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