hadoop配置 - secondarynamenode配置与恢复

一、配置：

secondary namenoded 配置很容易被忽视，如果jps检查都正常，大家通常不会太关心，除非namenode发生问题的时候，才会想起还有个secondary namenode，它的配置共两步：

1.      集群配置文件conf/master中添加secondarynamenode的机器
2.      修改/添加 hdfs-site.xml中如下属性：

	<property>
		<name>dfs.http.address</name>
		<value>192.168.1.11:50070</value>
		<description>
		The address and the base port where the dfs namenode web ui will listen on.
		If the port is 0 then the server will start on a free port.
		</description>
	</property>

	<property>
		<name>dfs.secondary.http.address</name>
		<value>192.168.1.12:50090</value>
		<description>
		The secondary namenode http server address and port.
		If the port is 0 then the server will start on a free port.
		</description>
	</property>

这两项配置OK后，启动集群。进入secondary namenode 机器，检查fs.checkpoint.dir（core-site.xml文件，默认为${hadoop.tmp.dir}/dfs/namesecondary）目录同步状态是否和namenode一致的。

如果不配置第二项则，secondary namenode同步文件夹永远为空，这时查看secondary namenode的log显示错误为：

2013-10-07 00:01:58,490 INFO org.apache.hadoop.hdfs.server.namenode.TransferFsImage: Opening connection to http://0.0.0.0:50070/getimage?getimage=1
2013-10-07 00:01:58,492 ERROR org.apache.hadoop.security.UserGroupInformation: PriviledgedActionException as:root cause:java.net.ConnectException: Connection refused
2013-10-07 00:01:58,492 ERROR org.apache.hadoop.hdfs.server.namenode.SecondaryNameNode: Exception in doCheckpoint: 
2013-10-07 00:01:58,493 ERROR org.apache.hadoop.hdfs.server.namenode.SecondaryNameNode: java.net.ConnectException: Connection refused
	at java.net.PlainSocketImpl.socketConnect(Native Method)
	at java.net.AbstractPlainSocketImpl.doConnect(AbstractPlainSocketImpl.java:339)
	at java.net.AbstractPlainSocketImpl.connectToAddress(AbstractPlainSocketImpl.java:198)
	at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:182)
	at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:391)
	at java.net.Socket.connect(Socket.java:579)
	at java.net.Socket.connect(Socket.java:528)
	at sun.net.NetworkClient.doConnect(NetworkClient.java:180)
	at sun.net.www.http.HttpClient.openServer(HttpClient.java:378)
	at sun.net.www.http.HttpClient.openServer(HttpClient.java:473)
	at sun.net.www.http.HttpClient.<init>(HttpClient.java:203)
	at sun.net.www.http.HttpClient.New(HttpClient.java:290)
	at sun.net.www.http.HttpClient.New(HttpClient.java:306)
	at sun.net.www.protocol.http.HttpURLConnection.getNewHttpClient(HttpURLConnection.java:995)
	at sun.net.www.protocol.http.HttpURLConnection.plainConnect(HttpURLConnection.java:931)
	at sun.net.www.protocol.http.HttpURLConnection.connect(HttpURLConnection.java:849)
	at sun.net.www.protocol.http.HttpURLConnection.getInputStream(HttpURLConnection.java:1299)
	at org.apache.hadoop.hdfs.server.namenode.TransferFsImage.getFileClient(TransferFsImage.java:172)
	at org.apache.hadoop.hdfs.server.namenode.SecondaryNameNode$4.run(SecondaryNameNode.java:404)
	at org.apache.hadoop.hdfs.server.namenode.SecondaryNameNode$4.run(SecondaryNameNode.java:393)
	at java.security.AccessController.doPrivileged(Native Method)
	at javax.security.auth.Subject.doAs(Subject.java:415)
	at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1149)
	at org.apache.hadoop.hdfs.server.namenode.SecondaryNameNode.downloadCheckpointFiles(SecondaryNameNode.java:393)
	at org.apache.hadoop.hdfs.server.namenode.SecondaryNameNode.doCheckpoint(SecondaryNameNode.java:494)
	at org.apache.hadoop.hdfs.server.namenode.SecondaryNameNode.doWork(SecondaryNameNode.java:369)
	at org.apache.hadoop.hdfs.server.namenode.SecondaryNameNode.run(SecondaryNameNode.java:332)
	at java.lang.Thread.run(Thread.java:722)

可能用到的core-site.xml文件相关属性：

	<property>  
		<name>fs.checkpoint.dir</name>  
		<value>${hadoop.tmp.dir}/dfs/namesecondary</value>  
		<description>Determines where on the local filesystem the DFS secondary  
		name node should store the temporary images to merge.  
		If this is a comma-delimited list of directories then the image is  
		replicated in all of the directories for redundancy.  
		</description>  
	</property>  

	<property>
		<name>fs.checkpoint.period</name>
		<value>3600</value>
		<description>The number of seconds between two periodic checkpoints.
		</description>
	</property>

	<property>
		<name>fs.checkpoint.size</name>
		<value>67108864</value>
		<description>The size of the current edit log (in bytes) that triggers
		a periodic checkpoint even if the fs.checkpoint.period hasn't expired.
		</description>
	</property>

二、配置检查:

配置完成之后，我们需要检查一下是否成功。我们可以通过查看运行secondarynamenode的机器上文件目录来确定是否成功配置。首先输入jps查看是否存在secondarynamenode进程。如果存在，在查看对应的目录下是否有备份记录。如下图：

该目录一般存在于hadoop.tmp.dir/dfs/namesecondary/下面。

三、恢复：

1、配置完成了，如何恢复。首先我们kill掉namenode进程，然后将hadoop.tmp.dir目录下的数据删除掉。制造master挂掉情况。

2、在配置参数dfs.name.dir指定的位置建立一个空文件夹； 把检查点目录的位置赋值给配置参数fs.checkpoint.dir； 启动NameNode，并加上-importCheckpoint。（这句话抄袭的是hadoop-0.20.2/hadoop-0.20.2/docs/cn/hdfs_user_guide.html#Secondary+NameNode，看看文档，有说明）

3、启动namenode的时候采用hadoop namenode –importCheckpoint

4、如果namenode的IP配置有修改，手动重启各datanode节点

四、总结：

1、secondarynamenode可以配置多个，master文件里面多写几个就可以。

2、千万记得如果要恢复数据是需要手动拷贝到namenode机器上的。不是自动的（参看上面写的恢复操作）。

3、镜像备份的周期时间是可以修改的，如果不想一个小时备份一次，可以改的时间短点。core-site.xml中的fs.checkpoint.period值。