[merge] document the pack format

[Robert Collins]

On Wed, 2007-10-24 at 19:57 +0100, James Westby wrote:
> On (24/10/07 10:53), Martin Pool wrote:
> > +obsolete_packs/      packs that have been repacked and are no 
> > +                     longer normally needed
> 
> When do packs enter here? When are they removed?
> 
> I am guessing this is in a repack operation. Does it just build up cruft?
> 
> There was a recent git conversation where they realised that all
> operations need to be automatic by default, as only 0.1% of developers
> will ever actually run the maintenance commands, if they even realise
> they are supposed to.

Yup, Someone mentioned this to me when I was developing packs, and I was
very happy to be able to say 'well we already do this' :).

> I applaud the automatic repack then, I would just be wary of the
> (only disk?) overhead that would arise from too much accumulating here.

https://bugs.edge.launchpad.net/bzr/+bug/153789

> Along the same lines, I guess a repack operation will still no nothing
> for unreferenced revisions, as they repository doesn't know about the
> branches, and packs don't change that.

The 'gc' command is the one I have proposed for cleaning this sort of
thing up.

The existing 'pack' command will allow a user to cause a full pack of
their repository rather than the automatically managed maintenance.
Currently the only difference between automatic packing and running
'pack' is that automatic packing uses the revision count in base 10 as a
histogram for the number and revision count of each pack, whereas
running pack causes bzr to create a single large pack.

-Rob
-- 
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