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Date: Mon, 8 Jul 2013 11:09:28 -0700
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Subject: GC recommendations for large Region Server heaps
From: Suraj Varma <svarma.ng@gmail.com>
To: user@hbase.apache.org
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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-0.94.6.1)

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).

Thanks in advance,
--Suraj

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