v2writable: short-circuit is_ancestor check on equality

We don't need to use git to check ancestry if object IDs
match on a string comparison.

This saves 100ms or so and brings down the ~0.5s no-op time on
lore.kernel.org/lkml down to ~0.4s.

1 files changed, 6 insertions, 0 deletions

diff --git a/lib/PublicInbox/V2Writable.pm b/lib/PublicInbox/V2Writable.pm
index fd93ac27..76844cd4 100644
--- a/lib/PublicInbox/V2Writable.pm
+++ b/lib/PublicInbox/V2Writable.pm
@@ -831,6 +831,12 @@ sub log_range ($$$$$) {
                 return $tip; # all of it
         };
 
+        # fast equality check to avoid (v)fork+execve overhead
+        if ($cur eq $tip) {
+                $sync->{ranges}->[$i] = undef;
+                return;
+        }
+
         my $range = "$cur..$tip";
         $pr->("$i.git checking contiguity... ") if $pr;
         if (is_ancestor($git, $cur, $tip)) { # common case