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From "Andrew Wang (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-4923) Save namespace when the namenode is stopped
Date Mon, 24 Jun 2013 18:35:20 GMT

    [ https://issues.apache.org/jira/browse/HDFS-4923?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13692225#comment-13692225
] 

Andrew Wang commented on HDFS-4923:
-----------------------------------

bq. 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.

When HA is configured, the namenode doesn't do a saveNamespace on startup.

{code:java}
      // We shouldn't be calling saveNamespace if we've come up in standby state.
      MetaRecoveryContext recovery = startOpt.createRecoveryContext();
      if (fsImage.recoverTransitionRead(startOpt, this, recovery) && !haEnabled) {
        fsImage.saveNamespace(this);
      }
{code}
                
> 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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