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Source: /includes/db/LoadBalancer.php - 1146 lines - 32613 bytes - Summary - Text - Print

Description: Database load balancing. This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version.

   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      private $mServers, $mConns, $mLoads, $mGroupLoads;
  32      private $mErrorConnection;
  33      private $mReadIndex, $mAllowLagged;
  34      private $mWaitForPos, $mWaitTimeout;
  35      private $mLaggedSlaveMode, $mLastError = 'Unknown error';
  36      private $mParentInfo, $mLagTimes;
  37      private $mLoadMonitorClass, $mLoadMonitor;
  38  
  39      /**
  40       * @param array $params with keys:
  41       *    servers           Required. Array of server info structures.
  42       *    masterWaitTimeout Replication lag wait timeout
  43       *    loadMonitor       Name of a class used to fetch server lag and load.
  44       * @throws MWException
  45       */
  46  	function __construct( $params ) {
  47          if ( !isset( $params['servers'] ) ) {
  48              throw new MWException( __CLASS__ . ': missing servers parameter' );
  49          }
  50          $this->mServers = $params['servers'];
  51  
  52          if ( isset( $params['waitTimeout'] ) ) {
  53              $this->mWaitTimeout = $params['waitTimeout'];
  54          } else {
  55              $this->mWaitTimeout = 10;
  56          }
  57  
  58          $this->mReadIndex = -1;
  59          $this->mWriteIndex = -1;
  60          $this->mConns = array(
  61              'local' => array(),
  62              'foreignUsed' => array(),
  63              'foreignFree' => array() );
  64          $this->mLoads = array();
  65          $this->mWaitForPos = false;
  66          $this->mLaggedSlaveMode = false;
  67          $this->mErrorConnection = false;
  68          $this->mAllowLagged = false;
  69  
  70          if ( isset( $params['loadMonitor'] ) ) {
  71              $this->mLoadMonitorClass = $params['loadMonitor'];
  72          } else {
  73              $master = reset( $params['servers'] );
  74              if ( isset( $master['type'] ) && $master['type'] === 'mysql' ) {
  75                  $this->mLoadMonitorClass = 'LoadMonitor_MySQL';
  76              } else {
  77                  $this->mLoadMonitorClass = 'LoadMonitor_Null';
  78              }
  79          }
  80  
  81          foreach ( $params['servers'] as $i => $server ) {
  82              $this->mLoads[$i] = $server['load'];
  83              if ( isset( $server['groupLoads'] ) ) {
  84                  foreach ( $server['groupLoads'] as $group => $ratio ) {
  85                      if ( !isset( $this->mGroupLoads[$group] ) ) {
  86                          $this->mGroupLoads[$group] = array();
  87                      }
  88                      $this->mGroupLoads[$group][$i] = $ratio;
  89                  }
  90              }
  91          }
  92      }
  93  
  94      /**
  95       * Get a LoadMonitor instance
  96       *
  97       * @return LoadMonitor
  98       */
  99  	function getLoadMonitor() {
 100          if ( !isset( $this->mLoadMonitor ) ) {
 101              $class = $this->mLoadMonitorClass;
 102              $this->mLoadMonitor = new $class( $this );
 103          }
 104          return $this->mLoadMonitor;
 105      }
 106  
 107      /**
 108       * Get or set arbitrary data used by the parent object, usually an LBFactory
 109       * @param $x
 110       * @return Mixed
 111       */
 112  	function parentInfo( $x = null ) {
 113          return wfSetVar( $this->mParentInfo, $x );
 114      }
 115  
 116      /**
 117       * Given an array of non-normalised probabilities, this function will select
 118       * an element and return the appropriate key
 119       *
 120       * @deprecated since 1.21, use ArrayUtils::pickRandom()
 121       *
 122       * @param $weights array
 123       *
 124       * @return bool|int|string
 125       */
 126  	function pickRandom( $weights ) {
 127          return ArrayUtils::pickRandom( $weights );
 128      }
 129  
 130      /**
 131       * @param $loads array
 132       * @param $wiki bool
 133       * @return bool|int|string
 134       */
 135  	function getRandomNonLagged( $loads, $wiki = false ) {
 136          # Unset excessively lagged servers
 137          $lags = $this->getLagTimes( $wiki );
 138          foreach ( $lags as $i => $lag ) {
 139              if ( $i != 0 ) {
 140                  if ( $lag === false ) {
 141                      wfDebugLog( 'replication', "Server #$i is not replicating\n" );
 142                      unset( $loads[$i] );
 143                  } elseif ( isset( $this->mServers[$i]['max lag'] ) && $lag > $this->mServers[$i]['max lag'] ) {
 144                      wfDebugLog( 'replication', "Server #$i is excessively lagged ($lag seconds)\n" );
 145                      unset( $loads[$i] );
 146                  }
 147              }
 148          }
 149  
 150          # Find out if all the slaves with non-zero load are lagged
 151          $sum = 0;
 152          foreach ( $loads as $load ) {
 153              $sum += $load;
 154          }
 155          if ( $sum == 0 ) {
 156              # No appropriate DB servers except maybe the master and some slaves with zero load
 157              # Do NOT use the master
 158              # Instead, this function will return false, triggering read-only mode,
 159              # and a lagged slave will be used instead.
 160              return false;
 161          }
 162  
 163          if ( count( $loads ) == 0 ) {
 164              return false;
 165          }
 166  
 167          #wfDebugLog( 'connect', var_export( $loads, true ) );
 168  
 169          # Return a random representative of the remainder
 170          return ArrayUtils::pickRandom( $loads );
 171      }
 172  
 173      /**
 174       * Get the index of the reader connection, which may be a slave
 175       * This takes into account load ratios and lag times. It should
 176       * always return a consistent index during a given invocation
 177       *
 178       * Side effect: opens connections to databases
 179       * @param $group bool
 180       * @param $wiki bool
 181       * @throws MWException
 182       * @return bool|int|string
 183       */
 184  	function getReaderIndex( $group = false, $wiki = false ) {
 185          global $wgReadOnly, $wgDBClusterTimeout, $wgDBAvgStatusPoll, $wgDBtype;
 186  
 187          # @todo FIXME: For now, only go through all this for mysql databases
 188          if ( $wgDBtype != 'mysql' ) {
 189              return $this->getWriterIndex();
 190          }
 191  
 192          if ( count( $this->mServers ) == 1 ) {
 193              # Skip the load balancing if there's only one server
 194              return 0;
 195          } elseif ( $group === false and $this->mReadIndex >= 0 ) {
 196              # Shortcut if generic reader exists already
 197              return $this->mReadIndex;
 198          }
 199  
 200          wfProfileIn( __METHOD__ );
 201  
 202          $totalElapsed = 0;
 203  
 204          # convert from seconds to microseconds
 205          $timeout = $wgDBClusterTimeout * 1e6;
 206  
 207          # Find the relevant load array
 208          if ( $group !== false ) {
 209              if ( isset( $this->mGroupLoads[$group] ) ) {
 210                  $nonErrorLoads = $this->mGroupLoads[$group];
 211              } else {
 212                  # No loads for this group, return false and the caller can use some other group
 213                  wfDebug( __METHOD__ . ": no loads for group $group\n" );
 214                  wfProfileOut( __METHOD__ );
 215                  return false;
 216              }
 217          } else {
 218              $nonErrorLoads = $this->mLoads;
 219          }
 220  
 221          if ( !$nonErrorLoads ) {
 222              wfProfileOut( __METHOD__ );
 223              throw new MWException( "Empty server array given to LoadBalancer" );
 224          }
 225  
 226          # Scale the configured load ratios according to the dynamic load (if the load monitor supports it)
 227          $this->getLoadMonitor()->scaleLoads( $nonErrorLoads, $group, $wiki );
 228  
 229          $laggedSlaveMode = false;
 230  
 231          # First try quickly looking through the available servers for a server that
 232          # meets our criteria
 233          do {
 234              $totalThreadsConnected = 0;
 235              $overloadedServers = 0;
 236              $currentLoads = $nonErrorLoads;
 237              while ( count( $currentLoads ) ) {
 238                  if ( $wgReadOnly || $this->mAllowLagged || $laggedSlaveMode ) {
 239                      $i = ArrayUtils::pickRandom( $currentLoads );
 240                  } else {
 241                      $i = $this->getRandomNonLagged( $currentLoads, $wiki );
 242                      if ( $i === false && count( $currentLoads ) != 0 ) {
 243                          # All slaves lagged. Switch to read-only mode
 244                          wfDebugLog( 'replication', "All slaves lagged. Switch to read-only mode\n" );
 245                          $wgReadOnly = 'The database has been automatically locked ' .
 246                              'while the slave database servers catch up to the master';
 247                          $i = ArrayUtils::pickRandom( $currentLoads );
 248                          $laggedSlaveMode = true;
 249                      }
 250                  }
 251  
 252                  if ( $i === false ) {
 253                      # pickRandom() returned false
 254                      # This is permanent and means the configuration or the load monitor
 255                      # wants us to return false.
 256                      wfDebugLog( 'connect', __METHOD__ . ": pickRandom() returned false\n" );
 257                      wfProfileOut( __METHOD__ );
 258                      return false;
 259                  }
 260  
 261                  wfDebugLog( 'connect', __METHOD__ . ": Using reader #$i: {$this->mServers[$i]['host']}...\n" );
 262                  $conn = $this->openConnection( $i, $wiki );
 263  
 264                  if ( !$conn ) {
 265                      wfDebugLog( 'connect', __METHOD__ . ": Failed connecting to $i/$wiki\n" );
 266                      unset( $nonErrorLoads[$i] );
 267                      unset( $currentLoads[$i] );
 268                      continue;
 269                  }
 270  
 271                  // Perform post-connection backoff
 272                  $threshold = isset( $this->mServers[$i]['max threads'] )
 273                      ? $this->mServers[$i]['max threads'] : false;
 274                  $backoff = $this->getLoadMonitor()->postConnectionBackoff( $conn, $threshold );
 275  
 276                  // Decrement reference counter, we are finished with this connection.
 277                  // It will be incremented for the caller later.
 278                  if ( $wiki !== false ) {
 279                      $this->reuseConnection( $conn );
 280                  }
 281  
 282                  if ( $backoff ) {
 283                      # Post-connection overload, don't use this server for now
 284                      $totalThreadsConnected += $backoff;
 285                      $overloadedServers++;
 286                      unset( $currentLoads[$i] );
 287                  } else {
 288                      # Return this server
 289                      break 2;
 290                  }
 291              }
 292  
 293              # No server found yet
 294              $i = false;
 295  
 296              # If all servers were down, quit now
 297              if ( !count( $nonErrorLoads ) ) {
 298                  wfDebugLog( 'connect', "All servers down\n" );
 299                  break;
 300              }
 301  
 302              # Some servers must have been overloaded
 303              if ( $overloadedServers == 0 ) {
 304                  throw new MWException( __METHOD__ . ": unexpectedly found no overloaded servers" );
 305              }
 306              # Back off for a while
 307              # Scale the sleep time by the number of connected threads, to produce a
 308              # roughly constant global poll rate
 309              $avgThreads = $totalThreadsConnected / $overloadedServers;
 310              $totalElapsed += $this->sleep( $wgDBAvgStatusPoll * $avgThreads );
 311          } while ( $totalElapsed < $timeout );
 312  
 313          if ( $totalElapsed >= $timeout ) {
 314              wfDebugLog( 'connect', "All servers busy\n" );
 315              $this->mErrorConnection = false;
 316              $this->mLastError = 'All servers busy';
 317          }
 318  
 319          if ( $i !== false ) {
 320              # Slave connection successful
 321              # Wait for the session master pos for a short time
 322              if ( $this->mWaitForPos && $i > 0 ) {
 323                  if ( !$this->doWait( $i ) ) {
 324                      $this->mServers[$i]['slave pos'] = $conn->getSlavePos();
 325                  }
 326              }
 327              if ( $this->mReadIndex <= 0 && $this->mLoads[$i] > 0 && $i !== false ) {
 328                  $this->mReadIndex = $i;
 329              }
 330          }
 331          wfProfileOut( __METHOD__ );
 332          return $i;
 333      }
 334  
 335      /**
 336       * Wait for a specified number of microseconds, and return the period waited
 337       * @param $t int
 338       * @return int
 339       */
 340  	function sleep( $t ) {
 341          wfProfileIn( __METHOD__ );
 342          wfDebug( __METHOD__ . ": waiting $t us\n" );
 343          usleep( $t );
 344          wfProfileOut( __METHOD__ );
 345          return $t;
 346      }
 347  
 348      /**
 349       * Set the master wait position
 350       * If a DB_SLAVE connection has been opened already, waits
 351       * Otherwise sets a variable telling it to wait if such a connection is opened
 352       * @param $pos DBMasterPos
 353       */
 354  	public function waitFor( $pos ) {
 355          wfProfileIn( __METHOD__ );
 356          $this->mWaitForPos = $pos;
 357          $i = $this->mReadIndex;
 358  
 359          if ( $i > 0 ) {
 360              if ( !$this->doWait( $i ) ) {
 361                  $this->mServers[$i]['slave pos'] = $this->getAnyOpenConnection( $i )->getSlavePos();
 362                  $this->mLaggedSlaveMode = true;
 363              }
 364          }
 365          wfProfileOut( __METHOD__ );
 366      }
 367  
 368      /**
 369       * Set the master wait position and wait for ALL slaves to catch up to it
 370       * @param $pos DBMasterPos
 371       */
 372  	public function waitForAll( $pos ) {
 373          wfProfileIn( __METHOD__ );
 374          $this->mWaitForPos = $pos;
 375          for ( $i = 1; $i < count( $this->mServers ); $i++ ) {
 376              $this->doWait( $i, true );
 377          }
 378          wfProfileOut( __METHOD__ );
 379      }
 380  
 381      /**
 382       * Get any open connection to a given server index, local or foreign
 383       * Returns false if there is no connection open
 384       *
 385       * @param $i int
 386       * @return DatabaseBase|bool False on failure
 387       */
 388  	function getAnyOpenConnection( $i ) {
 389          foreach ( $this->mConns as $conns ) {
 390              if ( !empty( $conns[$i] ) ) {
 391                  return reset( $conns[$i] );
 392              }
 393          }
 394          return false;
 395      }
 396  
 397      /**
 398       * Wait for a given slave to catch up to the master pos stored in $this
 399       * @param $index
 400       * @param $open bool
 401       * @return bool
 402       */
 403  	protected function doWait( $index, $open = false ) {
 404          # Find a connection to wait on
 405          $conn = $this->getAnyOpenConnection( $index );
 406          if ( !$conn ) {
 407              if ( !$open ) {
 408                  wfDebug( __METHOD__ . ": no connection open\n" );
 409                  return false;
 410              } else {
 411                  $conn = $this->openConnection( $index, '' );
 412                  if ( !$conn ) {
 413                      wfDebug( __METHOD__ . ": failed to open connection\n" );
 414                      return false;
 415                  }
 416              }
 417          }
 418  
 419          wfDebug( __METHOD__ . ": Waiting for slave #$index to catch up...\n" );
 420          $result = $conn->masterPosWait( $this->mWaitForPos, $this->mWaitTimeout );
 421  
 422          if ( $result == -1 || is_null( $result ) ) {
 423              # Timed out waiting for slave, use master instead
 424              wfDebug( __METHOD__ . ": Timed out waiting for slave #$index pos {$this->mWaitForPos}\n" );
 425              return false;
 426          } else {
 427              wfDebug( __METHOD__ . ": Done\n" );
 428              return true;
 429          }
 430      }
 431  
 432      /**
 433       * Get a connection by index
 434       * This is the main entry point for this class.
 435       *
 436       * @param $i Integer: server index
 437       * @param array $groups query groups
 438       * @param bool|string $wiki Wiki ID
 439       *
 440       * @throws MWException
 441       * @return DatabaseBase
 442       */
 443      public function &getConnection( $i, $groups = array(), $wiki = false ) {
 444          wfProfileIn( __METHOD__ );
 445  
 446          if ( $i == DB_LAST ) {
 447              wfProfileOut( __METHOD__ );
 448              throw new MWException( 'Attempt to call ' . __METHOD__ . ' with deprecated server index DB_LAST' );
 449          } elseif ( $i === null || $i === false ) {
 450              wfProfileOut( __METHOD__ );
 451              throw new MWException( 'Attempt to call ' . __METHOD__ . ' with invalid server index' );
 452          }
 453  
 454          if ( $wiki === wfWikiID() ) {
 455              $wiki = false;
 456          }
 457  
 458          # Query groups
 459          if ( $i == DB_MASTER ) {
 460              $i = $this->getWriterIndex();
 461          } elseif ( !is_array( $groups ) ) {
 462              $groupIndex = $this->getReaderIndex( $groups, $wiki );
 463              if ( $groupIndex !== false ) {
 464                  $serverName = $this->getServerName( $groupIndex );
 465                  wfDebug( __METHOD__ . ": using server $serverName for group $groups\n" );
 466                  $i = $groupIndex;
 467              }
 468          } else {
 469              foreach ( $groups as $group ) {
 470                  $groupIndex = $this->getReaderIndex( $group, $wiki );
 471                  if ( $groupIndex !== false ) {
 472                      $serverName = $this->getServerName( $groupIndex );
 473                      wfDebug( __METHOD__ . ": using server $serverName for group $group\n" );
 474                      $i = $groupIndex;
 475                      break;
 476                  }
 477              }
 478          }
 479  
 480          # Operation-based index
 481          if ( $i == DB_SLAVE ) {
 482              $this->mLastError = 'Unknown error'; // reset error string
 483              $i = $this->getReaderIndex( false, $wiki );
 484              # Couldn't find a working server in getReaderIndex()?
 485              if ( $i === false ) {
 486                  $this->mLastError = 'No working slave server: ' . $this->mLastError;
 487                  wfProfileOut( __METHOD__ );
 488                  return $this->reportConnectionError();
 489              }
 490          }
 491  
 492          # Now we have an explicit index into the servers array
 493          $conn = $this->openConnection( $i, $wiki );
 494          if ( !$conn ) {
 495              wfProfileOut( __METHOD__ );
 496              return $this->reportConnectionError();
 497          }
 498  
 499          wfProfileOut( __METHOD__ );
 500          return $conn;
 501      }
 502  
 503      /**
 504       * Mark a foreign connection as being available for reuse under a different
 505       * DB name or prefix. This mechanism is reference-counted, and must be called
 506       * the same number of times as getConnection() to work.
 507       *
 508       * @param DatabaseBase $conn
 509       * @throws MWException
 510       */
 511  	public function reuseConnection( $conn ) {
 512          $serverIndex = $conn->getLBInfo( 'serverIndex' );
 513          $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 514          $dbName = $conn->getDBname();
 515          $prefix = $conn->tablePrefix();
 516          if ( strval( $prefix ) !== '' ) {
 517              $wiki = "$dbName-$prefix";
 518          } else {
 519              $wiki = $dbName;
 520          }
 521          if ( $serverIndex === null || $refCount === null ) {
 522              wfDebug( __METHOD__ . ": this connection was not opened as a foreign connection\n" );
 523              /**
 524               * This can happen in code like:
 525               *   foreach ( $dbs as $db ) {
 526               *     $conn = $lb->getConnection( DB_SLAVE, array(), $db );
 527               *     ...
 528               *     $lb->reuseConnection( $conn );
 529               *   }
 530               * When a connection to the local DB is opened in this way, reuseConnection()
 531               * should be ignored
 532               */
 533              return;
 534          }
 535          if ( $this->mConns['foreignUsed'][$serverIndex][$wiki] !== $conn ) {
 536              throw new MWException( __METHOD__ . ": connection not found, has the connection been freed already?" );
 537          }
 538          $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
 539          if ( $refCount <= 0 ) {
 540              $this->mConns['foreignFree'][$serverIndex][$wiki] = $conn;
 541              unset( $this->mConns['foreignUsed'][$serverIndex][$wiki] );
 542              wfDebug( __METHOD__ . ": freed connection $serverIndex/$wiki\n" );
 543          } else {
 544              wfDebug( __METHOD__ . ": reference count for $serverIndex/$wiki reduced to $refCount\n" );
 545          }
 546      }
 547  
 548      /**
 549       * Get a database connection handle reference
 550       *
 551       * The handle's methods wrap simply wrap those of a DatabaseBase handle
 552       *
 553       * @see LoadBalancer::getConnection() for parameter information
 554       *
 555       * @param integer $db
 556       * @param mixed $groups
 557       * @param string $wiki
 558       * @return DBConnRef
 559       */
 560  	public function getConnectionRef( $db, $groups = array(), $wiki = false ) {
 561          return new DBConnRef( $this, $this->getConnection( $db, $groups, $wiki ) );
 562      }
 563  
 564      /**
 565       * Get a database connection handle reference without connecting yet
 566       *
 567       * The handle's methods wrap simply wrap those of a DatabaseBase handle
 568       *
 569       * @see LoadBalancer::getConnection() for parameter information
 570       *
 571       * @param integer $db
 572       * @param mixed $groups
 573       * @param string $wiki
 574       * @return DBConnRef
 575       */
 576  	public function getLazyConnectionRef( $db, $groups = array(), $wiki = false ) {
 577          return new DBConnRef( $this, array( $db, $groups, $wiki ) );
 578      }
 579  
 580      /**
 581       * Open a connection to the server given by the specified index
 582       * Index must be an actual index into the array.
 583       * If the server is already open, returns it.
 584       *
 585       * On error, returns false, and the connection which caused the
 586       * error will be available via $this->mErrorConnection.
 587       *
 588       * @param $i Integer server index
 589       * @param string $wiki wiki ID to open
 590       * @return DatabaseBase
 591       *
 592       * @access private
 593       */
 594  	function openConnection( $i, $wiki = false ) {
 595          wfProfileIn( __METHOD__ );
 596          if ( $wiki !== false ) {
 597              $conn = $this->openForeignConnection( $i, $wiki );
 598              wfProfileOut( __METHOD__ );
 599              return $conn;
 600          }
 601          if ( isset( $this->mConns['local'][$i][0] ) ) {
 602              $conn = $this->mConns['local'][$i][0];
 603          } else {
 604              $server = $this->mServers[$i];
 605              $server['serverIndex'] = $i;
 606              $conn = $this->reallyOpenConnection( $server, false );
 607              if ( $conn->isOpen() ) {
 608                  wfDebug( "Connected to database $i at {$this->mServers[$i]['host']}\n" );
 609                  $this->mConns['local'][$i][0] = $conn;
 610              } else {
 611                  wfDebug( "Failed to connect to database $i at {$this->mServers[$i]['host']}\n" );
 612                  $this->mErrorConnection = $conn;
 613                  $conn = false;
 614              }
 615          }
 616          wfProfileOut( __METHOD__ );
 617          return $conn;
 618      }
 619  
 620      /**
 621       * Open a connection to a foreign DB, or return one if it is already open.
 622       *
 623       * Increments a reference count on the returned connection which locks the
 624       * connection to the requested wiki. This reference count can be
 625       * decremented by calling reuseConnection().
 626       *
 627       * If a connection is open to the appropriate server already, but with the wrong
 628       * database, it will be switched to the right database and returned, as long as
 629       * it has been freed first with reuseConnection().
 630       *
 631       * On error, returns false, and the connection which caused the
 632       * error will be available via $this->mErrorConnection.
 633       *
 634       * @param $i Integer: server index
 635       * @param string $wiki wiki ID to open
 636       * @return DatabaseBase
 637       */
 638  	function openForeignConnection( $i, $wiki ) {
 639          wfProfileIn( __METHOD__ );
 640          list( $dbName, $prefix ) = wfSplitWikiID( $wiki );
 641          if ( isset( $this->mConns['foreignUsed'][$i][$wiki] ) ) {
 642              // Reuse an already-used connection
 643              $conn = $this->mConns['foreignUsed'][$i][$wiki];
 644              wfDebug( __METHOD__ . ": reusing connection $i/$wiki\n" );
 645          } elseif ( isset( $this->mConns['foreignFree'][$i][$wiki] ) ) {
 646              // Reuse a free connection for the same wiki
 647              $conn = $this->mConns['foreignFree'][$i][$wiki];
 648              unset( $this->mConns['foreignFree'][$i][$wiki] );
 649              $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 650              wfDebug( __METHOD__ . ": reusing free connection $i/$wiki\n" );
 651          } elseif ( !empty( $this->mConns['foreignFree'][$i] ) ) {
 652              // Reuse a connection from another wiki
 653              $conn = reset( $this->mConns['foreignFree'][$i] );
 654              $oldWiki = key( $this->mConns['foreignFree'][$i] );
 655  
 656              if ( !$conn->selectDB( $dbName ) ) {
 657                  $this->mLastError = "Error selecting database $dbName on server " .
 658                      $conn->getServer() . " from client host " . wfHostname() . "\n";
 659                  $this->mErrorConnection = $conn;
 660                  $conn = false;
 661              } else {
 662                  $conn->tablePrefix( $prefix );
 663                  unset( $this->mConns['foreignFree'][$i][$oldWiki] );
 664                  $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 665                  wfDebug( __METHOD__ . ": reusing free connection from $oldWiki for $wiki\n" );
 666              }
 667          } else {
 668              // Open a new connection
 669              $server = $this->mServers[$i];
 670              $server['serverIndex'] = $i;
 671              $server['foreignPoolRefCount'] = 0;
 672              $server['foreign'] = true;
 673              $conn = $this->reallyOpenConnection( $server, $dbName );
 674              if ( !$conn->isOpen() ) {
 675                  wfDebug( __METHOD__ . ": error opening connection for $i/$wiki\n" );
 676                  $this->mErrorConnection = $conn;
 677                  $conn = false;
 678              } else {
 679                  $conn->tablePrefix( $prefix );
 680                  $this->mConns['foreignUsed'][$i][$wiki] = $conn;
 681                  wfDebug( __METHOD__ . ": opened new connection for $i/$wiki\n" );
 682              }
 683          }
 684  
 685          // Increment reference count
 686          if ( $conn ) {
 687              $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 688              $conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
 689          }
 690          wfProfileOut( __METHOD__ );
 691          return $conn;
 692      }
 693  
 694      /**
 695       * Test if the specified index represents an open connection
 696       *
 697       * @param $index Integer: server index
 698       * @access private
 699       * @return bool
 700       */
 701  	function isOpen( $index ) {
 702          if ( !is_integer( $index ) ) {
 703              return false;
 704          }
 705          return (bool)$this->getAnyOpenConnection( $index );
 706      }
 707  
 708      /**
 709       * Really opens a connection. Uncached.
 710       * Returns a Database object whether or not the connection was successful.
 711       * @access private
 712       *
 713       * @param $server
 714       * @param $dbNameOverride bool
 715       * @throws MWException
 716       * @return DatabaseBase
 717       */
 718  	function reallyOpenConnection( $server, $dbNameOverride = false ) {
 719          if ( !is_array( $server ) ) {
 720              throw new MWException( 'You must update your load-balancing configuration. ' .
 721                  'See DefaultSettings.php entry for $wgDBservers.' );
 722          }
 723  
 724          if ( $dbNameOverride !== false ) {
 725              $server['dbname'] = $dbNameOverride;
 726          }
 727  
 728          # Create object
 729          try {
 730              $db = DatabaseBase::factory( $server['type'], $server );
 731          } catch ( DBConnectionError $e ) {
 732              // FIXME: This is probably the ugliest thing I have ever done to
 733              // PHP. I'm half-expecting it to segfault, just out of disgust. -- TS
 734              $db = $e->db;
 735          }
 736  
 737          $db->setLBInfo( $server );
 738          if ( isset( $server['fakeSlaveLag'] ) ) {
 739              $db->setFakeSlaveLag( $server['fakeSlaveLag'] );
 740          }
 741          if ( isset( $server['fakeMaster'] ) ) {
 742              $db->setFakeMaster( true );
 743          }
 744          return $db;
 745      }
 746  
 747      /**
 748       * @throws DBConnectionError
 749       * @return bool
 750       */
 751  	private function reportConnectionError() {
 752          $conn = $this->mErrorConnection; // The connection which caused the error
 753  
 754          if ( !is_object( $conn ) ) {
 755              // No last connection, probably due to all servers being too busy
 756              wfLogDBError( "LB failure with no last connection. Connection error: {$this->mLastError}\n" );
 757  
 758              // If all servers were busy, mLastError will contain something sensible
 759              throw new DBConnectionError( null, $this->mLastError );
 760          } else {
 761              $server = $conn->getProperty( 'mServer' );
 762              wfLogDBError( "Connection error: {$this->mLastError} ({$server})\n" );
 763              $conn->reportConnectionError( "{$this->mLastError} ({$server})" ); // throws DBConnectionError
 764          }
 765          return false; /* not reached */
 766      }
 767  
 768      /**
 769       * @return int
 770       */
 771  	function getWriterIndex() {
 772          return 0;
 773      }
 774  
 775      /**
 776       * Returns true if the specified index is a valid server index
 777       *
 778       * @param $i
 779       * @return bool
 780       */
 781  	function haveIndex( $i ) {
 782          return array_key_exists( $i, $this->mServers );
 783      }
 784  
 785      /**
 786       * Returns true if the specified index is valid and has non-zero load
 787       *
 788       * @param $i
 789       * @return bool
 790       */
 791  	function isNonZeroLoad( $i ) {
 792          return array_key_exists( $i, $this->mServers ) && $this->mLoads[$i] != 0;
 793      }
 794  
 795      /**
 796       * Get the number of defined servers (not the number of open connections)
 797       *
 798       * @return int
 799       */
 800  	function getServerCount() {
 801          return count( $this->mServers );
 802      }
 803  
 804      /**
 805       * Get the host name or IP address of the server with the specified index
 806       * Prefer a readable name if available.
 807       * @param $i
 808       * @return string
 809       */
 810  	function getServerName( $i ) {
 811          if ( isset( $this->mServers[$i]['hostName'] ) ) {
 812              return $this->mServers[$i]['hostName'];
 813          } elseif ( isset( $this->mServers[$i]['host'] ) ) {
 814              return $this->mServers[$i]['host'];
 815          } else {
 816              return '';
 817          }
 818      }
 819  
 820      /**
 821       * Return the server info structure for a given index, or false if the index is invalid.
 822       * @param $i
 823       * @return bool
 824       */
 825  	function getServerInfo( $i ) {
 826          if ( isset( $this->mServers[$i] ) ) {
 827              return $this->mServers[$i];
 828          } else {
 829              return false;
 830          }
 831      }
 832  
 833      /**
 834       * Sets the server info structure for the given index. Entry at index $i is created if it doesn't exist
 835       * @param $i
 836       * @param $serverInfo
 837       */
 838  	function setServerInfo( $i, $serverInfo ) {
 839          $this->mServers[$i] = $serverInfo;
 840      }
 841  
 842      /**
 843       * Get the current master position for chronology control purposes
 844       * @return mixed
 845       */
 846  	function getMasterPos() {
 847          # If this entire request was served from a slave without opening a connection to the
 848          # master (however unlikely that may be), then we can fetch the position from the slave.
 849          $masterConn = $this->getAnyOpenConnection( 0 );
 850          if ( !$masterConn ) {
 851              for ( $i = 1; $i < count( $this->mServers ); $i++ ) {
 852                  $conn = $this->getAnyOpenConnection( $i );
 853                  if ( $conn ) {
 854                      wfDebug( "Master pos fetched from slave\n" );
 855                      return $conn->getSlavePos();
 856                  }
 857              }
 858          } else {
 859              wfDebug( "Master pos fetched from master\n" );
 860              return $masterConn->getMasterPos();
 861          }
 862          return false;
 863      }
 864  
 865      /**
 866       * Close all open connections
 867       */
 868  	function closeAll() {
 869          foreach ( $this->mConns as $conns2 ) {
 870              foreach ( $conns2 as $conns3 ) {
 871                  foreach ( $conns3 as $conn ) {
 872                      $conn->close();
 873                  }
 874              }
 875          }
 876          $this->mConns = array(
 877              'local' => array(),
 878              'foreignFree' => array(),
 879              'foreignUsed' => array(),
 880          );
 881      }
 882  
 883      /**
 884       * Deprecated function, typo in function name
 885       *
 886       * @deprecated in 1.18
 887       * @param $conn
 888       */
 889  	function closeConnecton( $conn ) {
 890          wfDeprecated( __METHOD__, '1.18' );
 891          $this->closeConnection( $conn );
 892      }
 893  
 894      /**
 895       * Close a connection
 896       * Using this function makes sure the LoadBalancer knows the connection is closed.
 897       * If you use $conn->close() directly, the load balancer won't update its state.
 898       * @param $conn DatabaseBase
 899       */
 900  	function closeConnection( $conn ) {
 901          $done = false;
 902          foreach ( $this->mConns as $i1 => $conns2 ) {
 903              foreach ( $conns2 as $i2 => $conns3 ) {
 904                  foreach ( $conns3 as $i3 => $candidateConn ) {
 905                      if ( $conn === $candidateConn ) {
 906                          $conn->close();
 907                          unset( $this->mConns[$i1][$i2][$i3] );
 908                          $done = true;
 909                          break;
 910                      }
 911                  }
 912              }
 913          }
 914          if ( !$done ) {
 915              $conn->close();
 916          }
 917      }
 918  
 919      /**
 920       * Commit transactions on all open connections
 921       */
 922  	function commitAll() {
 923          foreach ( $this->mConns as $conns2 ) {
 924              foreach ( $conns2 as $conns3 ) {
 925                  foreach ( $conns3 as $conn ) {
 926                      if ( $conn->trxLevel() ) {
 927                          $conn->commit( __METHOD__, 'flush' );
 928                      }
 929                  }
 930              }
 931          }
 932      }
 933  
 934      /**
 935       *  Issue COMMIT only on master, only if queries were done on connection
 936       */
 937  	function commitMasterChanges() {
 938          // Always 0, but who knows.. :)
 939          $masterIndex = $this->getWriterIndex();
 940          foreach ( $this->mConns as $conns2 ) {
 941              if ( empty( $conns2[$masterIndex] ) ) {
 942                  continue;
 943              }
 944              foreach ( $conns2[$masterIndex] as $conn ) {
 945                  if ( $conn->trxLevel() && $conn->writesOrCallbacksPending() ) {
 946                      $conn->commit( __METHOD__, 'flush' );
 947                  }
 948              }
 949          }
 950      }
 951  
 952      /**
 953       * @param $value null
 954       * @return Mixed
 955       */
 956  	function waitTimeout( $value = null ) {
 957          return wfSetVar( $this->mWaitTimeout, $value );
 958      }
 959  
 960      /**
 961       * @return bool
 962       */
 963  	function getLaggedSlaveMode() {
 964          return $this->mLaggedSlaveMode;
 965      }
 966  
 967      /**
 968       * Disables/enables lag checks
 969       * @param $mode null
 970       * @return bool
 971       */
 972  	function allowLagged( $mode = null ) {
 973          if ( $mode === null ) {
 974              return $this->mAllowLagged;
 975          }
 976          $this->mAllowLagged = $mode;
 977          return $this->mAllowLagged;
 978      }
 979  
 980      /**
 981       * @return bool
 982       */
 983  	function pingAll() {
 984          $success = true;
 985          foreach ( $this->mConns as $conns2 ) {
 986              foreach ( $conns2 as $conns3 ) {
 987                  foreach ( $conns3 as $conn ) {
 988                      if ( !$conn->ping() ) {
 989                          $success = false;
 990                      }
 991                  }
 992              }
 993          }
 994          return $success;
 995      }
 996  
 997      /**
 998       * Call a function with each open connection object
 999       * @param $callback
1000       * @param array $params
1001       */
1002  	function forEachOpenConnection( $callback, $params = array() ) {
1003          foreach ( $this->mConns as $conns2 ) {
1004              foreach ( $conns2 as $conns3 ) {
1005                  foreach ( $conns3 as $conn ) {
1006                      $mergedParams = array_merge( array( $conn ), $params );
1007                      call_user_func_array( $callback, $mergedParams );
1008                  }
1009              }
1010          }
1011      }
1012  
1013      /**
1014       * Get the hostname and lag time of the most-lagged slave.
1015       * This is useful for maintenance scripts that need to throttle their updates.
1016       * May attempt to open connections to slaves on the default DB. If there is
1017       * no lag, the maximum lag will be reported as -1.
1018       *
1019       * @param string $wiki Wiki ID, or false for the default database
1020       *
1021       * @return array ( host, max lag, index of max lagged host )
1022       */
1023  	function getMaxLag( $wiki = false ) {
1024          $maxLag = -1;
1025          $host = '';
1026          $maxIndex = 0;
1027          if ( $this->getServerCount() > 1 ) { // no replication = no lag
1028              foreach ( $this->mServers as $i => $conn ) {
1029                  $conn = false;
1030                  if ( $wiki === false ) {
1031                      $conn = $this->getAnyOpenConnection( $i );
1032                  }
1033                  if ( !$conn ) {
1034                      $conn = $this->openConnection( $i, $wiki );
1035                  }
1036                  if ( !$conn ) {
1037                      continue;
1038                  }
1039                  $lag = $conn->getLag();
1040                  if ( $lag > $maxLag ) {
1041                      $maxLag = $lag;
1042                      $host = $this->mServers[$i]['host'];
1043                      $maxIndex = $i;
1044                  }
1045              }
1046          }
1047          return array( $host, $maxLag, $maxIndex );
1048      }
1049  
1050      /**
1051       * Get lag time for each server
1052       * Results are cached for a short time in memcached, and indefinitely in the process cache
1053       *
1054       * @param $wiki
1055       *
1056       * @return array
1057       */
1058  	function getLagTimes( $wiki = false ) {
1059          # Try process cache
1060          if ( isset( $this->mLagTimes ) ) {
1061              return $this->mLagTimes;
1062          }
1063          if ( $this->getServerCount() == 1 ) {
1064              # No replication
1065              $this->mLagTimes = array( 0 => 0 );
1066          } else {
1067              # Send the request to the load monitor
1068              $this->mLagTimes = $this->getLoadMonitor()->getLagTimes(
1069                  array_keys( $this->mServers ), $wiki );
1070          }
1071          return $this->mLagTimes;
1072      }
1073  
1074      /**
1075       * Get the lag in seconds for a given connection, or zero if this load
1076       * balancer does not have replication enabled.
1077       *
1078       * This should be used in preference to Database::getLag() in cases where
1079       * replication may not be in use, since there is no way to determine if
1080       * replication is in use at the connection level without running
1081       * potentially restricted queries such as SHOW SLAVE STATUS. Using this
1082       * function instead of Database::getLag() avoids a fatal error in this
1083       * case on many installations.
1084       *
1085       * @param $conn DatabaseBase
1086       *
1087       * @return int
1088       */
1089  	function safeGetLag( $conn ) {
1090          if ( $this->getServerCount() == 1 ) {
1091              return 0;
1092          } else {
1093              return $conn->getLag();
1094          }
1095      }
1096  
1097      /**
1098       * Clear the cache for getLagTimes
1099       */
1100  	function clearLagTimeCache() {
1101          $this->mLagTimes = null;
1102      }
1103  }
1104  
1105  /**
1106   * Helper class to handle automatically marking connectons as reusable (via RAII pattern)
1107   * as well handling deferring the actual network connection until the handle is used
1108   *
1109   * @ingroup Database
1110   * @since 1.22
1111   */
1112  class DBConnRef implements IDatabase {
1113      /** @var LoadBalancer */
1114      protected $lb;
1115      /** @var DatabaseBase|null */
1116      protected $conn;
1117      /** @var Array|null */
1118      protected $params;
1119  
1120      /**
1121       * @param $lb LoadBalancer
1122       * @param $conn DatabaseBase|array Connection or (server index, group, wiki ID) array
1123       */
1124  	public function __construct( LoadBalancer $lb, $conn ) {
1125          $this->lb = $lb;
1126          if ( $conn instanceof DatabaseBase ) {
1127              $this->conn = $conn;
1128          } else {
1129              $this->params = $conn;
1130          }
1131      }
1132  
1133  	public function __call( $name, $arguments ) {
1134          if ( $this->conn === null ) {
1135              list( $db, $groups, $wiki ) = $this->params;
1136              $this->conn = $this->lb->getConnection( $db, $groups, $wiki );
1137          }
1138          return call_user_func_array( array( $this->conn, $name ), $arguments );
1139      }
1140  
1141  	function __destruct() {
1142          if ( $this->conn !== null ) {
1143              $this->lb->reuseConnection( $this->conn );
1144          }
1145      }
1146  }

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