Performance Considerations › System Generation Parameters › Specifying the Number of Internal and External Run Units

Specifying the Number of Internal and External Run Units

The MAXIMUM TASKS and MAXIMUM ERUS parameters specify the maximum number of user tasks and external request units that can be active concurrently. The size of these parameters can affect the amount of time spent by the DC/UCF system in searching the queues for tasks that are waiting to be executed.

The numbers that should be specified are a site-specific determination and are dependent upon factors such as the number of tasks processed each hour in a particular environment. When setting the MAXIMUM TASKS and MAXIMUM ERUS parameters on the SYSTEM statement, the following statistics should be considered:

• Increasing the MAXIMUM TASKS or MAXIMUM ERUS parameters by one (1) causes virtual storage requirements to increase as shown below:

  Resource Size of resource Total
  TCE 736 bytes 736 bytes
  STACKSIZE 320 words 1,280 bytes
  DCE 64 bytes 64 bytes
  ECB *  3 8 bytes 24 bytes
  DPE * 20 16 bytes 320 bytes
  RCE * 15 24 bytes 360 bytes
  RLE * 25 12 bytes 300 bytes
                                             
                   Total increase per task:  3,084 bytes

  Note: A value larger than the default (420) should be specified for the STACKSIZE when using CA ADS. If the STACKSIZE is at 420 and two tasks exceed stacksize and go into abend storage at the same time, the system will abort with an abend code of 3995.

• The following DC/UCF system parameters should be increased as specified for every increment of one (1) in the size of MAXIMUM TASKS or MAXIMUM ERUS:

  Parameter Amount increased

  ECB LIST 3

  DPE COUNT 20

  RCE COUNT 15

  RLE COUNT 25