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From Antony Blakey <>
Subject Re: couchdb transactions changes
Date Sun, 08 Feb 2009 05:37:15 GMT

On 08/02/2009, at 3:52 PM, Damien Katz wrote:

> No, CouchDB replication doesn't support replicating the  
> transactions. Never has, never will. That's more like transaction  
> log replication that's in traditonal dbs, a different beast.

So just to be clear, replication ignores MVCC? And there is therefore  
no way to achieve any form of consistency, even the weaker ACID you've  
proposed - which sounds like it's really only Durability. I presume it  
at least replicates according to update_seq? If so, would it be  
difficult to ensure that the update_seq that the replicator sees is  
always on an MVCC boundary? That would allow for transactional  
replication of the form I'm talking about.

> For the new bulk transaction model, I'm only proposing supporting  
> eventual consistency. All changes are safe to disk, but the db may  
> not be in a consistent state right away.

Or indeed, ever.

>> Not necessarily, and even if they did, it's likely that they'll  
>> have multiple browser windows open.
> What's the front end written in?

On OSX, an Objective-C app that	provides an embedded Safari connecting  
to an embedded Ruby/Merb admin server, although I'm thinking of  
changing to Yaws et al. That provides a traditional OS app, with a GUI  
that looks like iTunes, provided via HTML. The admin app can then  
replicate/download web applications written in e.g. Ruby (for now)  
which do the real work.

On Windows, something similar, I presume .NET/C++/Gecko. Discussed in  
the contract RFI I posted.

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

Human beings, who are almost unique in having the ability to learn  
from the experience of others, are also remarkable for their apparent  
disinclination to do so.
   -- Douglas Adams

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