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From "Jonathan Gray (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HBASE-3303) Lower hbase.regionserver.handler.count from 25 back to 10
Date Fri, 03 Dec 2010 05:14:11 GMT

    [ https://issues.apache.org/jira/browse/HBASE-3303?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12966415#action_12966415
] 

Jonathan Gray commented on HBASE-3303:
--------------------------------------

I disagree that this is not an important configuration.  We've definitely had to put this
way up to handle more concurrent clients.  These Put throughput tests are just one type of
workload.

> 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
>
>         Attachments: 3303.txt, 3303.txt
>
>
> 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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