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From: Jonathan Ellis <jbellis@gmail.com>
Date: Tue, 9 Feb 2010 10:21:10 -0600
Message-ID: <e06563881002090821n31c56ce9n82f56a3487919b9@mail.gmail.com>
Subject: Re: loadbalance and different strategies
To: cassandra-dev@incubator.apache.org
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On Tue, Feb 9, 2010 at 3:13 AM, Jaakko <rosvopaallikko@gmail.com> wrote:
> What they probably should do, is to just
> consider nodes in the DC they are booting to, and try to balance load
> evenly in that DC.

I'm not sure what problem that would solve.  It seems to me there are two goals:

 1. don't transfer data across data centers
 2. improve ring balance when you add nodes

(1) should always be the case no matter where on the ring the node is
since there will be at least one replica of each range in each DC.

(2) is where we get into trouble here no matter which DC we add to.
 (a) if we add to G's DC, X will get all the replicas G has, remaining
unbalanced
 (b) if we add to the other DC, G will still be hit from all the
replicas from the other DC

So ISTM that the only real solution is to do what we say in the
Operations page, and make sure that nodes on the ring alternate DCs.
I don't think only considering nodes in the same DC helps with that.

-Jonathan