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From "Tom White (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (YARN-230) Make changes for RM restart phase 1
Date Tue, 27 Nov 2012 17:05:59 GMT

    [ https://issues.apache.org/jira/browse/YARN-230?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13504765#comment-13504765

Tom White commented on YARN-230:

The store and remove methods have been made mirrors because it helps maintain symmetry of
operations that is logically clear. An actual implementation could choose to remove the entire
app data including attempts in removeApplication() making removeApplicationAttempt() a no-op.
So that alternative is not precluded in the current interface while still maintaining flexibility
at the interface.

Why is this flexibility needed? I can't see why it makes sense to remove an application and
leave some application attempts around.

bq. I chose to not use directories for FileSystem because one could put a key value store
behind a FileSystem interface and I am not sure how directories would work in them.

That's reasonable. With the orphan handling (deletion) on restart, the flat structure you
have should work fine. (However, I don't think you need the removeApplicationAttempt() method.)

bq. One improvement would be to update the store with an attempts final state (failed/killed/succeeded)
and wait for it to be recorded before completing the state machine.

I agree this can be done later.

bq. Could you please help by providing a good system path.

How about something like ${hadoop.tmp.dir}/yarn/system/rm-store?
> Make changes for RM restart phase 1
> -----------------------------------
>                 Key: YARN-230
>                 URL: https://issues.apache.org/jira/browse/YARN-230
>             Project: Hadoop YARN
>          Issue Type: Sub-task
>          Components: resourcemanager
>            Reporter: Bikas Saha
>            Assignee: Bikas Saha
>         Attachments: PB-impl.patch, Recovery.patch, Store.patch, Test.patch, YARN-230.1.patch
> As described in YARN-128, phase 1 of RM restart puts in place mechanisms to save application
state and read them back after restart. Upon restart, the NM's are asked to reboot and the
previously running AM's are restarted.
> After this is done, RM HA and work preserving restart can continue in parallel. For more
details please refer to the design document in YARN-128

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