Answer 1

The parallel hint is one of the "good" hints, such as the cardinality and ordered hints.

- The target table or index must be doing a full-scan operation,
- A starting point for the parallel degree us cpu_count-1 (the truly fastest degree is determined empirically via timing the query).
- If the table is aliased, the parallel hint must also be aliased.

The parallel hint accepts a table name an an optional "degree" argument to tell how many factotum (slave) processes to use in the parallel hinted query.
Setting parallel at the table level avoids the need to use hints, but it has the downside of causing the optimizer to start favoring full scan operations.