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From "luoge123 (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-12555) HDFS federation should support configure secondary directory
Date Thu, 12 Oct 2017 06:13:00 GMT

    [ https://issues.apache.org/jira/browse/HDFS-12555?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16201505#comment-16201505
] 

luoge123 commented on HDFS-12555:
---------------------------------

In current federation function, if the /user directory has been configured as follows :
   <property>
       <name>fs.viewfs.mounttable.nsX.link./user</name>
       <value>hdfs://nn1:8020/user</value>
    </property>
then, we can't add the follow /user/hive configuration to core-site.xml any more.
    <property>
       <name>fs.viewfs.mounttable.nsX.link./user/hive</name>
       <value>hdfs://nn2:8020/user/hive</value>
    </property>

My improvement is that the two configuration items all exist in core-site.xml at same time.
After support this configuration, we need copy data from hdfs://nn1:8020/user/hive to hdfs://nn2:8020/user/hive,
fastcp or distcp tools can help us. And then we can delete hdfs://nn1:8020/user/hive. 
After we done this, the meta data in /user directory except /user/hive all manager by nn1,
and read and write requests are send to nn1. The meta data for /user/hive manager by nn2,
read and write requests for /user/hive are send to nn2.

I'm not sure this explanation could answer your question or not, if you have any questions,
please fell free to contact me.

> HDFS federation should support configure secondary directory 
> -------------------------------------------------------------
>
>                 Key: HDFS-12555
>                 URL: https://issues.apache.org/jira/browse/HDFS-12555
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: federation
>         Environment: 2.6.0-cdh5.10.0
>            Reporter: luoge123
>             Fix For: 2.6.0
>
>         Attachments: HDFS-12555.001.patch
>
>
> HDFS federation support multiple namenodes horizontally scales the file system namespace.
As the amount of data grows, using a single group of namenodes to manage a single directory,
namenode still achieves performance bottlenecks. In order to reduce the pressure of namenode,
we can split out the secondary directory, and manager it by a new namenode. This is  transparent
for users. 
> For example, nn1 only manager the /user directory, when nn1 achieve performance bottlenecks,
we can split out /user/hive directory, and ues nn2 to manager it.
> That means core-site.xml should support as follows configuration.
>    <property>
>        <name>fs.viewfs.mounttable.nsX.link./user</name>
>        <value>hdfs://nn1:8020/user</value>
>     </property>
>     <property>
>        <name>fs.viewfs.mounttable.nsX.link./user/hive</name>
>        <value>hdfs://nn2:8020/user/hive</value>
>     </property>



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