What does requestRepaintAll() does?

My Application has become very slow, This function —> ( requestRepaintAll() ) takes a lot of time. Kindly help me Out. I am new to vaadin and i am still learning it.

It is an old method that was used in Vaadin 6 if you wanted to rerender the UI (and thus ofcourse it is heavy)

https://vaadin.com/api/framework/8.5.1/com/vaadin/server/ClientConnector.html#requestRepaintAll--