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