Determine the number of CPU virtual processors needed

The right number of CPU virtual processors is the number at which they are all kept busy but not so busy that they cannot keep pace with incoming requests. You must not allocate more CPU virtual processors than the number of hardware processors in the computer.

When the database server starts, the number of CPU virtual processors is automatically increased to half the number of CPU processors on the database server computer, unless the SINGLE_CPU_VP configuration parameter is enabled. However, you can adjust the number of CPU VPs based on your system.

You can configure the database server to automatically add CPU VPs when needed, up to the number of CPU processors.

To evaluate the performance of the CPU virtual processors while the database server is running, repeat the following command at regular intervals over a set period:
onstat -g glo

If the accumulated usercpu and syscpu times, taken together, approach 100 percent of the actual elapsed time for the period of the test, add another CPU virtual processor if you have a CPU available to run it.

Use the VPCLASS configuration parameter to specify the following information about CPU virtual processors:
  • The number of virtual processors to start initially for a class
  • The maximum number of virtual processors to run for the class
  • Processor affinity for CPU class virtual processors
  • Disabling of priority aging, if applicable
  • Whether the database server automatically adds CPU virtual processors as needed

In addition to considering the number of CPUs in the computer and the number of users who connect to the database server, also consider that user-defined routines and DataBlade modules, which are collections of user-defined routines, run on either CPU virtual processors or user-defined virtual processors.

Note: Use the VPCLASS configuration parameter instead of the following discontinued configuration parameters: AFF_SPROC, AFFNPROCS, NOAGE, NUMCPUVPS, and NUMAIOVPS.

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