commit | 88473c8baeefafe6b95ab0f62eb2f12e2b098ac7 | [log] [tgz] |
---|---|---|
author | Jeff King <peff@peff.net> | Tue Jun 22 13:06:48 2021 -0400 |
committer | Junio C Hamano <gitster@pobox.com> | Mon Jun 28 20:31:40 2021 -0700 |
tree | 2cacfa9c322765de2dedce9520ee1b2ec3a12698 | |
parent | 7463064b28086c0a765e247bc8336f8e32356494 [diff] |
load_ref_decorations(): avoid parsing non-tag objects When we load the ref decorations, we parse the object pointed to by each ref in order to get a "struct object". This is unnecessarily expensive; we really only need the object struct, and don't even look at the parsed contents. The exception is tags, which we do need to peel. We can improve this by looking up the object type first (which is much cheaper), and skipping the parse entirely for non-tags. This increases the work slightly for annotated tags (which now do a type lookup _and_ a parse), but decreases it a lot for other types. On balance, this seems to be a good tradeoff. In my git.git clone, with ~2k refs, most of which are branches, the time to run "git log -1 --decorate" drops from 34ms to 11ms. Even on my linux.git clone, which contains mostly tags and only a handful of branches, the time drops from 30ms to 19ms. And on a more extreme real-world case with ~220k refs, mostly non-tags, the time drops from 2.6s to 650ms. That command is a lop-sided example, of course, because it does as little non-loading work as possible. But it does show the absolute time improvement. Even in something like a full "git log --decorate" on that extreme repo, we'd still be saving 2s of CPU time. Ideally we could push this even further, and avoid parsing even tags, by relying on the packed-refs "peel" optimization (which we could do by calling peel_iterated_oid() instead of peeling manually). But we can't do that here. The packed-refs file only stores the bottom-layer of the peel (so in a "tag->tag->commit" chain, it stores only the commit as the peel result). But the decoration code wants to peel the layers individually, annotating the middle layers of the chain. If the packed-refs file ever learns to store all of the peeled layers, then we could switch to it. Or even if it stored a flag to indicate the peel was not multi-layer (because most of them aren't), then we could use it most of the time and fall back to a manual peel for the rare cases. Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>
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