lei: avoid SQLite COUNT() for dedupe

SQLite COUNT() is a slow operation that does a full table scan
with no conditions.  There's no need for it, since lei dedupe
only needs to know if it's empty or not to decide between
new/ and cur/ for Maildir outputs.

1 files changed, 7 insertions, 0 deletions

diff --git a/lib/PublicInbox/SharedKV.pm b/lib/PublicInbox/SharedKV.pm
index 8347b195..3487e820 100644
--- a/lib/PublicInbox/SharedKV.pm
+++ b/lib/PublicInbox/SharedKV.pm
@@ -154,6 +154,13 @@ SELECT COUNT(k) FROM kv
         $sth->fetchrow_array;
 }
 
+# faster than ->count due to how SQLite works
+sub has_entries {
+        my ($self) = @_;
+        my @n = $self->{dbh}->selectrow_array('SELECT k FROM kv LIMIT 1');
+        scalar(@n) ? 1 : undef;
+}
+
 sub dbh_release {
         my ($self, $lock) = @_;
         my $dbh = delete $self->{dbh} or return;