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From "Liu, Raymond" <raymond....@intel.com>
Subject RE: what's the typical scan latency?
Date Tue, 04 Jun 2013 01:02:05 GMT
Thanks Amit

In my envionment, I run a dozens of client to read about 5-20K data per scan concurrently,
And the average read latency for cached data is around 5-20ms.
So it seems there must be something wrong with my cluster env or application. Or did you run
that with multiple client?


>Depends on so much environment related variables and on data as well.
>But to give you a number after all:
>One of our clusters is on EC2, 6 RS, on m1.xlarge machines (network performance 'high'
according to aws), with 90% of the time we do reads; our avg data size is 2K, block cache
at 20K, 100 rows per scan avg, bloom filters 'on' at the 'ROW' level, 40% of heap dedicated
to block cache (note that it contains several other bits and pieces) and I would say our average
latency for cached data (~97% blockCacheHitCachingRatio) is 3-4ms. File system access is much
much painful, especially on ec2 m1.xlarge where you really can't tell what's going on, as
far as I can tell. To tell you the truth as I see it, this is an abuse (for our use case)
of the HBase store and for cache like behavior I would recommend going to something like Redis.


On Mon, Jun 3, 2013 at 12:13 PM, ramkrishna vasudevan < ramkrishna.s.vasudevan@gmail.com>
wrote:

> What is that you are observing now?
>
> Regards
> Ram
>
>
> On Mon, Jun 3, 2013 at 2:00 PM, Liu, Raymond <raymond.liu@intel.com>
> wrote:
>
> > Hi
> >
> >         If all the data is already in RS blockcache.
> >         Then what's the typical scan latency for scan a few rows 
> > from a say several GB table ( with dozens of regions ) on a small 
> > cluster with
> say
> > 4 RS ?
> >
> >         A few ms? Tens of ms? Or more?
> >
> > Best Regards,
> > Raymond Liu
> >
>

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