[PATCH] fetch: pass transport to post-fetch connectivity check

["Kristofer Karlsson via GitGitGadget" <gitgitgadget@gmail.com>]

From: Kristofer Karlsson <krka@spotify.com>

When fetching with a transport that sets `self_contained_and_connected`
(as index-pack does for self-contained packs), check_connected() can
use find_pack_entry_one() to skip connectivity verification for refs
whose objects exist in the new pack. This avoids sending those OIDs to
the rev-list child process.

However, store_updated_refs() never passed the transport to
check_connected(), so opt.transport was always NULL and this
optimization was dead code for post-fetch connectivity checks.

Thread the transport parameter through store_updated_refs() and set
opt.transport so that check_connected() can take advantage of
self-contained packs.

On a large repository (2.4M commits, 374K files, 10.9K local refs),
fetching 200 new commits:

  Before: rev-list connectivity check  22s,  total fetch  36s
  After:  rev-list connectivity check   5s,  total fetch  14s

The remaining 5s is spent verifying refs not contained in the new pack.

Signed-off-by: Kristofer Karlsson <krka@spotify.com>
---
    fetch: pass transport to post-fetch connectivity check
    
    We're working on reducing git fetch times on a large monorepo (2.4M
    commits, 374K files, 10.9K local refs). Profiling showed the post-fetch
    connectivity check (rev-list --objects --stdin --not --all) dominating
    wall time when there are new objects.
    
    While investigating, I noticed that check_connected() already has a fast
    path for self-contained packs — it uses find_pack_entry_one() to skip
    refs whose objects are in the new pack. builtin/clone.c passes the
    transport to enable this, but store_updated_refs() in builtin/fetch.c
    does not, making the optimization dead code for fetches.
    
    The fix is a three-line change to thread the transport through.

Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-2123%2Fspkrka%2Ffetch-transport-fix-v1
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-2123/spkrka/fetch-transport-fix-v1
Pull-Request: https://github.com/gitgitgadget/git/pull/2123

 builtin/fetch.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/builtin/fetch.c b/builtin/fetch.c
index a22c319467..647fd1c30c 100644
--- a/builtin/fetch.c
+++ b/builtin/fetch.c
@@ -1213,6 +1213,7 @@ N_("it took %.2f seconds to check forced updates; you can use\n"
    "to avoid this check\n");
 
 static int store_updated_refs(struct display_state *display_state,
+			      struct transport *transport,
 			      int connectivity_checked,
 			      struct ref_transaction *transaction, struct ref *ref_map,
 			      struct fetch_head *fetch_head,
@@ -1228,6 +1229,7 @@ static int store_updated_refs(struct display_state *display_state,
 	if (!connectivity_checked) {
 		struct check_connected_options opt = CHECK_CONNECTED_INIT;
 
+		opt.transport = transport;
 		opt.exclude_hidden_refs_section = "fetch";
 		rm = ref_map;
 		if (check_connected(iterate_ref_map, &rm, &opt)) {
@@ -1432,7 +1434,7 @@ static int fetch_and_consume_refs(struct display_state *display_state,
 	}
 
 	trace2_region_enter("fetch", "consume_refs", the_repository);
-	ret = store_updated_refs(display_state, connectivity_checked,
+	ret = store_updated_refs(display_state, transport, connectivity_checked,
 				 transaction, ref_map, fetch_head, config,
 				 display_array);
 	trace2_region_leave("fetch", "consume_refs", the_repository);

base-commit: 6a4418c36d6bad69a599044b3cf49dcbd049cb45
-- 
gitgitgadget