git/t/t7704-repack-cruft.sh

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#!/bin/sh
test_description='git repack works correctly'
. ./test-lib.sh
objdir=.git/objects
builtin/repack.c: implement support for `--max-cruft-size` Cruft packs are an alternative mechanism for storing a collection of unreachable objects whose mtimes are recent enough to avoid being pruned out of the repository. When cruft packs were first introduced back in b757353676 (builtin/pack-objects.c: --cruft without expiration, 2022-05-20) and a7d493833f (builtin/pack-objects.c: --cruft with expiration, 2022-05-20), the recommended workflow consisted of: - Repacking periodically, either by packing anything loose in the repository (via `git repack -d`) or producing a geometric sequence of packs (via `git repack --geometric=<d> -d`). - Every so often, splitting the repository into two packs, one cruft to store the unreachable objects, and another non-cruft pack to store the reachable objects. Repositories may (out of band with the above) choose periodically to prune out some unreachable objects which have aged out of the grace period by generating a pack with `--cruft-expiration=<approxidate>`. This allowed repositories to maintain relatively few packs on average, and quarantine unreachable objects together in a cruft pack, avoiding the pitfalls of holding unreachable objects as loose while they age out (for more, see some of the details in 3d89a8c118 (Documentation/technical: add cruft-packs.txt, 2022-05-20)). This all works, but can be costly from an I/O-perspective when frequently repacking a repository that has many unreachable objects. This problem is exacerbated when those unreachable objects are rarely (if every) pruned. Since there is at most one cruft pack in the above scheme, each time we update the cruft pack it must be rewritten from scratch. Because much of the pack is reused, this is a relatively inexpensive operation from a CPU-perspective, but is very costly in terms of I/O since we end up rewriting basically the same pack (plus any new unreachable objects that have entered the repository since the last time a cruft pack was generated). At the time, we decided against implementing more robust support for multiple cruft packs. This patch implements that support which we were lacking. Introduce a new option `--max-cruft-size` which allows repositories to accumulate cruft packs up to a given size, after which point a new generation of cruft packs can accumulate until it reaches the maximum size, and so on. To generate a new cruft pack, the process works like so: - Sort a list of any existing cruft packs in ascending order of pack size. - Starting from the beginning of the list, group cruft packs together while the accumulated size is smaller than the maximum specified pack size. - Combine the objects in these cruft packs together into a new cruft pack, along with any other unreachable objects which have since entered the repository. Once a cruft pack grows beyond the size specified via `--max-cruft-size` the pack is effectively frozen. This limits the I/O churn up to a quadratic function of the value specified by the `--max-cruft-size` option, instead of behaving quadratically in the number of total unreachable objects. When pruning unreachable objects, we bypass the new code paths which combine small cruft packs together, and instead start from scratch, passing in the appropriate `--max-pack-size` down to `pack-objects`, putting it in charge of keeping the resulting set of cruft packs sized correctly. This may seem like further I/O churn, but in practice it isn't so bad. We could prune old cruft packs for whom all or most objects are removed, and then generate a new cruft pack with just the remaining set of objects. But this additional complexity buys us relatively little, because most objects end up being pruned anyway, so the I/O churn is well contained. Signed-off-by: Taylor Blau <me@ttaylorr.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2023-10-03 00:44:32 +00:00
packdir=$objdir/pack
test_expect_success '--expire-to stores pruned objects (now)' '
git init expire-to-now &&
(
cd expire-to-now &&
git branch -M main &&
test_commit base &&
git checkout -b cruft &&
test_commit --no-tag cruft &&
git rev-list --objects --no-object-names main..cruft >moved.raw &&
sort moved.raw >moved.want &&
git rev-list --all --objects --no-object-names >expect.raw &&
sort expect.raw >expect &&
git checkout main &&
git branch -D cruft &&
git reflog expire --all --expire=all &&
git init --bare expired.git &&
git repack -d \
--cruft --cruft-expiration="now" \
--expire-to="expired.git/objects/pack/pack" &&
expired="$(ls expired.git/objects/pack/pack-*.idx)" &&
test_path_is_file "${expired%.idx}.mtimes" &&
# Since the `--cruft-expiration` is "now", the effective
# behavior is to move _all_ unreachable objects out to
# the location in `--expire-to`.
git show-index <$expired >expired.raw &&
cut -d" " -f2 expired.raw | sort >expired.objects &&
git rev-list --all --objects --no-object-names \
>remaining.objects &&
# ...in other words, the combined contents of this
# repository and expired.git should be the same as the
# set of objects we started with.
cat expired.objects remaining.objects | sort >actual &&
test_cmp expect actual &&
# The "moved" objects (i.e., those in expired.git)
# should be the same as the cruft objects which were
# expired in the previous step.
test_cmp moved.want expired.objects
)
'
test_expect_success '--expire-to stores pruned objects (5.minutes.ago)' '
git init expire-to-5.minutes.ago &&
(
cd expire-to-5.minutes.ago &&
git branch -M main &&
test_commit base &&
# Create two classes of unreachable objects, one which
# is older than 5 minutes (stale), and another which is
# newer (recent).
for kind in stale recent
do
git checkout -b $kind main &&
test_commit --no-tag $kind || return 1
done &&
git rev-list --objects --no-object-names main..stale >in &&
stale="$(git pack-objects $objdir/pack/pack <in)" &&
mtime="$(test-tool chmtime --get =-600 $objdir/pack/pack-$stale.pack)" &&
# expect holds the set of objects we expect to find in
# this repository after repacking
git rev-list --objects --no-object-names recent >expect.raw &&
sort expect.raw >expect &&
# moved.want holds the set of objects we expect to find
# in expired.git
git rev-list --objects --no-object-names main..stale >out &&
sort out >moved.want &&
git checkout main &&
git branch -D stale recent &&
git reflog expire --all --expire=all &&
git prune-packed &&
git init --bare expired.git &&
git repack -d \
--cruft --cruft-expiration=5.minutes.ago \
--expire-to="expired.git/objects/pack/pack" &&
# Some of the remaining objects in this repository are
# unreachable, so use `cat-file --batch-all-objects`
# instead of `rev-list` to get their names
git cat-file --batch-all-objects --batch-check="%(objectname)" \
>remaining.objects &&
sort remaining.objects >actual &&
test_cmp expect actual &&
(
cd expired.git &&
expired="$(ls objects/pack/pack-*.mtimes)" &&
test-tool pack-mtimes $(basename $expired) >out &&
cut -d" " -f1 out | sort >../moved.got &&
# Ensure that there are as many objects with the
# expected mtime as were moved to expired.git.
#
# In other words, ensure that the recorded
# mtimes of any moved objects was written
# correctly.
grep " $mtime$" out >matching &&
test_line_count = $(wc -l <../moved.want) matching
) &&
test_cmp moved.want moved.got
)
'
builtin/repack.c: implement support for `--max-cruft-size` Cruft packs are an alternative mechanism for storing a collection of unreachable objects whose mtimes are recent enough to avoid being pruned out of the repository. When cruft packs were first introduced back in b757353676 (builtin/pack-objects.c: --cruft without expiration, 2022-05-20) and a7d493833f (builtin/pack-objects.c: --cruft with expiration, 2022-05-20), the recommended workflow consisted of: - Repacking periodically, either by packing anything loose in the repository (via `git repack -d`) or producing a geometric sequence of packs (via `git repack --geometric=<d> -d`). - Every so often, splitting the repository into two packs, one cruft to store the unreachable objects, and another non-cruft pack to store the reachable objects. Repositories may (out of band with the above) choose periodically to prune out some unreachable objects which have aged out of the grace period by generating a pack with `--cruft-expiration=<approxidate>`. This allowed repositories to maintain relatively few packs on average, and quarantine unreachable objects together in a cruft pack, avoiding the pitfalls of holding unreachable objects as loose while they age out (for more, see some of the details in 3d89a8c118 (Documentation/technical: add cruft-packs.txt, 2022-05-20)). This all works, but can be costly from an I/O-perspective when frequently repacking a repository that has many unreachable objects. This problem is exacerbated when those unreachable objects are rarely (if every) pruned. Since there is at most one cruft pack in the above scheme, each time we update the cruft pack it must be rewritten from scratch. Because much of the pack is reused, this is a relatively inexpensive operation from a CPU-perspective, but is very costly in terms of I/O since we end up rewriting basically the same pack (plus any new unreachable objects that have entered the repository since the last time a cruft pack was generated). At the time, we decided against implementing more robust support for multiple cruft packs. This patch implements that support which we were lacking. Introduce a new option `--max-cruft-size` which allows repositories to accumulate cruft packs up to a given size, after which point a new generation of cruft packs can accumulate until it reaches the maximum size, and so on. To generate a new cruft pack, the process works like so: - Sort a list of any existing cruft packs in ascending order of pack size. - Starting from the beginning of the list, group cruft packs together while the accumulated size is smaller than the maximum specified pack size. - Combine the objects in these cruft packs together into a new cruft pack, along with any other unreachable objects which have since entered the repository. Once a cruft pack grows beyond the size specified via `--max-cruft-size` the pack is effectively frozen. This limits the I/O churn up to a quadratic function of the value specified by the `--max-cruft-size` option, instead of behaving quadratically in the number of total unreachable objects. When pruning unreachable objects, we bypass the new code paths which combine small cruft packs together, and instead start from scratch, passing in the appropriate `--max-pack-size` down to `pack-objects`, putting it in charge of keeping the resulting set of cruft packs sized correctly. This may seem like further I/O churn, but in practice it isn't so bad. We could prune old cruft packs for whom all or most objects are removed, and then generate a new cruft pack with just the remaining set of objects. But this additional complexity buys us relatively little, because most objects end up being pruned anyway, so the I/O churn is well contained. Signed-off-by: Taylor Blau <me@ttaylorr.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2023-10-03 00:44:32 +00:00
generate_random_blob() {
test-tool genrandom "$@" >blob &&
git hash-object -w -t blob blob &&
rm blob
}
pack_random_blob () {
generate_random_blob "$@" &&
git repack -d -q >/dev/null
}
generate_cruft_pack () {
pack_random_blob "$@" >/dev/null &&
ls $packdir/pack-*.pack | xargs -n 1 basename >in &&
pack="$(git pack-objects --cruft $packdir/pack <in)" &&
git prune-packed &&
echo "$packdir/pack-$pack.mtimes"
}
test_expect_success '--max-cruft-size creates new packs when above threshold' '
git init max-cruft-size-large &&
(
cd max-cruft-size-large &&
test_commit base &&
foo="$(pack_random_blob foo $((1*1024*1024)))" &&
git repack --cruft -d &&
cruft_foo="$(ls $packdir/pack-*.mtimes)" &&
bar="$(pack_random_blob bar $((1*1024*1024)))" &&
git repack --cruft -d --max-cruft-size=1M &&
cruft_bar="$(ls $packdir/pack-*.mtimes | grep -v $cruft_foo)" &&
test-tool pack-mtimes $(basename "$cruft_foo") >foo.objects &&
test-tool pack-mtimes $(basename "$cruft_bar") >bar.objects &&
grep "^$foo" foo.objects &&
test_line_count = 1 foo.objects &&
grep "^$bar" bar.objects &&
test_line_count = 1 bar.objects
)
'
test_expect_success '--max-cruft-size combines existing packs when below threshold' '
git init max-cruft-size-small &&
(
cd max-cruft-size-small &&
test_commit base &&
foo="$(pack_random_blob foo $((1*1024*1024)))" &&
git repack --cruft -d &&
bar="$(pack_random_blob bar $((1*1024*1024)))" &&
git repack --cruft -d --max-cruft-size=10M &&
cruft=$(ls $packdir/pack-*.mtimes) &&
test-tool pack-mtimes $(basename "$cruft") >cruft.objects &&
grep "^$foo" cruft.objects &&
grep "^$bar" cruft.objects &&
test_line_count = 2 cruft.objects
)
'
test_expect_success '--max-cruft-size combines smaller packs first' '
git init max-cruft-size-consume-small &&
(
cd max-cruft-size-consume-small &&
test_commit base &&
git repack -ad &&
cruft_foo="$(generate_cruft_pack foo 524288)" && # 0.5 MiB
cruft_bar="$(generate_cruft_pack bar 524288)" && # 0.5 MiB
cruft_baz="$(generate_cruft_pack baz 1048576)" && # 1.0 MiB
cruft_quux="$(generate_cruft_pack quux 1572864)" && # 1.5 MiB
test-tool pack-mtimes "$(basename $cruft_foo)" >expect.raw &&
test-tool pack-mtimes "$(basename $cruft_bar)" >>expect.raw &&
sort expect.raw >expect.objects &&
# repacking with `--max-cruft-size=2M` should combine
# both 0.5 MiB packs together, instead of, say, one of
# the 0.5 MiB packs with the 1.0 MiB pack
ls $packdir/pack-*.mtimes | sort >cruft.before &&
git repack -d --cruft --max-cruft-size=2M &&
ls $packdir/pack-*.mtimes | sort >cruft.after &&
comm -13 cruft.before cruft.after >cruft.new &&
comm -23 cruft.before cruft.after >cruft.removed &&
test_line_count = 1 cruft.new &&
test_line_count = 2 cruft.removed &&
# the two smaller packs should be rolled up first
printf "%s\n" $cruft_foo $cruft_bar | sort >expect.removed &&
test_cmp expect.removed cruft.removed &&
# ...and contain the set of objects rolled up
test-tool pack-mtimes "$(basename $(cat cruft.new))" >actual.raw &&
sort actual.raw >actual.objects &&
test_cmp expect.objects actual.objects
)
'
test_expect_success 'setup --max-cruft-size with freshened objects' '
git init max-cruft-size-freshen &&
(
cd max-cruft-size-freshen &&
test_commit base &&
git repack -ad &&
foo="$(generate_random_blob foo 64)" &&
test-tool chmtime --get -10000 \
"$objdir/$(test_oid_to_path "$foo")" >foo.mtime &&
git repack --cruft -d &&
cruft="$(ls $packdir/pack-*.mtimes)" &&
test-tool pack-mtimes "$(basename $cruft)" >actual &&
echo "$foo $(cat foo.mtime)" >expect &&
test_cmp expect actual
)
'
test_expect_success '--max-cruft-size with freshened objects (loose)' '
(
cd max-cruft-size-freshen &&
# regenerate the object, setting its mtime to be more recent
foo="$(generate_random_blob foo 64)" &&
test-tool chmtime --get -100 \
"$objdir/$(test_oid_to_path "$foo")" >foo.mtime &&
git repack --cruft -d &&
cruft="$(ls $packdir/pack-*.mtimes)" &&
test-tool pack-mtimes "$(basename $cruft)" >actual &&
echo "$foo $(cat foo.mtime)" >expect &&
test_cmp expect actual
)
'
test_expect_success '--max-cruft-size with freshened objects (packed)' '
(
cd max-cruft-size-freshen &&
# regenerate the object and store it in a packfile,
# setting its mtime to be more recent
#
# store it alongside another cruft object so that we
# do not create an identical copy of the existing
# cruft pack (which contains $foo).
foo="$(generate_random_blob foo 64)" &&
bar="$(generate_random_blob bar 64)" &&
foo_pack="$(printf "%s\n" $foo $bar | git pack-objects $packdir/pack)" &&
git prune-packed &&
test-tool chmtime --get -10 \
"$packdir/pack-$foo_pack.pack" >foo.mtime &&
git repack --cruft -d &&
cruft="$(ls $packdir/pack-*.mtimes)" &&
test-tool pack-mtimes "$(basename $cruft)" >actual &&
echo "$foo $(cat foo.mtime)" >expect.raw &&
echo "$bar $(cat foo.mtime)" >>expect.raw &&
sort expect.raw >expect &&
test_cmp expect actual
)
'
test_expect_success '--max-cruft-size with pruning' '
git init max-cruft-size-prune &&
(
cd max-cruft-size-prune &&
test_commit base &&
foo="$(generate_random_blob foo $((1024*1024)))" &&
bar="$(generate_random_blob bar $((1024*1024)))" &&
baz="$(generate_random_blob baz $((1024*1024)))" &&
test-tool chmtime -10000 "$objdir/$(test_oid_to_path "$foo")" &&
git repack -d --cruft --max-cruft-size=1M &&
# backdate the mtimes of all cruft packs to validate
# that they were rewritten as a result of pruning
ls $packdir/pack-*.mtimes | sort >cruft.before &&
for cruft in $(cat cruft.before)
do
mtime="$(test-tool chmtime --get -10000 "$cruft")" &&
echo $cruft $mtime >>mtimes || return 1
done &&
# repack (and prune) with a --max-cruft-size to ensure
# that we appropriately split the resulting set of packs
git repack -d --cruft --max-cruft-size=1M \
--cruft-expiration=10.seconds.ago &&
ls $packdir/pack-*.mtimes | sort >cruft.after &&
for cruft in $(cat cruft.after)
do
old_mtime="$(grep $cruft mtimes | cut -d" " -f2)" &&
new_mtime="$(test-tool chmtime --get $cruft)" &&
test $old_mtime -lt $new_mtime || return 1
done &&
test_line_count = 3 cruft.before &&
test_line_count = 2 cruft.after &&
test_must_fail git cat-file -e $foo &&
git cat-file -e $bar &&
git cat-file -e $baz
)
'
test_expect_success '--max-cruft-size ignores non-local packs' '
repo="max-cruft-size-non-local" &&
git init $repo &&
(
cd $repo &&
test_commit base &&
generate_random_blob foo 64 &&
git repack --cruft -d
) &&
git clone --reference=$repo $repo $repo-alt &&
(
cd $repo-alt &&
test_commit other &&
generate_random_blob bar 64 &&
# ensure that we do not attempt to pick up packs from
# the non-alternated repository, which would result in a
# crash
git repack --cruft --max-cruft-size=1M -d
)
'
test_expect_success 'reachable packs are preferred over cruft ones' '
repo="cruft-preferred-packs" &&
git init "$repo" &&
(
cd "$repo" &&
# This test needs to exercise careful control over when a MIDX
# is and is not written. Unset the corresponding TEST variable
# accordingly.
sane_unset GIT_TEST_MULTI_PACK_INDEX &&
test_commit base &&
test_commit --no-tag cruft &&
non_cruft="$(echo base | git pack-objects --revs $packdir/pack)" &&
# Write a cruft pack which both (a) sorts ahead of the non-cruft
# pack in lexical order, and (b) has an older mtime to appease
# the MIDX preferred pack selection routine.
cruft="$(echo pack-$non_cruft.pack | git pack-objects --cruft $packdir/pack-A)" &&
test-tool chmtime -1000 $packdir/pack-A-$cruft.pack &&
test_commit other &&
git repack -d &&
git repack --geometric 2 -d --write-midx --write-bitmap-index &&
# After repacking, there are two packs left: one reachable one
# (which is the result of combining both of the existing two
# non-cruft packs), and one cruft pack.
find .git/objects/pack -type f -name "*.pack" >packs &&
test_line_count = 2 packs &&
# Make sure that the pack we just wrote is marked as preferred,
# not the cruft one.
pack="$(test-tool read-midx --preferred-pack $objdir)" &&
test_path_is_missing "$packdir/$(basename "$pack" ".idx").mtimes"
)
'
test_done