[jira] Commented: (CASSANDRA-48) test-and-set

["Sandeep Tata (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CASSANDRA-48?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12713234#action_12713234 ] 

Sandeep Tata commented on CASSANDRA-48:
---------------------------------------

Looks like it is much too tricky to guarantee convergence without somewhat stronger consistency if we admit a test-and-set instruction.

I've started work on a simple implementation without these additional repair mechanisms -- apps can use it safely if they either
a) manage concurrency in the app (bad assumption -- I don't expect apps to be able to do this, if they can, T&S doesn't really provide much value)
b) can expect to dial up the consistency if they want to use this part of the API (very useful if they can do this without losing performance for those parts of the app that don't need consistency)



> test-and-set
> ------------
>
>                 Key: CASSANDRA-48
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-48
>             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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