remote: repack packed-refs once when deleting multiple refs

When 'git remote rm' or 'git remote prune' were used in a repository
with many refs, and needed to delete many remote-tracking refs, a lot
of time was spent deleting those refs since for each deleted ref,
repack_without_refs() was called to rewrite packed-refs without just
that deleted ref.

To avoid this, call repack_without_refs() first to repack without all
the refs that will be deleted, before calling delete_ref() to delete
each one completely.  The call to repack_without_ref() in delete_ref()
then becomes a no-op, since packed-refs already won't contain any of
the deleted refs.
Signed-off-by: NJens Lindström <jl@opera.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

builtin/remote.c

@@ -749,15 +749,23 @@ static int mv(int argc, const char **argv)
 
 static int remove_branches(struct string_list *branches)
 {
+	const char **branch_names;
 	int i, result = 0;
+
+	branch_names = xmalloc(branches->nr * sizeof(*branch_names));
+	for (i = 0; i < branches->nr; i++)
+		branch_names[i] = branches->items[i].string;
+	result |= repack_without_refs(branch_names, branches->nr);
+	free(branch_names);
+
 	for (i = 0; i < branches->nr; i++) {
 		struct string_list_item *item = branches->items + i;
 		const char *refname = item->string;
-		unsigned char *sha1 = item->util;
 
-		if (delete_ref(refname, sha1, 0))
+		if (delete_ref(refname, NULL, 0))
 			result |= error(_("Could not remove branch %s"), refname);
 	}
+
 	return result;
 }
 
@@ -1305,6 +1313,7 @@ static int prune_remote(const char *remote, int dry_run)
 {
 	int result = 0, i;
 	struct ref_states states;
+	const char **delete_refs;
 	const char *dangling_msg = dry_run
 		? _(" %s will become dangling!")
 		: _(" %s has become dangling!");
@@ -1318,6 +1327,13 @@ static int prune_remote(const char *remote, int dry_run)
 		       states.remote->url_nr
 		       ? states.remote->url[0]
 		       : _("(no URL)"));
+
+		delete_refs = xmalloc(states.stale.nr * sizeof(*delete_refs));
+		for (i = 0; i < states.stale.nr; i++)
+			delete_refs[i] = states.stale.items[i].util;
+		if (!dry_run)
+			result |= repack_without_refs(delete_refs, states.stale.nr);
+		free(delete_refs);
 	}
 
 	for (i = 0; i < states.stale.nr; i++) {

refs.c

@@ -2431,7 +2431,7 @@ static int curate_packed_ref_fn(struct ref_entry *entry, void *cb_data)
 	return 0;
 }
 
-static int repack_without_refs(const char **refnames, int n)
+int repack_without_refs(const char **refnames, int n)
 {
 	struct ref_dir *packed;
 	struct string_list refs_to_delete = STRING_LIST_INIT_DUP;

refs.h

@@ -132,6 +132,8 @@ extern void rollback_packed_refs(void);
  */
 int pack_refs(unsigned int flags);
 
+extern int repack_without_refs(const char **refnames, int n);
+
 extern int ref_exists(const char *);
 
 /*