Specifies "consistent read explicit" (CRE). This subparameter
requests serialization of the record access with update or erase of
the record by another unit of recovery. CRE read provides the application
a means of ensuring that records read by a unit of recovery are not
changed by other units of recovery until the reading unit of recovery
issues a syncpoint. For VSAM record-level sharing (RLS), CRE is
valid only for an application that supports commit and backout. With DFSMS Transactional
VSAM Services (DFSMStvs), if a batch (non-CICS) application specifies
CRE as the value of the JCL RLS keyword or specifies CRE through the
ACB, the data set is opened for DFSMStvs access.
After a batch
application opens a data set for RLS access with the NRI or CR subparameter,
it is an error for the application to request CRE through the RPL.
CRE
does not inhibit update or erase of the record by the unit of recovery
that issued the CRE request. The consistent-read explicit GET request
obtains a SHARE lock on the record. The SHARE lock remains held until
a commit or backout request is processed.
CRE readers should
issue frequent commits to reduce contention with updaters. CRE read
does not affect update locking rules. Deadlocks are possible when
a mixture of CRE read and update is used.