Re: [PATCH 0/5] Suggested for PU: revision caching system to significantly speed up packing/walking

[Nicolas Pitre <nico@cam.org>]

On Fri, 7 Aug 2009, Sam Vilain wrote:

> Johannes Schindelin wrote:
> >> the short answer is that cache slices are totally independant of pack 
> >> files.
> >>     
> >
> > My idea with that was that you already have a SHA-1 map in the pack index, 
> > and if all you want to be able to accelerate the revision walker, you'd 
> > probably need something that adds yet another mapping, from commit to 
> > parents and tree, and from tree to sub-tree and blob (so you can avoid 
> > unpacking commit and tree objects).
> >   
> 
> Tying indexes together like that is not a good idea in the database
> world. Especially as in this case as Nick mentions, the domain is subtly
> different (ie pack vs dag). Unfortunately you just can't try to pretend
> that they will always be the same; you can't force a full repack on
> every ref change!

Right.  And the rev cache must work even if the repository is not 
packed. So pack index and rev caching are orthogonal things and are best 
kept separate on disk.

How big this cache might get would be interesting indeed.


Nicolas