IBM SC34-7012-01 manual Recovery for files, VSAM files, Sharing data sets with batch jobs

Recovery for files

A CICS file is a logical view of a physical data set, defined to CICS in a file resource definition with an 8-character file name.

A CICS file is associated with a VSAM or BDAM data set by one of the following:

vBy dynamic allocation, where the data set name is predefined on the DSNAME parameter in the file definition (or set by a CEMT, or EXEC CICS, SET FILE DSNAME(name) command)

vBy allocation by JES at job step initiation, where the data set name is defined on a DD statement

More than one file can refer to the same data set.

A data set is defined to be the physical object residing on DASD. It has a

44-character DSNAME. A VSAM data set, for example, is defined using VSAM access method services (AMS).

When designing your applications, ensure that application data is protected from transaction failures that could lead to data corruption, and that you can recover from accidental damage to storage devices.

When deciding on the access method, consider the recovery and restart facilities provided by each. These considerations are discussed in the following topics.

VSAM files

CICS file control supports three VSAM access modes—local shared resources (LSR), non-shared resources (NSR), and record-level sharing (RLS).

Sharing data sets with batch jobs

Sharing data sets directly between online CICS update transactions and batch update programs using VSAM share options (where available) or job control sharing is not recommended for non-RLS access modes. Sharing risks the integrity of the data with the result that application programs may appear to function correctly, but with incorrect data. Such loss of data integrity can occur, for example, if a CICS unit of work updates a record that is later updated by a non-CICS job while the CICS unit of work is still running. If the CICS unit of work abends, CICS backs out the record to the value it had at the start of the CICS unit of work, thus destroying the update from the non-CICS job.

File-owning regions and RLS access

To share data sets between more than one CICS region, use the RLS access mode or use a file-owning region (FOR) with function shipping from the application-owning regions (AORs). From a recovery point of view, RLS does not create distributed units of work, as happens between the AOR and FOR, because files accessed in RLS mode are all regarded as local to each CICS region. The SMSVSAM server takes the place of the FOR. However, there are special recovery considerations for data sets accessed in RLS mode, in connection with the role of SMSVSAM and its lock management.

Chapter 12. Defining recoverability for CICS-managed resources 125