Re: [PATCH] send-pack: use OBJECT_INFO_QUICK to check negative objects

> Subject: [PATCH] send-pack: use OBJECT_INFO_QUICK to check negative objects
>
> When pushing, we feed pack-objects a list of both positive and negative
> objects. The positive objects are what we want to send, and the negative
> objects are what the other side told us they have, which we can use to
> limit the size of the push.
>
> Before passing along a negative object, send_pack() will make sure we
> actually have it (since we only know about it because the remote
> mentioned it, not because it's one of our refs). So it's expected that
> some of these objects will be missing on the local side. But looking for
> a missing object is more expensive than one that we have: it triggers
> reprepare_packed_git() to handle a racy repack, plus it has to explore
> every alternate's loose object tree (which can be slow if you have a lot
> of them, or have a high-latency filesystem).

> This isn't usually a big problem, since repositories you're pushing to
> don't generally have a large number of refs that are unrelated to what
> the client has. But there's no reason such a setup is wrong, and it
> currently performs poorly.
>
> We can fix this by using OBJECT_INFO_QUICK, which tells the lookup
> code that we expect objects to be missing. Notably, it will not re-scan
> the packs, and it will use the loose cache from 61c7711cfe (sha1-file:
> use loose object cache for quick existence check, 2018-11-12).

> ---
> Interestingly, upload-pack does not use OBJECT_INFO_QUICK when it's
> getting oids from the other side. But I think it could possibly benefit
> in the same way. Nobody seems to have noticed. Perhaps it simply comes
> up less, as servers would tend to have more objects than their clients?