Thanks to everyone who gave comments on v1. I tried my best to respond to all of the feedback, but may have missed some while I was doing several renames, including: * builtin/graph.c -> builtin/commit-graph.c * packed-graph.[c|h] -> commit-graph.[c|h] * t/t5319-graph.sh -> t/t5318-commit-graph.sh Because of these renames (and several type/function renames) the diff is too large to conveniently share here. Some issues that came up and are addressed: * Use <hash> instead of <oid> when referring to the graph-<hash>.graph filenames and the contents of graph-head. * 32-bit timestamps will not cause undefined behavior. * timestamp_t is unsigned, so they are never negative. * The config setting "core.commitgraph" now only controls consuming the graph during normal operations and will not block the commit-graph plumbing command. * The --stdin-commits is better about sanitizing the input for strings that do not parse to OIDs or are OIDs for non-commit objects. One unresolved comment that I would like consensus on is the use of globals to store the config setting and the graph state. I'm currently using the pattern from packed_git instead of putting these values in the_repository. However, we want to eventually remove globals like packed_git. Should I deviate from the pattern _now_ in order to keep the problem from growing, or should I keep to the known pattern? Finally, I tried to clean up my incorrect style as I was recreating these commits. Feel free to be merciless in style feedback now that the architecture is more stable. Thanks, -Stolee -- >8 -- As promised [1], 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. Here are some performance results for a copy of the Linux repository where 'master' has 704,766 reachable commits and is behind 'origin/master' by 19,610 commits. | Command | Before | After | Rel % | |----------------------------------|--------|--------|-------| | log --oneline --topo-order -1000 | 5.9s | 0.7s | -88% | | branch -vv | 0.42s | 0.27s | -35% | | rev-list --all | 6.4s | 1.0s | -84% | | rev-list --all --objects | 32.6s | 27.6s | -15% | To test this yourself, run the following on your repo: git config core.commitgraph true git show-ref -s | git graph --write --update-head --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 comparisions by toggling the 'core.commitgraph' setting. [1] https://public-inbox.org/git/d154319e-bb9e-b300-7c37-27b1dcd2a2ce@xxxxxxxxxxxxxxxxx/ Re: What's cooking in git.git (Jan 2018, #03; Tue, 23) [2] https://github.com/derrickstolee/git/pull/2 A GitHub pull request containing the latest version of this patch. Derrick Stolee (14): commit-graph: add format document graph: add commit graph design document commit-graph: create git-commit-graph builtin commit-graph: implement construct_commit_graph() commit-graph: implement git-commit-graph --write commit-graph: implement git-commit-graph --read commit-graph: implement git-commit-graph --update-head commit-graph: implement git-commit-graph --clear commit-graph: teach git-commit-graph --delete-expired commit-graph: add core.commitgraph setting commit: integrate commit graph with commit parsing commit-graph: read only from specific pack-indexes commit-graph: close under reachability commit-graph: build graph from starting commits .gitignore | 1 + Documentation/config.txt | 3 + Documentation/git-commit-graph.txt | 100 +++ Documentation/technical/commit-graph-format.txt | 89 +++ Documentation/technical/commit-graph.txt | 189 ++++++ Makefile | 2 + alloc.c | 1 + builtin.h | 1 + builtin/commit-graph.c | 229 +++++++ cache.h | 1 + command-list.txt | 1 + commit-graph.c | 841 ++++++++++++++++++++++++ commit-graph.h | 69 ++ commit.c | 10 +- commit.h | 4 + config.c | 5 + environment.c | 1 + git.c | 1 + log-tree.c | 3 +- packfile.c | 4 +- packfile.h | 2 + t/t5318-commit-graph.sh | 272 ++++++++ 22 files changed, 1824 insertions(+), 5 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 -- 2.16.0
