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 IDatabase;
  29 use Database;
  30 use DBConnRef;
  31 use MaintainableDBConnRef;
  32 use BagOStuff;
  33 use EmptyBagOStuff;
  34 use WANObjectCache;
  35 use ArrayUtils;
  36 use DBError;
  37 use DBAccessError;
  38 use DBExpectedError;
  39 use DBUnexpectedError;
  40 use DBTransactionError;
  41 use DBTransactionSizeError;
  42 use DBConnectionError;
  43 use InvalidArgumentException;
  44 use RuntimeException;
  45 use Exception;
  46
  47 /**
  48  * Database connection, tracking, load balancing, and transaction manager for a cluster
  49  *
  50  * @ingroup Database
  51  */
  52 class LoadBalancer implements ILoadBalancer {
  53         /** @var array[] Map of (server index => server config array) */
  54         private $mServers;
  55         /** @var \Database[][][] Map of local/foreignUsed/foreignFree => server index => IDatabase array */
  56         private $mConns;
  57         /** @var float[] Map of (server index => weight) */
  58         private $mLoads;
  59         /** @var array[] Map of (group => server index => weight) */
  60         private $mGroupLoads;
  61         /** @var bool Whether to disregard replica DB lag as a factor in replica DB selection */
  62         private $mAllowLagged;
  63         /** @var integer Seconds to spend waiting on replica DB lag to resolve */
  64         private $mWaitTimeout;
  65         /** @var array The LoadMonitor configuration */
  66         private $loadMonitorConfig;
  67         /** @var array[] $aliases Map of (table => (dbname, schema, prefix) map) */
  68         private $tableAliases = [];
  69
  70         /** @var ILoadMonitor */
  71         private $loadMonitor;
  72         /** @var ChronologyProtector|null */
  73         private $chronProt;
  74         /** @var BagOStuff */
  75         private $srvCache;
  76         /** @var BagOStuff */
  77         private $memCache;
  78         /** @var WANObjectCache */
  79         private $wanCache;
  80         /** @var object|string Class name or object With profileIn/profileOut methods */
  81         protected $profiler;
  82         /** @var TransactionProfiler */
  83         protected $trxProfiler;
  84         /** @var LoggerInterface */
  85         protected $replLogger;
  86         /** @var LoggerInterface */
  87         protected $connLogger;
  88         /** @var LoggerInterface */
  89         protected $queryLogger;
  90         /** @var LoggerInterface */
  91         protected $perfLogger;
  92
  93         /** @var \Database Database connection that caused a problem */
  94         private $errorConnection;
  95         /** @var integer The generic (not query grouped) replica DB index (of $mServers) */
  96         private $mReadIndex;
  97         /** @var bool|DBMasterPos False if not set */
  98         private $mWaitForPos;
  99         /** @var bool Whether the generic reader fell back to a lagged replica DB */
 100         private $laggedReplicaMode = false;
 101         /** @var bool Whether the generic reader fell back to a lagged replica DB */
 102         private $allReplicasDownMode = false;
 103         /** @var string The last DB selection or connection error */
 104         private $mLastError = 'Unknown error';
 105         /** @var string|bool Reason the LB is read-only or false if not */
 106         private $readOnlyReason = false;
 107         /** @var integer Total connections opened */
 108         private $connsOpened = 0;
 109         /** @var string|bool String if a requested DBO_TRX transaction round is active */
 110         private $trxRoundId = false;
 111         /** @var array[] Map of (name => callable) */
 112         private $trxRecurringCallbacks = [];
 113         /** @var DatabaseDomain Local Domain ID and default for selectDB() calls */
 114         private $localDomain;
 115         /** @var string Alternate ID string for the domain instead of DatabaseDomain::getId() */
 116         private $localDomainIdAlias;
 117         /** @var string Current server name */
 118         private $host;
 119         /** @var bool Whether this PHP instance is for a CLI script */
 120         protected $cliMode;
 121         /** @var string Agent name for query profiling */
 122         protected $agent;
 123
 124         /** @var callable Exception logger */
 125         private $errorLogger;
 126
 127         /** @var boolean */
 128         private $disabled = false;
 129         /** @var boolean */
 130         private $chronProtInitialized = false;
 131
 132         /** @var integer Warn when this many connection are held */
 133         const CONN_HELD_WARN_THRESHOLD = 10;
 134
 135         /** @var integer Default 'max lag' when unspecified */
 136         const MAX_LAG_DEFAULT = 10;
 137         /** @var integer Seconds to cache master server read-only status */
 138         const TTL_CACHE_READONLY = 5;
 139
 140         public function __construct( array $params ) {
 141                 if ( !isset( $params['servers'] ) ) {
 142                         throw new InvalidArgumentException( __CLASS__ . ': missing servers parameter' );
 143                 }
 144                 $this->mServers = $params['servers'];
 145
 146                 $this->localDomain = isset( $params['localDomain'] )
 147                         ? DatabaseDomain::newFromId( $params['localDomain'] )
 148                         : DatabaseDomain::newUnspecified();
 149                 // In case a caller assumes that the domain ID is simply <db>-<prefix>, which is almost
 150                 // always true, gracefully handle the case when they fail to account for escaping.
 151                 if ( $this->localDomain->getTablePrefix() != '' ) {
 152                         $this->localDomainIdAlias =
 153                                 $this->localDomain->getDatabase() . '-' . $this->localDomain->getTablePrefix();
 154                 } else {
 155                         $this->localDomainIdAlias = $this->localDomain->getDatabase();
 156                 }
 157
 158                 $this->mWaitTimeout = isset( $params['waitTimeout'] ) ? $params['waitTimeout'] : 10;
 159
 160                 $this->mReadIndex = -1;
 161                 $this->mConns = [
 162                         'local'       => [],
 163                         'foreignUsed' => [],
 164                         'foreignFree' => []
 165                 ];
 166                 $this->mLoads = [];
 167                 $this->mWaitForPos = false;
 168                 $this->mAllowLagged = false;
 169
 170                 if ( isset( $params['readOnlyReason'] ) && is_string( $params['readOnlyReason'] ) ) {
 171                         $this->readOnlyReason = $params['readOnlyReason'];
 172                 }
 173
 174                 if ( isset( $params['loadMonitor'] ) ) {
 175                         $this->loadMonitorConfig = $params['loadMonitor'];
 176                 } else {
 177                         $this->loadMonitorConfig = [ 'class' => 'LoadMonitorNull' ];
 178                 }
 179
 180                 foreach ( $params['servers'] as $i => $server ) {
 181                         $this->mLoads[$i] = $server['load'];
 182                         if ( isset( $server['groupLoads'] ) ) {
 183                                 foreach ( $server['groupLoads'] as $group => $ratio ) {
 184                                         if ( !isset( $this->mGroupLoads[$group] ) ) {
 185                                                 $this->mGroupLoads[$group] = [];
 186                                         }
 187                                         $this->mGroupLoads[$group][$i] = $ratio;
 188                                 }
 189                         }
 190                 }
 191
 192                 if ( isset( $params['srvCache'] ) ) {
 193                         $this->srvCache = $params['srvCache'];
 194                 } else {
 195                         $this->srvCache = new EmptyBagOStuff();
 196                 }
 197                 if ( isset( $params['memCache'] ) ) {
 198                         $this->memCache = $params['memCache'];
 199                 } else {
 200                         $this->memCache = new EmptyBagOStuff();
 201                 }
 202                 if ( isset( $params['wanCache'] ) ) {
 203                         $this->wanCache = $params['wanCache'];
 204                 } else {
 205                         $this->wanCache = WANObjectCache::newEmpty();
 206                 }
 207                 $this->profiler = isset( $params['profiler'] ) ? $params['profiler'] : null;
 208                 if ( isset( $params['trxProfiler'] ) ) {
 209                         $this->trxProfiler = $params['trxProfiler'];
 210                 } else {
 211                         $this->trxProfiler = new TransactionProfiler();
 212                 }
 213
 214                 $this->errorLogger = isset( $params['errorLogger'] )
 215                         ? $params['errorLogger']
 216                         : function ( Exception $e ) {
 217                                 trigger_error( get_class( $e ) . ': ' . $e->getMessage(), E_USER_WARNING );
 218                         };
 219
 220                 foreach ( [ 'replLogger', 'connLogger', 'queryLogger', 'perfLogger' ] as $key ) {
 221                         $this->$key = isset( $params[$key] ) ? $params[$key] : new NullLogger();
 222                 }
 223
 224                 $this->host = isset( $params['hostname'] )
 225                         ? $params['hostname']
 226                         : ( gethostname() ?: 'unknown' );
 227                 $this->cliMode = isset( $params['cliMode'] ) ? $params['cliMode'] : PHP_SAPI === 'cli';
 228                 $this->agent = isset( $params['agent'] ) ? $params['agent'] : '';
 229
 230                 if ( isset( $params['chronologyProtector'] ) ) {
 231                         $this->chronProt = $params['chronologyProtector'];
 232                 }
 233         }
 234
 235         /**
 236          * Get a LoadMonitor instance
 237          *
 238          * @return ILoadMonitor
 239          */
 240         private function getLoadMonitor() {
 241                 if ( !isset( $this->loadMonitor ) ) {
 242                         $compat = [
 243                                 'LoadMonitor' => LoadMonitor::class,
 244                                 'LoadMonitorNull' => LoadMonitorNull::class,
 245                                 'LoadMonitorMySQL' => LoadMonitorMySQL::class,
 246                         ];
 247
 248                         $class = $this->loadMonitorConfig['class'];
 249                         if ( isset( $compat[$class] ) ) {
 250                                 $class = $compat[$class];
 251                         }
 252
 253                         $this->loadMonitor = new $class(
 254                                 $this, $this->srvCache, $this->memCache, $this->loadMonitorConfig );
 255                         $this->loadMonitor->setLogger( $this->replLogger );
 256                 }
 257
 258                 return $this->loadMonitor;
 259         }
 260
 261         /**
 262          * @param array $loads
 263          * @param bool|string $domain Domain to get non-lagged for
 264          * @param int $maxLag Restrict the maximum allowed lag to this many seconds
 265          * @return bool|int|string
 266          */
 267         private function getRandomNonLagged( array $loads, $domain = false, $maxLag = INF ) {
 268                 $lags = $this->getLagTimes( $domain );
 269
 270                 # Unset excessively lagged servers
 271                 foreach ( $lags as $i => $lag ) {
 272                         if ( $i != 0 ) {
 273                                 # How much lag this server nominally is allowed to have
 274                                 $maxServerLag = isset( $this->mServers[$i]['max lag'] )
 275                                         ? $this->mServers[$i]['max lag']
 276                                         : self::MAX_LAG_DEFAULT; // default
 277                                 # Constrain that futher by $maxLag argument
 278                                 $maxServerLag = min( $maxServerLag, $maxLag );
 279
 280                                 $host = $this->getServerName( $i );
 281                                 if ( $lag === false && !is_infinite( $maxServerLag ) ) {
 282                                         $this->replLogger->error(
 283                                                 "Server {host} (#$i) is not replicating?", [ 'host' => $host ] );
 284                                         unset( $loads[$i] );
 285                                 } elseif ( $lag > $maxServerLag ) {
 286                                         $this->replLogger->warning(
 287                                                 "Server {host} (#$i) has {lag} seconds of lag (>= {maxlag})",
 288                                                 [ 'host' => $host, 'lag' => $lag, 'maxlag' => $maxServerLag ]
 289                                         );
 290                                         unset( $loads[$i] );
 291                                 }
 292                         }
 293                 }
 294
 295                 # Find out if all the replica DBs with non-zero load are lagged
 296                 $sum = 0;
 297                 foreach ( $loads as $load ) {
 298                         $sum += $load;
 299                 }
 300                 if ( $sum == 0 ) {
 301                         # No appropriate DB servers except maybe the master and some replica DBs with zero load
 302                         # Do NOT use the master
 303                         # Instead, this function will return false, triggering read-only mode,
 304                         # and a lagged replica DB will be used instead.
 305                         return false;
 306                 }
 307
 308                 if ( count( $loads ) == 0 ) {
 309                         return false;
 310                 }
 311
 312                 # Return a random representative of the remainder
 313                 return ArrayUtils::pickRandom( $loads );
 314         }
 315
 316         public function getReaderIndex( $group = false, $domain = false ) {
 317                 if ( count( $this->mServers ) == 1 ) {
 318                         # Skip the load balancing if there's only one server
 319                         return $this->getWriterIndex();
 320                 } elseif ( $group === false && $this->mReadIndex >= 0 ) {
 321                         # Shortcut if generic reader exists already
 322                         return $this->mReadIndex;
 323                 }
 324
 325                 # Find the relevant load array
 326                 if ( $group !== false ) {
 327                         if ( isset( $this->mGroupLoads[$group] ) ) {
 328                                 $nonErrorLoads = $this->mGroupLoads[$group];
 329                         } else {
 330                                 # No loads for this group, return false and the caller can use some other group
 331                                 $this->connLogger->info( __METHOD__ . ": no loads for group $group" );
 332
 333                                 return false;
 334                         }
 335                 } else {
 336                         $nonErrorLoads = $this->mLoads;
 337                 }
 338
 339                 if ( !count( $nonErrorLoads ) ) {
 340                         throw new InvalidArgumentException( "Empty server array given to LoadBalancer" );
 341                 }
 342
 343                 # Scale the configured load ratios according to the dynamic load if supported
 344                 $this->getLoadMonitor()->scaleLoads( $nonErrorLoads, $domain );
 345
 346                 $laggedReplicaMode = false;
 347
 348                 # No server found yet
 349                 $i = false;
 350                 # First try quickly looking through the available servers for a server that
 351                 # meets our criteria
 352                 $currentLoads = $nonErrorLoads;
 353                 while ( count( $currentLoads ) ) {
 354                         if ( $this->mAllowLagged || $laggedReplicaMode ) {
 355                                 $i = ArrayUtils::pickRandom( $currentLoads );
 356                         } else {
 357                                 $i = false;
 358                                 if ( $this->mWaitForPos && $this->mWaitForPos->asOfTime() ) {
 359                                         # ChronologyProtecter causes mWaitForPos to be set via sessions.
 360                                         # This triggers doWait() after connect, so it's especially good to
 361                                         # avoid lagged servers so as to avoid just blocking in that method.
 362                                         $ago = microtime( true ) - $this->mWaitForPos->asOfTime();
 363                                         # Aim for <= 1 second of waiting (being too picky can backfire)
 364                                         $i = $this->getRandomNonLagged( $currentLoads, $domain, $ago + 1 );
 365                                 }
 366                                 if ( $i === false ) {
 367                                         # Any server with less lag than it's 'max lag' param is preferable
 368                                         $i = $this->getRandomNonLagged( $currentLoads, $domain );
 369                                 }
 370                                 if ( $i === false && count( $currentLoads ) != 0 ) {
 371                                         # All replica DBs lagged. Switch to read-only mode
 372                                         $this->replLogger->error( "All replica DBs lagged. Switch to read-only mode" );
 373                                         $i = ArrayUtils::pickRandom( $currentLoads );
 374                                         $laggedReplicaMode = true;
 375                                 }
 376                         }
 377
 378                         if ( $i === false ) {
 379                                 # pickRandom() returned false
 380                                 # This is permanent and means the configuration or the load monitor
 381                                 # wants us to return false.
 382                                 $this->connLogger->debug( __METHOD__ . ": pickRandom() returned false" );
 383
 384                                 return false;
 385                         }
 386
 387                         $serverName = $this->getServerName( $i );
 388                         $this->connLogger->debug( __METHOD__ . ": Using reader #$i: $serverName..." );
 389
 390                         $conn = $this->openConnection( $i, $domain );
 391                         if ( !$conn ) {
 392                                 $this->connLogger->warning( __METHOD__ . ": Failed connecting to $i/$domain" );
 393                                 unset( $nonErrorLoads[$i] );
 394                                 unset( $currentLoads[$i] );
 395                                 $i = false;
 396                                 continue;
 397                         }
 398
 399                         // Decrement reference counter, we are finished with this connection.
 400                         // It will be incremented for the caller later.
 401                         if ( $domain !== false ) {
 402                                 $this->reuseConnection( $conn );
 403                         }
 404
 405                         # Return this server
 406                         break;
 407                 }
 408
 409                 # If all servers were down, quit now
 410                 if ( !count( $nonErrorLoads ) ) {
 411                         $this->connLogger->error( "All servers down" );
 412                 }
 413
 414                 if ( $i !== false ) {
 415                         # Replica DB connection successful.
 416                         # Wait for the session master pos for a short time.
 417                         if ( $this->mWaitForPos && $i > 0 ) {
 418                                 $this->doWait( $i );
 419                         }
 420                         if ( $this->mReadIndex <= 0 && $this->mLoads[$i] > 0 && $group === false ) {
 421                                 $this->mReadIndex = $i;
 422                                 # Record if the generic reader index is in "lagged replica DB" mode
 423                                 if ( $laggedReplicaMode ) {
 424                                         $this->laggedReplicaMode = true;
 425                                 }
 426                         }
 427                         $serverName = $this->getServerName( $i );
 428                         $this->connLogger->debug(
 429                                 __METHOD__ . ": using server $serverName for group '$group'" );
 430                 }
 431
 432                 return $i;
 433         }
 434
 435         public function waitFor( $pos ) {
 436                 $oldPos = $this->mWaitForPos;
 437                 $this->mWaitForPos = $pos;
 438
 439                 // If a generic reader connection was already established, then wait now
 440                 $i = $this->mReadIndex;
 441                 if ( $i > 0 ) {
 442                         if ( !$this->doWait( $i ) ) {
 443                                 $this->laggedReplicaMode = true;
 444                         }
 445                 }
 446
 447                 // Restore the older position if it was higher
 448                 $this->setWaitForPositionIfHigher( $oldPos );
 449         }
 450
 451         public function waitForOne( $pos, $timeout = null ) {
 452                 $oldPos = $this->mWaitForPos;
 453                 $this->mWaitForPos = $pos;
 454
 455                 $i = $this->mReadIndex;
 456                 if ( $i <= 0 ) {
 457                         // Pick a generic replica DB if there isn't one yet
 458                         $readLoads = $this->mLoads;
 459                         unset( $readLoads[$this->getWriterIndex()] ); // replica DBs only
 460                         $readLoads = array_filter( $readLoads ); // with non-zero load
 461                         $i = ArrayUtils::pickRandom( $readLoads );
 462                 }
 463
 464                 if ( $i > 0 ) {
 465                         $ok = $this->doWait( $i, true, $timeout );
 466                 } else {
 467                         $ok = true; // no applicable loads
 468                 }
 469
 470                 // Restore the older position if it was higher
 471                 $this->setWaitForPositionIfHigher( $oldPos );
 472
 473                 return $ok;
 474         }
 475
 476         public function waitForAll( $pos, $timeout = null ) {
 477                 $oldPos = $this->mWaitForPos;
 478                 $this->mWaitForPos = $pos;
 479                 $serverCount = count( $this->mServers );
 480
 481                 $ok = true;
 482                 for ( $i = 1; $i < $serverCount; $i++ ) {
 483                         if ( $this->mLoads[$i] > 0 ) {
 484                                 $ok = $this->doWait( $i, true, $timeout ) && $ok;
 485                         }
 486                 }
 487
 488                 // Restore the older position if it was higher
 489                 $this->setWaitForPositionIfHigher( $oldPos );
 490
 491                 return $ok;
 492         }
 493
 494         /**
 495          * @param DBMasterPos|bool $pos
 496          */
 497         private function setWaitForPositionIfHigher( $pos ) {
 498                 if ( !$pos ) {
 499                         return;
 500                 }
 501
 502                 if ( !$this->mWaitForPos || $pos->hasReached( $this->mWaitForPos ) ) {
 503                         $this->mWaitForPos = $pos;
 504                 }
 505         }
 506
 507         /**
 508          * @param int $i
 509          * @return IDatabase|bool
 510          */
 511         public function getAnyOpenConnection( $i ) {
 512                 foreach ( $this->mConns as $connsByServer ) {
 513                         if ( !empty( $connsByServer[$i] ) ) {
 514                                 /** @var $serverConns IDatabase[] */
 515                                 $serverConns = $connsByServer[$i];
 516
 517                                 return reset( $serverConns );
 518                         }
 519                 }
 520
 521                 return false;
 522         }
 523
 524         /**
 525          * Wait for a given replica DB to catch up to the master pos stored in $this
 526          * @param int $index Server index
 527          * @param bool $open Check the server even if a new connection has to be made
 528          * @param int $timeout Max seconds to wait; default is mWaitTimeout
 529          * @return bool
 530          */
 531         protected function doWait( $index, $open = false, $timeout = null ) {
 532                 $close = false; // close the connection afterwards
 533
 534                 // Check if we already know that the DB has reached this point
 535                 $server = $this->getServerName( $index );
 536                 $key = $this->srvCache->makeGlobalKey( __CLASS__, 'last-known-pos', $server, 'v1' );
 537                 /** @var DBMasterPos $knownReachedPos */
 538                 $knownReachedPos = $this->srvCache->get( $key );
 539                 if (
 540                         $knownReachedPos instanceof DBMasterPos &&
 541                         $knownReachedPos->hasReached( $this->mWaitForPos )
 542                 ) {
 543                         $this->replLogger->debug( __METHOD__ .
 544                                 ": replica DB $server known to be caught up (pos >= $knownReachedPos)." );
 545                         return true;
 546                 }
 547
 548                 // Find a connection to wait on, creating one if needed and allowed
 549                 $conn = $this->getAnyOpenConnection( $index );
 550                 if ( !$conn ) {
 551                         if ( !$open ) {
 552                                 $this->replLogger->debug( __METHOD__ . ": no connection open for $server" );
 553
 554                                 return false;
 555                         } else {
 556                                 $conn = $this->openConnection( $index, self::DOMAIN_ANY );
 557                                 if ( !$conn ) {
 558                                         $this->replLogger->warning( __METHOD__ . ": failed to connect to $server" );
 559
 560                                         return false;
 561                                 }
 562                                 // Avoid connection spam in waitForAll() when connections
 563                                 // are made just for the sake of doing this lag check.
 564                                 $close = true;
 565                         }
 566                 }
 567
 568                 $this->replLogger->info( __METHOD__ . ": Waiting for replica DB $server to catch up..." );
 569                 $timeout = $timeout ?: $this->mWaitTimeout;
 570                 $result = $conn->masterPosWait( $this->mWaitForPos, $timeout );
 571
 572                 if ( $result == -1 || is_null( $result ) ) {
 573                         // Timed out waiting for replica DB, use master instead
 574                         $this->replLogger->warning(
 575                                 __METHOD__ . ": Timed out waiting on {host} pos {$this->mWaitForPos}",
 576                                 [ 'host' => $server ]
 577                         );
 578                         $ok = false;
 579                 } else {
 580                         $this->replLogger->info( __METHOD__ . ": Done" );
 581                         $ok = true;
 582                         // Remember that the DB reached this point
 583                         $this->srvCache->set( $key, $this->mWaitForPos, BagOStuff::TTL_DAY );
 584                 }
 585
 586                 if ( $close ) {
 587                         $this->closeConnection( $conn );
 588                 }
 589
 590                 return $ok;
 591         }
 592
 593         /**
 594          * @see ILoadBalancer::getConnection()
 595          *
 596          * @param int $i
 597          * @param array $groups
 598          * @param bool $domain
 599          * @return Database
 600          * @throws DBConnectionError
 601          */
 602         public function getConnection( $i, $groups = [], $domain = false ) {
 603                 if ( $i === null || $i === false ) {
 604                         throw new InvalidArgumentException( 'Attempt to call ' . __METHOD__ .
 605                                 ' with invalid server index' );
 606                 }
 607
 608                 if ( $this->localDomain->equals( $domain ) || $domain === $this->localDomainIdAlias ) {
 609                         $domain = false; // local connection requested
 610                 }
 611
 612                 $groups = ( $groups === false || $groups === [] )
 613                         ? [ false ] // check one "group": the generic pool
 614                         : (array)$groups;
 615
 616                 $masterOnly = ( $i == self::DB_MASTER || $i == $this->getWriterIndex() );
 617                 $oldConnsOpened = $this->connsOpened; // connections open now
 618
 619                 if ( $i == self::DB_MASTER ) {
 620                         $i = $this->getWriterIndex();
 621                 } else {
 622                         # Try to find an available server in any the query groups (in order)
 623                         foreach ( $groups as $group ) {
 624                                 $groupIndex = $this->getReaderIndex( $group, $domain );
 625                                 if ( $groupIndex !== false ) {
 626                                         $i = $groupIndex;
 627                                         break;
 628                                 }
 629                         }
 630                 }
 631
 632                 # Operation-based index
 633                 if ( $i == self::DB_REPLICA ) {
 634                         $this->mLastError = 'Unknown error'; // reset error string
 635                         # Try the general server pool if $groups are unavailable.
 636                         $i = ( $groups === [ false ] )
 637                                 ? false // don't bother with this if that is what was tried above
 638                                 : $this->getReaderIndex( false, $domain );
 639                         # Couldn't find a working server in getReaderIndex()?
 640                         if ( $i === false ) {
 641                                 $this->mLastError = 'No working replica DB server: ' . $this->mLastError;
 642                                 // Throw an exception
 643                                 $this->reportConnectionError();
 644                                 return null; // not reached
 645                         }
 646                 }
 647
 648                 # Now we have an explicit index into the servers array
 649                 $conn = $this->openConnection( $i, $domain );
 650                 if ( !$conn ) {
 651                         // Throw an exception
 652                         $this->reportConnectionError();
 653                         return null; // not reached
 654                 }
 655
 656                 # Profile any new connections that happen
 657                 if ( $this->connsOpened > $oldConnsOpened ) {
 658                         $host = $conn->getServer();
 659                         $dbname = $conn->getDBname();
 660                         $this->trxProfiler->recordConnection( $host, $dbname, $masterOnly );
 661                 }
 662
 663                 if ( $masterOnly ) {
 664                         # Make master-requested DB handles inherit any read-only mode setting
 665                         $conn->setLBInfo( 'readOnlyReason', $this->getReadOnlyReason( $domain, $conn ) );
 666                 }
 667
 668                 return $conn;
 669         }
 670
 671         public function reuseConnection( $conn ) {
 672                 $serverIndex = $conn->getLBInfo( 'serverIndex' );
 673                 $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 674                 if ( $serverIndex === null || $refCount === null ) {
 675                         /**
 676                          * This can happen in code like:
 677                          *   foreach ( $dbs as $db ) {
 678                          *     $conn = $lb->getConnection( $lb::DB_REPLICA, [], $db );
 679                          *     ...
 680                          *     $lb->reuseConnection( $conn );
 681                          *   }
 682                          * When a connection to the local DB is opened in this way, reuseConnection()
 683                          * should be ignored
 684                          */
 685                         return;
 686                 } elseif ( $conn instanceof DBConnRef ) {
 687                         // DBConnRef already handles calling reuseConnection() and only passes the live
 688                         // Database instance to this method. Any caller passing in a DBConnRef is broken.
 689                         $this->connLogger->error( __METHOD__ . ": got DBConnRef instance.\n" .
 690                                 ( new RuntimeException() )->getTraceAsString() );
 691
 692                         return;
 693                 }
 694
 695                 if ( $this->disabled ) {
 696                         return; // DBConnRef handle probably survived longer than the LoadBalancer
 697                 }
 698
 699                 $domain = $conn->getDomainID();
 700                 if ( !isset( $this->mConns['foreignUsed'][$serverIndex][$domain] ) ) {
 701                         throw new InvalidArgumentException( __METHOD__ .
 702                                 ": connection $serverIndex/$domain not found; it may have already been freed." );
 703                 } elseif ( $this->mConns['foreignUsed'][$serverIndex][$domain] !== $conn ) {
 704                         throw new InvalidArgumentException( __METHOD__ .
 705                                 ": connection $serverIndex/$domain mismatched; it may have already been freed." );
 706                 }
 707                 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
 708                 if ( $refCount <= 0 ) {
 709                         $this->mConns['foreignFree'][$serverIndex][$domain] = $conn;
 710                         unset( $this->mConns['foreignUsed'][$serverIndex][$domain] );
 711                         if ( !$this->mConns['foreignUsed'][$serverIndex] ) {
 712                                 unset( $this->mConns[ 'foreignUsed' ][$serverIndex] ); // clean up
 713                         }
 714                         $this->connLogger->debug( __METHOD__ . ": freed connection $serverIndex/$domain" );
 715                 } else {
 716                         $this->connLogger->debug( __METHOD__ .
 717                                 ": reference count for $serverIndex/$domain reduced to $refCount" );
 718                 }
 719         }
 720
 721         public function getConnectionRef( $db, $groups = [], $domain = false ) {
 722                 $domain = ( $domain !== false ) ? $domain : $this->localDomain;
 723
 724                 return new DBConnRef( $this, $this->getConnection( $db, $groups, $domain ) );
 725         }
 726
 727         public function getLazyConnectionRef( $db, $groups = [], $domain = false ) {
 728                 $domain = ( $domain !== false ) ? $domain : $this->localDomain;
 729
 730                 return new DBConnRef( $this, [ $db, $groups, $domain ] );
 731         }
 732
 733         public function getMaintenanceConnectionRef( $db, $groups = [], $domain = false ) {
 734                 $domain = ( $domain !== false ) ? $domain : $this->localDomain;
 735
 736                 return new MaintainableDBConnRef( $this, $this->getConnection( $db, $groups, $domain ) );
 737         }
 738
 739         /**
 740          * @see ILoadBalancer::openConnection()
 741          *
 742          * @param int $i
 743          * @param bool $domain
 744          * @return bool|Database
 745          * @throws DBAccessError
 746          */
 747         public function openConnection( $i, $domain = false ) {
 748                 if ( $this->localDomain->equals( $domain ) || $domain === $this->localDomainIdAlias ) {
 749                         $domain = false; // local connection requested
 750                 }
 751
 752                 if ( !$this->chronProtInitialized && $this->chronProt ) {
 753                         $this->connLogger->debug( __METHOD__ . ': calling initLB() before first connection.' );
 754                         // Load CP positions before connecting so that doWait() triggers later if needed
 755                         $this->chronProtInitialized = true;
 756                         $this->chronProt->initLB( $this );
 757                 }
 758
 759                 if ( $domain !== false ) {
 760                         $conn = $this->openForeignConnection( $i, $domain );
 761                 } elseif ( isset( $this->mConns['local'][$i][0] ) ) {
 762                         $conn = $this->mConns['local'][$i][0];
 763                 } else {
 764                         if ( !isset( $this->mServers[$i] ) || !is_array( $this->mServers[$i] ) ) {
 765                                 throw new InvalidArgumentException( "No server with index '$i'." );
 766                         }
 767                         // Open a new connection
 768                         $server = $this->mServers[$i];
 769                         $server['serverIndex'] = $i;
 770                         $conn = $this->reallyOpenConnection( $server, false );
 771                         $serverName = $this->getServerName( $i );
 772                         if ( $conn->isOpen() ) {
 773                                 $this->connLogger->debug( "Connected to database $i at '$serverName'." );
 774                                 $this->mConns['local'][$i][0] = $conn;
 775                         } else {
 776                                 $this->connLogger->warning( "Failed to connect to database $i at '$serverName'." );
 777                                 $this->errorConnection = $conn;
 778                                 $conn = false;
 779                         }
 780                 }
 781
 782                 if ( $conn instanceof IDatabase && !$conn->isOpen() ) {
 783                         // Connection was made but later unrecoverably lost for some reason.
 784                         // Do not return a handle that will just throw exceptions on use,
 785                         // but let the calling code (e.g. getReaderIndex) try another server.
 786                         // See DatabaseMyslBase::ping() for how this can happen.
 787                         $this->errorConnection = $conn;
 788                         $conn = false;
 789                 }
 790
 791                 return $conn;
 792         }
 793
 794         /**
 795          * Open a connection to a foreign DB, or return one if it is already open.
 796          *
 797          * Increments a reference count on the returned connection which locks the
 798          * connection to the requested domain. This reference count can be
 799          * decremented by calling reuseConnection().
 800          *
 801          * If a connection is open to the appropriate server already, but with the wrong
 802          * database, it will be switched to the right database and returned, as long as
 803          * it has been freed first with reuseConnection().
 804          *
 805          * On error, returns false, and the connection which caused the
 806          * error will be available via $this->errorConnection.
 807          *
 808          * @note If disable() was called on this LoadBalancer, this method will throw a DBAccessError.
 809          *
 810          * @param int $i Server index
 811          * @param string $domain Domain ID to open
 812          * @return Database
 813          */
 814         private function openForeignConnection( $i, $domain ) {
 815                 $domainInstance = DatabaseDomain::newFromId( $domain );
 816                 $dbName = $domainInstance->getDatabase();
 817                 $prefix = $domainInstance->getTablePrefix();
 818
 819                 if ( isset( $this->mConns['foreignUsed'][$i][$domain] ) ) {
 820                         // Reuse an already-used connection
 821                         $conn = $this->mConns['foreignUsed'][$i][$domain];
 822                         $this->connLogger->debug( __METHOD__ . ": reusing connection $i/$domain" );
 823                 } elseif ( isset( $this->mConns['foreignFree'][$i][$domain] ) ) {
 824                         // Reuse a free connection for the same domain
 825                         $conn = $this->mConns['foreignFree'][$i][$domain];
 826                         unset( $this->mConns['foreignFree'][$i][$domain] );
 827                         $this->mConns['foreignUsed'][$i][$domain] = $conn;
 828                         $this->connLogger->debug( __METHOD__ . ": reusing free connection $i/$domain" );
 829                 } elseif ( !empty( $this->mConns['foreignFree'][$i] ) ) {
 830                         // Reuse a connection from another domain
 831                         $conn = reset( $this->mConns['foreignFree'][$i] );
 832                         $oldDomain = key( $this->mConns['foreignFree'][$i] );
 833                         // The empty string as a DB name means "don't care".
 834                         // DatabaseMysqlBase::open() already handle this on connection.
 835                         if ( strlen( $dbName ) && !$conn->selectDB( $dbName ) ) {
 836                                 $this->mLastError = "Error selecting database '$dbName' on server " .
 837                                         $conn->getServer() . " from client host {$this->host}";
 838                                 $this->errorConnection = $conn;
 839                                 $conn = false;
 840                         } else {
 841                                 $conn->tablePrefix( $prefix );
 842                                 unset( $this->mConns['foreignFree'][$i][$oldDomain] );
 843                                 $this->mConns['foreignUsed'][$i][$domain] = $conn;
 844                                 $this->connLogger->debug( __METHOD__ .
 845                                         ": reusing free connection from $oldDomain for $domain" );
 846                         }
 847                 } else {
 848                         if ( !isset( $this->mServers[$i] ) || !is_array( $this->mServers[$i] ) ) {
 849                                 throw new InvalidArgumentException( "No server with index '$i'." );
 850                         }
 851                         // Open a new connection
 852                         $server = $this->mServers[$i];
 853                         $server['serverIndex'] = $i;
 854                         $server['foreignPoolRefCount'] = 0;
 855                         $server['foreign'] = true;
 856                         $conn = $this->reallyOpenConnection( $server, $dbName );
 857                         if ( !$conn->isOpen() ) {
 858                                 $this->connLogger->warning( __METHOD__ . ": connection error for $i/$domain" );
 859                                 $this->errorConnection = $conn;
 860                                 $conn = false;
 861                         } else {
 862                                 $conn->tablePrefix( $prefix );
 863                                 $this->mConns['foreignUsed'][$i][$domain] = $conn;
 864                                 $this->connLogger->debug( __METHOD__ . ": opened new connection for $i/$domain" );
 865                         }
 866                 }
 867
 868                 // Increment reference count
 869                 if ( $conn instanceof IDatabase ) {
 870                         $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 871                         $conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
 872                 }
 873
 874                 return $conn;
 875         }
 876
 877         /**
 878          * Test if the specified index represents an open connection
 879          *
 880          * @param int $index Server index
 881          * @access private
 882          * @return bool
 883          */
 884         private function isOpen( $index ) {
 885                 if ( !is_integer( $index ) ) {
 886                         return false;
 887                 }
 888
 889                 return (bool)$this->getAnyOpenConnection( $index );
 890         }
 891
 892         /**
 893          * Really opens a connection. Uncached.
 894          * Returns a Database object whether or not the connection was successful.
 895          * @access private
 896          *
 897          * @param array $server
 898          * @param string|bool $dbNameOverride Use "" to not select any database
 899          * @return Database
 900          * @throws DBAccessError
 901          * @throws InvalidArgumentException
 902          */
 903         protected function reallyOpenConnection( array $server, $dbNameOverride = false ) {
 904                 if ( $this->disabled ) {
 905                         throw new DBAccessError();
 906                 }
 907
 908                 if ( $dbNameOverride !== false ) {
 909                         $server['dbname'] = $dbNameOverride;
 910                 }
 911
 912                 // Let the handle know what the cluster master is (e.g. "db1052")
 913                 $masterName = $this->getServerName( $this->getWriterIndex() );
 914                 $server['clusterMasterHost'] = $masterName;
 915
 916                 // Log when many connection are made on requests
 917                 if ( ++$this->connsOpened >= self::CONN_HELD_WARN_THRESHOLD ) {
 918                         $this->perfLogger->warning( __METHOD__ . ": " .
 919                                 "{$this->connsOpened}+ connections made (master=$masterName)" );
 920                 }
 921
 922                 $server['srvCache'] = $this->srvCache;
 923                 // Set loggers and profilers
 924                 $server['connLogger'] = $this->connLogger;
 925                 $server['queryLogger'] = $this->queryLogger;
 926                 $server['errorLogger'] = $this->errorLogger;
 927                 $server['profiler'] = $this->profiler;
 928                 $server['trxProfiler'] = $this->trxProfiler;
 929                 // Use the same agent and PHP mode for all DB handles
 930                 $server['cliMode'] = $this->cliMode;
 931                 $server['agent'] = $this->agent;
 932                 // Use DBO_DEFAULT flags by default for LoadBalancer managed databases. Assume that the
 933                 // application calls LoadBalancer::commitMasterChanges() before the PHP script completes.
 934                 $server['flags'] = isset( $server['flags'] ) ? $server['flags'] : IDatabase::DBO_DEFAULT;
 935
 936                 // Create a live connection object
 937                 try {
 938                         $db = Database::factory( $server['type'], $server );
 939                 } catch ( DBConnectionError $e ) {
 940                         // FIXME: This is probably the ugliest thing I have ever done to
 941                         // PHP. I'm half-expecting it to segfault, just out of disgust. -- TS
 942                         $db = $e->db;
 943                 }
 944
 945                 $db->setLBInfo( $server );
 946                 $db->setLazyMasterHandle(
 947                         $this->getLazyConnectionRef( self::DB_MASTER, [], $db->getDomainID() )
 948                 );
 949                 $db->setTableAliases( $this->tableAliases );
 950
 951                 if ( $server['serverIndex'] === $this->getWriterIndex() ) {
 952                         if ( $this->trxRoundId !== false ) {
 953                                 $this->applyTransactionRoundFlags( $db );
 954                         }
 955                         foreach ( $this->trxRecurringCallbacks as $name => $callback ) {
 956                                 $db->setTransactionListener( $name, $callback );
 957                         }
 958                 }
 959
 960                 return $db;
 961         }
 962
 963         /**
 964          * @throws DBConnectionError
 965          */
 966         private function reportConnectionError() {
 967                 $conn = $this->errorConnection; // the connection which caused the error
 968                 $context = [
 969                         'method' => __METHOD__,
 970                         'last_error' => $this->mLastError,
 971                 ];
 972
 973                 if ( $conn instanceof IDatabase ) {
 974                         $context['db_server'] = $conn->getServer();
 975                         $this->connLogger->warning(
 976                                 "Connection error: {last_error} ({db_server})",
 977                                 $context
 978                         );
 979
 980                         // throws DBConnectionError
 981                         $conn->reportConnectionError( "{$this->mLastError} ({$context['db_server']})" );
 982                 } else {
 983                         // No last connection, probably due to all servers being too busy
 984                         $this->connLogger->error(
 985                                 "LB failure with no last connection. Connection error: {last_error}",
 986                                 $context
 987                         );
 988
 989                         // If all servers were busy, mLastError will contain something sensible
 990                         throw new DBConnectionError( null, $this->mLastError );
 991                 }
 992         }
 993
 994         public function getWriterIndex() {
 995                 return 0;
 996         }
 997
 998         public function haveIndex( $i ) {
 999                 return array_key_exists( $i, $this->mServers );
1000         }
1001
1002         public function isNonZeroLoad( $i ) {
1003                 return array_key_exists( $i, $this->mServers ) && $this->mLoads[$i] != 0;
1004         }
1005
1006         public function getServerCount() {
1007                 return count( $this->mServers );
1008         }
1009
1010         public function getServerName( $i ) {
1011                 if ( isset( $this->mServers[$i]['hostName'] ) ) {
1012                         $name = $this->mServers[$i]['hostName'];
1013                 } elseif ( isset( $this->mServers[$i]['host'] ) ) {
1014                         $name = $this->mServers[$i]['host'];
1015                 } else {
1016                         $name = '';
1017                 }
1018
1019                 return ( $name != '' ) ? $name : 'localhost';
1020         }
1021
1022         public function getServerInfo( $i ) {
1023                 if ( isset( $this->mServers[$i] ) ) {
1024                         return $this->mServers[$i];
1025                 } else {
1026                         return false;
1027                 }
1028         }
1029
1030         public function setServerInfo( $i, array $serverInfo ) {
1031                 $this->mServers[$i] = $serverInfo;
1032         }
1033
1034         public function getMasterPos() {
1035                 # If this entire request was served from a replica DB without opening a connection to the
1036                 # master (however unlikely that may be), then we can fetch the position from the replica DB.
1037                 $masterConn = $this->getAnyOpenConnection( $this->getWriterIndex() );
1038                 if ( !$masterConn ) {
1039                         $serverCount = count( $this->mServers );
1040                         for ( $i = 1; $i < $serverCount; $i++ ) {
1041                                 $conn = $this->getAnyOpenConnection( $i );
1042                                 if ( $conn ) {
1043                                         return $conn->getReplicaPos();
1044                                 }
1045                         }
1046                 } else {
1047                         return $masterConn->getMasterPos();
1048                 }
1049
1050                 return false;
1051         }
1052
1053         public function disable() {
1054                 $this->closeAll();
1055                 $this->disabled = true;
1056         }
1057
1058         public function closeAll() {
1059                 $this->forEachOpenConnection( function ( IDatabase $conn ) {
1060                         $host = $conn->getServer();
1061                         $this->connLogger->debug( "Closing connection to database '$host'." );
1062                         $conn->close();
1063                 } );
1064
1065                 $this->mConns = [
1066                         'local' => [],
1067                         'foreignFree' => [],
1068                         'foreignUsed' => [],
1069                 ];
1070                 $this->connsOpened = 0;
1071         }
1072
1073         public function closeConnection( IDatabase $conn ) {
1074                 $serverIndex = $conn->getLBInfo( 'serverIndex' ); // second index level of mConns
1075                 foreach ( $this->mConns as $type => $connsByServer ) {
1076                         if ( !isset( $connsByServer[$serverIndex] ) ) {
1077                                 continue;
1078                         }
1079
1080                         foreach ( $connsByServer[$serverIndex] as $i => $trackedConn ) {
1081                                 if ( $conn === $trackedConn ) {
1082                                         $host = $this->getServerName( $i );
1083                                         $this->connLogger->debug( "Closing connection to database $i at '$host'." );
1084                                         unset( $this->mConns[$type][$serverIndex][$i] );
1085                                         --$this->connsOpened;
1086                                         break 2;
1087                                 }
1088                         }
1089                 }
1090
1091                 $conn->close();
1092         }
1093
1094         public function commitAll( $fname = __METHOD__ ) {
1095                 $failures = [];
1096
1097                 $restore = ( $this->trxRoundId !== false );
1098                 $this->trxRoundId = false;
1099                 $this->forEachOpenConnection(
1100                         function ( IDatabase $conn ) use ( $fname, $restore, &$failures ) {
1101                                 try {
1102                                         $conn->commit( $fname, $conn::FLUSHING_ALL_PEERS );
1103                                 } catch ( DBError $e ) {
1104                                         call_user_func( $this->errorLogger, $e );
1105                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1106                                 }
1107                                 if ( $restore && $conn->getLBInfo( 'master' ) ) {
1108                                         $this->undoTransactionRoundFlags( $conn );
1109                                 }
1110                         }
1111                 );
1112
1113                 if ( $failures ) {
1114                         throw new DBExpectedError(
1115                                 null,
1116                                 "Commit failed on server(s) " . implode( "\n", array_unique( $failures ) )
1117                         );
1118                 }
1119         }
1120
1121         public function finalizeMasterChanges() {
1122                 $this->forEachOpenMasterConnection( function ( Database $conn ) {
1123                         // Any error should cause all DB transactions to be rolled back together
1124                         $conn->setTrxEndCallbackSuppression( false );
1125                         $conn->runOnTransactionPreCommitCallbacks();
1126                         // Defer post-commit callbacks until COMMIT finishes for all DBs
1127                         $conn->setTrxEndCallbackSuppression( true );
1128                 } );
1129         }
1130
1131         public function approveMasterChanges( array $options ) {
1132                 $limit = isset( $options['maxWriteDuration'] ) ? $options['maxWriteDuration'] : 0;
1133                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( $limit ) {
1134                         // If atomic sections or explicit transactions are still open, some caller must have
1135                         // caught an exception but failed to properly rollback any changes. Detect that and
1136                         // throw and error (causing rollback).
1137                         if ( $conn->explicitTrxActive() ) {
1138                                 throw new DBTransactionError(
1139                                         $conn,
1140                                         "Explicit transaction still active. A caller may have caught an error."
1141                                 );
1142                         }
1143                         // Assert that the time to replicate the transaction will be sane.
1144                         // If this fails, then all DB transactions will be rollback back together.
1145                         $time = $conn->pendingWriteQueryDuration( $conn::ESTIMATE_DB_APPLY );
1146                         if ( $limit > 0 && $time > $limit ) {
1147                                 throw new DBTransactionSizeError(
1148                                         $conn,
1149                                         "Transaction spent $time second(s) in writes, exceeding the $limit limit.",
1150                                         [ $time, $limit ]
1151                                 );
1152                         }
1153                         // If a connection sits idle while slow queries execute on another, that connection
1154                         // may end up dropped before the commit round is reached. Ping servers to detect this.
1155                         if ( $conn->writesOrCallbacksPending() && !$conn->ping() ) {
1156                                 throw new DBTransactionError(
1157                                         $conn,
1158                                         "A connection to the {$conn->getDBname()} database was lost before commit."
1159                                 );
1160                         }
1161                 } );
1162         }
1163
1164         public function beginMasterChanges( $fname = __METHOD__ ) {
1165                 if ( $this->trxRoundId !== false ) {
1166                         throw new DBTransactionError(
1167                                 null,
1168                                 "$fname: Transaction round '{$this->trxRoundId}' already started."
1169                         );
1170                 }
1171                 $this->trxRoundId = $fname;
1172
1173                 $failures = [];
1174                 $this->forEachOpenMasterConnection(
1175                         function ( Database $conn ) use ( $fname, &$failures ) {
1176                                 $conn->setTrxEndCallbackSuppression( true );
1177                                 try {
1178                                         $conn->flushSnapshot( $fname );
1179                                 } catch ( DBError $e ) {
1180                                         call_user_func( $this->errorLogger, $e );
1181                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1182                                 }
1183                                 $conn->setTrxEndCallbackSuppression( false );
1184                                 $this->applyTransactionRoundFlags( $conn );
1185                         }
1186                 );
1187
1188                 if ( $failures ) {
1189                         throw new DBExpectedError(
1190                                 null,
1191                                 "$fname: Flush failed on server(s) " . implode( "\n", array_unique( $failures ) )
1192                         );
1193                 }
1194         }
1195
1196         public function commitMasterChanges( $fname = __METHOD__ ) {
1197                 $failures = [];
1198
1199                 /** @noinspection PhpUnusedLocalVariableInspection */
1200                 $scope = $this->getScopedPHPBehaviorForCommit(); // try to ignore client aborts
1201
1202                 $restore = ( $this->trxRoundId !== false );
1203                 $this->trxRoundId = false;
1204                 $this->forEachOpenMasterConnection(
1205                         function ( IDatabase $conn ) use ( $fname, $restore, &$failures ) {
1206                                 try {
1207                                         if ( $conn->writesOrCallbacksPending() ) {
1208                                                 $conn->commit( $fname, $conn::FLUSHING_ALL_PEERS );
1209                                         } elseif ( $restore ) {
1210                                                 $conn->flushSnapshot( $fname );
1211                                         }
1212                                 } catch ( DBError $e ) {
1213                                         call_user_func( $this->errorLogger, $e );
1214                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1215                                 }
1216                                 if ( $restore ) {
1217                                         $this->undoTransactionRoundFlags( $conn );
1218                                 }
1219                         }
1220                 );
1221
1222                 if ( $failures ) {
1223                         throw new DBExpectedError(
1224                                 null,
1225                                 "$fname: Commit failed on server(s) " . implode( "\n", array_unique( $failures ) )
1226                         );
1227                 }
1228         }
1229
1230         public function runMasterPostTrxCallbacks( $type ) {
1231                 $e = null; // first exception
1232                 $this->forEachOpenMasterConnection( function ( Database $conn ) use ( $type, &$e ) {
1233                         $conn->setTrxEndCallbackSuppression( false );
1234                         if ( $conn->writesOrCallbacksPending() ) {
1235                                 // This happens if onTransactionIdle() callbacks leave callbacks on *another* DB
1236                                 // (which finished its callbacks already). Warn and recover in this case. Let the
1237                                 // callbacks run in the final commitMasterChanges() in LBFactory::shutdown().
1238                                 $this->queryLogger->error( __METHOD__ . ": found writes/callbacks pending." );
1239                                 return;
1240                         } elseif ( $conn->trxLevel() ) {
1241                                 // This happens for single-DB setups where DB_REPLICA uses the master DB,
1242                                 // thus leaving an implicit read-only transaction open at this point. It
1243                                 // also happens if onTransactionIdle() callbacks leave implicit transactions
1244                                 // open on *other* DBs (which is slightly improper). Let these COMMIT on the
1245                                 // next call to commitMasterChanges(), possibly in LBFactory::shutdown().
1246                                 return;
1247                         }
1248                         try {
1249                                 $conn->runOnTransactionIdleCallbacks( $type );
1250                         } catch ( Exception $ex ) {
1251                                 $e = $e ?: $ex;
1252                         }
1253                         try {
1254                                 $conn->runTransactionListenerCallbacks( $type );
1255                         } catch ( Exception $ex ) {
1256                                 $e = $e ?: $ex;
1257                         }
1258                 } );
1259
1260                 return $e;
1261         }
1262
1263         public function rollbackMasterChanges( $fname = __METHOD__ ) {
1264                 $restore = ( $this->trxRoundId !== false );
1265                 $this->trxRoundId = false;
1266                 $this->forEachOpenMasterConnection(
1267                         function ( IDatabase $conn ) use ( $fname, $restore ) {
1268                                 if ( $conn->writesOrCallbacksPending() ) {
1269                                         $conn->rollback( $fname, $conn::FLUSHING_ALL_PEERS );
1270                                 }
1271                                 if ( $restore ) {
1272                                         $this->undoTransactionRoundFlags( $conn );
1273                                 }
1274                         }
1275                 );
1276         }
1277
1278         public function suppressTransactionEndCallbacks() {
1279                 $this->forEachOpenMasterConnection( function ( Database $conn ) {
1280                         $conn->setTrxEndCallbackSuppression( true );
1281                 } );
1282         }
1283
1284         /**
1285          * @param IDatabase $conn
1286          */
1287         private function applyTransactionRoundFlags( IDatabase $conn ) {
1288                 if ( $conn->getFlag( $conn::DBO_DEFAULT ) ) {
1289                         // DBO_TRX is controlled entirely by CLI mode presence with DBO_DEFAULT.
1290                         // Force DBO_TRX even in CLI mode since a commit round is expected soon.
1291                         $conn->setFlag( $conn::DBO_TRX, $conn::REMEMBER_PRIOR );
1292                         // If config has explicitly requested DBO_TRX be either on or off by not
1293                         // setting DBO_DEFAULT, then respect that. Forcing no transactions is useful
1294                         // for things like blob stores (ExternalStore) which want auto-commit mode.
1295                 }
1296         }
1297
1298         /**
1299          * @param IDatabase $conn
1300          */
1301         private function undoTransactionRoundFlags( IDatabase $conn ) {
1302                 if ( $conn->getFlag( $conn::DBO_DEFAULT ) ) {
1303                         $conn->restoreFlags( $conn::RESTORE_PRIOR );
1304                 }
1305         }
1306
1307         public function flushReplicaSnapshots( $fname = __METHOD__ ) {
1308                 $this->forEachOpenReplicaConnection( function ( IDatabase $conn ) {
1309                         $conn->flushSnapshot( __METHOD__ );
1310                 } );
1311         }
1312
1313         public function hasMasterConnection() {
1314                 return $this->isOpen( $this->getWriterIndex() );
1315         }
1316
1317         public function hasMasterChanges() {
1318                 $pending = 0;
1319                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$pending ) {
1320                         $pending |= $conn->writesOrCallbacksPending();
1321                 } );
1322
1323                 return (bool)$pending;
1324         }
1325
1326         public function lastMasterChangeTimestamp() {
1327                 $lastTime = false;
1328                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$lastTime ) {
1329                         $lastTime = max( $lastTime, $conn->lastDoneWrites() );
1330                 } );
1331
1332                 return $lastTime;
1333         }
1334
1335         public function hasOrMadeRecentMasterChanges( $age = null ) {
1336                 $age = ( $age === null ) ? $this->mWaitTimeout : $age;
1337
1338                 return ( $this->hasMasterChanges()
1339                         || $this->lastMasterChangeTimestamp() > microtime( true ) - $age );
1340         }
1341
1342         public function pendingMasterChangeCallers() {
1343                 $fnames = [];
1344                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$fnames ) {
1345                         $fnames = array_merge( $fnames, $conn->pendingWriteCallers() );
1346                 } );
1347
1348                 return $fnames;
1349         }
1350
1351         public function getLaggedReplicaMode( $domain = false ) {
1352                 // No-op if there is only one DB (also avoids recursion)
1353                 if ( !$this->laggedReplicaMode && $this->getServerCount() > 1 ) {
1354                         try {
1355                                 // See if laggedReplicaMode gets set
1356                                 $conn = $this->getConnection( self::DB_REPLICA, false, $domain );
1357                                 $this->reuseConnection( $conn );
1358                         } catch ( DBConnectionError $e ) {
1359                                 // Avoid expensive re-connect attempts and failures
1360                                 $this->allReplicasDownMode = true;
1361                                 $this->laggedReplicaMode = true;
1362                         }
1363                 }
1364
1365                 return $this->laggedReplicaMode;
1366         }
1367
1368         /**
1369          * @param bool $domain
1370          * @return bool
1371          * @deprecated 1.28; use getLaggedReplicaMode()
1372          */
1373         public function getLaggedSlaveMode( $domain = false ) {
1374                 return $this->getLaggedReplicaMode( $domain );
1375         }
1376
1377         public function laggedReplicaUsed() {
1378                 return $this->laggedReplicaMode;
1379         }
1380
1381         /**
1382          * @return bool
1383          * @since 1.27
1384          * @deprecated Since 1.28; use laggedReplicaUsed()
1385          */
1386         public function laggedSlaveUsed() {
1387                 return $this->laggedReplicaUsed();
1388         }
1389
1390         public function getReadOnlyReason( $domain = false, IDatabase $conn = null ) {
1391                 if ( $this->readOnlyReason !== false ) {
1392                         return $this->readOnlyReason;
1393                 } elseif ( $this->getLaggedReplicaMode( $domain ) ) {
1394                         if ( $this->allReplicasDownMode ) {
1395                                 return 'The database has been automatically locked ' .
1396                                         'until the replica database servers become available';
1397                         } else {
1398                                 return 'The database has been automatically locked ' .
1399                                         'while the replica database servers catch up to the master.';
1400                         }
1401                 } elseif ( $this->masterRunningReadOnly( $domain, $conn ) ) {
1402                         return 'The database master is running in read-only mode.';
1403                 }
1404
1405                 return false;
1406         }
1407
1408         /**
1409          * @param string $domain Domain ID, or false for the current domain
1410          * @param IDatabase|null $conn DB master connectionl used to avoid loops [optional]
1411          * @return bool
1412          */
1413         private function masterRunningReadOnly( $domain, IDatabase $conn = null ) {
1414                 $cache = $this->wanCache;
1415                 $masterServer = $this->getServerName( $this->getWriterIndex() );
1416
1417                 return (bool)$cache->getWithSetCallback(
1418                         $cache->makeGlobalKey( __CLASS__, 'server-read-only', $masterServer ),
1419                         self::TTL_CACHE_READONLY,
1420                         function () use ( $domain, $conn ) {
1421                                 $old = $this->trxProfiler->setSilenced( true );
1422                                 try {
1423                                         $dbw = $conn ?: $this->getConnection( self::DB_MASTER, [], $domain );
1424                                         $readOnly = (int)$dbw->serverIsReadOnly();
1425                                         if ( !$conn ) {
1426                                                 $this->reuseConnection( $dbw );
1427                                         }
1428                                 } catch ( DBError $e ) {
1429                                         $readOnly = 0;
1430                                 }
1431                                 $this->trxProfiler->setSilenced( $old );
1432                                 return $readOnly;
1433                         },
1434                         [ 'pcTTL' => $cache::TTL_PROC_LONG, 'busyValue' => 0 ]
1435                 );
1436         }
1437
1438         public function allowLagged( $mode = null ) {
1439                 if ( $mode === null ) {
1440                         return $this->mAllowLagged;
1441                 }
1442                 $this->mAllowLagged = $mode;
1443
1444                 return $this->mAllowLagged;
1445         }
1446
1447         public function pingAll() {
1448                 $success = true;
1449                 $this->forEachOpenConnection( function ( IDatabase $conn ) use ( &$success ) {
1450                         if ( !$conn->ping() ) {
1451                                 $success = false;
1452                         }
1453                 } );
1454
1455                 return $success;
1456         }
1457
1458         public function forEachOpenConnection( $callback, array $params = [] ) {
1459                 foreach ( $this->mConns as $connsByServer ) {
1460                         foreach ( $connsByServer as $serverConns ) {
1461                                 foreach ( $serverConns as $conn ) {
1462                                         $mergedParams = array_merge( [ $conn ], $params );
1463                                         call_user_func_array( $callback, $mergedParams );
1464                                 }
1465                         }
1466                 }
1467         }
1468
1469         public function forEachOpenMasterConnection( $callback, array $params = [] ) {
1470                 $masterIndex = $this->getWriterIndex();
1471                 foreach ( $this->mConns as $connsByServer ) {
1472                         if ( isset( $connsByServer[$masterIndex] ) ) {
1473                                 /** @var IDatabase $conn */
1474                                 foreach ( $connsByServer[$masterIndex] as $conn ) {
1475                                         $mergedParams = array_merge( [ $conn ], $params );
1476                                         call_user_func_array( $callback, $mergedParams );
1477                                 }
1478                         }
1479                 }
1480         }
1481
1482         public function forEachOpenReplicaConnection( $callback, array $params = [] ) {
1483                 foreach ( $this->mConns as $connsByServer ) {
1484                         foreach ( $connsByServer as $i => $serverConns ) {
1485                                 if ( $i === $this->getWriterIndex() ) {
1486                                         continue; // skip master
1487                                 }
1488                                 foreach ( $serverConns as $conn ) {
1489                                         $mergedParams = array_merge( [ $conn ], $params );
1490                                         call_user_func_array( $callback, $mergedParams );
1491                                 }
1492                         }
1493                 }
1494         }
1495
1496         public function getMaxLag( $domain = false ) {
1497                 $maxLag = -1;
1498                 $host = '';
1499                 $maxIndex = 0;
1500
1501                 if ( $this->getServerCount() <= 1 ) {
1502                         return [ $host, $maxLag, $maxIndex ]; // no replication = no lag
1503                 }
1504
1505                 $lagTimes = $this->getLagTimes( $domain );
1506                 foreach ( $lagTimes as $i => $lag ) {
1507                         if ( $this->mLoads[$i] > 0 && $lag > $maxLag ) {
1508                                 $maxLag = $lag;
1509                                 $host = $this->mServers[$i]['host'];
1510                                 $maxIndex = $i;
1511                         }
1512                 }
1513
1514                 return [ $host, $maxLag, $maxIndex ];
1515         }
1516
1517         public function getLagTimes( $domain = false ) {
1518                 if ( $this->getServerCount() <= 1 ) {
1519                         return [ $this->getWriterIndex() => 0 ]; // no replication = no lag
1520                 }
1521
1522                 $knownLagTimes = []; // map of (server index => 0 seconds)
1523                 $indexesWithLag = [];
1524                 foreach ( $this->mServers as $i => $server ) {
1525                         if ( empty( $server['is static'] ) ) {
1526                                 $indexesWithLag[] = $i; // DB server might have replication lag
1527                         } else {
1528                                 $knownLagTimes[$i] = 0; // DB server is a non-replicating and read-only archive
1529                         }
1530                 }
1531
1532                 return $this->getLoadMonitor()->getLagTimes( $indexesWithLag, $domain ) + $knownLagTimes;
1533         }
1534
1535         public function safeGetLag( IDatabase $conn ) {
1536                 if ( $this->getServerCount() <= 1 ) {
1537                         return 0;
1538                 } else {
1539                         return $conn->getLag();
1540                 }
1541         }
1542
1543         /**
1544          * @param IDatabase $conn
1545          * @param DBMasterPos|bool $pos
1546          * @param int $timeout
1547          * @return bool
1548          */
1549         public function safeWaitForMasterPos( IDatabase $conn, $pos = false, $timeout = 10 ) {
1550                 if ( $this->getServerCount() <= 1 || !$conn->getLBInfo( 'replica' ) ) {
1551                         return true; // server is not a replica DB
1552                 }
1553
1554                 if ( !$pos ) {
1555                         // Get the current master position, opening a connection if needed
1556                         $masterConn = $this->getAnyOpenConnection( $this->getWriterIndex() );
1557                         if ( $masterConn ) {
1558                                 $pos = $masterConn->getMasterPos();
1559                         } else {
1560                                 $masterConn = $this->openConnection( $this->getWriterIndex(), self::DOMAIN_ANY );
1561                                 $pos = $masterConn->getMasterPos();
1562                                 $this->closeConnection( $masterConn );
1563                         }
1564                 }
1565
1566                 if ( $pos instanceof DBMasterPos ) {
1567                         $result = $conn->masterPosWait( $pos, $timeout );
1568                         if ( $result == -1 || is_null( $result ) ) {
1569                                 $msg = __METHOD__ . ": Timed out waiting on {$conn->getServer()} pos {$pos}";
1570                                 $this->replLogger->warning( "$msg" );
1571                                 $ok = false;
1572                         } else {
1573                                 $this->replLogger->info( __METHOD__ . ": Done" );
1574                                 $ok = true;
1575                         }
1576                 } else {
1577                         $ok = false; // something is misconfigured
1578                         $this->replLogger->error( "Could not get master pos for {$conn->getServer()}." );
1579                 }
1580
1581                 return $ok;
1582         }
1583
1584         public function setTransactionListener( $name, callable $callback = null ) {
1585                 if ( $callback ) {
1586                         $this->trxRecurringCallbacks[$name] = $callback;
1587                 } else {
1588                         unset( $this->trxRecurringCallbacks[$name] );
1589                 }
1590                 $this->forEachOpenMasterConnection(
1591                         function ( IDatabase $conn ) use ( $name, $callback ) {
1592                                 $conn->setTransactionListener( $name, $callback );
1593                         }
1594                 );
1595         }
1596
1597         public function setTableAliases( array $aliases ) {
1598                 $this->tableAliases = $aliases;
1599         }
1600
1601         public function setDomainPrefix( $prefix ) {
1602                 if ( $this->mConns['foreignUsed'] ) {
1603                         // Do not switch connections to explicit foreign domains unless marked as free
1604                         $domains = [];
1605                         foreach ( $this->mConns['foreignUsed'] as $i => $connsByDomain ) {
1606                                 $domains = array_merge( $domains, array_keys( $connsByDomain ) );
1607                         }
1608                         $domains = implode( ', ', $domains );
1609                         throw new DBUnexpectedError( null,
1610                                 "Foreign domain connections are still in use ($domains)." );
1611                 }
1612
1613                 $this->localDomain = new DatabaseDomain(
1614                         $this->localDomain->getDatabase(),
1615                         null,
1616                         $prefix
1617                 );
1618
1619                 $this->forEachOpenConnection( function ( IDatabase $db ) use ( $prefix ) {
1620                         $db->tablePrefix( $prefix );
1621                 } );
1622         }
1623
1624         /**
1625          * Make PHP ignore user aborts/disconnects until the returned
1626          * value leaves scope. This returns null and does nothing in CLI mode.
1627          *
1628          * @return ScopedCallback|null
1629          */
1630         final protected function getScopedPHPBehaviorForCommit() {
1631                 if ( PHP_SAPI != 'cli' ) { // https://bugs.php.net/bug.php?id=47540
1632                         $old = ignore_user_abort( true ); // avoid half-finished operations
1633                         return new ScopedCallback( function () use ( $old ) {
1634                                 ignore_user_abort( $old );
1635                         } );
1636                 }
1637
1638                 return null;
1639         }
1640
1641         function __destruct() {
1642                 // Avoid connection leaks for sanity
1643                 $this->disable();
1644         }
1645 }
1646
1647 class_alias( LoadBalancer::class, 'LoadBalancer' );