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From "Karthik Kambatla (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (YARN-1222) Make improvements in ZKRMStateStore for fencing
Date Wed, 06 Nov 2013 04:33:20 GMT

    [ https://issues.apache.org/jira/browse/YARN-1222?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13814596#comment-13814596

Karthik Kambatla commented on YARN-1222:

bq. Thinking aloud, using HAServiceTarget in RMStateStore to transitionToStandby() may not
be the right solution. 
My bad. I should  have explained the choice. Post YARN-1318, I think RMStateStore constructor
should take RMContext. Then, we should be able to replace the RPC approach with rmContext.getHAService.transitionToStandby().

bq. The store should inform the higher entity about the fenced state and not take action on
the higher entity by fencing it. 
I think it is a trade-off between pushing higher-level concepts like HA down versus spreading
the logic of handling the FencedException across multiple entities. If we push it all the
way down to the store implementation (ZKRMStateStore), we can get away with handling at one
location. The other extreme would be to handle it at every location where a store operation
is triggered. I think handling it in RMStateStore and not an implementation is a good compromise.
A completely different approach might to be keep {{handleStoreFencedException()}} in {{ResourceManager}}
and the store implementation to call it when it realizes it got fenced. Thoughts?

> Make improvements in ZKRMStateStore for fencing
> -----------------------------------------------
>                 Key: YARN-1222
>                 URL: https://issues.apache.org/jira/browse/YARN-1222
>             Project: Hadoop YARN
>          Issue Type: Sub-task
>            Reporter: Bikas Saha
>            Assignee: Karthik Kambatla
>         Attachments: yarn-1222-1.patch, yarn-1222-2.patch, yarn-1222-3.patch, yarn-1222-4.patch,
> Using multi-operations for every ZK interaction. 
> In every operation, automatically creating/deleting a lock znode that is the child of
the root znode. This is to achieve fencing by modifying the create/delete permissions on the
root znode.

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