Re: upload-pack is slow with lots of refs

On Thu, Oct 4, 2012 at 1:21 AM, Jeff King [off-list ref] wrote:

On Thu, Oct 04, 2012 at 12:32:35AM +0200, Ævar Arnfjörð Bjarmason wrote:

quoted

On Wed, Oct 3, 2012 at 8:03 PM, Jeff King [off-list ref] wrote:

quoted

What version of git are you using?  In the past year or so, I've made
several tweaks to speed up large numbers of refs, including:

  - cff38a5 (receive-pack: eliminate duplicate .have refs, v1.7.6); note
    that this only helps if they are being pulled in by an alternates
    repo. And even then, it only helps if they are mostly duplicates;
    distinct ones are still O(n^2).

  - 7db8d53 (fetch-pack: avoid quadratic behavior in remove_duplicates)
    a0de288 (fetch-pack: avoid quadratic loop in filter_refs)
    Both in v1.7.11. I think there is still a potential quadratic loop
    in mark_complete()

  - 90108a2 (upload-pack: avoid parsing tag destinations)
    926f1dd (upload-pack: avoid parsing objects during ref advertisement)
    Both in v1.7.10. Note that tag objects are more expensive to
    advertise than commits, because we have to load and peel them.

Even with those patches, though, I found that it was something like ~2s
to advertise 100,000 refs.

FWIW I bisected between 1.7.9 and 1.7.10 and found that the point at
which it went from 1.5/s to 2.5/s upload-pack runs on the pathological
git.git repository was none of those, but:

    ccdc6037fe - parse_object: try internal cache before reading object db

Ah, yeah, I forgot about that one. That implies that you have a lot of
refs pointing to the same objects (since the benefit of that commit is
to avoid reading from disk when we have already seen it).

Out of curiosity, what does your repo contain? I saw a lot of speedup
with that commit because my repos are big object stores, where we have
the same duplicated tag refs for every fork of the repo.

Things are much faster with your monkeypatch, got up to around 10
runs/s.

The repository mainly contains a lot of git-deploy[1] generated tags
which are added for every rollout to several subsystems.

Of the ~50k references in the repo 75% point to a commit that no other
reference points to. Around 98% of the references are annotated tags,
the rest are branches.

1. https://github.com/git-deploy/git-deploy