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From Eric Evans <eev...@acunu.com>
Subject Re: RFC: Cassandra Virtual Nodes
Date Tue, 20 Mar 2012 13:37:13 GMT
On Tue, Mar 20, 2012 at 6:40 AM, Sam Overton <sam@acunu.com> wrote:
> On 20 March 2012 04:35, Vijay <vijay2win@gmail.com> wrote:
>> On Mon, Mar 19, 2012 at 8:24 PM, Eric Evans <eevans@acunu.com> wrote:
>>
>>> I'm guessing you're referring to Rick's proposal about ranges per node?
>>>
>>
>> May be, what i mean is little more simple than that... We can consider
>> every node having a multiple conservative ranges and moving those ranges
>> for bootstrap etc, instead of finding the mid point etc in the bootstrap
>> code. Once we get that working all the way to the FS/Streaming then we can
>> move those ranges and assign those ranges to nodes in random orders. Hope
>> it makes sense.
>
> I agree that this should be approached in incremental steps. Rick
> already raised concerns about stability issues which might arise from
> changing large parts of code at once.
>
> I would anticipate the first step to be, exactly as you suggest, to
> support multiple tokens per host instead of just one. Presumably in
> your suggestion you imagine these tokens to define contiguous ranges
> for a given host, so that the distribution model is the same as
> before, but bootstrap can be done incrementally.
>
> This would be a great first step. The extension to a virtual node
> scheme as described previously is then fairly trivial. The only
> additional change needed is to assign the tokens in some other way
> which does not restrict the ranges to being contiguous.

Sounds good to me.

What can an upgrading user expect in the way of disruption?  What
would be required to move an existing cluster from one token per node
to virtual nodes?  Could this be made transparent?

-- 
Eric Evans
Acunu | http://www.acunu.com | @acunu

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