Monitor parallel UDRs

When PDQ is turned on, the SET EXPLAIN output shows whether the optimizer chose to execute a query in parallel. If the optimizer chose parallel scans, the output shows PARALLEL. If PDQ is turned off, the output shows SERIAL.

You can monitor the parallel execution of PDQs and parallel UDRs with the following options of the onstat utility:
  • onstat -g ath

    This option shows the threads currently executing for each session. Each session has a primary (sqlexec) thread. If the query is executing in parallel, onstat -g ath shows secondary threads, such as scan and sort.

  • onstat -g mem

    This option shows pool sizes allocated to sessions. This output can provide hints about how much memory the UDR uses.

  • onstat -g ses

    This option shows the number of threads allocated and the amount of memory used for each session. This output can also provide hints about how much memory the UDR uses.

For more information about interpreting the output of these onstat options, refer to the Informix® Performance Guide.