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From "Jimmy Xiang (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-9095) AssignmentManager's handleRegion should respect the single threaded nature of the processing
Date Fri, 02 Aug 2013 17:55:48 GMT

    [ https://issues.apache.org/jira/browse/HBASE-9095?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13727880#comment-13727880

Jimmy Xiang commented on HBASE-9095:

Now, since we have multiple threads to process assignment events,  I think it is good to run
these handlers synchronously.

+1 for the patch

> AssignmentManager's handleRegion should respect the single threaded nature of the processing
> --------------------------------------------------------------------------------------------
>                 Key: HBASE-9095
>                 URL: https://issues.apache.org/jira/browse/HBASE-9095
>             Project: HBase
>          Issue Type: Bug
>          Components: Region Assignment
>            Reporter: Devaraj Das
>            Assignee: Devaraj Das
>             Fix For: 0.95.2
>         Attachments: 9095-1.txt, 9095-1.txt
> While debugging a case where a region was getting opened on a RegionServer and then closed
soon after (and then never re-opened anywhere thereafter), it seemed like the processing in
handleRegion to do with deletion of ZK nodes should be non-asynchronous. This achieves two
> 1. The synchronous deletion prevents more than one processing on the same event data
twice. Assuming that we do get more than one notification (on let's say, region OPENED event),
the subsequent processing(s) in handleRegion for the same znode would end up with a zookeeper
node not found exception. The return value of the data read would be null and that's already
handled. If it is asynchronous, it leads to issues like - master opens a region on a certain
RegionServer and soon after it sends that RegionServer a close for the same region, and then
the znode is deleted.
> 2. The deletion is currently handled in an executor service. This is problematic since
by design the events for a given region should be processed in order. By delegating a part
of the processing to executor service we are somewhat violating this contract since there
is no guarantee of the ordering in the executor service executions...
> Thanks to [~jeffreyz] and [~enis] for the discussions on this issue.

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