Re: [PATCH 00/11] pack-bitmap: convert offset to ref deltas where possible

From: Jeff King <peff@peff.net>
Date: Oct 11, 2024, 08:38 UTC
Message-ID: <20241011083838.GI18010@coredump.intra.peff.net>
In-Reply-To: <cover.1728505840.git.me@ttaylorr.com>

On Wed, Oct 09, 2024 at 04:30:52PM -0400, Taylor Blau wrote:

Show 10 quoted lines

> The first optimization (cross-pack deltas) should help clones and
> fetches, but the second optimization (thin deltas) will only help
> fetches, since the 'haves' bitmap will necessarily be empty for
> clones.
> 
> Of course, REF_DELTAs have a less compact representation than
> OFS_DELTAs, so the resulting packs will trade off some CPU time for a
> slightly larger pack. But we're only talking about a handful of extra
> bytes, and network bandwidth is pretty cheap, so I think the
> optimization is worthwhile here too.

It would be nice to see some numbers, even simulated ones from t/perf. Of course we'd like to show off any reduced server CPU for generating a fetch response. But I'd also like to see if the extra steps to find the cross-pack bases have any measurable negative effect (so the ideal there would be a big midx repo that doesn't have a lot of those bases, as it would not be helped much by the optimization and would be hurt by the time spent trying to apply it).

-Peff