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From "Sylvain Lebresne (JIRA)" <>
Subject [jira] [Commented] (CASSANDRA-5062) Support CAS
Date Tue, 05 Mar 2013 08:04:14 GMT


Sylvain Lebresne commented on CASSANDRA-5062:

bq. When Acceptor receives proposal, if it doesn't check R, if Tm > Tn (clock mismatch)
according to paxos it needs to send it's old accepted value

In my solution/proposal, a round is a fully separated Paxos instance (it's not just a proposal
round for instance). Meaning that comparing a proposal timestamp Tn for Round R with a proposal
timestamp Tm for another round R-1 (which is the case you are talking about) makes no sense
whatsoever and is thus never done. And it doesn't break Paxos exactly because we don't mix
things from 2 completely separated instance of the raw Paxos algorithm.

> Support CAS
> -----------
>                 Key: CASSANDRA-5062
>                 URL:
>             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
> "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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