When creating a database using Database Configuration Assistant (DBCA), you can choose the server pools to host policy-managed databases.
During Database creation, you have the option to select an existing server pool or create a new server pool.
Parallel query server pool is a server pool that consists of only Leaf Nodes. Specify a parallel query server pool to ensure load balancing for Hub Nodes, and to enhance performance of the database. If you specify a parallel query server pool, then DBCA starts database instances on Leaf Nodes also.