Symbolic CHKP and XRST with GSAM

To checkpoint GSAM databases, use symbolic CHKP and XRST calls.

By using GSAM to read or write the data set, symbolic CHKP and XRST calls can be used to reposition the data set at the time of restart, enabling you to make your program restartable. When you use an XRST call, IMS repositions GSAM databases for processing. CHKP and XRST calls are available to application programs that can run as batch programs, batch-oriented BMPs, or transaction-oriented BMPs.

Restriction: When restarting GSAM databases:
  • You cannot use temporary data sets with a symbolic CHKP or XRST call.
  • A SYSOUT data set at restart time may give duplicate output data.
  • You cannot restart a program that is loading a GSAM or VSAM database.
  • The GSAM database data set must have the same data set format (BASIC or LARGE) as when the symbolic CHKP call was issued.

When IMS restores the data areas specified in the XRST call, it also repositions any GSAM databases that your program was using when it issued the symbolic CHKP call. If your program was loading GSAM databases when the symbolic CHKP call was issued, IMS repositions them (if they are accessed by BSAM). If you make a copy of the GSAM data set for use as input to the restart process, ensure that the short blocks are written to the new data set as short blocks, for example, using IEBGENER with RECFM=U for SYSUT1. You can also do the restart using the original GSAM data set.

During GSAM XRST processing, a check is made to determine if the GSAM output data set to be repositioned is empty, and if the abending job had previously inserted records into the data set.