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From shankarpnsn <>
Subject Re: What does ReadRepair exactly do?
Date Wed, 24 Oct 2012 14:02:13 GMT
Hiller, Dean wrote
> in general it is okay to get the older or newer value.  If you are reading
> 2 rows however instead of one, that may change.

This is certainly interesting, as it could mean that the user could see a
value that never met the required consistency. For instance with 3 replicas
<R1,R2,R3> and a quorum consistency, assume that R1 is initiating a read
(becomes the coordinator) - notices a conflict with R2 (assume R1 has a more
recent value) and initiates a read repair with its value. Meanwhile R2 and
R3 have seen two different writes with newer values than what was computed
by the read repair. If R1 were to respond back to the user with the value
that was computed at the time of read repair, wouldn't it be a value that
never met the consistency constraint? I was thinking if this should trigger
another round of repair that tries to reach the consistency constraint with
a newer value or time-out, which is the expected case when you don't meet
the required consistency. Please let me know if I'm missing something here. 

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