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https://issues.apache.org/jira/browse/HBASE-7246?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Andrew Kyle Purtell resolved HBASE-7246.
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Resolution: Incomplete
> Assignment#nodeChildrenChanged calls listChildrenAndWatchForNewChildren,
> overloading master & zookeper needlessly
> -----------------------------------------------------------------------------------------------------------------
>
> Key: HBASE-7246
> URL: https://issues.apache.org/jira/browse/HBASE-7246
> Project: HBase
> Issue Type: Improvement
> Components: master, Region Assignment
> Affects Versions: 0.95.2
> Reporter: Nicolas Liochon
> Priority: Major
>
> Assignment#nodeChildrenChanged listens to change event on hbase/unassigned,
> then calls listChildrenAndWatchForNewChildren. As its name says, this
> function gets the whole list of unnasigned regions from ZK.
> The internal comments says it's only for split creation. I tried to remove
> it, it seems to work.
> The point is:
> - ZK does not allow us to know upfront if it's a split or not
> - 50% of the events will be deletions, we don't care about them but we can't
> know in advance
> - for large assignment, we will have a lot of children (hence events). Common
> practise in ZK is to limit the number of subnodes (see the threads
> http://www.mail-archive.com/[email protected]/msg01954.html)
> Monitoring the master, it was spending 10% of it's time on this during
> assignment. It seems it was not on the critical path (yet...), so removing it
> did not change the overall performances on a test scenario. In real life
> however, this typically adds workload to ZK, and ZK workload is precious on
> large failures... Same as master actually.
> If it's used only for split, we should have a znode specific for split and
> not a global znode.
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