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From Otis Gospodnetic <otis.gospodne...@gmail.com>
Subject Re: GC recommendations for large Region Server heaps
Date Tue, 09 Jul 2013 05:12:17 GMT

Check http://blog.sematext.com/2013/06/24/g1-cms-java-garbage-collector/

Those graphs show RegionServer before and after switch to G1.  The
dashboard screenshot further below shows CMS (top row) vs. G1 (bottom
row).  After those tests we ended up switching to G1 across the whole
cluster and haven't had issues or major pauses since.... knock on

Solr & ElasticSearch Support -- http://sematext.com/
Performance Monitoring -- http://sematext.com/spm

On Mon, Jul 8, 2013 at 2:56 PM, Stack <stack@duboce.net> wrote:
> On Mon, Jul 8, 2013 at 11:09 AM, Suraj Varma <svarma.ng@gmail.com> wrote:
>> Hello:
>> We have an HBase cluster with region servers running on 8GB heap size with
>> a 0.6 block cache (it is a read heavy cluster, with bursty write traffic
>> via MR jobs). (version: hbase-
>> During HBaseCon, while speaking to a few attendees, I heard some folks were
>> running region servers as high as 24GB and some others in the 16GB range.
>> So - question: Are there any special GC recommendations (tuning parameters,
>> flags, etc) that folks who run at these large heaps can recommend while
>> moving up from an 8GB heap? i.e. for 16GB and for 24GB RS heaps ... ?
>> I'm especially concerned about long pauses causing zk session timeouts and
>> consequent RS shutdowns. Our boxes do have a lot of RAM and we are
>> exploring how we can use more of it for the cluster while maintaining
>> overall stability.
>> Also - if there are clusters running multiple region servers per host, I'd
>> be very interested to know what RS heap sizes those are being run at ...
>> and whether this was chosen as an alternative to running a single RS with
>> large heap.
>> (I know I'll have to test the GC stuff out on my cluster and for my
>> workloads anyway ... but just trying to get a feel of what sort of tuning
>> options had to be used to have a stable HBase cluster with 16 or 24GB RS
>> heaps).
> You hit full GC in this 8G heap Suraj?  Can you try running one server at
> 24G to see how it does (with GC logging enabled so you can watch it over
> time)?  On one hand, more heap may make it so you avoid full GC -- if you
> are hitting them now at 8G -- because application has more head room.  On
> other hand, yes, if a full GC hits, it will be gone for proportionally
> longer than for your 8G heap.
> St.Ack

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