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https://issues.apache.org/jira/browse/CASSANDRA-5062?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13593463#comment-13593463
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Cristian Opris commented on CASSANDRA-5062:
-------------------------------------------
Let me rewrite the example with your terminology:
{code}
X Y Z
1. L0 L0 L0 //initial state committed R=0
2. P/C(R=1)< P/C(R=1)< //Z sends propose/commit (i.e. paxos
round) R=1
3. L1 //Z has majority with Y, learns locally
L1 but X and Y fail to learn
4. P/C(R=2)< P/C(R=2)< //Z leads R=2
5. L2 L2 //Z has majority with X, both learn L2
but not Y
6. P/C(R=3)< P/C(R=3)< //Z leads R=3
5. L3 //Z has majority with Y, learsn locally
L3 but X and Y fail to learn
{code}
> 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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