Jeff King <peff@xxxxxxxx> 于2021年9月4日周六 下午8:40写道： > > Somebody complained to me off-list recently that for-each-ref was slow > when doing a trivial listing (like refname + objectname) of a large > number of refs, even though you could get mostly the same output by > just dumping the packed-refs file. > > So I was nerd-sniped into making this horrible series, which does speed > up some cases. It was a combination of "how fast can we easily get it", > plus I was curious _which_ parts of for-each-ref were actually slow. > > In this version there are 2 patches, tested against 'git for-each-ref > --format="%(objectname) %(refname)"' on a fully packed repo with 500k > refs: > Regarding this 500k refs, is there any way I can reproduce it? > - directly outputting items rather than building up a ref_array yields > about a 1.5x speedup > > - avoiding the whole atom-formatting system yields a 2.5x speedup on > top of that > > I had originally written it against a slightly older version of Git, > before show_ref_array_item() was inlined. In that version, there was a > middle ground where we still created a ref_array_item for each ref, and > then fed it to the "quick" formatter (so we could see the cost of > having to malloc/free a bunch of ref_array_item structs). The numbers > there wre: > > - streaming out items gave a 1.5x speedup > > - using the "quick" formatter gave a 1.8x speedup > > - avoiding the extra malloc/free for each item gave a 1.4x > > which makes sense; 1.8 * 1.4 is ~2.5, so it's the same speedup just > broken down further. > > I'm not sure I'm really advocating that we should do something like > this, though it is tempting because it does make some common queries > much faster. But I wanted to share it here to give some insight on where > the time may be going in ref-filter / for-each-ref. > Well, this acceleration looks gratifying. But so far I haven't seen its effect on git cat-file --batch | --batch-check. > [1/2]: ref-filter: hacky "streaming" mode > [2/2]: ref-filter: implement "quick" formats > > builtin/for-each-ref.c | 7 +++ > ref-filter.c | 113 +++++++++++++++++++++++++++++++++++++---- > ref-filter.h | 21 ++++++++ > 3 files changed, 132 insertions(+), 9 deletions(-) > > -Peff
