IBM SC34-7012-01 manual Recoverable resources, CICS backward recovery backout

Another way is to shut down CICS with an immediate shutdown and perform the forward recovery, after which a CICS emergency restart performs the backward recovery.

Recoverable resources

In CICS, a recoverable resource is any resource with recorded recovery information that can be recovered by backout.

The following resources can be made recoverable:

vCICS files that relate to:

–VSAM data sets

–BDAM data sets

vData tables (but user-maintained data tables are not recovered after a CICS failure, only after a transaction failure)

vCoupling facility data tables

vThe CICS system definition (CSD) file

vIntrapartition transient data destinations

vAuxiliary temporary storage queues

vResource definitions dynamically installed using resource definition online (RDO)

In some environments, a VSAM file managed by CICS file control might need to remain online and open for update for extended periods. You can use a backup manager, such as DFSMSdss, in a separate job under MVS™, to back up a VSAM file at regular intervals while it is open for update by CICS applications. This operation is known as backup-while-open (BWO). Even changes made to the VSAM file while the backup is in progress are recorded.

DFSMSdss is a functional component of DFSMS/MVS, and is the primary data mover. When used with supporting hardware, DFSMSdss also provides a concurrent copy capability. This capability enables you to copy or back up data while that data is being used.

If a data set failure occurs, you can use a backup of the data set and a forward recovery utility, such as CICS VSAM Recovery (CICSVR), to recover the VSAM file.

CICS backward recovery (backout)

Backward recovery, or backout, is a way of undoing changes made to resources such as files or databases.

Backout is one of the fundamental recovery mechanisms of CICS. It relies on recovery information recorded while CICS and its transactions are running normally.

Before a change is made to a resource, the recovery information for backout, in the form of a before-image, is recorded on the CICS system log. A before-image is a record of what the resource was like before the change. These before-images are used by CICS to perform backout in two situations:

vIn the event of failure of an individual in-flight transaction, which CICS backs out dynamically at the time of failure (dynamic transaction backout)

Chapter 1. Recovery and restart facilities 5