gtpd1m35Database Reference

Elements of a Coupling Facility Cache Structure

The TPF system supports directory-only CF cache structures. Directory-only cache users do not store data in the CF cache structure. Rather, directory-only users use the CF cache structure to maintain the consistency of data in their local caches.

The directory is a directory for the CF cache structure where the TPF system keeps control information about data shared among cache users. There is one directory entry for each piece of data that is shared. Shared data is maintained in the local cache buffer of each TPF system.

If a directory entry exists in the cache for a piece of shared data (that is, the TPF system has assigned a directory entry to the piece of shared data), the data is said to be identified to the CF cache structure. When a piece of shared data is identified to the CF cache structure, each TPF system receives notification through the local cache vector about the validity of the data. As long as the piece of shared data is identified by a directory entry, the CF can be notified that the data associated with the directory entry has been changed and is, therefore, no longer valid. A CF cache structure that contains directory entries but no pieces of shared data is referred to as a directory-only cache.

Accessing the Data

A directory-only user needs to access permanent storage frequently.