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From "Jean-Daniel Cryans (JIRA)" <j...@apache.org>
Subject [jira] Created: (HBASE-3303) Lower hbase.regionserver.handler.count from 25 back to 10
Date Thu, 02 Dec 2010 22:02:10 GMT
Lower hbase.regionserver.handler.count from 25 back to 10

                 Key: HBASE-3303
                 URL: https://issues.apache.org/jira/browse/HBASE-3303
             Project: HBase
          Issue Type: Improvement
            Reporter: Jean-Daniel Cryans
            Assignee: Jean-Daniel Cryans
             Fix For: 0.90.0

With HBASE-2506 in mind, I tested a low-memory environment (2GB of heap) with a lot of concurrent
writers using the default write buffer to verify if a lower number of handlers actually helps
reducing the occurrence full GCs. Very unscientifically, at this moment I think it's safe
to say that yes, it helps.

With the defaults, I saw a region server struggling more and more because the random inserters
at some point started filling up all the handlers and were all BLOCKED trying to sync the
WAL. It's safe to say that each of those clients carried a payload that the GC cannot get
rid of and it's one that we don't account for (as opposed to MemStore and the block cache).

With a much lower setting of 5, I didn't see the situation.

It kind of confirms my hypothesis but I need to do more proper testing. In the mean time,
in order to lower the onslaught of users that write to the ML complaining about either GCs
or OOMEs, I think we should set the handlers back to what it was originally (10) for 0.90.0
and add some documentation about configuring hbase.regionserver.handler.count

I'd like to hear others' thoughts.

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