From: Derrick Stolee <stolee@xxxxxxxxx>
This test helps inform someone as to the behavior of the name-hash
algorithms for their repo based on the paths at HEAD.
For example, the microsoft/fluentui repo had these statistics at time of
committing:
Test this tree
-----------------------------------------------------------------
5314.1: paths at head 19.6K
5314.2: number of distinct name-hashes 8.2K
5314.3: number of distinct full-name-hashes 19.6K
5314.4: maximum multiplicity of name-hashes 279
5314.5: maximum multiplicity of fullname-hashes 1
That demonstrates that of the nearly twenty thousand path names, they
are assigned around eight thousand distinct values. 279 paths are
assigned to a single value, leading the packing algorithm to sort
objects from those paths together, by size.
In this repository, no collisions occur for the full-name-hash
algorithm.
In a more extreme example, an internal monorepo had a much worse
collision rate:
Test this tree
-----------------------------------------------------------------
5314.1: paths at head 221.6K
5314.2: number of distinct name-hashes 72.0K
5314.3: number of distinct full-name-hashes 221.6K
5314.4: maximum multiplicity of name-hashes 14.4K
5314.5: maximum multiplicity of fullname-hashes 2
Even in this repository with many more paths at HEAD, the collision rate
was low and the maximum number of paths being grouped into a single
bucket by the full-path-name algorithm was two.
Signed-off-by: Derrick Stolee <stolee@xxxxxxxxx>
---
t/perf/p5314-name-hash.sh | 41 +++++++++++++++++++++++++++++++++++++++
1 file changed, 41 insertions(+)
create mode 100755 t/perf/p5314-name-hash.sh
diff --git a/t/perf/p5314-name-hash.sh b/t/perf/p5314-name-hash.sh
new file mode 100755
index 00000000000..9fe26612fac
--- /dev/null
+++ b/t/perf/p5314-name-hash.sh
@@ -0,0 +1,41 @@
+#!/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_size 'paths at head' '
+ git ls-tree -r --name-only HEAD >path-list &&
+ wc -l <path-list
+'
+
+test_size 'number of distinct name-hashes' '
+ cat path-list | test-tool name-hash >name-hashes &&
+ cat name-hashes | awk "{ print \$1; }" | sort -n | uniq -c >name-hash-count &&
+ wc -l <name-hash-count
+'
+
+test_size 'number of distinct full-name-hashes' '
+ cat name-hashes | awk "{ print \$2; }" | sort -n | uniq -c >full-name-hash-count &&
+ wc -l <full-name-hash-count
+'
+
+test_size 'maximum multiplicity of name-hashes' '
+ cat name-hash-count | \
+ sort -nr | \
+ head -n 1 | \
+ awk "{ print \$1; }"
+'
+
+test_size 'maximum multiplicity of fullname-hashes' '
+ cat full-name-hash-count | \
+ sort -nr | \
+ head -n 1 | \
+ awk "{ print \$1; }"
+'
+
+test_done
--
gitgitgadget
