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  * @ingroup Database
  22  */
  23 namespace Wikimedia\Rdbms;
  24
  25 use Psr\Log\LoggerInterface;
  26 use Psr\Log\NullLogger;
  27 use Wikimedia\ScopedCallback;
  28 use BagOStuff;
  29 use EmptyBagOStuff;
  30 use WANObjectCache;
  31 use ArrayUtils;
  32 use InvalidArgumentException;
  33 use RuntimeException;
  34 use Exception;
  35
  36 /**
  37  * Database connection, tracking, load balancing, and transaction manager for a cluster
  38  *
  39  * @ingroup Database
  40  */
  41 class LoadBalancer implements ILoadBalancer {
  42         /** @var array[] Map of (server index => server config array) */
  43         private $mServers;
  44         /** @var Database[][][] Map of local/foreignUsed/foreignFree => server index => IDatabase[] */
  45         private $mConns;
  46         /** @var float[] Map of (server index => weight) */
  47         private $mLoads;
  48         /** @var array[] Map of (group => server index => weight) */
  49         private $mGroupLoads;
  50         /** @var bool Whether to disregard replica DB lag as a factor in replica DB selection */
  51         private $mAllowLagged;
  52         /** @var integer Seconds to spend waiting on replica DB lag to resolve */
  53         private $mWaitTimeout;
  54         /** @var array The LoadMonitor configuration */
  55         private $loadMonitorConfig;
  56         /** @var array[] $aliases Map of (table => (dbname, schema, prefix) map) */
  57         private $tableAliases = [];
  58
  59         /** @var ILoadMonitor */
  60         private $loadMonitor;
  61         /** @var ChronologyProtector|null */
  62         private $chronProt;
  63         /** @var BagOStuff */
  64         private $srvCache;
  65         /** @var WANObjectCache */
  66         private $wanCache;
  67         /** @var object|string Class name or object With profileIn/profileOut methods */
  68         protected $profiler;
  69         /** @var TransactionProfiler */
  70         protected $trxProfiler;
  71         /** @var LoggerInterface */
  72         protected $replLogger;
  73         /** @var LoggerInterface */
  74         protected $connLogger;
  75         /** @var LoggerInterface */
  76         protected $queryLogger;
  77         /** @var LoggerInterface */
  78         protected $perfLogger;
  79
  80         /** @var Database DB connection object that caused a problem */
  81         private $errorConnection;
  82         /** @var integer The generic (not query grouped) replica DB index (of $mServers) */
  83         private $mReadIndex;
  84         /** @var bool|DBMasterPos False if not set */
  85         private $mWaitForPos;
  86         /** @var bool Whether the generic reader fell back to a lagged replica DB */
  87         private $laggedReplicaMode = false;
  88         /** @var bool Whether the generic reader fell back to a lagged replica DB */
  89         private $allReplicasDownMode = false;
  90         /** @var string The last DB selection or connection error */
  91         private $mLastError = 'Unknown error';
  92         /** @var string|bool Reason the LB is read-only or false if not */
  93         private $readOnlyReason = false;
  94         /** @var integer Total connections opened */
  95         private $connsOpened = 0;
  96         /** @var string|bool String if a requested DBO_TRX transaction round is active */
  97         private $trxRoundId = false;
  98         /** @var array[] Map of (name => callable) */
  99         private $trxRecurringCallbacks = [];
 100         /** @var DatabaseDomain Local Domain ID and default for selectDB() calls */
 101         private $localDomain;
 102         /** @var string Alternate ID string for the domain instead of DatabaseDomain::getId() */
 103         private $localDomainIdAlias;
 104         /** @var string Current server name */
 105         private $host;
 106         /** @var bool Whether this PHP instance is for a CLI script */
 107         protected $cliMode;
 108         /** @var string Agent name for query profiling */
 109         protected $agent;
 110
 111         /** @var callable Exception logger */
 112         private $errorLogger;
 113
 114         /** @var boolean */
 115         private $disabled = false;
 116         /** @var boolean */
 117         private $chronProtInitialized = false;
 118
 119         /** @var integer Warn when this many connection are held */
 120         const CONN_HELD_WARN_THRESHOLD = 10;
 121
 122         /** @var integer Default 'max lag' when unspecified */
 123         const MAX_LAG_DEFAULT = 10;
 124         /** @var integer Seconds to cache master server read-only status */
 125         const TTL_CACHE_READONLY = 5;
 126
 127         const KEY_LOCAL = 'local';
 128         const KEY_FOREIGN_FREE = 'foreignFree';
 129         const KEY_FOREIGN_INUSE = 'foreignInUse';
 130
 131         public function __construct( array $params ) {
 132                 if ( !isset( $params['servers'] ) ) {
 133                         throw new InvalidArgumentException( __CLASS__ . ': missing servers parameter' );
 134                 }
 135                 $this->mServers = $params['servers'];
 136
 137                 $this->localDomain = isset( $params['localDomain'] )
 138                         ? DatabaseDomain::newFromId( $params['localDomain'] )
 139                         : DatabaseDomain::newUnspecified();
 140                 // In case a caller assumes that the domain ID is simply <db>-<prefix>, which is almost
 141                 // always true, gracefully handle the case when they fail to account for escaping.
 142                 if ( $this->localDomain->getTablePrefix() != '' ) {
 143                         $this->localDomainIdAlias =
 144                                 $this->localDomain->getDatabase() . '-' . $this->localDomain->getTablePrefix();
 145                 } else {
 146                         $this->localDomainIdAlias = $this->localDomain->getDatabase();
 147                 }
 148
 149                 $this->mWaitTimeout = isset( $params['waitTimeout'] ) ? $params['waitTimeout'] : 10;
 150
 151                 $this->mReadIndex = -1;
 152                 $this->mConns = [
 153                         self::KEY_LOCAL => [],
 154                         self::KEY_FOREIGN_INUSE => [],
 155                         self::KEY_FOREIGN_FREE => []
 156                 ];
 157                 $this->mLoads = [];
 158                 $this->mWaitForPos = false;
 159                 $this->mAllowLagged = false;
 160
 161                 if ( isset( $params['readOnlyReason'] ) && is_string( $params['readOnlyReason'] ) ) {
 162                         $this->readOnlyReason = $params['readOnlyReason'];
 163                 }
 164
 165                 if ( isset( $params['loadMonitor'] ) ) {
 166                         $this->loadMonitorConfig = $params['loadMonitor'];
 167                 } else {
 168                         $this->loadMonitorConfig = [ 'class' => 'LoadMonitorNull' ];
 169                 }
 170
 171                 foreach ( $params['servers'] as $i => $server ) {
 172                         $this->mLoads[$i] = $server['load'];
 173                         if ( isset( $server['groupLoads'] ) ) {
 174                                 foreach ( $server['groupLoads'] as $group => $ratio ) {
 175                                         if ( !isset( $this->mGroupLoads[$group] ) ) {
 176                                                 $this->mGroupLoads[$group] = [];
 177                                         }
 178                                         $this->mGroupLoads[$group][$i] = $ratio;
 179                                 }
 180                         }
 181                 }
 182
 183                 if ( isset( $params['srvCache'] ) ) {
 184                         $this->srvCache = $params['srvCache'];
 185                 } else {
 186                         $this->srvCache = new EmptyBagOStuff();
 187                 }
 188                 if ( isset( $params['wanCache'] ) ) {
 189                         $this->wanCache = $params['wanCache'];
 190                 } else {
 191                         $this->wanCache = WANObjectCache::newEmpty();
 192                 }
 193                 $this->profiler = isset( $params['profiler'] ) ? $params['profiler'] : null;
 194                 if ( isset( $params['trxProfiler'] ) ) {
 195                         $this->trxProfiler = $params['trxProfiler'];
 196                 } else {
 197                         $this->trxProfiler = new TransactionProfiler();
 198                 }
 199
 200                 $this->errorLogger = isset( $params['errorLogger'] )
 201                         ? $params['errorLogger']
 202                         : function ( Exception $e ) {
 203                                 trigger_error( get_class( $e ) . ': ' . $e->getMessage(), E_USER_WARNING );
 204                         };
 205
 206                 foreach ( [ 'replLogger', 'connLogger', 'queryLogger', 'perfLogger' ] as $key ) {
 207                         $this->$key = isset( $params[$key] ) ? $params[$key] : new NullLogger();
 208                 }
 209
 210                 $this->host = isset( $params['hostname'] )
 211                         ? $params['hostname']
 212                         : ( gethostname() ?: 'unknown' );
 213                 $this->cliMode = isset( $params['cliMode'] ) ? $params['cliMode'] : PHP_SAPI === 'cli';
 214                 $this->agent = isset( $params['agent'] ) ? $params['agent'] : '';
 215
 216                 if ( isset( $params['chronologyProtector'] ) ) {
 217                         $this->chronProt = $params['chronologyProtector'];
 218                 }
 219         }
 220
 221         /**
 222          * Get a LoadMonitor instance
 223          *
 224          * @return ILoadMonitor
 225          */
 226         private function getLoadMonitor() {
 227                 if ( !isset( $this->loadMonitor ) ) {
 228                         $compat = [
 229                                 'LoadMonitor' => LoadMonitor::class,
 230                                 'LoadMonitorNull' => LoadMonitorNull::class,
 231                                 'LoadMonitorMySQL' => LoadMonitorMySQL::class,
 232                         ];
 233
 234                         $class = $this->loadMonitorConfig['class'];
 235                         if ( isset( $compat[$class] ) ) {
 236                                 $class = $compat[$class];
 237                         }
 238
 239                         $this->loadMonitor = new $class(
 240                                 $this, $this->srvCache, $this->wanCache, $this->loadMonitorConfig );
 241                         $this->loadMonitor->setLogger( $this->replLogger );
 242                 }
 243
 244                 return $this->loadMonitor;
 245         }
 246
 247         /**
 248          * @param array $loads
 249          * @param bool|string $domain Domain to get non-lagged for
 250          * @param int $maxLag Restrict the maximum allowed lag to this many seconds
 251          * @return bool|int|string
 252          */
 253         private function getRandomNonLagged( array $loads, $domain = false, $maxLag = INF ) {
 254                 $lags = $this->getLagTimes( $domain );
 255
 256                 # Unset excessively lagged servers
 257                 foreach ( $lags as $i => $lag ) {
 258                         if ( $i != 0 ) {
 259                                 # How much lag this server nominally is allowed to have
 260                                 $maxServerLag = isset( $this->mServers[$i]['max lag'] )
 261                                         ? $this->mServers[$i]['max lag']
 262                                         : self::MAX_LAG_DEFAULT; // default
 263                                 # Constrain that futher by $maxLag argument
 264                                 $maxServerLag = min( $maxServerLag, $maxLag );
 265
 266                                 $host = $this->getServerName( $i );
 267                                 if ( $lag === false && !is_infinite( $maxServerLag ) ) {
 268                                         $this->replLogger->error(
 269                                                 "Server {host} is not replicating?", [ 'host' => $host ] );
 270                                         unset( $loads[$i] );
 271                                 } elseif ( $lag > $maxServerLag ) {
 272                                         $this->replLogger->warning(
 273                                                 "Server {host} has {lag} seconds of lag (>= {maxlag})",
 274                                                 [ 'host' => $host, 'lag' => $lag, 'maxlag' => $maxServerLag ]
 275                                         );
 276                                         unset( $loads[$i] );
 277                                 }
 278                         }
 279                 }
 280
 281                 # Find out if all the replica DBs with non-zero load are lagged
 282                 $sum = 0;
 283                 foreach ( $loads as $load ) {
 284                         $sum += $load;
 285                 }
 286                 if ( $sum == 0 ) {
 287                         # No appropriate DB servers except maybe the master and some replica DBs with zero load
 288                         # Do NOT use the master
 289                         # Instead, this function will return false, triggering read-only mode,
 290                         # and a lagged replica DB will be used instead.
 291                         return false;
 292                 }
 293
 294                 if ( count( $loads ) == 0 ) {
 295                         return false;
 296                 }
 297
 298                 # Return a random representative of the remainder
 299                 return ArrayUtils::pickRandom( $loads );
 300         }
 301
 302         public function getReaderIndex( $group = false, $domain = false ) {
 303                 if ( count( $this->mServers ) == 1 ) {
 304                         // Skip the load balancing if there's only one server
 305                         return $this->getWriterIndex();
 306                 } elseif ( $group === false && $this->mReadIndex >= 0 ) {
 307                         // Shortcut if the generic reader index was already cached
 308                         return $this->mReadIndex;
 309                 }
 310
 311                 if ( $group !== false ) {
 312                         // Use the server weight array for this load group
 313                         if ( isset( $this->mGroupLoads[$group] ) ) {
 314                                 $loads = $this->mGroupLoads[$group];
 315                         } else {
 316                                 // No loads for this group, return false and the caller can use some other group
 317                                 $this->connLogger->info( __METHOD__ . ": no loads for group $group" );
 318
 319                                 return false;
 320                         }
 321                 } else {
 322                         // Use the generic load group
 323                         $loads = $this->mLoads;
 324                 }
 325
 326                 // Scale the configured load ratios according to each server's load and state
 327                 $this->getLoadMonitor()->scaleLoads( $loads, $domain );
 328
 329                 // Pick a server to use, accounting for weights, load, lag, and mWaitForPos
 330                 list( $i, $laggedReplicaMode ) = $this->pickReaderIndex( $loads, $domain );
 331                 if ( $i === false ) {
 332                         // Replica DB connection unsuccessful
 333                         return false;
 334                 }
 335
 336                 if ( $this->mWaitForPos && $i != $this->getWriterIndex() ) {
 337                         // Before any data queries are run, wait for the server to catch up to the
 338                         // specified position. This is used to improve session consistency. Note that
 339                         // when LoadBalancer::waitFor() sets mWaitForPos, the waiting triggers here,
 340                         // so update laggedReplicaMode as needed for consistency.
 341                         if ( !$this->doWait( $i ) ) {
 342                                 $laggedReplicaMode = true;
 343                         }
 344                 }
 345
 346                 if ( $this->mReadIndex <= 0 && $this->mLoads[$i] > 0 && $group === false ) {
 347                         // Cache the generic reader index for future ungrouped DB_REPLICA handles
 348                         $this->mReadIndex = $i;
 349                         // Record if the generic reader index is in "lagged replica DB" mode
 350                         if ( $laggedReplicaMode ) {
 351                                 $this->laggedReplicaMode = true;
 352                         }
 353                 }
 354
 355                 $serverName = $this->getServerName( $i );
 356                 $this->connLogger->debug( __METHOD__ . ": using server $serverName for group '$group'" );
 357
 358                 return $i;
 359         }
 360
 361         /**
 362          * @param array $loads List of server weights
 363          * @param string|bool $domain
 364          * @return array (reader index, lagged replica mode) or false on failure
 365          */
 366         private function pickReaderIndex( array $loads, $domain = false ) {
 367                 if ( !count( $loads ) ) {
 368                         throw new InvalidArgumentException( "Empty server array given to LoadBalancer" );
 369                 }
 370
 371                 /** @var $i int|bool Index of selected server */
 372                 $i = false;
 373                 /** @var $laggedReplicaMode bool Whether server is considered lagged */
 374                 $laggedReplicaMode = false;
 375
 376                 // Quickly look through the available servers for a server that meets criteria...
 377                 $currentLoads = $loads;
 378                 while ( count( $currentLoads ) ) {
 379                         if ( $this->mAllowLagged || $laggedReplicaMode ) {
 380                                 $i = ArrayUtils::pickRandom( $currentLoads );
 381                         } else {
 382                                 $i = false;
 383                                 if ( $this->mWaitForPos && $this->mWaitForPos->asOfTime() ) {
 384                                         // ChronologyProtecter sets mWaitForPos for session consistency.
 385                                         // This triggers doWait() after connect, so it's especially good to
 386                                         // avoid lagged servers so as to avoid excessive delay in that method.
 387                                         $ago = microtime( true ) - $this->mWaitForPos->asOfTime();
 388                                         // Aim for <= 1 second of waiting (being too picky can backfire)
 389                                         $i = $this->getRandomNonLagged( $currentLoads, $domain, $ago + 1 );
 390                                 }
 391                                 if ( $i === false ) {
 392                                         // Any server with less lag than it's 'max lag' param is preferable
 393                                         $i = $this->getRandomNonLagged( $currentLoads, $domain );
 394                                 }
 395                                 if ( $i === false && count( $currentLoads ) != 0 ) {
 396                                         // All replica DBs lagged. Switch to read-only mode
 397                                         $this->replLogger->error( "All replica DBs lagged. Switch to read-only mode" );
 398                                         $i = ArrayUtils::pickRandom( $currentLoads );
 399                                         $laggedReplicaMode = true;
 400                                 }
 401                         }
 402
 403                         if ( $i === false ) {
 404                                 // pickRandom() returned false.
 405                                 // This is permanent and means the configuration or the load monitor
 406                                 // wants us to return false.
 407                                 $this->connLogger->debug( __METHOD__ . ": pickRandom() returned false" );
 408
 409                                 return [ false, false ];
 410                         }
 411
 412                         $serverName = $this->getServerName( $i );
 413                         $this->connLogger->debug( __METHOD__ . ": Using reader #$i: $serverName..." );
 414
 415                         $conn = $this->openConnection( $i, $domain );
 416                         if ( !$conn ) {
 417                                 $this->connLogger->warning( __METHOD__ . ": Failed connecting to $i/$domain" );
 418                                 unset( $currentLoads[$i] ); // avoid this server next iteration
 419                                 $i = false;
 420                                 continue;
 421                         }
 422
 423                         // Decrement reference counter, we are finished with this connection.
 424                         // It will be incremented for the caller later.
 425                         if ( $domain !== false ) {
 426                                 $this->reuseConnection( $conn );
 427                         }
 428
 429                         // Return this server
 430                         break;
 431                 }
 432
 433                 // If all servers were down, quit now
 434                 if ( !count( $currentLoads ) ) {
 435                         $this->connLogger->error( "All servers down" );
 436                 }
 437
 438                 return [ $i, $laggedReplicaMode ];
 439         }
 440
 441         public function waitFor( $pos ) {
 442                 $oldPos = $this->mWaitForPos;
 443                 try {
 444                         $this->mWaitForPos = $pos;
 445                         // If a generic reader connection was already established, then wait now
 446                         $i = $this->mReadIndex;
 447                         if ( $i > 0 ) {
 448                                 if ( !$this->doWait( $i ) ) {
 449                                         $this->laggedReplicaMode = true;
 450                                 }
 451                         }
 452                 } finally {
 453                         // Restore the older position if it was higher since this is used for lag-protection
 454                         $this->setWaitForPositionIfHigher( $oldPos );
 455                 }
 456         }
 457
 458         public function waitForOne( $pos, $timeout = null ) {
 459                 $oldPos = $this->mWaitForPos;
 460                 try {
 461                         $this->mWaitForPos = $pos;
 462
 463                         $i = $this->mReadIndex;
 464                         if ( $i <= 0 ) {
 465                                 // Pick a generic replica DB if there isn't one yet
 466                                 $readLoads = $this->mLoads;
 467                                 unset( $readLoads[$this->getWriterIndex()] ); // replica DBs only
 468                                 $readLoads = array_filter( $readLoads ); // with non-zero load
 469                                 $i = ArrayUtils::pickRandom( $readLoads );
 470                         }
 471
 472                         if ( $i > 0 ) {
 473                                 $ok = $this->doWait( $i, true, $timeout );
 474                         } else {
 475                                 $ok = true; // no applicable loads
 476                         }
 477                 } finally {
 478                         # Restore the old position, as this is not used for lag-protection but for throttling
 479                         $this->mWaitForPos = $oldPos;
 480                 }
 481
 482                 return $ok;
 483         }
 484
 485         public function waitForAll( $pos, $timeout = null ) {
 486                 $oldPos = $this->mWaitForPos;
 487                 try {
 488                         $this->mWaitForPos = $pos;
 489                         $serverCount = count( $this->mServers );
 490
 491                         $ok = true;
 492                         for ( $i = 1; $i < $serverCount; $i++ ) {
 493                                 if ( $this->mLoads[$i] > 0 ) {
 494                                         $ok = $this->doWait( $i, true, $timeout ) && $ok;
 495                                 }
 496                         }
 497                 } finally {
 498                         # Restore the old position, as this is not used for lag-protection but for throttling
 499                         $this->mWaitForPos = $oldPos;
 500                 }
 501
 502                 return $ok;
 503         }
 504
 505         /**
 506          * @param DBMasterPos|bool $pos
 507          */
 508         private function setWaitForPositionIfHigher( $pos ) {
 509                 if ( !$pos ) {
 510                         return;
 511                 }
 512
 513                 if ( !$this->mWaitForPos || $pos->hasReached( $this->mWaitForPos ) ) {
 514                         $this->mWaitForPos = $pos;
 515                 }
 516         }
 517
 518         /**
 519          * @param int $i
 520          * @return IDatabase|bool
 521          */
 522         public function getAnyOpenConnection( $i ) {
 523                 foreach ( $this->mConns as $connsByServer ) {
 524                         if ( !empty( $connsByServer[$i] ) ) {
 525                                 /** @var $serverConns IDatabase[] */
 526                                 $serverConns = $connsByServer[$i];
 527
 528                                 return reset( $serverConns );
 529                         }
 530                 }
 531
 532                 return false;
 533         }
 534
 535         /**
 536          * Wait for a given replica DB to catch up to the master pos stored in $this
 537          * @param int $index Server index
 538          * @param bool $open Check the server even if a new connection has to be made
 539          * @param int $timeout Max seconds to wait; default is mWaitTimeout
 540          * @return bool
 541          */
 542         protected function doWait( $index, $open = false, $timeout = null ) {
 543                 $close = false; // close the connection afterwards
 544
 545                 // Check if we already know that the DB has reached this point
 546                 $server = $this->getServerName( $index );
 547                 $key = $this->srvCache->makeGlobalKey( __CLASS__, 'last-known-pos', $server, 'v1' );
 548                 /** @var DBMasterPos $knownReachedPos */
 549                 $knownReachedPos = $this->srvCache->get( $key );
 550                 if (
 551                         $knownReachedPos instanceof DBMasterPos &&
 552                         $knownReachedPos->hasReached( $this->mWaitForPos )
 553                 ) {
 554                         $this->replLogger->debug( __METHOD__ .
 555                                 ": replica DB $server known to be caught up (pos >= $knownReachedPos)." );
 556                         return true;
 557                 }
 558
 559                 // Find a connection to wait on, creating one if needed and allowed
 560                 $conn = $this->getAnyOpenConnection( $index );
 561                 if ( !$conn ) {
 562                         if ( !$open ) {
 563                                 $this->replLogger->debug( __METHOD__ . ": no connection open for $server" );
 564
 565                                 return false;
 566                         } else {
 567                                 $conn = $this->openConnection( $index, self::DOMAIN_ANY );
 568                                 if ( !$conn ) {
 569                                         $this->replLogger->warning( __METHOD__ . ": failed to connect to $server" );
 570
 571                                         return false;
 572                                 }
 573                                 // Avoid connection spam in waitForAll() when connections
 574                                 // are made just for the sake of doing this lag check.
 575                                 $close = true;
 576                         }
 577                 }
 578
 579                 $this->replLogger->info( __METHOD__ . ": Waiting for replica DB $server to catch up..." );
 580                 $timeout = $timeout ?: $this->mWaitTimeout;
 581                 $result = $conn->masterPosWait( $this->mWaitForPos, $timeout );
 582
 583                 if ( $result == -1 || is_null( $result ) ) {
 584                         // Timed out waiting for replica DB, use master instead
 585                         $this->replLogger->warning(
 586                                 __METHOD__ . ": Timed out waiting on {host} pos {$this->mWaitForPos}",
 587                                 [ 'host' => $server ]
 588                         );
 589                         $ok = false;
 590                 } else {
 591                         $this->replLogger->info( __METHOD__ . ": Done" );
 592                         $ok = true;
 593                         // Remember that the DB reached this point
 594                         $this->srvCache->set( $key, $this->mWaitForPos, BagOStuff::TTL_DAY );
 595                 }
 596
 597                 if ( $close ) {
 598                         $this->closeConnection( $conn );
 599                 }
 600
 601                 return $ok;
 602         }
 603
 604         /**
 605          * @see ILoadBalancer::getConnection()
 606          *
 607          * @param int $i
 608          * @param array $groups
 609          * @param bool $domain
 610          * @return Database
 611          * @throws DBConnectionError
 612          */
 613         public function getConnection( $i, $groups = [], $domain = false ) {
 614                 if ( $i === null || $i === false ) {
 615                         throw new InvalidArgumentException( 'Attempt to call ' . __METHOD__ .
 616                                 ' with invalid server index' );
 617                 }
 618
 619                 if ( $this->localDomain->equals( $domain ) || $domain === $this->localDomainIdAlias ) {
 620                         $domain = false; // local connection requested
 621                 }
 622
 623                 $groups = ( $groups === false || $groups === [] )
 624                         ? [ false ] // check one "group": the generic pool
 625                         : (array)$groups;
 626
 627                 $masterOnly = ( $i == self::DB_MASTER || $i == $this->getWriterIndex() );
 628                 $oldConnsOpened = $this->connsOpened; // connections open now
 629
 630                 if ( $i == self::DB_MASTER ) {
 631                         $i = $this->getWriterIndex();
 632                 } else {
 633                         # Try to find an available server in any the query groups (in order)
 634                         foreach ( $groups as $group ) {
 635                                 $groupIndex = $this->getReaderIndex( $group, $domain );
 636                                 if ( $groupIndex !== false ) {
 637                                         $i = $groupIndex;
 638                                         break;
 639                                 }
 640                         }
 641                 }
 642
 643                 # Operation-based index
 644                 if ( $i == self::DB_REPLICA ) {
 645                         $this->mLastError = 'Unknown error'; // reset error string
 646                         # Try the general server pool if $groups are unavailable.
 647                         $i = ( $groups === [ false ] )
 648                                 ? false // don't bother with this if that is what was tried above
 649                                 : $this->getReaderIndex( false, $domain );
 650                         # Couldn't find a working server in getReaderIndex()?
 651                         if ( $i === false ) {
 652                                 $this->mLastError = 'No working replica DB server: ' . $this->mLastError;
 653                                 // Throw an exception
 654                                 $this->reportConnectionError();
 655                                 return null; // not reached
 656                         }
 657                 }
 658
 659                 # Now we have an explicit index into the servers array
 660                 $conn = $this->openConnection( $i, $domain );
 661                 if ( !$conn ) {
 662                         // Throw an exception
 663                         $this->reportConnectionError();
 664                         return null; // not reached
 665                 }
 666
 667                 # Profile any new connections that happen
 668                 if ( $this->connsOpened > $oldConnsOpened ) {
 669                         $host = $conn->getServer();
 670                         $dbname = $conn->getDBname();
 671                         $this->trxProfiler->recordConnection( $host, $dbname, $masterOnly );
 672                 }
 673
 674                 if ( $masterOnly ) {
 675                         # Make master-requested DB handles inherit any read-only mode setting
 676                         $conn->setLBInfo( 'readOnlyReason', $this->getReadOnlyReason( $domain, $conn ) );
 677                 }
 678
 679                 return $conn;
 680         }
 681
 682         public function reuseConnection( $conn ) {
 683                 $serverIndex = $conn->getLBInfo( 'serverIndex' );
 684                 $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 685                 if ( $serverIndex === null || $refCount === null ) {
 686                         /**
 687                          * This can happen in code like:
 688                          *   foreach ( $dbs as $db ) {
 689                          *     $conn = $lb->getConnection( $lb::DB_REPLICA, [], $db );
 690                          *     ...
 691                          *     $lb->reuseConnection( $conn );
 692                          *   }
 693                          * When a connection to the local DB is opened in this way, reuseConnection()
 694                          * should be ignored
 695                          */
 696                         return;
 697                 } elseif ( $conn instanceof DBConnRef ) {
 698                         // DBConnRef already handles calling reuseConnection() and only passes the live
 699                         // Database instance to this method. Any caller passing in a DBConnRef is broken.
 700                         $this->connLogger->error( __METHOD__ . ": got DBConnRef instance.\n" .
 701                                 ( new RuntimeException() )->getTraceAsString() );
 702
 703                         return;
 704                 }
 705
 706                 if ( $this->disabled ) {
 707                         return; // DBConnRef handle probably survived longer than the LoadBalancer
 708                 }
 709
 710                 $domain = $conn->getDomainID();
 711                 if ( !isset( $this->mConns[self::KEY_FOREIGN_INUSE][$serverIndex][$domain] ) ) {
 712                         throw new InvalidArgumentException( __METHOD__ .
 713                                 ": connection $serverIndex/$domain not found; it may have already been freed." );
 714                 } elseif ( $this->mConns[self::KEY_FOREIGN_INUSE][$serverIndex][$domain] !== $conn ) {
 715                         throw new InvalidArgumentException( __METHOD__ .
 716                                 ": connection $serverIndex/$domain mismatched; it may have already been freed." );
 717                 }
 718                 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
 719                 if ( $refCount <= 0 ) {
 720                         $this->mConns[self::KEY_FOREIGN_FREE][$serverIndex][$domain] = $conn;
 721                         unset( $this->mConns[self::KEY_FOREIGN_INUSE][$serverIndex][$domain] );
 722                         if ( !$this->mConns[self::KEY_FOREIGN_INUSE][$serverIndex] ) {
 723                                 unset( $this->mConns[ self::KEY_FOREIGN_INUSE ][$serverIndex] ); // clean up
 724                         }
 725                         $this->connLogger->debug( __METHOD__ . ": freed connection $serverIndex/$domain" );
 726                 } else {
 727                         $this->connLogger->debug( __METHOD__ .
 728                                 ": reference count for $serverIndex/$domain reduced to $refCount" );
 729                 }
 730         }
 731
 732         public function getConnectionRef( $db, $groups = [], $domain = false ) {
 733                 $domain = ( $domain !== false ) ? $domain : $this->localDomain;
 734
 735                 return new DBConnRef( $this, $this->getConnection( $db, $groups, $domain ) );
 736         }
 737
 738         public function getLazyConnectionRef( $db, $groups = [], $domain = false ) {
 739                 $domain = ( $domain !== false ) ? $domain : $this->localDomain;
 740
 741                 return new DBConnRef( $this, [ $db, $groups, $domain ] );
 742         }
 743
 744         public function getMaintenanceConnectionRef( $db, $groups = [], $domain = false ) {
 745                 $domain = ( $domain !== false ) ? $domain : $this->localDomain;
 746
 747                 return new MaintainableDBConnRef( $this, $this->getConnection( $db, $groups, $domain ) );
 748         }
 749
 750         /**
 751          * @see ILoadBalancer::openConnection()
 752          *
 753          * @param int $i
 754          * @param bool $domain
 755          * @return bool|Database
 756          * @throws DBAccessError
 757          */
 758         public function openConnection( $i, $domain = false ) {
 759                 if ( $this->localDomain->equals( $domain ) || $domain === $this->localDomainIdAlias ) {
 760                         $domain = false; // local connection requested
 761                 }
 762
 763                 if ( !$this->chronProtInitialized && $this->chronProt ) {
 764                         $this->connLogger->debug( __METHOD__ . ': calling initLB() before first connection.' );
 765                         // Load CP positions before connecting so that doWait() triggers later if needed
 766                         $this->chronProtInitialized = true;
 767                         $this->chronProt->initLB( $this );
 768                 }
 769
 770                 if ( $domain !== false ) {
 771                         $conn = $this->openForeignConnection( $i, $domain );
 772                 } elseif ( isset( $this->mConns[self::KEY_LOCAL][$i][0] ) ) {
 773                         $conn = $this->mConns[self::KEY_LOCAL][$i][0];
 774                 } else {
 775                         if ( !isset( $this->mServers[$i] ) || !is_array( $this->mServers[$i] ) ) {
 776                                 throw new InvalidArgumentException( "No server with index '$i'." );
 777                         }
 778                         // Open a new connection
 779                         $server = $this->mServers[$i];
 780                         $server['serverIndex'] = $i;
 781                         $conn = $this->reallyOpenConnection( $server, false );
 782                         $serverName = $this->getServerName( $i );
 783                         if ( $conn->isOpen() ) {
 784                                 $this->connLogger->debug( "Connected to database $i at '$serverName'." );
 785                                 $this->mConns[self::KEY_LOCAL][$i][0] = $conn;
 786                         } else {
 787                                 $this->connLogger->warning( "Failed to connect to database $i at '$serverName'." );
 788                                 $this->errorConnection = $conn;
 789                                 $conn = false;
 790                         }
 791                 }
 792
 793                 if ( $conn instanceof IDatabase && !$conn->isOpen() ) {
 794                         // Connection was made but later unrecoverably lost for some reason.
 795                         // Do not return a handle that will just throw exceptions on use,
 796                         // but let the calling code (e.g. getReaderIndex) try another server.
 797                         // See DatabaseMyslBase::ping() for how this can happen.
 798                         $this->errorConnection = $conn;
 799                         $conn = false;
 800                 }
 801
 802                 return $conn;
 803         }
 804
 805         /**
 806          * Open a connection to a foreign DB, or return one if it is already open.
 807          *
 808          * Increments a reference count on the returned connection which locks the
 809          * connection to the requested domain. This reference count can be
 810          * decremented by calling reuseConnection().
 811          *
 812          * If a connection is open to the appropriate server already, but with the wrong
 813          * database, it will be switched to the right database and returned, as long as
 814          * it has been freed first with reuseConnection().
 815          *
 816          * On error, returns false, and the connection which caused the
 817          * error will be available via $this->errorConnection.
 818          *
 819          * @note If disable() was called on this LoadBalancer, this method will throw a DBAccessError.
 820          *
 821          * @param int $i Server index
 822          * @param string $domain Domain ID to open
 823          * @return Database
 824          */
 825         private function openForeignConnection( $i, $domain ) {
 826                 $domainInstance = DatabaseDomain::newFromId( $domain );
 827                 $dbName = $domainInstance->getDatabase();
 828                 $prefix = $domainInstance->getTablePrefix();
 829
 830                 if ( isset( $this->mConns[self::KEY_FOREIGN_INUSE][$i][$domain] ) ) {
 831                         // Reuse an in-use connection for the same domain that is not in-use
 832                         $conn = $this->mConns[self::KEY_FOREIGN_INUSE][$i][$domain];
 833                         $this->connLogger->debug( __METHOD__ . ": reusing connection $i/$domain" );
 834                 } elseif ( isset( $this->mConns[self::KEY_FOREIGN_FREE][$i][$domain] ) ) {
 835                         // Reuse a free connection for the same domain that is not in-use
 836                         $conn = $this->mConns[self::KEY_FOREIGN_FREE][$i][$domain];
 837                         unset( $this->mConns[self::KEY_FOREIGN_FREE][$i][$domain] );
 838                         $this->mConns[self::KEY_FOREIGN_INUSE][$i][$domain] = $conn;
 839                         $this->connLogger->debug( __METHOD__ . ": reusing free connection $i/$domain" );
 840                 } elseif ( !empty( $this->mConns[self::KEY_FOREIGN_FREE][$i] ) ) {
 841                         // Reuse a connection from another domain
 842                         $conn = reset( $this->mConns[self::KEY_FOREIGN_FREE][$i] );
 843                         $oldDomain = key( $this->mConns[self::KEY_FOREIGN_FREE][$i] );
 844                         // The empty string as a DB name means "don't care".
 845                         // DatabaseMysqlBase::open() already handle this on connection.
 846                         if ( strlen( $dbName ) && !$conn->selectDB( $dbName ) ) {
 847                                 $this->mLastError = "Error selecting database '$dbName' on server " .
 848                                         $conn->getServer() . " from client host {$this->host}";
 849                                 $this->errorConnection = $conn;
 850                                 $conn = false;
 851                         } else {
 852                                 $conn->tablePrefix( $prefix );
 853                                 unset( $this->mConns[self::KEY_FOREIGN_FREE][$i][$oldDomain] );
 854                                 $this->mConns[self::KEY_FOREIGN_INUSE][$i][$domain] = $conn;
 855                                 $this->connLogger->debug( __METHOD__ .
 856                                         ": reusing free connection from $oldDomain for $domain" );
 857                         }
 858                 } else {
 859                         if ( !isset( $this->mServers[$i] ) || !is_array( $this->mServers[$i] ) ) {
 860                                 throw new InvalidArgumentException( "No server with index '$i'." );
 861                         }
 862                         // Open a new connection
 863                         $server = $this->mServers[$i];
 864                         $server['serverIndex'] = $i;
 865                         $server['foreignPoolRefCount'] = 0;
 866                         $server['foreign'] = true;
 867                         $conn = $this->reallyOpenConnection( $server, $dbName );
 868                         if ( !$conn->isOpen() ) {
 869                                 $this->connLogger->warning( __METHOD__ . ": connection error for $i/$domain" );
 870                                 $this->errorConnection = $conn;
 871                                 $conn = false;
 872                         } else {
 873                                 $conn->tablePrefix( $prefix );
 874                                 $this->mConns[self::KEY_FOREIGN_INUSE][$i][$domain] = $conn;
 875                                 $this->connLogger->debug( __METHOD__ . ": opened new connection for $i/$domain" );
 876                         }
 877                 }
 878
 879                 // Increment reference count
 880                 if ( $conn instanceof IDatabase ) {
 881                         $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 882                         $conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
 883                 }
 884
 885                 return $conn;
 886         }
 887
 888         /**
 889          * Test if the specified index represents an open connection
 890          *
 891          * @param int $index Server index
 892          * @access private
 893          * @return bool
 894          */
 895         private function isOpen( $index ) {
 896                 if ( !is_integer( $index ) ) {
 897                         return false;
 898                 }
 899
 900                 return (bool)$this->getAnyOpenConnection( $index );
 901         }
 902
 903         /**
 904          * Really opens a connection. Uncached.
 905          * Returns a Database object whether or not the connection was successful.
 906          * @access private
 907          *
 908          * @param array $server
 909          * @param string|bool $dbNameOverride Use "" to not select any database
 910          * @return Database
 911          * @throws DBAccessError
 912          * @throws InvalidArgumentException
 913          */
 914         protected function reallyOpenConnection( array $server, $dbNameOverride = false ) {
 915                 if ( $this->disabled ) {
 916                         throw new DBAccessError();
 917                 }
 918
 919                 if ( $dbNameOverride !== false ) {
 920                         $server['dbname'] = $dbNameOverride;
 921                 }
 922
 923                 // Let the handle know what the cluster master is (e.g. "db1052")
 924                 $masterName = $this->getServerName( $this->getWriterIndex() );
 925                 $server['clusterMasterHost'] = $masterName;
 926
 927                 // Log when many connection are made on requests
 928                 if ( ++$this->connsOpened >= self::CONN_HELD_WARN_THRESHOLD ) {
 929                         $this->perfLogger->warning( __METHOD__ . ": " .
 930                                 "{$this->connsOpened}+ connections made (master=$masterName)" );
 931                 }
 932
 933                 $server['srvCache'] = $this->srvCache;
 934                 // Set loggers and profilers
 935                 $server['connLogger'] = $this->connLogger;
 936                 $server['queryLogger'] = $this->queryLogger;
 937                 $server['errorLogger'] = $this->errorLogger;
 938                 $server['profiler'] = $this->profiler;
 939                 $server['trxProfiler'] = $this->trxProfiler;
 940                 // Use the same agent and PHP mode for all DB handles
 941                 $server['cliMode'] = $this->cliMode;
 942                 $server['agent'] = $this->agent;
 943                 // Use DBO_DEFAULT flags by default for LoadBalancer managed databases. Assume that the
 944                 // application calls LoadBalancer::commitMasterChanges() before the PHP script completes.
 945                 $server['flags'] = isset( $server['flags'] ) ? $server['flags'] : IDatabase::DBO_DEFAULT;
 946
 947                 // Create a live connection object
 948                 try {
 949                         $db = Database::factory( $server['type'], $server );
 950                 } catch ( DBConnectionError $e ) {
 951                         // FIXME: This is probably the ugliest thing I have ever done to
 952                         // PHP. I'm half-expecting it to segfault, just out of disgust. -- TS
 953                         $db = $e->db;
 954                 }
 955
 956                 $db->setLBInfo( $server );
 957                 $db->setLazyMasterHandle(
 958                         $this->getLazyConnectionRef( self::DB_MASTER, [], $db->getDomainID() )
 959                 );
 960                 $db->setTableAliases( $this->tableAliases );
 961
 962                 if ( $server['serverIndex'] === $this->getWriterIndex() ) {
 963                         if ( $this->trxRoundId !== false ) {
 964                                 $this->applyTransactionRoundFlags( $db );
 965                         }
 966                         foreach ( $this->trxRecurringCallbacks as $name => $callback ) {
 967                                 $db->setTransactionListener( $name, $callback );
 968                         }
 969                 }
 970
 971                 return $db;
 972         }
 973
 974         /**
 975          * @throws DBConnectionError
 976          */
 977         private function reportConnectionError() {
 978                 $conn = $this->errorConnection; // the connection which caused the error
 979                 $context = [
 980                         'method' => __METHOD__,
 981                         'last_error' => $this->mLastError,
 982                 ];
 983
 984                 if ( $conn instanceof IDatabase ) {
 985                         $context['db_server'] = $conn->getServer();
 986                         $this->connLogger->warning(
 987                                 "Connection error: {last_error} ({db_server})",
 988                                 $context
 989                         );
 990
 991                         // throws DBConnectionError
 992                         $conn->reportConnectionError( "{$this->mLastError} ({$context['db_server']})" );
 993                 } else {
 994                         // No last connection, probably due to all servers being too busy
 995                         $this->connLogger->error(
 996                                 "LB failure with no last connection. Connection error: {last_error}",
 997                                 $context
 998                         );
 999
1000                         // If all servers were busy, mLastError will contain something sensible
1001                         throw new DBConnectionError( null, $this->mLastError );
1002                 }
1003         }
1004
1005         public function getWriterIndex() {
1006                 return 0;
1007         }
1008
1009         public function haveIndex( $i ) {
1010                 return array_key_exists( $i, $this->mServers );
1011         }
1012
1013         public function isNonZeroLoad( $i ) {
1014                 return array_key_exists( $i, $this->mServers ) && $this->mLoads[$i] != 0;
1015         }
1016
1017         public function getServerCount() {
1018                 return count( $this->mServers );
1019         }
1020
1021         public function getServerName( $i ) {
1022                 if ( isset( $this->mServers[$i]['hostName'] ) ) {
1023                         $name = $this->mServers[$i]['hostName'];
1024                 } elseif ( isset( $this->mServers[$i]['host'] ) ) {
1025                         $name = $this->mServers[$i]['host'];
1026                 } else {
1027                         $name = '';
1028                 }
1029
1030                 return ( $name != '' ) ? $name : 'localhost';
1031         }
1032
1033         /**
1034          * @deprecated Since 1.30, no alternative
1035          */
1036         public function getServerInfo( $i ) {
1037                 wfDeprecated( __METHOD__, '1.30' );
1038                 if ( isset( $this->mServers[$i] ) ) {
1039                         return $this->mServers[$i];
1040                 } else {
1041                         return false;
1042                 }
1043         }
1044
1045         /**
1046          * @deprecated Since 1.30, construct new object
1047          */
1048         public function setServerInfo( $i, array $serverInfo ) {
1049                 wfDeprecated( __METHOD__, '1.30' );
1050                 $this->mServers[$i] = $serverInfo;
1051         }
1052
1053         public function getMasterPos() {
1054                 # If this entire request was served from a replica DB without opening a connection to the
1055                 # master (however unlikely that may be), then we can fetch the position from the replica DB.
1056                 $masterConn = $this->getAnyOpenConnection( $this->getWriterIndex() );
1057                 if ( !$masterConn ) {
1058                         $serverCount = count( $this->mServers );
1059                         for ( $i = 1; $i < $serverCount; $i++ ) {
1060                                 $conn = $this->getAnyOpenConnection( $i );
1061                                 if ( $conn ) {
1062                                         return $conn->getReplicaPos();
1063                                 }
1064                         }
1065                 } else {
1066                         return $masterConn->getMasterPos();
1067                 }
1068
1069                 return false;
1070         }
1071
1072         public function disable() {
1073                 $this->closeAll();
1074                 $this->disabled = true;
1075         }
1076
1077         public function closeAll() {
1078                 $this->forEachOpenConnection( function ( IDatabase $conn ) {
1079                         $host = $conn->getServer();
1080                         $this->connLogger->debug( "Closing connection to database '$host'." );
1081                         $conn->close();
1082                 } );
1083
1084                 $this->mConns = [
1085                         self::KEY_LOCAL => [],
1086                         self::KEY_FOREIGN_FREE => [],
1087                         self::KEY_FOREIGN_INUSE => [],
1088                 ];
1089                 $this->connsOpened = 0;
1090         }
1091
1092         public function closeConnection( IDatabase $conn ) {
1093                 $serverIndex = $conn->getLBInfo( 'serverIndex' ); // second index level of mConns
1094                 foreach ( $this->mConns as $type => $connsByServer ) {
1095                         if ( !isset( $connsByServer[$serverIndex] ) ) {
1096                                 continue;
1097                         }
1098
1099                         foreach ( $connsByServer[$serverIndex] as $i => $trackedConn ) {
1100                                 if ( $conn === $trackedConn ) {
1101                                         $host = $this->getServerName( $i );
1102                                         $this->connLogger->debug( "Closing connection to database $i at '$host'." );
1103                                         unset( $this->mConns[$type][$serverIndex][$i] );
1104                                         --$this->connsOpened;
1105                                         break 2;
1106                                 }
1107                         }
1108                 }
1109
1110                 $conn->close();
1111         }
1112
1113         public function commitAll( $fname = __METHOD__ ) {
1114                 $failures = [];
1115
1116                 $restore = ( $this->trxRoundId !== false );
1117                 $this->trxRoundId = false;
1118                 $this->forEachOpenConnection(
1119                         function ( IDatabase $conn ) use ( $fname, $restore, &$failures ) {
1120                                 try {
1121                                         $conn->commit( $fname, $conn::FLUSHING_ALL_PEERS );
1122                                 } catch ( DBError $e ) {
1123                                         call_user_func( $this->errorLogger, $e );
1124                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1125                                 }
1126                                 if ( $restore && $conn->getLBInfo( 'master' ) ) {
1127                                         $this->undoTransactionRoundFlags( $conn );
1128                                 }
1129                         }
1130                 );
1131
1132                 if ( $failures ) {
1133                         throw new DBExpectedError(
1134                                 null,
1135                                 "Commit failed on server(s) " . implode( "\n", array_unique( $failures ) )
1136                         );
1137                 }
1138         }
1139
1140         public function finalizeMasterChanges() {
1141                 $this->forEachOpenMasterConnection( function ( Database $conn ) {
1142                         // Any error should cause all DB transactions to be rolled back together
1143                         $conn->setTrxEndCallbackSuppression( false );
1144                         $conn->runOnTransactionPreCommitCallbacks();
1145                         // Defer post-commit callbacks until COMMIT finishes for all DBs
1146                         $conn->setTrxEndCallbackSuppression( true );
1147                 } );
1148         }
1149
1150         public function approveMasterChanges( array $options ) {
1151                 $limit = isset( $options['maxWriteDuration'] ) ? $options['maxWriteDuration'] : 0;
1152                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( $limit ) {
1153                         // If atomic sections or explicit transactions are still open, some caller must have
1154                         // caught an exception but failed to properly rollback any changes. Detect that and
1155                         // throw and error (causing rollback).
1156                         if ( $conn->explicitTrxActive() ) {
1157                                 throw new DBTransactionError(
1158                                         $conn,
1159                                         "Explicit transaction still active. A caller may have caught an error."
1160                                 );
1161                         }
1162                         // Assert that the time to replicate the transaction will be sane.
1163                         // If this fails, then all DB transactions will be rollback back together.
1164                         $time = $conn->pendingWriteQueryDuration( $conn::ESTIMATE_DB_APPLY );
1165                         if ( $limit > 0 && $time > $limit ) {
1166                                 throw new DBTransactionSizeError(
1167                                         $conn,
1168                                         "Transaction spent $time second(s) in writes, exceeding the limit of $limit.",
1169                                         [ $time, $limit ]
1170                                 );
1171                         }
1172                         // If a connection sits idle while slow queries execute on another, that connection
1173                         // may end up dropped before the commit round is reached. Ping servers to detect this.
1174                         if ( $conn->writesOrCallbacksPending() && !$conn->ping() ) {
1175                                 throw new DBTransactionError(
1176                                         $conn,
1177                                         "A connection to the {$conn->getDBname()} database was lost before commit."
1178                                 );
1179                         }
1180                 } );
1181         }
1182
1183         public function beginMasterChanges( $fname = __METHOD__ ) {
1184                 if ( $this->trxRoundId !== false ) {
1185                         throw new DBTransactionError(
1186                                 null,
1187                                 "$fname: Transaction round '{$this->trxRoundId}' already started."
1188                         );
1189                 }
1190                 $this->trxRoundId = $fname;
1191
1192                 $failures = [];
1193                 $this->forEachOpenMasterConnection(
1194                         function ( Database $conn ) use ( $fname, &$failures ) {
1195                                 $conn->setTrxEndCallbackSuppression( true );
1196                                 try {
1197                                         $conn->flushSnapshot( $fname );
1198                                 } catch ( DBError $e ) {
1199                                         call_user_func( $this->errorLogger, $e );
1200                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1201                                 }
1202                                 $conn->setTrxEndCallbackSuppression( false );
1203                                 $this->applyTransactionRoundFlags( $conn );
1204                         }
1205                 );
1206
1207                 if ( $failures ) {
1208                         throw new DBExpectedError(
1209                                 null,
1210                                 "$fname: Flush failed on server(s) " . implode( "\n", array_unique( $failures ) )
1211                         );
1212                 }
1213         }
1214
1215         public function commitMasterChanges( $fname = __METHOD__ ) {
1216                 $failures = [];
1217
1218                 /** @noinspection PhpUnusedLocalVariableInspection */
1219                 $scope = $this->getScopedPHPBehaviorForCommit(); // try to ignore client aborts
1220
1221                 $restore = ( $this->trxRoundId !== false );
1222                 $this->trxRoundId = false;
1223                 $this->forEachOpenMasterConnection(
1224                         function ( IDatabase $conn ) use ( $fname, $restore, &$failures ) {
1225                                 try {
1226                                         if ( $conn->writesOrCallbacksPending() ) {
1227                                                 $conn->commit( $fname, $conn::FLUSHING_ALL_PEERS );
1228                                         } elseif ( $restore ) {
1229                                                 $conn->flushSnapshot( $fname );
1230                                         }
1231                                 } catch ( DBError $e ) {
1232                                         call_user_func( $this->errorLogger, $e );
1233                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1234                                 }
1235                                 if ( $restore ) {
1236                                         $this->undoTransactionRoundFlags( $conn );
1237                                 }
1238                         }
1239                 );
1240
1241                 if ( $failures ) {
1242                         throw new DBExpectedError(
1243                                 null,
1244                                 "$fname: Commit failed on server(s) " . implode( "\n", array_unique( $failures ) )
1245                         );
1246                 }
1247         }
1248
1249         public function runMasterPostTrxCallbacks( $type ) {
1250                 $e = null; // first exception
1251                 $this->forEachOpenMasterConnection( function ( Database $conn ) use ( $type, &$e ) {
1252                         $conn->setTrxEndCallbackSuppression( false );
1253                         if ( $conn->writesOrCallbacksPending() ) {
1254                                 // This happens if onTransactionIdle() callbacks leave callbacks on *another* DB
1255                                 // (which finished its callbacks already). Warn and recover in this case. Let the
1256                                 // callbacks run in the final commitMasterChanges() in LBFactory::shutdown().
1257                                 $this->queryLogger->info( __METHOD__ . ": found writes/callbacks pending." );
1258                                 return;
1259                         } elseif ( $conn->trxLevel() ) {
1260                                 // This happens for single-DB setups where DB_REPLICA uses the master DB,
1261                                 // thus leaving an implicit read-only transaction open at this point. It
1262                                 // also happens if onTransactionIdle() callbacks leave implicit transactions
1263                                 // open on *other* DBs (which is slightly improper). Let these COMMIT on the
1264                                 // next call to commitMasterChanges(), possibly in LBFactory::shutdown().
1265                                 return;
1266                         }
1267                         try {
1268                                 $conn->runOnTransactionIdleCallbacks( $type );
1269                         } catch ( Exception $ex ) {
1270                                 $e = $e ?: $ex;
1271                         }
1272                         try {
1273                                 $conn->runTransactionListenerCallbacks( $type );
1274                         } catch ( Exception $ex ) {
1275                                 $e = $e ?: $ex;
1276                         }
1277                 } );
1278
1279                 return $e;
1280         }
1281
1282         public function rollbackMasterChanges( $fname = __METHOD__ ) {
1283                 $restore = ( $this->trxRoundId !== false );
1284                 $this->trxRoundId = false;
1285                 $this->forEachOpenMasterConnection(
1286                         function ( IDatabase $conn ) use ( $fname, $restore ) {
1287                                 if ( $conn->writesOrCallbacksPending() ) {
1288                                         $conn->rollback( $fname, $conn::FLUSHING_ALL_PEERS );
1289                                 }
1290                                 if ( $restore ) {
1291                                         $this->undoTransactionRoundFlags( $conn );
1292                                 }
1293                         }
1294                 );
1295         }
1296
1297         public function suppressTransactionEndCallbacks() {
1298                 $this->forEachOpenMasterConnection( function ( Database $conn ) {
1299                         $conn->setTrxEndCallbackSuppression( true );
1300                 } );
1301         }
1302
1303         /**
1304          * @param IDatabase $conn
1305          */
1306         private function applyTransactionRoundFlags( IDatabase $conn ) {
1307                 if ( $conn->getFlag( $conn::DBO_DEFAULT ) ) {
1308                         // DBO_TRX is controlled entirely by CLI mode presence with DBO_DEFAULT.
1309                         // Force DBO_TRX even in CLI mode since a commit round is expected soon.
1310                         $conn->setFlag( $conn::DBO_TRX, $conn::REMEMBER_PRIOR );
1311                         // If config has explicitly requested DBO_TRX be either on or off by not
1312                         // setting DBO_DEFAULT, then respect that. Forcing no transactions is useful
1313                         // for things like blob stores (ExternalStore) which want auto-commit mode.
1314                 }
1315         }
1316
1317         /**
1318          * @param IDatabase $conn
1319          */
1320         private function undoTransactionRoundFlags( IDatabase $conn ) {
1321                 if ( $conn->getFlag( $conn::DBO_DEFAULT ) ) {
1322                         $conn->restoreFlags( $conn::RESTORE_PRIOR );
1323                 }
1324         }
1325
1326         public function flushReplicaSnapshots( $fname = __METHOD__ ) {
1327                 $this->forEachOpenReplicaConnection( function ( IDatabase $conn ) {
1328                         $conn->flushSnapshot( __METHOD__ );
1329                 } );
1330         }
1331
1332         public function hasMasterConnection() {
1333                 return $this->isOpen( $this->getWriterIndex() );
1334         }
1335
1336         public function hasMasterChanges() {
1337                 $pending = 0;
1338                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$pending ) {
1339                         $pending |= $conn->writesOrCallbacksPending();
1340                 } );
1341
1342                 return (bool)$pending;
1343         }
1344
1345         public function lastMasterChangeTimestamp() {
1346                 $lastTime = false;
1347                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$lastTime ) {
1348                         $lastTime = max( $lastTime, $conn->lastDoneWrites() );
1349                 } );
1350
1351                 return $lastTime;
1352         }
1353
1354         public function hasOrMadeRecentMasterChanges( $age = null ) {
1355                 $age = ( $age === null ) ? $this->mWaitTimeout : $age;
1356
1357                 return ( $this->hasMasterChanges()
1358                         || $this->lastMasterChangeTimestamp() > microtime( true ) - $age );
1359         }
1360
1361         public function pendingMasterChangeCallers() {
1362                 $fnames = [];
1363                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$fnames ) {
1364                         $fnames = array_merge( $fnames, $conn->pendingWriteCallers() );
1365                 } );
1366
1367                 return $fnames;
1368         }
1369
1370         public function getLaggedReplicaMode( $domain = false ) {
1371                 // No-op if there is only one DB (also avoids recursion)
1372                 if ( !$this->laggedReplicaMode && $this->getServerCount() > 1 ) {
1373                         try {
1374                                 // See if laggedReplicaMode gets set
1375                                 $conn = $this->getConnection( self::DB_REPLICA, false, $domain );
1376                                 $this->reuseConnection( $conn );
1377                         } catch ( DBConnectionError $e ) {
1378                                 // Avoid expensive re-connect attempts and failures
1379                                 $this->allReplicasDownMode = true;
1380                                 $this->laggedReplicaMode = true;
1381                         }
1382                 }
1383
1384                 return $this->laggedReplicaMode;
1385         }
1386
1387         /**
1388          * @param bool $domain
1389          * @return bool
1390          * @deprecated 1.28; use getLaggedReplicaMode()
1391          */
1392         public function getLaggedSlaveMode( $domain = false ) {
1393                 return $this->getLaggedReplicaMode( $domain );
1394         }
1395
1396         public function laggedReplicaUsed() {
1397                 return $this->laggedReplicaMode;
1398         }
1399
1400         /**
1401          * @return bool
1402          * @since 1.27
1403          * @deprecated Since 1.28; use laggedReplicaUsed()
1404          */
1405         public function laggedSlaveUsed() {
1406                 return $this->laggedReplicaUsed();
1407         }
1408
1409         public function getReadOnlyReason( $domain = false, IDatabase $conn = null ) {
1410                 if ( $this->readOnlyReason !== false ) {
1411                         return $this->readOnlyReason;
1412                 } elseif ( $this->getLaggedReplicaMode( $domain ) ) {
1413                         if ( $this->allReplicasDownMode ) {
1414                                 return 'The database has been automatically locked ' .
1415                                         'until the replica database servers become available';
1416                         } else {
1417                                 return 'The database has been automatically locked ' .
1418                                         'while the replica database servers catch up to the master.';
1419                         }
1420                 } elseif ( $this->masterRunningReadOnly( $domain, $conn ) ) {
1421                         return 'The database master is running in read-only mode.';
1422                 }
1423
1424                 return false;
1425         }
1426
1427         /**
1428          * @param string $domain Domain ID, or false for the current domain
1429          * @param IDatabase|null $conn DB master connectionl used to avoid loops [optional]
1430          * @return bool
1431          */
1432         private function masterRunningReadOnly( $domain, IDatabase $conn = null ) {
1433                 $cache = $this->wanCache;
1434                 $masterServer = $this->getServerName( $this->getWriterIndex() );
1435
1436                 return (bool)$cache->getWithSetCallback(
1437                         $cache->makeGlobalKey( __CLASS__, 'server-read-only', $masterServer ),
1438                         self::TTL_CACHE_READONLY,
1439                         function () use ( $domain, $conn ) {
1440                                 $old = $this->trxProfiler->setSilenced( true );
1441                                 try {
1442                                         $dbw = $conn ?: $this->getConnection( self::DB_MASTER, [], $domain );
1443                                         $readOnly = (int)$dbw->serverIsReadOnly();
1444                                         if ( !$conn ) {
1445                                                 $this->reuseConnection( $dbw );
1446                                         }
1447                                 } catch ( DBError $e ) {
1448                                         $readOnly = 0;
1449                                 }
1450                                 $this->trxProfiler->setSilenced( $old );
1451                                 return $readOnly;
1452                         },
1453                         [ 'pcTTL' => $cache::TTL_PROC_LONG, 'busyValue' => 0 ]
1454                 );
1455         }
1456
1457         public function allowLagged( $mode = null ) {
1458                 if ( $mode === null ) {
1459                         return $this->mAllowLagged;
1460                 }
1461                 $this->mAllowLagged = $mode;
1462
1463                 return $this->mAllowLagged;
1464         }
1465
1466         public function pingAll() {
1467                 $success = true;
1468                 $this->forEachOpenConnection( function ( IDatabase $conn ) use ( &$success ) {
1469                         if ( !$conn->ping() ) {
1470                                 $success = false;
1471                         }
1472                 } );
1473
1474                 return $success;
1475         }
1476
1477         public function forEachOpenConnection( $callback, array $params = [] ) {
1478                 foreach ( $this->mConns as $connsByServer ) {
1479                         foreach ( $connsByServer as $serverConns ) {
1480                                 foreach ( $serverConns as $conn ) {
1481                                         $mergedParams = array_merge( [ $conn ], $params );
1482                                         call_user_func_array( $callback, $mergedParams );
1483                                 }
1484                         }
1485                 }
1486         }
1487
1488         public function forEachOpenMasterConnection( $callback, array $params = [] ) {
1489                 $masterIndex = $this->getWriterIndex();
1490                 foreach ( $this->mConns as $connsByServer ) {
1491                         if ( isset( $connsByServer[$masterIndex] ) ) {
1492                                 /** @var IDatabase $conn */
1493                                 foreach ( $connsByServer[$masterIndex] as $conn ) {
1494                                         $mergedParams = array_merge( [ $conn ], $params );
1495                                         call_user_func_array( $callback, $mergedParams );
1496                                 }
1497                         }
1498                 }
1499         }
1500
1501         public function forEachOpenReplicaConnection( $callback, array $params = [] ) {
1502                 foreach ( $this->mConns as $connsByServer ) {
1503                         foreach ( $connsByServer as $i => $serverConns ) {
1504                                 if ( $i === $this->getWriterIndex() ) {
1505                                         continue; // skip master
1506                                 }
1507                                 foreach ( $serverConns as $conn ) {
1508                                         $mergedParams = array_merge( [ $conn ], $params );
1509                                         call_user_func_array( $callback, $mergedParams );
1510                                 }
1511                         }
1512                 }
1513         }
1514
1515         public function getMaxLag( $domain = false ) {
1516                 $maxLag = -1;
1517                 $host = '';
1518                 $maxIndex = 0;
1519
1520                 if ( $this->getServerCount() <= 1 ) {
1521                         return [ $host, $maxLag, $maxIndex ]; // no replication = no lag
1522                 }
1523
1524                 $lagTimes = $this->getLagTimes( $domain );
1525                 foreach ( $lagTimes as $i => $lag ) {
1526                         if ( $this->mLoads[$i] > 0 && $lag > $maxLag ) {
1527                                 $maxLag = $lag;
1528                                 $host = $this->mServers[$i]['host'];
1529                                 $maxIndex = $i;
1530                         }
1531                 }
1532
1533                 return [ $host, $maxLag, $maxIndex ];
1534         }
1535
1536         public function getLagTimes( $domain = false ) {
1537                 if ( $this->getServerCount() <= 1 ) {
1538                         return [ $this->getWriterIndex() => 0 ]; // no replication = no lag
1539                 }
1540
1541                 $knownLagTimes = []; // map of (server index => 0 seconds)
1542                 $indexesWithLag = [];
1543                 foreach ( $this->mServers as $i => $server ) {
1544                         if ( empty( $server['is static'] ) ) {
1545                                 $indexesWithLag[] = $i; // DB server might have replication lag
1546                         } else {
1547                                 $knownLagTimes[$i] = 0; // DB server is a non-replicating and read-only archive
1548                         }
1549                 }
1550
1551                 return $this->getLoadMonitor()->getLagTimes( $indexesWithLag, $domain ) + $knownLagTimes;
1552         }
1553
1554         public function safeGetLag( IDatabase $conn ) {
1555                 if ( $this->getServerCount() <= 1 ) {
1556                         return 0;
1557                 } else {
1558                         return $conn->getLag();
1559                 }
1560         }
1561
1562         /**
1563          * @param IDatabase $conn
1564          * @param DBMasterPos|bool $pos
1565          * @param int $timeout
1566          * @return bool
1567          */
1568         public function safeWaitForMasterPos( IDatabase $conn, $pos = false, $timeout = 10 ) {
1569                 if ( $this->getServerCount() <= 1 || !$conn->getLBInfo( 'replica' ) ) {
1570                         return true; // server is not a replica DB
1571                 }
1572
1573                 if ( !$pos ) {
1574                         // Get the current master position, opening a connection if needed
1575                         $masterConn = $this->getAnyOpenConnection( $this->getWriterIndex() );
1576                         if ( $masterConn ) {
1577                                 $pos = $masterConn->getMasterPos();
1578                         } else {
1579                                 $masterConn = $this->openConnection( $this->getWriterIndex(), self::DOMAIN_ANY );
1580                                 $pos = $masterConn->getMasterPos();
1581                                 $this->closeConnection( $masterConn );
1582                         }
1583                 }
1584
1585                 if ( $pos instanceof DBMasterPos ) {
1586                         $result = $conn->masterPosWait( $pos, $timeout );
1587                         if ( $result == -1 || is_null( $result ) ) {
1588                                 $msg = __METHOD__ . ": Timed out waiting on {$conn->getServer()} pos {$pos}";
1589                                 $this->replLogger->warning( "$msg" );
1590                                 $ok = false;
1591                         } else {
1592                                 $this->replLogger->info( __METHOD__ . ": Done" );
1593                                 $ok = true;
1594                         }
1595                 } else {
1596                         $ok = false; // something is misconfigured
1597                         $this->replLogger->error( "Could not get master pos for {$conn->getServer()}." );
1598                 }
1599
1600                 return $ok;
1601         }
1602
1603         public function setTransactionListener( $name, callable $callback = null ) {
1604                 if ( $callback ) {
1605                         $this->trxRecurringCallbacks[$name] = $callback;
1606                 } else {
1607                         unset( $this->trxRecurringCallbacks[$name] );
1608                 }
1609                 $this->forEachOpenMasterConnection(
1610                         function ( IDatabase $conn ) use ( $name, $callback ) {
1611                                 $conn->setTransactionListener( $name, $callback );
1612                         }
1613                 );
1614         }
1615
1616         public function setTableAliases( array $aliases ) {
1617                 $this->tableAliases = $aliases;
1618         }
1619
1620         public function setDomainPrefix( $prefix ) {
1621                 // Find connections to explicit foreign domains still marked as in-use...
1622                 $domainsInUse = [];
1623                 $this->forEachOpenConnection( function ( IDatabase $conn ) use ( &$domainsInUse ) {
1624                         // Once reuseConnection() is called on a handle, its reference count goes from 1 to 0.
1625                         // Until then, it is still in use by the caller (explicitly or via DBConnRef scope).
1626                         if ( $conn->getLBInfo( 'foreignPoolRefCount' ) > 0 ) {
1627                                 $domainsInUse[] = $conn->getDomainID();
1628                         }
1629                 } );
1630
1631                 // Do not switch connections to explicit foreign domains unless marked as safe
1632                 if ( $domainsInUse ) {
1633                         $domains = implode( ', ', $domainsInUse );
1634                         throw new DBUnexpectedError( null,
1635                                 "Foreign domain connections are still in use ($domains)." );
1636                 }
1637
1638                 $this->localDomain = new DatabaseDomain(
1639                         $this->localDomain->getDatabase(),
1640                         null,
1641                         $prefix
1642                 );
1643
1644                 $this->forEachOpenConnection( function ( IDatabase $db ) use ( $prefix ) {
1645                         $db->tablePrefix( $prefix );
1646                 } );
1647         }
1648
1649         /**
1650          * Make PHP ignore user aborts/disconnects until the returned
1651          * value leaves scope. This returns null and does nothing in CLI mode.
1652          *
1653          * @return ScopedCallback|null
1654          */
1655         final protected function getScopedPHPBehaviorForCommit() {
1656                 if ( PHP_SAPI != 'cli' ) { // https://bugs.php.net/bug.php?id=47540
1657                         $old = ignore_user_abort( true ); // avoid half-finished operations
1658                         return new ScopedCallback( function () use ( $old ) {
1659                                 ignore_user_abort( $old );
1660                         } );
1661                 }
1662
1663                 return null;
1664         }
1665
1666         function __destruct() {
1667                 // Avoid connection leaks for sanity
1668                 $this->disable();
1669         }
1670 }
1671
1672 class_alias( LoadBalancer::class, 'LoadBalancer' );