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HBase >> mail # user >> GC recommendations for large Region Server heaps


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Re: GC recommendations for large Region Server heaps
On Mon, Jul 8, 2013 at 11:09 AM, Suraj Varma <[EMAIL PROTECTED]> 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-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).
>
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