Re: Preferring shallower deltas on repack

[bdowning@lavos.net (Brian Downing)]

On Mon, Jul 09, 2007 at 12:27:24AM -0700, Junio C Hamano wrote:
> >> It would become worrysome (*BUT* infinitely more interesting)
> >> once you start talking about a tradeoff between slightly larger
> >> delta and much shorter delta.  Such a tradeoff, if done right,
> >> would make a lot of sense, but I do not offhand think of a way
> >> to strike a proper balance between them efficiently.
> >
> > Yeah, I was thinking about that too, and came to the same conclusion.
> > I suspect you'd have to save a /lot/ of delta depth to want to pay any
> > more I/O, though.
> 
> That may not be so.  Deeper delta also means more I/O (and
> worse, because they can be from discontiguous areas) plus delta
> application.

Good point.

I guess if I were to think about a metric for deciding whether to go for
a small deep delta or a larger shallow one, I would probably keep track
of the total path size (the sum of the base size and all the delta sizes)
for each entry, and play with a weighting formula of single delta size
verses total path size.

-bcd