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From aaron morton <>
Subject Re: Replica data distributing between racks
Date Wed, 04 May 2011 10:33:19 GMT
	Jonathan is suggesting the approach Jeremiah was using. 

	Calculate the tokens the nodes in each DC independantly, and then add 1 to the tokens if
there are two nodes with the same tokens. 

	In your case with 2 DC's with 2 nodes each. 

In DC 1
node 1 = 0
node 2 = 85070591730234615865843651857942052864

In DC 2
node 1 = 1
node 2 =  85070591730234615865843651857942052865

This will evenly distribute the keys in each DC, which is what the NetworkTopologyStrategy
is trying to do. 

You can make this change using nodetool move. 

Hope that helps. 

Aaron Morton
Freelance Cassandra Developer

On 4 May 2011, at 08:20, Eric tamme wrote:

> On Tue, May 3, 2011 at 4:08 PM, Jonathan Ellis <> wrote:
>> On Tue, May 3, 2011 at 2:46 PM, aaron morton <> wrote:
>>> Jonathan,
>>>        I think you are saying each DC should have it's own (logical) token ring.
>> Right. (Only with NTS, although you'd usually end up with a similar
>> effect if you alternate DC locations for nodes in a ONTS cluster.)
>>>        But currently two endpoints cannot have the same token regardless of the
DC they are in.
>> Also right.
>>> Or should people just bump the tokens in extra DC's to avoid the collision?
>> Yes.
> I am sorry, but I do not understand fully.  I would appreciate it if
> some one could explain with more verbosity for me.
> I do not understand why data insertion is even, but replication is not.
> I do not understand how to solve the problem.  What does "bumping"
> tokens entail - Is that going to change my insertion distribution?  I
> had no idea you can create different logical keyspaces ... and I am
> not sure what that exactly means... or that I even want to do it.  Is
> there a clear solution to "fixing" the problem I laid out, and getting
> replication data evenly distributed between racks in each DC?
> Sorry again for needing more verbosity - I am learning as I go with
> this stuff.  I appreciate everyones help.
> -Eric

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