Subject: Re: [PATCH] connected: always use partial clone optimization

From: Junio C Hamano <[email-masked]>
Date: Fri, 20 Mar 2020 15:54:41 -0700

Jonathan Tan <[email-masked]> writes:

> The addition of the fast path might cause performance reductions in
> these cases:
>
>  - If a partial clone or a fetch into a partial clone fails, Git will
>    fruitlessly run rev-list (it is expected that everything fetched
>    would go into promisor packs, so if that didn't happen, it is most
>    likely that rev-list will fail too).

I agree that it is reasonable not to optimize the system for the
failure case---it is pointless to fail as quick as possible ;-)

>  - Any connectivity checks done by receive-pack, in the (in my opinion,
>    unlikely) event that a partial clone serves receive-pack.

Meaning "I created this repository by partially cloning, and now
I want to update it by pushing into it"?  I am not sure how rare
such a use case is, so I won't be a good judge on this one.

> diff --git a/builtin/clone.c b/builtin/clone.c
> index 1ad26f4d8c..4b2b14ff61 100644
> --- a/builtin/clone.c
> +++ b/builtin/clone.c
> @@ -672,8 +672,7 @@ static void update_remote_refs(const struct ref *refs,
>  			       const char *branch_top,
>  			       const char *msg,
>  			       struct transport *transport,
> -			       int check_connectivity,
> -			       int check_refs_are_promisor_objects_only)
> +			       int check_connectivity)
>  {
>  	const struct ref *rm = mapped_refs;
>  
> @@ -682,8 +681,6 @@ static void update_remote_refs(const struct ref *refs,
>  
>  		opt.transport = transport;
>  		opt.progress = transport->progress;
> -		opt.check_refs_are_promisor_objects_only =
> -			!!check_refs_are_promisor_objects_only;
>  
>  		if (check_connected(iterate_ref_map, &rm, &opt))
>  			die(_("remote did not send all necessary objects"));
> @@ -1275,7 +1272,7 @@ int cmd_clone(int argc, const char **argv, const char *prefix)
>  
>  	update_remote_refs(refs, mapped_refs, remote_head_points_at,
>  			   branch_top.buf, reflog_msg.buf, transport,
> -			   !is_local, filter_options.choice);
> +			   !is_local);
>  
>  	update_head(our_head_points_at, remote_head, reflog_msg.buf);
>  
> diff --git a/builtin/fetch.c b/builtin/fetch.c
> index bf6bab80fa..1097e1e512 100644
> --- a/builtin/fetch.c
> +++ b/builtin/fetch.c
> @@ -908,13 +908,6 @@ static int store_updated_refs(const char *raw_url, const char *remote_name,
>  	if (!connectivity_checked) {
>  		struct check_connected_options opt = CHECK_CONNECTED_INIT;
>  
> -		if (filter_options.choice)
> -			/*
> -			 * Since a filter is specified, objects indirectly
> -			 * referenced by refs are allowed to be absent.
> -			 */
> -			opt.check_refs_are_promisor_objects_only = 1;
> -
>  		rm = ref_map;
>  		if (check_connected(iterate_ref_map, &rm, &opt)) {
>  			rc = error(_("%s did not send all necessary objects\n"), url);
> diff --git a/connected.c b/connected.c
> index 7e9bd1bc62..846f2e4eef 100644
> --- a/connected.c
> +++ b/connected.c
> @@ -52,7 +52,7 @@ int check_connected(oid_iterate_fn fn, void *cb_data,
>  		strbuf_release(&idx_file);
>  	}
>  
> -	if (opt->check_refs_are_promisor_objects_only) {
> +	if (has_promisor_remote()) {

Earlier we would have this bit on only when filter_options.choice
was non-NULL but this allows us to take the branch as long as we
are lazily populated.  Makes sense.

> @@ -71,13 +71,18 @@ int check_connected(oid_iterate_fn fn, void *cb_data,
>  				if (find_pack_entry_one(oid.hash, p))
>  					goto promisor_pack_found;
>  			}
> -			return 1;
> +			/*
> +			 * Fallback to rev-list with oid and the rest of the
> +			 * object IDs provided by fn.
> +			 */
> +			goto no_promisor_pack_found;

OK.  This is the "fallback" thing you mentioned in the log message.
Makes sense.

>  promisor_pack_found:
>  			;
>  		} while (!fn(cb_data, &oid));
>  		return 0;
>  	}
>  
> +no_promisor_pack_found:
>  	if (opt->shallow_file) {
>  		argv_array_push(&rev_list.args, "--shallow-file");
>  		argv_array_push(&rev_list.args, opt->shallow_file);