Application compatibility and interoperability with earlier versions of IBM MQ

Connecting an application that is built against libraries shipped with a later version of IBM® MQ to an earlier version IBM MQ is not supported. Avoid building applications against a later version, and redeploying them to a queue manager running at an earlier version, although some applications do work in practice.

IBM MQ applications do interoperate with applications running on earlier versions of IBM MQ, as long as they use no new function. IBM MQ clients can connect to queue managers running at an earlier version than the client, as long as the client uses no new functions.

An IBM MQ application that uses only functions provided by an earlier version of a queue manager can continue to send messages to the earlier version. It does not matter what version of IBM MQ an application is built on and connected to. It can exchange messages with an application connected to an earlier version of IBM MQ, as long as it does not use new function.

Consider these four cases; the first two cases are not supported though they might work in practice, the last two cases are supported. The first two cases require compatibility with an earlier version of IBM MQ. The last two cases rely on the interoperability between all versions of IBM MQ

Running an IBM MQ server application, built with a later version of IBM MQ, connecting to a queue manager running on a server with an earlier version of IBM MQ installed.
Running an IBM MQ client application, built with a later version of IBM MQ, on a client platform with an earlier client installation, connecting to a queue manager running on a server with a later version of IBM MQ installed.
Running an IBM MQ client application, built with a later version of IBM MQ, on a client platform with the later client installation, connecting to a queue manager running on a server with an earlier version of IBM MQ installed.
Exchanging messages between an IBM MQ client or server application, connected to a queue manager running on a server with a later version of IBM MQ installed, with applications connected to a queue manager running on a server with an earlier version of IBM MQ installed.

Plan to avoid the first two cases, as they are not guaranteed to work all the time. If you are running an incompatible configuration and you encounter a problem, you must rebuild your applications with the correct level of IBM MQ. You can then continue with problem diagnosis.

Multi-installation and application loading

The new loading capability of IBM MQ libraries in Version 7.1, or later, does not relax the restriction that an application compiled and linked at a later release level must not directly load an IBM MQ library at an earlier release level. In practice the restriction is of less significance than in earlier releases, because as long as the operating system loads a library at the same or later level than the library the application was compiled and linked with, IBM MQ can call any other level of IBM MQ on the same server from Version 7.0.1 upwards.

For example, suppose you recompile and link an application that is to connect to a Version 7.0.1 queue manager using the libraries shipped with Version 7.1. At run time the operating system must load the Version 7.1 libraries for the application, even though the application connects to a Version 7.0.1 queue manager. IBM WebSphere® MQ 7.1 detects the inconsistency and loads the Version 7.0.1 library for the application. The same applies to any future release. If the application is recompiled and linked against a later release, then the application must load an IBM MQ library that matches the later release, even if it continues to connect to a Version 7.1 queue manager.

Examples

You decide to rebuild a client application. Can you deploy it to your production environment that contains some earlier versions of client and server platforms?

The answer is no, you must upgrade all the client workstations you deploy to, at least to the version of the client you have built. The queue managers running on earlier versions of IBM MQ do not have to be upgraded. In practice all the clients are likely to work, but for maintainability you must avoid running incompatible levels of an application and the IBM MQ client.
You deploy some IBM MQ queue managers at a new version level. You have an existing IBM MQ application that you use to send messages between the servers. Do you rebuild the application to deploy it onto the new servers? Can you deploy the old version onto the new servers?

The answer is, either. You can continue to deploy the existing version of the application onto all your servers, or you can deploy the rebuilt application onto the new servers. Either configuration works. IBM MQ supports running the existing application on later servers and sending messages from later application versions to earlier ones. What you must not do is to rebuild the application on the later version and redeploy it onto both the earlier and newer servers. IBM MQ does not support compatibility with earlier versions.

z/OS® application stubs

The stub modules that are listed are link-edited with applications and exits. The version 7 stub modules might not work with Version 6.

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