@matheusbsbs / matheus-bagliano / commits / 90108a2441

upload-pack: avoid parsing tag destinations

When upload-pack advertises refs, it dereferences any tags it sees, and shows the resulting sha1 to the client. It does this by calling deref_tag. That function must load and parse each tag object to find the sha1 of the tagged object. However, it also ends up parsing the tagged object itself, which is not strictly necessary for upload-pack's use. Each tag produces two object loads (assuming it is not a recursive tag), when it could get away with only a single one. Dropping the second load halves the effort we spend. The downside is that we are no longer verifying the resulting object by loading it. In particular: 1. We never cross-check the "type" field given in the tag object with the type of the pointed-to object. If the tag says it points to a tag but doesn't, then we will keep peeling and realize the error. If the tag says it points to a non-tag but actually points to a tag, we will stop peeling and just advertise the pointed-to tag. 2. If we are missing the pointed-to object, we will not realize (because we never even look it up in the object db). However, both of these are errors in the object database, and both will be detected if a client actually requests the broken objects in question. So we are simply pushing the verification away from the advertising stage, and down to the actual fetching stage. On my test repo with 120K refs, this drops the time to advertise the refs from ~3.2s to ~2.0s. Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>

Jeff King committed Jan 6, 2012 at 14:18 UTC 90108a2441fb57f69c3f25d072d1952b306b77ab

3 files changed +14 -2

tag.c

+12

@@ -24,6 +24,18 @@ struct object *deref_tag(struct object *o, const char *warn, int warnlen)

24 return o;

25 }

27 +struct object *deref_tag_noverify(struct object *o)

28 +{

29 + while (o && o->type == OBJ_TAG) {

30 + o = parse_object(o->sha1);

31 + if (o && o->type == OBJ_TAG && ((struct tag *)o)->tagged)

32 + o = ((struct tag *)o)->tagged;

33 + else

34 + o = NULL;

35 + }

36 + return o;

37 +}

38 +

39 struct tag *lookup_tag(const unsigned char *sha1)

40 {

41 struct object *obj = lookup_object(sha1);

tag.h

@@ -16,6 +16,7 @@ extern struct tag *lookup_tag(const unsigned char *sha1);

16 extern int parse_tag_buffer(struct tag *item, const void *data, unsigned long size);

17 extern int parse_tag(struct tag *item);

18 extern struct object *deref_tag(struct object *, const char *, int);

19 +extern struct object *deref_tag_noverify(struct object *);

20 extern size_t parse_signature(const char *buf, unsigned long size);

22 #endif /* TAG_H */

upload-pack.c

+1 -2

@@ -741,8 +741,7 @@ static int send_ref(const char *refname, const unsigned char *sha1, int flag, vo

741 nr_our_refs++;

742 }

743 if (o->type == OBJ_TAG) {

744 - o = parse_object(o->sha1);

745 - o = deref_tag(o, refname, 0);

744 + o = deref_tag_noverify(o);

745 if (o)

746 packet_write(1, "%s %s^{}\n", sha1_to_hex(o->sha1), refname_nons);

747 }