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From Chuan-Heng Hsiao <hsiao.chuanh...@gmail.com>
Subject Re: Quorum read after quorum write guarantee
Date Sun, 10 Mar 2013 16:49:20 GMT
Hi André,

I am just a user of cassandra and did not look into the code deeply.

However, my guess is that cassandra only guarantee that
if you successfully write and you successfully read, then quorum will
give you the latest data.

not finding the just inserted data may be due to the failure of
successfully write or the failure of successfully read.
if it is the failure of successfully write, then pycassa should give
you some error message.
if it is the failure of successfully read, then pycassa may give you
timeout error or not-found error.

To test it fairly, it is better to setup the scenario as continuously
write/read same key/column name,
but with different column value. Then you should be able to see that
when you read,
either you read the latest data (successful write/read), or you read
the old data (fail write/success read),
or you read nothing (fail read)

Hopefully my guess is on the right track, and hopefully you understand
what I mean.

Sincerely,
Hsiao


On Mon, Mar 11, 2013 at 12:00 AM, André Cruz <andre.cruz@co.sapo.pt> wrote:
> Hello.
>
> In my application it sometimes happens that I execute a multiget (I use pycassa) to fetch
data that I have just inserted. I use quorum writes and reads, and my RF is 3.
>
> I've noticed that sometimes (1 in 1000 perhaps) an insert followed (300ms after) by a
multiget will not find the just inserted data. Is this normal? Or is something wrong? Can
there be some delay to obtain the inserted data even with quorum?
>
> Best regards,
> André

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