From: Taylor Blau <me@ttaylorr.com>
To: "Ævar Arnfjörð Bjarmason" <avarab@gmail.com>
Cc: Taylor Blau <ttaylorr@github.com>, Sun Chao <16657101987@163.com>,
Sun Chao via GitGitGadget <gitgitgadget@gmail.com>,
git@vger.kernel.org
Subject: Re: [PATCH v2] packfile: freshen the mtime of packfile by configuration
Date: Wed, 14 Jul 2021 15:30:51 -0400 [thread overview]
Message-ID: <YO87ax2JpLndc5Ly@nand.local> (raw)
In-Reply-To: <877dhs20x3.fsf@evledraar.gmail.com>
On Wed, Jul 14, 2021 at 08:19:15PM +0200, Ævar Arnfjörð Bjarmason wrote:
> >> The reason why we want to avoid freshen the mtime of ".pack" file is to
> >> improve the reading speed of Git Servers.
> >
> > That's surprising behavior to me. Are you saying that calling utime(2)
> > causes the *page* cache to be invalidated and that most reads are
> > cache-misses lowering overall IOPS?
>
> I think you may be right narrowly, but wrong in this context :)
>
> I.e. my understanding of this problem is that they have some incremental
> backup job, e.g. rsync without --checksum (not that doing that would
> help, chicken & egg issue)..
Ah, thanks for explaining. That's helpful, and changes my thinking.
Ideally, Sun would be able to use --checksum (if they are using rsync)
or some equivalent (if they are not). In other words, this seems like a
problem that Git shouldn't be bending over backwards for.
But if that isn't possible, then I find introducing a new file to
redefine the pack's mtime just to accommodate a backup system that
doesn't know better to be a poor justification for adding this
complexity. Especially since we agree that rsync-ing live Git
repositories is a bad idea in the first place ;).
If it were me, I would probably stop here and avoid pursuing this
further. But an OK middle ground might be core.freshenPackfiles=<bool>
to indicate whether or not packs can be freshened, or the objects
contained within them should just be rewritten loose.
Sun could then set this configuration to "false", implying:
- That they would have more random loose objects, leading to some
redundant work by their backup system.
- But they wouldn't have to resync their huge packfiles.
...and we wouldn't have to introduce any new formats/file types to do
it. To me, that seems like a net-positive outcome.
Thanks,
Taylor
next prev parent reply other threads:[~2021-07-14 19:30 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-10 19:01 [PATCH] packfile: enhance the mtime of packfile by idx file Sun Chao via GitGitGadget
2021-07-11 23:44 ` Ævar Arnfjörð Bjarmason
2021-07-12 16:17 ` Sun Chao
2021-07-14 1:28 ` [PATCH v2] packfile: freshen the mtime of packfile by configuration Sun Chao via GitGitGadget
2021-07-14 1:39 ` Ævar Arnfjörð Bjarmason
2021-07-14 2:52 ` Taylor Blau
2021-07-14 16:46 ` Sun Chao
2021-07-14 17:04 ` Taylor Blau
2021-07-14 18:19 ` Ævar Arnfjörð Bjarmason
2021-07-14 19:11 ` Martin Fick
2021-07-14 19:41 ` Ævar Arnfjörð Bjarmason
2021-07-14 20:20 ` Martin Fick
2021-07-20 6:32 ` Ævar Arnfjörð Bjarmason
2021-07-15 8:23 ` Son Luong Ngoc
2021-07-20 6:29 ` Ævar Arnfjörð Bjarmason
2021-07-14 19:30 ` Taylor Blau [this message]
2021-07-14 19:32 ` Ævar Arnfjörð Bjarmason
2021-07-14 19:52 ` Taylor Blau
2021-07-14 21:40 ` Junio C Hamano
2021-07-15 16:30 ` Sun Chao
2021-07-15 16:42 ` Taylor Blau
2021-07-15 16:48 ` Sun Chao
2021-07-14 16:11 ` Sun Chao
2021-07-19 19:53 ` [PATCH v3] " Sun Chao via GitGitGadget
2021-07-19 20:51 ` Taylor Blau
2021-07-20 0:07 ` Junio C Hamano
2021-07-20 15:07 ` Sun Chao
2021-07-20 6:19 ` Ævar Arnfjörð Bjarmason
2021-07-20 15:34 ` Sun Chao
2021-07-20 15:00 ` Sun Chao
2021-07-20 16:53 ` Taylor Blau
2021-08-15 17:08 ` [PATCH v4 0/2] " Sun Chao via GitGitGadget
2021-08-15 17:08 ` [PATCH v4 1/2] packfile: rename `derive_filename()` to `derive_pack_filename()` Sun Chao via GitGitGadget
2021-08-15 17:08 ` [PATCH v4 2/2] packfile: freshen the mtime of packfile by bump file Sun Chao via GitGitGadget
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