On Sat, 2011-04-09 at 10:42 +0100, Robert Newson wrote:
> CouchDB does not provide revisioning or history features to the end
> user at all. This is a common mistake.
> 
> The use of _rev and MVCC is purely a mechanism to enable sane
> replication between servers where writes are permitted everywhere.
> CouchDB's replication will only ensure that the current version* of
> any document is replicated, earlier revisions are *not* replicated.

I'm not interested in replicating earlier revisions.

I'm interested in receiving the change notification (either because of
replication or because of a local update) and showing what changed.

I'm pretty sure that:
- in the case of a local update, the previous revision is still there at
the moment the change notification happens
- in the case of a replication update, the previous local revision is
still locally available too.

Those are the changes I'm interested in showing, and hence I see no
reason why couchdb couldn't inform both the new revid and the revid just
before the change.

> Earlier revisions are also removed on compaction, which is an
> essential maintenance operation.

Essential how ? It's not going to stop working if you don't compact,
just slow down.  Depends on your usage model.  And in any case,
compaction is triggered, so I would be completely ok with once in a
while not being able to get an older revision and not correctly show
changes because I triggered compaction.  99% of the time this wouldn't
be the case.

Thomas

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