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https://issues.apache.org/jira/browse/HBASE-3789?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Jean-Daniel Cryans updated HBASE-3789:
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Attachment: HBASE-3789-v4-0.90.patch
Attaching the 0.90 patch refreshed for that branch. It's not meant for
inclusion, leaving it here if it's of use to anyone. Remember it breaks rolling
restarts if you plan on deploying it.
> Cleanup the locking contention in the master
> --------------------------------------------
>
> Key: HBASE-3789
> URL: https://issues.apache.org/jira/browse/HBASE-3789
> Project: HBase
> Issue Type: Improvement
> Affects Versions: 0.90.2
> Reporter: Jean-Daniel Cryans
> Assignee: Jean-Daniel Cryans
> Priority: Blocker
> Fix For: 0.92.0
>
> Attachments: HBASE-3789-trunk.patch, HBASE-3789-v4-0.90.patch
>
>
> The new master uses a lot of synchronized blocks to be safe, but it only
> takes a few jstacks to see that there's multiple layers of lock contention
> when a bunch of regions are moving (like when the balancer runs). The main
> culprits are regionInTransition in AssignmentManager, ZKAssign that uses
> ZKW.getZNnodes (basically another set of region in transitions), and locking
> at the RegionState level.
> My understanding is that even tho we have multiple threads to handle regions
> in transition, everything is actually serialized. Most of the time, lock
> holders are talking to ZK or a region server, which can take a few
> milliseconds.
> A simple example is when AssignmentManager wants to update the timers for all
> the regions on a RS, it will usually be waiting on another thread that's
> holding the lock while talking to ZK.
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