METHOD__ ) {
1209                 $restore = ( $this->trxRoundId !== false );
1210                 $this->trxRoundId = false;
1211                 $this->forEachOpenMasterConnection(
1212                         function ( IDatabase $conn ) use ( $fname, $restore ) {
1213                                 if ( $conn->writesOrCallbacksPending() ) {
1214                                         $conn->rollback( $fname, $conn::FLUSHING_ALL_PEERS );
1215                                 }
1216                                 if ( $restore ) {
1217                                         $this->undoTransactionRoundFlags( $conn );
1218                                 }
1219                         }
1220                 );
1221         }
1222
1223         public function suppressTransactionEndCallbacks() {
1224                 $this->forEachOpenMasterConnection( function ( Database $conn ) {
1225                         $conn->setTrxEndCallbackSuppression( true );
1226                 } );
1227         }
1228
1229         /**
1230          * @param IDatabase $conn
1231          */
1232         private function applyTransactionRoundFlags( IDatabase $conn ) {
1233                 if ( $conn->getFlag( $conn::DBO_DEFAULT ) ) {
1234                         // DBO_TRX is controlled entirely by CLI mode presence with DBO_DEFAULT.
1235                         // Force DBO_TRX even in CLI mode since a commit round is expected soon.
1236                         $conn->setFlag( $conn::DBO_TRX, $conn::REMEMBER_PRIOR );
1237                         // If config has explicitly requested DBO_TRX be either on or off by not
1238                         // setting DBO_DEFAULT, then respect that. Forcing no transactions is useful
1239                         // for things like blob stores (ExternalStore) which want auto-commit mode.
1240                 }
1241         }
1242
1243         /**
1244          * @param IDatabase $conn
1245          */
1246         private function undoTransactionRoundFlags( IDatabase $conn ) {
1247                 if ( $conn->getFlag( $conn::DBO_DEFAULT ) ) {
1248                         $conn->restoreFlags( $conn::RESTORE_PRIOR );
1249                 }
1250         }
1251
1252         public function flushReplicaSnapshots( $fname = __METHOD__ ) {
1253                 $this->forEachOpenReplicaConnection( function ( IDatabase $conn ) {
1254                         $conn->flushSnapshot( __METHOD__ );
1255                 } );
1256         }
1257
1258         public function hasMasterConnection() {
1259                 return $this->isOpen( $this->getWriterIndex() );
1260         }
1261
1262         public function hasMasterChanges() {
1263                 $pending = 0;
1264                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$pending ) {
1265                         $pending |= $conn->writesOrCallbacksPending();
1266                 } );
1267
1268                 return (bool)$pending;
1269         }
1270
1271         public function lastMasterChangeTimestamp() {
1272                 $lastTime = false;
1273                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$lastTime ) {
1274                         $lastTime = max( $lastTime, $conn->lastDoneWrites() );
1275                 } );
1276
1277                 return $lastTime;
1278         }
1279
1280         public function hasOrMadeRecentMasterChanges( $age = null ) {
1281                 $age = ( $age === null ) ? $this->mWaitTimeout : $age;
1282
1283                 return ( $this->hasMasterChanges()
1284                         || $this->lastMasterChangeTimestamp() > microtime( true ) - $age );
1285         }
1286
1287         public function pendingMasterChangeCallers() {
1288                 $fnames = [];
1289                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$fnames ) {
1290                         $fnames = array_merge( $fnames, $conn->pendingWriteCallers() );
1291                 } );
1292
1293                 return $fnames;
1294         }
1295
1296         public function getLaggedReplicaMode( $domain = false ) {
1297                 // No-op if there is only one DB (also avoids recursion)
1298                 if ( !$this->laggedReplicaMode && $this->getServerCount() > 1 ) {
1299                         try {
1300                                 // See if laggedReplicaMode gets set
1301                                 $conn = $this->getConnection( self::DB_REPLICA, false, $domain );
1302                                 $this->reuseConnection( $conn );
1303                         } catch ( DBConnectionError $e ) {
1304                                 // Avoid expensive re-connect attempts and failures
1305                                 $this->allReplicasDownMode = true;
1306                                 $this->laggedReplicaMode = true;
1307                         }
1308                 }
1309
1310                 return $this->laggedReplicaMode;
1311         }
1312
1313         /**
1314          * @param bool $domain
1315          * @return bool
1316          * @deprecated 1.28; use getLaggedReplicaMode()
1317          */
1318         public function getLaggedSlaveMode( $domain = false ) {
1319                 return $this->getLaggedReplicaMode( $domain );
1320         }
1321
1322         public function laggedReplicaUsed() {
1323                 return $this->laggedReplicaMode;
1324         }
1325
1326         /**
1327          * @return bool
1328          * @since 1.27
1329          * @deprecated Since 1.28; use laggedReplicaUsed()
1330          */
1331         public function laggedSlaveUsed() {
1332                 return $this->laggedReplicaUsed();
1333         }
1334
1335         public function getReadOnlyReason( $domain = false, IDatabase $conn = null ) {
1336                 if ( $this->readOnlyReason !== false ) {
1337                         return $this->readOnlyReason;
1338                 } elseif ( $this->getLaggedReplicaMode( $domain ) ) {
1339                         if ( $this->allReplicasDownMode ) {
1340                                 return 'The database has been automatically locked ' .
1341                                         'until the replica database servers become available';
1342                         } else {
1343                                 return 'The database has been automatically locked ' .
1344                                         'while the replica database servers catch up to the master.';
1345                         }
1346                 } elseif ( $this->masterRunningReadOnly( $domain, $conn ) ) {
1347                         return 'The database master is running in read-only mode.';
1348                 }
1349
1350                 return false;
1351         }
1352
1353         /**
1354          * @param string $domain Domain ID, or false for the current domain
1355          * @param IDatabase|null DB master connectionl used to avoid loops [optional]
1356          * @return bool
1357          */
1358         private function masterRunningReadOnly( $domain, IDatabase $conn = null ) {
1359                 $cache = $this->wanCache;
1360                 $masterServer = $this->getServerName( $this->getWriterIndex() );
1361
1362                 return (bool)$cache->getWithSetCallback(
1363                         $cache->makeGlobalKey( __CLASS__, 'server-read-only', $masterServer ),
1364                         self::TTL_CACHE_READONLY,
1365                         function () use ( $domain, $conn ) {
1366                                 $old = $this->trxProfiler->setSilenced( true );
1367                                 try {
1368                                         $dbw = $conn ?: $this->getConnection( self::DB_MASTER, [], $domain );
1369                                         $readOnly = (int)$dbw->serverIsReadOnly();
1370                                         if ( !$conn ) {
1371                                                 $this->reuseConnection( $dbw );
1372                                         }
1373                                 } catch ( DBError $e ) {
1374                                         $readOnly = 0;
1375                                 }
1376                                 $this->trxProfiler->setSilenced( $old );
1377                                 return $readOnly;
1378                         },
1379                         [ 'pcTTL' => $cache::TTL_PROC_LONG, 'busyValue' => 0 ]
1380                 );
1381         }
1382
1383         public function allowLagged( $mode = null ) {
1384                 if ( $mode === null ) {
1385                         return $this->mAllowLagged;
1386                 }
1387                 $this->mAllowLagged = $mode;
1388
1389                 return $this->mAllowLagged;
1390         }
1391
1392         public function pingAll() {
1393                 $success = true;
1394                 $this->forEachOpenConnection( function ( IDatabase $conn ) use ( &$success ) {
1395                         if ( !$conn->ping() ) {
1396                                 $success = false;
1397                         }
1398                 } );
1399
1400                 return $success;
1401         }
1402
1403         public function forEachOpenConnection( $callback, array $params = [] ) {
1404                 foreach ( $this->mConns as $connsByServer ) {
1405                         foreach ( $connsByServer as $serverConns ) {
1406                                 foreach ( $serverConns as $conn ) {
1407                                         $mergedParams = array_merge( [ $conn ], $params );
1408                                         call_user_func_array( $callback, $mergedParams );
1409                                 }
1410                         }
1411                 }
1412         }
1413
1414         public function forEachOpenMasterConnection( $callback, array $params = [] ) {
1415                 $masterIndex = $this->getWriterIndex();
1416                 foreach ( $this->mConns as $connsByServer ) {
1417                         if ( isset( $connsByServer[$masterIndex] ) ) {
1418                                 /** @var IDatabase $conn */
1419                                 foreach ( $connsByServer[$masterIndex] as $conn ) {
1420                                         $mergedParams = array_merge( [ $conn ], $params );
1421                                         call_user_func_array( $callback, $mergedParams );
1422                                 }
1423                         }
1424                 }
1425         }
1426
1427         public function forEachOpenReplicaConnection( $callback, array $params = [] ) {
1428                 foreach ( $this->mConns as $connsByServer ) {
1429                         foreach ( $connsByServer as $i => $serverConns ) {
1430                                 if ( $i === $this->getWriterIndex() ) {
1431                                         continue; // skip master
1432                                 }
1433                                 foreach ( $serverConns as $conn ) {
1434                                         $mergedParams = array_merge( [ $conn ], $params );
1435                                         call_user_func_array( $callback, $mergedParams );
1436                                 }
1437                         }
1438                 }
1439         }
1440
1441         public function getMaxLag( $domain = false ) {
1442                 $maxLag = -1;
1443                 $host = '';
1444                 $maxIndex = 0;
1445
1446                 if ( $this->getServerCount() <= 1 ) {
1447                         return [ $host, $maxLag, $maxIndex ]; // no replication = no lag
1448                 }
1449
1450                 $lagTimes = $this->getLagTimes( $domain );
1451                 foreach ( $lagTimes as $i => $lag ) {
1452                         if ( $this->mLoads[$i] > 0 && $lag > $maxLag ) {
1453                                 $maxLag = $lag;
1454                                 $host = $this->mServers[$i]['host'];
1455                                 $maxIndex = $i;
1456                         }
1457                 }
1458
1459                 return [ $host, $maxLag, $maxIndex ];
1460         }
1461
1462         public function getLagTimes( $domain = false ) {
1463                 if ( $this->getServerCount() <= 1 ) {
1464                         return [ $this->getWriterIndex() => 0 ]; // no replication = no lag
1465                 }
1466
1467                 $knownLagTimes = []; // map of (server index => 0 seconds)
1468                 $indexesWithLag = [];
1469                 foreach ( $this->mServers as $i => $server ) {
1470                         if ( empty( $server['is static'] ) ) {
1471                                 $indexesWithLag[] = $i; // DB server might have replication lag
1472                         } else {
1473                                 $knownLagTimes[$i] = 0; // DB server is a non-replicating and read-only archive
1474                         }
1475                 }
1476
1477                 return $this->getLoadMonitor()->getLagTimes( $indexesWithLag, $domain ) + $knownLagTimes;
1478         }
1479
1480         public function safeGetLag( IDatabase $conn ) {
1481                 if ( $this->getServerCount() <= 1 ) {
1482                         return 0;
1483                 } else {
1484                         return $conn->getLag();
1485                 }
1486         }
1487
1488         /**
1489          * @param IDatabase $conn
1490          * @param DBMasterPos|bool $pos
1491          * @param int $timeout
1492          * @return bool
1493          */
1494         public function safeWaitForMasterPos( IDatabase $conn, $pos = false, $timeout = 10 ) {
1495                 if ( $this->getServerCount() <= 1 || !$conn->getLBInfo( 'replica' ) ) {
1496                         return true; // server is not a replica DB
1497                 }
1498
1499                 if ( !$pos ) {
1500                         // Get the current master position, opening a connection if needed
1501                         $masterConn = $this->getAnyOpenConnection( $this->getWriterIndex() );
1502                         if ( $masterConn ) {
1503                                 $pos = $masterConn->getMasterPos();
1504                         } else {
1505                                 $masterConn = $this->openConnection( $this->getWriterIndex(), self::DOMAIN_ANY );
1506                                 $pos = $masterConn->getMasterPos();
1507                                 $this->closeConnection( $masterConn );
1508                         }
1509                 }
1510
1511                 if ( $pos instanceof DBMasterPos ) {
1512                         $result = $conn->masterPosWait( $pos, $timeout );
1513                         if ( $result == -1 || is_null( $result ) ) {
1514                                 $msg = __METHOD__ . ": Timed out waiting on {$conn->getServer()} pos {$pos}";
1515                                 $this->replLogger->warning( "$msg" );
1516                                 $ok = false;
1517                         } else {
1518                                 $this->replLogger->info( __METHOD__ . ": Done" );
1519                                 $ok = true;
1520                         }
1521                 } else {
1522                         $ok = false; // something is misconfigured
1523                         $this->replLogger->error( "Could not get master pos for {$conn->getServer()}." );
1524                 }
1525
1526                 return $ok;
1527         }
1528
1529         public function setTransactionListener( $name, callable $callback = null ) {
1530                 if ( $callback ) {
1531                         $this->trxRecurringCallbacks[$name] = $callback;
1532                 } else {
1533                         unset( $this->trxRecurringCallbacks[$name] );
1534                 }
1535                 $this->forEachOpenMasterConnection(
1536                         function ( IDatabase $conn ) use ( $name, $callback ) {
1537                                 $conn->setTransactionListener( $name, $callback );
1538                         }
1539                 );
1540         }
1541
1542         public function setTableAliases( array $aliases ) {
1543                 $this->tableAliases = $aliases;
1544         }
1545
1546         public function setDomainPrefix( $prefix ) {
1547                 if ( $this->mConns['foreignUsed'] ) {
1548                         // Do not switch connections to explicit foreign domains unless marked as free
1549                         $domains = [];
1550                         foreach ( $this->mConns['foreignUsed'] as $i => $connsByDomain ) {
1551                                 $domains = array_merge( $domains, array_keys( $connsByDomain ) );
1552                         }
1553                         $domains = implode( ', ', $domains );
1554                         throw new DBUnexpectedError( null,
1555                                 "Foreign domain connections are still in use ($domains)." );
1556                 }
1557
1558                 $this->localDomain = new DatabaseDomain(
1559                         $this->localDomain->getDatabase(),
1560                         null,
1561                         $prefix
1562                 );
1563
1564                 $this->forEachOpenConnection( function ( IDatabase $db ) use ( $prefix ) {
1565                         $db->tablePrefix( $prefix );
1566                 } );
1567         }
1568
1569         /**
1570          * Make PHP ignore user aborts/disconnects until the returned
1571          * value leaves scope. This returns null and does nothing in CLI mode.
1572          *
1573          * @return ScopedCallback|null
1574          */
1575         final protected function getScopedPHPBehaviorForCommit() {
1576                 if ( PHP_SAPI != 'cli' ) { // https://bugs.php.net/bug.php?id=47540
1577                         $old = ignore_user_abort( true ); // avoid half-finished operations
1578                         return new ScopedCallback( function () use ( $old ) {
1579                                 ignore_user_abort( $old );
1580                         } );
1581                 }
1582
1583                 return null;
1584         }
1585
1586         function __destruct() {
1587                 // Avoid connection leaks for sanity
1588                 $this->disable();
1589         }
1590 }