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From Niclas Hedhman <nic...@hedhman.org>
Subject Re: [replication] Master slave replication will not suffice
Date Fri, 25 Feb 2005 02:59:40 GMT
On Thursday 24 February 2005 09:15, Alex Karasulu wrote:
> So what we need is multimaster replication.  This is an order of
> magnitude more complex than master slave replication.

I don't have the formal MMR academia under my belt, and I make a general 
disclaimer of having any clue of how this should be solved. However, since I 
have implemented system fault tolerant systems in process control networks, I 
would like to share an approach that I *think* may work rather well here as 
well. (perhaps someone have suggested this already, and I have missed it, 
then sorry for the noise)

Instead of trying to do P2P replication, conflict resolution and so forth, I 
would investigate a "negotiated Master" approach instead.
I.e. all peers in the cluster negotiates who is the master, and forwards all 
CUD requests there, and the replication flows downstream.
Also, all peers monitors the master, and if any peer have communication 
problems with the master, it initiates the 'negotiation process'.

I think this limits the problem domain quite a bit, but there are still some 
of the MMR issues around;

 * What happens to Peer-to-Master-CUD and Master-to-Peer-replication 
operations in progress when the Master dies?

 * What happens to Master-to-Peer-replication operations in progress when a 
Peer no longer can be reached by the Master, but the Peer itself is 
operational and will initiate 'negotiation' (probably a very rare condition, 
but completely possible)?

And possibly others. Note that these are still present in full MMR situations 
as well (together with heaps of other failure situations).


Cheers
Niclas

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