PQO and the rule-based optimizer

One of the databases I'm working with has a large (3GB) table that must be scanned (full table scans) for a number of queries. Assuming sufficient cpu and disk resources, I understand that that the Parallel Query Option (PQO) can be used to divide the work among a number of servers, reducing query elapsed times.

Oracle documentation leads me to believe that the query plan chosen for such operations relates to the distribution of data in the table, implying cost-based optimization.

The vendor of this software insists on the use of the rule-based optimizer. We have specified such in init.ora, but we and also analyze all tables periodically for maintenance info and for "hint" optimizations (where the cost-based optimizer is used).

The question is how does Oracle determine how to partition the query? Is the cost-based optimizer used under the sheets? Or is the table simply divided according to the number of data blocks?

Oracle 7.1.6 is being used with HP/UX 10.10. The machine has 10 processors.

Thanks,

• Jim