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https://issues.apache.org/jira/browse/CASSANDRA-48?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12695475#action_12695475
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Jun Rao commented on CASSANDRA-48:
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Here is a contrived but simple example. Suppose that some shopping cart info is
stored in a column and multiple clients are updating it. A client may want to
update the column value only if the value hasn't changed since he last read it.
If the column value has indeed changed, he wants to read the latest value back
and MERGE it with the local value he has and then reinsert. This will be hard
to do with the current test-and-set insert semantic.
> 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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