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From "Cristian Opris (JIRA)" <j...@apache.org>
Subject [jira] [Comment Edited] (CASSANDRA-5062) Support CAS
Date Tue, 26 Feb 2013 18:26:14 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-5062?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13586394#comment-13586394
] 

Cristian Opris edited comment on CASSANDRA-5062 at 2/26/13 6:24 PM:
--------------------------------------------------------------------

So I guess what I'm proposing is similar to what Piotr said above: each CAS is a round of
Paxos.
With some cleverness this can be collapsed to Multi-Paxos. 
 
Spinnaker does leader election with ZK precisely because they did not want to implement Paxos
themselves. 

>From the paper, section 5: "The replication protocol has two phases: a leader election
phase, followed by a quorum phase where the leader proposes a write and the followers accept
it."

-That is Multi-Paxos, with first phase (leader election) handled by ZK and second phase being
the steady state (propose/accept) with the actual write/commit-
Edit: it's not, see below
                
      was (Author: onetoinfinity@yahoo.com):
    So I guess what I'm proposing is similar to what Piotr said above: each CAS is a round
of Paxos.
With some cleverness this can be collapsed to Multi-Paxos. 
 

Spinnaker does leader election with ZK precisely because they did not want to implement Paxos
themselves. 

>From the paper, section 5: "The replication protocol has two phases: a leader election
phase, followed by a quorum phase where the leader proposes a write and the followers accept
it."

That is Multi-Paxos, with first phase (leader election) handled by ZK and second phase being
the steady state (propose/accept) with the actual write/commit
                  
> 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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