Use global units of work

A global unit of work is implemented as a TMF transaction. An application starts a global unit of work by calling BEGINTRANSACTION, and either commits the unit of work by calling ENDTRANSACTION or backs out the unit of work by calling ABORTTRANSACTION. An application can use other TMF API calls as well.

An application can inherit a TMF transaction from another application. For example, an application (the first application) can perform work within the transaction before replying and passing the transaction back to a second application for further processing. Both the first and the second applications can therefore participate in the same global unit of work that involves updates to IBM MQ queues and updates to files and databases. The ability to pass a TMF transaction between applications means that several IBM MQ applications can perform messaging operations within the same global unit of work.

An application can manage and control multiple active TMF transactions at the same time. The transactions can be started by the application itself, or inherited from other applications, or both. This means that an application can participate in multiple global units of work at the same time.

The maximum number of concurrent active TMF transactions per process is 1000, which is an architectural limit. If an application is managing multiple TMF transactions, only one transaction can be current at any point in time. Alternatively, none of the transactions can be current. The application can use TMF API calls such as RESUMETRANSACTION, ACTIVATERECEIVETRANSID, and TMF_SET_TX_ID to move the state of being current from one transaction to another, or to designate that no transaction is current. The application uses this level of control to determine whether a messaging operation is performed within a local unit of work, a global unit of work, or outside of syncpoint control:

  • If an application calls MQPUT, MQPUT1, or MQGET within syncpoint control when no TMF transaction is current, IBM MQ processes the call within a local unit of work.
  • If an application calls MQPUT, MQPUT1, or MQGET within syncpoint control when the application has a current TMF transaction, IBM MQ processes the call within the global unit of work that is implemented by the current TMF transaction.
  • If an application calls MQPUT, MQPUT1, or MQGET outside of syncpoint control, IBM MQ processes the call outside of syncpoint control, irrespective of whether the application has a current TMF transaction at the time of the call.

IBM MQ never changes the state of an application's TMF transaction during an MQI call, except when a software or hardware failure occurs during processing and IBM MQ or the operating system determines that the transaction must be backed out to preserve data integrity. Every MQI call restores the transaction state of the application just before returning control to the application.