When do nodes sync their subtangle with the neighbours?

Question

Does this happen after every transaction? In discrete steps?

Is it always synced with neighbours only, or is there some super tangle that it syncs with? Is that the case as long as the coordinator is up?

Answer 1

After looking into code of IRI : all incoming transactions that aren't known yet (i.e. not already stored in the local tangle) are immediately stored in the local tangle and broadcasted to all neighbors.

There is a send_limit parameter that can be used to reduce the broadcast rate, but the default behavior is the broadcast every new transaction ASAP (including milestone).

There is no preferred/super neighbor.