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From Stack <st...@duboce.net>
Subject Re: 0.90 latency performance, cdh3b4
Date Wed, 20 Apr 2011 17:02:05 GMT
On Tue, Apr 19, 2011 at 4:46 PM, Dmitriy Lyubimov <dlyubimov@apache.org> wrote:
> Right now i am shooting scans returning between 3 and 40 rows and
> regardless of data size, approximately 500-400 QPS. The data tables
> are almost empty and in-memory, so they surely should fit in those 40%
> heap dedicated to them.

LRU in the regionserver logs its hit rate.  You might check it.

> As soon as i go to our 10-node cluster, the response times drop to
> 25ms per scan, regardless of # of records. I set scan block cache size
> to 100 (rows?), otherwise i was getting outrages numbers reaching as
> far out as 300-400ms.

Otherwise you are doing an rpc per fetch.

> It's my understanding the timing should be actually still much closer
> to my local tests than to 25ms.

Yes.  I would think so.

> So... how do i attack this ? increase regionserver handler count? What
> the latency should i be able to reach for extremely small data records
> (<=200bytes)?

40 rows of < 200 bytes each coming out of cache should be fast...
around the times you are seeing for local.


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