CPU virtual-processor class

The CPU virtual-processor class is the primary VP class of the database server. It runs the following kinds of threads:

• All session threads

  Session threads process requests from the SQL client applications.

• Some internal threads

  Internal threads perform services internal to the database server.

SPL routines must always run in the CPU VP. Therefore, you do not need to specify the CLASS routine modifier for an SPL routine. The following CREATE FUNCTION statement registers the getTotal() SPL routine, which runs in the CPU VP:

CREATE FUNCTION getTotal(order_num, state_code)
   RETURNS MONEY
...
END FUNCTION

By default, a C UDR runs in the CPU VP class. Generally, UDRs perform best in the CPU VP class because threads do not have to migrate among operating-system processes during query execution. However, to run in the CPU VP, the C UDR must be well behaved; that is, it must adhere to the following programming requirements:

• Preserves concurrency of the CPU VP
  • Yields the CPU VP for intense calculations
  • Does not perform blocking operating-system calls
• Is thread safe:
  • Does not modify static or global data
  • Does not allocate local resources
  • Does not modify the global VP state
• Does not make unsafe operating-system calls