MediaWiki 1.7.1 wiederhergestellt

1 files changed, 666 insertions, 0 deletions

diff --git a/includes/LoadBalancer.php b/includes/LoadBalancer.php
new file mode 100644
index 00000000..f985a7b4
--- /dev/null
+++ b/includes/LoadBalancer.php
@@ -0,0 +1,666 @@
+<?php
+/**
+ *
+ * @package MediaWiki
+ */
+
+/**
+ * Depends on the database object
+ */
+require_once( 'Database.php' );
+
+# Valid database indexes
+# Operation-based indexes
+define( 'DB_SLAVE', -1 );     # Read from the slave (or only server)
+define( 'DB_MASTER', -2 );    # Write to master (or only server)
+define( 'DB_LAST', -3 );     # Whatever database was used last
+
+# Obsolete aliases
+define( 'DB_READ', -1 );
+define( 'DB_WRITE', -2 );
+
+
+# Scale polling time so that under overload conditions, the database server
+# receives a SHOW STATUS query at an average interval of this many microseconds
+define( 'AVG_STATUS_POLL', 2000 );
+
+
+/**
+ * Database load balancing object
+ *
+ * @todo document
+ * @package MediaWiki
+ */
+class LoadBalancer {
+	/* private */ var $mServers, $mConnections, $mLoads, $mGroupLoads;
+	/* private */ var $mFailFunction, $mErrorConnection;
+	/* private */ var $mForce, $mReadIndex, $mLastIndex, $mAllowLagged;
+	/* private */ var $mWaitForFile, $mWaitForPos, $mWaitTimeout;
+	/* private */ var $mLaggedSlaveMode, $mLastError = 'Unknown error';
+
+	function LoadBalancer()
+	{
+		$this->mServers = array();
+		$this->mConnections = array();
+		$this->mFailFunction = false;
+		$this->mReadIndex = -1;
+		$this->mForce = -1;
+		$this->mLastIndex = -1;
+		$this->mErrorConnection = false;
+		$this->mAllowLag = false;
+	}
+
+	function newFromParams( $servers, $failFunction = false, $waitTimeout = 10 )
+	{
+		$lb = new LoadBalancer;
+		$lb->initialise( $servers, $failFunction, $waitTimeout );
+		return $lb;
+	}
+
+	function initialise( $servers, $failFunction = false, $waitTimeout = 10 )
+	{
+		$this->mServers = $servers;
+		$this->mFailFunction = $failFunction;
+		$this->mReadIndex = -1;
+		$this->mWriteIndex = -1;
+		$this->mForce = -1;
+		$this->mConnections = array();
+		$this->mLastIndex = 1;
+		$this->mLoads = array();
+		$this->mWaitForFile = false;
+		$this->mWaitForPos = false;
+		$this->mWaitTimeout = $waitTimeout;
+		$this->mLaggedSlaveMode = false;
+
+		foreach( $servers as $i => $server ) {
+			$this->mLoads[$i] = $server['load'];
+			if ( isset( $server['groupLoads'] ) ) {
+				foreach ( $server['groupLoads'] as $group => $ratio ) {
+					if ( !isset( $this->mGroupLoads[$group] ) ) {
+						$this->mGroupLoads[$group] = array();
+					}
+					$this->mGroupLoads[$group][$i] = $ratio;
+				}
+			}
+		}
+	}
+
+	/**
+	 * Given an array of non-normalised probabilities, this function will select
+	 * an element and return the appropriate key
+	 */
+	function pickRandom( $weights )
+	{
+		if ( !is_array( $weights ) || count( $weights ) == 0 ) {
+			return false;
+		}
+
+		$sum = array_sum( $weights );
+		if ( $sum == 0 ) {
+			# No loads on any of them
+			# In previous versions, this triggered an unweighted random selection,
+			# but this feature has been removed as of April 2006 to allow for strict 
+			# separation of query groups. 
+			return false;
+		}
+		$max = mt_getrandmax();
+		$rand = mt_rand(0, $max) / $max * $sum;
+
+		$sum = 0;
+		foreach ( $weights as $i => $w ) {
+			$sum += $w;
+			if ( $sum >= $rand ) {
+				break;
+			}
+		}
+		return $i;
+	}
+
+	function getRandomNonLagged( $loads ) {
+		# Unset excessively lagged servers
+		$lags = $this->getLagTimes();
+		foreach ( $lags as $i => $lag ) {
+			if ( isset( $this->mServers[$i]['max lag'] ) && $lag > $this->mServers[$i]['max lag'] ) {
+				unset( $loads[$i] );
+			}
+		}
+
+		# Find out if all the slaves with non-zero load are lagged
+		$sum = 0;
+		foreach ( $loads as $load ) {
+			$sum += $load;
+		}
+		if ( $sum == 0 ) {
+			# No appropriate DB servers except maybe the master and some slaves with zero load
+			# Do NOT use the master
+			# Instead, this function will return false, triggering read-only mode,
+			# and a lagged slave will be used instead.
+			return false;
+		}
+
+		if ( count( $loads ) == 0 ) {
+			return false;
+		}
+
+		#wfDebugLog( 'connect', var_export( $loads, true ) );
+
+		# Return a random representative of the remainder
+		return $this->pickRandom( $loads );
+	}
+
+	/**
+	 * Get the index of the reader connection, which may be a slave
+	 * This takes into account load ratios and lag times. It should
+	 * always return a consistent index during a given invocation
+	 *
+	 * Side effect: opens connections to databases
+	 */
+	function getReaderIndex() {
+		global $wgReadOnly, $wgDBClusterTimeout;
+
+		$fname = 'LoadBalancer::getReaderIndex';
+		wfProfileIn( $fname );
+
+		$i = false;
+		if ( $this->mForce >= 0 ) {
+			$i = $this->mForce;
+		} else {
+			if ( $this->mReadIndex >= 0 ) {
+				$i = $this->mReadIndex;
+			} else {
+				# $loads is $this->mLoads except with elements knocked out if they
+				# don't work
+				$loads = $this->mLoads;
+				$done = false;
+				$totalElapsed = 0;
+				do {
+					if ( $wgReadOnly or $this->mAllowLagged ) {
+						$i = $this->pickRandom( $loads );
+					} else {
+						$i = $this->getRandomNonLagged( $loads );
+						if ( $i === false && count( $loads ) != 0 )  {
+							# All slaves lagged. Switch to read-only mode
+							$wgReadOnly = wfMsgNoDB( 'readonly_lag' );
+							$i = $this->pickRandom( $loads );
+						}
+					}
+					$serverIndex = $i;
+					if ( $i !== false ) {
+						wfDebugLog( 'connect', "$fname: Using reader #$i: {$this->mServers[$i]['host']}...\n" );
+						$this->openConnection( $i );
+
+						if ( !$this->isOpen( $i ) ) {
+							wfDebug( "$fname: Failed\n" );
+							unset( $loads[$i] );
+							$sleepTime = 0;
+						} else {
+							$status = $this->mConnections[$i]->getStatus("Thread%");
+							if ( isset( $this->mServers[$i]['max threads'] ) &&
+							  $status['Threads_running'] > $this->mServers[$i]['max threads'] )
+							{
+								# Too much load, back off and wait for a while.
+								# The sleep time is scaled by the number of threads connected,
+								# to produce a roughly constant global poll rate.
+								$sleepTime = AVG_STATUS_POLL * $status['Threads_connected'];
+
+								# If we reach the timeout and exit the loop, don't use it
+								$i = false;
+							} else {
+								$done = true;
+								$sleepTime = 0;
+							}
+						}
+					} else {
+						$sleepTime = 500000;
+					}
+					if ( $sleepTime ) {
+							$totalElapsed += $sleepTime;
+							$x = "{$this->mServers[$serverIndex]['host']} [$serverIndex]";
+							wfProfileIn( "$fname-sleep $x" );
+							usleep( $sleepTime );
+							wfProfileOut( "$fname-sleep $x" );
+					}
+				} while ( count( $loads ) && !$done && $totalElapsed / 1e6 < $wgDBClusterTimeout );
+
+				if ( $totalElapsed / 1e6 >= $wgDBClusterTimeout ) {
+					$this->mErrorConnection = false;
+					$this->mLastError = 'All servers busy';
+				}
+
+				if ( $i !== false && $this->isOpen( $i ) ) {
+					# Wait for the session master pos for a short time
+					if ( $this->mWaitForFile ) {
+						if ( !$this->doWait( $i ) ) {
+							$this->mServers[$i]['slave pos'] = $this->mConnections[$i]->getSlavePos();
+						}
+					}
+					if ( $i !== false ) {
+						$this->mReadIndex = $i;
+					}
+				} else {
+					$i = false;
+				}
+			}
+		}
+		wfProfileOut( $fname );
+		return $i;
+	}
+
+	/**
+	 * Get a random server to use in a query group
+	 */
+	function getGroupIndex( $group ) {
+		if ( isset( $this->mGroupLoads[$group] ) ) {
+			$i = $this->pickRandom( $this->mGroupLoads[$group] );
+		} else {
+			$i = false;
+		}
+		wfDebug( "Query group $group => $i\n" );
+		return $i;
+	}
+
+	/**
+	 * Set the master wait position
+	 * If a DB_SLAVE connection has been opened already, waits
+	 * Otherwise sets a variable telling it to wait if such a connection is opened
+	 */
+	function waitFor( $file, $pos ) {
+		$fname = 'LoadBalancer::waitFor';
+		wfProfileIn( $fname );
+
+		wfDebug( "User master pos: $file $pos\n" );
+		$this->mWaitForFile = false;
+		$this->mWaitForPos = false;
+
+		if ( count( $this->mServers ) > 1 ) {
+			$this->mWaitForFile = $file;
+			$this->mWaitForPos = $pos;
+			$i = $this->mReadIndex;
+
+			if ( $i > 0 ) {
+				if ( !$this->doWait( $i ) ) {
+					$this->mServers[$i]['slave pos'] = $this->mConnections[$i]->getSlavePos();
+					$this->mLaggedSlaveMode = true;
+				}
+			}
+		}
+		wfProfileOut( $fname );
+	}
+
+	/**
+	 * Wait for a given slave to catch up to the master pos stored in $this
+	 */
+	function doWait( $index ) {
+		global $wgMemc;
+
+		$retVal = false;
+
+		# Debugging hacks
+		if ( isset( $this->mServers[$index]['lagged slave'] ) ) {
+			return false;
+		} elseif ( isset( $this->mServers[$index]['fake slave'] ) ) {
+			return true;
+		}
+
+		$key = 'masterpos:' . $index;
+		$memcPos = $wgMemc->get( $key );
+		if ( $memcPos ) {
+			list( $file, $pos ) = explode( ' ', $memcPos );
+			# If the saved position is later than the requested position, return now
+			if ( $file == $this->mWaitForFile && $this->mWaitForPos <= $pos ) {
+				$retVal = true;
+			}
+		}
+
+		if ( !$retVal && $this->isOpen( $index ) ) {
+			$conn =& $this->mConnections[$index];
+			wfDebug( "Waiting for slave #$index to catch up...\n" );
+			$result = $conn->masterPosWait( $this->mWaitForFile, $this->mWaitForPos, $this->mWaitTimeout );
+
+			if ( $result == -1 || is_null( $result ) ) {
+				# Timed out waiting for slave, use master instead
+				wfDebug( "Timed out waiting for slave #$index pos {$this->mWaitForFile} {$this->mWaitForPos}\n" );
+				$retVal = false;
+			} else {
+				$retVal = true;
+				wfDebug( "Done\n" );
+			}
+		}
+		return $retVal;
+	}
+
+	/**
+	 * Get a connection by index
+	 */
+	function &getConnection( $i, $fail = true, $groups = array() )
+	{
+		global $wgDBtype;
+		$fname = 'LoadBalancer::getConnection';
+		wfProfileIn( $fname );
+
+
+		# Query groups
+		if ( !is_array( $groups ) ) {
+			$groupIndex = $this->getGroupIndex( $groups, $i );
+			if ( $groupIndex !== false ) {
+				$i = $groupIndex;
+			}
+		} else {
+			foreach ( $groups as $group ) {
+				$groupIndex = $this->getGroupIndex( $group, $i );
+				if ( $groupIndex !== false ) {
+					$i = $groupIndex;
+					break;
+				}
+			}
+		}
+
+		# For now, only go through all this for mysql databases
+		if ($wgDBtype != 'mysql') {
+			$i = $this->getWriterIndex();
+		}
+		# Operation-based index
+		elseif ( $i == DB_SLAVE ) {
+			$i = $this->getReaderIndex();
+		} elseif ( $i == DB_MASTER ) {
+			$i = $this->getWriterIndex();
+		} elseif ( $i == DB_LAST ) {
+			# Just use $this->mLastIndex, which should already be set
+			$i = $this->mLastIndex;
+			if ( $i === -1 ) {
+				# Oh dear, not set, best to use the writer for safety
+				wfDebug( "Warning: DB_LAST used when there was no previous index\n" );
+				$i = $this->getWriterIndex();
+			}
+		}
+		# Couldn't find a working server in getReaderIndex()?
+		if ( $i === false ) {
+			$this->reportConnectionError( $this->mErrorConnection );
+		}
+		# Now we have an explicit index into the servers array
+		$this->openConnection( $i, $fail );
+
+		wfProfileOut( $fname );
+		return $this->mConnections[$i];
+	}
+
+	/**
+	 * Open a connection to the server given by the specified index
+	 * Index must be an actual index into the array
+	 * Returns success
+	 * @access private
+	 */
+	function openConnection( $i, $fail = false ) {
+		$fname = 'LoadBalancer::openConnection';
+		wfProfileIn( $fname );
+		$success = true;
+
+		if ( !$this->isOpen( $i ) ) {
+			$this->mConnections[$i] = $this->reallyOpenConnection( $this->mServers[$i] );
+		}
+
+		if ( !$this->isOpen( $i ) ) {
+			wfDebug( "Failed to connect to database $i at {$this->mServers[$i]['host']}\n" );
+			if ( $fail ) {
+				$this->reportConnectionError( $this->mConnections[$i] );
+			}
+			$this->mErrorConnection = $this->mConnections[$i];
+			$this->mConnections[$i] = false;
+			$success = false;
+		}
+		$this->mLastIndex = $i;
+		wfProfileOut( $fname );
+		return $success;
+	}
+
+	/**
+	 * Test if the specified index represents an open connection
+	 * @access private
+	 */
+	function isOpen( $index ) {
+		if( !is_integer( $index ) ) {
+			return false;
+		}
+		if ( array_key_exists( $index, $this->mConnections ) && is_object( $this->mConnections[$index] ) &&
+		  $this->mConnections[$index]->isOpen() )
+		{
+			return true;
+		} else {
+			return false;
+		}
+	}
+
+	/**
+	 * Really opens a connection
+	 * @access private
+	 */
+	function reallyOpenConnection( &$server ) {
+		if( !is_array( $server ) ) {
+			throw new MWException( 'You must update your load-balancing configuration. See DefaultSettings.php entry for $wgDBservers.' );
+		}
+
+		extract( $server );
+		# Get class for this database type
+		$class = 'Database' . ucfirst( $type );
+		if ( !class_exists( $class ) ) {
+			require_once( "$class.php" );
+		}
+
+		# Create object
+		$db = new $class( $host, $user, $password, $dbname, 1, $flags );
+		$db->setLBInfo( $server );
+		return $db;
+	}
+
+	function reportConnectionError( &$conn )
+	{
+		$fname = 'LoadBalancer::reportConnectionError';
+		wfProfileIn( $fname );
+		# Prevent infinite recursion
+
+		static $reporting = false;
+		if ( !$reporting ) {
+			$reporting = true;
+			if ( !is_object( $conn ) ) {
+				// No last connection, probably due to all servers being too busy
+				$conn = new Database;
+				if ( $this->mFailFunction ) {
+					$conn->failFunction( $this->mFailFunction );
+					$conn->reportConnectionError( $this->mLastError );
+				} else {
+					// If all servers were busy, mLastError will contain something sensible
+					throw new DBConnectionError( $conn, $this->mLastError );
+				}
+			} else {
+				if ( $this->mFailFunction ) {
+					$conn->failFunction( $this->mFailFunction );
+				} else {
+					$conn->failFunction( false );
+				}
+				$server = $conn->getProperty( 'mServer' );
+				$conn->reportConnectionError( "{$this->mLastError} ({$server})" );
+			}
+			$reporting = false;
+		}
+		wfProfileOut( $fname );
+	}
+
+	function getWriterIndex() {
+		return 0;
+	}
+
+	/**
+	 * Force subsequent calls to getConnection(DB_SLAVE) to return the 
+	 * given index. Set to -1 to restore the original load balancing
+	 * behaviour. I thought this was a good idea when I originally 
+	 * wrote this class, but it has never been used.
+	 */
+	function force( $i ) {
+		$this->mForce = $i;
+	}
+
+	/**
+	 * Returns true if the specified index is a valid server index
+	 */
+	function haveIndex( $i ) {
+		return array_key_exists( $i, $this->mServers );
+	}
+
+	/**
+	 * Returns true if the specified index is valid and has non-zero load
+	 */
+	function isNonZeroLoad( $i ) {
+		return array_key_exists( $i, $this->mServers ) && $this->mLoads[$i] != 0;
+	}
+
+	/**
+	 * Get the number of defined servers (not the number of open connections)
+	 */
+	function getServerCount() {
+		return count( $this->mServers );
+	}
+
+	/**
+	 * Save master pos to the session and to memcached, if the session exists
+	 */
+	function saveMasterPos() {
+		global $wgSessionStarted;
+		if ( $wgSessionStarted && count( $this->mServers ) > 1 ) {
+			# If this entire request was served from a slave without opening a connection to the
+			# master (however unlikely that may be), then we can fetch the position from the slave.
+			if ( empty( $this->mConnections[0] ) ) {
+				$conn =& $this->getConnection( DB_SLAVE );
+				list( $file, $pos ) = $conn->getSlavePos();
+				wfDebug( "Saving master pos fetched from slave: $file $pos\n" );
+			} else {
+				$conn =& $this->getConnection( 0 );
+				list( $file, $pos ) = $conn->getMasterPos();
+				wfDebug( "Saving master pos: $file $pos\n" );
+			}
+			if ( $file !== false ) {
+				$_SESSION['master_log_file'] = $file;
+				$_SESSION['master_pos'] = $pos;
+			}
+		}
+	}
+
+	/**
+	 * Loads the master pos from the session, waits for it if necessary
+	 */
+	function loadMasterPos() {
+		if ( isset( $_SESSION['master_log_file'] ) && isset( $_SESSION['master_pos'] ) ) {
+			$this->waitFor( $_SESSION['master_log_file'], $_SESSION['master_pos'] );
+		}
+	}
+
+	/**
+	 * Close all open connections
+	 */
+	function closeAll() {
+		foreach( $this->mConnections as $i => $conn ) {
+			if ( $this->isOpen( $i ) ) {
+				// Need to use this syntax because $conn is a copy not a reference
+				$this->mConnections[$i]->close();
+			}
+		}
+	}
+
+	function commitAll() {
+		foreach( $this->mConnections as $i => $conn ) {
+			if ( $this->isOpen( $i ) ) {
+				// Need to use this syntax because $conn is a copy not a reference
+				$this->mConnections[$i]->immediateCommit();
+			}
+		}
+	}
+
+	function waitTimeout( $value = NULL ) {
+		return wfSetVar( $this->mWaitTimeout, $value );
+	}
+
+	function getLaggedSlaveMode() {
+		return $this->mLaggedSlaveMode;
+	}
+
+	/* Disables/enables lag checks */
+	function allowLagged($mode=null) {
+		if ($mode===null)
+			return $this->mAllowLagged;
+		$this->mAllowLagged=$mode;
+	}
+
+	function pingAll() {
+		$success = true;
+		foreach ( $this->mConnections as $i => $conn ) {
+			if ( $this->isOpen( $i ) ) {
+				if ( !$this->mConnections[$i]->ping() ) {
+					$success = false;
+				}
+			}
+		}
+		return $success;
+	}
+
+	/**
+	 * Get the hostname and lag time of the most-lagged slave
+	 * This is useful for maintenance scripts that need to throttle their updates
+	 */
+	function getMaxLag() {
+		$maxLag = -1;
+		$host = '';
+		foreach ( $this->mServers as $i => $conn ) {
+			if ( $this->openConnection( $i ) ) {
+				$lag = $this->mConnections[$i]->getLag();
+				if ( $lag > $maxLag ) {
+					$maxLag = $lag;
+					$host = $this->mServers[$i]['host'];
+				}
+			}
+		}
+		return array( $host, $maxLag );
+	}
+
+	/**
+	 * Get lag time for each DB
+	 * Results are cached for a short time in memcached
+	 */
+	function getLagTimes() {
+		global $wgDBname;
+
+		$expiry = 5;
+		$requestRate = 10;
+
+		global $wgMemc;
+		$times = $wgMemc->get( "$wgDBname:lag_times" );
+		if ( $times ) {
+			# Randomly recache with probability rising over $expiry
+			$elapsed = time() - $times['timestamp'];
+			$chance = max( 0, ( $expiry - $elapsed ) * $requestRate );
+			if ( mt_rand( 0, $chance ) != 0 ) {
+				unset( $times['timestamp'] );
+				return $times;
+			}
+		}
+
+		# Cache key missing or expired
+
+		$times = array();
+		foreach ( $this->mServers as $i => $conn ) {
+			if ($i==0) { # Master
+				$times[$i] = 0;
+			} elseif ( $this->openConnection( $i ) ) {
+				$times[$i] = $this->mConnections[$i]->getLag();
+			}
+		}
+
+		# Add a timestamp key so we know when it was cached
+		$times['timestamp'] = time();
+		$wgMemc->set( "$wgDBname:lag_times", $times, $expiry );
+
+		# But don't give the timestamp to the caller
+		unset($times['timestamp']);
+		return $times;
+	}
+}
+
+?>