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From Jack Krupansky <jack.krupan...@gmail.com>
Subject Re: Counter values become under-counted when running repair.
Date Thu, 24 Mar 2016 14:17:58 GMT
What CL do you read and write with?

Normally, RF=2 is not recommended since it doesn't give you HA within a
data center - there is no way to achieve quorum in the data center if a
node goes down.

I suppose you can achieve a quorum if your request is spread across all
three data centers, but normally apps try to issue requests to a local data
center for performance. Having to ping all data centers on all requests to
achieve a quorum seems a bit excessive.

Can you advise us on your thinking when you selected RF=2?


-- Jack Krupansky

On Thu, Mar 24, 2016 at 2:17 AM, Dikang Gu <dikang85@gmail.com> wrote:

> Hello there,
>
> We are experimenting Counters in Cassandra 2.2.5. Our setup is that we
> have 6 nodes, across three different regions, and in each region, the
> replication factor is 2. Basically, each nodes holds a full copy of the
> data.
>
> When are doing 30k/s counter increment/decrement per node, and at the
> meanwhile, we are double writing to our mysql tier, so that we can measure
> the accuracy of C* counter, compared to mysql.
>
> The experiment result was great at the beginning, the counter value in C*
> and mysql are very close. The difference is less than 0.1%.
>
> But when we start to run the repair on one node, the counter value in C*
> become much less than the value in mysql,  the difference becomes larger
> than 1%.
>
> My question is that is it a known problem that the counter value will
> become under-counted if repair is running? Should we avoid running repair
> for counter tables?
>
> Thanks.
>
> --
> Dikang
>
>

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