Understanding dynamic output for print data sets

IMS can use the z/OS® services for Dynamic Output (SVC109) for print data sets. IMS uses this service to specify the attributes provided by the application for the print data sets being created. The service can be used on the CHNG call with the PRTO, TXTU, and OUTN options.

Related reading: For more information, see z/OS MVS Programming: Assembler Services Guide.

CHNG call with PRTO option

When you use the CHNG call and PRTO option, IMS activates SJF to verify the print options to call z/OS services for Dynamic Output. This creates the output descriptors that are used when the print data set is allocated. This is the simplest way for the application to provide print data set characteristics. However, it also uses the most overhead because parsing must occur for each CHNG call. If your application is WFI or creates multiple data sets with the same print options, use another option to reduce the parsing impact. You must specify the IAFP option keyword with this option.

CHNG call with TXTU option

If your application can manage the text units necessary for Dynamic Output, then you can avoid parsing for many of the print data sets. You can do this in one of two ways:

  • The application can build the text unit in the necessary format within the application area and pass these text units to IMS with the CHNG call and TXTU option.
  • The application can provide the print options to IMS with a SETO call and provide a work area for the construction of the text units. After z/OS has finished parsing and text construction, the work area passed will contain the text units necessary for Dynamic Output after a successful SETO call. The application must not relocate this work area because the work area contains address sensitive information.

Regardless of the method the application uses to manage the text units, applications that can reuse the text units can often achieve better performance by using the TXTU option on the CHNG call.

You must specify the IAFP option keyword with this option.

CHNG call with OUTN option

The dependent region JCL can contain OUTPUT JCL statements. If your application can use this method, you can use the CHNG call and OUTN option to reference OUTPUT JCL statements. When you use the OUTN option, IMS will reference the OUTPUT JCL statements at dynamic allocation. JES will obtain the print data set characteristics from the OUTPUT JCL statement. You must specify the IAFP option keyword with this option.