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From Chris Anderson <jch...@apache.org>
Subject Re: Trouble with replication
Date Fri, 30 Jan 2009 06:47:55 GMT
On Thu, Jan 29, 2009 at 9:23 PM, Antony Blakey <antony.blakey@gmail.com> wrote:
>
> On 30/01/2009, at 9:49 AM, Chris Anderson wrote:
>
>> What's happening in this scenario is that B is not getting any revs
>> from A. Replication is one-way. I think if you always trigger
>> replication both ways, then your nodes will be consistent (assuming
>> they accept the same set of updates as valid).
>
> If you have > 2 nodes then that is no longer true. Consider three nodes A, B
> and C where
>
> A: has a validation function F
> B: a document that is invalid under F
>
> Replicating B -> C, A -> C is different than A -> C, B -> C, and there is
no
> global steady state that can be reached.

I think it is the responsibility of the application to write sane
validation functions. Also, I don't see how the order of incoming
replications to C matters. Maybe you can spell it out for me.

>
> Without these non-functional additions, A, B, C will tend to a global steady
> state assuming full replication coverage, regardless of ordering. At least
> that's what I assume from the wiki statement about the determinism of
> conflict resolution. Have I made the wrong assumption about that?
>
> Antony Blakey
> -------------
> CTO, Linkuistics Pty Ltd
> Ph: 0438 840 787
>
> The intuitive mind is a sacred gift and the rational mind is a faithful
> servant. We have created a society that honours the servant and has
> forgotten the gift.
>  -- Albert Einstein
>
>
>



-- 
Chris Anderson
http://jchris.mfdz.com

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