If the database is not tuned properly, the results may not make the session any quicker. You can test the database to ensure it is tuned properly.
To verify that the database is tuned properly:
Create a pipeline with one partition.
Measure the reader throughput in the Workflow Monitor.
Add the partitions.
Verify that the throughput scales linearly.
For example, if the session has two partitions, the reader throughput should be twice as fast. If the throughput does not scale linearly, you probably need to tune the database.