I am definitely interested in taking this work up. I believe the CAS
functionality would help in a lot of different scenarios and could help avoid
use of other external services (like zookeeper) to provide similar
functionality. I am new at Cassandra development and would really appreciate
pointers from the dev. community about how to approach/start on this project.
Also how feasible is the approach mentioned below to implement the CAS
functionality? It would be great if we could have a discussion on the pros and
cons.
Thanks,
Rishi
________________________________
From: Sriram Srinivasan <sri...@malhar.net>
To: dev@cassandra.apache.org
Sent: Sun, June 20, 2010 9:47:37 PM
Subject: Re: Atomic Compare and Swap
I too am interested in a CAS facility.
I like Rishi's proposal. One could simply use a version number as the logical
timestamp. If we promote CAS to a consistency level, it would rate higher than
a quorum. One pays the price for a more complex write path to obtain the
requisite guarantee.
On Jun 21, 2010, at 4:03 AM, Rishi Bhardwaj wrote:
>
> Heres another thought I had, if say the user always wrote with quorum (or to
> all) nodes then can't we implement CAS (compare and swap) assuming that user
> employs logical timestamp and Cassandra doesn't allow writes to a column with
> same or older timestamp. Here's the scenario I am thinking about:
> Say we use logical timestamp for a column value and lets assume the current
> timestamp is t. Now say two clients read this column and generate concurrent
> CAS (compare and swap) operations on timestamp t and for both the writes the
> resulting new timestamp would become (t+1). Now if we don't allow writes to a
> column with same timestamp then only one of these writes would succeed. Of
> course another assumption is that if a third CAS write with compare on
> logical timestamp (t - 1) came in, that would be denied as I believe
> Cassandra doesn't allow "older" writes to win over "newer" writes. Do you
> think such a thing can be accomplished?
