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From "Tyler Hobbs (JIRA)" <>
Subject [jira] [Created] (CASSANDRA-8119) More Expressive Consistency Levels
Date Tue, 14 Oct 2014 21:01:33 GMT
Tyler Hobbs created CASSANDRA-8119:

             Summary: More Expressive Consistency Levels
                 Key: CASSANDRA-8119
             Project: Cassandra
          Issue Type: New Feature
          Components: API
            Reporter: Tyler Hobbs

For some multi-datacenter environments, the current set of consistency levels are too restrictive.
 For example, the following consistency requirements cannot be expressed:
* LOCAL_QUORUM in two specific DCs
* LOCAL_QUORUM in the local DC plus LOCAL_QUORUM in at least one other DC
* LOCAL_QUORUM in the local DC plus N remote replicas in any DC

I propose that we add a new consistency level: CUSTOM.  In the v4 (or v5) protocol, this would
be accompanied by an additional map argument.  A map of {DC: CL} or a map of {DC: int} is
sufficient to cover the first example.  If we accept a special keys to represent "any datacenter",
the second case can be handled.  A similar technique could be used for "any other nodes".

I'm not in love with the special keys, so if anybody has ideas for something more elegant,
feel free to propose them.  The main idea is that we want to be flexible enough to cover any
reasonable consistency or durability requirements.

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