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From "Sandeep Tata (JIRA)" <>
Subject [jira] Commented: (CASSANDRA-48) test-and-set
Date Tue, 26 May 2009 21:03:45 GMT


Sandeep Tata commented on CASSANDRA-48:

Yup, I'm planning to submit a "dial-up the consistency patch" first (modulo some failure scenarios,
it's not super hard). I'm testing it on a local cluster today .. I'll open a ticket and describe
the design. Just wanted to give you guys a heads up about the status on this one and reasons
for the consistency patch.

Using ZK to implement concurrency control is not a great option:

If you expect high level of conflicts, you're in trouble with a shared nothing architecture
anyway. Talking to ZK for this is going to kill performance.

If you expect low level of conflicts, you're better off with optimistic concurrency control,
and T&S is the right primitive for that.

> test-and-set
> ------------
>                 Key: CASSANDRA-48
>                 URL:
>             Project: Cassandra
>          Issue Type: Improvement
>            Reporter: Jonathan Ellis
> Atomic test-and-set insert operation would be nice: "set value to X but only if the current
value is still Y."  This allows a sort of optimistic consistency: perform a GET, then perform
test-and-set with the value of that GET as Y.
> I do not think that this requires strong consistency to be useful.

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