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From Viktor Jevdokimov <Viktor.Jevdoki...@adform.com>
Subject RE: Sorting keys for batch reads to minimize seeks
Date Fri, 18 Oct 2013 15:54:06 GMT
Read latency depends on many factors, don't forget "physics".
If it meets your requirements, it is good.


-----Original Message-----
From: Artur Kronenberg [mailto:artur.kronenberg@openmarket.com] 
Sent: Friday, October 18, 2013 1:03 PM
To: user@cassandra.apache.org
Subject: Re: Sorting keys for batch reads to minimize seeks

Hi,

Thanks for your reply. Our latency currently is 23.618ms. However I simply read that off one
node just now while it wasn't under a load test. I am going to be able to get a better number
after the next test run.

What is a good value for read latency?


On 18/10/13 08:31, Viktor Jevdokimov wrote:
> The only thing you may win - avoid unnecessary network hops if:
> - request sorted keys (by token) from appropriate replica with ConsistencyLevel.ONE and
"dynamic_snitch: false".
> - nodes has the same load
> - replica not doing GC, and GC pauses are much higher than internode communication.
>
> For multiple keys request C* will do multiple single key reads, except for range scan
requests, where only starting key and batch size is used in request.
>
> Consider multiple key request as a slow request by design, try to model your data for
low latency single key requests.
>
> So, what latencies do you want to achieve?
>
>
>
> Best regards / Pagarbiai
>
> Viktor Jevdokimov
> Senior Developer
>
> Email: Viktor.Jevdokimov@adform.com
> Phone: +370 5 212 3063
> Fax: +370 5 261 0453
>
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>
>
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> copies.-----Original Message-----
> From: Artur Kronenberg [mailto:artur.kronenberg@openmarket.com]
> Sent: Thursday, October 17, 2013 7:40 PM
> To: user@cassandra.apache.org
> Subject: Sorting keys for batch reads to minimize seeks
>
> Hi,
>
> I am looking to somehow increase read performance on cassandra. We are still playing
with configurations but I was thinking if there would be solutions in software that might
help us speed up our read performance.
>
> E.g. one idea, not sure how sane that is, was to sort read-batches by row-keys before
submitting them to cassandra. The idea is that row-keys should be closer together on the physical
disk and therefor this may minimize the amount of random seeks we have to do when querying
say 1000 entries from cassandra. Does that make any sense?
>
> Is there anything else that we can do in software to improve performance? Like specific
batch sizes for reads? We are using the astyanax library to access cassandra.
>
> Thanks!
>
>


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