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.
- You cannot use temporary data sets with a symbolic
CHKP
orXRST
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.