includes/libs/rdbms/loadbalancer/LoadBalancer.php

   1 <?php
   2 /**
   3  * Database load balancing manager
   4  *
   5  * This program is free software; you can redistribute it and/or modify
   6  * it under the terms of the GNU General Public License as published by
   7  * the Free Software Foundation; either version 2 of the License, or
   8  * (at your option) any later version.
   9  *
  10  * This program is distributed in the hope that it will be useful,
  11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  13  * GNU General Public License for more details.
  14  *
  15  * You should have received a copy of the GNU General Public License along
  16  * with this program; if not, write to the Free Software Foundation, Inc.,
  17  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
  18  * http://www.gnu.org/copyleft/gpl.html
  19  *
  20  * @file
  21  * @ingroup Database
  22  */
  23 namespace Wikimedia\Rdbms;
  24
  25 use Psr\Log\LoggerInterface;
  26 use Psr\Log\NullLogger;
  27 use Wikimedia\ScopedCallback;
  28 use Database;
  29 use BagOStuff;
  30 use EmptyBagOStuff;
  31 use WANObjectCache;
  32 use ArrayUtils;
  33 use DBError;
  34 use DBAccessError;
  35 use DBExpectedError;
  36 use DBUnexpectedError;
  37 use DBTransactionError;
  38 use DBTransactionSizeError;
  39 use DBConnectionError;
  40 use InvalidArgumentException;
  41 use RuntimeException;
  42 use Exception;
  43
  44 /**
  45  * Database connection, tracking, load balancing, and transaction manager for a cluster
  46  *
  47  * @ingroup Database
  48  */
  49 class LoadBalancer implements ILoadBalancer {
  50         /** @var array[] Map of (server index => server config array) */
  51         private $mServers;
  52         /** @var \Database[][][] Map of local/foreignUsed/foreignFree => server index => IDatabase array */
  53         private $mConns;
  54         /** @var float[] Map of (server index => weight) */
  55         private $mLoads;
  56         /** @var array[] Map of (group => server index => weight) */
  57         private $mGroupLoads;
  58         /** @var bool Whether to disregard replica DB lag as a factor in replica DB selection */
  59         private $mAllowLagged;
  60         /** @var integer Seconds to spend waiting on replica DB lag to resolve */
  61         private $mWaitTimeout;
  62         /** @var array The LoadMonitor configuration */
  63         private $loadMonitorConfig;
  64         /** @var array[] $aliases Map of (table => (dbname, schema, prefix) map) */
  65         private $tableAliases = [];
  66
  67         /** @var ILoadMonitor */
  68         private $loadMonitor;
  69         /** @var ChronologyProtector|null */
  70         private $chronProt;
  71         /** @var BagOStuff */
  72         private $srvCache;
  73         /** @var BagOStuff */
  74         private $memCache;
  75         /** @var WANObjectCache */
  76         private $wanCache;
  77         /** @var object|string Class name or object With profileIn/profileOut methods */
  78         protected $profiler;
  79         /** @var TransactionProfiler */
  80         protected $trxProfiler;
  81         /** @var LoggerInterface */
  82         protected $replLogger;
  83         /** @var LoggerInterface */
  84         protected $connLogger;
  85         /** @var LoggerInterface */
  86         protected $queryLogger;
  87         /** @var LoggerInterface */
  88         protected $perfLogger;
  89
  90         /** @var \Database Database connection that caused a problem */
  91         private $errorConnection;
  92         /** @var integer The generic (not query grouped) replica DB index (of $mServers) */
  93         private $mReadIndex;
  94         /** @var bool|DBMasterPos False if not set */
  95         private $mWaitForPos;
  96         /** @var bool Whether the generic reader fell back to a lagged replica DB */
  97         private $laggedReplicaMode = false;
  98         /** @var bool Whether the generic reader fell back to a lagged replica DB */
  99         private $allReplicasDownMode = false;
 100         /** @var string The last DB selection or connection error */
 101         private $mLastError = 'Unknown error';
 102         /** @var string|bool Reason the LB is read-only or false if not */
 103         private $readOnlyReason = false;
 104         /** @var integer Total connections opened */
 105         private $connsOpened = 0;
 106         /** @var string|bool String if a requested DBO_TRX transaction round is active */
 107         private $trxRoundId = false;
 108         /** @var array[] Map of (name => callable) */
 109         private $trxRecurringCallbacks = [];
 110         /** @var DatabaseDomain Local Domain ID and default for selectDB() calls */
 111         private $localDomain;
 112         /** @var string Alternate ID string for the domain instead of DatabaseDomain::getId() */
 113         private $localDomainIdAlias;
 114         /** @var string Current server name */
 115         private $host;
 116         /** @var bool Whether this PHP instance is for a CLI script */
 117         protected $cliMode;
 118         /** @var string Agent name for query profiling */
 119         protected $agent;
 120
 121         /** @var callable Exception logger */
 122         private $errorLogger;
 123
 124         /** @var boolean */
 125         private $disabled = false;
 126         /** @var boolean */
 127         private $chronProtInitialized = false;
 128
 129         /** @var integer Warn when this many connection are held */
 130         const CONN_HELD_WARN_THRESHOLD = 10;
 131
 132         /** @var integer Default 'max lag' when unspecified */
 133         const MAX_LAG_DEFAULT = 10;
 134         /** @var integer Seconds to cache master server read-only status */
 135         const TTL_CACHE_READONLY = 5;
 136
 137         public function __construct( array $params ) {
 138                 if ( !isset( $params['servers'] ) ) {
 139                         throw new InvalidArgumentException( __CLASS__ . ': missing servers parameter' );
 140                 }
 141                 $this->mServers = $params['servers'];
 142
 143                 $this->localDomain = isset( $params['localDomain'] )
 144                         ? DatabaseDomain::newFromId( $params['localDomain'] )
 145                         : DatabaseDomain::newUnspecified();
 146                 // In case a caller assumes that the domain ID is simply <db>-<prefix>, which is almost
 147                 // always true, gracefully handle the case when they fail to account for escaping.
 148                 if ( $this->localDomain->getTablePrefix() != '' ) {
 149                         $this->localDomainIdAlias =
 150                                 $this->localDomain->getDatabase() . '-' . $this->localDomain->getTablePrefix();
 151                 } else {
 152                         $this->localDomainIdAlias = $this->localDomain->getDatabase();
 153                 }
 154
 155                 $this->mWaitTimeout = isset( $params['waitTimeout'] ) ? $params['waitTimeout'] : 10;
 156
 157                 $this->mReadIndex = -1;
 158                 $this->mConns = [
 159                         'local'       => [],
 160                         'foreignUsed' => [],
 161                         'foreignFree' => []
 162                 ];
 163                 $this->mLoads = [];
 164                 $this->mWaitForPos = false;
 165                 $this->mAllowLagged = false;
 166
 167                 if ( isset( $params['readOnlyReason'] ) && is_string( $params['readOnlyReason'] ) ) {
 168                         $this->readOnlyReason = $params['readOnlyReason'];
 169                 }
 170
 171                 if ( isset( $params['loadMonitor'] ) ) {
 172                         $this->loadMonitorConfig = $params['loadMonitor'];
 173                 } else {
 174                         $this->loadMonitorConfig = [ 'class' => 'LoadMonitorNull' ];
 175                 }
 176
 177                 foreach ( $params['servers'] as $i => $server ) {
 178                         $this->mLoads[$i] = $server['load'];
 179                         if ( isset( $server['groupLoads'] ) ) {
 180                                 foreach ( $server['groupLoads'] as $group => $ratio ) {
 181                                         if ( !isset( $this->mGroupLoads[$group] ) ) {
 182                                                 $this->mGroupLoads[$group] = [];
 183                                         }
 184                                         $this->mGroupLoads[$group][$i] = $ratio;
 185                                 }
 186                         }
 187                 }
 188
 189                 if ( isset( $params['srvCache'] ) ) {
 190                         $this->srvCache = $params['srvCache'];
 191                 } else {
 192                         $this->srvCache = new EmptyBagOStuff();
 193                 }
 194                 if ( isset( $params['memCache'] ) ) {
 195                         $this->memCache = $params['memCache'];
 196                 } else {
 197                         $this->memCache = new EmptyBagOStuff();
 198                 }
 199                 if ( isset( $params['wanCache'] ) ) {
 200                         $this->wanCache = $params['wanCache'];
 201                 } else {
 202                         $this->wanCache = WANObjectCache::newEmpty();
 203                 }
 204                 $this->profiler = isset( $params['profiler'] ) ? $params['profiler'] : null;
 205                 if ( isset( $params['trxProfiler'] ) ) {
 206                         $this->trxProfiler = $params['trxProfiler'];
 207                 } else {
 208                         $this->trxProfiler = new TransactionProfiler();
 209                 }
 210
 211                 $this->errorLogger = isset( $params['errorLogger'] )
 212                         ? $params['errorLogger']
 213                         : function ( Exception $e ) {
 214                                 trigger_error( get_class( $e ) . ': ' . $e->getMessage(), E_USER_WARNING );
 215                         };
 216
 217                 foreach ( [ 'replLogger', 'connLogger', 'queryLogger', 'perfLogger' ] as $key ) {
 218                         $this->$key = isset( $params[$key] ) ? $params[$key] : new NullLogger();
 219                 }
 220
 221                 $this->host = isset( $params['hostname'] )
 222                         ? $params['hostname']
 223                         : ( gethostname() ?: 'unknown' );
 224                 $this->cliMode = isset( $params['cliMode'] ) ? $params['cliMode'] : PHP_SAPI === 'cli';
 225                 $this->agent = isset( $params['agent'] ) ? $params['agent'] : '';
 226
 227                 if ( isset( $params['chronologyProtector'] ) ) {
 228                         $this->chronProt = $params['chronologyProtector'];
 229                 }
 230         }
 231
 232         /**
 233          * Get a LoadMonitor instance
 234          *
 235          * @return ILoadMonitor
 236          */
 237         private function getLoadMonitor() {
 238                 if ( !isset( $this->loadMonitor ) ) {
 239                         $compat = [
 240                                 'LoadMonitor' => LoadMonitor::class,
 241                                 'LoadMonitorNull' => LoadMonitorNull::class,
 242                                 'LoadMonitorMySQL' => LoadMonitorMySQL::class,
 243                         ];
 244
 245                         $class = $this->loadMonitorConfig['class'];
 246                         if ( isset( $compat[$class] ) ) {
 247                                 $class = $compat[$class];
 248                         }
 249
 250                         $this->loadMonitor = new $class(
 251                                 $this, $this->srvCache, $this->memCache, $this->loadMonitorConfig );
 252                         $this->loadMonitor->setLogger( $this->replLogger );
 253                 }
 254
 255                 return $this->loadMonitor;
 256         }
 257
 258         /**
 259          * @param array $loads
 260          * @param bool|string $domain Domain to get non-lagged for
 261          * @param int $maxLag Restrict the maximum allowed lag to this many seconds
 262          * @return bool|int|string
 263          */
 264         private function getRandomNonLagged( array $loads, $domain = false, $maxLag = INF ) {
 265                 $lags = $this->getLagTimes( $domain );
 266
 267                 # Unset excessively lagged servers
 268                 foreach ( $lags as $i => $lag ) {
 269                         if ( $i != 0 ) {
 270                                 # How much lag this server nominally is allowed to have
 271                                 $maxServerLag = isset( $this->mServers[$i]['max lag'] )
 272                                         ? $this->mServers[$i]['max lag']
 273                                         : self::MAX_LAG_DEFAULT; // default
 274                                 # Constrain that futher by $maxLag argument
 275                                 $maxServerLag = min( $maxServerLag, $maxLag );
 276
 277                                 $host = $this->getServerName( $i );
 278                                 if ( $lag === false && !is_infinite( $maxServerLag ) ) {
 279                                         $this->replLogger->error(
 280                                                 "Server {host} (#$i) is not replicating?", [ 'host' => $host ] );
 281                                         unset( $loads[$i] );
 282                                 } elseif ( $lag > $maxServerLag ) {
 283                                         $this->replLogger->warning(
 284                                                 "Server {host} (#$i) has {lag} seconds of lag (>= {maxlag})",
 285                                                 [ 'host' => $host, 'lag' => $lag, 'maxlag' => $maxServerLag ]
 286                                         );
 287                                         unset( $loads[$i] );
 288                                 }
 289                         }
 290                 }
 291
 292                 # Find out if all the replica DBs with non-zero load are lagged
 293                 $sum = 0;
 294                 foreach ( $loads as $load ) {
 295                         $sum += $load;
 296                 }
 297                 if ( $sum == 0 ) {
 298                         # No appropriate DB servers except maybe the master and some replica DBs with zero load
 299                         # Do NOT use the master
 300                         # Instead, this function will return false, triggering read-only mode,
 301                         # and a lagged replica DB will be used instead.
 302                         return false;
 303                 }
 304
 305                 if ( count( $loads ) == 0 ) {
 306                         return false;
 307                 }
 308
 309                 # Return a random representative of the remainder
 310                 return ArrayUtils::pickRandom( $loads );
 311         }
 312
 313         public function getReaderIndex( $group = false, $domain = false ) {
 314                 if ( count( $this->mServers ) == 1 ) {
 315                         # Skip the load balancing if there's only one server
 316                         return $this->getWriterIndex();
 317                 } elseif ( $group === false && $this->mReadIndex >= 0 ) {
 318                         # Shortcut if generic reader exists already
 319                         return $this->mReadIndex;
 320                 }
 321
 322                 # Find the relevant load array
 323                 if ( $group !== false ) {
 324                         if ( isset( $this->mGroupLoads[$group] ) ) {
 325                                 $nonErrorLoads = $this->mGroupLoads[$group];
 326                         } else {
 327                                 # No loads for this group, return false and the caller can use some other group
 328                                 $this->connLogger->info( __METHOD__ . ": no loads for group $group" );
 329
 330                                 return false;
 331                         }
 332                 } else {
 333                         $nonErrorLoads = $this->mLoads;
 334                 }
 335
 336                 if ( !count( $nonErrorLoads ) ) {
 337                         throw new InvalidArgumentException( "Empty server array given to LoadBalancer" );
 338                 }
 339
 340                 # Scale the configured load ratios according to the dynamic load if supported
 341                 $this->getLoadMonitor()->scaleLoads( $nonErrorLoads, $domain );
 342
 343                 $laggedReplicaMode = false;
 344
 345                 # No server found yet
 346                 $i = false;
 347                 # First try quickly looking through the available servers for a server that
 348                 # meets our criteria
 349                 $currentLoads = $nonErrorLoads;
 350                 while ( count( $currentLoads ) ) {
 351                         if ( $this->mAllowLagged || $laggedReplicaMode ) {
 352                                 $i = ArrayUtils::pickRandom( $currentLoads );
 353                         } else {
 354                                 $i = false;
 355                                 if ( $this->mWaitForPos && $this->mWaitForPos->asOfTime() ) {
 356                                         # ChronologyProtecter causes mWaitForPos to be set via sessions.
 357                                         # This triggers doWait() after connect, so it's especially good to
 358                                         # avoid lagged servers so as to avoid just blocking in that method.
 359                                         $ago = microtime( true ) - $this->mWaitForPos->asOfTime();
 360                                         # Aim for <= 1 second of waiting (being too picky can backfire)
 361                                         $i = $this->getRandomNonLagged( $currentLoads, $domain, $ago + 1 );
 362                                 }
 363                                 if ( $i === false ) {
 364                                         # Any server with less lag than it's 'max lag' param is preferable
 365                                         $i = $this->getRandomNonLagged( $currentLoads, $domain );
 366                                 }
 367                                 if ( $i === false && count( $currentLoads ) != 0 ) {
 368                                         # All replica DBs lagged. Switch to read-only mode
 369                                         $this->replLogger->error( "All replica DBs lagged. Switch to read-only mode" );
 370                                         $i = ArrayUtils::pickRandom( $currentLoads );
 371                                         $laggedReplicaMode = true;
 372                                 }
 373                         }
 374
 375                         if ( $i === false ) {
 376                                 # pickRandom() returned false
 377                                 # This is permanent and means the configuration or the load monitor
 378                                 # wants us to return false.
 379                                 $this->connLogger->debug( __METHOD__ . ": pickRandom() returned false" );
 380
 381                                 return false;
 382                         }
 383
 384                         $serverName = $this->getServerName( $i );
 385                         $this->connLogger->debug( __METHOD__ . ": Using reader #$i: $serverName..." );
 386
 387                         $conn = $this->openConnection( $i, $domain );
 388                         if ( !$conn ) {
 389                                 $this->connLogger->warning( __METHOD__ . ": Failed connecting to $i/$domain" );
 390                                 unset( $nonErrorLoads[$i] );
 391                                 unset( $currentLoads[$i] );
 392                                 $i = false;
 393                                 continue;
 394                         }
 395
 396                         // Decrement reference counter, we are finished with this connection.
 397                         // It will be incremented for the caller later.
 398                         if ( $domain !== false ) {
 399                                 $this->reuseConnection( $conn );
 400                         }
 401
 402                         # Return this server
 403                         break;
 404                 }
 405
 406                 # If all servers were down, quit now
 407                 if ( !count( $nonErrorLoads ) ) {
 408                         $this->connLogger->error( "All servers down" );
 409                 }
 410
 411                 if ( $i !== false ) {
 412                         # Replica DB connection successful.
 413                         # Wait for the session master pos for a short time.
 414                         if ( $this->mWaitForPos && $i > 0 ) {
 415                                 $this->doWait( $i );
 416                         }
 417                         if ( $this->mReadIndex <= 0 && $this->mLoads[$i] > 0 && $group === false ) {
 418                                 $this->mReadIndex = $i;
 419                                 # Record if the generic reader index is in "lagged replica DB" mode
 420                                 if ( $laggedReplicaMode ) {
 421                                         $this->laggedReplicaMode = true;
 422                                 }
 423                         }
 424                         $serverName = $this->getServerName( $i );
 425                         $this->connLogger->debug(
 426                                 __METHOD__ . ": using server $serverName for group '$group'" );
 427                 }
 428
 429                 return $i;
 430         }
 431
 432         public function waitFor( $pos ) {
 433                 $oldPos = $this->mWaitForPos;
 434                 $this->mWaitForPos = $pos;
 435
 436                 // If a generic reader connection was already established, then wait now
 437                 $i = $this->mReadIndex;
 438                 if ( $i > 0 ) {
 439                         if ( !$this->doWait( $i ) ) {
 440                                 $this->laggedReplicaMode = true;
 441                         }
 442                 }
 443
 444                 // Restore the older position if it was higher
 445                 $this->setWaitForPositionIfHigher( $oldPos );
 446         }
 447
 448         public function waitForOne( $pos, $timeout = null ) {
 449                 $oldPos = $this->mWaitForPos;
 450                 $this->mWaitForPos = $pos;
 451
 452                 $i = $this->mReadIndex;
 453                 if ( $i <= 0 ) {
 454                         // Pick a generic replica DB if there isn't one yet
 455                         $readLoads = $this->mLoads;
 456                         unset( $readLoads[$this->getWriterIndex()] ); // replica DBs only
 457                         $readLoads = array_filter( $readLoads ); // with non-zero load
 458                         $i = ArrayUtils::pickRandom( $readLoads );
 459                 }
 460
 461                 if ( $i > 0 ) {
 462                         $ok = $this->doWait( $i, true, $timeout );
 463                 } else {
 464                         $ok = true; // no applicable loads
 465                 }
 466
 467                 // Restore the older position if it was higher
 468                 $this->setWaitForPositionIfHigher( $oldPos );
 469
 470                 return $ok;
 471         }
 472
 473         public function waitForAll( $pos, $timeout = null ) {
 474                 $oldPos = $this->mWaitForPos;
 475                 $this->mWaitForPos = $pos;
 476                 $serverCount = count( $this->mServers );
 477
 478                 $ok = true;
 479                 for ( $i = 1; $i < $serverCount; $i++ ) {
 480                         if ( $this->mLoads[$i] > 0 ) {
 481                                 $ok = $this->doWait( $i, true, $timeout ) && $ok;
 482                         }
 483                 }
 484
 485                 // Restore the older position if it was higher
 486                 $this->setWaitForPositionIfHigher( $oldPos );
 487
 488                 return $ok;
 489         }
 490
 491         /**
 492          * @param DBMasterPos|bool $pos
 493          */
 494         private function setWaitForPositionIfHigher( $pos ) {
 495                 if ( !$pos ) {
 496                         return;
 497                 }
 498
 499                 if ( !$this->mWaitForPos || $pos->hasReached( $this->mWaitForPos ) ) {
 500                         $this->mWaitForPos = $pos;
 501                 }
 502         }
 503
 504         /**
 505          * @param int $i
 506          * @return IDatabase|bool
 507          */
 508         public function getAnyOpenConnection( $i ) {
 509                 foreach ( $this->mConns as $connsByServer ) {
 510                         if ( !empty( $connsByServer[$i] ) ) {
 511                                 /** @var $serverConns IDatabase[] */
 512                                 $serverConns = $connsByServer[$i];
 513
 514                                 return reset( $serverConns );
 515                         }
 516                 }
 517
 518                 return false;
 519         }
 520
 521         /**
 522          * Wait for a given replica DB to catch up to the master pos stored in $this
 523          * @param int $index Server index
 524          * @param bool $open Check the server even if a new connection has to be made
 525          * @param int $timeout Max seconds to wait; default is mWaitTimeout
 526          * @return bool
 527          */
 528         protected function doWait( $index, $open = false, $timeout = null ) {
 529                 $close = false; // close the connection afterwards
 530
 531                 // Check if we already know that the DB has reached this point
 532                 $server = $this->getServerName( $index );
 533                 $key = $this->srvCache->makeGlobalKey( __CLASS__, 'last-known-pos', $server, 'v1' );
 534                 /** @var DBMasterPos $knownReachedPos */
 535                 $knownReachedPos = $this->srvCache->get( $key );
 536                 if (
 537                         $knownReachedPos instanceof DBMasterPos &&
 538                         $knownReachedPos->hasReached( $this->mWaitForPos )
 539                 ) {
 540                         $this->replLogger->debug( __METHOD__ .
 541                                 ": replica DB $server known to be caught up (pos >= $knownReachedPos)." );
 542                         return true;
 543                 }
 544
 545                 // Find a connection to wait on, creating one if needed and allowed
 546                 $conn = $this->getAnyOpenConnection( $index );
 547                 if ( !$conn ) {
 548                         if ( !$open ) {
 549                                 $this->replLogger->debug( __METHOD__ . ": no connection open for $server" );
 550
 551                                 return false;
 552                         } else {
 553                                 $conn = $this->openConnection( $index, self::DOMAIN_ANY );
 554                                 if ( !$conn ) {
 555                                         $this->replLogger->warning( __METHOD__ . ": failed to connect to $server" );
 556
 557                                         return false;
 558                                 }
 559                                 // Avoid connection spam in waitForAll() when connections
 560                                 // are made just for the sake of doing this lag check.
 561                                 $close = true;
 562                         }
 563                 }
 564
 565                 $this->replLogger->info( __METHOD__ . ": Waiting for replica DB $server to catch up..." );
 566                 $timeout = $timeout ?: $this->mWaitTimeout;
 567                 $result = $conn->masterPosWait( $this->mWaitForPos, $timeout );
 568
 569                 if ( $result == -1 || is_null( $result ) ) {
 570                         // Timed out waiting for replica DB, use master instead
 571                         $this->replLogger->warning(
 572                                 __METHOD__ . ": Timed out waiting on {host} pos {$this->mWaitForPos}",
 573                                 [ 'host' => $server ]
 574                         );
 575                         $ok = false;
 576                 } else {
 577                         $this->replLogger->info( __METHOD__ . ": Done" );
 578                         $ok = true;
 579                         // Remember that the DB reached this point
 580                         $this->srvCache->set( $key, $this->mWaitForPos, BagOStuff::TTL_DAY );
 581                 }
 582
 583                 if ( $close ) {
 584                         $this->closeConnection( $conn );
 585                 }
 586
 587                 return $ok;
 588         }
 589
 590         /**
 591          * @see ILoadBalancer::getConnection()
 592          *
 593          * @param int $i
 594          * @param array $groups
 595          * @param bool $domain
 596          * @return Database
 597          * @throws DBConnectionError
 598          */
 599         public function getConnection( $i, $groups = [], $domain = false ) {
 600                 if ( $i === null || $i === false ) {
 601                         throw new InvalidArgumentException( 'Attempt to call ' . __METHOD__ .
 602                                 ' with invalid server index' );
 603                 }
 604
 605                 if ( $this->localDomain->equals( $domain ) || $domain === $this->localDomainIdAlias ) {
 606                         $domain = false; // local connection requested
 607                 }
 608
 609                 $groups = ( $groups === false || $groups === [] )
 610                         ? [ false ] // check one "group": the generic pool
 611                         : (array)$groups;
 612
 613                 $masterOnly = ( $i == self::DB_MASTER || $i == $this->getWriterIndex() );
 614                 $oldConnsOpened = $this->connsOpened; // connections open now
 615
 616                 if ( $i == self::DB_MASTER ) {
 617                         $i = $this->getWriterIndex();
 618                 } else {
 619                         # Try to find an available server in any the query groups (in order)
 620                         foreach ( $groups as $group ) {
 621                                 $groupIndex = $this->getReaderIndex( $group, $domain );
 622                                 if ( $groupIndex !== false ) {
 623                                         $i = $groupIndex;
 624                                         break;
 625                                 }
 626                         }
 627                 }
 628
 629                 # Operation-based index
 630                 if ( $i == self::DB_REPLICA ) {
 631                         $this->mLastError = 'Unknown error'; // reset error string
 632                         # Try the general server pool if $groups are unavailable.
 633                         $i = ( $groups === [ false ] )
 634                                 ? false // don't bother with this if that is what was tried above
 635                                 : $this->getReaderIndex( false, $domain );
 636                         # Couldn't find a working server in getReaderIndex()?
 637                         if ( $i === false ) {
 638                                 $this->mLastError = 'No working replica DB server: ' . $this->mLastError;
 639                                 // Throw an exception
 640                                 $this->reportConnectionError();
 641                                 return null; // not reached
 642                         }
 643                 }
 644
 645                 # Now we have an explicit index into the servers array
 646                 $conn = $this->openConnection( $i, $domain );
 647                 if ( !$conn ) {
 648                         // Throw an exception
 649                         $this->reportConnectionError();
 650                         return null; // not reached
 651                 }
 652
 653                 # Profile any new connections that happen
 654                 if ( $this->connsOpened > $oldConnsOpened ) {
 655                         $host = $conn->getServer();
 656                         $dbname = $conn->getDBname();
 657                         $this->trxProfiler->recordConnection( $host, $dbname, $masterOnly );
 658                 }
 659
 660                 if ( $masterOnly ) {
 661                         # Make master-requested DB handles inherit any read-only mode setting
 662                         $conn->setLBInfo( 'readOnlyReason', $this->getReadOnlyReason( $domain, $conn ) );
 663                 }
 664
 665                 return $conn;
 666         }
 667
 668         public function reuseConnection( $conn ) {
 669                 $serverIndex = $conn->getLBInfo( 'serverIndex' );
 670                 $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 671                 if ( $serverIndex === null || $refCount === null ) {
 672                         /**
 673                          * This can happen in code like:
 674                          *   foreach ( $dbs as $db ) {
 675                          *     $conn = $lb->getConnection( $lb::DB_REPLICA, [], $db );
 676                          *     ...
 677                          *     $lb->reuseConnection( $conn );
 678                          *   }
 679                          * When a connection to the local DB is opened in this way, reuseConnection()
 680                          * should be ignored
 681                          */
 682                         return;
 683                 } elseif ( $conn instanceof DBConnRef ) {
 684                         // DBConnRef already handles calling reuseConnection() and only passes the live
 685                         // Database instance to this method. Any caller passing in a DBConnRef is broken.
 686                         $this->connLogger->error( __METHOD__ . ": got DBConnRef instance.\n" .
 687                                 ( new RuntimeException() )->getTraceAsString() );
 688
 689                         return;
 690                 }
 691
 692                 if ( $this->disabled ) {
 693                         return; // DBConnRef handle probably survived longer than the LoadBalancer
 694                 }
 695
 696                 $domain = $conn->getDomainID();
 697                 if ( !isset( $this->mConns['foreignUsed'][$serverIndex][$domain] ) ) {
 698                         throw new InvalidArgumentException( __METHOD__ .
 699                                 ": connection $serverIndex/$domain not found; it may have already been freed." );
 700                 } elseif ( $this->mConns['foreignUsed'][$serverIndex][$domain] !== $conn ) {
 701                         throw new InvalidArgumentException( __METHOD__ .
 702                                 ": connection $serverIndex/$domain mismatched; it may have already been freed." );
 703                 }
 704                 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
 705                 if ( $refCount <= 0 ) {
 706                         $this->mConns['foreignFree'][$serverIndex][$domain] = $conn;
 707                         unset( $this->mConns['foreignUsed'][$serverIndex][$domain] );
 708                         if ( !$this->mConns['foreignUsed'][$serverIndex] ) {
 709                                 unset( $this->mConns[ 'foreignUsed' ][$serverIndex] ); // clean up
 710                         }
 711                         $this->connLogger->debug( __METHOD__ . ": freed connection $serverIndex/$domain" );
 712                 } else {
 713                         $this->connLogger->debug( __METHOD__ .
 714                                 ": reference count for $serverIndex/$domain reduced to $refCount" );
 715                 }
 716         }
 717
 718         public function getConnectionRef( $db, $groups = [], $domain = false ) {
 719                 $domain = ( $domain !== false ) ? $domain : $this->localDomain;
 720
 721                 return new DBConnRef( $this, $this->getConnection( $db, $groups, $domain ) );
 722         }
 723
 724         public function getLazyConnectionRef( $db, $groups = [], $domain = false ) {
 725                 $domain = ( $domain !== false ) ? $domain : $this->localDomain;
 726
 727                 return new DBConnRef( $this, [ $db, $groups, $domain ] );
 728         }
 729
 730         public function getMaintenanceConnectionRef( $db, $groups = [], $domain = false ) {
 731                 $domain = ( $domain !== false ) ? $domain : $this->localDomain;
 732
 733                 return new MaintainableDBConnRef( $this, $this->getConnection( $db, $groups, $domain ) );
 734         }
 735
 736         /**
 737          * @see ILoadBalancer::openConnection()
 738          *
 739          * @param int $i
 740          * @param bool $domain
 741          * @return bool|Database
 742          * @throws DBAccessError
 743          */
 744         public function openConnection( $i, $domain = false ) {
 745                 if ( $this->localDomain->equals( $domain ) || $domain === $this->localDomainIdAlias ) {
 746                         $domain = false; // local connection requested
 747                 }
 748
 749                 if ( !$this->chronProtInitialized && $this->chronProt ) {
 750                         $this->connLogger->debug( __METHOD__ . ': calling initLB() before first connection.' );
 751                         // Load CP positions before connecting so that doWait() triggers later if needed
 752                         $this->chronProtInitialized = true;
 753                         $this->chronProt->initLB( $this );
 754                 }
 755
 756                 if ( $domain !== false ) {
 757                         $conn = $this->openForeignConnection( $i, $domain );
 758                 } elseif ( isset( $this->mConns['local'][$i][0] ) ) {
 759                         $conn = $this->mConns['local'][$i][0];
 760                 } else {
 761                         if ( !isset( $this->mServers[$i] ) || !is_array( $this->mServers[$i] ) ) {
 762                                 throw new InvalidArgumentException( "No server with index '$i'." );
 763                         }
 764                         // Open a new connection
 765                         $server = $this->mServers[$i];
 766                         $server['serverIndex'] = $i;
 767                         $conn = $this->reallyOpenConnection( $server, false );
 768                         $serverName = $this->getServerName( $i );
 769                         if ( $conn->isOpen() ) {
 770                                 $this->connLogger->debug( "Connected to database $i at '$serverName'." );
 771                                 $this->mConns['local'][$i][0] = $conn;
 772                         } else {
 773                                 $this->connLogger->warning( "Failed to connect to database $i at '$serverName'." );
 774                                 $this->errorConnection = $conn;
 775                                 $conn = false;
 776                         }
 777                 }
 778
 779                 if ( $conn instanceof IDatabase && !$conn->isOpen() ) {
 780                         // Connection was made but later unrecoverably lost for some reason.
 781                         // Do not return a handle that will just throw exceptions on use,
 782                         // but let the calling code (e.g. getReaderIndex) try another server.
 783                         // See DatabaseMyslBase::ping() for how this can happen.
 784                         $this->errorConnection = $conn;
 785                         $conn = false;
 786                 }
 787
 788                 return $conn;
 789         }
 790
 791         /**
 792          * Open a connection to a foreign DB, or return one if it is already open.
 793          *
 794          * Increments a reference count on the returned connection which locks the
 795          * connection to the requested domain. This reference count can be
 796          * decremented by calling reuseConnection().
 797          *
 798          * If a connection is open to the appropriate server already, but with the wrong
 799          * database, it will be switched to the right database and returned, as long as
 800          * it has been freed first with reuseConnection().
 801          *
 802          * On error, returns false, and the connection which caused the
 803          * error will be available via $this->errorConnection.
 804          *
 805          * @note If disable() was called on this LoadBalancer, this method will throw a DBAccessError.
 806          *
 807          * @param int $i Server index
 808          * @param string $domain Domain ID to open
 809          * @return Database
 810          */
 811         private function openForeignConnection( $i, $domain ) {
 812                 $domainInstance = DatabaseDomain::newFromId( $domain );
 813                 $dbName = $domainInstance->getDatabase();
 814                 $prefix = $domainInstance->getTablePrefix();
 815
 816                 if ( isset( $this->mConns['foreignUsed'][$i][$domain] ) ) {
 817                         // Reuse an already-used connection
 818                         $conn = $this->mConns['foreignUsed'][$i][$domain];
 819                         $this->connLogger->debug( __METHOD__ . ": reusing connection $i/$domain" );
 820                 } elseif ( isset( $this->mConns['foreignFree'][$i][$domain] ) ) {
 821                         // Reuse a free connection for the same domain
 822                         $conn = $this->mConns['foreignFree'][$i][$domain];
 823                         unset( $this->mConns['foreignFree'][$i][$domain] );
 824                         $this->mConns['foreignUsed'][$i][$domain] = $conn;
 825                         $this->connLogger->debug( __METHOD__ . ": reusing free connection $i/$domain" );
 826                 } elseif ( !empty( $this->mConns['foreignFree'][$i] ) ) {
 827                         // Reuse a connection from another domain
 828                         $conn = reset( $this->mConns['foreignFree'][$i] );
 829                         $oldDomain = key( $this->mConns['foreignFree'][$i] );
 830                         // The empty string as a DB name means "don't care".
 831                         // DatabaseMysqlBase::open() already handle this on connection.
 832                         if ( strlen( $dbName ) && !$conn->selectDB( $dbName ) ) {
 833                                 $this->mLastError = "Error selecting database '$dbName' on server " .
 834                                         $conn->getServer() . " from client host {$this->host}";
 835                                 $this->errorConnection = $conn;
 836                                 $conn = false;
 837                         } else {
 838                                 $conn->tablePrefix( $prefix );
 839                                 unset( $this->mConns['foreignFree'][$i][$oldDomain] );
 840                                 $this->mConns['foreignUsed'][$i][$domain] = $conn;
 841                                 $this->connLogger->debug( __METHOD__ .
 842                                         ": reusing free connection from $oldDomain for $domain" );
 843                         }
 844                 } else {
 845                         if ( !isset( $this->mServers[$i] ) || !is_array( $this->mServers[$i] ) ) {
 846                                 throw new InvalidArgumentException( "No server with index '$i'." );
 847                         }
 848                         // Open a new connection
 849                         $server = $this->mServers[$i];
 850                         $server['serverIndex'] = $i;
 851                         $server['foreignPoolRefCount'] = 0;
 852                         $server['foreign'] = true;
 853                         $conn = $this->reallyOpenConnection( $server, $dbName );
 854                         if ( !$conn->isOpen() ) {
 855                                 $this->connLogger->warning( __METHOD__ . ": connection error for $i/$domain" );
 856                                 $this->errorConnection = $conn;
 857                                 $conn = false;
 858                         } else {
 859                                 $conn->tablePrefix( $prefix );
 860                                 $this->mConns['foreignUsed'][$i][$domain] = $conn;
 861                                 $this->connLogger->debug( __METHOD__ . ": opened new connection for $i/$domain" );
 862                         }
 863                 }
 864
 865                 // Increment reference count
 866                 if ( $conn instanceof IDatabase ) {
 867                         $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 868                         $conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
 869                 }
 870
 871                 return $conn;
 872         }
 873
 874         /**
 875          * Test if the specified index represents an open connection
 876          *
 877          * @param int $index Server index
 878          * @access private
 879          * @return bool
 880          */
 881         private function isOpen( $index ) {
 882                 if ( !is_integer( $index ) ) {
 883                         return false;
 884                 }
 885
 886                 return (bool)$this->getAnyOpenConnection( $index );
 887         }
 888
 889         /**
 890          * Really opens a connection. Uncached.
 891          * Returns a Database object whether or not the connection was successful.
 892          * @access private
 893          *
 894          * @param array $server
 895          * @param string|bool $dbNameOverride Use "" to not select any database
 896          * @return Database
 897          * @throws DBAccessError
 898          * @throws InvalidArgumentException
 899          */
 900         protected function reallyOpenConnection( array $server, $dbNameOverride = false ) {
 901                 if ( $this->disabled ) {
 902                         throw new DBAccessError();
 903                 }
 904
 905                 if ( $dbNameOverride !== false ) {
 906                         $server['dbname'] = $dbNameOverride;
 907                 }
 908
 909                 // Let the handle know what the cluster master is (e.g. "db1052")
 910                 $masterName = $this->getServerName( $this->getWriterIndex() );
 911                 $server['clusterMasterHost'] = $masterName;
 912
 913                 // Log when many connection are made on requests
 914                 if ( ++$this->connsOpened >= self::CONN_HELD_WARN_THRESHOLD ) {
 915                         $this->perfLogger->warning( __METHOD__ . ": " .
 916                                 "{$this->connsOpened}+ connections made (master=$masterName)" );
 917                 }
 918
 919                 $server['srvCache'] = $this->srvCache;
 920                 // Set loggers and profilers
 921                 $server['connLogger'] = $this->connLogger;
 922                 $server['queryLogger'] = $this->queryLogger;
 923                 $server['errorLogger'] = $this->errorLogger;
 924                 $server['profiler'] = $this->profiler;
 925                 $server['trxProfiler'] = $this->trxProfiler;
 926                 // Use the same agent and PHP mode for all DB handles
 927                 $server['cliMode'] = $this->cliMode;
 928                 $server['agent'] = $this->agent;
 929                 // Use DBO_DEFAULT flags by default for LoadBalancer managed databases. Assume that the
 930                 // application calls LoadBalancer::commitMasterChanges() before the PHP script completes.
 931                 $server['flags'] = isset( $server['flags'] ) ? $server['flags'] : IDatabase::DBO_DEFAULT;
 932
 933                 // Create a live connection object
 934                 try {
 935                         $db = Database::factory( $server['type'], $server );
 936                 } catch ( DBConnectionError $e ) {
 937                         // FIXME: This is probably the ugliest thing I have ever done to
 938                         // PHP. I'm half-expecting it to segfault, just out of disgust. -- TS
 939                         $db = $e->db;
 940                 }
 941
 942                 $db->setLBInfo( $server );
 943                 $db->setLazyMasterHandle(
 944                         $this->getLazyConnectionRef( self::DB_MASTER, [], $db->getDomainID() )
 945                 );
 946                 $db->setTableAliases( $this->tableAliases );
 947
 948                 if ( $server['serverIndex'] === $this->getWriterIndex() ) {
 949                         if ( $this->trxRoundId !== false ) {
 950                                 $this->applyTransactionRoundFlags( $db );
 951                         }
 952                         foreach ( $this->trxRecurringCallbacks as $name => $callback ) {
 953                                 $db->setTransactionListener( $name, $callback );
 954                         }
 955                 }
 956
 957                 return $db;
 958         }
 959
 960         /**
 961          * @throws DBConnectionError
 962          */
 963         private function reportConnectionError() {
 964                 $conn = $this->errorConnection; // the connection which caused the error
 965                 $context = [
 966                         'method' => __METHOD__,
 967                         'last_error' => $this->mLastError,
 968                 ];
 969
 970                 if ( $conn instanceof IDatabase ) {
 971                         $context['db_server'] = $conn->getServer();
 972                         $this->connLogger->warning(
 973                                 "Connection error: {last_error} ({db_server})",
 974                                 $context
 975                         );
 976
 977                         // throws DBConnectionError
 978                         $conn->reportConnectionError( "{$this->mLastError} ({$context['db_server']})" );
 979                 } else {
 980                         // No last connection, probably due to all servers being too busy
 981                         $this->connLogger->error(
 982                                 "LB failure with no last connection. Connection error: {last_error}",
 983                                 $context
 984                         );
 985
 986                         // If all servers were busy, mLastError will contain something sensible
 987                         throw new DBConnectionError( null, $this->mLastError );
 988                 }
 989         }
 990
 991         public function getWriterIndex() {
 992                 return 0;
 993         }
 994
 995         public function haveIndex( $i ) {
 996                 return array_key_exists( $i, $this->mServers );
 997         }
 998
 999         public function isNonZeroLoad( $i ) {
1000                 return array_key_exists( $i, $this->mServers ) && $this->mLoads[$i] != 0;
1001         }
1002
1003         public function getServerCount() {
1004                 return count( $this->mServers );
1005         }
1006
1007         public function getServerName( $i ) {
1008                 if ( isset( $this->mServers[$i]['hostName'] ) ) {
1009                         $name = $this->mServers[$i]['hostName'];
1010                 } elseif ( isset( $this->mServers[$i]['host'] ) ) {
1011                         $name = $this->mServers[$i]['host'];
1012                 } else {
1013                         $name = '';
1014                 }
1015
1016                 return ( $name != '' ) ? $name : 'localhost';
1017         }
1018
1019         public function getServerInfo( $i ) {
1020                 if ( isset( $this->mServers[$i] ) ) {
1021                         return $this->mServers[$i];
1022                 } else {
1023                         return false;
1024                 }
1025         }
1026
1027         public function setServerInfo( $i, array $serverInfo ) {
1028                 $this->mServers[$i] = $serverInfo;
1029         }
1030
1031         public function getMasterPos() {
1032                 # If this entire request was served from a replica DB without opening a connection to the
1033                 # master (however unlikely that may be), then we can fetch the position from the replica DB.
1034                 $masterConn = $this->getAnyOpenConnection( $this->getWriterIndex() );
1035                 if ( !$masterConn ) {
1036                         $serverCount = count( $this->mServers );
1037                         for ( $i = 1; $i < $serverCount; $i++ ) {
1038                                 $conn = $this->getAnyOpenConnection( $i );
1039                                 if ( $conn ) {
1040                                         return $conn->getReplicaPos();
1041                                 }
1042                         }
1043                 } else {
1044                         return $masterConn->getMasterPos();
1045                 }
1046
1047                 return false;
1048         }
1049
1050         public function disable() {
1051                 $this->closeAll();
1052                 $this->disabled = true;
1053         }
1054
1055         public function closeAll() {
1056                 $this->forEachOpenConnection( function ( IDatabase $conn ) {
1057                         $host = $conn->getServer();
1058                         $this->connLogger->debug( "Closing connection to database '$host'." );
1059                         $conn->close();
1060                 } );
1061
1062                 $this->mConns = [
1063                         'local' => [],
1064                         'foreignFree' => [],
1065                         'foreignUsed' => [],
1066                 ];
1067                 $this->connsOpened = 0;
1068         }
1069
1070         public function closeConnection( IDatabase $conn ) {
1071                 $serverIndex = $conn->getLBInfo( 'serverIndex' ); // second index level of mConns
1072                 foreach ( $this->mConns as $type => $connsByServer ) {
1073                         if ( !isset( $connsByServer[$serverIndex] ) ) {
1074                                 continue;
1075                         }
1076
1077                         foreach ( $connsByServer[$serverIndex] as $i => $trackedConn ) {
1078                                 if ( $conn === $trackedConn ) {
1079                                         $host = $this->getServerName( $i );
1080                                         $this->connLogger->debug( "Closing connection to database $i at '$host'." );
1081                                         unset( $this->mConns[$type][$serverIndex][$i] );
1082                                         --$this->connsOpened;
1083                                         break 2;
1084                                 }
1085                         }
1086                 }
1087
1088                 $conn->close();
1089         }
1090
1091         public function commitAll( $fname = __METHOD__ ) {
1092                 $failures = [];
1093
1094                 $restore = ( $this->trxRoundId !== false );
1095                 $this->trxRoundId = false;
1096                 $this->forEachOpenConnection(
1097                         function ( IDatabase $conn ) use ( $fname, $restore, &$failures ) {
1098                                 try {
1099                                         $conn->commit( $fname, $conn::FLUSHING_ALL_PEERS );
1100                                 } catch ( DBError $e ) {
1101                                         call_user_func( $this->errorLogger, $e );
1102                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1103                                 }
1104                                 if ( $restore && $conn->getLBInfo( 'master' ) ) {
1105                                         $this->undoTransactionRoundFlags( $conn );
1106                                 }
1107                         }
1108                 );
1109
1110                 if ( $failures ) {
1111                         throw new DBExpectedError(
1112                                 null,
1113                                 "Commit failed on server(s) " . implode( "\n", array_unique( $failures ) )
1114                         );
1115                 }
1116         }
1117
1118         public function finalizeMasterChanges() {
1119                 $this->forEachOpenMasterConnection( function ( Database $conn ) {
1120                         // Any error should cause all DB transactions to be rolled back together
1121                         $conn->setTrxEndCallbackSuppression( false );
1122                         $conn->runOnTransactionPreCommitCallbacks();
1123                         // Defer post-commit callbacks until COMMIT finishes for all DBs
1124                         $conn->setTrxEndCallbackSuppression( true );
1125                 } );
1126         }
1127
1128         public function approveMasterChanges( array $options ) {
1129                 $limit = isset( $options['maxWriteDuration'] ) ? $options['maxWriteDuration'] : 0;
1130                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( $limit ) {
1131                         // If atomic sections or explicit transactions are still open, some caller must have
1132                         // caught an exception but failed to properly rollback any changes. Detect that and
1133                         // throw and error (causing rollback).
1134                         if ( $conn->explicitTrxActive() ) {
1135                                 throw new DBTransactionError(
1136                                         $conn,
1137                                         "Explicit transaction still active. A caller may have caught an error."
1138                                 );
1139                         }
1140                         // Assert that the time to replicate the transaction will be sane.
1141                         // If this fails, then all DB transactions will be rollback back together.
1142                         $time = $conn->pendingWriteQueryDuration( $conn::ESTIMATE_DB_APPLY );
1143                         if ( $limit > 0 && $time > $limit ) {
1144                                 throw new DBTransactionSizeError(
1145                                         $conn,
1146                                         "Transaction spent $time second(s) in writes, exceeding the $limit limit.",
1147                                         [ $time, $limit ]
1148                                 );
1149                         }
1150                         // If a connection sits idle while slow queries execute on another, that connection
1151                         // may end up dropped before the commit round is reached. Ping servers to detect this.
1152                         if ( $conn->writesOrCallbacksPending() && !$conn->ping() ) {
1153                                 throw new DBTransactionError(
1154                                         $conn,
1155                                         "A connection to the {$conn->getDBname()} database was lost before commit."
1156                                 );
1157                         }
1158                 } );
1159         }
1160
1161         public function beginMasterChanges( $fname = __METHOD__ ) {
1162                 if ( $this->trxRoundId !== false ) {
1163                         throw new DBTransactionError(
1164                                 null,
1165                                 "$fname: Transaction round '{$this->trxRoundId}' already started."
1166                         );
1167                 }
1168                 $this->trxRoundId = $fname;
1169
1170                 $failures = [];
1171                 $this->forEachOpenMasterConnection(
1172                         function ( Database $conn ) use ( $fname, &$failures ) {
1173                                 $conn->setTrxEndCallbackSuppression( true );
1174                                 try {
1175                                         $conn->flushSnapshot( $fname );
1176                                 } catch ( DBError $e ) {
1177                                         call_user_func( $this->errorLogger, $e );
1178                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1179                                 }
1180                                 $conn->setTrxEndCallbackSuppression( false );
1181                                 $this->applyTransactionRoundFlags( $conn );
1182                         }
1183                 );
1184
1185                 if ( $failures ) {
1186                         throw new DBExpectedError(
1187                                 null,
1188                                 "$fname: Flush failed on server(s) " . implode( "\n", array_unique( $failures ) )
1189                         );
1190                 }
1191         }
1192
1193         public function commitMasterChanges( $fname = __METHOD__ ) {
1194                 $failures = [];
1195
1196                 /** @noinspection PhpUnusedLocalVariableInspection */
1197                 $scope = $this->getScopedPHPBehaviorForCommit(); // try to ignore client aborts
1198
1199                 $restore = ( $this->trxRoundId !== false );
1200                 $this->trxRoundId = false;
1201                 $this->forEachOpenMasterConnection(
1202                         function ( IDatabase $conn ) use ( $fname, $restore, &$failures ) {
1203                                 try {
1204                                         if ( $conn->writesOrCallbacksPending() ) {
1205                                                 $conn->commit( $fname, $conn::FLUSHING_ALL_PEERS );
1206                                         } elseif ( $restore ) {
1207                                                 $conn->flushSnapshot( $fname );
1208                                         }
1209                                 } catch ( DBError $e ) {
1210                                         call_user_func( $this->errorLogger, $e );
1211                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1212                                 }
1213                                 if ( $restore ) {
1214                                         $this->undoTransactionRoundFlags( $conn );
1215                                 }
1216                         }
1217                 );
1218
1219                 if ( $failures ) {
1220                         throw new DBExpectedError(
1221                                 null,
1222                                 "$fname: Commit failed on server(s) " . implode( "\n", array_unique( $failures ) )
1223                         );
1224                 }
1225         }
1226
1227         public function runMasterPostTrxCallbacks( $type ) {
1228                 $e = null; // first exception
1229                 $this->forEachOpenMasterConnection( function ( Database $conn ) use ( $type, &$e ) {
1230                         $conn->setTrxEndCallbackSuppression( false );
1231                         if ( $conn->writesOrCallbacksPending() ) {
1232                                 // This happens if onTransactionIdle() callbacks leave callbacks on *another* DB
1233                                 // (which finished its callbacks already). Warn and recover in this case. Let the
1234                                 // callbacks run in the final commitMasterChanges() in LBFactory::shutdown().
1235                                 $this->queryLogger->error( __METHOD__ . ": found writes/callbacks pending." );
1236                                 return;
1237                         } elseif ( $conn->trxLevel() ) {
1238                                 // This happens for single-DB setups where DB_REPLICA uses the master DB,
1239                                 // thus leaving an implicit read-only transaction open at this point. It
1240                                 // also happens if onTransactionIdle() callbacks leave implicit transactions
1241                                 // open on *other* DBs (which is slightly improper). Let these COMMIT on the
1242                                 // next call to commitMasterChanges(), possibly in LBFactory::shutdown().
1243                                 return;
1244                         }
1245                         try {
1246                                 $conn->runOnTransactionIdleCallbacks( $type );
1247                         } catch ( Exception $ex ) {
1248                                 $e = $e ?: $ex;
1249                         }
1250                         try {
1251                                 $conn->runTransactionListenerCallbacks( $type );
1252                         } catch ( Exception $ex ) {
1253                                 $e = $e ?: $ex;
1254                         }
1255                 } );
1256
1257                 return $e;
1258         }
1259
1260         public function rollbackMasterChanges( $fname = __METHOD__ ) {
1261                 $restore = ( $this->trxRoundId !== false );
1262                 $this->trxRoundId = false;
1263                 $this->forEachOpenMasterConnection(
1264                         function ( IDatabase $conn ) use ( $fname, $restore ) {
1265                                 if ( $conn->writesOrCallbacksPending() ) {
1266                                         $conn->rollback( $fname, $conn::FLUSHING_ALL_PEERS );
1267                                 }
1268                                 if ( $restore ) {
1269                                         $this->undoTransactionRoundFlags( $conn );
1270                                 }
1271                         }
1272                 );
1273         }
1274
1275         public function suppressTransactionEndCallbacks() {
1276                 $this->forEachOpenMasterConnection( function ( Database $conn ) {
1277                         $conn->setTrxEndCallbackSuppression( true );
1278                 } );
1279         }
1280
1281         /**
1282          * @param IDatabase $conn
1283          */
1284         private function applyTransactionRoundFlags( IDatabase $conn ) {
1285                 if ( $conn->getFlag( $conn::DBO_DEFAULT ) ) {
1286                         // DBO_TRX is controlled entirely by CLI mode presence with DBO_DEFAULT.
1287                         // Force DBO_TRX even in CLI mode since a commit round is expected soon.
1288                         $conn->setFlag( $conn::DBO_TRX, $conn::REMEMBER_PRIOR );
1289                         // If config has explicitly requested DBO_TRX be either on or off by not
1290                         // setting DBO_DEFAULT, then respect that. Forcing no transactions is useful
1291                         // for things like blob stores (ExternalStore) which want auto-commit mode.
1292                 }
1293         }
1294
1295         /**
1296          * @param IDatabase $conn
1297          */
1298         private function undoTransactionRoundFlags( IDatabase $conn ) {
1299                 if ( $conn->getFlag( $conn::DBO_DEFAULT ) ) {
1300                         $conn->restoreFlags( $conn::RESTORE_PRIOR );
1301                 }
1302         }
1303
1304         public function flushReplicaSnapshots( $fname = __METHOD__ ) {
1305                 $this->forEachOpenReplicaConnection( function ( IDatabase $conn ) {
1306                         $conn->flushSnapshot( __METHOD__ );
1307                 } );
1308         }
1309
1310         public function hasMasterConnection() {
1311                 return $this->isOpen( $this->getWriterIndex() );
1312         }
1313
1314         public function hasMasterChanges() {
1315                 $pending = 0;
1316                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$pending ) {
1317                         $pending |= $conn->writesOrCallbacksPending();
1318                 } );
1319
1320                 return (bool)$pending;
1321         }
1322
1323         public function lastMasterChangeTimestamp() {
1324                 $lastTime = false;
1325                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$lastTime ) {
1326                         $lastTime = max( $lastTime, $conn->lastDoneWrites() );
1327                 } );
1328
1329                 return $lastTime;
1330         }
1331
1332         public function hasOrMadeRecentMasterChanges( $age = null ) {
1333                 $age = ( $age === null ) ? $this->mWaitTimeout : $age;
1334
1335                 return ( $this->hasMasterChanges()
1336                         || $this->lastMasterChangeTimestamp() > microtime( true ) - $age );
1337         }
1338
1339         public function pendingMasterChangeCallers() {
1340                 $fnames = [];
1341                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$fnames ) {
1342                         $fnames = array_merge( $fnames, $conn->pendingWriteCallers() );
1343                 } );
1344
1345                 return $fnames;
1346         }
1347
1348         public function getLaggedReplicaMode( $domain = false ) {
1349                 // No-op if there is only one DB (also avoids recursion)
1350                 if ( !$this->laggedReplicaMode && $this->getServerCount() > 1 ) {
1351                         try {
1352                                 // See if laggedReplicaMode gets set
1353                                 $conn = $this->getConnection( self::DB_REPLICA, false, $domain );
1354                                 $this->reuseConnection( $conn );
1355                         } catch ( DBConnectionError $e ) {
1356                                 // Avoid expensive re-connect attempts and failures
1357                                 $this->allReplicasDownMode = true;
1358                                 $this->laggedReplicaMode = true;
1359                         }
1360                 }
1361
1362                 return $this->laggedReplicaMode;
1363         }
1364
1365         /**
1366          * @param bool $domain
1367          * @return bool
1368          * @deprecated 1.28; use getLaggedReplicaMode()
1369          */
1370         public function getLaggedSlaveMode( $domain = false ) {
1371                 return $this->getLaggedReplicaMode( $domain );
1372         }
1373
1374         public function laggedReplicaUsed() {
1375                 return $this->laggedReplicaMode;
1376         }
1377
1378         /**
1379          * @return bool
1380          * @since 1.27
1381          * @deprecated Since 1.28; use laggedReplicaUsed()
1382          */
1383         public function laggedSlaveUsed() {
1384                 return $this->laggedReplicaUsed();
1385         }
1386
1387         public function getReadOnlyReason( $domain = false, IDatabase $conn = null ) {
1388                 if ( $this->readOnlyReason !== false ) {
1389                         return $this->readOnlyReason;
1390                 } elseif ( $this->getLaggedReplicaMode( $domain ) ) {
1391                         if ( $this->allReplicasDownMode ) {
1392                                 return 'The database has been automatically locked ' .
1393                                         'until the replica database servers become available';
1394                         } else {
1395                                 return 'The database has been automatically locked ' .
1396                                         'while the replica database servers catch up to the master.';
1397                         }
1398                 } elseif ( $this->masterRunningReadOnly( $domain, $conn ) ) {
1399                         return 'The database master is running in read-only mode.';
1400                 }
1401
1402                 return false;
1403         }
1404
1405         /**
1406          * @param string $domain Domain ID, or false for the current domain
1407          * @param IDatabase|null $conn DB master connectionl used to avoid loops [optional]
1408          * @return bool
1409          */
1410         private function masterRunningReadOnly( $domain, IDatabase $conn = null ) {
1411                 $cache = $this->wanCache;
1412                 $masterServer = $this->getServerName( $this->getWriterIndex() );
1413
1414                 return (bool)$cache->getWithSetCallback(
1415                         $cache->makeGlobalKey( __CLASS__, 'server-read-only', $masterServer ),
1416                         self::TTL_CACHE_READONLY,
1417                         function () use ( $domain, $conn ) {
1418                                 $old = $this->trxProfiler->setSilenced( true );
1419                                 try {
1420                                         $dbw = $conn ?: $this->getConnection( self::DB_MASTER, [], $domain );
1421                                         $readOnly = (int)$dbw->serverIsReadOnly();
1422                                         if ( !$conn ) {
1423                                                 $this->reuseConnection( $dbw );
1424                                         }
1425                                 } catch ( DBError $e ) {
1426                                         $readOnly = 0;
1427                                 }
1428                                 $this->trxProfiler->setSilenced( $old );
1429                                 return $readOnly;
1430                         },
1431                         [ 'pcTTL' => $cache::TTL_PROC_LONG, 'busyValue' => 0 ]
1432                 );
1433         }
1434
1435         public function allowLagged( $mode = null ) {
1436                 if ( $mode === null ) {
1437                         return $this->mAllowLagged;
1438                 }
1439                 $this->mAllowLagged = $mode;
1440
1441                 return $this->mAllowLagged;
1442         }
1443
1444         public function pingAll() {
1445                 $success = true;
1446                 $this->forEachOpenConnection( function ( IDatabase $conn ) use ( &$success ) {
1447                         if ( !$conn->ping() ) {
1448                                 $success = false;
1449                         }
1450                 } );
1451
1452                 return $success;
1453         }
1454
1455         public function forEachOpenConnection( $callback, array $params = [] ) {
1456                 foreach ( $this->mConns as $connsByServer ) {
1457                         foreach ( $connsByServer as $serverConns ) {
1458                                 foreach ( $serverConns as $conn ) {
1459                                         $mergedParams = array_merge( [ $conn ], $params );
1460                                         call_user_func_array( $callback, $mergedParams );
1461                                 }
1462                         }
1463                 }
1464         }
1465
1466         public function forEachOpenMasterConnection( $callback, array $params = [] ) {
1467                 $masterIndex = $this->getWriterIndex();
1468                 foreach ( $this->mConns as $connsByServer ) {
1469                         if ( isset( $connsByServer[$masterIndex] ) ) {
1470                                 /** @var IDatabase $conn */
1471                                 foreach ( $connsByServer[$masterIndex] as $conn ) {
1472                                         $mergedParams = array_merge( [ $conn ], $params );
1473                                         call_user_func_array( $callback, $mergedParams );
1474                                 }
1475                         }
1476                 }
1477         }
1478
1479         public function forEachOpenReplicaConnection( $callback, array $params = [] ) {
1480                 foreach ( $this->mConns as $connsByServer ) {
1481                         foreach ( $connsByServer as $i => $serverConns ) {
1482                                 if ( $i === $this->getWriterIndex() ) {
1483                                         continue; // skip master
1484                                 }
1485                                 foreach ( $serverConns as $conn ) {
1486                                         $mergedParams = array_merge( [ $conn ], $params );
1487                                         call_user_func_array( $callback, $mergedParams );
1488                                 }
1489                         }
1490                 }
1491         }
1492
1493         public function getMaxLag( $domain = false ) {
1494                 $maxLag = -1;
1495                 $host = '';
1496                 $maxIndex = 0;
1497
1498                 if ( $this->getServerCount() <= 1 ) {
1499                         return [ $host, $maxLag, $maxIndex ]; // no replication = no lag
1500                 }
1501
1502                 $lagTimes = $this->getLagTimes( $domain );
1503                 foreach ( $lagTimes as $i => $lag ) {
1504                         if ( $this->mLoads[$i] > 0 && $lag > $maxLag ) {
1505                                 $maxLag = $lag;
1506                                 $host = $this->mServers[$i]['host'];
1507                                 $maxIndex = $i;
1508                         }
1509                 }
1510
1511                 return [ $host, $maxLag, $maxIndex ];
1512         }
1513
1514         public function getLagTimes( $domain = false ) {
1515                 if ( $this->getServerCount() <= 1 ) {
1516                         return [ $this->getWriterIndex() => 0 ]; // no replication = no lag
1517                 }
1518
1519                 $knownLagTimes = []; // map of (server index => 0 seconds)
1520                 $indexesWithLag = [];
1521                 foreach ( $this->mServers as $i => $server ) {
1522                         if ( empty( $server['is static'] ) ) {
1523                                 $indexesWithLag[] = $i; // DB server might have replication lag
1524                         } else {
1525                                 $knownLagTimes[$i] = 0; // DB server is a non-replicating and read-only archive
1526                         }
1527                 }
1528
1529                 return $this->getLoadMonitor()->getLagTimes( $indexesWithLag, $domain ) + $knownLagTimes;
1530         }
1531
1532         public function safeGetLag( IDatabase $conn ) {
1533                 if ( $this->getServerCount() <= 1 ) {
1534                         return 0;
1535                 } else {
1536                         return $conn->getLag();
1537                 }
1538         }
1539
1540         /**
1541          * @param IDatabase $conn
1542          * @param DBMasterPos|bool $pos
1543          * @param int $timeout
1544          * @return bool
1545          */
1546         public function safeWaitForMasterPos( IDatabase $conn, $pos = false, $timeout = 10 ) {
1547                 if ( $this->getServerCount() <= 1 || !$conn->getLBInfo( 'replica' ) ) {
1548                         return true; // server is not a replica DB
1549                 }
1550
1551                 if ( !$pos ) {
1552                         // Get the current master position, opening a connection if needed
1553                         $masterConn = $this->getAnyOpenConnection( $this->getWriterIndex() );
1554                         if ( $masterConn ) {
1555                                 $pos = $masterConn->getMasterPos();
1556                         } else {
1557                                 $masterConn = $this->openConnection( $this->getWriterIndex(), self::DOMAIN_ANY );
1558                                 $pos = $masterConn->getMasterPos();
1559                                 $this->closeConnection( $masterConn );
1560                         }
1561                 }
1562
1563                 if ( $pos instanceof DBMasterPos ) {
1564                         $result = $conn->masterPosWait( $pos, $timeout );
1565                         if ( $result == -1 || is_null( $result ) ) {
1566                                 $msg = __METHOD__ . ": Timed out waiting on {$conn->getServer()} pos {$pos}";
1567                                 $this->replLogger->warning( "$msg" );
1568                                 $ok = false;
1569                         } else {
1570                                 $this->replLogger->info( __METHOD__ . ": Done" );
1571                                 $ok = true;
1572                         }
1573                 } else {
1574                         $ok = false; // something is misconfigured
1575                         $this->replLogger->error( "Could not get master pos for {$conn->getServer()}." );
1576                 }
1577
1578                 return $ok;
1579         }
1580
1581         public function setTransactionListener( $name, callable $callback = null ) {
1582                 if ( $callback ) {
1583                         $this->trxRecurringCallbacks[$name] = $callback;
1584                 } else {
1585                         unset( $this->trxRecurringCallbacks[$name] );
1586                 }
1587                 $this->forEachOpenMasterConnection(
1588                         function ( IDatabase $conn ) use ( $name, $callback ) {
1589                                 $conn->setTransactionListener( $name, $callback );
1590                         }
1591                 );
1592         }
1593
1594         public function setTableAliases( array $aliases ) {
1595                 $this->tableAliases = $aliases;
1596         }
1597
1598         public function setDomainPrefix( $prefix ) {
1599                 if ( $this->mConns['foreignUsed'] ) {
1600                         // Do not switch connections to explicit foreign domains unless marked as free
1601                         $domains = [];
1602                         foreach ( $this->mConns['foreignUsed'] as $i => $connsByDomain ) {
1603                                 $domains = array_merge( $domains, array_keys( $connsByDomain ) );
1604                         }
1605                         $domains = implode( ', ', $domains );
1606                         throw new DBUnexpectedError( null,
1607                                 "Foreign domain connections are still in use ($domains)." );
1608                 }
1609
1610                 $this->localDomain = new DatabaseDomain(
1611                         $this->localDomain->getDatabase(),
1612                         null,
1613                         $prefix
1614                 );
1615
1616                 $this->forEachOpenConnection( function ( IDatabase $db ) use ( $prefix ) {
1617                         $db->tablePrefix( $prefix );
1618                 } );
1619         }
1620
1621         /**
1622          * Make PHP ignore user aborts/disconnects until the returned
1623          * value leaves scope. This returns null and does nothing in CLI mode.
1624          *
1625          * @return ScopedCallback|null
1626          */
1627         final protected function getScopedPHPBehaviorForCommit() {
1628                 if ( PHP_SAPI != 'cli' ) { // https://bugs.php.net/bug.php?id=47540
1629                         $old = ignore_user_abort( true ); // avoid half-finished operations
1630                         return new ScopedCallback( function () use ( $old ) {
1631                                 ignore_user_abort( $old );
1632                         } );
1633                 }
1634
1635                 return null;
1636         }
1637
1638         function __destruct() {
1639                 // Avoid connection leaks for sanity
1640                 $this->disable();
1641         }
1642 }
1643
1644 class_alias( LoadBalancer::class, 'LoadBalancer' );