[PATCH v2 10/17] p5313: add performance tests for --path-walk

["Derrick Stolee via GitGitGadget" <gitgitgadget@gmail.com>]

From: Derrick Stolee <stolee@gmail.com>

The previous change added a --path-walk option to 'git pack-objects'.
Create a performance test that demonstrates the time and space benefits
of the feature.

In order to get an appropriate comparison, we need to avoid reusing
deltas and recompute them from scratch.

Compare the creation of a thin pack representing a small push and the
creation of a relatively large non-thin pack.

Running on my copy of the Git repository results in this data:

Test                                      this tree
---------------------------------------------------------
5313.2: thin pack                         0.01(0.00+0.00)
5313.3: thin pack size                               1.1K
5313.4: thin pack with --path-walk        0.01(0.01+0.00)
5313.5: thin pack size with --path-walk              1.1K
5313.6: big pack                          2.52(6.59+0.38)
5313.7: big pack size                               14.1M
5313.8: big pack with --path-walk         4.90(5.76+0.26)
5313.9: big pack size with --path-walk              13.2M

Note that the timing is slower because there is no threading in the
--path-walk case (yet).

The cases where the --path-walk option really shines is when the default
name-hash is overwhelmed with collisions. An open source example can be
found in the microsoft/fluentui repo [1] at a certain commit [2].

[1] https://github.com/microsoft/fluentui
[2] e70848ebac1cd720875bccaa3026f4a9ed700e08

Running the tests on this repo results in the following output:

Test                                      this tree
----------------------------------------------------------
5313.2: thin pack                         0.28(0.38+0.02)
5313.3: thin pack size                               1.2M
5313.4: thin pack with --path-walk        0.08(0.06+0.01)
5313.5: thin pack size with --path-walk             18.4K
5313.6: big pack                          4.05(29.62+0.43)
5313.7: big pack size                               20.0M
5313.8: big pack with --path-walk         5.99(9.06+0.24)
5313.9: big pack size with --path-walk              16.4M

Notice in particular that in the small thin pack, the time performance
has improved from 0.28s to 0.08s and this is likely due to the improved
size of the resulting pack: 18.4K instead of 1.2M.

Finally, running this on a copy of the Linux kernel repository results
in these data points:

Test                                      this tree
-----------------------------------------------------------
5313.2: thin pack                         0.00(0.00+0.00)
5313.3: thin pack size                               5.8K
5313.4: thin pack with --path-walk        0.00(0.01+0.00)
5313.5: thin pack size with --path-walk              5.8K
5313.6: big pack                          24.39(65.81+1.31)
5313.7: big pack size                              155.7M
5313.8: big pack with --path-walk         41.07(60.69+0.68)
5313.9: big pack size with --path-walk             150.8M

Signed-off-by: Derrick Stolee <stolee@gmail.com>
---
 t/perf/p5313-pack-objects.sh | 59 ++++++++++++++++++++++++++++++++++++
 1 file changed, 59 insertions(+)
 create mode 100755 t/perf/p5313-pack-objects.sh

diff --git a/t/perf/p5313-pack-objects.sh b/t/perf/p5313-pack-objects.sh
new file mode 100755
index 00000000000..840075f5691
--- /dev/null
+++ b/t/perf/p5313-pack-objects.sh
@@ -0,0 +1,59 @@
+#!/bin/sh
+
+test_description='Tests pack performance using bitmaps'
+. ./perf-lib.sh
+
+GIT_TEST_PASSING_SANITIZE_LEAK=0
+export GIT_TEST_PASSING_SANITIZE_LEAK
+
+test_perf_large_repo
+
+test_expect_success 'create rev input' '
+	cat >in-thin <<-EOF &&
+	$(git rev-parse HEAD)
+	^$(git rev-parse HEAD~1)
+	EOF
+
+	cat >in-big <<-EOF
+	$(git rev-parse HEAD)
+	^$(git rev-parse HEAD~1000)
+	EOF
+'
+
+test_perf 'thin pack' '
+	git pack-objects --thin --stdout --no-reuse-delta \
+		--revs --sparse <in-thin >out
+'
+
+test_size 'thin pack size' '
+	test_file_size out
+'
+
+test_perf 'thin pack with --path-walk' '
+	git pack-objects --thin --stdout --no-reuse-delta \
+		--revs --sparse --path-walk <in-thin >out
+'
+
+test_size 'thin pack size with --path-walk' '
+	test_file_size out
+'
+
+test_perf 'big pack' '
+	git pack-objects --stdout --no-reuse-delta --revs \
+		--sparse <in-big >out
+'
+
+test_size 'big pack size' '
+	test_file_size out
+'
+
+test_perf 'big pack with --path-walk' '
+	git pack-objects --stdout --no-reuse-delta --revs \
+		--sparse --path-walk <in-big >out
+'
+
+test_size 'big pack size with --path-walk' '
+	test_file_size out
+'
+
+test_done
-- 
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