includes/libs/rdbms/loadbalancer/LoadBalancer.php

   1 <?php
   2 /**
   3  * Database load balancing manager
   4  *
   5  * This program is free software; you can redistribute it and/or modify
   6  * it under the terms of the GNU General Public License as published by
   7  * the Free Software Foundation; either version 2 of the License, or
   8  * (at your option) any later version.
   9  *
  10  * This program is distributed in the hope that it will be useful,
  11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  13  * GNU General Public License for more details.
  14  *
  15  * You should have received a copy of the GNU General Public License along
  16  * with this program; if not, write to the Free Software Foundation, Inc.,
  17  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
  18  * http://www.gnu.org/copyleft/gpl.html
  19  *
  20  * @file
  21  */
  22 namespace Wikimedia\Rdbms;
  23
  24 use Psr\Log\LoggerInterface;
  25 use Psr\Log\NullLogger;
  26 use Wikimedia\ScopedCallback;
  27 use BagOStuff;
  28 use EmptyBagOStuff;
  29 use WANObjectCache;
  30 use ArrayUtils;
  31 use InvalidArgumentException;
  32 use RuntimeException;
  33 use Exception;
  34
  35 /**
  36  * Database connection, tracking, load balancing, and transaction manager for a cluster
  37  *
  38  * @ingroup Database
  39  */
  40 class LoadBalancer implements ILoadBalancer {
  41         /** @var ILoadMonitor */
  42         private $loadMonitor;
  43         /** @var callable|null Callback to run before the first connection attempt */
  44         private $chronologyCallback;
  45         /** @var BagOStuff */
  46         private $srvCache;
  47         /** @var WANObjectCache */
  48         private $wanCache;
  49         /** @var object|string Class name or object With profileIn/profileOut methods */
  50         private $profiler;
  51         /** @var TransactionProfiler */
  52         private $trxProfiler;
  53         /** @var LoggerInterface */
  54         private $replLogger;
  55         /** @var LoggerInterface */
  56         private $connLogger;
  57         /** @var LoggerInterface */
  58         private $queryLogger;
  59         /** @var LoggerInterface */
  60         private $perfLogger;
  61         /** @var callable Exception logger */
  62         private $errorLogger;
  63         /** @var callable Deprecation logger */
  64         private $deprecationLogger;
  65
  66         /** @var DatabaseDomain Local Domain ID and default for selectDB() calls */
  67         private $localDomain;
  68
  69         /** @var Database[][][] Map of (connection category => server index => IDatabase[]) */
  70         private $conns;
  71
  72         /** @var array[] Map of (server index => server config array) */
  73         private $servers;
  74         /** @var float[] Map of (server index => weight) */
  75         private $loads;
  76         /** @var array[] Map of (group => server index => weight) */
  77         private $groupLoads;
  78         /** @var bool Whether to disregard replica DB lag as a factor in replica DB selection */
  79         private $allowLagged;
  80         /** @var int Seconds to spend waiting on replica DB lag to resolve */
  81         private $waitTimeout;
  82         /** @var array The LoadMonitor configuration */
  83         private $loadMonitorConfig;
  84         /** @var string Alternate ID string for the domain instead of DatabaseDomain::getId() */
  85         private $localDomainIdAlias;
  86         /** @var int */
  87         private $maxLag = self::MAX_LAG_DEFAULT;
  88
  89         /** @var string Current server name */
  90         private $hostname;
  91         /** @var bool Whether this PHP instance is for a CLI script */
  92         private $cliMode;
  93         /** @var string Agent name for query profiling */
  94         private $agent;
  95
  96         /** @var array[] $aliases Map of (table => (dbname, schema, prefix) map) */
  97         private $tableAliases = [];
  98         /** @var string[] Map of (index alias => index) */
  99         private $indexAliases = [];
 100         /** @var array[] Map of (name => callable) */
 101         private $trxRecurringCallbacks = [];
 102
 103         /** @var Database DB connection object that caused a problem */
 104         private $errorConnection;
 105         /** @var int The generic (not query grouped) replica DB index (of $mServers) */
 106         private $readIndex;
 107         /** @var bool|DBMasterPos False if not set */
 108         private $waitForPos;
 109         /** @var bool Whether the generic reader fell back to a lagged replica DB */
 110         private $laggedReplicaMode = false;
 111         /** @var bool Whether the generic reader fell back to a lagged replica DB */
 112         private $allReplicasDownMode = false;
 113         /** @var string The last DB selection or connection error */
 114         private $lastError = 'Unknown error';
 115         /** @var string|bool Reason the LB is read-only or false if not */
 116         private $readOnlyReason = false;
 117         /** @var int Total connections opened */
 118         private $connsOpened = 0;
 119         /** @var bool */
 120         private $disabled = false;
 121         /** @var bool Whether any connection has been attempted yet */
 122         private $connectionAttempted = false;
 123
 124         /** @var string|bool String if a requested DBO_TRX transaction round is active */
 125         private $trxRoundId = false;
 126         /** @var string Stage of the current transaction round in the transaction round life-cycle */
 127         private $trxRoundStage = self::ROUND_CURSORY;
 128
 129         /** @var string|null */
 130         private $defaultGroup = null;
 131
 132         /** @var int Warn when this many connection are held */
 133         const CONN_HELD_WARN_THRESHOLD = 10;
 134
 135         /** @var int Default 'maxLag' when unspecified */
 136         const MAX_LAG_DEFAULT = 10;
 137         /** @var int Default 'waitTimeout' when unspecified */
 138         const MAX_WAIT_DEFAULT = 10;
 139         /** @var int Seconds to cache master server read-only status */
 140         const TTL_CACHE_READONLY = 5;
 141
 142         const KEY_LOCAL = 'local';
 143         const KEY_FOREIGN_FREE = 'foreignFree';
 144         const KEY_FOREIGN_INUSE = 'foreignInUse';
 145
 146         const KEY_LOCAL_NOROUND = 'localAutoCommit';
 147         const KEY_FOREIGN_FREE_NOROUND = 'foreignFreeAutoCommit';
 148         const KEY_FOREIGN_INUSE_NOROUND = 'foreignInUseAutoCommit';
 149
 150         /** @var string Transaction round, explicit or implicit, has not finished writing */
 151         const ROUND_CURSORY = 'cursory';
 152         /** @var string Transaction round writes are complete and ready for pre-commit checks */
 153         const ROUND_FINALIZED = 'finalized';
 154         /** @var string Transaction round passed final pre-commit checks */
 155         const ROUND_APPROVED = 'approved';
 156         /** @var string Transaction round was committed and post-commit callbacks must be run */
 157         const ROUND_COMMIT_CALLBACKS = 'commit-callbacks';
 158         /** @var string Transaction round was rolled back and post-rollback callbacks must be run */
 159         const ROUND_ROLLBACK_CALLBACKS = 'rollback-callbacks';
 160         /** @var string Transaction round encountered an error */
 161         const ROUND_ERROR = 'error';
 162
 163         public function __construct( array $params ) {
 164                 if ( !isset( $params['servers'] ) ) {
 165                         throw new InvalidArgumentException( __CLASS__ . ': missing servers parameter' );
 166                 }
 167                 $this->servers = $params['servers'];
 168                 foreach ( $this->servers as $i => $server ) {
 169                         if ( $i == 0 ) {
 170                                 $this->servers[$i]['master'] = true;
 171                         } else {
 172                                 $this->servers[$i]['replica'] = true;
 173                         }
 174                 }
 175
 176                 $localDomain = isset( $params['localDomain'] )
 177                         ? DatabaseDomain::newFromId( $params['localDomain'] )
 178                         : DatabaseDomain::newUnspecified();
 179                 $this->setLocalDomain( $localDomain );
 180
 181                 $this->waitTimeout = $params['waitTimeout'] ?? self::MAX_WAIT_DEFAULT;
 182
 183                 $this->readIndex = -1;
 184                 $this->conns = [
 185                         // Connection were transaction rounds may be applied
 186                         self::KEY_LOCAL => [],
 187                         self::KEY_FOREIGN_INUSE => [],
 188                         self::KEY_FOREIGN_FREE => [],
 189                         // Auto-committing counterpart connections that ignore transaction rounds
 190                         self::KEY_LOCAL_NOROUND => [],
 191                         self::KEY_FOREIGN_INUSE_NOROUND => [],
 192                         self::KEY_FOREIGN_FREE_NOROUND => []
 193                 ];
 194                 $this->loads = [];
 195                 $this->waitForPos = false;
 196                 $this->allowLagged = false;
 197
 198                 if ( isset( $params['readOnlyReason'] ) && is_string( $params['readOnlyReason'] ) ) {
 199                         $this->readOnlyReason = $params['readOnlyReason'];
 200                 }
 201
 202                 if ( isset( $params['maxLag'] ) ) {
 203                         $this->maxLag = $params['maxLag'];
 204                 }
 205
 206                 if ( isset( $params['loadMonitor'] ) ) {
 207                         $this->loadMonitorConfig = $params['loadMonitor'];
 208                 } else {
 209                         $this->loadMonitorConfig = [ 'class' => 'LoadMonitorNull' ];
 210                 }
 211                 $this->loadMonitorConfig += [ 'lagWarnThreshold' => $this->maxLag ];
 212
 213                 foreach ( $params['servers'] as $i => $server ) {
 214                         $this->loads[$i] = $server['load'];
 215                         if ( isset( $server['groupLoads'] ) ) {
 216                                 foreach ( $server['groupLoads'] as $group => $ratio ) {
 217                                         if ( !isset( $this->groupLoads[$group] ) ) {
 218                                                 $this->groupLoads[$group] = [];
 219                                         }
 220                                         $this->groupLoads[$group][$i] = $ratio;
 221                                 }
 222                         }
 223                 }
 224
 225                 if ( isset( $params['srvCache'] ) ) {
 226                         $this->srvCache = $params['srvCache'];
 227                 } else {
 228                         $this->srvCache = new EmptyBagOStuff();
 229                 }
 230                 if ( isset( $params['wanCache'] ) ) {
 231                         $this->wanCache = $params['wanCache'];
 232                 } else {
 233                         $this->wanCache = WANObjectCache::newEmpty();
 234                 }
 235                 $this->profiler = $params['profiler'] ?? null;
 236                 if ( isset( $params['trxProfiler'] ) ) {
 237                         $this->trxProfiler = $params['trxProfiler'];
 238                 } else {
 239                         $this->trxProfiler = new TransactionProfiler();
 240                 }
 241
 242                 $this->errorLogger = $params['errorLogger'] ?? function ( Exception $e ) {
 243                         trigger_error( get_class( $e ) . ': ' . $e->getMessage(), E_USER_WARNING );
 244                 };
 245                 $this->deprecationLogger = $params['deprecationLogger'] ?? function ( $msg ) {
 246                         trigger_error( $msg, E_USER_DEPRECATED );
 247                 };
 248
 249                 foreach ( [ 'replLogger', 'connLogger', 'queryLogger', 'perfLogger' ] as $key ) {
 250                         $this->$key = $params[$key] ?? new NullLogger();
 251                 }
 252
 253                 $this->hostname = $params['hostname'] ?? ( gethostname() ?: 'unknown' );
 254                 $this->cliMode = $params['cliMode'] ?? ( PHP_SAPI === 'cli' || PHP_SAPI === 'phpdbg' );
 255                 $this->agent = $params['agent'] ?? '';
 256
 257                 if ( isset( $params['chronologyCallback'] ) ) {
 258                         $this->chronologyCallback = $params['chronologyCallback'];
 259                 }
 260
 261                 if ( isset( $params['roundStage'] ) ) {
 262                         if ( $params['roundStage'] === self::STAGE_POSTCOMMIT_CALLBACKS ) {
 263                                 $this->trxRoundStage = self::ROUND_COMMIT_CALLBACKS;
 264                         } elseif ( $params['roundStage'] === self::STAGE_POSTROLLBACK_CALLBACKS ) {
 265                                 $this->trxRoundStage = self::ROUND_ROLLBACK_CALLBACKS;
 266                         }
 267                 }
 268
 269                 $this->defaultGroup = $params['defaultGroup'] ?? null;
 270         }
 271
 272         public function getLocalDomainID() {
 273                 return $this->localDomain->getId();
 274         }
 275
 276         public function resolveDomainID( $domain ) {
 277                 return ( $domain !== false ) ? (string)$domain : $this->getLocalDomainID();
 278         }
 279
 280         /**
 281          * Get a LoadMonitor instance
 282          *
 283          * @return ILoadMonitor
 284          */
 285         private function getLoadMonitor() {
 286                 if ( !isset( $this->loadMonitor ) ) {
 287                         $compat = [
 288                                 'LoadMonitor' => LoadMonitor::class,
 289                                 'LoadMonitorNull' => LoadMonitorNull::class,
 290                                 'LoadMonitorMySQL' => LoadMonitorMySQL::class,
 291                         ];
 292
 293                         $class = $this->loadMonitorConfig['class'];
 294                         if ( isset( $compat[$class] ) ) {
 295                                 $class = $compat[$class];
 296                         }
 297
 298                         $this->loadMonitor = new $class(
 299                                 $this, $this->srvCache, $this->wanCache, $this->loadMonitorConfig );
 300                         $this->loadMonitor->setLogger( $this->replLogger );
 301                 }
 302
 303                 return $this->loadMonitor;
 304         }
 305
 306         /**
 307          * @param array $loads
 308          * @param bool|string $domain Domain to get non-lagged for
 309          * @param int $maxLag Restrict the maximum allowed lag to this many seconds
 310          * @return bool|int|string
 311          */
 312         private function getRandomNonLagged( array $loads, $domain = false, $maxLag = INF ) {
 313                 $lags = $this->getLagTimes( $domain );
 314
 315                 # Unset excessively lagged servers
 316                 foreach ( $lags as $i => $lag ) {
 317                         if ( $i != 0 ) {
 318                                 # How much lag this server nominally is allowed to have
 319                                 $maxServerLag = $this->servers[$i]['max lag'] ?? $this->maxLag; // default
 320                                 # Constrain that futher by $maxLag argument
 321                                 $maxServerLag = min( $maxServerLag, $maxLag );
 322
 323                                 $host = $this->getServerName( $i );
 324                                 if ( $lag === false && !is_infinite( $maxServerLag ) ) {
 325                                         $this->replLogger->error(
 326                                                 __METHOD__ .
 327                                                 ": server {host} is not replicating?", [ 'host' => $host ] );
 328                                         unset( $loads[$i] );
 329                                 } elseif ( $lag > $maxServerLag ) {
 330                                         $this->replLogger->info(
 331                                                 __METHOD__ .
 332                                                 ": server {host} has {lag} seconds of lag (>= {maxlag})",
 333                                                 [ 'host' => $host, 'lag' => $lag, 'maxlag' => $maxServerLag ]
 334                                         );
 335                                         unset( $loads[$i] );
 336                                 }
 337                         }
 338                 }
 339
 340                 # Find out if all the replica DBs with non-zero load are lagged
 341                 $sum = 0;
 342                 foreach ( $loads as $load ) {
 343                         $sum += $load;
 344                 }
 345                 if ( $sum == 0 ) {
 346                         # No appropriate DB servers except maybe the master and some replica DBs with zero load
 347                         # Do NOT use the master
 348                         # Instead, this function will return false, triggering read-only mode,
 349                         # and a lagged replica DB will be used instead.
 350                         return false;
 351                 }
 352
 353                 if ( count( $loads ) == 0 ) {
 354                         return false;
 355                 }
 356
 357                 # Return a random representative of the remainder
 358                 return ArrayUtils::pickRandom( $loads );
 359         }
 360
 361         public function getReaderIndex( $group = false, $domain = false ) {
 362                 if ( count( $this->servers ) == 1 ) {
 363                         // Skip the load balancing if there's only one server
 364                         return $this->getWriterIndex();
 365                 } elseif ( $group === false && $this->readIndex >= 0 ) {
 366                         // Shortcut if the generic reader index was already cached
 367                         return $this->readIndex;
 368                 }
 369
 370                 if ( $group !== false ) {
 371                         // Use the server weight array for this load group
 372                         if ( isset( $this->groupLoads[$group] ) ) {
 373                                 $loads = $this->groupLoads[$group];
 374                         } else {
 375                                 // No loads for this group, return false and the caller can use some other group
 376                                 $this->connLogger->info( __METHOD__ . ": no loads for group $group" );
 377
 378                                 return false;
 379                         }
 380                 } else {
 381                         // Use the generic load group
 382                         $loads = $this->loads;
 383                 }
 384
 385                 // Scale the configured load ratios according to each server's load and state
 386                 $this->getLoadMonitor()->scaleLoads( $loads, $domain );
 387
 388                 // Pick a server to use, accounting for weights, load, lag, and "waitForPos"
 389                 list( $i, $laggedReplicaMode ) = $this->pickReaderIndex( $loads, $domain );
 390                 if ( $i === false ) {
 391                         // Replica DB connection unsuccessful
 392                         return false;
 393                 }
 394
 395                 if ( $this->waitForPos && $i != $this->getWriterIndex() ) {
 396                         // Before any data queries are run, wait for the server to catch up to the
 397                         // specified position. This is used to improve session consistency. Note that
 398                         // when LoadBalancer::waitFor() sets "waitForPos", the waiting triggers here,
 399                         // so update laggedReplicaMode as needed for consistency.
 400                         if ( !$this->doWait( $i ) ) {
 401                                 $laggedReplicaMode = true;
 402                         }
 403                 }
 404
 405                 if ( $this->readIndex <= 0 && $this->loads[$i] > 0 && $group === false ) {
 406                         // Cache the generic reader index for future ungrouped DB_REPLICA handles
 407                         $this->readIndex = $i;
 408                         // Record if the generic reader index is in "lagged replica DB" mode
 409                         if ( $laggedReplicaMode ) {
 410                                 $this->laggedReplicaMode = true;
 411                         }
 412                 }
 413
 414                 $serverName = $this->getServerName( $i );
 415                 $this->connLogger->debug( __METHOD__ . ": using server $serverName for group '$group'" );
 416
 417                 return $i;
 418         }
 419
 420         /**
 421          * @param array $loads List of server weights
 422          * @param string|bool $domain
 423          * @return array (reader index, lagged replica mode) or false on failure
 424          */
 425         private function pickReaderIndex( array $loads, $domain = false ) {
 426                 if ( !count( $loads ) ) {
 427                         throw new InvalidArgumentException( "Empty server array given to LoadBalancer" );
 428                 }
 429
 430                 /** @var int|bool $i Index of selected server */
 431                 $i = false;
 432                 /** @var bool $laggedReplicaMode Whether server is considered lagged */
 433                 $laggedReplicaMode = false;
 434
 435                 // Quickly look through the available servers for a server that meets criteria...
 436                 $currentLoads = $loads;
 437                 while ( count( $currentLoads ) ) {
 438                         if ( $this->allowLagged || $laggedReplicaMode ) {
 439                                 $i = ArrayUtils::pickRandom( $currentLoads );
 440                         } else {
 441                                 $i = false;
 442                                 if ( $this->waitForPos && $this->waitForPos->asOfTime() ) {
 443                                         // "chronologyCallback" sets "waitForPos" for session consistency.
 444                                         // This triggers doWait() after connect, so it's especially good to
 445                                         // avoid lagged servers so as to avoid excessive delay in that method.
 446                                         $ago = microtime( true ) - $this->waitForPos->asOfTime();
 447                                         // Aim for <= 1 second of waiting (being too picky can backfire)
 448                                         $i = $this->getRandomNonLagged( $currentLoads, $domain, $ago + 1 );
 449                                 }
 450                                 if ( $i === false ) {
 451                                         // Any server with less lag than it's 'max lag' param is preferable
 452                                         $i = $this->getRandomNonLagged( $currentLoads, $domain );
 453                                 }
 454                                 if ( $i === false && count( $currentLoads ) != 0 ) {
 455                                         // All replica DBs lagged. Switch to read-only mode
 456                                         $this->replLogger->error(
 457                                                 __METHOD__ . ": all replica DBs lagged. Switch to read-only mode" );
 458                                         $i = ArrayUtils::pickRandom( $currentLoads );
 459                                         $laggedReplicaMode = true;
 460                                 }
 461                         }
 462
 463                         if ( $i === false ) {
 464                                 // pickRandom() returned false.
 465                                 // This is permanent and means the configuration or the load monitor
 466                                 // wants us to return false.
 467                                 $this->connLogger->debug( __METHOD__ . ": pickRandom() returned false" );
 468
 469                                 return [ false, false ];
 470                         }
 471
 472                         $serverName = $this->getServerName( $i );
 473                         $this->connLogger->debug( __METHOD__ . ": Using reader #$i: $serverName..." );
 474
 475                         $conn = $this->openConnection( $i, $domain );
 476                         if ( !$conn ) {
 477                                 $this->connLogger->warning( __METHOD__ . ": Failed connecting to $i/$domain" );
 478                                 unset( $currentLoads[$i] ); // avoid this server next iteration
 479                                 $i = false;
 480                                 continue;
 481                         }
 482
 483                         // Decrement reference counter, we are finished with this connection.
 484                         // It will be incremented for the caller later.
 485                         if ( $domain !== false ) {
 486                                 $this->reuseConnection( $conn );
 487                         }
 488
 489                         // Return this server
 490                         break;
 491                 }
 492
 493                 // If all servers were down, quit now
 494                 if ( !count( $currentLoads ) ) {
 495                         $this->connLogger->error( __METHOD__ . ": all servers down" );
 496                 }
 497
 498                 return [ $i, $laggedReplicaMode ];
 499         }
 500
 501         public function waitFor( $pos ) {
 502                 $oldPos = $this->waitForPos;
 503                 try {
 504                         $this->waitForPos = $pos;
 505                         // If a generic reader connection was already established, then wait now
 506                         $i = $this->readIndex;
 507                         if ( $i > 0 ) {
 508                                 if ( !$this->doWait( $i ) ) {
 509                                         $this->laggedReplicaMode = true;
 510                                 }
 511                         }
 512                 } finally {
 513                         // Restore the older position if it was higher since this is used for lag-protection
 514                         $this->setWaitForPositionIfHigher( $oldPos );
 515                 }
 516         }
 517
 518         public function waitForOne( $pos, $timeout = null ) {
 519                 $oldPos = $this->waitForPos;
 520                 try {
 521                         $this->waitForPos = $pos;
 522
 523                         $i = $this->readIndex;
 524                         if ( $i <= 0 ) {
 525                                 // Pick a generic replica DB if there isn't one yet
 526                                 $readLoads = $this->loads;
 527                                 unset( $readLoads[$this->getWriterIndex()] ); // replica DBs only
 528                                 $readLoads = array_filter( $readLoads ); // with non-zero load
 529                                 $i = ArrayUtils::pickRandom( $readLoads );
 530                         }
 531
 532                         if ( $i > 0 ) {
 533                                 $ok = $this->doWait( $i, true, $timeout );
 534                         } else {
 535                                 $ok = true; // no applicable loads
 536                         }
 537                 } finally {
 538                         # Restore the old position, as this is not used for lag-protection but for throttling
 539                         $this->waitForPos = $oldPos;
 540                 }
 541
 542                 return $ok;
 543         }
 544
 545         public function waitForAll( $pos, $timeout = null ) {
 546                 $timeout = $timeout ?: $this->waitTimeout;
 547
 548                 $oldPos = $this->waitForPos;
 549                 try {
 550                         $this->waitForPos = $pos;
 551                         $serverCount = count( $this->servers );
 552
 553                         $ok = true;
 554                         for ( $i = 1; $i < $serverCount; $i++ ) {
 555                                 if ( $this->loads[$i] > 0 ) {
 556                                         $start = microtime( true );
 557                                         $ok = $this->doWait( $i, true, $timeout ) && $ok;
 558                                         $timeout -= intval( microtime( true ) - $start );
 559                                         if ( $timeout <= 0 ) {
 560                                                 break; // timeout reached
 561                                         }
 562                                 }
 563                         }
 564                 } finally {
 565                         # Restore the old position, as this is not used for lag-protection but for throttling
 566                         $this->waitForPos = $oldPos;
 567                 }
 568
 569                 return $ok;
 570         }
 571
 572         /**
 573          * @param DBMasterPos|bool $pos
 574          */
 575         private function setWaitForPositionIfHigher( $pos ) {
 576                 if ( !$pos ) {
 577                         return;
 578                 }
 579
 580                 if ( !$this->waitForPos || $pos->hasReached( $this->waitForPos ) ) {
 581                         $this->waitForPos = $pos;
 582                 }
 583         }
 584
 585         public function getAnyOpenConnection( $i, $flags = 0 ) {
 586                 $autocommit = ( ( $flags & self::CONN_TRX_AUTOCOMMIT ) == self::CONN_TRX_AUTOCOMMIT );
 587                 foreach ( $this->conns as $connsByServer ) {
 588                         if ( !isset( $connsByServer[$i] ) ) {
 589                                 continue;
 590                         }
 591
 592                         foreach ( $connsByServer[$i] as $conn ) {
 593                                 if ( !$autocommit || $conn->getLBInfo( 'autoCommitOnly' ) ) {
 594                                         return $conn;
 595                                 }
 596                         }
 597                 }
 598
 599                 return false;
 600         }
 601
 602         /**
 603          * Wait for a given replica DB to catch up to the master pos stored in $this
 604          * @param int $index Server index
 605          * @param bool $open Check the server even if a new connection has to be made
 606          * @param int|null $timeout Max seconds to wait; default is "waitTimeout" given to __construct()
 607          * @return bool
 608          */
 609         protected function doWait( $index, $open = false, $timeout = null ) {
 610                 $timeout = max( 1, intval( $timeout ?: $this->waitTimeout ) );
 611
 612                 // Check if we already know that the DB has reached this point
 613                 $server = $this->getServerName( $index );
 614                 $key = $this->srvCache->makeGlobalKey( __CLASS__, 'last-known-pos', $server, 'v1' );
 615                 /** @var DBMasterPos $knownReachedPos */
 616                 $knownReachedPos = $this->srvCache->get( $key );
 617                 if (
 618                         $knownReachedPos instanceof DBMasterPos &&
 619                         $knownReachedPos->hasReached( $this->waitForPos )
 620                 ) {
 621                         $this->replLogger->debug(
 622                                 __METHOD__ .
 623                                 ': replica DB {dbserver} known to be caught up (pos >= $knownReachedPos).',
 624                                 [ 'dbserver' => $server ]
 625                         );
 626                         return true;
 627                 }
 628
 629                 // Find a connection to wait on, creating one if needed and allowed
 630                 $close = false; // close the connection afterwards
 631                 $conn = $this->getAnyOpenConnection( $index );
 632                 if ( !$conn ) {
 633                         if ( !$open ) {
 634                                 $this->replLogger->debug(
 635                                         __METHOD__ . ': no connection open for {dbserver}',
 636                                         [ 'dbserver' => $server ]
 637                                 );
 638
 639                                 return false;
 640                         } else {
 641                                 $conn = $this->openConnection( $index, self::DOMAIN_ANY );
 642                                 if ( !$conn ) {
 643                                         $this->replLogger->warning(
 644                                                 __METHOD__ . ': failed to connect to {dbserver}',
 645                                                 [ 'dbserver' => $server ]
 646                                         );
 647
 648                                         return false;
 649                                 }
 650                                 // Avoid connection spam in waitForAll() when connections
 651                                 // are made just for the sake of doing this lag check.
 652                                 $close = true;
 653                         }
 654                 }
 655
 656                 $this->replLogger->info(
 657                         __METHOD__ .
 658                         ': waiting for replica DB {dbserver} to catch up...',
 659                         [ 'dbserver' => $server ]
 660                 );
 661
 662                 $result = $conn->masterPosWait( $this->waitForPos, $timeout );
 663
 664                 if ( $result === null ) {
 665                         $this->replLogger->warning(
 666                                 __METHOD__ . ': Errored out waiting on {host} pos {pos}',
 667                                 [
 668                                         'host' => $server,
 669                                         'pos' => $this->waitForPos,
 670                                         'trace' => ( new RuntimeException() )->getTraceAsString()
 671                                 ]
 672                         );
 673                         $ok = false;
 674                 } elseif ( $result == -1 ) {
 675                         $this->replLogger->warning(
 676                                 __METHOD__ . ': Timed out waiting on {host} pos {pos}',
 677                                 [
 678                                         'host' => $server,
 679                                         'pos' => $this->waitForPos,
 680                                         'trace' => ( new RuntimeException() )->getTraceAsString()
 681                                 ]
 682                         );
 683                         $ok = false;
 684                 } else {
 685                         $this->replLogger->debug( __METHOD__ . ": done waiting" );
 686                         $ok = true;
 687                         // Remember that the DB reached this point
 688                         $this->srvCache->set( $key, $this->waitForPos, BagOStuff::TTL_DAY );
 689                 }
 690
 691                 if ( $close ) {
 692                         $this->closeConnection( $conn );
 693                 }
 694
 695                 return $ok;
 696         }
 697
 698         public function getConnection( $i, $groups = [], $domain = false, $flags = 0 ) {
 699                 if ( $i === null || $i === false ) {
 700                         throw new InvalidArgumentException( 'Attempt to call ' . __METHOD__ .
 701                                 ' with invalid server index' );
 702                 }
 703
 704                 if ( $this->localDomain->equals( $domain ) || $domain === $this->localDomainIdAlias ) {
 705                         $domain = false; // local connection requested
 706                 }
 707
 708                 if ( ( $flags & self::CONN_TRX_AUTOCOMMIT ) === self::CONN_TRX_AUTOCOMMIT ) {
 709                         // Assuming all servers are of the same type (or similar), which is overwhelmingly
 710                         // the case, use the master server information to get the attributes. The information
 711                         // for $i cannot be used since it might be DB_REPLICA, which might require connection
 712                         // attempts in order to be resolved into a real server index.
 713                         $attributes = $this->getServerAttributes( $this->getWriterIndex() );
 714                         if ( $attributes[Database::ATTR_DB_LEVEL_LOCKING] ) {
 715                                 // Callers sometimes want to (a) escape REPEATABLE-READ stateness without locking
 716                                 // rows (e.g. FOR UPDATE) or (b) make small commits during a larger transactions
 717                                 // to reduce lock contention. None of these apply for sqlite and using separate
 718                                 // connections just causes self-deadlocks.
 719                                 $flags &= ~self::CONN_TRX_AUTOCOMMIT;
 720                                 $this->connLogger->info( __METHOD__ .
 721                                         ': ignoring CONN_TRX_AUTOCOMMIT to avoid deadlocks.' );
 722                         }
 723                 }
 724
 725                 // Check one "group" per default: the generic pool
 726                 $defaultGroups = $this->defaultGroup ? [ $this->defaultGroup ] : [ false ];
 727
 728                 $groups = ( $groups === false || $groups === [] )
 729                         ? $defaultGroups
 730                         : (array)$groups;
 731
 732                 $masterOnly = ( $i == self::DB_MASTER || $i == $this->getWriterIndex() );
 733                 $oldConnsOpened = $this->connsOpened; // connections open now
 734
 735                 if ( $i == self::DB_MASTER ) {
 736                         $i = $this->getWriterIndex();
 737                 } elseif ( $i == self::DB_REPLICA ) {
 738                         # Try to find an available server in any the query groups (in order)
 739                         foreach ( $groups as $group ) {
 740                                 $groupIndex = $this->getReaderIndex( $group, $domain );
 741                                 if ( $groupIndex !== false ) {
 742                                         $i = $groupIndex;
 743                                         break;
 744                                 }
 745                         }
 746                 }
 747
 748                 # Operation-based index
 749                 if ( $i == self::DB_REPLICA ) {
 750                         $this->lastError = 'Unknown error'; // reset error string
 751                         # Try the general server pool if $groups are unavailable.
 752                         $i = ( $groups === [ false ] )
 753                                 ? false // don't bother with this if that is what was tried above
 754                                 : $this->getReaderIndex( false, $domain );
 755                         # Couldn't find a working server in getReaderIndex()?
 756                         if ( $i === false ) {
 757                                 $this->lastError = 'No working replica DB server: ' . $this->lastError;
 758                                 // Throw an exception
 759                                 $this->reportConnectionError();
 760                                 return null; // not reached
 761                         }
 762                 }
 763
 764                 # Now we have an explicit index into the servers array
 765                 $conn = $this->openConnection( $i, $domain, $flags );
 766                 if ( !$conn ) {
 767                         // Throw an exception
 768                         $this->reportConnectionError();
 769                         return null; // not reached
 770                 }
 771
 772                 # Profile any new connections that happen
 773                 if ( $this->connsOpened > $oldConnsOpened ) {
 774                         $host = $conn->getServer();
 775                         $dbname = $conn->getDBname();
 776                         $this->trxProfiler->recordConnection( $host, $dbname, $masterOnly );
 777                 }
 778
 779                 if ( $masterOnly ) {
 780                         # Make master-requested DB handles inherit any read-only mode setting
 781                         $conn->setLBInfo( 'readOnlyReason', $this->getReadOnlyReason( $domain, $conn ) );
 782                 }
 783
 784                 return $conn;
 785         }
 786
 787         public function reuseConnection( IDatabase $conn ) {
 788                 $serverIndex = $conn->getLBInfo( 'serverIndex' );
 789                 $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 790                 if ( $serverIndex === null || $refCount === null ) {
 791                         /**
 792                          * This can happen in code like:
 793                          *   foreach ( $dbs as $db ) {
 794                          *     $conn = $lb->getConnection( $lb::DB_REPLICA, [], $db );
 795                          *     ...
 796                          *     $lb->reuseConnection( $conn );
 797                          *   }
 798                          * When a connection to the local DB is opened in this way, reuseConnection()
 799                          * should be ignored
 800                          */
 801                         return;
 802                 } elseif ( $conn instanceof DBConnRef ) {
 803                         // DBConnRef already handles calling reuseConnection() and only passes the live
 804                         // Database instance to this method. Any caller passing in a DBConnRef is broken.
 805                         $this->connLogger->error(
 806                                 __METHOD__ . ": got DBConnRef instance.\n" .
 807                                 ( new RuntimeException() )->getTraceAsString() );
 808
 809                         return;
 810                 }
 811
 812                 if ( $this->disabled ) {
 813                         return; // DBConnRef handle probably survived longer than the LoadBalancer
 814                 }
 815
 816                 if ( $conn->getLBInfo( 'autoCommitOnly' ) ) {
 817                         $connFreeKey = self::KEY_FOREIGN_FREE_NOROUND;
 818                         $connInUseKey = self::KEY_FOREIGN_INUSE_NOROUND;
 819                 } else {
 820                         $connFreeKey = self::KEY_FOREIGN_FREE;
 821                         $connInUseKey = self::KEY_FOREIGN_INUSE;
 822                 }
 823
 824                 $domain = $conn->getDomainID();
 825                 if ( !isset( $this->conns[$connInUseKey][$serverIndex][$domain] ) ) {
 826                         throw new InvalidArgumentException( __METHOD__ .
 827                                 ": connection $serverIndex/$domain not found; it may have already been freed." );
 828                 } elseif ( $this->conns[$connInUseKey][$serverIndex][$domain] !== $conn ) {
 829                         throw new InvalidArgumentException( __METHOD__ .
 830                                 ": connection $serverIndex/$domain mismatched; it may have already been freed." );
 831                 }
 832
 833                 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
 834                 if ( $refCount <= 0 ) {
 835                         $this->conns[$connFreeKey][$serverIndex][$domain] = $conn;
 836                         unset( $this->conns[$connInUseKey][$serverIndex][$domain] );
 837                         if ( !$this->conns[$connInUseKey][$serverIndex] ) {
 838                                 unset( $this->conns[$connInUseKey][$serverIndex] ); // clean up
 839                         }
 840                         $this->connLogger->debug( __METHOD__ . ": freed connection $serverIndex/$domain" );
 841                 } else {
 842                         $this->connLogger->debug( __METHOD__ .
 843                                 ": reference count for $serverIndex/$domain reduced to $refCount" );
 844                 }
 845         }
 846
 847         public function getConnectionRef( $db, $groups = [], $domain = false, $flags = 0 ) {
 848                 $domain = $this->resolveDomainID( $domain );
 849
 850                 return new DBConnRef( $this, $this->getConnection( $db, $groups, $domain, $flags ) );
 851         }
 852
 853         public function getLazyConnectionRef( $db, $groups = [], $domain = false, $flags = 0 ) {
 854                 $domain = $this->resolveDomainID( $domain );
 855
 856                 return new DBConnRef( $this, [ $db, $groups, $domain, $flags ] );
 857         }
 858
 859         public function getMaintenanceConnectionRef( $db, $groups = [], $domain = false, $flags = 0 ) {
 860                 $domain = $this->resolveDomainID( $domain );
 861
 862                 return new MaintainableDBConnRef(
 863                         $this, $this->getConnection( $db, $groups, $domain, $flags ) );
 864         }
 865
 866         public function openConnection( $i, $domain = false, $flags = 0 ) {
 867                 if ( $this->localDomain->equals( $domain ) || $domain === $this->localDomainIdAlias ) {
 868                         $domain = false; // local connection requested
 869                 }
 870
 871                 if ( !$this->connectionAttempted && $this->chronologyCallback ) {
 872                         $this->connLogger->debug( __METHOD__ . ': calling initLB() before first connection.' );
 873                         // Load any "waitFor" positions before connecting so that doWait() is triggered
 874                         $this->connectionAttempted = true;
 875                         ( $this->chronologyCallback )( $this );
 876                 }
 877
 878                 // Check if an auto-commit connection is being requested. If so, it will not reuse the
 879                 // main set of DB connections but rather its own pool since:
 880                 // a) those are usually set to implicitly use transaction rounds via DBO_TRX
 881                 // b) those must support the use of explicit transaction rounds via beginMasterChanges()
 882                 $autoCommit = ( ( $flags & self::CONN_TRX_AUTOCOMMIT ) == self::CONN_TRX_AUTOCOMMIT );
 883
 884                 if ( $domain !== false ) {
 885                         // Connection is to a foreign domain
 886                         $conn = $this->openForeignConnection( $i, $domain, $flags );
 887                 } else {
 888                         // Connection is to the local domain
 889                         $connKey = $autoCommit ? self::KEY_LOCAL_NOROUND : self::KEY_LOCAL;
 890                         if ( isset( $this->conns[$connKey][$i][0] ) ) {
 891                                 $conn = $this->conns[$connKey][$i][0];
 892                         } else {
 893                                 if ( !isset( $this->servers[$i] ) || !is_array( $this->servers[$i] ) ) {
 894                                         throw new InvalidArgumentException( "No server with index '$i'." );
 895                                 }
 896                                 // Open a new connection
 897                                 $server = $this->servers[$i];
 898                                 $server['serverIndex'] = $i;
 899                                 $server['autoCommitOnly'] = $autoCommit;
 900                                 if ( $this->localDomain->getDatabase() !== null ) {
 901                                         // Use the local domain table prefix if the local domain is specified
 902                                         $server['tablePrefix'] = $this->localDomain->getTablePrefix();
 903                                 }
 904                                 $conn = $this->reallyOpenConnection( $server, $this->localDomain );
 905                                 $host = $this->getServerName( $i );
 906                                 if ( $conn->isOpen() ) {
 907                                         $this->connLogger->debug(
 908                                                 __METHOD__ . ": connected to database $i at '$host'." );
 909                                         $this->conns[$connKey][$i][0] = $conn;
 910                                 } else {
 911                                         $this->connLogger->warning(
 912                                                 __METHOD__ . ": failed to connect to database $i at '$host'." );
 913                                         $this->errorConnection = $conn;
 914                                         $conn = false;
 915                                 }
 916                         }
 917                 }
 918
 919                 if ( $conn instanceof IDatabase && !$conn->isOpen() ) {
 920                         // Connection was made but later unrecoverably lost for some reason.
 921                         // Do not return a handle that will just throw exceptions on use,
 922                         // but let the calling code (e.g. getReaderIndex) try another server.
 923                         // See DatabaseMyslBase::ping() for how this can happen.
 924                         $this->errorConnection = $conn;
 925                         $conn = false;
 926                 }
 927
 928                 if ( $autoCommit && $conn instanceof IDatabase ) {
 929                         $conn->clearFlag( $conn::DBO_TRX ); // auto-commit mode
 930                 }
 931
 932                 return $conn;
 933         }
 934
 935         /**
 936          * Open a connection to a foreign DB, or return one if it is already open.
 937          *
 938          * Increments a reference count on the returned connection which locks the
 939          * connection to the requested domain. This reference count can be
 940          * decremented by calling reuseConnection().
 941          *
 942          * If a connection is open to the appropriate server already, but with the wrong
 943          * database, it will be switched to the right database and returned, as long as
 944          * it has been freed first with reuseConnection().
 945          *
 946          * On error, returns false, and the connection which caused the
 947          * error will be available via $this->errorConnection.
 948          *
 949          * @note If disable() was called on this LoadBalancer, this method will throw a DBAccessError.
 950          *
 951          * @param int $i Server index
 952          * @param string $domain Domain ID to open
 953          * @param int $flags Class CONN_* constant bitfield
 954          * @return Database
 955          */
 956         private function openForeignConnection( $i, $domain, $flags = 0 ) {
 957                 $domainInstance = DatabaseDomain::newFromId( $domain );
 958                 $dbName = $domainInstance->getDatabase();
 959                 $prefix = $domainInstance->getTablePrefix();
 960                 $autoCommit = ( ( $flags & self::CONN_TRX_AUTOCOMMIT ) == self::CONN_TRX_AUTOCOMMIT );
 961
 962                 if ( $autoCommit ) {
 963                         $connFreeKey = self::KEY_FOREIGN_FREE_NOROUND;
 964                         $connInUseKey = self::KEY_FOREIGN_INUSE_NOROUND;
 965                 } else {
 966                         $connFreeKey = self::KEY_FOREIGN_FREE;
 967                         $connInUseKey = self::KEY_FOREIGN_INUSE;
 968                 }
 969
 970                 if ( isset( $this->conns[$connInUseKey][$i][$domain] ) ) {
 971                         // Reuse an in-use connection for the same domain
 972                         $conn = $this->conns[$connInUseKey][$i][$domain];
 973                         $this->connLogger->debug( __METHOD__ . ": reusing connection $i/$domain" );
 974                 } elseif ( isset( $this->conns[$connFreeKey][$i][$domain] ) ) {
 975                         // Reuse a free connection for the same domain
 976                         $conn = $this->conns[$connFreeKey][$i][$domain];
 977                         unset( $this->conns[$connFreeKey][$i][$domain] );
 978                         $this->conns[$connInUseKey][$i][$domain] = $conn;
 979                         $this->connLogger->debug( __METHOD__ . ": reusing free connection $i/$domain" );
 980                 } elseif ( !empty( $this->conns[$connFreeKey][$i] ) ) {
 981                         // Reuse a free connection from another domain
 982                         $conn = reset( $this->conns[$connFreeKey][$i] );
 983                         $oldDomain = key( $this->conns[$connFreeKey][$i] );
 984                         if ( strlen( $dbName ) && !$conn->selectDB( $dbName ) ) {
 985                                 $this->lastError = "Error selecting database '$dbName' on server " .
 986                                         $conn->getServer() . " from client host {$this->hostname}";
 987                                 $this->errorConnection = $conn;
 988                                 $conn = false;
 989                         } else {
 990                                 $conn->tablePrefix( $prefix );
 991                                 unset( $this->conns[$connFreeKey][$i][$oldDomain] );
 992                                 // Note that if $domain is an empty string, getDomainID() might not match it
 993                                 $this->conns[$connInUseKey][$i][$conn->getDomainId()] = $conn;
 994                                 $this->connLogger->debug( __METHOD__ .
 995                                         ": reusing free connection from $oldDomain for $domain" );
 996                         }
 997                 } else {
 998                         if ( !isset( $this->servers[$i] ) || !is_array( $this->servers[$i] ) ) {
 999                                 throw new InvalidArgumentException( "No server with index '$i'." );
1000                         }
1001                         // Open a new connection
1002                         $server = $this->servers[$i];
1003                         $server['serverIndex'] = $i;
1004                         $server['foreignPoolRefCount'] = 0;
1005                         $server['foreign'] = true;
1006                         $server['autoCommitOnly'] = $autoCommit;
1007                         $conn = $this->reallyOpenConnection( $server, $domainInstance );
1008                         if ( !$conn->isOpen() ) {
1009                                 $this->connLogger->warning( __METHOD__ . ": connection error for $i/$domain" );
1010                                 $this->errorConnection = $conn;
1011                                 $conn = false;
1012                         } else {
1013                                 $conn->tablePrefix( $prefix ); // as specified
1014                                 // Note that if $domain is an empty string, getDomainID() might not match it
1015                                 $this->conns[$connInUseKey][$i][$conn->getDomainID()] = $conn;
1016                                 $this->connLogger->debug( __METHOD__ . ": opened new connection for $i/$domain" );
1017                         }
1018                 }
1019
1020                 // Increment reference count
1021                 if ( $conn instanceof IDatabase ) {
1022                         $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
1023                         $conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
1024                 }
1025
1026                 return $conn;
1027         }
1028
1029         public function getServerAttributes( $i ) {
1030                 return Database::attributesFromType(
1031                         $this->getServerType( $i ),
1032                         $this->servers[$i]['driver'] ?? null
1033                 );
1034         }
1035
1036         /**
1037          * Test if the specified index represents an open connection
1038          *
1039          * @param int $index Server index
1040          * @access private
1041          * @return bool
1042          */
1043         private function isOpen( $index ) {
1044                 if ( !is_int( $index ) ) {
1045                         return false;
1046                 }
1047
1048                 return (bool)$this->getAnyOpenConnection( $index );
1049         }
1050
1051         /**
1052          * Open a new network connection to a server (uncached)
1053          *
1054          * Returns a Database object whether or not the connection was successful.
1055          *
1056          * @param array $server
1057          * @param DatabaseDomain $domainOverride Use an unspecified domain to not select any database
1058          * @return Database
1059          * @throws DBAccessError
1060          * @throws InvalidArgumentException
1061          */
1062         protected function reallyOpenConnection( array $server, DatabaseDomain $domainOverride ) {
1063                 if ( $this->disabled ) {
1064                         throw new DBAccessError();
1065                 }
1066
1067                 // Handle $domainOverride being a specified or an unspecified domain
1068                 if ( $domainOverride->getDatabase() === null ) {
1069                         // Normally, an RDBMS requires a DB name specified on connection and the $server
1070                         // configuration array is assumed to already specify an appropriate DB name.
1071                         if ( $server['type'] === 'mysql' ) {
1072                                 // For MySQL, DATABASE and SCHEMA are synonyms, connections need not specify a DB,
1073                                 // and the DB name in $server might not exist due to legacy reasons (the default
1074                                 // domain used to ignore the local LB domain, even when mismatched).
1075                                 $server['dbname'] = null;
1076                         }
1077                 } else {
1078                         $server['dbname'] = $domainOverride->getDatabase();
1079                         $server['schema'] = $domainOverride->getSchema();
1080                 }
1081
1082                 // Let the handle know what the cluster master is (e.g. "db1052")
1083                 $masterName = $this->getServerName( $this->getWriterIndex() );
1084                 $server['clusterMasterHost'] = $masterName;
1085
1086                 // Log when many connection are made on requests
1087                 if ( ++$this->connsOpened >= self::CONN_HELD_WARN_THRESHOLD ) {
1088                         $this->perfLogger->warning( __METHOD__ . ": " .
1089                                 "{$this->connsOpened}+ connections made (master=$masterName)" );
1090                 }
1091
1092                 $server['srvCache'] = $this->srvCache;
1093                 // Set loggers and profilers
1094                 $server['connLogger'] = $this->connLogger;
1095                 $server['queryLogger'] = $this->queryLogger;
1096                 $server['errorLogger'] = $this->errorLogger;
1097                 $server['deprecationLogger'] = $this->deprecationLogger;
1098                 $server['profiler'] = $this->profiler;
1099                 $server['trxProfiler'] = $this->trxProfiler;
1100                 // Use the same agent and PHP mode for all DB handles
1101                 $server['cliMode'] = $this->cliMode;
1102                 $server['agent'] = $this->agent;
1103                 // Use DBO_DEFAULT flags by default for LoadBalancer managed databases. Assume that the
1104                 // application calls LoadBalancer::commitMasterChanges() before the PHP script completes.
1105                 $server['flags'] = $server['flags'] ?? IDatabase::DBO_DEFAULT;
1106
1107                 // Create a live connection object
1108                 try {
1109                         $db = Database::factory( $server['type'], $server );
1110                 } catch ( DBConnectionError $e ) {
1111                         // FIXME: This is probably the ugliest thing I have ever done to
1112                         // PHP. I'm half-expecting it to segfault, just out of disgust. -- TS
1113                         $db = $e->db;
1114                 }
1115
1116                 $db->setLBInfo( $server );
1117                 $db->setLazyMasterHandle(
1118                         $this->getLazyConnectionRef( self::DB_MASTER, [], $db->getDomainID() )
1119                 );
1120                 $db->setTableAliases( $this->tableAliases );
1121                 $db->setIndexAliases( $this->indexAliases );
1122
1123                 if ( $server['serverIndex'] === $this->getWriterIndex() ) {
1124                         if ( $this->trxRoundId !== false ) {
1125                                 $this->applyTransactionRoundFlags( $db );
1126                         }
1127                         foreach ( $this->trxRecurringCallbacks as $name => $callback ) {
1128                                 $db->setTransactionListener( $name, $callback );
1129                         }
1130                 }
1131
1132                 return $db;
1133         }
1134
1135         /**
1136          * @throws DBConnectionError
1137          */
1138         private function reportConnectionError() {
1139                 $conn = $this->errorConnection; // the connection which caused the error
1140                 $context = [
1141                         'method' => __METHOD__,
1142                         'last_error' => $this->lastError,
1143                 ];
1144
1145                 if ( $conn instanceof IDatabase ) {
1146                         $context['db_server'] = $conn->getServer();
1147                         $this->connLogger->warning(
1148                                 __METHOD__ . ": connection error: {last_error} ({db_server})",
1149                                 $context
1150                         );
1151
1152                         throw new DBConnectionError( $conn, "{$this->lastError} ({$context['db_server']})" );
1153                 } else {
1154                         // No last connection, probably due to all servers being too busy
1155                         $this->connLogger->error(
1156                                 __METHOD__ .
1157                                 ": LB failure with no last connection. Connection error: {last_error}",
1158                                 $context
1159                         );
1160
1161                         // If all servers were busy, "lastError" will contain something sensible
1162                         throw new DBConnectionError( null, $this->lastError );
1163                 }
1164         }
1165
1166         public function getWriterIndex() {
1167                 return 0;
1168         }
1169
1170         public function haveIndex( $i ) {
1171                 return array_key_exists( $i, $this->servers );
1172         }
1173
1174         public function isNonZeroLoad( $i ) {
1175                 return array_key_exists( $i, $this->servers ) && $this->loads[$i] != 0;
1176         }
1177
1178         public function getServerCount() {
1179                 return count( $this->servers );
1180         }
1181
1182         public function getServerName( $i ) {
1183                 if ( isset( $this->servers[$i]['hostName'] ) ) {
1184                         $name = $this->servers[$i]['hostName'];
1185                 } elseif ( isset( $this->servers[$i]['host'] ) ) {
1186                         $name = $this->servers[$i]['host'];
1187                 } else {
1188                         $name = '';
1189                 }
1190
1191                 return ( $name != '' ) ? $name : 'localhost';
1192         }
1193
1194         public function getServerInfo( $i ) {
1195                 if ( isset( $this->servers[$i] ) ) {
1196                         return $this->servers[$i];
1197                 } else {
1198                         return false;
1199                 }
1200         }
1201
1202         public function getServerType( $i ) {
1203                 return $this->servers[$i]['type'] ?? 'unknown';
1204         }
1205
1206         public function getMasterPos() {
1207                 # If this entire request was served from a replica DB without opening a connection to the
1208                 # master (however unlikely that may be), then we can fetch the position from the replica DB.
1209                 $masterConn = $this->getAnyOpenConnection( $this->getWriterIndex() );
1210                 if ( !$masterConn ) {
1211                         $serverCount = count( $this->servers );
1212                         for ( $i = 1; $i < $serverCount; $i++ ) {
1213                                 $conn = $this->getAnyOpenConnection( $i );
1214                                 if ( $conn ) {
1215                                         return $conn->getReplicaPos();
1216                                 }
1217                         }
1218                 } else {
1219                         return $masterConn->getMasterPos();
1220                 }
1221
1222                 return false;
1223         }
1224
1225         public function disable() {
1226                 $this->closeAll();
1227                 $this->disabled = true;
1228         }
1229
1230         public function closeAll() {
1231                 $this->forEachOpenConnection( function ( IDatabase $conn ) {
1232                         $host = $conn->getServer();
1233                         $this->connLogger->debug(
1234                                 __METHOD__ . ": closing connection to database '$host'." );
1235                         $conn->close();
1236                 } );
1237
1238                 $this->conns = [
1239                         self::KEY_LOCAL => [],
1240                         self::KEY_FOREIGN_INUSE => [],
1241                         self::KEY_FOREIGN_FREE => [],
1242                         self::KEY_LOCAL_NOROUND => [],
1243                         self::KEY_FOREIGN_INUSE_NOROUND => [],
1244                         self::KEY_FOREIGN_FREE_NOROUND => []
1245                 ];
1246                 $this->connsOpened = 0;
1247         }
1248
1249         public function closeConnection( IDatabase $conn ) {
1250                 $serverIndex = $conn->getLBInfo( 'serverIndex' );
1251                 foreach ( $this->conns as $type => $connsByServer ) {
1252                         if ( !isset( $connsByServer[$serverIndex] ) ) {
1253                                 continue;
1254                         }
1255
1256                         foreach ( $connsByServer[$serverIndex] as $i => $trackedConn ) {
1257                                 if ( $conn === $trackedConn ) {
1258                                         $host = $this->getServerName( $i );
1259                                         $this->connLogger->debug(
1260                                                 __METHOD__ . ": closing connection to database $i at '$host'." );
1261                                         unset( $this->conns[$type][$serverIndex][$i] );
1262                                         --$this->connsOpened;
1263                                         break 2;
1264                                 }
1265                         }
1266                 }
1267
1268                 $conn->close();
1269         }
1270
1271         public function commitAll( $fname = __METHOD__ ) {
1272                 $this->commitMasterChanges( $fname );
1273                 $this->flushMasterSnapshots( $fname );
1274                 $this->flushReplicaSnapshots( $fname );
1275         }
1276
1277         public function finalizeMasterChanges() {
1278                 $this->assertTransactionRoundStage( [ self::ROUND_CURSORY, self::ROUND_FINALIZED ] );
1279
1280                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1281                 // Loop until callbacks stop adding callbacks on other connections
1282                 $total = 0;
1283                 do {
1284                         $count = 0; // callbacks execution attempts
1285                         $this->forEachOpenMasterConnection( function ( Database $conn ) use ( &$count ) {
1286                                 // Run any pre-commit callbacks while leaving the post-commit ones suppressed.
1287                                 // Any error should cause all (peer) transactions to be rolled back together.
1288                                 $count += $conn->runOnTransactionPreCommitCallbacks();
1289                         } );
1290                         $total += $count;
1291                 } while ( $count > 0 );
1292                 // Defer post-commit callbacks until after COMMIT/ROLLBACK happens on all handles
1293                 $this->forEachOpenMasterConnection( function ( Database $conn ) {
1294                         $conn->setTrxEndCallbackSuppression( true );
1295                 } );
1296                 $this->trxRoundStage = self::ROUND_FINALIZED;
1297
1298                 return $total;
1299         }
1300
1301         public function approveMasterChanges( array $options ) {
1302                 $this->assertTransactionRoundStage( self::ROUND_FINALIZED );
1303
1304                 $limit = $options['maxWriteDuration'] ?? 0;
1305
1306                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1307                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( $limit ) {
1308                         // If atomic sections or explicit transactions are still open, some caller must have
1309                         // caught an exception but failed to properly rollback any changes. Detect that and
1310                         // throw and error (causing rollback).
1311                         if ( $conn->explicitTrxActive() ) {
1312                                 throw new DBTransactionError(
1313                                         $conn,
1314                                         "Explicit transaction still active. A caller may have caught an error."
1315                                 );
1316                         }
1317                         // Assert that the time to replicate the transaction will be sane.
1318                         // If this fails, then all DB transactions will be rollback back together.
1319                         $time = $conn->pendingWriteQueryDuration( $conn::ESTIMATE_DB_APPLY );
1320                         if ( $limit > 0 && $time > $limit ) {
1321                                 throw new DBTransactionSizeError(
1322                                         $conn,
1323                                         "Transaction spent $time second(s) in writes, exceeding the limit of $limit.",
1324                                         [ $time, $limit ]
1325                                 );
1326                         }
1327                         // If a connection sits idle while slow queries execute on another, that connection
1328                         // may end up dropped before the commit round is reached. Ping servers to detect this.
1329                         if ( $conn->writesOrCallbacksPending() && !$conn->ping() ) {
1330                                 throw new DBTransactionError(
1331                                         $conn,
1332                                         "A connection to the {$conn->getDBname()} database was lost before commit."
1333                                 );
1334                         }
1335                 } );
1336                 $this->trxRoundStage = self::ROUND_APPROVED;
1337         }
1338
1339         public function beginMasterChanges( $fname = __METHOD__ ) {
1340                 if ( $this->trxRoundId !== false ) {
1341                         throw new DBTransactionError(
1342                                 null,
1343                                 "$fname: Transaction round '{$this->trxRoundId}' already started."
1344                         );
1345                 }
1346                 $this->assertTransactionRoundStage( self::ROUND_CURSORY );
1347
1348                 // Clear any empty transactions (no writes/callbacks) from the implicit round
1349                 $this->flushMasterSnapshots( $fname );
1350
1351                 $this->trxRoundId = $fname;
1352                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1353                 // Mark applicable handles as participating in this explicit transaction round.
1354                 // For each of these handles, any writes and callbacks will be tied to a single
1355                 // transaction. The (peer) handles will reject begin()/commit() calls unless they
1356                 // are part of an en masse commit or an en masse rollback.
1357                 $this->forEachOpenMasterConnection( function ( Database $conn ) {
1358                         $this->applyTransactionRoundFlags( $conn );
1359                 } );
1360                 $this->trxRoundStage = self::ROUND_CURSORY;
1361         }
1362
1363         public function commitMasterChanges( $fname = __METHOD__ ) {
1364                 $this->assertTransactionRoundStage( self::ROUND_APPROVED );
1365
1366                 $failures = [];
1367
1368                 /** @noinspection PhpUnusedLocalVariableInspection */
1369                 $scope = $this->getScopedPHPBehaviorForCommit(); // try to ignore client aborts
1370
1371                 $restore = ( $this->trxRoundId !== false );
1372                 $this->trxRoundId = false;
1373                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1374                 // Commit any writes and clear any snapshots as well (callbacks require AUTOCOMMIT).
1375                 // Note that callbacks should already be suppressed due to finalizeMasterChanges().
1376                 $this->forEachOpenMasterConnection(
1377                         function ( IDatabase $conn ) use ( $fname, &$failures ) {
1378                                 try {
1379                                         $conn->commit( $fname, $conn::FLUSHING_ALL_PEERS );
1380                                 } catch ( DBError $e ) {
1381                                         ( $this->errorLogger )( $e );
1382                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1383                                 }
1384                         }
1385                 );
1386                 if ( $failures ) {
1387                         throw new DBTransactionError(
1388                                 null,
1389                                 "$fname: Commit failed on server(s) " . implode( "\n", array_unique( $failures ) )
1390                         );
1391                 }
1392                 if ( $restore ) {
1393                         // Unmark handles as participating in this explicit transaction round
1394                         $this->forEachOpenMasterConnection( function ( Database $conn ) {
1395                                 $this->undoTransactionRoundFlags( $conn );
1396                         } );
1397                 }
1398                 $this->trxRoundStage = self::ROUND_COMMIT_CALLBACKS;
1399         }
1400
1401         public function runMasterTransactionIdleCallbacks() {
1402                 if ( $this->trxRoundStage === self::ROUND_COMMIT_CALLBACKS ) {
1403                         $type = IDatabase::TRIGGER_COMMIT;
1404                 } elseif ( $this->trxRoundStage === self::ROUND_ROLLBACK_CALLBACKS ) {
1405                         $type = IDatabase::TRIGGER_ROLLBACK;
1406                 } else {
1407                         throw new DBTransactionError(
1408                                 null,
1409                                 "Transaction should be in the callback stage (not '{$this->trxRoundStage}')"
1410                         );
1411                 }
1412
1413                 $oldStage = $this->trxRoundStage;
1414                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1415
1416                 // Now that the COMMIT/ROLLBACK step is over, enable post-commit callback runs
1417                 $this->forEachOpenMasterConnection( function ( Database $conn ) {
1418                         $conn->setTrxEndCallbackSuppression( false );
1419                 } );
1420
1421                 $e = null; // first exception
1422                 // Loop until callbacks stop adding callbacks on other connections
1423                 do {
1424                         // Run any pending callbacks for each connection...
1425                         $count = 0; // callback execution attempts
1426                         $this->forEachOpenMasterConnection(
1427                                 function ( Database $conn ) use ( $type, &$e, &$count ) {
1428                                         if ( $conn->trxLevel() ) {
1429                                                 return; // retry in the next iteration, after commit() is called
1430                                         }
1431                                         try {
1432                                                 $count += $conn->runOnTransactionIdleCallbacks( $type );
1433                                         } catch ( Exception $ex ) {
1434                                                 $e = $e ?: $ex;
1435                                         }
1436                                 }
1437                         );
1438                         // Clear out any active transactions left over from callbacks...
1439                         $this->forEachOpenMasterConnection( function ( Database $conn ) use ( &$e ) {
1440                                 if ( $conn->writesPending() ) {
1441                                         // A callback from another handle wrote to this one and DBO_TRX is set
1442                                         $this->queryLogger->warning( __METHOD__ . ": found writes pending." );
1443                                         $fnames = implode( ', ', $conn->pendingWriteAndCallbackCallers() );
1444                                         $this->queryLogger->warning(
1445                                                 __METHOD__ . ": found writes pending ($fnames).",
1446                                                 [
1447                                                         'db_server' => $conn->getServer(),
1448                                                         'db_name' => $conn->getDBname()
1449                                                 ]
1450                                         );
1451                                 } elseif ( $conn->trxLevel() ) {
1452                                         // A callback from another handle read from this one and DBO_TRX is set,
1453                                         // which can easily happen if there is only one DB (no replicas)
1454                                         $this->queryLogger->debug( __METHOD__ . ": found empty transaction." );
1455                                 }
1456                                 try {
1457                                         $conn->commit( __METHOD__, $conn::FLUSHING_ALL_PEERS );
1458                                 } catch ( Exception $ex ) {
1459                                         $e = $e ?: $ex;
1460                                 }
1461                         } );
1462                 } while ( $count > 0 );
1463
1464                 $this->trxRoundStage = $oldStage;
1465
1466                 return $e;
1467         }
1468
1469         public function runMasterTransactionListenerCallbacks() {
1470                 if ( $this->trxRoundStage === self::ROUND_COMMIT_CALLBACKS ) {
1471                         $type = IDatabase::TRIGGER_COMMIT;
1472                 } elseif ( $this->trxRoundStage === self::ROUND_ROLLBACK_CALLBACKS ) {
1473                         $type = IDatabase::TRIGGER_ROLLBACK;
1474                 } else {
1475                         throw new DBTransactionError(
1476                                 null,
1477                                 "Transaction should be in the callback stage (not '{$this->trxRoundStage}')"
1478                         );
1479                 }
1480
1481                 $e = null;
1482
1483                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1484                 $this->forEachOpenMasterConnection( function ( Database $conn ) use ( $type, &$e ) {
1485                         try {
1486                                 $conn->runTransactionListenerCallbacks( $type );
1487                         } catch ( Exception $ex ) {
1488                                 $e = $e ?: $ex;
1489                         }
1490                 } );
1491                 $this->trxRoundStage = self::ROUND_CURSORY;
1492
1493                 return $e;
1494         }
1495
1496         public function rollbackMasterChanges( $fname = __METHOD__ ) {
1497                 $restore = ( $this->trxRoundId !== false );
1498                 $this->trxRoundId = false;
1499                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1500                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( $fname ) {
1501                         $conn->rollback( $fname, $conn::FLUSHING_ALL_PEERS );
1502                 } );
1503                 if ( $restore ) {
1504                         // Unmark handles as participating in this explicit transaction round
1505                         $this->forEachOpenMasterConnection( function ( Database $conn ) {
1506                                 $this->undoTransactionRoundFlags( $conn );
1507                         } );
1508                 }
1509                 $this->trxRoundStage = self::ROUND_ROLLBACK_CALLBACKS;
1510         }
1511
1512         /**
1513          * @param string|string[] $stage
1514          */
1515         private function assertTransactionRoundStage( $stage ) {
1516                 $stages = (array)$stage;
1517
1518                 if ( !in_array( $this->trxRoundStage, $stages, true ) ) {
1519                         $stageList = implode(
1520                                 '/',
1521                                 array_map( function ( $v ) {
1522                                         return "'$v'";
1523                                 }, $stages )
1524                         );
1525                         throw new DBTransactionError(
1526                                 null,
1527                                 "Transaction round stage must be $stageList (not '{$this->trxRoundStage}')"
1528                         );
1529                 }
1530         }
1531
1532         /**
1533          * Make all DB servers with DBO_DEFAULT/DBO_TRX set join the transaction round
1534          *
1535          * Some servers may have neither flag enabled, meaning that they opt out of such
1536          * transaction rounds and remain in auto-commit mode. Such behavior might be desired
1537          * when a DB server is used for something like simple key/value storage.
1538          *
1539          * @param Database $conn
1540          */
1541         private function applyTransactionRoundFlags( Database $conn ) {
1542                 if ( $conn->getLBInfo( 'autoCommitOnly' ) ) {
1543                         return; // transaction rounds do not apply to these connections
1544                 }
1545
1546                 if ( $conn->getFlag( $conn::DBO_DEFAULT ) ) {
1547                         // DBO_TRX is controlled entirely by CLI mode presence with DBO_DEFAULT.
1548                         // Force DBO_TRX even in CLI mode since a commit round is expected soon.
1549                         $conn->setFlag( $conn::DBO_TRX, $conn::REMEMBER_PRIOR );
1550                 }
1551
1552                 if ( $conn->getFlag( $conn::DBO_TRX ) ) {
1553                         $conn->setLBInfo( 'trxRoundId', $this->trxRoundId );
1554                 }
1555         }
1556
1557         /**
1558          * @param Database $conn
1559          */
1560         private function undoTransactionRoundFlags( Database $conn ) {
1561                 if ( $conn->getLBInfo( 'autoCommitOnly' ) ) {
1562                         return; // transaction rounds do not apply to these connections
1563                 }
1564
1565                 if ( $conn->getFlag( $conn::DBO_TRX ) ) {
1566                         $conn->setLBInfo( 'trxRoundId', false );
1567                 }
1568
1569                 if ( $conn->getFlag( $conn::DBO_DEFAULT ) ) {
1570                         $conn->restoreFlags( $conn::RESTORE_PRIOR );
1571                 }
1572         }
1573
1574         public function flushReplicaSnapshots( $fname = __METHOD__ ) {
1575                 $this->forEachOpenReplicaConnection( function ( IDatabase $conn ) use ( $fname ) {
1576                         $conn->flushSnapshot( $fname );
1577                 } );
1578         }
1579
1580         public function flushMasterSnapshots( $fname = __METHOD__ ) {
1581                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( $fname ) {
1582                         $conn->flushSnapshot( $fname );
1583                 } );
1584         }
1585
1586         /**
1587          * @return string
1588          * @since 1.32
1589          */
1590         public function getTransactionRoundStage() {
1591                 return $this->trxRoundStage;
1592         }
1593
1594         public function hasMasterConnection() {
1595                 return $this->isOpen( $this->getWriterIndex() );
1596         }
1597
1598         public function hasMasterChanges() {
1599                 $pending = 0;
1600                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$pending ) {
1601                         $pending |= $conn->writesOrCallbacksPending();
1602                 } );
1603
1604                 return (bool)$pending;
1605         }
1606
1607         public function lastMasterChangeTimestamp() {
1608                 $lastTime = false;
1609                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$lastTime ) {
1610                         $lastTime = max( $lastTime, $conn->lastDoneWrites() );
1611                 } );
1612
1613                 return $lastTime;
1614         }
1615
1616         public function hasOrMadeRecentMasterChanges( $age = null ) {
1617                 $age = ( $age === null ) ? $this->waitTimeout : $age;
1618
1619                 return ( $this->hasMasterChanges()
1620                         || $this->lastMasterChangeTimestamp() > microtime( true ) - $age );
1621         }
1622
1623         public function pendingMasterChangeCallers() {
1624                 $fnames = [];
1625                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$fnames ) {
1626                         $fnames = array_merge( $fnames, $conn->pendingWriteCallers() );
1627                 } );
1628
1629                 return $fnames;
1630         }
1631
1632         public function getLaggedReplicaMode( $domain = false ) {
1633                 // No-op if there is only one DB (also avoids recursion)
1634                 if ( !$this->laggedReplicaMode && $this->getServerCount() > 1 ) {
1635                         try {
1636                                 // See if laggedReplicaMode gets set
1637                                 $conn = $this->getConnection( self::DB_REPLICA, false, $domain );
1638                                 $this->reuseConnection( $conn );
1639                         } catch ( DBConnectionError $e ) {
1640                                 // Avoid expensive re-connect attempts and failures
1641                                 $this->allReplicasDownMode = true;
1642                                 $this->laggedReplicaMode = true;
1643                         }
1644                 }
1645
1646                 return $this->laggedReplicaMode;
1647         }
1648
1649         public function laggedReplicaUsed() {
1650                 return $this->laggedReplicaMode;
1651         }
1652
1653         /**
1654          * @return bool
1655          * @since 1.27
1656          * @deprecated Since 1.28; use laggedReplicaUsed()
1657          */
1658         public function laggedSlaveUsed() {
1659                 return $this->laggedReplicaUsed();
1660         }
1661
1662         public function getReadOnlyReason( $domain = false, IDatabase $conn = null ) {
1663                 if ( $this->readOnlyReason !== false ) {
1664                         return $this->readOnlyReason;
1665                 } elseif ( $this->getLaggedReplicaMode( $domain ) ) {
1666                         if ( $this->allReplicasDownMode ) {
1667                                 return 'The database has been automatically locked ' .
1668                                         'until the replica database servers become available';
1669                         } else {
1670                                 return 'The database has been automatically locked ' .
1671                                         'while the replica database servers catch up to the master.';
1672                         }
1673                 } elseif ( $this->masterRunningReadOnly( $domain, $conn ) ) {
1674                         return 'The database master is running in read-only mode.';
1675                 }
1676
1677                 return false;
1678         }
1679
1680         /**
1681          * @param string $domain Domain ID, or false for the current domain
1682          * @param IDatabase|null $conn DB master connectionl used to avoid loops [optional]
1683          * @return bool
1684          */
1685         private function masterRunningReadOnly( $domain, IDatabase $conn = null ) {
1686                 $cache = $this->wanCache;
1687                 $masterServer = $this->getServerName( $this->getWriterIndex() );
1688
1689                 return (bool)$cache->getWithSetCallback(
1690                         $cache->makeGlobalKey( __CLASS__, 'server-read-only', $masterServer ),
1691                         self::TTL_CACHE_READONLY,
1692                         function () use ( $domain, $conn ) {
1693                                 $old = $this->trxProfiler->setSilenced( true );
1694                                 try {
1695                                         $dbw = $conn ?: $this->getConnection( self::DB_MASTER, [], $domain );
1696                                         $readOnly = (int)$dbw->serverIsReadOnly();
1697                                         if ( !$conn ) {
1698                                                 $this->reuseConnection( $dbw );
1699                                         }
1700                                 } catch ( DBError $e ) {
1701                                         $readOnly = 0;
1702                                 }
1703                                 $this->trxProfiler->setSilenced( $old );
1704                                 return $readOnly;
1705                         },
1706                         [ 'pcTTL' => $cache::TTL_PROC_LONG, 'busyValue' => 0 ]
1707                 );
1708         }
1709
1710         public function allowLagged( $mode = null ) {
1711                 if ( $mode === null ) {
1712                         return $this->allowLagged;
1713                 }
1714                 $this->allowLagged = $mode;
1715
1716                 return $this->allowLagged;
1717         }
1718
1719         public function pingAll() {
1720                 $success = true;
1721                 $this->forEachOpenConnection( function ( IDatabase $conn ) use ( &$success ) {
1722                         if ( !$conn->ping() ) {
1723                                 $success = false;
1724                         }
1725                 } );
1726
1727                 return $success;
1728         }
1729
1730         public function forEachOpenConnection( $callback, array $params = [] ) {
1731                 foreach ( $this->conns as $connsByServer ) {
1732                         foreach ( $connsByServer as $serverConns ) {
1733                                 foreach ( $serverConns as $conn ) {
1734                                         $callback( $conn, ...$params );
1735                                 }
1736                         }
1737                 }
1738         }
1739
1740         public function forEachOpenMasterConnection( $callback, array $params = [] ) {
1741                 $masterIndex = $this->getWriterIndex();
1742                 foreach ( $this->conns as $connsByServer ) {
1743                         if ( isset( $connsByServer[$masterIndex] ) ) {
1744                                 /** @var IDatabase $conn */
1745                                 foreach ( $connsByServer[$masterIndex] as $conn ) {
1746                                         $callback( $conn, ...$params );
1747                                 }
1748                         }
1749                 }
1750         }
1751
1752         public function forEachOpenReplicaConnection( $callback, array $params = [] ) {
1753                 foreach ( $this->conns as $connsByServer ) {
1754                         foreach ( $connsByServer as $i => $serverConns ) {
1755                                 if ( $i === $this->getWriterIndex() ) {
1756                                         continue; // skip master
1757                                 }
1758                                 foreach ( $serverConns as $conn ) {
1759                                         $callback( $conn, ...$params );
1760                                 }
1761                         }
1762                 }
1763         }
1764
1765         public function getMaxLag( $domain = false ) {
1766                 $maxLag = -1;
1767                 $host = '';
1768                 $maxIndex = 0;
1769
1770                 if ( $this->getServerCount() <= 1 ) {
1771                         return [ $host, $maxLag, $maxIndex ]; // no replication = no lag
1772                 }
1773
1774                 $lagTimes = $this->getLagTimes( $domain );
1775                 foreach ( $lagTimes as $i => $lag ) {
1776                         if ( $this->loads[$i] > 0 && $lag > $maxLag ) {
1777                                 $maxLag = $lag;
1778                                 $host = $this->servers[$i]['host'];
1779                                 $maxIndex = $i;
1780                         }
1781                 }
1782
1783                 return [ $host, $maxLag, $maxIndex ];
1784         }
1785
1786         public function getLagTimes( $domain = false ) {
1787                 if ( $this->getServerCount() <= 1 ) {
1788                         return [ $this->getWriterIndex() => 0 ]; // no replication = no lag
1789                 }
1790
1791                 $knownLagTimes = []; // map of (server index => 0 seconds)
1792                 $indexesWithLag = [];
1793                 foreach ( $this->servers as $i => $server ) {
1794                         if ( empty( $server['is static'] ) ) {
1795                                 $indexesWithLag[] = $i; // DB server might have replication lag
1796                         } else {
1797                                 $knownLagTimes[$i] = 0; // DB server is a non-replicating and read-only archive
1798                         }
1799                 }
1800
1801                 return $this->getLoadMonitor()->getLagTimes( $indexesWithLag, $domain ) + $knownLagTimes;
1802         }
1803
1804         public function safeGetLag( IDatabase $conn ) {
1805                 if ( $this->getServerCount() <= 1 ) {
1806                         return 0;
1807                 } else {
1808                         return $conn->getLag();
1809                 }
1810         }
1811
1812         /**
1813          * @param IDatabase $conn
1814          * @param DBMasterPos|bool $pos
1815          * @param int|null $timeout
1816          * @return bool
1817          */
1818         public function safeWaitForMasterPos( IDatabase $conn, $pos = false, $timeout = null ) {
1819                 $timeout = max( 1, $timeout ?: $this->waitTimeout );
1820
1821                 if ( $this->getServerCount() <= 1 || !$conn->getLBInfo( 'replica' ) ) {
1822                         return true; // server is not a replica DB
1823                 }
1824
1825                 if ( !$pos ) {
1826                         // Get the current master position, opening a connection if needed
1827                         $masterConn = $this->getAnyOpenConnection( $this->getWriterIndex() );
1828                         if ( $masterConn ) {
1829                                 $pos = $masterConn->getMasterPos();
1830                         } else {
1831                                 $masterConn = $this->openConnection( $this->getWriterIndex(), self::DOMAIN_ANY );
1832                                 $pos = $masterConn->getMasterPos();
1833                                 $this->closeConnection( $masterConn );
1834                         }
1835                 }
1836
1837                 if ( $pos instanceof DBMasterPos ) {
1838                         $result = $conn->masterPosWait( $pos, $timeout );
1839                         if ( $result == -1 || is_null( $result ) ) {
1840                                 $msg = __METHOD__ . ': timed out waiting on {host} pos {pos}';
1841                                 $this->replLogger->warning( $msg, [
1842                                         'host' => $conn->getServer(),
1843                                         'pos' => $pos,
1844                                         'trace' => ( new RuntimeException() )->getTraceAsString()
1845                                 ] );
1846                                 $ok = false;
1847                         } else {
1848                                 $this->replLogger->debug( __METHOD__ . ': done waiting' );
1849                                 $ok = true;
1850                         }
1851                 } else {
1852                         $ok = false; // something is misconfigured
1853                         $this->replLogger->error(
1854                                 __METHOD__ . ': could not get master pos for {host}',
1855                                 [
1856                                         'host' => $conn->getServer(),
1857                                         'trace' => ( new RuntimeException() )->getTraceAsString()
1858                                 ]
1859                         );
1860                 }
1861
1862                 return $ok;
1863         }
1864
1865         public function setTransactionListener( $name, callable $callback = null ) {
1866                 if ( $callback ) {
1867                         $this->trxRecurringCallbacks[$name] = $callback;
1868                 } else {
1869                         unset( $this->trxRecurringCallbacks[$name] );
1870                 }
1871                 $this->forEachOpenMasterConnection(
1872                         function ( IDatabase $conn ) use ( $name, $callback ) {
1873                                 $conn->setTransactionListener( $name, $callback );
1874                         }
1875                 );
1876         }
1877
1878         public function setTableAliases( array $aliases ) {
1879                 $this->tableAliases = $aliases;
1880         }
1881
1882         public function setIndexAliases( array $aliases ) {
1883                 $this->indexAliases = $aliases;
1884         }
1885
1886         public function setDomainPrefix( $prefix ) {
1887                 // Find connections to explicit foreign domains still marked as in-use...
1888                 $domainsInUse = [];
1889                 $this->forEachOpenConnection( function ( IDatabase $conn ) use ( &$domainsInUse ) {
1890                         // Once reuseConnection() is called on a handle, its reference count goes from 1 to 0.
1891                         // Until then, it is still in use by the caller (explicitly or via DBConnRef scope).
1892                         if ( $conn->getLBInfo( 'foreignPoolRefCount' ) > 0 ) {
1893                                 $domainsInUse[] = $conn->getDomainID();
1894                         }
1895                 } );
1896
1897                 // Do not switch connections to explicit foreign domains unless marked as safe
1898                 if ( $domainsInUse ) {
1899                         $domains = implode( ', ', $domainsInUse );
1900                         throw new DBUnexpectedError( null,
1901                                 "Foreign domain connections are still in use ($domains)." );
1902                 }
1903
1904                 $oldDomain = $this->localDomain->getId();
1905                 $this->setLocalDomain( new DatabaseDomain(
1906                         $this->localDomain->getDatabase(),
1907                         $this->localDomain->getSchema(),
1908                         $prefix
1909                 ) );
1910
1911                 $this->forEachOpenConnection( function ( IDatabase $db ) use ( $prefix, $oldDomain ) {
1912                         if ( !$db->getLBInfo( 'foreign' ) ) {
1913                                 $db->tablePrefix( $prefix );
1914                         }
1915                 } );
1916         }
1917
1918         /**
1919          * @param DatabaseDomain $domain
1920          */
1921         private function setLocalDomain( DatabaseDomain $domain ) {
1922                 $this->localDomain = $domain;
1923                 // In case a caller assumes that the domain ID is simply <db>-<prefix>, which is almost
1924                 // always true, gracefully handle the case when they fail to account for escaping.
1925                 if ( $this->localDomain->getTablePrefix() != '' ) {
1926                         $this->localDomainIdAlias =
1927                                 $this->localDomain->getDatabase() . '-' . $this->localDomain->getTablePrefix();
1928                 } else {
1929                         $this->localDomainIdAlias = $this->localDomain->getDatabase();
1930                 }
1931         }
1932
1933         /**
1934          * Make PHP ignore user aborts/disconnects until the returned
1935          * value leaves scope. This returns null and does nothing in CLI mode.
1936          *
1937          * @return ScopedCallback|null
1938          */
1939         final protected function getScopedPHPBehaviorForCommit() {
1940                 if ( PHP_SAPI != 'cli' ) { // https://bugs.php.net/bug.php?id=47540
1941                         $old = ignore_user_abort( true ); // avoid half-finished operations
1942                         return new ScopedCallback( function () use ( $old ) {
1943                                 ignore_user_abort( $old );
1944                         } );
1945                 }
1946
1947                 return null;
1948         }
1949
1950         function __destruct() {
1951                 // Avoid connection leaks for sanity
1952                 $this->disable();
1953         }
1954 }
1955
1956 /**
1957  * @deprecated since 1.29
1958  */
1959 class_alias( LoadBalancer::class, 'LoadBalancer' );