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From Andrew Purtell <apurt...@apache.org>
Subject Re: [jira] Created: (HBASE-3303) Lower hbase.regionserver.handler.count from 25 back to 10
Date Thu, 02 Dec 2010 23:17:57 GMT

Your hypothesis is interesting. 

I took the same step -- change 100 -> 10 -- to reduce the probability that regionservers
would OOME under high write load as generated by an end simulation I have been developing,
to model an application we plan to deploy. (Stack, this is the next generation of the monster
that led us to find the problem with ByteArrayOutputStream buffer management in the 0.19 time
frame. It's baaaaack, bigger than before.)

Reducing handler.count did move the needle, but sooner or later they are all dead, at 4G heap,
or 8G heap... and the usual GC tuning tricks are not helping. 

When I get back from this latest tour of Asia next week I need to dig in with jhat and jprofiler.

Best regards,

    - Andy

--- On Thu, 12/2/10, Jean-Daniel Cryans (JIRA) <jira@apache.org> wrote:

> From: Jean-Daniel Cryans (JIRA) <jira@apache.org>
> Subject: [jira] Created: (HBASE-3303) Lower hbase.regionserver.handler.count from 25
back to 10
> To: issues@hbase.apache.org
> Date: Thursday, December 2, 2010, 2:02 PM
> 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.
> -- 
> This message is automatically generated by JIRA.
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