fetch-pack: use ref adv. to prune "have" sent

In negotiation using protocol v2, fetch-pack sometimes does not make
full use of the information obtained in the ref advertisement:
specifically, that if the server advertises a commit that the client
also has, the client never needs to inform the server that it has the
commit's parents, since it can just tell the server that it has the
advertised commit and it knows that the server can and will infer the
rest.

This is because, in do_fetch_pack_v2(), rev_list_insert_ref_oid() is
invoked before mark_complete_and_common_ref(). This means that if we
have a commit that is both our ref and their ref, it would be enqueued
by rev_list_insert_ref_oid() as SEEN, and since it is thus already SEEN,
mark_complete_and_common_ref() would not enqueue it.

If mark_complete_and_common_ref() were invoked first, as it is in
do_fetch_pack() for protocol v0, then mark_complete_and_common_ref()
would enqueue it with COMMON_REF | SEEN. The addition of COMMON_REF
ensures that its parents are not sent as "have" lines.

Change the order in do_fetch_pack_v2() to be consistent with
do_fetch_pack(), and to avoid sending unnecessary "have" lines.

Signed-off-by: Jonathan Tan <jonathantanmy@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/fetch-pack.c b/fetch-pack.c
index 60adfc073a8cd46f38b5f355e5af8b202f65a859..806c40021f0d3602566f28344de4a4c08ffd649e 100644 (file)
--- a/fetch-pack.c
+++ b/fetch-pack.c
@@ -1392,9 +1392,6 @@ static struct ref *do_fetch_pack_v2(struct fetch_pack_args *args,
                                for_each_ref(clear_marks, NULL);
                        marked = 1;
 
-                       for_each_ref(rev_list_insert_ref_oid, NULL);
-                       for_each_cached_alternate(insert_one_alternate_object);
-
                        /* Filter 'ref' by 'sought' and those that aren't local */
                        mark_complete_and_common_ref(args, &ref);
                        filter_refs(args, &ref, sought, nr_sought);
@@ -1402,6 +1399,9 @@ static struct ref *do_fetch_pack_v2(struct fetch_pack_args *args,
                                state = FETCH_DONE;
                        else
                                state = FETCH_SEND_REQUEST;
+
+                       for_each_ref(rev_list_insert_ref_oid, NULL);
+                       for_each_cached_alternate(insert_one_alternate_object);
                        break;
                case FETCH_SEND_REQUEST:
                        if (send_fetch_request(fd[1], args, ref, &common,

diff --git a/t/t5500-fetch-pack.sh b/t/t5500-fetch-pack.sh
index d4f435155f5c9350f196904b910e2b5466c3ffd6..e0cdc295d8f4522960cf34ed61da21b9e0cb8587 100755 (executable)
--- a/t/t5500-fetch-pack.sh
+++ b/t/t5500-fetch-pack.sh
@@ -755,6 +755,39 @@ test_expect_success 'fetching deepen' '
        )
 '
 
+test_expect_success 'use ref advertisement to prune "have" lines sent' '
+       rm -rf server client &&
+       git init server &&
+       test_commit -C server both_have_1 &&
+       git -C server tag -d both_have_1 &&
+       test_commit -C server both_have_2 &&
+
+       git clone server client &&
+       test_commit -C server server_has &&
+       test_commit -C client client_has &&
+
+       # In both protocol v0 and v2, ensure that the parent of both_have_2 is
+       # not sent as a "have" line. The client should know that the server has
+       # both_have_2, so it only needs to inform the server that it has
+       # both_have_2, and the server can infer the rest.
+
+       rm -f trace &&
+       cp -r client clientv0 &&
+       GIT_TRACE_PACKET="$(pwd)/trace" git -C clientv0 \
+               fetch origin server_has both_have_2 &&
+       grep "have $(git -C client rev-parse client_has)" trace &&
+       grep "have $(git -C client rev-parse both_have_2)" trace &&
+       ! grep "have $(git -C client rev-parse both_have_2^)" trace &&
+
+       rm -f trace &&
+       cp -r client clientv2 &&
+       GIT_TRACE_PACKET="$(pwd)/trace" git -C clientv2 -c protocol.version=2 \
+               fetch origin server_has both_have_2 &&
+       grep "have $(git -C client rev-parse client_has)" trace &&
+       grep "have $(git -C client rev-parse both_have_2)" trace &&
+       ! grep "have $(git -C client rev-parse both_have_2^)" trace
+'
+
 test_expect_success 'filtering by size' '
        rm -rf server client &&
        test_create_repo server &&