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https://issues.apache.org/jira/browse/CASSANDRA-5062?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13591828#comment-13591828
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Cristian Opris commented on CASSANDRA-5062:
-------------------------------------------
One more example of how mostRecentCommit is ambiguous:
{code}
R1 R2 R3
Ct0 Ct0 Ct0 //initial state at t0
Atn< Atn < //accept at Tn > t0
Atn -> Ctn //R3 commits Ctn, mostRecentCommit = tn,
Accept is cleared !
>Atn+m >Atn+m //R3 accepts new value at tn+m > tn, this is
>valid since accept has been cleared
Atn+m -> Ctn+m //ambiguous state with R1=Ctn+m, R2=Ct0,
R3=Ctn, needs read ALL to resolve
{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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