includes/db/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 use Psr\Log\LoggerInterface;
  24
  25 /**
  26  * Database load balancing, tracking, and transaction management object
  27  *
  28  * @ingroup Database
  29  */
  30 class LoadBalancer {
  31         /** @var array[] Map of (server index => server config array) */
  32         private $mServers;
  33         /** @var array[] Map of (local/foreignUsed/foreignFree => server index => DatabaseBase array) */
  34         private $mConns;
  35         /** @var array Map of (server index => weight) */
  36         private $mLoads;
  37         /** @var array[] Map of (group => server index => weight) */
  38         private $mGroupLoads;
  39         /** @var bool Whether to disregard replica DB lag as a factor in replica DB selection */
  40         private $mAllowLagged;
  41         /** @var integer Seconds to spend waiting on replica DB lag to resolve */
  42         private $mWaitTimeout;
  43         /** @var string The LoadMonitor subclass name */
  44         private $mLoadMonitorClass;
  45
  46         /** @var LoadMonitor */
  47         private $mLoadMonitor;
  48         /** @var BagOStuff */
  49         private $srvCache;
  50         /** @var WANObjectCache */
  51         private $wanCache;
  52         /** @var TransactionProfiler */
  53         protected $trxProfiler;
  54         /** @var LoggerInterface */
  55         protected $replLogger;
  56         /** @var LoggerInterface */
  57         protected $connLogger;
  58         /** @var LoggerInterface */
  59         protected $queryLogger;
  60         /** @var LoggerInterface */
  61         protected $perfLogger;
  62
  63         /** @var bool|DatabaseBase Database connection that caused a problem */
  64         private $mErrorConnection;
  65         /** @var integer The generic (not query grouped) replica DB index (of $mServers) */
  66         private $mReadIndex;
  67         /** @var bool|DBMasterPos False if not set */
  68         private $mWaitForPos;
  69         /** @var bool Whether the generic reader fell back to a lagged replica DB */
  70         private $laggedReplicaMode = false;
  71         /** @var bool Whether the generic reader fell back to a lagged replica DB */
  72         private $allReplicasDownMode = false;
  73         /** @var string The last DB selection or connection error */
  74         private $mLastError = 'Unknown error';
  75         /** @var string|bool Reason the LB is read-only or false if not */
  76         private $readOnlyReason = false;
  77         /** @var integer Total connections opened */
  78         private $connsOpened = 0;
  79         /** @var string|bool String if a requested DBO_TRX transaction round is active */
  80         private $trxRoundId = false;
  81         /** @var array[] Map of (name => callable) */
  82         private $trxRecurringCallbacks = [];
  83         /** @var string Local Wiki ID and default for selectDB() calls */
  84         private $localDomain;
  85         /** @var callable Exception logger */
  86         private $errorLogger;
  87
  88         /** @var boolean */
  89         private $disabled = false;
  90
  91         /** @var integer Warn when this many connection are held */
  92         const CONN_HELD_WARN_THRESHOLD = 10;
  93         /** @var integer Default 'max lag' when unspecified */
  94         const MAX_LAG_DEFAULT = 10;
  95         /** @var integer Max time to wait for a replica DB to catch up (e.g. ChronologyProtector) */
  96         const POS_WAIT_TIMEOUT = 10;
  97         /** @var integer Seconds to cache master server read-only status */
  98         const TTL_CACHE_READONLY = 5;
  99
 100         /**
 101          * @param array $params Array with keys:
 102          *  - servers : Required. Array of server info structures.
 103          *  - loadMonitor : Name of a class used to fetch server lag and load.
 104          *  - readOnlyReason : Reason the master DB is read-only if so [optional]
 105          *  - waitTimeout : Maximum time to wait for replicas for consistency [optional]
 106          *  - srvCache : BagOStuff object [optional]
 107          *  - wanCache : WANObjectCache object [optional]
 108          *  - localDomain: The wiki ID of the "local"/"current" wiki [optional]
 109          *  - errorLogger: Callback that takes an Exception and logs it [optional]
 110          *  - connLogger : LoggerInterface object [optional]
 111          *  - queryLogger : LoggerInterface object [optional]
 112          *  - replLogger : LoggerInterface object [optional]
 113          *  - perfLogger : LoggerInterface object [optional]
 114          * @throws InvalidArgumentException
 115          */
 116         public function __construct( array $params ) {
 117                 if ( !isset( $params['servers'] ) ) {
 118                         throw new InvalidArgumentException( __CLASS__ . ': missing servers parameter' );
 119                 }
 120                 $this->mServers = $params['servers'];
 121                 $this->mWaitTimeout = isset( $params['waitTimeout'] )
 122                         ? $params['waitTimeout']
 123                         : self::POS_WAIT_TIMEOUT;
 124                 $this->localDomain = isset( $params['localDomain'] ) ? $params['localDomain'] : '';
 125
 126                 $this->mReadIndex = -1;
 127                 $this->mConns = [
 128                         'local' => [],
 129                         'foreignUsed' => [],
 130                         'foreignFree' => [] ];
 131                 $this->mLoads = [];
 132                 $this->mWaitForPos = false;
 133                 $this->mErrorConnection = false;
 134                 $this->mAllowLagged = false;
 135
 136                 if ( isset( $params['readOnlyReason'] ) && is_string( $params['readOnlyReason'] ) ) {
 137                         $this->readOnlyReason = $params['readOnlyReason'];
 138                 }
 139
 140                 if ( isset( $params['loadMonitor'] ) ) {
 141                         $this->mLoadMonitorClass = $params['loadMonitor'];
 142                 } else {
 143                         $master = reset( $params['servers'] );
 144                         if ( isset( $master['type'] ) && $master['type'] === 'mysql' ) {
 145                                 $this->mLoadMonitorClass = 'LoadMonitorMySQL';
 146                         } else {
 147                                 $this->mLoadMonitorClass = 'LoadMonitorNull';
 148                         }
 149                 }
 150
 151                 foreach ( $params['servers'] as $i => $server ) {
 152                         $this->mLoads[$i] = $server['load'];
 153                         if ( isset( $server['groupLoads'] ) ) {
 154                                 foreach ( $server['groupLoads'] as $group => $ratio ) {
 155                                         if ( !isset( $this->mGroupLoads[$group] ) ) {
 156                                                 $this->mGroupLoads[$group] = [];
 157                                         }
 158                                         $this->mGroupLoads[$group][$i] = $ratio;
 159                                 }
 160                         }
 161                 }
 162
 163                 if ( isset( $params['srvCache'] ) ) {
 164                         $this->srvCache = $params['srvCache'];
 165                 } else {
 166                         $this->srvCache = new EmptyBagOStuff();
 167                 }
 168                 if ( isset( $params['wanCache'] ) ) {
 169                         $this->wanCache = $params['wanCache'];
 170                 } else {
 171                         $this->wanCache = WANObjectCache::newEmpty();
 172                 }
 173                 if ( isset( $params['trxProfiler'] ) ) {
 174                         $this->trxProfiler = $params['trxProfiler'];
 175                 } else {
 176                         $this->trxProfiler = new TransactionProfiler();
 177                 }
 178
 179                 $this->errorLogger = isset( $params['errorLogger'] )
 180                         ? $params['errorLogger']
 181                         : function ( Exception $e ) {
 182                                 trigger_error( E_WARNING, $e->getMessage() );
 183                         };
 184
 185                 foreach ( [ 'replLogger', 'connLogger', 'queryLogger', 'perfLogger' ] as $key ) {
 186                         $this->$key = isset( $params[$key] ) ? $params[$key] : new \Psr\Log\NullLogger();
 187                 }
 188         }
 189
 190         /**
 191          * Get a LoadMonitor instance
 192          *
 193          * @return LoadMonitor
 194          */
 195         private function getLoadMonitor() {
 196                 if ( !isset( $this->mLoadMonitor ) ) {
 197                         $class = $this->mLoadMonitorClass;
 198                         $this->mLoadMonitor = new $class( $this );
 199                         $this->mLoadMonitor->setLogger( $this->replLogger );
 200                 }
 201
 202                 return $this->mLoadMonitor;
 203         }
 204
 205         /**
 206          * @param array $loads
 207          * @param bool|string $wiki Wiki to get non-lagged for
 208          * @param int $maxLag Restrict the maximum allowed lag to this many seconds
 209          * @return bool|int|string
 210          */
 211         private function getRandomNonLagged( array $loads, $wiki = false, $maxLag = INF ) {
 212                 $lags = $this->getLagTimes( $wiki );
 213
 214                 # Unset excessively lagged servers
 215                 foreach ( $lags as $i => $lag ) {
 216                         if ( $i != 0 ) {
 217                                 # How much lag this server nominally is allowed to have
 218                                 $maxServerLag = isset( $this->mServers[$i]['max lag'] )
 219                                         ? $this->mServers[$i]['max lag']
 220                                         : self::MAX_LAG_DEFAULT; // default
 221                                 # Constrain that futher by $maxLag argument
 222                                 $maxServerLag = min( $maxServerLag, $maxLag );
 223
 224                                 $host = $this->getServerName( $i );
 225                                 if ( $lag === false && !is_infinite( $maxServerLag ) ) {
 226                                         $this->replLogger->error( "Server $host (#$i) is not replicating?" );
 227                                         unset( $loads[$i] );
 228                                 } elseif ( $lag > $maxServerLag ) {
 229                                         $this->replLogger->warning( "Server $host (#$i) has >= $lag seconds of lag" );
 230                                         unset( $loads[$i] );
 231                                 }
 232                         }
 233                 }
 234
 235                 # Find out if all the replica DBs with non-zero load are lagged
 236                 $sum = 0;
 237                 foreach ( $loads as $load ) {
 238                         $sum += $load;
 239                 }
 240                 if ( $sum == 0 ) {
 241                         # No appropriate DB servers except maybe the master and some replica DBs with zero load
 242                         # Do NOT use the master
 243                         # Instead, this function will return false, triggering read-only mode,
 244                         # and a lagged replica DB will be used instead.
 245                         return false;
 246                 }
 247
 248                 if ( count( $loads ) == 0 ) {
 249                         return false;
 250                 }
 251
 252                 # Return a random representative of the remainder
 253                 return ArrayUtils::pickRandom( $loads );
 254         }
 255
 256         /**
 257          * Get the index of the reader connection, which may be a replica DB
 258          * This takes into account load ratios and lag times. It should
 259          * always return a consistent index during a given invocation
 260          *
 261          * Side effect: opens connections to databases
 262          * @param string|bool $group Query group, or false for the generic reader
 263          * @param string|bool $wiki Wiki ID, or false for the current wiki
 264          * @throws MWException
 265          * @return bool|int|string
 266          */
 267         public function getReaderIndex( $group = false, $wiki = false ) {
 268                 if ( count( $this->mServers ) == 1 ) {
 269                         # Skip the load balancing if there's only one server
 270                         return $this->getWriterIndex();
 271                 } elseif ( $group === false && $this->mReadIndex >= 0 ) {
 272                         # Shortcut if generic reader exists already
 273                         return $this->mReadIndex;
 274                 }
 275
 276                 # Find the relevant load array
 277                 if ( $group !== false ) {
 278                         if ( isset( $this->mGroupLoads[$group] ) ) {
 279                                 $nonErrorLoads = $this->mGroupLoads[$group];
 280                         } else {
 281                                 # No loads for this group, return false and the caller can use some other group
 282                                 $this->connLogger->info( __METHOD__ . ": no loads for group $group" );
 283
 284                                 return false;
 285                         }
 286                 } else {
 287                         $nonErrorLoads = $this->mLoads;
 288                 }
 289
 290                 if ( !count( $nonErrorLoads ) ) {
 291                         throw new MWException( "Empty server array given to LoadBalancer" );
 292                 }
 293
 294                 # Scale the configured load ratios according to the dynamic load if supported
 295                 $this->getLoadMonitor()->scaleLoads( $nonErrorLoads, $group, $wiki );
 296
 297                 $laggedReplicaMode = false;
 298
 299                 # No server found yet
 300                 $i = false;
 301                 # First try quickly looking through the available servers for a server that
 302                 # meets our criteria
 303                 $currentLoads = $nonErrorLoads;
 304                 while ( count( $currentLoads ) ) {
 305                         if ( $this->mAllowLagged || $laggedReplicaMode ) {
 306                                 $i = ArrayUtils::pickRandom( $currentLoads );
 307                         } else {
 308                                 $i = false;
 309                                 if ( $this->mWaitForPos && $this->mWaitForPos->asOfTime() ) {
 310                                         # ChronologyProtecter causes mWaitForPos to be set via sessions.
 311                                         # This triggers doWait() after connect, so it's especially good to
 312                                         # avoid lagged servers so as to avoid just blocking in that method.
 313                                         $ago = microtime( true ) - $this->mWaitForPos->asOfTime();
 314                                         # Aim for <= 1 second of waiting (being too picky can backfire)
 315                                         $i = $this->getRandomNonLagged( $currentLoads, $wiki, $ago + 1 );
 316                                 }
 317                                 if ( $i === false ) {
 318                                         # Any server with less lag than it's 'max lag' param is preferable
 319                                         $i = $this->getRandomNonLagged( $currentLoads, $wiki );
 320                                 }
 321                                 if ( $i === false && count( $currentLoads ) != 0 ) {
 322                                         # All replica DBs lagged. Switch to read-only mode
 323                                         $this->replLogger->error( "All replica DBs lagged. Switch to read-only mode" );
 324                                         $i = ArrayUtils::pickRandom( $currentLoads );
 325                                         $laggedReplicaMode = true;
 326                                 }
 327                         }
 328
 329                         if ( $i === false ) {
 330                                 # pickRandom() returned false
 331                                 # This is permanent and means the configuration or the load monitor
 332                                 # wants us to return false.
 333                                 $this->connLogger->debug( __METHOD__ . ": pickRandom() returned false" );
 334
 335                                 return false;
 336                         }
 337
 338                         $serverName = $this->getServerName( $i );
 339                         $this->connLogger->debug( __METHOD__ . ": Using reader #$i: $serverName..." );
 340
 341                         $conn = $this->openConnection( $i, $wiki );
 342                         if ( !$conn ) {
 343                                 $this->connLogger->warning( __METHOD__ . ": Failed connecting to $i/$wiki" );
 344                                 unset( $nonErrorLoads[$i] );
 345                                 unset( $currentLoads[$i] );
 346                                 $i = false;
 347                                 continue;
 348                         }
 349
 350                         // Decrement reference counter, we are finished with this connection.
 351                         // It will be incremented for the caller later.
 352                         if ( $wiki !== false ) {
 353                                 $this->reuseConnection( $conn );
 354                         }
 355
 356                         # Return this server
 357                         break;
 358                 }
 359
 360                 # If all servers were down, quit now
 361                 if ( !count( $nonErrorLoads ) ) {
 362                         $this->connLogger->error( "All servers down" );
 363                 }
 364
 365                 if ( $i !== false ) {
 366                         # Replica DB connection successful.
 367                         # Wait for the session master pos for a short time.
 368                         if ( $this->mWaitForPos && $i > 0 ) {
 369                                 $this->doWait( $i );
 370                         }
 371                         if ( $this->mReadIndex <= 0 && $this->mLoads[$i] > 0 && $group === false ) {
 372                                 $this->mReadIndex = $i;
 373                                 # Record if the generic reader index is in "lagged replica DB" mode
 374                                 if ( $laggedReplicaMode ) {
 375                                         $this->laggedReplicaMode = true;
 376                                 }
 377                         }
 378                         $serverName = $this->getServerName( $i );
 379                         $this->connLogger->debug(
 380                                 __METHOD__ . ": using server $serverName for group '$group'\n" );
 381                 }
 382
 383                 return $i;
 384         }
 385
 386         /**
 387          * Set the master wait position
 388          * If a DB_REPLICA connection has been opened already, waits
 389          * Otherwise sets a variable telling it to wait if such a connection is opened
 390          * @param DBMasterPos $pos
 391          */
 392         public function waitFor( $pos ) {
 393                 $this->mWaitForPos = $pos;
 394                 $i = $this->mReadIndex;
 395
 396                 if ( $i > 0 ) {
 397                         if ( !$this->doWait( $i ) ) {
 398                                 $this->laggedReplicaMode = true;
 399                         }
 400                 }
 401         }
 402
 403         /**
 404          * Set the master wait position and wait for a "generic" replica DB to catch up to it
 405          *
 406          * This can be used a faster proxy for waitForAll()
 407          *
 408          * @param DBMasterPos $pos
 409          * @param int $timeout Max seconds to wait; default is mWaitTimeout
 410          * @return bool Success (able to connect and no timeouts reached)
 411          * @since 1.26
 412          */
 413         public function waitForOne( $pos, $timeout = null ) {
 414                 $this->mWaitForPos = $pos;
 415
 416                 $i = $this->mReadIndex;
 417                 if ( $i <= 0 ) {
 418                         // Pick a generic replica DB if there isn't one yet
 419                         $readLoads = $this->mLoads;
 420                         unset( $readLoads[$this->getWriterIndex()] ); // replica DBs only
 421                         $readLoads = array_filter( $readLoads ); // with non-zero load
 422                         $i = ArrayUtils::pickRandom( $readLoads );
 423                 }
 424
 425                 if ( $i > 0 ) {
 426                         $ok = $this->doWait( $i, true, $timeout );
 427                 } else {
 428                         $ok = true; // no applicable loads
 429                 }
 430
 431                 return $ok;
 432         }
 433
 434         /**
 435          * Set the master wait position and wait for ALL replica DBs to catch up to it
 436          * @param DBMasterPos $pos
 437          * @param int $timeout Max seconds to wait; default is mWaitTimeout
 438          * @return bool Success (able to connect and no timeouts reached)
 439          */
 440         public function waitForAll( $pos, $timeout = null ) {
 441                 $this->mWaitForPos = $pos;
 442                 $serverCount = count( $this->mServers );
 443
 444                 $ok = true;
 445                 for ( $i = 1; $i < $serverCount; $i++ ) {
 446                         if ( $this->mLoads[$i] > 0 ) {
 447                                 $ok = $this->doWait( $i, true, $timeout ) && $ok;
 448                         }
 449                 }
 450
 451                 return $ok;
 452         }
 453
 454         /**
 455          * Get any open connection to a given server index, local or foreign
 456          * Returns false if there is no connection open
 457          *
 458          * @param int $i Server index
 459          * @return DatabaseBase|bool False on failure
 460          */
 461         public function getAnyOpenConnection( $i ) {
 462                 foreach ( $this->mConns as $connsByServer ) {
 463                         if ( !empty( $connsByServer[$i] ) ) {
 464                                 return reset( $connsByServer[$i] );
 465                         }
 466                 }
 467
 468                 return false;
 469         }
 470
 471         /**
 472          * Wait for a given replica DB to catch up to the master pos stored in $this
 473          * @param int $index Server index
 474          * @param bool $open Check the server even if a new connection has to be made
 475          * @param int $timeout Max seconds to wait; default is mWaitTimeout
 476          * @return bool
 477          */
 478         protected function doWait( $index, $open = false, $timeout = null ) {
 479                 $close = false; // close the connection afterwards
 480
 481                 // Check if we already know that the DB has reached this point
 482                 $server = $this->getServerName( $index );
 483                 $key = $this->srvCache->makeGlobalKey( __CLASS__, 'last-known-pos', $server );
 484                 /** @var DBMasterPos $knownReachedPos */
 485                 $knownReachedPos = $this->srvCache->get( $key );
 486                 if ( $knownReachedPos && $knownReachedPos->hasReached( $this->mWaitForPos ) ) {
 487                         $this->replLogger->debug( __METHOD__ .
 488                                 ": replica DB $server known to be caught up (pos >= $knownReachedPos).\n" );
 489                         return true;
 490                 }
 491
 492                 // Find a connection to wait on, creating one if needed and allowed
 493                 $conn = $this->getAnyOpenConnection( $index );
 494                 if ( !$conn ) {
 495                         if ( !$open ) {
 496                                 $this->replLogger->debug( __METHOD__ . ": no connection open for $server\n" );
 497
 498                                 return false;
 499                         } else {
 500                                 $conn = $this->openConnection( $index, '' );
 501                                 if ( !$conn ) {
 502                                         $this->replLogger->warning( __METHOD__ . ": failed to connect to $server\n" );
 503
 504                                         return false;
 505                                 }
 506                                 // Avoid connection spam in waitForAll() when connections
 507                                 // are made just for the sake of doing this lag check.
 508                                 $close = true;
 509                         }
 510                 }
 511
 512                 $this->replLogger->info( __METHOD__ . ": Waiting for replica DB $server to catch up...\n" );
 513                 $timeout = $timeout ?: $this->mWaitTimeout;
 514                 $result = $conn->masterPosWait( $this->mWaitForPos, $timeout );
 515
 516                 if ( $result == -1 || is_null( $result ) ) {
 517                         // Timed out waiting for replica DB, use master instead
 518                         $msg = __METHOD__ . ": Timed out waiting on $server pos {$this->mWaitForPos}";
 519                         $this->replLogger->warning( "$msg\n" );
 520                         $this->perfLogger->warning( "$msg:\n" . wfBacktrace( true ) );
 521                         $ok = false;
 522                 } else {
 523                         $this->replLogger->info( __METHOD__ . ": Done\n" );
 524                         $ok = true;
 525                         // Remember that the DB reached this point
 526                         $this->srvCache->set( $key, $this->mWaitForPos, BagOStuff::TTL_DAY );
 527                 }
 528
 529                 if ( $close ) {
 530                         $this->closeConnection( $conn );
 531                 }
 532
 533                 return $ok;
 534         }
 535
 536         /**
 537          * Get a connection by index
 538          * This is the main entry point for this class.
 539          *
 540          * @param int $i Server index
 541          * @param array|string|bool $groups Query group(s), or false for the generic reader
 542          * @param string|bool $wiki Wiki ID, or false for the current wiki
 543          *
 544          * @throws MWException
 545          * @return DatabaseBase
 546          */
 547         public function getConnection( $i, $groups = [], $wiki = false ) {
 548                 if ( $i === null || $i === false ) {
 549                         throw new MWException( 'Attempt to call ' . __METHOD__ .
 550                                 ' with invalid server index' );
 551                 }
 552
 553                 if ( $wiki === $this->localDomain ) {
 554                         $wiki = false;
 555                 }
 556
 557                 $groups = ( $groups === false || $groups === [] )
 558                         ? [ false ] // check one "group": the generic pool
 559                         : (array)$groups;
 560
 561                 $masterOnly = ( $i == DB_MASTER || $i == $this->getWriterIndex() );
 562                 $oldConnsOpened = $this->connsOpened; // connections open now
 563
 564                 if ( $i == DB_MASTER ) {
 565                         $i = $this->getWriterIndex();
 566                 } else {
 567                         # Try to find an available server in any the query groups (in order)
 568                         foreach ( $groups as $group ) {
 569                                 $groupIndex = $this->getReaderIndex( $group, $wiki );
 570                                 if ( $groupIndex !== false ) {
 571                                         $i = $groupIndex;
 572                                         break;
 573                                 }
 574                         }
 575                 }
 576
 577                 # Operation-based index
 578                 if ( $i == DB_REPLICA ) {
 579                         $this->mLastError = 'Unknown error'; // reset error string
 580                         # Try the general server pool if $groups are unavailable.
 581                         $i = in_array( false, $groups, true )
 582                                 ? false // don't bother with this if that is what was tried above
 583                                 : $this->getReaderIndex( false, $wiki );
 584                         # Couldn't find a working server in getReaderIndex()?
 585                         if ( $i === false ) {
 586                                 $this->mLastError = 'No working replica DB server: ' . $this->mLastError;
 587
 588                                 return $this->reportConnectionError();
 589                         }
 590                 }
 591
 592                 # Now we have an explicit index into the servers array
 593                 $conn = $this->openConnection( $i, $wiki );
 594                 if ( !$conn ) {
 595                         return $this->reportConnectionError();
 596                 }
 597
 598                 # Profile any new connections that happen
 599                 if ( $this->connsOpened > $oldConnsOpened ) {
 600                         $host = $conn->getServer();
 601                         $dbname = $conn->getDBname();
 602                         $this->trxProfiler->recordConnection( $host, $dbname, $masterOnly );
 603                 }
 604
 605                 if ( $masterOnly ) {
 606                         # Make master-requested DB handles inherit any read-only mode setting
 607                         $conn->setLBInfo( 'readOnlyReason', $this->getReadOnlyReason( $wiki, $conn ) );
 608                 }
 609
 610                 return $conn;
 611         }
 612
 613         /**
 614          * Mark a foreign connection as being available for reuse under a different
 615          * DB name or prefix. This mechanism is reference-counted, and must be called
 616          * the same number of times as getConnection() to work.
 617          *
 618          * @param DatabaseBase $conn
 619          * @throws MWException
 620          */
 621         public function reuseConnection( $conn ) {
 622                 $serverIndex = $conn->getLBInfo( 'serverIndex' );
 623                 $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 624                 if ( $serverIndex === null || $refCount === null ) {
 625                         /**
 626                          * This can happen in code like:
 627                          *   foreach ( $dbs as $db ) {
 628                          *     $conn = $lb->getConnection( DB_REPLICA, [], $db );
 629                          *     ...
 630                          *     $lb->reuseConnection( $conn );
 631                          *   }
 632                          * When a connection to the local DB is opened in this way, reuseConnection()
 633                          * should be ignored
 634                          */
 635                         return;
 636                 }
 637
 638                 $dbName = $conn->getDBname();
 639                 $prefix = $conn->tablePrefix();
 640                 if ( strval( $prefix ) !== '' ) {
 641                         $wiki = "$dbName-$prefix";
 642                 } else {
 643                         $wiki = $dbName;
 644                 }
 645                 if ( $this->mConns['foreignUsed'][$serverIndex][$wiki] !== $conn ) {
 646                         throw new MWException( __METHOD__ . ": connection not found, has " .
 647                                 "the connection been freed already?" );
 648                 }
 649                 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
 650                 if ( $refCount <= 0 ) {
 651                         $this->mConns['foreignFree'][$serverIndex][$wiki] = $conn;
 652                         unset( $this->mConns['foreignUsed'][$serverIndex][$wiki] );
 653                         wfDebug( __METHOD__ . ": freed connection $serverIndex/$wiki\n" );
 654                 } else {
 655                         wfDebug( __METHOD__ . ": reference count for $serverIndex/$wiki reduced to $refCount\n" );
 656                 }
 657         }
 658
 659         /**
 660          * Get a database connection handle reference
 661          *
 662          * The handle's methods wrap simply wrap those of a DatabaseBase handle
 663          *
 664          * @see LoadBalancer::getConnection() for parameter information
 665          *
 666          * @param int $db
 667          * @param array|string|bool $groups Query group(s), or false for the generic reader
 668          * @param string|bool $wiki Wiki ID, or false for the current wiki
 669          * @return DBConnRef
 670          */
 671         public function getConnectionRef( $db, $groups = [], $wiki = false ) {
 672                 return new DBConnRef( $this, $this->getConnection( $db, $groups, $wiki ) );
 673         }
 674
 675         /**
 676          * Get a database connection handle reference without connecting yet
 677          *
 678          * The handle's methods wrap simply wrap those of a DatabaseBase handle
 679          *
 680          * @see LoadBalancer::getConnection() for parameter information
 681          *
 682          * @param int $db
 683          * @param array|string|bool $groups Query group(s), or false for the generic reader
 684          * @param string|bool $wiki Wiki ID, or false for the current wiki
 685          * @return DBConnRef
 686          */
 687         public function getLazyConnectionRef( $db, $groups = [], $wiki = false ) {
 688                 $wiki = ( $wiki !== false ) ? $wiki : $this->localDomain;
 689
 690                 return new DBConnRef( $this, [ $db, $groups, $wiki ] );
 691         }
 692
 693         /**
 694          * Open a connection to the server given by the specified index
 695          * Index must be an actual index into the array.
 696          * If the server is already open, returns it.
 697          *
 698          * On error, returns false, and the connection which caused the
 699          * error will be available via $this->mErrorConnection.
 700          *
 701          * @note If disable() was called on this LoadBalancer, this method will throw a DBAccessError.
 702          *
 703          * @param int $i Server index
 704          * @param string|bool $wiki Wiki ID, or false for the current wiki
 705          * @return DatabaseBase|bool Returns false on errors
 706          */
 707         public function openConnection( $i, $wiki = false ) {
 708                 if ( $wiki !== false ) {
 709                         $conn = $this->openForeignConnection( $i, $wiki );
 710                 } elseif ( isset( $this->mConns['local'][$i][0] ) ) {
 711                         $conn = $this->mConns['local'][$i][0];
 712                 } else {
 713                         $server = $this->mServers[$i];
 714                         $server['serverIndex'] = $i;
 715                         $conn = $this->reallyOpenConnection( $server, false );
 716                         $serverName = $this->getServerName( $i );
 717                         if ( $conn->isOpen() ) {
 718                                 $this->connLogger->debug( "Connected to database $i at '$serverName'." );
 719                                 $this->mConns['local'][$i][0] = $conn;
 720                         } else {
 721                                 $this->connLogger->warning( "Failed to connect to database $i at '$serverName'." );
 722                                 $this->mErrorConnection = $conn;
 723                                 $conn = false;
 724                         }
 725                 }
 726
 727                 if ( $conn && !$conn->isOpen() ) {
 728                         // Connection was made but later unrecoverably lost for some reason.
 729                         // Do not return a handle that will just throw exceptions on use,
 730                         // but let the calling code (e.g. getReaderIndex) try another server.
 731                         // See DatabaseMyslBase::ping() for how this can happen.
 732                         $this->mErrorConnection = $conn;
 733                         $conn = false;
 734                 }
 735
 736                 return $conn;
 737         }
 738
 739         /**
 740          * Open a connection to a foreign DB, or return one if it is already open.
 741          *
 742          * Increments a reference count on the returned connection which locks the
 743          * connection to the requested wiki. This reference count can be
 744          * decremented by calling reuseConnection().
 745          *
 746          * If a connection is open to the appropriate server already, but with the wrong
 747          * database, it will be switched to the right database and returned, as long as
 748          * it has been freed first with reuseConnection().
 749          *
 750          * On error, returns false, and the connection which caused the
 751          * error will be available via $this->mErrorConnection.
 752          *
 753          * @note If disable() was called on this LoadBalancer, this method will throw a DBAccessError.
 754          *
 755          * @param int $i Server index
 756          * @param string $wiki Wiki ID to open
 757          * @return DatabaseBase
 758          */
 759         private function openForeignConnection( $i, $wiki ) {
 760                 list( $dbName, $prefix ) = explode( '-', $wiki, 2 ) + [ '', '' ];
 761
 762                 if ( isset( $this->mConns['foreignUsed'][$i][$wiki] ) ) {
 763                         // Reuse an already-used connection
 764                         $conn = $this->mConns['foreignUsed'][$i][$wiki];
 765                         wfDebug( __METHOD__ . ": reusing connection $i/$wiki\n" );
 766                 } elseif ( isset( $this->mConns['foreignFree'][$i][$wiki] ) ) {
 767                         // Reuse a free connection for the same wiki
 768                         $conn = $this->mConns['foreignFree'][$i][$wiki];
 769                         unset( $this->mConns['foreignFree'][$i][$wiki] );
 770                         $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 771                         wfDebug( __METHOD__ . ": reusing free connection $i/$wiki\n" );
 772                 } elseif ( !empty( $this->mConns['foreignFree'][$i] ) ) {
 773                         // Reuse a connection from another wiki
 774                         $conn = reset( $this->mConns['foreignFree'][$i] );
 775                         $oldWiki = key( $this->mConns['foreignFree'][$i] );
 776
 777                         // The empty string as a DB name means "don't care".
 778                         // DatabaseMysqlBase::open() already handle this on connection.
 779                         if ( $dbName !== '' && !$conn->selectDB( $dbName ) ) {
 780                                 $this->mLastError = "Error selecting database $dbName on server " .
 781                                         $conn->getServer() . " from client host " . wfHostname() . "\n";
 782                                 $this->mErrorConnection = $conn;
 783                                 $conn = false;
 784                         } else {
 785                                 $conn->tablePrefix( $prefix );
 786                                 unset( $this->mConns['foreignFree'][$i][$oldWiki] );
 787                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 788                                 wfDebug( __METHOD__ . ": reusing free connection from $oldWiki for $wiki\n" );
 789                         }
 790                 } else {
 791                         // Open a new connection
 792                         $server = $this->mServers[$i];
 793                         $server['serverIndex'] = $i;
 794                         $server['foreignPoolRefCount'] = 0;
 795                         $server['foreign'] = true;
 796                         $conn = $this->reallyOpenConnection( $server, $dbName );
 797                         if ( !$conn->isOpen() ) {
 798                                 wfDebug( __METHOD__ . ": error opening connection for $i/$wiki\n" );
 799                                 $this->mErrorConnection = $conn;
 800                                 $conn = false;
 801                         } else {
 802                                 $conn->tablePrefix( $prefix );
 803                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 804                                 wfDebug( __METHOD__ . ": opened new connection for $i/$wiki\n" );
 805                         }
 806                 }
 807
 808                 // Increment reference count
 809                 if ( $conn ) {
 810                         $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 811                         $conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
 812                 }
 813
 814                 return $conn;
 815         }
 816
 817         /**
 818          * Test if the specified index represents an open connection
 819          *
 820          * @param int $index Server index
 821          * @access private
 822          * @return bool
 823          */
 824         private function isOpen( $index ) {
 825                 if ( !is_integer( $index ) ) {
 826                         return false;
 827                 }
 828
 829                 return (bool)$this->getAnyOpenConnection( $index );
 830         }
 831
 832         /**
 833          * Really opens a connection. Uncached.
 834          * Returns a Database object whether or not the connection was successful.
 835          * @access private
 836          *
 837          * @param array $server
 838          * @param bool $dbNameOverride
 839          * @throws MWException
 840          * @return DatabaseBase
 841          */
 842         protected function reallyOpenConnection( $server, $dbNameOverride = false ) {
 843                 if ( $this->disabled ) {
 844                         throw new DBAccessError();
 845                 }
 846
 847                 if ( !is_array( $server ) ) {
 848                         throw new MWException( 'You must update your load-balancing configuration. ' .
 849                                 'See DefaultSettings.php entry for $wgDBservers.' );
 850                 }
 851
 852                 if ( $dbNameOverride !== false ) {
 853                         $server['dbname'] = $dbNameOverride;
 854                 }
 855
 856                 // Let the handle know what the cluster master is (e.g. "db1052")
 857                 $masterName = $this->getServerName( $this->getWriterIndex() );
 858                 $server['clusterMasterHost'] = $masterName;
 859
 860                 // Log when many connection are made on requests
 861                 if ( ++$this->connsOpened >= self::CONN_HELD_WARN_THRESHOLD ) {
 862                         $this->perfLogger->warning( __METHOD__ . ": " .
 863                                 "{$this->connsOpened}+ connections made (master=$masterName)\n" .
 864                                 wfBacktrace( true ) );
 865                 }
 866
 867                 // Set loggers
 868                 $server['connLogger'] = $this->connLogger;
 869                 $server['queryLogger'] = $this->queryLogger;
 870
 871                 // Create a live connection object
 872                 try {
 873                         $db = DatabaseBase::factory( $server['type'], $server );
 874                 } catch ( DBConnectionError $e ) {
 875                         // FIXME: This is probably the ugliest thing I have ever done to
 876                         // PHP. I'm half-expecting it to segfault, just out of disgust. -- TS
 877                         $db = $e->db;
 878                 }
 879
 880                 $db->setLBInfo( $server );
 881                 $db->setLazyMasterHandle(
 882                         $this->getLazyConnectionRef( DB_MASTER, [], $db->getWikiID() )
 883                 );
 884                 $db->setTransactionProfiler( $this->trxProfiler );
 885
 886                 if ( $server['serverIndex'] === $this->getWriterIndex() ) {
 887                         if ( $this->trxRoundId !== false ) {
 888                                 $this->applyTransactionRoundFlags( $db );
 889                         }
 890                         foreach ( $this->trxRecurringCallbacks as $name => $callback ) {
 891                                 $db->setTransactionListener( $name, $callback );
 892                         }
 893                 }
 894
 895                 return $db;
 896         }
 897
 898         /**
 899          * @throws DBConnectionError
 900          * @return bool
 901          */
 902         private function reportConnectionError() {
 903                 $conn = $this->mErrorConnection; // The connection which caused the error
 904                 $context = [
 905                         'method' => __METHOD__,
 906                         'last_error' => $this->mLastError,
 907                 ];
 908
 909                 if ( !is_object( $conn ) ) {
 910                         // No last connection, probably due to all servers being too busy
 911                         wfLogDBError(
 912                                 "LB failure with no last connection. Connection error: {last_error}",
 913                                 $context
 914                         );
 915
 916                         // If all servers were busy, mLastError will contain something sensible
 917                         throw new DBConnectionError( null, $this->mLastError );
 918                 } else {
 919                         $context['db_server'] = $conn->getProperty( 'mServer' );
 920                         wfLogDBError(
 921                                 "Connection error: {last_error} ({db_server})",
 922                                 $context
 923                         );
 924
 925                         // throws DBConnectionError
 926                         $conn->reportConnectionError( "{$this->mLastError} ({$context['db_server']})" );
 927                 }
 928
 929                 return false; /* not reached */
 930         }
 931
 932         /**
 933          * @return int
 934          * @since 1.26
 935          */
 936         public function getWriterIndex() {
 937                 return 0;
 938         }
 939
 940         /**
 941          * Returns true if the specified index is a valid server index
 942          *
 943          * @param string $i
 944          * @return bool
 945          */
 946         public function haveIndex( $i ) {
 947                 return array_key_exists( $i, $this->mServers );
 948         }
 949
 950         /**
 951          * Returns true if the specified index is valid and has non-zero load
 952          *
 953          * @param string $i
 954          * @return bool
 955          */
 956         public function isNonZeroLoad( $i ) {
 957                 return array_key_exists( $i, $this->mServers ) && $this->mLoads[$i] != 0;
 958         }
 959
 960         /**
 961          * Get the number of defined servers (not the number of open connections)
 962          *
 963          * @return int
 964          */
 965         public function getServerCount() {
 966                 return count( $this->mServers );
 967         }
 968
 969         /**
 970          * Get the host name or IP address of the server with the specified index
 971          * Prefer a readable name if available.
 972          * @param string $i
 973          * @return string
 974          */
 975         public function getServerName( $i ) {
 976                 if ( isset( $this->mServers[$i]['hostName'] ) ) {
 977                         $name = $this->mServers[$i]['hostName'];
 978                 } elseif ( isset( $this->mServers[$i]['host'] ) ) {
 979                         $name = $this->mServers[$i]['host'];
 980                 } else {
 981                         $name = '';
 982                 }
 983
 984                 return ( $name != '' ) ? $name : 'localhost';
 985         }
 986
 987         /**
 988          * Return the server info structure for a given index, or false if the index is invalid.
 989          * @param int $i
 990          * @return array|bool
 991          */
 992         public function getServerInfo( $i ) {
 993                 if ( isset( $this->mServers[$i] ) ) {
 994                         return $this->mServers[$i];
 995                 } else {
 996                         return false;
 997                 }
 998         }
 999
1000         /**
1001          * Sets the server info structure for the given index. Entry at index $i
1002          * is created if it doesn't exist
1003          * @param int $i
1004          * @param array $serverInfo
1005          */
1006         public function setServerInfo( $i, array $serverInfo ) {
1007                 $this->mServers[$i] = $serverInfo;
1008         }
1009
1010         /**
1011          * Get the current master position for chronology control purposes
1012          * @return DBMasterPos|bool Returns false if not applicable
1013          */
1014         public function getMasterPos() {
1015                 # If this entire request was served from a replica DB without opening a connection to the
1016                 # master (however unlikely that may be), then we can fetch the position from the replica DB.
1017                 $masterConn = $this->getAnyOpenConnection( $this->getWriterIndex() );
1018                 if ( !$masterConn ) {
1019                         $serverCount = count( $this->mServers );
1020                         for ( $i = 1; $i < $serverCount; $i++ ) {
1021                                 $conn = $this->getAnyOpenConnection( $i );
1022                                 if ( $conn ) {
1023                                         return $conn->getSlavePos();
1024                                 }
1025                         }
1026                 } else {
1027                         return $masterConn->getMasterPos();
1028                 }
1029
1030                 return false;
1031         }
1032
1033         /**
1034          * Disable this load balancer. All connections are closed, and any attempt to
1035          * open a new connection will result in a DBAccessError.
1036          *
1037          * @since 1.27
1038          */
1039         public function disable() {
1040                 $this->closeAll();
1041                 $this->disabled = true;
1042         }
1043
1044         /**
1045          * Close all open connections
1046          */
1047         public function closeAll() {
1048                 $this->forEachOpenConnection( function ( DatabaseBase $conn ) {
1049                         $conn->close();
1050                 } );
1051
1052                 $this->mConns = [
1053                         'local' => [],
1054                         'foreignFree' => [],
1055                         'foreignUsed' => [],
1056                 ];
1057                 $this->connsOpened = 0;
1058         }
1059
1060         /**
1061          * Close a connection
1062          *
1063          * Using this function makes sure the LoadBalancer knows the connection is closed.
1064          * If you use $conn->close() directly, the load balancer won't update its state.
1065          *
1066          * @param DatabaseBase $conn
1067          */
1068         public function closeConnection( DatabaseBase $conn ) {
1069                 $serverIndex = $conn->getLBInfo( 'serverIndex' ); // second index level of mConns
1070                 foreach ( $this->mConns as $type => $connsByServer ) {
1071                         if ( !isset( $connsByServer[$serverIndex] ) ) {
1072                                 continue;
1073                         }
1074
1075                         foreach ( $connsByServer[$serverIndex] as $i => $trackedConn ) {
1076                                 if ( $conn === $trackedConn ) {
1077                                         unset( $this->mConns[$type][$serverIndex][$i] );
1078                                         --$this->connsOpened;
1079                                         break 2;
1080                                 }
1081                         }
1082                 }
1083
1084                 $conn->close();
1085         }
1086
1087         /**
1088          * Commit transactions on all open connections
1089          * @param string $fname Caller name
1090          * @throws DBExpectedError
1091          */
1092         public function commitAll( $fname = __METHOD__ ) {
1093                 $failures = [];
1094
1095                 $restore = ( $this->trxRoundId !== false );
1096                 $this->trxRoundId = false;
1097                 $this->forEachOpenConnection(
1098                         function ( DatabaseBase $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         /**
1120          * Perform all pre-commit callbacks that remain part of the atomic transactions
1121          * and disable any post-commit callbacks until runMasterPostTrxCallbacks()
1122          * @since 1.28
1123          */
1124         public function finalizeMasterChanges() {
1125                 $this->forEachOpenMasterConnection( function ( DatabaseBase $conn ) {
1126                         // Any error should cause all DB transactions to be rolled back together
1127                         $conn->setTrxEndCallbackSuppression( false );
1128                         $conn->runOnTransactionPreCommitCallbacks();
1129                         // Defer post-commit callbacks until COMMIT finishes for all DBs
1130                         $conn->setTrxEndCallbackSuppression( true );
1131                 } );
1132         }
1133
1134         /**
1135          * Perform all pre-commit checks for things like replication safety
1136          * @param array $options Includes:
1137          *   - maxWriteDuration : max write query duration time in seconds
1138          * @throws DBTransactionError
1139          * @since 1.28
1140          */
1141         public function approveMasterChanges( array $options ) {
1142                 $limit = isset( $options['maxWriteDuration'] ) ? $options['maxWriteDuration'] : 0;
1143                 $this->forEachOpenMasterConnection( function ( DatabaseBase $conn ) use ( $limit ) {
1144                         // If atomic sections or explicit transactions are still open, some caller must have
1145                         // caught an exception but failed to properly rollback any changes. Detect that and
1146                         // throw and error (causing rollback).
1147                         if ( $conn->explicitTrxActive() ) {
1148                                 throw new DBTransactionError(
1149                                         $conn,
1150                                         "Explicit transaction still active. A caller may have caught an error."
1151                                 );
1152                         }
1153                         // Assert that the time to replicate the transaction will be sane.
1154                         // If this fails, then all DB transactions will be rollback back together.
1155                         $time = $conn->pendingWriteQueryDuration( $conn::ESTIMATE_DB_APPLY );
1156                         if ( $limit > 0 && $time > $limit ) {
1157                                 throw new DBTransactionError(
1158                                         $conn,
1159                                         wfMessage( 'transaction-duration-limit-exceeded', $time, $limit )->text()
1160                                 );
1161                         }
1162                         // If a connection sits idle while slow queries execute on another, that connection
1163                         // may end up dropped before the commit round is reached. Ping servers to detect this.
1164                         if ( $conn->writesOrCallbacksPending() && !$conn->ping() ) {
1165                                 throw new DBTransactionError(
1166                                         $conn,
1167                                         "A connection to the {$conn->getDBname()} database was lost before commit."
1168                                 );
1169                         }
1170                 } );
1171         }
1172
1173         /**
1174          * Flush any master transaction snapshots and set DBO_TRX (if DBO_DEFAULT is set)
1175          *
1176          * The DBO_TRX setting will be reverted to the default in each of these methods:
1177          *   - commitMasterChanges()
1178          *   - rollbackMasterChanges()
1179          *   - commitAll()
1180          * This allows for custom transaction rounds from any outer transaction scope.
1181          *
1182          * @param string $fname
1183          * @throws DBExpectedError
1184          * @since 1.28
1185          */
1186         public function beginMasterChanges( $fname = __METHOD__ ) {
1187                 if ( $this->trxRoundId !== false ) {
1188                         throw new DBTransactionError(
1189                                 null,
1190                                 "$fname: Transaction round '{$this->trxRoundId}' already started."
1191                         );
1192                 }
1193                 $this->trxRoundId = $fname;
1194
1195                 $failures = [];
1196                 $this->forEachOpenMasterConnection(
1197                         function ( DatabaseBase $conn ) use ( $fname, &$failures ) {
1198                                 $conn->setTrxEndCallbackSuppression( true );
1199                                 try {
1200                                         $conn->flushSnapshot( $fname );
1201                                 } catch ( DBError $e ) {
1202                                         call_user_func( $this->errorLogger, $e );
1203                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1204                                 }
1205                                 $conn->setTrxEndCallbackSuppression( false );
1206                                 $this->applyTransactionRoundFlags( $conn );
1207                         }
1208                 );
1209
1210                 if ( $failures ) {
1211                         throw new DBExpectedError(
1212                                 null,
1213                                 "$fname: Flush failed on server(s) " . implode( "\n", array_unique( $failures ) )
1214                         );
1215                 }
1216         }
1217
1218         /**
1219          * Issue COMMIT on all master connections where writes where done
1220          * @param string $fname Caller name
1221          * @throws DBExpectedError
1222          */
1223         public function commitMasterChanges( $fname = __METHOD__ ) {
1224                 $failures = [];
1225
1226                 $restore = ( $this->trxRoundId !== false );
1227                 $this->trxRoundId = false;
1228                 $this->forEachOpenMasterConnection(
1229                         function ( DatabaseBase $conn ) use ( $fname, $restore, &$failures ) {
1230                                 try {
1231                                         if ( $conn->writesOrCallbacksPending() ) {
1232                                                 $conn->commit( $fname, $conn::FLUSHING_ALL_PEERS );
1233                                         } elseif ( $restore ) {
1234                                                 $conn->flushSnapshot( $fname );
1235                                         }
1236                                 } catch ( DBError $e ) {
1237                                         call_user_func( $this->errorLogger, $e );
1238                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1239                                 }
1240                                 if ( $restore ) {
1241                                         $this->undoTransactionRoundFlags( $conn );
1242                                 }
1243                         }
1244                 );
1245
1246                 if ( $failures ) {
1247                         throw new DBExpectedError(
1248                                 null,
1249                                 "$fname: Commit failed on server(s) " . implode( "\n", array_unique( $failures ) )
1250                         );
1251                 }
1252         }
1253
1254         /**
1255          * Issue all pending post-COMMIT/ROLLBACK callbacks
1256          * @param integer $type IDatabase::TRIGGER_* constant
1257          * @return Exception|null The first exception or null if there were none
1258          * @since 1.28
1259          */
1260         public function runMasterPostTrxCallbacks( $type ) {
1261                 $e = null; // first exception
1262                 $this->forEachOpenMasterConnection( function ( DatabaseBase $conn ) use ( $type, &$e ) {
1263                         $conn->setTrxEndCallbackSuppression( false );
1264                         if ( $conn->writesOrCallbacksPending() ) {
1265                                 // This happens if onTransactionIdle() callbacks leave callbacks on *another* DB
1266                                 // (which finished its callbacks already). Warn and recover in this case. Let the
1267                                 // callbacks run in the final commitMasterChanges() in LBFactory::shutdown().
1268                                 wfWarn( __METHOD__ . ": did not expect writes/callbacks pending." );
1269                                 return;
1270                         } elseif ( $conn->trxLevel() ) {
1271                                 // This happens for single-DB setups where DB_REPLICA uses the master DB,
1272                                 // thus leaving an implicit read-only transaction open at this point. It
1273                                 // also happens if onTransactionIdle() callbacks leave implicit transactions
1274                                 // open on *other* DBs (which is slightly improper). Let these COMMIT on the
1275                                 // next call to commitMasterChanges(), possibly in LBFactory::shutdown().
1276                                 return;
1277                         }
1278                         try {
1279                                 $conn->runOnTransactionIdleCallbacks( $type );
1280                         } catch ( Exception $ex ) {
1281                                 $e = $e ?: $ex;
1282                         }
1283                         try {
1284                                 $conn->runTransactionListenerCallbacks( $type );
1285                         } catch ( Exception $ex ) {
1286                                 $e = $e ?: $ex;
1287                         }
1288                 } );
1289
1290                 return $e;
1291         }
1292
1293         /**
1294          * Issue ROLLBACK only on master, only if queries were done on connection
1295          * @param string $fname Caller name
1296          * @throws DBExpectedError
1297          * @since 1.23
1298          */
1299         public function rollbackMasterChanges( $fname = __METHOD__ ) {
1300                 $restore = ( $this->trxRoundId !== false );
1301                 $this->trxRoundId = false;
1302                 $this->forEachOpenMasterConnection(
1303                         function ( DatabaseBase $conn ) use ( $fname, $restore ) {
1304                                 if ( $conn->writesOrCallbacksPending() ) {
1305                                         $conn->rollback( $fname, $conn::FLUSHING_ALL_PEERS );
1306                                 }
1307                                 if ( $restore ) {
1308                                         $this->undoTransactionRoundFlags( $conn );
1309                                 }
1310                         }
1311                 );
1312         }
1313
1314         /**
1315          * Suppress all pending post-COMMIT/ROLLBACK callbacks
1316          * @return Exception|null The first exception or null if there were none
1317          * @since 1.28
1318          */
1319         public function suppressTransactionEndCallbacks() {
1320                 $this->forEachOpenMasterConnection( function ( DatabaseBase $conn ) {
1321                         $conn->setTrxEndCallbackSuppression( true );
1322                 } );
1323         }
1324
1325         /**
1326          * @param DatabaseBase $conn
1327          */
1328         private function applyTransactionRoundFlags( DatabaseBase $conn ) {
1329                 if ( $conn->getFlag( DBO_DEFAULT ) ) {
1330                         // DBO_TRX is controlled entirely by CLI mode presence with DBO_DEFAULT.
1331                         // Force DBO_TRX even in CLI mode since a commit round is expected soon.
1332                         $conn->setFlag( DBO_TRX, $conn::REMEMBER_PRIOR );
1333                         // If config has explicitly requested DBO_TRX be either on or off by not
1334                         // setting DBO_DEFAULT, then respect that. Forcing no transactions is useful
1335                         // for things like blob stores (ExternalStore) which want auto-commit mode.
1336                 }
1337         }
1338
1339         /**
1340          * @param DatabaseBase $conn
1341          */
1342         private function undoTransactionRoundFlags( DatabaseBase $conn ) {
1343                 if ( $conn->getFlag( DBO_DEFAULT ) ) {
1344                         $conn->restoreFlags( $conn::RESTORE_PRIOR );
1345                 }
1346         }
1347
1348         /**
1349          * Commit all replica DB transactions so as to flush any REPEATABLE-READ or SSI snapshot
1350          *
1351          * @param string $fname Caller name
1352          * @since 1.28
1353          */
1354         public function flushReplicaSnapshots( $fname = __METHOD__ ) {
1355                 $this->forEachOpenReplicaConnection( function ( DatabaseBase $conn ) {
1356                         $conn->flushSnapshot( __METHOD__ );
1357                 } );
1358         }
1359
1360         /**
1361          * @return bool Whether a master connection is already open
1362          * @since 1.24
1363          */
1364         public function hasMasterConnection() {
1365                 return $this->isOpen( $this->getWriterIndex() );
1366         }
1367
1368         /**
1369          * Determine if there are pending changes in a transaction by this thread
1370          * @since 1.23
1371          * @return bool
1372          */
1373         public function hasMasterChanges() {
1374                 $pending = 0;
1375                 $this->forEachOpenMasterConnection( function ( DatabaseBase $conn ) use ( &$pending ) {
1376                         $pending |= $conn->writesOrCallbacksPending();
1377                 } );
1378
1379                 return (bool)$pending;
1380         }
1381
1382         /**
1383          * Get the timestamp of the latest write query done by this thread
1384          * @since 1.25
1385          * @return float|bool UNIX timestamp or false
1386          */
1387         public function lastMasterChangeTimestamp() {
1388                 $lastTime = false;
1389                 $this->forEachOpenMasterConnection( function ( DatabaseBase $conn ) use ( &$lastTime ) {
1390                         $lastTime = max( $lastTime, $conn->lastDoneWrites() );
1391                 } );
1392
1393                 return $lastTime;
1394         }
1395
1396         /**
1397          * Check if this load balancer object had any recent or still
1398          * pending writes issued against it by this PHP thread
1399          *
1400          * @param float $age How many seconds ago is "recent" [defaults to mWaitTimeout]
1401          * @return bool
1402          * @since 1.25
1403          */
1404         public function hasOrMadeRecentMasterChanges( $age = null ) {
1405                 $age = ( $age === null ) ? $this->mWaitTimeout : $age;
1406
1407                 return ( $this->hasMasterChanges()
1408                         || $this->lastMasterChangeTimestamp() > microtime( true ) - $age );
1409         }
1410
1411         /**
1412          * Get the list of callers that have pending master changes
1413          *
1414          * @return string[] List of method names
1415          * @since 1.27
1416          */
1417         public function pendingMasterChangeCallers() {
1418                 $fnames = [];
1419                 $this->forEachOpenMasterConnection( function ( DatabaseBase $conn ) use ( &$fnames ) {
1420                         $fnames = array_merge( $fnames, $conn->pendingWriteCallers() );
1421                 } );
1422
1423                 return $fnames;
1424         }
1425
1426         /**
1427          * @note This method will trigger a DB connection if not yet done
1428          * @param string|bool $wiki Wiki ID, or false for the current wiki
1429          * @return bool Whether the generic connection for reads is highly "lagged"
1430          */
1431         public function getLaggedReplicaMode( $wiki = false ) {
1432                 // No-op if there is only one DB (also avoids recursion)
1433                 if ( !$this->laggedReplicaMode && $this->getServerCount() > 1 ) {
1434                         try {
1435                                 // See if laggedReplicaMode gets set
1436                                 $conn = $this->getConnection( DB_REPLICA, false, $wiki );
1437                                 $this->reuseConnection( $conn );
1438                         } catch ( DBConnectionError $e ) {
1439                                 // Avoid expensive re-connect attempts and failures
1440                                 $this->allReplicasDownMode = true;
1441                                 $this->laggedReplicaMode = true;
1442                         }
1443                 }
1444
1445                 return $this->laggedReplicaMode;
1446         }
1447
1448         /**
1449          * @param bool $wiki
1450          * @return bool
1451          * @deprecated 1.28; use getLaggedReplicaMode()
1452          */
1453         public function getLaggedSlaveMode( $wiki = false ) {
1454                 return $this->getLaggedReplicaMode( $wiki );
1455         }
1456
1457         /**
1458          * @note This method will never cause a new DB connection
1459          * @return bool Whether any generic connection used for reads was highly "lagged"
1460          * @since 1.28
1461          */
1462         public function laggedReplicaUsed() {
1463                 return $this->laggedReplicaMode;
1464         }
1465
1466         /**
1467          * @return bool
1468          * @since 1.27
1469          * @deprecated Since 1.28; use laggedReplicaUsed()
1470          */
1471         public function laggedSlaveUsed() {
1472                 return $this->laggedReplicaUsed();
1473         }
1474
1475         /**
1476          * @note This method may trigger a DB connection if not yet done
1477          * @param string|bool $wiki Wiki ID, or false for the current wiki
1478          * @param DatabaseBase|null DB master connection; used to avoid loops [optional]
1479          * @return string|bool Reason the master is read-only or false if it is not
1480          * @since 1.27
1481          */
1482         public function getReadOnlyReason( $wiki = false, DatabaseBase $conn = null ) {
1483                 if ( $this->readOnlyReason !== false ) {
1484                         return $this->readOnlyReason;
1485                 } elseif ( $this->getLaggedReplicaMode( $wiki ) ) {
1486                         if ( $this->allReplicasDownMode ) {
1487                                 return 'The database has been automatically locked ' .
1488                                         'until the replica database servers become available';
1489                         } else {
1490                                 return 'The database has been automatically locked ' .
1491                                         'while the replica database servers catch up to the master.';
1492                         }
1493                 } elseif ( $this->masterRunningReadOnly( $wiki, $conn ) ) {
1494                         return 'The database master is running in read-only mode.';
1495                 }
1496
1497                 return false;
1498         }
1499
1500         /**
1501          * @param string $wiki Wiki ID, or false for the current wiki
1502          * @param DatabaseBase|null DB master connectionl used to avoid loops [optional]
1503          * @return bool
1504          */
1505         private function masterRunningReadOnly( $wiki, DatabaseBase $conn = null ) {
1506                 $cache = $this->wanCache;
1507                 $masterServer = $this->getServerName( $this->getWriterIndex() );
1508
1509                 return (bool)$cache->getWithSetCallback(
1510                         $cache->makeGlobalKey( __CLASS__, 'server-read-only', $masterServer ),
1511                         self::TTL_CACHE_READONLY,
1512                         function () use ( $wiki, $conn ) {
1513                                 $this->trxProfiler->setSilenced( true );
1514                                 try {
1515                                         $dbw = $conn ?: $this->getConnection( DB_MASTER, [], $wiki );
1516                                         $readOnly = (int)$dbw->serverIsReadOnly();
1517                                 } catch ( DBError $e ) {
1518                                         $readOnly = 0;
1519                                 }
1520                                 $this->trxProfiler->setSilenced( false );
1521                                 return $readOnly;
1522                         },
1523                         [ 'pcTTL' => $cache::TTL_PROC_LONG, 'busyValue' => 0 ]
1524                 );
1525         }
1526
1527         /**
1528          * Disables/enables lag checks
1529          * @param null|bool $mode
1530          * @return bool
1531          */
1532         public function allowLagged( $mode = null ) {
1533                 if ( $mode === null ) {
1534                         return $this->mAllowLagged;
1535                 }
1536                 $this->mAllowLagged = $mode;
1537
1538                 return $this->mAllowLagged;
1539         }
1540
1541         /**
1542          * @return bool
1543          */
1544         public function pingAll() {
1545                 $success = true;
1546                 $this->forEachOpenConnection( function ( DatabaseBase $conn ) use ( &$success ) {
1547                         if ( !$conn->ping() ) {
1548                                 $success = false;
1549                         }
1550                 } );
1551
1552                 return $success;
1553         }
1554
1555         /**
1556          * Call a function with each open connection object
1557          * @param callable $callback
1558          * @param array $params
1559          */
1560         public function forEachOpenConnection( $callback, array $params = [] ) {
1561                 foreach ( $this->mConns as $connsByServer ) {
1562                         foreach ( $connsByServer as $serverConns ) {
1563                                 foreach ( $serverConns as $conn ) {
1564                                         $mergedParams = array_merge( [ $conn ], $params );
1565                                         call_user_func_array( $callback, $mergedParams );
1566                                 }
1567                         }
1568                 }
1569         }
1570
1571         /**
1572          * Call a function with each open connection object to a master
1573          * @param callable $callback
1574          * @param array $params
1575          * @since 1.28
1576          */
1577         public function forEachOpenMasterConnection( $callback, array $params = [] ) {
1578                 $masterIndex = $this->getWriterIndex();
1579                 foreach ( $this->mConns as $connsByServer ) {
1580                         if ( isset( $connsByServer[$masterIndex] ) ) {
1581                                 /** @var DatabaseBase $conn */
1582                                 foreach ( $connsByServer[$masterIndex] as $conn ) {
1583                                         $mergedParams = array_merge( [ $conn ], $params );
1584                                         call_user_func_array( $callback, $mergedParams );
1585                                 }
1586                         }
1587                 }
1588         }
1589
1590         /**
1591          * Call a function with each open replica DB connection object
1592          * @param callable $callback
1593          * @param array $params
1594          * @since 1.28
1595          */
1596         public function forEachOpenReplicaConnection( $callback, array $params = [] ) {
1597                 foreach ( $this->mConns as $connsByServer ) {
1598                         foreach ( $connsByServer as $i => $serverConns ) {
1599                                 if ( $i === $this->getWriterIndex() ) {
1600                                         continue; // skip master
1601                                 }
1602                                 foreach ( $serverConns as $conn ) {
1603                                         $mergedParams = array_merge( [ $conn ], $params );
1604                                         call_user_func_array( $callback, $mergedParams );
1605                                 }
1606                         }
1607                 }
1608         }
1609
1610         /**
1611          * Get the hostname and lag time of the most-lagged replica DB
1612          *
1613          * This is useful for maintenance scripts that need to throttle their updates.
1614          * May attempt to open connections to replica DBs on the default DB. If there is
1615          * no lag, the maximum lag will be reported as -1.
1616          *
1617          * @param bool|string $wiki Wiki ID, or false for the default database
1618          * @return array ( host, max lag, index of max lagged host )
1619          */
1620         public function getMaxLag( $wiki = false ) {
1621                 $maxLag = -1;
1622                 $host = '';
1623                 $maxIndex = 0;
1624
1625                 if ( $this->getServerCount() <= 1 ) {
1626                         return [ $host, $maxLag, $maxIndex ]; // no replication = no lag
1627                 }
1628
1629                 $lagTimes = $this->getLagTimes( $wiki );
1630                 foreach ( $lagTimes as $i => $lag ) {
1631                         if ( $this->mLoads[$i] > 0 && $lag > $maxLag ) {
1632                                 $maxLag = $lag;
1633                                 $host = $this->mServers[$i]['host'];
1634                                 $maxIndex = $i;
1635                         }
1636                 }
1637
1638                 return [ $host, $maxLag, $maxIndex ];
1639         }
1640
1641         /**
1642          * Get an estimate of replication lag (in seconds) for each server
1643          *
1644          * Results are cached for a short time in memcached/process cache
1645          *
1646          * Values may be "false" if replication is too broken to estimate
1647          *
1648          * @param string|bool $wiki
1649          * @return int[] Map of (server index => float|int|bool)
1650          */
1651         public function getLagTimes( $wiki = false ) {
1652                 if ( $this->getServerCount() <= 1 ) {
1653                         return [ 0 => 0 ]; // no replication = no lag
1654                 }
1655
1656                 # Send the request to the load monitor
1657                 return $this->getLoadMonitor()->getLagTimes( array_keys( $this->mServers ), $wiki );
1658         }
1659
1660         /**
1661          * Get the lag in seconds for a given connection, or zero if this load
1662          * balancer does not have replication enabled.
1663          *
1664          * This should be used in preference to Database::getLag() in cases where
1665          * replication may not be in use, since there is no way to determine if
1666          * replication is in use at the connection level without running
1667          * potentially restricted queries such as SHOW SLAVE STATUS. Using this
1668          * function instead of Database::getLag() avoids a fatal error in this
1669          * case on many installations.
1670          *
1671          * @param IDatabase $conn
1672          * @return int|bool Returns false on error
1673          */
1674         public function safeGetLag( IDatabase $conn ) {
1675                 if ( $this->getServerCount() == 1 ) {
1676                         return 0;
1677                 } else {
1678                         return $conn->getLag();
1679                 }
1680         }
1681
1682         /**
1683          * Wait for a replica DB to reach a specified master position
1684          *
1685          * This will connect to the master to get an accurate position if $pos is not given
1686          *
1687          * @param IDatabase $conn Replica DB
1688          * @param DBMasterPos|bool $pos Master position; default: current position
1689          * @param integer $timeout Timeout in seconds
1690          * @return bool Success
1691          * @since 1.27
1692          */
1693         public function safeWaitForMasterPos( IDatabase $conn, $pos = false, $timeout = 10 ) {
1694                 if ( $this->getServerCount() == 1 || !$conn->getLBInfo( 'replica' ) ) {
1695                         return true; // server is not a replica DB
1696                 }
1697
1698                 $pos = $pos ?: $this->getConnection( DB_MASTER )->getMasterPos();
1699                 if ( !( $pos instanceof DBMasterPos ) ) {
1700                         return false; // something is misconfigured
1701                 }
1702
1703                 $result = $conn->masterPosWait( $pos, $timeout );
1704                 if ( $result == -1 || is_null( $result ) ) {
1705                         $msg = __METHOD__ . ": Timed out waiting on {$conn->getServer()} pos {$pos}";
1706                         $this->replLogger->warning( "$msg\n" );
1707                         $this->perfLogger->warning( "$msg:\n" . wfBacktrace( true ) );
1708                         $ok = false;
1709                 } else {
1710                         $this->replLogger->info( __METHOD__ . ": Done\n" );
1711                         $ok = true;
1712                 }
1713
1714                 return $ok;
1715         }
1716
1717         /**
1718          * Clear the cache for slag lag delay times
1719          *
1720          * This is only used for testing
1721          */
1722         public function clearLagTimeCache() {
1723                 $this->getLoadMonitor()->clearCaches();
1724         }
1725
1726         /**
1727          * Set a callback via DatabaseBase::setTransactionListener() on
1728          * all current and future master connections of this load balancer
1729          *
1730          * @param string $name Callback name
1731          * @param callable|null $callback
1732          * @since 1.28
1733          */
1734         public function setTransactionListener( $name, callable $callback = null ) {
1735                 if ( $callback ) {
1736                         $this->trxRecurringCallbacks[$name] = $callback;
1737                 } else {
1738                         unset( $this->trxRecurringCallbacks[$name] );
1739                 }
1740                 $this->forEachOpenMasterConnection(
1741                         function ( DatabaseBase $conn ) use ( $name, $callback ) {
1742                                 $conn->setTransactionListener( $name, $callback );
1743                         }
1744                 );
1745         }
1746
1747         /**
1748          * Set a new table prefix for the existing local wiki ID for testing
1749          *
1750          * @param string $prefix
1751          * @since 1.28
1752          */
1753         public function setDomainPrefix( $prefix ) {
1754                 list( $dbName, ) = explode( '-', $this->localDomain, 2 );
1755
1756                 $this->localDomain = "{$dbName}-{$prefix}";
1757         }
1758 }