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From "Jean-Daniel Cryans (JIRA)" <j...@apache.org>
Subject [jira] [Resolved] (HBASE-3789) Cleanup the locking contention in the master
Date Wed, 15 Jun 2011 18:24:47 GMT

     [ https://issues.apache.org/jira/browse/HBASE-3789?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Jean-Daniel Cryans resolved HBASE-3789.
---------------------------------------

      Resolution: Fixed
    Release Note: 
The master now creates the znode when closing a region, which is an incompatible change.
SplitTransaction now waits on the master to delete the znode that it created before it can
finish.
The master doesn't keep track of znodes being deleted and created anymore, it was getting
out of sync too easily. 
    Hadoop Flags: [Incompatible change, Reviewed]

Committed to trunk, thanks for the review Stack.

> 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-v3-0.90.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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