includes/libs/rdbms/loadbalancer/LoadBalancer.php

   1 <?php
   2 /**
   3  * Database load balancing manager
   4  *
   5  * This program is free software; you can redistribute it and/or modify
   6  * it under the terms of the GNU General Public License as published by
   7  * the Free Software Foundation; either version 2 of the License, or
   8  * (at your option) any later version.
   9  *
  10  * This program is distributed in the hope that it will be useful,
  11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  13  * GNU General Public License for more details.
  14  *
  15  * You should have received a copy of the GNU General Public License along
  16  * with this program; if not, write to the Free Software Foundation, Inc.,
  17  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
  18  * http://www.gnu.org/copyleft/gpl.html
  19  *
  20  * @file
  21  * @ingroup Database
  22  */
  23 namespace Wikimedia\Rdbms;
  24
  25 use Psr\Log\LoggerInterface;
  26 use Psr\Log\NullLogger;
  27 use Wikimedia\ScopedCallback;
  28 use BagOStuff;
  29 use EmptyBagOStuff;
  30 use WANObjectCache;
  31 use ArrayUtils;
  32 use InvalidArgumentException;
  33 use RuntimeException;
  34 use Exception;
  35
  36 /**
  37  * Database connection, tracking, load balancing, and transaction manager for a cluster
  38  *
  39  * @ingroup Database
  40  */
  41 class LoadBalancer implements ILoadBalancer {
  42         /** @var array[] Map of (server index => server config array) */
  43         private $mServers;
  44         /** @var Database[][][] Map of (connection category => server index => IDatabase[]) */
  45         private $mConns;
  46         /** @var float[] Map of (server index => weight) */
  47         private $mLoads;
  48         /** @var array[] Map of (group => server index => weight) */
  49         private $mGroupLoads;
  50         /** @var bool Whether to disregard replica DB lag as a factor in replica DB selection */
  51         private $mAllowLagged;
  52         /** @var integer Seconds to spend waiting on replica DB lag to resolve */
  53         private $mWaitTimeout;
  54         /** @var array The LoadMonitor configuration */
  55         private $loadMonitorConfig;
  56         /** @var array[] $aliases Map of (table => (dbname, schema, prefix) map) */
  57         private $tableAliases = [];
  58
  59         /** @var ILoadMonitor */
  60         private $loadMonitor;
  61         /** @var ChronologyProtector|null */
  62         private $chronProt;
  63         /** @var BagOStuff */
  64         private $srvCache;
  65         /** @var WANObjectCache */
  66         private $wanCache;
  67         /** @var object|string Class name or object With profileIn/profileOut methods */
  68         protected $profiler;
  69         /** @var TransactionProfiler */
  70         protected $trxProfiler;
  71         /** @var LoggerInterface */
  72         protected $replLogger;
  73         /** @var LoggerInterface */
  74         protected $connLogger;
  75         /** @var LoggerInterface */
  76         protected $queryLogger;
  77         /** @var LoggerInterface */
  78         protected $perfLogger;
  79
  80         /** @var Database DB connection object that caused a problem */
  81         private $errorConnection;
  82         /** @var integer The generic (not query grouped) replica DB index (of $mServers) */
  83         private $mReadIndex;
  84         /** @var bool|DBMasterPos False if not set */
  85         private $mWaitForPos;
  86         /** @var bool Whether the generic reader fell back to a lagged replica DB */
  87         private $laggedReplicaMode = false;
  88         /** @var bool Whether the generic reader fell back to a lagged replica DB */
  89         private $allReplicasDownMode = false;
  90         /** @var string The last DB selection or connection error */
  91         private $mLastError = 'Unknown error';
  92         /** @var string|bool Reason the LB is read-only or false if not */
  93         private $readOnlyReason = false;
  94         /** @var integer Total connections opened */
  95         private $connsOpened = 0;
  96         /** @var string|bool String if a requested DBO_TRX transaction round is active */
  97         private $trxRoundId = false;
  98         /** @var array[] Map of (name => callable) */
  99         private $trxRecurringCallbacks = [];
 100         /** @var DatabaseDomain Local Domain ID and default for selectDB() calls */
 101         private $localDomain;
 102         /** @var string Alternate ID string for the domain instead of DatabaseDomain::getId() */
 103         private $localDomainIdAlias;
 104         /** @var string Current server name */
 105         private $host;
 106         /** @var bool Whether this PHP instance is for a CLI script */
 107         protected $cliMode;
 108         /** @var string Agent name for query profiling */
 109         protected $agent;
 110
 111         /** @var callable Exception logger */
 112         private $errorLogger;
 113
 114         /** @var boolean */
 115         private $disabled = false;
 116         /** @var boolean */
 117         private $chronProtInitialized = false;
 118
 119         /** @var integer Warn when this many connection are held */
 120         const CONN_HELD_WARN_THRESHOLD = 10;
 121
 122         /** @var integer Default 'max lag' when unspecified */
 123         const MAX_LAG_DEFAULT = 10;
 124         /** @var integer Seconds to cache master server read-only status */
 125         const TTL_CACHE_READONLY = 5;
 126
 127         const KEY_LOCAL = 'local';
 128         const KEY_FOREIGN_FREE = 'foreignFree';
 129         const KEY_FOREIGN_INUSE = 'foreignInUse';
 130
 131         const KEY_LOCAL_NOROUND = 'localAutoCommit';
 132         const KEY_FOREIGN_FREE_NOROUND = 'foreignFreeAutoCommit';
 133         const KEY_FOREIGN_INUSE_NOROUND = 'foreignInUseAutoCommit';
 134
 135         public function __construct( array $params ) {
 136                 if ( !isset( $params['servers'] ) ) {
 137                         throw new InvalidArgumentException( __CLASS__ . ': missing servers parameter' );
 138                 }
 139                 $this->mServers = $params['servers'];
 140                 foreach ( $this->mServers as $i => $server ) {
 141                         if ( $i == 0 ) {
 142                                 $this->mServers[$i]['master'] = true;
 143                         } else {
 144                                 $this->mServers[$i]['replica'] = true;
 145                         }
 146                 }
 147
 148                 $this->localDomain = isset( $params['localDomain'] )
 149                         ? DatabaseDomain::newFromId( $params['localDomain'] )
 150                         : DatabaseDomain::newUnspecified();
 151                 // In case a caller assumes that the domain ID is simply <db>-<prefix>, which is almost
 152                 // always true, gracefully handle the case when they fail to account for escaping.
 153                 if ( $this->localDomain->getTablePrefix() != '' ) {
 154                         $this->localDomainIdAlias =
 155                                 $this->localDomain->getDatabase() . '-' . $this->localDomain->getTablePrefix();
 156                 } else {
 157                         $this->localDomainIdAlias = $this->localDomain->getDatabase();
 158                 }
 159
 160                 $this->mWaitTimeout = isset( $params['waitTimeout'] ) ? $params['waitTimeout'] : 10;
 161
 162                 $this->mReadIndex = -1;
 163                 $this->mConns = [
 164                         // Connection were transaction rounds may be applied
 165                         self::KEY_LOCAL => [],
 166                         self::KEY_FOREIGN_INUSE => [],
 167                         self::KEY_FOREIGN_FREE => [],
 168                         // Auto-committing counterpart connections that ignore transaction rounds
 169                         self::KEY_LOCAL_NOROUND => [],
 170                         self::KEY_FOREIGN_INUSE_NOROUND => [],
 171                         self::KEY_FOREIGN_FREE_NOROUND => []
 172                 ];
 173                 $this->mLoads = [];
 174                 $this->mWaitForPos = false;
 175                 $this->mAllowLagged = false;
 176
 177                 if ( isset( $params['readOnlyReason'] ) && is_string( $params['readOnlyReason'] ) ) {
 178                         $this->readOnlyReason = $params['readOnlyReason'];
 179                 }
 180
 181                 if ( isset( $params['loadMonitor'] ) ) {
 182                         $this->loadMonitorConfig = $params['loadMonitor'];
 183                 } else {
 184                         $this->loadMonitorConfig = [ 'class' => 'LoadMonitorNull' ];
 185                 }
 186
 187                 foreach ( $params['servers'] as $i => $server ) {
 188                         $this->mLoads[$i] = $server['load'];
 189                         if ( isset( $server['groupLoads'] ) ) {
 190                                 foreach ( $server['groupLoads'] as $group => $ratio ) {
 191                                         if ( !isset( $this->mGroupLoads[$group] ) ) {
 192                                                 $this->mGroupLoads[$group] = [];
 193                                         }
 194                                         $this->mGroupLoads[$group][$i] = $ratio;
 195                                 }
 196                         }
 197                 }
 198
 199                 if ( isset( $params['srvCache'] ) ) {
 200                         $this->srvCache = $params['srvCache'];
 201                 } else {
 202                         $this->srvCache = new EmptyBagOStuff();
 203                 }
 204                 if ( isset( $params['wanCache'] ) ) {
 205                         $this->wanCache = $params['wanCache'];
 206                 } else {
 207                         $this->wanCache = WANObjectCache::newEmpty();
 208                 }
 209                 $this->profiler = isset( $params['profiler'] ) ? $params['profiler'] : null;
 210                 if ( isset( $params['trxProfiler'] ) ) {
 211                         $this->trxProfiler = $params['trxProfiler'];
 212                 } else {
 213                         $this->trxProfiler = new TransactionProfiler();
 214                 }
 215
 216                 $this->errorLogger = isset( $params['errorLogger'] )
 217                         ? $params['errorLogger']
 218                         : function ( Exception $e ) {
 219                                 trigger_error( get_class( $e ) . ': ' . $e->getMessage(), E_USER_WARNING );
 220                         };
 221
 222                 foreach ( [ 'replLogger', 'connLogger', 'queryLogger', 'perfLogger' ] as $key ) {
 223                         $this->$key = isset( $params[$key] ) ? $params[$key] : new NullLogger();
 224                 }
 225
 226                 $this->host = isset( $params['hostname'] )
 227                         ? $params['hostname']
 228                         : ( gethostname() ?: 'unknown' );
 229                 $this->cliMode = isset( $params['cliMode'] ) ? $params['cliMode'] : PHP_SAPI === 'cli';
 230                 $this->agent = isset( $params['agent'] ) ? $params['agent'] : '';
 231
 232                 if ( isset( $params['chronologyProtector'] ) ) {
 233                         $this->chronProt = $params['chronologyProtector'];
 234                 }
 235         }
 236
 237         /**
 238          * Get a LoadMonitor instance
 239          *
 240          * @return ILoadMonitor
 241          */
 242         private function getLoadMonitor() {
 243                 if ( !isset( $this->loadMonitor ) ) {
 244                         $compat = [
 245                                 'LoadMonitor' => LoadMonitor::class,
 246                                 'LoadMonitorNull' => LoadMonitorNull::class,
 247                                 'LoadMonitorMySQL' => LoadMonitorMySQL::class,
 248                         ];
 249
 250                         $class = $this->loadMonitorConfig['class'];
 251                         if ( isset( $compat[$class] ) ) {
 252                                 $class = $compat[$class];
 253                         }
 254
 255                         $this->loadMonitor = new $class(
 256                                 $this, $this->srvCache, $this->wanCache, $this->loadMonitorConfig );
 257                         $this->loadMonitor->setLogger( $this->replLogger );
 258                 }
 259
 260                 return $this->loadMonitor;
 261         }
 262
 263         /**
 264          * @param array $loads
 265          * @param bool|string $domain Domain to get non-lagged for
 266          * @param int $maxLag Restrict the maximum allowed lag to this many seconds
 267          * @return bool|int|string
 268          */
 269         private function getRandomNonLagged( array $loads, $domain = false, $maxLag = INF ) {
 270                 $lags = $this->getLagTimes( $domain );
 271
 272                 # Unset excessively lagged servers
 273                 foreach ( $lags as $i => $lag ) {
 274                         if ( $i != 0 ) {
 275                                 # How much lag this server nominally is allowed to have
 276                                 $maxServerLag = isset( $this->mServers[$i]['max lag'] )
 277                                         ? $this->mServers[$i]['max lag']
 278                                         : self::MAX_LAG_DEFAULT; // default
 279                                 # Constrain that futher by $maxLag argument
 280                                 $maxServerLag = min( $maxServerLag, $maxLag );
 281
 282                                 $host = $this->getServerName( $i );
 283                                 if ( $lag === false && !is_infinite( $maxServerLag ) ) {
 284                                         $this->replLogger->error(
 285                                                 "Server {host} is not replicating?", [ 'host' => $host ] );
 286                                         unset( $loads[$i] );
 287                                 } elseif ( $lag > $maxServerLag ) {
 288                                         $this->replLogger->warning(
 289                                                 "Server {host} has {lag} seconds of lag (>= {maxlag})",
 290                                                 [ 'host' => $host, 'lag' => $lag, 'maxlag' => $maxServerLag ]
 291                                         );
 292                                         unset( $loads[$i] );
 293                                 }
 294                         }
 295                 }
 296
 297                 # Find out if all the replica DBs with non-zero load are lagged
 298                 $sum = 0;
 299                 foreach ( $loads as $load ) {
 300                         $sum += $load;
 301                 }
 302                 if ( $sum == 0 ) {
 303                         # No appropriate DB servers except maybe the master and some replica DBs with zero load
 304                         # Do NOT use the master
 305                         # Instead, this function will return false, triggering read-only mode,
 306                         # and a lagged replica DB will be used instead.
 307                         return false;
 308                 }
 309
 310                 if ( count( $loads ) == 0 ) {
 311                         return false;
 312                 }
 313
 314                 # Return a random representative of the remainder
 315                 return ArrayUtils::pickRandom( $loads );
 316         }
 317
 318         public function getReaderIndex( $group = false, $domain = false ) {
 319                 if ( count( $this->mServers ) == 1 ) {
 320                         // Skip the load balancing if there's only one server
 321                         return $this->getWriterIndex();
 322                 } elseif ( $group === false && $this->mReadIndex >= 0 ) {
 323                         // Shortcut if the generic reader index was already cached
 324                         return $this->mReadIndex;
 325                 }
 326
 327                 if ( $group !== false ) {
 328                         // Use the server weight array for this load group
 329                         if ( isset( $this->mGroupLoads[$group] ) ) {
 330                                 $loads = $this->mGroupLoads[$group];
 331                         } else {
 332                                 // No loads for this group, return false and the caller can use some other group
 333                                 $this->connLogger->info( __METHOD__ . ": no loads for group $group" );
 334
 335                                 return false;
 336                         }
 337                 } else {
 338                         // Use the generic load group
 339                         $loads = $this->mLoads;
 340                 }
 341
 342                 // Scale the configured load ratios according to each server's load and state
 343                 $this->getLoadMonitor()->scaleLoads( $loads, $domain );
 344
 345                 // Pick a server to use, accounting for weights, load, lag, and mWaitForPos
 346                 list( $i, $laggedReplicaMode ) = $this->pickReaderIndex( $loads, $domain );
 347                 if ( $i === false ) {
 348                         // Replica DB connection unsuccessful
 349                         return false;
 350                 }
 351
 352                 if ( $this->mWaitForPos && $i != $this->getWriterIndex() ) {
 353                         // Before any data queries are run, wait for the server to catch up to the
 354                         // specified position. This is used to improve session consistency. Note that
 355                         // when LoadBalancer::waitFor() sets mWaitForPos, the waiting triggers here,
 356                         // so update laggedReplicaMode as needed for consistency.
 357                         if ( !$this->doWait( $i ) ) {
 358                                 $laggedReplicaMode = true;
 359                         }
 360                 }
 361
 362                 if ( $this->mReadIndex <= 0 && $this->mLoads[$i] > 0 && $group === false ) {
 363                         // Cache the generic reader index for future ungrouped DB_REPLICA handles
 364                         $this->mReadIndex = $i;
 365                         // Record if the generic reader index is in "lagged replica DB" mode
 366                         if ( $laggedReplicaMode ) {
 367                                 $this->laggedReplicaMode = true;
 368                         }
 369                 }
 370
 371                 $serverName = $this->getServerName( $i );
 372                 $this->connLogger->debug( __METHOD__ . ": using server $serverName for group '$group'" );
 373
 374                 return $i;
 375         }
 376
 377         /**
 378          * @param array $loads List of server weights
 379          * @param string|bool $domain
 380          * @return array (reader index, lagged replica mode) or false on failure
 381          */
 382         private function pickReaderIndex( array $loads, $domain = false ) {
 383                 if ( !count( $loads ) ) {
 384                         throw new InvalidArgumentException( "Empty server array given to LoadBalancer" );
 385                 }
 386
 387                 /** @var $i int|bool Index of selected server */
 388                 $i = false;
 389                 /** @var $laggedReplicaMode bool Whether server is considered lagged */
 390                 $laggedReplicaMode = false;
 391
 392                 // Quickly look through the available servers for a server that meets criteria...
 393                 $currentLoads = $loads;
 394                 while ( count( $currentLoads ) ) {
 395                         if ( $this->mAllowLagged || $laggedReplicaMode ) {
 396                                 $i = ArrayUtils::pickRandom( $currentLoads );
 397                         } else {
 398                                 $i = false;
 399                                 if ( $this->mWaitForPos && $this->mWaitForPos->asOfTime() ) {
 400                                         // ChronologyProtecter sets mWaitForPos for session consistency.
 401                                         // This triggers doWait() after connect, so it's especially good to
 402                                         // avoid lagged servers so as to avoid excessive delay in that method.
 403                                         $ago = microtime( true ) - $this->mWaitForPos->asOfTime();
 404                                         // Aim for <= 1 second of waiting (being too picky can backfire)
 405                                         $i = $this->getRandomNonLagged( $currentLoads, $domain, $ago + 1 );
 406                                 }
 407                                 if ( $i === false ) {
 408                                         // Any server with less lag than it's 'max lag' param is preferable
 409                                         $i = $this->getRandomNonLagged( $currentLoads, $domain );
 410                                 }
 411                                 if ( $i === false && count( $currentLoads ) != 0 ) {
 412                                         // All replica DBs lagged. Switch to read-only mode
 413                                         $this->replLogger->error( "All replica DBs lagged. Switch to read-only mode" );
 414                                         $i = ArrayUtils::pickRandom( $currentLoads );
 415                                         $laggedReplicaMode = true;
 416                                 }
 417                         }
 418
 419                         if ( $i === false ) {
 420                                 // pickRandom() returned false.
 421                                 // This is permanent and means the configuration or the load monitor
 422                                 // wants us to return false.
 423                                 $this->connLogger->debug( __METHOD__ . ": pickRandom() returned false" );
 424
 425                                 return [ false, false ];
 426                         }
 427
 428                         $serverName = $this->getServerName( $i );
 429                         $this->connLogger->debug( __METHOD__ . ": Using reader #$i: $serverName..." );
 430
 431                         $conn = $this->openConnection( $i, $domain );
 432                         if ( !$conn ) {
 433                                 $this->connLogger->warning( __METHOD__ . ": Failed connecting to $i/$domain" );
 434                                 unset( $currentLoads[$i] ); // avoid this server next iteration
 435                                 $i = false;
 436                                 continue;
 437                         }
 438
 439                         // Decrement reference counter, we are finished with this connection.
 440                         // It will be incremented for the caller later.
 441                         if ( $domain !== false ) {
 442                                 $this->reuseConnection( $conn );
 443                         }
 444
 445                         // Return this server
 446                         break;
 447                 }
 448
 449                 // If all servers were down, quit now
 450                 if ( !count( $currentLoads ) ) {
 451                         $this->connLogger->error( "All servers down" );
 452                 }
 453
 454                 return [ $i, $laggedReplicaMode ];
 455         }
 456
 457         public function waitFor( $pos ) {
 458                 $oldPos = $this->mWaitForPos;
 459                 try {
 460                         $this->mWaitForPos = $pos;
 461                         // If a generic reader connection was already established, then wait now
 462                         $i = $this->mReadIndex;
 463                         if ( $i > 0 ) {
 464                                 if ( !$this->doWait( $i ) ) {
 465                                         $this->laggedReplicaMode = true;
 466                                 }
 467                         }
 468                 } finally {
 469                         // Restore the older position if it was higher since this is used for lag-protection
 470                         $this->setWaitForPositionIfHigher( $oldPos );
 471                 }
 472         }
 473
 474         public function waitForOne( $pos, $timeout = null ) {
 475                 $oldPos = $this->mWaitForPos;
 476                 try {
 477                         $this->mWaitForPos = $pos;
 478
 479                         $i = $this->mReadIndex;
 480                         if ( $i <= 0 ) {
 481                                 // Pick a generic replica DB if there isn't one yet
 482                                 $readLoads = $this->mLoads;
 483                                 unset( $readLoads[$this->getWriterIndex()] ); // replica DBs only
 484                                 $readLoads = array_filter( $readLoads ); // with non-zero load
 485                                 $i = ArrayUtils::pickRandom( $readLoads );
 486                         }
 487
 488                         if ( $i > 0 ) {
 489                                 $ok = $this->doWait( $i, true, $timeout );
 490                         } else {
 491                                 $ok = true; // no applicable loads
 492                         }
 493                 } finally {
 494                         # Restore the old position, as this is not used for lag-protection but for throttling
 495                         $this->mWaitForPos = $oldPos;
 496                 }
 497
 498                 return $ok;
 499         }
 500
 501         public function waitForAll( $pos, $timeout = null ) {
 502                 $oldPos = $this->mWaitForPos;
 503                 try {
 504                         $this->mWaitForPos = $pos;
 505                         $serverCount = count( $this->mServers );
 506
 507                         $ok = true;
 508                         for ( $i = 1; $i < $serverCount; $i++ ) {
 509                                 if ( $this->mLoads[$i] > 0 ) {
 510                                         $ok = $this->doWait( $i, true, $timeout ) && $ok;
 511                                 }
 512                         }
 513                 } finally {
 514                         # Restore the old position, as this is not used for lag-protection but for throttling
 515                         $this->mWaitForPos = $oldPos;
 516                 }
 517
 518                 return $ok;
 519         }
 520
 521         /**
 522          * @param DBMasterPos|bool $pos
 523          */
 524         private function setWaitForPositionIfHigher( $pos ) {
 525                 if ( !$pos ) {
 526                         return;
 527                 }
 528
 529                 if ( !$this->mWaitForPos || $pos->hasReached( $this->mWaitForPos ) ) {
 530                         $this->mWaitForPos = $pos;
 531                 }
 532         }
 533
 534         /**
 535          * @param int $i
 536          * @return IDatabase|bool
 537          */
 538         public function getAnyOpenConnection( $i ) {
 539                 foreach ( $this->mConns as $connsByServer ) {
 540                         if ( !empty( $connsByServer[$i] ) ) {
 541                                 /** @var $serverConns IDatabase[] */
 542                                 $serverConns = $connsByServer[$i];
 543
 544                                 return reset( $serverConns );
 545                         }
 546                 }
 547
 548                 return false;
 549         }
 550
 551         /**
 552          * Wait for a given replica DB to catch up to the master pos stored in $this
 553          * @param int $index Server index
 554          * @param bool $open Check the server even if a new connection has to be made
 555          * @param int $timeout Max seconds to wait; default is mWaitTimeout
 556          * @return bool
 557          */
 558         protected function doWait( $index, $open = false, $timeout = null ) {
 559                 $close = false; // close the connection afterwards
 560
 561                 // Check if we already know that the DB has reached this point
 562                 $server = $this->getServerName( $index );
 563                 $key = $this->srvCache->makeGlobalKey( __CLASS__, 'last-known-pos', $server, 'v1' );
 564                 /** @var DBMasterPos $knownReachedPos */
 565                 $knownReachedPos = $this->srvCache->get( $key );
 566                 if (
 567                         $knownReachedPos instanceof DBMasterPos &&
 568                         $knownReachedPos->hasReached( $this->mWaitForPos )
 569                 ) {
 570                         $this->replLogger->debug( __METHOD__ .
 571                                 ": replica DB $server known to be caught up (pos >= $knownReachedPos)." );
 572                         return true;
 573                 }
 574
 575                 // Find a connection to wait on, creating one if needed and allowed
 576                 $conn = $this->getAnyOpenConnection( $index );
 577                 if ( !$conn ) {
 578                         if ( !$open ) {
 579                                 $this->replLogger->debug( __METHOD__ . ": no connection open for $server" );
 580
 581                                 return false;
 582                         } else {
 583                                 $conn = $this->openConnection( $index, self::DOMAIN_ANY );
 584                                 if ( !$conn ) {
 585                                         $this->replLogger->warning( __METHOD__ . ": failed to connect to $server" );
 586
 587                                         return false;
 588                                 }
 589                                 // Avoid connection spam in waitForAll() when connections
 590                                 // are made just for the sake of doing this lag check.
 591                                 $close = true;
 592                         }
 593                 }
 594
 595                 $this->replLogger->info( __METHOD__ . ": Waiting for replica DB $server to catch up..." );
 596                 $timeout = $timeout ?: $this->mWaitTimeout;
 597                 $result = $conn->masterPosWait( $this->mWaitForPos, $timeout );
 598
 599                 if ( $result == -1 || is_null( $result ) ) {
 600                         // Timed out waiting for replica DB, use master instead
 601                         $this->replLogger->warning(
 602                                 __METHOD__ . ": Timed out waiting on {host} pos {$this->mWaitForPos}",
 603                                 [ 'host' => $server ]
 604                         );
 605                         $ok = false;
 606                 } else {
 607                         $this->replLogger->info( __METHOD__ . ": Done" );
 608                         $ok = true;
 609                         // Remember that the DB reached this point
 610                         $this->srvCache->set( $key, $this->mWaitForPos, BagOStuff::TTL_DAY );
 611                 }
 612
 613                 if ( $close ) {
 614                         $this->closeConnection( $conn );
 615                 }
 616
 617                 return $ok;
 618         }
 619
 620         public function getConnection( $i, $groups = [], $domain = false, $flags = 0 ) {
 621                 if ( $i === null || $i === false ) {
 622                         throw new InvalidArgumentException( 'Attempt to call ' . __METHOD__ .
 623                                 ' with invalid server index' );
 624                 }
 625
 626                 if ( $this->localDomain->equals( $domain ) || $domain === $this->localDomainIdAlias ) {
 627                         $domain = false; // local connection requested
 628                 }
 629
 630                 $groups = ( $groups === false || $groups === [] )
 631                         ? [ false ] // check one "group": the generic pool
 632                         : (array)$groups;
 633
 634                 $masterOnly = ( $i == self::DB_MASTER || $i == $this->getWriterIndex() );
 635                 $oldConnsOpened = $this->connsOpened; // connections open now
 636
 637                 if ( $i == self::DB_MASTER ) {
 638                         $i = $this->getWriterIndex();
 639                 } else {
 640                         # Try to find an available server in any the query groups (in order)
 641                         foreach ( $groups as $group ) {
 642                                 $groupIndex = $this->getReaderIndex( $group, $domain );
 643                                 if ( $groupIndex !== false ) {
 644                                         $i = $groupIndex;
 645                                         break;
 646                                 }
 647                         }
 648                 }
 649
 650                 # Operation-based index
 651                 if ( $i == self::DB_REPLICA ) {
 652                         $this->mLastError = 'Unknown error'; // reset error string
 653                         # Try the general server pool if $groups are unavailable.
 654                         $i = ( $groups === [ false ] )
 655                                 ? false // don't bother with this if that is what was tried above
 656                                 : $this->getReaderIndex( false, $domain );
 657                         # Couldn't find a working server in getReaderIndex()?
 658                         if ( $i === false ) {
 659                                 $this->mLastError = 'No working replica DB server: ' . $this->mLastError;
 660                                 // Throw an exception
 661                                 $this->reportConnectionError();
 662                                 return null; // not reached
 663                         }
 664                 }
 665
 666                 # Now we have an explicit index into the servers array
 667                 $conn = $this->openConnection( $i, $domain, $flags );
 668                 if ( !$conn ) {
 669                         // Throw an exception
 670                         $this->reportConnectionError();
 671                         return null; // not reached
 672                 }
 673
 674                 # Profile any new connections that happen
 675                 if ( $this->connsOpened > $oldConnsOpened ) {
 676                         $host = $conn->getServer();
 677                         $dbname = $conn->getDBname();
 678                         $this->trxProfiler->recordConnection( $host, $dbname, $masterOnly );
 679                 }
 680
 681                 if ( $masterOnly ) {
 682                         # Make master-requested DB handles inherit any read-only mode setting
 683                         $conn->setLBInfo( 'readOnlyReason', $this->getReadOnlyReason( $domain, $conn ) );
 684                 }
 685
 686                 return $conn;
 687         }
 688
 689         public function reuseConnection( $conn ) {
 690                 $serverIndex = $conn->getLBInfo( 'serverIndex' );
 691                 $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 692                 if ( $serverIndex === null || $refCount === null ) {
 693                         /**
 694                          * This can happen in code like:
 695                          *   foreach ( $dbs as $db ) {
 696                          *     $conn = $lb->getConnection( $lb::DB_REPLICA, [], $db );
 697                          *     ...
 698                          *     $lb->reuseConnection( $conn );
 699                          *   }
 700                          * When a connection to the local DB is opened in this way, reuseConnection()
 701                          * should be ignored
 702                          */
 703                         return;
 704                 } elseif ( $conn instanceof DBConnRef ) {
 705                         // DBConnRef already handles calling reuseConnection() and only passes the live
 706                         // Database instance to this method. Any caller passing in a DBConnRef is broken.
 707                         $this->connLogger->error( __METHOD__ . ": got DBConnRef instance.\n" .
 708                                 ( new RuntimeException() )->getTraceAsString() );
 709
 710                         return;
 711                 }
 712
 713                 if ( $this->disabled ) {
 714                         return; // DBConnRef handle probably survived longer than the LoadBalancer
 715                 }
 716
 717                 if ( $conn->getLBInfo( 'autoCommitOnly' ) ) {
 718                         $connFreeKey = self::KEY_FOREIGN_FREE_NOROUND;
 719                         $connInUseKey = self::KEY_FOREIGN_INUSE_NOROUND;
 720                 } else {
 721                         $connFreeKey = self::KEY_FOREIGN_FREE;
 722                         $connInUseKey = self::KEY_FOREIGN_INUSE;
 723                 }
 724
 725                 $domain = $conn->getDomainID();
 726                 if ( !isset( $this->mConns[$connInUseKey][$serverIndex][$domain] ) ) {
 727                         throw new InvalidArgumentException( __METHOD__ .
 728                                 ": connection $serverIndex/$domain not found; it may have already been freed." );
 729                 } elseif ( $this->mConns[$connInUseKey][$serverIndex][$domain] !== $conn ) {
 730                         throw new InvalidArgumentException( __METHOD__ .
 731                                 ": connection $serverIndex/$domain mismatched; it may have already been freed." );
 732                 }
 733
 734                 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
 735                 if ( $refCount <= 0 ) {
 736                         $this->mConns[$connFreeKey][$serverIndex][$domain] = $conn;
 737                         unset( $this->mConns[$connInUseKey][$serverIndex][$domain] );
 738                         if ( !$this->mConns[$connInUseKey][$serverIndex] ) {
 739                                 unset( $this->mConns[$connInUseKey][$serverIndex] ); // clean up
 740                         }
 741                         $this->connLogger->debug( __METHOD__ . ": freed connection $serverIndex/$domain" );
 742                 } else {
 743                         $this->connLogger->debug( __METHOD__ .
 744                                 ": reference count for $serverIndex/$domain reduced to $refCount" );
 745                 }
 746         }
 747
 748         public function getConnectionRef( $db, $groups = [], $domain = false, $flags = 0 ) {
 749                 $domain = ( $domain !== false ) ? $domain : $this->localDomain;
 750
 751                 return new DBConnRef( $this, $this->getConnection( $db, $groups, $domain, $flags ) );
 752         }
 753
 754         public function getLazyConnectionRef( $db, $groups = [], $domain = false, $flags = 0 ) {
 755                 $domain = ( $domain !== false ) ? $domain : $this->localDomain;
 756
 757                 return new DBConnRef( $this, [ $db, $groups, $domain, $flags ] );
 758         }
 759
 760         public function getMaintenanceConnectionRef( $db, $groups = [], $domain = false, $flags = 0 ) {
 761                 $domain = ( $domain !== false ) ? $domain : $this->localDomain;
 762
 763                 return new MaintainableDBConnRef(
 764                         $this, $this->getConnection( $db, $groups, $domain, $flags ) );
 765         }
 766
 767         public function openConnection( $i, $domain = false, $flags = 0 ) {
 768                 if ( $this->localDomain->equals( $domain ) || $domain === $this->localDomainIdAlias ) {
 769                         $domain = false; // local connection requested
 770                 }
 771
 772                 if ( !$this->chronProtInitialized && $this->chronProt ) {
 773                         $this->connLogger->debug( __METHOD__ . ': calling initLB() before first connection.' );
 774                         // Load CP positions before connecting so that doWait() triggers later if needed
 775                         $this->chronProtInitialized = true;
 776                         $this->chronProt->initLB( $this );
 777                 }
 778
 779                 // Check if an auto-commit connection is being requested. If so, it will not reuse the
 780                 // main set of DB connections but rather its own pool since:
 781                 // a) those are usually set to implicitly use transaction rounds via DBO_TRX
 782                 // b) those must support the use of explicit transaction rounds via beginMasterChanges()
 783                 $autoCommit = ( ( $flags & self::CONN_TRX_AUTO ) == self::CONN_TRX_AUTO );
 784
 785                 if ( $domain !== false ) {
 786                         // Connection is to a foreign domain
 787                         $conn = $this->openForeignConnection( $i, $domain, $flags );
 788                 } else {
 789                         // Connection is to the local domain
 790                         $connKey = $autoCommit ? self::KEY_LOCAL_NOROUND : self::KEY_LOCAL;
 791                         if ( isset( $this->mConns[$connKey][$i][0] ) ) {
 792                                 $conn = $this->mConns[$connKey][$i][0];
 793                         } else {
 794                                 if ( !isset( $this->mServers[$i] ) || !is_array( $this->mServers[$i] ) ) {
 795                                         throw new InvalidArgumentException( "No server with index '$i'." );
 796                                 }
 797                                 // Open a new connection
 798                                 $server = $this->mServers[$i];
 799                                 $server['serverIndex'] = $i;
 800                                 $server['autoCommitOnly'] = $autoCommit;
 801                                 $conn = $this->reallyOpenConnection( $server, false );
 802                                 $host = $this->getServerName( $i );
 803                                 if ( $conn->isOpen() ) {
 804                                         $this->connLogger->debug( "Connected to database $i at '$host'." );
 805                                         $this->mConns[$connKey][$i][0] = $conn;
 806                                 } else {
 807                                         $this->connLogger->warning( "Failed to connect to database $i at '$host'." );
 808                                         $this->errorConnection = $conn;
 809                                         $conn = false;
 810                                 }
 811                         }
 812                 }
 813
 814                 if ( $conn instanceof IDatabase && !$conn->isOpen() ) {
 815                         // Connection was made but later unrecoverably lost for some reason.
 816                         // Do not return a handle that will just throw exceptions on use,
 817                         // but let the calling code (e.g. getReaderIndex) try another server.
 818                         // See DatabaseMyslBase::ping() for how this can happen.
 819                         $this->errorConnection = $conn;
 820                         $conn = false;
 821                 }
 822
 823                 if ( $autoCommit && $conn instanceof IDatabase ) {
 824                         $conn->clearFlag( $conn::DBO_TRX ); // auto-commit mode
 825                 }
 826
 827                 return $conn;
 828         }
 829
 830         /**
 831          * Open a connection to a foreign DB, or return one if it is already open.
 832          *
 833          * Increments a reference count on the returned connection which locks the
 834          * connection to the requested domain. This reference count can be
 835          * decremented by calling reuseConnection().
 836          *
 837          * If a connection is open to the appropriate server already, but with the wrong
 838          * database, it will be switched to the right database and returned, as long as
 839          * it has been freed first with reuseConnection().
 840          *
 841          * On error, returns false, and the connection which caused the
 842          * error will be available via $this->errorConnection.
 843          *
 844          * @note If disable() was called on this LoadBalancer, this method will throw a DBAccessError.
 845          *
 846          * @param int $i Server index
 847          * @param string $domain Domain ID to open
 848          * @param integer $flags Class CONN_* constant bitfield
 849          * @return Database
 850          */
 851         private function openForeignConnection( $i, $domain, $flags = 0 ) {
 852                 $domainInstance = DatabaseDomain::newFromId( $domain );
 853                 $dbName = $domainInstance->getDatabase();
 854                 $prefix = $domainInstance->getTablePrefix();
 855                 $autoCommit = ( ( $flags & self::CONN_TRX_AUTO ) == self::CONN_TRX_AUTO );
 856
 857                 if ( $autoCommit ) {
 858                         $connFreeKey = self::KEY_FOREIGN_FREE_NOROUND;
 859                         $connInUseKey = self::KEY_FOREIGN_INUSE_NOROUND;
 860                 } else {
 861                         $connFreeKey = self::KEY_FOREIGN_FREE;
 862                         $connInUseKey = self::KEY_FOREIGN_INUSE;
 863                 }
 864
 865                 if ( isset( $this->mConns[$connInUseKey][$i][$domain] ) ) {
 866                         // Reuse an in-use connection for the same domain
 867                         $conn = $this->mConns[$connInUseKey][$i][$domain];
 868                         $this->connLogger->debug( __METHOD__ . ": reusing connection $i/$domain" );
 869                 } elseif ( isset( $this->mConns[$connFreeKey][$i][$domain] ) ) {
 870                         // Reuse a free connection for the same domain
 871                         $conn = $this->mConns[$connFreeKey][$i][$domain];
 872                         unset( $this->mConns[$connFreeKey][$i][$domain] );
 873                         $this->mConns[$connInUseKey][$i][$domain] = $conn;
 874                         $this->connLogger->debug( __METHOD__ . ": reusing free connection $i/$domain" );
 875                 } elseif ( !empty( $this->mConns[$connFreeKey][$i] ) ) {
 876                         // Reuse a free connection from another domain
 877                         $conn = reset( $this->mConns[$connFreeKey][$i] );
 878                         $oldDomain = key( $this->mConns[$connFreeKey][$i] );
 879                         // The empty string as a DB name means "don't care".
 880                         // DatabaseMysqlBase::open() already handle this on connection.
 881                         if ( strlen( $dbName ) && !$conn->selectDB( $dbName ) ) {
 882                                 $this->mLastError = "Error selecting database '$dbName' on server " .
 883                                         $conn->getServer() . " from client host {$this->host}";
 884                                 $this->errorConnection = $conn;
 885                                 $conn = false;
 886                         } else {
 887                                 $conn->tablePrefix( $prefix );
 888                                 unset( $this->mConns[$connFreeKey][$i][$oldDomain] );
 889                                 $this->mConns[$connInUseKey][$i][$domain] = $conn;
 890                                 $this->connLogger->debug( __METHOD__ .
 891                                         ": reusing free connection from $oldDomain for $domain" );
 892                         }
 893                 } else {
 894                         if ( !isset( $this->mServers[$i] ) || !is_array( $this->mServers[$i] ) ) {
 895                                 throw new InvalidArgumentException( "No server with index '$i'." );
 896                         }
 897                         // Open a new connection
 898                         $server = $this->mServers[$i];
 899                         $server['serverIndex'] = $i;
 900                         $server['foreignPoolRefCount'] = 0;
 901                         $server['foreign'] = true;
 902                         $server['autoCommitOnly'] = $autoCommit;
 903                         $conn = $this->reallyOpenConnection( $server, $dbName );
 904                         if ( !$conn->isOpen() ) {
 905                                 $this->connLogger->warning( __METHOD__ . ": connection error for $i/$domain" );
 906                                 $this->errorConnection = $conn;
 907                                 $conn = false;
 908                         } else {
 909                                 $conn->tablePrefix( $prefix );
 910                                 $this->mConns[$connInUseKey][$i][$domain] = $conn;
 911                                 $this->connLogger->debug( __METHOD__ . ": opened new connection for $i/$domain" );
 912                         }
 913                 }
 914
 915                 // Increment reference count
 916                 if ( $conn instanceof IDatabase ) {
 917                         $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 918                         $conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
 919                 }
 920
 921                 return $conn;
 922         }
 923
 924         /**
 925          * Test if the specified index represents an open connection
 926          *
 927          * @param int $index Server index
 928          * @access private
 929          * @return bool
 930          */
 931         private function isOpen( $index ) {
 932                 if ( !is_integer( $index ) ) {
 933                         return false;
 934                 }
 935
 936                 return (bool)$this->getAnyOpenConnection( $index );
 937         }
 938
 939         /**
 940          * Really opens a connection. Uncached.
 941          * Returns a Database object whether or not the connection was successful.
 942          * @access private
 943          *
 944          * @param array $server
 945          * @param string|bool $dbNameOverride Use "" to not select any database
 946          * @return Database
 947          * @throws DBAccessError
 948          * @throws InvalidArgumentException
 949          */
 950         protected function reallyOpenConnection( array $server, $dbNameOverride = false ) {
 951                 if ( $this->disabled ) {
 952                         throw new DBAccessError();
 953                 }
 954
 955                 if ( $dbNameOverride !== false ) {
 956                         $server['dbname'] = $dbNameOverride;
 957                 }
 958
 959                 // Let the handle know what the cluster master is (e.g. "db1052")
 960                 $masterName = $this->getServerName( $this->getWriterIndex() );
 961                 $server['clusterMasterHost'] = $masterName;
 962
 963                 // Log when many connection are made on requests
 964                 if ( ++$this->connsOpened >= self::CONN_HELD_WARN_THRESHOLD ) {
 965                         $this->perfLogger->warning( __METHOD__ . ": " .
 966                                 "{$this->connsOpened}+ connections made (master=$masterName)" );
 967                 }
 968
 969                 $server['srvCache'] = $this->srvCache;
 970                 // Set loggers and profilers
 971                 $server['connLogger'] = $this->connLogger;
 972                 $server['queryLogger'] = $this->queryLogger;
 973                 $server['errorLogger'] = $this->errorLogger;
 974                 $server['profiler'] = $this->profiler;
 975                 $server['trxProfiler'] = $this->trxProfiler;
 976                 // Use the same agent and PHP mode for all DB handles
 977                 $server['cliMode'] = $this->cliMode;
 978                 $server['agent'] = $this->agent;
 979                 // Use DBO_DEFAULT flags by default for LoadBalancer managed databases. Assume that the
 980                 // application calls LoadBalancer::commitMasterChanges() before the PHP script completes.
 981                 $server['flags'] = isset( $server['flags'] ) ? $server['flags'] : IDatabase::DBO_DEFAULT;
 982
 983                 // Create a live connection object
 984                 try {
 985                         $db = Database::factory( $server['type'], $server );
 986                 } catch ( DBConnectionError $e ) {
 987                         // FIXME: This is probably the ugliest thing I have ever done to
 988                         // PHP. I'm half-expecting it to segfault, just out of disgust. -- TS
 989                         $db = $e->db;
 990                 }
 991
 992                 $db->setLBInfo( $server );
 993                 $db->setLazyMasterHandle(
 994                         $this->getLazyConnectionRef( self::DB_MASTER, [], $db->getDomainID() )
 995                 );
 996                 $db->setTableAliases( $this->tableAliases );
 997
 998                 if ( $server['serverIndex'] === $this->getWriterIndex() ) {
 999                         if ( $this->trxRoundId !== false ) {
1000                                 $this->applyTransactionRoundFlags( $db );
1001                         }
1002                         foreach ( $this->trxRecurringCallbacks as $name => $callback ) {
1003                                 $db->setTransactionListener( $name, $callback );
1004                         }
1005                 }
1006
1007                 return $db;
1008         }
1009
1010         /**
1011          * @throws DBConnectionError
1012          */
1013         private function reportConnectionError() {
1014                 $conn = $this->errorConnection; // the connection which caused the error
1015                 $context = [
1016                         'method' => __METHOD__,
1017                         'last_error' => $this->mLastError,
1018                 ];
1019
1020                 if ( $conn instanceof IDatabase ) {
1021                         $context['db_server'] = $conn->getServer();
1022                         $this->connLogger->warning(
1023                                 "Connection error: {last_error} ({db_server})",
1024                                 $context
1025                         );
1026
1027                         // throws DBConnectionError
1028                         $conn->reportConnectionError( "{$this->mLastError} ({$context['db_server']})" );
1029                 } else {
1030                         // No last connection, probably due to all servers being too busy
1031                         $this->connLogger->error(
1032                                 "LB failure with no last connection. Connection error: {last_error}",
1033                                 $context
1034                         );
1035
1036                         // If all servers were busy, mLastError will contain something sensible
1037                         throw new DBConnectionError( null, $this->mLastError );
1038                 }
1039         }
1040
1041         public function getWriterIndex() {
1042                 return 0;
1043         }
1044
1045         public function haveIndex( $i ) {
1046                 return array_key_exists( $i, $this->mServers );
1047         }
1048
1049         public function isNonZeroLoad( $i ) {
1050                 return array_key_exists( $i, $this->mServers ) && $this->mLoads[$i] != 0;
1051         }
1052
1053         public function getServerCount() {
1054                 return count( $this->mServers );
1055         }
1056
1057         public function getServerName( $i ) {
1058                 if ( isset( $this->mServers[$i]['hostName'] ) ) {
1059                         $name = $this->mServers[$i]['hostName'];
1060                 } elseif ( isset( $this->mServers[$i]['host'] ) ) {
1061                         $name = $this->mServers[$i]['host'];
1062                 } else {
1063                         $name = '';
1064                 }
1065
1066                 return ( $name != '' ) ? $name : 'localhost';
1067         }
1068
1069         public function getServerType( $i ) {
1070                 return isset( $this->mServers[$i]['type'] ) ? $this->mServers[$i]['type'] : 'unknown';
1071         }
1072
1073         /**
1074          * @deprecated Since 1.30, no alternative
1075          */
1076         public function getServerInfo( $i ) {
1077                 wfDeprecated( __METHOD__, '1.30' );
1078                 if ( isset( $this->mServers[$i] ) ) {
1079                         return $this->mServers[$i];
1080                 } else {
1081                         return false;
1082                 }
1083         }
1084
1085         /**
1086          * @deprecated Since 1.30, construct new object
1087          */
1088         public function setServerInfo( $i, array $serverInfo ) {
1089                 wfDeprecated( __METHOD__, '1.30' );
1090                 $this->mServers[$i] = $serverInfo;
1091         }
1092
1093         public function getMasterPos() {
1094                 # If this entire request was served from a replica DB without opening a connection to the
1095                 # master (however unlikely that may be), then we can fetch the position from the replica DB.
1096                 $masterConn = $this->getAnyOpenConnection( $this->getWriterIndex() );
1097                 if ( !$masterConn ) {
1098                         $serverCount = count( $this->mServers );
1099                         for ( $i = 1; $i < $serverCount; $i++ ) {
1100                                 $conn = $this->getAnyOpenConnection( $i );
1101                                 if ( $conn ) {
1102                                         return $conn->getReplicaPos();
1103                                 }
1104                         }
1105                 } else {
1106                         return $masterConn->getMasterPos();
1107                 }
1108
1109                 return false;
1110         }
1111
1112         public function disable() {
1113                 $this->closeAll();
1114                 $this->disabled = true;
1115         }
1116
1117         public function closeAll() {
1118                 $this->forEachOpenConnection( function ( IDatabase $conn ) {
1119                         $host = $conn->getServer();
1120                         $this->connLogger->debug( "Closing connection to database '$host'." );
1121                         $conn->close();
1122                 } );
1123
1124                 $this->mConns = [
1125                         self::KEY_LOCAL => [],
1126                         self::KEY_FOREIGN_INUSE => [],
1127                         self::KEY_FOREIGN_FREE => [],
1128                         self::KEY_LOCAL_NOROUND => [],
1129                         self::KEY_FOREIGN_INUSE_NOROUND => [],
1130                         self::KEY_FOREIGN_FREE_NOROUND => []
1131                 ];
1132                 $this->connsOpened = 0;
1133         }
1134
1135         public function closeConnection( IDatabase $conn ) {
1136                 $serverIndex = $conn->getLBInfo( 'serverIndex' ); // second index level of mConns
1137                 foreach ( $this->mConns as $type => $connsByServer ) {
1138                         if ( !isset( $connsByServer[$serverIndex] ) ) {
1139                                 continue;
1140                         }
1141
1142                         foreach ( $connsByServer[$serverIndex] as $i => $trackedConn ) {
1143                                 if ( $conn === $trackedConn ) {
1144                                         $host = $this->getServerName( $i );
1145                                         $this->connLogger->debug( "Closing connection to database $i at '$host'." );
1146                                         unset( $this->mConns[$type][$serverIndex][$i] );
1147                                         --$this->connsOpened;
1148                                         break 2;
1149                                 }
1150                         }
1151                 }
1152
1153                 $conn->close();
1154         }
1155
1156         public function commitAll( $fname = __METHOD__ ) {
1157                 $failures = [];
1158
1159                 $restore = ( $this->trxRoundId !== false );
1160                 $this->trxRoundId = false;
1161                 $this->forEachOpenConnection(
1162                         function ( IDatabase $conn ) use ( $fname, $restore, &$failures ) {
1163                                 try {
1164                                         $conn->commit( $fname, $conn::FLUSHING_ALL_PEERS );
1165                                 } catch ( DBError $e ) {
1166                                         call_user_func( $this->errorLogger, $e );
1167                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1168                                 }
1169                                 if ( $restore && $conn->getLBInfo( 'master' ) ) {
1170                                         $this->undoTransactionRoundFlags( $conn );
1171                                 }
1172                         }
1173                 );
1174
1175                 if ( $failures ) {
1176                         throw new DBExpectedError(
1177                                 null,
1178                                 "Commit failed on server(s) " . implode( "\n", array_unique( $failures ) )
1179                         );
1180                 }
1181         }
1182
1183         public function finalizeMasterChanges() {
1184                 $this->forEachOpenMasterConnection( function ( Database $conn ) {
1185                         // Any error should cause all DB transactions to be rolled back together
1186                         $conn->setTrxEndCallbackSuppression( false );
1187                         $conn->runOnTransactionPreCommitCallbacks();
1188                         // Defer post-commit callbacks until COMMIT finishes for all DBs
1189                         $conn->setTrxEndCallbackSuppression( true );
1190                 } );
1191         }
1192
1193         public function approveMasterChanges( array $options ) {
1194                 $limit = isset( $options['maxWriteDuration'] ) ? $options['maxWriteDuration'] : 0;
1195                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( $limit ) {
1196                         // If atomic sections or explicit transactions are still open, some caller must have
1197                         // caught an exception but failed to properly rollback any changes. Detect that and
1198                         // throw and error (causing rollback).
1199                         if ( $conn->explicitTrxActive() ) {
1200                                 throw new DBTransactionError(
1201                                         $conn,
1202                                         "Explicit transaction still active. A caller may have caught an error."
1203                                 );
1204                         }
1205                         // Assert that the time to replicate the transaction will be sane.
1206                         // If this fails, then all DB transactions will be rollback back together.
1207                         $time = $conn->pendingWriteQueryDuration( $conn::ESTIMATE_DB_APPLY );
1208                         if ( $limit > 0 && $time > $limit ) {
1209                                 throw new DBTransactionSizeError(
1210                                         $conn,
1211                                         "Transaction spent $time second(s) in writes, exceeding the limit of $limit.",
1212                                         [ $time, $limit ]
1213                                 );
1214                         }
1215                         // If a connection sits idle while slow queries execute on another, that connection
1216                         // may end up dropped before the commit round is reached. Ping servers to detect this.
1217                         if ( $conn->writesOrCallbacksPending() && !$conn->ping() ) {
1218                                 throw new DBTransactionError(
1219                                         $conn,
1220                                         "A connection to the {$conn->getDBname()} database was lost before commit."
1221                                 );
1222                         }
1223                 } );
1224         }
1225
1226         public function beginMasterChanges( $fname = __METHOD__ ) {
1227                 if ( $this->trxRoundId !== false ) {
1228                         throw new DBTransactionError(
1229                                 null,
1230                                 "$fname: Transaction round '{$this->trxRoundId}' already started."
1231                         );
1232                 }
1233                 $this->trxRoundId = $fname;
1234
1235                 $failures = [];
1236                 $this->forEachOpenMasterConnection(
1237                         function ( Database $conn ) use ( $fname, &$failures ) {
1238                                 $conn->setTrxEndCallbackSuppression( true );
1239                                 try {
1240                                         $conn->flushSnapshot( $fname );
1241                                 } catch ( DBError $e ) {
1242                                         call_user_func( $this->errorLogger, $e );
1243                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1244                                 }
1245                                 $conn->setTrxEndCallbackSuppression( false );
1246                                 $this->applyTransactionRoundFlags( $conn );
1247                         }
1248                 );
1249
1250                 if ( $failures ) {
1251                         throw new DBExpectedError(
1252                                 null,
1253                                 "$fname: Flush failed on server(s) " . implode( "\n", array_unique( $failures ) )
1254                         );
1255                 }
1256         }
1257
1258         public function commitMasterChanges( $fname = __METHOD__ ) {
1259                 $failures = [];
1260
1261                 /** @noinspection PhpUnusedLocalVariableInspection */
1262                 $scope = $this->getScopedPHPBehaviorForCommit(); // try to ignore client aborts
1263
1264                 $restore = ( $this->trxRoundId !== false );
1265                 $this->trxRoundId = false;
1266                 $this->forEachOpenMasterConnection(
1267                         function ( IDatabase $conn ) use ( $fname, $restore, &$failures ) {
1268                                 try {
1269                                         if ( $conn->writesOrCallbacksPending() ) {
1270                                                 $conn->commit( $fname, $conn::FLUSHING_ALL_PEERS );
1271                                         } elseif ( $restore ) {
1272                                                 $conn->flushSnapshot( $fname );
1273                                         }
1274                                 } catch ( DBError $e ) {
1275                                         call_user_func( $this->errorLogger, $e );
1276                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1277                                 }
1278                                 if ( $restore ) {
1279                                         $this->undoTransactionRoundFlags( $conn );
1280                                 }
1281                         }
1282                 );
1283
1284                 if ( $failures ) {
1285                         throw new DBExpectedError(
1286                                 null,
1287                                 "$fname: Commit failed on server(s) " . implode( "\n", array_unique( $failures ) )
1288                         );
1289                 }
1290         }
1291
1292         public function runMasterPostTrxCallbacks( $type ) {
1293                 $e = null; // first exception
1294                 $this->forEachOpenMasterConnection( function ( Database $conn ) use ( $type, &$e ) {
1295                         $conn->setTrxEndCallbackSuppression( false );
1296                         if ( $conn->writesOrCallbacksPending() ) {
1297                                 // This happens if onTransactionIdle() callbacks leave callbacks on *another* DB
1298                                 // (which finished its callbacks already). Warn and recover in this case. Let the
1299                                 // callbacks run in the final commitMasterChanges() in LBFactory::shutdown().
1300                                 $this->queryLogger->info( __METHOD__ . ": found writes/callbacks pending." );
1301                                 return;
1302                         } elseif ( $conn->trxLevel() ) {
1303                                 // This happens for single-DB setups where DB_REPLICA uses the master DB,
1304                                 // thus leaving an implicit read-only transaction open at this point. It
1305                                 // also happens if onTransactionIdle() callbacks leave implicit transactions
1306                                 // open on *other* DBs (which is slightly improper). Let these COMMIT on the
1307                                 // next call to commitMasterChanges(), possibly in LBFactory::shutdown().
1308                                 return;
1309                         }
1310                         try {
1311                                 $conn->runOnTransactionIdleCallbacks( $type );
1312                         } catch ( Exception $ex ) {
1313                                 $e = $e ?: $ex;
1314                         }
1315                         try {
1316                                 $conn->runTransactionListenerCallbacks( $type );
1317                         } catch ( Exception $ex ) {
1318                                 $e = $e ?: $ex;
1319                         }
1320                 } );
1321
1322                 return $e;
1323         }
1324
1325         public function rollbackMasterChanges( $fname = __METHOD__ ) {
1326                 $restore = ( $this->trxRoundId !== false );
1327                 $this->trxRoundId = false;
1328                 $this->forEachOpenMasterConnection(
1329                         function ( IDatabase $conn ) use ( $fname, $restore ) {
1330                                 if ( $conn->writesOrCallbacksPending() ) {
1331                                         $conn->rollback( $fname, $conn::FLUSHING_ALL_PEERS );
1332                                 }
1333                                 if ( $restore ) {
1334                                         $this->undoTransactionRoundFlags( $conn );
1335                                 }
1336                         }
1337                 );
1338         }
1339
1340         public function suppressTransactionEndCallbacks() {
1341                 $this->forEachOpenMasterConnection( function ( Database $conn ) {
1342                         $conn->setTrxEndCallbackSuppression( true );
1343                 } );
1344         }
1345
1346         /**
1347          * @param IDatabase $conn
1348          */
1349         private function applyTransactionRoundFlags( IDatabase $conn ) {
1350                 if ( $conn->getLBInfo( 'autoCommitOnly' ) ) {
1351                         return; // transaction rounds do not apply to these connections
1352                 }
1353
1354                 if ( $conn->getFlag( $conn::DBO_DEFAULT ) ) {
1355                         // DBO_TRX is controlled entirely by CLI mode presence with DBO_DEFAULT.
1356                         // Force DBO_TRX even in CLI mode since a commit round is expected soon.
1357                         $conn->setFlag( $conn::DBO_TRX, $conn::REMEMBER_PRIOR );
1358                         // If config has explicitly requested DBO_TRX be either on or off by not
1359                         // setting DBO_DEFAULT, then respect that. Forcing no transactions is useful
1360                         // for things like blob stores (ExternalStore) which want auto-commit mode.
1361                 }
1362         }
1363
1364         /**
1365          * @param IDatabase $conn
1366          */
1367         private function undoTransactionRoundFlags( IDatabase $conn ) {
1368                 if ( $conn->getLBInfo( 'autoCommitOnly' ) ) {
1369                         return; // transaction rounds do not apply to these connections
1370                 }
1371
1372                 if ( $conn->getFlag( $conn::DBO_DEFAULT ) ) {
1373                         $conn->restoreFlags( $conn::RESTORE_PRIOR );
1374                 }
1375         }
1376
1377         public function flushReplicaSnapshots( $fname = __METHOD__ ) {
1378                 $this->forEachOpenReplicaConnection( function ( IDatabase $conn ) {
1379                         $conn->flushSnapshot( __METHOD__ );
1380                 } );
1381         }
1382
1383         public function hasMasterConnection() {
1384                 return $this->isOpen( $this->getWriterIndex() );
1385         }
1386
1387         public function hasMasterChanges() {
1388                 $pending = 0;
1389                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$pending ) {
1390                         $pending |= $conn->writesOrCallbacksPending();
1391                 } );
1392
1393                 return (bool)$pending;
1394         }
1395
1396         public function lastMasterChangeTimestamp() {
1397                 $lastTime = false;
1398                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$lastTime ) {
1399                         $lastTime = max( $lastTime, $conn->lastDoneWrites() );
1400                 } );
1401
1402                 return $lastTime;
1403         }
1404
1405         public function hasOrMadeRecentMasterChanges( $age = null ) {
1406                 $age = ( $age === null ) ? $this->mWaitTimeout : $age;
1407
1408                 return ( $this->hasMasterChanges()
1409                         || $this->lastMasterChangeTimestamp() > microtime( true ) - $age );
1410         }
1411
1412         public function pendingMasterChangeCallers() {
1413                 $fnames = [];
1414                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$fnames ) {
1415                         $fnames = array_merge( $fnames, $conn->pendingWriteCallers() );
1416                 } );
1417
1418                 return $fnames;
1419         }
1420
1421         public function getLaggedReplicaMode( $domain = false ) {
1422                 // No-op if there is only one DB (also avoids recursion)
1423                 if ( !$this->laggedReplicaMode && $this->getServerCount() > 1 ) {
1424                         try {
1425                                 // See if laggedReplicaMode gets set
1426                                 $conn = $this->getConnection( self::DB_REPLICA, false, $domain );
1427                                 $this->reuseConnection( $conn );
1428                         } catch ( DBConnectionError $e ) {
1429                                 // Avoid expensive re-connect attempts and failures
1430                                 $this->allReplicasDownMode = true;
1431                                 $this->laggedReplicaMode = true;
1432                         }
1433                 }
1434
1435                 return $this->laggedReplicaMode;
1436         }
1437
1438         /**
1439          * @param bool $domain
1440          * @return bool
1441          * @deprecated 1.28; use getLaggedReplicaMode()
1442          */
1443         public function getLaggedSlaveMode( $domain = false ) {
1444                 return $this->getLaggedReplicaMode( $domain );
1445         }
1446
1447         public function laggedReplicaUsed() {
1448                 return $this->laggedReplicaMode;
1449         }
1450
1451         /**
1452          * @return bool
1453          * @since 1.27
1454          * @deprecated Since 1.28; use laggedReplicaUsed()
1455          */
1456         public function laggedSlaveUsed() {
1457                 return $this->laggedReplicaUsed();
1458         }
1459
1460         public function getReadOnlyReason( $domain = false, IDatabase $conn = null ) {
1461                 if ( $this->readOnlyReason !== false ) {
1462                         return $this->readOnlyReason;
1463                 } elseif ( $this->getLaggedReplicaMode( $domain ) ) {
1464                         if ( $this->allReplicasDownMode ) {
1465                                 return 'The database has been automatically locked ' .
1466                                         'until the replica database servers become available';
1467                         } else {
1468                                 return 'The database has been automatically locked ' .
1469                                         'while the replica database servers catch up to the master.';
1470                         }
1471                 } elseif ( $this->masterRunningReadOnly( $domain, $conn ) ) {
1472                         return 'The database master is running in read-only mode.';
1473                 }
1474
1475                 return false;
1476         }
1477
1478         /**
1479          * @param string $domain Domain ID, or false for the current domain
1480          * @param IDatabase|null $conn DB master connectionl used to avoid loops [optional]
1481          * @return bool
1482          */
1483         private function masterRunningReadOnly( $domain, IDatabase $conn = null ) {
1484                 $cache = $this->wanCache;
1485                 $masterServer = $this->getServerName( $this->getWriterIndex() );
1486
1487                 return (bool)$cache->getWithSetCallback(
1488                         $cache->makeGlobalKey( __CLASS__, 'server-read-only', $masterServer ),
1489                         self::TTL_CACHE_READONLY,
1490                         function () use ( $domain, $conn ) {
1491                                 $old = $this->trxProfiler->setSilenced( true );
1492                                 try {
1493                                         $dbw = $conn ?: $this->getConnection( self::DB_MASTER, [], $domain );
1494                                         $readOnly = (int)$dbw->serverIsReadOnly();
1495                                         if ( !$conn ) {
1496                                                 $this->reuseConnection( $dbw );
1497                                         }
1498                                 } catch ( DBError $e ) {
1499                                         $readOnly = 0;
1500                                 }
1501                                 $this->trxProfiler->setSilenced( $old );
1502                                 return $readOnly;
1503                         },
1504                         [ 'pcTTL' => $cache::TTL_PROC_LONG, 'busyValue' => 0 ]
1505                 );
1506         }
1507
1508         public function allowLagged( $mode = null ) {
1509                 if ( $mode === null ) {
1510                         return $this->mAllowLagged;
1511                 }
1512                 $this->mAllowLagged = $mode;
1513
1514                 return $this->mAllowLagged;
1515         }
1516
1517         public function pingAll() {
1518                 $success = true;
1519                 $this->forEachOpenConnection( function ( IDatabase $conn ) use ( &$success ) {
1520                         if ( !$conn->ping() ) {
1521                                 $success = false;
1522                         }
1523                 } );
1524
1525                 return $success;
1526         }
1527
1528         public function forEachOpenConnection( $callback, array $params = [] ) {
1529                 foreach ( $this->mConns as $connsByServer ) {
1530                         foreach ( $connsByServer as $serverConns ) {
1531                                 foreach ( $serverConns as $conn ) {
1532                                         $mergedParams = array_merge( [ $conn ], $params );
1533                                         call_user_func_array( $callback, $mergedParams );
1534                                 }
1535                         }
1536                 }
1537         }
1538
1539         public function forEachOpenMasterConnection( $callback, array $params = [] ) {
1540                 $masterIndex = $this->getWriterIndex();
1541                 foreach ( $this->mConns as $connsByServer ) {
1542                         if ( isset( $connsByServer[$masterIndex] ) ) {
1543                                 /** @var IDatabase $conn */
1544                                 foreach ( $connsByServer[$masterIndex] as $conn ) {
1545                                         $mergedParams = array_merge( [ $conn ], $params );
1546                                         call_user_func_array( $callback, $mergedParams );
1547                                 }
1548                         }
1549                 }
1550         }
1551
1552         public function forEachOpenReplicaConnection( $callback, array $params = [] ) {
1553                 foreach ( $this->mConns as $connsByServer ) {
1554                         foreach ( $connsByServer as $i => $serverConns ) {
1555                                 if ( $i === $this->getWriterIndex() ) {
1556                                         continue; // skip master
1557                                 }
1558                                 foreach ( $serverConns as $conn ) {
1559                                         $mergedParams = array_merge( [ $conn ], $params );
1560                                         call_user_func_array( $callback, $mergedParams );
1561                                 }
1562                         }
1563                 }
1564         }
1565
1566         public function getMaxLag( $domain = false ) {
1567                 $maxLag = -1;
1568                 $host = '';
1569                 $maxIndex = 0;
1570
1571                 if ( $this->getServerCount() <= 1 ) {
1572                         return [ $host, $maxLag, $maxIndex ]; // no replication = no lag
1573                 }
1574
1575                 $lagTimes = $this->getLagTimes( $domain );
1576                 foreach ( $lagTimes as $i => $lag ) {
1577                         if ( $this->mLoads[$i] > 0 && $lag > $maxLag ) {
1578                                 $maxLag = $lag;
1579                                 $host = $this->mServers[$i]['host'];
1580                                 $maxIndex = $i;
1581                         }
1582                 }
1583
1584                 return [ $host, $maxLag, $maxIndex ];
1585         }
1586
1587         public function getLagTimes( $domain = false ) {
1588                 if ( $this->getServerCount() <= 1 ) {
1589                         return [ $this->getWriterIndex() => 0 ]; // no replication = no lag
1590                 }
1591
1592                 $knownLagTimes = []; // map of (server index => 0 seconds)
1593                 $indexesWithLag = [];
1594                 foreach ( $this->mServers as $i => $server ) {
1595                         if ( empty( $server['is static'] ) ) {
1596                                 $indexesWithLag[] = $i; // DB server might have replication lag
1597                         } else {
1598                                 $knownLagTimes[$i] = 0; // DB server is a non-replicating and read-only archive
1599                         }
1600                 }
1601
1602                 return $this->getLoadMonitor()->getLagTimes( $indexesWithLag, $domain ) + $knownLagTimes;
1603         }
1604
1605         public function safeGetLag( IDatabase $conn ) {
1606                 if ( $this->getServerCount() <= 1 ) {
1607                         return 0;
1608                 } else {
1609                         return $conn->getLag();
1610                 }
1611         }
1612
1613         /**
1614          * @param IDatabase $conn
1615          * @param DBMasterPos|bool $pos
1616          * @param int $timeout
1617          * @return bool
1618          */
1619         public function safeWaitForMasterPos( IDatabase $conn, $pos = false, $timeout = 10 ) {
1620                 if ( $this->getServerCount() <= 1 || !$conn->getLBInfo( 'replica' ) ) {
1621                         return true; // server is not a replica DB
1622                 }
1623
1624                 if ( !$pos ) {
1625                         // Get the current master position, opening a connection if needed
1626                         $masterConn = $this->getAnyOpenConnection( $this->getWriterIndex() );
1627                         if ( $masterConn ) {
1628                                 $pos = $masterConn->getMasterPos();
1629                         } else {
1630                                 $masterConn = $this->openConnection( $this->getWriterIndex(), self::DOMAIN_ANY );
1631                                 $pos = $masterConn->getMasterPos();
1632                                 $this->closeConnection( $masterConn );
1633                         }
1634                 }
1635
1636                 if ( $pos instanceof DBMasterPos ) {
1637                         $result = $conn->masterPosWait( $pos, $timeout );
1638                         if ( $result == -1 || is_null( $result ) ) {
1639                                 $msg = __METHOD__ . ": Timed out waiting on {$conn->getServer()} pos {$pos}";
1640                                 $this->replLogger->warning( "$msg" );
1641                                 $ok = false;
1642                         } else {
1643                                 $this->replLogger->info( __METHOD__ . ": Done" );
1644                                 $ok = true;
1645                         }
1646                 } else {
1647                         $ok = false; // something is misconfigured
1648                         $this->replLogger->error( "Could not get master pos for {$conn->getServer()}." );
1649                 }
1650
1651                 return $ok;
1652         }
1653
1654         public function setTransactionListener( $name, callable $callback = null ) {
1655                 if ( $callback ) {
1656                         $this->trxRecurringCallbacks[$name] = $callback;
1657                 } else {
1658                         unset( $this->trxRecurringCallbacks[$name] );
1659                 }
1660                 $this->forEachOpenMasterConnection(
1661                         function ( IDatabase $conn ) use ( $name, $callback ) {
1662                                 $conn->setTransactionListener( $name, $callback );
1663                         }
1664                 );
1665         }
1666
1667         public function setTableAliases( array $aliases ) {
1668                 $this->tableAliases = $aliases;
1669         }
1670
1671         public function setDomainPrefix( $prefix ) {
1672                 // Find connections to explicit foreign domains still marked as in-use...
1673                 $domainsInUse = [];
1674                 $this->forEachOpenConnection( function ( IDatabase $conn ) use ( &$domainsInUse ) {
1675                         // Once reuseConnection() is called on a handle, its reference count goes from 1 to 0.
1676                         // Until then, it is still in use by the caller (explicitly or via DBConnRef scope).
1677                         if ( $conn->getLBInfo( 'foreignPoolRefCount' ) > 0 ) {
1678                                 $domainsInUse[] = $conn->getDomainID();
1679                         }
1680                 } );
1681
1682                 // Do not switch connections to explicit foreign domains unless marked as safe
1683                 if ( $domainsInUse ) {
1684                         $domains = implode( ', ', $domainsInUse );
1685                         throw new DBUnexpectedError( null,
1686                                 "Foreign domain connections are still in use ($domains)." );
1687                 }
1688
1689                 $this->localDomain = new DatabaseDomain(
1690                         $this->localDomain->getDatabase(),
1691                         null,
1692                         $prefix
1693                 );
1694
1695                 $this->forEachOpenConnection( function ( IDatabase $db ) use ( $prefix ) {
1696                         $db->tablePrefix( $prefix );
1697                 } );
1698         }
1699
1700         /**
1701          * Make PHP ignore user aborts/disconnects until the returned
1702          * value leaves scope. This returns null and does nothing in CLI mode.
1703          *
1704          * @return ScopedCallback|null
1705          */
1706         final protected function getScopedPHPBehaviorForCommit() {
1707                 if ( PHP_SAPI != 'cli' ) { // https://bugs.php.net/bug.php?id=47540
1708                         $old = ignore_user_abort( true ); // avoid half-finished operations
1709                         return new ScopedCallback( function () use ( $old ) {
1710                                 ignore_user_abort( $old );
1711                         } );
1712                 }
1713
1714                 return null;
1715         }
1716
1717         function __destruct() {
1718                 // Avoid connection leaks for sanity
1719                 $this->disable();
1720         }
1721 }
1722
1723 class_alias( LoadBalancer::class, 'LoadBalancer' );