includes/db/LoadBalancer.php

   1 <?php
   2 /**
   3  * Database load balancing.
   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
  24 /**
  25  * Database load balancing object
  26  *
  27  * @todo document
  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 slave lag as a factor in slave selection */
  40         private $mAllowLagged;
  41         /** @var integer Seconds to spend waiting on slave lag to resolve */
  42         private $mWaitTimeout;
  43
  44         /** @var array LBFactory information */
  45         private $mParentInfo;
  46         /** @var string The LoadMonitor subclass name */
  47         private $mLoadMonitorClass;
  48         /** @var LoadMonitor */
  49         private $mLoadMonitor;
  50
  51         /** @var bool|DatabaseBase Database connection that caused a problem */
  52         private $mErrorConnection;
  53         /** @var integer The generic (not query grouped) slave index (of $mServers) */
  54         private $mReadIndex;
  55         /** @var bool|DBMasterPos False if not set */
  56         private $mWaitForPos;
  57         /** @var bool Whether the generic reader fell back to a lagged slave */
  58         private $mLaggedSlaveMode;
  59         /** @var string The last DB selection or connection error */
  60         private $mLastError = 'Unknown error';
  61         /** @var integer Total connections opened */
  62         private $connsOpened = 0;
  63         /** @var ProcessCacheLRU */
  64         private $mProcCache;
  65
  66         /** @var integer Warn when this many connection are held */
  67         const CONN_HELD_WARN_THRESHOLD = 10;
  68
  69         /**
  70          * @param array $params Array with keys:
  71          *   servers           Required. Array of server info structures.
  72          *   loadMonitor       Name of a class used to fetch server lag and load.
  73          * @throws MWException
  74          */
  75         public function __construct( array $params ) {
  76                 if ( !isset( $params['servers'] ) ) {
  77                         throw new MWException( __CLASS__ . ': missing servers parameter' );
  78                 }
  79                 $this->mServers = $params['servers'];
  80                 $this->mWaitTimeout = 10;
  81
  82                 $this->mReadIndex = -1;
  83                 $this->mWriteIndex = -1;
  84                 $this->mConns = array(
  85                         'local' => array(),
  86                         'foreignUsed' => array(),
  87                         'foreignFree' => array() );
  88                 $this->mLoads = array();
  89                 $this->mWaitForPos = false;
  90                 $this->mLaggedSlaveMode = false;
  91                 $this->mErrorConnection = false;
  92                 $this->mAllowLagged = false;
  93
  94                 if ( isset( $params['loadMonitor'] ) ) {
  95                         $this->mLoadMonitorClass = $params['loadMonitor'];
  96                 } else {
  97                         $master = reset( $params['servers'] );
  98                         if ( isset( $master['type'] ) && $master['type'] === 'mysql' ) {
  99                                 $this->mLoadMonitorClass = 'LoadMonitorMySQL';
 100                         } else {
 101                                 $this->mLoadMonitorClass = 'LoadMonitorNull';
 102                         }
 103                 }
 104
 105                 foreach ( $params['servers'] as $i => $server ) {
 106                         $this->mLoads[$i] = $server['load'];
 107                         if ( isset( $server['groupLoads'] ) ) {
 108                                 foreach ( $server['groupLoads'] as $group => $ratio ) {
 109                                         if ( !isset( $this->mGroupLoads[$group] ) ) {
 110                                                 $this->mGroupLoads[$group] = array();
 111                                         }
 112                                         $this->mGroupLoads[$group][$i] = $ratio;
 113                                 }
 114                         }
 115                 }
 116
 117                 $this->mProcCache = new ProcessCacheLRU( 30 );
 118         }
 119
 120         /**
 121          * Get a LoadMonitor instance
 122          *
 123          * @return LoadMonitor
 124          */
 125         private function getLoadMonitor() {
 126                 if ( !isset( $this->mLoadMonitor ) ) {
 127                         $class = $this->mLoadMonitorClass;
 128                         $this->mLoadMonitor = new $class( $this );
 129                 }
 130
 131                 return $this->mLoadMonitor;
 132         }
 133
 134         /**
 135          * Get or set arbitrary data used by the parent object, usually an LBFactory
 136          * @param mixed $x
 137          * @return mixed
 138          */
 139         public function parentInfo( $x = null ) {
 140                 return wfSetVar( $this->mParentInfo, $x );
 141         }
 142
 143         /**
 144          * Given an array of non-normalised probabilities, this function will select
 145          * an element and return the appropriate key
 146          *
 147          * @deprecated since 1.21, use ArrayUtils::pickRandom()
 148          *
 149          * @param array $weights
 150          * @return bool|int|string
 151          */
 152         public function pickRandom( array $weights ) {
 153                 return ArrayUtils::pickRandom( $weights );
 154         }
 155
 156         /**
 157          * @param array $loads
 158          * @param bool|string $wiki Wiki to get non-lagged for
 159          * @param float $maxLag Restrict the maximum allowed lag to this many seconds
 160          * @return bool|int|string
 161          */
 162         private function getRandomNonLagged( array $loads, $wiki = false, $maxLag = INF ) {
 163                 $lags = $this->getLagTimes( $wiki );
 164
 165                 # Unset excessively lagged servers
 166                 foreach ( $lags as $i => $lag ) {
 167                         if ( $i != 0 ) {
 168                                 $maxServerLag = $maxLag;
 169                                 if ( isset( $this->mServers[$i]['max lag'] ) ) {
 170                                         $maxServerLag = min( $maxServerLag, $this->mServers[$i]['max lag'] );
 171                                 }
 172                                 if ( $lag === false ) {
 173                                         wfDebugLog( 'replication', "Server #$i is not replicating" );
 174                                         unset( $loads[$i] );
 175                                 } elseif ( $lag > $maxServerLag ) {
 176                                         wfDebugLog( 'replication', "Server #$i is excessively lagged ($lag seconds)" );
 177                                         unset( $loads[$i] );
 178                                 }
 179                         }
 180                 }
 181
 182                 # Find out if all the slaves with non-zero load are lagged
 183                 $sum = 0;
 184                 foreach ( $loads as $load ) {
 185                         $sum += $load;
 186                 }
 187                 if ( $sum == 0 ) {
 188                         # No appropriate DB servers except maybe the master and some slaves with zero load
 189                         # Do NOT use the master
 190                         # Instead, this function will return false, triggering read-only mode,
 191                         # and a lagged slave will be used instead.
 192                         return false;
 193                 }
 194
 195                 if ( count( $loads ) == 0 ) {
 196                         return false;
 197                 }
 198
 199                 #wfDebugLog( 'connect', var_export( $loads, true ) );
 200
 201                 # Return a random representative of the remainder
 202                 return ArrayUtils::pickRandom( $loads );
 203         }
 204
 205         /**
 206          * Get the index of the reader connection, which may be a slave
 207          * This takes into account load ratios and lag times. It should
 208          * always return a consistent index during a given invocation
 209          *
 210          * Side effect: opens connections to databases
 211          * @param string|bool $group Query group, or false for the generic reader
 212          * @param string|bool $wiki Wiki ID, or false for the current wiki
 213          * @throws MWException
 214          * @return bool|int|string
 215          */
 216         public function getReaderIndex( $group = false, $wiki = false ) {
 217                 global $wgReadOnly, $wgDBtype;
 218
 219                 # @todo FIXME: For now, only go through all this for mysql databases
 220                 if ( $wgDBtype != 'mysql' ) {
 221                         return $this->getWriterIndex();
 222                 }
 223
 224                 if ( count( $this->mServers ) == 1 ) {
 225                         # Skip the load balancing if there's only one server
 226                         return 0;
 227                 } elseif ( $group === false && $this->mReadIndex >= 0 ) {
 228                         # Shortcut if generic reader exists already
 229                         return $this->mReadIndex;
 230                 }
 231
 232                 # Find the relevant load array
 233                 if ( $group !== false ) {
 234                         if ( isset( $this->mGroupLoads[$group] ) ) {
 235                                 $nonErrorLoads = $this->mGroupLoads[$group];
 236                         } else {
 237                                 # No loads for this group, return false and the caller can use some other group
 238                                 wfDebug( __METHOD__ . ": no loads for group $group\n" );
 239
 240                                 return false;
 241                         }
 242                 } else {
 243                         $nonErrorLoads = $this->mLoads;
 244                 }
 245
 246                 if ( !count( $nonErrorLoads ) ) {
 247                         throw new MWException( "Empty server array given to LoadBalancer" );
 248                 }
 249
 250                 # Scale the configured load ratios according to the dynamic load (if the load monitor supports it)
 251                 $this->getLoadMonitor()->scaleLoads( $nonErrorLoads, $group, $wiki );
 252
 253                 $laggedSlaveMode = false;
 254
 255                 # No server found yet
 256                 $i = false;
 257                 # First try quickly looking through the available servers for a server that
 258                 # meets our criteria
 259                 $currentLoads = $nonErrorLoads;
 260                 while ( count( $currentLoads ) ) {
 261                         if ( $wgReadOnly || $this->mAllowLagged || $laggedSlaveMode ) {
 262                                 $i = ArrayUtils::pickRandom( $currentLoads );
 263                         } else {
 264                                 $i = false;
 265                                 if ( $this->mWaitForPos && $this->mWaitForPos->asOfTime() ) {
 266                                         # ChronologyProtecter causes mWaitForPos to be set via sessions.
 267                                         # This triggers doWait() after connect, so it's especially good to
 268                                         # avoid lagged servers so as to avoid just blocking in that method.
 269                                         $ago = microtime( true ) - $this->mWaitForPos->asOfTime();
 270                                         # Aim for <= 1 second of waiting (being too picky can backfire)
 271                                         $i = $this->getRandomNonLagged( $currentLoads, $wiki, $ago + 1 );
 272                                 }
 273                                 if ( $i === false ) {
 274                                         # Any server with less lag than it's 'max lag' param is preferable
 275                                         $i = $this->getRandomNonLagged( $currentLoads, $wiki );
 276                                 }
 277                                 if ( $i === false && count( $currentLoads ) != 0 ) {
 278                                         # All slaves lagged. Switch to read-only mode
 279                                         wfDebugLog( 'replication', "All slaves lagged. Switch to read-only mode" );
 280                                         $wgReadOnly = 'The database has been automatically locked ' .
 281                                                 'while the slave database servers catch up to the master';
 282                                         $i = ArrayUtils::pickRandom( $currentLoads );
 283                                         $laggedSlaveMode = true;
 284                                 }
 285                         }
 286
 287                         if ( $i === false ) {
 288                                 # pickRandom() returned false
 289                                 # This is permanent and means the configuration or the load monitor
 290                                 # wants us to return false.
 291                                 wfDebugLog( 'connect', __METHOD__ . ": pickRandom() returned false" );
 292
 293                                 return false;
 294                         }
 295
 296                         wfDebugLog( 'connect', __METHOD__ .
 297                                 ": Using reader #$i: {$this->mServers[$i]['host']}..." );
 298
 299                         $conn = $this->openConnection( $i, $wiki );
 300                         if ( !$conn ) {
 301                                 wfDebugLog( 'connect', __METHOD__ . ": Failed connecting to $i/$wiki" );
 302                                 unset( $nonErrorLoads[$i] );
 303                                 unset( $currentLoads[$i] );
 304                                 $i = false;
 305                                 continue;
 306                         }
 307
 308                         // Decrement reference counter, we are finished with this connection.
 309                         // It will be incremented for the caller later.
 310                         if ( $wiki !== false ) {
 311                                 $this->reuseConnection( $conn );
 312                         }
 313
 314                         # Return this server
 315                         break;
 316                 }
 317
 318                 # If all servers were down, quit now
 319                 if ( !count( $nonErrorLoads ) ) {
 320                         wfDebugLog( 'connect', "All servers down" );
 321                 }
 322
 323                 if ( $i !== false ) {
 324                         # Slave connection successful
 325                         # Wait for the session master pos for a short time
 326                         if ( $this->mWaitForPos && $i > 0 ) {
 327                                 if ( !$this->doWait( $i ) ) {
 328                                         $this->mServers[$i]['slave pos'] = $conn->getSlavePos();
 329                                 }
 330                         }
 331                         if ( $this->mReadIndex <= 0 && $this->mLoads[$i] > 0 && $group !== false ) {
 332                                 $this->mReadIndex = $i;
 333                         }
 334                 }
 335
 336                 return $i;
 337         }
 338
 339         /**
 340          * Set the master wait position
 341          * If a DB_SLAVE connection has been opened already, waits
 342          * Otherwise sets a variable telling it to wait if such a connection is opened
 343          * @param DBMasterPos $pos
 344          */
 345         public function waitFor( $pos ) {
 346                 $this->mWaitForPos = $pos;
 347                 $i = $this->mReadIndex;
 348
 349                 if ( $i > 0 ) {
 350                         if ( !$this->doWait( $i ) ) {
 351                                 $this->mServers[$i]['slave pos'] = $this->getAnyOpenConnection( $i )->getSlavePos();
 352                                 $this->mLaggedSlaveMode = true;
 353                         }
 354                 }
 355         }
 356
 357         /**
 358          * Set the master wait position and wait for ALL slaves to catch up to it
 359          * @param DBMasterPos $pos
 360          * @param int $timeout Max seconds to wait; default is mWaitTimeout
 361          * @return bool Success (able to connect and no timeouts reached)
 362          */
 363         public function waitForAll( $pos, $timeout = null ) {
 364                 $this->mWaitForPos = $pos;
 365                 $serverCount = count( $this->mServers );
 366
 367                 $ok = true;
 368                 for ( $i = 1; $i < $serverCount; $i++ ) {
 369                         if ( $this->mLoads[$i] > 0 ) {
 370                                 $ok = $this->doWait( $i, true, $timeout ) && $ok;
 371                         }
 372                 }
 373
 374                 return $ok;
 375         }
 376
 377         /**
 378          * Get any open connection to a given server index, local or foreign
 379          * Returns false if there is no connection open
 380          *
 381          * @param int $i
 382          * @return DatabaseBase|bool False on failure
 383          */
 384         public function getAnyOpenConnection( $i ) {
 385                 foreach ( $this->mConns as $conns ) {
 386                         if ( !empty( $conns[$i] ) ) {
 387                                 return reset( $conns[$i] );
 388                         }
 389                 }
 390
 391                 return false;
 392         }
 393
 394         /**
 395          * Wait for a given slave to catch up to the master pos stored in $this
 396          * @param int $index Server index
 397          * @param bool $open Check the server even if a new connection has to be made
 398          * @param int $timeout Max seconds to wait; default is mWaitTimeout
 399          * @return bool
 400          */
 401         protected function doWait( $index, $open = false, $timeout = null ) {
 402                 $close = false; // close the connection afterwards
 403
 404                 # Find a connection to wait on, creating one if needed and allowed
 405                 $conn = $this->getAnyOpenConnection( $index );
 406                 if ( !$conn ) {
 407                         if ( !$open ) {
 408                                 wfDebug( __METHOD__ . ": no connection open\n" );
 409
 410                                 return false;
 411                         } else {
 412                                 $conn = $this->openConnection( $index, '' );
 413                                 if ( !$conn ) {
 414                                         wfDebug( __METHOD__ . ": failed to open connection\n" );
 415
 416                                         return false;
 417                                 }
 418                                 // Avoid connection spam in waitForAll() when connections
 419                                 // are made just for the sake of doing this lag check.
 420                                 $close = true;
 421                         }
 422                 }
 423
 424                 wfDebug( __METHOD__ . ": Waiting for slave #$index to catch up...\n" );
 425                 $timeout = $timeout ?: $this->mWaitTimeout;
 426                 $result = $conn->masterPosWait( $this->mWaitForPos, $timeout );
 427
 428                 if ( $result == -1 || is_null( $result ) ) {
 429                         # Timed out waiting for slave, use master instead
 430                         $server = $this->mServers[$index]['host'];
 431                         $msg = __METHOD__ . ": Timed out waiting on $server pos {$this->mWaitForPos}";
 432                         wfDebug( "$msg\n" );
 433                         wfDebugLog( 'DBPerformance', "$msg:\n" . wfBacktrace( true ) );
 434                         $ok = false;
 435                 } else {
 436                         wfDebug( __METHOD__ . ": Done\n" );
 437                         $ok = true;
 438                 }
 439
 440                 if ( $close ) {
 441                         $this->closeConnection( $conn );
 442                 }
 443
 444                 return $ok;
 445         }
 446
 447         /**
 448          * Get a connection by index
 449          * This is the main entry point for this class.
 450          *
 451          * @param int $i Server index
 452          * @param array|string|bool $groups Query group(s), or false for the generic reader
 453          * @param string|bool $wiki Wiki ID, or false for the current wiki
 454          *
 455          * @throws MWException
 456          * @return DatabaseBase
 457          */
 458         public function getConnection( $i, $groups = array(), $wiki = false ) {
 459                 if ( $i === null || $i === false ) {
 460                         throw new MWException( 'Attempt to call ' . __METHOD__ .
 461                                 ' with invalid server index' );
 462                 }
 463
 464                 if ( $wiki === wfWikiID() ) {
 465                         $wiki = false;
 466                 }
 467
 468                 $groups = ( $groups === false || $groups === array() )
 469                         ? array( false ) // check one "group": the generic pool
 470                         : (array)$groups;
 471
 472                 if ( $i == DB_MASTER ) {
 473                         $i = $this->getWriterIndex();
 474                 } else {
 475                         # Try to find an available server in any the query groups (in order)
 476                         foreach ( $groups as $group ) {
 477                                 $groupIndex = $this->getReaderIndex( $group, $wiki );
 478                                 if ( $groupIndex !== false ) {
 479                                         $serverName = $this->getServerName( $groupIndex );
 480                                         wfDebug( __METHOD__ . ": using server $serverName for group $group\n" );
 481                                         $i = $groupIndex;
 482                                         break;
 483                                 }
 484                         }
 485                 }
 486
 487                 # Operation-based index
 488                 if ( $i == DB_SLAVE ) {
 489                         $this->mLastError = 'Unknown error'; // reset error string
 490                         # Try the general server pool if $groups are unavailable.
 491                         $i = in_array( false, $groups, true )
 492                                 ? false // don't bother with this if that is what was tried above
 493                                 : $this->getReaderIndex( false, $wiki );
 494                         # Couldn't find a working server in getReaderIndex()?
 495                         if ( $i === false ) {
 496                                 $this->mLastError = 'No working slave server: ' . $this->mLastError;
 497
 498                                 return $this->reportConnectionError();
 499                         }
 500                 }
 501
 502                 # Now we have an explicit index into the servers array
 503                 $conn = $this->openConnection( $i, $wiki );
 504                 if ( !$conn ) {
 505
 506                         return $this->reportConnectionError();
 507                 }
 508
 509                 return $conn;
 510         }
 511
 512         /**
 513          * Mark a foreign connection as being available for reuse under a different
 514          * DB name or prefix. This mechanism is reference-counted, and must be called
 515          * the same number of times as getConnection() to work.
 516          *
 517          * @param DatabaseBase $conn
 518          * @throws MWException
 519          */
 520         public function reuseConnection( $conn ) {
 521                 $serverIndex = $conn->getLBInfo( 'serverIndex' );
 522                 $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 523                 if ( $serverIndex === null || $refCount === null ) {
 524                         wfDebug( __METHOD__ . ": this connection was not opened as a foreign connection\n" );
 525
 526                         /**
 527                          * This can happen in code like:
 528                          *   foreach ( $dbs as $db ) {
 529                          *     $conn = $lb->getConnection( DB_SLAVE, array(), $db );
 530                          *     ...
 531                          *     $lb->reuseConnection( $conn );
 532                          *   }
 533                          * When a connection to the local DB is opened in this way, reuseConnection()
 534                          * should be ignored
 535                          */
 536
 537                         return;
 538                 }
 539
 540                 $dbName = $conn->getDBname();
 541                 $prefix = $conn->tablePrefix();
 542                 if ( strval( $prefix ) !== '' ) {
 543                         $wiki = "$dbName-$prefix";
 544                 } else {
 545                         $wiki = $dbName;
 546                 }
 547                 if ( $this->mConns['foreignUsed'][$serverIndex][$wiki] !== $conn ) {
 548                         throw new MWException( __METHOD__ . ": connection not found, has " .
 549                                 "the connection been freed already?" );
 550                 }
 551                 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
 552                 if ( $refCount <= 0 ) {
 553                         $this->mConns['foreignFree'][$serverIndex][$wiki] = $conn;
 554                         unset( $this->mConns['foreignUsed'][$serverIndex][$wiki] );
 555                         wfDebug( __METHOD__ . ": freed connection $serverIndex/$wiki\n" );
 556                 } else {
 557                         wfDebug( __METHOD__ . ": reference count for $serverIndex/$wiki reduced to $refCount\n" );
 558                 }
 559         }
 560
 561         /**
 562          * Get a database connection handle reference
 563          *
 564          * The handle's methods wrap simply wrap those of a DatabaseBase handle
 565          *
 566          * @see LoadBalancer::getConnection() for parameter information
 567          *
 568          * @param int $db
 569          * @param array|string|bool $groups Query group(s), or false for the generic reader
 570          * @param string|bool $wiki Wiki ID, or false for the current wiki
 571          * @return DBConnRef
 572          */
 573         public function getConnectionRef( $db, $groups = array(), $wiki = false ) {
 574                 return new DBConnRef( $this, $this->getConnection( $db, $groups, $wiki ) );
 575         }
 576
 577         /**
 578          * Get a database connection handle reference without connecting yet
 579          *
 580          * The handle's methods wrap simply wrap those of a DatabaseBase handle
 581          *
 582          * @see LoadBalancer::getConnection() for parameter information
 583          *
 584          * @param int $db
 585          * @param array|string|bool $groups Query group(s), or false for the generic reader
 586          * @param string|bool $wiki Wiki ID, or false for the current wiki
 587          * @return DBConnRef
 588          */
 589         public function getLazyConnectionRef( $db, $groups = array(), $wiki = false ) {
 590                 return new DBConnRef( $this, array( $db, $groups, $wiki ) );
 591         }
 592
 593         /**
 594          * Open a connection to the server given by the specified index
 595          * Index must be an actual index into the array.
 596          * If the server is already open, returns it.
 597          *
 598          * On error, returns false, and the connection which caused the
 599          * error will be available via $this->mErrorConnection.
 600          *
 601          * @param int $i Server index
 602          * @param string|bool $wiki Wiki ID, or false for the current wiki
 603          * @return DatabaseBase
 604          *
 605          * @access private
 606          */
 607         public function openConnection( $i, $wiki = false ) {
 608                 if ( $wiki !== false ) {
 609                         $conn = $this->openForeignConnection( $i, $wiki );
 610
 611                         return $conn;
 612                 }
 613                 if ( isset( $this->mConns['local'][$i][0] ) ) {
 614                         $conn = $this->mConns['local'][$i][0];
 615                 } else {
 616                         $server = $this->mServers[$i];
 617                         $server['serverIndex'] = $i;
 618                         $conn = $this->reallyOpenConnection( $server, false );
 619                         if ( $conn->isOpen() ) {
 620                                 wfDebug( "Connected to database $i at {$this->mServers[$i]['host']}\n" );
 621                                 $this->mConns['local'][$i][0] = $conn;
 622                         } else {
 623                                 wfDebug( "Failed to connect to database $i at {$this->mServers[$i]['host']}\n" );
 624                                 $this->mErrorConnection = $conn;
 625                                 $conn = false;
 626                         }
 627                 }
 628
 629                 return $conn;
 630         }
 631
 632         /**
 633          * Open a connection to a foreign DB, or return one if it is already open.
 634          *
 635          * Increments a reference count on the returned connection which locks the
 636          * connection to the requested wiki. This reference count can be
 637          * decremented by calling reuseConnection().
 638          *
 639          * If a connection is open to the appropriate server already, but with the wrong
 640          * database, it will be switched to the right database and returned, as long as
 641          * it has been freed first with reuseConnection().
 642          *
 643          * On error, returns false, and the connection which caused the
 644          * error will be available via $this->mErrorConnection.
 645          *
 646          * @param int $i Server index
 647          * @param string $wiki Wiki ID to open
 648          * @return DatabaseBase
 649          */
 650         private function openForeignConnection( $i, $wiki ) {
 651                 list( $dbName, $prefix ) = wfSplitWikiID( $wiki );
 652                 if ( isset( $this->mConns['foreignUsed'][$i][$wiki] ) ) {
 653                         // Reuse an already-used connection
 654                         $conn = $this->mConns['foreignUsed'][$i][$wiki];
 655                         wfDebug( __METHOD__ . ": reusing connection $i/$wiki\n" );
 656                 } elseif ( isset( $this->mConns['foreignFree'][$i][$wiki] ) ) {
 657                         // Reuse a free connection for the same wiki
 658                         $conn = $this->mConns['foreignFree'][$i][$wiki];
 659                         unset( $this->mConns['foreignFree'][$i][$wiki] );
 660                         $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 661                         wfDebug( __METHOD__ . ": reusing free connection $i/$wiki\n" );
 662                 } elseif ( !empty( $this->mConns['foreignFree'][$i] ) ) {
 663                         // Reuse a connection from another wiki
 664                         $conn = reset( $this->mConns['foreignFree'][$i] );
 665                         $oldWiki = key( $this->mConns['foreignFree'][$i] );
 666
 667                         // The empty string as a DB name means "don't care".
 668                         // DatabaseMysqlBase::open() already handle this on connection.
 669                         if ( $dbName !== '' && !$conn->selectDB( $dbName ) ) {
 670                                 $this->mLastError = "Error selecting database $dbName on server " .
 671                                         $conn->getServer() . " from client host " . wfHostname() . "\n";
 672                                 $this->mErrorConnection = $conn;
 673                                 $conn = false;
 674                         } else {
 675                                 $conn->tablePrefix( $prefix );
 676                                 unset( $this->mConns['foreignFree'][$i][$oldWiki] );
 677                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 678                                 wfDebug( __METHOD__ . ": reusing free connection from $oldWiki for $wiki\n" );
 679                         }
 680                 } else {
 681                         // Open a new connection
 682                         $server = $this->mServers[$i];
 683                         $server['serverIndex'] = $i;
 684                         $server['foreignPoolRefCount'] = 0;
 685                         $server['foreign'] = true;
 686                         $conn = $this->reallyOpenConnection( $server, $dbName );
 687                         if ( !$conn->isOpen() ) {
 688                                 wfDebug( __METHOD__ . ": error opening connection for $i/$wiki\n" );
 689                                 $this->mErrorConnection = $conn;
 690                                 $conn = false;
 691                         } else {
 692                                 $conn->tablePrefix( $prefix );
 693                                 $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 694                                 wfDebug( __METHOD__ . ": opened new connection for $i/$wiki\n" );
 695                         }
 696                 }
 697
 698                 // Increment reference count
 699                 if ( $conn ) {
 700                         $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 701                         $conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
 702                 }
 703
 704                 return $conn;
 705         }
 706
 707         /**
 708          * Test if the specified index represents an open connection
 709          *
 710          * @param int $index Server index
 711          * @access private
 712          * @return bool
 713          */
 714         private function isOpen( $index ) {
 715                 if ( !is_integer( $index ) ) {
 716                         return false;
 717                 }
 718
 719                 return (bool)$this->getAnyOpenConnection( $index );
 720         }
 721
 722         /**
 723          * Really opens a connection. Uncached.
 724          * Returns a Database object whether or not the connection was successful.
 725          * @access private
 726          *
 727          * @param array $server
 728          * @param bool $dbNameOverride
 729          * @throws MWException
 730          * @return DatabaseBase
 731          */
 732         protected function reallyOpenConnection( $server, $dbNameOverride = false ) {
 733                 if ( !is_array( $server ) ) {
 734                         throw new MWException( 'You must update your load-balancing configuration. ' .
 735                                 'See DefaultSettings.php entry for $wgDBservers.' );
 736                 }
 737
 738                 if ( $dbNameOverride !== false ) {
 739                         $server['dbname'] = $dbNameOverride;
 740                 }
 741
 742                 // Log when many connection are made on requests
 743                 if ( ++$this->connsOpened >= self::CONN_HELD_WARN_THRESHOLD ) {
 744                         $masterAddr = $this->getServerName( 0 );
 745                         wfDebugLog( 'DBPerformance', __METHOD__ . ": " .
 746                                 "{$this->connsOpened}+ connections made (master=$masterAddr)\n" .
 747                                 wfBacktrace( true ) );
 748                 }
 749
 750                 # Create object
 751                 try {
 752                         $db = DatabaseBase::factory( $server['type'], $server );
 753                 } catch ( DBConnectionError $e ) {
 754                         // FIXME: This is probably the ugliest thing I have ever done to
 755                         // PHP. I'm half-expecting it to segfault, just out of disgust. -- TS
 756                         $db = $e->db;
 757                 }
 758
 759                 $db->setLBInfo( $server );
 760                 if ( isset( $server['fakeSlaveLag'] ) ) {
 761                         $db->setFakeSlaveLag( $server['fakeSlaveLag'] );
 762                 }
 763                 if ( isset( $server['fakeMaster'] ) ) {
 764                         $db->setFakeMaster( true );
 765                 }
 766
 767                 return $db;
 768         }
 769
 770         /**
 771          * @throws DBConnectionError
 772          * @return bool
 773          */
 774         private function reportConnectionError() {
 775                 $conn = $this->mErrorConnection; // The connection which caused the error
 776                 $context = array(
 777                         'method' => __METHOD__,
 778                         'last_error' => $this->mLastError,
 779                 );
 780
 781                 if ( !is_object( $conn ) ) {
 782                         // No last connection, probably due to all servers being too busy
 783                         wfLogDBError(
 784                                 "LB failure with no last connection. Connection error: {last_error}",
 785                                 $context
 786                         );
 787
 788                         // If all servers were busy, mLastError will contain something sensible
 789                         throw new DBConnectionError( null, $this->mLastError );
 790                 } else {
 791                         $context['db_server'] = $conn->getProperty( 'mServer' );
 792                         wfLogDBError(
 793                                 "Connection error: {last_error} ({db_server})",
 794                                 $context
 795                         );
 796                         $conn->reportConnectionError( "{$this->mLastError} ({$context['db_server']})" ); // throws DBConnectionError
 797                 }
 798
 799                 return false; /* not reached */
 800         }
 801
 802         /**
 803          * @return int
 804          */
 805         private function getWriterIndex() {
 806                 return 0;
 807         }
 808
 809         /**
 810          * Returns true if the specified index is a valid server index
 811          *
 812          * @param string $i
 813          * @return bool
 814          */
 815         public function haveIndex( $i ) {
 816                 return array_key_exists( $i, $this->mServers );
 817         }
 818
 819         /**
 820          * Returns true if the specified index is valid and has non-zero load
 821          *
 822          * @param string $i
 823          * @return bool
 824          */
 825         public function isNonZeroLoad( $i ) {
 826                 return array_key_exists( $i, $this->mServers ) && $this->mLoads[$i] != 0;
 827         }
 828
 829         /**
 830          * Get the number of defined servers (not the number of open connections)
 831          *
 832          * @return int
 833          */
 834         public function getServerCount() {
 835                 return count( $this->mServers );
 836         }
 837
 838         /**
 839          * Get the host name or IP address of the server with the specified index
 840          * Prefer a readable name if available.
 841          * @param string $i
 842          * @return string
 843          */
 844         public function getServerName( $i ) {
 845                 if ( isset( $this->mServers[$i]['hostName'] ) ) {
 846                         return $this->mServers[$i]['hostName'];
 847                 } elseif ( isset( $this->mServers[$i]['host'] ) ) {
 848                         return $this->mServers[$i]['host'];
 849                 } else {
 850                         return '';
 851                 }
 852         }
 853
 854         /**
 855          * Return the server info structure for a given index, or false if the index is invalid.
 856          * @param int $i
 857          * @return array|bool
 858          */
 859         public function getServerInfo( $i ) {
 860                 if ( isset( $this->mServers[$i] ) ) {
 861                         return $this->mServers[$i];
 862                 } else {
 863                         return false;
 864                 }
 865         }
 866
 867         /**
 868          * Sets the server info structure for the given index. Entry at index $i
 869          * is created if it doesn't exist
 870          * @param int $i
 871          * @param array $serverInfo
 872          */
 873         public function setServerInfo( $i, array $serverInfo ) {
 874                 $this->mServers[$i] = $serverInfo;
 875         }
 876
 877         /**
 878          * Get the current master position for chronology control purposes
 879          * @return mixed
 880          */
 881         public function getMasterPos() {
 882                 # If this entire request was served from a slave without opening a connection to the
 883                 # master (however unlikely that may be), then we can fetch the position from the slave.
 884                 $masterConn = $this->getAnyOpenConnection( 0 );
 885                 if ( !$masterConn ) {
 886                         $serverCount = count( $this->mServers );
 887                         for ( $i = 1; $i < $serverCount; $i++ ) {
 888                                 $conn = $this->getAnyOpenConnection( $i );
 889                                 if ( $conn ) {
 890                                         wfDebug( "Master pos fetched from slave\n" );
 891
 892                                         return $conn->getSlavePos();
 893                                 }
 894                         }
 895                 } else {
 896                         wfDebug( "Master pos fetched from master\n" );
 897
 898                         return $masterConn->getMasterPos();
 899                 }
 900
 901                 return false;
 902         }
 903
 904         /**
 905          * Close all open connections
 906          */
 907         public function closeAll() {
 908                 foreach ( $this->mConns as $conns2 ) {
 909                         foreach ( $conns2 as $conns3 ) {
 910                                 /** @var DatabaseBase $conn */
 911                                 foreach ( $conns3 as $conn ) {
 912                                         $conn->close();
 913                                 }
 914                         }
 915                 }
 916                 $this->mConns = array(
 917                         'local' => array(),
 918                         'foreignFree' => array(),
 919                         'foreignUsed' => array(),
 920                 );
 921                 $this->connsOpened = 0;
 922         }
 923
 924         /**
 925          * Close a connection
 926          * Using this function makes sure the LoadBalancer knows the connection is closed.
 927          * If you use $conn->close() directly, the load balancer won't update its state.
 928          * @param DatabaseBase $conn
 929          */
 930         public function closeConnection( $conn ) {
 931                 $done = false;
 932                 foreach ( $this->mConns as $i1 => $conns2 ) {
 933                         foreach ( $conns2 as $i2 => $conns3 ) {
 934                                 foreach ( $conns3 as $i3 => $candidateConn ) {
 935                                         if ( $conn === $candidateConn ) {
 936                                                 $conn->close();
 937                                                 unset( $this->mConns[$i1][$i2][$i3] );
 938                                                 --$this->connsOpened;
 939                                                 $done = true;
 940                                                 break;
 941                                         }
 942                                 }
 943                         }
 944                 }
 945                 if ( !$done ) {
 946                         $conn->close();
 947                 }
 948         }
 949
 950         /**
 951          * Commit transactions on all open connections
 952          */
 953         public function commitAll() {
 954                 foreach ( $this->mConns as $conns2 ) {
 955                         foreach ( $conns2 as $conns3 ) {
 956                                 /** @var DatabaseBase[] $conns3 */
 957                                 foreach ( $conns3 as $conn ) {
 958                                         if ( $conn->trxLevel() ) {
 959                                                 $conn->commit( __METHOD__, 'flush' );
 960                                         }
 961                                 }
 962                         }
 963                 }
 964         }
 965
 966         /**
 967          *  Issue COMMIT only on master, only if queries were done on connection
 968          */
 969         public function commitMasterChanges() {
 970                 // Always 0, but who knows.. :)
 971                 $masterIndex = $this->getWriterIndex();
 972                 foreach ( $this->mConns as $conns2 ) {
 973                         if ( empty( $conns2[$masterIndex] ) ) {
 974                                 continue;
 975                         }
 976                         /** @var DatabaseBase $conn */
 977                         foreach ( $conns2[$masterIndex] as $conn ) {
 978                                 if ( $conn->trxLevel() && $conn->writesOrCallbacksPending() ) {
 979                                         $conn->commit( __METHOD__, 'flush' );
 980                                 }
 981                         }
 982                 }
 983         }
 984
 985         /**
 986          * Issue ROLLBACK only on master, only if queries were done on connection
 987          * @since 1.23
 988          */
 989         public function rollbackMasterChanges() {
 990                 // Always 0, but who knows.. :)
 991                 $masterIndex = $this->getWriterIndex();
 992                 foreach ( $this->mConns as $conns2 ) {
 993                         if ( empty( $conns2[$masterIndex] ) ) {
 994                                 continue;
 995                         }
 996                         /** @var DatabaseBase $conn */
 997                         foreach ( $conns2[$masterIndex] as $conn ) {
 998                                 if ( $conn->trxLevel() && $conn->writesOrCallbacksPending() ) {
 999                                         $conn->rollback( __METHOD__, 'flush' );
1000                                 }
1001                         }
1002                 }
1003         }
1004
1005         /**
1006          * @return bool Whether a master connection is already open
1007          * @since 1.24
1008          */
1009         public function hasMasterConnection() {
1010                 return $this->isOpen( $this->getWriterIndex() );
1011         }
1012
1013         /**
1014          * Determine if there are any pending changes that need to be rolled back
1015          * or committed.
1016          * @since 1.23
1017          * @return bool
1018          */
1019         public function hasMasterChanges() {
1020                 // Always 0, but who knows.. :)
1021                 $masterIndex = $this->getWriterIndex();
1022                 foreach ( $this->mConns as $conns2 ) {
1023                         if ( empty( $conns2[$masterIndex] ) ) {
1024                                 continue;
1025                         }
1026                         /** @var DatabaseBase $conn */
1027                         foreach ( $conns2[$masterIndex] as $conn ) {
1028                                 if ( $conn->trxLevel() && $conn->writesOrCallbacksPending() ) {
1029                                         return true;
1030                                 }
1031                         }
1032                 }
1033                 return false;
1034         }
1035
1036         /**
1037          * @param mixed $value
1038          * @return mixed
1039          */
1040         public function waitTimeout( $value = null ) {
1041                 return wfSetVar( $this->mWaitTimeout, $value );
1042         }
1043
1044         /**
1045          * @return bool
1046          */
1047         public function getLaggedSlaveMode() {
1048                 return $this->mLaggedSlaveMode;
1049         }
1050
1051         /**
1052          * Disables/enables lag checks
1053          * @param null|bool $mode
1054          * @return bool
1055          */
1056         public function allowLagged( $mode = null ) {
1057                 if ( $mode === null ) {
1058                         return $this->mAllowLagged;
1059                 }
1060                 $this->mAllowLagged = $mode;
1061
1062                 return $this->mAllowLagged;
1063         }
1064
1065         /**
1066          * @return bool
1067          */
1068         public function pingAll() {
1069                 $success = true;
1070                 foreach ( $this->mConns as $conns2 ) {
1071                         foreach ( $conns2 as $conns3 ) {
1072                                 /** @var DatabaseBase[] $conns3 */
1073                                 foreach ( $conns3 as $conn ) {
1074                                         if ( !$conn->ping() ) {
1075                                                 $success = false;
1076                                         }
1077                                 }
1078                         }
1079                 }
1080
1081                 return $success;
1082         }
1083
1084         /**
1085          * Call a function with each open connection object
1086          * @param callable $callback
1087          * @param array $params
1088          */
1089         public function forEachOpenConnection( $callback, array $params = array() ) {
1090                 foreach ( $this->mConns as $conns2 ) {
1091                         foreach ( $conns2 as $conns3 ) {
1092                                 foreach ( $conns3 as $conn ) {
1093                                         $mergedParams = array_merge( array( $conn ), $params );
1094                                         call_user_func_array( $callback, $mergedParams );
1095                                 }
1096                         }
1097                 }
1098         }
1099
1100         /**
1101          * Get the hostname and lag time of the most-lagged slave
1102          *
1103          * This is useful for maintenance scripts that need to throttle their updates.
1104          * May attempt to open connections to slaves on the default DB. If there is
1105          * no lag, the maximum lag will be reported as -1.
1106          *
1107          * @param bool|string $wiki Wiki ID, or false for the default database
1108          * @return array ( host, max lag, index of max lagged host )
1109          */
1110         public function getMaxLag( $wiki = false ) {
1111                 $maxLag = -1;
1112                 $host = '';
1113                 $maxIndex = 0;
1114
1115                 if ( $this->getServerCount() <= 1 ) {
1116                         return array( $host, $maxLag, $maxIndex ); // no replication = no lag
1117                 }
1118
1119                 $lagTimes = $this->getLagTimes( $wiki );
1120                 foreach ( $lagTimes as $i => $lag ) {
1121                         if ( $lag > $maxLag ) {
1122                                 $maxLag = $lag;
1123                                 $host = $this->mServers[$i]['host'];
1124                                 $maxIndex = $i;
1125                         }
1126                 }
1127
1128                 return array( $host, $maxLag, $maxIndex );
1129         }
1130
1131         /**
1132          * Get lag time for each server
1133          *
1134          * Results are cached for a short time in memcached/process cache
1135          *
1136          * @param string|bool $wiki
1137          * @return int[] Map of (server index => seconds)
1138          */
1139         public function getLagTimes( $wiki = false ) {
1140                 if ( $this->getServerCount() <= 1 ) {
1141                         return array( 0 => 0 ); // no replication = no lag
1142                 }
1143
1144                 if ( $this->mProcCache->has( 'slave_lag', 'times', 1 ) ) {
1145                         return $this->mProcCache->get( 'slave_lag', 'times' );
1146                 }
1147
1148                 # Send the request to the load monitor
1149                 $times = $this->getLoadMonitor()->getLagTimes( array_keys( $this->mServers ), $wiki );
1150
1151                 $this->mProcCache->set( 'slave_lag', 'times', $times );
1152
1153                 return $times;
1154         }
1155
1156         /**
1157          * Get the lag in seconds for a given connection, or zero if this load
1158          * balancer does not have replication enabled.
1159          *
1160          * This should be used in preference to Database::getLag() in cases where
1161          * replication may not be in use, since there is no way to determine if
1162          * replication is in use at the connection level without running
1163          * potentially restricted queries such as SHOW SLAVE STATUS. Using this
1164          * function instead of Database::getLag() avoids a fatal error in this
1165          * case on many installations.
1166          *
1167          * @param DatabaseBase $conn
1168          * @return int
1169          */
1170         public function safeGetLag( $conn ) {
1171                 if ( $this->getServerCount() == 1 ) {
1172                         return 0;
1173                 } else {
1174                         return $conn->getLag();
1175                 }
1176         }
1177
1178         /**
1179          * Clear the cache for slag lag delay times
1180          */
1181         public function clearLagTimeCache() {
1182                 $this->mProcCache->clear( 'slave_lag' );
1183         }
1184 }
1185
1186 /**
1187  * Helper class to handle automatically marking connections as reusable (via RAII pattern)
1188  * as well handling deferring the actual network connection until the handle is used
1189  *
1190  * @ingroup Database
1191  * @since 1.22
1192  */
1193 class DBConnRef implements IDatabase {
1194         /** @var LoadBalancer */
1195         private $lb;
1196
1197         /** @var DatabaseBase|null */
1198         private $conn;
1199
1200         /** @var array|null */
1201         private $params;
1202
1203         /**
1204          * @param LoadBalancer $lb
1205          * @param DatabaseBase|array $conn Connection or (server index, group, wiki ID) array
1206          */
1207         public function __construct( LoadBalancer $lb, $conn ) {
1208                 $this->lb = $lb;
1209                 if ( $conn instanceof DatabaseBase ) {
1210                         $this->conn = $conn;
1211                 } else {
1212                         $this->params = $conn;
1213                 }
1214         }
1215
1216         public function __call( $name, $arguments ) {
1217                 if ( $this->conn === null ) {
1218                         list( $db, $groups, $wiki ) = $this->params;
1219                         $this->conn = $this->lb->getConnection( $db, $groups, $wiki );
1220                 }
1221
1222                 return call_user_func_array( array( $this->conn, $name ), $arguments );
1223         }
1224
1225         public function __destruct() {
1226                 if ( $this->conn !== null ) {
1227                         $this->lb->reuseConnection( $this->conn );
1228                 }
1229         }
1230 }