code: func (h *hawkularSink) checkCache(key string, hash uint64) bool {
  	h.regLock.Lock()
  	defer h.regLock.Unlock()
  	_, found := h.expReg[key]
  	if !found || h.expReg[key].hash != hash {
  		return false
  	}
  	// Update the TTL
  	h.expReg[key].ttl = h.runId
  	return true
  }
docs: // checkCache returns false if the cached instance is not current. Updates the TTL in the cache