commit-reach: use the decoration hash for tips_reachable_from_bases()#2116
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spkrka wants to merge 1 commit into
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commit-reach: use the decoration hash for tips_reachable_from_bases()#2116spkrka wants to merge 1 commit into
spkrka wants to merge 1 commit into
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tips_reachable_from_bases() walks the commit graph from a set of base commits to find which tip commits are reachable. The inner loop does a linear scan over the tips array to check whether each visited commit is a tip, making the overall cost O(C * T) where C is commits walked and T is the number of tips. Replace the linear scan with the decoration hash for lookups, reducing the per-commit tip check from O(T) to O(1) and the overall cost from O(C * T) to O(C + T). This function is called by `git for-each-ref --merged` and `git branch/tag --contains/--no-contains` via reach_filter() in ref-filter.c. Benchmark on a merge-heavy monorepo (2.3M commits, 10,000 refs): Command Before After Speedup for-each-ref --merged HEAD 6.64s 1.66s 4.0x for-each-ref --no-merged HEAD 6.75s 1.74s 3.9x branch --merged HEAD 0.68s 0.61s 10% branch --no-merged HEAD 0.65s 0.61s 8% tag --merged HEAD 0.12s 0.12s - The large speedup for for-each-ref is because it checks all 10,000 refs as tips, making the O(T) inner loop expensive. The branch subcommand only checks local branches (fewer tips), so the improvement is smaller. Signed-off-by: Kristofer Karlsson <[email protected]>
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This is a single small commit that replaces an O(C*T) linear scan in
tips_reachable_from_bases()with an O(1) lookup using the decoration hash.The function is called by
git for-each-ref --mergedandgit branch/tag --contains/--no-containsviareach_filter()inref-filter.c. On a merge-heavy monorepo with 2.3M commits and 10,000
refs,
git for-each-ref --merged HEADgoes from 6.6s to 1.7s (4x).The diff is intentionally minimal (+9/-6) to make the idea easy to
discuss before polishing. Things I'm not fully happy about:
{ }just to preserve indentation of the inner body(void *)(i + 1)instead of storing a proper pointer
- 1on asize_t0) to check fornot-found via
j < tips_nrHappy to clean all of these up in a follow-up commit if the approach
makes sense.