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

For more information about SET EXPLAIN, see its description in the Informix® Guide to SQL: Syntax and your Informix Performance Guide.

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.

For more information about the onstat utility, see the .