Jeff King writes: > I suspect the issue may be quite subtle. Even you asked for > "--no-patch", the underlying diff may still be used for other things. > For example, simplifying away TREESAME commits. I.e., ones which did not > change anything from their parents after applying path restrictions, > diff-filters, etc. There may be other cases, too (e.g., --follow). > > I think the code could be written to realize that none of those features > are in use, and disable the diff entirely in favor of checking whether > the two trees has the same object id. That would yield _mostly_ the same > behavior, though there are probably corner cases (e.g., a tree with an > odd mode entry, say, may get parsed so as to produce an empty diff, even > though it's not byte for byte identical). That may be an acceptable > tradeoff. But I think the code would be a bit brittle (it needs to know > about all the cases where a diff might matter, and we may add more > later). Do you think it'd be safe to make --no-patch imply --diff-merges=off, as Tao suggested elsewhere in this thread? https://lore.kernel.org/git/CAPMMpog-7eDOrgSU9GjV4G9rk5RkL-PJhaUAO3_0p2YxfRf=LA@xxxxxxxxxxxxxx If so, it seems like that'd be a good way to get speedups for some merge commits. For example, here are hyperfine timings for the current tip of git.git's master branch: Benchmark #1: git show --no-patch --format=%h 1e59178e3f Time (mean ± σ): 47.8 ms ± 1.5 ms [User: 43.2 ms, System: 4.6 ms] Range (min … max): 46.8 ms … 54.4 ms 59 runs Warning: Statistical outliers were detected. Consider re-running this benchmark on a quiet PC without any interferences from other programs. It might help to use the '--warmup' or '--prepare' options. Benchmark #2: git show --no-patch --diff-merges=off --format=%h 1e59178e3f Time (mean ± σ): 3.2 ms ± 0.2 ms [User: 2.5 ms, System: 0.8 ms] Range (min … max): 2.9 ms … 6.8 ms 688 runs Warning: Command took less than 5 ms to complete. Results might be inaccurate. Warning: Statistical outliers were detected. Consider [...] options. Benchmark #3: git log --no-walk --format=%h 1e59178e3f Time (mean ± σ): 3.2 ms ± 0.1 ms [User: 2.4 ms, System: 0.8 ms] Range (min … max): 2.9 ms … 4.2 ms 697 runs Warning: Command took less than 5 ms to complete. Results might [...] Warning: Statistical outliers were detected. Consider [...] Summary 'git log --no-walk --format=%h 1e59178e3f' ran 1.01 ± 0.08 times faster than 'git show --no-patch --diff-merges=off --format=%h 1e59178e3f' 14.98 ± 0.79 times faster than 'git show --no-patch --format=%h 1e59178e3f'
