Recoverable and Nonrecoverable Data Sets

CICS file control supports recoverable or nonrecoverable data sets. DFSMStvs supports only recoverable data sets; it allows batch update of recoverable VSAM data sets, even while CICS is processing the data sets. A data set definition includes a LOG attribute that denotes whether the data set is recoverable. The attribute options are specified as follows:

LOG(NONE)—nonrecoverable
Specifies the data set as nonrecoverable. CICS does not perform any logging of changes for a data set that has this attribute. Neither rollback nor forward recovery is provided.
LOG(UNDO)—recoverable
Specifies the data set as commit or rollback recoverable. CICS and DFSMStvs log the before (UNDO) images of changes to the data set and backs out the changes if the application requests rollback or if the transaction terminates abnormally.
LOG(ALL)—recoverable
Specifies the data set as both commit or rollback recoverable and forward recoverable. In addition to the logging and recovery functions provided for LOG(UNDO), CICS logs the after image of changes (REDO record) to the data set. The redo log records are used by forward recovery programs or products such as CICS VSAM Recovery (CICSVR) to reconstruct the data set in the event of hardware or software damage to the data set.

Attention: Specifying LOG(NONE) is different from not specifying LOG at all. If you do not specify LOG, RLS cannot access the data set.

You can specify VSAM recoverable data set control attributes in IDCAMS (access method services) DEFINE and ALTER commands. In the data class, you can specify LOG along with the BWO and LOGSTREAMID parameters. If you want to be able to back up a data set while it is open, you should define them using the IDCAMS BWO(TYPECICS) parameter. Only a CICS application or DFSMStvs can open a recoverable data set for output because VSAM RLS does not provide the logging and other transactional functions required for writing to a recoverable data set.

When a data set is opened in a non-RLS access mode (NSR, LSR, or GSR), the recoverable attributes of the data set do not apply and are ignored. The recoverable data set rules have no impact on existing programs that do not use RLS access.