Re: upload-pack is slow with lots of refs

["Ævar Arnfjörð Bjarmason" <avarab@gmail.com>]

On Wed, Oct 3, 2012 at 8:03 PM, Jeff King <peff@peff.net> wrote:
> 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