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From: Derrick Stolee <stolee@gmail.com>
To: "Ævar Arnfjörð Bjarmason" <avarab@gmail.com>
Cc: "Git List" <git@vger.kernel.org>,
	"Nguyễn Thái Ngọc Duy" <pclouds@gmail.com>,
	"SZEDER Gábor" <szeder.dev@gmail.com>,
	"Jeff King" <peff@peff.net>, "Stefan Beller" <sbeller@google.com>
Subject: Re: [RFC PATCH] We should add a "git gc --auto" after "git clone" due to commit graph
Date: Fri, 5 Oct 2018 09:45:47 -0400
Message-ID: <05fefab0-4012-4ef0-5df1-2430eea2bf4d@gmail.com> (raw)
In-Reply-To: <87ftxkh7bf.fsf@evledraar.gmail.com>

On 10/5/2018 9:05 AM, Ævar Arnfjörð Bjarmason wrote:
> On Fri, Oct 05 2018, Derrick Stolee wrote:
>
>> On 10/4/2018 5:42 PM, Ævar Arnfjörð Bjarmason wrote:
>>> I don't have time to polish this up for submission now, but here's a WIP
>>> patch that implements this, highlights:
>>>
>>>    * There's a gc.clone.autoDetach=false default setting which overrides
>>>      gc.autoDetach if 'git gc --auto' is run via git-clone (we just pass a
>>>      --cloning option to indicate this).
>> I'll repeat that it could make sense to do the same thing on clone
>> _and_ fetch. Perhaps a "--post-fetch" flag would be good here to
>> communicate that we just downloaded a pack from a remote.
> I don't think that makes sense, but let's talk about why, because maybe
> I've missed something, you're certainly more familiar with the
> commit-graph than I am.
>
> The reason to do it on clone as a special-case or when the file is
> missing, is because we know the file is desired (via the GC config), and
> presumably is expected to help performance, and we have 0% of it. So by
> going from 0% to 100% on clone we'll get fast --contains and other
> goodies the graph helps with.
>
> But when we're doing a fetch, or really anything else that runs "git gc
> --auto" we can safely assume that we have a recent enough graph, because
> it will have been run whenever auto-gc kicked in.
>
> I.e.:
>
>      # Slow, if we assume background forked commit-graph generation
>      # (which I'm avoiding)
>      git clone x && cd x && git tag --contains
>      # Fast enough, since we have an existing commit-graph
>      cd x && git fetch && git tag --contains
>
> I *do* think it might make sense to in general split off parts of "gc
> --auto" that we'd like to be more aggressive about, simply because the
> ratio of how long it takes to do, and how much it helps with performance
> makes more sense than a full repack, which is what the current heuristic
> is based on.
>
> And maybe when we run in that mode we should run in the foreground, but
> I don't see why git-fetch should be a special case there, and in this
> regard, the gc.clone.autoDetach=false setting I've made doesn't make
> much sence. I.e. maybe we should also skip forking to the background in
> such a mode when we trigger such a "mini gc" via git-commit or whatever.

My misunderstanding was that your proposed change to gc computes the 
commit-graph in either of these two cases:

(1) The auto-GC threshold is met.

(2) There is no commit-graph file.

And what I hope to have instead of (2) is (3):

(3) The commit-graph file is "sufficiently behind" the tip refs.

This condition is intentionally vague at the moment. It could be that we 
hint that (3) holds by saying "--post-fetch" (i.e. "We just downloaded a 
pack, and it probably contains a lot of new commits") or we could create 
some more complicated condition based on counting reachable commits with 
infinite generation number (the number of commits not in the 
commit-graph file).

I like that you are moving forward to make the commit-graph be written 
more frequently, but I'm trying to push us in a direction of writing it 
even more often than your proposed strategy. We should avoid creating 
too many orthogonal conditions that trigger the commit-graph write, 
which is why I'm pushing on your design here.

Anyone else have thoughts on this direction?

Thanks,

-Stolee


  reply index

Thread overview: 76+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-10-03 13:23 Ævar Arnfjörð Bjarmason
2018-10-03 13:36 ` SZEDER Gábor
2018-10-03 13:42   ` Derrick Stolee
2018-10-03 14:18     ` Ævar Arnfjörð Bjarmason
2018-10-03 14:01   ` Ævar Arnfjörð Bjarmason
2018-10-03 14:17     ` SZEDER Gábor
2018-10-03 14:22       ` Ævar Arnfjörð Bjarmason
2018-10-03 14:53         ` SZEDER Gábor
2018-10-03 15:19           ` Ævar Arnfjörð Bjarmason
2018-10-03 16:59             ` SZEDER Gábor
2018-10-05  6:09               ` Junio C Hamano
2018-10-10 22:07                 ` SZEDER Gábor
2018-10-10 23:01                   ` Ævar Arnfjörð Bjarmason
2018-10-03 19:08           ` Stefan Beller
2018-10-03 19:21             ` Jeff King
2018-10-03 20:35               ` Ævar Arnfjörð Bjarmason
2018-10-03 17:47         ` Stefan Beller
2018-10-03 18:47           ` Ævar Arnfjörð Bjarmason
2018-10-03 18:51             ` Jeff King
2018-10-03 18:59               ` Derrick Stolee
2018-10-03 19:18                 ` Jeff King
2018-10-08 16:41                   ` SZEDER Gábor
2018-10-08 16:57                     ` Derrick Stolee
2018-10-08 18:10                       ` SZEDER Gábor
2018-10-08 18:29                         ` Derrick Stolee
2018-10-09  3:08                           ` Jeff King
2018-10-09 13:48                             ` Bloom Filters (was Re: We should add a "git gc --auto" after "git clone" due to commit graph) Derrick Stolee
2018-10-09 18:45                               ` Ævar Arnfjörð Bjarmason
2018-10-09 18:46                               ` Jeff King
2018-10-09 19:03                                 ` Derrick Stolee
2018-10-09 21:14                                   ` Jeff King
2018-10-09 23:12                                     ` Bloom Filters Jeff King
2018-10-09 23:13                                       ` [PoC -- do not apply 1/3] initial tree-bitmap proof of concept Jeff King
2018-10-09 23:14                                       ` [PoC -- do not apply 2/3] test-tree-bitmap: add "dump" mode Jeff King
2018-10-10  0:48                                         ` Junio C Hamano
2018-10-11  3:13                                           ` Jeff King
2018-10-09 23:14                                       ` [PoC -- do not apply 3/3] test-tree-bitmap: replace ewah with custom rle encoding Jeff King
2018-10-10  0:58                                         ` Junio C Hamano
2018-10-11  3:20                                           ` Jeff King
2018-10-11 12:33                                       ` Bloom Filters Derrick Stolee
2018-10-11 13:43                                         ` Jeff King
2018-10-09 21:30                             ` We should add a "git gc --auto" after "git clone" due to commit graph SZEDER Gábor
2018-10-09 19:34                       ` [PATCH 0/4] Bloom filter experiment SZEDER Gábor
2018-10-09 19:34                         ` [PATCH 1/4] Add a (very) barebones Bloom filter implementation SZEDER Gábor
2018-10-09 19:34                         ` [PATCH 2/4] commit-graph: write a Bloom filter containing changed paths for each commit SZEDER Gábor
2018-10-09 21:06                           ` Jeff King
2018-10-09 21:37                             ` SZEDER Gábor
2018-10-09 19:34                         ` [PATCH 3/4] revision.c: use the Bloom filter to speed up path-limited revision walks SZEDER Gábor
2018-10-09 19:34                         ` [PATCH 4/4] revision.c: add GIT_TRACE_BLOOM_FILTER for a bit of statistics SZEDER Gábor
2018-10-09 19:47                         ` [PATCH 0/4] Bloom filter experiment Derrick Stolee
2018-10-11  1:21                         ` [PATCH 0/2] Per-commit filter proof of concept Jonathan Tan
2018-10-11  1:21                           ` [PATCH 1/2] One filter per commit Jonathan Tan
2018-10-11  1:21                           ` [PATCH 2/2] Only make bloom filter for first parent Jonathan Tan
2018-10-11  7:37                           ` [PATCH 0/2] Per-commit filter proof of concept Ævar Arnfjörð Bjarmason
2018-10-15 14:39                         ` [PATCH 0/4] Bloom filter experiment Derrick Stolee
2018-10-16  4:45                           ` Junio C Hamano
2018-10-16 11:13                             ` Derrick Stolee
2018-10-16 12:57                               ` Ævar Arnfjörð Bjarmason
2018-10-16 13:03                                 ` Derrick Stolee
2018-10-18  2:00                                 ` Junio C Hamano
2018-10-16 23:41                           ` Jonathan Tan
2018-10-08 23:02                     ` We should add a "git gc --auto" after "git clone" due to commit graph Junio C Hamano
2018-10-03 14:32     ` Duy Nguyen
2018-10-03 16:45 ` Duy Nguyen
2018-10-04 21:42 ` [RFC PATCH] " Ævar Arnfjörð Bjarmason
2018-10-05 12:05   ` Derrick Stolee
2018-10-05 13:05     ` Ævar Arnfjörð Bjarmason
2018-10-05 13:45       ` Derrick Stolee [this message]
2018-10-05 14:04         ` Ævar Arnfjörð Bjarmason
2018-10-05 19:21         ` Jeff King
2018-10-05 19:41           ` Derrick Stolee
2018-10-05 19:47             ` Jeff King
2018-10-05 20:00               ` Derrick Stolee
2018-10-05 20:02                 ` Jeff King
2018-10-05 20:01               ` Ævar Arnfjörð Bjarmason
2018-10-05 20:09                 ` Jeff King
2018-10-11 12:49 [PATCH 1/2] One filter per commit Derrick Stolee
2018-10-11 19:11 ` [PATCH] Per-commit and per-parent filters for 2 parents Jonathan Tan

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