The shared-queues environment

Operating in a shared-queues environment allows multiple IMS systems in a sysplex environment to share IMS message queues and EMH message queues. The IMS systems work together as an IMSplex providing a single-image view of multiple IMS systems.

The shared-queues environment distributes processing loads between the IMS systems in the IMSplex. Transactions that are entered on one IMS can be made available on the shared queues to any other IMS that can process them. Results of these transactions are then returned to the initiating terminal. End users need not be aware of these activities; they view the processing as if they were operating a single-system.

Definitions:
  • A shared queue is a collection of messages that are associated by the same queue name. A shared queue is managed by a Common Queue Server (CQS) and can be shared by CQS clients in a IMSplex.
  • A Common Queue Server receives, maintains, and distributes data objects from a shared queue that resides in a coupling facility list structure for its client.
  • A CQS client is an IMS DB/DC or DCCTL system that accesses shared queues through its own CQS.
  • A coupling facility is a special, logical partition that provides high-speed caching, list processing, and locking functions in a sysplex environment.
  • A sysplex environment is a set of z/OS® systems that communicate and cooperate with one another through certain multisystem hardware components and software services in order to process workloads.
  • An IMSplex is one or more IMS control regions, managers, or servers that work together as a unit. Typically, but not always, IMS systems in an IMSplex:
    • Share either databases or resources or message queues (or any combination)
    • Run in a z/OS Parallel Sysplex® environment
    • Include an IMS Common Service Layer (CSL)

In general, IMS handles messages in the following manner:

  1. IMS systems register interest in those queues for which they are able to process messages.
  2. When an IMS receives a message and places it on the shared queue, all IMS systems that have registered interest in that queue are notified.
  3. One IMS retrieves the message and processes it.
  4. The IMS that processes the message places a response on the queue.
  5. The IMS that submitted the original message is notified that the response message was placed on the queue.
  6. The IMS that submitted the original message sends the response message to the originating terminal.
Figure 1. Basic shared-queues environment
Four IMS systems connect to a shared queue on a coupling facility through four CQS's.