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From: Jeff King <peff@peff.net>
To: Jonathan Tan <jonathantanmy@google.com>
Cc: git@vger.kernel.org, gitster@pobox.com
Subject: Re: [PATCH v2] send-pack: never fetch when checking exclusions
Date: Fri, 11 Oct 2019 02:12:57 -0400
Message-ID: <20191011061257.GD20094@sigill.intra.peff.net> (raw)
In-Reply-To: <20191008183739.194714-1-jonathantanmy@google.com>

On Tue, Oct 08, 2019 at 11:37:39AM -0700, Jonathan Tan wrote:

> When building the packfile to be sent, send_pack() is given a list of
> remote refs to be used as exclusions. For each ref, it first checks if
> the ref exists locally, and if it does, passes it with a "^" prefix to
> pack-objects. However, in a partial clone, the check may trigger a lazy
> fetch.
> 
> The additional commit ancestry information obtained during such fetches
> may show that certain objects that would have been sent are already
> known to the server, resulting in a smaller pack being sent. But this is
> at the cost of fetching from many possibly unrelated refs, and the lazy
> fetches do not help at all in the typical case where the client is
> up-to-date with the upstream of the branch being pushed.
> 
> 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.

-Peff

  reply index

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 [this message]
2019-10-11 12:31       ` Derrick Stolee
2019-10-11 16:15         ` Jeff King
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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