The Netezza machine is an AMPP (asymmetric MPP) not an SMP, although it has an SMP host running Linux

When you submit a query, the query is sent to all SPUs and executed on all SPUs. Any SPU with data that answers the query will return that data.

But each query activates all SPUs, and this is why it is important to remember that Netezza is not a transactional machine. One-record inserts and one-record queries will still activate all SPUs, even if only one will ultimately do work. So you can insert one record in one second, or a million records in one second. It's a matter of how you will use the second.