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