From: Junio C Hamano <gitster@pobox.com>
To: Jeff King <peff@peff.net>
Cc: git@vger.kernel.org
Subject: Re: [PATCH 0/2] optimizing pack access on "read only" fetch repos
Date: Sat, 26 Jan 2013 22:32:42 -0800 [thread overview]
Message-ID: <7vlibfxhit.fsf@alter.siamese.dyndns.org> (raw)
In-Reply-To: <20130126224011.GA20675@sigill.intra.peff.net> (Jeff King's message of "Sat, 26 Jan 2013 17:40:11 -0500")
Jeff King <peff@peff.net> writes:
> This is a repost from here:
>
> http://thread.gmane.org/gmane.comp.version-control.git/211176
>
> which got no response initially. Basically the issue is that read-only
> repos (e.g., a CI server) whose workflow is something like:
>
> git fetch $some_branch &&
> git checkout -f $some_branch &&
> make test
>
> will never run git-gc, and will accumulate a bunch of small packs and
> loose objects, leading to poor performance.
>
> Patch 1 runs "gc --auto" on fetch, which I think is sane to do.
>
> Patch 2 optimizes our pack dir re-scanning for fetch-pack (which, unlike
> the rest of git, should expect to be missing lots of objects, since we
> are deciding what to fetch).
>
> I think 1 is a no-brainer. If your repo is packed, patch 2 matters less,
> but it still seems like a sensible optimization to me.
>
> [1/2]: fetch: run gc --auto after fetching
> [2/2]: fetch-pack: avoid repeatedly re-scanning pack directory
>
> -Peff
Both makes sense to me.
I also wonder if we would be helped by another "repack" mode that
coalesces small packs into a single one with minimum overhead, and
run that often from "gc --auto", so that we do not end up having to
have 50 packfiles.
When we have 2 or more small and young packs, we could:
- iterate over idx files for these packs to enumerate the objects
to be packed, replacing read_object_list_from_stdin() step;
- always choose to copy the data we have in these existing packs,
instead of doing a full prepare_pack(); and
- use the order the objects appear in the original packs, bypassing
compute_write_order().
The procedure cannot be a straight byte-for-byte copy, because some
objects may appear in multiple packs, and extra copies of the same
object have to be excised from the result. OFS_DELTA offsets need
to be adjusted for objects that appear later in the output and for
objects that were deltified against such an object that recorded its
base with OFS_DELTA format.
But other than such OFS_DELTA adjustments, it feels that such an
"only coalesce multiple packs into one" mode should be fairly quick.
next prev parent reply other threads:[~2013-01-27 6:33 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-01-26 22:40 [PATCH 0/2] optimizing pack access on "read only" fetch repos Jeff King
2013-01-26 22:40 ` [PATCH 1/2] fetch: run gc --auto after fetching Jeff King
2013-01-27 1:51 ` Jonathan Nieder
[not found] ` <87bmopzbqx.fsf@gmail.com>
2017-07-12 20:00 ` git gc --auto aquires *.lock files that make a subsequent git-fetch error out Jeff King
2017-07-12 20:30 ` Ævar Arnfjörð Bjarmason
2017-07-12 20:43 ` Jeff King
2013-01-26 22:40 ` [PATCH 2/2] fetch-pack: avoid repeatedly re-scanning pack directory Jeff King
2013-01-27 10:27 ` Jonathan Nieder
2013-01-27 20:09 ` Junio C Hamano
2013-01-27 23:20 ` Jonathan Nieder
2013-01-27 6:32 ` Junio C Hamano [this message]
2013-01-29 8:06 ` [PATCH 0/2] optimizing pack access on "read only" fetch repos Shawn Pearce
2013-01-29 8:29 ` Jeff King
2013-01-29 15:25 ` Martin Fick
2013-01-29 15:58 ` Junio C Hamano
2013-01-29 21:19 ` Jeff King
2013-01-29 22:26 ` Junio C Hamano
2013-01-31 16:47 ` Shawn Pearce
2013-02-01 9:14 ` Jeff King
2013-02-02 10:07 ` Shawn Pearce
2013-01-29 11:01 ` Duy Nguyen
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