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From Piotr Kołaczkowski (JIRA) <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-5062) Support CAS
Date Sun, 24 Feb 2013 23:42:13 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-5062?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13585536#comment-13585536
] 

Piotr Kołaczkowski commented on CASSANDRA-5062:
-----------------------------------------------

Another option is optimistic versioning and vector clocks:
1. Check for expected value and get its version vector.
2. Write the new value with the updated version.
3. Reread the value. If value and version matches, we got CAS.

The problem I can see with this approach is that if we timeout in step 2. or 3. (e.g. no quorum),
the new value might have been written, although we didn't get a CAS. I'm not sure how a big
problem it is.


                
> 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
>
>
> "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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