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

Hi Victoria,

On Tue, Oct 5, 2021 at 6:20 AM Victoria Dye via GitGitGadget
[off-list ref] 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.