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From "dhruba borthakur (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HDFS-1508) Ability to do savenamespace without being in safemode
Date Thu, 16 Dec 2010 06:19:01 GMT

    [ https://issues.apache.org/jira/browse/HDFS-1508?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12971976#action_12971976
] 

dhruba borthakur commented on HDFS-1508:
----------------------------------------

> Q. If saveNamespace fails, why will checkpoint run into a problem? 

savenamespace fails if all directories listed in fs.name.dir are bad. In this case, the succeeding
checkpoint will fail too.

> Q. In the past a saveNamespace in progress aborted a checkpoint because the NN was in
safemode.

In the new code, the saveNamespace call aborts an existing checkpoint. The savenamespace command
clears out the edits log. This causes the checkpoint to fail because the rollFSImage call
expects to find a edits.new file. That's why a new variable called "saveNamespaceInProgress"
is not needed.

Also, like you said, the existing behaviour is that if an operator wants to run the savenamespace
command, he/she first puts the namenode is safemode. This causes a concurrently running checkpoint
to fail. This behaviour is retained by this patch. do you think this patch is good to go in
its current incantation?

> Ability to do savenamespace without being in safemode
> -----------------------------------------------------
>
>                 Key: HDFS-1508
>                 URL: https://issues.apache.org/jira/browse/HDFS-1508
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: name-node
>            Reporter: dhruba borthakur
>            Assignee: dhruba borthakur
>         Attachments: savenamespaceWithoutSafemode.txt, savenamespaceWithoutSafemode2.txt,
savenamespaceWithoutSafemode3.txt, savenamespaceWithoutSafemode4.txt
>
>
> In the current code, the administrator can run savenamespace only after putting the namenode
in safemode. This means that applications that are writing to HDFS encounters errors because
the NN is in safemode. We would like to allow saveNamespace even when the namenode is not
in safemode.
> The savenamespace command already acquires the FSNamesystem writelock. There is no need
to require that the namenode is in safemode too.

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