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Sylvain Lebresne commented on CASSANDRA-7296:
---------------------------------------------
I can certainly agree that having the dynamic snitch getting in the way of
local queries is not always desirable, but I'm less convinced that adding a new
consistency level is the cleanest way to circumvent that.
First, I'm not even entirely sure than letting the dynamic snitch bypass the
coordinator if it's a replica is a good idea in the first place. Everyone more
or less agree that doing token-aware routing is a good thing nowadays, and it's
certainly confusing that the dynamic snitch may screw that up. If the dynamic
snitch was a perfect and instantaneous view of latencies, then that could make
sense, but it's not. Anyway, I think it's worth at least evaluating making even
the dynamic snitch always pick the local node if it's a replica, as I'm not
sure the benefit of not doing so outweigh the confusion it creates.
But short of that, why not directly attack the problem we're trying to solve
and add a (protocol) option to queries to force the behavior ("always pick the
coordinator as one replica if it's one"). That sounds less confusing to me than
have a new CL that will confuse newcomers (as the difference with ONE is
somewhat subtle for a newcomer). As a bonus, it would also work for CL > ONE
(since again, it'll just be about forcing the dynamic snitch to pick the
coordinator if it's a replica).
We could also have a table option to do the same: force the dynamic snitch to
pick the coordinator if it's a replica for all queries on that table, which
would be a tad more convenient for request pinning (of course, I get that for
troubleshooting you still want to per-query option).
> Add CL.COORDINATOR_ONLY
> -----------------------
>
> Key: CASSANDRA-7296
> URL: https://issues.apache.org/jira/browse/CASSANDRA-7296
> 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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