Sharing of VSO DEDB areas

Sharing of VSO DEDB areas allows multiple IMS systems to concurrently read and update the same VSO DEDB area. The three main participants are the coupling facility hardware, the coupling facility policy software, and the XES and z/OS® services.

The coupling facility hardware provides high-performance, random-access shared storage in which IMS systems can share data in a sysplex environment. The shared storage area in the coupling facility is divided into sections, called structures. For VSO DEDB data, the structure type used is called a cache structure, as opposed to a list structure or a lock structure. The cache structure is designed for high-performance read reference reuse and deferred write of modified data. The coupling facility and structures are defined in a common z/OS data set, the couple data set (COUPLExx).

The coupling facility policy software and its cache structure services provide interfaces and services to z/OS that allow sharing of VSO DEDB data in shared storage. Shared storage controls VSO DEDB reads and writes:

• A read of a VSO CI brings the CI into the coupling facility from DASD.
• A write of an updated VSO CI copies the CI to the coupling facility from main storage, and marks it as changed.
• Changed CI data is periodically written back to DASD.

The XES and z/OS services provide a way of manipulating the data within the cache structures. They provide high performance, data integrity, and data consistency for multiple IMS systems sharing data.