DBRC and Data Sharing

Concurrent access to databases by systems in one or more operating systems is controlled with a common (shared) Database Recovery Control (DBRC) facility RECON data set. IMSs perform an automatic sign-on to DBRC, and this action ensures that DBRC knows which IMSs and utilities are currently participating in shared access. Subsequently, a system's eligibility to be authorized for access to a database depends on the declared degree of sharing permitted and other status indicators in the RECON data set.

To maintain data integrity, status indicators in the RECON data set control concurrent access and recovery actions for the databases. This common RECON data set is required in a data sharing IMSplex^[1] because a given database must have a database management block (DMB) number that uniquely identifies it to all the sharing subsystems. The DMB number that DBRC records in its RECON data set is related to the order in which databases are registered to DBRC. Using multiple RECON data sets can result in the same DMB number existing in each RECON data set for different databases, which in turn can result in damage to databases.

^[1] For an overview of IMSplexes, see Chapter 28 "IMSplexes," on page 495.

Databases that are to take part in data sharing must be registered in the RECON data set. Each registered database has a current status that reflects whether it can take part in sharing and the scope of the sharing. The concept of scope combines several ideas:

• The type of access: read or update

• Whether more than one access can occur within the database simultaneously

• Whether an IMS that needs access is in the same or a different z/OS image

Related Reading: For more information about DBRC, see Chapter 23, "Database Recovery Control (DBRC) Facility," on page 375.