From f559d6d45e7e58ae1f922213948723de77ea77bd Mon Sep 17 00:00:00 2001 From: Patrick Steinhardt Date: Mon, 9 Aug 2021 10:12:03 +0200 Subject: revision: avoid hitting packfiles when commits are in commit-graph MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit When queueing references in git-rev-list(1), we try to optimize parsing of commits via the commit-graph. To do so, we first look up the object's type, and if it is a commit we call `repo_parse_commit()` instead of `parse_object()`. This is quite inefficient though given that we're always uncompressing the object header in order to determine the type. Instead, we can opportunistically search the commit-graph for the object ID: in case it's found, we know it's a commit and can directly fill in the commit object without having to uncompress the object header. Expose a new function `lookup_commit_in_graph()`, which tries to find a commit in the commit-graph by ID, and convert `get_reference()` to use this function. This provides a big performance win in cases where we load references in a repository with lots of references pointing to commits. The following has been executed in a real-world repository with about 2.2 million refs: Benchmark #1: HEAD~: rev-list --unsorted-input --objects --quiet --not --all --not $newrev Time (mean ± σ): 4.458 s ± 0.044 s [User: 4.115 s, System: 0.342 s] Range (min … max): 4.409 s … 4.534 s 10 runs Benchmark #2: HEAD: rev-list --unsorted-input --objects --quiet --not --all --not $newrev Time (mean ± σ): 3.089 s ± 0.015 s [User: 2.768 s, System: 0.321 s] Range (min … max): 3.061 s … 3.105 s 10 runs Summary 'HEAD: rev-list --unsorted-input --objects --quiet --not --all --not $newrev' ran 1.44 ± 0.02 times faster than 'HEAD~: rev-list --unsorted-input --objects --quiet --not --all --not $newrev' Signed-off-by: Patrick Steinhardt Signed-off-by: Junio C Hamano --- commit-graph.h | 8 ++++++++ 1 file changed, 8 insertions(+) (limited to 'commit-graph.h') diff --git a/commit-graph.h b/commit-graph.h index 96c24fb577..04a94e1830 100644 --- a/commit-graph.h +++ b/commit-graph.h @@ -40,6 +40,14 @@ int open_commit_graph(const char *graph_file, int *fd, struct stat *st); */ int parse_commit_in_graph(struct repository *r, struct commit *item); +/* + * Look up the given commit ID in the commit-graph. This will only return a + * commit if the ID exists both in the graph and in the object database such + * that we don't return commits whose object has been pruned. Otherwise, this + * function returns `NULL`. + */ +struct commit *lookup_commit_in_graph(struct repository *repo, const struct object_id *id); + /* * It is possible that we loaded commit contents from the commit buffer, * but we also want to ensure the commit-graph content is correctly -- cgit v1.2.3