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From: Jeff King <peff@peff.net>
To: git@vger.kernel.org
Cc: "Junio C Hamano" <gitster@pobox.com>,
	"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>
Subject: [RFC/PATCHv2 6/6] limit "contains" traversals based on commit generation
Date: Wed, 13 Jul 2011 03:06:44 -0400
Message-ID: <20110713070644.GF18566@sigill.intra.peff.net> (raw)
In-Reply-To: <20110713064709.GA18499@sigill.intra.peff.net>

When looking for commits that contain other commits (e.g.,
via "git tag --contains"), we can end up traversing useless
portions of the graph. For example, if I am looking for a
tag that contains a commit made last week, there is not much
point in traversing portions of the history graph made five
years ago.

This optimization can provide massive speedups. For example,
doing "git tag --contains HEAD~1000" in the linux-2.6
repository goes from:

  real    0m3.139s
  user    0m3.044s
  sys     0m0.092s

to:

  real    0m0.035s
  user    0m0.028s
  sys     0m0.004s

We could use commit timestamps to know when we are going too
far back in history, but they are sometimes not trustworthy.
Extreme clock skew on committers' machines (or bugs in
commit-generating software) mean that we may stop the
traversal too early when seeing commits skewed into the
past.

Instead, we use the calculated commit generation, which is a
propery of the graph itself (but since we cache it, it's
still cheap to consult).

Signed-off-by: Jeff King <peff@peff.net>
---
Same as previous version.

 builtin/tag.c |   20 +++++++++++++++++---
 1 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/builtin/tag.c b/builtin/tag.c
index 63bce6e..df6de47 100644
--- a/builtin/tag.c
+++ b/builtin/tag.c
@@ -40,7 +40,8 @@ static int in_commit_list(const struct commit_list *want, struct commit *c)
 }
 
 static int contains_recurse(struct commit *candidate,
-			    const struct commit_list *want)
+			    const struct commit_list *want,
+			    unsigned long cutoff)
 {
 	struct commit_list *p;
 
@@ -57,9 +58,13 @@ static int contains_recurse(struct commit *candidate,
 	if (parse_commit(candidate) < 0)
 		return 0;
 
+	/* stop searching if we go too far back in time */
+	if (commit_generation(candidate) < cutoff)
+		return 0;
+
 	/* Otherwise recurse and mark ourselves for future traversals. */
 	for (p = candidate->parents; p; p = p->next) {
-		if (contains_recurse(p->item, want)) {
+		if (contains_recurse(p->item, want, cutoff)) {
 			candidate->object.flags |= TMP_MARK;
 			return 1;
 		}
@@ -70,7 +75,16 @@ static int contains_recurse(struct commit *candidate,
 
 static int contains(struct commit *candidate, const struct commit_list *want)
 {
-	return contains_recurse(candidate, want);
+	unsigned long cutoff = ULONG_MAX;
+	const struct commit_list *c;
+
+	for (c = want; c; c = c->next) {
+		unsigned long g = commit_generation(c->item);
+		if (g < cutoff)
+			cutoff = g;
+	}
+
+	return contains_recurse(candidate, want, cutoff);
 }
 
 static int show_reference(const char *refname, const unsigned char *sha1,
-- 
1.7.6.37.g989c6

  parent reply index

Thread overview: 56+ 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
2011-08-05 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 ` Jeff King [this message]
2011-07-13  7:23   ` [RFC/PATCHv2 6/6] limit "contains" traversals based on commit generation 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
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
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

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