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