Re: [PATCH v2 0/7] Sparse Index: integrate with reset

[Elijah Newren <newren@gmail.com>]

Hi Victoria,

On Tue, Oct 5, 2021 at 6:20 AM Victoria Dye via GitGitGadget
<gitgitgadget@gmail.com> wrote:
>
> This series integrates the sparse index with git reset and provides
> miscellaneous fixes and improvements to the command in sparse checkouts.
> This includes:
>
>  1. tests added to t1092 and p2000 to establish the baseline functionality
>     of the command
>  2. repository settings to enable the sparse index with ensure_full_index
>     guarding any code paths that break tests without other compatibility
>     updates.
>  3. modifications to remove or reduce the scope in which ensure_full_index
>     must be called.
>
> The sparse index updates are predicated on a fix originating from the
> microsoft/git fork [1], correcting how git reset --mixed handles resetting
> entries outside the sparse checkout definition. Additionally, a performance
> "bug" in next_cache_entry with sparse index is corrected, preventing
> repeatedly looping over already-searched entries.
>
> The p2000 tests demonstrate an overall ~70% execution time reduction across
> all tested usages of git reset using a sparse index:
>
> Test                                               before   after
> ------------------------------------------------------------------------
> 2000.22: git reset (full-v3)                       0.48     0.51 +6.3%
> 2000.23: git reset (full-v4)                       0.47     0.50 +6.4%
> 2000.24: git reset (sparse-v3)                     0.93     0.30 -67.7%
> 2000.25: git reset (sparse-v4)                     0.94     0.29 -69.1%
> 2000.26: git reset --hard (full-v3)                0.69     0.68 -1.4%
> 2000.27: git reset --hard (full-v4)                0.75     0.68 -9.3%
> 2000.28: git reset --hard (sparse-v3)              1.29     0.34 -73.6%
> 2000.29: git reset --hard (sparse-v4)              1.31     0.34 -74.0%
> 2000.30: git reset -- does-not-exist (full-v3)     0.54     0.51 -5.6%
> 2000.31: git reset -- does-not-exist (full-v4)     0.54     0.52 -3.7%
> 2000.32: git reset -- does-not-exist (sparse-v3)   1.02     0.31 -69.6%
> 2000.33: git reset -- does-not-exist (sparse-v4)   1.07     0.30 -72.0%
>
>
>
> Changes since V1
> ================
>
>  * Add --force-full-index option to update-index. The option is used
>    circumvent changing command_requires_full_index from its default value -
>    right now this is effectively a no-op, but will change once update-index
>    is integrated with sparse index. By using this option in the t1092
>    expand/collapse test, the command used to test will not need to be
>    updated with subsequent sparse index integrations.
>  * Update implementation of mixed reset for entries outside sparse checkout
>    definition. The condition in which a file should be checked out before
>    index reset is simplified to "if it has skip-worktree enabled and a reset
>    would change the file, check it out".
>    * After checking the behavior of update_index_from_diff with renames,
>      found that the diff used by reset does not produce diff queue entries
>      with different pathnames for one and two. Because of this, and that
>      nothing in the implementation seems to rely on identical path names, no
>      BUG check is added.
>  * Correct a bug in the sparse index is not expanded tests in t1092 where
>    failure of a git reset --mixed test was not being reported. Test now
>    verifies an appropriate scenario with corrected failure-checking.

I read over the first six patches.  I tried to read over the seventh,
but I've never figured out cache_bottom for some reason and I did
nothing beyond spot checking when Stolee touched that area either.

Anyway, I had lots of little comments, tweaks to the way to fix the
inconsistency in patch 1, various questions, etc.  It probably adds up
to a lot, but it's all small fixable stuff; overall it looks like you
(and Kevin) are making a solid contribution on the sparse-checkout
stuff; I look forward to reading the next round.