Re: [PATCH v3 0/5] Avoid spawning gzip in git archive

From: Jeff King <peff@peff.net>
Date: Jul 1, 2022, 16:27 UTC
Message-ID: <Yr8gZT6dbCpzaR9n@coredump.intra.peff.net>
In-Reply-To: <038r075o-5s5r-9sop-5o02-8s84428o0r54@tzk.qr>

On Fri, Jul 01, 2022 at 06:05:59PM +0200, Johannes Schindelin wrote:

> Stolee pointed out to me that objects inside pack files are also
> zlib-compressed, and that measuring the speed of `git rev-list --objects
> --all --count` might therefore be a better test.

That will spend quite a lot of time doing hash-lookups for each tree entry. A better raw zlib test might be:

  git cat-file --batch --batch-all-objects --unordered >/dev/null

which will just dump each object, and should mostly be zlib and delta reconstruction (the --unordered is important to hit the deltas in the right order).

> And this is where things get a little messy: in the context of Git for
> Windows, my local measurements indicate that zlib is better, with ~41
> seconds using zlib vs ~52 seconds using zlib-ng (but the latter has a
> rather large variance).

That is a surprising slow-down between the two. I'd expect the command above to show even more pronounced results, though, as it's spending less time doing non-zlib things. But it's still just inflating (as opposed to git-archive, which is both inflating and deflating).

-Peff