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From Tom van den Berge <>
Subject Re: How to prevent queries being routed to new DC?
Date Thu, 03 Sep 2015 18:53:11 GMT
Hi Bryan,

I'm using the PropertyFileSnitch, and it contains entries for all nodes in
the old DC, and all nodes in the new DC. The replication factor for both
DCs is 1.

With the first approach I described, the new nodes join the cluster, and
show up correctly under the new DC, so all seems to be fine.
With the second approach (join_ring=false), they don't show up at all,
which is also what I expected.

On Thu, Sep 3, 2015 at 8:44 PM, Bryan Cheng <> wrote:

> 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 <
>> 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
>> 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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