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                 $this->localDomain = isset( $params['localDomain'] )
 150                         ? DatabaseDomain::newFromId( $params['localDomain'] )
 151                         : DatabaseDomain::newUnspecified();
 152                 // In case a caller assumes that the domain ID is simply <db>-<prefix>, which is almost
 153                 // always true, gracefully handle the case when they fail to account for escaping.
 154                 if ( $this->localDomain->getTablePrefix() != '' ) {
 155                         $this->localDomainIdAlias =
 156                                 $this->localDomain->getDatabase() . '-' . $this->localDomain->getTablePrefix();
 157                 } else {
 158                         $this->localDomainIdAlias = $this->localDomain->getDatabase();
 159                 }
 160
 161                 $this->mWaitTimeout = isset( $params['waitTimeout'] ) ? $params['waitTimeout'] : 10;
 162
 163                 $this->mReadIndex = -1;
 164                 $this->mConns = [
 165                         // Connection were transaction rounds may be applied
 166                         self::KEY_LOCAL => [],
 167                         self::KEY_FOREIGN_INUSE => [],
 168                         self::KEY_FOREIGN_FREE => [],
 169                         // Auto-committing counterpart connections that ignore transaction rounds
 170                         self::KEY_LOCAL_NOROUND => [],
 171                         self::KEY_FOREIGN_INUSE_NOROUND => [],
 172                         self::KEY_FOREIGN_FREE_NOROUND => []
 173                 ];
 174                 $this->mLoads = [];
 175                 $this->mWaitForPos = false;
 176                 $this->mAllowLagged = false;
 177
 178                 if ( isset( $params['readOnlyReason'] ) && is_string( $params['readOnlyReason'] ) ) {
 179                         $this->readOnlyReason = $params['readOnlyReason'];
 180                 }
 181
 182                 if ( isset( $params['maxLag'] ) ) {
 183                         $this->maxLag = $params['maxLag'];
 184                 }
 185
 186                 if ( isset( $params['loadMonitor'] ) ) {
 187                         $this->loadMonitorConfig = $params['loadMonitor'];
 188                 } else {
 189                         $this->loadMonitorConfig = [ 'class' => 'LoadMonitorNull' ];
 190                 }
 191                 $this->loadMonitorConfig += [ 'lagWarnThreshold' => $this->maxLag ];
 192
 193                 foreach ( $params['servers'] as $i => $server ) {
 194                         $this->mLoads[$i] = $server['load'];
 195                         if ( isset( $server['groupLoads'] ) ) {
 196                                 foreach ( $server['groupLoads'] as $group => $ratio ) {
 197                                         if ( !isset( $this->mGroupLoads[$group] ) ) {
 198                                                 $this->mGroupLoads[$group] = [];
 199                                         }
 200                                         $this->mGroupLoads[$group][$i] = $ratio;
 201                                 }
 202                         }
 203                 }
 204
 205                 if ( isset( $params['srvCache'] ) ) {
 206                         $this->srvCache = $params['srvCache'];
 207                 } else {
 208                         $this->srvCache = new EmptyBagOStuff();
 209                 }
 210                 if ( isset( $params['wanCache'] ) ) {
 211                         $this->wanCache = $params['wanCache'];
 212                 } else {
 213                         $this->wanCache = WANObjectCache::newEmpty();
 214                 }
 215                 $this->profiler = isset( $params['profiler'] ) ? $params['profiler'] : null;
 216                 if ( isset( $params['trxProfiler'] ) ) {
 217                         $this->trxProfiler = $params['trxProfiler'];
 218                 } else {
 219                         $this->trxProfiler = new TransactionProfiler();
 220                 }
 221
 222                 $this->errorLogger = isset( $params['errorLogger'] )
 223                         ? $params['errorLogger']
 224                         : function ( Exception $e ) {
 225                                 trigger_error( get_class( $e ) . ': ' . $e->getMessage(), E_USER_WARNING );
 226                         };
 227
 228                 foreach ( [ 'replLogger', 'connLogger', 'queryLogger', 'perfLogger' ] as $key ) {
 229                         $this->$key = isset( $params[$key] ) ? $params[$key] : new NullLogger();
 230                 }
 231
 232                 $this->host = isset( $params['hostname'] )
 233                         ? $params['hostname']
 234                         : ( gethostname() ?: 'unknown' );
 235                 $this->cliMode = isset( $params['cliMode'] ) ? $params['cliMode'] : PHP_SAPI === 'cli';
 236                 $this->agent = isset( $params['agent'] ) ? $params['agent'] : '';
 237
 238                 if ( isset( $params['chronologyProtector'] ) ) {
 239                         $this->chronProt = $params['chronologyProtector'];
 240                 }
 241         }
 242
 243         /**
 244          * Get a LoadMonitor instance
 245          *
 246          * @return ILoadMonitor
 247          */
 248         private function getLoadMonitor() {
 249                 if ( !isset( $this->loadMonitor ) ) {
 250                         $compat = [
 251                                 'LoadMonitor' => LoadMonitor::class,
 252                                 'LoadMonitorNull' => LoadMonitorNull::class,
 253                                 'LoadMonitorMySQL' => LoadMonitorMySQL::class,
 254                         ];
 255
 256                         $class = $this->loadMonitorConfig['class'];
 257                         if ( isset( $compat[$class] ) ) {
 258                                 $class = $compat[$class];
 259                         }
 260
 261                         $this->loadMonitor = new $class(
 262                                 $this, $this->srvCache, $this->wanCache, $this->loadMonitorConfig );
 263                         $this->loadMonitor->setLogger( $this->replLogger );
 264                 }
 265
 266                 return $this->loadMonitor;
 267         }
 268
 269         /**
 270          * @param array $loads
 271          * @param bool|string $domain Domain to get non-lagged for
 272          * @param int $maxLag Restrict the maximum allowed lag to this many seconds
 273          * @return bool|int|string
 274          */
 275         private function getRandomNonLagged( array $loads, $domain = false, $maxLag = INF ) {
 276                 $lags = $this->getLagTimes( $domain );
 277
 278                 # Unset excessively lagged servers
 279                 foreach ( $lags as $i => $lag ) {
 280                         if ( $i != 0 ) {
 281                                 # How much lag this server nominally is allowed to have
 282                                 $maxServerLag = isset( $this->mServers[$i]['max lag'] )
 283                                         ? $this->mServers[$i]['max lag']
 284                                         : $this->maxLag; // default
 285                                 # Constrain that futher by $maxLag argument
 286                                 $maxServerLag = min( $maxServerLag, $maxLag );
 287
 288                                 $host = $this->getServerName( $i );
 289                                 if ( $lag === false && !is_infinite( $maxServerLag ) ) {
 290                                         $this->replLogger->error(
 291                                                 "Server {host} is not replicating?", [ 'host' => $host ] );
 292                                         unset( $loads[$i] );
 293                                 } elseif ( $lag > $maxServerLag ) {
 294                                         $this->replLogger->info(
 295                                                 "Server {host} has {lag} seconds of lag (>= {maxlag})",
 296                                                 [ 'host' => $host, 'lag' => $lag, 'maxlag' => $maxServerLag ]
 297                                         );
 298                                         unset( $loads[$i] );
 299                                 }
 300                         }
 301                 }
 302
 303                 # Find out if all the replica DBs with non-zero load are lagged
 304                 $sum = 0;
 305                 foreach ( $loads as $load ) {
 306                         $sum += $load;
 307                 }
 308                 if ( $sum == 0 ) {
 309                         # No appropriate DB servers except maybe the master and some replica DBs with zero load
 310                         # Do NOT use the master
 311                         # Instead, this function will return false, triggering read-only mode,
 312                         # and a lagged replica DB will be used instead.
 313                         return false;
 314                 }
 315
 316                 if ( count( $loads ) == 0 ) {
 317                         return false;
 318                 }
 319
 320                 # Return a random representative of the remainder
 321                 return ArrayUtils::pickRandom( $loads );
 322         }
 323
 324         public function getReaderIndex( $group = false, $domain = false ) {
 325                 if ( count( $this->mServers ) == 1 ) {
 326                         // Skip the load balancing if there's only one server
 327                         return $this->getWriterIndex();
 328                 } elseif ( $group === false && $this->mReadIndex >= 0 ) {
 329                         // Shortcut if the generic reader index was already cached
 330                         return $this->mReadIndex;
 331                 }
 332
 333                 if ( $group !== false ) {
 334                         // Use the server weight array for this load group
 335                         if ( isset( $this->mGroupLoads[$group] ) ) {
 336                                 $loads = $this->mGroupLoads[$group];
 337                         } else {
 338                                 // No loads for this group, return false and the caller can use some other group
 339                                 $this->connLogger->info( __METHOD__ . ": no loads for group $group" );
 340
 341                                 return false;
 342                         }
 343                 } else {
 344                         // Use the generic load group
 345                         $loads = $this->mLoads;
 346                 }
 347
 348                 // Scale the configured load ratios according to each server's load and state
 349                 $this->getLoadMonitor()->scaleLoads( $loads, $domain );
 350
 351                 // Pick a server to use, accounting for weights, load, lag, and mWaitForPos
 352                 list( $i, $laggedReplicaMode ) = $this->pickReaderIndex( $loads, $domain );
 353                 if ( $i === false ) {
 354                         // Replica DB connection unsuccessful
 355                         return false;
 356                 }
 357
 358                 if ( $this->mWaitForPos && $i != $this->getWriterIndex() ) {
 359                         // Before any data queries are run, wait for the server to catch up to the
 360                         // specified position. This is used to improve session consistency. Note that
 361                         // when LoadBalancer::waitFor() sets mWaitForPos, the waiting triggers here,
 362                         // so update laggedReplicaMode as needed for consistency.
 363                         if ( !$this->doWait( $i ) ) {
 364                                 $laggedReplicaMode = true;
 365                         }
 366                 }
 367
 368                 if ( $this->mReadIndex <= 0 && $this->mLoads[$i] > 0 && $group === false ) {
 369                         // Cache the generic reader index for future ungrouped DB_REPLICA handles
 370                         $this->mReadIndex = $i;
 371                         // Record if the generic reader index is in "lagged replica DB" mode
 372                         if ( $laggedReplicaMode ) {
 373                                 $this->laggedReplicaMode = true;
 374                         }
 375                 }
 376
 377                 $serverName = $this->getServerName( $i );
 378                 $this->connLogger->debug( __METHOD__ . ": using server $serverName for group '$group'" );
 379
 380                 return $i;
 381         }
 382
 383         /**
 384          * @param array $loads List of server weights
 385          * @param string|bool $domain
 386          * @return array (reader index, lagged replica mode) or false on failure
 387          */
 388         private function pickReaderIndex( array $loads, $domain = false ) {
 389                 if ( !count( $loads ) ) {
 390                         throw new InvalidArgumentException( "Empty server array given to LoadBalancer" );
 391                 }
 392
 393                 /** @var int|bool $i Index of selected server */
 394                 $i = false;
 395                 /** @var bool $laggedReplicaMode Whether server is considered lagged */
 396                 $laggedReplicaMode = false;
 397
 398                 // Quickly look through the available servers for a server that meets criteria...
 399                 $currentLoads = $loads;
 400                 while ( count( $currentLoads ) ) {
 401                         if ( $this->mAllowLagged || $laggedReplicaMode ) {
 402                                 $i = ArrayUtils::pickRandom( $currentLoads );
 403                         } else {
 404                                 $i = false;
 405                                 if ( $this->mWaitForPos && $this->mWaitForPos->asOfTime() ) {
 406                                         // ChronologyProtecter sets mWaitForPos for session consistency.
 407                                         // This triggers doWait() after connect, so it's especially good to
 408                                         // avoid lagged servers so as to avoid excessive delay in that method.
 409                                         $ago = microtime( true ) - $this->mWaitForPos->asOfTime();
 410                                         // Aim for <= 1 second of waiting (being too picky can backfire)
 411                                         $i = $this->getRandomNonLagged( $currentLoads, $domain, $ago + 1 );
 412                                 }
 413                                 if ( $i === false ) {
 414                                         // Any server with less lag than it's 'max lag' param is preferable
 415                                         $i = $this->getRandomNonLagged( $currentLoads, $domain );
 416                                 }
 417                                 if ( $i === false && count( $currentLoads ) != 0 ) {
 418                                         // All replica DBs lagged. Switch to read-only mode
 419                                         $this->replLogger->error( "All replica DBs lagged. Switch to read-only mode" );
 420                                         $i = ArrayUtils::pickRandom( $currentLoads );
 421                                         $laggedReplicaMode = true;
 422                                 }
 423                         }
 424
 425                         if ( $i === false ) {
 426                                 // pickRandom() returned false.
 427                                 // This is permanent and means the configuration or the load monitor
 428                                 // wants us to return false.
 429                                 $this->connLogger->debug( __METHOD__ . ": pickRandom() returned false" );
 430
 431                                 return [ false, false ];
 432                         }
 433
 434                         $serverName = $this->getServerName( $i );
 435                         $this->connLogger->debug( __METHOD__ . ": Using reader #$i: $serverName..." );
 436
 437                         $conn = $this->openConnection( $i, $domain );
 438                         if ( !$conn ) {
 439                                 $this->connLogger->warning( __METHOD__ . ": Failed connecting to $i/$domain" );
 440                                 unset( $currentLoads[$i] ); // avoid this server next iteration
 441                                 $i = false;
 442                                 continue;
 443                         }
 444
 445                         // Decrement reference counter, we are finished with this connection.
 446                         // It will be incremented for the caller later.
 447                         if ( $domain !== false ) {
 448                                 $this->reuseConnection( $conn );
 449                         }
 450
 451                         // Return this server
 452                         break;
 453                 }
 454
 455                 // If all servers were down, quit now
 456                 if ( !count( $currentLoads ) ) {
 457                         $this->connLogger->error( "All servers down" );
 458                 }
 459
 460                 return [ $i, $laggedReplicaMode ];
 461         }
 462
 463         public function waitFor( $pos ) {
 464                 $oldPos = $this->mWaitForPos;
 465                 try {
 466                         $this->mWaitForPos = $pos;
 467                         // If a generic reader connection was already established, then wait now
 468                         $i = $this->mReadIndex;
 469                         if ( $i > 0 ) {
 470                                 if ( !$this->doWait( $i ) ) {
 471                                         $this->laggedReplicaMode = true;
 472                                 }
 473                         }
 474                 } finally {
 475                         // Restore the older position if it was higher since this is used for lag-protection
 476                         $this->setWaitForPositionIfHigher( $oldPos );
 477                 }
 478         }
 479
 480         public function waitForOne( $pos, $timeout = null ) {
 481                 $oldPos = $this->mWaitForPos;
 482                 try {
 483                         $this->mWaitForPos = $pos;
 484
 485                         $i = $this->mReadIndex;
 486                         if ( $i <= 0 ) {
 487                                 // Pick a generic replica DB if there isn't one yet
 488                                 $readLoads = $this->mLoads;
 489                                 unset( $readLoads[$this->getWriterIndex()] ); // replica DBs only
 490                                 $readLoads = array_filter( $readLoads ); // with non-zero load
 491                                 $i = ArrayUtils::pickRandom( $readLoads );
 492                         }
 493
 494                         if ( $i > 0 ) {
 495                                 $ok = $this->doWait( $i, true, $timeout );
 496                         } else {
 497                                 $ok = true; // no applicable loads
 498                         }
 499                 } finally {
 500                         # Restore the old position, as this is not used for lag-protection but for throttling
 501                         $this->mWaitForPos = $oldPos;
 502                 }
 503
 504                 return $ok;
 505         }
 506
 507         public function waitForAll( $pos, $timeout = null ) {
 508                 $oldPos = $this->mWaitForPos;
 509                 try {
 510                         $this->mWaitForPos = $pos;
 511                         $serverCount = count( $this->mServers );
 512
 513                         $ok = true;
 514                         for ( $i = 1; $i < $serverCount; $i++ ) {
 515                                 if ( $this->mLoads[$i] > 0 ) {
 516                                         $ok = $this->doWait( $i, true, $timeout ) && $ok;
 517                                 }
 518                         }
 519                 } finally {
 520                         # Restore the old position, as this is not used for lag-protection but for throttling
 521                         $this->mWaitForPos = $oldPos;
 522                 }
 523
 524                 return $ok;
 525         }
 526
 527         /**
 528          * @param DBMasterPos|bool $pos
 529          */
 530         private function setWaitForPositionIfHigher( $pos ) {
 531                 if ( !$pos ) {
 532                         return;
 533                 }
 534
 535                 if ( !$this->mWaitForPos || $pos->hasReached( $this->mWaitForPos ) ) {
 536                         $this->mWaitForPos = $pos;
 537                 }
 538         }
 539
 540         /**
 541          * @param int $i
 542          * @return IDatabase|bool
 543          */
 544         public function getAnyOpenConnection( $i ) {
 545                 foreach ( $this->mConns as $connsByServer ) {
 546                         if ( !empty( $connsByServer[$i] ) ) {
 547                                 /** @var IDatabase[] $serverConns */
 548                                 $serverConns = $connsByServer[$i];
 549
 550                                 return reset( $serverConns );
 551                         }
 552                 }
 553
 554                 return false;
 555         }
 556
 557         /**
 558          * Wait for a given replica DB to catch up to the master pos stored in $this
 559          * @param int $index Server index
 560          * @param bool $open Check the server even if a new connection has to be made
 561          * @param int $timeout Max seconds to wait; default is mWaitTimeout
 562          * @return bool
 563          */
 564         protected function doWait( $index, $open = false, $timeout = null ) {
 565                 $close = false; // close the connection afterwards
 566
 567                 // Check if we already know that the DB has reached this point
 568                 $server = $this->getServerName( $index );
 569                 $key = $this->srvCache->makeGlobalKey( __CLASS__, 'last-known-pos', $server, 'v1' );
 570                 /** @var DBMasterPos $knownReachedPos */
 571                 $knownReachedPos = $this->srvCache->get( $key );
 572                 if (
 573                         $knownReachedPos instanceof DBMasterPos &&
 574                         $knownReachedPos->hasReached( $this->mWaitForPos )
 575                 ) {
 576                         $this->replLogger->debug( __METHOD__ .
 577                                 ': replica DB {dbserver} known to be caught up (pos >= $knownReachedPos).',
 578                                 [ 'dbserver' => $server ] );
 579                         return true;
 580                 }
 581
 582                 // Find a connection to wait on, creating one if needed and allowed
 583                 $conn = $this->getAnyOpenConnection( $index );
 584                 if ( !$conn ) {
 585                         if ( !$open ) {
 586                                 $this->replLogger->debug( __METHOD__ . ': no connection open for {dbserver}',
 587                                         [ 'dbserver' => $server ] );
 588
 589                                 return false;
 590                         } else {
 591                                 $conn = $this->openConnection( $index, self::DOMAIN_ANY );
 592                                 if ( !$conn ) {
 593                                         $this->replLogger->warning( __METHOD__ . ': failed to connect to {dbserver}',
 594                                                 [ 'dbserver' => $server ] );
 595
 596                                         return false;
 597                                 }
 598                                 // Avoid connection spam in waitForAll() when connections
 599                                 // are made just for the sake of doing this lag check.
 600                                 $close = true;
 601                         }
 602                 }
 603
 604                 $this->replLogger->info( __METHOD__ . ': Waiting for replica DB {dbserver} to catch up...',
 605                         [ 'dbserver' => $server ] );
 606                 $timeout = $timeout ?: $this->mWaitTimeout;
 607                 $result = $conn->masterPosWait( $this->mWaitForPos, $timeout );
 608
 609                 if ( $result == -1 || is_null( $result ) ) {
 610                         // Timed out waiting for replica DB, use master instead
 611                         $this->replLogger->warning(
 612                                 __METHOD__ . ': Timed out waiting on {host} pos {pos}',
 613                                 [ 'host' => $server, 'pos' => $this->mWaitForPos ]
 614                         );
 615                         $ok = false;
 616                 } else {
 617                         $this->replLogger->info( __METHOD__ . ": Done" );
 618                         $ok = true;
 619                         // Remember that the DB reached this point
 620                         $this->srvCache->set( $key, $this->mWaitForPos, BagOStuff::TTL_DAY );
 621                 }
 622
 623                 if ( $close ) {
 624                         $this->closeConnection( $conn );
 625                 }
 626
 627                 return $ok;
 628         }
 629
 630         public function getConnection( $i, $groups = [], $domain = false, $flags = 0 ) {
 631                 if ( $i === null || $i === false ) {
 632                         throw new InvalidArgumentException( 'Attempt to call ' . __METHOD__ .
 633                                 ' with invalid server index' );
 634                 }
 635
 636                 if ( $this->localDomain->equals( $domain ) || $domain === $this->localDomainIdAlias ) {
 637                         $domain = false; // local connection requested
 638                 }
 639
 640                 $groups = ( $groups === false || $groups === [] )
 641                         ? [ false ] // check one "group": the generic pool
 642                         : (array)$groups;
 643
 644                 $masterOnly = ( $i == self::DB_MASTER || $i == $this->getWriterIndex() );
 645                 $oldConnsOpened = $this->connsOpened; // connections open now
 646
 647                 if ( $i == self::DB_MASTER ) {
 648                         if ( $flags & self::CONN_NO_WRITE ) {
 649                                 throw new InvalidArgumentException(
 650                                         'Cannot set CONN_NO_WRITE flag on master connection!'
 651                                 );
 652                         }
 653
 654                         $i = $this->getWriterIndex();
 655                 } else {
 656                         # Try to find an available server in any the query groups (in order)
 657                         foreach ( $groups as $group ) {
 658                                 $groupIndex = $this->getReaderIndex( $group, $domain );
 659                                 if ( $groupIndex !== false ) {
 660                                         $i = $groupIndex;
 661                                         break;
 662                                 }
 663                         }
 664
 665                         // Request no-write connection, even if $i == $this->getWriterIndex().
 666                         $flags |= self::CONN_NO_WRITE;
 667                 }
 668
 669                 # Operation-based index
 670                 if ( $i == self::DB_REPLICA ) {
 671                         $this->mLastError = 'Unknown error'; // reset error string
 672                         # Try the general server pool if $groups are unavailable.
 673                         $i = ( $groups === [ false ] )
 674                                 ? false // don't bother with this if that is what was tried above
 675                                 : $this->getReaderIndex( false, $domain );
 676                         # Couldn't find a working server in getReaderIndex()?
 677                         if ( $i === false ) {
 678                                 $this->mLastError = 'No working replica DB server: ' . $this->mLastError;
 679                                 // Throw an exception
 680                                 $this->reportConnectionError();
 681                                 return null; // not reached
 682                         }
 683
 684                         // Request no-write connection, even if $i == $this->getWriterIndex().
 685                         $flags |= self::CONN_NO_WRITE;
 686                 }
 687
 688                 # Now we have an explicit index into the servers array
 689                 $conn = $this->openConnection( $i, $domain, $flags );
 690                 if ( !$conn ) {
 691                         // Throw an exception
 692                         $this->reportConnectionError();
 693                         return null; // not reached
 694                 }
 695
 696                 # Profile any new connections that happen
 697                 if ( $this->connsOpened > $oldConnsOpened ) {
 698                         $host = $conn->getServer();
 699                         $dbname = $conn->getDBname();
 700                         $this->trxProfiler->recordConnection( $host, $dbname, $masterOnly );
 701                 }
 702
 703                 if ( $masterOnly ) {
 704                         # Make master-requested DB handles inherit any read-only mode setting
 705                         $conn->setLBInfo( 'readOnlyReason', $this->getReadOnlyReason( $domain, $conn ) );
 706                 }
 707
 708                 return $conn;
 709         }
 710
 711         public function reuseConnection( $conn ) {
 712                 $serverIndex = $conn->getLBInfo( 'serverIndex' );
 713                 $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 714                 if ( $serverIndex === null || $refCount === null ) {
 715                         /**
 716                          * This can happen in code like:
 717                          *   foreach ( $dbs as $db ) {
 718                          *     $conn = $lb->getConnection( $lb::DB_REPLICA, [], $db );
 719                          *     ...
 720                          *     $lb->reuseConnection( $conn );
 721                          *   }
 722                          * When a connection to the local DB is opened in this way, reuseConnection()
 723                          * should be ignored
 724                          */
 725                         return;
 726                 } elseif ( $conn instanceof DBConnRef ) {
 727                         // DBConnRef already handles calling reuseConnection() and only passes the live
 728                         // Database instance to this method. Any caller passing in a DBConnRef is broken.
 729                         $this->connLogger->error( __METHOD__ . ": got DBConnRef instance.\n" .
 730                                 ( new RuntimeException() )->getTraceAsString() );
 731
 732                         return;
 733                 }
 734
 735                 if ( $this->disabled ) {
 736                         return; // DBConnRef handle probably survived longer than the LoadBalancer
 737                 }
 738
 739                 if ( $conn->getLBInfo( 'autoCommitOnly' ) ) {
 740                         $connFreeKey = self::KEY_FOREIGN_FREE_NOROUND;
 741                         $connInUseKey = self::KEY_FOREIGN_INUSE_NOROUND;
 742                 } else {
 743                         $connFreeKey = self::KEY_FOREIGN_FREE;
 744                         $connInUseKey = self::KEY_FOREIGN_INUSE;
 745                 }
 746
 747                 $domain = $conn->getDomainID();
 748                 if ( !isset( $this->mConns[$connInUseKey][$serverIndex][$domain] ) ) {
 749                         throw new InvalidArgumentException( __METHOD__ .
 750                                 ": connection $serverIndex/$domain not found; it may have already been freed." );
 751                 } elseif ( $this->mConns[$connInUseKey][$serverIndex][$domain] !== $conn ) {
 752                         throw new InvalidArgumentException( __METHOD__ .
 753                                 ": connection $serverIndex/$domain mismatched; it may have already been freed." );
 754                 }
 755
 756                 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
 757                 if ( $refCount <= 0 ) {
 758                         $this->mConns[$connFreeKey][$serverIndex][$domain] = $conn;
 759                         unset( $this->mConns[$connInUseKey][$serverIndex][$domain] );
 760                         if ( !$this->mConns[$connInUseKey][$serverIndex] ) {
 761                                 unset( $this->mConns[$connInUseKey][$serverIndex] ); // clean up
 762                         }
 763                         $this->connLogger->debug( __METHOD__ . ": freed connection $serverIndex/$domain" );
 764                 } else {
 765                         $this->connLogger->debug( __METHOD__ .
 766                                 ": reference count for $serverIndex/$domain reduced to $refCount" );
 767                 }
 768         }
 769
 770         public function getConnectionRef( $db, $groups = [], $domain = false, $flags = 0 ) {
 771                 $domain = ( $domain !== false ) ? $domain : $this->localDomain;
 772
 773                 return new DBConnRef( $this, $this->getConnection( $db, $groups, $domain, $flags ) );
 774         }
 775
 776         public function getLazyConnectionRef( $db, $groups = [], $domain = false, $flags = 0 ) {
 777                 $domain = ( $domain !== false ) ? $domain : $this->localDomain;
 778
 779                 return new DBConnRef( $this, [ $db, $groups, $domain, $flags ] );
 780         }
 781
 782         public function getMaintenanceConnectionRef( $db, $groups = [], $domain = false, $flags = 0 ) {
 783                 $domain = ( $domain !== false ) ? $domain : $this->localDomain;
 784
 785                 return new MaintainableDBConnRef(
 786                         $this, $this->getConnection( $db, $groups, $domain, $flags ) );
 787         }
 788
 789         public function openConnection( $i, $domain = false, $flags = 0 ) {
 790                 if ( $this->localDomain->equals( $domain ) || $domain === $this->localDomainIdAlias ) {
 791                         $domain = false; // local connection requested
 792                 }
 793
 794                 if ( !$this->chronProtInitialized && $this->chronProt ) {
 795                         $this->connLogger->debug( __METHOD__ . ': calling initLB() before first connection.' );
 796                         // Load CP positions before connecting so that doWait() triggers later if needed
 797                         $this->chronProtInitialized = true;
 798                         $this->chronProt->initLB( $this );
 799                 }
 800
 801                 // Check if an auto-commit connection is being requested. If so, it will not reuse the
 802                 // main set of DB connections but rather its own pool since:
 803                 // a) those are usually set to implicitly use transaction rounds via DBO_TRX
 804                 // b) those must support the use of explicit transaction rounds via beginMasterChanges()
 805                 $autoCommit = ( ( $flags & self::CONN_TRX_AUTO ) == self::CONN_TRX_AUTO );
 806                 $noWrite = ( ( $flags & self::CONN_NO_WRITE ) == self::CONN_NO_WRITE );
 807
 808                 if ( $noWrite && $i === $this->getWriterIndex() ) {
 809                         // We can't disable writes on the master connection!
 810                         // TODO: Wrap the master connection, so write operations fail!
 811                         $noWrite = false;
 812                 }
 813
 814                 if ( $domain !== false ) {
 815                         // Connection is to a foreign domain
 816                         $conn = $this->openForeignConnection( $i, $domain, $flags );
 817                 } else {
 818                         // Connection is to the local domain
 819                         $connKey = $autoCommit ? self::KEY_LOCAL_NOROUND : self::KEY_LOCAL;
 820                         if ( isset( $this->mConns[$connKey][$i][0] ) ) {
 821                                 $conn = $this->mConns[$connKey][$i][0];
 822                         } else {
 823                                 if ( !isset( $this->mServers[$i] ) || !is_array( $this->mServers[$i] ) ) {
 824                                         throw new InvalidArgumentException( "No server with index '$i'." );
 825                                 }
 826                                 // Open a new connection
 827                                 $server = $this->mServers[$i];
 828                                 $server['serverIndex'] = $i;
 829                                 $server['noWrite'] = $noWrite;
 830                                 $server['autoCommitOnly'] = $autoCommit;
 831                                 $conn = $this->reallyOpenConnection( $server, false );
 832                                 $host = $this->getServerName( $i );
 833                                 if ( $conn->isOpen() ) {
 834                                         $this->connLogger->debug( "Connected to database $i at '$host'." );
 835                                         $this->mConns[$connKey][$i][0] = $conn;
 836                                 } else {
 837                                         $this->connLogger->warning( "Failed to connect to database $i at '$host'." );
 838                                         $this->errorConnection = $conn;
 839                                         $conn = false;
 840                                 }
 841                         }
 842                 }
 843
 844                 if ( $conn instanceof IDatabase && !$conn->isOpen() ) {
 845                         // Connection was made but later unrecoverably lost for some reason.
 846                         // Do not return a handle that will just throw exceptions on use,
 847                         // but let the calling code (e.g. getReaderIndex) try another server.
 848                         // See DatabaseMyslBase::ping() for how this can happen.
 849                         $this->errorConnection = $conn;
 850                         $conn = false;
 851                 }
 852
 853                 if ( $autoCommit && $conn instanceof IDatabase ) {
 854                         $conn->clearFlag( $conn::DBO_TRX ); // auto-commit mode
 855                 }
 856
 857                 return $conn;
 858         }
 859
 860         /**
 861          * Open a connection to a foreign DB, or return one if it is already open.
 862          *
 863          * Increments a reference count on the returned connection which locks the
 864          * connection to the requested domain. This reference count can be
 865          * decremented by calling reuseConnection().
 866          *
 867          * If a connection is open to the appropriate server already, but with the wrong
 868          * database, it will be switched to the right database and returned, as long as
 869          * it has been freed first with reuseConnection().
 870          *
 871          * On error, returns false, and the connection which caused the
 872          * error will be available via $this->errorConnection.
 873          *
 874          * @note If disable() was called on this LoadBalancer, this method will throw a DBAccessError.
 875          *
 876          * @param int $i Server index
 877          * @param string $domain Domain ID to open
 878          * @param int $flags Class CONN_* constant bitfield
 879          * @return Database
 880          */
 881         private function openForeignConnection( $i, $domain, $flags = 0 ) {
 882                 $domainInstance = DatabaseDomain::newFromId( $domain );
 883                 $dbName = $domainInstance->getDatabase();
 884                 $prefix = $domainInstance->getTablePrefix();
 885                 $autoCommit = ( ( $flags & self::CONN_TRX_AUTO ) == self::CONN_TRX_AUTO );
 886                 $noWrite = ( ( $flags & self::CONN_NO_WRITE ) == self::CONN_NO_WRITE );
 887
 888                 if ( $noWrite && $i === $this->getWriterIndex() ) {
 889                         // We can't disable writes on the master connection!
 890                         // TODO: Wrap the master connection, so write operations fail!
 891                         $noWrite = false;
 892                 }
 893
 894                 if ( $autoCommit ) {
 895                         $connFreeKey = self::KEY_FOREIGN_FREE_NOROUND;
 896                         $connInUseKey = self::KEY_FOREIGN_INUSE_NOROUND;
 897                 } else {
 898                         $connFreeKey = self::KEY_FOREIGN_FREE;
 899                         $connInUseKey = self::KEY_FOREIGN_INUSE;
 900                 }
 901
 902                 if ( isset( $this->mConns[$connInUseKey][$i][$domain] ) ) {
 903                         // Reuse an in-use connection for the same domain
 904                         $conn = $this->mConns[$connInUseKey][$i][$domain];
 905                         $this->connLogger->debug( __METHOD__ . ": reusing connection $i/$domain" );
 906                 } elseif ( isset( $this->mConns[$connFreeKey][$i][$domain] ) ) {
 907                         // Reuse a free connection for the same domain
 908                         $conn = $this->mConns[$connFreeKey][$i][$domain];
 909                         unset( $this->mConns[$connFreeKey][$i][$domain] );
 910                         $this->mConns[$connInUseKey][$i][$domain] = $conn;
 911                         $this->connLogger->debug( __METHOD__ . ": reusing free connection $i/$domain" );
 912                 } elseif ( !empty( $this->mConns[$connFreeKey][$i] ) ) {
 913                         // Reuse a free connection from another domain
 914                         $conn = reset( $this->mConns[$connFreeKey][$i] );
 915                         $oldDomain = key( $this->mConns[$connFreeKey][$i] );
 916                         // The empty string as a DB name means "don't care".
 917                         // DatabaseMysqlBase::open() already handle this on connection.
 918                         if ( strlen( $dbName ) && !$conn->selectDB( $dbName ) ) {
 919                                 $this->mLastError = "Error selecting database '$dbName' on server " .
 920                                         $conn->getServer() . " from client host {$this->host}";
 921                                 $this->errorConnection = $conn;
 922                                 $conn = false;
 923                         } else {
 924                                 $conn->tablePrefix( $prefix );
 925                                 unset( $this->mConns[$connFreeKey][$i][$oldDomain] );
 926                                 $this->mConns[$connInUseKey][$i][$domain] = $conn;
 927                                 $this->connLogger->debug( __METHOD__ .
 928                                         ": reusing free connection from $oldDomain for $domain" );
 929                         }
 930                 } else {
 931                         if ( !isset( $this->mServers[$i] ) || !is_array( $this->mServers[$i] ) ) {
 932                                 throw new InvalidArgumentException( "No server with index '$i'." );
 933                         }
 934                         // Open a new connection
 935                         $server = $this->mServers[$i];
 936                         $server['serverIndex'] = $i;
 937                         $server['foreignPoolRefCount'] = 0;
 938                         $server['foreign'] = true;
 939                         $server['autoCommitOnly'] = $autoCommit;
 940                         $server['noWrite'] = $noWrite;
 941                         $conn = $this->reallyOpenConnection( $server, $dbName );
 942                         if ( !$conn->isOpen() ) {
 943                                 $this->connLogger->warning( __METHOD__ . ": connection error for $i/$domain" );
 944                                 $this->errorConnection = $conn;
 945                                 $conn = false;
 946                         } else {
 947                                 $conn->tablePrefix( $prefix );
 948                                 $this->mConns[$connInUseKey][$i][$domain] = $conn;
 949                                 $this->connLogger->debug( __METHOD__ . ": opened new connection for $i/$domain" );
 950                         }
 951                 }
 952
 953                 // Increment reference count
 954                 if ( $conn instanceof IDatabase ) {
 955                         $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 956                         $conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
 957                 }
 958
 959                 return $conn;
 960         }
 961
 962         /**
 963          * Test if the specified index represents an open connection
 964          *
 965          * @param int $index Server index
 966          * @access private
 967          * @return bool
 968          */
 969         private function isOpen( $index ) {
 970                 if ( !is_integer( $index ) ) {
 971                         return false;
 972                 }
 973
 974                 return (bool)$this->getAnyOpenConnection( $index );
 975         }
 976
 977         /**
 978          * Really opens a connection. Uncached.
 979          * Returns a Database object whether or not the connection was successful.
 980          * @access private
 981          *
 982          * @param array $server
 983          * @param string|bool $dbNameOverride Use "" to not select any database
 984          * @return Database
 985          * @throws DBAccessError
 986          * @throws InvalidArgumentException
 987          */
 988         protected function reallyOpenConnection( array $server, $dbNameOverride = false ) {
 989                 if ( $this->disabled ) {
 990                         throw new DBAccessError();
 991                 }
 992
 993                 if ( $dbNameOverride !== false ) {
 994                         $server['dbname'] = $dbNameOverride;
 995                 }
 996
 997                 // Let the handle know what the cluster master is (e.g. "db1052")
 998                 $masterName = $this->getServerName( $this->getWriterIndex() );
 999                 $server['clusterMasterHost'] = $masterName;
1000
1001                 // Log when many connection are made on requests
1002                 if ( ++$this->connsOpened >= self::CONN_HELD_WARN_THRESHOLD ) {
1003                         $this->perfLogger->warning( __METHOD__ . ": " .
1004                                 "{$this->connsOpened}+ connections made (master=$masterName)" );
1005                 }
1006
1007                 $server['srvCache'] = $this->srvCache;
1008                 // Set loggers and profilers
1009                 $server['connLogger'] = $this->connLogger;
1010                 $server['queryLogger'] = $this->queryLogger;
1011                 $server['errorLogger'] = $this->errorLogger;
1012                 $server['profiler'] = $this->profiler;
1013                 $server['trxProfiler'] = $this->trxProfiler;
1014                 // Use the same agent and PHP mode for all DB handles
1015                 $server['cliMode'] = $this->cliMode;
1016                 $server['agent'] = $this->agent;
1017                 // Use DBO_DEFAULT flags by default for LoadBalancer managed databases. Assume that the
1018                 // application calls LoadBalancer::commitMasterChanges() before the PHP script completes.
1019                 $server['flags'] = isset( $server['flags'] ) ? $server['flags'] : IDatabase::DBO_DEFAULT;
1020
1021                 // Create a live connection object
1022                 try {
1023                         $db = Database::factory( $server['type'], $server );
1024                 } catch ( DBConnectionError $e ) {
1025                         // FIXME: This is probably the ugliest thing I have ever done to
1026                         // PHP. I'm half-expecting it to segfault, just out of disgust. -- TS
1027                         $db = $e->db;
1028                 }
1029
1030                 $db->setLBInfo( $server );
1031                 $db->setLazyMasterHandle(
1032                         $this->getLazyConnectionRef( self::DB_MASTER, [], $db->getDomainID() )
1033                 );
1034                 $db->setTableAliases( $this->tableAliases );
1035
1036                 if ( $server['serverIndex'] === $this->getWriterIndex() ) {
1037                         if ( $this->trxRoundId !== false ) {
1038                                 $this->applyTransactionRoundFlags( $db );
1039                         }
1040                         foreach ( $this->trxRecurringCallbacks as $name => $callback ) {
1041                                 $db->setTransactionListener( $name, $callback );
1042                         }
1043                 }
1044
1045                 return $db;
1046         }
1047
1048         /**
1049          * @throws DBConnectionError
1050          */
1051         private function reportConnectionError() {
1052                 $conn = $this->errorConnection; // the connection which caused the error
1053                 $context = [
1054                         'method' => __METHOD__,
1055                         'last_error' => $this->mLastError,
1056                 ];
1057
1058                 if ( $conn instanceof IDatabase ) {
1059                         $context['db_server'] = $conn->getServer();
1060                         $this->connLogger->warning(
1061                                 "Connection error: {last_error} ({db_server})",
1062                                 $context
1063                         );
1064
1065                         // throws DBConnectionError
1066                         $conn->reportConnectionError( "{$this->mLastError} ({$context['db_server']})" );
1067                 } else {
1068                         // No last connection, probably due to all servers being too busy
1069                         $this->connLogger->error(
1070                                 "LB failure with no last connection. Connection error: {last_error}",
1071                                 $context
1072                         );
1073
1074                         // If all servers were busy, mLastError will contain something sensible
1075                         throw new DBConnectionError( null, $this->mLastError );
1076                 }
1077         }
1078
1079         public function getWriterIndex() {
1080                 return 0;
1081         }
1082
1083         public function haveIndex( $i ) {
1084                 return array_key_exists( $i, $this->mServers );
1085         }
1086
1087         public function isNonZeroLoad( $i ) {
1088                 return array_key_exists( $i, $this->mServers ) && $this->mLoads[$i] != 0;
1089         }
1090
1091         public function getServerCount() {
1092                 return count( $this->mServers );
1093         }
1094
1095         public function getServerName( $i ) {
1096                 if ( isset( $this->mServers[$i]['hostName'] ) ) {
1097                         $name = $this->mServers[$i]['hostName'];
1098                 } elseif ( isset( $this->mServers[$i]['host'] ) ) {
1099                         $name = $this->mServers[$i]['host'];
1100                 } else {
1101                         $name = '';
1102                 }
1103
1104                 return ( $name != '' ) ? $name : 'localhost';
1105         }
1106
1107         public function getServerType( $i ) {
1108                 return isset( $this->mServers[$i]['type'] ) ? $this->mServers[$i]['type'] : 'unknown';
1109         }
1110
1111         /**
1112          * @deprecated Since 1.30, no alternative
1113          */
1114         public function getServerInfo( $i ) {
1115                 wfDeprecated( __METHOD__, '1.30' );
1116                 if ( isset( $this->mServers[$i] ) ) {
1117                         return $this->mServers[$i];
1118                 } else {
1119                         return false;
1120                 }
1121         }
1122
1123         /**
1124          * @deprecated Since 1.30, construct new object
1125          */
1126         public function setServerInfo( $i, array $serverInfo ) {
1127                 wfDeprecated( __METHOD__, '1.30' );
1128                 $this->mServers[$i] = $serverInfo;
1129         }
1130
1131         public function getMasterPos() {
1132                 # If this entire request was served from a replica DB without opening a connection to the
1133                 # master (however unlikely that may be), then we can fetch the position from the replica DB.
1134                 $masterConn = $this->getAnyOpenConnection( $this->getWriterIndex() );
1135                 if ( !$masterConn ) {
1136                         $serverCount = count( $this->mServers );
1137                         for ( $i = 1; $i < $serverCount; $i++ ) {
1138                                 $conn = $this->getAnyOpenConnection( $i );
1139                                 if ( $conn ) {
1140                                         return $conn->getReplicaPos();
1141                                 }
1142                         }
1143                 } else {
1144                         return $masterConn->getMasterPos();
1145                 }
1146
1147                 return false;
1148         }
1149
1150         public function disable() {
1151                 $this->closeAll();
1152                 $this->disabled = true;
1153         }
1154
1155         public function closeAll() {
1156                 $this->forEachOpenConnection( function ( IDatabase $conn ) {
1157                         $host = $conn->getServer();
1158                         $this->connLogger->debug( "Closing connection to database '$host'." );
1159                         $conn->close();
1160                 } );
1161
1162                 $this->mConns = [
1163                         self::KEY_LOCAL => [],
1164                         self::KEY_FOREIGN_INUSE => [],
1165                         self::KEY_FOREIGN_FREE => [],
1166                         self::KEY_LOCAL_NOROUND => [],
1167                         self::KEY_FOREIGN_INUSE_NOROUND => [],
1168                         self::KEY_FOREIGN_FREE_NOROUND => []
1169                 ];
1170                 $this->connsOpened = 0;
1171         }
1172
1173         public function closeConnection( IDatabase $conn ) {
1174                 $serverIndex = $conn->getLBInfo( 'serverIndex' ); // second index level of mConns
1175                 foreach ( $this->mConns as $type => $connsByServer ) {
1176                         if ( !isset( $connsByServer[$serverIndex] ) ) {
1177                                 continue;
1178                         }
1179
1180                         foreach ( $connsByServer[$serverIndex] as $i => $trackedConn ) {
1181                                 if ( $conn === $trackedConn ) {
1182                                         $host = $this->getServerName( $i );
1183                                         $this->connLogger->debug( "Closing connection to database $i at '$host'." );
1184                                         unset( $this->mConns[$type][$serverIndex][$i] );
1185                                         --$this->connsOpened;
1186                                         break 2;
1187                                 }
1188                         }
1189                 }
1190
1191                 $conn->close();
1192         }
1193
1194         public function commitAll( $fname = __METHOD__ ) {
1195                 $failures = [];
1196
1197                 $restore = ( $this->trxRoundId !== false );
1198                 $this->trxRoundId = false;
1199                 $this->forEachOpenConnection(
1200                         function ( IDatabase $conn ) use ( $fname, $restore, &$failures ) {
1201                                 try {
1202                                         $conn->commit( $fname, $conn::FLUSHING_ALL_PEERS );
1203                                 } catch ( DBError $e ) {
1204                                         call_user_func( $this->errorLogger, $e );
1205                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1206                                 }
1207                                 if ( $restore && $conn->getLBInfo( 'master' ) ) {
1208                                         $this->undoTransactionRoundFlags( $conn );
1209                                 }
1210                         }
1211                 );
1212
1213                 if ( $failures ) {
1214                         throw new DBExpectedError(
1215                                 null,
1216                                 "Commit failed on server(s) " . implode( "\n", array_unique( $failures ) )
1217                         );
1218                 }
1219         }
1220
1221         public function finalizeMasterChanges() {
1222                 $this->forEachOpenMasterConnection( function ( Database $conn ) {
1223                         // Any error should cause all DB transactions to be rolled back together
1224                         $conn->setTrxEndCallbackSuppression( false );
1225                         $conn->runOnTransactionPreCommitCallbacks();
1226                         // Defer post-commit callbacks until COMMIT finishes for all DBs
1227                         $conn->setTrxEndCallbackSuppression( true );
1228                 } );
1229         }
1230
1231         public function approveMasterChanges( array $options ) {
1232                 $limit = isset( $options['maxWriteDuration'] ) ? $options['maxWriteDuration'] : 0;
1233                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( $limit ) {
1234                         // If atomic sections or explicit transactions are still open, some caller must have
1235                         // caught an exception but failed to properly rollback any changes. Detect that and
1236                         // throw and error (causing rollback).
1237                         if ( $conn->explicitTrxActive() ) {
1238                                 throw new DBTransactionError(
1239                                         $conn,
1240                                         "Explicit transaction still active. A caller may have caught an error."
1241                                 );
1242                         }
1243                         // Assert that the time to replicate the transaction will be sane.
1244                         // If this fails, then all DB transactions will be rollback back together.
1245                         $time = $conn->pendingWriteQueryDuration( $conn::ESTIMATE_DB_APPLY );
1246                         if ( $limit > 0 && $time > $limit ) {
1247                                 throw new DBTransactionSizeError(
1248                                         $conn,
1249                                         "Transaction spent $time second(s) in writes, exceeding the limit of $limit.",
1250                                         [ $time, $limit ]
1251                                 );
1252                         }
1253                         // If a connection sits idle while slow queries execute on another, that connection
1254                         // may end up dropped before the commit round is reached. Ping servers to detect this.
1255                         if ( $conn->writesOrCallbacksPending() && !$conn->ping() ) {
1256                                 throw new DBTransactionError(
1257                                         $conn,
1258                                         "A connection to the {$conn->getDBname()} database was lost before commit."
1259                                 );
1260                         }
1261                 } );
1262         }
1263
1264         public function beginMasterChanges( $fname = __METHOD__ ) {
1265                 if ( $this->trxRoundId !== false ) {
1266                         throw new DBTransactionError(
1267                                 null,
1268                                 "$fname: Transaction round '{$this->trxRoundId}' already started."
1269                         );
1270                 }
1271                 $this->trxRoundId = $fname;
1272
1273                 $failures = [];
1274                 $this->forEachOpenMasterConnection(
1275                         function ( Database $conn ) use ( $fname, &$failures ) {
1276                                 $conn->setTrxEndCallbackSuppression( true );
1277                                 try {
1278                                         $conn->flushSnapshot( $fname );
1279                                 } catch ( DBError $e ) {
1280                                         call_user_func( $this->errorLogger, $e );
1281                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1282                                 }
1283                                 $conn->setTrxEndCallbackSuppression( false );
1284                                 $this->applyTransactionRoundFlags( $conn );
1285                         }
1286                 );
1287
1288                 if ( $failures ) {
1289                         throw new DBExpectedError(
1290                                 null,
1291                                 "$fname: Flush failed on server(s) " . implode( "\n", array_unique( $failures ) )
1292                         );
1293                 }
1294         }
1295
1296         public function commitMasterChanges( $fname = __METHOD__ ) {
1297                 $failures = [];
1298
1299                 /** @noinspection PhpUnusedLocalVariableInspection */
1300                 $scope = $this->getScopedPHPBehaviorForCommit(); // try to ignore client aborts
1301
1302                 $restore = ( $this->trxRoundId !== false );
1303                 $this->trxRoundId = false;
1304                 $this->forEachOpenMasterConnection(
1305                         function ( IDatabase $conn ) use ( $fname, $restore, &$failures ) {
1306                                 try {
1307                                         if ( $conn->writesOrCallbacksPending() ) {
1308                                                 $conn->commit( $fname, $conn::FLUSHING_ALL_PEERS );
1309                                         } elseif ( $restore ) {
1310                                                 $conn->flushSnapshot( $fname );
1311                                         }
1312                                 } catch ( DBError $e ) {
1313                                         call_user_func( $this->errorLogger, $e );
1314                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1315                                 }
1316                                 if ( $restore ) {
1317                                         $this->undoTransactionRoundFlags( $conn );
1318                                 }
1319                         }
1320                 );
1321
1322                 if ( $failures ) {
1323                         throw new DBExpectedError(
1324                                 null,
1325                                 "$fname: Commit failed on server(s) " . implode( "\n", array_unique( $failures ) )
1326                         );
1327                 }
1328         }
1329
1330         public function runMasterPostTrxCallbacks( $type ) {
1331                 $e = null; // first exception
1332                 $this->forEachOpenMasterConnection( function ( Database $conn ) use ( $type, &$e ) {
1333                         $conn->setTrxEndCallbackSuppression( false );
1334                         if ( $conn->writesOrCallbacksPending() ) {
1335                                 // This happens if onTransactionIdle() callbacks leave callbacks on *another* DB
1336                                 // (which finished its callbacks already). Warn and recover in this case. Let the
1337                                 // callbacks run in the final commitMasterChanges() in LBFactory::shutdown().
1338                                 $this->queryLogger->info( __METHOD__ . ": found writes/callbacks pending." );
1339                                 return;
1340                         } elseif ( $conn->trxLevel() ) {
1341                                 // This happens for single-DB setups where DB_REPLICA uses the master DB,
1342                                 // thus leaving an implicit read-only transaction open at this point. It
1343                                 // also happens if onTransactionIdle() callbacks leave implicit transactions
1344                                 // open on *other* DBs (which is slightly improper). Let these COMMIT on the
1345                                 // next call to commitMasterChanges(), possibly in LBFactory::shutdown().
1346                                 return;
1347                         }
1348                         try {
1349                                 $conn->runOnTransactionIdleCallbacks( $type );
1350                         } catch ( Exception $ex ) {
1351                                 $e = $e ?: $ex;
1352                         }
1353                         try {
1354                                 $conn->runTransactionListenerCallbacks( $type );
1355                         } catch ( Exception $ex ) {
1356                                 $e = $e ?: $ex;
1357                         }
1358                 } );
1359
1360                 return $e;
1361         }
1362
1363         public function rollbackMasterChanges( $fname = __METHOD__ ) {
1364                 $restore = ( $this->trxRoundId !== false );
1365                 $this->trxRoundId = false;
1366                 $this->forEachOpenMasterConnection(
1367                         function ( IDatabase $conn ) use ( $fname, $restore ) {
1368                                 if ( $conn->writesOrCallbacksPending() ) {
1369                                         $conn->rollback( $fname, $conn::FLUSHING_ALL_PEERS );
1370                                 }
1371                                 if ( $restore ) {
1372                                         $this->undoTransactionRoundFlags( $conn );
1373                                 }
1374                         }
1375                 );
1376         }
1377
1378         public function suppressTransactionEndCallbacks() {
1379                 $this->forEachOpenMasterConnection( function ( Database $conn ) {
1380                         $conn->setTrxEndCallbackSuppression( true );
1381                 } );
1382         }
1383
1384         /**
1385          * @param IDatabase $conn
1386          */
1387         private function applyTransactionRoundFlags( IDatabase $conn ) {
1388                 if ( $conn->getLBInfo( 'autoCommitOnly' ) ) {
1389                         return; // transaction rounds do not apply to these connections
1390                 }
1391
1392                 if ( $conn->getFlag( $conn::DBO_DEFAULT ) ) {
1393                         // DBO_TRX is controlled entirely by CLI mode presence with DBO_DEFAULT.
1394                         // Force DBO_TRX even in CLI mode since a commit round is expected soon.
1395                         $conn->setFlag( $conn::DBO_TRX, $conn::REMEMBER_PRIOR );
1396                         // If config has explicitly requested DBO_TRX be either on or off by not
1397                         // setting DBO_DEFAULT, then respect that. Forcing no transactions is useful
1398                         // for things like blob stores (ExternalStore) which want auto-commit mode.
1399                 }
1400         }
1401
1402         /**
1403          * @param IDatabase $conn
1404          */
1405         private function undoTransactionRoundFlags( IDatabase $conn ) {
1406                 if ( $conn->getLBInfo( 'autoCommitOnly' ) ) {
1407                         return; // transaction rounds do not apply to these connections
1408                 }
1409
1410                 if ( $conn->getFlag( $conn::DBO_DEFAULT ) ) {
1411                         $conn->restoreFlags( $conn::RESTORE_PRIOR );
1412                 }
1413         }
1414
1415         public function flushReplicaSnapshots( $fname = __METHOD__ ) {
1416                 $this->forEachOpenReplicaConnection( function ( IDatabase $conn ) {
1417                         $conn->flushSnapshot( __METHOD__ );
1418                 } );
1419         }
1420
1421         public function hasMasterConnection() {
1422                 return $this->isOpen( $this->getWriterIndex() );
1423         }
1424
1425         public function hasMasterChanges() {
1426                 $pending = 0;
1427                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$pending ) {
1428                         $pending |= $conn->writesOrCallbacksPending();
1429                 } );
1430
1431                 return (bool)$pending;
1432         }
1433
1434         public function lastMasterChangeTimestamp() {
1435                 $lastTime = false;
1436                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$lastTime ) {
1437                         $lastTime = max( $lastTime, $conn->lastDoneWrites() );
1438                 } );
1439
1440                 return $lastTime;
1441         }
1442
1443         public function hasOrMadeRecentMasterChanges( $age = null ) {
1444                 $age = ( $age === null ) ? $this->mWaitTimeout : $age;
1445
1446                 return ( $this->hasMasterChanges()
1447                         || $this->lastMasterChangeTimestamp() > microtime( true ) - $age );
1448         }
1449
1450         public function pendingMasterChangeCallers() {
1451                 $fnames = [];
1452                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$fnames ) {
1453                         $fnames = array_merge( $fnames, $conn->pendingWriteCallers() );
1454                 } );
1455
1456                 return $fnames;
1457         }
1458
1459         public function getLaggedReplicaMode( $domain = false ) {
1460                 // No-op if there is only one DB (also avoids recursion)
1461                 if ( !$this->laggedReplicaMode && $this->getServerCount() > 1 ) {
1462                         try {
1463                                 // See if laggedReplicaMode gets set
1464                                 $conn = $this->getConnection( self::DB_REPLICA, false, $domain );
1465                                 $this->reuseConnection( $conn );
1466                         } catch ( DBConnectionError $e ) {
1467                                 // Avoid expensive re-connect attempts and failures
1468                                 $this->allReplicasDownMode = true;
1469                                 $this->laggedReplicaMode = true;
1470                         }
1471                 }
1472
1473                 return $this->laggedReplicaMode;
1474         }
1475
1476         /**
1477          * @param bool $domain
1478          * @return bool
1479          * @deprecated 1.28; use getLaggedReplicaMode()
1480          */
1481         public function getLaggedSlaveMode( $domain = false ) {
1482                 return $this->getLaggedReplicaMode( $domain );
1483         }
1484
1485         public function laggedReplicaUsed() {
1486                 return $this->laggedReplicaMode;
1487         }
1488
1489         /**
1490          * @return bool
1491          * @since 1.27
1492          * @deprecated Since 1.28; use laggedReplicaUsed()
1493          */
1494         public function laggedSlaveUsed() {
1495                 return $this->laggedReplicaUsed();
1496         }
1497
1498         public function getReadOnlyReason( $domain = false, IDatabase $conn = null ) {
1499                 if ( $this->readOnlyReason !== false ) {
1500                         return $this->readOnlyReason;
1501                 } elseif ( $this->getLaggedReplicaMode( $domain ) ) {
1502                         if ( $this->allReplicasDownMode ) {
1503                                 return 'The database has been automatically locked ' .
1504                                         'until the replica database servers become available';
1505                         } else {
1506                                 return 'The database has been automatically locked ' .
1507                                         'while the replica database servers catch up to the master.';
1508                         }
1509                 } elseif ( $this->masterRunningReadOnly( $domain, $conn ) ) {
1510                         return 'The database master is running in read-only mode.';
1511                 }
1512
1513                 return false;
1514         }
1515
1516         /**
1517          * @param string $domain Domain ID, or false for the current domain
1518          * @param IDatabase|null $conn DB master connectionl used to avoid loops [optional]
1519          * @return bool
1520          */
1521         private function masterRunningReadOnly( $domain, IDatabase $conn = null ) {
1522                 $cache = $this->wanCache;
1523                 $masterServer = $this->getServerName( $this->getWriterIndex() );
1524
1525                 return (bool)$cache->getWithSetCallback(
1526                         $cache->makeGlobalKey( __CLASS__, 'server-read-only', $masterServer ),
1527                         self::TTL_CACHE_READONLY,
1528                         function () use ( $domain, $conn ) {
1529                                 $old = $this->trxProfiler->setSilenced( true );
1530                                 try {
1531                                         $dbw = $conn ?: $this->getConnection( self::DB_MASTER, [], $domain );
1532                                         $readOnly = (int)$dbw->serverIsReadOnly();
1533                                         if ( !$conn ) {
1534                                                 $this->reuseConnection( $dbw );
1535                                         }
1536                                 } catch ( DBError $e ) {
1537                                         $readOnly = 0;
1538                                 }
1539                                 $this->trxProfiler->setSilenced( $old );
1540                                 return $readOnly;
1541                         },
1542                         [ 'pcTTL' => $cache::TTL_PROC_LONG, 'busyValue' => 0 ]
1543                 );
1544         }
1545
1546         public function allowLagged( $mode = null ) {
1547                 if ( $mode === null ) {
1548                         return $this->mAllowLagged;
1549                 }
1550                 $this->mAllowLagged = $mode;
1551
1552                 return $this->mAllowLagged;
1553         }
1554
1555         public function pingAll() {
1556                 $success = true;
1557                 $this->forEachOpenConnection( function ( IDatabase $conn ) use ( &$success ) {
1558                         if ( !$conn->ping() ) {
1559                                 $success = false;
1560                         }
1561                 } );
1562
1563                 return $success;
1564         }
1565
1566         public function forEachOpenConnection( $callback, array $params = [] ) {
1567                 foreach ( $this->mConns as $connsByServer ) {
1568                         foreach ( $connsByServer as $serverConns ) {
1569                                 foreach ( $serverConns as $conn ) {
1570                                         $mergedParams = array_merge( [ $conn ], $params );
1571                                         call_user_func_array( $callback, $mergedParams );
1572                                 }
1573                         }
1574                 }
1575         }
1576
1577         public function forEachOpenMasterConnection( $callback, array $params = [] ) {
1578                 $masterIndex = $this->getWriterIndex();
1579                 foreach ( $this->mConns as $connsByServer ) {
1580                         if ( isset( $connsByServer[$masterIndex] ) ) {
1581                                 /** @var IDatabase $conn */
1582                                 foreach ( $connsByServer[$masterIndex] as $conn ) {
1583                                         $mergedParams = array_merge( [ $conn ], $params );
1584                                         call_user_func_array( $callback, $mergedParams );
1585                                 }
1586                         }
1587                 }
1588         }
1589
1590         public function forEachOpenReplicaConnection( $callback, array $params = [] ) {
1591                 foreach ( $this->mConns as $connsByServer ) {
1592                         foreach ( $connsByServer as $i => $serverConns ) {
1593                                 if ( $i === $this->getWriterIndex() ) {
1594                                         continue; // skip master
1595                                 }
1596                                 foreach ( $serverConns as $conn ) {
1597                                         $mergedParams = array_merge( [ $conn ], $params );
1598                                         call_user_func_array( $callback, $mergedParams );
1599                                 }
1600                         }
1601                 }
1602         }
1603
1604         public function getMaxLag( $domain = false ) {
1605                 $maxLag = -1;
1606                 $host = '';
1607                 $maxIndex = 0;
1608
1609                 if ( $this->getServerCount() <= 1 ) {
1610                         return [ $host, $maxLag, $maxIndex ]; // no replication = no lag
1611                 }
1612
1613                 $lagTimes = $this->getLagTimes( $domain );
1614                 foreach ( $lagTimes as $i => $lag ) {
1615                         if ( $this->mLoads[$i] > 0 && $lag > $maxLag ) {
1616                                 $maxLag = $lag;
1617                                 $host = $this->mServers[$i]['host'];
1618                                 $maxIndex = $i;
1619                         }
1620                 }
1621
1622                 return [ $host, $maxLag, $maxIndex ];
1623         }
1624
1625         public function getLagTimes( $domain = false ) {
1626                 if ( $this->getServerCount() <= 1 ) {
1627                         return [ $this->getWriterIndex() => 0 ]; // no replication = no lag
1628                 }
1629
1630                 $knownLagTimes = []; // map of (server index => 0 seconds)
1631                 $indexesWithLag = [];
1632                 foreach ( $this->mServers as $i => $server ) {
1633                         if ( empty( $server['is static'] ) ) {
1634                                 $indexesWithLag[] = $i; // DB server might have replication lag
1635                         } else {
1636                                 $knownLagTimes[$i] = 0; // DB server is a non-replicating and read-only archive
1637                         }
1638                 }
1639
1640                 return $this->getLoadMonitor()->getLagTimes( $indexesWithLag, $domain ) + $knownLagTimes;
1641         }
1642
1643         public function safeGetLag( IDatabase $conn ) {
1644                 if ( $this->getServerCount() <= 1 ) {
1645                         return 0;
1646                 } else {
1647                         return $conn->getLag();
1648                 }
1649         }
1650
1651         /**
1652          * @param IDatabase $conn
1653          * @param DBMasterPos|bool $pos
1654          * @param int $timeout
1655          * @return bool
1656          */
1657         public function safeWaitForMasterPos( IDatabase $conn, $pos = false, $timeout = 10 ) {
1658                 if ( $this->getServerCount() <= 1 || !$conn->getLBInfo( 'replica' ) ) {
1659                         return true; // server is not a replica DB
1660                 }
1661
1662                 if ( !$pos ) {
1663                         // Get the current master position, opening a connection if needed
1664                         $masterConn = $this->getAnyOpenConnection( $this->getWriterIndex() );
1665                         if ( $masterConn ) {
1666                                 $pos = $masterConn->getMasterPos();
1667                         } else {
1668                                 $masterConn = $this->openConnection( $this->getWriterIndex(), self::DOMAIN_ANY );
1669                                 $pos = $masterConn->getMasterPos();
1670                                 $this->closeConnection( $masterConn );
1671                         }
1672                 }
1673
1674                 if ( $pos instanceof DBMasterPos ) {
1675                         $result = $conn->masterPosWait( $pos, $timeout );
1676                         if ( $result == -1 || is_null( $result ) ) {
1677                                 $msg = __METHOD__ . ': Timed out waiting on {host} pos {pos}';
1678                                 $this->replLogger->warning( $msg,
1679                                         [ 'host' => $conn->getServer(), 'pos' => $pos ] );
1680                                 $ok = false;
1681                         } else {
1682                                 $this->replLogger->info( __METHOD__ . ': Done' );
1683                                 $ok = true;
1684                         }
1685                 } else {
1686                         $ok = false; // something is misconfigured
1687                         $this->replLogger->error( 'Could not get master pos for {host}',
1688                                 [ 'host' => $conn->getServer() ] );
1689                 }
1690
1691                 return $ok;
1692         }
1693
1694         public function setTransactionListener( $name, callable $callback = null ) {
1695                 if ( $callback ) {
1696                         $this->trxRecurringCallbacks[$name] = $callback;
1697                 } else {
1698                         unset( $this->trxRecurringCallbacks[$name] );
1699                 }
1700                 $this->forEachOpenMasterConnection(
1701                         function ( IDatabase $conn ) use ( $name, $callback ) {
1702                                 $conn->setTransactionListener( $name, $callback );
1703                         }
1704                 );
1705         }
1706
1707         public function setTableAliases( array $aliases ) {
1708                 $this->tableAliases = $aliases;
1709         }
1710
1711         public function setDomainPrefix( $prefix ) {
1712                 // Find connections to explicit foreign domains still marked as in-use...
1713                 $domainsInUse = [];
1714                 $this->forEachOpenConnection( function ( IDatabase $conn ) use ( &$domainsInUse ) {
1715                         // Once reuseConnection() is called on a handle, its reference count goes from 1 to 0.
1716                         // Until then, it is still in use by the caller (explicitly or via DBConnRef scope).
1717                         if ( $conn->getLBInfo( 'foreignPoolRefCount' ) > 0 ) {
1718                                 $domainsInUse[] = $conn->getDomainID();
1719                         }
1720                 } );
1721
1722                 // Do not switch connections to explicit foreign domains unless marked as safe
1723                 if ( $domainsInUse ) {
1724                         $domains = implode( ', ', $domainsInUse );
1725                         throw new DBUnexpectedError( null,
1726                                 "Foreign domain connections are still in use ($domains)." );
1727                 }
1728
1729                 $this->localDomain = new DatabaseDomain(
1730                         $this->localDomain->getDatabase(),
1731                         null,
1732                         $prefix
1733                 );
1734
1735                 $this->forEachOpenConnection( function ( IDatabase $db ) use ( $prefix ) {
1736                         $db->tablePrefix( $prefix );
1737                 } );
1738         }
1739
1740         /**
1741          * Make PHP ignore user aborts/disconnects until the returned
1742          * value leaves scope. This returns null and does nothing in CLI mode.
1743          *
1744          * @return ScopedCallback|null
1745          */
1746         final protected function getScopedPHPBehaviorForCommit() {
1747                 if ( PHP_SAPI != 'cli' ) { // https://bugs.php.net/bug.php?id=47540
1748                         $old = ignore_user_abort( true ); // avoid half-finished operations
1749                         return new ScopedCallback( function () use ( $old ) {
1750                                 ignore_user_abort( $old );
1751                         } );
1752                 }
1753
1754                 return null;
1755         }
1756
1757         function __destruct() {
1758                 // Avoid connection leaks for sanity
1759                 $this->disable();
1760         }
1761 }
1762
1763 class_alias( LoadBalancer::class, 'LoadBalancer' );