Still confused about the full_state_update parameter

[ChongWei905]

I'm still very confused about the full_state_update parameter after reading all kinds of docs.
Could anyone make a plot or sth else to show what's the difference between one or two updates?
Is it about distributed computing?
Is the global only about global of multiple batches? Or it's about global of multiple batches and devices?
And the implemented metrics' update methods has no difference about "the metric state of one batch is completely independent of the state of other batches".
Is there any example? like what metric has to do 2 updates or what