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From "Suresh Srinivas (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-4923) Save namespace when the namenode is stopped
Date Fri, 21 Jun 2013 21:32:23 GMT

    [ https://issues.apache.org/jira/browse/HDFS-4923?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13690744#comment-13690744
] 

Suresh Srinivas commented on HDFS-4923:
---------------------------------------

bq. In general though, I'm in favor of giving the admin flexibility. I'd rather not block
exit on writing out a multi-GB file. This might actually make overall restart time slower
if there aren't many edits.
I think this probably is less of a concern. Either you save the namespace when you stop the
namenode or when you start the namenode. The cost of writing multi-GB file cannot be avoided,
at least as of now.

bq. My $0.02, definitely, but this should be default 'true'.
I agree.

                
> Save namespace when the namenode is stopped
> -------------------------------------------
>
>                 Key: HDFS-4923
>                 URL: https://issues.apache.org/jira/browse/HDFS-4923
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>    Affects Versions: 3.0.0
>            Reporter: Suresh Srinivas
>            Assignee: Suresh Srinivas
>
> In rare instances the namenode fails to load editlog due to corruption during startup.
This has more severe impact if editlog segment to be checkpointed has corruption, as checkpointing
fails because the editlog with corruption cannot be consumed. If an administrator does not
notice this and address it by saving the namespace, recovering the namespace would involve
complex file editing, using previous backups or losing last set of modifications.
> The other issue that also happens frequently is, checkpointing fails and has not happened
for a long time, resulting in long editlogs and even corrupt editlogs.
> To handle these issues, when namenode is stopped, we can put it in safemode and save
the namespace, before the process is shutdown. As an added benefit, the namenode restart would
be faster, given there is no editlog to consume.
> What do folks think?

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