review tweaks

db.go

@@ -575,11 +575,11 @@ type Stats struct {
 // This is useful when obtaining stats at two different points and time and
 // you need the performance counters that occurred within that time span.
 func (s *Stats) Sub(other *Stats) Stats {
-	var diff = *s
 	if other == nil {
-		return diff
+		return *s
 	}
-	diff.TxN = other.TxN - diff.TxN
+	var diff Stat
+	diff.TxN = other.TxN - s.TxN
 	diff.TxStats = s.TxStats.Sub(&other.TxStats)
 	return diff
 }