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