This patch has only a few changes since v6: * Fixed whitespace issues using 'git rebase --whitespace=fix' * The --stdin-packs docs now refer to "pack-indexes" insead of "packs" * Modified description of --object-dir option to warn use is rare * Replaced '--additive' with '--append' * In "commit-graph: close under reachability" I greatly simplified the check that every reachable commit is included. While running tests I noticed that the revision walk machinery could not keep up with a very large queue created when combined with the '--append' option that added all commits from the existing file as starting points for the walk. The new algorithm simply appends missing commits to the end of the list, which are then iterated to ensure their parents are in the list. I have a few patch series prepared that provide further performance improvments following this patch. -- >8 -- This patch contains a way to serialize the commit graph. The current implementation defines a new file format to store the graph structure (parent relationships) and basic commit metadata (commit date, root tree OID) in order to prevent parsing raw commits while performing basic graph walks. For example, we do not need to parse the full commit when performing these walks: * 'git log --topo-order -1000' walks all reachable commits to avoid incorrect topological orders, but only needs the commit message for the top 1000 commits. * 'git merge-base <A> <B>' may walk many commits to find the correct boundary between the commits reachable from A and those reachable from B. No commit messages are needed. * 'git branch -vv' checks ahead/behind status for all local branches compared to their upstream remote branches. This is essentially as hard as computing merge bases for each. The current patch speeds up these calculations by injecting a check in parse_commit_gently() to check if there is a graph file and using that to provide the required metadata to the struct commit. The file format has room to store generation numbers, which will be provided as a patch after this framework is merged. Generation numbers are referenced by the design document but not implemented in order to make the current patch focus on the graph construction process. Once that is stable, it will be easier to add generation numbers and make graph walks aware of generation numbers one-by-one. By loading commits from the graph instead of parsing commit buffers, we save a lot of time on long commit walks. Here are some performance results for a copy of the Linux repository where 'master' has 678,653 reachable commits and is behind 'origin/master' by 59,929 commits. | Command | Before | After | Rel % | |----------------------------------|--------|--------|-------| | log --oneline --topo-order -1000 | 8.31s | 0.94s | -88% | | branch -vv | 1.02s | 0.14s | -86% | | rev-list --all | 5.89s | 1.07s | -81% | | rev-list --all --objects | 66.15s | 58.45s | -11% | To test this yourself, run the following on your repo: git config core.commitGraph true git show-ref -s | git commit-graph write --stdin-commits The second command writes a commit graph file containing every commit reachable from your refs. Now, all git commands that walk commits will check your graph first before consulting the ODB. You can run your own performance comparisons by toggling the 'core.commitGraph' setting. [1] https://github.com/derrickstolee/git/pull/2 A GitHub pull request containing the latest version of this patch. Derrick Stolee (14): csum-file: rename hashclose() to finalize_hashfile() csum-file: refactor finalize_hashfile() method commit-graph: add format document graph: add commit graph design document commit-graph: create git-commit-graph builtin commit-graph: implement write_commit_graph() commit-graph: implement git-commit-graph write commit-graph: implement git commit-graph read commit-graph: add core.commitGraph setting commit-graph: close under reachability commit: integrate commit graph with commit parsing commit-graph: read only from specific pack-indexes commit-graph: build graph from starting commits commit-graph: implement "--additive" option .gitignore | 1 + Documentation/config.txt | 4 + Documentation/git-commit-graph.txt | 94 +++ .../technical/commit-graph-format.txt | 97 +++ Documentation/technical/commit-graph.txt | 163 ++++ Makefile | 2 + alloc.c | 1 + builtin.h | 1 + builtin/commit-graph.c | 171 ++++ builtin/index-pack.c | 2 +- builtin/pack-objects.c | 6 +- bulk-checkin.c | 4 +- cache.h | 1 + command-list.txt | 1 + commit-graph.c | 738 ++++++++++++++++++ commit-graph.h | 46 ++ commit.c | 3 + commit.h | 3 + config.c | 5 + contrib/completion/git-completion.bash | 2 + csum-file.c | 10 +- csum-file.h | 9 +- environment.c | 1 + fast-import.c | 2 +- git.c | 1 + pack-bitmap-write.c | 2 +- pack-write.c | 5 +- packfile.c | 4 +- packfile.h | 2 + t/t5318-commit-graph.sh | 224 ++++++ 30 files changed, 1584 insertions(+), 21 deletions(-) create mode 100644 Documentation/git-commit-graph.txt create mode 100644 Documentation/technical/commit-graph-format.txt create mode 100644 Documentation/technical/commit-graph.txt create mode 100644 builtin/commit-graph.c create mode 100644 commit-graph.c create mode 100644 commit-graph.h create mode 100755 t/t5318-commit-graph.sh base-commit: 468165c1d8a442994a825f3684528361727cd8c0 -- 2.17.0.14.gba1221a8ce
