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https://issues.apache.org/jira/browse/HBASE-7247?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13510389#comment-13510389
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nkeywal commented on HBASE-7247:
--------------------------------

The issue comes from mixing asynchronous writes with synchronous writes & 
reads. My patch is now working but adds some complexity because of the added 
resynchronisation. I'm gonna do simpler. The ideal solution would be to be full 
async for the region opening (and I'm not gonna do that here :-) )
                
> Assignment performances decreased by 50% because of 
> regionserver.OpenRegionHandler#tickleOpening
> ------------------------------------------------------------------------------------------------
>
>                 Key: HBASE-7247
>                 URL: https://issues.apache.org/jira/browse/HBASE-7247
>             Project: HBase
>          Issue Type: Improvement
>          Components: master, Region Assignment, regionserver
>    Affects Versions: 0.96.0
>            Reporter: nkeywal
>            Assignee: nkeywal
>            Priority: Critical
>
> The regionserver.OpenRegionHandler#tickleOpening updates the region znode as 
> "Do this so master doesn't timeout this region-in-transition.".
> However, on the usual test, this makes the assignment time of 1500 regions 
> goes from 70s to 100s, that is, we're 50% slower because of this.
> More generally, ZooKeper commits to disk all the data update, and this takes 
> time. Using it to provide a keep alive seems overkill. At the very list, it 
> could be made asynchronous.
> I'm not sure how necessary these updates are required (I need to go deeper in 
> the internal, feedback welcome), but it seems very important to optimize 
> this... The trival fix would be to make this optional.

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