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revision: use commit graph in get_reference() 

When fetching into a repository, a connectivity check is first made by
check_exist_and_connected() in builtin/fetch.c that runs:

  git rev-list --objects --stdin --not --all --quiet <(list of objects)

If the client repository has many refs, this command can be slow,
regardless of the nature of the server repository or what is being
fetched. A profiler reveals that most of the time is spent in
setup_revisions() (approx. 60/63), and of the time spent in
setup_revisions(), most of it is spent in parse_object() (approx.
49/60). This is because setup_revisions() parses the target of every ref
(from "--all"), and parse_object() reads the buffer of the object.

Reading the buffer is unnecessary if the repository has a commit graph
and if the ref points to a commit (which is typically the case). This
patch uses the commit graph wherever possible; on my computer, when I
run the above command with a list of 1 object on a many-ref repository,
I get a speedup from 1.8s to 1.0s.

Another way to accomplish this effect would be to modify parse_object()
to use the commit graph if possible; however, I did not want to change
parse_object()'s current behavior of always checking the object
signature of the returned object.

Signed-off-by: Jonathan Tan <jonathantanmy@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Jonathan Tan 2018-12-04 14:42:38 -08:00 committed by Junio C Hamano
parent ff509c585e
commit ec0c5798ee
1 changed files with 14 additions and 1 deletions
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15
revision.c
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@ -212,7 +212,20 @@ static struct object *get_reference(struct rev_info *revs, const char *name,
{
struct object *object;
object = parse_object(revs->repo, oid);
/*
* If the repository has commit graphs, repo_parse_commit() avoids
* reading the object buffer, so use it whenever possible.
*/
if (oid_object_info(revs->repo, oid, NULL) == OBJ_COMMIT) {
struct commit *c = lookup_commit(revs->repo, oid);
if (!repo_parse_commit(revs->repo, c))
object = (struct object *) c;
else
object = NULL;
} else {
object = parse_object(revs->repo, oid);
}
if (!object) {
if (revs->ignore_missing)
return object;