promisor-remote: die upon failing fetch

In a partial clone, an attempt to read a missing object results in an
attempt to fetch that single object. In order to avoid multiple
sequential fetches, which would occur when multiple objects are missing
(which is the typical case), some commands have been taught to prefetch
in a batch: such a command would, in a partial clone, notice that
several objects that it will eventually need are missing, and call
promisor_remote_get_direct() with all such objects at once.

When this batch prefetch fails, these commands fall back to the
sequential fetches. But at $DAYJOB we have noticed that this results in
a bad user experience: a command would take unexpectedly long to finish
(and possibly use up a lot of bandwidth) if the batch prefetch would
fail for some intermittent reason, but all subsequent fetches would
work. It would be a better user experience for such a command would
just fail.

Therefore, make it a fatal error if the prefetch fails and at least one
object being fetched is known to be a promisor object. (The latter
criterion is to make sure that we are not misleading the user that such
an object would be present from the promisor remote. For example, a
missing object may be a result of repository corruption and not because
it is expectedly missing due to the repository being a partial clone.)

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

1 files changed, 10 insertions, 1 deletions

diff --git a/promisor-remote.c b/promisor-remote.c
index 8b4d650b4c..faa7612941 100644
--- a/promisor-remote.c
+++ b/promisor-remote.c
@@ -4,6 +4,7 @@
 #include "config.h"
 #include "transport.h"
 #include "strvec.h"
+#include "packfile.h"
 
 struct promisor_remote_config {
 	struct promisor_remote *promisors;
@@ -238,6 +239,7 @@ void promisor_remote_get_direct(struct repository *repo,
 	struct object_id *remaining_oids = (struct object_id *)oids;
 	int remaining_nr = oid_nr;
 	int to_free = 0;
+	int i;
 
 	if (oid_nr == 0)
 		return;
@@ -255,9 +257,16 @@ void promisor_remote_get_direct(struct repository *repo,
 				continue;
 			}
 		}
-		break;
+		goto all_fetched;
+	}
+
+	for (i = 0; i < remaining_nr; i++) {
+		if (is_promisor_object(&remaining_oids[i]))
+			die(_("could not fetch %s from promisor remote"),
+			    oid_to_hex(&remaining_oids[i]));
 	}
 
+all_fetched:
 	if (to_free)
 		free(remaining_oids);
 }