This figure illustrates a partial partition-wise join between sales and customers. This is described in the accompanying text. In addition:
Sales are partitions P1, P2, ... P16.
Parallel execution serv er set 2 illustrates joins to all servers in parallel execution server set 1. This is where hash(c_customerid) occurs.
Parallel execution server set 1 illustrates joins to all in server set 2.
The customers table, which is where the SELECT is.