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From Jabbar Azam <aja...@gmail.com>
Subject Re: idempotent counters
Date Mon, 19 May 2014 09:49:45 GMT
Thanks Aaron. I've mitigated this by removing the dependency on idempotent
counters. But its good to know the limitations of counters.

Thanks

Jabbar Azam
On 19 May 2014 08:36, "Aaron Morton" <aaron@thelastpickle.com> wrote:

> Does anybody else use another technique for achieving this idempotency
> with counters?
>
>
> The idempotency problem with counters has to do with what will happen when
> you get a timeout. If you reply the write there is a chance of the
> increment been applied twice. This is inherent in the current design.
>
> Cheers
> Aaron
>
>
> -----------------
> Aaron Morton
> New Zealand
> @aaronmorton
>
> Co-Founder & Principal Consultant
> Apache Cassandra Consulting
> http://www.thelastpickle.com
>
> On 9/05/2014, at 1:07 am, Jabbar Azam <ajazam@gmail.com> wrote:
>
> Hello,
>
> Do people use counters when they want to have idempotent operations in
> cassandra?
>
> I have a use case for using a counter to check for a count of objects in a
> partition. If the counter is more than some value then the data in the
> partition is moved into two different partitions. I can't work out how to
> do this splitting and recover if a problem happens during modification of
> the counter.
>
>
> http://www.ebaytechblog.com/2012/08/14/cassandra-data-modeling-best-practices-part-2explains
that counters shouldn't be used if you want idempotency. I would
> agree, but the alternative  is not very elegant. I would have to manully
> count the objects in a partition and then move the data and repeat the
> operation if something went wrong.
>
> It is less resource intensive to read a counter value to see if a
> partition needs splitting then to read all the objects in a partition. The
> counter value can be stored in its own table sorting in descending order of
> the counter value.
>
> Does anybody else use another technique for achieving this idempotency
> with counters?
>
> I'm using cassandra 2.0.7.
>
>
>
> Thanks
>
> Jabbar Azam
>
>
>

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