[PATCH] fetch-pack: binary search when storing wanted-refs

[Jonathan Tan]

In do_fetch_pack_v2(), the "sought" array is sorted by name, and it is
not subsequently reordered (within the function). Therefore,
receive_wanted_refs() can assume that "sought" is sorted, and can thus
use a binary search when storing wanted-refs retrieved from the server.

Replace the existing linear search with a binary search. This improves
performance significantly when mirror cloning a repository with more
than 1 million refs.

Signed-off-by: Jonathan Tan <jonathanta...@google.com>
---
 fetch-pack.c | 19 ++++++++++---------
 1 file changed, 10 insertions(+), 9 deletions(-)

diff --git a/fetch-pack.c b/fetch-pack.c
index e69993b2eb..e8266bd45a 100644
--- a/fetch-pack.c
+++ b/fetch-pack.c
@@ -1298,6 +1298,11 @@ static void receive_shallow_info(struct fetch_pack_args 
*args,
        }
 }
 
+static int cmp_name_ref(const void *name, const void *ref)
+{
+       return strcmp(name, (*(struct ref **)ref)->name);
+}
+
 static void receive_wanted_refs(struct packet_reader *reader,
                                struct ref **sought, int nr_sought)
 {
@@ -1305,20 +1310,16 @@ static void receive_wanted_refs(struct packet_reader 
*reader,
        while (packet_reader_read(reader) == PACKET_READ_NORMAL) {
                struct object_id oid;
                const char *end;
-               int i;
+               struct ref **found;
 
                if (parse_oid_hex(reader->line, &oid, &end) || *end++ != ' ')
                        die(_("expected wanted-ref, got '%s'"), reader->line);
 
-               for (i = 0; i < nr_sought; i++) {
-                       if (!strcmp(end, sought[i]->name)) {
-                               oidcpy(&sought[i]->old_oid, &oid);
-                               break;
-                       }
-               }
-
-               if (i == nr_sought)
+               found = bsearch(end, sought, nr_sought, sizeof(*sought),
+                               cmp_name_ref);
+               if (!found)
                        die(_("unexpected wanted-ref: '%s'"), reader->line);
+               oidcpy(&(*found)->old_oid, &oid);
        }
 
        if (reader->status != PACKET_READ_DELIM)
-- 
2.21.0.197.gd478713db0