Debug the parallelizable UDR

You can use the SQL statement SET EXPLAIN to determine whether a parallelizable query is actually being executed in parallel. The SET EXPLAIN statement executes when the database server optimizes a statement. It creates a file that contains:

• A copy of the SQL statement
• The plan of execution that the optimizer has chosen
• An estimate of the amount of work

The following onstat options are useful to track execution of parallel activities:

• The -g ath option shows the session thread and any additional scan threads for each fragment that is scanned for a statement that is running in parallel. You can use the -g ses option to help find the relationship between the threads.
• The -g stk option dumps the stack of a specified thread. This option can be helpful in tracing exactly what the thread is doing.