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fast-export: do not load blob objects twice

Browse source 
When fast-export wants to export a blob object, it first
calls parse_object to get a "struct object" and check
whether we have already shown the object.  If we haven't
shown it, we then use read_sha1_file to pull it from disk
and write it out.

That means we load each blob from disk twice: once for
parse_object to find its type and check its sha1, and a
second time when we actually output it. We can drop this to
a single load by using lookup_object to check the SHOWN
flag, and then checking the signature on and outputting a
single buffer.

This provides modest speedups on git.git (best-of-five, "git
fast-export HEAD >/dev/null"):

  [before]                [after]
  real    0m14.347s       real    0m13.780s
  user    0m14.084s       user    0m13.620s
  sys     0m0.208s        sys     0m0.100s

and somewhat more on more blob-heavy repos (this is a
repository full of media files):

  [before]                [after]
  real    0m52.236s       real    0m44.451s
  user    0m50.568s       user    0m43.000s
  sys     0m1.536s        sys     0m1.284s

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Jeff King 2013-03-17 04:38:57 -04:00 committed by Junio C Hamano
parent f9b54e2630
commit 30b939c33a
1 changed files with 10 additions and 6 deletions
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14
builtin/fast-export.c
View file

@ -119,6 +119,7 @@ static void export_blob(const unsigned char *sha1)
enum object_type type;
char *buf;
struct object *object;
int eaten;
if (no_data)
return;
@ -126,16 +127,18 @@ static void export_blob(const unsigned char *sha1)
if (is_null_sha1(sha1))
return;
object = parse_object(sha1);
if (!object)
die ("Could not read blob %s", sha1_to_hex(sha1));
if (object->flags & SHOWN)
object = lookup_object(sha1);
if (object && object->flags & SHOWN)
return;
buf = read_sha1_file(sha1, &type, &size);
if (!buf)
die ("Could not read blob %s", sha1_to_hex(sha1));
if (check_sha1_signature(sha1, buf, size, typename(type)) < 0)
die("sha1 mismatch in blob %s", sha1_to_hex(sha1));
object = parse_object_buffer(sha1, type, size, buf, &eaten);
if (!object)
die("Could not read blob %s", sha1_to_hex(sha1));
mark_next_object(object);
@ -147,6 +150,7 @@ static void export_blob(const unsigned char *sha1)
show_progress();
object->flags |= SHOWN;
if (!eaten)
free(buf);
}