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  */
  22 namespace Wikimedia\Rdbms;
  23
  24 use Psr\Log\LoggerInterface;
  25 use Psr\Log\NullLogger;
  26 use Wikimedia\ScopedCallback;
  27 use BagOStuff;
  28 use EmptyBagOStuff;
  29 use WANObjectCache;
  30 use ArrayUtils;
  31 use InvalidArgumentException;
  32 use RuntimeException;
  33 use Exception;
  34
  35 /**
  36  * Database connection, tracking, load balancing, and transaction manager for a cluster
  37  *
  38  * @ingroup Database
  39  */
  40 class LoadBalancer implements ILoadBalancer {
  41         /** @var array[] Map of (server index => server config array) */
  42         private $mServers;
  43         /** @var Database[][][] Map of (connection category => server index => IDatabase[]) */
  44         private $mConns;
  45         /** @var float[] Map of (server index => weight) */
  46         private $mLoads;
  47         /** @var array[] Map of (group => server index => weight) */
  48         private $mGroupLoads;
  49         /** @var bool Whether to disregard replica DB lag as a factor in replica DB selection */
  50         private $mAllowLagged;
  51         /** @var int Seconds to spend waiting on replica DB lag to resolve */
  52         private $mWaitTimeout;
  53         /** @var array The LoadMonitor configuration */
  54         private $loadMonitorConfig;
  55         /** @var array[] $aliases Map of (table => (dbname, schema, prefix) map) */
  56         private $tableAliases = [];
  57
  58         /** @var ILoadMonitor */
  59         private $loadMonitor;
  60         /** @var ChronologyProtector|null */
  61         private $chronProt;
  62         /** @var BagOStuff */
  63         private $srvCache;
  64         /** @var WANObjectCache */
  65         private $wanCache;
  66         /** @var object|string Class name or object With profileIn/profileOut methods */
  67         protected $profiler;
  68         /** @var TransactionProfiler */
  69         protected $trxProfiler;
  70         /** @var LoggerInterface */
  71         protected $replLogger;
  72         /** @var LoggerInterface */
  73         protected $connLogger;
  74         /** @var LoggerInterface */
  75         protected $queryLogger;
  76         /** @var LoggerInterface */
  77         protected $perfLogger;
  78
  79         /** @var Database DB connection object that caused a problem */
  80         private $errorConnection;
  81         /** @var int The generic (not query grouped) replica DB index (of $mServers) */
  82         private $mReadIndex;
  83         /** @var bool|DBMasterPos False if not set */
  84         private $mWaitForPos;
  85         /** @var bool Whether the generic reader fell back to a lagged replica DB */
  86         private $laggedReplicaMode = false;
  87         /** @var bool Whether the generic reader fell back to a lagged replica DB */
  88         private $allReplicasDownMode = false;
  89         /** @var string The last DB selection or connection error */
  90         private $mLastError = 'Unknown error';
  91         /** @var string|bool Reason the LB is read-only or false if not */
  92         private $readOnlyReason = false;
  93         /** @var int Total connections opened */
  94         private $connsOpened = 0;
  95         /** @var string|bool String if a requested DBO_TRX transaction round is active */
  96         private $trxRoundId = false;
  97         /** @var array[] Map of (name => callable) */
  98         private $trxRecurringCallbacks = [];
  99         /** @var DatabaseDomain Local Domain ID and default for selectDB() calls */
 100         private $localDomain;
 101         /** @var string Alternate ID string for the domain instead of DatabaseDomain::getId() */
 102         private $localDomainIdAlias;
 103         /** @var string Current server name */
 104         private $host;
 105         /** @var bool Whether this PHP instance is for a CLI script */
 106         protected $cliMode;
 107         /** @var string Agent name for query profiling */
 108         protected $agent;
 109
 110         /** @var callable Exception logger */
 111         private $errorLogger;
 112
 113         /** @var bool */
 114         private $disabled = false;
 115         /** @var bool */
 116         private $chronProtInitialized = false;
 117         /** @var int */
 118         private $maxLag = self::MAX_LAG_DEFAULT;
 119
 120         /** @var int Warn when this many connection are held */
 121         const CONN_HELD_WARN_THRESHOLD = 10;
 122
 123         /** @var int Default 'maxLag' when unspecified */
 124         const MAX_LAG_DEFAULT = 10;
 125         /** @var int Seconds to cache master server read-only status */
 126         const TTL_CACHE_READONLY = 5;
 127
 128         const KEY_LOCAL = 'local';
 129         const KEY_FOREIGN_FREE = 'foreignFree';
 130         const KEY_FOREIGN_INUSE = 'foreignInUse';
 131
 132         const KEY_LOCAL_NOROUND = 'localAutoCommit';
 133         const KEY_FOREIGN_FREE_NOROUND = 'foreignFreeAutoCommit';
 134         const KEY_FOREIGN_INUSE_NOROUND = 'foreignInUseAutoCommit';
 135
 136         public function __construct( array $params ) {
 137                 if ( !isset( $params['servers'] ) ) {
 138                         throw new InvalidArgumentException( __CLASS__ . ': missing servers parameter' );
 139                 }
 140                 $this->mServers = $params['servers'];
 141                 foreach ( $this->mServers as $i => $server ) {
 142                         if ( $i == 0 ) {
 143                                 $this->mServers[$i]['master'] = true;
 144                         } else {
 145                                 $this->mServers[$i]['replica'] = true;
 146                         }
 147                 }
 148
 149                 $localDomain = isset( $params['localDomain'] )
 150                         ? DatabaseDomain::newFromId( $params['localDomain'] )
 151                         : DatabaseDomain::newUnspecified();
 152                 $this->setLocalDomain( $localDomain );
 153
 154                 $this->mWaitTimeout = isset( $params['waitTimeout'] ) ? $params['waitTimeout'] : 10;
 155
 156                 $this->mReadIndex = -1;
 157                 $this->mConns = [
 158                         // Connection were transaction rounds may be applied
 159                         self::KEY_LOCAL => [],
 160                         self::KEY_FOREIGN_INUSE => [],
 161                         self::KEY_FOREIGN_FREE => [],
 162                         // Auto-committing counterpart connections that ignore transaction rounds
 163                         self::KEY_LOCAL_NOROUND => [],
 164                         self::KEY_FOREIGN_INUSE_NOROUND => [],
 165                         self::KEY_FOREIGN_FREE_NOROUND => []
 166                 ];
 167                 $this->mLoads = [];
 168                 $this->mWaitForPos = false;
 169                 $this->mAllowLagged = false;
 170
 171                 if ( isset( $params['readOnlyReason'] ) && is_string( $params['readOnlyReason'] ) ) {
 172                         $this->readOnlyReason = $params['readOnlyReason'];
 173                 }
 174
 175                 if ( isset( $params['maxLag'] ) ) {
 176                         $this->maxLag = $params['maxLag'];
 177                 }
 178
 179                 if ( isset( $params['loadMonitor'] ) ) {
 180                         $this->loadMonitorConfig = $params['loadMonitor'];
 181                 } else {
 182                         $this->loadMonitorConfig = [ 'class' => 'LoadMonitorNull' ];
 183                 }
 184                 $this->loadMonitorConfig += [ 'lagWarnThreshold' => $this->maxLag ];
 185
 186                 foreach ( $params['servers'] as $i => $server ) {
 187                         $this->mLoads[$i] = $server['load'];
 188                         if ( isset( $server['groupLoads'] ) ) {
 189                                 foreach ( $server['groupLoads'] as $group => $ratio ) {
 190                                         if ( !isset( $this->mGroupLoads[$group] ) ) {
 191                                                 $this->mGroupLoads[$group] = [];
 192                                         }
 193                                         $this->mGroupLoads[$group][$i] = $ratio;
 194                                 }
 195                         }
 196                 }
 197
 198                 if ( isset( $params['srvCache'] ) ) {
 199                         $this->srvCache = $params['srvCache'];
 200                 } else {
 201                         $this->srvCache = new EmptyBagOStuff();
 202                 }
 203                 if ( isset( $params['wanCache'] ) ) {
 204                         $this->wanCache = $params['wanCache'];
 205                 } else {
 206                         $this->wanCache = WANObjectCache::newEmpty();
 207                 }
 208                 $this->profiler = isset( $params['profiler'] ) ? $params['profiler'] : null;
 209                 if ( isset( $params['trxProfiler'] ) ) {
 210                         $this->trxProfiler = $params['trxProfiler'];
 211                 } else {
 212                         $this->trxProfiler = new TransactionProfiler();
 213                 }
 214
 215                 $this->errorLogger = isset( $params['errorLogger'] )
 216                         ? $params['errorLogger']
 217                         : function ( Exception $e ) {
 218                                 trigger_error( get_class( $e ) . ': ' . $e->getMessage(), E_USER_WARNING );
 219                         };
 220
 221                 foreach ( [ 'replLogger', 'connLogger', 'queryLogger', 'perfLogger' ] as $key ) {
 222                         $this->$key = isset( $params[$key] ) ? $params[$key] : new NullLogger();
 223                 }
 224
 225                 $this->host = isset( $params['hostname'] )
 226                         ? $params['hostname']
 227                         : ( gethostname() ?: 'unknown' );
 228                 $this->cliMode = isset( $params['cliMode'] )
 229                         ? $params['cliMode']
 230                         : ( PHP_SAPI === 'cli' || PHP_SAPI === 'phpdbg' );
 231                 $this->agent = isset( $params['agent'] ) ? $params['agent'] : '';
 232
 233                 if ( isset( $params['chronologyProtector'] ) ) {
 234                         $this->chronProt = $params['chronologyProtector'];
 235                 }
 236         }
 237
 238         /**
 239          * Get the local (and default) database domain ID of connection handles
 240          *
 241          * @see DatabaseDomain
 242          * @return string Database domain ID; this specifies DB name, schema, and table prefix
 243          * @since 1.31
 244          */
 245         public function getLocalDomainID() {
 246                 return $this->localDomain->getId();
 247         }
 248
 249         /**
 250          * Get a LoadMonitor instance
 251          *
 252          * @return ILoadMonitor
 253          */
 254         private function getLoadMonitor() {
 255                 if ( !isset( $this->loadMonitor ) ) {
 256                         $compat = [
 257                                 'LoadMonitor' => LoadMonitor::class,
 258                                 'LoadMonitorNull' => LoadMonitorNull::class,
 259                                 'LoadMonitorMySQL' => LoadMonitorMySQL::class,
 260                         ];
 261
 262                         $class = $this->loadMonitorConfig['class'];
 263                         if ( isset( $compat[$class] ) ) {
 264                                 $class = $compat[$class];
 265                         }
 266
 267                         $this->loadMonitor = new $class(
 268                                 $this, $this->srvCache, $this->wanCache, $this->loadMonitorConfig );
 269                         $this->loadMonitor->setLogger( $this->replLogger );
 270                 }
 271
 272                 return $this->loadMonitor;
 273         }
 274
 275         /**
 276          * @param array $loads
 277          * @param bool|string $domain Domain to get non-lagged for
 278          * @param int $maxLag Restrict the maximum allowed lag to this many seconds
 279          * @return bool|int|string
 280          */
 281         private function getRandomNonLagged( array $loads, $domain = false, $maxLag = INF ) {
 282                 $lags = $this->getLagTimes( $domain );
 283
 284                 # Unset excessively lagged servers
 285                 foreach ( $lags as $i => $lag ) {
 286                         if ( $i != 0 ) {
 287                                 # How much lag this server nominally is allowed to have
 288                                 $maxServerLag = isset( $this->mServers[$i]['max lag'] )
 289                                         ? $this->mServers[$i]['max lag']
 290                                         : $this->maxLag; // default
 291                                 # Constrain that futher by $maxLag argument
 292                                 $maxServerLag = min( $maxServerLag, $maxLag );
 293
 294                                 $host = $this->getServerName( $i );
 295                                 if ( $lag === false && !is_infinite( $maxServerLag ) ) {
 296                                         $this->replLogger->error(
 297                                                 "Server {host} is not replicating?", [ 'host' => $host ] );
 298                                         unset( $loads[$i] );
 299                                 } elseif ( $lag > $maxServerLag ) {
 300                                         $this->replLogger->info(
 301                                                 "Server {host} has {lag} seconds of lag (>= {maxlag})",
 302                                                 [ 'host' => $host, 'lag' => $lag, 'maxlag' => $maxServerLag ]
 303                                         );
 304                                         unset( $loads[$i] );
 305                                 }
 306                         }
 307                 }
 308
 309                 # Find out if all the replica DBs with non-zero load are lagged
 310                 $sum = 0;
 311                 foreach ( $loads as $load ) {
 312                         $sum += $load;
 313                 }
 314                 if ( $sum == 0 ) {
 315                         # No appropriate DB servers except maybe the master and some replica DBs with zero load
 316                         # Do NOT use the master
 317                         # Instead, this function will return false, triggering read-only mode,
 318                         # and a lagged replica DB will be used instead.
 319                         return false;
 320                 }
 321
 322                 if ( count( $loads ) == 0 ) {
 323                         return false;
 324                 }
 325
 326                 # Return a random representative of the remainder
 327                 return ArrayUtils::pickRandom( $loads );
 328         }
 329
 330         public function getReaderIndex( $group = false, $domain = false ) {
 331                 if ( count( $this->mServers ) == 1 ) {
 332                         // Skip the load balancing if there's only one server
 333                         return $this->getWriterIndex();
 334                 } elseif ( $group === false && $this->mReadIndex >= 0 ) {
 335                         // Shortcut if the generic reader index was already cached
 336                         return $this->mReadIndex;
 337                 }
 338
 339                 if ( $group !== false ) {
 340                         // Use the server weight array for this load group
 341                         if ( isset( $this->mGroupLoads[$group] ) ) {
 342                                 $loads = $this->mGroupLoads[$group];
 343                         } else {
 344                                 // No loads for this group, return false and the caller can use some other group
 345                                 $this->connLogger->info( __METHOD__ . ": no loads for group $group" );
 346
 347                                 return false;
 348                         }
 349                 } else {
 350                         // Use the generic load group
 351                         $loads = $this->mLoads;
 352                 }
 353
 354                 // Scale the configured load ratios according to each server's load and state
 355                 $this->getLoadMonitor()->scaleLoads( $loads, $domain );
 356
 357                 // Pick a server to use, accounting for weights, load, lag, and mWaitForPos
 358                 list( $i, $laggedReplicaMode ) = $this->pickReaderIndex( $loads, $domain );
 359                 if ( $i === false ) {
 360                         // Replica DB connection unsuccessful
 361                         return false;
 362                 }
 363
 364                 if ( $this->mWaitForPos && $i != $this->getWriterIndex() ) {
 365                         // Before any data queries are run, wait for the server to catch up to the
 366                         // specified position. This is used to improve session consistency. Note that
 367                         // when LoadBalancer::waitFor() sets mWaitForPos, the waiting triggers here,
 368                         // so update laggedReplicaMode as needed for consistency.
 369                         if ( !$this->doWait( $i ) ) {
 370                                 $laggedReplicaMode = true;
 371                         }
 372                 }
 373
 374                 if ( $this->mReadIndex <= 0 && $this->mLoads[$i] > 0 && $group === false ) {
 375                         // Cache the generic reader index for future ungrouped DB_REPLICA handles
 376                         $this->mReadIndex = $i;
 377                         // Record if the generic reader index is in "lagged replica DB" mode
 378                         if ( $laggedReplicaMode ) {
 379                                 $this->laggedReplicaMode = true;
 380                         }
 381                 }
 382
 383                 $serverName = $this->getServerName( $i );
 384                 $this->connLogger->debug( __METHOD__ . ": using server $serverName for group '$group'" );
 385
 386                 return $i;
 387         }
 388
 389         /**
 390          * @param array $loads List of server weights
 391          * @param string|bool $domain
 392          * @return array (reader index, lagged replica mode) or false on failure
 393          */
 394         private function pickReaderIndex( array $loads, $domain = false ) {
 395                 if ( !count( $loads ) ) {
 396                         throw new InvalidArgumentException( "Empty server array given to LoadBalancer" );
 397                 }
 398
 399                 /** @var int|bool $i Index of selected server */
 400                 $i = false;
 401                 /** @var bool $laggedReplicaMode Whether server is considered lagged */
 402                 $laggedReplicaMode = false;
 403
 404                 // Quickly look through the available servers for a server that meets criteria...
 405                 $currentLoads = $loads;
 406                 while ( count( $currentLoads ) ) {
 407                         if ( $this->mAllowLagged || $laggedReplicaMode ) {
 408                                 $i = ArrayUtils::pickRandom( $currentLoads );
 409                         } else {
 410                                 $i = false;
 411                                 if ( $this->mWaitForPos && $this->mWaitForPos->asOfTime() ) {
 412                                         // ChronologyProtecter sets mWaitForPos for session consistency.
 413                                         // This triggers doWait() after connect, so it's especially good to
 414                                         // avoid lagged servers so as to avoid excessive delay in that method.
 415                                         $ago = microtime( true ) - $this->mWaitForPos->asOfTime();
 416                                         // Aim for <= 1 second of waiting (being too picky can backfire)
 417                                         $i = $this->getRandomNonLagged( $currentLoads, $domain, $ago + 1 );
 418                                 }
 419                                 if ( $i === false ) {
 420                                         // Any server with less lag than it's 'max lag' param is preferable
 421                                         $i = $this->getRandomNonLagged( $currentLoads, $domain );
 422                                 }
 423                                 if ( $i === false && count( $currentLoads ) != 0 ) {
 424                                         // All replica DBs lagged. Switch to read-only mode
 425                                         $this->replLogger->error( "All replica DBs lagged. Switch to read-only mode" );
 426                                         $i = ArrayUtils::pickRandom( $currentLoads );
 427                                         $laggedReplicaMode = true;
 428                                 }
 429                         }
 430
 431                         if ( $i === false ) {
 432                                 // pickRandom() returned false.
 433                                 // This is permanent and means the configuration or the load monitor
 434                                 // wants us to return false.
 435                                 $this->connLogger->debug( __METHOD__ . ": pickRandom() returned false" );
 436
 437                                 return [ false, false ];
 438                         }
 439
 440                         $serverName = $this->getServerName( $i );
 441                         $this->connLogger->debug( __METHOD__ . ": Using reader #$i: $serverName..." );
 442
 443                         $conn = $this->openConnection( $i, $domain );
 444                         if ( !$conn ) {
 445                                 $this->connLogger->warning( __METHOD__ . ": Failed connecting to $i/$domain" );
 446                                 unset( $currentLoads[$i] ); // avoid this server next iteration
 447                                 $i = false;
 448                                 continue;
 449                         }
 450
 451                         // Decrement reference counter, we are finished with this connection.
 452                         // It will be incremented for the caller later.
 453                         if ( $domain !== false ) {
 454                                 $this->reuseConnection( $conn );
 455                         }
 456
 457                         // Return this server
 458                         break;
 459                 }
 460
 461                 // If all servers were down, quit now
 462                 if ( !count( $currentLoads ) ) {
 463                         $this->connLogger->error( "All servers down" );
 464                 }
 465
 466                 return [ $i, $laggedReplicaMode ];
 467         }
 468
 469         public function waitFor( $pos ) {
 470                 $oldPos = $this->mWaitForPos;
 471                 try {
 472                         $this->mWaitForPos = $pos;
 473                         // If a generic reader connection was already established, then wait now
 474                         $i = $this->mReadIndex;
 475                         if ( $i > 0 ) {
 476                                 if ( !$this->doWait( $i ) ) {
 477                                         $this->laggedReplicaMode = true;
 478                                 }
 479                         }
 480                 } finally {
 481                         // Restore the older position if it was higher since this is used for lag-protection
 482                         $this->setWaitForPositionIfHigher( $oldPos );
 483                 }
 484         }
 485
 486         public function waitForOne( $pos, $timeout = null ) {
 487                 $oldPos = $this->mWaitForPos;
 488                 try {
 489                         $this->mWaitForPos = $pos;
 490
 491                         $i = $this->mReadIndex;
 492                         if ( $i <= 0 ) {
 493                                 // Pick a generic replica DB if there isn't one yet
 494                                 $readLoads = $this->mLoads;
 495                                 unset( $readLoads[$this->getWriterIndex()] ); // replica DBs only
 496                                 $readLoads = array_filter( $readLoads ); // with non-zero load
 497                                 $i = ArrayUtils::pickRandom( $readLoads );
 498                         }
 499
 500                         if ( $i > 0 ) {
 501                                 $ok = $this->doWait( $i, true, $timeout );
 502                         } else {
 503                                 $ok = true; // no applicable loads
 504                         }
 505                 } finally {
 506                         # Restore the old position, as this is not used for lag-protection but for throttling
 507                         $this->mWaitForPos = $oldPos;
 508                 }
 509
 510                 return $ok;
 511         }
 512
 513         public function waitForAll( $pos, $timeout = null ) {
 514                 $oldPos = $this->mWaitForPos;
 515                 try {
 516                         $this->mWaitForPos = $pos;
 517                         $serverCount = count( $this->mServers );
 518
 519                         $ok = true;
 520                         for ( $i = 1; $i < $serverCount; $i++ ) {
 521                                 if ( $this->mLoads[$i] > 0 ) {
 522                                         $ok = $this->doWait( $i, true, $timeout ) && $ok;
 523                                 }
 524                         }
 525                 } finally {
 526                         # Restore the old position, as this is not used for lag-protection but for throttling
 527                         $this->mWaitForPos = $oldPos;
 528                 }
 529
 530                 return $ok;
 531         }
 532
 533         /**
 534          * @param DBMasterPos|bool $pos
 535          */
 536         private function setWaitForPositionIfHigher( $pos ) {
 537                 if ( !$pos ) {
 538                         return;
 539                 }
 540
 541                 if ( !$this->mWaitForPos || $pos->hasReached( $this->mWaitForPos ) ) {
 542                         $this->mWaitForPos = $pos;
 543                 }
 544         }
 545
 546         /**
 547          * @param int $i
 548          * @return IDatabase|bool
 549          */
 550         public function getAnyOpenConnection( $i ) {
 551                 foreach ( $this->mConns as $connsByServer ) {
 552                         if ( !empty( $connsByServer[$i] ) ) {
 553                                 /** @var IDatabase[] $serverConns */
 554                                 $serverConns = $connsByServer[$i];
 555
 556                                 return reset( $serverConns );
 557                         }
 558                 }
 559
 560                 return false;
 561         }
 562
 563         /**
 564          * Wait for a given replica DB to catch up to the master pos stored in $this
 565          * @param int $index Server index
 566          * @param bool $open Check the server even if a new connection has to be made
 567          * @param int $timeout Max seconds to wait; default is mWaitTimeout
 568          * @return bool
 569          */
 570         protected function doWait( $index, $open = false, $timeout = null ) {
 571                 $close = false; // close the connection afterwards
 572
 573                 // Check if we already know that the DB has reached this point
 574                 $server = $this->getServerName( $index );
 575                 $key = $this->srvCache->makeGlobalKey( __CLASS__, 'last-known-pos', $server, 'v1' );
 576                 /** @var DBMasterPos $knownReachedPos */
 577                 $knownReachedPos = $this->srvCache->get( $key );
 578                 if (
 579                         $knownReachedPos instanceof DBMasterPos &&
 580                         $knownReachedPos->hasReached( $this->mWaitForPos )
 581                 ) {
 582                         $this->replLogger->debug( __METHOD__ .
 583                                 ': replica DB {dbserver} known to be caught up (pos >= $knownReachedPos).',
 584                                 [ 'dbserver' => $server ] );
 585                         return true;
 586                 }
 587
 588                 // Find a connection to wait on, creating one if needed and allowed
 589                 $conn = $this->getAnyOpenConnection( $index );
 590                 if ( !$conn ) {
 591                         if ( !$open ) {
 592                                 $this->replLogger->debug( __METHOD__ . ': no connection open for {dbserver}',
 593                                         [ 'dbserver' => $server ] );
 594
 595                                 return false;
 596                         } else {
 597                                 $conn = $this->openConnection( $index, self::DOMAIN_ANY );
 598                                 if ( !$conn ) {
 599                                         $this->replLogger->warning( __METHOD__ . ': failed to connect to {dbserver}',
 600                                                 [ 'dbserver' => $server ] );
 601
 602                                         return false;
 603                                 }
 604                                 // Avoid connection spam in waitForAll() when connections
 605                                 // are made just for the sake of doing this lag check.
 606                                 $close = true;
 607                         }
 608                 }
 609
 610                 $this->replLogger->info( __METHOD__ . ': Waiting for replica DB {dbserver} to catch up...',
 611                         [ 'dbserver' => $server ] );
 612                 $timeout = $timeout ?: $this->mWaitTimeout;
 613                 $result = $conn->masterPosWait( $this->mWaitForPos, $timeout );
 614
 615                 if ( $result == -1 || is_null( $result ) ) {
 616                         // Timed out waiting for replica DB, use master instead
 617                         $this->replLogger->warning(
 618                                 __METHOD__ . ': Timed out waiting on {host} pos {pos}',
 619                                 [ 'host' => $server, 'pos' => $this->mWaitForPos ]
 620                         );
 621                         $ok = false;
 622                 } else {
 623                         $this->replLogger->info( __METHOD__ . ": Done" );
 624                         $ok = true;
 625                         // Remember that the DB reached this point
 626                         $this->srvCache->set( $key, $this->mWaitForPos, BagOStuff::TTL_DAY );
 627                 }
 628
 629                 if ( $close ) {
 630                         $this->closeConnection( $conn );
 631                 }
 632
 633                 return $ok;
 634         }
 635
 636         public function getConnection( $i, $groups = [], $domain = false, $flags = 0 ) {
 637                 if ( $i === null || $i === false ) {
 638                         throw new InvalidArgumentException( 'Attempt to call ' . __METHOD__ .
 639                                 ' with invalid server index' );
 640                 }
 641
 642                 if ( $this->localDomain->equals( $domain ) || $domain === $this->localDomainIdAlias ) {
 643                         $domain = false; // local connection requested
 644                 }
 645
 646                 $groups = ( $groups === false || $groups === [] )
 647                         ? [ false ] // check one "group": the generic pool
 648                         : (array)$groups;
 649
 650                 $masterOnly = ( $i == self::DB_MASTER || $i == $this->getWriterIndex() );
 651                 $oldConnsOpened = $this->connsOpened; // connections open now
 652
 653                 if ( $i == self::DB_MASTER ) {
 654                         $i = $this->getWriterIndex();
 655                 } else {
 656                         # Try to find an available server in any the query groups (in order)
 657                         foreach ( $groups as $group ) {
 658                                 $groupIndex = $this->getReaderIndex( $group, $domain );
 659                                 if ( $groupIndex !== false ) {
 660                                         $i = $groupIndex;
 661                                         break;
 662                                 }
 663                         }
 664                 }
 665
 666                 # Operation-based index
 667                 if ( $i == self::DB_REPLICA ) {
 668                         $this->mLastError = 'Unknown error'; // reset error string
 669                         # Try the general server pool if $groups are unavailable.
 670                         $i = ( $groups === [ false ] )
 671                                 ? false // don't bother with this if that is what was tried above
 672                                 : $this->getReaderIndex( false, $domain );
 673                         # Couldn't find a working server in getReaderIndex()?
 674                         if ( $i === false ) {
 675                                 $this->mLastError = 'No working replica DB server: ' . $this->mLastError;
 676                                 // Throw an exception
 677                                 $this->reportConnectionError();
 678                                 return null; // not reached
 679                         }
 680                 }
 681
 682                 # Now we have an explicit index into the servers array
 683                 $conn = $this->openConnection( $i, $domain, $flags );
 684                 if ( !$conn ) {
 685                         // Throw an exception
 686                         $this->reportConnectionError();
 687                         return null; // not reached
 688                 }
 689
 690                 # Profile any new connections that happen
 691                 if ( $this->connsOpened > $oldConnsOpened ) {
 692                         $host = $conn->getServer();
 693                         $dbname = $conn->getDBname();
 694                         $this->trxProfiler->recordConnection( $host, $dbname, $masterOnly );
 695                 }
 696
 697                 if ( $masterOnly ) {
 698                         # Make master-requested DB handles inherit any read-only mode setting
 699                         $conn->setLBInfo( 'readOnlyReason', $this->getReadOnlyReason( $domain, $conn ) );
 700                 }
 701
 702                 return $conn;
 703         }
 704
 705         public function reuseConnection( $conn ) {
 706                 $serverIndex = $conn->getLBInfo( 'serverIndex' );
 707                 $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 708                 if ( $serverIndex === null || $refCount === null ) {
 709                         /**
 710                          * This can happen in code like:
 711                          *   foreach ( $dbs as $db ) {
 712                          *     $conn = $lb->getConnection( $lb::DB_REPLICA, [], $db );
 713                          *     ...
 714                          *     $lb->reuseConnection( $conn );
 715                          *   }
 716                          * When a connection to the local DB is opened in this way, reuseConnection()
 717                          * should be ignored
 718                          */
 719                         return;
 720                 } elseif ( $conn instanceof DBConnRef ) {
 721                         // DBConnRef already handles calling reuseConnection() and only passes the live
 722                         // Database instance to this method. Any caller passing in a DBConnRef is broken.
 723                         $this->connLogger->error( __METHOD__ . ": got DBConnRef instance.\n" .
 724                                 ( new RuntimeException() )->getTraceAsString() );
 725
 726                         return;
 727                 }
 728
 729                 if ( $this->disabled ) {
 730                         return; // DBConnRef handle probably survived longer than the LoadBalancer
 731                 }
 732
 733                 if ( $conn->getLBInfo( 'autoCommitOnly' ) ) {
 734                         $connFreeKey = self::KEY_FOREIGN_FREE_NOROUND;
 735                         $connInUseKey = self::KEY_FOREIGN_INUSE_NOROUND;
 736                 } else {
 737                         $connFreeKey = self::KEY_FOREIGN_FREE;
 738                         $connInUseKey = self::KEY_FOREIGN_INUSE;
 739                 }
 740
 741                 $domain = $conn->getDomainID();
 742                 if ( !isset( $this->mConns[$connInUseKey][$serverIndex][$domain] ) ) {
 743                         throw new InvalidArgumentException( __METHOD__ .
 744                                 ": connection $serverIndex/$domain not found; it may have already been freed." );
 745                 } elseif ( $this->mConns[$connInUseKey][$serverIndex][$domain] !== $conn ) {
 746                         throw new InvalidArgumentException( __METHOD__ .
 747                                 ": connection $serverIndex/$domain mismatched; it may have already been freed." );
 748                 }
 749
 750                 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
 751                 if ( $refCount <= 0 ) {
 752                         $this->mConns[$connFreeKey][$serverIndex][$domain] = $conn;
 753                         unset( $this->mConns[$connInUseKey][$serverIndex][$domain] );
 754                         if ( !$this->mConns[$connInUseKey][$serverIndex] ) {
 755                                 unset( $this->mConns[$connInUseKey][$serverIndex] ); // clean up
 756                         }
 757                         $this->connLogger->debug( __METHOD__ . ": freed connection $serverIndex/$domain" );
 758                 } else {
 759                         $this->connLogger->debug( __METHOD__ .
 760                                 ": reference count for $serverIndex/$domain reduced to $refCount" );
 761                 }
 762         }
 763
 764         public function getConnectionRef( $db, $groups = [], $domain = false, $flags = 0 ) {
 765                 $domain = ( $domain !== false ) ? $domain : $this->localDomain;
 766
 767                 return new DBConnRef( $this, $this->getConnection( $db, $groups, $domain, $flags ) );
 768         }
 769
 770         public function getLazyConnectionRef( $db, $groups = [], $domain = false, $flags = 0 ) {
 771                 $domain = ( $domain !== false ) ? $domain : $this->localDomain;
 772
 773                 return new DBConnRef( $this, [ $db, $groups, $domain, $flags ] );
 774         }
 775
 776         public function getMaintenanceConnectionRef( $db, $groups = [], $domain = false, $flags = 0 ) {
 777                 $domain = ( $domain !== false ) ? $domain : $this->localDomain;
 778
 779                 return new MaintainableDBConnRef(
 780                         $this, $this->getConnection( $db, $groups, $domain, $flags ) );
 781         }
 782
 783         public function openConnection( $i, $domain = false, $flags = 0 ) {
 784                 if ( $this->localDomain->equals( $domain ) || $domain === $this->localDomainIdAlias ) {
 785                         $domain = false; // local connection requested
 786                 }
 787
 788                 if ( !$this->chronProtInitialized && $this->chronProt ) {
 789                         $this->connLogger->debug( __METHOD__ . ': calling initLB() before first connection.' );
 790                         // Load CP positions before connecting so that doWait() triggers later if needed
 791                         $this->chronProtInitialized = true;
 792                         $this->chronProt->initLB( $this );
 793                 }
 794
 795                 // Check if an auto-commit connection is being requested. If so, it will not reuse the
 796                 // main set of DB connections but rather its own pool since:
 797                 // a) those are usually set to implicitly use transaction rounds via DBO_TRX
 798                 // b) those must support the use of explicit transaction rounds via beginMasterChanges()
 799                 $autoCommit = ( ( $flags & self::CONN_TRX_AUTO ) == self::CONN_TRX_AUTO );
 800
 801                 if ( $domain !== false ) {
 802                         // Connection is to a foreign domain
 803                         $conn = $this->openForeignConnection( $i, $domain, $flags );
 804                 } else {
 805                         // Connection is to the local domain
 806                         $connKey = $autoCommit ? self::KEY_LOCAL_NOROUND : self::KEY_LOCAL;
 807                         if ( isset( $this->mConns[$connKey][$i][0] ) ) {
 808                                 $conn = $this->mConns[$connKey][$i][0];
 809                         } else {
 810                                 if ( !isset( $this->mServers[$i] ) || !is_array( $this->mServers[$i] ) ) {
 811                                         throw new InvalidArgumentException( "No server with index '$i'." );
 812                                 }
 813                                 // Open a new connection
 814                                 $server = $this->mServers[$i];
 815                                 $server['serverIndex'] = $i;
 816                                 $server['autoCommitOnly'] = $autoCommit;
 817                                 if ( $this->localDomain->getDatabase() !== null ) {
 818                                         // Use the local domain table prefix if the local domain is specified
 819                                         $server['tablePrefix'] = $this->localDomain->getTablePrefix();
 820                                 }
 821                                 $conn = $this->reallyOpenConnection( $server, $this->localDomain->getDatabase() );
 822                                 $host = $this->getServerName( $i );
 823                                 if ( $conn->isOpen() ) {
 824                                         $this->connLogger->debug( "Connected to database $i at '$host'." );
 825                                         $this->mConns[$connKey][$i][0] = $conn;
 826                                 } else {
 827                                         $this->connLogger->warning( "Failed to connect to database $i at '$host'." );
 828                                         $this->errorConnection = $conn;
 829                                         $conn = false;
 830                                 }
 831                         }
 832                 }
 833
 834                 if ( $conn instanceof IDatabase && !$conn->isOpen() ) {
 835                         // Connection was made but later unrecoverably lost for some reason.
 836                         // Do not return a handle that will just throw exceptions on use,
 837                         // but let the calling code (e.g. getReaderIndex) try another server.
 838                         // See DatabaseMyslBase::ping() for how this can happen.
 839                         $this->errorConnection = $conn;
 840                         $conn = false;
 841                 }
 842
 843                 if ( $autoCommit && $conn instanceof IDatabase ) {
 844                         $conn->clearFlag( $conn::DBO_TRX ); // auto-commit mode
 845                 }
 846
 847                 return $conn;
 848         }
 849
 850         /**
 851          * Open a connection to a foreign DB, or return one if it is already open.
 852          *
 853          * Increments a reference count on the returned connection which locks the
 854          * connection to the requested domain. This reference count can be
 855          * decremented by calling reuseConnection().
 856          *
 857          * If a connection is open to the appropriate server already, but with the wrong
 858          * database, it will be switched to the right database and returned, as long as
 859          * it has been freed first with reuseConnection().
 860          *
 861          * On error, returns false, and the connection which caused the
 862          * error will be available via $this->errorConnection.
 863          *
 864          * @note If disable() was called on this LoadBalancer, this method will throw a DBAccessError.
 865          *
 866          * @param int $i Server index
 867          * @param string $domain Domain ID to open
 868          * @param int $flags Class CONN_* constant bitfield
 869          * @return Database
 870          */
 871         private function openForeignConnection( $i, $domain, $flags = 0 ) {
 872                 $domainInstance = DatabaseDomain::newFromId( $domain );
 873                 $dbName = $domainInstance->getDatabase();
 874                 $prefix = $domainInstance->getTablePrefix();
 875                 $autoCommit = ( ( $flags & self::CONN_TRX_AUTO ) == self::CONN_TRX_AUTO );
 876
 877                 if ( $autoCommit ) {
 878                         $connFreeKey = self::KEY_FOREIGN_FREE_NOROUND;
 879                         $connInUseKey = self::KEY_FOREIGN_INUSE_NOROUND;
 880                 } else {
 881                         $connFreeKey = self::KEY_FOREIGN_FREE;
 882                         $connInUseKey = self::KEY_FOREIGN_INUSE;
 883                 }
 884
 885                 if ( isset( $this->mConns[$connInUseKey][$i][$domain] ) ) {
 886                         // Reuse an in-use connection for the same domain
 887                         $conn = $this->mConns[$connInUseKey][$i][$domain];
 888                         $this->connLogger->debug( __METHOD__ . ": reusing connection $i/$domain" );
 889                 } elseif ( isset( $this->mConns[$connFreeKey][$i][$domain] ) ) {
 890                         // Reuse a free connection for the same domain
 891                         $conn = $this->mConns[$connFreeKey][$i][$domain];
 892                         unset( $this->mConns[$connFreeKey][$i][$domain] );
 893                         $this->mConns[$connInUseKey][$i][$domain] = $conn;
 894                         $this->connLogger->debug( __METHOD__ . ": reusing free connection $i/$domain" );
 895                 } elseif ( !empty( $this->mConns[$connFreeKey][$i] ) ) {
 896                         // Reuse a free connection from another domain
 897                         $conn = reset( $this->mConns[$connFreeKey][$i] );
 898                         $oldDomain = key( $this->mConns[$connFreeKey][$i] );
 899                         if ( strlen( $dbName ) && !$conn->selectDB( $dbName ) ) {
 900                                 $this->mLastError = "Error selecting database '$dbName' on server " .
 901                                         $conn->getServer() . " from client host {$this->host}";
 902                                 $this->errorConnection = $conn;
 903                                 $conn = false;
 904                         } else {
 905                                 $conn->tablePrefix( $prefix );
 906                                 unset( $this->mConns[$connFreeKey][$i][$oldDomain] );
 907                                 // Note that if $domain is an empty string, getDomainID() might not match it
 908                                 $this->mConns[$connInUseKey][$i][$conn->getDomainId()] = $conn;
 909                                 $this->connLogger->debug( __METHOD__ .
 910                                         ": reusing free connection from $oldDomain for $domain" );
 911                         }
 912                 } else {
 913                         if ( !isset( $this->mServers[$i] ) || !is_array( $this->mServers[$i] ) ) {
 914                                 throw new InvalidArgumentException( "No server with index '$i'." );
 915                         }
 916                         // Open a new connection
 917                         $server = $this->mServers[$i];
 918                         $server['serverIndex'] = $i;
 919                         $server['foreignPoolRefCount'] = 0;
 920                         $server['foreign'] = true;
 921                         $server['autoCommitOnly'] = $autoCommit;
 922                         $conn = $this->reallyOpenConnection( $server, $dbName );
 923                         if ( !$conn->isOpen() ) {
 924                                 $this->connLogger->warning( __METHOD__ . ": connection error for $i/$domain" );
 925                                 $this->errorConnection = $conn;
 926                                 $conn = false;
 927                         } else {
 928                                 $conn->tablePrefix( $prefix ); // as specified
 929                                 // Note that if $domain is an empty string, getDomainID() might not match it
 930                                 $this->mConns[$connInUseKey][$i][$conn->getDomainID()] = $conn;
 931                                 $this->connLogger->debug( __METHOD__ . ": opened new connection for $i/$domain" );
 932                         }
 933                 }
 934
 935                 // Increment reference count
 936                 if ( $conn instanceof IDatabase ) {
 937                         $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 938                         $conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
 939                 }
 940
 941                 return $conn;
 942         }
 943
 944         /**
 945          * Test if the specified index represents an open connection
 946          *
 947          * @param int $index Server index
 948          * @access private
 949          * @return bool
 950          */
 951         private function isOpen( $index ) {
 952                 if ( !is_int( $index ) ) {
 953                         return false;
 954                 }
 955
 956                 return (bool)$this->getAnyOpenConnection( $index );
 957         }
 958
 959         /**
 960          * Open a new network connection to a server (uncached)
 961          *
 962          * Returns a Database object whether or not the connection was successful.
 963          *
 964          * @param array $server
 965          * @param string|null $dbNameOverride Use "" to not select any database
 966          * @return Database
 967          * @throws DBAccessError
 968          * @throws InvalidArgumentException
 969          */
 970         protected function reallyOpenConnection( array $server, $dbNameOverride ) {
 971                 if ( $this->disabled ) {
 972                         throw new DBAccessError();
 973                 }
 974
 975                 if ( $dbNameOverride !== null ) {
 976                         $server['dbname'] = $dbNameOverride;
 977                 }
 978
 979                 // Let the handle know what the cluster master is (e.g. "db1052")
 980                 $masterName = $this->getServerName( $this->getWriterIndex() );
 981                 $server['clusterMasterHost'] = $masterName;
 982
 983                 // Log when many connection are made on requests
 984                 if ( ++$this->connsOpened >= self::CONN_HELD_WARN_THRESHOLD ) {
 985                         $this->perfLogger->warning( __METHOD__ . ": " .
 986                                 "{$this->connsOpened}+ connections made (master=$masterName)" );
 987                 }
 988
 989                 $server['srvCache'] = $this->srvCache;
 990                 // Set loggers and profilers
 991                 $server['connLogger'] = $this->connLogger;
 992                 $server['queryLogger'] = $this->queryLogger;
 993                 $server['errorLogger'] = $this->errorLogger;
 994                 $server['profiler'] = $this->profiler;
 995                 $server['trxProfiler'] = $this->trxProfiler;
 996                 // Use the same agent and PHP mode for all DB handles
 997                 $server['cliMode'] = $this->cliMode;
 998                 $server['agent'] = $this->agent;
 999                 // Use DBO_DEFAULT flags by default for LoadBalancer managed databases. Assume that the
1000                 // application calls LoadBalancer::commitMasterChanges() before the PHP script completes.
1001                 $server['flags'] = isset( $server['flags'] ) ? $server['flags'] : IDatabase::DBO_DEFAULT;
1002
1003                 // Create a live connection object
1004                 try {
1005                         $db = Database::factory( $server['type'], $server );
1006                 } catch ( DBConnectionError $e ) {
1007                         // FIXME: This is probably the ugliest thing I have ever done to
1008                         // PHP. I'm half-expecting it to segfault, just out of disgust. -- TS
1009                         $db = $e->db;
1010                 }
1011
1012                 $db->setLBInfo( $server );
1013                 $db->setLazyMasterHandle(
1014                         $this->getLazyConnectionRef( self::DB_MASTER, [], $db->getDomainID() )
1015                 );
1016                 $db->setTableAliases( $this->tableAliases );
1017
1018                 if ( $server['serverIndex'] === $this->getWriterIndex() ) {
1019                         if ( $this->trxRoundId !== false ) {
1020                                 $this->applyTransactionRoundFlags( $db );
1021                         }
1022                         foreach ( $this->trxRecurringCallbacks as $name => $callback ) {
1023                                 $db->setTransactionListener( $name, $callback );
1024                         }
1025                 }
1026
1027                 return $db;
1028         }
1029
1030         /**
1031          * @throws DBConnectionError
1032          */
1033         private function reportConnectionError() {
1034                 $conn = $this->errorConnection; // the connection which caused the error
1035                 $context = [
1036                         'method' => __METHOD__,
1037                         'last_error' => $this->mLastError,
1038                 ];
1039
1040                 if ( $conn instanceof IDatabase ) {
1041                         $context['db_server'] = $conn->getServer();
1042                         $this->connLogger->warning(
1043                                 "Connection error: {last_error} ({db_server})",
1044                                 $context
1045                         );
1046
1047                         // throws DBConnectionError
1048                         $conn->reportConnectionError( "{$this->mLastError} ({$context['db_server']})" );
1049                 } else {
1050                         // No last connection, probably due to all servers being too busy
1051                         $this->connLogger->error(
1052                                 "LB failure with no last connection. Connection error: {last_error}",
1053                                 $context
1054                         );
1055
1056                         // If all servers were busy, mLastError will contain something sensible
1057                         throw new DBConnectionError( null, $this->mLastError );
1058                 }
1059         }
1060
1061         public function getWriterIndex() {
1062                 return 0;
1063         }
1064
1065         public function haveIndex( $i ) {
1066                 return array_key_exists( $i, $this->mServers );
1067         }
1068
1069         public function isNonZeroLoad( $i ) {
1070                 return array_key_exists( $i, $this->mServers ) && $this->mLoads[$i] != 0;
1071         }
1072
1073         public function getServerCount() {
1074                 return count( $this->mServers );
1075         }
1076
1077         public function getServerName( $i ) {
1078                 if ( isset( $this->mServers[$i]['hostName'] ) ) {
1079                         $name = $this->mServers[$i]['hostName'];
1080                 } elseif ( isset( $this->mServers[$i]['host'] ) ) {
1081                         $name = $this->mServers[$i]['host'];
1082                 } else {
1083                         $name = '';
1084                 }
1085
1086                 return ( $name != '' ) ? $name : 'localhost';
1087         }
1088
1089         public function getServerType( $i ) {
1090                 return isset( $this->mServers[$i]['type'] ) ? $this->mServers[$i]['type'] : 'unknown';
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 {host} pos {pos}';
1640                                 $this->replLogger->warning( $msg,
1641                                         [ 'host' => $conn->getServer(), 'pos' => $pos ] );
1642                                 $ok = false;
1643                         } else {
1644                                 $this->replLogger->info( __METHOD__ . ': Done' );
1645                                 $ok = true;
1646                         }
1647                 } else {
1648                         $ok = false; // something is misconfigured
1649                         $this->replLogger->error( 'Could not get master pos for {host}',
1650                                 [ 'host' => $conn->getServer() ] );
1651                 }
1652
1653                 return $ok;
1654         }
1655
1656         public function setTransactionListener( $name, callable $callback = null ) {
1657                 if ( $callback ) {
1658                         $this->trxRecurringCallbacks[$name] = $callback;
1659                 } else {
1660                         unset( $this->trxRecurringCallbacks[$name] );
1661                 }
1662                 $this->forEachOpenMasterConnection(
1663                         function ( IDatabase $conn ) use ( $name, $callback ) {
1664                                 $conn->setTransactionListener( $name, $callback );
1665                         }
1666                 );
1667         }
1668
1669         public function setTableAliases( array $aliases ) {
1670                 $this->tableAliases = $aliases;
1671         }
1672
1673         public function setDomainPrefix( $prefix ) {
1674                 // Find connections to explicit foreign domains still marked as in-use...
1675                 $domainsInUse = [];
1676                 $this->forEachOpenConnection( function ( IDatabase $conn ) use ( &$domainsInUse ) {
1677                         // Once reuseConnection() is called on a handle, its reference count goes from 1 to 0.
1678                         // Until then, it is still in use by the caller (explicitly or via DBConnRef scope).
1679                         if ( $conn->getLBInfo( 'foreignPoolRefCount' ) > 0 ) {
1680                                 $domainsInUse[] = $conn->getDomainID();
1681                         }
1682                 } );
1683
1684                 // Do not switch connections to explicit foreign domains unless marked as safe
1685                 if ( $domainsInUse ) {
1686                         $domains = implode( ', ', $domainsInUse );
1687                         throw new DBUnexpectedError( null,
1688                                 "Foreign domain connections are still in use ($domains)." );
1689                 }
1690
1691                 $oldDomain = $this->localDomain->getId();
1692                 $this->setLocalDomain( new DatabaseDomain(
1693                         $this->localDomain->getDatabase(),
1694                         null,
1695                         $prefix
1696                 ) );
1697
1698                 $this->forEachOpenConnection( function ( IDatabase $db ) use ( $prefix, $oldDomain ) {
1699                         if ( !$db->getLBInfo( 'foreign' ) ) {
1700                                 $db->tablePrefix( $prefix );
1701                         }
1702                 } );
1703         }
1704
1705         /**
1706          * @param DatabaseDomain $domain
1707          */
1708         private function setLocalDomain( DatabaseDomain $domain ) {
1709                 $this->localDomain = $domain;
1710                 // In case a caller assumes that the domain ID is simply <db>-<prefix>, which is almost
1711                 // always true, gracefully handle the case when they fail to account for escaping.
1712                 if ( $this->localDomain->getTablePrefix() != '' ) {
1713                         $this->localDomainIdAlias =
1714                                 $this->localDomain->getDatabase() . '-' . $this->localDomain->getTablePrefix();
1715                 } else {
1716                         $this->localDomainIdAlias = $this->localDomain->getDatabase();
1717                 }
1718         }
1719
1720         /**
1721          * Make PHP ignore user aborts/disconnects until the returned
1722          * value leaves scope. This returns null and does nothing in CLI mode.
1723          *
1724          * @return ScopedCallback|null
1725          */
1726         final protected function getScopedPHPBehaviorForCommit() {
1727                 if ( PHP_SAPI != 'cli' ) { // https://bugs.php.net/bug.php?id=47540
1728                         $old = ignore_user_abort( true ); // avoid half-finished operations
1729                         return new ScopedCallback( function () use ( $old ) {
1730                                 ignore_user_abort( $old );
1731                         } );
1732                 }
1733
1734                 return null;
1735         }
1736
1737         function __destruct() {
1738                 // Avoid connection leaks for sanity
1739                 $this->disable();
1740         }
1741 }
1742
1743 class_alias( LoadBalancer::class, 'LoadBalancer' );