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 = $params['waitTimeout'] ?? self::MAX_WAIT_DEFAULT;
 176
 177                 $this->readIndex = -1;
 178                 $this->conns = [
 179                         // Connection were transaction rounds may be applied
 180                         self::KEY_LOCAL => [],
 181                         self::KEY_FOREIGN_INUSE => [],
 182                         self::KEY_FOREIGN_FREE => [],
 183                         // Auto-committing counterpart connections that ignore transaction rounds
 184                         self::KEY_LOCAL_NOROUND => [],
 185                         self::KEY_FOREIGN_INUSE_NOROUND => [],
 186                         self::KEY_FOREIGN_FREE_NOROUND => []
 187                 ];
 188                 $this->loads = [];
 189                 $this->waitForPos = false;
 190                 $this->allowLagged = false;
 191
 192                 if ( isset( $params['readOnlyReason'] ) && is_string( $params['readOnlyReason'] ) ) {
 193                         $this->readOnlyReason = $params['readOnlyReason'];
 194                 }
 195
 196                 if ( isset( $params['maxLag'] ) ) {
 197                         $this->maxLag = $params['maxLag'];
 198                 }
 199
 200                 if ( isset( $params['loadMonitor'] ) ) {
 201                         $this->loadMonitorConfig = $params['loadMonitor'];
 202                 } else {
 203                         $this->loadMonitorConfig = [ 'class' => 'LoadMonitorNull' ];
 204                 }
 205                 $this->loadMonitorConfig += [ 'lagWarnThreshold' => $this->maxLag ];
 206
 207                 foreach ( $params['servers'] as $i => $server ) {
 208                         $this->loads[$i] = $server['load'];
 209                         if ( isset( $server['groupLoads'] ) ) {
 210                                 foreach ( $server['groupLoads'] as $group => $ratio ) {
 211                                         if ( !isset( $this->groupLoads[$group] ) ) {
 212                                                 $this->groupLoads[$group] = [];
 213                                         }
 214                                         $this->groupLoads[$group][$i] = $ratio;
 215                                 }
 216                         }
 217                 }
 218
 219                 if ( isset( $params['srvCache'] ) ) {
 220                         $this->srvCache = $params['srvCache'];
 221                 } else {
 222                         $this->srvCache = new EmptyBagOStuff();
 223                 }
 224                 if ( isset( $params['wanCache'] ) ) {
 225                         $this->wanCache = $params['wanCache'];
 226                 } else {
 227                         $this->wanCache = WANObjectCache::newEmpty();
 228                 }
 229                 $this->profiler = $params['profiler'] ?? null;
 230                 if ( isset( $params['trxProfiler'] ) ) {
 231                         $this->trxProfiler = $params['trxProfiler'];
 232                 } else {
 233                         $this->trxProfiler = new TransactionProfiler();
 234                 }
 235
 236                 $this->errorLogger = $params['errorLogger'] ?? function ( Exception $e ) {
 237                         trigger_error( get_class( $e ) . ': ' . $e->getMessage(), E_USER_WARNING );
 238                 };
 239                 $this->deprecationLogger = $params['deprecationLogger'] ?? function ( $msg ) {
 240                         trigger_error( $msg, E_USER_DEPRECATED );
 241                 };
 242
 243                 foreach ( [ 'replLogger', 'connLogger', 'queryLogger', 'perfLogger' ] as $key ) {
 244                         $this->$key = $params[$key] ?? new NullLogger();
 245                 }
 246
 247                 $this->host = $params['hostname'] ?? ( gethostname() ?: 'unknown' );
 248                 $this->cliMode = $params['cliMode'] ?? ( PHP_SAPI === 'cli' || PHP_SAPI === 'phpdbg' );
 249                 $this->agent = $params['agent'] ?? '';
 250
 251                 if ( isset( $params['chronologyCallback'] ) ) {
 252                         $this->chronologyCallback = $params['chronologyCallback'];
 253                 }
 254
 255                 if ( isset( $params['roundStage'] ) ) {
 256                         if ( $params['roundStage'] === self::STAGE_POSTCOMMIT_CALLBACKS ) {
 257                                 $this->trxRoundStage = self::ROUND_COMMIT_CALLBACKS;
 258                         } elseif ( $params['roundStage'] === self::STAGE_POSTROLLBACK_CALLBACKS ) {
 259                                 $this->trxRoundStage = self::ROUND_ROLLBACK_CALLBACKS;
 260                         }
 261                 }
 262         }
 263
 264         /**
 265          * Get the local (and default) database domain ID of connection handles
 266          *
 267          * @see DatabaseDomain
 268          * @return string Database domain ID; this specifies DB name, schema, and table prefix
 269          * @since 1.31
 270          */
 271         public function getLocalDomainID() {
 272                 return $this->localDomain->getId();
 273         }
 274
 275         /**
 276          * Get a LoadMonitor instance
 277          *
 278          * @return ILoadMonitor
 279          */
 280         private function getLoadMonitor() {
 281                 if ( !isset( $this->loadMonitor ) ) {
 282                         $compat = [
 283                                 'LoadMonitor' => LoadMonitor::class,
 284                                 'LoadMonitorNull' => LoadMonitorNull::class,
 285                                 'LoadMonitorMySQL' => LoadMonitorMySQL::class,
 286                         ];
 287
 288                         $class = $this->loadMonitorConfig['class'];
 289                         if ( isset( $compat[$class] ) ) {
 290                                 $class = $compat[$class];
 291                         }
 292
 293                         $this->loadMonitor = new $class(
 294                                 $this, $this->srvCache, $this->wanCache, $this->loadMonitorConfig );
 295                         $this->loadMonitor->setLogger( $this->replLogger );
 296                 }
 297
 298                 return $this->loadMonitor;
 299         }
 300
 301         /**
 302          * @param array $loads
 303          * @param bool|string $domain Domain to get non-lagged for
 304          * @param int $maxLag Restrict the maximum allowed lag to this many seconds
 305          * @return bool|int|string
 306          */
 307         private function getRandomNonLagged( array $loads, $domain = false, $maxLag = INF ) {
 308                 $lags = $this->getLagTimes( $domain );
 309
 310                 # Unset excessively lagged servers
 311                 foreach ( $lags as $i => $lag ) {
 312                         if ( $i != 0 ) {
 313                                 # How much lag this server nominally is allowed to have
 314                                 $maxServerLag = $this->servers[$i]['max lag'] ?? $this->maxLag; // default
 315                                 # Constrain that futher by $maxLag argument
 316                                 $maxServerLag = min( $maxServerLag, $maxLag );
 317
 318                                 $host = $this->getServerName( $i );
 319                                 if ( $lag === false && !is_infinite( $maxServerLag ) ) {
 320                                         $this->replLogger->error(
 321                                                 __METHOD__ .
 322                                                 ": server {host} is not replicating?", [ 'host' => $host ] );
 323                                         unset( $loads[$i] );
 324                                 } elseif ( $lag > $maxServerLag ) {
 325                                         $this->replLogger->info(
 326                                                 __METHOD__ .
 327                                                 ": server {host} has {lag} seconds of lag (>= {maxlag})",
 328                                                 [ 'host' => $host, 'lag' => $lag, 'maxlag' => $maxServerLag ]
 329                                         );
 330                                         unset( $loads[$i] );
 331                                 }
 332                         }
 333                 }
 334
 335                 # Find out if all the replica DBs with non-zero load are lagged
 336                 $sum = 0;
 337                 foreach ( $loads as $load ) {
 338                         $sum += $load;
 339                 }
 340                 if ( $sum == 0 ) {
 341                         # No appropriate DB servers except maybe the master and some replica DBs with zero load
 342                         # Do NOT use the master
 343                         # Instead, this function will return false, triggering read-only mode,
 344                         # and a lagged replica DB will be used instead.
 345                         return false;
 346                 }
 347
 348                 if ( count( $loads ) == 0 ) {
 349                         return false;
 350                 }
 351
 352                 # Return a random representative of the remainder
 353                 return ArrayUtils::pickRandom( $loads );
 354         }
 355
 356         public function getReaderIndex( $group = false, $domain = false ) {
 357                 if ( count( $this->servers ) == 1 ) {
 358                         // Skip the load balancing if there's only one server
 359                         return $this->getWriterIndex();
 360                 } elseif ( $group === false && $this->readIndex >= 0 ) {
 361                         // Shortcut if the generic reader index was already cached
 362                         return $this->readIndex;
 363                 }
 364
 365                 if ( $group !== false ) {
 366                         // Use the server weight array for this load group
 367                         if ( isset( $this->groupLoads[$group] ) ) {
 368                                 $loads = $this->groupLoads[$group];
 369                         } else {
 370                                 // No loads for this group, return false and the caller can use some other group
 371                                 $this->connLogger->info( __METHOD__ . ": no loads for group $group" );
 372
 373                                 return false;
 374                         }
 375                 } else {
 376                         // Use the generic load group
 377                         $loads = $this->loads;
 378                 }
 379
 380                 // Scale the configured load ratios according to each server's load and state
 381                 $this->getLoadMonitor()->scaleLoads( $loads, $domain );
 382
 383                 // Pick a server to use, accounting for weights, load, lag, and "waitForPos"
 384                 list( $i, $laggedReplicaMode ) = $this->pickReaderIndex( $loads, $domain );
 385                 if ( $i === false ) {
 386                         // Replica DB connection unsuccessful
 387                         return false;
 388                 }
 389
 390                 if ( $this->waitForPos && $i != $this->getWriterIndex() ) {
 391                         // Before any data queries are run, wait for the server to catch up to the
 392                         // specified position. This is used to improve session consistency. Note that
 393                         // when LoadBalancer::waitFor() sets "waitForPos", the waiting triggers here,
 394                         // so update laggedReplicaMode as needed for consistency.
 395                         if ( !$this->doWait( $i ) ) {
 396                                 $laggedReplicaMode = true;
 397                         }
 398                 }
 399
 400                 if ( $this->readIndex <= 0 && $this->loads[$i] > 0 && $group === false ) {
 401                         // Cache the generic reader index for future ungrouped DB_REPLICA handles
 402                         $this->readIndex = $i;
 403                         // Record if the generic reader index is in "lagged replica DB" mode
 404                         if ( $laggedReplicaMode ) {
 405                                 $this->laggedReplicaMode = true;
 406                         }
 407                 }
 408
 409                 $serverName = $this->getServerName( $i );
 410                 $this->connLogger->debug( __METHOD__ . ": using server $serverName for group '$group'" );
 411
 412                 return $i;
 413         }
 414
 415         /**
 416          * @param array $loads List of server weights
 417          * @param string|bool $domain
 418          * @return array (reader index, lagged replica mode) or false on failure
 419          */
 420         private function pickReaderIndex( array $loads, $domain = false ) {
 421                 if ( !count( $loads ) ) {
 422                         throw new InvalidArgumentException( "Empty server array given to LoadBalancer" );
 423                 }
 424
 425                 /** @var int|bool $i Index of selected server */
 426                 $i = false;
 427                 /** @var bool $laggedReplicaMode Whether server is considered lagged */
 428                 $laggedReplicaMode = false;
 429
 430                 // Quickly look through the available servers for a server that meets criteria...
 431                 $currentLoads = $loads;
 432                 while ( count( $currentLoads ) ) {
 433                         if ( $this->allowLagged || $laggedReplicaMode ) {
 434                                 $i = ArrayUtils::pickRandom( $currentLoads );
 435                         } else {
 436                                 $i = false;
 437                                 if ( $this->waitForPos && $this->waitForPos->asOfTime() ) {
 438                                         // "chronologyCallback" sets "waitForPos" for session consistency.
 439                                         // This triggers doWait() after connect, so it's especially good to
 440                                         // avoid lagged servers so as to avoid excessive delay in that method.
 441                                         $ago = microtime( true ) - $this->waitForPos->asOfTime();
 442                                         // Aim for <= 1 second of waiting (being too picky can backfire)
 443                                         $i = $this->getRandomNonLagged( $currentLoads, $domain, $ago + 1 );
 444                                 }
 445                                 if ( $i === false ) {
 446                                         // Any server with less lag than it's 'max lag' param is preferable
 447                                         $i = $this->getRandomNonLagged( $currentLoads, $domain );
 448                                 }
 449                                 if ( $i === false && count( $currentLoads ) != 0 ) {
 450                                         // All replica DBs lagged. Switch to read-only mode
 451                                         $this->replLogger->error(
 452                                                 __METHOD__ . ": all replica DBs lagged. Switch to read-only mode" );
 453                                         $i = ArrayUtils::pickRandom( $currentLoads );
 454                                         $laggedReplicaMode = true;
 455                                 }
 456                         }
 457
 458                         if ( $i === false ) {
 459                                 // pickRandom() returned false.
 460                                 // This is permanent and means the configuration or the load monitor
 461                                 // wants us to return false.
 462                                 $this->connLogger->debug( __METHOD__ . ": pickRandom() returned false" );
 463
 464                                 return [ false, false ];
 465                         }
 466
 467                         $serverName = $this->getServerName( $i );
 468                         $this->connLogger->debug( __METHOD__ . ": Using reader #$i: $serverName..." );
 469
 470                         $conn = $this->openConnection( $i, $domain );
 471                         if ( !$conn ) {
 472                                 $this->connLogger->warning( __METHOD__ . ": Failed connecting to $i/$domain" );
 473                                 unset( $currentLoads[$i] ); // avoid this server next iteration
 474                                 $i = false;
 475                                 continue;
 476                         }
 477
 478                         // Decrement reference counter, we are finished with this connection.
 479                         // It will be incremented for the caller later.
 480                         if ( $domain !== false ) {
 481                                 $this->reuseConnection( $conn );
 482                         }
 483
 484                         // Return this server
 485                         break;
 486                 }
 487
 488                 // If all servers were down, quit now
 489                 if ( !count( $currentLoads ) ) {
 490                         $this->connLogger->error( __METHOD__ . ": all servers down" );
 491                 }
 492
 493                 return [ $i, $laggedReplicaMode ];
 494         }
 495
 496         public function waitFor( $pos ) {
 497                 $oldPos = $this->waitForPos;
 498                 try {
 499                         $this->waitForPos = $pos;
 500                         // If a generic reader connection was already established, then wait now
 501                         $i = $this->readIndex;
 502                         if ( $i > 0 ) {
 503                                 if ( !$this->doWait( $i ) ) {
 504                                         $this->laggedReplicaMode = true;
 505                                 }
 506                         }
 507                 } finally {
 508                         // Restore the older position if it was higher since this is used for lag-protection
 509                         $this->setWaitForPositionIfHigher( $oldPos );
 510                 }
 511         }
 512
 513         public function waitForOne( $pos, $timeout = null ) {
 514                 $oldPos = $this->waitForPos;
 515                 try {
 516                         $this->waitForPos = $pos;
 517
 518                         $i = $this->readIndex;
 519                         if ( $i <= 0 ) {
 520                                 // Pick a generic replica DB if there isn't one yet
 521                                 $readLoads = $this->loads;
 522                                 unset( $readLoads[$this->getWriterIndex()] ); // replica DBs only
 523                                 $readLoads = array_filter( $readLoads ); // with non-zero load
 524                                 $i = ArrayUtils::pickRandom( $readLoads );
 525                         }
 526
 527                         if ( $i > 0 ) {
 528                                 $ok = $this->doWait( $i, true, $timeout );
 529                         } else {
 530                                 $ok = true; // no applicable loads
 531                         }
 532                 } finally {
 533                         # Restore the old position, as this is not used for lag-protection but for throttling
 534                         $this->waitForPos = $oldPos;
 535                 }
 536
 537                 return $ok;
 538         }
 539
 540         public function waitForAll( $pos, $timeout = null ) {
 541                 $timeout = $timeout ?: $this->waitTimeout;
 542
 543                 $oldPos = $this->waitForPos;
 544                 try {
 545                         $this->waitForPos = $pos;
 546                         $serverCount = count( $this->servers );
 547
 548                         $ok = true;
 549                         for ( $i = 1; $i < $serverCount; $i++ ) {
 550                                 if ( $this->loads[$i] > 0 ) {
 551                                         $start = microtime( true );
 552                                         $ok = $this->doWait( $i, true, $timeout ) && $ok;
 553                                         $timeout -= intval( microtime( true ) - $start );
 554                                         if ( $timeout <= 0 ) {
 555                                                 break; // timeout reached
 556                                         }
 557                                 }
 558                         }
 559                 } finally {
 560                         # Restore the old position, as this is not used for lag-protection but for throttling
 561                         $this->waitForPos = $oldPos;
 562                 }
 563
 564                 return $ok;
 565         }
 566
 567         /**
 568          * @param DBMasterPos|bool $pos
 569          */
 570         private function setWaitForPositionIfHigher( $pos ) {
 571                 if ( !$pos ) {
 572                         return;
 573                 }
 574
 575                 if ( !$this->waitForPos || $pos->hasReached( $this->waitForPos ) ) {
 576                         $this->waitForPos = $pos;
 577                 }
 578         }
 579
 580         public function getAnyOpenConnection( $i, $flags = 0 ) {
 581                 $autocommit = ( ( $flags & self::CONN_TRX_AUTOCOMMIT ) == self::CONN_TRX_AUTOCOMMIT );
 582                 foreach ( $this->conns as $connsByServer ) {
 583                         if ( !isset( $connsByServer[$i] ) ) {
 584                                 continue;
 585                         }
 586
 587                         foreach ( $connsByServer[$i] as $conn ) {
 588                                 if ( !$autocommit || $conn->getLBInfo( 'autoCommitOnly' ) ) {
 589                                         return $conn;
 590                                 }
 591                         }
 592                 }
 593
 594                 return false;
 595         }
 596
 597         /**
 598          * Wait for a given replica DB to catch up to the master pos stored in $this
 599          * @param int $index Server index
 600          * @param bool $open Check the server even if a new connection has to be made
 601          * @param int $timeout Max seconds to wait; default is "waitTimeout" given to __construct()
 602          * @return bool
 603          */
 604         protected function doWait( $index, $open = false, $timeout = null ) {
 605                 $timeout = max( 1, intval( $timeout ?: $this->waitTimeout ) );
 606
 607                 // Check if we already know that the DB has reached this point
 608                 $server = $this->getServerName( $index );
 609                 $key = $this->srvCache->makeGlobalKey( __CLASS__, 'last-known-pos', $server, 'v1' );
 610                 /** @var DBMasterPos $knownReachedPos */
 611                 $knownReachedPos = $this->srvCache->get( $key );
 612                 if (
 613                         $knownReachedPos instanceof DBMasterPos &&
 614                         $knownReachedPos->hasReached( $this->waitForPos )
 615                 ) {
 616                         $this->replLogger->debug(
 617                                 __METHOD__ .
 618                                 ': replica DB {dbserver} known to be caught up (pos >= $knownReachedPos).',
 619                                 [ 'dbserver' => $server ]
 620                         );
 621                         return true;
 622                 }
 623
 624                 // Find a connection to wait on, creating one if needed and allowed
 625                 $close = false; // close the connection afterwards
 626                 $conn = $this->getAnyOpenConnection( $index );
 627                 if ( !$conn ) {
 628                         if ( !$open ) {
 629                                 $this->replLogger->debug(
 630                                         __METHOD__ . ': no connection open for {dbserver}',
 631                                         [ 'dbserver' => $server ]
 632                                 );
 633
 634                                 return false;
 635                         } else {
 636                                 $conn = $this->openConnection( $index, self::DOMAIN_ANY );
 637                                 if ( !$conn ) {
 638                                         $this->replLogger->warning(
 639                                                 __METHOD__ . ': failed to connect to {dbserver}',
 640                                                 [ 'dbserver' => $server ]
 641                                         );
 642
 643                                         return false;
 644                                 }
 645                                 // Avoid connection spam in waitForAll() when connections
 646                                 // are made just for the sake of doing this lag check.
 647                                 $close = true;
 648                         }
 649                 }
 650
 651                 $this->replLogger->info(
 652                         __METHOD__ .
 653                         ': waiting for replica DB {dbserver} to catch up...',
 654                         [ 'dbserver' => $server ]
 655                 );
 656
 657                 $result = $conn->masterPosWait( $this->waitForPos, $timeout );
 658
 659                 if ( $result === null ) {
 660                         $this->replLogger->warning(
 661                                 __METHOD__ . ': Errored out waiting on {host} pos {pos}',
 662                                 [
 663                                         'host' => $server,
 664                                         'pos' => $this->waitForPos,
 665                                         'trace' => ( new RuntimeException() )->getTraceAsString()
 666                                 ]
 667                         );
 668                         $ok = false;
 669                 } elseif ( $result == -1 ) {
 670                         $this->replLogger->warning(
 671                                 __METHOD__ . ': Timed out waiting on {host} pos {pos}',
 672                                 [
 673                                         'host' => $server,
 674                                         'pos' => $this->waitForPos,
 675                                         'trace' => ( new RuntimeException() )->getTraceAsString()
 676                                 ]
 677                         );
 678                         $ok = false;
 679                 } else {
 680                         $this->replLogger->debug( __METHOD__ . ": done waiting" );
 681                         $ok = true;
 682                         // Remember that the DB reached this point
 683                         $this->srvCache->set( $key, $this->waitForPos, BagOStuff::TTL_DAY );
 684                 }
 685
 686                 if ( $close ) {
 687                         $this->closeConnection( $conn );
 688                 }
 689
 690                 return $ok;
 691         }
 692
 693         public function getConnection( $i, $groups = [], $domain = false, $flags = 0 ) {
 694                 if ( $i === null || $i === false ) {
 695                         throw new InvalidArgumentException( 'Attempt to call ' . __METHOD__ .
 696                                 ' with invalid server index' );
 697                 }
 698
 699                 if ( $this->localDomain->equals( $domain ) || $domain === $this->localDomainIdAlias ) {
 700                         $domain = false; // local connection requested
 701                 }
 702
 703                 if ( ( $flags & self::CONN_TRX_AUTOCOMMIT ) === self::CONN_TRX_AUTOCOMMIT ) {
 704                         // Assuming all servers are of the same type (or similar), which is overwhelmingly
 705                         // the case, use the master server information to get the attributes. The information
 706                         // for $i cannot be used since it might be DB_REPLICA, which might require connection
 707                         // attempts in order to be resolved into a real server index.
 708                         $attributes = $this->getServerAttributes( $this->getWriterIndex() );
 709                         if ( $attributes[Database::ATTR_DB_LEVEL_LOCKING] ) {
 710                                 // Callers sometimes want to (a) escape REPEATABLE-READ stateness without locking
 711                                 // rows (e.g. FOR UPDATE) or (b) make small commits during a larger transactions
 712                                 // to reduce lock contention. None of these apply for sqlite and using separate
 713                                 // connections just causes self-deadlocks.
 714                                 $flags &= ~self::CONN_TRX_AUTOCOMMIT;
 715                                 $this->connLogger->info( __METHOD__ .
 716                                         ': ignoring CONN_TRX_AUTOCOMMIT to avoid deadlocks.' );
 717                         }
 718                 }
 719
 720                 $groups = ( $groups === false || $groups === [] )
 721                         ? [ false ] // check one "group": the generic pool
 722                         : (array)$groups;
 723
 724                 $masterOnly = ( $i == self::DB_MASTER || $i == $this->getWriterIndex() );
 725                 $oldConnsOpened = $this->connsOpened; // connections open now
 726
 727                 if ( $i == self::DB_MASTER ) {
 728                         $i = $this->getWriterIndex();
 729                 } elseif ( $i == self::DB_REPLICA ) {
 730                         # Try to find an available server in any the query groups (in order)
 731                         foreach ( $groups as $group ) {
 732                                 $groupIndex = $this->getReaderIndex( $group, $domain );
 733                                 if ( $groupIndex !== false ) {
 734                                         $i = $groupIndex;
 735                                         break;
 736                                 }
 737                         }
 738                 }
 739
 740                 # Operation-based index
 741                 if ( $i == self::DB_REPLICA ) {
 742                         $this->lastError = 'Unknown error'; // reset error string
 743                         # Try the general server pool if $groups are unavailable.
 744                         $i = ( $groups === [ false ] )
 745                                 ? false // don't bother with this if that is what was tried above
 746                                 : $this->getReaderIndex( false, $domain );
 747                         # Couldn't find a working server in getReaderIndex()?
 748                         if ( $i === false ) {
 749                                 $this->lastError = 'No working replica DB server: ' . $this->lastError;
 750                                 // Throw an exception
 751                                 $this->reportConnectionError();
 752                                 return null; // not reached
 753                         }
 754                 }
 755
 756                 # Now we have an explicit index into the servers array
 757                 $conn = $this->openConnection( $i, $domain, $flags );
 758                 if ( !$conn ) {
 759                         // Throw an exception
 760                         $this->reportConnectionError();
 761                         return null; // not reached
 762                 }
 763
 764                 # Profile any new connections that happen
 765                 if ( $this->connsOpened > $oldConnsOpened ) {
 766                         $host = $conn->getServer();
 767                         $dbname = $conn->getDBname();
 768                         $this->trxProfiler->recordConnection( $host, $dbname, $masterOnly );
 769                 }
 770
 771                 if ( $masterOnly ) {
 772                         # Make master-requested DB handles inherit any read-only mode setting
 773                         $conn->setLBInfo( 'readOnlyReason', $this->getReadOnlyReason( $domain, $conn ) );
 774                 }
 775
 776                 return $conn;
 777         }
 778
 779         public function reuseConnection( IDatabase $conn ) {
 780                 $serverIndex = $conn->getLBInfo( 'serverIndex' );
 781                 $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 782                 if ( $serverIndex === null || $refCount === null ) {
 783                         /**
 784                          * This can happen in code like:
 785                          *   foreach ( $dbs as $db ) {
 786                          *     $conn = $lb->getConnection( $lb::DB_REPLICA, [], $db );
 787                          *     ...
 788                          *     $lb->reuseConnection( $conn );
 789                          *   }
 790                          * When a connection to the local DB is opened in this way, reuseConnection()
 791                          * should be ignored
 792                          */
 793                         return;
 794                 } elseif ( $conn instanceof DBConnRef ) {
 795                         // DBConnRef already handles calling reuseConnection() and only passes the live
 796                         // Database instance to this method. Any caller passing in a DBConnRef is broken.
 797                         $this->connLogger->error(
 798                                 __METHOD__ . ": got DBConnRef instance.\n" .
 799                                 ( new RuntimeException() )->getTraceAsString() );
 800
 801                         return;
 802                 }
 803
 804                 if ( $this->disabled ) {
 805                         return; // DBConnRef handle probably survived longer than the LoadBalancer
 806                 }
 807
 808                 if ( $conn->getLBInfo( 'autoCommitOnly' ) ) {
 809                         $connFreeKey = self::KEY_FOREIGN_FREE_NOROUND;
 810                         $connInUseKey = self::KEY_FOREIGN_INUSE_NOROUND;
 811                 } else {
 812                         $connFreeKey = self::KEY_FOREIGN_FREE;
 813                         $connInUseKey = self::KEY_FOREIGN_INUSE;
 814                 }
 815
 816                 $domain = $conn->getDomainID();
 817                 if ( !isset( $this->conns[$connInUseKey][$serverIndex][$domain] ) ) {
 818                         throw new InvalidArgumentException( __METHOD__ .
 819                                 ": connection $serverIndex/$domain not found; it may have already been freed." );
 820                 } elseif ( $this->conns[$connInUseKey][$serverIndex][$domain] !== $conn ) {
 821                         throw new InvalidArgumentException( __METHOD__ .
 822                                 ": connection $serverIndex/$domain mismatched; it may have already been freed." );
 823                 }
 824
 825                 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
 826                 if ( $refCount <= 0 ) {
 827                         $this->conns[$connFreeKey][$serverIndex][$domain] = $conn;
 828                         unset( $this->conns[$connInUseKey][$serverIndex][$domain] );
 829                         if ( !$this->conns[$connInUseKey][$serverIndex] ) {
 830                                 unset( $this->conns[$connInUseKey][$serverIndex] ); // clean up
 831                         }
 832                         $this->connLogger->debug( __METHOD__ . ": freed connection $serverIndex/$domain" );
 833                 } else {
 834                         $this->connLogger->debug( __METHOD__ .
 835                                 ": reference count for $serverIndex/$domain reduced to $refCount" );
 836                 }
 837         }
 838
 839         public function getConnectionRef( $db, $groups = [], $domain = false, $flags = 0 ) {
 840                 $domain = ( $domain !== false ) ? $domain : $this->localDomain;
 841
 842                 return new DBConnRef( $this, $this->getConnection( $db, $groups, $domain, $flags ) );
 843         }
 844
 845         public function getLazyConnectionRef( $db, $groups = [], $domain = false, $flags = 0 ) {
 846                 $domain = ( $domain !== false ) ? $domain : $this->localDomain;
 847
 848                 return new DBConnRef( $this, [ $db, $groups, $domain, $flags ] );
 849         }
 850
 851         public function getMaintenanceConnectionRef( $db, $groups = [], $domain = false, $flags = 0 ) {
 852                 $domain = ( $domain !== false ) ? $domain : $this->localDomain;
 853
 854                 return new MaintainableDBConnRef(
 855                         $this, $this->getConnection( $db, $groups, $domain, $flags ) );
 856         }
 857
 858         public function openConnection( $i, $domain = false, $flags = 0 ) {
 859                 if ( $this->localDomain->equals( $domain ) || $domain === $this->localDomainIdAlias ) {
 860                         $domain = false; // local connection requested
 861                 }
 862
 863                 if ( !$this->connectionAttempted && $this->chronologyCallback ) {
 864                         $this->connLogger->debug( __METHOD__ . ': calling initLB() before first connection.' );
 865                         // Load any "waitFor" positions before connecting so that doWait() is triggered
 866                         $this->connectionAttempted = true;
 867                         call_user_func( $this->chronologyCallback, $this );
 868                 }
 869
 870                 // Check if an auto-commit connection is being requested. If so, it will not reuse the
 871                 // main set of DB connections but rather its own pool since:
 872                 // a) those are usually set to implicitly use transaction rounds via DBO_TRX
 873                 // b) those must support the use of explicit transaction rounds via beginMasterChanges()
 874                 $autoCommit = ( ( $flags & self::CONN_TRX_AUTOCOMMIT ) == self::CONN_TRX_AUTOCOMMIT );
 875
 876                 if ( $domain !== false ) {
 877                         // Connection is to a foreign domain
 878                         $conn = $this->openForeignConnection( $i, $domain, $flags );
 879                 } else {
 880                         // Connection is to the local domain
 881                         $connKey = $autoCommit ? self::KEY_LOCAL_NOROUND : self::KEY_LOCAL;
 882                         if ( isset( $this->conns[$connKey][$i][0] ) ) {
 883                                 $conn = $this->conns[$connKey][$i][0];
 884                         } else {
 885                                 if ( !isset( $this->servers[$i] ) || !is_array( $this->servers[$i] ) ) {
 886                                         throw new InvalidArgumentException( "No server with index '$i'." );
 887                                 }
 888                                 // Open a new connection
 889                                 $server = $this->servers[$i];
 890                                 $server['serverIndex'] = $i;
 891                                 $server['autoCommitOnly'] = $autoCommit;
 892                                 if ( $this->localDomain->getDatabase() !== null ) {
 893                                         // Use the local domain table prefix if the local domain is specified
 894                                         $server['tablePrefix'] = $this->localDomain->getTablePrefix();
 895                                 }
 896                                 $conn = $this->reallyOpenConnection( $server, $this->localDomain );
 897                                 $host = $this->getServerName( $i );
 898                                 if ( $conn->isOpen() ) {
 899                                         $this->connLogger->debug(
 900                                                 __METHOD__ . ": connected to database $i at '$host'." );
 901                                         $this->conns[$connKey][$i][0] = $conn;
 902                                 } else {
 903                                         $this->connLogger->warning(
 904                                                 __METHOD__ . ": failed to connect to database $i at '$host'." );
 905                                         $this->errorConnection = $conn;
 906                                         $conn = false;
 907                                 }
 908                         }
 909                 }
 910
 911                 if ( $conn instanceof IDatabase && !$conn->isOpen() ) {
 912                         // Connection was made but later unrecoverably lost for some reason.
 913                         // Do not return a handle that will just throw exceptions on use,
 914                         // but let the calling code (e.g. getReaderIndex) try another server.
 915                         // See DatabaseMyslBase::ping() for how this can happen.
 916                         $this->errorConnection = $conn;
 917                         $conn = false;
 918                 }
 919
 920                 if ( $autoCommit && $conn instanceof IDatabase ) {
 921                         $conn->clearFlag( $conn::DBO_TRX ); // auto-commit mode
 922                 }
 923
 924                 return $conn;
 925         }
 926
 927         /**
 928          * Open a connection to a foreign DB, or return one if it is already open.
 929          *
 930          * Increments a reference count on the returned connection which locks the
 931          * connection to the requested domain. This reference count can be
 932          * decremented by calling reuseConnection().
 933          *
 934          * If a connection is open to the appropriate server already, but with the wrong
 935          * database, it will be switched to the right database and returned, as long as
 936          * it has been freed first with reuseConnection().
 937          *
 938          * On error, returns false, and the connection which caused the
 939          * error will be available via $this->errorConnection.
 940          *
 941          * @note If disable() was called on this LoadBalancer, this method will throw a DBAccessError.
 942          *
 943          * @param int $i Server index
 944          * @param string $domain Domain ID to open
 945          * @param int $flags Class CONN_* constant bitfield
 946          * @return Database
 947          */
 948         private function openForeignConnection( $i, $domain, $flags = 0 ) {
 949                 $domainInstance = DatabaseDomain::newFromId( $domain );
 950                 $dbName = $domainInstance->getDatabase();
 951                 $prefix = $domainInstance->getTablePrefix();
 952                 $autoCommit = ( ( $flags & self::CONN_TRX_AUTOCOMMIT ) == self::CONN_TRX_AUTOCOMMIT );
 953
 954                 if ( $autoCommit ) {
 955                         $connFreeKey = self::KEY_FOREIGN_FREE_NOROUND;
 956                         $connInUseKey = self::KEY_FOREIGN_INUSE_NOROUND;
 957                 } else {
 958                         $connFreeKey = self::KEY_FOREIGN_FREE;
 959                         $connInUseKey = self::KEY_FOREIGN_INUSE;
 960                 }
 961
 962                 if ( isset( $this->conns[$connInUseKey][$i][$domain] ) ) {
 963                         // Reuse an in-use connection for the same domain
 964                         $conn = $this->conns[$connInUseKey][$i][$domain];
 965                         $this->connLogger->debug( __METHOD__ . ": reusing connection $i/$domain" );
 966                 } elseif ( isset( $this->conns[$connFreeKey][$i][$domain] ) ) {
 967                         // Reuse a free connection for the same domain
 968                         $conn = $this->conns[$connFreeKey][$i][$domain];
 969                         unset( $this->conns[$connFreeKey][$i][$domain] );
 970                         $this->conns[$connInUseKey][$i][$domain] = $conn;
 971                         $this->connLogger->debug( __METHOD__ . ": reusing free connection $i/$domain" );
 972                 } elseif ( !empty( $this->conns[$connFreeKey][$i] ) ) {
 973                         // Reuse a free connection from another domain
 974                         $conn = reset( $this->conns[$connFreeKey][$i] );
 975                         $oldDomain = key( $this->conns[$connFreeKey][$i] );
 976                         if ( strlen( $dbName ) && !$conn->selectDB( $dbName ) ) {
 977                                 $this->lastError = "Error selecting database '$dbName' on server " .
 978                                         $conn->getServer() . " from client host {$this->host}";
 979                                 $this->errorConnection = $conn;
 980                                 $conn = false;
 981                         } else {
 982                                 $conn->tablePrefix( $prefix );
 983                                 unset( $this->conns[$connFreeKey][$i][$oldDomain] );
 984                                 // Note that if $domain is an empty string, getDomainID() might not match it
 985                                 $this->conns[$connInUseKey][$i][$conn->getDomainId()] = $conn;
 986                                 $this->connLogger->debug( __METHOD__ .
 987                                         ": reusing free connection from $oldDomain for $domain" );
 988                         }
 989                 } else {
 990                         if ( !isset( $this->servers[$i] ) || !is_array( $this->servers[$i] ) ) {
 991                                 throw new InvalidArgumentException( "No server with index '$i'." );
 992                         }
 993                         // Open a new connection
 994                         $server = $this->servers[$i];
 995                         $server['serverIndex'] = $i;
 996                         $server['foreignPoolRefCount'] = 0;
 997                         $server['foreign'] = true;
 998                         $server['autoCommitOnly'] = $autoCommit;
 999                         $conn = $this->reallyOpenConnection( $server, $domainInstance );
1000                         if ( !$conn->isOpen() ) {
1001                                 $this->connLogger->warning( __METHOD__ . ": connection error for $i/$domain" );
1002                                 $this->errorConnection = $conn;
1003                                 $conn = false;
1004                         } else {
1005                                 $conn->tablePrefix( $prefix ); // as specified
1006                                 // Note that if $domain is an empty string, getDomainID() might not match it
1007                                 $this->conns[$connInUseKey][$i][$conn->getDomainID()] = $conn;
1008                                 $this->connLogger->debug( __METHOD__ . ": opened new connection for $i/$domain" );
1009                         }
1010                 }
1011
1012                 // Increment reference count
1013                 if ( $conn instanceof IDatabase ) {
1014                         $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
1015                         $conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
1016                 }
1017
1018                 return $conn;
1019         }
1020
1021         public function getServerAttributes( $i ) {
1022                 return Database::attributesFromType(
1023                         $this->getServerType( $i ),
1024                         $this->servers[$i]['driver'] ?? null
1025                 );
1026         }
1027
1028         /**
1029          * Test if the specified index represents an open connection
1030          *
1031          * @param int $index Server index
1032          * @access private
1033          * @return bool
1034          */
1035         private function isOpen( $index ) {
1036                 if ( !is_int( $index ) ) {
1037                         return false;
1038                 }
1039
1040                 return (bool)$this->getAnyOpenConnection( $index );
1041         }
1042
1043         /**
1044          * Open a new network connection to a server (uncached)
1045          *
1046          * Returns a Database object whether or not the connection was successful.
1047          *
1048          * @param array $server
1049          * @param DatabaseDomain $domainOverride Use an unspecified domain to not select any database
1050          * @return Database
1051          * @throws DBAccessError
1052          * @throws InvalidArgumentException
1053          */
1054         protected function reallyOpenConnection( array $server, DatabaseDomain $domainOverride ) {
1055                 if ( $this->disabled ) {
1056                         throw new DBAccessError();
1057                 }
1058
1059                 // Handle $domainOverride being a specified or an unspecified domain
1060                 if ( $domainOverride->getDatabase() === null ) {
1061                         // Normally, an RDBMS requires a DB name specified on connection and the $server
1062                         // configuration array is assumed to already specify an appropriate DB name.
1063                         if ( $server['type'] === 'mysql' ) {
1064                                 // For MySQL, DATABASE and SCHEMA are synonyms, connections need not specify a DB,
1065                                 // and the DB name in $server might not exist due to legacy reasons (the default
1066                                 // domain used to ignore the local LB domain, even when mismatched).
1067                                 $server['dbname'] = null;
1068                         }
1069                 } else {
1070                         $server['dbname'] = $domainOverride->getDatabase();
1071                         $server['schema'] = $domainOverride->getSchema();
1072                 }
1073
1074                 // Let the handle know what the cluster master is (e.g. "db1052")
1075                 $masterName = $this->getServerName( $this->getWriterIndex() );
1076                 $server['clusterMasterHost'] = $masterName;
1077
1078                 // Log when many connection are made on requests
1079                 if ( ++$this->connsOpened >= self::CONN_HELD_WARN_THRESHOLD ) {
1080                         $this->perfLogger->warning( __METHOD__ . ": " .
1081                                 "{$this->connsOpened}+ connections made (master=$masterName)" );
1082                 }
1083
1084                 $server['srvCache'] = $this->srvCache;
1085                 // Set loggers and profilers
1086                 $server['connLogger'] = $this->connLogger;
1087                 $server['queryLogger'] = $this->queryLogger;
1088                 $server['errorLogger'] = $this->errorLogger;
1089                 $server['deprecationLogger'] = $this->deprecationLogger;
1090                 $server['profiler'] = $this->profiler;
1091                 $server['trxProfiler'] = $this->trxProfiler;
1092                 // Use the same agent and PHP mode for all DB handles
1093                 $server['cliMode'] = $this->cliMode;
1094                 $server['agent'] = $this->agent;
1095                 // Use DBO_DEFAULT flags by default for LoadBalancer managed databases. Assume that the
1096                 // application calls LoadBalancer::commitMasterChanges() before the PHP script completes.
1097                 $server['flags'] = $server['flags'] ?? IDatabase::DBO_DEFAULT;
1098
1099                 // Create a live connection object
1100                 try {
1101                         $db = Database::factory( $server['type'], $server );
1102                 } catch ( DBConnectionError $e ) {
1103                         // FIXME: This is probably the ugliest thing I have ever done to
1104                         // PHP. I'm half-expecting it to segfault, just out of disgust. -- TS
1105                         $db = $e->db;
1106                 }
1107
1108                 $db->setLBInfo( $server );
1109                 $db->setLazyMasterHandle(
1110                         $this->getLazyConnectionRef( self::DB_MASTER, [], $db->getDomainID() )
1111                 );
1112                 $db->setTableAliases( $this->tableAliases );
1113                 $db->setIndexAliases( $this->indexAliases );
1114
1115                 if ( $server['serverIndex'] === $this->getWriterIndex() ) {
1116                         if ( $this->trxRoundId !== false ) {
1117                                 $this->applyTransactionRoundFlags( $db );
1118                         }
1119                         foreach ( $this->trxRecurringCallbacks as $name => $callback ) {
1120                                 $db->setTransactionListener( $name, $callback );
1121                         }
1122                 }
1123
1124                 return $db;
1125         }
1126
1127         /**
1128          * @throws DBConnectionError
1129          */
1130         private function reportConnectionError() {
1131                 $conn = $this->errorConnection; // the connection which caused the error
1132                 $context = [
1133                         'method' => __METHOD__,
1134                         'last_error' => $this->lastError,
1135                 ];
1136
1137                 if ( $conn instanceof IDatabase ) {
1138                         $context['db_server'] = $conn->getServer();
1139                         $this->connLogger->warning(
1140                                 __METHOD__ . ": connection error: {last_error} ({db_server})",
1141                                 $context
1142                         );
1143
1144                         throw new DBConnectionError( $conn, "{$this->lastError} ({$context['db_server']})" );
1145                 } else {
1146                         // No last connection, probably due to all servers being too busy
1147                         $this->connLogger->error(
1148                                 __METHOD__ .
1149                                 ": LB failure with no last connection. Connection error: {last_error}",
1150                                 $context
1151                         );
1152
1153                         // If all servers were busy, "lastError" will contain something sensible
1154                         throw new DBConnectionError( null, $this->lastError );
1155                 }
1156         }
1157
1158         public function getWriterIndex() {
1159                 return 0;
1160         }
1161
1162         public function haveIndex( $i ) {
1163                 return array_key_exists( $i, $this->servers );
1164         }
1165
1166         public function isNonZeroLoad( $i ) {
1167                 return array_key_exists( $i, $this->servers ) && $this->loads[$i] != 0;
1168         }
1169
1170         public function getServerCount() {
1171                 return count( $this->servers );
1172         }
1173
1174         public function getServerName( $i ) {
1175                 if ( isset( $this->servers[$i]['hostName'] ) ) {
1176                         $name = $this->servers[$i]['hostName'];
1177                 } elseif ( isset( $this->servers[$i]['host'] ) ) {
1178                         $name = $this->servers[$i]['host'];
1179                 } else {
1180                         $name = '';
1181                 }
1182
1183                 return ( $name != '' ) ? $name : 'localhost';
1184         }
1185
1186         public function getServerType( $i ) {
1187                 return $this->servers[$i]['type'] ?? 'unknown';
1188         }
1189
1190         public function getMasterPos() {
1191                 # If this entire request was served from a replica DB without opening a connection to the
1192                 # master (however unlikely that may be), then we can fetch the position from the replica DB.
1193                 $masterConn = $this->getAnyOpenConnection( $this->getWriterIndex() );
1194                 if ( !$masterConn ) {
1195                         $serverCount = count( $this->servers );
1196                         for ( $i = 1; $i < $serverCount; $i++ ) {
1197                                 $conn = $this->getAnyOpenConnection( $i );
1198                                 if ( $conn ) {
1199                                         return $conn->getReplicaPos();
1200                                 }
1201                         }
1202                 } else {
1203                         return $masterConn->getMasterPos();
1204                 }
1205
1206                 return false;
1207         }
1208
1209         public function disable() {
1210                 $this->closeAll();
1211                 $this->disabled = true;
1212         }
1213
1214         public function closeAll() {
1215                 $this->forEachOpenConnection( function ( IDatabase $conn ) {
1216                         $host = $conn->getServer();
1217                         $this->connLogger->debug(
1218                                 __METHOD__ . ": closing connection to database '$host'." );
1219                         $conn->close();
1220                 } );
1221
1222                 $this->conns = [
1223                         self::KEY_LOCAL => [],
1224                         self::KEY_FOREIGN_INUSE => [],
1225                         self::KEY_FOREIGN_FREE => [],
1226                         self::KEY_LOCAL_NOROUND => [],
1227                         self::KEY_FOREIGN_INUSE_NOROUND => [],
1228                         self::KEY_FOREIGN_FREE_NOROUND => []
1229                 ];
1230                 $this->connsOpened = 0;
1231         }
1232
1233         public function closeConnection( IDatabase $conn ) {
1234                 $serverIndex = $conn->getLBInfo( 'serverIndex' );
1235                 foreach ( $this->conns as $type => $connsByServer ) {
1236                         if ( !isset( $connsByServer[$serverIndex] ) ) {
1237                                 continue;
1238                         }
1239
1240                         foreach ( $connsByServer[$serverIndex] as $i => $trackedConn ) {
1241                                 if ( $conn === $trackedConn ) {
1242                                         $host = $this->getServerName( $i );
1243                                         $this->connLogger->debug(
1244                                                 __METHOD__ . ": closing connection to database $i at '$host'." );
1245                                         unset( $this->conns[$type][$serverIndex][$i] );
1246                                         --$this->connsOpened;
1247                                         break 2;
1248                                 }
1249                         }
1250                 }
1251
1252                 $conn->close();
1253         }
1254
1255         public function commitAll( $fname = __METHOD__ ) {
1256                 $this->commitMasterChanges( $fname );
1257                 $this->flushMasterSnapshots( $fname );
1258                 $this->flushReplicaSnapshots( $fname );
1259         }
1260
1261         public function finalizeMasterChanges() {
1262                 $this->assertTransactionRoundStage( [ self::ROUND_CURSORY, self::ROUND_FINALIZED ] );
1263
1264                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1265                 // Loop until callbacks stop adding callbacks on other connections
1266                 $total = 0;
1267                 do {
1268                         $count = 0; // callbacks execution attempts
1269                         $this->forEachOpenMasterConnection( function ( Database $conn ) use ( &$count ) {
1270                                 // Run any pre-commit callbacks while leaving the post-commit ones suppressed.
1271                                 // Any error should cause all (peer) transactions to be rolled back together.
1272                                 $count += $conn->runOnTransactionPreCommitCallbacks();
1273                         } );
1274                         $total += $count;
1275                 } while ( $count > 0 );
1276                 // Defer post-commit callbacks until after COMMIT/ROLLBACK happens on all handles
1277                 $this->forEachOpenMasterConnection( function ( Database $conn ) {
1278                         $conn->setTrxEndCallbackSuppression( true );
1279                 } );
1280                 $this->trxRoundStage = self::ROUND_FINALIZED;
1281
1282                 return $total;
1283         }
1284
1285         public function approveMasterChanges( array $options ) {
1286                 $this->assertTransactionRoundStage( self::ROUND_FINALIZED );
1287
1288                 $limit = $options['maxWriteDuration'] ?? 0;
1289
1290                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1291                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( $limit ) {
1292                         // If atomic sections or explicit transactions are still open, some caller must have
1293                         // caught an exception but failed to properly rollback any changes. Detect that and
1294                         // throw and error (causing rollback).
1295                         if ( $conn->explicitTrxActive() ) {
1296                                 throw new DBTransactionError(
1297                                         $conn,
1298                                         "Explicit transaction still active. A caller may have caught an error."
1299                                 );
1300                         }
1301                         // Assert that the time to replicate the transaction will be sane.
1302                         // If this fails, then all DB transactions will be rollback back together.
1303                         $time = $conn->pendingWriteQueryDuration( $conn::ESTIMATE_DB_APPLY );
1304                         if ( $limit > 0 && $time > $limit ) {
1305                                 throw new DBTransactionSizeError(
1306                                         $conn,
1307                                         "Transaction spent $time second(s) in writes, exceeding the limit of $limit.",
1308                                         [ $time, $limit ]
1309                                 );
1310                         }
1311                         // If a connection sits idle while slow queries execute on another, that connection
1312                         // may end up dropped before the commit round is reached. Ping servers to detect this.
1313                         if ( $conn->writesOrCallbacksPending() && !$conn->ping() ) {
1314                                 throw new DBTransactionError(
1315                                         $conn,
1316                                         "A connection to the {$conn->getDBname()} database was lost before commit."
1317                                 );
1318                         }
1319                 } );
1320                 $this->trxRoundStage = self::ROUND_APPROVED;
1321         }
1322
1323         public function beginMasterChanges( $fname = __METHOD__ ) {
1324                 if ( $this->trxRoundId !== false ) {
1325                         throw new DBTransactionError(
1326                                 null,
1327                                 "$fname: Transaction round '{$this->trxRoundId}' already started."
1328                         );
1329                 }
1330                 $this->assertTransactionRoundStage( self::ROUND_CURSORY );
1331
1332                 // Clear any empty transactions (no writes/callbacks) from the implicit round
1333                 $this->flushMasterSnapshots( $fname );
1334
1335                 $this->trxRoundId = $fname;
1336                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1337                 // Mark applicable handles as participating in this explicit transaction round.
1338                 // For each of these handles, any writes and callbacks will be tied to a single
1339                 // transaction. The (peer) handles will reject begin()/commit() calls unless they
1340                 // are part of an en masse commit or an en masse rollback.
1341                 $this->forEachOpenMasterConnection( function ( Database $conn ) {
1342                         $this->applyTransactionRoundFlags( $conn );
1343                 } );
1344                 $this->trxRoundStage = self::ROUND_CURSORY;
1345         }
1346
1347         public function commitMasterChanges( $fname = __METHOD__ ) {
1348                 $this->assertTransactionRoundStage( self::ROUND_APPROVED );
1349
1350                 $failures = [];
1351
1352                 /** @noinspection PhpUnusedLocalVariableInspection */
1353                 $scope = $this->getScopedPHPBehaviorForCommit(); // try to ignore client aborts
1354
1355                 $restore = ( $this->trxRoundId !== false );
1356                 $this->trxRoundId = false;
1357                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1358                 // Commit any writes and clear any snapshots as well (callbacks require AUTOCOMMIT).
1359                 // Note that callbacks should already be suppressed due to finalizeMasterChanges().
1360                 $this->forEachOpenMasterConnection(
1361                         function ( IDatabase $conn ) use ( $fname, &$failures ) {
1362                                 try {
1363                                         $conn->commit( $fname, $conn::FLUSHING_ALL_PEERS );
1364                                 } catch ( DBError $e ) {
1365                                         call_user_func( $this->errorLogger, $e );
1366                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1367                                 }
1368                         }
1369                 );
1370                 if ( $failures ) {
1371                         throw new DBTransactionError(
1372                                 null,
1373                                 "$fname: Commit failed on server(s) " . implode( "\n", array_unique( $failures ) )
1374                         );
1375                 }
1376                 if ( $restore ) {
1377                         // Unmark handles as participating in this explicit transaction round
1378                         $this->forEachOpenMasterConnection( function ( Database $conn ) {
1379                                 $this->undoTransactionRoundFlags( $conn );
1380                         } );
1381                 }
1382                 $this->trxRoundStage = self::ROUND_COMMIT_CALLBACKS;
1383         }
1384
1385         public function runMasterTransactionIdleCallbacks() {
1386                 if ( $this->trxRoundStage === self::ROUND_COMMIT_CALLBACKS ) {
1387                         $type = IDatabase::TRIGGER_COMMIT;
1388                 } elseif ( $this->trxRoundStage === self::ROUND_ROLLBACK_CALLBACKS ) {
1389                         $type = IDatabase::TRIGGER_ROLLBACK;
1390                 } else {
1391                         throw new DBTransactionError(
1392                                 null,
1393                                 "Transaction should be in the callback stage (not '{$this->trxRoundStage}')"
1394                         );
1395                 }
1396
1397                 $oldStage = $this->trxRoundStage;
1398                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1399
1400                 // Now that the COMMIT/ROLLBACK step is over, enable post-commit callback runs
1401                 $this->forEachOpenMasterConnection( function ( Database $conn ) {
1402                         $conn->setTrxEndCallbackSuppression( false );
1403                 } );
1404
1405                 $e = null; // first exception
1406                 // Loop until callbacks stop adding callbacks on other connections
1407                 do {
1408                         // Run any pending callbacks for each connection...
1409                         $count = 0; // callback execution attempts
1410                         $this->forEachOpenMasterConnection(
1411                                 function ( Database $conn ) use ( $type, &$e, &$count ) {
1412                                         if ( $conn->trxLevel() ) {
1413                                                 return; // retry in the next iteration, after commit() is called
1414                                         }
1415                                         try {
1416                                                 $count += $conn->runOnTransactionIdleCallbacks( $type );
1417                                         } catch ( Exception $ex ) {
1418                                                 $e = $e ?: $ex;
1419                                         }
1420                                 }
1421                         );
1422                         // Clear out any active transactions left over from callbacks...
1423                         $this->forEachOpenMasterConnection( function ( Database $conn ) use ( &$e ) {
1424                                 if ( $conn->writesPending() ) {
1425                                         // A callback from another handle wrote to this one and DBO_TRX is set
1426                                         $this->queryLogger->warning( __METHOD__ . ": found writes pending." );
1427                                         $fnames = implode( ', ', $conn->pendingWriteAndCallbackCallers() );
1428                                         $this->queryLogger->warning(
1429                                                 __METHOD__ . ": found writes pending ($fnames).",
1430                                                 [
1431                                                         'db_server' => $conn->getServer(),
1432                                                         'db_name' => $conn->getDBname()
1433                                                 ]
1434                                         );
1435                                 } elseif ( $conn->trxLevel() ) {
1436                                         // A callback from another handle read from this one and DBO_TRX is set,
1437                                         // which can easily happen if there is only one DB (no replicas)
1438                                         $this->queryLogger->debug( __METHOD__ . ": found empty transaction." );
1439                                 }
1440                                 try {
1441                                         $conn->commit( __METHOD__, $conn::FLUSHING_ALL_PEERS );
1442                                 } catch ( Exception $ex ) {
1443                                         $e = $e ?: $ex;
1444                                 }
1445                         } );
1446                 } while ( $count > 0 );
1447
1448                 $this->trxRoundStage = $oldStage;
1449
1450                 return $e;
1451         }
1452
1453         public function runMasterTransactionListenerCallbacks() {
1454                 if ( $this->trxRoundStage === self::ROUND_COMMIT_CALLBACKS ) {
1455                         $type = IDatabase::TRIGGER_COMMIT;
1456                 } elseif ( $this->trxRoundStage === self::ROUND_ROLLBACK_CALLBACKS ) {
1457                         $type = IDatabase::TRIGGER_ROLLBACK;
1458                 } else {
1459                         throw new DBTransactionError(
1460                                 null,
1461                                 "Transaction should be in the callback stage (not '{$this->trxRoundStage}')"
1462                         );
1463                 }
1464
1465                 $e = null;
1466
1467                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1468                 $this->forEachOpenMasterConnection( function ( Database $conn ) use ( $type, &$e ) {
1469                         try {
1470                                 $conn->runTransactionListenerCallbacks( $type );
1471                         } catch ( Exception $ex ) {
1472                                 $e = $e ?: $ex;
1473                         }
1474                 } );
1475                 $this->trxRoundStage = self::ROUND_CURSORY;
1476
1477                 return $e;
1478         }
1479
1480         public function rollbackMasterChanges( $fname = __METHOD__ ) {
1481                 $restore = ( $this->trxRoundId !== false );
1482                 $this->trxRoundId = false;
1483                 $this->trxRoundStage = self::ROUND_ERROR; // "failed" until proven otherwise
1484                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( $fname ) {
1485                         $conn->rollback( $fname, $conn::FLUSHING_ALL_PEERS );
1486                 } );
1487                 if ( $restore ) {
1488                         // Unmark handles as participating in this explicit transaction round
1489                         $this->forEachOpenMasterConnection( function ( Database $conn ) {
1490                                 $this->undoTransactionRoundFlags( $conn );
1491                         } );
1492                 }
1493                 $this->trxRoundStage = self::ROUND_ROLLBACK_CALLBACKS;
1494         }
1495
1496         /**
1497          * @param string|string[] $stage
1498          */
1499         private function assertTransactionRoundStage( $stage ) {
1500                 $stages = (array)$stage;
1501
1502                 if ( !in_array( $this->trxRoundStage, $stages, true ) ) {
1503                         $stageList = implode(
1504                                 '/',
1505                                 array_map( function ( $v ) {
1506                                         return "'$v'";
1507                                 }, $stages )
1508                         );
1509                         throw new DBTransactionError(
1510                                 null,
1511                                 "Transaction round stage must be $stageList (not '{$this->trxRoundStage}')"
1512                         );
1513                 }
1514         }
1515
1516         /**
1517          * Make all DB servers with DBO_DEFAULT/DBO_TRX set join the transaction round
1518          *
1519          * Some servers may have neither flag enabled, meaning that they opt out of such
1520          * transaction rounds and remain in auto-commit mode. Such behavior might be desired
1521          * when a DB server is used for something like simple key/value storage.
1522          *
1523          * @param Database $conn
1524          */
1525         private function applyTransactionRoundFlags( Database $conn ) {
1526                 if ( $conn->getLBInfo( 'autoCommitOnly' ) ) {
1527                         return; // transaction rounds do not apply to these connections
1528                 }
1529
1530                 if ( $conn->getFlag( $conn::DBO_DEFAULT ) ) {
1531                         // DBO_TRX is controlled entirely by CLI mode presence with DBO_DEFAULT.
1532                         // Force DBO_TRX even in CLI mode since a commit round is expected soon.
1533                         $conn->setFlag( $conn::DBO_TRX, $conn::REMEMBER_PRIOR );
1534                 }
1535
1536                 if ( $conn->getFlag( $conn::DBO_TRX ) ) {
1537                         $conn->setLBInfo( 'trxRoundId', $this->trxRoundId );
1538                 }
1539         }
1540
1541         /**
1542          * @param Database $conn
1543          */
1544         private function undoTransactionRoundFlags( Database $conn ) {
1545                 if ( $conn->getLBInfo( 'autoCommitOnly' ) ) {
1546                         return; // transaction rounds do not apply to these connections
1547                 }
1548
1549                 if ( $conn->getFlag( $conn::DBO_TRX ) ) {
1550                         $conn->setLBInfo( 'trxRoundId', false );
1551                 }
1552
1553                 if ( $conn->getFlag( $conn::DBO_DEFAULT ) ) {
1554                         $conn->restoreFlags( $conn::RESTORE_PRIOR );
1555                 }
1556         }
1557
1558         public function flushReplicaSnapshots( $fname = __METHOD__ ) {
1559                 $this->forEachOpenReplicaConnection( function ( IDatabase $conn ) use ( $fname ) {
1560                         $conn->flushSnapshot( $fname );
1561                 } );
1562         }
1563
1564         public function flushMasterSnapshots( $fname = __METHOD__ ) {
1565                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( $fname ) {
1566                         $conn->flushSnapshot( $fname );
1567                 } );
1568         }
1569
1570         /**
1571          * @return string
1572          * @since 1.32
1573          */
1574         public function getTransactionRoundStage() {
1575                 return $this->trxRoundStage;
1576         }
1577
1578         public function hasMasterConnection() {
1579                 return $this->isOpen( $this->getWriterIndex() );
1580         }
1581
1582         public function hasMasterChanges() {
1583                 $pending = 0;
1584                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$pending ) {
1585                         $pending |= $conn->writesOrCallbacksPending();
1586                 } );
1587
1588                 return (bool)$pending;
1589         }
1590
1591         public function lastMasterChangeTimestamp() {
1592                 $lastTime = false;
1593                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$lastTime ) {
1594                         $lastTime = max( $lastTime, $conn->lastDoneWrites() );
1595                 } );
1596
1597                 return $lastTime;
1598         }
1599
1600         public function hasOrMadeRecentMasterChanges( $age = null ) {
1601                 $age = ( $age === null ) ? $this->waitTimeout : $age;
1602
1603                 return ( $this->hasMasterChanges()
1604                         || $this->lastMasterChangeTimestamp() > microtime( true ) - $age );
1605         }
1606
1607         public function pendingMasterChangeCallers() {
1608                 $fnames = [];
1609                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$fnames ) {
1610                         $fnames = array_merge( $fnames, $conn->pendingWriteCallers() );
1611                 } );
1612
1613                 return $fnames;
1614         }
1615
1616         public function getLaggedReplicaMode( $domain = false ) {
1617                 // No-op if there is only one DB (also avoids recursion)
1618                 if ( !$this->laggedReplicaMode && $this->getServerCount() > 1 ) {
1619                         try {
1620                                 // See if laggedReplicaMode gets set
1621                                 $conn = $this->getConnection( self::DB_REPLICA, false, $domain );
1622                                 $this->reuseConnection( $conn );
1623                         } catch ( DBConnectionError $e ) {
1624                                 // Avoid expensive re-connect attempts and failures
1625                                 $this->allReplicasDownMode = true;
1626                                 $this->laggedReplicaMode = true;
1627                         }
1628                 }
1629
1630                 return $this->laggedReplicaMode;
1631         }
1632
1633         public function laggedReplicaUsed() {
1634                 return $this->laggedReplicaMode;
1635         }
1636
1637         /**
1638          * @return bool
1639          * @since 1.27
1640          * @deprecated Since 1.28; use laggedReplicaUsed()
1641          */
1642         public function laggedSlaveUsed() {
1643                 return $this->laggedReplicaUsed();
1644         }
1645
1646         public function getReadOnlyReason( $domain = false, IDatabase $conn = null ) {
1647                 if ( $this->readOnlyReason !== false ) {
1648                         return $this->readOnlyReason;
1649                 } elseif ( $this->getLaggedReplicaMode( $domain ) ) {
1650                         if ( $this->allReplicasDownMode ) {
1651                                 return 'The database has been automatically locked ' .
1652                                         'until the replica database servers become available';
1653                         } else {
1654                                 return 'The database has been automatically locked ' .
1655                                         'while the replica database servers catch up to the master.';
1656                         }
1657                 } elseif ( $this->masterRunningReadOnly( $domain, $conn ) ) {
1658                         return 'The database master is running in read-only mode.';
1659                 }
1660
1661                 return false;
1662         }
1663
1664         /**
1665          * @param string $domain Domain ID, or false for the current domain
1666          * @param IDatabase|null $conn DB master connectionl used to avoid loops [optional]
1667          * @return bool
1668          */
1669         private function masterRunningReadOnly( $domain, IDatabase $conn = null ) {
1670                 $cache = $this->wanCache;
1671                 $masterServer = $this->getServerName( $this->getWriterIndex() );
1672
1673                 return (bool)$cache->getWithSetCallback(
1674                         $cache->makeGlobalKey( __CLASS__, 'server-read-only', $masterServer ),
1675                         self::TTL_CACHE_READONLY,
1676                         function () use ( $domain, $conn ) {
1677                                 $old = $this->trxProfiler->setSilenced( true );
1678                                 try {
1679                                         $dbw = $conn ?: $this->getConnection( self::DB_MASTER, [], $domain );
1680                                         $readOnly = (int)$dbw->serverIsReadOnly();
1681                                         if ( !$conn ) {
1682                                                 $this->reuseConnection( $dbw );
1683                                         }
1684                                 } catch ( DBError $e ) {
1685                                         $readOnly = 0;
1686                                 }
1687                                 $this->trxProfiler->setSilenced( $old );
1688                                 return $readOnly;
1689                         },
1690                         [ 'pcTTL' => $cache::TTL_PROC_LONG, 'busyValue' => 0 ]
1691                 );
1692         }
1693
1694         public function allowLagged( $mode = null ) {
1695                 if ( $mode === null ) {
1696                         return $this->allowLagged;
1697                 }
1698                 $this->allowLagged = $mode;
1699
1700                 return $this->allowLagged;
1701         }
1702
1703         public function pingAll() {
1704                 $success = true;
1705                 $this->forEachOpenConnection( function ( IDatabase $conn ) use ( &$success ) {
1706                         if ( !$conn->ping() ) {
1707                                 $success = false;
1708                         }
1709                 } );
1710
1711                 return $success;
1712         }
1713
1714         public function forEachOpenConnection( $callback, array $params = [] ) {
1715                 foreach ( $this->conns as $connsByServer ) {
1716                         foreach ( $connsByServer as $serverConns ) {
1717                                 foreach ( $serverConns as $conn ) {
1718                                         $mergedParams = array_merge( [ $conn ], $params );
1719                                         call_user_func_array( $callback, $mergedParams );
1720                                 }
1721                         }
1722                 }
1723         }
1724
1725         public function forEachOpenMasterConnection( $callback, array $params = [] ) {
1726                 $masterIndex = $this->getWriterIndex();
1727                 foreach ( $this->conns as $connsByServer ) {
1728                         if ( isset( $connsByServer[$masterIndex] ) ) {
1729                                 /** @var IDatabase $conn */
1730                                 foreach ( $connsByServer[$masterIndex] as $conn ) {
1731                                         $mergedParams = array_merge( [ $conn ], $params );
1732                                         call_user_func_array( $callback, $mergedParams );
1733                                 }
1734                         }
1735                 }
1736         }
1737
1738         public function forEachOpenReplicaConnection( $callback, array $params = [] ) {
1739                 foreach ( $this->conns as $connsByServer ) {
1740                         foreach ( $connsByServer as $i => $serverConns ) {
1741                                 if ( $i === $this->getWriterIndex() ) {
1742                                         continue; // skip master
1743                                 }
1744                                 foreach ( $serverConns as $conn ) {
1745                                         $mergedParams = array_merge( [ $conn ], $params );
1746                                         call_user_func_array( $callback, $mergedParams );
1747                                 }
1748                         }
1749                 }
1750         }
1751
1752         public function getMaxLag( $domain = false ) {
1753                 $maxLag = -1;
1754                 $host = '';
1755                 $maxIndex = 0;
1756
1757                 if ( $this->getServerCount() <= 1 ) {
1758                         return [ $host, $maxLag, $maxIndex ]; // no replication = no lag
1759                 }
1760
1761                 $lagTimes = $this->getLagTimes( $domain );
1762                 foreach ( $lagTimes as $i => $lag ) {
1763                         if ( $this->loads[$i] > 0 && $lag > $maxLag ) {
1764                                 $maxLag = $lag;
1765                                 $host = $this->servers[$i]['host'];
1766                                 $maxIndex = $i;
1767                         }
1768                 }
1769
1770                 return [ $host, $maxLag, $maxIndex ];
1771         }
1772
1773         public function getLagTimes( $domain = false ) {
1774                 if ( $this->getServerCount() <= 1 ) {
1775                         return [ $this->getWriterIndex() => 0 ]; // no replication = no lag
1776                 }
1777
1778                 $knownLagTimes = []; // map of (server index => 0 seconds)
1779                 $indexesWithLag = [];
1780                 foreach ( $this->servers as $i => $server ) {
1781                         if ( empty( $server['is static'] ) ) {
1782                                 $indexesWithLag[] = $i; // DB server might have replication lag
1783                         } else {
1784                                 $knownLagTimes[$i] = 0; // DB server is a non-replicating and read-only archive
1785                         }
1786                 }
1787
1788                 return $this->getLoadMonitor()->getLagTimes( $indexesWithLag, $domain ) + $knownLagTimes;
1789         }
1790
1791         public function safeGetLag( IDatabase $conn ) {
1792                 if ( $this->getServerCount() <= 1 ) {
1793                         return 0;
1794                 } else {
1795                         return $conn->getLag();
1796                 }
1797         }
1798
1799         /**
1800          * @param IDatabase $conn
1801          * @param DBMasterPos|bool $pos
1802          * @param int|null $timeout
1803          * @return bool
1804          */
1805         public function safeWaitForMasterPos( IDatabase $conn, $pos = false, $timeout = null ) {
1806                 $timeout = max( 1, $timeout ?: $this->waitTimeout );
1807
1808                 if ( $this->getServerCount() <= 1 || !$conn->getLBInfo( 'replica' ) ) {
1809                         return true; // server is not a replica DB
1810                 }
1811
1812                 if ( !$pos ) {
1813                         // Get the current master position, opening a connection if needed
1814                         $masterConn = $this->getAnyOpenConnection( $this->getWriterIndex() );
1815                         if ( $masterConn ) {
1816                                 $pos = $masterConn->getMasterPos();
1817                         } else {
1818                                 $masterConn = $this->openConnection( $this->getWriterIndex(), self::DOMAIN_ANY );
1819                                 $pos = $masterConn->getMasterPos();
1820                                 $this->closeConnection( $masterConn );
1821                         }
1822                 }
1823
1824                 if ( $pos instanceof DBMasterPos ) {
1825                         $result = $conn->masterPosWait( $pos, $timeout );
1826                         if ( $result == -1 || is_null( $result ) ) {
1827                                 $msg = __METHOD__ . ': timed out waiting on {host} pos {pos}';
1828                                 $this->replLogger->warning( $msg, [
1829                                         'host' => $conn->getServer(),
1830                                         'pos' => $pos,
1831                                         'trace' => ( new RuntimeException() )->getTraceAsString()
1832                                 ] );
1833                                 $ok = false;
1834                         } else {
1835                                 $this->replLogger->debug( __METHOD__ . ': done waiting' );
1836                                 $ok = true;
1837                         }
1838                 } else {
1839                         $ok = false; // something is misconfigured
1840                         $this->replLogger->error(
1841                                 __METHOD__ . ': could not get master pos for {host}',
1842                                 [
1843                                         'host' => $conn->getServer(),
1844                                         'trace' => ( new RuntimeException() )->getTraceAsString()
1845                                 ]
1846                         );
1847                 }
1848
1849                 return $ok;
1850         }
1851
1852         public function setTransactionListener( $name, callable $callback = null ) {
1853                 if ( $callback ) {
1854                         $this->trxRecurringCallbacks[$name] = $callback;
1855                 } else {
1856                         unset( $this->trxRecurringCallbacks[$name] );
1857                 }
1858                 $this->forEachOpenMasterConnection(
1859                         function ( IDatabase $conn ) use ( $name, $callback ) {
1860                                 $conn->setTransactionListener( $name, $callback );
1861                         }
1862                 );
1863         }
1864
1865         public function setTableAliases( array $aliases ) {
1866                 $this->tableAliases = $aliases;
1867         }
1868
1869         public function setIndexAliases( array $aliases ) {
1870                 $this->indexAliases = $aliases;
1871         }
1872
1873         public function setDomainPrefix( $prefix ) {
1874                 // Find connections to explicit foreign domains still marked as in-use...
1875                 $domainsInUse = [];
1876                 $this->forEachOpenConnection( function ( IDatabase $conn ) use ( &$domainsInUse ) {
1877                         // Once reuseConnection() is called on a handle, its reference count goes from 1 to 0.
1878                         // Until then, it is still in use by the caller (explicitly or via DBConnRef scope).
1879                         if ( $conn->getLBInfo( 'foreignPoolRefCount' ) > 0 ) {
1880                                 $domainsInUse[] = $conn->getDomainID();
1881                         }
1882                 } );
1883
1884                 // Do not switch connections to explicit foreign domains unless marked as safe
1885                 if ( $domainsInUse ) {
1886                         $domains = implode( ', ', $domainsInUse );
1887                         throw new DBUnexpectedError( null,
1888                                 "Foreign domain connections are still in use ($domains)." );
1889                 }
1890
1891                 $oldDomain = $this->localDomain->getId();
1892                 $this->setLocalDomain( new DatabaseDomain(
1893                         $this->localDomain->getDatabase(),
1894                         $this->localDomain->getSchema(),
1895                         $prefix
1896                 ) );
1897
1898                 $this->forEachOpenConnection( function ( IDatabase $db ) use ( $prefix, $oldDomain ) {
1899                         if ( !$db->getLBInfo( 'foreign' ) ) {
1900                                 $db->tablePrefix( $prefix );
1901                         }
1902                 } );
1903         }
1904
1905         /**
1906          * @param DatabaseDomain $domain
1907          */
1908         private function setLocalDomain( DatabaseDomain $domain ) {
1909                 $this->localDomain = $domain;
1910                 // In case a caller assumes that the domain ID is simply <db>-<prefix>, which is almost
1911                 // always true, gracefully handle the case when they fail to account for escaping.
1912                 if ( $this->localDomain->getTablePrefix() != '' ) {
1913                         $this->localDomainIdAlias =
1914                                 $this->localDomain->getDatabase() . '-' . $this->localDomain->getTablePrefix();
1915                 } else {
1916                         $this->localDomainIdAlias = $this->localDomain->getDatabase();
1917                 }
1918         }
1919
1920         /**
1921          * Make PHP ignore user aborts/disconnects until the returned
1922          * value leaves scope. This returns null and does nothing in CLI mode.
1923          *
1924          * @return ScopedCallback|null
1925          */
1926         final protected function getScopedPHPBehaviorForCommit() {
1927                 if ( PHP_SAPI != 'cli' ) { // https://bugs.php.net/bug.php?id=47540
1928                         $old = ignore_user_abort( true ); // avoid half-finished operations
1929                         return new ScopedCallback( function () use ( $old ) {
1930                                 ignore_user_abort( $old );
1931                         } );
1932                 }
1933
1934                 return null;
1935         }
1936
1937         function __destruct() {
1938                 // Avoid connection leaks for sanity
1939                 $this->disable();
1940         }
1941 }
1942
1943 /**
1944  * @deprecated since 1.29
1945  */
1946 class_alias( LoadBalancer::class, 'LoadBalancer' );