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From "Sylvain Lebresne (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-5062) Support CAS
Date Tue, 05 Mar 2013 17:34:15 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-5062?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13593635#comment-13593635
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Sylvain Lebresne commented on CASSANDRA-5062:
---------------------------------------------

bq. That could work

Not only it could work, but that's exactly what the pseudo-code in my document does (I'm sorry
to be rude, but I took the pain of writing 500 lines of explanation/pseudo-code in a separate
document to avoid "spamming" the JIRA with my whole train of though. It would have been nice
of you to make sure you understand what's there before shooting a comment here every other
minute, because this will make it very hard to follow for other people interested in the issue).

And I don't pretend my proposal can't be optimized, only that it's correct. But truth being
told, in practice, learn messages won't be lost randomly as in your example, so I'm not even
sure it's worth optimizing in practice (or that it will be an optimization in the first place,
"ensuring you always have a quorum that has learned" during accept won't have 0 cost).
                
> Support CAS
> -----------
>
>                 Key: CASSANDRA-5062
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-5062
>             Project: Cassandra
>          Issue Type: New Feature
>          Components: API, Core
>            Reporter: Jonathan Ellis
>             Fix For: 2.0
>
>         Attachments: half-baked commit 1.jpg, half-baked commit 2.jpg, half-baked commit
3.jpg
>
>
> "Strong" consistency is not enough to prevent race conditions.  The classic example is
user account creation: we want to ensure usernames are unique, so we only want to signal account
creation success if nobody else has created the account yet.  But naive read-then-write allows
clients to race and both think they have a green light to create.

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