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From "Harsh J (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-3886) Shutdown requests can possibly check for checkpoint issues (corrupted edits) and save a good namespace copy before closing down?
Date Sat, 08 Sep 2012 18:40:07 GMT

    [ https://issues.apache.org/jira/browse/HDFS-3886?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13451385#comment-13451385

Harsh J commented on HDFS-3886:

Yeah, sorry if my 'Shutdown requests' in title was too ambiguous. I am mostly talking of the
NN shutdown itself. I'd thought the simple init.d framework itself had a kill -9'er (like
a supervisor would) but I was wrong.

bq. This would indeed make an RPC to the NN to enter safemode, perform a save namespace, and
then shut itself down.

So this is currently a simple:
sudo -u hdfs hdfs dfsadmin -safemode enter
sudo -u hdfs hdfs dfsadmin -saveNamespace

However, my only caveat with this is that client logs for clients still active, will start
showing SafeModeExceptions rather than Connection Refused/etc.. Is that fine to have, when
doing a clean-stop? Would it be better if we shut off the client RPC and then issued a namespace

I've also not thought of this in HA terms yet.
> Shutdown requests can possibly check for checkpoint issues (corrupted edits) and save
a good namespace copy before closing down?
> --------------------------------------------------------------------------------------------------------------------------------
>                 Key: HDFS-3886
>                 URL: https://issues.apache.org/jira/browse/HDFS-3886
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: name-node
>    Affects Versions: 2.0.0-alpha
>            Reporter: Harsh J
>            Priority: Minor
> HDFS-3878 sorta gives me this idea. Aside of having a method to download it to a different
location, we can also lock up the namesystem (or deactivate the client rpc server) and save
the namesystem before we complete up the shutdown.
> The init.d/shutdown scripts would have to work with this somehow though, to not kill
-9 it when in-process. Also, the new image may be stored in a shutdown.chkpt directory, to
not interfere in the regular dirs, but still allow easier recovery.
> Obviously this will still not work if all directories are broken. So maybe we could have
some configs to tackle that as well?
> I haven't thought this through, so let me know what part is wrong to do :)

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