includes/libs/rdbms/loadbalancer/LoadBalancer.php

   1 <?php
   2 /**
   3  * Database load balancing manager
   4  *
   5  * This program is free software; you can redistribute it and/or modify
   6  * it under the terms of the GNU General Public License as published by
   7  * the Free Software Foundation; either version 2 of the License, or
   8  * (at your option) any later version.
   9  *
  10  * This program is distributed in the hope that it will be useful,
  11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  13  * GNU General Public License for more details.
  14  *
  15  * You should have received a copy of the GNU General Public License along
  16  * with this program; if not, write to the Free Software Foundation, Inc.,
  17  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
  18  * http://www.gnu.org/copyleft/gpl.html
  19  *
  20  * @file
  21  * @ingroup Database
  22  */
  23 use Psr\Log\LoggerInterface;
  24
  25 /**
  26  * Database connection, tracking, load balancing, and transaction manager for a cluster
  27  *
  28  * @ingroup Database
  29  */
  30 class LoadBalancer implements ILoadBalancer {
  31         /** @var array[] Map of (server index => server config array) */
  32         private $mServers;
  33         /** @var array[] Map of (local/foreignUsed/foreignFree => server index => IDatabase array) */
  34         private $mConns;
  35         /** @var float[] Map of (server index => weight) */
  36         private $mLoads;
  37         /** @var array[] Map of (group => server index => weight) */
  38         private $mGroupLoads;
  39         /** @var bool Whether to disregard replica DB lag as a factor in replica DB selection */
  40         private $mAllowLagged;
  41         /** @var integer Seconds to spend waiting on replica DB lag to resolve */
  42         private $mWaitTimeout;
  43         /** @var array The LoadMonitor configuration */
  44         private $loadMonitorConfig;
  45         /** @var array[] $aliases Map of (table => (dbname, schema, prefix) map) */
  46         private $tableAliases = [];
  47
  48         /** @var ILoadMonitor */
  49         private $loadMonitor;
  50         /** @var BagOStuff */
  51         private $srvCache;
  52         /** @var BagOStuff */
  53         private $memCache;
  54         /** @var WANObjectCache */
  55         private $wanCache;
  56         /** @var object|string Class name or object With profileIn/profileOut methods */
  57         protected $profiler;
  58         /** @var TransactionProfiler */
  59         protected $trxProfiler;
  60         /** @var LoggerInterface */
  61         protected $replLogger;
  62         /** @var LoggerInterface */
  63         protected $connLogger;
  64         /** @var LoggerInterface */
  65         protected $queryLogger;
  66         /** @var LoggerInterface */
  67         protected $perfLogger;
  68
  69         /** @var bool|IDatabase Database connection that caused a problem */
  70         private $mErrorConnection;
  71         /** @var integer The generic (not query grouped) replica DB index (of $mServers) */
  72         private $mReadIndex;
  73         /** @var bool|DBMasterPos False if not set */
  74         private $mWaitForPos;
  75         /** @var bool Whether the generic reader fell back to a lagged replica DB */
  76         private $laggedReplicaMode = false;
  77         /** @var bool Whether the generic reader fell back to a lagged replica DB */
  78         private $allReplicasDownMode = false;
  79         /** @var string The last DB selection or connection error */
  80         private $mLastError = 'Unknown error';
  81         /** @var string|bool Reason the LB is read-only or false if not */
  82         private $readOnlyReason = false;
  83         /** @var integer Total connections opened */
  84         private $connsOpened = 0;
  85         /** @var string|bool String if a requested DBO_TRX transaction round is active */
  86         private $trxRoundId = false;
  87         /** @var array[] Map of (name => callable) */
  88         private $trxRecurringCallbacks = [];
  89         /** @var DatabaseDomain Local Domain ID and default for selectDB() calls */
  90         private $localDomain;
  91         /** @var string Alternate ID string for the domain instead of DatabaseDomain::getId() */
  92         private $localDomainIdAlias;
  93         /** @var string Current server name */
  94         private $host;
  95         /** @var bool Whether this PHP instance is for a CLI script */
  96         protected $cliMode;
  97         /** @var string Agent name for query profiling */
  98         protected $agent;
  99
 100         /** @var callable Exception logger */
 101         private $errorLogger;
 102
 103         /** @var boolean */
 104         private $disabled = false;
 105
 106         /** @var integer Warn when this many connection are held */
 107         const CONN_HELD_WARN_THRESHOLD = 10;
 108
 109         /** @var integer Default 'max lag' when unspecified */
 110         const MAX_LAG_DEFAULT = 10;
 111         /** @var integer Seconds to cache master server read-only status */
 112         const TTL_CACHE_READONLY = 5;
 113
 114         public function __construct( array $params ) {
 115                 if ( !isset( $params['servers'] ) ) {
 116                         throw new InvalidArgumentException( __CLASS__ . ': missing servers parameter' );
 117                 }
 118                 $this->mServers = $params['servers'];
 119
 120                 $this->localDomain = isset( $params['localDomain'] )
 121                         ? DatabaseDomain::newFromId( $params['localDomain'] )
 122                         : DatabaseDomain::newUnspecified();
 123                 // In case a caller assumes that the domain ID is simply <db>-<prefix>, which is almost
 124                 // always true, gracefully handle the case when they fail to account for escaping.
 125                 if ( $this->localDomain->getTablePrefix() != '' ) {
 126                         $this->localDomainIdAlias =
 127                                 $this->localDomain->getDatabase() . '-' . $this->localDomain->getTablePrefix();
 128                 } else {
 129                         $this->localDomainIdAlias = $this->localDomain->getDatabase();
 130                 }
 131
 132                 $this->mWaitTimeout = isset( $params['waitTimeout'] ) ? $params['waitTimeout'] : 10;
 133
 134                 $this->mReadIndex = -1;
 135                 $this->mConns = [
 136                         'local'       => [],
 137                         'foreignUsed' => [],
 138                         'foreignFree' => []
 139                 ];
 140                 $this->mLoads = [];
 141                 $this->mWaitForPos = false;
 142                 $this->mErrorConnection = false;
 143                 $this->mAllowLagged = false;
 144
 145                 if ( isset( $params['readOnlyReason'] ) && is_string( $params['readOnlyReason'] ) ) {
 146                         $this->readOnlyReason = $params['readOnlyReason'];
 147                 }
 148
 149                 if ( isset( $params['loadMonitor'] ) ) {
 150                         $this->loadMonitorConfig = $params['loadMonitor'];
 151                 } else {
 152                         $this->loadMonitorConfig = [ 'class' => 'LoadMonitorNull' ];
 153                 }
 154
 155                 foreach ( $params['servers'] as $i => $server ) {
 156                         $this->mLoads[$i] = $server['load'];
 157                         if ( isset( $server['groupLoads'] ) ) {
 158                                 foreach ( $server['groupLoads'] as $group => $ratio ) {
 159                                         if ( !isset( $this->mGroupLoads[$group] ) ) {
 160                                                 $this->mGroupLoads[$group] = [];
 161                                         }
 162                                         $this->mGroupLoads[$group][$i] = $ratio;
 163                                 }
 164                         }
 165                 }
 166
 167                 if ( isset( $params['srvCache'] ) ) {
 168                         $this->srvCache = $params['srvCache'];
 169                 } else {
 170                         $this->srvCache = new EmptyBagOStuff();
 171                 }
 172                 if ( isset( $params['memCache'] ) ) {
 173                         $this->memCache = $params['memCache'];
 174                 } else {
 175                         $this->memCache = new EmptyBagOStuff();
 176                 }
 177                 if ( isset( $params['wanCache'] ) ) {
 178                         $this->wanCache = $params['wanCache'];
 179                 } else {
 180                         $this->wanCache = WANObjectCache::newEmpty();
 181                 }
 182                 $this->profiler = isset( $params['profiler'] ) ? $params['profiler'] : null;
 183                 if ( isset( $params['trxProfiler'] ) ) {
 184                         $this->trxProfiler = $params['trxProfiler'];
 185                 } else {
 186                         $this->trxProfiler = new TransactionProfiler();
 187                 }
 188
 189                 $this->errorLogger = isset( $params['errorLogger'] )
 190                         ? $params['errorLogger']
 191                         : function ( Exception $e ) {
 192                                 trigger_error( get_class( $e ) . ': ' . $e->getMessage(), E_WARNING );
 193                         };
 194
 195                 foreach ( [ 'replLogger', 'connLogger', 'queryLogger', 'perfLogger' ] as $key ) {
 196                         $this->$key = isset( $params[$key] ) ? $params[$key] : new \Psr\Log\NullLogger();
 197                 }
 198
 199                 $this->host = isset( $params['hostname'] )
 200                         ? $params['hostname']
 201                         : ( gethostname() ?: 'unknown' );
 202                 $this->cliMode = isset( $params['cliMode'] ) ? $params['cliMode'] : PHP_SAPI === 'cli';
 203                 $this->agent = isset( $params['agent'] ) ? $params['agent'] : '';
 204         }
 205
 206         /**
 207          * Get a LoadMonitor instance
 208          *
 209          * @return ILoadMonitor
 210          */
 211         private function getLoadMonitor() {
 212                 if ( !isset( $this->loadMonitor ) ) {
 213                         $class = $this->loadMonitorConfig['class'];
 214                         $this->loadMonitor = new $class(
 215                                 $this, $this->srvCache, $this->memCache, $this->loadMonitorConfig );
 216                         $this->loadMonitor->setLogger( $this->replLogger );
 217                 }
 218
 219                 return $this->loadMonitor;
 220         }
 221
 222         /**
 223          * @param array $loads
 224          * @param bool|string $domain Domain to get non-lagged for
 225          * @param int $maxLag Restrict the maximum allowed lag to this many seconds
 226          * @return bool|int|string
 227          */
 228         private function getRandomNonLagged( array $loads, $domain = false, $maxLag = INF ) {
 229                 $lags = $this->getLagTimes( $domain );
 230
 231                 # Unset excessively lagged servers
 232                 foreach ( $lags as $i => $lag ) {
 233                         if ( $i != 0 ) {
 234                                 # How much lag this server nominally is allowed to have
 235                                 $maxServerLag = isset( $this->mServers[$i]['max lag'] )
 236                                         ? $this->mServers[$i]['max lag']
 237                                         : self::MAX_LAG_DEFAULT; // default
 238                                 # Constrain that futher by $maxLag argument
 239                                 $maxServerLag = min( $maxServerLag, $maxLag );
 240
 241                                 $host = $this->getServerName( $i );
 242                                 if ( $lag === false && !is_infinite( $maxServerLag ) ) {
 243                                         $this->replLogger->error( "Server $host (#$i) is not replicating?" );
 244                                         unset( $loads[$i] );
 245                                 } elseif ( $lag > $maxServerLag ) {
 246                                         $this->replLogger->warning( "Server $host (#$i) has >= $lag seconds of lag" );
 247                                         unset( $loads[$i] );
 248                                 }
 249                         }
 250                 }
 251
 252                 # Find out if all the replica DBs with non-zero load are lagged
 253                 $sum = 0;
 254                 foreach ( $loads as $load ) {
 255                         $sum += $load;
 256                 }
 257                 if ( $sum == 0 ) {
 258                         # No appropriate DB servers except maybe the master and some replica DBs with zero load
 259                         # Do NOT use the master
 260                         # Instead, this function will return false, triggering read-only mode,
 261                         # and a lagged replica DB will be used instead.
 262                         return false;
 263                 }
 264
 265                 if ( count( $loads ) == 0 ) {
 266                         return false;
 267                 }
 268
 269                 # Return a random representative of the remainder
 270                 return ArrayUtils::pickRandom( $loads );
 271         }
 272
 273         public function getReaderIndex( $group = false, $domain = false ) {
 274                 if ( count( $this->mServers ) == 1 ) {
 275                         # Skip the load balancing if there's only one server
 276                         return $this->getWriterIndex();
 277                 } elseif ( $group === false && $this->mReadIndex >= 0 ) {
 278                         # Shortcut if generic reader exists already
 279                         return $this->mReadIndex;
 280                 }
 281
 282                 # Find the relevant load array
 283                 if ( $group !== false ) {
 284                         if ( isset( $this->mGroupLoads[$group] ) ) {
 285                                 $nonErrorLoads = $this->mGroupLoads[$group];
 286                         } else {
 287                                 # No loads for this group, return false and the caller can use some other group
 288                                 $this->connLogger->info( __METHOD__ . ": no loads for group $group" );
 289
 290                                 return false;
 291                         }
 292                 } else {
 293                         $nonErrorLoads = $this->mLoads;
 294                 }
 295
 296                 if ( !count( $nonErrorLoads ) ) {
 297                         throw new InvalidArgumentException( "Empty server array given to LoadBalancer" );
 298                 }
 299
 300                 # Scale the configured load ratios according to the dynamic load if supported
 301                 $this->getLoadMonitor()->scaleLoads( $nonErrorLoads, $domain );
 302
 303                 $laggedReplicaMode = false;
 304
 305                 # No server found yet
 306                 $i = false;
 307                 # First try quickly looking through the available servers for a server that
 308                 # meets our criteria
 309                 $currentLoads = $nonErrorLoads;
 310                 while ( count( $currentLoads ) ) {
 311                         if ( $this->mAllowLagged || $laggedReplicaMode ) {
 312                                 $i = ArrayUtils::pickRandom( $currentLoads );
 313                         } else {
 314                                 $i = false;
 315                                 if ( $this->mWaitForPos && $this->mWaitForPos->asOfTime() ) {
 316                                         # ChronologyProtecter causes mWaitForPos to be set via sessions.
 317                                         # This triggers doWait() after connect, so it's especially good to
 318                                         # avoid lagged servers so as to avoid just blocking in that method.
 319                                         $ago = microtime( true ) - $this->mWaitForPos->asOfTime();
 320                                         # Aim for <= 1 second of waiting (being too picky can backfire)
 321                                         $i = $this->getRandomNonLagged( $currentLoads, $domain, $ago + 1 );
 322                                 }
 323                                 if ( $i === false ) {
 324                                         # Any server with less lag than it's 'max lag' param is preferable
 325                                         $i = $this->getRandomNonLagged( $currentLoads, $domain );
 326                                 }
 327                                 if ( $i === false && count( $currentLoads ) != 0 ) {
 328                                         # All replica DBs lagged. Switch to read-only mode
 329                                         $this->replLogger->error( "All replica DBs lagged. Switch to read-only mode" );
 330                                         $i = ArrayUtils::pickRandom( $currentLoads );
 331                                         $laggedReplicaMode = true;
 332                                 }
 333                         }
 334
 335                         if ( $i === false ) {
 336                                 # pickRandom() returned false
 337                                 # This is permanent and means the configuration or the load monitor
 338                                 # wants us to return false.
 339                                 $this->connLogger->debug( __METHOD__ . ": pickRandom() returned false" );
 340
 341                                 return false;
 342                         }
 343
 344                         $serverName = $this->getServerName( $i );
 345                         $this->connLogger->debug( __METHOD__ . ": Using reader #$i: $serverName..." );
 346
 347                         $conn = $this->openConnection( $i, $domain );
 348                         if ( !$conn ) {
 349                                 $this->connLogger->warning( __METHOD__ . ": Failed connecting to $i/$domain" );
 350                                 unset( $nonErrorLoads[$i] );
 351                                 unset( $currentLoads[$i] );
 352                                 $i = false;
 353                                 continue;
 354                         }
 355
 356                         // Decrement reference counter, we are finished with this connection.
 357                         // It will be incremented for the caller later.
 358                         if ( $domain !== false ) {
 359                                 $this->reuseConnection( $conn );
 360                         }
 361
 362                         # Return this server
 363                         break;
 364                 }
 365
 366                 # If all servers were down, quit now
 367                 if ( !count( $nonErrorLoads ) ) {
 368                         $this->connLogger->error( "All servers down" );
 369                 }
 370
 371                 if ( $i !== false ) {
 372                         # Replica DB connection successful.
 373                         # Wait for the session master pos for a short time.
 374                         if ( $this->mWaitForPos && $i > 0 ) {
 375                                 $this->doWait( $i );
 376                         }
 377                         if ( $this->mReadIndex <= 0 && $this->mLoads[$i] > 0 && $group === false ) {
 378                                 $this->mReadIndex = $i;
 379                                 # Record if the generic reader index is in "lagged replica DB" mode
 380                                 if ( $laggedReplicaMode ) {
 381                                         $this->laggedReplicaMode = true;
 382                                 }
 383                         }
 384                         $serverName = $this->getServerName( $i );
 385                         $this->connLogger->debug(
 386                                 __METHOD__ . ": using server $serverName for group '$group'" );
 387                 }
 388
 389                 return $i;
 390         }
 391
 392         public function waitFor( $pos ) {
 393                 $this->mWaitForPos = $pos;
 394                 $i = $this->mReadIndex;
 395
 396                 if ( $i > 0 ) {
 397                         if ( !$this->doWait( $i ) ) {
 398                                 $this->laggedReplicaMode = true;
 399                         }
 400                 }
 401         }
 402
 403         public function waitForOne( $pos, $timeout = null ) {
 404                 $this->mWaitForPos = $pos;
 405
 406                 $i = $this->mReadIndex;
 407                 if ( $i <= 0 ) {
 408                         // Pick a generic replica DB if there isn't one yet
 409                         $readLoads = $this->mLoads;
 410                         unset( $readLoads[$this->getWriterIndex()] ); // replica DBs only
 411                         $readLoads = array_filter( $readLoads ); // with non-zero load
 412                         $i = ArrayUtils::pickRandom( $readLoads );
 413                 }
 414
 415                 if ( $i > 0 ) {
 416                         $ok = $this->doWait( $i, true, $timeout );
 417                 } else {
 418                         $ok = true; // no applicable loads
 419                 }
 420
 421                 return $ok;
 422         }
 423
 424         public function waitForAll( $pos, $timeout = null ) {
 425                 $this->mWaitForPos = $pos;
 426                 $serverCount = count( $this->mServers );
 427
 428                 $ok = true;
 429                 for ( $i = 1; $i < $serverCount; $i++ ) {
 430                         if ( $this->mLoads[$i] > 0 ) {
 431                                 $ok = $this->doWait( $i, true, $timeout ) && $ok;
 432                         }
 433                 }
 434
 435                 return $ok;
 436         }
 437
 438         public function getAnyOpenConnection( $i ) {
 439                 foreach ( $this->mConns as $connsByServer ) {
 440                         if ( !empty( $connsByServer[$i] ) ) {
 441                                 return reset( $connsByServer[$i] );
 442                         }
 443                 }
 444
 445                 return false;
 446         }
 447
 448         /**
 449          * Wait for a given replica DB to catch up to the master pos stored in $this
 450          * @param int $index Server index
 451          * @param bool $open Check the server even if a new connection has to be made
 452          * @param int $timeout Max seconds to wait; default is mWaitTimeout
 453          * @return bool
 454          */
 455         protected function doWait( $index, $open = false, $timeout = null ) {
 456                 $close = false; // close the connection afterwards
 457
 458                 // Check if we already know that the DB has reached this point
 459                 $server = $this->getServerName( $index );
 460                 $key = $this->srvCache->makeGlobalKey( __CLASS__, 'last-known-pos', $server );
 461                 /** @var DBMasterPos $knownReachedPos */
 462                 $knownReachedPos = $this->srvCache->get( $key );
 463                 if ( $knownReachedPos && $knownReachedPos->hasReached( $this->mWaitForPos ) ) {
 464                         $this->replLogger->debug( __METHOD__ .
 465                                 ": replica DB $server known to be caught up (pos >= $knownReachedPos)." );
 466                         return true;
 467                 }
 468
 469                 // Find a connection to wait on, creating one if needed and allowed
 470                 $conn = $this->getAnyOpenConnection( $index );
 471                 if ( !$conn ) {
 472                         if ( !$open ) {
 473                                 $this->replLogger->debug( __METHOD__ . ": no connection open for $server" );
 474
 475                                 return false;
 476                         } else {
 477                                 $conn = $this->openConnection( $index, self::DOMAIN_ANY );
 478                                 if ( !$conn ) {
 479                                         $this->replLogger->warning( __METHOD__ . ": failed to connect to $server" );
 480
 481                                         return false;
 482                                 }
 483                                 // Avoid connection spam in waitForAll() when connections
 484                                 // are made just for the sake of doing this lag check.
 485                                 $close = true;
 486                         }
 487                 }
 488
 489                 $this->replLogger->info( __METHOD__ . ": Waiting for replica DB $server to catch up..." );
 490                 $timeout = $timeout ?: $this->mWaitTimeout;
 491                 $result = $conn->masterPosWait( $this->mWaitForPos, $timeout );
 492
 493                 if ( $result == -1 || is_null( $result ) ) {
 494                         // Timed out waiting for replica DB, use master instead
 495                         $msg = __METHOD__ . ": Timed out waiting on $server pos {$this->mWaitForPos}";
 496                         $this->replLogger->warning( "$msg" );
 497                         $ok = false;
 498                 } else {
 499                         $this->replLogger->info( __METHOD__ . ": Done" );
 500                         $ok = true;
 501                         // Remember that the DB reached this point
 502                         $this->srvCache->set( $key, $this->mWaitForPos, BagOStuff::TTL_DAY );
 503                 }
 504
 505                 if ( $close ) {
 506                         $this->closeConnection( $conn );
 507                 }
 508
 509                 return $ok;
 510         }
 511
 512         /**
 513          * @see ILoadBalancer::getConnection()
 514          *
 515          * @param int $i
 516          * @param array $groups
 517          * @param bool $domain
 518          * @return Database
 519          * @throws DBConnectionError
 520          */
 521         public function getConnection( $i, $groups = [], $domain = false ) {
 522                 if ( $i === null || $i === false ) {
 523                         throw new InvalidArgumentException( 'Attempt to call ' . __METHOD__ .
 524                                 ' with invalid server index' );
 525                 }
 526
 527                 if ( $this->localDomain->equals( $domain ) || $domain === $this->localDomainIdAlias ) {
 528                         $domain = false; // local connection requested
 529                 }
 530
 531                 $groups = ( $groups === false || $groups === [] )
 532                         ? [ false ] // check one "group": the generic pool
 533                         : (array)$groups;
 534
 535                 $masterOnly = ( $i == self::DB_MASTER || $i == $this->getWriterIndex() );
 536                 $oldConnsOpened = $this->connsOpened; // connections open now
 537
 538                 if ( $i == self::DB_MASTER ) {
 539                         $i = $this->getWriterIndex();
 540                 } else {
 541                         # Try to find an available server in any the query groups (in order)
 542                         foreach ( $groups as $group ) {
 543                                 $groupIndex = $this->getReaderIndex( $group, $domain );
 544                                 if ( $groupIndex !== false ) {
 545                                         $i = $groupIndex;
 546                                         break;
 547                                 }
 548                         }
 549                 }
 550
 551                 # Operation-based index
 552                 if ( $i == self::DB_REPLICA ) {
 553                         $this->mLastError = 'Unknown error'; // reset error string
 554                         # Try the general server pool if $groups are unavailable.
 555                         $i = in_array( false, $groups, true )
 556                                 ? false // don't bother with this if that is what was tried above
 557                                 : $this->getReaderIndex( false, $domain );
 558                         # Couldn't find a working server in getReaderIndex()?
 559                         if ( $i === false ) {
 560                                 $this->mLastError = 'No working replica DB server: ' . $this->mLastError;
 561                                 // Throw an exception
 562                                 $this->reportConnectionError();
 563                                 return null; // not reached
 564                         }
 565                 }
 566
 567                 # Now we have an explicit index into the servers array
 568                 $conn = $this->openConnection( $i, $domain );
 569                 if ( !$conn ) {
 570                         // Throw an exception
 571                         $this->reportConnectionError();
 572                         return null; // not reached
 573                 }
 574
 575                 # Profile any new connections that happen
 576                 if ( $this->connsOpened > $oldConnsOpened ) {
 577                         $host = $conn->getServer();
 578                         $dbname = $conn->getDBname();
 579                         $this->trxProfiler->recordConnection( $host, $dbname, $masterOnly );
 580                 }
 581
 582                 if ( $masterOnly ) {
 583                         # Make master-requested DB handles inherit any read-only mode setting
 584                         $conn->setLBInfo( 'readOnlyReason', $this->getReadOnlyReason( $domain, $conn ) );
 585                 }
 586
 587                 return $conn;
 588         }
 589
 590         public function reuseConnection( $conn ) {
 591                 $serverIndex = $conn->getLBInfo( 'serverIndex' );
 592                 $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 593                 if ( $serverIndex === null || $refCount === null ) {
 594                         /**
 595                          * This can happen in code like:
 596                          *   foreach ( $dbs as $db ) {
 597                          *     $conn = $lb->getConnection( $lb::DB_REPLICA, [], $db );
 598                          *     ...
 599                          *     $lb->reuseConnection( $conn );
 600                          *   }
 601                          * When a connection to the local DB is opened in this way, reuseConnection()
 602                          * should be ignored
 603                          */
 604                         return;
 605                 } elseif ( $conn instanceof DBConnRef ) {
 606                         // DBConnRef already handles calling reuseConnection() and only passes the live
 607                         // Database instance to this method. Any caller passing in a DBConnRef is broken.
 608                         $this->connLogger->error( __METHOD__ . ": got DBConnRef instance.\n" .
 609                                 ( new RuntimeException() )->getTraceAsString() );
 610
 611                         return;
 612                 }
 613
 614                 if ( $this->disabled ) {
 615                         return; // DBConnRef handle probably survived longer than the LoadBalancer
 616                 }
 617
 618                 $domain = $conn->getDomainID();
 619                 if ( !isset( $this->mConns['foreignUsed'][$serverIndex][$domain] ) ) {
 620                         throw new InvalidArgumentException( __METHOD__ .
 621                                 ": connection $serverIndex/$domain not found; it may have already been freed." );
 622                 } elseif ( $this->mConns['foreignUsed'][$serverIndex][$domain] !== $conn ) {
 623                         throw new InvalidArgumentException( __METHOD__ .
 624                                 ": connection $serverIndex/$domain mismatched; it may have already been freed." );
 625                 }
 626                 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
 627                 if ( $refCount <= 0 ) {
 628                         $this->mConns['foreignFree'][$serverIndex][$domain] = $conn;
 629                         unset( $this->mConns['foreignUsed'][$serverIndex][$domain] );
 630                         if ( !$this->mConns['foreignUsed'][$serverIndex] ) {
 631                                 unset( $this->mConns[ 'foreignUsed' ][$serverIndex] ); // clean up
 632                         }
 633                         $this->connLogger->debug( __METHOD__ . ": freed connection $serverIndex/$domain" );
 634                 } else {
 635                         $this->connLogger->debug( __METHOD__ .
 636                                 ": reference count for $serverIndex/$domain reduced to $refCount" );
 637                 }
 638         }
 639
 640         public function getConnectionRef( $db, $groups = [], $domain = false ) {
 641                 $domain = ( $domain !== false ) ? $domain : $this->localDomain;
 642
 643                 return new DBConnRef( $this, $this->getConnection( $db, $groups, $domain ) );
 644         }
 645
 646         public function getLazyConnectionRef( $db, $groups = [], $domain = false ) {
 647                 $domain = ( $domain !== false ) ? $domain : $this->localDomain;
 648
 649                 return new DBConnRef( $this, [ $db, $groups, $domain ] );
 650         }
 651
 652         /**
 653          * @see ILoadBalancer::openConnection()
 654          *
 655          * @param int $i
 656          * @param bool $domain
 657          * @return bool|Database
 658          * @throws DBAccessError
 659          */
 660         public function openConnection( $i, $domain = false ) {
 661                 if ( $this->localDomain->equals( $domain ) || $domain === $this->localDomainIdAlias ) {
 662                         $domain = false; // local connection requested
 663                 }
 664
 665                 if ( $domain !== false ) {
 666                         $conn = $this->openForeignConnection( $i, $domain );
 667                 } elseif ( isset( $this->mConns['local'][$i][0] ) ) {
 668                         $conn = $this->mConns['local'][$i][0];
 669                 } else {
 670                         if ( !isset( $this->mServers[$i] ) || !is_array( $this->mServers[$i] ) ) {
 671                                 throw new InvalidArgumentException( "No server with index '$i'." );
 672                         }
 673                         // Open a new connection
 674                         $server = $this->mServers[$i];
 675                         $server['serverIndex'] = $i;
 676                         $conn = $this->reallyOpenConnection( $server, false );
 677                         $serverName = $this->getServerName( $i );
 678                         if ( $conn->isOpen() ) {
 679                                 $this->connLogger->debug( "Connected to database $i at '$serverName'." );
 680                                 $this->mConns['local'][$i][0] = $conn;
 681                         } else {
 682                                 $this->connLogger->warning( "Failed to connect to database $i at '$serverName'." );
 683                                 $this->mErrorConnection = $conn;
 684                                 $conn = false;
 685                         }
 686                 }
 687
 688                 if ( $conn && !$conn->isOpen() ) {
 689                         // Connection was made but later unrecoverably lost for some reason.
 690                         // Do not return a handle that will just throw exceptions on use,
 691                         // but let the calling code (e.g. getReaderIndex) try another server.
 692                         // See DatabaseMyslBase::ping() for how this can happen.
 693                         $this->mErrorConnection = $conn;
 694                         $conn = false;
 695                 }
 696
 697                 return $conn;
 698         }
 699
 700         /**
 701          * Open a connection to a foreign DB, or return one if it is already open.
 702          *
 703          * Increments a reference count on the returned connection which locks the
 704          * connection to the requested domain. This reference count can be
 705          * decremented by calling reuseConnection().
 706          *
 707          * If a connection is open to the appropriate server already, but with the wrong
 708          * database, it will be switched to the right database and returned, as long as
 709          * it has been freed first with reuseConnection().
 710          *
 711          * On error, returns false, and the connection which caused the
 712          * error will be available via $this->mErrorConnection.
 713          *
 714          * @note If disable() was called on this LoadBalancer, this method will throw a DBAccessError.
 715          *
 716          * @param int $i Server index
 717          * @param string $domain Domain ID to open
 718          * @return Database
 719          */
 720         private function openForeignConnection( $i, $domain ) {
 721                 $domainInstance = DatabaseDomain::newFromId( $domain );
 722                 $dbName = $domainInstance->getDatabase();
 723                 $prefix = $domainInstance->getTablePrefix();
 724
 725                 if ( isset( $this->mConns['foreignUsed'][$i][$domain] ) ) {
 726                         // Reuse an already-used connection
 727                         $conn = $this->mConns['foreignUsed'][$i][$domain];
 728                         $this->connLogger->debug( __METHOD__ . ": reusing connection $i/$domain" );
 729                 } elseif ( isset( $this->mConns['foreignFree'][$i][$domain] ) ) {
 730                         // Reuse a free connection for the same domain
 731                         $conn = $this->mConns['foreignFree'][$i][$domain];
 732                         unset( $this->mConns['foreignFree'][$i][$domain] );
 733                         $this->mConns['foreignUsed'][$i][$domain] = $conn;
 734                         $this->connLogger->debug( __METHOD__ . ": reusing free connection $i/$domain" );
 735                 } elseif ( !empty( $this->mConns['foreignFree'][$i] ) ) {
 736                         // Reuse a connection from another domain
 737                         $conn = reset( $this->mConns['foreignFree'][$i] );
 738                         $oldDomain = key( $this->mConns['foreignFree'][$i] );
 739                         // The empty string as a DB name means "don't care".
 740                         // DatabaseMysqlBase::open() already handle this on connection.
 741                         if ( strlen( $dbName ) && !$conn->selectDB( $dbName ) ) {
 742                                 $this->mLastError = "Error selecting database '$dbName' on server " .
 743                                         $conn->getServer() . " from client host {$this->host}";
 744                                 $this->mErrorConnection = $conn;
 745                                 $conn = false;
 746                         } else {
 747                                 $conn->tablePrefix( $prefix );
 748                                 unset( $this->mConns['foreignFree'][$i][$oldDomain] );
 749                                 $this->mConns['foreignUsed'][$i][$domain] = $conn;
 750                                 $this->connLogger->debug( __METHOD__ .
 751                                         ": reusing free connection from $oldDomain for $domain" );
 752                         }
 753                 } else {
 754                         if ( !isset( $this->mServers[$i] ) || !is_array( $this->mServers[$i] ) ) {
 755                                 throw new InvalidArgumentException( "No server with index '$i'." );
 756                         }
 757                         // Open a new connection
 758                         $server = $this->mServers[$i];
 759                         $server['serverIndex'] = $i;
 760                         $server['foreignPoolRefCount'] = 0;
 761                         $server['foreign'] = true;
 762                         $conn = $this->reallyOpenConnection( $server, $dbName );
 763                         if ( !$conn->isOpen() ) {
 764                                 $this->connLogger->warning( __METHOD__ . ": connection error for $i/$domain" );
 765                                 $this->mErrorConnection = $conn;
 766                                 $conn = false;
 767                         } else {
 768                                 $conn->tablePrefix( $prefix );
 769                                 $this->mConns['foreignUsed'][$i][$domain] = $conn;
 770                                 $this->connLogger->debug( __METHOD__ . ": opened new connection for $i/$domain" );
 771                         }
 772                 }
 773
 774                 // Increment reference count
 775                 if ( $conn ) {
 776                         $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 777                         $conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
 778                 }
 779
 780                 return $conn;
 781         }
 782
 783         /**
 784          * Test if the specified index represents an open connection
 785          *
 786          * @param int $index Server index
 787          * @access private
 788          * @return bool
 789          */
 790         private function isOpen( $index ) {
 791                 if ( !is_integer( $index ) ) {
 792                         return false;
 793                 }
 794
 795                 return (bool)$this->getAnyOpenConnection( $index );
 796         }
 797
 798         /**
 799          * Really opens a connection. Uncached.
 800          * Returns a Database object whether or not the connection was successful.
 801          * @access private
 802          *
 803          * @param array $server
 804          * @param string|bool $dbNameOverride Use "" to not select any database
 805          * @return Database
 806          * @throws DBAccessError
 807          * @throws InvalidArgumentException
 808          */
 809         protected function reallyOpenConnection( array $server, $dbNameOverride = false ) {
 810                 if ( $this->disabled ) {
 811                         throw new DBAccessError();
 812                 }
 813
 814                 if ( $dbNameOverride !== false ) {
 815                         $server['dbname'] = $dbNameOverride;
 816                 }
 817
 818                 // Let the handle know what the cluster master is (e.g. "db1052")
 819                 $masterName = $this->getServerName( $this->getWriterIndex() );
 820                 $server['clusterMasterHost'] = $masterName;
 821
 822                 // Log when many connection are made on requests
 823                 if ( ++$this->connsOpened >= self::CONN_HELD_WARN_THRESHOLD ) {
 824                         $this->perfLogger->warning( __METHOD__ . ": " .
 825                                 "{$this->connsOpened}+ connections made (master=$masterName)" );
 826                 }
 827
 828                 $server['srvCache'] = $this->srvCache;
 829                 // Set loggers and profilers
 830                 $server['connLogger'] = $this->connLogger;
 831                 $server['queryLogger'] = $this->queryLogger;
 832                 $server['errorLogger'] = $this->errorLogger;
 833                 $server['profiler'] = $this->profiler;
 834                 $server['trxProfiler'] = $this->trxProfiler;
 835                 // Use the same agent and PHP mode for all DB handles
 836                 $server['cliMode'] = $this->cliMode;
 837                 $server['agent'] = $this->agent;
 838                 // Use DBO_DEFAULT flags by default for LoadBalancer managed databases. Assume that the
 839                 // application calls LoadBalancer::commitMasterChanges() before the PHP script completes.
 840                 $server['flags'] = isset( $server['flags'] ) ? $server['flags'] : IDatabase::DBO_DEFAULT;
 841
 842                 // Create a live connection object
 843                 try {
 844                         $db = Database::factory( $server['type'], $server );
 845                 } catch ( DBConnectionError $e ) {
 846                         // FIXME: This is probably the ugliest thing I have ever done to
 847                         // PHP. I'm half-expecting it to segfault, just out of disgust. -- TS
 848                         $db = $e->db;
 849                 }
 850
 851                 $db->setLBInfo( $server );
 852                 $db->setLazyMasterHandle(
 853                         $this->getLazyConnectionRef( self::DB_MASTER, [], $db->getDomainID() )
 854                 );
 855                 $db->setTableAliases( $this->tableAliases );
 856
 857                 if ( $server['serverIndex'] === $this->getWriterIndex() ) {
 858                         if ( $this->trxRoundId !== false ) {
 859                                 $this->applyTransactionRoundFlags( $db );
 860                         }
 861                         foreach ( $this->trxRecurringCallbacks as $name => $callback ) {
 862                                 $db->setTransactionListener( $name, $callback );
 863                         }
 864                 }
 865
 866                 return $db;
 867         }
 868
 869         /**
 870          * @throws DBConnectionError
 871          */
 872         private function reportConnectionError() {
 873                 $conn = $this->mErrorConnection; // the connection which caused the error
 874                 $context = [
 875                         'method' => __METHOD__,
 876                         'last_error' => $this->mLastError,
 877                 ];
 878
 879                 if ( !is_object( $conn ) ) {
 880                         // No last connection, probably due to all servers being too busy
 881                         $this->connLogger->error(
 882                                 "LB failure with no last connection. Connection error: {last_error}",
 883                                 $context
 884                         );
 885
 886                         // If all servers were busy, mLastError will contain something sensible
 887                         throw new DBConnectionError( null, $this->mLastError );
 888                 } else {
 889                         $context['db_server'] = $conn->getProperty( 'mServer' );
 890                         $this->connLogger->warning(
 891                                 "Connection error: {last_error} ({db_server})",
 892                                 $context
 893                         );
 894
 895                         // throws DBConnectionError
 896                         $conn->reportConnectionError( "{$this->mLastError} ({$context['db_server']})" );
 897                 }
 898         }
 899
 900         public function getWriterIndex() {
 901                 return 0;
 902         }
 903
 904         public function haveIndex( $i ) {
 905                 return array_key_exists( $i, $this->mServers );
 906         }
 907
 908         public function isNonZeroLoad( $i ) {
 909                 return array_key_exists( $i, $this->mServers ) && $this->mLoads[$i] != 0;
 910         }
 911
 912         public function getServerCount() {
 913                 return count( $this->mServers );
 914         }
 915
 916         public function getServerName( $i ) {
 917                 if ( isset( $this->mServers[$i]['hostName'] ) ) {
 918                         $name = $this->mServers[$i]['hostName'];
 919                 } elseif ( isset( $this->mServers[$i]['host'] ) ) {
 920                         $name = $this->mServers[$i]['host'];
 921                 } else {
 922                         $name = '';
 923                 }
 924
 925                 return ( $name != '' ) ? $name : 'localhost';
 926         }
 927
 928         public function getServerInfo( $i ) {
 929                 if ( isset( $this->mServers[$i] ) ) {
 930                         return $this->mServers[$i];
 931                 } else {
 932                         return false;
 933                 }
 934         }
 935
 936         public function setServerInfo( $i, array $serverInfo ) {
 937                 $this->mServers[$i] = $serverInfo;
 938         }
 939
 940         public function getMasterPos() {
 941                 # If this entire request was served from a replica DB without opening a connection to the
 942                 # master (however unlikely that may be), then we can fetch the position from the replica DB.
 943                 $masterConn = $this->getAnyOpenConnection( $this->getWriterIndex() );
 944                 if ( !$masterConn ) {
 945                         $serverCount = count( $this->mServers );
 946                         for ( $i = 1; $i < $serverCount; $i++ ) {
 947                                 $conn = $this->getAnyOpenConnection( $i );
 948                                 if ( $conn ) {
 949                                         return $conn->getReplicaPos();
 950                                 }
 951                         }
 952                 } else {
 953                         return $masterConn->getMasterPos();
 954                 }
 955
 956                 return false;
 957         }
 958
 959         public function disable() {
 960                 $this->closeAll();
 961                 $this->disabled = true;
 962         }
 963
 964         public function closeAll() {
 965                 $this->forEachOpenConnection( function ( IDatabase $conn ) {
 966                         $host = $conn->getServer();
 967                         $this->connLogger->debug( "Closing connection to database '$host'." );
 968                         $conn->close();
 969                 } );
 970
 971                 $this->mConns = [
 972                         'local' => [],
 973                         'foreignFree' => [],
 974                         'foreignUsed' => [],
 975                 ];
 976                 $this->connsOpened = 0;
 977         }
 978
 979         public function closeConnection( IDatabase $conn ) {
 980                 $serverIndex = $conn->getLBInfo( 'serverIndex' ); // second index level of mConns
 981                 foreach ( $this->mConns as $type => $connsByServer ) {
 982                         if ( !isset( $connsByServer[$serverIndex] ) ) {
 983                                 continue;
 984                         }
 985
 986                         foreach ( $connsByServer[$serverIndex] as $i => $trackedConn ) {
 987                                 if ( $conn === $trackedConn ) {
 988                                         $host = $this->getServerName( $i );
 989                                         $this->connLogger->debug( "Closing connection to database $i at '$host'." );
 990                                         unset( $this->mConns[$type][$serverIndex][$i] );
 991                                         --$this->connsOpened;
 992                                         break 2;
 993                                 }
 994                         }
 995                 }
 996
 997                 $conn->close();
 998         }
 999
1000         public function commitAll( $fname = __METHOD__ ) {
1001                 $failures = [];
1002
1003                 $restore = ( $this->trxRoundId !== false );
1004                 $this->trxRoundId = false;
1005                 $this->forEachOpenConnection(
1006                         function ( IDatabase $conn ) use ( $fname, $restore, &$failures ) {
1007                                 try {
1008                                         $conn->commit( $fname, $conn::FLUSHING_ALL_PEERS );
1009                                 } catch ( DBError $e ) {
1010                                         call_user_func( $this->errorLogger, $e );
1011                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1012                                 }
1013                                 if ( $restore && $conn->getLBInfo( 'master' ) ) {
1014                                         $this->undoTransactionRoundFlags( $conn );
1015                                 }
1016                         }
1017                 );
1018
1019                 if ( $failures ) {
1020                         throw new DBExpectedError(
1021                                 null,
1022                                 "Commit failed on server(s) " . implode( "\n", array_unique( $failures ) )
1023                         );
1024                 }
1025         }
1026
1027         public function finalizeMasterChanges() {
1028                 $this->forEachOpenMasterConnection( function ( Database $conn ) {
1029                         // Any error should cause all DB transactions to be rolled back together
1030                         $conn->setTrxEndCallbackSuppression( false );
1031                         $conn->runOnTransactionPreCommitCallbacks();
1032                         // Defer post-commit callbacks until COMMIT finishes for all DBs
1033                         $conn->setTrxEndCallbackSuppression( true );
1034                 } );
1035         }
1036
1037         public function approveMasterChanges( array $options ) {
1038                 $limit = isset( $options['maxWriteDuration'] ) ? $options['maxWriteDuration'] : 0;
1039                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( $limit ) {
1040                         // If atomic sections or explicit transactions are still open, some caller must have
1041                         // caught an exception but failed to properly rollback any changes. Detect that and
1042                         // throw and error (causing rollback).
1043                         if ( $conn->explicitTrxActive() ) {
1044                                 throw new DBTransactionError(
1045                                         $conn,
1046                                         "Explicit transaction still active. A caller may have caught an error."
1047                                 );
1048                         }
1049                         // Assert that the time to replicate the transaction will be sane.
1050                         // If this fails, then all DB transactions will be rollback back together.
1051                         $time = $conn->pendingWriteQueryDuration( $conn::ESTIMATE_DB_APPLY );
1052                         if ( $limit > 0 && $time > $limit ) {
1053                                 throw new DBTransactionSizeError(
1054                                         $conn,
1055                                         "Transaction spent $time second(s) in writes, exceeding the $limit limit.",
1056                                         [ $time, $limit ]
1057                                 );
1058                         }
1059                         // If a connection sits idle while slow queries execute on another, that connection
1060                         // may end up dropped before the commit round is reached. Ping servers to detect this.
1061                         if ( $conn->writesOrCallbacksPending() && !$conn->ping() ) {
1062                                 throw new DBTransactionError(
1063                                         $conn,
1064                                         "A connection to the {$conn->getDBname()} database was lost before commit."
1065                                 );
1066                         }
1067                 } );
1068         }
1069
1070         public function beginMasterChanges( $fname = __METHOD__ ) {
1071                 if ( $this->trxRoundId !== false ) {
1072                         throw new DBTransactionError(
1073                                 null,
1074                                 "$fname: Transaction round '{$this->trxRoundId}' already started."
1075                         );
1076                 }
1077                 $this->trxRoundId = $fname;
1078
1079                 $failures = [];
1080                 $this->forEachOpenMasterConnection(
1081                         function ( Database $conn ) use ( $fname, &$failures ) {
1082                                 $conn->setTrxEndCallbackSuppression( true );
1083                                 try {
1084                                         $conn->flushSnapshot( $fname );
1085                                 } catch ( DBError $e ) {
1086                                         call_user_func( $this->errorLogger, $e );
1087                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1088                                 }
1089                                 $conn->setTrxEndCallbackSuppression( false );
1090                                 $this->applyTransactionRoundFlags( $conn );
1091                         }
1092                 );
1093
1094                 if ( $failures ) {
1095                         throw new DBExpectedError(
1096                                 null,
1097                                 "$fname: Flush failed on server(s) " . implode( "\n", array_unique( $failures ) )
1098                         );
1099                 }
1100         }
1101
1102         public function commitMasterChanges( $fname = __METHOD__ ) {
1103                 $failures = [];
1104
1105                 /** @noinspection PhpUnusedLocalVariableInspection */
1106                 $scope = $this->getScopedPHPBehaviorForCommit(); // try to ignore client aborts
1107
1108                 $restore = ( $this->trxRoundId !== false );
1109                 $this->trxRoundId = false;
1110                 $this->forEachOpenMasterConnection(
1111                         function ( IDatabase $conn ) use ( $fname, $restore, &$failures ) {
1112                                 try {
1113                                         if ( $conn->writesOrCallbacksPending() ) {
1114                                                 $conn->commit( $fname, $conn::FLUSHING_ALL_PEERS );
1115                                         } elseif ( $restore ) {
1116                                                 $conn->flushSnapshot( $fname );
1117                                         }
1118                                 } catch ( DBError $e ) {
1119                                         call_user_func( $this->errorLogger, $e );
1120                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1121                                 }
1122                                 if ( $restore ) {
1123                                         $this->undoTransactionRoundFlags( $conn );
1124                                 }
1125                         }
1126                 );
1127
1128                 if ( $failures ) {
1129                         throw new DBExpectedError(
1130                                 null,
1131                                 "$fname: Commit failed on server(s) " . implode( "\n", array_unique( $failures ) )
1132                         );
1133                 }
1134         }
1135
1136         public function runMasterPostTrxCallbacks( $type ) {
1137                 $e = null; // first exception
1138                 $this->forEachOpenMasterConnection( function ( Database $conn ) use ( $type, &$e ) {
1139                         $conn->setTrxEndCallbackSuppression( false );
1140                         if ( $conn->writesOrCallbacksPending() ) {
1141                                 // This happens if onTransactionIdle() callbacks leave callbacks on *another* DB
1142                                 // (which finished its callbacks already). Warn and recover in this case. Let the
1143                                 // callbacks run in the final commitMasterChanges() in LBFactory::shutdown().
1144                                 $this->queryLogger->error( __METHOD__ . ": found writes/callbacks pending." );
1145                                 return;
1146                         } elseif ( $conn->trxLevel() ) {
1147                                 // This happens for single-DB setups where DB_REPLICA uses the master DB,
1148                                 // thus leaving an implicit read-only transaction open at this point. It
1149                                 // also happens if onTransactionIdle() callbacks leave implicit transactions
1150                                 // open on *other* DBs (which is slightly improper). Let these COMMIT on the
1151                                 // next call to commitMasterChanges(), possibly in LBFactory::shutdown().
1152                                 return;
1153                         }
1154                         try {
1155                                 $conn->runOnTransactionIdleCallbacks( $type );
1156                         } catch ( Exception $ex ) {
1157                                 $e = $e ?: $ex;
1158                         }
1159                         try {
1160                                 $conn->runTransactionListenerCallbacks( $type );
1161                         } catch ( Exception $ex ) {
1162                                 $e = $e ?: $ex;
1163                         }
1164                 } );
1165
1166                 return $e;
1167         }
1168
1169         public function rollbackMasterChanges( $fname = __METHOD__ ) {
1170                 $restore = ( $this->trxRoundId !== false );
1171                 $this->trxRoundId = false;
1172                 $this->forEachOpenMasterConnection(
1173                         function ( IDatabase $conn ) use ( $fname, $restore ) {
1174                                 if ( $conn->writesOrCallbacksPending() ) {
1175                                         $conn->rollback( $fname, $conn::FLUSHING_ALL_PEERS );
1176                                 }
1177                                 if ( $restore ) {
1178                                         $this->undoTransactionRoundFlags( $conn );
1179                                 }
1180                         }
1181                 );
1182         }
1183
1184         public function suppressTransactionEndCallbacks() {
1185                 $this->forEachOpenMasterConnection( function ( Database $conn ) {
1186                         $conn->setTrxEndCallbackSuppression( true );
1187                 } );
1188         }
1189
1190         /**
1191          * @param IDatabase $conn
1192          */
1193         private function applyTransactionRoundFlags( IDatabase $conn ) {
1194                 if ( $conn->getFlag( $conn::DBO_DEFAULT ) ) {
1195                         // DBO_TRX is controlled entirely by CLI mode presence with DBO_DEFAULT.
1196                         // Force DBO_TRX even in CLI mode since a commit round is expected soon.
1197                         $conn->setFlag( $conn::DBO_TRX, $conn::REMEMBER_PRIOR );
1198                         // If config has explicitly requested DBO_TRX be either on or off by not
1199                         // setting DBO_DEFAULT, then respect that. Forcing no transactions is useful
1200                         // for things like blob stores (ExternalStore) which want auto-commit mode.
1201                 }
1202         }
1203
1204         /**
1205          * @param IDatabase $conn
1206          */
1207         private function undoTransactionRoundFlags( IDatabase $conn ) {
1208                 if ( $conn->getFlag( $conn::DBO_DEFAULT ) ) {
1209                         $conn->restoreFlags( $conn::RESTORE_PRIOR );
1210                 }
1211         }
1212
1213         public function flushReplicaSnapshots( $fname = __METHOD__ ) {
1214                 $this->forEachOpenReplicaConnection( function ( IDatabase $conn ) {
1215                         $conn->flushSnapshot( __METHOD__ );
1216                 } );
1217         }
1218
1219         public function hasMasterConnection() {
1220                 return $this->isOpen( $this->getWriterIndex() );
1221         }
1222
1223         public function hasMasterChanges() {
1224                 $pending = 0;
1225                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$pending ) {
1226                         $pending |= $conn->writesOrCallbacksPending();
1227                 } );
1228
1229                 return (bool)$pending;
1230         }
1231
1232         public function lastMasterChangeTimestamp() {
1233                 $lastTime = false;
1234                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$lastTime ) {
1235                         $lastTime = max( $lastTime, $conn->lastDoneWrites() );
1236                 } );
1237
1238                 return $lastTime;
1239         }
1240
1241         public function hasOrMadeRecentMasterChanges( $age = null ) {
1242                 $age = ( $age === null ) ? $this->mWaitTimeout : $age;
1243
1244                 return ( $this->hasMasterChanges()
1245                         || $this->lastMasterChangeTimestamp() > microtime( true ) - $age );
1246         }
1247
1248         public function pendingMasterChangeCallers() {
1249                 $fnames = [];
1250                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$fnames ) {
1251                         $fnames = array_merge( $fnames, $conn->pendingWriteCallers() );
1252                 } );
1253
1254                 return $fnames;
1255         }
1256
1257         public function getLaggedReplicaMode( $domain = false ) {
1258                 // No-op if there is only one DB (also avoids recursion)
1259                 if ( !$this->laggedReplicaMode && $this->getServerCount() > 1 ) {
1260                         try {
1261                                 // See if laggedReplicaMode gets set
1262                                 $conn = $this->getConnection( self::DB_REPLICA, false, $domain );
1263                                 $this->reuseConnection( $conn );
1264                         } catch ( DBConnectionError $e ) {
1265                                 // Avoid expensive re-connect attempts and failures
1266                                 $this->allReplicasDownMode = true;
1267                                 $this->laggedReplicaMode = true;
1268                         }
1269                 }
1270
1271                 return $this->laggedReplicaMode;
1272         }
1273
1274         /**
1275          * @param bool $domain
1276          * @return bool
1277          * @deprecated 1.28; use getLaggedReplicaMode()
1278          */
1279         public function getLaggedSlaveMode( $domain = false ) {
1280                 return $this->getLaggedReplicaMode( $domain );
1281         }
1282
1283         public function laggedReplicaUsed() {
1284                 return $this->laggedReplicaMode;
1285         }
1286
1287         /**
1288          * @return bool
1289          * @since 1.27
1290          * @deprecated Since 1.28; use laggedReplicaUsed()
1291          */
1292         public function laggedSlaveUsed() {
1293                 return $this->laggedReplicaUsed();
1294         }
1295
1296         public function getReadOnlyReason( $domain = false, IDatabase $conn = null ) {
1297                 if ( $this->readOnlyReason !== false ) {
1298                         return $this->readOnlyReason;
1299                 } elseif ( $this->getLaggedReplicaMode( $domain ) ) {
1300                         if ( $this->allReplicasDownMode ) {
1301                                 return 'The database has been automatically locked ' .
1302                                         'until the replica database servers become available';
1303                         } else {
1304                                 return 'The database has been automatically locked ' .
1305                                         'while the replica database servers catch up to the master.';
1306                         }
1307                 } elseif ( $this->masterRunningReadOnly( $domain, $conn ) ) {
1308                         return 'The database master is running in read-only mode.';
1309                 }
1310
1311                 return false;
1312         }
1313
1314         /**
1315          * @param string $domain Domain ID, or false for the current domain
1316          * @param IDatabase|null DB master connectionl used to avoid loops [optional]
1317          * @return bool
1318          */
1319         private function masterRunningReadOnly( $domain, IDatabase $conn = null ) {
1320                 $cache = $this->wanCache;
1321                 $masterServer = $this->getServerName( $this->getWriterIndex() );
1322
1323                 return (bool)$cache->getWithSetCallback(
1324                         $cache->makeGlobalKey( __CLASS__, 'server-read-only', $masterServer ),
1325                         self::TTL_CACHE_READONLY,
1326                         function () use ( $domain, $conn ) {
1327                                 $this->trxProfiler->setSilenced( true );
1328                                 try {
1329                                         $dbw = $conn ?: $this->getConnection( self::DB_MASTER, [], $domain );
1330                                         $readOnly = (int)$dbw->serverIsReadOnly();
1331                                         if ( !$conn ) {
1332                                                 $this->reuseConnection( $dbw );
1333                                         }
1334                                 } catch ( DBError $e ) {
1335                                         $readOnly = 0;
1336                                 }
1337                                 $this->trxProfiler->setSilenced( false );
1338                                 return $readOnly;
1339                         },
1340                         [ 'pcTTL' => $cache::TTL_PROC_LONG, 'busyValue' => 0 ]
1341                 );
1342         }
1343
1344         public function allowLagged( $mode = null ) {
1345                 if ( $mode === null ) {
1346                         return $this->mAllowLagged;
1347                 }
1348                 $this->mAllowLagged = $mode;
1349
1350                 return $this->mAllowLagged;
1351         }
1352
1353         public function pingAll() {
1354                 $success = true;
1355                 $this->forEachOpenConnection( function ( IDatabase $conn ) use ( &$success ) {
1356                         if ( !$conn->ping() ) {
1357                                 $success = false;
1358                         }
1359                 } );
1360
1361                 return $success;
1362         }
1363
1364         public function forEachOpenConnection( $callback, array $params = [] ) {
1365                 foreach ( $this->mConns as $connsByServer ) {
1366                         foreach ( $connsByServer as $serverConns ) {
1367                                 foreach ( $serverConns as $conn ) {
1368                                         $mergedParams = array_merge( [ $conn ], $params );
1369                                         call_user_func_array( $callback, $mergedParams );
1370                                 }
1371                         }
1372                 }
1373         }
1374
1375         public function forEachOpenMasterConnection( $callback, array $params = [] ) {
1376                 $masterIndex = $this->getWriterIndex();
1377                 foreach ( $this->mConns as $connsByServer ) {
1378                         if ( isset( $connsByServer[$masterIndex] ) ) {
1379                                 /** @var IDatabase $conn */
1380                                 foreach ( $connsByServer[$masterIndex] as $conn ) {
1381                                         $mergedParams = array_merge( [ $conn ], $params );
1382                                         call_user_func_array( $callback, $mergedParams );
1383                                 }
1384                         }
1385                 }
1386         }
1387
1388         public function forEachOpenReplicaConnection( $callback, array $params = [] ) {
1389                 foreach ( $this->mConns as $connsByServer ) {
1390                         foreach ( $connsByServer as $i => $serverConns ) {
1391                                 if ( $i === $this->getWriterIndex() ) {
1392                                         continue; // skip master
1393                                 }
1394                                 foreach ( $serverConns as $conn ) {
1395                                         $mergedParams = array_merge( [ $conn ], $params );
1396                                         call_user_func_array( $callback, $mergedParams );
1397                                 }
1398                         }
1399                 }
1400         }
1401
1402         public function getMaxLag( $domain = false ) {
1403                 $maxLag = -1;
1404                 $host = '';
1405                 $maxIndex = 0;
1406
1407                 if ( $this->getServerCount() <= 1 ) {
1408                         return [ $host, $maxLag, $maxIndex ]; // no replication = no lag
1409                 }
1410
1411                 $lagTimes = $this->getLagTimes( $domain );
1412                 foreach ( $lagTimes as $i => $lag ) {
1413                         if ( $this->mLoads[$i] > 0 && $lag > $maxLag ) {
1414                                 $maxLag = $lag;
1415                                 $host = $this->mServers[$i]['host'];
1416                                 $maxIndex = $i;
1417                         }
1418                 }
1419
1420                 return [ $host, $maxLag, $maxIndex ];
1421         }
1422
1423         public function getLagTimes( $domain = false ) {
1424                 if ( $this->getServerCount() <= 1 ) {
1425                         return [ $this->getWriterIndex() => 0 ]; // no replication = no lag
1426                 }
1427
1428                 $knownLagTimes = []; // map of (server index => 0 seconds)
1429                 $indexesWithLag = [];
1430                 foreach ( $this->mServers as $i => $server ) {
1431                         if ( empty( $server['is static'] ) ) {
1432                                 $indexesWithLag[] = $i; // DB server might have replication lag
1433                         } else {
1434                                 $knownLagTimes[$i] = 0; // DB server is a non-replicating and read-only archive
1435                         }
1436                 }
1437
1438                 return $this->getLoadMonitor()->getLagTimes( $indexesWithLag, $domain ) + $knownLagTimes;
1439         }
1440
1441         public function safeGetLag( IDatabase $conn ) {
1442                 if ( $this->getServerCount() <= 1 ) {
1443                         return 0;
1444                 } else {
1445                         return $conn->getLag();
1446                 }
1447         }
1448
1449         public function safeWaitForMasterPos( IDatabase $conn, $pos = false, $timeout = 10 ) {
1450                 if ( $this->getServerCount() <= 1 || !$conn->getLBInfo( 'replica' ) ) {
1451                         return true; // server is not a replica DB
1452                 }
1453
1454                 if ( !$pos ) {
1455                         // Get the current master position, opening a connection if needed
1456                         $masterConn = $this->getAnyOpenConnection( $this->getWriterIndex() );
1457                         if ( $masterConn ) {
1458                                 $pos = $masterConn->getMasterPos();
1459                         } else {
1460                                 $masterConn = $this->openConnection( $this->getWriterIndex(), self::DOMAIN_ANY );
1461                                 $pos = $masterConn->getMasterPos();
1462                                 $this->closeConnection( $masterConn );
1463                         }
1464                 }
1465
1466                 if ( $pos instanceof DBMasterPos ) {
1467                         $result = $conn->masterPosWait( $pos, $timeout );
1468                         if ( $result == -1 || is_null( $result ) ) {
1469                                 $msg = __METHOD__ . ": Timed out waiting on {$conn->getServer()} pos {$pos}";
1470                                 $this->replLogger->warning( "$msg" );
1471                                 $ok = false;
1472                         } else {
1473                                 $this->replLogger->info( __METHOD__ . ": Done" );
1474                                 $ok = true;
1475                         }
1476                 } else {
1477                         $ok = false; // something is misconfigured
1478                         $this->replLogger->error( "Could not get master pos for {$conn->getServer()}." );
1479                 }
1480
1481                 return $ok;
1482         }
1483
1484         public function setTransactionListener( $name, callable $callback = null ) {
1485                 if ( $callback ) {
1486                         $this->trxRecurringCallbacks[$name] = $callback;
1487                 } else {
1488                         unset( $this->trxRecurringCallbacks[$name] );
1489                 }
1490                 $this->forEachOpenMasterConnection(
1491                         function ( IDatabase $conn ) use ( $name, $callback ) {
1492                                 $conn->setTransactionListener( $name, $callback );
1493                         }
1494                 );
1495         }
1496
1497         public function setTableAliases( array $aliases ) {
1498                 $this->tableAliases = $aliases;
1499         }
1500
1501         public function setDomainPrefix( $prefix ) {
1502                 if ( $this->mConns['foreignUsed'] ) {
1503                         // Do not switch connections to explicit foreign domains unless marked as free
1504                         $domains = [];
1505                         foreach ( $this->mConns['foreignUsed'] as $i => $connsByDomain ) {
1506                                 $domains = array_merge( $domains, array_keys( $connsByDomain ) );
1507                         }
1508                         $domains = implode( ', ', $domains );
1509                         throw new DBUnexpectedError( null,
1510                                 "Foreign domain connections are still in use ($domains)." );
1511                 }
1512
1513                 $this->localDomain = new DatabaseDomain(
1514                         $this->localDomain->getDatabase(),
1515                         null,
1516                         $prefix
1517                 );
1518
1519                 $this->forEachOpenConnection( function ( IDatabase $db ) use ( $prefix ) {
1520                         $db->tablePrefix( $prefix );
1521                 } );
1522         }
1523
1524         /**
1525          * Make PHP ignore user aborts/disconnects until the returned
1526          * value leaves scope. This returns null and does nothing in CLI mode.
1527          *
1528          * @return ScopedCallback|null
1529          */
1530         final protected function getScopedPHPBehaviorForCommit() {
1531                 if ( PHP_SAPI != 'cli' ) { // http://bugs.php.net/bug.php?id=47540
1532                         $old = ignore_user_abort( true ); // avoid half-finished operations
1533                         return new ScopedCallback( function () use ( $old ) {
1534                                 ignore_user_abort( $old );
1535                         } );
1536                 }
1537
1538                 return null;
1539         }
1540
1541         function __destruct() {
1542                 // Avoid connection leaks for sanity
1543                 $this->disable();
1544         }
1545 }