org.apache.hadoop.hdfs.server.namenode

Class SecondaryNameNode

java.lang.Object

org.apache.hadoop.hdfs.server.namenode.SecondaryNameNode

All Implemented Interfaces:

Runnable

@InterfaceAudience.Private
public class SecondaryNameNode
extends Object
implements Runnable

The Secondary NameNode is a helper to the primary NameNode. The Secondary is responsible for supporting periodic checkpoints of the HDFS metadata. The current design allows only one Secondary NameNode per HDFs cluster. The Secondary NameNode is a daemon that periodically wakes up (determined by the schedule specified in the configuration), triggers a periodic checkpoint and then goes back to sleep. The Secondary NameNode uses the ClientProtocol to talk to the primary NameNode.

Field Summary

Fields

Modifier and Type	Field and Description
static org.apache.commons.logging.Log	LOG

Constructor Summary

Constructors

Constructor and Description
SecondaryNameNode(Configuration conf) Create a connection to the primary namenode.
SecondaryNameNode(Configuration conf, org.apache.hadoop.hdfs.server.namenode.SecondaryNameNode.CommandLineOpts commandLineOpts)

Method Summary

Methods

Modifier and Type	Method and Description
void	doWork()
static InetSocketAddress	getHttpAddress(Configuration conf)
static void	main(String[] argv) main() has some simple utility methods.
void	run()
void	shutdown() Shut down this instance of the datanode.
void	startCheckpointThread()
String	toString()

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Field Detail

LOG

public static final org.apache.commons.logging.Log LOG

Constructor Detail

SecondaryNameNode

public SecondaryNameNode(Configuration conf)
                  throws IOException

Create a connection to the primary namenode.

Throws:

IOException

SecondaryNameNode

public SecondaryNameNode(Configuration conf,
                 org.apache.hadoop.hdfs.server.namenode.SecondaryNameNode.CommandLineOpts commandLineOpts)
                  throws IOException

Throws:

IOException

Method Detail

toString

public String toString()

Overrides:

toString in class Object

getHttpAddress

public static InetSocketAddress getHttpAddress(Configuration conf)

shutdown

public void shutdown()

Shut down this instance of the datanode. Returns only after shutdown is complete.

run

public void run()

Specified by:

run in interface Runnable

doWork

public void doWork()

main

public static void main(String[] argv)
                 throws Exception

main() has some simple utility methods.

Parameters:

argv - Command line parameters.

Throws:

Exception - if the filesystem does not exist.

startCheckpointThread

public void startCheckpointThread()