Query broadcast load balancing is accomplished by having a program intercept every query and send it to all servers. Read-only queries can be sent to a single server because there is no need for all servers to process it. This is unusual because most replication solutions have each write server propagate its changes to the other servers. With query broadcasting, each server operates independently.
This can be complex to set up because functions like random() and CURRENT_TIMESTAMP will have different values on different servers, and sequences should be consistent across servers. Care must also be taken that all transactions either commit or abort on all servers Pgpool is an example of this type of replication.