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From: Matheus Tavares Bernardino <matheus.bernardino@usp.br>
To: Elijah Newren <newren@gmail.com>
Cc: Git Mailing List <git@vger.kernel.org>,
	Derrick Stolee <dstolee@microsoft.com>,
	"brian m. carlson" <sandals@crustytoothpaste.net>,
	Stefan Beller <stefanbeller@gmail.com>,
	Jonathan Nieder <jrnieder@gmail.com>
Subject: Re: [RFC PATCH 2/3] grep: honor sparse checkout patterns
Date: Thu, 23 Apr 2020 03:09:30 -0300	[thread overview]
Message-ID: <CAHd-oW7xaLcBskLM6bgqgnLukXnwW+bWvGM24Ao_9UxKwdXi3A@mail.gmail.com> (raw)
In-Reply-To: <CABPp-BGUf-4exGW23xka1twf2D=nFOz1CkD_f-rDX_AGdVEeDA@mail.gmail.com>

On Tue, Apr 21, 2020 at 12:08 AM Elijah Newren <newren@gmail.com> wrote:
>
> On Mon, Apr 20, 2020 at 7:11 PM Matheus Tavares Bernardino
> <matheus.bernardino@usp.br> wrote:
> >
> > I've been working on the file skipping mechanism using the sparsity
> > patterns directly. But I'm uncertain about some implementation
> > details. So I wanted to share my current plan with you, to get some
> > feedback before going deeper.
> >
> > The first idea was to load the sparsity patterns a priori and pass
> > them to grep_tree(), which recursively greps the entries of a given
> > tree object. If --recurse-submodules is given, however, we would also
> > need to load each surepo's sparse-checkout file on the fly (as the
> > subrepos are lazily initialized in grep_tree()'s call chain). That's
> > not a problem on its own. But in the most naive implementation, this
> > means unnecessarily re-loading the sparse-checkout files of the
> > submodules for each tree given to git-grep (as grep_tree() is called
> > separately for each one of them).
>
> Wouldn't loading the sparse-checkout files be fast compared to
> grepping a submodule for matching strings?  And not just fast, but
> essentially in the noise and hard to even measure?  I have a hard time
> fathoming parsing the sparse-checkout file for a submodule somehow
> appreciably affecting the cost of grepping through that submodule.  If
> the submodule has a huge number of sparse-checkout patterns, that'll
> be because it has a ginormous number of files and grepping through
> them all would be way, way longer.  If the submodule only has a few
> files, then the sparse-checkout file is only going to be a few lines
> at most.

Yeah, makes sense.

> Also, from another angle: I think the original intent of submodules
> was an alternate form of sparse-checkout/partial-clone, letting people
> deal with just their piece of the repo.  As such, do we really even
> expect people to use sparse-checkouts and submodules together, let
> alone use them very heavily together?  Sure, someone will use them,
> but I have a hard time imagining the scale of use of both features
> heavily enough for this to matter, especially since it also requires
> specifying multiple trees to grep (which is slightly unusual) in
> addition to the combination of these other features before your
> optimization here could kick in and be worthwhile.
>
> I'd be very tempted to just implement the most naive implementation
> and maybe leave a TODO note in the code for some future person to come
> along and optimize if it really matters, but I'd like to see numbers
> before we spend the development and maintenance effort on it because
> I'm having a hard time imagining any scale where it could matter.

You're right. I guess I got a little too excited about the
optimizations possibilities and neglected the fact that they might not
even be needed here.

Just to take a look at some numbers, I prototyped the naive
implementation and downloaded a testing repository[1] containing 8
submodules (or 14 counting the nested ones). For each of the
non-nested submodules, I added its .gitignore rules to the
sparse-checkout file (of course this doesn't make any sense for a
real-world usage, but I just wanted to populate the file with a large
quantity of valid rules, to test the parsing time). I also added the
rule '/*'. Then I ran:

git-grep --threads=1 --recurse-submodules -E "config_[a-z]+\(" $(cat /tmp/trees)

Where /tmp/trees contained about 120 trees in the said repository
(again, a probably unreal case, for testing purposes only). Then,
measuring the time spent only inside the function I created to load a
sparse-checkout file for a given 'struct repository', I got to the
following numbers:

Number of calls: 1531 (makes sense: ~120 trees and 14 submodules)
Percentage over the total time: 0.015%
Number of matches: 300897

And using 8 threads, I got the same numbers except for the percentage,
which was a little higher: 0.05%.

So, indeed, the overhead of re-loading the files is too insignificant.
And my cache idea was a premature and unnecessary optimization.

> > So my next idea was to implement a cache, mapping 'struct repository's
> > to 'struct pattern_list'. Well, not 'struct repository' itself, but
> > repo->gitdir. This way we could load each file once, store the pattern
> > list, and quickly retrieve the one that affect the repository
> > currently being grepped, whether it is a submodule or not. But, is
> > gitidir unique per repository? If not, could we use
> > repo_git_path(repo, "info/sparse-checkout") as the key?
> >
> > I already have a prototype implementation of the last idea (using
> > repo_git_path()). But I wanted to make sure, does this seem like a
> > good path? Or should we avoid the work of having this hashmap here and
> > do something else, as adding a 'struct pattern_list' to 'struct
> > repository', directly?
>
> Honestly, it sounds a bit like premature optimization to me.  Sorry if
> that's disappointing since you've apparently already put some effort
> into this, and it sounds like you're on a good track for optimizing
> this if it were necessary, but I'm just having a hard time figuring
> out whether it'd really help and be worth the code complexity.

No problem! I'm glad to have this feedback now, while I'm still
working on v2  :) Now I can focus on what's really relevant. So thanks
again!

[1]: https://github.com/surevine/Metre

  parent reply	other threads:[~2020-04-23  6:09 UTC|newest]

Thread overview: 123+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-03-24  6:04 [RFC PATCH 0/3] grep: honor sparse checkout and add option to ignore it Matheus Tavares
2020-03-24  6:11 ` [RFC PATCH 1/3] doc: grep: unify info on configuration variables Matheus Tavares
2020-03-24  7:57   ` Elijah Newren
2020-03-24 21:26     ` Junio C Hamano
2020-03-24 23:38       ` Matheus Tavares
2020-03-24  6:12 ` [RFC PATCH 2/3] grep: honor sparse checkout patterns Matheus Tavares
2020-03-24  7:15   ` Elijah Newren
2020-03-24 15:12     ` Derrick Stolee
2020-03-24 16:16       ` Elijah Newren
2020-03-24 17:02         ` Derrick Stolee
2020-03-24 23:01       ` Matheus Tavares Bernardino
2020-03-24 22:55     ` Matheus Tavares Bernardino
2020-04-21  2:10       ` Matheus Tavares Bernardino
2020-04-21  3:08         ` Elijah Newren
2020-04-22 12:08           ` Derrick Stolee
2020-04-23  6:09           ` Matheus Tavares Bernardino [this message]
2020-03-24  6:13 ` [RFC PATCH 3/3] grep: add option to ignore sparsity patterns Matheus Tavares
2020-03-24  7:54   ` Elijah Newren
2020-03-24 18:30     ` Junio C Hamano
2020-03-24 19:07       ` Elijah Newren
2020-03-25 20:18         ` Junio C Hamano
2020-03-30  3:23       ` Matheus Tavares Bernardino
2020-03-31 19:12         ` Elijah Newren
2020-03-31 20:02           ` Derrick Stolee
2020-04-27 17:15             ` Matheus Tavares Bernardino
2020-04-29 16:46               ` Elijah Newren
2020-04-29 17:21             ` Elijah Newren
2020-03-25 23:15     ` Matheus Tavares Bernardino
2020-03-26  6:02       ` Elijah Newren
2020-03-27 15:51         ` Junio C Hamano
2020-03-27 19:01           ` Elijah Newren
2020-03-30  1:12         ` Matheus Tavares Bernardino
2020-03-31 16:48           ` Elijah Newren
2020-05-10  0:41 ` [RFC PATCH v2 0/4] grep: honor sparse checkout and add option to ignore it Matheus Tavares
2020-05-10  0:41   ` [RFC PATCH v2 1/4] doc: grep: unify info on configuration variables Matheus Tavares
2020-05-10  0:41   ` [RFC PATCH v2 2/4] config: load the correct config.worktree file Matheus Tavares
2020-05-11 19:10     ` Junio C Hamano
2020-05-12 22:55       ` Matheus Tavares Bernardino
2020-05-12 23:22         ` Junio C Hamano
2020-05-10  0:41   ` [RFC PATCH v2 3/4] grep: honor sparse checkout patterns Matheus Tavares
2020-05-11 19:35     ` Junio C Hamano
2020-05-13  0:05       ` Matheus Tavares Bernardino
2020-05-13  0:17         ` Junio C Hamano
2020-05-21  7:26           ` Elijah Newren
2020-05-21 17:35             ` Matheus Tavares Bernardino
2020-05-21 17:52               ` Elijah Newren
2020-05-22  5:49                 ` Matheus Tavares Bernardino
2020-05-22 14:26                   ` Elijah Newren
2020-05-22 15:36                     ` Elijah Newren
2020-05-22 20:54                       ` Matheus Tavares Bernardino
2020-05-22 21:06                         ` Elijah Newren
2020-06-10 11:40                     ` Derrick Stolee
2020-06-10 16:22                       ` Matheus Tavares Bernardino
2020-06-10 17:42                         ` Derrick Stolee
2020-06-10 18:14                           ` Matheus Tavares Bernardino
2020-06-10 20:12                         ` Elijah Newren
2020-06-10 19:58                       ` Elijah Newren
2020-05-21  7:36       ` Elijah Newren
2020-05-10  0:41   ` [RFC PATCH v2 4/4] config: add setting to ignore sparsity patterns in some cmds Matheus Tavares
2020-05-10  4:23     ` Matheus Tavares Bernardino
2020-05-21 17:18       ` Elijah Newren
2020-05-21  7:09     ` Elijah Newren
2020-05-28  1:12   ` [PATCH v3 0/5] grep: honor sparse checkout and add option to ignore it Matheus Tavares
2020-05-28  1:12     ` [PATCH v3 1/5] doc: grep: unify info on configuration variables Matheus Tavares
2020-05-28  1:13     ` [PATCH v3 2/5] t/helper/test-config: return exit codes consistently Matheus Tavares
2020-05-30 14:29       ` Elijah Newren
2020-06-01  4:36         ` Matheus Tavares Bernardino
2020-05-28  1:13     ` [PATCH v3 3/5] config: correctly read worktree configs in submodules Matheus Tavares
2020-05-30 14:49       ` Elijah Newren
2020-06-01  4:38         ` Matheus Tavares Bernardino
2020-05-28  1:13     ` [PATCH v3 4/5] grep: honor sparse checkout patterns Matheus Tavares
2020-05-30 15:48       ` Elijah Newren
2020-06-01  4:44         ` Matheus Tavares Bernardino
2020-06-03  2:38           ` Elijah Newren
2020-06-10 17:08             ` Matheus Tavares Bernardino
2020-05-28  1:13     ` [PATCH v3 5/5] config: add setting to ignore sparsity patterns in some cmds Matheus Tavares
2020-05-30 16:18       ` Elijah Newren
2020-06-01  4:45         ` Matheus Tavares Bernardino
2020-06-03  2:39           ` Elijah Newren
2020-06-10 21:15             ` Matheus Tavares Bernardino
2020-06-11  0:35               ` Elijah Newren
2020-06-12 15:44     ` [PATCH v4 0/6] grep: honor sparse checkout and add option to ignore it Matheus Tavares
2020-06-12 15:44       ` [PATCH v4 1/6] doc: grep: unify info on configuration variables Matheus Tavares
2020-06-12 15:45       ` [PATCH v4 2/6] t/helper/test-config: return exit codes consistently Matheus Tavares
2020-06-12 15:45       ` [PATCH v4 3/6] t/helper/test-config: facilitate addition of new cli options Matheus Tavares
2020-06-12 15:45       ` [PATCH v4 4/6] config: correctly read worktree configs in submodules Matheus Tavares
2020-06-16 19:13         ` Elijah Newren
2020-06-21 16:05           ` Matheus Tavares Bernardino
2020-09-01  2:41         ` Jonathan Nieder
2020-09-01 21:44           ` Matheus Tavares Bernardino
2020-06-12 15:45       ` [PATCH v4 5/6] grep: honor sparse checkout patterns Matheus Tavares
2020-06-12 15:45       ` [PATCH v4 6/6] config: add setting to ignore sparsity patterns in some cmds Matheus Tavares
2020-06-16 22:31       ` [PATCH v4 0/6] grep: honor sparse checkout and add option to ignore it Elijah Newren
2020-09-02  6:17       ` [PATCH v5 0/8] " Matheus Tavares
2020-09-02  6:17         ` [PATCH v5 1/8] doc: grep: unify info on configuration variables Matheus Tavares
2020-09-02  6:17         ` [PATCH v5 2/8] t1308-config-set: avoid false positives when using test-config Matheus Tavares
2020-09-02  6:57           ` Eric Sunshine
2020-09-02 16:16             ` Matheus Tavares Bernardino
2020-09-02 16:38               ` Eric Sunshine
2020-09-02  6:17         ` [PATCH v5 3/8] t/helper/test-config: be consistent with exit codes Matheus Tavares
2020-09-02  6:17         ` [PATCH v5 4/8] t/helper/test-config: check argc before accessing argv Matheus Tavares
2020-09-02  7:18           ` Eric Sunshine
2020-09-02  6:17         ` [PATCH v5 5/8] t/helper/test-config: unify exit labels Matheus Tavares
2020-09-02  7:30           ` Eric Sunshine
2020-09-02  6:17         ` [PATCH v5 6/8] config: correctly read worktree configs in submodules Matheus Tavares
2020-09-02 20:15           ` Jonathan Nieder
2020-09-09 13:04             ` Matheus Tavares Bernardino
2020-09-09 23:32               ` Jonathan Nieder
2020-09-02  6:17         ` [PATCH v5 7/8] grep: honor sparse checkout patterns Matheus Tavares
2020-09-02  6:17         ` [PATCH v5 8/8] config: add setting to ignore sparsity patterns in some cmds Matheus Tavares
2020-09-10 17:21         ` [PATCH v6 0/9] grep: honor sparse checkout and add option to ignore it Matheus Tavares
2020-09-10 17:21           ` [PATCH v6 1/9] doc: grep: unify info on configuration variables Matheus Tavares
2020-09-10 17:21           ` [PATCH v6 2/9] t1308-config-set: avoid false positives when using test-config Matheus Tavares
2020-09-10 17:21           ` [PATCH v6 3/9] t/helper/test-config: be consistent with exit codes Matheus Tavares
2020-09-10 17:21           ` [PATCH v6 4/9] t/helper/test-config: diagnose missing arguments Matheus Tavares
2020-09-10 17:21           ` [PATCH v6 5/9] t/helper/test-config: unify exit labels Matheus Tavares
2020-09-10 17:21           ` [PATCH v6 6/9] config: make do_git_config_sequence receive a 'struct repository' Matheus Tavares
2020-09-10 17:21           ` [PATCH v6 7/9] config: correctly read worktree configs in submodules Matheus Tavares
2020-09-10 17:21           ` [PATCH v6 8/9] grep: honor sparse checkout patterns Matheus Tavares
2020-09-10 17:21           ` [PATCH v6 9/9] config: add setting to ignore sparsity patterns in some cmds Matheus Tavares
2021-02-09 21:33           ` [PATCH v7] grep: honor sparse-checkout on working tree searches Matheus Tavares
2021-02-09 23:23             ` Junio C Hamano
2021-02-10  6:12               ` Elijah Newren

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