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From Gary Dusbabek <>
Subject Re: Write consistency
Date Thu, 08 Apr 2010 13:16:57 GMT
On Thu, Apr 8, 2010 at 02:55, Paul Prescod <> 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.

> If this is still true (even for ConsistencyLevel.ALL) then I would
> like to add it to the API documentation. I'd also be curious about if
> there have been discussions about for an optional 2PC mode for use on
> fast LANs.

None recently.  I think 2PC would be at odds with Cassandra's goal to
"keep writes really fast".  That being said, we have zookeeper support
in contrib which would get you most of the way there.  My zookeeper
knowledge is pretty weak though, but I don't think it would let you
rollback if things went south during the actual commit.


>  Paul Prescod
> ¹

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