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 $loads;
  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 (of $mServers) */
 107         private $readIndex;
 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->readIndex = -1;
 185                 $this->conns = [
 186                         // Connection were transaction rounds may be applied
 187                         self::KEY_LOCAL => [],
 188                         self::KEY_FOREIGN_INUSE => [],
 189                         self::KEY_FOREIGN_FREE => [],
 190                         // Auto-committing counterpart connections that ignore transaction rounds
 191                         self::KEY_LOCAL_NOROUND => [],
 192                         self::KEY_FOREIGN_INUSE_NOROUND => [],
 193                         self::KEY_FOREIGN_FREE_NOROUND => []
 194                 ];
 195                 $this->loads = [];
 196                 $this->waitForPos = false;
 197                 $this->allowLagged = false;
 198
 199                 if ( isset( $params['readOnlyReason'] ) && is_string( $params['readOnlyReason'] ) ) {
 200                         $this->readOnlyReason = $params['readOnlyReason'];
 201                 }
 202
 203                 $this->maxLag = $params['maxLag'] ?? self::MAX_LAG_DEFAULT;
 204
 205                 $this->loadMonitorConfig = $params['loadMonitor'] ?? [ 'class' => 'LoadMonitorNull' ];
 206                 $this->loadMonitorConfig += [ 'lagWarnThreshold' => $this->maxLag ];
 207
 208                 foreach ( $params['servers'] as $i => $server ) {
 209                         $this->loads[$i] = $server['load'];
 210                         if ( isset( $server['groupLoads'] ) ) {
 211                                 foreach ( $server['groupLoads'] as $group => $ratio ) {
 212                                         if ( !isset( $this->groupLoads[$group] ) ) {
 213                                                 $this->groupLoads[$group] = [];
 214                                         }
 215                                         $this->groupLoads[$group][$i] = $ratio;
 216                                 }
 217                         }
 218                 }
 219
 220                 $this->srvCache = $params['srvCache'] ?? new EmptyBagOStuff();
 221                 $this->wanCache = $params['wanCache'] ?? WANObjectCache::newEmpty();
 222                 $this->profiler = $params['profiler'] ?? null;
 223                 $this->trxProfiler = $params['trxProfiler'] ?? new TransactionProfiler();
 224
 225                 $this->errorLogger = $params['errorLogger'] ?? function ( Exception $e ) {
 226                         trigger_error( get_class( $e ) . ': ' . $e->getMessage(), E_USER_WARNING );
 227                 };
 228                 $this->deprecationLogger = $params['deprecationLogger'] ?? function ( $msg ) {
 229                         trigger_error( $msg, E_USER_DEPRECATED );
 230                 };
 231
 232                 foreach ( [ 'replLogger', 'connLogger', 'queryLogger', 'perfLogger' ] as $key ) {
 233                         $this->$key = $params[$key] ?? new NullLogger();
 234                 }
 235
 236                 $this->hostname = $params['hostname'] ?? ( gethostname() ?: 'unknown' );
 237                 $this->cliMode = $params['cliMode'] ?? ( PHP_SAPI === 'cli' || PHP_SAPI === 'phpdbg' );
 238                 $this->agent = $params['agent'] ?? '';
 239
 240                 if ( isset( $params['chronologyCallback'] ) ) {
 241                         $this->chronologyCallback = $params['chronologyCallback'];
 242                 }
 243
 244                 if ( isset( $params['roundStage'] ) ) {
 245                         if ( $params['roundStage'] === self::STAGE_POSTCOMMIT_CALLBACKS ) {
 246                                 $this->trxRoundStage = self::ROUND_COMMIT_CALLBACKS;
 247                         } elseif ( $params['roundStage'] === self::STAGE_POSTROLLBACK_CALLBACKS ) {
 248                                 $this->trxRoundStage = self::ROUND_ROLLBACK_CALLBACKS;
 249                         }
 250                 }
 251
 252                 $this->defaultGroup = $params['defaultGroup'] ?? null;
 253         }
 254
 255         public function getLocalDomainID() {
 256                 return $this->localDomain->getId();
 257         }
 258
 259         public function resolveDomainID( $domain ) {
 260                 if ( $domain === $this->localDomainIdAlias || $domain === false ) {
 261                         // Local connection requested via some backwards-compatibility domain alias
 262                         return $this->getLocalDomainID();
 263                 }
 264
 265                 return (string)$domain;
 266         }
 267
 268         /**
 269          * Get a LoadMonitor instance
 270          *
 271          * @return ILoadMonitor
 272          */
 273         private function getLoadMonitor() {
 274                 if ( !isset( $this->loadMonitor ) ) {
 275                         $compat = [
 276                                 'LoadMonitor' => LoadMonitor::class,
 277                                 'LoadMonitorNull' => LoadMonitorNull::class,
 278                                 'LoadMonitorMySQL' => LoadMonitorMySQL::class,
 279                         ];
 280
 281                         $class = $this->loadMonitorConfig['class'];
 282                         if ( isset( $compat[$class] ) ) {
 283                                 $class = $compat[$class];
 284                         }
 285
 286                         $this->loadMonitor = new $class(
 287                                 $this, $this->srvCache, $this->wanCache, $this->loadMonitorConfig );
 288                         $this->loadMonitor->setLogger( $this->replLogger );
 289                 }
 290
 291                 return $this->loadMonitor;
 292         }
 293
 294         /**
 295          * @param array $loads
 296          * @param bool|string $domain Domain to get non-lagged for
 297          * @param int $maxLag Restrict the maximum allowed lag to this many seconds
 298          * @return bool|int|string
 299          */
 300         private function getRandomNonLagged( array $loads, $domain = false, $maxLag = INF ) {
 301                 $lags = $this->getLagTimes( $domain );
 302
 303                 # Unset excessively lagged servers
 304                 foreach ( $lags as $i => $lag ) {
 305                         if ( $i != 0 ) {
 306                                 # How much lag this server nominally is allowed to have
 307                                 $maxServerLag = $this->servers[$i]['max lag'] ?? $this->maxLag; // default
 308                                 # Constrain that futher by $maxLag argument
 309                                 $maxServerLag = min( $maxServerLag, $maxLag );
 310
 311                                 $host = $this->getServerName( $i );
 312                                 if ( $lag === false && !is_infinite( $maxServerLag ) ) {
 313                                         $this->replLogger->debug(
 314                                                 __METHOD__ .
 315                                                 ": server {host} is not replicating?", [ 'host' => $host ] );
 316                                         unset( $loads[$i] );
 317                                 } elseif ( $lag > $maxServerLag ) {
 318                                         $this->replLogger->debug(
 319                                                 __METHOD__ .
 320                                                 ": server {host} has {lag} seconds of lag (>= {maxlag})",
 321                                                 [ 'host' => $host, 'lag' => $lag, 'maxlag' => $maxServerLag ]
 322                                         );
 323                                         unset( $loads[$i] );
 324                                 }
 325                         }
 326                 }
 327
 328                 # Find out if all the replica DBs with non-zero load are lagged
 329                 $sum = 0;
 330                 foreach ( $loads as $load ) {
 331                         $sum += $load;
 332                 }
 333                 if ( $sum == 0 ) {
 334                         # No appropriate DB servers except maybe the master and some replica DBs with zero load
 335                         # Do NOT use the master
 336                         # Instead, this function will return false, triggering read-only mode,
 337                         # and a lagged replica DB will be used instead.
 338                         return false;
 339                 }
 340
 341                 if ( count( $loads ) == 0 ) {
 342                         return false;
 343                 }
 344
 345                 # Return a random representative of the remainder
 346                 return ArrayUtils::pickRandom( $loads );
 347         }
 348
 349         /**
 350          * @param int $i
 351          * @param array $groups
 352          * @param string|bool $domain
 353          * @return int
 354          */
 355         private function getConnectionIndex( $i, $groups, $domain ) {
 356                 // Check one "group" per default: the generic pool
 357                 $defaultGroups = $this->defaultGroup ? [ $this->defaultGroup ] : [ false ];
 358
 359                 $groups = ( $groups === false || $groups === [] )
 360                         ? $defaultGroups
 361                         : (array)$groups;
 362
 363                 if ( $i == self::DB_MASTER ) {
 364                         $i = $this->getWriterIndex();
 365                 } elseif ( $i == self::DB_REPLICA ) {
 366                         # Try to find an available server in any the query groups (in order)
 367                         foreach ( $groups as $group ) {
 368                                 $groupIndex = $this->getReaderIndex( $group, $domain );
 369                                 if ( $groupIndex !== false ) {
 370                                         $i = $groupIndex;
 371                                         break;
 372                                 }
 373                         }
 374                 }
 375
 376                 # Operation-based index
 377                 if ( $i == self::DB_REPLICA ) {
 378                         $this->lastError = 'Unknown error'; // reset error string
 379                         # Try the general server pool if $groups are unavailable.
 380                         $i = ( $groups === [ false ] )
 381                                 ? false // don't bother with this if that is what was tried above
 382                                 : $this->getReaderIndex( false, $domain );
 383                         # Couldn't find a working server in getReaderIndex()?
 384                         if ( $i === false ) {
 385                                 $this->lastError = 'No working replica DB server: ' . $this->lastError;
 386                                 // Throw an exception
 387                                 $this->reportConnectionError();
 388                                 return null; // not reached
 389                         }
 390                 }
 391
 392                 return $i;
 393         }
 394
 395         public function getReaderIndex( $group = false, $domain = false ) {
 396                 if ( count( $this->servers ) == 1 ) {
 397                         // Skip the load balancing if there's only one server
 398                         return $this->getWriterIndex();
 399                 } elseif ( $group === false && $this->readIndex >= 0 ) {
 400                         // Shortcut if the generic reader index was already cached
 401                         return $this->readIndex;
 402                 }
 403
 404                 if ( $group !== false ) {
 405                         // Use the server weight array for this load group
 406                         if ( isset( $this->groupLoads[$group] ) ) {
 407                                 $loads = $this->groupLoads[$group];
 408                         } else {
 409                                 // No loads for this group, return false and the caller can use some other group
 410                                 $this->connLogger->info( __METHOD__ . ": no loads for group $group" );
 411
 412                                 return false;
 413                         }
 414                 } else {
 415                         // Use the generic load group
 416                         $loads = $this->loads;
 417                 }
 418
 419                 // Scale the configured load ratios according to each server's load and state
 420                 $this->getLoadMonitor()->scaleLoads( $loads, $domain );
 421
 422                 // Pick a server to use, accounting for weights, load, lag, and "waitForPos"
 423                 list( $i, $laggedReplicaMode ) = $this->pickReaderIndex( $loads, $domain );
 424                 if ( $i === false ) {
 425                         // Replica DB connection unsuccessful
 426                         return false;
 427                 }
 428
 429                 if ( $this->waitForPos && $i != $this->getWriterIndex() ) {
 430                         // Before any data queries are run, wait for the server to catch up to the
 431                         // specified position. This is used to improve session consistency. Note that
 432                         // when LoadBalancer::waitFor() sets "waitForPos", the waiting triggers here,
 433                         // so update laggedReplicaMode as needed for consistency.
 434                         if ( !$this->doWait( $i ) ) {
 435                                 $laggedReplicaMode = true;
 436                         }
 437                 }
 438
 439                 if ( $this->readIndex <= 0 && $this->loads[$i] > 0 && $group === false ) {
 440                         // Cache the generic reader index for future ungrouped DB_REPLICA handles
 441                         $this->readIndex = $i;
 442                         // Record if the generic reader index is in "lagged replica DB" mode
 443                         if ( $laggedReplicaMode ) {
 444                                 $this->laggedReplicaMode = true;
 445                         }
 446                 }
 447
 448                 $serverName = $this->getServerName( $i );
 449                 $this->connLogger->debug( __METHOD__ . ": using server $serverName for group '$group'" );
 450
 451                 return $i;
 452         }
 453
 454         /**
 455          * @param array $loads List of server weights
 456          * @param string|bool $domain
 457          * @return array (reader index, lagged replica mode) or false on failure
 458          */
 459         private function pickReaderIndex( array $loads, $domain = false ) {
 460                 if ( $loads === [] ) {
 461                         throw new InvalidArgumentException( "Server configuration array is empty" );
 462                 }
 463
 464                 /** @var int|bool $i Index of selected server */
 465                 $i = false;
 466                 /** @var bool $laggedReplicaMode Whether server is considered lagged */
 467                 $laggedReplicaMode = false;
 468
 469                 // Quickly look through the available servers for a server that meets criteria...
 470                 $currentLoads = $loads;
 471                 while ( count( $currentLoads ) ) {
 472                         if ( $this->allowLagged || $laggedReplicaMode ) {
 473                                 $i = ArrayUtils::pickRandom( $currentLoads );
 474                         } else {
 475                                 $i = false;
 476                                 if ( $this->waitForPos && $this->waitForPos->asOfTime() ) {
 477                                         // "chronologyCallback" sets "waitForPos" for session consistency.
 478                                         // This triggers doWait() after connect, so it's especially good to
 479                                         // avoid lagged servers so as to avoid excessive delay in that method.
 480                                         $ago = microtime( true ) - $this->waitForPos->asOfTime();
 481                                         // Aim for <= 1 second of waiting (being too picky can backfire)
 482                                         $i = $this->getRandomNonLagged( $currentLoads, $domain, $ago + 1 );
 483                                 }
 484                                 if ( $i === false ) {
 485                                         // Any server with less lag than it's 'max lag' param is preferable
 486                                         $i = $this->getRandomNonLagged( $currentLoads, $domain );
 487                                 }
 488                                 if ( $i === false && count( $currentLoads ) != 0 ) {
 489                                         // All replica DBs lagged. Switch to read-only mode
 490                                         $this->replLogger->error(
 491                                                 __METHOD__ . ": all replica DBs lagged. Switch to read-only mode" );
 492                                         $i = ArrayUtils::pickRandom( $currentLoads );
 493                                         $laggedReplicaMode = true;
 494                                 }
 495                         }
 496
 497                         if ( $i === false ) {
 498                                 // pickRandom() returned false.
 499                                 // This is permanent and means the configuration or the load monitor
 500                                 // wants us to return false.
 501                                 $this->connLogger->debug( __METHOD__ . ": pickRandom() returned false" );
 502
 503                                 return [ false, false ];
 504                         }
 505
 506                         $serverName = $this->getServerName( $i );
 507                         $this->connLogger->debug( __METHOD__ . ": Using reader #$i: $serverName..." );
 508
 509                         $conn = $this->openConnection( $i, $domain );
 510                         if ( !$conn ) {
 511                                 $this->connLogger->warning( __METHOD__ . ": Failed connecting to $i/$domain" );
 512                                 unset( $currentLoads[$i] ); // avoid this server next iteration
 513                                 $i = false;
 514                                 continue;
 515                         }
 516
 517                         // Decrement reference counter, we are finished with this connection.
 518                         // It will be incremented for the caller later.
 519                         if ( $domain !== false ) {
 520                                 $this->reuseConnection( $conn );
 521                         }
 522
 523                         // Return this server
 524                         break;
 525                 }
 526
 527                 // If all servers were down, quit now
 528                 if ( $currentLoads === [] ) {
 529                         $this->connLogger->error( __METHOD__ . ": all servers down" );
 530                 }
 531
 532                 return [ $i, $laggedReplicaMode ];
 533         }
 534
 535         public function waitFor( $pos ) {
 536                 $oldPos = $this->waitForPos;
 537                 try {
 538                         $this->waitForPos = $pos;
 539                         // If a generic reader connection was already established, then wait now
 540                         $i = $this->readIndex;
 541                         if ( ( $i > 0 ) && !$this->doWait( $i ) ) {
 542                                 $this->laggedReplicaMode = true;
 543                         }
 544                 } finally {
 545                         // Restore the older position if it was higher since this is used for lag-protection
 546                         $this->setWaitForPositionIfHigher( $oldPos );
 547                 }
 548         }
 549
 550         public function waitForOne( $pos, $timeout = null ) {
 551                 $oldPos = $this->waitForPos;
 552                 try {
 553                         $this->waitForPos = $pos;
 554
 555                         $i = $this->readIndex;
 556                         if ( $i <= 0 ) {
 557                                 // Pick a generic replica DB if there isn't one yet
 558                                 $readLoads = $this->loads;
 559                                 unset( $readLoads[$this->getWriterIndex()] ); // replica DBs only
 560                                 $readLoads = array_filter( $readLoads ); // with non-zero load
 561                                 $i = ArrayUtils::pickRandom( $readLoads );
 562                         }
 563
 564                         if ( $i > 0 ) {
 565                                 $ok = $this->doWait( $i, true, $timeout );
 566                         } else {
 567                                 $ok = true; // no applicable loads
 568                         }
 569                 } finally {
 570                         # Restore the old position, as this is not used for lag-protection but for throttling
 571                         $this->waitForPos = $oldPos;
 572                 }
 573
 574                 return $ok;
 575         }
 576
 577         public function waitForAll( $pos, $timeout = null ) {
 578                 $timeout = $timeout ?: $this->waitTimeout;
 579
 580                 $oldPos = $this->waitForPos;
 581                 try {
 582                         $this->waitForPos = $pos;
 583                         $serverCount = count( $this->servers );
 584
 585                         $ok = true;
 586                         for ( $i = 1; $i < $serverCount; $i++ ) {
 587                                 if ( $this->loads[$i] > 0 ) {
 588                                         $start = microtime( true );
 589                                         $ok = $this->doWait( $i, true, $timeout ) && $ok;
 590                                         $timeout -= intval( microtime( true ) - $start );
 591                                         if ( $timeout <= 0 ) {
 592                                                 break; // timeout reached
 593                                         }
 594                                 }
 595                         }
 596                 } finally {
 597                         # Restore the old position, as this is not used for lag-protection but for throttling
 598                         $this->waitForPos = $oldPos;
 599                 }
 600
 601                 return $ok;
 602         }
 603
 604         /**
 605          * @param DBMasterPos|bool $pos
 606          */
 607         private function setWaitForPositionIfHigher( $pos ) {
 608                 if ( !$pos ) {
 609                         return;
 610                 }
 611
 612                 if ( !$this->waitForPos || $pos->hasReached( $this->waitForPos ) ) {
 613                         $this->waitForPos = $pos;
 614                 }
 615         }
 616
 617         public function getAnyOpenConnection( $i, $flags = 0 ) {
 618                 $i = ( $i === self::DB_MASTER ) ? $this->getWriterIndex() : $i;
 619                 $autocommit = ( ( $flags & self::CONN_TRX_AUTOCOMMIT ) == self::CONN_TRX_AUTOCOMMIT );
 620
 621                 foreach ( $this->conns as $connsByServer ) {
 622                         if ( $i === self::DB_REPLICA ) {
 623                                 $indexes = array_keys( $connsByServer );
 624                         } else {
 625                                 $indexes = isset( $connsByServer[$i] ) ? [ $i ] : [];
 626                         }
 627
 628                         foreach ( $indexes as $index ) {
 629                                 foreach ( $connsByServer[$index] as $conn ) {
 630                                         if ( !$conn->isOpen() ) {
 631                                                 continue; // some sort of error occured?
 632                                         }
 633                                         if ( !$autocommit || $conn->getLBInfo( 'autoCommitOnly' ) ) {
 634                                                 return $conn;
 635                                         }
 636                                 }
 637                         }
 638                 }
 639
 640                 return false;
 641         }
 642
 643         /**
 644          * Wait for a given replica DB to catch up to the master pos stored in $this
 645          * @param int $index Server index
 646          * @param bool $open Check the server even if a new connection has to be made
 647          * @param int|null $timeout Max seconds to wait; default is "waitTimeout" given to __construct()
 648          * @return bool
 649          */
 650         protected function doWait( $index, $open = false, $timeout = null ) {
 651                 $timeout = max( 1, intval( $timeout ?: $this->waitTimeout ) );
 652
 653                 // Check if we already know that the DB has reached this point
 654                 $server = $this->getServerName( $index );
 655                 $key = $this->srvCache->makeGlobalKey( __CLASS__, 'last-known-pos', $server, 'v1' );
 656                 /** @var DBMasterPos $knownReachedPos */
 657                 $knownReachedPos = $this->srvCache->get( $key );
 658                 if (
 659                         $knownReachedPos instanceof DBMasterPos &&
 660                         $knownReachedPos->hasReached( $this->waitForPos )
 661                 ) {
 662                         $this->replLogger->debug(
 663                                 __METHOD__ .
 664                                 ': replica DB {dbserver} known to be caught up (pos >= $knownReachedPos).',
 665                                 [ 'dbserver' => $server ]
 666                         );
 667                         return true;
 668                 }
 669
 670                 // Find a connection to wait on, creating one if needed and allowed
 671                 $close = false; // close the connection afterwards
 672                 $conn = $this->getAnyOpenConnection( $index );
 673                 if ( !$conn ) {
 674                         if ( !$open ) {
 675                                 $this->replLogger->debug(
 676                                         __METHOD__ . ': no connection open for {dbserver}',
 677                                         [ 'dbserver' => $server ]
 678                                 );
 679
 680                                 return false;
 681                         } else {
 682                                 $conn = $this->openConnection( $index, self::DOMAIN_ANY );
 683                                 if ( !$conn ) {
 684                                         $this->replLogger->warning(
 685                                                 __METHOD__ . ': failed to connect to {dbserver}',
 686                                                 [ 'dbserver' => $server ]
 687                                         );
 688
 689                                         return false;
 690                                 }
 691                                 // Avoid connection spam in waitForAll() when connections
 692                                 // are made just for the sake of doing this lag check.
 693                                 $close = true;
 694                         }
 695                 }
 696
 697                 $this->replLogger->info(
 698                         __METHOD__ .
 699                         ': waiting for replica DB {dbserver} to catch up...',
 700                         [ 'dbserver' => $server ]
 701                 );
 702
 703                 $result = $conn->masterPosWait( $this->waitForPos, $timeout );
 704
 705                 if ( $result === null ) {
 706                         $this->replLogger->warning(
 707                                 __METHOD__ . ': Errored out waiting on {host} pos {pos}',
 708                                 [
 709                                         'host' => $server,
 710                                         'pos' => $this->waitForPos,
 711                                         'trace' => ( new RuntimeException() )->getTraceAsString()
 712                                 ]
 713                         );
 714                         $ok = false;
 715                 } elseif ( $result == -1 ) {
 716                         $this->replLogger->warning(
 717                                 __METHOD__ . ': Timed out waiting on {host} pos {pos}',
 718                                 [
 719                                         'host' => $server,
 720                                         'pos' => $this->waitForPos,
 721                                         'trace' => ( new RuntimeException() )->getTraceAsString()
 722                                 ]
 723                         );
 724                         $ok = false;
 725                 } else {
 726                         $this->replLogger->debug( __METHOD__ . ": done waiting" );
 727                         $ok = true;
 728                         // Remember that the DB reached this point
 729                         $this->srvCache->set( $key, $this->waitForPos, BagOStuff::TTL_DAY );
 730                 }
 731
 732                 if ( $close ) {
 733                         $this->closeConnection( $conn );
 734                 }
 735
 736                 return $ok;
 737         }
 738
 739         public function getConnection( $i, $groups = [], $domain = false, $flags = 0 ) {
 740                 if ( $i === null || $i === false ) {
 741                         throw new InvalidArgumentException( "Cannot connect without a server index" );
 742                 }
 743
 744                 $domain = $this->resolveDomainID( $domain );
 745                 $masterOnly = ( $i == self::DB_MASTER || $i == $this->getWriterIndex() );
 746
 747                 if ( ( $flags & self::CONN_TRX_AUTOCOMMIT ) === self::CONN_TRX_AUTOCOMMIT ) {
 748                         // Assuming all servers are of the same type (or similar), which is overwhelmingly
 749                         // the case, use the master server information to get the attributes. The information
 750                         // for $i cannot be used since it might be DB_REPLICA, which might require connection
 751                         // attempts in order to be resolved into a real server index.
 752                         $attributes = $this->getServerAttributes( $this->getWriterIndex() );
 753                         if ( $attributes[Database::ATTR_DB_LEVEL_LOCKING] ) {
 754                                 // Callers sometimes want to (a) escape REPEATABLE-READ stateness without locking
 755                                 // rows (e.g. FOR UPDATE) or (b) make small commits during a larger transactions
 756                                 // to reduce lock contention. None of these apply for sqlite and using separate
 757                                 // connections just causes self-deadlocks.
 758                                 $flags &= ~self::CONN_TRX_AUTOCOMMIT;
 759                                 $this->connLogger->info( __METHOD__ .
 760                                         ': ignoring CONN_TRX_AUTOCOMMIT to avoid deadlocks.' );
 761                         }
 762                 }
 763
 764                 // Number of connections made before getting the server index and handle
 765                 $priorConnectionsMade = $this->connsOpened;
 766                 // Decide which server to use (might trigger new connections)
 767                 $serverIndex = $this->getConnectionIndex( $i, $groups, $domain );
 768                 // Get an open connection to that server (might trigger a new connection)
 769                 $conn = $this->openConnection( $serverIndex, $domain, $flags );
 770                 if ( !$conn ) {
 771                         $this->reportConnectionError();
 772                         return null; // unreachable due to exception
 773                 }
 774
 775                 // Profile any new connections caused by this method
 776                 if ( $this->connsOpened > $priorConnectionsMade ) {
 777                         $host = $conn->getServer();
 778                         $dbname = $conn->getDBname();
 779                         $this->trxProfiler->recordConnection( $host, $dbname, $masterOnly );
 780                 }
 781
 782                 if ( $masterOnly ) {
 783                         // If the load balancer is read-only, perhaps due to replication lag, then master
 784                         // DB handles will reflect that. Note that Database::assertIsWritableMaster() takes
 785                         // care of replica DB handles whereas getReadOnlyReason() would cause infinite loops.
 786                         $conn->setLBInfo( 'readOnlyReason', $this->getReadOnlyReason( $domain, $conn ) );
 787                 }
 788
 789                 return $conn;
 790         }
 791
 792         public function reuseConnection( IDatabase $conn ) {
 793                 $serverIndex = $conn->getLBInfo( 'serverIndex' );
 794                 $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 795                 if ( $serverIndex === null || $refCount === null ) {
 796                         /**
 797                          * This can happen in code like:
 798                          *   foreach ( $dbs as $db ) {
 799                          *     $conn = $lb->getConnection( $lb::DB_REPLICA, [], $db );
 800                          *     ...
 801                          *     $lb->reuseConnection( $conn );
 802                          *   }
 803                          * When a connection to the local DB is opened in this way, reuseConnection()
 804                          * should be ignored
 805                          */
 806                         return;
 807                 } elseif ( $conn instanceof DBConnRef ) {
 808                         // DBConnRef already handles calling reuseConnection() and only passes the live
 809                         // Database instance to this method. Any caller passing in a DBConnRef is broken.
 810                         $this->connLogger->error(
 811                                 __METHOD__ . ": got DBConnRef instance.\n" .
 812                                 ( new RuntimeException() )->getTraceAsString() );
 813
 814                         return;
 815                 }
 816
 817                 if ( $this->disabled ) {
 818                         return; // DBConnRef handle probably survived longer than the LoadBalancer
 819                 }
 820
 821                 if ( $conn->getLBInfo( 'autoCommitOnly' ) ) {
 822                         $connFreeKey = self::KEY_FOREIGN_FREE_NOROUND;
 823                         $connInUseKey = self::KEY_FOREIGN_INUSE_NOROUND;
 824                 } else {
 825                         $connFreeKey = self::KEY_FOREIGN_FREE;
 826                         $connInUseKey = self::KEY_FOREIGN_INUSE;
 827                 }
 828
 829                 $domain = $conn->getDomainID();
 830                 if ( !isset( $this->conns[$connInUseKey][$serverIndex][$domain] ) ) {
 831                         throw new InvalidArgumentException(
 832                                 "Connection $serverIndex/$domain not found; it may have already been freed" );
 833                 } elseif ( $this->conns[$connInUseKey][$serverIndex][$domain] !== $conn ) {
 834                         throw new InvalidArgumentException(
 835                                 "Connection $serverIndex/$domain mismatched; it may have already been freed" );
 836                 }
 837
 838                 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
 839                 if ( $refCount <= 0 ) {
 840                         $this->conns[$connFreeKey][$serverIndex][$domain] = $conn;
 841                         unset( $this->conns[$connInUseKey][$serverIndex][$domain] );
 842                         if ( !$this->conns[$connInUseKey][$serverIndex] ) {
 843                                 unset( $this->conns[$connInUseKey][$serverIndex] ); // clean up
 844                         }
 845                         $this->connLogger->debug( __METHOD__ . ": freed connection $serverIndex/$domain" );
 846                 } else {
 847                         $this->connLogger->debug( __METHOD__ .
 848                                 ": reference count for $serverIndex/$domain reduced to $refCount" );
 849                 }
 850         }
 851
 852         public function getConnectionRef( $i, $groups = [], $domain = false, $flags = 0 ) {
 853                 $domain = $this->resolveDomainID( $domain );
 854                 $role = $this->getRoleFromIndex( $i );
 855
 856                 return new DBConnRef( $this, $this->getConnection( $i, $groups, $domain, $flags ), $role );
 857         }
 858
 859         public function getLazyConnectionRef( $i, $groups = [], $domain = false, $flags = 0 ) {
 860                 $domain = $this->resolveDomainID( $domain );
 861                 $role = $this->getRoleFromIndex( $i );
 862
 863                 return new DBConnRef( $this, [ $i, $groups, $domain, $flags ], $role );
 864         }
 865
 866         public function getMaintenanceConnectionRef( $i, $groups = [], $domain = false, $flags = 0 ) {
 867                 $domain = $this->resolveDomainID( $domain );
 868                 $role = $this->getRoleFromIndex( $i );
 869
 870                 return new MaintainableDBConnRef(
 871                         $this, $this->getConnection( $i, $groups, $domain, $flags ), $role );
 872         }
 873
 874         /**
 875          * @param int $i Server index or DB_MASTER/DB_REPLICA
 876          * @return int One of DB_MASTER/DB_REPLICA
 877          */
 878         private function getRoleFromIndex( $i ) {
 879                 return ( $i === self::DB_MASTER || $i === $this->getWriterIndex() )
 880                         ? self::DB_MASTER
 881                         : self::DB_REPLICA;
 882         }
 883
 884         public function openConnection( $i, $domain = false, $flags = 0 ) {
 885                 $domain = $this->resolveDomainID( $domain );
 886
 887                 if ( !$this->connectionAttempted && $this->chronologyCallback ) {
 888                         // Load any "waitFor" positions before connecting so that doWait() is triggered
 889                         $this->connLogger->debug( __METHOD__ . ': calling initLB() before first connection.' );
 890                         $this->connectionAttempted = true;
 891                         ( $this->chronologyCallback )( $this );
 892                 }
 893
 894                 $conn = $this->localDomain->equals( $domain )
 895                         ? $this->openLocalConnection( $i, $flags )
 896                         : $this->openForeignConnection( $i, $domain, $flags );
 897
 898                 if ( $conn instanceof IDatabase && !$conn->isOpen() ) {
 899                         // Connection was made but later unrecoverably lost for some reason.
 900                         // Do not return a handle that will just throw exceptions on use,
 901                         // but let the calling code (e.g. getReaderIndex) try another server.
 902                         $this->errorConnection = $conn;
 903                         $conn = false;
 904                 }
 905
 906                 if (
 907                         $conn instanceof IDatabase &&
 908                         ( ( $flags & self::CONN_TRX_AUTOCOMMIT ) == self::CONN_TRX_AUTOCOMMIT )
 909                 ) {
 910                         if ( $conn->trxLevel() ) { // sanity
 911                                 throw new DBUnexpectedError(
 912                                         $conn,
 913                                         'Handle requested with CONN_TRX_AUTOCOMMIT yet it has a transaction'
 914                                 );
 915                         }
 916
 917                         $conn->clearFlag( $conn::DBO_TRX ); // auto-commit mode
 918                 }
 919
 920                 return $conn;
 921         }
 922
 923         /**
 924          * Open a connection to a local DB, or return one if it is already open.
 925          *
 926          * On error, returns false, and the connection which caused the
 927          * error will be available via $this->errorConnection.
 928          *
 929          * @note If disable() was called on this LoadBalancer, this method will throw a DBAccessError.
 930          *
 931          * @param int $i Server index
 932          * @param int $flags Class CONN_* constant bitfield
 933          * @return Database
 934          */
 935         private function openLocalConnection( $i, $flags = 0 ) {
 936                 // Connection handles required to be in auto-commit mode use a separate connection
 937                 // pool since the main pool is effected by implicit and explicit transaction rounds
 938                 $autoCommit = ( ( $flags & self::CONN_TRX_AUTOCOMMIT ) == self::CONN_TRX_AUTOCOMMIT );
 939
 940                 $connKey = $autoCommit ? self::KEY_LOCAL_NOROUND : self::KEY_LOCAL;
 941                 if ( isset( $this->conns[$connKey][$i][0] ) ) {
 942                         $conn = $this->conns[$connKey][$i][0];
 943                 } else {
 944                         if ( !isset( $this->servers[$i] ) || !is_array( $this->servers[$i] ) ) {
 945                                 throw new InvalidArgumentException( "No server with index '$i'" );
 946                         }
 947                         // Open a new connection
 948                         $server = $this->servers[$i];
 949                         $server['serverIndex'] = $i;
 950                         $server['autoCommitOnly'] = $autoCommit;
 951                         $conn = $this->reallyOpenConnection( $server, $this->localDomain );
 952                         $host = $this->getServerName( $i );
 953                         if ( $conn->isOpen() ) {
 954                                 $this->connLogger->debug(
 955                                         __METHOD__ . ": connected to database $i at '$host'." );
 956                                 $this->conns[$connKey][$i][0] = $conn;
 957                         } else {
 958                                 $this->connLogger->warning(
 959                                         __METHOD__ . ": failed to connect to database $i at '$host'." );
 960                                 $this->errorConnection = $conn;
 961                                 $conn = false;
 962                         }
 963                 }
 964
 965                 // Final sanity check to make sure the right domain is selected
 966                 if (
 967                         $conn instanceof IDatabase &&
 968                         !$this->localDomain->isCompatible( $conn->getDomainID() )
 969                 ) {
 970                         throw new UnexpectedValueException(
 971                                 "Got connection to '{$conn->getDomainID()}', " .
 972                                 "but expected local domain ('{$this->localDomain}')" );
 973                 }
 974
 975                 return $conn;
 976         }
 977
 978         /**
 979          * Open a connection to a foreign DB, or return one if it is already open.
 980          *
 981          * Increments a reference count on the returned connection which locks the
 982          * connection to the requested domain. This reference count can be
 983          * decremented by calling reuseConnection().
 984          *
 985          * If a connection is open to the appropriate server already, but with the wrong
 986          * database, it will be switched to the right database and returned, as long as
 987          * it has been freed first with reuseConnection().
 988          *
 989          * On error, returns false, and the connection which caused the
 990          * error will be available via $this->errorConnection.
 991          *
 992          * @note If disable() was called on this LoadBalancer, this method will throw a DBAccessError.
 993          *
 994          * @param int $i Server index
 995          * @param string $domain Domain ID to open
 996          * @param int $flags Class CONN_* constant bitfield
 997          * @return Database|bool Returns false on connection error
 998          * @throws DBError When database selection fails
 999          */
1000         private function openForeignConnection( $i, $domain, $flags = 0 ) {
1001                 $domainInstance = DatabaseDomain::newFromId( $domain );
1002                 // Connection handles required to be in auto-commit mode use a separate connection
1003                 // pool since the main pool is effected by implicit and explicit transaction rounds
1004                 $autoCommit = ( ( $flags & self::CONN_TRX_AUTOCOMMIT ) == self::CONN_TRX_AUTOCOMMIT );
1005
1006                 if ( $autoCommit ) {
1007                         $connFreeKey = self::KEY_FOREIGN_FREE_NOROUND;
1008                         $connInUseKey = self::KEY_FOREIGN_INUSE_NOROUND;
1009                 } else {
1010                         $connFreeKey = self::KEY_FOREIGN_FREE;
1011                         $connInUseKey = self::KEY_FOREIGN_INUSE;
1012                 }
1013
1014                 /** @var Database $conn */
1015                 $conn = null;
1016
1017                 if ( isset( $this->conns[$connInUseKey][$i][$domain] ) ) {
1018                         // Reuse an in-use connection for the same domain
1019                         $conn = $this->conns[$connInUseKey][$i][$domain];
1020                         $this->connLogger->debug( __METHOD__ . ": reusing connection $i/$domain" );
1021                 } elseif ( isset( $this->conns[$connFreeKey][$i][$domain] ) ) {
1022                         // Reuse a free connection for the same domain
1023                         $conn = $this->conns[$connFreeKey][$i][$domain];
1024                         unset( $this->conns[$connFreeKey][$i][$domain] );
1025                         $this->conns[$connInUseKey][$i][$domain] = $conn;
1026                         $this->connLogger->debug( __METHOD__ . ": reusing free connection $i/$domain" );
1027                 } elseif ( !empty( $this->conns[$connFreeKey][$i] ) ) {
1028                         // Reuse a free connection from another domain if possible
1029                         foreach ( $this->conns[$connFreeKey][$i] as $oldDomain => $conn ) {
1030                                 if ( $domainInstance->getDatabase() !== null ) {
1031                                         // Check if changing the database will require a new connection.
1032                                         // In that case, leave the connection handle alone and keep looking.
1033                                         // This prevents connections from being closed mid-transaction and can
1034                                         // also avoid overhead if the same database will later be requested.
1035                                         if (
1036                                                 $conn->databasesAreIndependent() &&
1037                                                 $conn->getDBname() !== $domainInstance->getDatabase()
1038                                         ) {
1039                                                 continue;
1040                                         }
1041                                         // Select the new database, schema, and prefix
1042                                         $conn->selectDomain( $domainInstance );
1043                                 } else {
1044                                         // Stay on the current database, but update the schema/prefix
1045                                         $conn->dbSchema( $domainInstance->getSchema() );
1046                                         $conn->tablePrefix( $domainInstance->getTablePrefix() );
1047                                 }
1048                                 unset( $this->conns[$connFreeKey][$i][$oldDomain] );
1049                                 // Note that if $domain is an empty string, getDomainID() might not match it
1050                                 $this->conns[$connInUseKey][$i][$conn->getDomainID()] = $conn;
1051                                 $this->connLogger->debug( __METHOD__ .
1052                                         ": reusing free connection from $oldDomain for $domain" );
1053                                 break;
1054                         }
1055                 }
1056
1057                 if ( !$conn ) {
1058                         if ( !isset( $this->servers[$i] ) || !is_array( $this->servers[$i] ) ) {
1059                                 throw new InvalidArgumentException( "No server with index '$i'" );
1060                         }
1061                         // Open a new connection
1062                         $server = $this->servers[$i];
1063                         $server['serverIndex'] = $i;
1064                         $server['foreignPoolRefCount'] = 0;
1065                         $server['foreign'] = true;
1066                         $server['autoCommitOnly'] = $autoCommit;
1067                         $conn = $this->reallyOpenConnection( $server, $domainInstance );
1068                         if ( !$conn->isOpen() ) {
1069                                 $this->connLogger->warning( __METHOD__ . ": connection error for $i/$domain" );
1070                                 $this->errorConnection = $conn;
1071                                 $conn = false;
1072                         } else {
1073                                 // Note that if $domain is an empty string, getDomainID() might not match it
1074                                 $this->conns[$connInUseKey][$i][$conn->getDomainID()] = $conn;
1075                                 $this->connLogger->debug( __METHOD__ . ": opened new connection for $i/$domain" );
1076                         }
1077                 }
1078
1079                 if ( $conn instanceof IDatabase ) {
1080                         // Final sanity check to make sure the right domain is selected
1081                         if ( !$domainInstance->isCompatible( $conn->getDomainID() ) ) {
1082                                 throw new UnexpectedValueException(
1083                                         "Got connection to '{$conn->getDomainID()}', but expected '$domain'" );
1084                         }
1085                         // Increment reference count
1086                         $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
1087                         $conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
1088                 }
1089
1090                 return $conn;
1091         }
1092
1093         public function getServerAttributes( $i ) {
1094                 return Database::attributesFromType(
1095                         $this->getServerType( $i ),
1096                         $this->servers[$i]['driver'] ?? null
1097                 );
1098         }
1099
1100         /**
1101          * Test if the specified index represents an open connection
1102          *
1103          * @param int $index Server index
1104          * @private
1105          * @return bool
1106          */
1107         private function isOpen( $index ) {
1108                 if ( !is_int( $index ) ) {
1109                         return false;
1110                 }
1111
1112                 return (bool)$this->getAnyOpenConnection( $index );
1113         }
1114
1115         /**
1116          * Open a new network connection to a server (uncached)
1117          *
1118          * Returns a Database object whether or not the connection was successful.
1119          *
1120          * @param array $server
1121          * @param DatabaseDomain $domain Domain the connection is for, possibly unspecified
1122          * @return Database
1123          * @throws DBAccessError
1124          * @throws InvalidArgumentException
1125          */
1126         protected function reallyOpenConnection( array $server, DatabaseDomain $domain ) {
1127                 if ( $this->disabled ) {
1128                         throw new DBAccessError();
1129                 }
1130
1131                 if ( $domain->getDatabase() === null ) {
1132                         // The database domain does not specify a DB name and some database systems require a
1133                         // valid DB specified on connection. The $server configuration array contains a default
1134                         // DB name to use for connections in such cases.
1135                         if ( $server['type'] === 'mysql' ) {
1136                                 // For MySQL, DATABASE and SCHEMA are synonyms, connections need not specify a DB,
1137                                 // and the DB name in $server might not exist due to legacy reasons (the default
1138                                 // domain used to ignore the local LB domain, even when mismatched).
1139                                 $server['dbname'] = null;
1140                         }
1141                 } else {
1142                         $server['dbname'] = $domain->getDatabase();
1143                 }
1144
1145                 if ( $domain->getSchema() !== null ) {
1146                         $server['schema'] = $domain->getSchema();
1147                 }
1148
1149                 // It is always possible to connect with any prefix, even the empty string
1150                 $server['tablePrefix'] = $domain->getTablePrefix();
1151
1152                 // Let the handle know what the cluster master is (e.g. "db1052")
1153                 $masterName = $this->getServerName( $this->getWriterIndex() );
1154                 $server['clusterMasterHost'] = $masterName;
1155
1156                 // Log when many connection are made on requests
1157                 if ( ++$this->connsOpened >= self::CONN_HELD_WARN_THRESHOLD ) {
1158                         $this->perfLogger->warning( __METHOD__ . ": " .
1159                                 "{$this->connsOpened}+ connections made (master=$masterName)" );
1160                 }
1161
1162                 $server['srvCache'] = $this->srvCache;
1163                 // Set loggers and profilers
1164                 $server['connLogger'] = $this->connLogger;
1165                 $server['queryLogger'] = $this->queryLogger;
1166                 $server['errorLogger'] = $this->errorLogger;
1167                 $server['deprecationLogger'] = $this->deprecationLogger;
1168                 $server['profiler'] = $this->profiler;
1169                 $server['trxProfiler'] = $this->trxProfiler;
1170                 // Use the same agent and PHP mode for all DB handles
1171                 $server['cliMode'] = $this->cliMode;
1172                 $server['agent'] = $this->agent;
1173                 // Use DBO_DEFAULT flags by default for LoadBalancer managed databases. Assume that the
1174                 // application calls LoadBalancer::commitMasterChanges() before the PHP script completes.
1175                 $server['flags'] = $server['flags'] ?? IDatabase::DBO_DEFAULT;
1176
1177                 // Create a live connection object
1178                 try {
1179                         $db = Database::factory( $server['type'], $server );
1180                 } catch ( DBConnectionError $e ) {
1181                         // FIXME: This is probably the ugliest thing I have ever done to
1182                         // PHP. I'm half-expecting it to segfault, just out of disgust. -- TS
1183                         $db = $e->db;
1184                 }
1185
1186                 $db->setLBInfo( $server );
1187                 $db->setLazyMasterHandle(
1188                         $this->getLazyConnectionRef( self::DB_MASTER, [], $db->getDomainID() )
1189                 );
1190                 $db->setTableAliases( $this->tableAliases );
1191                 $db->setIndexAliases( $this->indexAliases );
1192
1193                 if ( $server['serverIndex'] === $this->getWriterIndex() ) {
1194                         if ( $this->trxRoundId !== false ) {
1195                                 $this->applyTransactionRoundFlags( $db );
1196                         }
1197                         foreach ( $this->trxRecurringCallbacks as $name => $callback ) {
1198                                 $db->setTransactionListener( $name, $callback );
1199                         }
1200                 }
1201
1202                 return $db;
1203         }
1204
1205         /**
1206          * @throws DBConnectionError
1207          */
1208         private function reportConnectionError() {
1209                 $conn = $this->errorConnection; // the connection which caused the error
1210                 $context = [
1211                         'method' => __METHOD__,
1212                         'last_error' => $this->lastError,
1213                 ];
1214
1215                 if ( $conn instanceof IDatabase ) {
1216                         $context['db_server'] = $conn->getServer();
1217                         $this->connLogger->warning(
1218                                 __METHOD__ . ": connection error: {last_error} ({db_server})",
1219                                 $context
1220                         );
1221
1222                         throw new DBConnectionError( $conn, "{$this->lastError} ({$context['db_server']})" );
1223                 } else {
1224                         // No last connection, probably due to all servers being too busy
1225                         $this->connLogger->error(
1226                                 __METHOD__ .
1227                                 ": LB failure with no last connection. Connection error: {last_error}",
1228                                 $context
1229                         );
1230
1231                         // If all servers were busy, "lastError" will contain something sensible
1232                         throw new DBConnectionError( null, $this->lastError );
1233                 }
1234         }
1235
1236         public function getWriterIndex() {
1237                 return 0;
1238         }
1239
1240         public function haveIndex( $i ) {
1241                 return array_key_exists( $i, $this->servers );
1242         }
1243
1244         public function isNonZeroLoad( $i ) {
1245                 return array_key_exists( $i, $this->servers ) && $this->loads[$i] != 0;
1246         }
1247
1248         public function getServerCount() {
1249                 return count( $this->servers );
1250         }
1251
1252         public function getServerName( $i ) {
1253                 $name = $this->servers[$i]['hostName'] ?? $this->servers[$i]['host'] ?? '';
1254
1255                 return ( $name != '' ) ? $name : 'localhost';
1256         }
1257
1258         public function getServerInfo( $i ) {
1259                 return $this->servers[$i] ?? false;
1260         }
1261
1262         public function getServerType( $i ) {
1263                 return $this->servers[$i]['type'] ?? 'unknown';
1264         }
1265
1266         public function getMasterPos() {
1267                 # If this entire request was served from a replica DB without opening a connection to the
1268                 # master (however unlikely that may be), then we can fetch the position from the replica DB.
1269                 $masterConn = $this->getAnyOpenConnection( $this->getWriterIndex() );
1270                 if ( !$masterConn ) {
1271                         $serverCount = count( $this->servers );
1272                         for ( $i = 1; $i < $serverCount; $i++ ) {
1273                                 $conn = $this->getAnyOpenConnection( $i );
1274                                 if ( $conn ) {
1275                                         return $conn->getReplicaPos();
1276                                 }
1277                         }
1278                 } else {
1279                         return $masterConn->getMasterPos();
1280                 }
1281
1282                 return false;
1283         }
1284
1285         public function disable() {
1286                 $this->closeAll();
1287                 $this->disabled = true;
1288         }
1289
1290         public function closeAll() {
1291                 $fname = __METHOD__;
1292                 $this->forEachOpenConnection( function ( IDatabase $conn ) use ( $fname ) {
1293                         $host = $conn->getServer();
1294                         $this->connLogger->debug(
1295                                 $fname . ": closing connection to database '$host'." );
1296                         $conn->close();
1297                 } );
1298
1299                 $this->conns = [
1300                         self::KEY_LOCAL => [],
1301                         self::KEY_FOREIGN_INUSE => [],
1302                         self::KEY_FOREIGN_FREE => [],
1303                         self::KEY_LOCAL_NOROUND => [],
1304                         self::KEY_FOREIGN_INUSE_NOROUND => [],
1305                         self::KEY_FOREIGN_FREE_NOROUND => []
1306                 ];
1307                 $this->connsOpened = 0;
1308         }
1309
1310         public function closeConnection( IDatabase $conn ) {
1311                 if ( $conn instanceof DBConnRef ) {
1312                         // Avoid calling close() but still leaving the handle in the pool
1313                         throw new RuntimeException( 'Cannot close DBConnRef instance; it must be shareable' );
1314                 }
1315
1316                 $serverIndex = $conn->getLBInfo( 'serverIndex' );
1317                 foreach ( $this->conns as $type => $connsByServer ) {
1318                         if ( !isset( $connsByServer[$serverIndex] ) ) {
1319                                 continue;
1320                         }
1321
1322                         foreach ( $connsByServer[$serverIndex] as $i => $trackedConn ) {
1323                                 if ( $conn === $trackedConn ) {
1324                                         $host = $this->getServerName( $i );
1325                                         $this->connLogger->debug(
1326                                                 __METHOD__ . ": closing connection to database $i at '$host'." );
1327                                         unset( $this->conns[$type][$serverIndex][$i] );
1328                                         --$this->connsOpened;
1329                                         break 2;
1330                                 }
1331                         }
1332                 }
1333
1334                 $conn->close();
1335         }
1336
1337         public function commitAll( $fname = __METHOD__ ) {
1338                 $this->commitMasterChanges( $fname );
1339                 $this->flushMasterSnapshots( $fname );
1340                 $this->flushReplicaSnapshots( $fname );
1341         }
1342
1343         public function finalizeMasterChanges() {
1344                 $this->assertTransactionRoundStage( [ self::ROUND_CURSORY, self::ROUND_FINALIZED ] );
1345
1346                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1347                 // Loop until callbacks stop adding callbacks on other connections
1348                 $total = 0;
1349                 do {
1350                         $count = 0; // callbacks execution attempts
1351                         $this->forEachOpenMasterConnection( function ( Database $conn ) use ( &$count ) {
1352                                 // Run any pre-commit callbacks while leaving the post-commit ones suppressed.
1353                                 // Any error should cause all (peer) transactions to be rolled back together.
1354                                 $count += $conn->runOnTransactionPreCommitCallbacks();
1355                         } );
1356                         $total += $count;
1357                 } while ( $count > 0 );
1358                 // Defer post-commit callbacks until after COMMIT/ROLLBACK happens on all handles
1359                 $this->forEachOpenMasterConnection( function ( Database $conn ) {
1360                         $conn->setTrxEndCallbackSuppression( true );
1361                 } );
1362                 $this->trxRoundStage = self::ROUND_FINALIZED;
1363
1364                 return $total;
1365         }
1366
1367         public function approveMasterChanges( array $options ) {
1368                 $this->assertTransactionRoundStage( self::ROUND_FINALIZED );
1369
1370                 $limit = $options['maxWriteDuration'] ?? 0;
1371
1372                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1373                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( $limit ) {
1374                         // If atomic sections or explicit transactions are still open, some caller must have
1375                         // caught an exception but failed to properly rollback any changes. Detect that and
1376                         // throw and error (causing rollback).
1377                         $conn->assertNoOpenTransactions();
1378                         // Assert that the time to replicate the transaction will be sane.
1379                         // If this fails, then all DB transactions will be rollback back together.
1380                         $time = $conn->pendingWriteQueryDuration( $conn::ESTIMATE_DB_APPLY );
1381                         if ( $limit > 0 && $time > $limit ) {
1382                                 throw new DBTransactionSizeError(
1383                                         $conn,
1384                                         "Transaction spent $time second(s) in writes, exceeding the limit of $limit",
1385                                         [ $time, $limit ]
1386                                 );
1387                         }
1388                         // If a connection sits idle while slow queries execute on another, that connection
1389                         // may end up dropped before the commit round is reached. Ping servers to detect this.
1390                         if ( $conn->writesOrCallbacksPending() && !$conn->ping() ) {
1391                                 throw new DBTransactionError(
1392                                         $conn,
1393                                         "A connection to the {$conn->getDBname()} database was lost before commit"
1394                                 );
1395                         }
1396                 } );
1397                 $this->trxRoundStage = self::ROUND_APPROVED;
1398         }
1399
1400         public function beginMasterChanges( $fname = __METHOD__ ) {
1401                 if ( $this->trxRoundId !== false ) {
1402                         throw new DBTransactionError(
1403                                 null,
1404                                 "$fname: Transaction round '{$this->trxRoundId}' already started"
1405                         );
1406                 }
1407                 $this->assertTransactionRoundStage( self::ROUND_CURSORY );
1408
1409                 // Clear any empty transactions (no writes/callbacks) from the implicit round
1410                 $this->flushMasterSnapshots( $fname );
1411
1412                 $this->trxRoundId = $fname;
1413                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1414                 // Mark applicable handles as participating in this explicit transaction round.
1415                 // For each of these handles, any writes and callbacks will be tied to a single
1416                 // transaction. The (peer) handles will reject begin()/commit() calls unless they
1417                 // are part of an en masse commit or an en masse rollback.
1418                 $this->forEachOpenMasterConnection( function ( Database $conn ) {
1419                         $this->applyTransactionRoundFlags( $conn );
1420                 } );
1421                 $this->trxRoundStage = self::ROUND_CURSORY;
1422         }
1423
1424         public function commitMasterChanges( $fname = __METHOD__ ) {
1425                 $this->assertTransactionRoundStage( self::ROUND_APPROVED );
1426
1427                 $failures = [];
1428
1429                 /** @noinspection PhpUnusedLocalVariableInspection */
1430                 $scope = ScopedCallback::newScopedIgnoreUserAbort(); // try to ignore client aborts
1431
1432                 $restore = ( $this->trxRoundId !== false );
1433                 $this->trxRoundId = false;
1434                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1435                 // Commit any writes and clear any snapshots as well (callbacks require AUTOCOMMIT).
1436                 // Note that callbacks should already be suppressed due to finalizeMasterChanges().
1437                 $this->forEachOpenMasterConnection(
1438                         function ( IDatabase $conn ) use ( $fname, &$failures ) {
1439                                 try {
1440                                         $conn->commit( $fname, $conn::FLUSHING_ALL_PEERS );
1441                                 } catch ( DBError $e ) {
1442                                         ( $this->errorLogger )( $e );
1443                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1444                                 }
1445                         }
1446                 );
1447                 if ( $failures ) {
1448                         throw new DBTransactionError(
1449                                 null,
1450                                 "$fname: Commit failed on server(s) " . implode( "\n", array_unique( $failures ) )
1451                         );
1452                 }
1453                 if ( $restore ) {
1454                         // Unmark handles as participating in this explicit transaction round
1455                         $this->forEachOpenMasterConnection( function ( Database $conn ) {
1456                                 $this->undoTransactionRoundFlags( $conn );
1457                         } );
1458                 }
1459                 $this->trxRoundStage = self::ROUND_COMMIT_CALLBACKS;
1460         }
1461
1462         public function runMasterTransactionIdleCallbacks() {
1463                 if ( $this->trxRoundStage === self::ROUND_COMMIT_CALLBACKS ) {
1464                         $type = IDatabase::TRIGGER_COMMIT;
1465                 } elseif ( $this->trxRoundStage === self::ROUND_ROLLBACK_CALLBACKS ) {
1466                         $type = IDatabase::TRIGGER_ROLLBACK;
1467                 } else {
1468                         throw new DBTransactionError(
1469                                 null,
1470                                 "Transaction should be in the callback stage (not '{$this->trxRoundStage}')"
1471                         );
1472                 }
1473
1474                 $oldStage = $this->trxRoundStage;
1475                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1476
1477                 // Now that the COMMIT/ROLLBACK step is over, enable post-commit callback runs
1478                 $this->forEachOpenMasterConnection( function ( Database $conn ) {
1479                         $conn->setTrxEndCallbackSuppression( false );
1480                 } );
1481
1482                 $e = null; // first exception
1483                 $fname = __METHOD__;
1484                 // Loop until callbacks stop adding callbacks on other connections
1485                 do {
1486                         // Run any pending callbacks for each connection...
1487                         $count = 0; // callback execution attempts
1488                         $this->forEachOpenMasterConnection(
1489                                 function ( Database $conn ) use ( $type, &$e, &$count ) {
1490                                         if ( $conn->trxLevel() ) {
1491                                                 return; // retry in the next iteration, after commit() is called
1492                                         }
1493                                         try {
1494                                                 $count += $conn->runOnTransactionIdleCallbacks( $type );
1495                                         } catch ( Exception $ex ) {
1496                                                 $e = $e ?: $ex;
1497                                         }
1498                                 }
1499                         );
1500                         // Clear out any active transactions left over from callbacks...
1501                         $this->forEachOpenMasterConnection( function ( Database $conn ) use ( &$e, $fname ) {
1502                                 if ( $conn->writesPending() ) {
1503                                         // A callback from another handle wrote to this one and DBO_TRX is set
1504                                         $this->queryLogger->warning( $fname . ": found writes pending." );
1505                                         $fnames = implode( ', ', $conn->pendingWriteAndCallbackCallers() );
1506                                         $this->queryLogger->warning(
1507                                                 $fname . ": found writes pending ($fnames).",
1508                                                 [
1509                                                         'db_server' => $conn->getServer(),
1510                                                         'db_name' => $conn->getDBname()
1511                                                 ]
1512                                         );
1513                                 } elseif ( $conn->trxLevel() ) {
1514                                         // A callback from another handle read from this one and DBO_TRX is set,
1515                                         // which can easily happen if there is only one DB (no replicas)
1516                                         $this->queryLogger->debug( $fname . ": found empty transaction." );
1517                                 }
1518                                 try {
1519                                         $conn->commit( $fname, $conn::FLUSHING_ALL_PEERS );
1520                                 } catch ( Exception $ex ) {
1521                                         $e = $e ?: $ex;
1522                                 }
1523                         } );
1524                 } while ( $count > 0 );
1525
1526                 $this->trxRoundStage = $oldStage;
1527
1528                 return $e;
1529         }
1530
1531         public function runMasterTransactionListenerCallbacks() {
1532                 if ( $this->trxRoundStage === self::ROUND_COMMIT_CALLBACKS ) {
1533                         $type = IDatabase::TRIGGER_COMMIT;
1534                 } elseif ( $this->trxRoundStage === self::ROUND_ROLLBACK_CALLBACKS ) {
1535                         $type = IDatabase::TRIGGER_ROLLBACK;
1536                 } else {
1537                         throw new DBTransactionError(
1538                                 null,
1539                                 "Transaction should be in the callback stage (not '{$this->trxRoundStage}')"
1540                         );
1541                 }
1542
1543                 $e = null;
1544
1545                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1546                 $this->forEachOpenMasterConnection( function ( Database $conn ) use ( $type, &$e ) {
1547                         try {
1548                                 $conn->runTransactionListenerCallbacks( $type );
1549                         } catch ( Exception $ex ) {
1550                                 $e = $e ?: $ex;
1551                         }
1552                 } );
1553                 $this->trxRoundStage = self::ROUND_CURSORY;
1554
1555                 return $e;
1556         }
1557
1558         public function rollbackMasterChanges( $fname = __METHOD__ ) {
1559                 $restore = ( $this->trxRoundId !== false );
1560                 $this->trxRoundId = false;
1561                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1562                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( $fname ) {
1563                         $conn->rollback( $fname, $conn::FLUSHING_ALL_PEERS );
1564                 } );
1565                 if ( $restore ) {
1566                         // Unmark handles as participating in this explicit transaction round
1567                         $this->forEachOpenMasterConnection( function ( Database $conn ) {
1568                                 $this->undoTransactionRoundFlags( $conn );
1569                         } );
1570                 }
1571                 $this->trxRoundStage = self::ROUND_ROLLBACK_CALLBACKS;
1572         }
1573
1574         /**
1575          * @param string|string[] $stage
1576          */
1577         private function assertTransactionRoundStage( $stage ) {
1578                 $stages = (array)$stage;
1579
1580                 if ( !in_array( $this->trxRoundStage, $stages, true ) ) {
1581                         $stageList = implode(
1582                                 '/',
1583                                 array_map( function ( $v ) {
1584                                         return "'$v'";
1585                                 }, $stages )
1586                         );
1587                         throw new DBTransactionError(
1588                                 null,
1589                                 "Transaction round stage must be $stageList (not '{$this->trxRoundStage}')"
1590                         );
1591                 }
1592         }
1593
1594         /**
1595          * Make all DB servers with DBO_DEFAULT/DBO_TRX set join the transaction round
1596          *
1597          * Some servers may have neither flag enabled, meaning that they opt out of such
1598          * transaction rounds and remain in auto-commit mode. Such behavior might be desired
1599          * when a DB server is used for something like simple key/value storage.
1600          *
1601          * @param Database $conn
1602          */
1603         private function applyTransactionRoundFlags( Database $conn ) {
1604                 if ( $conn->getLBInfo( 'autoCommitOnly' ) ) {
1605                         return; // transaction rounds do not apply to these connections
1606                 }
1607
1608                 if ( $conn->getFlag( $conn::DBO_DEFAULT ) ) {
1609                         // DBO_TRX is controlled entirely by CLI mode presence with DBO_DEFAULT.
1610                         // Force DBO_TRX even in CLI mode since a commit round is expected soon.
1611                         $conn->setFlag( $conn::DBO_TRX, $conn::REMEMBER_PRIOR );
1612                 }
1613
1614                 if ( $conn->getFlag( $conn::DBO_TRX ) ) {
1615                         $conn->setLBInfo( 'trxRoundId', $this->trxRoundId );
1616                 }
1617         }
1618
1619         /**
1620          * @param Database $conn
1621          */
1622         private function undoTransactionRoundFlags( Database $conn ) {
1623                 if ( $conn->getLBInfo( 'autoCommitOnly' ) ) {
1624                         return; // transaction rounds do not apply to these connections
1625                 }
1626
1627                 if ( $conn->getFlag( $conn::DBO_TRX ) ) {
1628                         $conn->setLBInfo( 'trxRoundId', false );
1629                 }
1630
1631                 if ( $conn->getFlag( $conn::DBO_DEFAULT ) ) {
1632                         $conn->restoreFlags( $conn::RESTORE_PRIOR );
1633                 }
1634         }
1635
1636         public function flushReplicaSnapshots( $fname = __METHOD__ ) {
1637                 $this->forEachOpenReplicaConnection( function ( IDatabase $conn ) use ( $fname ) {
1638                         $conn->flushSnapshot( $fname );
1639                 } );
1640         }
1641
1642         public function flushMasterSnapshots( $fname = __METHOD__ ) {
1643                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( $fname ) {
1644                         $conn->flushSnapshot( $fname );
1645                 } );
1646         }
1647
1648         /**
1649          * @return string
1650          * @since 1.32
1651          */
1652         public function getTransactionRoundStage() {
1653                 return $this->trxRoundStage;
1654         }
1655
1656         public function hasMasterConnection() {
1657                 return $this->isOpen( $this->getWriterIndex() );
1658         }
1659
1660         public function hasMasterChanges() {
1661                 $pending = 0;
1662                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$pending ) {
1663                         $pending |= $conn->writesOrCallbacksPending();
1664                 } );
1665
1666                 return (bool)$pending;
1667         }
1668
1669         public function lastMasterChangeTimestamp() {
1670                 $lastTime = false;
1671                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$lastTime ) {
1672                         $lastTime = max( $lastTime, $conn->lastDoneWrites() );
1673                 } );
1674
1675                 return $lastTime;
1676         }
1677
1678         public function hasOrMadeRecentMasterChanges( $age = null ) {
1679                 $age = ( $age === null ) ? $this->waitTimeout : $age;
1680
1681                 return ( $this->hasMasterChanges()
1682                         || $this->lastMasterChangeTimestamp() > microtime( true ) - $age );
1683         }
1684
1685         public function pendingMasterChangeCallers() {
1686                 $fnames = [];
1687                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$fnames ) {
1688                         $fnames = array_merge( $fnames, $conn->pendingWriteCallers() );
1689                 } );
1690
1691                 return $fnames;
1692         }
1693
1694         public function getLaggedReplicaMode( $domain = false ) {
1695                 if (
1696                         // Avoid recursion if there is only one DB
1697                         $this->getServerCount() > 1 &&
1698                         // Stay in lagged replica mode during the load balancer instance lifetime
1699                         !$this->laggedReplicaMode
1700                 ) {
1701                         try {
1702                                 // See if laggedReplicaMode gets set
1703                                 $conn = $this->getConnection( self::DB_REPLICA, false, $domain );
1704                                 $this->reuseConnection( $conn );
1705                         } catch ( DBConnectionError $e ) {
1706                                 // Avoid expensive re-connect attempts and failures
1707                                 $this->allReplicasDownMode = true;
1708                                 $this->laggedReplicaMode = true;
1709                         }
1710                 }
1711
1712                 return $this->laggedReplicaMode;
1713         }
1714
1715         public function laggedReplicaUsed() {
1716                 return $this->laggedReplicaMode;
1717         }
1718
1719         /**
1720          * @return bool
1721          * @since 1.27
1722          * @deprecated Since 1.28; use laggedReplicaUsed()
1723          */
1724         public function laggedSlaveUsed() {
1725                 return $this->laggedReplicaUsed();
1726         }
1727
1728         public function getReadOnlyReason( $domain = false, IDatabase $conn = null ) {
1729                 if ( $this->readOnlyReason !== false ) {
1730                         return $this->readOnlyReason;
1731                 } elseif ( $this->getLaggedReplicaMode( $domain ) ) {
1732                         if ( $this->allReplicasDownMode ) {
1733                                 return 'The database has been automatically locked ' .
1734                                         'until the replica database servers become available';
1735                         } else {
1736                                 return 'The database has been automatically locked ' .
1737                                         'while the replica database servers catch up to the master.';
1738                         }
1739                 } elseif ( $this->masterRunningReadOnly( $domain, $conn ) ) {
1740                         return 'The database master is running in read-only mode.';
1741                 }
1742
1743                 return false;
1744         }
1745
1746         /**
1747          * @param string $domain Domain ID, or false for the current domain
1748          * @param IDatabase|null $conn DB master connectionl used to avoid loops [optional]
1749          * @return bool
1750          */
1751         private function masterRunningReadOnly( $domain, IDatabase $conn = null ) {
1752                 $cache = $this->wanCache;
1753                 $masterServer = $this->getServerName( $this->getWriterIndex() );
1754
1755                 return (bool)$cache->getWithSetCallback(
1756                         $cache->makeGlobalKey( __CLASS__, 'server-read-only', $masterServer ),
1757                         self::TTL_CACHE_READONLY,
1758                         function () use ( $domain, $conn ) {
1759                                 $old = $this->trxProfiler->setSilenced( true );
1760                                 try {
1761                                         $dbw = $conn ?: $this->getConnection( self::DB_MASTER, [], $domain );
1762                                         $readOnly = (int)$dbw->serverIsReadOnly();
1763                                         if ( !$conn ) {
1764                                                 $this->reuseConnection( $dbw );
1765                                         }
1766                                 } catch ( DBError $e ) {
1767                                         $readOnly = 0;
1768                                 }
1769                                 $this->trxProfiler->setSilenced( $old );
1770                                 return $readOnly;
1771                         },
1772                         [ 'pcTTL' => $cache::TTL_PROC_LONG, 'busyValue' => 0 ]
1773                 );
1774         }
1775
1776         public function allowLagged( $mode = null ) {
1777                 if ( $mode === null ) {
1778                         return $this->allowLagged;
1779                 }
1780                 $this->allowLagged = $mode;
1781
1782                 return $this->allowLagged;
1783         }
1784
1785         public function pingAll() {
1786                 $success = true;
1787                 $this->forEachOpenConnection( function ( IDatabase $conn ) use ( &$success ) {
1788                         if ( !$conn->ping() ) {
1789                                 $success = false;
1790                         }
1791                 } );
1792
1793                 return $success;
1794         }
1795
1796         public function forEachOpenConnection( $callback, array $params = [] ) {
1797                 foreach ( $this->conns as $connsByServer ) {
1798                         foreach ( $connsByServer as $serverConns ) {
1799                                 foreach ( $serverConns as $conn ) {
1800                                         $callback( $conn, ...$params );
1801                                 }
1802                         }
1803                 }
1804         }
1805
1806         public function forEachOpenMasterConnection( $callback, array $params = [] ) {
1807                 $masterIndex = $this->getWriterIndex();
1808                 foreach ( $this->conns as $connsByServer ) {
1809                         if ( isset( $connsByServer[$masterIndex] ) ) {
1810                                 /** @var IDatabase $conn */
1811                                 foreach ( $connsByServer[$masterIndex] as $conn ) {
1812                                         $callback( $conn, ...$params );
1813                                 }
1814                         }
1815                 }
1816         }
1817
1818         public function forEachOpenReplicaConnection( $callback, array $params = [] ) {
1819                 foreach ( $this->conns as $connsByServer ) {
1820                         foreach ( $connsByServer as $i => $serverConns ) {
1821                                 if ( $i === $this->getWriterIndex() ) {
1822                                         continue; // skip master
1823                                 }
1824                                 foreach ( $serverConns as $conn ) {
1825                                         $callback( $conn, ...$params );
1826                                 }
1827                         }
1828                 }
1829         }
1830
1831         public function getMaxLag( $domain = false ) {
1832                 $maxLag = -1;
1833                 $host = '';
1834                 $maxIndex = 0;
1835
1836                 if ( $this->getServerCount() <= 1 ) {
1837                         return [ $host, $maxLag, $maxIndex ]; // no replication = no lag
1838                 }
1839
1840                 $lagTimes = $this->getLagTimes( $domain );
1841                 foreach ( $lagTimes as $i => $lag ) {
1842                         if ( $this->loads[$i] > 0 && $lag > $maxLag ) {
1843                                 $maxLag = $lag;
1844                                 $host = $this->servers[$i]['host'];
1845                                 $maxIndex = $i;
1846                         }
1847                 }
1848
1849                 return [ $host, $maxLag, $maxIndex ];
1850         }
1851
1852         public function getLagTimes( $domain = false ) {
1853                 if ( $this->getServerCount() <= 1 ) {
1854                         return [ $this->getWriterIndex() => 0 ]; // no replication = no lag
1855                 }
1856
1857                 $knownLagTimes = []; // map of (server index => 0 seconds)
1858                 $indexesWithLag = [];
1859                 foreach ( $this->servers as $i => $server ) {
1860                         if ( empty( $server['is static'] ) ) {
1861                                 $indexesWithLag[] = $i; // DB server might have replication lag
1862                         } else {
1863                                 $knownLagTimes[$i] = 0; // DB server is a non-replicating and read-only archive
1864                         }
1865                 }
1866
1867                 return $this->getLoadMonitor()->getLagTimes( $indexesWithLag, $domain ) + $knownLagTimes;
1868         }
1869
1870         public function safeGetLag( IDatabase $conn ) {
1871                 if ( $this->getServerCount() <= 1 ) {
1872                         return 0;
1873                 } else {
1874                         return $conn->getLag();
1875                 }
1876         }
1877
1878         public function safeWaitForMasterPos( IDatabase $conn, $pos = false, $timeout = null ) {
1879                 $timeout = max( 1, $timeout ?: $this->waitTimeout );
1880
1881                 if ( $this->getServerCount() <= 1 || !$conn->getLBInfo( 'replica' ) ) {
1882                         return true; // server is not a replica DB
1883                 }
1884
1885                 if ( !$pos ) {
1886                         // Get the current master position, opening a connection if needed
1887                         $masterConn = $this->getAnyOpenConnection( $this->getWriterIndex() );
1888                         if ( $masterConn ) {
1889                                 $pos = $masterConn->getMasterPos();
1890                         } else {
1891                                 $masterConn = $this->openConnection( $this->getWriterIndex(), self::DOMAIN_ANY );
1892                                 if ( !$masterConn ) {
1893                                         throw new DBReplicationWaitError(
1894                                                 null,
1895                                                 "Could not obtain a master database connection to get the position"
1896                                         );
1897                                 }
1898                                 $pos = $masterConn->getMasterPos();
1899                                 $this->closeConnection( $masterConn );
1900                         }
1901                 }
1902
1903                 if ( $pos instanceof DBMasterPos ) {
1904                         $result = $conn->masterPosWait( $pos, $timeout );
1905                         if ( $result == -1 || is_null( $result ) ) {
1906                                 $msg = __METHOD__ . ': timed out waiting on {host} pos {pos}';
1907                                 $this->replLogger->warning( $msg, [
1908                                         'host' => $conn->getServer(),
1909                                         'pos' => $pos,
1910                                         'trace' => ( new RuntimeException() )->getTraceAsString()
1911                                 ] );
1912                                 $ok = false;
1913                         } else {
1914                                 $this->replLogger->debug( __METHOD__ . ': done waiting' );
1915                                 $ok = true;
1916                         }
1917                 } else {
1918                         $ok = false; // something is misconfigured
1919                         $this->replLogger->error(
1920                                 __METHOD__ . ': could not get master pos for {host}',
1921                                 [
1922                                         'host' => $conn->getServer(),
1923                                         'trace' => ( new RuntimeException() )->getTraceAsString()
1924                                 ]
1925                         );
1926                 }
1927
1928                 return $ok;
1929         }
1930
1931         public function setTransactionListener( $name, callable $callback = null ) {
1932                 if ( $callback ) {
1933                         $this->trxRecurringCallbacks[$name] = $callback;
1934                 } else {
1935                         unset( $this->trxRecurringCallbacks[$name] );
1936                 }
1937                 $this->forEachOpenMasterConnection(
1938                         function ( IDatabase $conn ) use ( $name, $callback ) {
1939                                 $conn->setTransactionListener( $name, $callback );
1940                         }
1941                 );
1942         }
1943
1944         public function setTableAliases( array $aliases ) {
1945                 $this->tableAliases = $aliases;
1946         }
1947
1948         public function setIndexAliases( array $aliases ) {
1949                 $this->indexAliases = $aliases;
1950         }
1951
1952         /**
1953          * @param string $prefix
1954          * @deprecated Since 1.33
1955          */
1956         public function setDomainPrefix( $prefix ) {
1957                 $this->setLocalDomainPrefix( $prefix );
1958         }
1959
1960         public function setLocalDomainPrefix( $prefix ) {
1961                 // Find connections to explicit foreign domains still marked as in-use...
1962                 $domainsInUse = [];
1963                 $this->forEachOpenConnection( function ( IDatabase $conn ) use ( &$domainsInUse ) {
1964                         // Once reuseConnection() is called on a handle, its reference count goes from 1 to 0.
1965                         // Until then, it is still in use by the caller (explicitly or via DBConnRef scope).
1966                         if ( $conn->getLBInfo( 'foreignPoolRefCount' ) > 0 ) {
1967                                 $domainsInUse[] = $conn->getDomainID();
1968                         }
1969                 } );
1970
1971                 // Do not switch connections to explicit foreign domains unless marked as safe
1972                 if ( $domainsInUse ) {
1973                         $domains = implode( ', ', $domainsInUse );
1974                         throw new DBUnexpectedError( null,
1975                                 "Foreign domain connections are still in use ($domains)" );
1976                 }
1977
1978                 $this->setLocalDomain( new DatabaseDomain(
1979                         $this->localDomain->getDatabase(),
1980                         $this->localDomain->getSchema(),
1981                         $prefix
1982                 ) );
1983
1984                 // Update the prefix for all local connections...
1985                 $this->forEachOpenConnection( function ( IDatabase $db ) use ( $prefix ) {
1986                         if ( !$db->getLBInfo( 'foreign' ) ) {
1987                                 $db->tablePrefix( $prefix );
1988                         }
1989                 } );
1990         }
1991
1992         public function redefineLocalDomain( $domain ) {
1993                 $this->closeAll();
1994
1995                 $this->setLocalDomain( DatabaseDomain::newFromId( $domain ) );
1996         }
1997
1998         /**
1999          * @param DatabaseDomain $domain
2000          */
2001         private function setLocalDomain( DatabaseDomain $domain ) {
2002                 $this->localDomain = $domain;
2003                 // In case a caller assumes that the domain ID is simply <db>-<prefix>, which is almost
2004                 // always true, gracefully handle the case when they fail to account for escaping.
2005                 if ( $this->localDomain->getTablePrefix() != '' ) {
2006                         $this->localDomainIdAlias =
2007                                 $this->localDomain->getDatabase() . '-' . $this->localDomain->getTablePrefix();
2008                 } else {
2009                         $this->localDomainIdAlias = $this->localDomain->getDatabase();
2010                 }
2011         }
2012
2013         function __destruct() {
2014                 // Avoid connection leaks for sanity
2015                 $this->disable();
2016         }
2017 }
2018
2019 /**
2020  * @deprecated since 1.29
2021  */
2022 class_alias( LoadBalancer::class, 'LoadBalancer' );