Allocating the RECON Data Sets to an IMS System

You can use one of two methods to allocate the RECON data sets to an IMS system:

• Point to the RECON data sets by inserting the DD statements in the startup JCL for the IMS system.

• Use dynamic allocation.

If a DD statement is specified for the RECON data sets, DBRC does not use dynamic allocation. Otherwise, DBRC uses dynamic allocation.

Recommendation:

With multiple IMS systems sharing the same databases and RECON data sets, use dynamic allocation for both the RECON data sets and the associated databases. Doing so ensures that:

• Correct and current RECON data sets are used.

• Correct RECON data sets are associated with the correct set of databases.

Dynamic allocation also makes the recovery of a failed RECON data set easier because DBRC dynamically deallocates a RECON data set if a problem is encountered with it.

To establish dynamic allocation, you must add a special member that names the RECON data sets to the IMS.SDFSRESL library or to an authorized library that is concatenated to the IMS.SDFSRESL library. Add the member to IMS.SDFSRESL using the IMS DFSMDA macro. Figure 23-5 shows an example of the required DFSMDA macros for dynamic allocation of the RECON data sets.

Figure 23-5. Example JCL for Allocating RECON Data Sets Dynamically

 //DYNALL JOB.. //STEP     EXEC IMSDALOC //SYSIN    DD  *      DFSMDA TYPE=INITIAL      DFSMDA TYPE=RECON,DSNAME=PROD.RECON01,                  DDNAME=RECON1      DFSMDA TYPE=RECON,DSNAME=PROD.RECON02,                  DDNAME=RECON2      DFSMDA TYPE=RECON,DSNAME=PROD.RECON03, DDNAME=RECON3 

RECON data sets are always dynamically allocated with DISP=SHR specified.

When using multiple RECON data sets (for example, test and production), be sure that each IMS uses the correct RECON data set group. You can ensure that the correct RECON data set group is being used by altering the SYSLMOD DD statement in the IMSDALOC procedure to place the dynamic allocation parameter lists for the different RECON data set groups in different IMS.SDFSRESL libraries. The appropriate IMS.SDFSRESL or concatenated IMS.SDFSRESL libraries must be included for each IMS startup JCL.

Important:

When multiple IMSs running on different processors are accessing the same RECON data set, you must keep the dynamic allocation parameter lists being used by the different processors synchronized in the IMS.SDFSRESL libraries. This synchronization does not happen automatically. Also, using dynamic allocation in some IMS systems and JCL allocation in others is not recommended.