Hi,
To reach the full state, the OSPF routers should finish the LSDB exchanging. In other words, the LSDB of all the routers should be the same.
From the OSPF state machine, in the second-last state, which is the loading state, the OSPF routers send the LSR packets to request the missing LSAs from the remote peers, when all the LSAs are received and stored in the local LSDB, it will set the remote peer state to full.