Rajesh S

• Aug 10th, 2007

 

This option provides a high level of integrity (WRITE inegrity) for data being updated, while providing no special protection for data only being read. Many tasks in several VSE images can open the file for read access. Simultaneously, one or more than one task in one VSE image may open the file for output. All output users are granted WRITE integrity, but read-only tasks do not have READ integrity.

The cross-system image integrity checking is only done during OPEN and CLOSE, so this incurs little performance impact. However, in order to ensure READ and WRITE integrity for update processing, VSAM will always refresh buffer contents from disk for any GET, and then will LOCK the CI until PUT (or RELEASE) processing. In addition, from the time PUT processing begins until it finishes, the CA will be locked. The locking done is INTERNAL locking, using VSE's lock table.

The extra overhead processing time and I/O activity is as a result of the forced refresing of buffer contents, and not from locking per-se. Clearly, this option adds CPU time and I/O wait time to processing requests.