System Run Units

System run units are initiated by CA IDMS software components to satisfy requests for services. For example, loading a module from a load area or extracting message text from the message area.

Predefined System Run Units

A predefined system run unit is one which is defined in the DC/UCF system generation and is started during the DC/UCF system initialization.

System run units can be predefined for the following:

Load area (DDLDCLOD) processing. Use the RUNUNITS FOR LOADER parameter of the system generation SYSTEM statement to predefine load-area run units for the default dictionary. Use the system generation RUNUNITS statement to predefine load-area run units for an alternate dictionary.
Note: For more information about the RUNUNITS statement, see RUNUNITS Statement.
Message area (DDLDCMSG) processing by means of the RUNUNITS FOR MSGDICT parameter of the system generation SYSTEM statement.
Queue area (DDLDCRUN) processing by means of the RUNUNITS FOR QUEUE parameter of the system generation SYSTEM statement.
Signon processing in the user catalog by means of the RUNUNITS FOR SIGNON parameter of the system generation SYSTEM statement.
Destination processing by means of the RUNUNITS FOR DEST parameter of the system generation SYSTEM statement.
Security enforcement for system resources by means of the RUNUNITS FOR SECURITY parameter of the system generation SYSTEM statement.
Security enforcement for SQL by means of the SQL SECURITY parameter of the system generation RUNUNITS statement.
Load area (DDLCATLOD) processing for SQL by means of the SQL LOADER parameter of the system generation RUNUNITS statement.

How Predefined Run Units are Used

Predefined run units are initiated at startup and exist for the duration of system execution. At startup, the DC/UCF system allocates storage for each predefined run unit. The system maintains this storage until system shutdown.

Overflow Run Units

At runtime, if the number of predefined run units is insufficient to satisfy program processing requirements, the system initiates additional run units as needed. These additional run units are referred to as overflow run units. The system terminates overflow run units when they are no longer needed, freeing their storage.

An insufficient number of predefined run units can result in an excessive amount of journal activity. Only one BIND/FINISH sequence is issued for each predefined run unit, regardless of the number of requests the run unit is used to satisfy. Overflow run units, initiated on an as-needed basis, exist only to process individual requests. One BIND/FINISH sequence is issued per request. For example, if a single predefined run unit initiated at startup processes 100 signon requests, only one BIND/FINISH sequence is issued for those requests. If overflow run units process 100 signon requests, 100 BIND/FINISH sequences are issued.