From: Derrick Stolee <derrickstolee@github.com>
To: "Jeff King" <peff@peff.net>, 程洋 <chengyang@xiaomi.com>
Cc: "git@vger.kernel.org" <git@vger.kernel.org>,
何浩 <hehao@xiaomi.com>, "Xin7 Ma 马鑫" <maxin7@xiaomi.com>,
石奉兵 <shifengbing@xiaomi.com>, 凡军辉 <fanjunhui@xiaomi.com>,
王汉基 <wanghanji@xiaomi.com>
Subject: Re: [PATCH 2/3] upload-pack: skip parse-object re-hashing of "want" objects
Date: Wed, 7 Sep 2022 10:36:14 -0400 [thread overview]
Message-ID: <6018c526-4641-8374-8802-cfda5be330c3@github.com> (raw)
In-Reply-To: <YxfSRkEiiP4TyZTM@coredump.intra.peff.net>
On 9/6/2022 7:05 PM, Jeff King wrote:
> This patch teaches both code paths to use the new SKIP_HASH_CHECK flag
> for parse_object(). You can see the speed-up in p5600, which does a
> blob:none clone followed by a checkout. The savings for git.git are
> modest:
>
> Test HEAD^ HEAD
> ----------------------------------------------------------------------
> 5600.3: checkout of result 2.23(4.19+0.24) 1.72(3.79+0.18) -22.9%
>
> But the savings scale with the number of bytes. So on a repository like
> linux.git with more files, we see more improvement (in both absolute and
> relative numbers):
>
> Test HEAD^ HEAD
> ----------------------------------------------------------------------------
> 5600.3: checkout of result 51.62(77.26+2.76) 34.86(61.41+2.63) -32.5%
>
> And here's an even more extreme case. This is the android gradle-plugin
> repository, whose tip checkout has ~3.7GB of files:
>
> Test HEAD^ HEAD
> --------------------------------------------------------------------------
> 5600.3: checkout of result 79.51(90.84+5.55) 40.28(51.88+5.67) -49.3%
>
> Keep in mind that these timings are of the whole checkout operation.
These numbers are _very_ impressive for this user-facing scenario.
> Benchmark 1: GIT_PROTOCOL=version=2 git.old upload-pack ../gradle-plugin <input
> Time (mean ± σ): 50.884 s ± 0.239 s [User: 51.450 s, System: 1.726 s]
> Range (min … max): 50.608 s … 51.025 s 3 runs
>
> Benchmark 2: GIT_PROTOCOL=version=2 git.new upload-pack ../gradle-plugin <input
> Time (mean ± σ): 9.728 s ± 0.112 s [User: 10.466 s, System: 1.535 s]
> Range (min … max): 9.618 s … 9.842 s 3 runs
>
> Summary
> 'GIT_PROTOCOL=version=2 git.new upload-pack ../gradle-plugin <input' ran
> 5.23 ± 0.07 times faster than 'GIT_PROTOCOL=version=2 git.old upload-pack ../gradle-plugin <input'
>
> So a server would see an 80% reduction in CPU serving the initial
> checkout of a partial clone for this repository.
Very nice!
> In both cases skipping the extra hashing on the server should be pretty
> safe. The client doesn't trust the server anyway, so it will re-hash all
> of the objects via index-pack.
Definitely safe for this target scenario.
> There is one thing to note, though: the
> change in get_reference() affects not just pack-objects, but rev-list,
> git-log, etc. We could use a flag to limit to index-pack here, but we
> may already skip hash checks in this instance. For commits, we'd skip
> anything we load via the commit-graph. And while before this commit we
> would check a blob fed directly to rev-list on the command-line, we'd
> skip checking that same blob if we found it by traversing a tree.
It's worth also mentioning that since you isolated the change to
get_reference(), it is only skipping the parse for the requested tips
of the revision walk. As we follow commits and trees to other objects
we do not use parse_object() but instead use the appropriate method
(parse_commit(), parse_tree(), and do not even parse blobs).
This is additionally confirmed that p0001-rev-list.sh has no measurable
change in results with this commit, even when disabling the commit-graph.
> The exception for both is if --verify-objects is used. In that case,
> we'll skip this optimization, and the new test makes sure we do this
> correctly.
The test for this is clever. Thanks for adding it.
Code and test look good.
Thanks,
-Stolee
next prev parent reply other threads:[~2022-09-07 14:36 UTC|newest]
Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-08-11 8:09 Partial-clone cause big performance impact on server 程洋
2022-08-11 17:22 ` Jonathan Tan
2022-08-13 7:55 ` 回复: [External Mail]Re: " 程洋
2022-08-13 11:41 ` 程洋
2022-08-15 5:16 ` ZheNing Hu
2022-08-15 13:15 ` 程洋
2022-08-12 12:21 ` Derrick Stolee
2022-08-14 6:48 ` Jeff King
2022-08-15 13:18 ` Derrick Stolee
2022-08-15 14:50 ` [External Mail]Re: " 程洋
2022-08-17 10:22 ` 程洋
2022-08-17 13:41 ` Derrick Stolee
2022-08-18 5:49 ` Jeff King
2022-09-01 6:53 ` 程洋
2022-09-01 16:19 ` Jeff King
2022-09-05 11:17 ` 程洋
2022-09-06 18:38 ` Jeff King
2022-09-06 22:58 ` [PATCH 0/3] speeding up on-demand fetch for blobs in partial clone Jeff King
2022-09-06 23:01 ` [PATCH 1/3] parse_object(): allow skipping hash check Jeff King
2022-09-07 14:15 ` Derrick Stolee
2022-09-07 20:44 ` Jeff King
2022-09-06 23:05 ` [PATCH 2/3] upload-pack: skip parse-object re-hashing of "want" objects Jeff King
2022-09-07 14:36 ` Derrick Stolee [this message]
2022-09-07 14:45 ` Derrick Stolee
2022-09-07 20:50 ` Jeff King
2022-09-07 19:26 ` Junio C Hamano
2022-09-07 20:36 ` Jeff King
2022-09-07 20:48 ` [BUG] t1800: Fails for error text comparison rsbecker
2022-09-07 21:55 ` Junio C Hamano
2022-09-07 22:23 ` rsbecker
2022-09-07 21:02 ` [PATCH 2/3] upload-pack: skip parse-object re-hashing of "want" objects Jeff King
2022-09-07 22:07 ` Junio C Hamano
2022-09-08 5:04 ` Jeff King
2022-09-08 16:41 ` Junio C Hamano
2022-09-06 23:06 ` [PATCH 3/3] parse_object(): check commit-graph when skip_hash set Jeff King
2022-09-07 14:46 ` Derrick Stolee
2022-09-07 19:31 ` Junio C Hamano
2022-09-08 10:39 ` [External Mail]Re: " 程洋
2022-09-08 18:42 ` Jeff King
2022-09-07 14:48 ` [PATCH 0/3] speeding up on-demand fetch for blobs in partial clone Derrick Stolee
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