If a session contains multiple partitions, the throughput for each partition should be the same as the throughput for a single partition session. If you do not see this correlation, then the database is probably inserting rows into the database serially.
To ensure that the database inserts rows in parallel, check the following configuration options in the target database:
Set options in the database to enable parallel inserts.
For example, set the db_writer_processes and DB2 has max_agents options in an Oracle database to enable parallel inserts. Some databases may enable these options by default.
Consider partitioning the target table.
If possible, try to have each partition write to a single database partition using a Router transformation to do this. Also, have the database partitions on separate disks to prevent I/O contention among the pipeline partitions.
Set options in the database to enhance database scalability.
For example, disable archive logging and timed statistics in an Oracle database to enhance scalability.