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 namespace Wikimedia\Rdbms;
  24
  25 use Psr\Log\LoggerInterface;
  26 use Psr\Log\NullLogger;
  27 use Wikimedia\ScopedCallback;
  28 use Database;
  29 use DBConnRef;
  30 use MaintainableDBConnRef;
  31 use BagOStuff;
  32 use EmptyBagOStuff;
  33 use WANObjectCache;
  34 use ArrayUtils;
  35 use DBError;
  36 use DBAccessError;
  37 use DBExpectedError;
  38 use DBUnexpectedError;
  39 use DBTransactionError;
  40 use DBTransactionSizeError;
  41 use DBConnectionError;
  42 use InvalidArgumentException;
  43 use RuntimeException;
  44 use Exception;
  45
  46 /**
  47  * Database connection, tracking, load balancing, and transaction manager for a cluster
  48  *
  49  * @ingroup Database
  50  */
  51 class LoadBalancer implements ILoadBalancer {
  52         /** @var array[] Map of (server index => server config array) */
  53         private $mServers;
  54         /** @var \Database[][][] Map of local/foreignUsed/foreignFree => server index => IDatabase array */
  55         private $mConns;
  56         /** @var float[] Map of (server index => weight) */
  57         private $mLoads;
  58         /** @var array[] Map of (group => server index => weight) */
  59         private $mGroupLoads;
  60         /** @var bool Whether to disregard replica DB lag as a factor in replica DB selection */
  61         private $mAllowLagged;
  62         /** @var integer Seconds to spend waiting on replica DB lag to resolve */
  63         private $mWaitTimeout;
  64         /** @var array The LoadMonitor configuration */
  65         private $loadMonitorConfig;
  66         /** @var array[] $aliases Map of (table => (dbname, schema, prefix) map) */
  67         private $tableAliases = [];
  68
  69         /** @var ILoadMonitor */
  70         private $loadMonitor;
  71         /** @var ChronologyProtector|null */
  72         private $chronProt;
  73         /** @var BagOStuff */
  74         private $srvCache;
  75         /** @var BagOStuff */
  76         private $memCache;
  77         /** @var WANObjectCache */
  78         private $wanCache;
  79         /** @var object|string Class name or object With profileIn/profileOut methods */
  80         protected $profiler;
  81         /** @var TransactionProfiler */
  82         protected $trxProfiler;
  83         /** @var LoggerInterface */
  84         protected $replLogger;
  85         /** @var LoggerInterface */
  86         protected $connLogger;
  87         /** @var LoggerInterface */
  88         protected $queryLogger;
  89         /** @var LoggerInterface */
  90         protected $perfLogger;
  91
  92         /** @var \Database Database connection that caused a problem */
  93         private $errorConnection;
  94         /** @var integer The generic (not query grouped) replica DB index (of $mServers) */
  95         private $mReadIndex;
  96         /** @var bool|DBMasterPos False if not set */
  97         private $mWaitForPos;
  98         /** @var bool Whether the generic reader fell back to a lagged replica DB */
  99         private $laggedReplicaMode = false;
 100         /** @var bool Whether the generic reader fell back to a lagged replica DB */
 101         private $allReplicasDownMode = false;
 102         /** @var string The last DB selection or connection error */
 103         private $mLastError = 'Unknown error';
 104         /** @var string|bool Reason the LB is read-only or false if not */
 105         private $readOnlyReason = false;
 106         /** @var integer Total connections opened */
 107         private $connsOpened = 0;
 108         /** @var string|bool String if a requested DBO_TRX transaction round is active */
 109         private $trxRoundId = false;
 110         /** @var array[] Map of (name => callable) */
 111         private $trxRecurringCallbacks = [];
 112         /** @var DatabaseDomain Local Domain ID and default for selectDB() calls */
 113         private $localDomain;
 114         /** @var string Alternate ID string for the domain instead of DatabaseDomain::getId() */
 115         private $localDomainIdAlias;
 116         /** @var string Current server name */
 117         private $host;
 118         /** @var bool Whether this PHP instance is for a CLI script */
 119         protected $cliMode;
 120         /** @var string Agent name for query profiling */
 121         protected $agent;
 122
 123         /** @var callable Exception logger */
 124         private $errorLogger;
 125
 126         /** @var boolean */
 127         private $disabled = false;
 128         /** @var boolean */
 129         private $chronProtInitialized = false;
 130
 131         /** @var integer Warn when this many connection are held */
 132         const CONN_HELD_WARN_THRESHOLD = 10;
 133
 134         /** @var integer Default 'max lag' when unspecified */
 135         const MAX_LAG_DEFAULT = 10;
 136         /** @var integer Seconds to cache master server read-only status */
 137         const TTL_CACHE_READONLY = 5;
 138
 139         public function __construct( array $params ) {
 140                 if ( !isset( $params['servers'] ) ) {
 141                         throw new InvalidArgumentException( __CLASS__ . ': missing servers parameter' );
 142                 }
 143                 $this->mServers = $params['servers'];
 144
 145                 $this->localDomain = isset( $params['localDomain'] )
 146                         ? DatabaseDomain::newFromId( $params['localDomain'] )
 147                         : DatabaseDomain::newUnspecified();
 148                 // In case a caller assumes that the domain ID is simply <db>-<prefix>, which is almost
 149                 // always true, gracefully handle the case when they fail to account for escaping.
 150                 if ( $this->localDomain->getTablePrefix() != '' ) {
 151                         $this->localDomainIdAlias =
 152                                 $this->localDomain->getDatabase() . '-' . $this->localDomain->getTablePrefix();
 153                 } else {
 154                         $this->localDomainIdAlias = $this->localDomain->getDatabase();
 155                 }
 156
 157                 $this->mWaitTimeout = isset( $params['waitTimeout'] ) ? $params['waitTimeout'] : 10;
 158
 159                 $this->mReadIndex = -1;
 160                 $this->mConns = [
 161                         'local'       => [],
 162                         'foreignUsed' => [],
 163                         'foreignFree' => []
 164                 ];
 165                 $this->mLoads = [];
 166                 $this->mWaitForPos = false;
 167                 $this->mAllowLagged = false;
 168
 169                 if ( isset( $params['readOnlyReason'] ) && is_string( $params['readOnlyReason'] ) ) {
 170                         $this->readOnlyReason = $params['readOnlyReason'];
 171                 }
 172
 173                 if ( isset( $params['loadMonitor'] ) ) {
 174                         $this->loadMonitorConfig = $params['loadMonitor'];
 175                 } else {
 176                         $this->loadMonitorConfig = [ 'class' => 'LoadMonitorNull' ];
 177                 }
 178
 179                 foreach ( $params['servers'] as $i => $server ) {
 180                         $this->mLoads[$i] = $server['load'];
 181                         if ( isset( $server['groupLoads'] ) ) {
 182                                 foreach ( $server['groupLoads'] as $group => $ratio ) {
 183                                         if ( !isset( $this->mGroupLoads[$group] ) ) {
 184                                                 $this->mGroupLoads[$group] = [];
 185                                         }
 186                                         $this->mGroupLoads[$group][$i] = $ratio;
 187                                 }
 188                         }
 189                 }
 190
 191                 if ( isset( $params['srvCache'] ) ) {
 192                         $this->srvCache = $params['srvCache'];
 193                 } else {
 194                         $this->srvCache = new EmptyBagOStuff();
 195                 }
 196                 if ( isset( $params['memCache'] ) ) {
 197                         $this->memCache = $params['memCache'];
 198                 } else {
 199                         $this->memCache = new EmptyBagOStuff();
 200                 }
 201                 if ( isset( $params['wanCache'] ) ) {
 202                         $this->wanCache = $params['wanCache'];
 203                 } else {
 204                         $this->wanCache = WANObjectCache::newEmpty();
 205                 }
 206                 $this->profiler = isset( $params['profiler'] ) ? $params['profiler'] : null;
 207                 if ( isset( $params['trxProfiler'] ) ) {
 208                         $this->trxProfiler = $params['trxProfiler'];
 209                 } else {
 210                         $this->trxProfiler = new TransactionProfiler();
 211                 }
 212
 213                 $this->errorLogger = isset( $params['errorLogger'] )
 214                         ? $params['errorLogger']
 215                         : function ( Exception $e ) {
 216                                 trigger_error( get_class( $e ) . ': ' . $e->getMessage(), E_USER_WARNING );
 217                         };
 218
 219                 foreach ( [ 'replLogger', 'connLogger', 'queryLogger', 'perfLogger' ] as $key ) {
 220                         $this->$key = isset( $params[$key] ) ? $params[$key] : new NullLogger();
 221                 }
 222
 223                 $this->host = isset( $params['hostname'] )
 224                         ? $params['hostname']
 225                         : ( gethostname() ?: 'unknown' );
 226                 $this->cliMode = isset( $params['cliMode'] ) ? $params['cliMode'] : PHP_SAPI === 'cli';
 227                 $this->agent = isset( $params['agent'] ) ? $params['agent'] : '';
 228
 229                 if ( isset( $params['chronologyProtector'] ) ) {
 230                         $this->chronProt = $params['chronologyProtector'];
 231                 }
 232         }
 233
 234         /**
 235          * Get a LoadMonitor instance
 236          *
 237          * @return ILoadMonitor
 238          */
 239         private function getLoadMonitor() {
 240                 if ( !isset( $this->loadMonitor ) ) {
 241                         $compat = [
 242                                 'LoadMonitor' => LoadMonitor::class,
 243                                 'LoadMonitorNull' => LoadMonitorNull::class,
 244                                 'LoadMonitorMySQL' => LoadMonitorMySQL::class,
 245                         ];
 246
 247                         $class = $this->loadMonitorConfig['class'];
 248                         if ( isset( $compat[$class] ) ) {
 249                                 $class = $compat[$class];
 250                         }
 251
 252                         $this->loadMonitor = new $class(
 253                                 $this, $this->srvCache, $this->memCache, $this->loadMonitorConfig );
 254                         $this->loadMonitor->setLogger( $this->replLogger );
 255                 }
 256
 257                 return $this->loadMonitor;
 258         }
 259
 260         /**
 261          * @param array $loads
 262          * @param bool|string $domain Domain to get non-lagged for
 263          * @param int $maxLag Restrict the maximum allowed lag to this many seconds
 264          * @return bool|int|string
 265          */
 266         private function getRandomNonLagged( array $loads, $domain = false, $maxLag = INF ) {
 267                 $lags = $this->getLagTimes( $domain );
 268
 269                 # Unset excessively lagged servers
 270                 foreach ( $lags as $i => $lag ) {
 271                         if ( $i != 0 ) {
 272                                 # How much lag this server nominally is allowed to have
 273                                 $maxServerLag = isset( $this->mServers[$i]['max lag'] )
 274                                         ? $this->mServers[$i]['max lag']
 275                                         : self::MAX_LAG_DEFAULT; // default
 276                                 # Constrain that futher by $maxLag argument
 277                                 $maxServerLag = min( $maxServerLag, $maxLag );
 278
 279                                 $host = $this->getServerName( $i );
 280                                 if ( $lag === false && !is_infinite( $maxServerLag ) ) {
 281                                         $this->replLogger->error(
 282                                                 "Server {host} (#$i) is not replicating?", [ 'host' => $host ] );
 283                                         unset( $loads[$i] );
 284                                 } elseif ( $lag > $maxServerLag ) {
 285                                         $this->replLogger->warning(
 286                                                 "Server {host} (#$i) has {lag} seconds of lag (>= {maxlag})",
 287                                                 [ 'host' => $host, 'lag' => $lag, 'maxlag' => $maxServerLag ]
 288                                         );
 289                                         unset( $loads[$i] );
 290                                 }
 291                         }
 292                 }
 293
 294                 # Find out if all the replica DBs with non-zero load are lagged
 295                 $sum = 0;
 296                 foreach ( $loads as $load ) {
 297                         $sum += $load;
 298                 }
 299                 if ( $sum == 0 ) {
 300                         # No appropriate DB servers except maybe the master and some replica DBs with zero load
 301                         # Do NOT use the master
 302                         # Instead, this function will return false, triggering read-only mode,
 303                         # and a lagged replica DB will be used instead.
 304                         return false;
 305                 }
 306
 307                 if ( count( $loads ) == 0 ) {
 308                         return false;
 309                 }
 310
 311                 # Return a random representative of the remainder
 312                 return ArrayUtils::pickRandom( $loads );
 313         }
 314
 315         public function getReaderIndex( $group = false, $domain = false ) {
 316                 if ( count( $this->mServers ) == 1 ) {
 317                         # Skip the load balancing if there's only one server
 318                         return $this->getWriterIndex();
 319                 } elseif ( $group === false && $this->mReadIndex >= 0 ) {
 320                         # Shortcut if generic reader exists already
 321                         return $this->mReadIndex;
 322                 }
 323
 324                 # Find the relevant load array
 325                 if ( $group !== false ) {
 326                         if ( isset( $this->mGroupLoads[$group] ) ) {
 327                                 $nonErrorLoads = $this->mGroupLoads[$group];
 328                         } else {
 329                                 # No loads for this group, return false and the caller can use some other group
 330                                 $this->connLogger->info( __METHOD__ . ": no loads for group $group" );
 331
 332                                 return false;
 333                         }
 334                 } else {
 335                         $nonErrorLoads = $this->mLoads;
 336                 }
 337
 338                 if ( !count( $nonErrorLoads ) ) {
 339                         throw new InvalidArgumentException( "Empty server array given to LoadBalancer" );
 340                 }
 341
 342                 # Scale the configured load ratios according to the dynamic load if supported
 343                 $this->getLoadMonitor()->scaleLoads( $nonErrorLoads, $domain );
 344
 345                 $laggedReplicaMode = false;
 346
 347                 # No server found yet
 348                 $i = false;
 349                 # First try quickly looking through the available servers for a server that
 350                 # meets our criteria
 351                 $currentLoads = $nonErrorLoads;
 352                 while ( count( $currentLoads ) ) {
 353                         if ( $this->mAllowLagged || $laggedReplicaMode ) {
 354                                 $i = ArrayUtils::pickRandom( $currentLoads );
 355                         } else {
 356                                 $i = false;
 357                                 if ( $this->mWaitForPos && $this->mWaitForPos->asOfTime() ) {
 358                                         # ChronologyProtecter causes mWaitForPos to be set via sessions.
 359                                         # This triggers doWait() after connect, so it's especially good to
 360                                         # avoid lagged servers so as to avoid just blocking in that method.
 361                                         $ago = microtime( true ) - $this->mWaitForPos->asOfTime();
 362                                         # Aim for <= 1 second of waiting (being too picky can backfire)
 363                                         $i = $this->getRandomNonLagged( $currentLoads, $domain, $ago + 1 );
 364                                 }
 365                                 if ( $i === false ) {
 366                                         # Any server with less lag than it's 'max lag' param is preferable
 367                                         $i = $this->getRandomNonLagged( $currentLoads, $domain );
 368                                 }
 369                                 if ( $i === false && count( $currentLoads ) != 0 ) {
 370                                         # All replica DBs lagged. Switch to read-only mode
 371                                         $this->replLogger->error( "All replica DBs lagged. Switch to read-only mode" );
 372                                         $i = ArrayUtils::pickRandom( $currentLoads );
 373                                         $laggedReplicaMode = true;
 374                                 }
 375                         }
 376
 377                         if ( $i === false ) {
 378                                 # pickRandom() returned false
 379                                 # This is permanent and means the configuration or the load monitor
 380                                 # wants us to return false.
 381                                 $this->connLogger->debug( __METHOD__ . ": pickRandom() returned false" );
 382
 383                                 return false;
 384                         }
 385
 386                         $serverName = $this->getServerName( $i );
 387                         $this->connLogger->debug( __METHOD__ . ": Using reader #$i: $serverName..." );
 388
 389                         $conn = $this->openConnection( $i, $domain );
 390                         if ( !$conn ) {
 391                                 $this->connLogger->warning( __METHOD__ . ": Failed connecting to $i/$domain" );
 392                                 unset( $nonErrorLoads[$i] );
 393                                 unset( $currentLoads[$i] );
 394                                 $i = false;
 395                                 continue;
 396                         }
 397
 398                         // Decrement reference counter, we are finished with this connection.
 399                         // It will be incremented for the caller later.
 400                         if ( $domain !== false ) {
 401                                 $this->reuseConnection( $conn );
 402                         }
 403
 404                         # Return this server
 405                         break;
 406                 }
 407
 408                 # If all servers were down, quit now
 409                 if ( !count( $nonErrorLoads ) ) {
 410                         $this->connLogger->error( "All servers down" );
 411                 }
 412
 413                 if ( $i !== false ) {
 414                         # Replica DB connection successful.
 415                         # Wait for the session master pos for a short time.
 416                         if ( $this->mWaitForPos && $i > 0 ) {
 417                                 $this->doWait( $i );
 418                         }
 419                         if ( $this->mReadIndex <= 0 && $this->mLoads[$i] > 0 && $group === false ) {
 420                                 $this->mReadIndex = $i;
 421                                 # Record if the generic reader index is in "lagged replica DB" mode
 422                                 if ( $laggedReplicaMode ) {
 423                                         $this->laggedReplicaMode = true;
 424                                 }
 425                         }
 426                         $serverName = $this->getServerName( $i );
 427                         $this->connLogger->debug(
 428                                 __METHOD__ . ": using server $serverName for group '$group'" );
 429                 }
 430
 431                 return $i;
 432         }
 433
 434         public function waitFor( $pos ) {
 435                 $oldPos = $this->mWaitForPos;
 436                 $this->mWaitForPos = $pos;
 437
 438                 // If a generic reader connection was already established, then wait now
 439                 $i = $this->mReadIndex;
 440                 if ( $i > 0 ) {
 441                         if ( !$this->doWait( $i ) ) {
 442                                 $this->laggedReplicaMode = true;
 443                         }
 444                 }
 445
 446                 // Restore the older position if it was higher
 447                 $this->setWaitForPositionIfHigher( $oldPos );
 448         }
 449
 450         public function waitForOne( $pos, $timeout = null ) {
 451                 $oldPos = $this->mWaitForPos;
 452                 $this->mWaitForPos = $pos;
 453
 454                 $i = $this->mReadIndex;
 455                 if ( $i <= 0 ) {
 456                         // Pick a generic replica DB if there isn't one yet
 457                         $readLoads = $this->mLoads;
 458                         unset( $readLoads[$this->getWriterIndex()] ); // replica DBs only
 459                         $readLoads = array_filter( $readLoads ); // with non-zero load
 460                         $i = ArrayUtils::pickRandom( $readLoads );
 461                 }
 462
 463                 if ( $i > 0 ) {
 464                         $ok = $this->doWait( $i, true, $timeout );
 465                 } else {
 466                         $ok = true; // no applicable loads
 467                 }
 468
 469                 // Restore the older position if it was higher
 470                 $this->setWaitForPositionIfHigher( $oldPos );
 471
 472                 return $ok;
 473         }
 474
 475         public function waitForAll( $pos, $timeout = null ) {
 476                 $oldPos = $this->mWaitForPos;
 477                 $this->mWaitForPos = $pos;
 478                 $serverCount = count( $this->mServers );
 479
 480                 $ok = true;
 481                 for ( $i = 1; $i < $serverCount; $i++ ) {
 482                         if ( $this->mLoads[$i] > 0 ) {
 483                                 $ok = $this->doWait( $i, true, $timeout ) && $ok;
 484                         }
 485                 }
 486
 487                 // Restore the older position if it was higher
 488                 $this->setWaitForPositionIfHigher( $oldPos );
 489
 490                 return $ok;
 491         }
 492
 493         /**
 494          * @param DBMasterPos|bool $pos
 495          */
 496         private function setWaitForPositionIfHigher( $pos ) {
 497                 if ( !$pos ) {
 498                         return;
 499                 }
 500
 501                 if ( !$this->mWaitForPos || $pos->hasReached( $this->mWaitForPos ) ) {
 502                         $this->mWaitForPos = $pos;
 503                 }
 504         }
 505
 506         /**
 507          * @param int $i
 508          * @return IDatabase|bool
 509          */
 510         public function getAnyOpenConnection( $i ) {
 511                 foreach ( $this->mConns as $connsByServer ) {
 512                         if ( !empty( $connsByServer[$i] ) ) {
 513                                 /** @var $serverConns IDatabase[] */
 514                                 $serverConns = $connsByServer[$i];
 515
 516                                 return reset( $serverConns );
 517                         }
 518                 }
 519
 520                 return false;
 521         }
 522
 523         /**
 524          * Wait for a given replica DB to catch up to the master pos stored in $this
 525          * @param int $index Server index
 526          * @param bool $open Check the server even if a new connection has to be made
 527          * @param int $timeout Max seconds to wait; default is mWaitTimeout
 528          * @return bool
 529          */
 530         protected function doWait( $index, $open = false, $timeout = null ) {
 531                 $close = false; // close the connection afterwards
 532
 533                 // Check if we already know that the DB has reached this point
 534                 $server = $this->getServerName( $index );
 535                 $key = $this->srvCache->makeGlobalKey( __CLASS__, 'last-known-pos', $server, 'v1' );
 536                 /** @var DBMasterPos $knownReachedPos */
 537                 $knownReachedPos = $this->srvCache->get( $key );
 538                 if (
 539                         $knownReachedPos instanceof DBMasterPos &&
 540                         $knownReachedPos->hasReached( $this->mWaitForPos )
 541                 ) {
 542                         $this->replLogger->debug( __METHOD__ .
 543                                 ": replica DB $server known to be caught up (pos >= $knownReachedPos)." );
 544                         return true;
 545                 }
 546
 547                 // Find a connection to wait on, creating one if needed and allowed
 548                 $conn = $this->getAnyOpenConnection( $index );
 549                 if ( !$conn ) {
 550                         if ( !$open ) {
 551                                 $this->replLogger->debug( __METHOD__ . ": no connection open for $server" );
 552
 553                                 return false;
 554                         } else {
 555                                 $conn = $this->openConnection( $index, self::DOMAIN_ANY );
 556                                 if ( !$conn ) {
 557                                         $this->replLogger->warning( __METHOD__ . ": failed to connect to $server" );
 558
 559                                         return false;
 560                                 }
 561                                 // Avoid connection spam in waitForAll() when connections
 562                                 // are made just for the sake of doing this lag check.
 563                                 $close = true;
 564                         }
 565                 }
 566
 567                 $this->replLogger->info( __METHOD__ . ": Waiting for replica DB $server to catch up..." );
 568                 $timeout = $timeout ?: $this->mWaitTimeout;
 569                 $result = $conn->masterPosWait( $this->mWaitForPos, $timeout );
 570
 571                 if ( $result == -1 || is_null( $result ) ) {
 572                         // Timed out waiting for replica DB, use master instead
 573                         $this->replLogger->warning(
 574                                 __METHOD__ . ": Timed out waiting on {host} pos {$this->mWaitForPos}",
 575                                 [ 'host' => $server ]
 576                         );
 577                         $ok = false;
 578                 } else {
 579                         $this->replLogger->info( __METHOD__ . ": Done" );
 580                         $ok = true;
 581                         // Remember that the DB reached this point
 582                         $this->srvCache->set( $key, $this->mWaitForPos, BagOStuff::TTL_DAY );
 583                 }
 584
 585                 if ( $close ) {
 586                         $this->closeConnection( $conn );
 587                 }
 588
 589                 return $ok;
 590         }
 591
 592         /**
 593          * @see ILoadBalancer::getConnection()
 594          *
 595          * @param int $i
 596          * @param array $groups
 597          * @param bool $domain
 598          * @return Database
 599          * @throws DBConnectionError
 600          */
 601         public function getConnection( $i, $groups = [], $domain = false ) {
 602                 if ( $i === null || $i === false ) {
 603                         throw new InvalidArgumentException( 'Attempt to call ' . __METHOD__ .
 604                                 ' with invalid server index' );
 605                 }
 606
 607                 if ( $this->localDomain->equals( $domain ) || $domain === $this->localDomainIdAlias ) {
 608                         $domain = false; // local connection requested
 609                 }
 610
 611                 $groups = ( $groups === false || $groups === [] )
 612                         ? [ false ] // check one "group": the generic pool
 613                         : (array)$groups;
 614
 615                 $masterOnly = ( $i == self::DB_MASTER || $i == $this->getWriterIndex() );
 616                 $oldConnsOpened = $this->connsOpened; // connections open now
 617
 618                 if ( $i == self::DB_MASTER ) {
 619                         $i = $this->getWriterIndex();
 620                 } else {
 621                         # Try to find an available server in any the query groups (in order)
 622                         foreach ( $groups as $group ) {
 623                                 $groupIndex = $this->getReaderIndex( $group, $domain );
 624                                 if ( $groupIndex !== false ) {
 625                                         $i = $groupIndex;
 626                                         break;
 627                                 }
 628                         }
 629                 }
 630
 631                 # Operation-based index
 632                 if ( $i == self::DB_REPLICA ) {
 633                         $this->mLastError = 'Unknown error'; // reset error string
 634                         # Try the general server pool if $groups are unavailable.
 635                         $i = ( $groups === [ false ] )
 636                                 ? false // don't bother with this if that is what was tried above
 637                                 : $this->getReaderIndex( false, $domain );
 638                         # Couldn't find a working server in getReaderIndex()?
 639                         if ( $i === false ) {
 640                                 $this->mLastError = 'No working replica DB server: ' . $this->mLastError;
 641                                 // Throw an exception
 642                                 $this->reportConnectionError();
 643                                 return null; // not reached
 644                         }
 645                 }
 646
 647                 # Now we have an explicit index into the servers array
 648                 $conn = $this->openConnection( $i, $domain );
 649                 if ( !$conn ) {
 650                         // Throw an exception
 651                         $this->reportConnectionError();
 652                         return null; // not reached
 653                 }
 654
 655                 # Profile any new connections that happen
 656                 if ( $this->connsOpened > $oldConnsOpened ) {
 657                         $host = $conn->getServer();
 658                         $dbname = $conn->getDBname();
 659                         $this->trxProfiler->recordConnection( $host, $dbname, $masterOnly );
 660                 }
 661
 662                 if ( $masterOnly ) {
 663                         # Make master-requested DB handles inherit any read-only mode setting
 664                         $conn->setLBInfo( 'readOnlyReason', $this->getReadOnlyReason( $domain, $conn ) );
 665                 }
 666
 667                 return $conn;
 668         }
 669
 670         public function reuseConnection( $conn ) {
 671                 $serverIndex = $conn->getLBInfo( 'serverIndex' );
 672                 $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 673                 if ( $serverIndex === null || $refCount === null ) {
 674                         /**
 675                          * This can happen in code like:
 676                          *   foreach ( $dbs as $db ) {
 677                          *     $conn = $lb->getConnection( $lb::DB_REPLICA, [], $db );
 678                          *     ...
 679                          *     $lb->reuseConnection( $conn );
 680                          *   }
 681                          * When a connection to the local DB is opened in this way, reuseConnection()
 682                          * should be ignored
 683                          */
 684                         return;
 685                 } elseif ( $conn instanceof DBConnRef ) {
 686                         // DBConnRef already handles calling reuseConnection() and only passes the live
 687                         // Database instance to this method. Any caller passing in a DBConnRef is broken.
 688                         $this->connLogger->error( __METHOD__ . ": got DBConnRef instance.\n" .
 689                                 ( new RuntimeException() )->getTraceAsString() );
 690
 691                         return;
 692                 }
 693
 694                 if ( $this->disabled ) {
 695                         return; // DBConnRef handle probably survived longer than the LoadBalancer
 696                 }
 697
 698                 $domain = $conn->getDomainID();
 699                 if ( !isset( $this->mConns['foreignUsed'][$serverIndex][$domain] ) ) {
 700                         throw new InvalidArgumentException( __METHOD__ .
 701                                 ": connection $serverIndex/$domain not found; it may have already been freed." );
 702                 } elseif ( $this->mConns['foreignUsed'][$serverIndex][$domain] !== $conn ) {
 703                         throw new InvalidArgumentException( __METHOD__ .
 704                                 ": connection $serverIndex/$domain mismatched; it may have already been freed." );
 705                 }
 706                 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
 707                 if ( $refCount <= 0 ) {
 708                         $this->mConns['foreignFree'][$serverIndex][$domain] = $conn;
 709                         unset( $this->mConns['foreignUsed'][$serverIndex][$domain] );
 710                         if ( !$this->mConns['foreignUsed'][$serverIndex] ) {
 711                                 unset( $this->mConns[ 'foreignUsed' ][$serverIndex] ); // clean up
 712                         }
 713                         $this->connLogger->debug( __METHOD__ . ": freed connection $serverIndex/$domain" );
 714                 } else {
 715                         $this->connLogger->debug( __METHOD__ .
 716                                 ": reference count for $serverIndex/$domain reduced to $refCount" );
 717                 }
 718         }
 719
 720         public function getConnectionRef( $db, $groups = [], $domain = false ) {
 721                 $domain = ( $domain !== false ) ? $domain : $this->localDomain;
 722
 723                 return new DBConnRef( $this, $this->getConnection( $db, $groups, $domain ) );
 724         }
 725
 726         public function getLazyConnectionRef( $db, $groups = [], $domain = false ) {
 727                 $domain = ( $domain !== false ) ? $domain : $this->localDomain;
 728
 729                 return new DBConnRef( $this, [ $db, $groups, $domain ] );
 730         }
 731
 732         public function getMaintenanceConnectionRef( $db, $groups = [], $domain = false ) {
 733                 $domain = ( $domain !== false ) ? $domain : $this->localDomain;
 734
 735                 return new MaintainableDBConnRef( $this, $this->getConnection( $db, $groups, $domain ) );
 736         }
 737
 738         /**
 739          * @see ILoadBalancer::openConnection()
 740          *
 741          * @param int $i
 742          * @param bool $domain
 743          * @return bool|Database
 744          * @throws DBAccessError
 745          */
 746         public function openConnection( $i, $domain = false ) {
 747                 if ( $this->localDomain->equals( $domain ) || $domain === $this->localDomainIdAlias ) {
 748                         $domain = false; // local connection requested
 749                 }
 750
 751                 if ( !$this->chronProtInitialized && $this->chronProt ) {
 752                         $this->connLogger->debug( __METHOD__ . ': calling initLB() before first connection.' );
 753                         // Load CP positions before connecting so that doWait() triggers later if needed
 754                         $this->chronProtInitialized = true;
 755                         $this->chronProt->initLB( $this );
 756                 }
 757
 758                 if ( $domain !== false ) {
 759                         $conn = $this->openForeignConnection( $i, $domain );
 760                 } elseif ( isset( $this->mConns['local'][$i][0] ) ) {
 761                         $conn = $this->mConns['local'][$i][0];
 762                 } else {
 763                         if ( !isset( $this->mServers[$i] ) || !is_array( $this->mServers[$i] ) ) {
 764                                 throw new InvalidArgumentException( "No server with index '$i'." );
 765                         }
 766                         // Open a new connection
 767                         $server = $this->mServers[$i];
 768                         $server['serverIndex'] = $i;
 769                         $conn = $this->reallyOpenConnection( $server, false );
 770                         $serverName = $this->getServerName( $i );
 771                         if ( $conn->isOpen() ) {
 772                                 $this->connLogger->debug( "Connected to database $i at '$serverName'." );
 773                                 $this->mConns['local'][$i][0] = $conn;
 774                         } else {
 775                                 $this->connLogger->warning( "Failed to connect to database $i at '$serverName'." );
 776                                 $this->errorConnection = $conn;
 777                                 $conn = false;
 778                         }
 779                 }
 780
 781                 if ( $conn instanceof IDatabase && !$conn->isOpen() ) {
 782                         // Connection was made but later unrecoverably lost for some reason.
 783                         // Do not return a handle that will just throw exceptions on use,
 784                         // but let the calling code (e.g. getReaderIndex) try another server.
 785                         // See DatabaseMyslBase::ping() for how this can happen.
 786                         $this->errorConnection = $conn;
 787                         $conn = false;
 788                 }
 789
 790                 return $conn;
 791         }
 792
 793         /**
 794          * Open a connection to a foreign DB, or return one if it is already open.
 795          *
 796          * Increments a reference count on the returned connection which locks the
 797          * connection to the requested domain. This reference count can be
 798          * decremented by calling reuseConnection().
 799          *
 800          * If a connection is open to the appropriate server already, but with the wrong
 801          * database, it will be switched to the right database and returned, as long as
 802          * it has been freed first with reuseConnection().
 803          *
 804          * On error, returns false, and the connection which caused the
 805          * error will be available via $this->errorConnection.
 806          *
 807          * @note If disable() was called on this LoadBalancer, this method will throw a DBAccessError.
 808          *
 809          * @param int $i Server index
 810          * @param string $domain Domain ID to open
 811          * @return Database
 812          */
 813         private function openForeignConnection( $i, $domain ) {
 814                 $domainInstance = DatabaseDomain::newFromId( $domain );
 815                 $dbName = $domainInstance->getDatabase();
 816                 $prefix = $domainInstance->getTablePrefix();
 817
 818                 if ( isset( $this->mConns['foreignUsed'][$i][$domain] ) ) {
 819                         // Reuse an already-used connection
 820                         $conn = $this->mConns['foreignUsed'][$i][$domain];
 821                         $this->connLogger->debug( __METHOD__ . ": reusing connection $i/$domain" );
 822                 } elseif ( isset( $this->mConns['foreignFree'][$i][$domain] ) ) {
 823                         // Reuse a free connection for the same domain
 824                         $conn = $this->mConns['foreignFree'][$i][$domain];
 825                         unset( $this->mConns['foreignFree'][$i][$domain] );
 826                         $this->mConns['foreignUsed'][$i][$domain] = $conn;
 827                         $this->connLogger->debug( __METHOD__ . ": reusing free connection $i/$domain" );
 828                 } elseif ( !empty( $this->mConns['foreignFree'][$i] ) ) {
 829                         // Reuse a connection from another domain
 830                         $conn = reset( $this->mConns['foreignFree'][$i] );
 831                         $oldDomain = key( $this->mConns['foreignFree'][$i] );
 832                         // The empty string as a DB name means "don't care".
 833                         // DatabaseMysqlBase::open() already handle this on connection.
 834                         if ( strlen( $dbName ) && !$conn->selectDB( $dbName ) ) {
 835                                 $this->mLastError = "Error selecting database '$dbName' on server " .
 836                                         $conn->getServer() . " from client host {$this->host}";
 837                                 $this->errorConnection = $conn;
 838                                 $conn = false;
 839                         } else {
 840                                 $conn->tablePrefix( $prefix );
 841                                 unset( $this->mConns['foreignFree'][$i][$oldDomain] );
 842                                 $this->mConns['foreignUsed'][$i][$domain] = $conn;
 843                                 $this->connLogger->debug( __METHOD__ .
 844                                         ": reusing free connection from $oldDomain for $domain" );
 845                         }
 846                 } else {
 847                         if ( !isset( $this->mServers[$i] ) || !is_array( $this->mServers[$i] ) ) {
 848                                 throw new InvalidArgumentException( "No server with index '$i'." );
 849                         }
 850                         // Open a new connection
 851                         $server = $this->mServers[$i];
 852                         $server['serverIndex'] = $i;
 853                         $server['foreignPoolRefCount'] = 0;
 854                         $server['foreign'] = true;
 855                         $conn = $this->reallyOpenConnection( $server, $dbName );
 856                         if ( !$conn->isOpen() ) {
 857                                 $this->connLogger->warning( __METHOD__ . ": connection error for $i/$domain" );
 858                                 $this->errorConnection = $conn;
 859                                 $conn = false;
 860                         } else {
 861                                 $conn->tablePrefix( $prefix );
 862                                 $this->mConns['foreignUsed'][$i][$domain] = $conn;
 863                                 $this->connLogger->debug( __METHOD__ . ": opened new connection for $i/$domain" );
 864                         }
 865                 }
 866
 867                 // Increment reference count
 868                 if ( $conn instanceof IDatabase ) {
 869                         $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 870                         $conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
 871                 }
 872
 873                 return $conn;
 874         }
 875
 876         /**
 877          * Test if the specified index represents an open connection
 878          *
 879          * @param int $index Server index
 880          * @access private
 881          * @return bool
 882          */
 883         private function isOpen( $index ) {
 884                 if ( !is_integer( $index ) ) {
 885                         return false;
 886                 }
 887
 888                 return (bool)$this->getAnyOpenConnection( $index );
 889         }
 890
 891         /**
 892          * Really opens a connection. Uncached.
 893          * Returns a Database object whether or not the connection was successful.
 894          * @access private
 895          *
 896          * @param array $server
 897          * @param string|bool $dbNameOverride Use "" to not select any database
 898          * @return Database
 899          * @throws DBAccessError
 900          * @throws InvalidArgumentException
 901          */
 902         protected function reallyOpenConnection( array $server, $dbNameOverride = false ) {
 903                 if ( $this->disabled ) {
 904                         throw new DBAccessError();
 905                 }
 906
 907                 if ( $dbNameOverride !== false ) {
 908                         $server['dbname'] = $dbNameOverride;
 909                 }
 910
 911                 // Let the handle know what the cluster master is (e.g. "db1052")
 912                 $masterName = $this->getServerName( $this->getWriterIndex() );
 913                 $server['clusterMasterHost'] = $masterName;
 914
 915                 // Log when many connection are made on requests
 916                 if ( ++$this->connsOpened >= self::CONN_HELD_WARN_THRESHOLD ) {
 917                         $this->perfLogger->warning( __METHOD__ . ": " .
 918                                 "{$this->connsOpened}+ connections made (master=$masterName)" );
 919                 }
 920
 921                 $server['srvCache'] = $this->srvCache;
 922                 // Set loggers and profilers
 923                 $server['connLogger'] = $this->connLogger;
 924                 $server['queryLogger'] = $this->queryLogger;
 925                 $server['errorLogger'] = $this->errorLogger;
 926                 $server['profiler'] = $this->profiler;
 927                 $server['trxProfiler'] = $this->trxProfiler;
 928                 // Use the same agent and PHP mode for all DB handles
 929                 $server['cliMode'] = $this->cliMode;
 930                 $server['agent'] = $this->agent;
 931                 // Use DBO_DEFAULT flags by default for LoadBalancer managed databases. Assume that the
 932                 // application calls LoadBalancer::commitMasterChanges() before the PHP script completes.
 933                 $server['flags'] = isset( $server['flags'] ) ? $server['flags'] : IDatabase::DBO_DEFAULT;
 934
 935                 // Create a live connection object
 936                 try {
 937                         $db = Database::factory( $server['type'], $server );
 938                 } catch ( DBConnectionError $e ) {
 939                         // FIXME: This is probably the ugliest thing I have ever done to
 940                         // PHP. I'm half-expecting it to segfault, just out of disgust. -- TS
 941                         $db = $e->db;
 942                 }
 943
 944                 $db->setLBInfo( $server );
 945                 $db->setLazyMasterHandle(
 946                         $this->getLazyConnectionRef( self::DB_MASTER, [], $db->getDomainID() )
 947                 );
 948                 $db->setTableAliases( $this->tableAliases );
 949
 950                 if ( $server['serverIndex'] === $this->getWriterIndex() ) {
 951                         if ( $this->trxRoundId !== false ) {
 952                                 $this->applyTransactionRoundFlags( $db );
 953                         }
 954                         foreach ( $this->trxRecurringCallbacks as $name => $callback ) {
 955                                 $db->setTransactionListener( $name, $callback );
 956                         }
 957                 }
 958
 959                 return $db;
 960         }
 961
 962         /**
 963          * @throws DBConnectionError
 964          */
 965         private function reportConnectionError() {
 966                 $conn = $this->errorConnection; // the connection which caused the error
 967                 $context = [
 968                         'method' => __METHOD__,
 969                         'last_error' => $this->mLastError,
 970                 ];
 971
 972                 if ( $conn instanceof IDatabase ) {
 973                         $context['db_server'] = $conn->getServer();
 974                         $this->connLogger->warning(
 975                                 "Connection error: {last_error} ({db_server})",
 976                                 $context
 977                         );
 978
 979                         // throws DBConnectionError
 980                         $conn->reportConnectionError( "{$this->mLastError} ({$context['db_server']})" );
 981                 } else {
 982                         // No last connection, probably due to all servers being too busy
 983                         $this->connLogger->error(
 984                                 "LB failure with no last connection. Connection error: {last_error}",
 985                                 $context
 986                         );
 987
 988                         // If all servers were busy, mLastError will contain something sensible
 989                         throw new DBConnectionError( null, $this->mLastError );
 990                 }
 991         }
 992
 993         public function getWriterIndex() {
 994                 return 0;
 995         }
 996
 997         public function haveIndex( $i ) {
 998                 return array_key_exists( $i, $this->mServers );
 999         }
1000
1001         public function isNonZeroLoad( $i ) {
1002                 return array_key_exists( $i, $this->mServers ) && $this->mLoads[$i] != 0;
1003         }
1004
1005         public function getServerCount() {
1006                 return count( $this->mServers );
1007         }
1008
1009         public function getServerName( $i ) {
1010                 if ( isset( $this->mServers[$i]['hostName'] ) ) {
1011                         $name = $this->mServers[$i]['hostName'];
1012                 } elseif ( isset( $this->mServers[$i]['host'] ) ) {
1013                         $name = $this->mServers[$i]['host'];
1014                 } else {
1015                         $name = '';
1016                 }
1017
1018                 return ( $name != '' ) ? $name : 'localhost';
1019         }
1020
1021         public function getServerInfo( $i ) {
1022                 if ( isset( $this->mServers[$i] ) ) {
1023                         return $this->mServers[$i];
1024                 } else {
1025                         return false;
1026                 }
1027         }
1028
1029         public function setServerInfo( $i, array $serverInfo ) {
1030                 $this->mServers[$i] = $serverInfo;
1031         }
1032
1033         public function getMasterPos() {
1034                 # If this entire request was served from a replica DB without opening a connection to the
1035                 # master (however unlikely that may be), then we can fetch the position from the replica DB.
1036                 $masterConn = $this->getAnyOpenConnection( $this->getWriterIndex() );
1037                 if ( !$masterConn ) {
1038                         $serverCount = count( $this->mServers );
1039                         for ( $i = 1; $i < $serverCount; $i++ ) {
1040                                 $conn = $this->getAnyOpenConnection( $i );
1041                                 if ( $conn ) {
1042                                         return $conn->getReplicaPos();
1043                                 }
1044                         }
1045                 } else {
1046                         return $masterConn->getMasterPos();
1047                 }
1048
1049                 return false;
1050         }
1051
1052         public function disable() {
1053                 $this->closeAll();
1054                 $this->disabled = true;
1055         }
1056
1057         public function closeAll() {
1058                 $this->forEachOpenConnection( function ( IDatabase $conn ) {
1059                         $host = $conn->getServer();
1060                         $this->connLogger->debug( "Closing connection to database '$host'." );
1061                         $conn->close();
1062                 } );
1063
1064                 $this->mConns = [
1065                         'local' => [],
1066                         'foreignFree' => [],
1067                         'foreignUsed' => [],
1068                 ];
1069                 $this->connsOpened = 0;
1070         }
1071
1072         public function closeConnection( IDatabase $conn ) {
1073                 $serverIndex = $conn->getLBInfo( 'serverIndex' ); // second index level of mConns
1074                 foreach ( $this->mConns as $type => $connsByServer ) {
1075                         if ( !isset( $connsByServer[$serverIndex] ) ) {
1076                                 continue;
1077                         }
1078
1079                         foreach ( $connsByServer[$serverIndex] as $i => $trackedConn ) {
1080                                 if ( $conn === $trackedConn ) {
1081                                         $host = $this->getServerName( $i );
1082                                         $this->connLogger->debug( "Closing connection to database $i at '$host'." );
1083                                         unset( $this->mConns[$type][$serverIndex][$i] );
1084                                         --$this->connsOpened;
1085                                         break 2;
1086                                 }
1087                         }
1088                 }
1089
1090                 $conn->close();
1091         }
1092
1093         public function commitAll( $fname = __METHOD__ ) {
1094                 $failures = [];
1095
1096                 $restore = ( $this->trxRoundId !== false );
1097                 $this->trxRoundId = false;
1098                 $this->forEachOpenConnection(
1099                         function ( IDatabase $conn ) use ( $fname, $restore, &$failures ) {
1100                                 try {
1101                                         $conn->commit( $fname, $conn::FLUSHING_ALL_PEERS );
1102                                 } catch ( DBError $e ) {
1103                                         call_user_func( $this->errorLogger, $e );
1104                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1105                                 }
1106                                 if ( $restore && $conn->getLBInfo( 'master' ) ) {
1107                                         $this->undoTransactionRoundFlags( $conn );
1108                                 }
1109                         }
1110                 );
1111
1112                 if ( $failures ) {
1113                         throw new DBExpectedError(
1114                                 null,
1115                                 "Commit failed on server(s) " . implode( "\n", array_unique( $failures ) )
1116                         );
1117                 }
1118         }
1119
1120         public function finalizeMasterChanges() {
1121                 $this->forEachOpenMasterConnection( function ( Database $conn ) {
1122                         // Any error should cause all DB transactions to be rolled back together
1123                         $conn->setTrxEndCallbackSuppression( false );
1124                         $conn->runOnTransactionPreCommitCallbacks();
1125                         // Defer post-commit callbacks until COMMIT finishes for all DBs
1126                         $conn->setTrxEndCallbackSuppression( true );
1127                 } );
1128         }
1129
1130         public function approveMasterChanges( array $options ) {
1131                 $limit = isset( $options['maxWriteDuration'] ) ? $options['maxWriteDuration'] : 0;
1132                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( $limit ) {
1133                         // If atomic sections or explicit transactions are still open, some caller must have
1134                         // caught an exception but failed to properly rollback any changes. Detect that and
1135                         // throw and error (causing rollback).
1136                         if ( $conn->explicitTrxActive() ) {
1137                                 throw new DBTransactionError(
1138                                         $conn,
1139                                         "Explicit transaction still active. A caller may have caught an error."
1140                                 );
1141                         }
1142                         // Assert that the time to replicate the transaction will be sane.
1143                         // If this fails, then all DB transactions will be rollback back together.
1144                         $time = $conn->pendingWriteQueryDuration( $conn::ESTIMATE_DB_APPLY );
1145                         if ( $limit > 0 && $time > $limit ) {
1146                                 throw new DBTransactionSizeError(
1147                                         $conn,
1148                                         "Transaction spent $time second(s) in writes, exceeding the $limit limit.",
1149                                         [ $time, $limit ]
1150                                 );
1151                         }
1152                         // If a connection sits idle while slow queries execute on another, that connection
1153                         // may end up dropped before the commit round is reached. Ping servers to detect this.
1154                         if ( $conn->writesOrCallbacksPending() && !$conn->ping() ) {
1155                                 throw new DBTransactionError(
1156                                         $conn,
1157                                         "A connection to the {$conn->getDBname()} database was lost before commit."
1158                                 );
1159                         }
1160                 } );
1161         }
1162
1163         public function beginMasterChanges( $fname = __METHOD__ ) {
1164                 if ( $this->trxRoundId !== false ) {
1165                         throw new DBTransactionError(
1166                                 null,
1167                                 "$fname: Transaction round '{$this->trxRoundId}' already started."
1168                         );
1169                 }
1170                 $this->trxRoundId = $fname;
1171
1172                 $failures = [];
1173                 $this->forEachOpenMasterConnection(
1174                         function ( Database $conn ) use ( $fname, &$failures ) {
1175                                 $conn->setTrxEndCallbackSuppression( true );
1176                                 try {
1177                                         $conn->flushSnapshot( $fname );
1178                                 } catch ( DBError $e ) {
1179                                         call_user_func( $this->errorLogger, $e );
1180                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1181                                 }
1182                                 $conn->setTrxEndCallbackSuppression( false );
1183                                 $this->applyTransactionRoundFlags( $conn );
1184                         }
1185                 );
1186
1187                 if ( $failures ) {
1188                         throw new DBExpectedError(
1189                                 null,
1190                                 "$fname: Flush failed on server(s) " . implode( "\n", array_unique( $failures ) )
1191                         );
1192                 }
1193         }
1194
1195         public function commitMasterChanges( $fname = __METHOD__ ) {
1196                 $failures = [];
1197
1198                 /** @noinspection PhpUnusedLocalVariableInspection */
1199                 $scope = $this->getScopedPHPBehaviorForCommit(); // try to ignore client aborts
1200
1201                 $restore = ( $this->trxRoundId !== false );
1202                 $this->trxRoundId = false;
1203                 $this->forEachOpenMasterConnection(
1204                         function ( IDatabase $conn ) use ( $fname, $restore, &$failures ) {
1205                                 try {
1206                                         if ( $conn->writesOrCallbacksPending() ) {
1207                                                 $conn->commit( $fname, $conn::FLUSHING_ALL_PEERS );
1208                                         } elseif ( $restore ) {
1209                                                 $conn->flushSnapshot( $fname );
1210                                         }
1211                                 } catch ( DBError $e ) {
1212                                         call_user_func( $this->errorLogger, $e );
1213                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1214                                 }
1215                                 if ( $restore ) {
1216                                         $this->undoTransactionRoundFlags( $conn );
1217                                 }
1218                         }
1219                 );
1220
1221                 if ( $failures ) {
1222                         throw new DBExpectedError(
1223                                 null,
1224                                 "$fname: Commit failed on server(s) " . implode( "\n", array_unique( $failures ) )
1225                         );
1226                 }
1227         }
1228
1229         public function runMasterPostTrxCallbacks( $type ) {
1230                 $e = null; // first exception
1231                 $this->forEachOpenMasterConnection( function ( Database $conn ) use ( $type, &$e ) {
1232                         $conn->setTrxEndCallbackSuppression( false );
1233                         if ( $conn->writesOrCallbacksPending() ) {
1234                                 // This happens if onTransactionIdle() callbacks leave callbacks on *another* DB
1235                                 // (which finished its callbacks already). Warn and recover in this case. Let the
1236                                 // callbacks run in the final commitMasterChanges() in LBFactory::shutdown().
1237                                 $this->queryLogger->error( __METHOD__ . ": found writes/callbacks pending." );
1238                                 return;
1239                         } elseif ( $conn->trxLevel() ) {
1240                                 // This happens for single-DB setups where DB_REPLICA uses the master DB,
1241                                 // thus leaving an implicit read-only transaction open at this point. It
1242                                 // also happens if onTransactionIdle() callbacks leave implicit transactions
1243                                 // open on *other* DBs (which is slightly improper). Let these COMMIT on the
1244                                 // next call to commitMasterChanges(), possibly in LBFactory::shutdown().
1245                                 return;
1246                         }
1247                         try {
1248                                 $conn->runOnTransactionIdleCallbacks( $type );
1249                         } catch ( Exception $ex ) {
1250                                 $e = $e ?: $ex;
1251                         }
1252                         try {
1253                                 $conn->runTransactionListenerCallbacks( $type );
1254                         } catch ( Exception $ex ) {
1255                                 $e = $e ?: $ex;
1256                         }
1257                 } );
1258
1259                 return $e;
1260         }
1261
1262         public function rollbackMasterChanges( $fname = __METHOD__ ) {
1263                 $restore = ( $this->trxRoundId !== false );
1264                 $this->trxRoundId = false;
1265                 $this->forEachOpenMasterConnection(
1266                         function ( IDatabase $conn ) use ( $fname, $restore ) {
1267                                 if ( $conn->writesOrCallbacksPending() ) {
1268                                         $conn->rollback( $fname, $conn::FLUSHING_ALL_PEERS );
1269                                 }
1270                                 if ( $restore ) {
1271                                         $this->undoTransactionRoundFlags( $conn );
1272                                 }
1273                         }
1274                 );
1275         }
1276
1277         public function suppressTransactionEndCallbacks() {
1278                 $this->forEachOpenMasterConnection( function ( Database $conn ) {
1279                         $conn->setTrxEndCallbackSuppression( true );
1280                 } );
1281         }
1282
1283         /**
1284          * @param IDatabase $conn
1285          */
1286         private function applyTransactionRoundFlags( IDatabase $conn ) {
1287                 if ( $conn->getFlag( $conn::DBO_DEFAULT ) ) {
1288                         // DBO_TRX is controlled entirely by CLI mode presence with DBO_DEFAULT.
1289                         // Force DBO_TRX even in CLI mode since a commit round is expected soon.
1290                         $conn->setFlag( $conn::DBO_TRX, $conn::REMEMBER_PRIOR );
1291                         // If config has explicitly requested DBO_TRX be either on or off by not
1292                         // setting DBO_DEFAULT, then respect that. Forcing no transactions is useful
1293                         // for things like blob stores (ExternalStore) which want auto-commit mode.
1294                 }
1295         }
1296
1297         /**
1298          * @param IDatabase $conn
1299          */
1300         private function undoTransactionRoundFlags( IDatabase $conn ) {
1301                 if ( $conn->getFlag( $conn::DBO_DEFAULT ) ) {
1302                         $conn->restoreFlags( $conn::RESTORE_PRIOR );
1303                 }
1304         }
1305
1306         public function flushReplicaSnapshots( $fname = __METHOD__ ) {
1307                 $this->forEachOpenReplicaConnection( function ( IDatabase $conn ) {
1308                         $conn->flushSnapshot( __METHOD__ );
1309                 } );
1310         }
1311
1312         public function hasMasterConnection() {
1313                 return $this->isOpen( $this->getWriterIndex() );
1314         }
1315
1316         public function hasMasterChanges() {
1317                 $pending = 0;
1318                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$pending ) {
1319                         $pending |= $conn->writesOrCallbacksPending();
1320                 } );
1321
1322                 return (bool)$pending;
1323         }
1324
1325         public function lastMasterChangeTimestamp() {
1326                 $lastTime = false;
1327                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$lastTime ) {
1328                         $lastTime = max( $lastTime, $conn->lastDoneWrites() );
1329                 } );
1330
1331                 return $lastTime;
1332         }
1333
1334         public function hasOrMadeRecentMasterChanges( $age = null ) {
1335                 $age = ( $age === null ) ? $this->mWaitTimeout : $age;
1336
1337                 return ( $this->hasMasterChanges()
1338                         || $this->lastMasterChangeTimestamp() > microtime( true ) - $age );
1339         }
1340
1341         public function pendingMasterChangeCallers() {
1342                 $fnames = [];
1343                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$fnames ) {
1344                         $fnames = array_merge( $fnames, $conn->pendingWriteCallers() );
1345                 } );
1346
1347                 return $fnames;
1348         }
1349
1350         public function getLaggedReplicaMode( $domain = false ) {
1351                 // No-op if there is only one DB (also avoids recursion)
1352                 if ( !$this->laggedReplicaMode && $this->getServerCount() > 1 ) {
1353                         try {
1354                                 // See if laggedReplicaMode gets set
1355                                 $conn = $this->getConnection( self::DB_REPLICA, false, $domain );
1356                                 $this->reuseConnection( $conn );
1357                         } catch ( DBConnectionError $e ) {
1358                                 // Avoid expensive re-connect attempts and failures
1359                                 $this->allReplicasDownMode = true;
1360                                 $this->laggedReplicaMode = true;
1361                         }
1362                 }
1363
1364                 return $this->laggedReplicaMode;
1365         }
1366
1367         /**
1368          * @param bool $domain
1369          * @return bool
1370          * @deprecated 1.28; use getLaggedReplicaMode()
1371          */
1372         public function getLaggedSlaveMode( $domain = false ) {
1373                 return $this->getLaggedReplicaMode( $domain );
1374         }
1375
1376         public function laggedReplicaUsed() {
1377                 return $this->laggedReplicaMode;
1378         }
1379
1380         /**
1381          * @return bool
1382          * @since 1.27
1383          * @deprecated Since 1.28; use laggedReplicaUsed()
1384          */
1385         public function laggedSlaveUsed() {
1386                 return $this->laggedReplicaUsed();
1387         }
1388
1389         public function getReadOnlyReason( $domain = false, IDatabase $conn = null ) {
1390                 if ( $this->readOnlyReason !== false ) {
1391                         return $this->readOnlyReason;
1392                 } elseif ( $this->getLaggedReplicaMode( $domain ) ) {
1393                         if ( $this->allReplicasDownMode ) {
1394                                 return 'The database has been automatically locked ' .
1395                                         'until the replica database servers become available';
1396                         } else {
1397                                 return 'The database has been automatically locked ' .
1398                                         'while the replica database servers catch up to the master.';
1399                         }
1400                 } elseif ( $this->masterRunningReadOnly( $domain, $conn ) ) {
1401                         return 'The database master is running in read-only mode.';
1402                 }
1403
1404                 return false;
1405         }
1406
1407         /**
1408          * @param string $domain Domain ID, or false for the current domain
1409          * @param IDatabase|null $conn DB master connectionl used to avoid loops [optional]
1410          * @return bool
1411          */
1412         private function masterRunningReadOnly( $domain, IDatabase $conn = null ) {
1413                 $cache = $this->wanCache;
1414                 $masterServer = $this->getServerName( $this->getWriterIndex() );
1415
1416                 return (bool)$cache->getWithSetCallback(
1417                         $cache->makeGlobalKey( __CLASS__, 'server-read-only', $masterServer ),
1418                         self::TTL_CACHE_READONLY,
1419                         function () use ( $domain, $conn ) {
1420                                 $old = $this->trxProfiler->setSilenced( true );
1421                                 try {
1422                                         $dbw = $conn ?: $this->getConnection( self::DB_MASTER, [], $domain );
1423                                         $readOnly = (int)$dbw->serverIsReadOnly();
1424                                         if ( !$conn ) {
1425                                                 $this->reuseConnection( $dbw );
1426                                         }
1427                                 } catch ( DBError $e ) {
1428                                         $readOnly = 0;
1429                                 }
1430                                 $this->trxProfiler->setSilenced( $old );
1431                                 return $readOnly;
1432                         },
1433                         [ 'pcTTL' => $cache::TTL_PROC_LONG, 'busyValue' => 0 ]
1434                 );
1435         }
1436
1437         public function allowLagged( $mode = null ) {
1438                 if ( $mode === null ) {
1439                         return $this->mAllowLagged;
1440                 }
1441                 $this->mAllowLagged = $mode;
1442
1443                 return $this->mAllowLagged;
1444         }
1445
1446         public function pingAll() {
1447                 $success = true;
1448                 $this->forEachOpenConnection( function ( IDatabase $conn ) use ( &$success ) {
1449                         if ( !$conn->ping() ) {
1450                                 $success = false;
1451                         }
1452                 } );
1453
1454                 return $success;
1455         }
1456
1457         public function forEachOpenConnection( $callback, array $params = [] ) {
1458                 foreach ( $this->mConns as $connsByServer ) {
1459                         foreach ( $connsByServer as $serverConns ) {
1460                                 foreach ( $serverConns as $conn ) {
1461                                         $mergedParams = array_merge( [ $conn ], $params );
1462                                         call_user_func_array( $callback, $mergedParams );
1463                                 }
1464                         }
1465                 }
1466         }
1467
1468         public function forEachOpenMasterConnection( $callback, array $params = [] ) {
1469                 $masterIndex = $this->getWriterIndex();
1470                 foreach ( $this->mConns as $connsByServer ) {
1471                         if ( isset( $connsByServer[$masterIndex] ) ) {
1472                                 /** @var IDatabase $conn */
1473                                 foreach ( $connsByServer[$masterIndex] as $conn ) {
1474                                         $mergedParams = array_merge( [ $conn ], $params );
1475                                         call_user_func_array( $callback, $mergedParams );
1476                                 }
1477                         }
1478                 }
1479         }
1480
1481         public function forEachOpenReplicaConnection( $callback, array $params = [] ) {
1482                 foreach ( $this->mConns as $connsByServer ) {
1483                         foreach ( $connsByServer as $i => $serverConns ) {
1484                                 if ( $i === $this->getWriterIndex() ) {
1485                                         continue; // skip master
1486                                 }
1487                                 foreach ( $serverConns as $conn ) {
1488                                         $mergedParams = array_merge( [ $conn ], $params );
1489                                         call_user_func_array( $callback, $mergedParams );
1490                                 }
1491                         }
1492                 }
1493         }
1494
1495         public function getMaxLag( $domain = false ) {
1496                 $maxLag = -1;
1497                 $host = '';
1498                 $maxIndex = 0;
1499
1500                 if ( $this->getServerCount() <= 1 ) {
1501                         return [ $host, $maxLag, $maxIndex ]; // no replication = no lag
1502                 }
1503
1504                 $lagTimes = $this->getLagTimes( $domain );
1505                 foreach ( $lagTimes as $i => $lag ) {
1506                         if ( $this->mLoads[$i] > 0 && $lag > $maxLag ) {
1507                                 $maxLag = $lag;
1508                                 $host = $this->mServers[$i]['host'];
1509                                 $maxIndex = $i;
1510                         }
1511                 }
1512
1513                 return [ $host, $maxLag, $maxIndex ];
1514         }
1515
1516         public function getLagTimes( $domain = false ) {
1517                 if ( $this->getServerCount() <= 1 ) {
1518                         return [ $this->getWriterIndex() => 0 ]; // no replication = no lag
1519                 }
1520
1521                 $knownLagTimes = []; // map of (server index => 0 seconds)
1522                 $indexesWithLag = [];
1523                 foreach ( $this->mServers as $i => $server ) {
1524                         if ( empty( $server['is static'] ) ) {
1525                                 $indexesWithLag[] = $i; // DB server might have replication lag
1526                         } else {
1527                                 $knownLagTimes[$i] = 0; // DB server is a non-replicating and read-only archive
1528                         }
1529                 }
1530
1531                 return $this->getLoadMonitor()->getLagTimes( $indexesWithLag, $domain ) + $knownLagTimes;
1532         }
1533
1534         public function safeGetLag( IDatabase $conn ) {
1535                 if ( $this->getServerCount() <= 1 ) {
1536                         return 0;
1537                 } else {
1538                         return $conn->getLag();
1539                 }
1540         }
1541
1542         /**
1543          * @param IDatabase $conn
1544          * @param DBMasterPos|bool $pos
1545          * @param int $timeout
1546          * @return bool
1547          */
1548         public function safeWaitForMasterPos( IDatabase $conn, $pos = false, $timeout = 10 ) {
1549                 if ( $this->getServerCount() <= 1 || !$conn->getLBInfo( 'replica' ) ) {
1550                         return true; // server is not a replica DB
1551                 }
1552
1553                 if ( !$pos ) {
1554                         // Get the current master position, opening a connection if needed
1555                         $masterConn = $this->getAnyOpenConnection( $this->getWriterIndex() );
1556                         if ( $masterConn ) {
1557                                 $pos = $masterConn->getMasterPos();
1558                         } else {
1559                                 $masterConn = $this->openConnection( $this->getWriterIndex(), self::DOMAIN_ANY );
1560                                 $pos = $masterConn->getMasterPos();
1561                                 $this->closeConnection( $masterConn );
1562                         }
1563                 }
1564
1565                 if ( $pos instanceof DBMasterPos ) {
1566                         $result = $conn->masterPosWait( $pos, $timeout );
1567                         if ( $result == -1 || is_null( $result ) ) {
1568                                 $msg = __METHOD__ . ": Timed out waiting on {$conn->getServer()} pos {$pos}";
1569                                 $this->replLogger->warning( "$msg" );
1570                                 $ok = false;
1571                         } else {
1572                                 $this->replLogger->info( __METHOD__ . ": Done" );
1573                                 $ok = true;
1574                         }
1575                 } else {
1576                         $ok = false; // something is misconfigured
1577                         $this->replLogger->error( "Could not get master pos for {$conn->getServer()}." );
1578                 }
1579
1580                 return $ok;
1581         }
1582
1583         public function setTransactionListener( $name, callable $callback = null ) {
1584                 if ( $callback ) {
1585                         $this->trxRecurringCallbacks[$name] = $callback;
1586                 } else {
1587                         unset( $this->trxRecurringCallbacks[$name] );
1588                 }
1589                 $this->forEachOpenMasterConnection(
1590                         function ( IDatabase $conn ) use ( $name, $callback ) {
1591                                 $conn->setTransactionListener( $name, $callback );
1592                         }
1593                 );
1594         }
1595
1596         public function setTableAliases( array $aliases ) {
1597                 $this->tableAliases = $aliases;
1598         }
1599
1600         public function setDomainPrefix( $prefix ) {
1601                 if ( $this->mConns['foreignUsed'] ) {
1602                         // Do not switch connections to explicit foreign domains unless marked as free
1603                         $domains = [];
1604                         foreach ( $this->mConns['foreignUsed'] as $i => $connsByDomain ) {
1605                                 $domains = array_merge( $domains, array_keys( $connsByDomain ) );
1606                         }
1607                         $domains = implode( ', ', $domains );
1608                         throw new DBUnexpectedError( null,
1609                                 "Foreign domain connections are still in use ($domains)." );
1610                 }
1611
1612                 $this->localDomain = new DatabaseDomain(
1613                         $this->localDomain->getDatabase(),
1614                         null,
1615                         $prefix
1616                 );
1617
1618                 $this->forEachOpenConnection( function ( IDatabase $db ) use ( $prefix ) {
1619                         $db->tablePrefix( $prefix );
1620                 } );
1621         }
1622
1623         /**
1624          * Make PHP ignore user aborts/disconnects until the returned
1625          * value leaves scope. This returns null and does nothing in CLI mode.
1626          *
1627          * @return ScopedCallback|null
1628          */
1629         final protected function getScopedPHPBehaviorForCommit() {
1630                 if ( PHP_SAPI != 'cli' ) { // https://bugs.php.net/bug.php?id=47540
1631                         $old = ignore_user_abort( true ); // avoid half-finished operations
1632                         return new ScopedCallback( function () use ( $old ) {
1633                                 ignore_user_abort( $old );
1634                         } );
1635                 }
1636
1637                 return null;
1638         }
1639
1640         function __destruct() {
1641                 // Avoid connection leaks for sanity
1642                 $this->disable();
1643         }
1644 }
1645
1646 class_alias( LoadBalancer::class, 'LoadBalancer' );