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From Bryan Cheng <br...@blockcypher.com>
Subject Re: How to prevent queries being routed to new DC?
Date Thu, 03 Sep 2015 18:44:27 GMT
Hey Tom,

What's your replication strategy look like? When your new nodes join the
ring, can you verify that they show up under a new DC and not as part of
the old?

--Bryan

On Thu, Sep 3, 2015 at 11:27 AM, Tom van den Berge <
tom.vandenberge@gmail.com> wrote:

> I want to start using vnodes in my cluster. To do so, I've set up a new
> data center with the same number of nodes as the existing one, as described
> in
> http://docs.datastax.com/en/cassandra/2.0/cassandra/configuration/configVnodesProduction_t.html.
> The new DC is in the same physical location as the old one.
>
> The problem I'm running into is that as soon as the nodes in the new data
> center are started, the application that is using the nodes in the old data
> center is frequently getting error messages because queries don't return
> the expected data. I'm pretty sure this is because somehow these queries
> are routed to the new, empty data center. The application is not connecting
> to the nodes in the new DC.
>
> I've tried two different things to prevent this:
>
> 1) Ensure that all queries use either LOCAL_ONE or LOCAL_QUORUM
> consistency. Nevertheless, I'm still seeing failed queries.
> 2) Start the new nodes with -Dcassandra.join_ring=false, to prevent them
> from participating in the cluster. Although they don't show up in nodetool
> ring, I'm still seeing failed queries.
>
> If I understand it correctly, both measures should prevent queries from
> ending up in the new DC, but somehow they don't in my situation.
>
> How is it possible that queries are routed to the new, emtpy data center?
> And more importantly, how can I prevent it?
>
> Thanks,
> Tom
>

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