[PATCH v4 5/8] p5303: measure time to repack with keep
- From
Taylor Blau <me@ttaylorr.com>
- Date
- Feb 23, 2021, 02:25 UTC
- Message-ID
- <94e4f3ee3af3181c3805ee397d043e343038005a.1614047097.git.me@ttaylorr.com>
- In-Reply-To
- <cover.1614047097.git.me@ttaylorr.com>
From: Jeff King <peff@peff.net>
Add two new tests to measure repack performance. Both tests split the repository into synthetic "pushes", and then leave the remaining objects in a big base pack.
The first new test marks an empty pack as "kept" and then passes --honor-pack-keep to avoid including objects in it. That doesn't change the resulting pack, but it does let us compare to the normal repack case to see how much overhead we add to check whether objects are kept or not.
The other test is of --stdin-packs, which gives us a sense of how that number scales based on the number of packs we provide as input. In each of those tests, the empty pack isn't considered, but the residual pack (objects that were left over and not included in one of the synthetic push packs) is marked as kept.
(Note that in the single-pack case of the --stdin-packs test, there is nothing do since there are no non-excluded packs).
Here are some timings on a recent clone of the kernel:
5303.5: repack (1) 57.26(54.59+10.84) 5303.6: repack with kept (1) 57.33(54.80+10.51)
in the 50-pack case, things start to slow down:
5303.11: repack (50) 71.54(88.57+4.84) 5303.12: repack with kept (50) 85.12(102.05+4.94)
and by the time we hit 1,000 packs, things are substantially worse, even though the resulting pack produced is the same:
5303.17: repack (1000) 216.87(490.79+14.57) 5303.18: repack with kept (1000) 665.63(938.87+15.76)
That's because the code paths around handling .keep files are known to scale badly; they look in every single pack file to find each object. Our solution to that was to notice that most repos don't have keep files, and to make that case a fast path. But as soon as you add a single .keep, that part of pack-objects slows down again (even if we have fewer objects total to look at).
Likewise, the scaling is pretty extreme on --stdin-packs (but each subsequent test is also being asked to do more work):
5303.7: repack with --stdin-packs (1) 0.01(0.01+0.00) 5303.13: repack with --stdin-packs (50) 3.53(12.07+0.24) 5303.19: repack with --stdin-packs (1000) 195.83(371.82+8.10)
Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: Taylor Blau <me@ttaylorr.com> --- t/perf/p5303-many-packs.sh | 34 ++++++++++++++++++++++++++++++++-- 1 file changed, 32 insertions(+), 2 deletions(-)
diff --git a/t/perf/p5303-many-packs.sh b/t/perf/p5303-many-packs.sh index d90d714923..35c0cbdf49 100755 --- a/t/perf/p5303-many-packs.sh +++ b/t/perf/p5303-many-packs.sh @@ -31,8 +31,15 @@ repack_into_n () { ' "$1" >pushes && # create base packfile - head -n 1 pushes | - git pack-objects --delta-base-offset --revs staging/pack && + base_pack=$( + head -n 1 pushes | + git pack-objects --delta-base-offset --revs staging/pack + ) && + test_export base_pack && + + # create an empty packfile + empty_pack=$(git pack-objects staging/pack </dev/null) && + test_export empty_pack && # and then incrementals between each pair of commits last= && @@ -49,6 +56,12 @@ repack_into_n () { last=$rev done <pushes && + ( + find staging -type f -name 'pack-*.pack' | + xargs -n 1 basename | grep -v "$base_pack" && + printf "^pack-%s.pack\n" $base_pack + ) >stdin.packs + # and install the whole thing rm -f .git/objects/pack/* && mv staging/* .git/objects/pack/ @@ -91,6 +104,23 @@ do --reflog --indexed-objects --delta-base-offset \ --stdout </dev/null >/dev/null ' + + test_perf "repack with kept ($nr_packs)" ' + git pack-objects --keep-true-parents \ + --keep-pack=pack-$empty_pack.pack \ + --honor-pack-keep --non-empty --all \ + --reflog --indexed-objects --delta-base-offset \ + --stdout </dev/null >/dev/null + ' + + test_perf "repack with --stdin-packs ($nr_packs)" ' + git pack-objects \ + --keep-true-parents \ + --stdin-packs \ + --non-empty \ + --delta-base-offset \ + --stdout <stdin.packs >/dev/null + ' done # Measure pack loading with 10,000 packs.
-- 2.30.0.667.g81c0cbc6fd