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add: allow operating on a sparse-only index

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Disable command_requires_full_index for 'git add'. This does not require
any additional removals of ensure_full_index(). The main reason is that
'git add' discovers changes based on the pathspec and the worktree
itself. These are then inserted into the index directly, and calls to
index_name_pos() or index_file_exists() already call expand_to_path() at
the appropriate time to support a sparse-index.

Add a test to check that 'git add -A' and 'git add <file>' does not
expand the index at all, as long as <file> is not within a sparse
directory. This does not help the global 'git add .' case.

We can measure the improvement using p2000-sparse-operations.sh with
these results:

Test                                  HEAD~1           HEAD
------------------------------------------------------------------------------
2000.6: git add -A (full-index-v3)    0.35(0.30+0.05)  0.37(0.29+0.06) +5.7%
2000.7: git add -A (full-index-v4)    0.31(0.26+0.06)  0.33(0.27+0.06) +6.5%
2000.8: git add -A (sparse-index-v3)  0.57(0.53+0.07)  0.05(0.04+0.08) -91.2%
2000.9: git add -A (sparse-index-v4)  0.58(0.55+0.06)  0.05(0.05+0.06) -91.4%

While the 91% improvement seems impressive, it's important to recognize
that previously we had significant overhead for expanding the
sparse-index. Comparing to the full index case, 'git add -A' goes from
0.37s to 0.05s, which is "only" an 86% improvement.

This modification to 'git add' creates some behavior change depending on
the use of a sparse index. We modify a test in t1092 to demonstrate
these changes which will be remedied in future changes.

Reviewed-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Derrick Stolee
2021-07-29 14:52:04 +00:00
committed by Junio C Hamano
parent 83ad8ca596
commit 5e7cbab196
2 changed files with 21 additions and 7 deletions
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3
builtin/add.c
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@ -528,6 +528,9 @@ int cmd_add(int argc, const char **argv, const char *prefix)
add_new_files = !take_worktree_changes && !refresh_only && !add_renormalize;
require_pathspec = !(take_worktree_changes || (0 < addremove_explicit));
prepare_repo_settings(the_repository);
the_repository->settings.command_requires_full_index = 0;
hold_locked_index(&lock_file, LOCK_DIE_ON_ERROR);
/*