includes/libs/rdbms/loadbalancer/LoadBalancer.php

   1 <?php
   2 /**
   3  * Database load balancing manager
   4  *
   5  * This program is free software; you can redistribute it and/or modify
   6  * it under the terms of the GNU General Public License as published by
   7  * the Free Software Foundation; either version 2 of the License, or
   8  * (at your option) any later version.
   9  *
  10  * This program is distributed in the hope that it will be useful,
  11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  13  * GNU General Public License for more details.
  14  *
  15  * You should have received a copy of the GNU General Public License along
  16  * with this program; if not, write to the Free Software Foundation, Inc.,
  17  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
  18  * http://www.gnu.org/copyleft/gpl.html
  19  *
  20  * @file
  21  */
  22 namespace Wikimedia\Rdbms;
  23
  24 use Psr\Log\LoggerInterface;
  25 use Psr\Log\NullLogger;
  26 use Wikimedia\ScopedCallback;
  27 use BagOStuff;
  28 use EmptyBagOStuff;
  29 use WANObjectCache;
  30 use ArrayUtils;
  31 use InvalidArgumentException;
  32 use RuntimeException;
  33 use Exception;
  34
  35 /**
  36  * Database connection, tracking, load balancing, and transaction manager for a cluster
  37  *
  38  * @ingroup Database
  39  */
  40 class LoadBalancer implements ILoadBalancer {
  41         /** @var array[] Map of (server index => server config array) */
  42         private $servers;
  43         /** @var Database[][][] Map of (connection category => server index => IDatabase[]) */
  44         private $conns;
  45         /** @var float[] Map of (server index => weight) */
  46         private $loads;
  47         /** @var array[] Map of (group => server index => weight) */
  48         private $groupLoads;
  49         /** @var bool Whether to disregard replica DB lag as a factor in replica DB selection */
  50         private $allowLagged;
  51         /** @var int Seconds to spend waiting on replica DB lag to resolve */
  52         private $waitTimeout;
  53         /** @var array The LoadMonitor configuration */
  54         private $loadMonitorConfig;
  55         /** @var array[] $aliases Map of (table => (dbname, schema, prefix) map) */
  56         private $tableAliases = [];
  57         /** @var string[] Map of (index alias => index) */
  58         private $indexAliases = [];
  59
  60         /** @var ILoadMonitor */
  61         private $loadMonitor;
  62         /** @var callable|null Callback to run before the first connection attempt */
  63         private $chronologyCallback;
  64         /** @var BagOStuff */
  65         private $srvCache;
  66         /** @var WANObjectCache */
  67         private $wanCache;
  68         /** @var object|string Class name or object With profileIn/profileOut methods */
  69         protected $profiler;
  70         /** @var TransactionProfiler */
  71         protected $trxProfiler;
  72         /** @var LoggerInterface */
  73         protected $replLogger;
  74         /** @var LoggerInterface */
  75         protected $connLogger;
  76         /** @var LoggerInterface */
  77         protected $queryLogger;
  78         /** @var LoggerInterface */
  79         protected $perfLogger;
  80
  81         /** @var Database DB connection object that caused a problem */
  82         private $errorConnection;
  83         /** @var int The generic (not query grouped) replica DB index (of $mServers) */
  84         private $readIndex;
  85         /** @var bool|DBMasterPos False if not set */
  86         private $waitForPos;
  87         /** @var bool Whether the generic reader fell back to a lagged replica DB */
  88         private $laggedReplicaMode = false;
  89         /** @var bool Whether the generic reader fell back to a lagged replica DB */
  90         private $allReplicasDownMode = false;
  91         /** @var string The last DB selection or connection error */
  92         private $lastError = 'Unknown error';
  93         /** @var string|bool Reason the LB is read-only or false if not */
  94         private $readOnlyReason = false;
  95         /** @var int Total connections opened */
  96         private $connsOpened = 0;
  97         /** @var string|bool String if a requested DBO_TRX transaction round is active */
  98         private $trxRoundId = false;
  99         /** @var array[] Map of (name => callable) */
 100         private $trxRecurringCallbacks = [];
 101         /** @var DatabaseDomain Local Domain ID and default for selectDB() calls */
 102         private $localDomain;
 103         /** @var string Alternate ID string for the domain instead of DatabaseDomain::getId() */
 104         private $localDomainIdAlias;
 105         /** @var string Current server name */
 106         private $host;
 107         /** @var bool Whether this PHP instance is for a CLI script */
 108         protected $cliMode;
 109         /** @var string Agent name for query profiling */
 110         protected $agent;
 111
 112         /** @var callable Exception logger */
 113         private $errorLogger;
 114         /** @var callable Deprecation logger */
 115         private $deprecationLogger;
 116
 117         /** @var bool */
 118         private $disabled = false;
 119         /** @var bool Whether any connection has been attempted yet */
 120         private $connectionAttempted = false;
 121         /** @var int */
 122         private $maxLag = self::MAX_LAG_DEFAULT;
 123         /** @var string Stage of the current transaction round in the transaction round life-cycle */
 124         private $trxRoundStage = self::ROUND_CURSORY;
 125
 126         /** @var int Warn when this many connection are held */
 127         const CONN_HELD_WARN_THRESHOLD = 10;
 128
 129         /** @var int Default 'maxLag' when unspecified */
 130         const MAX_LAG_DEFAULT = 10;
 131         /** @var int Default 'waitTimeout' when unspecified */
 132         const MAX_WAIT_DEFAULT = 10;
 133         /** @var int Seconds to cache master server read-only status */
 134         const TTL_CACHE_READONLY = 5;
 135
 136         const KEY_LOCAL = 'local';
 137         const KEY_FOREIGN_FREE = 'foreignFree';
 138         const KEY_FOREIGN_INUSE = 'foreignInUse';
 139
 140         const KEY_LOCAL_NOROUND = 'localAutoCommit';
 141         const KEY_FOREIGN_FREE_NOROUND = 'foreignFreeAutoCommit';
 142         const KEY_FOREIGN_INUSE_NOROUND = 'foreignInUseAutoCommit';
 143
 144         /** @var string Transaction round, explicit or implicit, has not finished writing */
 145         const ROUND_CURSORY = 'cursory';
 146         /** @var string Transaction round writes are complete and ready for pre-commit checks */
 147         const ROUND_FINALIZED = 'finalized';
 148         /** @var string Transaction round passed final pre-commit checks */
 149         const ROUND_APPROVED = 'approved';
 150         /** @var string Transaction round was committed and post-commit callbacks must be run */
 151         const ROUND_COMMIT_CALLBACKS = 'commit-callbacks';
 152         /** @var string Transaction round was rolled back and post-rollback callbacks must be run */
 153         const ROUND_ROLLBACK_CALLBACKS = 'rollback-callbacks';
 154         /** @var string Transaction round encountered an error */
 155         const ROUND_ERROR = 'error';
 156
 157         public function __construct( array $params ) {
 158                 if ( !isset( $params['servers'] ) ) {
 159                         throw new InvalidArgumentException( __CLASS__ . ': missing servers parameter' );
 160                 }
 161                 $this->servers = $params['servers'];
 162                 foreach ( $this->servers as $i => $server ) {
 163                         if ( $i == 0 ) {
 164                                 $this->servers[$i]['master'] = true;
 165                         } else {
 166                                 $this->servers[$i]['replica'] = true;
 167                         }
 168                 }
 169
 170                 $localDomain = isset( $params['localDomain'] )
 171                         ? DatabaseDomain::newFromId( $params['localDomain'] )
 172                         : DatabaseDomain::newUnspecified();
 173                 $this->setLocalDomain( $localDomain );
 174
 175                 $this->waitTimeout = isset( $params['waitTimeout'] )
 176                         ? $params['waitTimeout']
 177                         : self::MAX_WAIT_DEFAULT;
 178
 179                 $this->readIndex = -1;
 180                 $this->conns = [
 181                         // Connection were transaction rounds may be applied
 182                         self::KEY_LOCAL => [],
 183                         self::KEY_FOREIGN_INUSE => [],
 184                         self::KEY_FOREIGN_FREE => [],
 185                         // Auto-committing counterpart connections that ignore transaction rounds
 186                         self::KEY_LOCAL_NOROUND => [],
 187                         self::KEY_FOREIGN_INUSE_NOROUND => [],
 188                         self::KEY_FOREIGN_FREE_NOROUND => []
 189                 ];
 190                 $this->loads = [];
 191                 $this->waitForPos = false;
 192                 $this->allowLagged = false;
 193
 194                 if ( isset( $params['readOnlyReason'] ) && is_string( $params['readOnlyReason'] ) ) {
 195                         $this->readOnlyReason = $params['readOnlyReason'];
 196                 }
 197
 198                 if ( isset( $params['maxLag'] ) ) {
 199                         $this->maxLag = $params['maxLag'];
 200                 }
 201
 202                 if ( isset( $params['loadMonitor'] ) ) {
 203                         $this->loadMonitorConfig = $params['loadMonitor'];
 204                 } else {
 205                         $this->loadMonitorConfig = [ 'class' => 'LoadMonitorNull' ];
 206                 }
 207                 $this->loadMonitorConfig += [ 'lagWarnThreshold' => $this->maxLag ];
 208
 209                 foreach ( $params['servers'] as $i => $server ) {
 210                         $this->loads[$i] = $server['load'];
 211                         if ( isset( $server['groupLoads'] ) ) {
 212                                 foreach ( $server['groupLoads'] as $group => $ratio ) {
 213                                         if ( !isset( $this->groupLoads[$group] ) ) {
 214                                                 $this->groupLoads[$group] = [];
 215                                         }
 216                                         $this->groupLoads[$group][$i] = $ratio;
 217                                 }
 218                         }
 219                 }
 220
 221                 if ( isset( $params['srvCache'] ) ) {
 222                         $this->srvCache = $params['srvCache'];
 223                 } else {
 224                         $this->srvCache = new EmptyBagOStuff();
 225                 }
 226                 if ( isset( $params['wanCache'] ) ) {
 227                         $this->wanCache = $params['wanCache'];
 228                 } else {
 229                         $this->wanCache = WANObjectCache::newEmpty();
 230                 }
 231                 $this->profiler = isset( $params['profiler'] ) ? $params['profiler'] : null;
 232                 if ( isset( $params['trxProfiler'] ) ) {
 233                         $this->trxProfiler = $params['trxProfiler'];
 234                 } else {
 235                         $this->trxProfiler = new TransactionProfiler();
 236                 }
 237
 238                 $this->errorLogger = isset( $params['errorLogger'] )
 239                         ? $params['errorLogger']
 240                         : function ( Exception $e ) {
 241                                 trigger_error( get_class( $e ) . ': ' . $e->getMessage(), E_USER_WARNING );
 242                         };
 243                 $this->deprecationLogger = isset( $params['deprecationLogger'] )
 244                         ? $params['deprecationLogger']
 245                         : function ( $msg ) {
 246                                 trigger_error( $msg, E_USER_DEPRECATED );
 247                         };
 248
 249                 foreach ( [ 'replLogger', 'connLogger', 'queryLogger', 'perfLogger' ] as $key ) {
 250                         $this->$key = isset( $params[$key] ) ? $params[$key] : new NullLogger();
 251                 }
 252
 253                 $this->host = isset( $params['hostname'] )
 254                         ? $params['hostname']
 255                         : ( gethostname() ?: 'unknown' );
 256                 $this->cliMode = isset( $params['cliMode'] )
 257                         ? $params['cliMode']
 258                         : ( PHP_SAPI === 'cli' || PHP_SAPI === 'phpdbg' );
 259                 $this->agent = isset( $params['agent'] ) ? $params['agent'] : '';
 260
 261                 if ( isset( $params['chronologyCallback'] ) ) {
 262                         $this->chronologyCallback = $params['chronologyCallback'];
 263                 }
 264         }
 265
 266         /**
 267          * Get the local (and default) database domain ID of connection handles
 268          *
 269          * @see DatabaseDomain
 270          * @return string Database domain ID; this specifies DB name, schema, and table prefix
 271          * @since 1.31
 272          */
 273         public function getLocalDomainID() {
 274                 return $this->localDomain->getId();
 275         }
 276
 277         /**
 278          * Get a LoadMonitor instance
 279          *
 280          * @return ILoadMonitor
 281          */
 282         private function getLoadMonitor() {
 283                 if ( !isset( $this->loadMonitor ) ) {
 284                         $compat = [
 285                                 'LoadMonitor' => LoadMonitor::class,
 286                                 'LoadMonitorNull' => LoadMonitorNull::class,
 287                                 'LoadMonitorMySQL' => LoadMonitorMySQL::class,
 288                         ];
 289
 290                         $class = $this->loadMonitorConfig['class'];
 291                         if ( isset( $compat[$class] ) ) {
 292                                 $class = $compat[$class];
 293                         }
 294
 295                         $this->loadMonitor = new $class(
 296                                 $this, $this->srvCache, $this->wanCache, $this->loadMonitorConfig );
 297                         $this->loadMonitor->setLogger( $this->replLogger );
 298                 }
 299
 300                 return $this->loadMonitor;
 301         }
 302
 303         /**
 304          * @param array $loads
 305          * @param bool|string $domain Domain to get non-lagged for
 306          * @param int $maxLag Restrict the maximum allowed lag to this many seconds
 307          * @return bool|int|string
 308          */
 309         private function getRandomNonLagged( array $loads, $domain = false, $maxLag = INF ) {
 310                 $lags = $this->getLagTimes( $domain );
 311
 312                 # Unset excessively lagged servers
 313                 foreach ( $lags as $i => $lag ) {
 314                         if ( $i != 0 ) {
 315                                 # How much lag this server nominally is allowed to have
 316                                 $maxServerLag = isset( $this->servers[$i]['max lag'] )
 317                                         ? $this->servers[$i]['max lag']
 318                                         : $this->maxLag; // default
 319                                 # Constrain that futher by $maxLag argument
 320                                 $maxServerLag = min( $maxServerLag, $maxLag );
 321
 322                                 $host = $this->getServerName( $i );
 323                                 if ( $lag === false && !is_infinite( $maxServerLag ) ) {
 324                                         $this->replLogger->error(
 325                                                 __METHOD__ .
 326                                                 ": server {host} is not replicating?", [ 'host' => $host ] );
 327                                         unset( $loads[$i] );
 328                                 } elseif ( $lag > $maxServerLag ) {
 329                                         $this->replLogger->info(
 330                                                 __METHOD__ .
 331                                                 ": server {host} has {lag} seconds of lag (>= {maxlag})",
 332                                                 [ 'host' => $host, 'lag' => $lag, 'maxlag' => $maxServerLag ]
 333                                         );
 334                                         unset( $loads[$i] );
 335                                 }
 336                         }
 337                 }
 338
 339                 # Find out if all the replica DBs with non-zero load are lagged
 340                 $sum = 0;
 341                 foreach ( $loads as $load ) {
 342                         $sum += $load;
 343                 }
 344                 if ( $sum == 0 ) {
 345                         # No appropriate DB servers except maybe the master and some replica DBs with zero load
 346                         # Do NOT use the master
 347                         # Instead, this function will return false, triggering read-only mode,
 348                         # and a lagged replica DB will be used instead.
 349                         return false;
 350                 }
 351
 352                 if ( count( $loads ) == 0 ) {
 353                         return false;
 354                 }
 355
 356                 # Return a random representative of the remainder
 357                 return ArrayUtils::pickRandom( $loads );
 358         }
 359
 360         public function getReaderIndex( $group = false, $domain = false ) {
 361                 if ( count( $this->servers ) == 1 ) {
 362                         // Skip the load balancing if there's only one server
 363                         return $this->getWriterIndex();
 364                 } elseif ( $group === false && $this->readIndex >= 0 ) {
 365                         // Shortcut if the generic reader index was already cached
 366                         return $this->readIndex;
 367                 }
 368
 369                 if ( $group !== false ) {
 370                         // Use the server weight array for this load group
 371                         if ( isset( $this->groupLoads[$group] ) ) {
 372                                 $loads = $this->groupLoads[$group];
 373                         } else {
 374                                 // No loads for this group, return false and the caller can use some other group
 375                                 $this->connLogger->info( __METHOD__ . ": no loads for group $group" );
 376
 377                                 return false;
 378                         }
 379                 } else {
 380                         // Use the generic load group
 381                         $loads = $this->loads;
 382                 }
 383
 384                 // Scale the configured load ratios according to each server's load and state
 385                 $this->getLoadMonitor()->scaleLoads( $loads, $domain );
 386
 387                 // Pick a server to use, accounting for weights, load, lag, and "waitForPos"
 388                 list( $i, $laggedReplicaMode ) = $this->pickReaderIndex( $loads, $domain );
 389                 if ( $i === false ) {
 390                         // Replica DB connection unsuccessful
 391                         return false;
 392                 }
 393
 394                 if ( $this->waitForPos && $i != $this->getWriterIndex() ) {
 395                         // Before any data queries are run, wait for the server to catch up to the
 396                         // specified position. This is used to improve session consistency. Note that
 397                         // when LoadBalancer::waitFor() sets "waitForPos", the waiting triggers here,
 398                         // so update laggedReplicaMode as needed for consistency.
 399                         if ( !$this->doWait( $i ) ) {
 400                                 $laggedReplicaMode = true;
 401                         }
 402                 }
 403
 404                 if ( $this->readIndex <= 0 && $this->loads[$i] > 0 && $group === false ) {
 405                         // Cache the generic reader index for future ungrouped DB_REPLICA handles
 406                         $this->readIndex = $i;
 407                         // Record if the generic reader index is in "lagged replica DB" mode
 408                         if ( $laggedReplicaMode ) {
 409                                 $this->laggedReplicaMode = true;
 410                         }
 411                 }
 412
 413                 $serverName = $this->getServerName( $i );
 414                 $this->connLogger->debug( __METHOD__ . ": using server $serverName for group '$group'" );
 415
 416                 return $i;
 417         }
 418
 419         /**
 420          * @param array $loads List of server weights
 421          * @param string|bool $domain
 422          * @return array (reader index, lagged replica mode) or false on failure
 423          */
 424         private function pickReaderIndex( array $loads, $domain = false ) {
 425                 if ( !count( $loads ) ) {
 426                         throw new InvalidArgumentException( "Empty server array given to LoadBalancer" );
 427                 }
 428
 429                 /** @var int|bool $i Index of selected server */
 430                 $i = false;
 431                 /** @var bool $laggedReplicaMode Whether server is considered lagged */
 432                 $laggedReplicaMode = false;
 433
 434                 // Quickly look through the available servers for a server that meets criteria...
 435                 $currentLoads = $loads;
 436                 while ( count( $currentLoads ) ) {
 437                         if ( $this->allowLagged || $laggedReplicaMode ) {
 438                                 $i = ArrayUtils::pickRandom( $currentLoads );
 439                         } else {
 440                                 $i = false;
 441                                 if ( $this->waitForPos && $this->waitForPos->asOfTime() ) {
 442                                         // "chronologyCallback" sets "waitForPos" for session consistency.
 443                                         // This triggers doWait() after connect, so it's especially good to
 444                                         // avoid lagged servers so as to avoid excessive delay in that method.
 445                                         $ago = microtime( true ) - $this->waitForPos->asOfTime();
 446                                         // Aim for <= 1 second of waiting (being too picky can backfire)
 447                                         $i = $this->getRandomNonLagged( $currentLoads, $domain, $ago + 1 );
 448                                 }
 449                                 if ( $i === false ) {
 450                                         // Any server with less lag than it's 'max lag' param is preferable
 451                                         $i = $this->getRandomNonLagged( $currentLoads, $domain );
 452                                 }
 453                                 if ( $i === false && count( $currentLoads ) != 0 ) {
 454                                         // All replica DBs lagged. Switch to read-only mode
 455                                         $this->replLogger->error(
 456                                                 __METHOD__ . ": all replica DBs lagged. Switch to read-only mode" );
 457                                         $i = ArrayUtils::pickRandom( $currentLoads );
 458                                         $laggedReplicaMode = true;
 459                                 }
 460                         }
 461
 462                         if ( $i === false ) {
 463                                 // pickRandom() returned false.
 464                                 // This is permanent and means the configuration or the load monitor
 465                                 // wants us to return false.
 466                                 $this->connLogger->debug( __METHOD__ . ": pickRandom() returned false" );
 467
 468                                 return [ false, false ];
 469                         }
 470
 471                         $serverName = $this->getServerName( $i );
 472                         $this->connLogger->debug( __METHOD__ . ": Using reader #$i: $serverName..." );
 473
 474                         $conn = $this->openConnection( $i, $domain );
 475                         if ( !$conn ) {
 476                                 $this->connLogger->warning( __METHOD__ . ": Failed connecting to $i/$domain" );
 477                                 unset( $currentLoads[$i] ); // avoid this server next iteration
 478                                 $i = false;
 479                                 continue;
 480                         }
 481
 482                         // Decrement reference counter, we are finished with this connection.
 483                         // It will be incremented for the caller later.
 484                         if ( $domain !== false ) {
 485                                 $this->reuseConnection( $conn );
 486                         }
 487
 488                         // Return this server
 489                         break;
 490                 }
 491
 492                 // If all servers were down, quit now
 493                 if ( !count( $currentLoads ) ) {
 494                         $this->connLogger->error( __METHOD__ . ": all servers down" );
 495                 }
 496
 497                 return [ $i, $laggedReplicaMode ];
 498         }
 499
 500         public function waitFor( $pos ) {
 501                 $oldPos = $this->waitForPos;
 502                 try {
 503                         $this->waitForPos = $pos;
 504                         // If a generic reader connection was already established, then wait now
 505                         $i = $this->readIndex;
 506                         if ( $i > 0 ) {
 507                                 if ( !$this->doWait( $i ) ) {
 508                                         $this->laggedReplicaMode = true;
 509                                 }
 510                         }
 511                 } finally {
 512                         // Restore the older position if it was higher since this is used for lag-protection
 513                         $this->setWaitForPositionIfHigher( $oldPos );
 514                 }
 515         }
 516
 517         public function waitForOne( $pos, $timeout = null ) {
 518                 $oldPos = $this->waitForPos;
 519                 try {
 520                         $this->waitForPos = $pos;
 521
 522                         $i = $this->readIndex;
 523                         if ( $i <= 0 ) {
 524                                 // Pick a generic replica DB if there isn't one yet
 525                                 $readLoads = $this->loads;
 526                                 unset( $readLoads[$this->getWriterIndex()] ); // replica DBs only
 527                                 $readLoads = array_filter( $readLoads ); // with non-zero load
 528                                 $i = ArrayUtils::pickRandom( $readLoads );
 529                         }
 530
 531                         if ( $i > 0 ) {
 532                                 $ok = $this->doWait( $i, true, $timeout );
 533                         } else {
 534                                 $ok = true; // no applicable loads
 535                         }
 536                 } finally {
 537                         # Restore the old position, as this is not used for lag-protection but for throttling
 538                         $this->waitForPos = $oldPos;
 539                 }
 540
 541                 return $ok;
 542         }
 543
 544         public function waitForAll( $pos, $timeout = null ) {
 545                 $timeout = $timeout ?: $this->waitTimeout;
 546
 547                 $oldPos = $this->waitForPos;
 548                 try {
 549                         $this->waitForPos = $pos;
 550                         $serverCount = count( $this->servers );
 551
 552                         $ok = true;
 553                         for ( $i = 1; $i < $serverCount; $i++ ) {
 554                                 if ( $this->loads[$i] > 0 ) {
 555                                         $start = microtime( true );
 556                                         $ok = $this->doWait( $i, true, $timeout ) && $ok;
 557                                         $timeout -= intval( microtime( true ) - $start );
 558                                         if ( $timeout <= 0 ) {
 559                                                 break; // timeout reached
 560                                         }
 561                                 }
 562                         }
 563                 } finally {
 564                         # Restore the old position, as this is not used for lag-protection but for throttling
 565                         $this->waitForPos = $oldPos;
 566                 }
 567
 568                 return $ok;
 569         }
 570
 571         /**
 572          * @param DBMasterPos|bool $pos
 573          */
 574         private function setWaitForPositionIfHigher( $pos ) {
 575                 if ( !$pos ) {
 576                         return;
 577                 }
 578
 579                 if ( !$this->waitForPos || $pos->hasReached( $this->waitForPos ) ) {
 580                         $this->waitForPos = $pos;
 581                 }
 582         }
 583
 584         public function getAnyOpenConnection( $i, $flags = 0 ) {
 585                 $autocommit = ( ( $flags & self::CONN_TRX_AUTOCOMMIT ) == self::CONN_TRX_AUTOCOMMIT );
 586                 foreach ( $this->conns as $connsByServer ) {
 587                         if ( !isset( $connsByServer[$i] ) ) {
 588                                 continue;
 589                         }
 590
 591                         foreach ( $connsByServer[$i] as $conn ) {
 592                                 if ( !$autocommit || $conn->getLBInfo( 'autoCommitOnly' ) ) {
 593                                         return $conn;
 594                                 }
 595                         }
 596                 }
 597
 598                 return false;
 599         }
 600
 601         /**
 602          * Wait for a given replica DB to catch up to the master pos stored in $this
 603          * @param int $index Server index
 604          * @param bool $open Check the server even if a new connection has to be made
 605          * @param int $timeout Max seconds to wait; default is "waitTimeout" given to __construct()
 606          * @return bool
 607          */
 608         protected function doWait( $index, $open = false, $timeout = null ) {
 609                 $timeout = max( 1, intval( $timeout ?: $this->waitTimeout ) );
 610
 611                 // Check if we already know that the DB has reached this point
 612                 $server = $this->getServerName( $index );
 613                 $key = $this->srvCache->makeGlobalKey( __CLASS__, 'last-known-pos', $server, 'v1' );
 614                 /** @var DBMasterPos $knownReachedPos */
 615                 $knownReachedPos = $this->srvCache->get( $key );
 616                 if (
 617                         $knownReachedPos instanceof DBMasterPos &&
 618                         $knownReachedPos->hasReached( $this->waitForPos )
 619                 ) {
 620                         $this->replLogger->debug(
 621                                 __METHOD__ .
 622                                 ': replica DB {dbserver} known to be caught up (pos >= $knownReachedPos).',
 623                                 [ 'dbserver' => $server ]
 624                         );
 625                         return true;
 626                 }
 627
 628                 // Find a connection to wait on, creating one if needed and allowed
 629                 $close = false; // close the connection afterwards
 630                 $conn = $this->getAnyOpenConnection( $index );
 631                 if ( !$conn ) {
 632                         if ( !$open ) {
 633                                 $this->replLogger->debug(
 634                                         __METHOD__ . ': no connection open for {dbserver}',
 635                                         [ 'dbserver' => $server ]
 636                                 );
 637
 638                                 return false;
 639                         } else {
 640                                 $conn = $this->openConnection( $index, self::DOMAIN_ANY );
 641                                 if ( !$conn ) {
 642                                         $this->replLogger->warning(
 643                                                 __METHOD__ . ': failed to connect to {dbserver}',
 644                                                 [ 'dbserver' => $server ]
 645                                         );
 646
 647                                         return false;
 648                                 }
 649                                 // Avoid connection spam in waitForAll() when connections
 650                                 // are made just for the sake of doing this lag check.
 651                                 $close = true;
 652                         }
 653                 }
 654
 655                 $this->replLogger->info(
 656                         __METHOD__ .
 657                         ': waiting for replica DB {dbserver} to catch up...',
 658                         [ 'dbserver' => $server ]
 659                 );
 660
 661                 $result = $conn->masterPosWait( $this->waitForPos, $timeout );
 662
 663                 if ( $result === null ) {
 664                         $this->replLogger->warning(
 665                                 __METHOD__ . ': Errored out waiting on {host} pos {pos}',
 666                                 [
 667                                         'host' => $server,
 668                                         'pos' => $this->waitForPos,
 669                                         'trace' => ( new RuntimeException() )->getTraceAsString()
 670                                 ]
 671                         );
 672                         $ok = false;
 673                 } elseif ( $result == -1 ) {
 674                         $this->replLogger->warning(
 675                                 __METHOD__ . ': Timed out waiting on {host} pos {pos}',
 676                                 [
 677                                         'host' => $server,
 678                                         'pos' => $this->waitForPos,
 679                                         'trace' => ( new RuntimeException() )->getTraceAsString()
 680                                 ]
 681                         );
 682                         $ok = false;
 683                 } else {
 684                         $this->replLogger->debug( __METHOD__ . ": done waiting" );
 685                         $ok = true;
 686                         // Remember that the DB reached this point
 687                         $this->srvCache->set( $key, $this->waitForPos, BagOStuff::TTL_DAY );
 688                 }
 689
 690                 if ( $close ) {
 691                         $this->closeConnection( $conn );
 692                 }
 693
 694                 return $ok;
 695         }
 696
 697         public function getConnection( $i, $groups = [], $domain = false, $flags = 0 ) {
 698                 if ( $i === null || $i === false ) {
 699                         throw new InvalidArgumentException( 'Attempt to call ' . __METHOD__ .
 700                                 ' with invalid server index' );
 701                 }
 702
 703                 if ( $this->localDomain->equals( $domain ) || $domain === $this->localDomainIdAlias ) {
 704                         $domain = false; // local connection requested
 705                 }
 706
 707                 if ( ( $flags & self::CONN_TRX_AUTOCOMMIT ) === self::CONN_TRX_AUTOCOMMIT ) {
 708                         // Assuming all servers are of the same type (or similar), which is overwhelmingly
 709                         // the case, use the master server information to get the attributes. The information
 710                         // for $i cannot be used since it might be DB_REPLICA, which might require connection
 711                         // attempts in order to be resolved into a real server index.
 712                         $attributes = $this->getServerAttributes( $this->getWriterIndex() );
 713                         if ( $attributes[Database::ATTR_DB_LEVEL_LOCKING] ) {
 714                                 // Callers sometimes want to (a) escape REPEATABLE-READ stateness without locking
 715                                 // rows (e.g. FOR UPDATE) or (b) make small commits during a larger transactions
 716                                 // to reduce lock contention. None of these apply for sqlite and using separate
 717                                 // connections just causes self-deadlocks.
 718                                 $flags &= ~self::CONN_TRX_AUTOCOMMIT;
 719                                 $this->connLogger->info( __METHOD__ .
 720                                         ': ignoring CONN_TRX_AUTOCOMMIT to avoid deadlocks.' );
 721                         }
 722                 }
 723
 724                 $groups = ( $groups === false || $groups === [] )
 725                         ? [ false ] // check one "group": the generic pool
 726                         : (array)$groups;
 727
 728                 $masterOnly = ( $i == self::DB_MASTER || $i == $this->getWriterIndex() );
 729                 $oldConnsOpened = $this->connsOpened; // connections open now
 730
 731                 if ( $i == self::DB_MASTER ) {
 732                         $i = $this->getWriterIndex();
 733                 } elseif ( $i == self::DB_REPLICA ) {
 734                         # Try to find an available server in any the query groups (in order)
 735                         foreach ( $groups as $group ) {
 736                                 $groupIndex = $this->getReaderIndex( $group, $domain );
 737                                 if ( $groupIndex !== false ) {
 738                                         $i = $groupIndex;
 739                                         break;
 740                                 }
 741                         }
 742                 }
 743
 744                 # Operation-based index
 745                 if ( $i == self::DB_REPLICA ) {
 746                         $this->lastError = 'Unknown error'; // reset error string
 747                         # Try the general server pool if $groups are unavailable.
 748                         $i = ( $groups === [ false ] )
 749                                 ? false // don't bother with this if that is what was tried above
 750                                 : $this->getReaderIndex( false, $domain );
 751                         # Couldn't find a working server in getReaderIndex()?
 752                         if ( $i === false ) {
 753                                 $this->lastError = 'No working replica DB server: ' . $this->lastError;
 754                                 // Throw an exception
 755                                 $this->reportConnectionError();
 756                                 return null; // not reached
 757                         }
 758                 }
 759
 760                 # Now we have an explicit index into the servers array
 761                 $conn = $this->openConnection( $i, $domain, $flags );
 762                 if ( !$conn ) {
 763                         // Throw an exception
 764                         $this->reportConnectionError();
 765                         return null; // not reached
 766                 }
 767
 768                 # Profile any new connections that happen
 769                 if ( $this->connsOpened > $oldConnsOpened ) {
 770                         $host = $conn->getServer();
 771                         $dbname = $conn->getDBname();
 772                         $this->trxProfiler->recordConnection( $host, $dbname, $masterOnly );
 773                 }
 774
 775                 if ( $masterOnly ) {
 776                         # Make master-requested DB handles inherit any read-only mode setting
 777                         $conn->setLBInfo( 'readOnlyReason', $this->getReadOnlyReason( $domain, $conn ) );
 778                 }
 779
 780                 return $conn;
 781         }
 782
 783         public function reuseConnection( IDatabase $conn ) {
 784                 $serverIndex = $conn->getLBInfo( 'serverIndex' );
 785                 $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 786                 if ( $serverIndex === null || $refCount === null ) {
 787                         /**
 788                          * This can happen in code like:
 789                          *   foreach ( $dbs as $db ) {
 790                          *     $conn = $lb->getConnection( $lb::DB_REPLICA, [], $db );
 791                          *     ...
 792                          *     $lb->reuseConnection( $conn );
 793                          *   }
 794                          * When a connection to the local DB is opened in this way, reuseConnection()
 795                          * should be ignored
 796                          */
 797                         return;
 798                 } elseif ( $conn instanceof DBConnRef ) {
 799                         // DBConnRef already handles calling reuseConnection() and only passes the live
 800                         // Database instance to this method. Any caller passing in a DBConnRef is broken.
 801                         $this->connLogger->error(
 802                                 __METHOD__ . ": got DBConnRef instance.\n" .
 803                                 ( new RuntimeException() )->getTraceAsString() );
 804
 805                         return;
 806                 }
 807
 808                 if ( $this->disabled ) {
 809                         return; // DBConnRef handle probably survived longer than the LoadBalancer
 810                 }
 811
 812                 if ( $conn->getLBInfo( 'autoCommitOnly' ) ) {
 813                         $connFreeKey = self::KEY_FOREIGN_FREE_NOROUND;
 814                         $connInUseKey = self::KEY_FOREIGN_INUSE_NOROUND;
 815                 } else {
 816                         $connFreeKey = self::KEY_FOREIGN_FREE;
 817                         $connInUseKey = self::KEY_FOREIGN_INUSE;
 818                 }
 819
 820                 $domain = $conn->getDomainID();
 821                 if ( !isset( $this->conns[$connInUseKey][$serverIndex][$domain] ) ) {
 822                         throw new InvalidArgumentException( __METHOD__ .
 823                                 ": connection $serverIndex/$domain not found; it may have already been freed." );
 824                 } elseif ( $this->conns[$connInUseKey][$serverIndex][$domain] !== $conn ) {
 825                         throw new InvalidArgumentException( __METHOD__ .
 826                                 ": connection $serverIndex/$domain mismatched; it may have already been freed." );
 827                 }
 828
 829                 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
 830                 if ( $refCount <= 0 ) {
 831                         $this->conns[$connFreeKey][$serverIndex][$domain] = $conn;
 832                         unset( $this->conns[$connInUseKey][$serverIndex][$domain] );
 833                         if ( !$this->conns[$connInUseKey][$serverIndex] ) {
 834                                 unset( $this->conns[$connInUseKey][$serverIndex] ); // clean up
 835                         }
 836                         $this->connLogger->debug( __METHOD__ . ": freed connection $serverIndex/$domain" );
 837                 } else {
 838                         $this->connLogger->debug( __METHOD__ .
 839                                 ": reference count for $serverIndex/$domain reduced to $refCount" );
 840                 }
 841         }
 842
 843         public function getConnectionRef( $db, $groups = [], $domain = false, $flags = 0 ) {
 844                 $domain = ( $domain !== false ) ? $domain : $this->localDomain;
 845
 846                 return new DBConnRef( $this, $this->getConnection( $db, $groups, $domain, $flags ) );
 847         }
 848
 849         public function getLazyConnectionRef( $db, $groups = [], $domain = false, $flags = 0 ) {
 850                 $domain = ( $domain !== false ) ? $domain : $this->localDomain;
 851
 852                 return new DBConnRef( $this, [ $db, $groups, $domain, $flags ] );
 853         }
 854
 855         public function getMaintenanceConnectionRef( $db, $groups = [], $domain = false, $flags = 0 ) {
 856                 $domain = ( $domain !== false ) ? $domain : $this->localDomain;
 857
 858                 return new MaintainableDBConnRef(
 859                         $this, $this->getConnection( $db, $groups, $domain, $flags ) );
 860         }
 861
 862         public function openConnection( $i, $domain = false, $flags = 0 ) {
 863                 if ( $this->localDomain->equals( $domain ) || $domain === $this->localDomainIdAlias ) {
 864                         $domain = false; // local connection requested
 865                 }
 866
 867                 if ( !$this->connectionAttempted && $this->chronologyCallback ) {
 868                         $this->connLogger->debug( __METHOD__ . ': calling initLB() before first connection.' );
 869                         // Load any "waitFor" positions before connecting so that doWait() is triggered
 870                         $this->connectionAttempted = true;
 871                         call_user_func( $this->chronologyCallback, $this );
 872                 }
 873
 874                 // Check if an auto-commit connection is being requested. If so, it will not reuse the
 875                 // main set of DB connections but rather its own pool since:
 876                 // a) those are usually set to implicitly use transaction rounds via DBO_TRX
 877                 // b) those must support the use of explicit transaction rounds via beginMasterChanges()
 878                 $autoCommit = ( ( $flags & self::CONN_TRX_AUTOCOMMIT ) == self::CONN_TRX_AUTOCOMMIT );
 879
 880                 if ( $domain !== false ) {
 881                         // Connection is to a foreign domain
 882                         $conn = $this->openForeignConnection( $i, $domain, $flags );
 883                 } else {
 884                         // Connection is to the local domain
 885                         $connKey = $autoCommit ? self::KEY_LOCAL_NOROUND : self::KEY_LOCAL;
 886                         if ( isset( $this->conns[$connKey][$i][0] ) ) {
 887                                 $conn = $this->conns[$connKey][$i][0];
 888                         } else {
 889                                 if ( !isset( $this->servers[$i] ) || !is_array( $this->servers[$i] ) ) {
 890                                         throw new InvalidArgumentException( "No server with index '$i'." );
 891                                 }
 892                                 // Open a new connection
 893                                 $server = $this->servers[$i];
 894                                 $server['serverIndex'] = $i;
 895                                 $server['autoCommitOnly'] = $autoCommit;
 896                                 if ( $this->localDomain->getDatabase() !== null ) {
 897                                         // Use the local domain table prefix if the local domain is specified
 898                                         $server['tablePrefix'] = $this->localDomain->getTablePrefix();
 899                                 }
 900                                 $conn = $this->reallyOpenConnection( $server, $this->localDomain );
 901                                 $host = $this->getServerName( $i );
 902                                 if ( $conn->isOpen() ) {
 903                                         $this->connLogger->debug(
 904                                                 __METHOD__ . ": connected to database $i at '$host'." );
 905                                         $this->conns[$connKey][$i][0] = $conn;
 906                                 } else {
 907                                         $this->connLogger->warning(
 908                                                 __METHOD__ . ": failed to connect to database $i at '$host'." );
 909                                         $this->errorConnection = $conn;
 910                                         $conn = false;
 911                                 }
 912                         }
 913                 }
 914
 915                 if ( $conn instanceof IDatabase && !$conn->isOpen() ) {
 916                         // Connection was made but later unrecoverably lost for some reason.
 917                         // Do not return a handle that will just throw exceptions on use,
 918                         // but let the calling code (e.g. getReaderIndex) try another server.
 919                         // See DatabaseMyslBase::ping() for how this can happen.
 920                         $this->errorConnection = $conn;
 921                         $conn = false;
 922                 }
 923
 924                 if ( $autoCommit && $conn instanceof IDatabase ) {
 925                         $conn->clearFlag( $conn::DBO_TRX ); // auto-commit mode
 926                 }
 927
 928                 return $conn;
 929         }
 930
 931         /**
 932          * Open a connection to a foreign DB, or return one if it is already open.
 933          *
 934          * Increments a reference count on the returned connection which locks the
 935          * connection to the requested domain. This reference count can be
 936          * decremented by calling reuseConnection().
 937          *
 938          * If a connection is open to the appropriate server already, but with the wrong
 939          * database, it will be switched to the right database and returned, as long as
 940          * it has been freed first with reuseConnection().
 941          *
 942          * On error, returns false, and the connection which caused the
 943          * error will be available via $this->errorConnection.
 944          *
 945          * @note If disable() was called on this LoadBalancer, this method will throw a DBAccessError.
 946          *
 947          * @param int $i Server index
 948          * @param string $domain Domain ID to open
 949          * @param int $flags Class CONN_* constant bitfield
 950          * @return Database
 951          */
 952         private function openForeignConnection( $i, $domain, $flags = 0 ) {
 953                 $domainInstance = DatabaseDomain::newFromId( $domain );
 954                 $dbName = $domainInstance->getDatabase();
 955                 $prefix = $domainInstance->getTablePrefix();
 956                 $autoCommit = ( ( $flags & self::CONN_TRX_AUTOCOMMIT ) == self::CONN_TRX_AUTOCOMMIT );
 957
 958                 if ( $autoCommit ) {
 959                         $connFreeKey = self::KEY_FOREIGN_FREE_NOROUND;
 960                         $connInUseKey = self::KEY_FOREIGN_INUSE_NOROUND;
 961                 } else {
 962                         $connFreeKey = self::KEY_FOREIGN_FREE;
 963                         $connInUseKey = self::KEY_FOREIGN_INUSE;
 964                 }
 965
 966                 if ( isset( $this->conns[$connInUseKey][$i][$domain] ) ) {
 967                         // Reuse an in-use connection for the same domain
 968                         $conn = $this->conns[$connInUseKey][$i][$domain];
 969                         $this->connLogger->debug( __METHOD__ . ": reusing connection $i/$domain" );
 970                 } elseif ( isset( $this->conns[$connFreeKey][$i][$domain] ) ) {
 971                         // Reuse a free connection for the same domain
 972                         $conn = $this->conns[$connFreeKey][$i][$domain];
 973                         unset( $this->conns[$connFreeKey][$i][$domain] );
 974                         $this->conns[$connInUseKey][$i][$domain] = $conn;
 975                         $this->connLogger->debug( __METHOD__ . ": reusing free connection $i/$domain" );
 976                 } elseif ( !empty( $this->conns[$connFreeKey][$i] ) ) {
 977                         // Reuse a free connection from another domain
 978                         $conn = reset( $this->conns[$connFreeKey][$i] );
 979                         $oldDomain = key( $this->conns[$connFreeKey][$i] );
 980                         if ( strlen( $dbName ) && !$conn->selectDB( $dbName ) ) {
 981                                 $this->lastError = "Error selecting database '$dbName' on server " .
 982                                         $conn->getServer() . " from client host {$this->host}";
 983                                 $this->errorConnection = $conn;
 984                                 $conn = false;
 985                         } else {
 986                                 $conn->tablePrefix( $prefix );
 987                                 unset( $this->conns[$connFreeKey][$i][$oldDomain] );
 988                                 // Note that if $domain is an empty string, getDomainID() might not match it
 989                                 $this->conns[$connInUseKey][$i][$conn->getDomainId()] = $conn;
 990                                 $this->connLogger->debug( __METHOD__ .
 991                                         ": reusing free connection from $oldDomain for $domain" );
 992                         }
 993                 } else {
 994                         if ( !isset( $this->servers[$i] ) || !is_array( $this->servers[$i] ) ) {
 995                                 throw new InvalidArgumentException( "No server with index '$i'." );
 996                         }
 997                         // Open a new connection
 998                         $server = $this->servers[$i];
 999                         $server['serverIndex'] = $i;
1000                         $server['foreignPoolRefCount'] = 0;
1001                         $server['foreign'] = true;
1002                         $server['autoCommitOnly'] = $autoCommit;
1003                         $conn = $this->reallyOpenConnection( $server, $domainInstance );
1004                         if ( !$conn->isOpen() ) {
1005                                 $this->connLogger->warning( __METHOD__ . ": connection error for $i/$domain" );
1006                                 $this->errorConnection = $conn;
1007                                 $conn = false;
1008                         } else {
1009                                 $conn->tablePrefix( $prefix ); // as specified
1010                                 // Note that if $domain is an empty string, getDomainID() might not match it
1011                                 $this->conns[$connInUseKey][$i][$conn->getDomainID()] = $conn;
1012                                 $this->connLogger->debug( __METHOD__ . ": opened new connection for $i/$domain" );
1013                         }
1014                 }
1015
1016                 // Increment reference count
1017                 if ( $conn instanceof IDatabase ) {
1018                         $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
1019                         $conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
1020                 }
1021
1022                 return $conn;
1023         }
1024
1025         public function getServerAttributes( $i ) {
1026                 return Database::attributesFromType(
1027                         $this->getServerType( $i ),
1028                         isset( $this->servers[$i]['driver'] ) ? $this->servers[$i]['driver'] : null
1029                 );
1030         }
1031
1032         /**
1033          * Test if the specified index represents an open connection
1034          *
1035          * @param int $index Server index
1036          * @access private
1037          * @return bool
1038          */
1039         private function isOpen( $index ) {
1040                 if ( !is_int( $index ) ) {
1041                         return false;
1042                 }
1043
1044                 return (bool)$this->getAnyOpenConnection( $index );
1045         }
1046
1047         /**
1048          * Open a new network connection to a server (uncached)
1049          *
1050          * Returns a Database object whether or not the connection was successful.
1051          *
1052          * @param array $server
1053          * @param DatabaseDomain $domainOverride Use an unspecified domain to not select any database
1054          * @return Database
1055          * @throws DBAccessError
1056          * @throws InvalidArgumentException
1057          */
1058         protected function reallyOpenConnection( array $server, DatabaseDomain $domainOverride ) {
1059                 if ( $this->disabled ) {
1060                         throw new DBAccessError();
1061                 }
1062
1063                 // Handle $domainOverride being a specified or an unspecified domain
1064                 if ( $domainOverride->getDatabase() === null ) {
1065                         // Normally, an RDBMS requires a DB name specified on connection and the $server
1066                         // configuration array is assumed to already specify an appropriate DB name.
1067                         if ( $server['type'] === 'mysql' ) {
1068                                 // For MySQL, DATABASE and SCHEMA are synonyms, connections need not specify a DB,
1069                                 // and the DB name in $server might not exist due to legacy reasons (the default
1070                                 // domain used to ignore the local LB domain, even when mismatched).
1071                                 $server['dbname'] = null;
1072                         }
1073                 } else {
1074                         $server['dbname'] = $domainOverride->getDatabase();
1075                         $server['schema'] = $domainOverride->getSchema();
1076                 }
1077
1078                 // Let the handle know what the cluster master is (e.g. "db1052")
1079                 $masterName = $this->getServerName( $this->getWriterIndex() );
1080                 $server['clusterMasterHost'] = $masterName;
1081
1082                 // Log when many connection are made on requests
1083                 if ( ++$this->connsOpened >= self::CONN_HELD_WARN_THRESHOLD ) {
1084                         $this->perfLogger->warning( __METHOD__ . ": " .
1085                                 "{$this->connsOpened}+ connections made (master=$masterName)" );
1086                 }
1087
1088                 $server['srvCache'] = $this->srvCache;
1089                 // Set loggers and profilers
1090                 $server['connLogger'] = $this->connLogger;
1091                 $server['queryLogger'] = $this->queryLogger;
1092                 $server['errorLogger'] = $this->errorLogger;
1093                 $server['deprecationLogger'] = $this->deprecationLogger;
1094                 $server['profiler'] = $this->profiler;
1095                 $server['trxProfiler'] = $this->trxProfiler;
1096                 // Use the same agent and PHP mode for all DB handles
1097                 $server['cliMode'] = $this->cliMode;
1098                 $server['agent'] = $this->agent;
1099                 // Use DBO_DEFAULT flags by default for LoadBalancer managed databases. Assume that the
1100                 // application calls LoadBalancer::commitMasterChanges() before the PHP script completes.
1101                 $server['flags'] = isset( $server['flags'] ) ? $server['flags'] : IDatabase::DBO_DEFAULT;
1102
1103                 // Create a live connection object
1104                 try {
1105                         $db = Database::factory( $server['type'], $server );
1106                 } catch ( DBConnectionError $e ) {
1107                         // FIXME: This is probably the ugliest thing I have ever done to
1108                         // PHP. I'm half-expecting it to segfault, just out of disgust. -- TS
1109                         $db = $e->db;
1110                 }
1111
1112                 $db->setLBInfo( $server );
1113                 $db->setLazyMasterHandle(
1114                         $this->getLazyConnectionRef( self::DB_MASTER, [], $db->getDomainID() )
1115                 );
1116                 $db->setTableAliases( $this->tableAliases );
1117                 $db->setIndexAliases( $this->indexAliases );
1118
1119                 if ( $server['serverIndex'] === $this->getWriterIndex() ) {
1120                         if ( $this->trxRoundId !== false ) {
1121                                 $this->applyTransactionRoundFlags( $db );
1122                         }
1123                         foreach ( $this->trxRecurringCallbacks as $name => $callback ) {
1124                                 $db->setTransactionListener( $name, $callback );
1125                         }
1126                 }
1127
1128                 return $db;
1129         }
1130
1131         /**
1132          * @throws DBConnectionError
1133          */
1134         private function reportConnectionError() {
1135                 $conn = $this->errorConnection; // the connection which caused the error
1136                 $context = [
1137                         'method' => __METHOD__,
1138                         'last_error' => $this->lastError,
1139                 ];
1140
1141                 if ( $conn instanceof IDatabase ) {
1142                         $context['db_server'] = $conn->getServer();
1143                         $this->connLogger->warning(
1144                                 __METHOD__ . ": connection error: {last_error} ({db_server})",
1145                                 $context
1146                         );
1147
1148                         throw new DBConnectionError( $conn, "{$this->lastError} ({$context['db_server']})" );
1149                 } else {
1150                         // No last connection, probably due to all servers being too busy
1151                         $this->connLogger->error(
1152                                 __METHOD__ .
1153                                 ": LB failure with no last connection. Connection error: {last_error}",
1154                                 $context
1155                         );
1156
1157                         // If all servers were busy, "lastError" will contain something sensible
1158                         throw new DBConnectionError( null, $this->lastError );
1159                 }
1160         }
1161
1162         public function getWriterIndex() {
1163                 return 0;
1164         }
1165
1166         public function haveIndex( $i ) {
1167                 return array_key_exists( $i, $this->servers );
1168         }
1169
1170         public function isNonZeroLoad( $i ) {
1171                 return array_key_exists( $i, $this->servers ) && $this->loads[$i] != 0;
1172         }
1173
1174         public function getServerCount() {
1175                 return count( $this->servers );
1176         }
1177
1178         public function getServerName( $i ) {
1179                 if ( isset( $this->servers[$i]['hostName'] ) ) {
1180                         $name = $this->servers[$i]['hostName'];
1181                 } elseif ( isset( $this->servers[$i]['host'] ) ) {
1182                         $name = $this->servers[$i]['host'];
1183                 } else {
1184                         $name = '';
1185                 }
1186
1187                 return ( $name != '' ) ? $name : 'localhost';
1188         }
1189
1190         public function getServerType( $i ) {
1191                 return isset( $this->servers[$i]['type'] ) ? $this->servers[$i]['type'] : 'unknown';
1192         }
1193
1194         public function getMasterPos() {
1195                 # If this entire request was served from a replica DB without opening a connection to the
1196                 # master (however unlikely that may be), then we can fetch the position from the replica DB.
1197                 $masterConn = $this->getAnyOpenConnection( $this->getWriterIndex() );
1198                 if ( !$masterConn ) {
1199                         $serverCount = count( $this->servers );
1200                         for ( $i = 1; $i < $serverCount; $i++ ) {
1201                                 $conn = $this->getAnyOpenConnection( $i );
1202                                 if ( $conn ) {
1203                                         return $conn->getReplicaPos();
1204                                 }
1205                         }
1206                 } else {
1207                         return $masterConn->getMasterPos();
1208                 }
1209
1210                 return false;
1211         }
1212
1213         public function disable() {
1214                 $this->closeAll();
1215                 $this->disabled = true;
1216         }
1217
1218         public function closeAll() {
1219                 $this->forEachOpenConnection( function ( IDatabase $conn ) {
1220                         $host = $conn->getServer();
1221                         $this->connLogger->debug(
1222                                 __METHOD__ . ": closing connection to database '$host'." );
1223                         $conn->close();
1224                 } );
1225
1226                 $this->conns = [
1227                         self::KEY_LOCAL => [],
1228                         self::KEY_FOREIGN_INUSE => [],
1229                         self::KEY_FOREIGN_FREE => [],
1230                         self::KEY_LOCAL_NOROUND => [],
1231                         self::KEY_FOREIGN_INUSE_NOROUND => [],
1232                         self::KEY_FOREIGN_FREE_NOROUND => []
1233                 ];
1234                 $this->connsOpened = 0;
1235         }
1236
1237         public function closeConnection( IDatabase $conn ) {
1238                 $serverIndex = $conn->getLBInfo( 'serverIndex' );
1239                 foreach ( $this->conns as $type => $connsByServer ) {
1240                         if ( !isset( $connsByServer[$serverIndex] ) ) {
1241                                 continue;
1242                         }
1243
1244                         foreach ( $connsByServer[$serverIndex] as $i => $trackedConn ) {
1245                                 if ( $conn === $trackedConn ) {
1246                                         $host = $this->getServerName( $i );
1247                                         $this->connLogger->debug(
1248                                                 __METHOD__ . ": closing connection to database $i at '$host'." );
1249                                         unset( $this->conns[$type][$serverIndex][$i] );
1250                                         --$this->connsOpened;
1251                                         break 2;
1252                                 }
1253                         }
1254                 }
1255
1256                 $conn->close();
1257         }
1258
1259         public function commitAll( $fname = __METHOD__ ) {
1260                 $this->commitMasterChanges( $fname );
1261                 $this->flushMasterSnapshots( $fname );
1262                 $this->flushReplicaSnapshots( $fname );
1263         }
1264
1265         public function finalizeMasterChanges() {
1266                 $this->assertTransactionRoundStage( [ self::ROUND_CURSORY, self::ROUND_FINALIZED ] );
1267
1268                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1269                 // Loop until callbacks stop adding callbacks on other connections
1270                 $total = 0;
1271                 do {
1272                         $count = 0; // callbacks execution attempts
1273                         $this->forEachOpenMasterConnection( function ( Database $conn ) use ( &$count ) {
1274                                 // Run any pre-commit callbacks while leaving the post-commit ones suppressed.
1275                                 // Any error should cause all (peer) transactions to be rolled back together.
1276                                 $count += $conn->runOnTransactionPreCommitCallbacks();
1277                         } );
1278                         $total += $count;
1279                 } while ( $count > 0 );
1280                 // Defer post-commit callbacks until after COMMIT/ROLLBACK happens on all handles
1281                 $this->forEachOpenMasterConnection( function ( Database $conn ) {
1282                         $conn->setTrxEndCallbackSuppression( true );
1283                 } );
1284                 $this->trxRoundStage = self::ROUND_FINALIZED;
1285
1286                 return $total;
1287         }
1288
1289         public function approveMasterChanges( array $options ) {
1290                 $this->assertTransactionRoundStage( self::ROUND_FINALIZED );
1291
1292                 $limit = isset( $options['maxWriteDuration'] ) ? $options['maxWriteDuration'] : 0;
1293
1294                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1295                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( $limit ) {
1296                         // If atomic sections or explicit transactions are still open, some caller must have
1297                         // caught an exception but failed to properly rollback any changes. Detect that and
1298                         // throw and error (causing rollback).
1299                         if ( $conn->explicitTrxActive() ) {
1300                                 throw new DBTransactionError(
1301                                         $conn,
1302                                         "Explicit transaction still active. A caller may have caught an error."
1303                                 );
1304                         }
1305                         // Assert that the time to replicate the transaction will be sane.
1306                         // If this fails, then all DB transactions will be rollback back together.
1307                         $time = $conn->pendingWriteQueryDuration( $conn::ESTIMATE_DB_APPLY );
1308                         if ( $limit > 0 && $time > $limit ) {
1309                                 throw new DBTransactionSizeError(
1310                                         $conn,
1311                                         "Transaction spent $time second(s) in writes, exceeding the limit of $limit.",
1312                                         [ $time, $limit ]
1313                                 );
1314                         }
1315                         // If a connection sits idle while slow queries execute on another, that connection
1316                         // may end up dropped before the commit round is reached. Ping servers to detect this.
1317                         if ( $conn->writesOrCallbacksPending() && !$conn->ping() ) {
1318                                 throw new DBTransactionError(
1319                                         $conn,
1320                                         "A connection to the {$conn->getDBname()} database was lost before commit."
1321                                 );
1322                         }
1323                 } );
1324                 $this->trxRoundStage = self::ROUND_APPROVED;
1325         }
1326
1327         public function beginMasterChanges( $fname = __METHOD__ ) {
1328                 if ( $this->trxRoundId !== false ) {
1329                         throw new DBTransactionError(
1330                                 null,
1331                                 "$fname: Transaction round '{$this->trxRoundId}' already started."
1332                         );
1333                 }
1334                 $this->assertTransactionRoundStage( self::ROUND_CURSORY );
1335
1336                 // Clear any empty transactions (no writes/callbacks) from the implicit round
1337                 $this->flushMasterSnapshots( $fname );
1338
1339                 $this->trxRoundId = $fname;
1340                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1341                 // Mark applicable handles as participating in this explicit transaction round.
1342                 // For each of these handles, any writes and callbacks will be tied to a single
1343                 // transaction. The (peer) handles will reject begin()/commit() calls unless they
1344                 // are part of an en masse commit or an en masse rollback.
1345                 $this->forEachOpenMasterConnection( function ( Database $conn ) {
1346                         $this->applyTransactionRoundFlags( $conn );
1347                 } );
1348                 $this->trxRoundStage = self::ROUND_CURSORY;
1349         }
1350
1351         public function commitMasterChanges( $fname = __METHOD__ ) {
1352                 $this->assertTransactionRoundStage( self::ROUND_APPROVED );
1353
1354                 $failures = [];
1355
1356                 /** @noinspection PhpUnusedLocalVariableInspection */
1357                 $scope = $this->getScopedPHPBehaviorForCommit(); // try to ignore client aborts
1358
1359                 $restore = ( $this->trxRoundId !== false );
1360                 $this->trxRoundId = false;
1361                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1362                 // Commit any writes and clear any snapshots as well (callbacks require AUTOCOMMIT).
1363                 // Note that callbacks should already be suppressed due to finalizeMasterChanges().
1364                 $this->forEachOpenMasterConnection(
1365                         function ( IDatabase $conn ) use ( $fname, &$failures ) {
1366                                 try {
1367                                         $conn->commit( $fname, $conn::FLUSHING_ALL_PEERS );
1368                                 } catch ( DBError $e ) {
1369                                         call_user_func( $this->errorLogger, $e );
1370                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1371                                 }
1372                         }
1373                 );
1374                 if ( $failures ) {
1375                         throw new DBTransactionError(
1376                                 null,
1377                                 "$fname: Commit failed on server(s) " . implode( "\n", array_unique( $failures ) )
1378                         );
1379                 }
1380                 if ( $restore ) {
1381                         // Unmark handles as participating in this explicit transaction round
1382                         $this->forEachOpenMasterConnection( function ( Database $conn ) {
1383                                 $this->undoTransactionRoundFlags( $conn );
1384                         } );
1385                 }
1386                 $this->trxRoundStage = self::ROUND_COMMIT_CALLBACKS;
1387         }
1388
1389         public function runMasterTransactionIdleCallbacks() {
1390                 if ( $this->trxRoundStage === self::ROUND_COMMIT_CALLBACKS ) {
1391                         $type = IDatabase::TRIGGER_COMMIT;
1392                 } elseif ( $this->trxRoundStage === self::ROUND_ROLLBACK_CALLBACKS ) {
1393                         $type = IDatabase::TRIGGER_ROLLBACK;
1394                 } else {
1395                         throw new DBTransactionError(
1396                                 null,
1397                                 "Transaction should be in the callback stage (not '{$this->trxRoundStage}')"
1398                         );
1399                 }
1400
1401                 $oldStage = $this->trxRoundStage;
1402                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1403
1404                 // Now that the COMMIT/ROLLBACK step is over, enable post-commit callback runs
1405                 $this->forEachOpenMasterConnection( function ( Database $conn ) {
1406                         $conn->setTrxEndCallbackSuppression( false );
1407                 } );
1408
1409                 $e = null; // first exception
1410                 // Loop until callbacks stop adding callbacks on other connections
1411                 do {
1412                         // Run any pending callbacks for each connection...
1413                         $count = 0; // callback execution attempts
1414                         $this->forEachOpenMasterConnection(
1415                                 function ( Database $conn ) use ( $type, &$e, &$count ) {
1416                                         if ( $conn->trxLevel() ) {
1417                                                 return; // retry in the next iteration, after commit() is called
1418                                         }
1419                                         try {
1420                                                 $count += $conn->runOnTransactionIdleCallbacks( $type );
1421                                         } catch ( Exception $ex ) {
1422                                                 $e = $e ?: $ex;
1423                                         }
1424                                 }
1425                         );
1426                         // Clear out any active transactions left over from callbacks...
1427                         $this->forEachOpenMasterConnection( function ( Database $conn ) use ( &$e ) {
1428                                 if ( $conn->writesPending() ) {
1429                                         // A callback from another handle wrote to this one and DBO_TRX is set
1430                                         $this->queryLogger->warning( __METHOD__ . ": found writes pending." );
1431                                         $fnames = implode( ', ', $conn->pendingWriteAndCallbackCallers() );
1432                                         $this->queryLogger->warning(
1433                                                 __METHOD__ . ": found writes pending ($fnames).",
1434                                                 [
1435                                                         'db_server' => $conn->getServer(),
1436                                                         'db_name' => $conn->getDBname()
1437                                                 ]
1438                                         );
1439                                 } elseif ( $conn->trxLevel() ) {
1440                                         // A callback from another handle read from this one and DBO_TRX is set,
1441                                         // which can easily happen if there is only one DB (no replicas)
1442                                         $this->queryLogger->debug( __METHOD__ . ": found empty transaction." );
1443                                 }
1444                                 try {
1445                                         $conn->commit( __METHOD__, $conn::FLUSHING_ALL_PEERS );
1446                                 } catch ( Exception $ex ) {
1447                                         $e = $e ?: $ex;
1448                                 }
1449                         } );
1450                 } while ( $count > 0 );
1451
1452                 $this->trxRoundStage = $oldStage;
1453
1454                 return $e;
1455         }
1456
1457         public function runMasterTransactionListenerCallbacks() {
1458                 if ( $this->trxRoundStage === self::ROUND_COMMIT_CALLBACKS ) {
1459                         $type = IDatabase::TRIGGER_COMMIT;
1460                 } elseif ( $this->trxRoundStage === self::ROUND_ROLLBACK_CALLBACKS ) {
1461                         $type = IDatabase::TRIGGER_ROLLBACK;
1462                 } else {
1463                         throw new DBTransactionError(
1464                                 null,
1465                                 "Transaction should be in the callback stage (not '{$this->trxRoundStage}')"
1466                         );
1467                 }
1468
1469                 $e = null;
1470
1471                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1472                 $this->forEachOpenMasterConnection( function ( Database $conn ) use ( $type, &$e ) {
1473                         try {
1474                                 $conn->runTransactionListenerCallbacks( $type );
1475                         } catch ( Exception $ex ) {
1476                                 $e = $e ?: $ex;
1477                         }
1478                 } );
1479                 $this->trxRoundStage = self::ROUND_CURSORY;
1480
1481                 return $e;
1482         }
1483
1484         public function rollbackMasterChanges( $fname = __METHOD__ ) {
1485                 $restore = ( $this->trxRoundId !== false );
1486                 $this->trxRoundId = false;
1487                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1488                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( $fname ) {
1489                         $conn->rollback( $fname, $conn::FLUSHING_ALL_PEERS );
1490                 } );
1491                 if ( $restore ) {
1492                         // Unmark handles as participating in this explicit transaction round
1493                         $this->forEachOpenMasterConnection( function ( Database $conn ) {
1494                                 $this->undoTransactionRoundFlags( $conn );
1495                         } );
1496                 }
1497                 $this->trxRoundStage = self::ROUND_ROLLBACK_CALLBACKS;
1498         }
1499
1500         /**
1501          * @param string|string[] $stage
1502          */
1503         private function assertTransactionRoundStage( $stage ) {
1504                 $stages = (array)$stage;
1505
1506                 if ( !in_array( $this->trxRoundStage, $stages, true ) ) {
1507                         $stageList = implode(
1508                                 '/',
1509                                 array_map( function ( $v ) {
1510                                         return "'$v'";
1511                                 }, $stages )
1512                         );
1513                         throw new DBTransactionError(
1514                                 null,
1515                                 "Transaction round stage must be $stageList (not '{$this->trxRoundStage}')"
1516                         );
1517                 }
1518         }
1519
1520         /**
1521          * Make all DB servers with DBO_DEFAULT/DBO_TRX set join the transaction round
1522          *
1523          * Some servers may have neither flag enabled, meaning that they opt out of such
1524          * transaction rounds and remain in auto-commit mode. Such behavior might be desired
1525          * when a DB server is used for something like simple key/value storage.
1526          *
1527          * @param Database $conn
1528          */
1529         private function applyTransactionRoundFlags( Database $conn ) {
1530                 if ( $conn->getLBInfo( 'autoCommitOnly' ) ) {
1531                         return; // transaction rounds do not apply to these connections
1532                 }
1533
1534                 if ( $conn->getFlag( $conn::DBO_DEFAULT ) ) {
1535                         // DBO_TRX is controlled entirely by CLI mode presence with DBO_DEFAULT.
1536                         // Force DBO_TRX even in CLI mode since a commit round is expected soon.
1537                         $conn->setFlag( $conn::DBO_TRX, $conn::REMEMBER_PRIOR );
1538                 }
1539
1540                 if ( $conn->getFlag( $conn::DBO_TRX ) ) {
1541                         $conn->setLBInfo( 'trxRoundId', $this->trxRoundId );
1542                 }
1543         }
1544
1545         /**
1546          * @param Database $conn
1547          */
1548         private function undoTransactionRoundFlags( Database $conn ) {
1549                 if ( $conn->getLBInfo( 'autoCommitOnly' ) ) {
1550                         return; // transaction rounds do not apply to these connections
1551                 }
1552
1553                 if ( $conn->getFlag( $conn::DBO_TRX ) ) {
1554                         $conn->setLBInfo( 'trxRoundId', false );
1555                 }
1556
1557                 if ( $conn->getFlag( $conn::DBO_DEFAULT ) ) {
1558                         $conn->restoreFlags( $conn::RESTORE_PRIOR );
1559                 }
1560         }
1561
1562         public function flushReplicaSnapshots( $fname = __METHOD__ ) {
1563                 $this->forEachOpenReplicaConnection( function ( IDatabase $conn ) use ( $fname ) {
1564                         $conn->flushSnapshot( $fname );
1565                 } );
1566         }
1567
1568         private function flushMasterSnapshots( $fname = __METHOD__ ) {
1569                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( $fname ) {
1570                         $conn->flushSnapshot( $fname );
1571                 } );
1572         }
1573
1574         /**
1575          * @return string
1576          * @since 1.32
1577          */
1578         public function getTransactionRoundStage() {
1579                 return $this->trxRoundStage;
1580         }
1581
1582         public function hasMasterConnection() {
1583                 return $this->isOpen( $this->getWriterIndex() );
1584         }
1585
1586         public function hasMasterChanges() {
1587                 $pending = 0;
1588                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$pending ) {
1589                         $pending |= $conn->writesOrCallbacksPending();
1590                 } );
1591
1592                 return (bool)$pending;
1593         }
1594
1595         public function lastMasterChangeTimestamp() {
1596                 $lastTime = false;
1597                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$lastTime ) {
1598                         $lastTime = max( $lastTime, $conn->lastDoneWrites() );
1599                 } );
1600
1601                 return $lastTime;
1602         }
1603
1604         public function hasOrMadeRecentMasterChanges( $age = null ) {
1605                 $age = ( $age === null ) ? $this->waitTimeout : $age;
1606
1607                 return ( $this->hasMasterChanges()
1608                         || $this->lastMasterChangeTimestamp() > microtime( true ) - $age );
1609         }
1610
1611         public function pendingMasterChangeCallers() {
1612                 $fnames = [];
1613                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$fnames ) {
1614                         $fnames = array_merge( $fnames, $conn->pendingWriteCallers() );
1615                 } );
1616
1617                 return $fnames;
1618         }
1619
1620         public function getLaggedReplicaMode( $domain = false ) {
1621                 // No-op if there is only one DB (also avoids recursion)
1622                 if ( !$this->laggedReplicaMode && $this->getServerCount() > 1 ) {
1623                         try {
1624                                 // See if laggedReplicaMode gets set
1625                                 $conn = $this->getConnection( self::DB_REPLICA, false, $domain );
1626                                 $this->reuseConnection( $conn );
1627                         } catch ( DBConnectionError $e ) {
1628                                 // Avoid expensive re-connect attempts and failures
1629                                 $this->allReplicasDownMode = true;
1630                                 $this->laggedReplicaMode = true;
1631                         }
1632                 }
1633
1634                 return $this->laggedReplicaMode;
1635         }
1636
1637         public function laggedReplicaUsed() {
1638                 return $this->laggedReplicaMode;
1639         }
1640
1641         /**
1642          * @return bool
1643          * @since 1.27
1644          * @deprecated Since 1.28; use laggedReplicaUsed()
1645          */
1646         public function laggedSlaveUsed() {
1647                 return $this->laggedReplicaUsed();
1648         }
1649
1650         public function getReadOnlyReason( $domain = false, IDatabase $conn = null ) {
1651                 if ( $this->readOnlyReason !== false ) {
1652                         return $this->readOnlyReason;
1653                 } elseif ( $this->getLaggedReplicaMode( $domain ) ) {
1654                         if ( $this->allReplicasDownMode ) {
1655                                 return 'The database has been automatically locked ' .
1656                                         'until the replica database servers become available';
1657                         } else {
1658                                 return 'The database has been automatically locked ' .
1659                                         'while the replica database servers catch up to the master.';
1660                         }
1661                 } elseif ( $this->masterRunningReadOnly( $domain, $conn ) ) {
1662                         return 'The database master is running in read-only mode.';
1663                 }
1664
1665                 return false;
1666         }
1667
1668         /**
1669          * @param string $domain Domain ID, or false for the current domain
1670          * @param IDatabase|null $conn DB master connectionl used to avoid loops [optional]
1671          * @return bool
1672          */
1673         private function masterRunningReadOnly( $domain, IDatabase $conn = null ) {
1674                 $cache = $this->wanCache;
1675                 $masterServer = $this->getServerName( $this->getWriterIndex() );
1676
1677                 return (bool)$cache->getWithSetCallback(
1678                         $cache->makeGlobalKey( __CLASS__, 'server-read-only', $masterServer ),
1679                         self::TTL_CACHE_READONLY,
1680                         function () use ( $domain, $conn ) {
1681                                 $old = $this->trxProfiler->setSilenced( true );
1682                                 try {
1683                                         $dbw = $conn ?: $this->getConnection( self::DB_MASTER, [], $domain );
1684                                         $readOnly = (int)$dbw->serverIsReadOnly();
1685                                         if ( !$conn ) {
1686                                                 $this->reuseConnection( $dbw );
1687                                         }
1688                                 } catch ( DBError $e ) {
1689                                         $readOnly = 0;
1690                                 }
1691                                 $this->trxProfiler->setSilenced( $old );
1692                                 return $readOnly;
1693                         },
1694                         [ 'pcTTL' => $cache::TTL_PROC_LONG, 'busyValue' => 0 ]
1695                 );
1696         }
1697
1698         public function allowLagged( $mode = null ) {
1699                 if ( $mode === null ) {
1700                         return $this->allowLagged;
1701                 }
1702                 $this->allowLagged = $mode;
1703
1704                 return $this->allowLagged;
1705         }
1706
1707         public function pingAll() {
1708                 $success = true;
1709                 $this->forEachOpenConnection( function ( IDatabase $conn ) use ( &$success ) {
1710                         if ( !$conn->ping() ) {
1711                                 $success = false;
1712                         }
1713                 } );
1714
1715                 return $success;
1716         }
1717
1718         public function forEachOpenConnection( $callback, array $params = [] ) {
1719                 foreach ( $this->conns as $connsByServer ) {
1720                         foreach ( $connsByServer as $serverConns ) {
1721                                 foreach ( $serverConns as $conn ) {
1722                                         $mergedParams = array_merge( [ $conn ], $params );
1723                                         call_user_func_array( $callback, $mergedParams );
1724                                 }
1725                         }
1726                 }
1727         }
1728
1729         public function forEachOpenMasterConnection( $callback, array $params = [] ) {
1730                 $masterIndex = $this->getWriterIndex();
1731                 foreach ( $this->conns as $connsByServer ) {
1732                         if ( isset( $connsByServer[$masterIndex] ) ) {
1733                                 /** @var IDatabase $conn */
1734                                 foreach ( $connsByServer[$masterIndex] as $conn ) {
1735                                         $mergedParams = array_merge( [ $conn ], $params );
1736                                         call_user_func_array( $callback, $mergedParams );
1737                                 }
1738                         }
1739                 }
1740         }
1741
1742         public function forEachOpenReplicaConnection( $callback, array $params = [] ) {
1743                 foreach ( $this->conns as $connsByServer ) {
1744                         foreach ( $connsByServer as $i => $serverConns ) {
1745                                 if ( $i === $this->getWriterIndex() ) {
1746                                         continue; // skip master
1747                                 }
1748                                 foreach ( $serverConns as $conn ) {
1749                                         $mergedParams = array_merge( [ $conn ], $params );
1750                                         call_user_func_array( $callback, $mergedParams );
1751                                 }
1752                         }
1753                 }
1754         }
1755
1756         public function getMaxLag( $domain = false ) {
1757                 $maxLag = -1;
1758                 $host = '';
1759                 $maxIndex = 0;
1760
1761                 if ( $this->getServerCount() <= 1 ) {
1762                         return [ $host, $maxLag, $maxIndex ]; // no replication = no lag
1763                 }
1764
1765                 $lagTimes = $this->getLagTimes( $domain );
1766                 foreach ( $lagTimes as $i => $lag ) {
1767                         if ( $this->loads[$i] > 0 && $lag > $maxLag ) {
1768                                 $maxLag = $lag;
1769                                 $host = $this->servers[$i]['host'];
1770                                 $maxIndex = $i;
1771                         }
1772                 }
1773
1774                 return [ $host, $maxLag, $maxIndex ];
1775         }
1776
1777         public function getLagTimes( $domain = false ) {
1778                 if ( $this->getServerCount() <= 1 ) {
1779                         return [ $this->getWriterIndex() => 0 ]; // no replication = no lag
1780                 }
1781
1782                 $knownLagTimes = []; // map of (server index => 0 seconds)
1783                 $indexesWithLag = [];
1784                 foreach ( $this->servers as $i => $server ) {
1785                         if ( empty( $server['is static'] ) ) {
1786                                 $indexesWithLag[] = $i; // DB server might have replication lag
1787                         } else {
1788                                 $knownLagTimes[$i] = 0; // DB server is a non-replicating and read-only archive
1789                         }
1790                 }
1791
1792                 return $this->getLoadMonitor()->getLagTimes( $indexesWithLag, $domain ) + $knownLagTimes;
1793         }
1794
1795         public function safeGetLag( IDatabase $conn ) {
1796                 if ( $this->getServerCount() <= 1 ) {
1797                         return 0;
1798                 } else {
1799                         return $conn->getLag();
1800                 }
1801         }
1802
1803         /**
1804          * @param IDatabase $conn
1805          * @param DBMasterPos|bool $pos
1806          * @param int|null $timeout
1807          * @return bool
1808          */
1809         public function safeWaitForMasterPos( IDatabase $conn, $pos = false, $timeout = null ) {
1810                 $timeout = max( 1, $timeout ?: $this->waitTimeout );
1811
1812                 if ( $this->getServerCount() <= 1 || !$conn->getLBInfo( 'replica' ) ) {
1813                         return true; // server is not a replica DB
1814                 }
1815
1816                 if ( !$pos ) {
1817                         // Get the current master position, opening a connection if needed
1818                         $masterConn = $this->getAnyOpenConnection( $this->getWriterIndex() );
1819                         if ( $masterConn ) {
1820                                 $pos = $masterConn->getMasterPos();
1821                         } else {
1822                                 $masterConn = $this->openConnection( $this->getWriterIndex(), self::DOMAIN_ANY );
1823                                 $pos = $masterConn->getMasterPos();
1824                                 $this->closeConnection( $masterConn );
1825                         }
1826                 }
1827
1828                 if ( $pos instanceof DBMasterPos ) {
1829                         $result = $conn->masterPosWait( $pos, $timeout );
1830                         if ( $result == -1 || is_null( $result ) ) {
1831                                 $msg = __METHOD__ . ': timed out waiting on {host} pos {pos}';
1832                                 $this->replLogger->warning( $msg, [
1833                                         'host' => $conn->getServer(),
1834                                         'pos' => $pos,
1835                                         'trace' => ( new RuntimeException() )->getTraceAsString()
1836                                 ] );
1837                                 $ok = false;
1838                         } else {
1839                                 $this->replLogger->debug( __METHOD__ . ': done waiting' );
1840                                 $ok = true;
1841                         }
1842                 } else {
1843                         $ok = false; // something is misconfigured
1844                         $this->replLogger->error(
1845                                 __METHOD__ . ': could not get master pos for {host}',
1846                                 [
1847                                         'host' => $conn->getServer(),
1848                                         'trace' => ( new RuntimeException() )->getTraceAsString()
1849                                 ]
1850                         );
1851                 }
1852
1853                 return $ok;
1854         }
1855
1856         public function setTransactionListener( $name, callable $callback = null ) {
1857                 if ( $callback ) {
1858                         $this->trxRecurringCallbacks[$name] = $callback;
1859                 } else {
1860                         unset( $this->trxRecurringCallbacks[$name] );
1861                 }
1862                 $this->forEachOpenMasterConnection(
1863                         function ( IDatabase $conn ) use ( $name, $callback ) {
1864                                 $conn->setTransactionListener( $name, $callback );
1865                         }
1866                 );
1867         }
1868
1869         public function setTableAliases( array $aliases ) {
1870                 $this->tableAliases = $aliases;
1871         }
1872
1873         public function setIndexAliases( array $aliases ) {
1874                 $this->indexAliases = $aliases;
1875         }
1876
1877         public function setDomainPrefix( $prefix ) {
1878                 // Find connections to explicit foreign domains still marked as in-use...
1879                 $domainsInUse = [];
1880                 $this->forEachOpenConnection( function ( IDatabase $conn ) use ( &$domainsInUse ) {
1881                         // Once reuseConnection() is called on a handle, its reference count goes from 1 to 0.
1882                         // Until then, it is still in use by the caller (explicitly or via DBConnRef scope).
1883                         if ( $conn->getLBInfo( 'foreignPoolRefCount' ) > 0 ) {
1884                                 $domainsInUse[] = $conn->getDomainID();
1885                         }
1886                 } );
1887
1888                 // Do not switch connections to explicit foreign domains unless marked as safe
1889                 if ( $domainsInUse ) {
1890                         $domains = implode( ', ', $domainsInUse );
1891                         throw new DBUnexpectedError( null,
1892                                 "Foreign domain connections are still in use ($domains)." );
1893                 }
1894
1895                 $oldDomain = $this->localDomain->getId();
1896                 $this->setLocalDomain( new DatabaseDomain(
1897                         $this->localDomain->getDatabase(),
1898                         $this->localDomain->getSchema(),
1899                         $prefix
1900                 ) );
1901
1902                 $this->forEachOpenConnection( function ( IDatabase $db ) use ( $prefix, $oldDomain ) {
1903                         if ( !$db->getLBInfo( 'foreign' ) ) {
1904                                 $db->tablePrefix( $prefix );
1905                         }
1906                 } );
1907         }
1908
1909         /**
1910          * @param DatabaseDomain $domain
1911          */
1912         private function setLocalDomain( DatabaseDomain $domain ) {
1913                 $this->localDomain = $domain;
1914                 // In case a caller assumes that the domain ID is simply <db>-<prefix>, which is almost
1915                 // always true, gracefully handle the case when they fail to account for escaping.
1916                 if ( $this->localDomain->getTablePrefix() != '' ) {
1917                         $this->localDomainIdAlias =
1918                                 $this->localDomain->getDatabase() . '-' . $this->localDomain->getTablePrefix();
1919                 } else {
1920                         $this->localDomainIdAlias = $this->localDomain->getDatabase();
1921                 }
1922         }
1923
1924         /**
1925          * Make PHP ignore user aborts/disconnects until the returned
1926          * value leaves scope. This returns null and does nothing in CLI mode.
1927          *
1928          * @return ScopedCallback|null
1929          */
1930         final protected function getScopedPHPBehaviorForCommit() {
1931                 if ( PHP_SAPI != 'cli' ) { // https://bugs.php.net/bug.php?id=47540
1932                         $old = ignore_user_abort( true ); // avoid half-finished operations
1933                         return new ScopedCallback( function () use ( $old ) {
1934                                 ignore_user_abort( $old );
1935                         } );
1936                 }
1937
1938                 return null;
1939         }
1940
1941         function __destruct() {
1942                 // Avoid connection leaks for sanity
1943                 $this->disable();
1944         }
1945 }
1946
1947 class_alias( LoadBalancer::class, 'LoadBalancer' );