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https://issues.apache.org/jira/browse/HADOOP-4826?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Konstantin Shvachko updated HADOOP-4826:
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Attachment: saveNamespace.patch
saveNamespace will save the namespace image directly to disk(s), it does not
need to replay the journal.
Since saving the image is much faster than digesting the edits the command can
substantially reduce the overall cluster restart time.
Recommended procedure for restarting the cluster:
# enter safe mode
# save namespace
# shutdown the cluster
# start the cluster
The patch introduces a new {{DFSAdmin}} command which is called using
{code}
hadoop dfsadmin -saveNamespace
{code}
As all other {{DFSAdmin}} commands it requires *superuser permissions*.
In addition, the name-node *must be in safe mode*, because we don't want to
allow changing namespace during the save.
In order to enter safe mode call
{code}
hadoop dfsadmin -safemode enter
{code}
The patch also corrects 2 warnings in TestCheckpoint, and 2 Javadoc warnings in
FSNamesystem.
> Admin command saveNamespace.
> ----------------------------
>
> Key: HADOOP-4826
> URL: https://issues.apache.org/jira/browse/HADOOP-4826
> Project: Hadoop Core
> Issue Type: New Feature
> Components: dfs
> Reporter: Konstantin Shvachko
> Assignee: Konstantin Shvachko
> Fix For: 0.20.0
>
> Attachments: saveNamespace.patch
>
>
> It would be useful to have an admin command that saves current namespace.
> This command can be used before regular (planned) cluster shutdown.
> The command will save the namespace into storage directory(s) and reset the
> name-node journal (edits file).
> It will also reduce name-node startup time, because edits do not need to be
> digest.
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