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From Ravikumar Govindarajan <ravikumar.govindara...@gmail.com>
Subject Nodetool ring and multiple dc
Date Fri, 10 Feb 2012 07:00:31 GMT
Hi,

I was trying to setup a backup DC from existing DC.

State of existing DC with SimpleStrategy & rep_factor=1.

./nodetool -h localhost ring
Address         DC          Rack        Status State   Load            Owns
   Token


   85070591730234615865843651857942052864
XXX.YYY        DC1         RAC1        Up     Normal  187.69 MB
50.00%  0
XXX.ZZZ       DC1         RAC1        Up     Normal  187.77 MB       50.00%
 85070591730234615865843651857942052864

After adding backup DC with NetworkTopologyStrategy {DC1:1,DC2:1}, the
output is as follows

./nodetool -h localhost ring
Address         DC          Rack        Status State   Load            Owns
   Token

   85070591730234615865843651857942052864
XXX.YYY    DC1         RAC1        Up     Normal  187.69 MB       50.00%  0

AAA.BBB    DC2         RAC1        Up     Normal  374.59 MB       11.99%
 20392907958956928593056220689159358496
XXX.ZZZ    DC1         RAC1        Up     Normal  187.77 MB       38.01%
 85070591730234615865843651857942052864

As per our app rules, all writes will first go through DC1 and then find
it's way to DC2. Since the "Owns" percentage has drastically changed, will
it mean that the DC1 nodes will become unbalanced for future writes?

We have a very balanced ring in our production with all nodes serving
almost equal volume data as of now in DC1. Will setting up a backup DC2
disturb the balance?

Thanks and Regards,
Ravi

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