Channels, clusters, and remote queuing

 

Introduction

A queue manager communicates with another queue manager by sending a message and, if required, receiving back a response. The receiving queue manager could be:

  • On the same machine
  • On another machine in the same location
  • Running on the same platform as the local queue manager
  • Running on another platform supported by WebSphere MQ

These messages might originate from:

  • User-written application programs that transfer data from one node to another

  • User-written administration applications that use PCF commands, the MQAI, or the ADSI

  • Queue managers sending:

    • Instrumentation event messages to another queue manager

    • MQSC commands issued from a runmqsc command in indirect mode (where the commands are run on another queue manager)

Before a message can be sent to a remote queue manager, the local queue manager needs a mechanism to detect the arrival of messages and transport them consisting of:

A channel is a one-way communication link between two queue managers and can carry messages destined for any number of queues at the remote queue manager.

Each end of the channel has a separate definition. For example, if one end is a sender or a server, the other end must be a receiver or a requester. A simple channel consists of a sender channel definition at the local queue manager end and a receiver channel definition at the remote queue manager end. The two definitions must have the same name and together constitute a single channel.

If you want the remote queue manager to respond to messages sent by the local queue manager, set up a second channel to send responses back to the local queue manager.

Use the MQSC command DEFINE CHANNEL to define channels.

There is a message channel agent (MCA) at each end of a channel, controlling the sending and receiving of messages. The MCA takes messages from the transmission queue and puts them on the communication link between the queue managers.

A transmission queue is a specialized local queue that temporarily holds messages before the MCA picks them up and sends them to the remote queue manager. You specify the name of the transmission queue on a remote queue definition.

You can allow an MCA to transfer messages using multiple threads. This process is known as pipelining. Pipelining enables the MCA to transfer messages more efficiently, improving channel performance.

 

Remote administration using clusters

In a WebSphere MQ network using distributed queuing, every queue manager is independent. If one queue manager needs to send messages to another queue manager, it must define a transmission queue, a channel to the remote queue manager, and a remote queue definition for every queue to which it wants to send messages.

A cluster is a group of queue managers set up in such a way that the queue managers can communicate directly with one another over a single network without complex transmission queue, channel, and queue definitions. Clusters can be set up, and typically contain queue managers that are logically related in some way and need to share data or applications. Even the smallest cluster reduces system administration overheads.

Establishing a network of queue managers in a cluster involves fewer definitions than establishing a traditional distributed queuing environment. With fewer definitions to make, you can set up or change your network more quickly and easily, and reduce the risk of making an error in your definitions.

To set up a cluster, you need one cluster sender (CLUSSDR) and one cluster receiver (CLUSRCVR) definition for each queue manager. You do not need any transmission queue definitions or remote queue definitions. The principles of remote administration are the same when used within a cluster, but the definitions themselves are greatly simplified.

 

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IBM is a trademark of the IBM Corporation in the United States, other countries, or both.