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From "Peter Schuller (Created) (JIRA)" <j...@apache.org>
Subject [jira] [Created] (CASSANDRA-3901) write endpoints are not treated correctly, breaking consistency guarantees
Date Mon, 13 Feb 2012 00:48:59 GMT
write endpoints are not treated correctly, breaking consistency guarantees
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                 Key: CASSANDRA-3901
                 URL: https://issues.apache.org/jira/browse/CASSANDRA-3901
             Project: Cassandra
          Issue Type: Sub-task
          Components: Core
            Reporter: Peter Schuller
            Assignee: Peter Schuller
            Priority: Critical


I had a nagging feeling this was the case ever since I started wanting CASSANDRA-3833 and
thinking about hot to handle the association between nodes in the read set and nodes in the
write set.

I may be wrong (please point me in the direct direction if so), but I see no code anywhere
that tries to (1) apply consistency level to currently normal endpoints only, and (2) "connect"
a given read endpoint with a future write endpoint such that they are tied together for consistency
purposes (parts of these concerns probably is covered by CASSANDRA-2434 but that ticket is
more general).

To be more clear about the problem: Suppose we have a ring of nodes, with a single node bootstrapping.
Now, for a given row key suppose reads are served by A, B and C while writes are to go to
A, B, C and D. In other words, D is the node bootstrapping. Suppose RF is 3 and A,B,C,D is
ring order. There are a few things required for correct behavior:

* Writes acked by D must never be treated as sufficient to satisfy consistency level since
until it is part of the read set it does not count towards CL on reads.
* Writes acked by B must *not* be treated as sufficient to satisfy consistency level *unless*
the same write is *also* acked by D, because once D enters the ring, B will no longer be counting
towards CL on reads. The only alternative is to make the read succeed and disallow D from
entering the ring.

We don't seem to be handling this at all (and it becomes more complicated with arbitrary transitions).



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