Required components of a shared-queues environment

Although you can operate many different configurations of a shared-queues environment, the required components of shared-queues processing, shown in Figure 1, include:

Common Queue Server (CQS)

One CQS is required for each client, though multiple IMS systems can share a CQS. Each CQS accesses the shared queues, which reside on coupling facility list structures.

CQS client

One or more IMS DB/DC or DCCTL subsystems that can access the shared queues using CQS client requests.

z/OS® coupling facility list structures

A type of coupling facility structure that maintains the shared queues.

Definitions:

• A list structure is an area of storage in a coupling facility that enables multisystem applications in a sysplex environment to share information that is organized as a set of lists or queues. The list structure consists of a set of lists and an optional lock table.
• CQS maintains list structures in pairs, called structure pairs, with a primary list structure and an overflow list structure.
• The primary list structure contains the shared queues.
• The overflow list structure, if defined, contains shared queues that overflow after the primary list structure reaches a predefined threshold.

z/OS system log

One z/OS system log is used for each structure pair. CQS places recovery information about the work it has processed and about the list structure pair in the z/OS log streams. These log streams are then shared by all CQSs that access the list structure pair.

CQS checkpoint data set

One CQS checkpoint data set is maintained for each structure pair of each CQS. The CQS checkpoint data set contains CQS system checkpoint information.

CQS structure recovery data sets (SRDSs)

CQS maintains two SRDSs for each structure pair so that shared queues on the structures can be recovered. The SRDSs maintain structure checkpoint information for the shared queues.