Specifying Db2 for z/OS groups for IMS online regions

IMS supports the use of Db2 for z/OS data sharing groups.

You can use Db2 for z/OS group names in all dependent regions. The Db2 for z/OS group name is used to call z/OS Name Services. If z/OS returns a positive response to the group inquiry, IMS selects a member of the Db2 for z/OS group that is connected to the IMS control region and connects that Db2 for z/OS to the dependent region under the following condition: The Db2 for z/OS name that was selected was not explicitly defined by another statement with the SSM member.

If that condition is not met, IMS ignores the statement that caused the z/OS Name Services call, and no message is issued.

IMS dependent regions examine the subsystem name that is specified in their SSM member. If the control region is connected to a Db2 for z/OS with that subsystem name, the dependent region connects to it. If the control region is not connected to it, the dependent region assumes that it might be a Db2 for z/OS group attach name. In this case, the dependent region uses this name to access the z/OS Name Services to find any Db2 for z/OS subsystem on the z/OS image that is using this group attach name. It also checks to see if its control region is connected to this Db2 for z/OS and, if so, connects to the specific Db2 for z/OS.

If you are using Db2 for z/OS groups:
  • SSM= must be specified when the dependent region starts.
  • The name specified on SSN= must be a one- to four-character Db2 for z/OS group name.
  • When CRC= is specified and a system is selected from a Db2 for z/OS group, the CRC is changed to that of the control region's corresponding SSM member statement.

IMS BMP, JMP, JBP, MPP, and IFP (dependent regions) support DB2® group attach. The control region does not. For the control region, you must point to the correct subsystem name running on the same LPAR with the IMS.

In the SSM for the control region, you include one of the Db2 for z/OS subsystems in the Db2 for z/OS group that you may use. The SSM for the control region can only specify one member of the group. You cannot specify the Db2 for z/OS group name in the SSM for the control region. In the SSM for the dependent region you can specify the Db2 for z/OS group name and IMS (with help from z/OS) determines if the Db2 for z/OS group can connect or not.

A Db2 for z/OS group name cannot be the same as any Db2 for z/OS subsystem name.

An IMS control region cannot connect to more than one Db2 for z/OS in the same group; however, different IMS control regions on the same z/OS can connect to different instances of Db2 for z/OS in the same group.

A BMP that accesses Db2 for z/OS can be submitted to run on any IMS system in a Parallel Sysplex® environment without requiring modification of the SSM parameter or the SSM member of the IMS PROCLIB data set. BMPs that run with different instances of Db2 for z/OS in a data sharing group can use the same SSM member referring to the same Db2 for z/OS. The IMS control region must specify the specific Db2 for z/OS subsystem name or names in its SSM member. IMS control regions cannot use the Db2 for z/OS group attach name.

Examples

For the following two examples, the Db2 for z/OS group name is GRP1 and contains Db2 for z/OS subsystems DB21 and DB22:

Example 1

  1. Specify the following in Control Region 1's SSM PROCLIB member: 
    SST=DB2,SSN=DB21,LIT=SYS1,ESMT=DSNMIN10,REO=R,CRC=-
  2. Specify the following in Dependent Region 1 of Control Region 1's PROCLIB member: 
    SST=DB2,SSN=GRP1,LIT=SYS1,ESMT=DSNMIN10,REO=R,CRC=-

    An application can run here and get to DB21.

  3. Specify the following in Control Region 2's SSM PROCLIB member: 
    SST=DB2,SSN=DB22,LIT=SYS1,ESMT=DSNMIN10,REO=R,CRC=-
  4. Specify the following in Dependent Region 2 of Control Region 2's PROCLIB member: 
    SST=DB2,SSN=GRP1,LIT=SYS1,ESMT=DSNMIN10,REO=R,CRC=-

Example 2

  1. Specify the following in Control Region 1's SSM PROCLIB member: 
    SST=DB2,SSN=DB21,LIT=SYS1,ESMT=DSNMIN10,REO=R,CRC=-
SST=DB2,SSN=DB22,LIT=SYS1,ESMT=DSNMIN10,REO=R,CRC=-
  2. Specify the following in Dependent Region 1 of Control Region 1's PROCLIB member: 
    SST=DB2,SSN=GRP1,LIT=SYS1,ESMT=DSNMIN10,REO=R,CRC=-

In this example, IMS connects to Db2 for z/OS subsystem DB21 or DB22, depending on which Db2 for z/OS is available. The dependent region uses z/OS Name Services to determine if GRP1 is a Db2 for z/OS group, check if any of the systems defined in the Control Region's SSM are within that group, and connect to the first one that is active. If both Db2 for z/OS systems are active, connected to IMS, and part of the same Db2 for z/OS group, then the connection is made to the first one in the list. If GRP1 is not found to be a Db2 for z/OS group using z/OS Name Services, then an attempt is made to connect to GRP1 as a specific Db2 for z/OS.