From: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Date: Thu, 27 Oct 2011 21:01:50 GMT
Subject: Re: [PATCH 2/2] pack-objects: optimize "recency order"
Message-ID: <CACBZZX6Ss4jLtdrDhLUNKCUjEHjHHKzfv-LMkOyTPDhRUXm4sQ@mail.gmail.com>
In-Reply-To: <1310084657-16790-3-git-send-email-gitster@pobox.com>

On Fri, Jul 8, 2011 at 02:24, Junio C Hamano <gitster@pobox.com> wrote:

>  - Commits at the tip of tags are written together, in the hope that
>   revision traversal done in incremental fetch (which starts by
>   putting them in a revision queue marked as UNINTERESTING) will see a
>   better locality of these objects;

We recently upgraded to 1.7.7 and I've traced a very large slowdown in
packing down to this commit.

On our repository packing used to take around 30 seconds, it now takes
about 4 minutes. Which means that cloning the repository went from
being slightly slow to pretty intolerable.

I haven't dug into why this is but I'm pretty sure it's because this
patch makes Git behave pathologically on repositories with a large
amount of tags. git.git itself has ~27k revs / and ~450 tags, or a tag
every ~60 revisions.

Try it on e.g. a repository with a couple of hundred thousand revs and
a tag every 10-20 revisions.