IBM SC34-7012-01 manual Coordinating updates in distributed units of work

others. This can happen, for example, if two data sets are updated and the UOW has to be backed out, and the following happens:

v One resource backs out successfully

v While committing this successful backout, the commit fails v The other resource fails to back out

These events leave one data set commit-failed, and the other backout-failed. In this situation, the overall status of the UOW is logged as backout-failed.

During emergency restart following a CICS failure, each UOW and its state is reconstructed from the system log. If any UOW is in the backout-failed or commit-failed state, CICS automatically retries the UOW to complete the backout or commit.

Coordinating updates in distributed units of work

If the execution of a UOW is distributed across more than one system, the CICS

recovery manager (or their non-CICS equivalents) in each pair of connected

systems ensure that the effects of the distributed UOW are atomic.

Each CICS recovery manager (or its non-CICS equivalent) issues the requests

necessary to effect two-phase syncpoint processing to each of the connected

systems with which a UOW may be in conversation.

Note: In this context, the non-CICS equivalent of a CICS recovery manager could

be the recovery component of a database manager, such as DBCTL or DB2®, or any

equivalent function where one of a pair of connected systems is not CICS.

In each connected system in a network, the CICS recovery manager uses interfaces

to its local recovery manager connectors (RMCs) to communicate with partner

recovery managers. The RMCs are the communication resource managers (IPIC,

LU6.2, LU6.1, MRO, and RMI) which have the function of understanding the

transport protocols and constructing the flows between the connected systems.

As remote resources are accessed during UOW execution, the CICS recovery

manager keeps track of data describing the status of its end of the conversation

with that RMC. The CICS recovery manager also assumes responsibility for the

coordination of two-phase syncpoint processing for the RMC.

Managing indoubt units of work

During the syncpoint phases, for each RMC, the CICS recovery manager records

the changes in the status of the conversation, and also writes, on behalf of the

RMC, equivalent information to the system log.

If a session fails at any time during the running of a UOW, it is the RMC

responsibility to notify the CICS recovery manager, which takes appropriate action

with regard to the unit of work as a whole. If the failure occurs during syncpoint

processing, the CICS recovery manager may be in doubt and unable to determine

immediately how to complete the UOW. In this case, the CICS recovery manager

causes the UOW to be shunted awaiting UOW resolution, which follows

notification from its RMC of successful resynchronization on the failed session.

During emergency restart following a CICS failure, each UOW and its state is

reconstructed from the system log. If any UOW is in the indoubt state, it remains

shunted awaiting resolution.

20CICS TS for z/OS 4.1: Recovery and Restart Guide