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1771be90c8
When searching for a commit in a commit-graph chain of G graphs with N
commits, the search takes O(G log N) time. If we always add a new tip
graph with every write, the linear G term will start to dominate and
slow the lookup process.
To keep lookups fast, but also keep most incremental writes fast, create
a strategy for merging levels of the commit-graph chain. The strategy is
detailed in the commit-graph design document, but is summarized by these
two conditions:
1. If the number of commits we are adding is more than half the number
of commits in the graph below, then merge with that graph.
2. If we are writing more than 64,000 commits into a single graph,
then merge with all lower graphs.
The numeric values in the conditions above are currently constant, but
can become config options in a future update.
As we merge levels of the commit-graph chain, check that the commits
still exist in the repository. A garbage-collection operation may have
removed those commits from the object store and we do not want to
persist them in the commit-graph chain. This is a non-issue if the
'git gc' process wrote a new, single-level commit-graph file.
After we merge levels, the old graph-{hash}.graph files are no longer
referenced by the commit-graph-chain file. We will expire these files in
a future change.
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
136 lines
3.4 KiB
Bash
Executable file
136 lines
3.4 KiB
Bash
Executable file
#!/bin/sh
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test_description='split commit graph'
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. ./test-lib.sh
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GIT_TEST_COMMIT_GRAPH=0
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test_expect_success 'setup repo' '
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git init &&
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git config core.commitGraph true &&
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infodir=".git/objects/info" &&
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graphdir="$infodir/commit-graphs" &&
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test_oid_init
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'
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graph_read_expect() {
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NUM_BASE=0
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if test ! -z $2
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then
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NUM_BASE=$2
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fi
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cat >expect <<- EOF
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header: 43475048 1 1 3 $NUM_BASE
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num_commits: $1
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chunks: oid_fanout oid_lookup commit_metadata
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EOF
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git commit-graph read >output &&
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test_cmp expect output
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}
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test_expect_success 'create commits and write commit-graph' '
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for i in $(test_seq 3)
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do
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test_commit $i &&
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git branch commits/$i || return 1
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done &&
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git commit-graph write --reachable &&
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test_path_is_file $infodir/commit-graph &&
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graph_read_expect 3
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'
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graph_git_two_modes() {
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git -c core.commitGraph=true $1 >output
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git -c core.commitGraph=false $1 >expect
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test_cmp expect output
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}
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graph_git_behavior() {
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MSG=$1
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BRANCH=$2
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COMPARE=$3
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test_expect_success "check normal git operations: $MSG" '
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graph_git_two_modes "log --oneline $BRANCH" &&
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graph_git_two_modes "log --topo-order $BRANCH" &&
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graph_git_two_modes "log --graph $COMPARE..$BRANCH" &&
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graph_git_two_modes "branch -vv" &&
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graph_git_two_modes "merge-base -a $BRANCH $COMPARE"
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'
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}
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graph_git_behavior 'graph exists' commits/3 commits/1
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verify_chain_files_exist() {
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for hash in $(cat $1/commit-graph-chain)
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do
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test_path_is_file $1/graph-$hash.graph || return 1
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done
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}
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test_expect_success 'add more commits, and write a new base graph' '
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git reset --hard commits/1 &&
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for i in $(test_seq 4 5)
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do
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test_commit $i &&
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git branch commits/$i || return 1
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done &&
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git reset --hard commits/2 &&
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for i in $(test_seq 6 10)
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do
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test_commit $i &&
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git branch commits/$i || return 1
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done &&
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git reset --hard commits/2 &&
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git merge commits/4 &&
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git branch merge/1 &&
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git reset --hard commits/4 &&
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git merge commits/6 &&
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git branch merge/2 &&
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git commit-graph write --reachable &&
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graph_read_expect 12
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'
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test_expect_success 'add three more commits, write a tip graph' '
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git reset --hard commits/3 &&
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git merge merge/1 &&
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git merge commits/5 &&
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git merge merge/2 &&
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git branch merge/3 &&
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git commit-graph write --reachable --split &&
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test_path_is_missing $infodir/commit-graph &&
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test_path_is_file $graphdir/commit-graph-chain &&
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ls $graphdir/graph-*.graph >graph-files &&
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test_line_count = 2 graph-files &&
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verify_chain_files_exist $graphdir
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'
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graph_git_behavior 'split commit-graph: merge 3 vs 2' merge/3 merge/2
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test_expect_success 'add one commit, write a tip graph' '
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test_commit 11 &&
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git branch commits/11 &&
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git commit-graph write --reachable --split &&
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test_path_is_missing $infodir/commit-graph &&
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test_path_is_file $graphdir/commit-graph-chain &&
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ls $graphdir/graph-*.graph >graph-files &&
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test_line_count = 3 graph-files &&
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verify_chain_files_exist $graphdir
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'
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graph_git_behavior 'three-layer commit-graph: commit 11 vs 6' commits/11 commits/6
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test_expect_success 'add one commit, write a merged graph' '
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test_commit 12 &&
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git branch commits/12 &&
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git commit-graph write --reachable --split &&
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test_path_is_file $graphdir/commit-graph-chain &&
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test_line_count = 2 $graphdir/commit-graph-chain &&
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ls $graphdir/graph-*.graph >graph-files &&
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test_line_count = 4 graph-files &&
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verify_chain_files_exist $graphdir
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'
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graph_git_behavior 'merged commit-graph: commit 12 vs 6' commits/12 commits/6
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test_done
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