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https://issues.apache.org/jira/browse/CASSANDRA-2494?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13021242#comment-13021242
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Jeremiah Jordan commented on CASSANDRA-2494:
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I would think that reads at QUORUM should never go backwards.  Even if the 
Write was at ZERO.  If there were writes to the cluster of a=1 time=5, a=2 
time=10, a=3 time=15, and I do a read at QUORUM which tells me a=3 time=15, I 
should not be able to do another read at QUORUM and get a=2 time=10.

> Quorum reads are not consistent
> -------------------------------
>
>                 Key: CASSANDRA-2494
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-2494
>             Project: Cassandra
>          Issue Type: Bug
>            Reporter: Sean Bridges
>
> As discussed in this thread,
> http://www.mail-archive.com/user@cassandra.apache.org/msg12421.html
> Quorum reads should be consistent.  Assume we have a cluster of 3 nodes 
> (X,Y,Z) and a replication factor of 3. If a write of N is committed to X, but 
> not Y and Z, then a read from X should not return N unless the read is 
> committed to at  least two nodes.  To ensure this, a read from X should wait 
> for an ack of the read repair write from either Y or Z before returning.
> Are there system tests for cassandra?  If so, there should be a test similar 
> to the original post in the email thread.  One thread should write 1,2,3... 
> at consistency level ONE.  Another thread should read at consistency level 
> QUORUM from a random host, and verify that each read is >= the last read.

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