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Sylvain Lebresne commented on CASSANDRA-2494:
---------------------------------------------
The problem is you are considering the consistency of reads but not write. The
guarantee is: "quorum reads will not see old quorum write once a quorum read
sees a new quorum". Period. I you don't consider the consistency of a write,
consider the case of a CL.ANY write. In this case, the update may not be at all
on any replica. How can we ensure the quorum read property that you want ? We
query all nodes for quorum reads in case there is an hint somewhere ?
If you look at the Consistency part of
http://wiki.apache.org/cassandra/ArchitectureOverview, it seems to me that it
is pretty clear that the consistency of reads *and* writes is involved to
achieve strong consistency. So I would hope 'most people' are aware of that.
> 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/[email protected]/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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