From: Josh Triplett <josh@joshtriplett.org>
To: Junio C Hamano <gitster@pobox.com>
Cc: git@vger.kernel.org
Subject: Re: gc and repack ignore .git/*HEAD when checking reachability
Date: Thu, 7 Jul 2016 23:44:49 -0700 [thread overview]
Message-ID: <20160708064448.GA18043@x> (raw)
In-Reply-To: <xmqq1t34oiit.fsf@gitster.mtv.corp.google.com>
On Thu, Jul 07, 2016 at 09:34:02PM -0700, Junio C Hamano wrote:
> Josh Triplett <josh@joshtriplett.org> writes:
> > This could result in data loss, if a user expected that having an object
> > referenced from those places would protect it from pruning.
>
> Yeah, luckily, nobody expects such. I do not think any of our
> document says nothing other than HEAD like CHERRY_PICK_HEAD is
> reachability anchoring point; they are designed to be transient.
I can imagine at least one scenario that would result in data loss here:
git pull a URL (not referenced via any ref other than
FETCH_HEAD/MERGE_HEAD), get a merge conflict, get halfway through
resolving it, set that repository aside for a while, do something that
triggers a gc, then attempt to finish and commit.
Unlikely, but not impossible. Same reason the reachability logic looks
at the index.
(I originally encountered this because I intended to add another
HEAD-like ref in .git, so I started investigating the logic around such
HEADs.)
> Because they are designed to be transient, I do not think there is
> any downside (other than the initial start-up cost) to including
> them in reachability computation. Because they are meant to be
> transient, the objects anchored by them would be reachable from
> other anchoring points anyway.
That sounds reasonable. And if they *do* end up taking any time to
traverse, it's because they weren't reachable from other anchoring
points, so taking the extra time to traverse them seems fine.
- Josh Triplett
next prev parent reply other threads:[~2016-07-08 6:44 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-07-08 2:59 gc and repack ignore .git/*HEAD when checking reachability Josh Triplett
2016-07-08 4:34 ` Junio C Hamano
2016-07-08 6:44 ` Josh Triplett [this message]
2016-07-08 17:14 ` Junio C Hamano
2016-07-08 19:25 ` Theodore Ts'o
2016-07-08 20:30 ` Junio C Hamano
2016-07-08 23:50 ` Theodore Ts'o
2016-07-09 5:23 ` Josh Triplett
2016-07-08 20:29 ` Josh Triplett
2016-07-09 7:35 ` Johannes Schindelin
2016-07-09 14:09 ` Josh Triplett
2016-07-09 16:45 ` Duy Nguyen
2016-07-10 10:59 ` Johannes Schindelin
2016-07-10 11:04 ` Duy Nguyen
2016-07-10 14:16 ` Johannes Schindelin
2016-07-10 15:01 ` Duy Nguyen
2016-07-11 6:07 ` Johannes Schindelin
2016-07-11 18:52 ` Junio C Hamano
2016-07-12 10:47 ` Johannes Schindelin
2016-07-12 15:26 ` Jeff King
2016-07-12 15:46 ` Duy Nguyen
2016-07-12 15:51 ` Jeff King
2016-07-12 16:13 ` Duy Nguyen
2016-07-13 8:20 ` Johannes Schindelin
2016-07-13 14:54 ` Duy Nguyen
2016-07-13 18:59 ` Johannes Schindelin
2016-07-15 15:46 ` Duy Nguyen
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