Reusing the global catalog to perform a cold start

If you need to perform a cold start, do not delete and redefine the global catalog data set. If you were to delete and redefine the global catalog, CICS® would perform an initial start, and all recovery information for remote systems would be lost. When remote systems reconnected, CICS would inform them that it had lost any information that they needed to resynchronize their units of work, and messages would be produced to record the fact, on both the local and the remote systems. Instead, to specify that the next start should be cold, use the DFHRMUTL utility with the SET_AUTO_START=AUTOCOLD option.

This approach has the following advantages:
  • You do not have to reset the START system initialization parameter from AUTO to COLD, and back again.
  • Because sufficient information is preserved on the global catalog and the system log, CICS is able to recover information for remote systems from the log, and to reply to remote systems in a way that enables them to resynchronize their units of work.

You can speed up a cold start by using the DFHRMUTL COLD_COPY option to copy only those records that are needed for the cold start to another catalog data set. If the return code set by DFHRMUTL indicates that the copy was successful, a subsequent job-step can copy the new (largely empty) catalog back to the original catalog data set. The performance gain occurs because, at startup, CICS does not have to spend time deleting all the definitional records from the catalog. This technique also speeds up initial starts, for the same reason. Figure 1 is an example of this technique. The COLD_COPY option is used to improve startup performance. Note that the NEWGCD and DFHGCD data sets must have been defined with the REUSE attribute. In the example JCL, the high level qualifier (CICSTSnn.CICS) assumes the release level of CICS TS beta. You must adapt it for your own CICS release.

Note: Before you use COLD_COPY, ensure that you want to perform a cold or initial start. As a safeguard, make a backup copy of the original global catalog before you copy the new catalog output by DFHRMUTL over it. For more information about the use of the global catalog in a cold start of CICS, see Controlling start and restart.
Figure 1. DFHRMUTL example: Setting the global catalog for a cold start
//RMUTL    EXEC PGM=DFHRMUTL,REGION=1M
//STEPLIB  DD DSNAME=CICSTS64.CICS.SDFHLOAD,DISP=SHR
//SYSPRINT DD SYSOUT=A
//DFHGCD   DD DSNAME=CICSTS64.CICS.applid.DFHGCD,DISP=OLD
//NEWGCD   DD DSNAME=CICSTS64.CICS.applid.COPY.DFHGCD,DISP=OLD
//SYSIN    DD *
SET_AUTO_START=AUTOCOLD,COLD_COPY
/*
//         IF (RMUTL.RC<16) THEN
//*  Steps to be performed if RMUTL was a success
//COPY     EXEC PGM=IDCAMS
//SYSPRINT DD SYSOUT=A
//DFHGCD   DD DSNAME=CICSTS64.CICS.applid.DFHGCD,DISP=OLD
//NEWGCD   DD DSNAME=CICSTS64.CICS.applid.COPY.DFHGCD,DISP=OLD
//SYSIN    DD *
   REPRO INFILE(NEWGCD) OUTFILE(DFHGCD) REUSE
/*
//*  End of steps to be performed if RMUTL was a success
//         ENDIF