Basic and Symbolic Checkpoint Calls

Enterprise Server supports basic checkpoint (CHKP) calls, and symbolic checkpoint and Extended Restart (XSRT) calls.

Basic CHKP Calls

The basic CHKP call is available from message-driven transactions as well as BMPs and batch programs. Basic CHKP commits the changes your program has made to the database and establishes places in your program from which you can restart your program in the event that it terminates abnormally.

Symbolic CHKP and XSRT Calls

Symbolic CHKP and XSRT calls are only available to BMPs and batch programs.

The symbolic CHKP call commits the changes your program has made to the database and establishes places in your program from which you can restart your program in the event that it terminates abnormally. In addition, the CHKP call:

Works with the XRST call to restart your program if it terminates abnormally. An XRST call is required before a CHKP call to indicate to IMS that symbolic check points are being taken.
Designates a checkpoint ID, which is a place within the program from which you can restart it should the program terminate abnormally.
Designates up to seven data areas in your program to be automatically restored when your program is restarted after an abnormal termination.

The checkpoint ID and save areas are stored in files named IMSLOGR.DAT and IMSLOGR.IDX.

If an XRST call indicates that a restart should take place, the save areas are restored into the program's Working-Storage section. The restart checkpoint ID can be specified in the XRST call itself or as part of the Batch Program Command used to start the batch program. All XSRT calls, successful or not, are logged in the IMS System Log.

If an XSRT call indicates that a restart should take place, the save areas are restored into the program's Working-Storage. The restart checkpoint ID can be specified in the XRST call itself or as part of the Batch Program Command used to start the batch program. All restart calls, successful or not, are logged in the IMS System Log.

When restarting a BMP using a symbolic checkpoint, the log file is searched to find a match not only on the provided checkpoint ID but also on the name of the application program being restarted. This is consistent with mainframe behavior; however, when restarting a program with a checkpoint ID of LAST, the mainframe enforces on JOB name, PSB name, and program name, Enterprise Server IMS only enforces a match on program name.[2]

Notes:

An input GSAM file position RBA is saved on a checkpoint call and restored on a restart call.
An XRST call does not reposition any databases, nor does it restore any PCB information.
GSAM updates are committed to the data file when the update call completes.