Re: pack-object's try_delta fast path for v2 trees?

From: Jeff King <peff@peff.net>
Date: Oct 15, 2013, 00:54 UTC
Message-ID: <20131015005417.GA16502@sigill.intra.peff.net>
In-Reply-To: <CACsJy8DgjCR+B+Bvbydns=bCZP5=TU1avPinnuDKqLZXS=4LNQ@mail.gmail.com>

On Tue, Oct 15, 2013 at 07:49:57AM +0700, Nguyen Thai Ngoc Duy wrote:

> I see this as pack-objects peformance improvements only. If we could
> make pack-objects run like 10% faster (even only with -adf), then it
> may be worth trying. The 10% is a total guess though as I haven't
> checked how much time we spend in searching deltas.

For "repack -ad", generally we don't spend that much time on deltas. It depends what your pre-repack state is, of course, but I find that most of the time goes to "counting objects". With "-adf", I would guess that we easily spend something like 95% of the time on compressing for a large repository (just try "repack -adf" on the kernel; even with 8 cores it's a half hour or more on my machine, versus about 25 seconds to count the objects).

So I think you could potentially get a lot of speedup for the "-adf" case (and likewise "git gc --aggressive").

-Peff