Re: RFC: New diff-delta.c implementation

From: Nicolas Pitre <nico@cam.org>
Date: Apr 22, 2006, 12:45 UTC
Message-ID: <Pine.LNX.4.64.0604220835190.2215@localhost.localdomain>
In-Reply-To: <7v7j5hkglq.fsf@assigned-by-dhcp.cox.net>

On Sat, 22 Apr 2006, Junio C Hamano wrote:

Show 9 quoted lines

> Geert Bosch <bosch@adacore.com> writes:
> 
> > BTW. It's a shame that we don't reuse the index when comparing one
> > source
> >      against multiple targets. Creating the index takes about 70% of
> > the time.
> 
> I think we tried that with Nico/Davide's delta already, and IIRC
> we had mixed results.

Well, actually I was measuring a 10% speed improvement with a quick and naive (not memory efficient) approach for pack-objects with the current algorithm.

> It really depends on how big an index for a source is.  Keep in
> mind that we keep --window (default=10) of the source text
> in-core, and you are suggesting to keep index in-core as well,
> so we need to take memory pressure into account.

The idea to avoid memory pressure is to reverse the window processing such that the object to delta against is constant for the entire window instead of the current logic where the target object is constant. This way there would be only one index in memory at all time.

Nicolas