Re: [PATCH] packfile: actually set approximate_object_count_valid

[Taylor Blau <me@ttaylorr.com>]

On Thu, Sep 17, 2020 at 12:47:43PM -0400, Jeff King wrote:
> So here it is wrapped up as a patch. I think it's worth fixing (as
> opposed to dropping the unused flag code). Thanks for finding it.

Yup, after reading the patch and performance timings below, I agree that
this is worth fixing and keeping instead of dropping.

> It doesn't help at all when we have 1 pack (5303.4), but we get a 10%
> speedup when there are 1000 packs (5303.12). That's a modest speedup for
> a case that's already slow and we'd hope to avoid in general (note how
> slow it is even after, because we have to look in each of those packs
> for abbreviations). But it's a one-line change that clearly matches the
> original intent, so it seems worth doing.

Excellent.

> The included perf test may also be useful for keeping an eye on any
> regressions in the overall abbreviation code.
>
> Reported-by: Rasmus Villemoes <rv@rasmusvillemoes.dk>
> Signed-off-by: Jeff King <peff@peff.net>
> ---
>  packfile.c                 | 1 +
>  t/perf/p5303-many-packs.sh | 4 ++++
>  2 files changed, 5 insertions(+)
>
> diff --git a/packfile.c b/packfile.c
> index 9ef27508f2..e69012e7f2 100644
> --- a/packfile.c
> +++ b/packfile.c
> @@ -923,6 +923,7 @@ unsigned long repo_approximate_object_count(struct repository *r)
>  			count += p->num_objects;
>  		}
>  		r->objects->approximate_object_count = count;
> +		r->objects->approximate_object_count_valid = 1;
>  	}
>  	return r->objects->approximate_object_count;
>  }
> diff --git a/t/perf/p5303-many-packs.sh b/t/perf/p5303-many-packs.sh
> index 7ee791669a..f4c2ab0584 100755
> --- a/t/perf/p5303-many-packs.sh
> +++ b/t/perf/p5303-many-packs.sh
> @@ -73,6 +73,10 @@ do
>  		git rev-list --objects --all >/dev/null
>  	'
>
> +	test_perf "abbrev-commit ($nr_packs)" '
> +		git rev-list --abbrev-commit HEAD >/dev/null
> +	'
> +
>  	# This simulates the interesting part of the repack, which is the
>  	# actual pack generation, without smudging the on-disk setup
>  	# between trials.
> --
> 2.28.0.982.gdd163d6eb1

Looks all very good to me. Thanks.

Thanks,
Taylor