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https://issues.apache.org/jira/browse/HBASE-9095?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13728250#comment-13728250
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Enis Soztutar commented on HBASE-9095:
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Agreed. If we find any slowness in assignment, we can address them later.
> 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 things:
> 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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