fetch: Speed up fetch by rewriting find_non_local_tags

When trying to get a list of remote tags to see if we need to fetch
any we were doing a linear search for the matching tag ref for the
tag^{} commit entries.  This proves to be incredibly slow for large
numbers of tags.  Rewrite the function so that we build up a
string_list of refs to fetch and then process that instead.

As an extreme example, for a repository with 50000 tags (and just a
single commit on a single branch), a fetch that does nothing goes from
~1m50s to ~4.1s.

Signed-off-by: Julian Phillips <julian@quantumfyre.co.uk>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/builtin-fetch.c b/builtin-fetch.c
index cb48c57ca3e66b7ec39a98128b2cfb058c2dad15..a35a6f8cb8030bf9be98a001da26fddf0efdb912 100644 (file)
--- a/builtin-fetch.c
+++ b/builtin-fetch.c
@@ -504,57 +504,98 @@ static int will_fetch(struct ref **head, const unsigned char *sha1)
        return 0;
 }
 
+struct tag_data {
+       struct ref **head;
+       struct ref ***tail;
+};
+
+static int add_to_tail(struct string_list_item *item, void *cb_data)
+{
+       struct tag_data *data = (struct tag_data *)cb_data;
+       struct ref *rm = NULL;
+
+       /* We have already decided to ignore this item */
+       if (!item->util)
+               return 0;
+
+       rm = alloc_ref(item->string);
+       rm->peer_ref = alloc_ref(item->string);
+       hashcpy(rm->old_sha1, item->util);
+
+       **data->tail = rm;
+       *data->tail = &rm->next;
+
+       return 0;
+}
+
 static void find_non_local_tags(struct transport *transport,
                        struct ref **head,
                        struct ref ***tail)
 {
        struct string_list existing_refs = { NULL, 0, 0, 0 };
-       struct string_list new_refs = { NULL, 0, 0, 1 };
-       char *ref_name;
-       int ref_name_len;
-       const unsigned char *ref_sha1;
-       const struct ref *tag_ref;
-       struct ref *rm = NULL;
+       struct string_list remote_refs = { NULL, 0, 0, 0 };
+       struct tag_data data = {head, tail};
        const struct ref *ref;
+       struct string_list_item *item = NULL;
 
        for_each_ref(add_existing, &existing_refs);
        for (ref = transport_get_remote_refs(transport); ref; ref = ref->next) {
                if (prefixcmp(ref->name, "refs/tags"))
                        continue;
 
-               ref_name = xstrdup(ref->name);
-               ref_name_len = strlen(ref_name);
-               ref_sha1 = ref->old_sha1;
-
-               if (!strcmp(ref_name + ref_name_len - 3, "^{}")) {
-                       ref_name[ref_name_len - 3] = 0;
-                       tag_ref = transport_get_remote_refs(transport);
-                       while (tag_ref) {
-                               if (!strcmp(tag_ref->name, ref_name)) {
-                                       ref_sha1 = tag_ref->old_sha1;
-                                       break;
-                               }
-                               tag_ref = tag_ref->next;
-                       }
+               /*
+                * The peeled ref always follows the matching base
+                * ref, so if we see a peeled ref that we don't want
+                * to fetch then we can mark the ref entry in the list
+                * as one to ignore by setting util to NULL.
+                */
+               if (!strcmp(ref->name + strlen(ref->name) - 3, "^{}")) {
+                       if (item && !has_sha1_file(ref->old_sha1) &&
+                           !will_fetch(head, ref->old_sha1) &&
+                           !has_sha1_file(item->util) &&
+                           !will_fetch(head, item->util))
+                               item->util = NULL;
+                       item = NULL;
+                       continue;
                }
 
-               if (!string_list_has_string(&existing_refs, ref_name) &&
-                   !string_list_has_string(&new_refs, ref_name) &&
-                   (has_sha1_file(ref->old_sha1) ||
-                    will_fetch(head, ref->old_sha1))) {
-                       string_list_insert(ref_name, &new_refs);
+               /*
+                * If item is non-NULL here, then we previously saw a
+                * ref not followed by a peeled reference, so we need
+                * to check if it is a lightweight tag that we want to
+                * fetch.
+                */
+               if (item && !has_sha1_file(item->util) &&
+                   !will_fetch(head, item->util))
+                       item->util = NULL;
 
-                       rm = alloc_ref(ref_name);
-                       rm->peer_ref = alloc_ref(ref_name);
-                       hashcpy(rm->old_sha1, ref_sha1);
+               item = NULL;
 
-                       **tail = rm;
-                       *tail = &rm->next;
-               }
-               free(ref_name);
+               /* skip duplicates and refs that we already have */
+               if (string_list_has_string(&remote_refs, ref->name) ||
+                   string_list_has_string(&existing_refs, ref->name))
+                       continue;
+
+               item = string_list_insert(ref->name, &remote_refs);
+               item->util = (void *)ref->old_sha1;
        }
        string_list_clear(&existing_refs, 0);
-       string_list_clear(&new_refs, 0);
+
+       /*
+        * We may have a final lightweight tag that needs to be
+        * checked to see if it needs fetching.
+        */
+       if (item && !has_sha1_file(item->util) &&
+           !will_fetch(head, item->util))
+               item->util = NULL;
+
+       /*
+        * For all the tags in the remote_refs string list, call
+        * add_to_tail to add them to the list of refs to be fetched
+        */
+       for_each_string_list(add_to_tail, &remote_refs, &data);
+
+       string_list_clear(&remote_refs, 0);
 }
 
 static void check_not_current_branch(struct ref *ref_map)