Optimize inner loop of activeExpireCycle() for no-expires case.

src/redis.c

@@ -671,9 +671,13 @@ void activeExpireCycle(void) {
         /* Continue to expire if at the end of the cycle more than 25%
          * of the keys were expired. */
         do {
-            unsigned long num = dictSize(db->expires);
-            unsigned long slots = dictSlots(db->expires);
-            long long now = mstime();
+            unsigned long num, slots;
+            long long now;
+
+            /* If there is nothing to expire try next DB ASAP. */
+            if ((num = dictSize(db->expires)) == 0) break;
+            slots = dictSlots(db->expires);
+            now = mstime();
 
             /* When there are less than 1% filled slots getting random
              * keys is expensive, so stop here waiting for better times...