prune_refs(): use delete_refs()

The old version just looped over the references to delete, calling
delete_ref() on each one. But that has quadratic behavior, because
each call to delete_ref() might have to rewrite the packed-refs file.
This can be very expensive in a repository with a large number of
references. In some (admittedly extreme) repositories, we've seen
cases where the ref-pruning part of fetch takes multiple tens of
minutes.

Instead call delete_refs(), which (aside from being less code) has the
optimization that it only rewrites the packed-refs file a single time.

Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/builtin/fetch.c b/builtin/fetch.c
index 8d5b2dba2bc4251a7c35bc6aa6ff260ea72b7455..34b6f5ebcad7a80901c60448a45e23b667ba7fbe 100644 (file)
--- a/builtin/fetch.c
+++ b/builtin/fetch.c
@@ -790,20 +790,29 @@ static int prune_refs(struct refspec *refs, int ref_count, struct ref *ref_map,
        if (4 < i && !strncmp(".git", url + i - 3, 4))
                url_len = i - 3;
 
-       for (ref = stale_refs; ref; ref = ref->next) {
-               if (!dry_run)
-                       result |= delete_ref(ref->name, NULL, 0);
-               if (verbosity >= 0 && !shown_url) {
-                       fprintf(stderr, _("From %.*s\n"), url_len, url);
-                       shown_url = 1;
-               }
-               if (verbosity >= 0) {
+       if (!dry_run) {
+               struct string_list refnames = STRING_LIST_INIT_NODUP;
+
+               for (ref = stale_refs; ref; ref = ref->next)
+                       string_list_append(&refnames, ref->name);
+
+               result = delete_refs(&refnames);
+               string_list_clear(&refnames, 0);
+       }
+
+       if (verbosity >= 0) {
+               for (ref = stale_refs; ref; ref = ref->next) {
+                       if (!shown_url) {
+                               fprintf(stderr, _("From %.*s\n"), url_len, url);
+                               shown_url = 1;
+                       }
                        fprintf(stderr, " x %-*s %-*s -> %s\n",
                                TRANSPORT_SUMMARY(_("[deleted]")),
                                REFCOL_WIDTH, _("(none)"), prettify_refname(ref->name));
                        warn_dangling_symref(stderr, dangling_msg, ref->name);
                }
        }
+
        free(url);
        free_refs(stale_refs);
        return result;