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From "Jun Rao (JIRA)" <j...@apache.org>
Subject [jira] Commented: (CASSANDRA-48) test-and-set
Date Fri, 03 Apr 2009 15:42:13 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-48?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12695459#action_12695459
] 

Jun Rao commented on CASSANDRA-48:
----------------------------------

That's when complexity comes in. Say N=3 and you insert to node A,B, and C. The insert succeeds
at A, but failed at B and C. You want to fail the insert. However, the insert already succeeds
at A. Now, you should roll back the insert made at A. Then, you need to remember the previous
version at A. You will be essentially doing some sort of 2-phase commit.

> 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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