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From: Junio C Hamano <gitster@pobox.com>
To: Jeff King <peff@peff.net>
Cc: "Rasmus Villemoes" <rv@rasmusvillemoes.dk>,
	"Git Mailing List" <git@vger.kernel.org>,
	"Stefan Beller" <stefanbeller@gmail.com>,
	"Nguyễn Thái Ngọc Duy" <pclouds@gmail.com>
Subject: Re: [PATCH] packfile: actually set approximate_object_count_valid
Date: Thu, 17 Sep 2020 11:26:21 -0700	[thread overview]
Message-ID: <xmqqy2l8qmya.fsf@gitster.c.googlers.com> (raw)
In-Reply-To: <20200917164743.GA3731633@coredump.intra.peff.net> (Jeff King's message of "Thu, 17 Sep 2020 12:47:43 -0400")

Jeff King <peff@peff.net> writes:

> Subject: [PATCH] packfile: actually set approximate_object_count_valid
>
> The approximate_object_count() function tries to compute the count only
> once per process. But ever since it was introduced in 8e3f52d778
> (find_unique_abbrev: move logic out of get_short_sha1(), 2016-10-03), we
> failed to actually set the "valid" flag, meaning we'd compute it fresh
> on every call.
> ...
>   Test                            origin              HEAD
>   ----------------------------------------------------------------------------
>   5303.3: rev-list (1)            28.91(28.46+0.44)   29.03(28.65+0.38) +0.4%
>   5303.4: abbrev-commit (1)       1.18(1.06+0.11)     1.17(1.02+0.14) -0.8%
>   5303.7: rev-list (50)           28.95(28.56+0.38)   29.50(29.17+0.32) +1.9%
>   5303.8: abbrev-commit (50)      3.67(3.56+0.10)     3.57(3.42+0.15) -2.7%
>   5303.11: rev-list (1000)        30.34(29.89+0.43)   30.82(30.35+0.46) +1.6%
>   5303.12: abbrev-commit (1000)   86.82(86.52+0.29)   77.82(77.59+0.22) -10.4%

Yuk, this is quite extreme.

>   5303.15: load 10,000 packs      0.08(0.02+0.05)     0.08(0.02+0.06) +0.0%
>
> 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.
>
> 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(+)

Thanks for finding and fixing.  I agree that this is worth doing.

      parent reply	other threads:[~2020-09-17 18:29 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-17  8:20 approximate_object_count_valid never set? Rasmus Villemoes
2020-09-17 11:58 ` Ævar Arnfjörð Bjarmason
2020-09-17 12:53 ` Jeff King
2020-09-17 16:47   ` [PATCH] packfile: actually set approximate_object_count_valid Jeff King
2020-09-17 16:53     ` Taylor Blau
2020-09-17 18:26     ` Junio C Hamano [this message]

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