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From "Sergio Bossa (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-5062) Support CAS
Date Sun, 03 Mar 2013 12:15:15 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-5062?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13591721#comment-13591721
] 

Sergio Bossa commented on CASSANDRA-5062:
-----------------------------------------

{quote}Sergio, the reason to go beyond pure Paxos by turning Learn into Commit is twofold:
To allow a fresh start for a new round of CAS; otherwise, each new proposal is stuck re-issuing
the first accepted value
To move the data from the Paxos "maybe it's accepted but we don't know until we get a majority"
limbo into a normal sstable cell{quote}

Yes, I get why it's there, I'm just not sure it's actually needed (which may well be due to
my limited knowledge of hardcore C* internals, in particular around HH, RR and AE).

By the way, I don't have enough time to do any more meaningful contributions to this ticket,
so I'm backing off: it is in good hands anyways :)
                
> 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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