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Date: Sun, 3 Mar 2013 18:03:14 +0000 (UTC)
From: "Cristian Opris (JIRA)" <jira@apache.org>
To: commits@cassandra.apache.org
Message-ID: <JIRA.12623764.1355412285561.372575.1362333794951@arcas>
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Subject: [jira] [Commented] (CASSANDRA-5062) Support CAS
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    [ https://issues.apache.org/jira/browse/CASSANDRA-5062?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13591811#comment-13591811 ] 

Cristian Opris commented on CASSANDRA-5062:
-------------------------------------------

Ok, but I think my point was that even if you can assume that (monotonic time) than it's still not
correct, because when a proposal with a new value and higher timestamp than last committed comes in,
accepting it over a previously accepted value would violate paxos. That is step 6 in my first example there. This at least breaks cas and cannot give consistent read

However I confess I don't fully understand your solution, could you summarize or formalize a bit ?
                
> 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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