Client side caching: show tracking slots usage in INFO.

src/server.c

@@ -4147,7 +4147,8 @@ sds genRedisInfoString(char *section) {
             "active_defrag_hits:%lld\r\n"
             "active_defrag_misses:%lld\r\n"
             "active_defrag_key_hits:%lld\r\n"
-            "active_defrag_key_misses:%lld\r\n",
+            "active_defrag_key_misses:%lld\r\n"
+            "tracking_used_slots:%lld\r\n",
             server.stat_numconnections,
             server.stat_numcommands,
             getInstantaneousMetric(STATS_METRIC_COMMAND),
@@ -4173,7 +4174,8 @@ sds genRedisInfoString(char *section) {
             server.stat_active_defrag_hits,
             server.stat_active_defrag_misses,
             server.stat_active_defrag_key_hits,
-            server.stat_active_defrag_key_misses);
+            server.stat_active_defrag_key_misses,
+            trackingGetUsedSlots());
     }
 
     /* Replication */

src/server.h

@@ -1642,6 +1642,7 @@ void trackingRememberKeys(client *c);
 void trackingInvalidateKey(robj *keyobj);
 void trackingInvalidateKeysOnFlush(int dbid);
 void trackingLimitUsedSlots(void);
+unsigned long long trackingGetUsedSlots(void);
 
 /* List data type */
 void listTypeTryConversion(robj *subject, robj *value);

src/tracking.c

@@ -288,3 +288,9 @@ void trackingLimitUsedSlots(void) {
     }
     timeout_counter++;
 }
+
+/* This is just used in order to access the amount of used slots in the
+ * tracking table. */
+unsigned long long trackingGetUsedSlots(void) {
+    return TrackingTableUsedSlots;
+}