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https://issues.apache.org/jira/browse/CASSANDRA-5062?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13611519#comment-13611519
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Jonathan Ellis commented on CASSANDRA-5062:
-------------------------------------------

I've posted a draft of a CAS method to 
https://github.com/jbellis/cassandra/commits/5062 following the outline I 
posted (way, way) above.

Stuff that is missing:
- We probably want to support passing CL.SERIAL to reads, to allow asking "What 
happened to the CAS operation I just tried, but then the coordinator died 
before replying to me?"  This would just do the prepare phase, and finish any 
in-progress updates, before performing a quorum read.
- May want to allow passing a CL to CAS to specify how many replicas you want 
to ack the commit before returning.
- Any form of CQL support
- Any testing

                
> 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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