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From Paul Davis <>
Subject Re: couchdb transactions changes
Date Tue, 10 Feb 2009 01:13:16 GMT
On Mon, Feb 9, 2009 at 7:29 PM, Antony Blakey <> wrote:
> On 10/02/2009, at 10:30 AM, Paul Davis wrote:
>>> Compaction and revision stemming (which is required to avoid unbounded
>>> growth) make intermediate states inconsistent because they can delete
>>> either
>>> the data of a document rev or the document rev itself. In the face of
>>> compaction, it's possible for consistency to only be achieved when the
>>> replication reaches the same MVCC commit point that the compaction was
>>> operating against. Revision stemming has a similar effect, although it
>>> has
>>> the further issue of being automatic i.e. not scheduled.
>>> That's ignoring replication failure, either temporary or permanent, which
>>> further complicates the picture. Given that intermediate states are not
>>> necessarily consistent, anything that leaves you in an intermediate state
>>> without a way forward, repudiates the guarantee of Eventual Consistency.
>> I'm pretty sure the rest of this is wrong though.
> I mean no offense, but I'm looking for something more than 'pretty sure'.
> I'm trying to work through these issues so that I understand the formal
> model and design intention completely and properly.

No offense taken. And I mean none as well.

The thing is, you're probably one of the most well informed people on
the subject as you've put so much effort into learning it. If you're
really committed on learning and improving the replication mechanisms
and the implications that has in general, I would suggest that you
start reading source code. I know you have the ability to make a
positive impact on CouchDB and having more people familiar with the
deeper internals will only be a win for the community.

Paul Davis

> Antony Blakey
> -------------
> CTO, Linkuistics Pty Ltd
> Ph: 0438 840 787
> Borrow money from pessimists - they don't expect it back.
>  -- Steven Wright

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