Re: [PATCH 0/3] Make add_missing_tags() linear

From: Derrick Stolee <stolee@gmail.com>
To: Elijah Newren <newren@gmail.com>
Cc: Git Mailing List <git@vger.kernel.org>,
	Junio C Hamano <gitster@pobox.com>, Jeff King <peff@peff.net>,
	Derrick Stolee <dstolee@microsoft.com>
Subject: Re: [PATCH 0/3] Make add_missing_tags() linear
Date: Fri, 2 Nov 2018 11:38:55 -0400	[thread overview]
Message-ID: <ba7ee399-029d-8cff-c582-c3e54ab61796@gmail.com> (raw)
In-Reply-To: <CABPp-BEa3U6m8jWrHJXjFo77T32LqEKkdDs7H89m0y_gjHgOWw@mail.gmail.com>

On 11/2/2018 10:58 AM, Elijah Newren wrote:
> On Thu, Nov 1, 2018 at 12:02 PM Derrick Stolee <stolee@gmail.com> wrote:
>> On 11/1/2018 2:57 PM, Elijah Newren wrote:
>>> On Thu, Nov 1, 2018 at 5:32 AM Derrick Stolee <stolee@gmail.com> wrote:
>>>> No rush. I'd just like to understand how removing the commit-graph file
>>>> can make the new algorithm faster. Putting a similar count in the old
>>>> algorithm would involve giving a count for every call to
>>>> in_merge_bases_many(), which would be very noisy.
>>> $ time git push --dry-run --follow-tags /home/newren/repo-mirror
>>> count: 92912
>>> To /home/newren/repo-mirror
>>>    * [new branch]              test5 -> test5
>>>
>>> real    0m3.024s
>>> user    0m2.752s
>>> sys    0m0.320s
>> Is the above test with or without the commit-graph file? Can you run it
>> in the other mode, too? I'd like to see if the "count" value changes
>> when the only difference is the presence of a commit-graph file.
> I apologize for providing misleading information earlier; this was an
> apples to oranges comparison.  Here's what I did:
>
> <build a version of git with your fixes>
> git clone coworker.bundle coworker-repo
> cd coworker-repo
> time git push --dry-run --follow-tags /home/newren/repo-mirror
> git config core.commitgraph true
> git config gc.writecommitgraph true
> git gc
> time git push --dry-run --follow-tags /home/newren/nucleus-mirror
>
>
> I figured I had just done a fresh clone, so surely the gc wouldn't do
> anything other than write the .git/objects/info/commit-graph file.
> However, the original bundle contained many references outside of
> refs/heads/ and refs/tags/:
>
> $ git bundle list-heads ../coworker.bundle | grep -v -e refs/heads/ -e
> refs/tags/ -e HEAD | wc -l
> 2396
>
> These other refs apparently referred to objects not otherwise
> referenced in refs/heads/ and refs/tags/, and caused the gc to explode
> lots of loose objects:
> $ git count-objects -v
> count: 147604
> size: 856416
> in-pack: 1180692
> packs: 1
> size-pack: 796143
> prune-packable: 0
> garbage: 0
> size-garbage: 0
>
>
> The slowdown with commit-graph was entirely due to there being lots of
> loose objects (147K of them).  If I add a git-prune before doing the
> timing with commit-graph, then the timing with commit-graph is faster
> than the run without a commit-graph.
>
> Sorry for the wild goose chase.
>
> And thanks for the fixes; get_reachable_subset() makes things much
> faster even without a commit-graph, and the commit-graph just improves
> it more.  :-)

Thanks for double-checking! It's good to have confidence that this is a good

algorithm to use.

Thanks,

-Stolee