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git/t/t5324-split-commit-graph.sh
Derrick Stolee 150f11574b commit-graph: ignore duplicates when merging layers 
Thomas reported [1] that a "git fetch" command was failing with an error
saying "unexpected duplicate commit id". The root cause is that they had
fetch.writeCommitGraph enabled which generates commit-graph chains, and
this instance was merging two layers that both contained the same commit
ID.

[1] https://lore.kernel.org/git/55f8f00c-a61c-67d4-889e-a9501c596c39@virtuell-zuhause.de/

The initial assumption is that Git would not write a commit ID into a
commit-graph layer if it already exists in a lower commit-graph layer.
Somehow, this specific case did get into that situation, leading to this
error.

While unexpected, this isn't actually invalid (as long as the two layers
agree on the metadata for the commit). When we parse a commit that does
not have a graph_pos in the commit_graph_data_slab, we use binary search
in the commit-graph layers to find the commit and set graph_pos. That
position is never used again in this case. However, when we parse a
commit from the commit-graph file, we load its parents from the
commit-graph and assign graph_pos at that point. If those parents were
already parsed from the commit-graph, then nothing needs to be done.
Otherwise, this graph_pos is a valid position in the commit-graph so we
can parse the parents, when necessary.

Thus, this die() is too aggressive. The easiest thing to do would be to
ignore the duplicates.

If we only ignore the duplicates, then we will produce a commit-graph
that has identical commit IDs listed in adjacent positions. This excess
data will never be removed from the commit-graph, which could cascade
into significantly bloated file sizes.

Thankfully, we can collapse the list to erase the duplicate commit
pointers. This allows us to get the end result we want without extra
memory costs and minimal CPU time.

The root cause is due to disabling core.commitGraph, which prevents
parsing commits from the lower layers during a 'git commit-graph write
--split' command. Since we use the 'graph_pos' value to determine
whether a commit is in a lower layer, we never discover that those
commits are already in the commit-graph chain and add them to the top
layer. This layer is then merged down, creating duplicates.

The test added in t5324-split-commit-graph.sh fails without this change.
However, we still have not completely removed the need for this
duplicate check. That will come in a follow-up change.

Reported-by: Thomas Braun <thomas.braun@virtuell-zuhause.de>
Helped-by: Taylor Blau <me@ttaylorr.com>
Co-authored-by: Jeff King <peff@peff.net>
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2020-10-09 14:16:23 -07:00

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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_init &&
test_oid_cache <<-EOM
shallow sha1:1760
shallow sha256:2064
base sha1:1376
base sha256:1496
EOM
'
graph_read_expect() {
NUM_BASE=0
if test ! -z $2
then
NUM_BASE=$2
fi
cat >expect <<- EOF
header: 43475048 1 1 3 $NUM_BASE
num_commits: $1
chunks: oid_fanout oid_lookup commit_metadata
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 &&
test_might_fail run_with_limited_open_files 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 config core.commitGraph false &&
git -C dup commit --allow-empty -m one &&
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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