Using ASAM services through GSAM replacement

• • GSAM replacement call overview
  • Data set options
  • Processing option values

GSAM replacement call overview

To use GSAM replacement, an application program issues IMS format GSAM calls. These calls are identical to IMS GSAM calls; if the program already uses GSAM calls, no change is necessary.

Keep the following information in mind as you set up the calls:

• AR/CTL replaces GSAM with ASAM for all GSAM data sets accessed by the job step; replacement is not selective by data set.
• At restart of a program that is using only ASAM services, the program does not need to open an ASAM data set if the data set was open at the time of the last checkpoint.
• If the data set uses output staging and a failure occurs, AR/CTL discards any records written since the last checkpoint (if the staging area has not overflowed). If the data set does not use output staging and a failure occurs, the records written since the last checkpoint may be present in the data set before restart. The records are overwritten after the restart.
• Sequential data set repositioning requires each volume of a multi-volume output tape data set to be mounted and unloaded. Although only the last volume is read, the other volumes must be mounted to keep the catalog and tape headers correct and complete for future use. This processing is consistent with GSAM processing.
• AR/CTL GSAM replacement supports the use of multi-volume GSAM data sets. Make sure that the FCB is defined using record level repositioning.

Data set options

A data set option member (FCB) can be created for the data set. If you do not set up a data set option member, AR/CTL uses default values for the data set options as described in the Reference section. For a GSAM-replacement data set that uses an IMS GSAM DBD, the default value for the Repositioning Options is RECORD. A program options member is not necessary for GSAM replacement; the program continues to use the IMS program specification block (PSB).

The name of the data set option member must be the same name as the GSAM database description (DBD) in the PCB that the application program uses with IMS. AR/CTL searches the AR/CTL control block libraries (ddname ARC) for a data set option member with the same name as the GSAM DBD. If AR/CTL finds this member, AR/CTL uses it instead of the IMS DBD; the data set option member completely replaces the GSAM DBD. If AR/CTL does not find this member, AR/CTL uses the GSAM DBD from the IMS control block libraries (ddname IMS).

To set up data set option members, you can use the AR/CTL ISPF interface, as described in the Reference section.

Processing option values

To enable GSAM replacement, the Replace IMS GSAM with ASAM processing option must be set to Y. The default value is N.