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From "Todd Lipcon (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-4774) Retain znodes for all regions in UNASSIGNED (zookeeper)
Date Fri, 11 Nov 2011 21:24:51 GMT

    [ https://issues.apache.org/jira/browse/HBASE-4774?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13148742#comment-13148742
] 

Todd Lipcon commented on HBASE-4774:
------------------------------------

I agree. I also would really like to define a proper FSM class for region state transitions
-- one for RegionOnMaster and another for RegionOnRS (the state machines are a bit different
between the two). The inputs into the state machines would be ZK state changes as well as
lifecycle events in the server. I've done a bit of hacking in this direction, but it's not
a simple project.
                
> Retain znodes for all regions in UNASSIGNED (zookeeper)
> -------------------------------------------------------
>
>                 Key: HBASE-4774
>                 URL: https://issues.apache.org/jira/browse/HBASE-4774
>             Project: HBase
>          Issue Type: Brainstorming
>          Components: master
>            Reporter: Karthik Ranganathan
>
> We delete znodes from UNASSIGNED once a region is opened and the open is entered into
META.
> A lot of multiple assignment issues arise from the fact that we delete this znode and
dont have state information after the region is opened. So one proposal is to always retain
the znodes in META and never delete the regions from UNASSIGNED. That way we can have a simple,
deterministic state machine for each region. We could bucket the regions into sub-directories
using a deterministic hash or the region prefixes. 
> Note that what we put in zk is not permanent state but just the state of the cluster
that is running. This state is invalid upon cluster restart - so we are still storing temporary
data in zk.
> Thoughts?

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