External syncpoint coordination

 

This occurs when a syncpoint coordinator other than WebSphere MQ has been selected; for example, CICS, Encina, or Tuxedo. In this situation, WebSphere MQ on UNIX systems and WebSphere MQ for Windows register their interest in the outcome of the unit of work with the syncpoint coordinator so that they can commit or roll back any uncommitted get or put operations as required. The external syncpoint coordinator determines whether one- or two-phase commitment protocols are provided.

When you use an external coordinator, MQCMIT, MQBACK, and MQBEGIN cannot be issued. Calls to these functions fail with the reason code MQRC_ENVIRONMENT_ERROR.

The way in which an externally-coordinated unit of work is started depends on the programming interface provided by the syncpoint coordinator. An explicit call might be required. If an explicit call is required, and you issue an MQPUT call specifying the MQPMO_SYNCPOINT option when a unit of work is not started, the completion code MQRC_SYNCPOINT_NOT_AVAILABLE is returned.

The scope of the unit of work is determined by the syncpoint coordinator. The state of the connection between the application and the queue manager affects the success or failure of MQI calls that an application issues, not the state of the unit of work. An application can, for example, disconnect and reconnect to a queue manager during an active unit of work and perform further MQGET and MQPUT operations inside the same unit of work. This is known as a pending disconnect.

We can use WebSphere MQ API calls in CICS programs, whether or not you choose to use the XA abilities of CICS. If you do not use XA, then the puts and gets of messages to and from queues will not be managed within CICS atomic units of work. One reason for choosing this method is that the overall consistency of the unit of work is not very important to you.

If the integrity of your units of work is important to you, then you must use XA. When you use XA, CICS uses a two-phase commit protocol to ensure all resources within the unit of work are updated together.

For more information about setting up setting up transactional support, see the WebSphere MQ System Administration Guide, and also TXSeries CICS documentation, for example, TXSeries for Multiplatforms CICS Administration Guide for Open Systems.

 

Parent topic:

Global units of work

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