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From: Jeff King <peff@peff.net>
To: Derrick Stolee <stolee@gmail.com>
Cc: Jonathan Tan <jonathantanmy@google.com>,
	git@vger.kernel.org, gitster@pobox.com
Subject: Re: [PATCH v2] send-pack: never fetch when checking exclusions
Date: Fri, 11 Oct 2019 12:15:05 -0400
Message-ID: <20191011161504.GB19741@sigill.intra.peff.net> (raw)
In-Reply-To: <a87cf3ce-fbff-ef4e-941e-bd2da0bf182f@gmail.com>

On Fri, Oct 11, 2019 at 08:31:30AM -0400, Derrick Stolee wrote:

> >> Ensure that these lazy fetches do not occur.
> > 
> > That makes sense. For similar reasons, should we be using
> > OBJECT_INFO_QUICK here? If the other side has a bunch of ref tips that
> > we don't have, we'll end up re-scanning the pack directory over and over
> > (which is _usually_ pretty quick, but can be slow if you have a lot of
> > packs locally). And it's OK if we racily miss out on an exclusion due to
> > somebody else repacking simultaneously.
> 
> That's a good idea. We can hint to the object store that we don't expect
> misses to be due to a concurrent repack, so we don't want to reprepare
> pack-files.

As a general rule (and why I'm raising this issue in reply to Jonathan's
patch), I think most or all sites that want OBJECT_INFO_QUICK will want
SKIP_FETCH_OBJECT as well, and vice versa. The reasoning is generally
the same:

  - it's OK to racily have a false negative (we'll still be correct, but
    possibly a little less optimal)

  - it's expected and normal to be missing the object, so spending time
    double-checking the pack store wastes measurable time in real-world
    cases

-Peff

  reply	other threads:[~2019-10-11 16:15 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-07 21:38 [PATCH] " Jonathan Tan
2019-10-08  4:10 ` Junio C Hamano
2019-10-08 18:37   ` [PATCH v2] " Jonathan Tan
2019-10-11  6:12     ` Jeff King
2019-10-11 12:31       ` Derrick Stolee
2019-10-11 16:15         ` Jeff King [this message]
2019-10-11 22:08           ` Jonathan Tan
2019-10-17  6:10             ` Jeff King
2019-10-12  0:47           ` Junio C Hamano

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