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From Antony Blakey <>
Subject Re: Replication and forms of weak consistency
Date Mon, 16 Feb 2009 22:37:49 GMT

On 16/02/2009, at 9:45 PM, Robert Newson wrote:

> I agree it may not be generally practical to carry a version vector in
> the client (specifically in a 2k cookie) but it may be practical in my
> specific case.

The problem is that the replica group you use from your client may not  
be able to achieve the Monotonic Writes guarantee even at the steady  
state within that group e.g. you would have to cover every replica  
that had ever been replicated from.

The point of doing it in the server is that every node guarantees  
Monotonic Writes, and you never have to worry about failing because  
you can't achieve it. Given the current server implementation, IMO  
it's more likely than not that you would fail.

Furthermore, this isn't a simple problem, and pushing it to the client  
just leads to multiple complicated client implementations, IMHO.

> I don't (yet) see why partial replication is a
> particular problem, though.

Because achieving the Monotonic Writes guarantee is more difficult  
with Partial Replication, and requires special support in the server.  
There's no indication that PRACTI can be implemented as a client  

Antony Blakey
CTO, Linkuistics Pty Ltd
Ph: 0438 840 787

If you pick up a starving dog and make him prosperous, he will not  
bite you. This is the principal difference between a man and a dog.
   -- Mark Twain

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