How to load markers instantly android - google-maps-markers

Question

I using googleMap and what i'm tring to do is to refresh markers from firebase database, and that mean i delete all the previous markers and add the new ones by using this methode
#Override
public void onKeyEntered(String key, GeoLocation location) {
try{
MyItem myItem = new MyItem(location.latitude, location.longitude);
if (!items.contains(myItem)) {
items.add(myItem);
}
Log.d("onKey","called");
}catch (ClassCastException e){
Log.d("classCastException","");
}
}
parseJsonToList methode :
private void parseJsonToList() {
itemss = clusterManagerAlgorithm.getItems();
try {
items.removeAll(itemss);
}catch (IndexOutOfBoundsException e){
Log.d("itemsDoesn't exist"," : ");
}
mClusterManager.clearItems();
mClusterManager.cluster();
mClusterManager.addItems(items);
Log.d("items"," : " + items);
}
So, my problem is that everytime I'm tring to clean and load data what happened is that all markers desapears for about 3 second to been reloaded again. How can i delete and reload data without markers dispear.
this is myItem class :
public class MyItem implements ClusterItem {
private final LatLng mPosition;
public MyItem(double lat, double lng) {
mPosition = new LatLng(lat, lng);
}
#Override
public LatLng getPosition() {
return mPosition;
}
#Override
public boolean equals(Object o) {
if (this == o) return true;
if (o == null || getClass() != o.getClass()) return false;
MyItem item = (MyItem) o;
return Objects.equals(mPosition, item.mPosition);
}
#Override
public int hashCode() {
return Objects.hash(mPosition);
}
}