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 UnexpectedValueException;
  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 ILoadMonitor */
  43         private $loadMonitor;
  44         /** @var callable|null Callback to run before the first connection attempt */
  45         private $chronologyCallback;
  46         /** @var BagOStuff */
  47         private $srvCache;
  48         /** @var WANObjectCache */
  49         private $wanCache;
  50         /** @var mixed Class name or object With profileIn/profileOut methods */
  51         private $profiler;
  52         /** @var TransactionProfiler */
  53         private $trxProfiler;
  54         /** @var LoggerInterface */
  55         private $replLogger;
  56         /** @var LoggerInterface */
  57         private $connLogger;
  58         /** @var LoggerInterface */
  59         private $queryLogger;
  60         /** @var LoggerInterface */
  61         private $perfLogger;
  62         /** @var callable Exception logger */
  63         private $errorLogger;
  64         /** @var callable Deprecation logger */
  65         private $deprecationLogger;
  66
  67         /** @var DatabaseDomain Local DB domain ID and default for selectDB() calls */
  68         private $localDomain;
  69
  70         /** @var Database[][][] Map of (connection category => server index => IDatabase[]) */
  71         private $conns;
  72
  73         /** @var array[] Map of (server index => server config array) */
  74         private $servers;
  75         /** @var float[] Map of (server index => weight) */
  76         private $genericLoads;
  77         /** @var array[] Map of (group => server index => weight) */
  78         private $groupLoads;
  79         /** @var bool Whether to disregard replica DB lag as a factor in replica DB selection */
  80         private $allowLagged;
  81         /** @var int Seconds to spend waiting on replica DB lag to resolve */
  82         private $waitTimeout;
  83         /** @var array The LoadMonitor configuration */
  84         private $loadMonitorConfig;
  85         /** @var string Alternate local DB domain instead of DatabaseDomain::getId() */
  86         private $localDomainIdAlias;
  87         /** @var int */
  88         private $maxLag;
  89
  90         /** @var string Current server name */
  91         private $hostname;
  92         /** @var bool Whether this PHP instance is for a CLI script */
  93         private $cliMode;
  94         /** @var string Agent name for query profiling */
  95         private $agent;
  96
  97         /** @var array[] $aliases Map of (table => (dbname, schema, prefix) map) */
  98         private $tableAliases = [];
  99         /** @var string[] Map of (index alias => index) */
 100         private $indexAliases = [];
 101         /** @var array[] Map of (name => callable) */
 102         private $trxRecurringCallbacks = [];
 103
 104         /** @var Database DB connection object that caused a problem */
 105         private $errorConnection;
 106         /** @var int The generic (not query grouped) replica DB index */
 107         private $genericReadIndex = -1;
 108         /** @var bool|DBMasterPos False if not set */
 109         private $waitForPos;
 110         /** @var bool Whether the generic reader fell back to a lagged replica DB */
 111         private $laggedReplicaMode = false;
 112         /** @var bool Whether the generic reader fell back to a lagged replica DB */
 113         private $allReplicasDownMode = false;
 114         /** @var string The last DB selection or connection error */
 115         private $lastError = 'Unknown error';
 116         /** @var string|bool Reason the LB is read-only or false if not */
 117         private $readOnlyReason = false;
 118         /** @var int Total connections opened */
 119         private $connsOpened = 0;
 120         /** @var bool */
 121         private $disabled = false;
 122         /** @var bool Whether any connection has been attempted yet */
 123         private $connectionAttempted = false;
 124
 125         /** @var string|bool String if a requested DBO_TRX transaction round is active */
 126         private $trxRoundId = false;
 127         /** @var string Stage of the current transaction round in the transaction round life-cycle */
 128         private $trxRoundStage = self::ROUND_CURSORY;
 129
 130         /** @var string|null */
 131         private $defaultGroup = null;
 132
 133         /** @var int Warn when this many connection are held */
 134         const CONN_HELD_WARN_THRESHOLD = 10;
 135
 136         /** @var int Default 'maxLag' when unspecified */
 137         const MAX_LAG_DEFAULT = 6;
 138         /** @var int Default 'waitTimeout' when unspecified */
 139         const MAX_WAIT_DEFAULT = 10;
 140         /** @var int Seconds to cache master server read-only status */
 141         const TTL_CACHE_READONLY = 5;
 142
 143         const KEY_LOCAL = 'local';
 144         const KEY_FOREIGN_FREE = 'foreignFree';
 145         const KEY_FOREIGN_INUSE = 'foreignInUse';
 146
 147         const KEY_LOCAL_NOROUND = 'localAutoCommit';
 148         const KEY_FOREIGN_FREE_NOROUND = 'foreignFreeAutoCommit';
 149         const KEY_FOREIGN_INUSE_NOROUND = 'foreignInUseAutoCommit';
 150
 151         /** @var string Transaction round, explicit or implicit, has not finished writing */
 152         const ROUND_CURSORY = 'cursory';
 153         /** @var string Transaction round writes are complete and ready for pre-commit checks */
 154         const ROUND_FINALIZED = 'finalized';
 155         /** @var string Transaction round passed final pre-commit checks */
 156         const ROUND_APPROVED = 'approved';
 157         /** @var string Transaction round was committed and post-commit callbacks must be run */
 158         const ROUND_COMMIT_CALLBACKS = 'commit-callbacks';
 159         /** @var string Transaction round was rolled back and post-rollback callbacks must be run */
 160         const ROUND_ROLLBACK_CALLBACKS = 'rollback-callbacks';
 161         /** @var string Transaction round encountered an error */
 162         const ROUND_ERROR = 'error';
 163
 164         public function __construct( array $params ) {
 165                 if ( !isset( $params['servers'] ) ) {
 166                         throw new InvalidArgumentException( __CLASS__ . ': missing "servers" parameter' );
 167                 }
 168                 $this->servers = $params['servers'];
 169                 foreach ( $this->servers as $i => $server ) {
 170                         if ( $i == 0 ) {
 171                                 $this->servers[$i]['master'] = true;
 172                         } else {
 173                                 $this->servers[$i]['replica'] = true;
 174                         }
 175                 }
 176
 177                 $localDomain = isset( $params['localDomain'] )
 178                         ? DatabaseDomain::newFromId( $params['localDomain'] )
 179                         : DatabaseDomain::newUnspecified();
 180                 $this->setLocalDomain( $localDomain );
 181
 182                 $this->waitTimeout = $params['waitTimeout'] ?? self::MAX_WAIT_DEFAULT;
 183
 184                 $this->conns = [
 185                         // Connection were transaction rounds may be applied
 186                         self::KEY_LOCAL => [],
 187                         self::KEY_FOREIGN_INUSE => [],
 188                         self::KEY_FOREIGN_FREE => [],
 189                         // Auto-committing counterpart connections that ignore transaction rounds
 190                         self::KEY_LOCAL_NOROUND => [],
 191                         self::KEY_FOREIGN_INUSE_NOROUND => [],
 192                         self::KEY_FOREIGN_FREE_NOROUND => []
 193                 ];
 194                 $this->genericLoads = [];
 195                 $this->waitForPos = false;
 196                 $this->allowLagged = false;
 197
 198                 if ( isset( $params['readOnlyReason'] ) && is_string( $params['readOnlyReason'] ) ) {
 199                         $this->readOnlyReason = $params['readOnlyReason'];
 200                 }
 201
 202                 $this->maxLag = $params['maxLag'] ?? self::MAX_LAG_DEFAULT;
 203
 204                 $this->loadMonitorConfig = $params['loadMonitor'] ?? [ 'class' => 'LoadMonitorNull' ];
 205                 $this->loadMonitorConfig += [ 'lagWarnThreshold' => $this->maxLag ];
 206
 207                 foreach ( $params['servers'] as $i => $server ) {
 208                         $this->genericLoads[$i] = $server['load'];
 209                         if ( isset( $server['groupLoads'] ) ) {
 210                                 foreach ( $server['groupLoads'] as $group => $ratio ) {
 211                                         if ( !isset( $this->groupLoads[$group] ) ) {
 212                                                 $this->groupLoads[$group] = [];
 213                                         }
 214                                         $this->groupLoads[$group][$i] = $ratio;
 215                                 }
 216                         }
 217                 }
 218
 219                 $this->srvCache = $params['srvCache'] ?? new EmptyBagOStuff();
 220                 $this->wanCache = $params['wanCache'] ?? WANObjectCache::newEmpty();
 221                 $this->profiler = $params['profiler'] ?? null;
 222                 $this->trxProfiler = $params['trxProfiler'] ?? new TransactionProfiler();
 223
 224                 $this->errorLogger = $params['errorLogger'] ?? function ( Exception $e ) {
 225                         trigger_error( get_class( $e ) . ': ' . $e->getMessage(), E_USER_WARNING );
 226                 };
 227                 $this->deprecationLogger = $params['deprecationLogger'] ?? function ( $msg ) {
 228                         trigger_error( $msg, E_USER_DEPRECATED );
 229                 };
 230
 231                 foreach ( [ 'replLogger', 'connLogger', 'queryLogger', 'perfLogger' ] as $key ) {
 232                         $this->$key = $params[$key] ?? new NullLogger();
 233                 }
 234
 235                 $this->hostname = $params['hostname'] ?? ( gethostname() ?: 'unknown' );
 236                 $this->cliMode = $params['cliMode'] ?? ( PHP_SAPI === 'cli' || PHP_SAPI === 'phpdbg' );
 237                 $this->agent = $params['agent'] ?? '';
 238
 239                 if ( isset( $params['chronologyCallback'] ) ) {
 240                         $this->chronologyCallback = $params['chronologyCallback'];
 241                 }
 242
 243                 if ( isset( $params['roundStage'] ) ) {
 244                         if ( $params['roundStage'] === self::STAGE_POSTCOMMIT_CALLBACKS ) {
 245                                 $this->trxRoundStage = self::ROUND_COMMIT_CALLBACKS;
 246                         } elseif ( $params['roundStage'] === self::STAGE_POSTROLLBACK_CALLBACKS ) {
 247                                 $this->trxRoundStage = self::ROUND_ROLLBACK_CALLBACKS;
 248                         }
 249                 }
 250
 251                 $this->defaultGroup = $params['defaultGroup'] ?? null;
 252         }
 253
 254         public function getLocalDomainID() {
 255                 return $this->localDomain->getId();
 256         }
 257
 258         public function resolveDomainID( $domain ) {
 259                 if ( $domain === $this->localDomainIdAlias || $domain === false ) {
 260                         // Local connection requested via some backwards-compatibility domain alias
 261                         return $this->getLocalDomainID();
 262                 }
 263
 264                 return (string)$domain;
 265         }
 266
 267         /**
 268          * Get a LoadMonitor instance
 269          *
 270          * @return ILoadMonitor
 271          */
 272         private function getLoadMonitor() {
 273                 if ( !isset( $this->loadMonitor ) ) {
 274                         $compat = [
 275                                 'LoadMonitor' => LoadMonitor::class,
 276                                 'LoadMonitorNull' => LoadMonitorNull::class,
 277                                 'LoadMonitorMySQL' => LoadMonitorMySQL::class,
 278                         ];
 279
 280                         $class = $this->loadMonitorConfig['class'];
 281                         if ( isset( $compat[$class] ) ) {
 282                                 $class = $compat[$class];
 283                         }
 284
 285                         $this->loadMonitor = new $class(
 286                                 $this, $this->srvCache, $this->wanCache, $this->loadMonitorConfig );
 287                         $this->loadMonitor->setLogger( $this->replLogger );
 288                 }
 289
 290                 return $this->loadMonitor;
 291         }
 292
 293         /**
 294          * @param array $loads
 295          * @param bool|string $domain Domain to get non-lagged for
 296          * @param int $maxLag Restrict the maximum allowed lag to this many seconds
 297          * @return bool|int|string
 298          */
 299         private function getRandomNonLagged( array $loads, $domain = false, $maxLag = INF ) {
 300                 $lags = $this->getLagTimes( $domain );
 301
 302                 # Unset excessively lagged servers
 303                 foreach ( $lags as $i => $lag ) {
 304                         if ( $i != 0 ) {
 305                                 # How much lag this server nominally is allowed to have
 306                                 $maxServerLag = $this->servers[$i]['max lag'] ?? $this->maxLag; // default
 307                                 # Constrain that futher by $maxLag argument
 308                                 $maxServerLag = min( $maxServerLag, $maxLag );
 309
 310                                 $host = $this->getServerName( $i );
 311                                 if ( $lag === false && !is_infinite( $maxServerLag ) ) {
 312                                         $this->replLogger->debug(
 313                                                 __METHOD__ .
 314                                                 ": server {host} is not replicating?", [ 'host' => $host ] );
 315                                         unset( $loads[$i] );
 316                                 } elseif ( $lag > $maxServerLag ) {
 317                                         $this->replLogger->debug(
 318                                                 __METHOD__ .
 319                                                 ": server {host} has {lag} seconds of lag (>= {maxlag})",
 320                                                 [ 'host' => $host, 'lag' => $lag, 'maxlag' => $maxServerLag ]
 321                                         );
 322                                         unset( $loads[$i] );
 323                                 }
 324                         }
 325                 }
 326
 327                 # Find out if all the replica DBs with non-zero load are lagged
 328                 $sum = 0;
 329                 foreach ( $loads as $load ) {
 330                         $sum += $load;
 331                 }
 332                 if ( $sum == 0 ) {
 333                         # No appropriate DB servers except maybe the master and some replica DBs with zero load
 334                         # Do NOT use the master
 335                         # Instead, this function will return false, triggering read-only mode,
 336                         # and a lagged replica DB will be used instead.
 337                         return false;
 338                 }
 339
 340                 if ( count( $loads ) == 0 ) {
 341                         return false;
 342                 }
 343
 344                 # Return a random representative of the remainder
 345                 return ArrayUtils::pickRandom( $loads );
 346         }
 347
 348         /**
 349          * @param int $i
 350          * @param array $groups
 351          * @param string|bool $domain
 352          * @return int
 353          */
 354         private function getConnectionIndex( $i, $groups, $domain ) {
 355                 // Check one "group" per default: the generic pool
 356                 $defaultGroups = $this->defaultGroup ? [ $this->defaultGroup ] : [ false ];
 357
 358                 $groups = ( $groups === false || $groups === [] )
 359                         ? $defaultGroups
 360                         : (array)$groups;
 361
 362                 if ( $i == self::DB_MASTER ) {
 363                         $i = $this->getWriterIndex();
 364                 } elseif ( $i == self::DB_REPLICA ) {
 365                         # Try to find an available server in any the query groups (in order)
 366                         foreach ( $groups as $group ) {
 367                                 $groupIndex = $this->getReaderIndex( $group, $domain );
 368                                 if ( $groupIndex !== false ) {
 369                                         $i = $groupIndex;
 370                                         break;
 371                                 }
 372                         }
 373                 }
 374
 375                 # Operation-based index
 376                 if ( $i == self::DB_REPLICA ) {
 377                         $this->lastError = 'Unknown error'; // reset error string
 378                         # Try the general server pool if $groups are unavailable.
 379                         $i = ( $groups === [ false ] )
 380                                 ? false // don't bother with this if that is what was tried above
 381                                 : $this->getReaderIndex( false, $domain );
 382                         # Couldn't find a working server in getReaderIndex()?
 383                         if ( $i === false ) {
 384                                 $this->lastError = 'No working replica DB server: ' . $this->lastError;
 385                                 // Throw an exception
 386                                 $this->reportConnectionError();
 387                                 return null; // not reached
 388                         }
 389                 }
 390
 391                 return $i;
 392         }
 393
 394         public function getReaderIndex( $group = false, $domain = false ) {
 395                 if ( count( $this->servers ) == 1 ) {
 396                         // Skip the load balancing if there's only one server
 397                         return $this->getWriterIndex();
 398                 } elseif ( $group === false && $this->genericReadIndex >= 0 ) {
 399                         // A generic reader index was already selected and "waitForPos" was handled
 400                         return $this->genericReadIndex;
 401                 }
 402
 403                 if ( $group !== false ) {
 404                         // Use the server weight array for this load group
 405                         if ( isset( $this->groupLoads[$group] ) ) {
 406                                 $loads = $this->groupLoads[$group];
 407                         } else {
 408                                 // No loads for this group, return false and the caller can use some other group
 409                                 $this->connLogger->info( __METHOD__ . ": no loads for group $group" );
 410
 411                                 return false;
 412                         }
 413                 } else {
 414                         // Use the generic load group
 415                         $loads = $this->genericLoads;
 416                 }
 417
 418                 // Scale the configured load ratios according to each server's load and state
 419                 $this->getLoadMonitor()->scaleLoads( $loads, $domain );
 420
 421                 // Pick a server to use, accounting for weights, load, lag, and "waitForPos"
 422                 list( $i, $laggedReplicaMode ) = $this->pickReaderIndex( $loads, $domain );
 423                 if ( $i === false ) {
 424                         // DB connection unsuccessful
 425                         return false;
 426                 }
 427
 428                 // If data seen by queries is expected to reflect the transactions committed as of
 429                 // or after a given replication position then wait for the DB to apply those changes
 430                 if ( $this->waitForPos && $i != $this->getWriterIndex() && !$this->doWait( $i ) ) {
 431                         // Data will be outdated compared to what was expected
 432                         $laggedReplicaMode = true;
 433                 }
 434
 435                 if ( $this->genericReadIndex < 0 && $this->genericLoads[$i] > 0 && $group === false ) {
 436                         // Cache the generic (ungrouped) reader index for future DB_REPLICA handles
 437                         $this->genericReadIndex = $i;
 438                         // Record if the generic reader index is in "lagged replica DB" mode
 439                         $this->laggedReplicaMode = ( $laggedReplicaMode || $this->laggedReplicaMode );
 440                 }
 441
 442                 $serverName = $this->getServerName( $i );
 443                 $this->connLogger->debug( __METHOD__ . ": using server $serverName for group '$group'" );
 444
 445                 return $i;
 446         }
 447
 448         /**
 449          * @param array $loads List of server weights
 450          * @param string|bool $domain
 451          * @return array (reader index, lagged replica mode) or false on failure
 452          */
 453         private function pickReaderIndex( array $loads, $domain = false ) {
 454                 if ( $loads === [] ) {
 455                         throw new InvalidArgumentException( "Server configuration array is empty" );
 456                 }
 457
 458                 /** @var int|bool $i Index of selected server */
 459                 $i = false;
 460                 /** @var bool $laggedReplicaMode Whether server is considered lagged */
 461                 $laggedReplicaMode = false;
 462
 463                 // Quickly look through the available servers for a server that meets criteria...
 464                 $currentLoads = $loads;
 465                 while ( count( $currentLoads ) ) {
 466                         if ( $this->allowLagged || $laggedReplicaMode ) {
 467                                 $i = ArrayUtils::pickRandom( $currentLoads );
 468                         } else {
 469                                 $i = false;
 470                                 if ( $this->waitForPos && $this->waitForPos->asOfTime() ) {
 471                                         // "chronologyCallback" sets "waitForPos" for session consistency.
 472                                         // This triggers doWait() after connect, so it's especially good to
 473                                         // avoid lagged servers so as to avoid excessive delay in that method.
 474                                         $ago = microtime( true ) - $this->waitForPos->asOfTime();
 475                                         // Aim for <= 1 second of waiting (being too picky can backfire)
 476                                         $i = $this->getRandomNonLagged( $currentLoads, $domain, $ago + 1 );
 477                                 }
 478                                 if ( $i === false ) {
 479                                         // Any server with less lag than it's 'max lag' param is preferable
 480                                         $i = $this->getRandomNonLagged( $currentLoads, $domain );
 481                                 }
 482                                 if ( $i === false && count( $currentLoads ) != 0 ) {
 483                                         // All replica DBs lagged. Switch to read-only mode
 484                                         $this->replLogger->error(
 485                                                 __METHOD__ . ": all replica DBs lagged. Switch to read-only mode" );
 486                                         $i = ArrayUtils::pickRandom( $currentLoads );
 487                                         $laggedReplicaMode = true;
 488                                 }
 489                         }
 490
 491                         if ( $i === false ) {
 492                                 // pickRandom() returned false.
 493                                 // This is permanent and means the configuration or the load monitor
 494                                 // wants us to return false.
 495                                 $this->connLogger->debug( __METHOD__ . ": pickRandom() returned false" );
 496
 497                                 return [ false, false ];
 498                         }
 499
 500                         $serverName = $this->getServerName( $i );
 501                         $this->connLogger->debug( __METHOD__ . ": Using reader #$i: $serverName..." );
 502
 503                         $conn = $this->openConnection( $i, $domain );
 504                         if ( !$conn ) {
 505                                 $this->connLogger->warning( __METHOD__ . ": Failed connecting to $i/$domain" );
 506                                 unset( $currentLoads[$i] ); // avoid this server next iteration
 507                                 $i = false;
 508                                 continue;
 509                         }
 510
 511                         // Decrement reference counter, we are finished with this connection.
 512                         // It will be incremented for the caller later.
 513                         if ( $domain !== false ) {
 514                                 $this->reuseConnection( $conn );
 515                         }
 516
 517                         // Return this server
 518                         break;
 519                 }
 520
 521                 // If all servers were down, quit now
 522                 if ( $currentLoads === [] ) {
 523                         $this->connLogger->error( __METHOD__ . ": all servers down" );
 524                 }
 525
 526                 return [ $i, $laggedReplicaMode ];
 527         }
 528
 529         public function waitFor( $pos ) {
 530                 $oldPos = $this->waitForPos;
 531                 try {
 532                         $this->waitForPos = $pos;
 533                         // If a generic reader connection was already established, then wait now
 534                         if ( $this->genericReadIndex > 0 && !$this->doWait( $this->genericReadIndex ) ) {
 535                                 $this->laggedReplicaMode = true;
 536                         }
 537                         // Otherwise, wait until a connection is established in getReaderIndex()
 538                 } finally {
 539                         // Restore the older position if it was higher since this is used for lag-protection
 540                         $this->setWaitForPositionIfHigher( $oldPos );
 541                 }
 542         }
 543
 544         public function waitForOne( $pos, $timeout = null ) {
 545                 $oldPos = $this->waitForPos;
 546                 try {
 547                         $this->waitForPos = $pos;
 548
 549                         $i = $this->genericReadIndex;
 550                         if ( $i <= 0 ) {
 551                                 // Pick a generic replica DB if there isn't one yet
 552                                 $readLoads = $this->genericLoads;
 553                                 unset( $readLoads[$this->getWriterIndex()] ); // replica DBs only
 554                                 $readLoads = array_filter( $readLoads ); // with non-zero load
 555                                 $i = ArrayUtils::pickRandom( $readLoads );
 556                         }
 557
 558                         if ( $i > 0 ) {
 559                                 $ok = $this->doWait( $i, true, $timeout );
 560                         } else {
 561                                 $ok = true; // no applicable loads
 562                         }
 563                 } finally {
 564                         # Restore the old position, as this is not used for lag-protection but for throttling
 565                         $this->waitForPos = $oldPos;
 566                 }
 567
 568                 return $ok;
 569         }
 570
 571         public function waitForAll( $pos, $timeout = null ) {
 572                 $timeout = $timeout ?: $this->waitTimeout;
 573
 574                 $oldPos = $this->waitForPos;
 575                 try {
 576                         $this->waitForPos = $pos;
 577                         $serverCount = count( $this->servers );
 578
 579                         $ok = true;
 580                         for ( $i = 1; $i < $serverCount; $i++ ) {
 581                                 if ( $this->genericLoads[$i] > 0 ) {
 582                                         $start = microtime( true );
 583                                         $ok = $this->doWait( $i, true, $timeout ) && $ok;
 584                                         $timeout -= intval( microtime( true ) - $start );
 585                                         if ( $timeout <= 0 ) {
 586                                                 break; // timeout reached
 587                                         }
 588                                 }
 589                         }
 590                 } finally {
 591                         # Restore the old position, as this is not used for lag-protection but for throttling
 592                         $this->waitForPos = $oldPos;
 593                 }
 594
 595                 return $ok;
 596         }
 597
 598         /**
 599          * @param DBMasterPos|bool $pos
 600          */
 601         private function setWaitForPositionIfHigher( $pos ) {
 602                 if ( !$pos ) {
 603                         return;
 604                 }
 605
 606                 if ( !$this->waitForPos || $pos->hasReached( $this->waitForPos ) ) {
 607                         $this->waitForPos = $pos;
 608                 }
 609         }
 610
 611         public function getAnyOpenConnection( $i, $flags = 0 ) {
 612                 $i = ( $i === self::DB_MASTER ) ? $this->getWriterIndex() : $i;
 613                 $autocommit = ( ( $flags & self::CONN_TRX_AUTOCOMMIT ) == self::CONN_TRX_AUTOCOMMIT );
 614
 615                 foreach ( $this->conns as $connsByServer ) {
 616                         if ( $i === self::DB_REPLICA ) {
 617                                 $indexes = array_keys( $connsByServer );
 618                         } else {
 619                                 $indexes = isset( $connsByServer[$i] ) ? [ $i ] : [];
 620                         }
 621
 622                         foreach ( $indexes as $index ) {
 623                                 foreach ( $connsByServer[$index] as $conn ) {
 624                                         if ( !$conn->isOpen() ) {
 625                                                 continue; // some sort of error occured?
 626                                         }
 627                                         if ( !$autocommit || $conn->getLBInfo( 'autoCommitOnly' ) ) {
 628                                                 return $conn;
 629                                         }
 630                                 }
 631                         }
 632                 }
 633
 634                 return false;
 635         }
 636
 637         /**
 638          * Wait for a given replica DB to catch up to the master pos stored in $this
 639          * @param int $index Server index
 640          * @param bool $open Check the server even if a new connection has to be made
 641          * @param int|null $timeout Max seconds to wait; default is "waitTimeout" given to __construct()
 642          * @return bool
 643          */
 644         protected function doWait( $index, $open = false, $timeout = null ) {
 645                 $timeout = max( 1, intval( $timeout ?: $this->waitTimeout ) );
 646
 647                 // Check if we already know that the DB has reached this point
 648                 $server = $this->getServerName( $index );
 649                 $key = $this->srvCache->makeGlobalKey( __CLASS__, 'last-known-pos', $server, 'v1' );
 650                 /** @var DBMasterPos $knownReachedPos */
 651                 $knownReachedPos = $this->srvCache->get( $key );
 652                 if (
 653                         $knownReachedPos instanceof DBMasterPos &&
 654                         $knownReachedPos->hasReached( $this->waitForPos )
 655                 ) {
 656                         $this->replLogger->debug(
 657                                 __METHOD__ .
 658                                 ': replica DB {dbserver} known to be caught up (pos >= $knownReachedPos).',
 659                                 [ 'dbserver' => $server ]
 660                         );
 661                         return true;
 662                 }
 663
 664                 // Find a connection to wait on, creating one if needed and allowed
 665                 $close = false; // close the connection afterwards
 666                 $conn = $this->getAnyOpenConnection( $index );
 667                 if ( !$conn ) {
 668                         if ( !$open ) {
 669                                 $this->replLogger->debug(
 670                                         __METHOD__ . ': no connection open for {dbserver}',
 671                                         [ 'dbserver' => $server ]
 672                                 );
 673
 674                                 return false;
 675                         } else {
 676                                 $conn = $this->openConnection( $index, self::DOMAIN_ANY );
 677                                 if ( !$conn ) {
 678                                         $this->replLogger->warning(
 679                                                 __METHOD__ . ': failed to connect to {dbserver}',
 680                                                 [ 'dbserver' => $server ]
 681                                         );
 682
 683                                         return false;
 684                                 }
 685                                 // Avoid connection spam in waitForAll() when connections
 686                                 // are made just for the sake of doing this lag check.
 687                                 $close = true;
 688                         }
 689                 }
 690
 691                 $this->replLogger->info(
 692                         __METHOD__ .
 693                         ': waiting for replica DB {dbserver} to catch up...',
 694                         [ 'dbserver' => $server ]
 695                 );
 696
 697                 $result = $conn->masterPosWait( $this->waitForPos, $timeout );
 698
 699                 if ( $result === null ) {
 700                         $this->replLogger->warning(
 701                                 __METHOD__ . ': Errored out waiting on {host} pos {pos}',
 702                                 [
 703                                         'host' => $server,
 704                                         'pos' => $this->waitForPos,
 705                                         'trace' => ( new RuntimeException() )->getTraceAsString()
 706                                 ]
 707                         );
 708                         $ok = false;
 709                 } elseif ( $result == -1 ) {
 710                         $this->replLogger->warning(
 711                                 __METHOD__ . ': Timed out waiting on {host} pos {pos}',
 712                                 [
 713                                         'host' => $server,
 714                                         'pos' => $this->waitForPos,
 715                                         'trace' => ( new RuntimeException() )->getTraceAsString()
 716                                 ]
 717                         );
 718                         $ok = false;
 719                 } else {
 720                         $this->replLogger->debug( __METHOD__ . ": done waiting" );
 721                         $ok = true;
 722                         // Remember that the DB reached this point
 723                         $this->srvCache->set( $key, $this->waitForPos, BagOStuff::TTL_DAY );
 724                 }
 725
 726                 if ( $close ) {
 727                         $this->closeConnection( $conn );
 728                 }
 729
 730                 return $ok;
 731         }
 732
 733         public function getConnection( $i, $groups = [], $domain = false, $flags = 0 ) {
 734                 if ( $i === null || $i === false ) {
 735                         throw new InvalidArgumentException( "Cannot connect without a server index" );
 736                 }
 737
 738                 $domain = $this->resolveDomainID( $domain );
 739                 $masterOnly = ( $i == self::DB_MASTER || $i == $this->getWriterIndex() );
 740
 741                 if ( ( $flags & self::CONN_TRX_AUTOCOMMIT ) === self::CONN_TRX_AUTOCOMMIT ) {
 742                         // Assuming all servers are of the same type (or similar), which is overwhelmingly
 743                         // the case, use the master server information to get the attributes. The information
 744                         // for $i cannot be used since it might be DB_REPLICA, which might require connection
 745                         // attempts in order to be resolved into a real server index.
 746                         $attributes = $this->getServerAttributes( $this->getWriterIndex() );
 747                         if ( $attributes[Database::ATTR_DB_LEVEL_LOCKING] ) {
 748                                 // Callers sometimes want to (a) escape REPEATABLE-READ stateness without locking
 749                                 // rows (e.g. FOR UPDATE) or (b) make small commits during a larger transactions
 750                                 // to reduce lock contention. None of these apply for sqlite and using separate
 751                                 // connections just causes self-deadlocks.
 752                                 $flags &= ~self::CONN_TRX_AUTOCOMMIT;
 753                                 $this->connLogger->info( __METHOD__ .
 754                                         ': ignoring CONN_TRX_AUTOCOMMIT to avoid deadlocks.' );
 755                         }
 756                 }
 757
 758                 // Number of connections made before getting the server index and handle
 759                 $priorConnectionsMade = $this->connsOpened;
 760                 // Decide which server to use (might trigger new connections)
 761                 $serverIndex = $this->getConnectionIndex( $i, $groups, $domain );
 762                 // Get an open connection to that server (might trigger a new connection)
 763                 $conn = $this->openConnection( $serverIndex, $domain, $flags );
 764                 if ( !$conn ) {
 765                         $this->reportConnectionError();
 766                         return null; // unreachable due to exception
 767                 }
 768
 769                 // Profile any new connections caused by this method
 770                 if ( $this->connsOpened > $priorConnectionsMade ) {
 771                         $host = $conn->getServer();
 772                         $dbname = $conn->getDBname();
 773                         $this->trxProfiler->recordConnection( $host, $dbname, $masterOnly );
 774                 }
 775
 776                 if ( $serverIndex == $this->getWriterIndex() ) {
 777                         // If the load balancer is read-only, perhaps due to replication lag, then master
 778                         // DB handles will reflect that. Note that Database::assertIsWritableMaster() takes
 779                         // care of replica DB handles whereas getReadOnlyReason() would cause infinite loops.
 780                         $conn->setLBInfo( 'readOnlyReason', $this->getReadOnlyReason( $domain, $conn ) );
 781                 }
 782
 783                 return $conn;
 784         }
 785
 786         public function reuseConnection( IDatabase $conn ) {
 787                 $serverIndex = $conn->getLBInfo( 'serverIndex' );
 788                 $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 789                 if ( $serverIndex === null || $refCount === null ) {
 790                         /**
 791                          * This can happen in code like:
 792                          *   foreach ( $dbs as $db ) {
 793                          *     $conn = $lb->getConnection( $lb::DB_REPLICA, [], $db );
 794                          *     ...
 795                          *     $lb->reuseConnection( $conn );
 796                          *   }
 797                          * When a connection to the local DB is opened in this way, reuseConnection()
 798                          * should be ignored
 799                          */
 800                         return;
 801                 } elseif ( $conn instanceof DBConnRef ) {
 802                         // DBConnRef already handles calling reuseConnection() and only passes the live
 803                         // Database instance to this method. Any caller passing in a DBConnRef is broken.
 804                         $this->connLogger->error(
 805                                 __METHOD__ . ": got DBConnRef instance.\n" .
 806                                 ( new RuntimeException() )->getTraceAsString() );
 807
 808                         return;
 809                 }
 810
 811                 if ( $this->disabled ) {
 812                         return; // DBConnRef handle probably survived longer than the LoadBalancer
 813                 }
 814
 815                 if ( $conn->getLBInfo( 'autoCommitOnly' ) ) {
 816                         $connFreeKey = self::KEY_FOREIGN_FREE_NOROUND;
 817                         $connInUseKey = self::KEY_FOREIGN_INUSE_NOROUND;
 818                 } else {
 819                         $connFreeKey = self::KEY_FOREIGN_FREE;
 820                         $connInUseKey = self::KEY_FOREIGN_INUSE;
 821                 }
 822
 823                 $domain = $conn->getDomainID();
 824                 if ( !isset( $this->conns[$connInUseKey][$serverIndex][$domain] ) ) {
 825                         throw new InvalidArgumentException(
 826                                 "Connection $serverIndex/$domain not found; it may have already been freed" );
 827                 } elseif ( $this->conns[$connInUseKey][$serverIndex][$domain] !== $conn ) {
 828                         throw new InvalidArgumentException(
 829                                 "Connection $serverIndex/$domain mismatched; it may have already been freed" );
 830                 }
 831
 832                 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
 833                 if ( $refCount <= 0 ) {
 834                         $this->conns[$connFreeKey][$serverIndex][$domain] = $conn;
 835                         unset( $this->conns[$connInUseKey][$serverIndex][$domain] );
 836                         if ( !$this->conns[$connInUseKey][$serverIndex] ) {
 837                                 unset( $this->conns[$connInUseKey][$serverIndex] ); // clean up
 838                         }
 839                         $this->connLogger->debug( __METHOD__ . ": freed connection $serverIndex/$domain" );
 840                 } else {
 841                         $this->connLogger->debug( __METHOD__ .
 842                                 ": reference count for $serverIndex/$domain reduced to $refCount" );
 843                 }
 844         }
 845
 846         public function getConnectionRef( $i, $groups = [], $domain = false, $flags = 0 ) {
 847                 $domain = $this->resolveDomainID( $domain );
 848                 $role = $this->getRoleFromIndex( $i );
 849
 850                 return new DBConnRef( $this, $this->getConnection( $i, $groups, $domain, $flags ), $role );
 851         }
 852
 853         public function getLazyConnectionRef( $i, $groups = [], $domain = false, $flags = 0 ) {
 854                 $domain = $this->resolveDomainID( $domain );
 855                 $role = $this->getRoleFromIndex( $i );
 856
 857                 return new DBConnRef( $this, [ $i, $groups, $domain, $flags ], $role );
 858         }
 859
 860         public function getMaintenanceConnectionRef( $i, $groups = [], $domain = false, $flags = 0 ) {
 861                 $domain = $this->resolveDomainID( $domain );
 862                 $role = $this->getRoleFromIndex( $i );
 863
 864                 return new MaintainableDBConnRef(
 865                         $this, $this->getConnection( $i, $groups, $domain, $flags ), $role );
 866         }
 867
 868         /**
 869          * @param int $i Server index or DB_MASTER/DB_REPLICA
 870          * @return int One of DB_MASTER/DB_REPLICA
 871          */
 872         private function getRoleFromIndex( $i ) {
 873                 return ( $i === self::DB_MASTER || $i === $this->getWriterIndex() )
 874                         ? self::DB_MASTER
 875                         : self::DB_REPLICA;
 876         }
 877
 878         public function openConnection( $i, $domain = false, $flags = 0 ) {
 879                 $domain = $this->resolveDomainID( $domain );
 880
 881                 if ( !$this->connectionAttempted && $this->chronologyCallback ) {
 882                         // Load any "waitFor" positions before connecting so that doWait() is triggered
 883                         $this->connLogger->debug( __METHOD__ . ': calling initLB() before first connection.' );
 884                         $this->connectionAttempted = true;
 885                         ( $this->chronologyCallback )( $this );
 886                 }
 887
 888                 $conn = $this->localDomain->equals( $domain )
 889                         ? $this->openLocalConnection( $i, $flags )
 890                         : $this->openForeignConnection( $i, $domain, $flags );
 891
 892                 if ( $conn instanceof IDatabase && !$conn->isOpen() ) {
 893                         // Connection was made but later unrecoverably lost for some reason.
 894                         // Do not return a handle that will just throw exceptions on use,
 895                         // but let the calling code (e.g. getReaderIndex) try another server.
 896                         $this->errorConnection = $conn;
 897                         $conn = false;
 898                 }
 899
 900                 if (
 901                         $conn instanceof IDatabase &&
 902                         ( ( $flags & self::CONN_TRX_AUTOCOMMIT ) == self::CONN_TRX_AUTOCOMMIT )
 903                 ) {
 904                         if ( $conn->trxLevel() ) { // sanity
 905                                 throw new DBUnexpectedError(
 906                                         $conn,
 907                                         'Handle requested with CONN_TRX_AUTOCOMMIT yet it has a transaction'
 908                                 );
 909                         }
 910
 911                         $conn->clearFlag( $conn::DBO_TRX ); // auto-commit mode
 912                 }
 913
 914                 return $conn;
 915         }
 916
 917         /**
 918          * Open a connection to a local DB, or return one if it is already open.
 919          *
 920          * On error, returns false, and the connection which caused the
 921          * error will be available via $this->errorConnection.
 922          *
 923          * @note If disable() was called on this LoadBalancer, this method will throw a DBAccessError.
 924          *
 925          * @param int $i Server index
 926          * @param int $flags Class CONN_* constant bitfield
 927          * @return Database
 928          */
 929         private function openLocalConnection( $i, $flags = 0 ) {
 930                 // Connection handles required to be in auto-commit mode use a separate connection
 931                 // pool since the main pool is effected by implicit and explicit transaction rounds
 932                 $autoCommit = ( ( $flags & self::CONN_TRX_AUTOCOMMIT ) == self::CONN_TRX_AUTOCOMMIT );
 933
 934                 $connKey = $autoCommit ? self::KEY_LOCAL_NOROUND : self::KEY_LOCAL;
 935                 if ( isset( $this->conns[$connKey][$i][0] ) ) {
 936                         $conn = $this->conns[$connKey][$i][0];
 937                 } else {
 938                         if ( !isset( $this->servers[$i] ) || !is_array( $this->servers[$i] ) ) {
 939                                 throw new InvalidArgumentException( "No server with index '$i'" );
 940                         }
 941                         // Open a new connection
 942                         $server = $this->servers[$i];
 943                         $server['serverIndex'] = $i;
 944                         $server['autoCommitOnly'] = $autoCommit;
 945                         $conn = $this->reallyOpenConnection( $server, $this->localDomain );
 946                         $host = $this->getServerName( $i );
 947                         if ( $conn->isOpen() ) {
 948                                 $this->connLogger->debug(
 949                                         __METHOD__ . ": connected to database $i at '$host'." );
 950                                 $this->conns[$connKey][$i][0] = $conn;
 951                         } else {
 952                                 $this->connLogger->warning(
 953                                         __METHOD__ . ": failed to connect to database $i at '$host'." );
 954                                 $this->errorConnection = $conn;
 955                                 $conn = false;
 956                         }
 957                 }
 958
 959                 // Final sanity check to make sure the right domain is selected
 960                 if (
 961                         $conn instanceof IDatabase &&
 962                         !$this->localDomain->isCompatible( $conn->getDomainID() )
 963                 ) {
 964                         throw new UnexpectedValueException(
 965                                 "Got connection to '{$conn->getDomainID()}', " .
 966                                 "but expected local domain ('{$this->localDomain}')" );
 967                 }
 968
 969                 return $conn;
 970         }
 971
 972         /**
 973          * Open a connection to a foreign DB, or return one if it is already open.
 974          *
 975          * Increments a reference count on the returned connection which locks the
 976          * connection to the requested domain. This reference count can be
 977          * decremented by calling reuseConnection().
 978          *
 979          * If a connection is open to the appropriate server already, but with the wrong
 980          * database, it will be switched to the right database and returned, as long as
 981          * it has been freed first with reuseConnection().
 982          *
 983          * On error, returns false, and the connection which caused the
 984          * error will be available via $this->errorConnection.
 985          *
 986          * @note If disable() was called on this LoadBalancer, this method will throw a DBAccessError.
 987          *
 988          * @param int $i Server index
 989          * @param string $domain Domain ID to open
 990          * @param int $flags Class CONN_* constant bitfield
 991          * @return Database|bool Returns false on connection error
 992          * @throws DBError When database selection fails
 993          */
 994         private function openForeignConnection( $i, $domain, $flags = 0 ) {
 995                 $domainInstance = DatabaseDomain::newFromId( $domain );
 996                 // Connection handles required to be in auto-commit mode use a separate connection
 997                 // pool since the main pool is effected by implicit and explicit transaction rounds
 998                 $autoCommit = ( ( $flags & self::CONN_TRX_AUTOCOMMIT ) == self::CONN_TRX_AUTOCOMMIT );
 999
1000                 if ( $autoCommit ) {
1001                         $connFreeKey = self::KEY_FOREIGN_FREE_NOROUND;
1002                         $connInUseKey = self::KEY_FOREIGN_INUSE_NOROUND;
1003                 } else {
1004                         $connFreeKey = self::KEY_FOREIGN_FREE;
1005                         $connInUseKey = self::KEY_FOREIGN_INUSE;
1006                 }
1007
1008                 /** @var Database $conn */
1009                 $conn = null;
1010
1011                 if ( isset( $this->conns[$connInUseKey][$i][$domain] ) ) {
1012                         // Reuse an in-use connection for the same domain
1013                         $conn = $this->conns[$connInUseKey][$i][$domain];
1014                         $this->connLogger->debug( __METHOD__ . ": reusing connection $i/$domain" );
1015                 } elseif ( isset( $this->conns[$connFreeKey][$i][$domain] ) ) {
1016                         // Reuse a free connection for the same domain
1017                         $conn = $this->conns[$connFreeKey][$i][$domain];
1018                         unset( $this->conns[$connFreeKey][$i][$domain] );
1019                         $this->conns[$connInUseKey][$i][$domain] = $conn;
1020                         $this->connLogger->debug( __METHOD__ . ": reusing free connection $i/$domain" );
1021                 } elseif ( !empty( $this->conns[$connFreeKey][$i] ) ) {
1022                         // Reuse a free connection from another domain if possible
1023                         foreach ( $this->conns[$connFreeKey][$i] as $oldDomain => $conn ) {
1024                                 if ( $domainInstance->getDatabase() !== null ) {
1025                                         // Check if changing the database will require a new connection.
1026                                         // In that case, leave the connection handle alone and keep looking.
1027                                         // This prevents connections from being closed mid-transaction and can
1028                                         // also avoid overhead if the same database will later be requested.
1029                                         if (
1030                                                 $conn->databasesAreIndependent() &&
1031                                                 $conn->getDBname() !== $domainInstance->getDatabase()
1032                                         ) {
1033                                                 continue;
1034                                         }
1035                                         // Select the new database, schema, and prefix
1036                                         $conn->selectDomain( $domainInstance );
1037                                 } else {
1038                                         // Stay on the current database, but update the schema/prefix
1039                                         $conn->dbSchema( $domainInstance->getSchema() );
1040                                         $conn->tablePrefix( $domainInstance->getTablePrefix() );
1041                                 }
1042                                 unset( $this->conns[$connFreeKey][$i][$oldDomain] );
1043                                 // Note that if $domain is an empty string, getDomainID() might not match it
1044                                 $this->conns[$connInUseKey][$i][$conn->getDomainID()] = $conn;
1045                                 $this->connLogger->debug( __METHOD__ .
1046                                         ": reusing free connection from $oldDomain for $domain" );
1047                                 break;
1048                         }
1049                 }
1050
1051                 if ( !$conn ) {
1052                         if ( !isset( $this->servers[$i] ) || !is_array( $this->servers[$i] ) ) {
1053                                 throw new InvalidArgumentException( "No server with index '$i'" );
1054                         }
1055                         // Open a new connection
1056                         $server = $this->servers[$i];
1057                         $server['serverIndex'] = $i;
1058                         $server['foreignPoolRefCount'] = 0;
1059                         $server['foreign'] = true;
1060                         $server['autoCommitOnly'] = $autoCommit;
1061                         $conn = $this->reallyOpenConnection( $server, $domainInstance );
1062                         if ( !$conn->isOpen() ) {
1063                                 $this->connLogger->warning( __METHOD__ . ": connection error for $i/$domain" );
1064                                 $this->errorConnection = $conn;
1065                                 $conn = false;
1066                         } else {
1067                                 // Note that if $domain is an empty string, getDomainID() might not match it
1068                                 $this->conns[$connInUseKey][$i][$conn->getDomainID()] = $conn;
1069                                 $this->connLogger->debug( __METHOD__ . ": opened new connection for $i/$domain" );
1070                         }
1071                 }
1072
1073                 if ( $conn instanceof IDatabase ) {
1074                         // Final sanity check to make sure the right domain is selected
1075                         if ( !$domainInstance->isCompatible( $conn->getDomainID() ) ) {
1076                                 throw new UnexpectedValueException(
1077                                         "Got connection to '{$conn->getDomainID()}', but expected '$domain'" );
1078                         }
1079                         // Increment reference count
1080                         $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
1081                         $conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
1082                 }
1083
1084                 return $conn;
1085         }
1086
1087         public function getServerAttributes( $i ) {
1088                 return Database::attributesFromType(
1089                         $this->getServerType( $i ),
1090                         $this->servers[$i]['driver'] ?? null
1091                 );
1092         }
1093
1094         /**
1095          * Test if the specified index represents an open connection
1096          *
1097          * @param int $index Server index
1098          * @private
1099          * @return bool
1100          */
1101         private function isOpen( $index ) {
1102                 if ( !is_int( $index ) ) {
1103                         return false;
1104                 }
1105
1106                 return (bool)$this->getAnyOpenConnection( $index );
1107         }
1108
1109         /**
1110          * Open a new network connection to a server (uncached)
1111          *
1112          * Returns a Database object whether or not the connection was successful.
1113          *
1114          * @param array $server
1115          * @param DatabaseDomain $domain Domain the connection is for, possibly unspecified
1116          * @return Database
1117          * @throws DBAccessError
1118          * @throws InvalidArgumentException
1119          */
1120         protected function reallyOpenConnection( array $server, DatabaseDomain $domain ) {
1121                 if ( $this->disabled ) {
1122                         throw new DBAccessError();
1123                 }
1124
1125                 if ( $domain->getDatabase() === null ) {
1126                         // The database domain does not specify a DB name and some database systems require a
1127                         // valid DB specified on connection. The $server configuration array contains a default
1128                         // DB name to use for connections in such cases.
1129                         if ( $server['type'] === 'mysql' ) {
1130                                 // For MySQL, DATABASE and SCHEMA are synonyms, connections need not specify a DB,
1131                                 // and the DB name in $server might not exist due to legacy reasons (the default
1132                                 // domain used to ignore the local LB domain, even when mismatched).
1133                                 $server['dbname'] = null;
1134                         }
1135                 } else {
1136                         $server['dbname'] = $domain->getDatabase();
1137                 }
1138
1139                 if ( $domain->getSchema() !== null ) {
1140                         $server['schema'] = $domain->getSchema();
1141                 }
1142
1143                 // It is always possible to connect with any prefix, even the empty string
1144                 $server['tablePrefix'] = $domain->getTablePrefix();
1145
1146                 // Let the handle know what the cluster master is (e.g. "db1052")
1147                 $masterName = $this->getServerName( $this->getWriterIndex() );
1148                 $server['clusterMasterHost'] = $masterName;
1149
1150                 // Log when many connection are made on requests
1151                 if ( ++$this->connsOpened >= self::CONN_HELD_WARN_THRESHOLD ) {
1152                         $this->perfLogger->warning( __METHOD__ . ": " .
1153                                 "{$this->connsOpened}+ connections made (master=$masterName)" );
1154                 }
1155
1156                 $server['srvCache'] = $this->srvCache;
1157                 // Set loggers and profilers
1158                 $server['connLogger'] = $this->connLogger;
1159                 $server['queryLogger'] = $this->queryLogger;
1160                 $server['errorLogger'] = $this->errorLogger;
1161                 $server['deprecationLogger'] = $this->deprecationLogger;
1162                 $server['profiler'] = $this->profiler;
1163                 $server['trxProfiler'] = $this->trxProfiler;
1164                 // Use the same agent and PHP mode for all DB handles
1165                 $server['cliMode'] = $this->cliMode;
1166                 $server['agent'] = $this->agent;
1167                 // Use DBO_DEFAULT flags by default for LoadBalancer managed databases. Assume that the
1168                 // application calls LoadBalancer::commitMasterChanges() before the PHP script completes.
1169                 $server['flags'] = $server['flags'] ?? IDatabase::DBO_DEFAULT;
1170
1171                 // Create a live connection object
1172                 try {
1173                         $db = Database::factory( $server['type'], $server );
1174                 } catch ( DBConnectionError $e ) {
1175                         // FIXME: This is probably the ugliest thing I have ever done to
1176                         // PHP. I'm half-expecting it to segfault, just out of disgust. -- TS
1177                         $db = $e->db;
1178                 }
1179
1180                 $db->setLBInfo( $server );
1181                 $db->setLazyMasterHandle(
1182                         $this->getLazyConnectionRef( self::DB_MASTER, [], $db->getDomainID() )
1183                 );
1184                 $db->setTableAliases( $this->tableAliases );
1185                 $db->setIndexAliases( $this->indexAliases );
1186
1187                 if ( $server['serverIndex'] === $this->getWriterIndex() ) {
1188                         if ( $this->trxRoundId !== false ) {
1189                                 $this->applyTransactionRoundFlags( $db );
1190                         }
1191                         foreach ( $this->trxRecurringCallbacks as $name => $callback ) {
1192                                 $db->setTransactionListener( $name, $callback );
1193                         }
1194                 }
1195
1196                 return $db;
1197         }
1198
1199         /**
1200          * @throws DBConnectionError
1201          */
1202         private function reportConnectionError() {
1203                 $conn = $this->errorConnection; // the connection which caused the error
1204                 $context = [
1205                         'method' => __METHOD__,
1206                         'last_error' => $this->lastError,
1207                 ];
1208
1209                 if ( $conn instanceof IDatabase ) {
1210                         $context['db_server'] = $conn->getServer();
1211                         $this->connLogger->warning(
1212                                 __METHOD__ . ": connection error: {last_error} ({db_server})",
1213                                 $context
1214                         );
1215
1216                         throw new DBConnectionError( $conn, "{$this->lastError} ({$context['db_server']})" );
1217                 } else {
1218                         // No last connection, probably due to all servers being too busy
1219                         $this->connLogger->error(
1220                                 __METHOD__ .
1221                                 ": LB failure with no last connection. Connection error: {last_error}",
1222                                 $context
1223                         );
1224
1225                         // If all servers were busy, "lastError" will contain something sensible
1226                         throw new DBConnectionError( null, $this->lastError );
1227                 }
1228         }
1229
1230         public function getWriterIndex() {
1231                 return 0;
1232         }
1233
1234         public function haveIndex( $i ) {
1235                 return array_key_exists( $i, $this->servers );
1236         }
1237
1238         public function isNonZeroLoad( $i ) {
1239                 return array_key_exists( $i, $this->servers ) && $this->genericLoads[$i] != 0;
1240         }
1241
1242         public function getServerCount() {
1243                 return count( $this->servers );
1244         }
1245
1246         public function getServerName( $i ) {
1247                 $name = $this->servers[$i]['hostName'] ?? $this->servers[$i]['host'] ?? '';
1248
1249                 return ( $name != '' ) ? $name : 'localhost';
1250         }
1251
1252         public function getServerInfo( $i ) {
1253                 return $this->servers[$i] ?? false;
1254         }
1255
1256         public function getServerType( $i ) {
1257                 return $this->servers[$i]['type'] ?? 'unknown';
1258         }
1259
1260         public function getMasterPos() {
1261                 # If this entire request was served from a replica DB without opening a connection to the
1262                 # master (however unlikely that may be), then we can fetch the position from the replica DB.
1263                 $masterConn = $this->getAnyOpenConnection( $this->getWriterIndex() );
1264                 if ( !$masterConn ) {
1265                         $serverCount = count( $this->servers );
1266                         for ( $i = 1; $i < $serverCount; $i++ ) {
1267                                 $conn = $this->getAnyOpenConnection( $i );
1268                                 if ( $conn ) {
1269                                         return $conn->getReplicaPos();
1270                                 }
1271                         }
1272                 } else {
1273                         return $masterConn->getMasterPos();
1274                 }
1275
1276                 return false;
1277         }
1278
1279         public function disable() {
1280                 $this->closeAll();
1281                 $this->disabled = true;
1282         }
1283
1284         public function closeAll() {
1285                 $fname = __METHOD__;
1286                 $this->forEachOpenConnection( function ( IDatabase $conn ) use ( $fname ) {
1287                         $host = $conn->getServer();
1288                         $this->connLogger->debug(
1289                                 $fname . ": closing connection to database '$host'." );
1290                         $conn->close();
1291                 } );
1292
1293                 $this->conns = [
1294                         self::KEY_LOCAL => [],
1295                         self::KEY_FOREIGN_INUSE => [],
1296                         self::KEY_FOREIGN_FREE => [],
1297                         self::KEY_LOCAL_NOROUND => [],
1298                         self::KEY_FOREIGN_INUSE_NOROUND => [],
1299                         self::KEY_FOREIGN_FREE_NOROUND => []
1300                 ];
1301                 $this->connsOpened = 0;
1302         }
1303
1304         public function closeConnection( IDatabase $conn ) {
1305                 if ( $conn instanceof DBConnRef ) {
1306                         // Avoid calling close() but still leaving the handle in the pool
1307                         throw new RuntimeException( 'Cannot close DBConnRef instance; it must be shareable' );
1308                 }
1309
1310                 $serverIndex = $conn->getLBInfo( 'serverIndex' );
1311                 foreach ( $this->conns as $type => $connsByServer ) {
1312                         if ( !isset( $connsByServer[$serverIndex] ) ) {
1313                                 continue;
1314                         }
1315
1316                         foreach ( $connsByServer[$serverIndex] as $i => $trackedConn ) {
1317                                 if ( $conn === $trackedConn ) {
1318                                         $host = $this->getServerName( $i );
1319                                         $this->connLogger->debug(
1320                                                 __METHOD__ . ": closing connection to database $i at '$host'." );
1321                                         unset( $this->conns[$type][$serverIndex][$i] );
1322                                         --$this->connsOpened;
1323                                         break 2;
1324                                 }
1325                         }
1326                 }
1327
1328                 $conn->close();
1329         }
1330
1331         public function commitAll( $fname = __METHOD__ ) {
1332                 $this->commitMasterChanges( $fname );
1333                 $this->flushMasterSnapshots( $fname );
1334                 $this->flushReplicaSnapshots( $fname );
1335         }
1336
1337         public function finalizeMasterChanges() {
1338                 $this->assertTransactionRoundStage( [ self::ROUND_CURSORY, self::ROUND_FINALIZED ] );
1339
1340                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1341                 // Loop until callbacks stop adding callbacks on other connections
1342                 $total = 0;
1343                 do {
1344                         $count = 0; // callbacks execution attempts
1345                         $this->forEachOpenMasterConnection( function ( Database $conn ) use ( &$count ) {
1346                                 // Run any pre-commit callbacks while leaving the post-commit ones suppressed.
1347                                 // Any error should cause all (peer) transactions to be rolled back together.
1348                                 $count += $conn->runOnTransactionPreCommitCallbacks();
1349                         } );
1350                         $total += $count;
1351                 } while ( $count > 0 );
1352                 // Defer post-commit callbacks until after COMMIT/ROLLBACK happens on all handles
1353                 $this->forEachOpenMasterConnection( function ( Database $conn ) {
1354                         $conn->setTrxEndCallbackSuppression( true );
1355                 } );
1356                 $this->trxRoundStage = self::ROUND_FINALIZED;
1357
1358                 return $total;
1359         }
1360
1361         public function approveMasterChanges( array $options ) {
1362                 $this->assertTransactionRoundStage( self::ROUND_FINALIZED );
1363
1364                 $limit = $options['maxWriteDuration'] ?? 0;
1365
1366                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1367                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( $limit ) {
1368                         // If atomic sections or explicit transactions are still open, some caller must have
1369                         // caught an exception but failed to properly rollback any changes. Detect that and
1370                         // throw and error (causing rollback).
1371                         $conn->assertNoOpenTransactions();
1372                         // Assert that the time to replicate the transaction will be sane.
1373                         // If this fails, then all DB transactions will be rollback back together.
1374                         $time = $conn->pendingWriteQueryDuration( $conn::ESTIMATE_DB_APPLY );
1375                         if ( $limit > 0 && $time > $limit ) {
1376                                 throw new DBTransactionSizeError(
1377                                         $conn,
1378                                         "Transaction spent $time second(s) in writes, exceeding the limit of $limit",
1379                                         [ $time, $limit ]
1380                                 );
1381                         }
1382                         // If a connection sits idle while slow queries execute on another, that connection
1383                         // may end up dropped before the commit round is reached. Ping servers to detect this.
1384                         if ( $conn->writesOrCallbacksPending() && !$conn->ping() ) {
1385                                 throw new DBTransactionError(
1386                                         $conn,
1387                                         "A connection to the {$conn->getDBname()} database was lost before commit"
1388                                 );
1389                         }
1390                 } );
1391                 $this->trxRoundStage = self::ROUND_APPROVED;
1392         }
1393
1394         public function beginMasterChanges( $fname = __METHOD__ ) {
1395                 if ( $this->trxRoundId !== false ) {
1396                         throw new DBTransactionError(
1397                                 null,
1398                                 "$fname: Transaction round '{$this->trxRoundId}' already started"
1399                         );
1400                 }
1401                 $this->assertTransactionRoundStage( self::ROUND_CURSORY );
1402
1403                 // Clear any empty transactions (no writes/callbacks) from the implicit round
1404                 $this->flushMasterSnapshots( $fname );
1405
1406                 $this->trxRoundId = $fname;
1407                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1408                 // Mark applicable handles as participating in this explicit transaction round.
1409                 // For each of these handles, any writes and callbacks will be tied to a single
1410                 // transaction. The (peer) handles will reject begin()/commit() calls unless they
1411                 // are part of an en masse commit or an en masse rollback.
1412                 $this->forEachOpenMasterConnection( function ( Database $conn ) {
1413                         $this->applyTransactionRoundFlags( $conn );
1414                 } );
1415                 $this->trxRoundStage = self::ROUND_CURSORY;
1416         }
1417
1418         public function commitMasterChanges( $fname = __METHOD__ ) {
1419                 $this->assertTransactionRoundStage( self::ROUND_APPROVED );
1420
1421                 $failures = [];
1422
1423                 /** @noinspection PhpUnusedLocalVariableInspection */
1424                 $scope = ScopedCallback::newScopedIgnoreUserAbort(); // try to ignore client aborts
1425
1426                 $restore = ( $this->trxRoundId !== false );
1427                 $this->trxRoundId = false;
1428                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1429                 // Commit any writes and clear any snapshots as well (callbacks require AUTOCOMMIT).
1430                 // Note that callbacks should already be suppressed due to finalizeMasterChanges().
1431                 $this->forEachOpenMasterConnection(
1432                         function ( IDatabase $conn ) use ( $fname, &$failures ) {
1433                                 try {
1434                                         $conn->commit( $fname, $conn::FLUSHING_ALL_PEERS );
1435                                 } catch ( DBError $e ) {
1436                                         ( $this->errorLogger )( $e );
1437                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1438                                 }
1439                         }
1440                 );
1441                 if ( $failures ) {
1442                         throw new DBTransactionError(
1443                                 null,
1444                                 "$fname: Commit failed on server(s) " . implode( "\n", array_unique( $failures ) )
1445                         );
1446                 }
1447                 if ( $restore ) {
1448                         // Unmark handles as participating in this explicit transaction round
1449                         $this->forEachOpenMasterConnection( function ( Database $conn ) {
1450                                 $this->undoTransactionRoundFlags( $conn );
1451                         } );
1452                 }
1453                 $this->trxRoundStage = self::ROUND_COMMIT_CALLBACKS;
1454         }
1455
1456         public function runMasterTransactionIdleCallbacks() {
1457                 if ( $this->trxRoundStage === self::ROUND_COMMIT_CALLBACKS ) {
1458                         $type = IDatabase::TRIGGER_COMMIT;
1459                 } elseif ( $this->trxRoundStage === self::ROUND_ROLLBACK_CALLBACKS ) {
1460                         $type = IDatabase::TRIGGER_ROLLBACK;
1461                 } else {
1462                         throw new DBTransactionError(
1463                                 null,
1464                                 "Transaction should be in the callback stage (not '{$this->trxRoundStage}')"
1465                         );
1466                 }
1467
1468                 $oldStage = $this->trxRoundStage;
1469                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1470
1471                 // Now that the COMMIT/ROLLBACK step is over, enable post-commit callback runs
1472                 $this->forEachOpenMasterConnection( function ( Database $conn ) {
1473                         $conn->setTrxEndCallbackSuppression( false );
1474                 } );
1475
1476                 $e = null; // first exception
1477                 $fname = __METHOD__;
1478                 // Loop until callbacks stop adding callbacks on other connections
1479                 do {
1480                         // Run any pending callbacks for each connection...
1481                         $count = 0; // callback execution attempts
1482                         $this->forEachOpenMasterConnection(
1483                                 function ( Database $conn ) use ( $type, &$e, &$count ) {
1484                                         if ( $conn->trxLevel() ) {
1485                                                 return; // retry in the next iteration, after commit() is called
1486                                         }
1487                                         try {
1488                                                 $count += $conn->runOnTransactionIdleCallbacks( $type );
1489                                         } catch ( Exception $ex ) {
1490                                                 $e = $e ?: $ex;
1491                                         }
1492                                 }
1493                         );
1494                         // Clear out any active transactions left over from callbacks...
1495                         $this->forEachOpenMasterConnection( function ( Database $conn ) use ( &$e, $fname ) {
1496                                 if ( $conn->writesPending() ) {
1497                                         // A callback from another handle wrote to this one and DBO_TRX is set
1498                                         $this->queryLogger->warning( $fname . ": found writes pending." );
1499                                         $fnames = implode( ', ', $conn->pendingWriteAndCallbackCallers() );
1500                                         $this->queryLogger->warning(
1501                                                 $fname . ": found writes pending ($fnames).",
1502                                                 [
1503                                                         'db_server' => $conn->getServer(),
1504                                                         'db_name' => $conn->getDBname()
1505                                                 ]
1506                                         );
1507                                 } elseif ( $conn->trxLevel() ) {
1508                                         // A callback from another handle read from this one and DBO_TRX is set,
1509                                         // which can easily happen if there is only one DB (no replicas)
1510                                         $this->queryLogger->debug( $fname . ": found empty transaction." );
1511                                 }
1512                                 try {
1513                                         $conn->commit( $fname, $conn::FLUSHING_ALL_PEERS );
1514                                 } catch ( Exception $ex ) {
1515                                         $e = $e ?: $ex;
1516                                 }
1517                         } );
1518                 } while ( $count > 0 );
1519
1520                 $this->trxRoundStage = $oldStage;
1521
1522                 return $e;
1523         }
1524
1525         public function runMasterTransactionListenerCallbacks() {
1526                 if ( $this->trxRoundStage === self::ROUND_COMMIT_CALLBACKS ) {
1527                         $type = IDatabase::TRIGGER_COMMIT;
1528                 } elseif ( $this->trxRoundStage === self::ROUND_ROLLBACK_CALLBACKS ) {
1529                         $type = IDatabase::TRIGGER_ROLLBACK;
1530                 } else {
1531                         throw new DBTransactionError(
1532                                 null,
1533                                 "Transaction should be in the callback stage (not '{$this->trxRoundStage}')"
1534                         );
1535                 }
1536
1537                 $e = null;
1538
1539                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1540                 $this->forEachOpenMasterConnection( function ( Database $conn ) use ( $type, &$e ) {
1541                         try {
1542                                 $conn->runTransactionListenerCallbacks( $type );
1543                         } catch ( Exception $ex ) {
1544                                 $e = $e ?: $ex;
1545                         }
1546                 } );
1547                 $this->trxRoundStage = self::ROUND_CURSORY;
1548
1549                 return $e;
1550         }
1551
1552         public function rollbackMasterChanges( $fname = __METHOD__ ) {
1553                 $restore = ( $this->trxRoundId !== false );
1554                 $this->trxRoundId = false;
1555                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1556                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( $fname ) {
1557                         $conn->rollback( $fname, $conn::FLUSHING_ALL_PEERS );
1558                 } );
1559                 if ( $restore ) {
1560                         // Unmark handles as participating in this explicit transaction round
1561                         $this->forEachOpenMasterConnection( function ( Database $conn ) {
1562                                 $this->undoTransactionRoundFlags( $conn );
1563                         } );
1564                 }
1565                 $this->trxRoundStage = self::ROUND_ROLLBACK_CALLBACKS;
1566         }
1567
1568         /**
1569          * @param string|string[] $stage
1570          */
1571         private function assertTransactionRoundStage( $stage ) {
1572                 $stages = (array)$stage;
1573
1574                 if ( !in_array( $this->trxRoundStage, $stages, true ) ) {
1575                         $stageList = implode(
1576                                 '/',
1577                                 array_map( function ( $v ) {
1578                                         return "'$v'";
1579                                 }, $stages )
1580                         );
1581                         throw new DBTransactionError(
1582                                 null,
1583                                 "Transaction round stage must be $stageList (not '{$this->trxRoundStage}')"
1584                         );
1585                 }
1586         }
1587
1588         /**
1589          * Make all DB servers with DBO_DEFAULT/DBO_TRX set join the transaction round
1590          *
1591          * Some servers may have neither flag enabled, meaning that they opt out of such
1592          * transaction rounds and remain in auto-commit mode. Such behavior might be desired
1593          * when a DB server is used for something like simple key/value storage.
1594          *
1595          * @param Database $conn
1596          */
1597         private function applyTransactionRoundFlags( Database $conn ) {
1598                 if ( $conn->getLBInfo( 'autoCommitOnly' ) ) {
1599                         return; // transaction rounds do not apply to these connections
1600                 }
1601
1602                 if ( $conn->getFlag( $conn::DBO_DEFAULT ) ) {
1603                         // DBO_TRX is controlled entirely by CLI mode presence with DBO_DEFAULT.
1604                         // Force DBO_TRX even in CLI mode since a commit round is expected soon.
1605                         $conn->setFlag( $conn::DBO_TRX, $conn::REMEMBER_PRIOR );
1606                 }
1607
1608                 if ( $conn->getFlag( $conn::DBO_TRX ) ) {
1609                         $conn->setLBInfo( 'trxRoundId', $this->trxRoundId );
1610                 }
1611         }
1612
1613         /**
1614          * @param Database $conn
1615          */
1616         private function undoTransactionRoundFlags( Database $conn ) {
1617                 if ( $conn->getLBInfo( 'autoCommitOnly' ) ) {
1618                         return; // transaction rounds do not apply to these connections
1619                 }
1620
1621                 if ( $conn->getFlag( $conn::DBO_TRX ) ) {
1622                         $conn->setLBInfo( 'trxRoundId', false );
1623                 }
1624
1625                 if ( $conn->getFlag( $conn::DBO_DEFAULT ) ) {
1626                         $conn->restoreFlags( $conn::RESTORE_PRIOR );
1627                 }
1628         }
1629
1630         public function flushReplicaSnapshots( $fname = __METHOD__ ) {
1631                 $this->forEachOpenReplicaConnection( function ( IDatabase $conn ) use ( $fname ) {
1632                         $conn->flushSnapshot( $fname );
1633                 } );
1634         }
1635
1636         public function flushMasterSnapshots( $fname = __METHOD__ ) {
1637                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( $fname ) {
1638                         $conn->flushSnapshot( $fname );
1639                 } );
1640         }
1641
1642         /**
1643          * @return string
1644          * @since 1.32
1645          */
1646         public function getTransactionRoundStage() {
1647                 return $this->trxRoundStage;
1648         }
1649
1650         public function hasMasterConnection() {
1651                 return $this->isOpen( $this->getWriterIndex() );
1652         }
1653
1654         public function hasMasterChanges() {
1655                 $pending = 0;
1656                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$pending ) {
1657                         $pending |= $conn->writesOrCallbacksPending();
1658                 } );
1659
1660                 return (bool)$pending;
1661         }
1662
1663         public function lastMasterChangeTimestamp() {
1664                 $lastTime = false;
1665                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$lastTime ) {
1666                         $lastTime = max( $lastTime, $conn->lastDoneWrites() );
1667                 } );
1668
1669                 return $lastTime;
1670         }
1671
1672         public function hasOrMadeRecentMasterChanges( $age = null ) {
1673                 $age = ( $age === null ) ? $this->waitTimeout : $age;
1674
1675                 return ( $this->hasMasterChanges()
1676                         || $this->lastMasterChangeTimestamp() > microtime( true ) - $age );
1677         }
1678
1679         public function pendingMasterChangeCallers() {
1680                 $fnames = [];
1681                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$fnames ) {
1682                         $fnames = array_merge( $fnames, $conn->pendingWriteCallers() );
1683                 } );
1684
1685                 return $fnames;
1686         }
1687
1688         public function getLaggedReplicaMode( $domain = false ) {
1689                 if (
1690                         // Avoid recursion if there is only one DB
1691                         $this->getServerCount() > 1 &&
1692                         // Avoid recursion if the (non-zero load) master DB was picked for generic reads
1693                         $this->genericReadIndex !== $this->getWriterIndex() &&
1694                         // Stay in lagged replica mode during the load balancer instance lifetime
1695                         !$this->laggedReplicaMode
1696                 ) {
1697                         try {
1698                                 // Calling this method will set "laggedReplicaMode" as needed
1699                                 $this->getReaderIndex( false, $domain );
1700                         } catch ( DBConnectionError $e ) {
1701                                 // Avoid expensive re-connect attempts and failures
1702                                 $this->allReplicasDownMode = true;
1703                                 $this->laggedReplicaMode = true;
1704                         }
1705                 }
1706
1707                 return $this->laggedReplicaMode;
1708         }
1709
1710         public function laggedReplicaUsed() {
1711                 return $this->laggedReplicaMode;
1712         }
1713
1714         /**
1715          * @return bool
1716          * @since 1.27
1717          * @deprecated Since 1.28; use laggedReplicaUsed()
1718          */
1719         public function laggedSlaveUsed() {
1720                 return $this->laggedReplicaUsed();
1721         }
1722
1723         public function getReadOnlyReason( $domain = false, IDatabase $conn = null ) {
1724                 if ( $this->readOnlyReason !== false ) {
1725                         return $this->readOnlyReason;
1726                 } elseif ( $this->getLaggedReplicaMode( $domain ) ) {
1727                         if ( $this->allReplicasDownMode ) {
1728                                 return 'The database has been automatically locked ' .
1729                                         'until the replica database servers become available';
1730                         } else {
1731                                 return 'The database has been automatically locked ' .
1732                                         'while the replica database servers catch up to the master.';
1733                         }
1734                 } elseif ( $this->masterRunningReadOnly( $domain, $conn ) ) {
1735                         return 'The database master is running in read-only mode.';
1736                 }
1737
1738                 return false;
1739         }
1740
1741         /**
1742          * @param string $domain Domain ID, or false for the current domain
1743          * @param IDatabase|null $conn DB master connectionl used to avoid loops [optional]
1744          * @return bool
1745          */
1746         private function masterRunningReadOnly( $domain, IDatabase $conn = null ) {
1747                 $cache = $this->wanCache;
1748                 $masterServer = $this->getServerName( $this->getWriterIndex() );
1749
1750                 return (bool)$cache->getWithSetCallback(
1751                         $cache->makeGlobalKey( __CLASS__, 'server-read-only', $masterServer ),
1752                         self::TTL_CACHE_READONLY,
1753                         function () use ( $domain, $conn ) {
1754                                 $old = $this->trxProfiler->setSilenced( true );
1755                                 try {
1756                                         $dbw = $conn ?: $this->getConnection( self::DB_MASTER, [], $domain );
1757                                         $readOnly = (int)$dbw->serverIsReadOnly();
1758                                         if ( !$conn ) {
1759                                                 $this->reuseConnection( $dbw );
1760                                         }
1761                                 } catch ( DBError $e ) {
1762                                         $readOnly = 0;
1763                                 }
1764                                 $this->trxProfiler->setSilenced( $old );
1765                                 return $readOnly;
1766                         },
1767                         [ 'pcTTL' => $cache::TTL_PROC_LONG, 'busyValue' => 0 ]
1768                 );
1769         }
1770
1771         public function allowLagged( $mode = null ) {
1772                 if ( $mode === null ) {
1773                         return $this->allowLagged;
1774                 }
1775                 $this->allowLagged = $mode;
1776
1777                 return $this->allowLagged;
1778         }
1779
1780         public function pingAll() {
1781                 $success = true;
1782                 $this->forEachOpenConnection( function ( IDatabase $conn ) use ( &$success ) {
1783                         if ( !$conn->ping() ) {
1784                                 $success = false;
1785                         }
1786                 } );
1787
1788                 return $success;
1789         }
1790
1791         public function forEachOpenConnection( $callback, array $params = [] ) {
1792                 foreach ( $this->conns as $connsByServer ) {
1793                         foreach ( $connsByServer as $serverConns ) {
1794                                 foreach ( $serverConns as $conn ) {
1795                                         $callback( $conn, ...$params );
1796                                 }
1797                         }
1798                 }
1799         }
1800
1801         public function forEachOpenMasterConnection( $callback, array $params = [] ) {
1802                 $masterIndex = $this->getWriterIndex();
1803                 foreach ( $this->conns as $connsByServer ) {
1804                         if ( isset( $connsByServer[$masterIndex] ) ) {
1805                                 /** @var IDatabase $conn */
1806                                 foreach ( $connsByServer[$masterIndex] as $conn ) {
1807                                         $callback( $conn, ...$params );
1808                                 }
1809                         }
1810                 }
1811         }
1812
1813         public function forEachOpenReplicaConnection( $callback, array $params = [] ) {
1814                 foreach ( $this->conns as $connsByServer ) {
1815                         foreach ( $connsByServer as $i => $serverConns ) {
1816                                 if ( $i === $this->getWriterIndex() ) {
1817                                         continue; // skip master
1818                                 }
1819                                 foreach ( $serverConns as $conn ) {
1820                                         $callback( $conn, ...$params );
1821                                 }
1822                         }
1823                 }
1824         }
1825
1826         public function getMaxLag( $domain = false ) {
1827                 $maxLag = -1;
1828                 $host = '';
1829                 $maxIndex = 0;
1830
1831                 if ( $this->getServerCount() <= 1 ) {
1832                         return [ $host, $maxLag, $maxIndex ]; // no replication = no lag
1833                 }
1834
1835                 $lagTimes = $this->getLagTimes( $domain );
1836                 foreach ( $lagTimes as $i => $lag ) {
1837                         if ( $this->genericLoads[$i] > 0 && $lag > $maxLag ) {
1838                                 $maxLag = $lag;
1839                                 $host = $this->servers[$i]['host'];
1840                                 $maxIndex = $i;
1841                         }
1842                 }
1843
1844                 return [ $host, $maxLag, $maxIndex ];
1845         }
1846
1847         public function getLagTimes( $domain = false ) {
1848                 if ( $this->getServerCount() <= 1 ) {
1849                         return [ $this->getWriterIndex() => 0 ]; // no replication = no lag
1850                 }
1851
1852                 $knownLagTimes = []; // map of (server index => 0 seconds)
1853                 $indexesWithLag = [];
1854                 foreach ( $this->servers as $i => $server ) {
1855                         if ( empty( $server['is static'] ) ) {
1856                                 $indexesWithLag[] = $i; // DB server might have replication lag
1857                         } else {
1858                                 $knownLagTimes[$i] = 0; // DB server is a non-replicating and read-only archive
1859                         }
1860                 }
1861
1862                 return $this->getLoadMonitor()->getLagTimes( $indexesWithLag, $domain ) + $knownLagTimes;
1863         }
1864
1865         public function safeGetLag( IDatabase $conn ) {
1866                 if ( $this->getServerCount() <= 1 ) {
1867                         return 0;
1868                 } else {
1869                         return $conn->getLag();
1870                 }
1871         }
1872
1873         public function safeWaitForMasterPos( IDatabase $conn, $pos = false, $timeout = null ) {
1874                 $timeout = max( 1, $timeout ?: $this->waitTimeout );
1875
1876                 if ( $this->getServerCount() <= 1 || !$conn->getLBInfo( 'replica' ) ) {
1877                         return true; // server is not a replica DB
1878                 }
1879
1880                 if ( !$pos ) {
1881                         // Get the current master position, opening a connection if needed
1882                         $masterConn = $this->getAnyOpenConnection( $this->getWriterIndex() );
1883                         if ( $masterConn ) {
1884                                 $pos = $masterConn->getMasterPos();
1885                         } else {
1886                                 $masterConn = $this->openConnection( $this->getWriterIndex(), self::DOMAIN_ANY );
1887                                 if ( !$masterConn ) {
1888                                         throw new DBReplicationWaitError(
1889                                                 null,
1890                                                 "Could not obtain a master database connection to get the position"
1891                                         );
1892                                 }
1893                                 $pos = $masterConn->getMasterPos();
1894                                 $this->closeConnection( $masterConn );
1895                         }
1896                 }
1897
1898                 if ( $pos instanceof DBMasterPos ) {
1899                         $result = $conn->masterPosWait( $pos, $timeout );
1900                         if ( $result == -1 || is_null( $result ) ) {
1901                                 $msg = __METHOD__ . ': timed out waiting on {host} pos {pos}';
1902                                 $this->replLogger->warning( $msg, [
1903                                         'host' => $conn->getServer(),
1904                                         'pos' => $pos,
1905                                         'trace' => ( new RuntimeException() )->getTraceAsString()
1906                                 ] );
1907                                 $ok = false;
1908                         } else {
1909                                 $this->replLogger->debug( __METHOD__ . ': done waiting' );
1910                                 $ok = true;
1911                         }
1912                 } else {
1913                         $ok = false; // something is misconfigured
1914                         $this->replLogger->error(
1915                                 __METHOD__ . ': could not get master pos for {host}',
1916                                 [
1917                                         'host' => $conn->getServer(),
1918                                         'trace' => ( new RuntimeException() )->getTraceAsString()
1919                                 ]
1920                         );
1921                 }
1922
1923                 return $ok;
1924         }
1925
1926         public function setTransactionListener( $name, callable $callback = null ) {
1927                 if ( $callback ) {
1928                         $this->trxRecurringCallbacks[$name] = $callback;
1929                 } else {
1930                         unset( $this->trxRecurringCallbacks[$name] );
1931                 }
1932                 $this->forEachOpenMasterConnection(
1933                         function ( IDatabase $conn ) use ( $name, $callback ) {
1934                                 $conn->setTransactionListener( $name, $callback );
1935                         }
1936                 );
1937         }
1938
1939         public function setTableAliases( array $aliases ) {
1940                 $this->tableAliases = $aliases;
1941         }
1942
1943         public function setIndexAliases( array $aliases ) {
1944                 $this->indexAliases = $aliases;
1945         }
1946
1947         /**
1948          * @param string $prefix
1949          * @deprecated Since 1.33
1950          */
1951         public function setDomainPrefix( $prefix ) {
1952                 $this->setLocalDomainPrefix( $prefix );
1953         }
1954
1955         public function setLocalDomainPrefix( $prefix ) {
1956                 // Find connections to explicit foreign domains still marked as in-use...
1957                 $domainsInUse = [];
1958                 $this->forEachOpenConnection( function ( IDatabase $conn ) use ( &$domainsInUse ) {
1959                         // Once reuseConnection() is called on a handle, its reference count goes from 1 to 0.
1960                         // Until then, it is still in use by the caller (explicitly or via DBConnRef scope).
1961                         if ( $conn->getLBInfo( 'foreignPoolRefCount' ) > 0 ) {
1962                                 $domainsInUse[] = $conn->getDomainID();
1963                         }
1964                 } );
1965
1966                 // Do not switch connections to explicit foreign domains unless marked as safe
1967                 if ( $domainsInUse ) {
1968                         $domains = implode( ', ', $domainsInUse );
1969                         throw new DBUnexpectedError( null,
1970                                 "Foreign domain connections are still in use ($domains)" );
1971                 }
1972
1973                 $this->setLocalDomain( new DatabaseDomain(
1974                         $this->localDomain->getDatabase(),
1975                         $this->localDomain->getSchema(),
1976                         $prefix
1977                 ) );
1978
1979                 // Update the prefix for all local connections...
1980                 $this->forEachOpenConnection( function ( IDatabase $db ) use ( $prefix ) {
1981                         if ( !$db->getLBInfo( 'foreign' ) ) {
1982                                 $db->tablePrefix( $prefix );
1983                         }
1984                 } );
1985         }
1986
1987         public function redefineLocalDomain( $domain ) {
1988                 $this->closeAll();
1989
1990                 $this->setLocalDomain( DatabaseDomain::newFromId( $domain ) );
1991         }
1992
1993         /**
1994          * @param DatabaseDomain $domain
1995          */
1996         private function setLocalDomain( DatabaseDomain $domain ) {
1997                 $this->localDomain = $domain;
1998                 // In case a caller assumes that the domain ID is simply <db>-<prefix>, which is almost
1999                 // always true, gracefully handle the case when they fail to account for escaping.
2000                 if ( $this->localDomain->getTablePrefix() != '' ) {
2001                         $this->localDomainIdAlias =
2002                                 $this->localDomain->getDatabase() . '-' . $this->localDomain->getTablePrefix();
2003                 } else {
2004                         $this->localDomainIdAlias = $this->localDomain->getDatabase();
2005                 }
2006         }
2007
2008         function __destruct() {
2009                 // Avoid connection leaks for sanity
2010                 $this->disable();
2011         }
2012 }
2013
2014 /**
2015  * @deprecated since 1.29
2016  */
2017 class_alias( LoadBalancer::class, 'LoadBalancer' );