Re: Performance regression on git fetch in 2.21

[Orgad Shaneh <orgads@gmail.com>]

On Fri, May 24, 2019 at 12:14 PM Orgad Shaneh <orgads@gmail.com> wrote:
>
> Hi,
>
> git fetch in my repository *when nothing new is received* takes 2.5x
> the time when comparing 2.20 against 2.21 (on Windows it's 4x).
>
> I have 5 initialized submodules in this working directory.
>
> I reported this issue on git-for-windows github:
> https://github.com/git-for-windows/git/issues/2199 but there is also
> an upstream change related.
>
> I bisected and found this commit to blame:
>
> Building... Fetching... Failed [10.7949124]
> Bisecting: 0 revisions left to test after this (roughly 0 steps)
> [a62387b3fc9f5aeeb04a2db278121d33a9caafa7] submodule.c: fetch in
> submodules git directory instead of in worktree
> running git-bisect.rb
> Building... Fetching... Success [4.303592]
> be76c2128234d94b47f7087152ee55d08bb65d88 is the first bad commit
> commit be76c2128234d94b47f7087152ee55d08bb65d88
> Author: Stefan Beller <sbeller@google.com>
> Date:   Thu Dec 6 13:26:55 2018 -0800
>
>     fetch: ensure submodule objects fetched
>
>     Currently when git-fetch is asked to recurse into submodules, it dispatches
>     a plain "git-fetch -C <submodule-dir>" (with some submodule related options
>     such as prefix and recusing strategy, but) without any information of the
>     remote or the tip that should be fetched.
>
>     But this default fetch is not sufficient, as a newly fetched commit in
>     the superproject could point to a commit in the submodule that is not
>     in the default refspec. This is common in workflows like Gerrit's.
>     When fetching a Gerrit change under review (from refs/changes/??), the
>     commits in that change likely point to submodule commits that have not
>     been merged to a branch yet.
>
>     Fetch a submodule object by id if the object that the superproject
>     points to, cannot be found. For now this object is fetched from the
>     'origin' remote as we defer getting the default remote to a later patch.
>
>     A list of new submodule commits are already generated in certain
>     conditions (by check_for_new_submodule_commits()); this new feature
>     invokes that function in more situations.
>
>     The submodule checks were done only when a ref in the superproject
>     changed, these checks were extended to also be performed when fetching
>     into FETCH_HEAD for completeness, and add a test for that too.
>
>     Signed-off-by: Stefan Beller <sbeller@google.com>
>     Signed-off-by: Junio C Hamano <gitster@pobox.com>
>
> :040000 040000 2bad86c248b79ef1e36ea5edaa423cd73445c9a2
> ad989a8f3e6f80d4f5a84ec3db0ff1ab00a7e210 M      builtin
> :100644 100644 d1b6646f42d5d12740a94f50a7d25aad4aa356bf
> b88343d977d78364b417e2015eaa352dec1501b9 M      submodule.c
> :040000 040000 a3c58919de0796b6467709a0f21fa21e28d4d13b
> cdf9514c9085efcbfcdba8efc765174f6455ce5d M      t
>
> Can you please suggest a fix? Is this the expected behavior?
>
> Thanks,
> - Orgad

ping

- Orgad