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From: Jeff King <peff@peff.net>
To: Junio C Hamano <gitster@pobox.com>
Cc: git@vger.kernel.org, "Jakub Narebski" <jnareb@gmail.com>,
	"Ted Ts'o" <tytso@mit.edu>,
	"Jonathan Nieder" <jrnieder@gmail.com>,
	"Ævar Arnfjörð Bjarmason" <avarab@gmail.com>,
	"Clemens Buchacher" <drizzd@aon.at>,
	"Shawn O. Pearce" <spearce@spearce.org>,
	"Linus Torvalds" <torvalds@linux-foundation.org>
Subject: Re: [RFC/PATCHv2 6/6] limit "contains" traversals based on commit generation
Date: Fri, 15 Jul 2011 17:14:41 -0400	[thread overview]
Message-ID: <20110715211441.GB1943@sigill.intra.peff.net> (raw)
In-Reply-To: <7vzkkfz261.fsf@alter.siamese.dyndns.org>

On Fri, Jul 15, 2011 at 02:04:06PM -0700, Junio C Hamano wrote:

> Jeff King <peff@peff.net> writes:
> 
> >>    So how about marking commits (using the metainfo-cache facility) that
> >>    has an ancestor (not necessarily its direct parent) that records a
> >>    younger timestamp (e.g. 1 is such a commit, as its ancestors include
> >>    things like 2 and 4)? There should be relatively small number of them,
> >>    and still_interesting() logic can be told to dig through such commits
> >>    even if everybody is uninteresting in the active list.
> > ...
> >>  * As to "tag --contains", when timestamp based heuristics breaks down is
> >>    when a tagged commit incorrectly records way young timestamp or the
> >>    "want" commit records way old timetsamp. I haven't thought things
> >>    through, but the same metainfo-cache may be useful to detect which
> >>    commit to dig through ignoring the cutoff heuristics.
> >
> > It can also break down if intermediate commits are wrong, because we
> > have to traverse backwards, and we may erroneously cutoff early.
> >
> > For example:
> >
> >    A--B--C
> >
> >    timestamp(A) = 2
> >    timestamp(B) = 1 # skewed!
> >    timestamp(C) = 3
> >
> > If tag=C and want=A, then we traverse backwards from C. We can't stop
> > immediately because we know that 2 < 3. But we go back to B, and see
> > that 2 > 1, and assume that A cannot possibly be an ancestor of B.
> 
> I envisioned that the metainfo-cache to help rev-list I mentioned earlier
> would mark B having an ancestor A that has a timestamp younger than it, so
> I think we can certainly notice that we have to "dig through" B.

Right. I thought you were talking about the case where we did not have
such a cache. But given your response, did you mean:

  If we have such a cache, then the only thing left to worry about is
  when we specifically ask about a commit (either a tag or a "want"
  commit) that is skewed.

That I agree with.

-Peff

  reply	other threads:[~2011-07-15 21:14 UTC|newest]

Thread overview: 57+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-07-13  6:47 [RFC/PATCHv2 0/6] generation numbers for faster traversals Jeff King
2011-07-13  6:57 ` [RFC/PATCHv2 1/6] decorate: allow storing values instead of pointers Jeff King
2011-07-13 17:52   ` Jonathan Nieder
2011-07-13 20:08     ` Jeff King
2011-07-14 17:34       ` Jeff King
2011-07-14 17:51         ` [PATCH 1/3] implement generic key/value map Jeff King
2011-07-14 18:52           ` Bert Wesarg
2011-07-14 18:54             ` Bert Wesarg
2011-07-14 18:55               ` Jeff King
2011-07-14 19:07                 ` Bert Wesarg
2011-07-14 19:14                   ` Jeff King
2011-07-14 19:18                     ` Bert Wesarg
2011-07-14 17:52         ` [PATCH 2/3] fast-export: use object to uint32 map instead of "decorate" Jeff King
2011-07-15  9:40           ` Sverre Rabbelier
2011-07-15 20:00             ` Jeff King
2011-07-14 17:53         ` [PATCH 3/3] decorate: use "map" for the underlying implementation Jeff King
2011-07-14 21:06         ` [RFC/PATCHv2 1/6] decorate: allow storing values instead of pointers Junio C Hamano
2011-08-04 22:43           ` [RFC/PATCH 0/5] macro-based key/value maps Jeff King
2011-08-04 22:45             ` [PATCH 1/5] implement generic key/value map Jeff King
2011-08-04 22:46             ` [PATCH 2/5] fast-export: use object to uint32 map instead of "decorate" Jeff King
2011-08-04 22:46             ` [PATCH 3/5] decorate: use "map" for the underlying implementation Jeff King
2011-08-04 22:46             ` [PATCH 4/5] map: implement persistent maps Jeff King
2011-08-04 22:46             ` [PATCH 5/5] implement metadata cache subsystem Jeff King
2011-08-04 22:48             ` [RFC/PATCH 0/2] patch-id caching Jeff King
2011-08-04 22:49               ` [PATCH 1/2] cherry: read default config Jeff King
2011-08-04 22:49               ` [PATCH 2/2] cache patch ids on disk Jeff King
2011-08-04 22:52                 ` Jeff King
2011-08-05 11:03             ` [RFC/PATCH 0/5] macro-based key/value maps Jeff King
2011-08-05 15:31               ` René Scharfe
2011-08-06  6:30                 ` Jeff King
2011-07-13  7:04 ` [RFC/PATCHv2 2/6] add metadata-cache infrastructure Jeff King
2011-07-13  8:18   ` Bert Wesarg
2011-07-13  8:31     ` Jeff King
2011-07-13  8:45       ` Bert Wesarg
2011-07-13 19:18         ` Jeff King
2011-07-13 19:40       ` Junio C Hamano
2011-07-13 19:33   ` Junio C Hamano
2011-07-13 20:25     ` Jeff King
2011-07-13  7:05 ` [RFC/PATCHv2 3/6] commit: add commit_generation function Jeff King
2011-07-13 14:26   ` Eric Sunshine
2011-07-13  7:05 ` [RFC/PATCHv2 4/6] pretty: support %G to show the generation number of a commit Jeff King
2011-07-13  7:06 ` [RFC/PATCHv2 5/6] check commit generation cache validity against grafts Jeff King
2011-07-13 14:26   ` Eric Sunshine
2011-07-13 19:35     ` Jeff King
2011-07-13  7:06 ` [RFC/PATCHv2 6/6] limit "contains" traversals based on commit generation Jeff King
2011-07-13  7:23   ` Jeff King
2011-07-13 20:33     ` Junio C Hamano
2011-07-13 20:58       ` Jeff King
2011-07-13 21:12         ` Junio C Hamano
2011-07-13 21:18           ` Jeff King
2011-07-15 18:22   ` Junio C Hamano
2011-07-15 20:40     ` Jeff King
2011-07-15 21:04       ` Junio C Hamano
2011-07-15 21:14         ` Jeff King [this message]
2011-07-15 21:01 ` Generation numbers and replacement objects Jakub Narebski
2011-07-15 21:10   ` Jeff King
2011-07-16 21:10     ` Jakub Narebski

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