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From "Nicolas Liochon (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-7247) Assignment performances decreased by 50% because of regionserver.OpenRegionHandler#tickleOpening
Date Wed, 10 Apr 2013 10:46:17 GMT

    [ https://issues.apache.org/jira/browse/HBASE-7247?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13627662#comment-13627662

Nicolas Liochon commented on HBASE-7247:

bq. This sync happens every time? Ain't it really expensive? More expensive that what used
to be there (a write?). Why we need it?
We already had the sync previously. We're just saving the final write.
The sync can be expensive, I don't know if it's always expensive or sometimes optimized by
ZK. My test hides its cost, because it's a single ZK node and the master is on the same node.
A real life system with 5 ZK would be more realistic. In any case, saving the write is good.

bq. Does this clear any existing watch?
No, it does not set a watcher but should not impact existing ones.

bq. Does the content of retransitionNodeOpening deserve to be generalized and moved back into
transitionNode but with a flag for whether to write the new state or not?

I don't know. Do we have a lot of case like this one?
Globally, the performance problem is that we check the state before writing, hence we sync
and we read. The next optimization I'm thinking about is to know that we were the previous
writer, or that we read the previous version already, so we can send the write without syncing/reading,
relying only on ZooKeeper versions. But it's easy to add bugs when doing this.

> 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: 0.95.2
>            Reporter: Nicolas Liochon
>            Assignee: Nicolas Liochon
>             Fix For: 0.98.0, 0.95.1
>         Attachments: 7247.v1.patch, 7247.v2.patch
> 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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