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From " Brian Hess (JIRA)" <>
Subject [jira] [Commented] (CASSANDRA-7296) Add CL.COORDINATOR_ONLY
Date Mon, 10 Oct 2016 19:38:20 GMT


 Brian Hess commented on CASSANDRA-7296:

Consistency Level does feel like the right approach. The THIS_ prefix is in line with LOCAL_
in that it would identify the locus of nodes that are available for consistency. With LOCAL_ONE,
we need just one replica from the data center of this coordinator. If no replicas exist (like
the RF=0) then you get UnavailableException. Namely, you don't reach out to other nodes and
proxy for another DC, etc. Also note that while the client can certainly see that it's talking
to a DC with no RF by looking at system tables or driver API calls, we still throw the UnavailableException.

In the THIS_ONE, we are saying that the locus of available nodes for consistency level is
just the coordonator itself. If that node is not a replica, then it should also throw an UnavailableException.
It should not silently go ask the actual replicas, just like in the LOCAL_ONE case we don't
ask other DCs. While it is true that the client could know that this node is not a replica,
it is the same as in LOCAL_ONE and RF. 

> -----------------------
>                 Key: CASSANDRA-7296
>                 URL:
>             Project: Cassandra
>          Issue Type: Improvement
>            Reporter: Tupshin Harper
> For reasons such as CASSANDRA-6340 and similar, it would be nice to have a read that
never gets distributed, and only works if the coordinator you are talking to is an owner of
the row.

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