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From "Jean-Daniel Cryans (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HBASE-3789) Cleanup the locking contention in the master
Date Fri, 15 Apr 2011 22:54:05 GMT
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
            Priority: Blocker
             Fix For: 0.92.0

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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