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git/t/t5324-split-commit-graph.sh
Abhishek Kumar e8b63005c4 commit-graph: implement generation data chunk 
As discovered by Ævar, we cannot increment graph version to
distinguish between generation numbers v1 and v2 [1]. Thus, one of
pre-requistes before implementing generation number v2 was to
distinguish between graph versions in a backwards compatible manner.

We are going to introduce a new chunk called Generation DATa chunk (or
GDAT). GDAT will store corrected committer date offsets whereas CDAT
will still store topological level.

Old Git does not understand GDAT chunk and would ignore it, reading
topological levels from CDAT. New Git can parse GDAT and take advantage
of newer generation numbers, falling back to topological levels when
GDAT chunk is missing (as it would happen with a commit-graph written
by old Git).

We introduce a test environment variable 'GIT_TEST_COMMIT_GRAPH_NO_GDAT'
which forces commit-graph file to be written without generation data
chunk to emulate a commit-graph file written by old Git.

To minimize the space required to store corrrected commit date, Git
stores corrected commit date offsets into the commit-graph file, instea
of corrected commit dates. This saves us 4 bytes per commit, decreasing
the GDAT chunk size by half, but it's possible for the offset to
overflow the 4-bytes allocated for storage. As such overflows are and
should be exceedingly rare, we use the following overflow management
scheme:

We introduce a new commit-graph chunk, Generation Data OVerflow ('GDOV')
to store corrected commit dates for commits with offsets greater than
GENERATION_NUMBER_V2_OFFSET_MAX.

If the offset is greater than GENERATION_NUMBER_V2_OFFSET_MAX, we set
the MSB of the offset and the other bits store the position of corrected
commit date in GDOV chunk, similar to how Extra Edge List is maintained.

We test the overflow-related code with the following repo history:

           F - N - U
          /         \
U - N - U            N
         \          /
	  N - F - N

Where the commits denoted by U have committer date of zero seconds
since Unix epoch, the commits denoted by N have committer date of
1112354055 (default committer date for the test suite) seconds since
Unix epoch and the commits denoted by F have committer date of
(2 ^ 31 - 2) seconds since Unix epoch.

The largest offset observed is 2 ^ 31, just large enough to overflow.

[1]: https://lore.kernel.org/git/87a7gdspo4.fsf@evledraar.gmail.com/

Signed-off-by: Abhishek Kumar <abhishekkumar8222@gmail.com>
Reviewed-by: Taylor Blau <me@ttaylorr.com>
Reviewed-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2021-01-18 16:21:18 -08:00

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#!/bin/sh
test_description='split commit graph'
. ./test-lib.sh
GIT_TEST_COMMIT_GRAPH=0
GIT_TEST_COMMIT_GRAPH_CHANGED_PATHS=0
test_expect_success 'setup repo' '
git init &&
git config core.commitGraph true &&
git config gc.writeCommitGraph false &&
infodir=".git/objects/info" &&
graphdir="$infodir/commit-graphs" &&
test_oid_cache <<-EOM
shallow sha1:2132
shallow sha256:2436
base sha1:1408
base sha256:1528
oid_version sha1:1
oid_version sha256:2
EOM
'
graph_read_expect() {
NUM_BASE=0
if test ! -z $2
then
NUM_BASE=$2
fi
cat >expect <<- EOF
header: 43475048 1 $(test_oid oid_version) 4 $NUM_BASE
num_commits: $1
chunks: oid_fanout oid_lookup commit_metadata generation_data
EOF
test-tool read-graph >output &&
test_cmp expect output
}
test_expect_success POSIXPERM 'tweak umask for modebit tests' '
umask 022
'
test_expect_success 'create commits and write commit-graph' '
for i in $(test_seq 3)
do
test_commit $i &&
git branch commits/$i || return 1
done &&
git commit-graph write --reachable &&
test_path_is_file $infodir/commit-graph &&
graph_read_expect 3
'
graph_git_two_modes() {
git -c core.commitGraph=true $1 >output
git -c core.commitGraph=false $1 >expect
test_cmp expect output
}
graph_git_behavior() {
MSG=$1
BRANCH=$2
COMPARE=$3
test_expect_success "check normal git operations: $MSG" '
graph_git_two_modes "log --oneline $BRANCH" &&
graph_git_two_modes "log --topo-order $BRANCH" &&
graph_git_two_modes "log --graph $COMPARE..$BRANCH" &&
graph_git_two_modes "branch -vv" &&
graph_git_two_modes "merge-base -a $BRANCH $COMPARE"
'
}
graph_git_behavior 'graph exists' commits/3 commits/1
verify_chain_files_exist() {
for hash in $(cat $1/commit-graph-chain)
do
test_path_is_file $1/graph-$hash.graph || return 1
done
}
test_expect_success 'add more commits, and write a new base graph' '
git reset --hard commits/1 &&
for i in $(test_seq 4 5)
do
test_commit $i &&
git branch commits/$i || return 1
done &&
git reset --hard commits/2 &&
for i in $(test_seq 6 10)
do
test_commit $i &&
git branch commits/$i || return 1
done &&
git reset --hard commits/2 &&
git merge commits/4 &&
git branch merge/1 &&
git reset --hard commits/4 &&
git merge commits/6 &&
git branch merge/2 &&
git commit-graph write --reachable &&
graph_read_expect 12
'
test_expect_success 'fork and fail to base a chain on a commit-graph file' '
test_when_finished rm -rf fork &&
git clone . fork &&
(
cd fork &&
rm .git/objects/info/commit-graph &&
echo "$(pwd)/../.git/objects" >.git/objects/info/alternates &&
test_commit new-commit &&
git commit-graph write --reachable --split &&
test_path_is_file $graphdir/commit-graph-chain &&
test_line_count = 1 $graphdir/commit-graph-chain &&
verify_chain_files_exist $graphdir
)
'
test_expect_success 'add three more commits, write a tip graph' '
git reset --hard commits/3 &&
git merge merge/1 &&
git merge commits/5 &&
git merge merge/2 &&
git branch merge/3 &&
git commit-graph write --reachable --split &&
test_path_is_missing $infodir/commit-graph &&
test_path_is_file $graphdir/commit-graph-chain &&
ls $graphdir/graph-*.graph >graph-files &&
test_line_count = 2 graph-files &&
verify_chain_files_exist $graphdir
'
graph_git_behavior 'split commit-graph: merge 3 vs 2' merge/3 merge/2
test_expect_success 'add one commit, write a tip graph' '
test_commit 11 &&
git branch commits/11 &&
git commit-graph write --reachable --split &&
test_path_is_missing $infodir/commit-graph &&
test_path_is_file $graphdir/commit-graph-chain &&
ls $graphdir/graph-*.graph >graph-files &&
test_line_count = 3 graph-files &&
verify_chain_files_exist $graphdir
'
graph_git_behavior 'three-layer commit-graph: commit 11 vs 6' commits/11 commits/6
test_expect_success 'add one commit, write a merged graph' '
test_commit 12 &&
git branch commits/12 &&
git commit-graph write --reachable --split &&
test_path_is_file $graphdir/commit-graph-chain &&
test_line_count = 2 $graphdir/commit-graph-chain &&
ls $graphdir/graph-*.graph >graph-files &&
test_line_count = 2 graph-files &&
verify_chain_files_exist $graphdir
'
graph_git_behavior 'merged commit-graph: commit 12 vs 6' commits/12 commits/6
test_expect_success 'create fork and chain across alternate' '
git clone . fork &&
(
cd fork &&
git config core.commitGraph true &&
rm -rf $graphdir &&
echo "$(pwd)/../.git/objects" >.git/objects/info/alternates &&
test_commit 13 &&
git branch commits/13 &&
git commit-graph write --reachable --split &&
test_path_is_file $graphdir/commit-graph-chain &&
test_line_count = 3 $graphdir/commit-graph-chain &&
ls $graphdir/graph-*.graph >graph-files &&
test_line_count = 1 graph-files &&
git -c core.commitGraph=true rev-list HEAD >expect &&
git -c core.commitGraph=false rev-list HEAD >actual &&
test_cmp expect actual &&
test_commit 14 &&
git commit-graph write --reachable --split --object-dir=.git/objects/ &&
test_line_count = 3 $graphdir/commit-graph-chain &&
ls $graphdir/graph-*.graph >graph-files &&
test_line_count = 1 graph-files
)
'
graph_git_behavior 'alternate: commit 13 vs 6' commits/13 commits/6
test_expect_success 'test merge stragety constants' '
git clone . merge-2 &&
(
cd merge-2 &&
git config core.commitGraph true &&
test_line_count = 2 $graphdir/commit-graph-chain &&
test_commit 14 &&
git commit-graph write --reachable --split --size-multiple=2 &&
test_line_count = 3 $graphdir/commit-graph-chain
) &&
git clone . merge-10 &&
(
cd merge-10 &&
git config core.commitGraph true &&
test_line_count = 2 $graphdir/commit-graph-chain &&
test_commit 14 &&
git commit-graph write --reachable --split --size-multiple=10 &&
test_line_count = 1 $graphdir/commit-graph-chain &&
ls $graphdir/graph-*.graph >graph-files &&
test_line_count = 1 graph-files
) &&
git clone . merge-10-expire &&
(
cd merge-10-expire &&
git config core.commitGraph true &&
test_line_count = 2 $graphdir/commit-graph-chain &&
test_commit 15 &&
touch $graphdir/to-delete.graph $graphdir/to-keep.graph &&
test-tool chmtime =1546362000 $graphdir/to-delete.graph &&
test-tool chmtime =1546362001 $graphdir/to-keep.graph &&
git commit-graph write --reachable --split --size-multiple=10 \
--expire-time="2019-01-01 12:00 -05:00" &&
test_line_count = 1 $graphdir/commit-graph-chain &&
test_path_is_missing $graphdir/to-delete.graph &&
test_path_is_file $graphdir/to-keep.graph &&
ls $graphdir/graph-*.graph >graph-files &&
test_line_count = 3 graph-files
) &&
git clone --no-hardlinks . max-commits &&
(
cd max-commits &&
git config core.commitGraph true &&
test_line_count = 2 $graphdir/commit-graph-chain &&
test_commit 16 &&
test_commit 17 &&
git commit-graph write --reachable --split --max-commits=1 &&
test_line_count = 1 $graphdir/commit-graph-chain &&
ls $graphdir/graph-*.graph >graph-files &&
test_line_count = 1 graph-files
)
'
test_expect_success 'remove commit-graph-chain file after flattening' '
git clone . flatten &&
(
cd flatten &&
test_line_count = 2 $graphdir/commit-graph-chain &&
git commit-graph write --reachable &&
test_path_is_missing $graphdir/commit-graph-chain &&
ls $graphdir >graph-files &&
test_line_count = 0 graph-files
)
'
corrupt_file() {
file=$1
pos=$2
data="${3:-\0}"
chmod a+w "$file" &&
printf "$data" | dd of="$file" bs=1 seek="$pos" conv=notrunc
}
test_expect_success 'verify hashes along chain, even in shallow' '
git clone --no-hardlinks . verify &&
(
cd verify &&
git commit-graph verify &&
base_file=$graphdir/graph-$(head -n 1 $graphdir/commit-graph-chain).graph &&
corrupt_file "$base_file" $(test_oid shallow) "\01" &&
test_must_fail git commit-graph verify --shallow 2>test_err &&
grep -v "^+" test_err >err &&
test_i18ngrep "incorrect checksum" err
)
'
test_expect_success 'verify --shallow does not check base contents' '
git clone --no-hardlinks . verify-shallow &&
(
cd verify-shallow &&
git commit-graph verify &&
base_file=$graphdir/graph-$(head -n 1 $graphdir/commit-graph-chain).graph &&
corrupt_file "$base_file" 1000 "\01" &&
git commit-graph verify --shallow &&
test_must_fail git commit-graph verify 2>test_err &&
grep -v "^+" test_err >err &&
test_i18ngrep "incorrect checksum" err
)
'
test_expect_success 'warn on base graph chunk incorrect' '
git clone --no-hardlinks . base-chunk &&
(
cd base-chunk &&
git commit-graph verify &&
base_file=$graphdir/graph-$(tail -n 1 $graphdir/commit-graph-chain).graph &&
corrupt_file "$base_file" $(test_oid base) "\01" &&
git commit-graph verify --shallow 2>test_err &&
grep -v "^+" test_err >err &&
test_i18ngrep "commit-graph chain does not match" err
)
'
test_expect_success 'verify after commit-graph-chain corruption' '
git clone --no-hardlinks . verify-chain &&
(
cd verify-chain &&
corrupt_file "$graphdir/commit-graph-chain" 60 "G" &&
git commit-graph verify 2>test_err &&
grep -v "^+" test_err >err &&
test_i18ngrep "invalid commit-graph chain" err &&
corrupt_file "$graphdir/commit-graph-chain" 60 "A" &&
git commit-graph verify 2>test_err &&
grep -v "^+" test_err >err &&
test_i18ngrep "unable to find all commit-graph files" err
)
'
test_expect_success 'verify across alternates' '
git clone --no-hardlinks . verify-alt &&
(
cd verify-alt &&
rm -rf $graphdir &&
altdir="$(pwd)/../.git/objects" &&
echo "$altdir" >.git/objects/info/alternates &&
git commit-graph verify --object-dir="$altdir/" &&
test_commit extra &&
git commit-graph write --reachable --split &&
tip_file=$graphdir/graph-$(tail -n 1 $graphdir/commit-graph-chain).graph &&
corrupt_file "$tip_file" 100 "\01" &&
test_must_fail git commit-graph verify --shallow 2>test_err &&
grep -v "^+" test_err >err &&
test_i18ngrep "commit-graph has incorrect fanout value" err
)
'
test_expect_success 'add octopus merge' '
git reset --hard commits/10 &&
git merge commits/3 commits/4 &&
git branch merge/octopus &&
git commit-graph write --reachable --split &&
git commit-graph verify --progress 2>err &&
test_line_count = 3 err &&
test_i18ngrep ! warning err &&
test_line_count = 3 $graphdir/commit-graph-chain
'
graph_git_behavior 'graph exists' merge/octopus commits/12
test_expect_success 'split across alternate where alternate is not split' '
git commit-graph write --reachable &&
test_path_is_file .git/objects/info/commit-graph &&
cp .git/objects/info/commit-graph . &&
git clone --no-hardlinks . alt-split &&
(
cd alt-split &&
rm -f .git/objects/info/commit-graph &&
echo "$(pwd)"/../.git/objects >.git/objects/info/alternates &&
test_commit 18 &&
git commit-graph write --reachable --split &&
test_line_count = 1 $graphdir/commit-graph-chain
) &&
test_cmp commit-graph .git/objects/info/commit-graph
'
test_expect_success '--split=no-merge always writes an incremental' '
test_when_finished rm -rf a b &&
rm -rf $graphdir $infodir/commit-graph &&
git reset --hard commits/2 &&
git rev-list HEAD~1 >a &&
git rev-list HEAD >b &&
git commit-graph write --split --stdin-commits <a &&
git commit-graph write --split=no-merge --stdin-commits <b &&
test_line_count = 2 $graphdir/commit-graph-chain
'
test_expect_success '--split=replace replaces the chain' '
rm -rf $graphdir $infodir/commit-graph &&
git reset --hard commits/3 &&
git rev-list -1 HEAD~2 >a &&
git rev-list -1 HEAD~1 >b &&
git rev-list -1 HEAD >c &&
git commit-graph write --split=no-merge --stdin-commits <a &&
git commit-graph write --split=no-merge --stdin-commits <b &&
git commit-graph write --split=no-merge --stdin-commits <c &&
test_line_count = 3 $graphdir/commit-graph-chain &&
git commit-graph write --stdin-commits --split=replace <b &&
test_path_is_missing $infodir/commit-graph &&
test_path_is_file $graphdir/commit-graph-chain &&
ls $graphdir/graph-*.graph >graph-files &&
test_line_count = 1 graph-files &&
verify_chain_files_exist $graphdir &&
graph_read_expect 2
'
test_expect_success ULIMIT_FILE_DESCRIPTORS 'handles file descriptor exhaustion' '
git init ulimit &&
(
cd ulimit &&
for i in $(test_seq 64)
do
test_commit $i &&
run_with_limited_open_files test_might_fail git commit-graph write \
--split=no-merge --reachable || return 1
done
)
'
while read mode modebits
do
test_expect_success POSIXPERM "split commit-graph respects core.sharedrepository $mode" '
rm -rf $graphdir $infodir/commit-graph &&
git reset --hard commits/1 &&
test_config core.sharedrepository "$mode" &&
git commit-graph write --split --reachable &&
ls $graphdir/graph-*.graph >graph-files &&
test_line_count = 1 graph-files &&
echo "$modebits" >expect &&
test_modebits $graphdir/graph-*.graph >actual &&
test_cmp expect actual &&
test_modebits $graphdir/commit-graph-chain >actual &&
test_cmp expect actual
'
done <<\EOF
0666 -r--r--r--
0600 -r--------
EOF
test_expect_success '--split=replace with partial Bloom data' '
rm -rf $graphdir $infodir/commit-graph &&
git reset --hard commits/3 &&
git rev-list -1 HEAD~2 >a &&
git rev-list -1 HEAD~1 >b &&
git commit-graph write --split=no-merge --stdin-commits --changed-paths <a &&
git commit-graph write --split=no-merge --stdin-commits <b &&
git commit-graph write --split=replace --stdin-commits --changed-paths <c &&
ls $graphdir/graph-*.graph >graph-files &&
test_line_count = 1 graph-files &&
verify_chain_files_exist $graphdir
'
test_expect_success 'prevent regression for duplicate commits across layers' '
git init dup &&
git -C dup commit --allow-empty -m one &&
git -C dup -c core.commitGraph=false commit-graph write --split=no-merge --reachable 2>err &&
test_i18ngrep "attempting to write a commit-graph" err &&
git -C dup commit-graph write --split=no-merge --reachable &&
git -C dup commit --allow-empty -m two &&
git -C dup commit-graph write --split=no-merge --reachable &&
git -C dup commit --allow-empty -m three &&
git -C dup commit-graph write --split --reachable &&
git -C dup commit-graph verify
'
test_done
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