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From "Sandeep Tata (JIRA)" <>
Subject [jira] Commented: (CASSANDRA-48) test-and-set
Date Fri, 03 Apr 2009 16:38:13 GMT


Sandeep Tata commented on CASSANDRA-48:

Say we have 2 processes doing test-and-set.

Read X              Read X
T&S X +1           T&S X+2

The two T&S are routed to A , B, C:

@A T&S X + 1
                            @B T&S X+2
                            @C T&S X+2
                            @A T&S X+2 <------Fail, A already updated X 
@B T&S X+1 <---- fail
@C T&S X+2 <---- fail

X+1 fails, X+2 succeeds.
A contains a bad value that can be repaired by majority read. Any holes ?

> test-and-set
> ------------
>                 Key: CASSANDRA-48
>                 URL:
>             Project: Cassandra
>          Issue Type: Improvement
>            Reporter: Jonathan Ellis
> Atomic test-and-set insert operation would be nice: "set value to X but only if the current
value is still Y."  This allows a sort of optimistic consistency: perform a GET, then perform
test-and-set with the value of that GET as Y.
> I do not think that this requires strong consistency to be useful.

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