[07/10] add: allow operating on a sparse-only index

Commit Message

Derrick Stolee April 13, 2021, 2:01 p.m. UTC

From: Derrick Stolee <[e-mail]>

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)    1.35(1.00+0.20)  1.33(0.98+0.19) -1.5%
2000.7: git add -A (full-index-v4)    1.25(0.97+0.17)  1.23(0.96+0.16) -1.6%
2000.8: git add -A (sparse-index-v3)  2.38(2.28+0.13)  0.06(0.04+0.08) -97.5%
2000.9: git add -A (sparse-index-v4)  2.39(2.25+0.18)  0.06(0.04+0.07) -97.5%

While the 97% 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
1.33s to 0.06s, which is "only" a 95% improvement.

Signed-off-by: Derrick Stolee <[e-mail]>
---
 builtin/add.c                            |  3 +++
 t/t1092-sparse-checkout-compatibility.sh | 12 ++++++++++++
 2 files changed, 15 insertions(+)

Patch

diff --git a/builtin/add.c b/builtin/add.c
index 58ee3f954ef7..0572d0344065 100644
--- a/builtin/add.c
+++ b/builtin/add.c
@@ -526,6 +526,9 @@  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);
 
 	/*
diff --git a/t/t1092-sparse-checkout-compatibility.sh b/t/t1092-sparse-checkout-compatibility.sh
index b937d7096afd..c210dba78067 100755
--- a/t/t1092-sparse-checkout-compatibility.sh
+++ b/t/t1092-sparse-checkout-compatibility.sh
@@ -459,6 +459,18 @@  test_expect_success 'sparse-index is not expanded' '
 	echo >>sparse-index/untracked.txt &&
 	GIT_TRACE2_EVENT="$(pwd)/trace2.txt" GIT_TRACE2_EVENT_NESTING=10 \
 		git -C sparse-index status &&
+	test_region ! index ensure_full_index trace2.txt &&
+
+	rm trace2.txt &&
+	echo >>sparse-index/README.md &&
+	GIT_TRACE2_EVENT="$(pwd)/trace2.txt" GIT_TRACE2_EVENT_NESTING=10 \
+		git -C sparse-index add -A &&
+	test_region ! index ensure_full_index trace2.txt &&
+
+	rm trace2.txt &&
+	echo >>sparse-index/extra.txt &&
+	GIT_TRACE2_EVENT="$(pwd)/trace2.txt" GIT_TRACE2_EVENT_NESTING=10 \
+		git -C sparse-index add extra.txt &&
 	test_region ! index ensure_full_index trace2.txt
 '