code: func (h *hawkularSink) expireCache(runId uint64) {
  	h.regLock.Lock()
  	defer h.regLock.Unlock()
  
  	for k, v := range h.expReg {
  		if (v.ttl + h.cacheAge) <= runId {
  			delete(h.expReg, k)
  		}
  	}
  }
docs: // expireCache will process the map and check for any item that has been expired and release it