cassandra-user mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From Mark Greene <green...@gmail.com>
Subject Re: Write consistency
Date Thu, 08 Apr 2010 16:36:06 GMT
So unless you re-try the write, the previous stale write stays on the other
two nodes? Would a read repair fix this eventually?

On Thu, Apr 8, 2010 at 11:36 AM, Avinash Lakshman <
avinash.lakshman@gmail.com> wrote:

> What your describing is a distributed transaction? Generally strong
> consistency is always associated with doing transactional writes where you
> never see the results of a failed write on a subsequent read no matter what
> happens. Cassandra has no notion of rollback. That is why no combination
> will give you strong consistency. The idea is you re-try the failed write
> and eventually the system would have gotten rid of the previous stale write.
>
> Avinash
>
>
> On Thu, Apr 8, 2010 at 8:29 AM, Jeremy Dunck <jdunck@gmail.com> wrote:
>
>> On Thu, Apr 8, 2010 at 7:16 AM, Gary Dusbabek <gdusbabek@gmail.com>
>> wrote:
>> > On Thu, Apr 8, 2010 at 02:55, Paul Prescod <paul@ayogo.com> wrote:
>> >> In this¹ debate, there seemed to be consensus on the following fact:
>> >>
>> >> "In Cassandra, say you use N=3, W=3 & R=1. Let’s say you managed to
>> >> only write to replicas A & B, but not C. In this case Cassandra will
>> >> return an error to the application saying the write failed- which is
>> >> acceptable given than W=3. But Cassandra does not cleanup/rollback the
>> >> writes that happened to A & B."
>> >>
>> >
>> > correct: no rolling back.  Cassandra does go out of its way to make
>> > sure the cluster is healthy enough to begin the write though.
>>
>> I think the general answer here is don't use R=1 if you can't tolerate
>> inconsistency?  Still the point of confusion -- if W=3 and the write
>> succeeds on 2 nodes but fails the 3rd, the write fails (to the
>> updating client), but is the data on the two successful nodes still
>> readable (i.e. reading from what was actually a failed write)?
>>
>
>

Mime
View raw message