Using ASAM services through the ASAM callable interface
This section describes the ASAM services of AR/CTL that are available through the ASAM callable interface and summarizes the requirements for implementing ASAM services through the ASAM callable interface. The ASAM callable interface is available with AR/CTL for DB2 and AR/CTL for VSAM. The callable interface supports physical sequential data sets, VSAM input and output ESDSs, and VSAM input KSDSs.
ASAM callable interface supported data set types
AR/CTL supports the following types of sequential data sets through the ASAM callable interface:
- tape input and output with repositioning on the basis of block count or record count
- sequential input and output on DASD
- print (output staging is especially valuable in simplifying the programming effort for print data sets)
- VSAM ESDS for input and output
- VSAM KSDS for input
- generation data groups (GDGs) for input and output
Some vendor products do not allow DASD data sets using the MVS NOTE/POINT macros to become multi-volume data sets. AR/CTL supports and can reposition multi-volume ASAM data sets.
ASAM call
To request ASAM services through the ASAM callable interface, an application program must issue ARCASAM calls. If you are replacing an existing sequential data set with ASAM, change the application program to remove any open calls, close calls, and access request calls (such as get, put, read, and write). Then make all data requests directly to AR/CTL using the ASAM callable interface.
Keep the following information in mind as you set up the calls:
- At restart of a program that is using ASAM services only, 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.
Data set and program options
A data set option member (FCB) must be created for each data set that the application program will access through ASAM services through the ASAM callable interface. A program option member (ASB) must be created to refer to the data set option members that the application program will use. For more information, see Reference.