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From: Jeff King <peff@peff.net>
To: "Ævar Arnfjörð Bjarmason" <avarab@gmail.com>
Cc: Git Mailing List <git@vger.kernel.org>
Subject: [PATCH 3/4] peel_ref: check object type before loading
Date: Thu, 4 Oct 2012 04:02:53 -0400	[thread overview]
Message-ID: <20121004080253.GC31325@sigill.intra.peff.net> (raw)
In-Reply-To: <20121004075609.GA1355@sigill.intra.peff.net>

The point of peel_ref is to dereference tags; if the base
object is not a tag, then we can return early without even
loading the object into memory.

This patch accomplishes that by checking sha1_object_info
for the type. For a packed object, we can get away with just
looking in the pack index. For a loose object, we only need
to inflate the first couple of header bytes.

This is a bit of a gamble; if we do find a tag object, then
we will end up loading the content anyway, and the extra
lookup will have been wasteful. However, if it is not a tag
object, then we save loading the object entirely. Depending
on the ratio of non-tags to tags in the input, this can be a
minor win or minor loss.

However, it does give us one potential major win: if a ref
points to a large blob (e.g., via an unannotated tag), then
we can avoid looking at it entirely.

Signed-off-by: Jeff King <peff@peff.net>
---
This optimization is the one that gave me the most pause. While
upload-pack does call peel_ref on everything, the other callers all
constrain themselves to refs/tags/. So for many projects, we will be
calling it mostly on annotated tags, and it may be a very small net
loss. But in practice, it will not matter for most projects with a sane
number of normal tags, and saving even one accidental giant blob load
can have a huge impact.

 refs.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/refs.c b/refs.c
index f672ad9..02e47b1 100644
--- a/refs.c
+++ b/refs.c
@@ -1225,8 +1225,15 @@ fallback:
 	}
 
 fallback:
-	o = parse_object(base);
-	if (o && o->type == OBJ_TAG) {
+	o = lookup_unknown_object(base);
+	if (o->type == OBJ_NONE) {
+		int type = sha1_object_info(base, NULL);
+		if (type < 0)
+			return -1;
+		o->type = type;
+	}
+
+	if (o->type == OBJ_TAG) {
 		o = deref_tag_noverify(o);
 		if (o) {
 			hashcpy(sha1, o->sha1);
-- 
1.8.0.rc0.10.g8dd2a92

  parent reply	other threads:[~2012-10-04 22:02 UTC|newest]

Thread overview: 38+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-10-03 12:36 upload-pack is slow with lots of refs Ævar Arnfjörð Bjarmason
2012-10-03 13:06 ` Nguyen Thai Ngoc Duy
2012-10-03 18:03 ` Jeff King
2012-10-03 18:53   ` Junio C Hamano
2012-10-03 18:55     ` Jeff King
2012-10-03 19:41       ` Shawn Pearce
2012-10-03 20:13         ` Jeff King
2012-10-04 21:52           ` Sascha Cunz
2012-10-05  0:20             ` Jeff King
2012-10-05  6:24         ` Johannes Sixt
2012-10-05 16:57           ` Shawn Pearce
2012-10-08 15:05             ` Johannes Sixt
2012-10-09  6:46               ` Shawn Pearce
2012-10-09 20:30                 ` Johannes Sixt
2012-10-09 20:46                   ` Johannes Sixt
2012-10-03 20:16   ` Ævar Arnfjörð Bjarmason
2012-10-03 21:20     ` Jeff King
2012-10-03 22:15       ` Ævar Arnfjörð Bjarmason
2012-10-03 23:15         ` Jeff King
2012-10-03 23:54           ` Ævar Arnfjörð Bjarmason
2012-10-04  7:56             ` [PATCH 0/4] optimizing upload-pack ref peeling Jeff King
2012-10-04  7:58               ` [PATCH 1/4] peel_ref: use faster deref_tag_noverify Jeff King
2012-10-04 18:24                 ` Junio C Hamano
2012-10-04  8:00               ` [PATCH 2/4] peel_ref: do not return a null sha1 Jeff King
2012-10-04 18:32                 ` Junio C Hamano
2012-10-04  8:02               ` Jeff King [this message]
2012-10-04 19:06                 ` [PATCH 3/4] peel_ref: check object type before loading Junio C Hamano
2012-10-04 19:41                   ` Jeff King
2012-10-04 20:41                     ` Junio C Hamano
2012-10-04 21:59                       ` Jeff King
2012-10-04  8:03               ` [PATCH 4/4] upload-pack: use peel_ref for ref advertisements Jeff King
2012-10-04  8:04               ` [PATCH 0/4] optimizing upload-pack ref peeling Jeff King
2012-10-04  9:01                 ` Ævar Arnfjörð Bjarmason
2012-10-04 12:14                   ` Nazri Ramliy
2012-10-03 22:32   ` upload-pack is slow with lots of refs Ævar Arnfjörð Bjarmason
2012-10-03 23:21     ` Jeff King
2012-10-03 23:47       ` Ævar Arnfjörð Bjarmason
2012-10-03 19:13 ` Junio C Hamano

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