Client side caching: implement full slot limit function.

src/tracking.c

@@ -251,4 +251,40 @@ void trackingInvalidateKeysOnFlush(int dbid) {
  * random caching slots, and send invalidation messages to clients like if
  * the key was modified. */
 void trackingLimitUsedSlots(void) {
+    static unsigned int timeout_counter = 0;
+
+    if (server.tracking_table_max_fill == 0) return; /* No limits set. */
+    unsigned int max_slots =
+        (TRACKING_TABLE_SIZE/100) * server.tracking_table_max_fill;
+    if (TrackingTableUsedSlots <= max_slots) {
+        timeout_counter = 0;
+        return; /* Limit not reached. */
+    }
+
+    /* We have to invalidate a few slots to reach the limit again. The effort
+     * we do here is proportional to the number of times we entered this
+     * function and found that we are still over the limit. */
+    int effort = 100 * (timeout_counter+1);
+
+    /* Let's start at a random position, and perform linear probing, in order
+     * to improve cache locality. However once we are able to find an used
+     * slot, jump again randomly, in order to avoid creating big holes in the
+     * table (that will make this funciton use more resourced later). */
+    while(effort > 0) {
+        unsigned int idx = rand() % TRACKING_TABLE_SIZE;
+        do {
+            effort--;
+            idx = (idx+1) % TRACKING_TABLE_SIZE;
+            if (TrackingTable[idx] != NULL) {
+                trackingInvalidateSlot(idx);
+                if (TrackingTableUsedSlots <= max_slots) {
+                    timeout_counter = 0;
+                    return; /* Return ASAP: we are again under the limit. */
+                } else {
+                    break; /* Jump to next random position. */
+                }
+            }
+        } while(effort > 0);
+    }
+    timeout_counter++;
 }