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