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From "Jeff Jirsa (JIRA)" <>
Subject [jira] [Commented] (CASSANDRA-7296) Add CL.COORDINATOR_ONLY
Date Mon, 10 Oct 2016 15:48:20 GMT


Jeff Jirsa commented on CASSANDRA-7296:

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.

Emotionally, I want this to be the right answer (principle of least astonishment), but I don't
think it is. I'm concerned it will prove to be a step backwards in real clusters, where coordinator
disk latencies may truly jump up up significantly (imagine all compaction threads running
scrub/cleanup, where not only is the disk likely completely utilized, but the # of sstables
on disk grows because all compaction threads are in use, so reads are more expensive than
normal - in this case, dsnitch DOES save us, and implementing this type of change would be
very hard to work around in production with most drivers).

> -----------------------
>                 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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