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 successfulSETO
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.