You can store data to be shared among multiple users in the cache structure on the coupling facility. You can also use the cache structure to keep track of data that resides in permanent storage and in local storage but is not stored in the cache structure itself.

However you store data that multiple users share, each user of the cache structure is expected to maintain a local cache buffer to contain a copy of the data. Through the use of a directory in the cache structure and a mechanism called “cross-invalidate” to inform users of changes to data, each MVS™ system in the sysplex can keep track of whether locally cached copies of the data are valid (that is, whether the copies contain the latest changes).

The directory allows you to refer to named data items that you can store in the cache structure itself or in local storage. Cross-invalidate processing involves setting an indicator in a local cache vector for each of the users to indicate whether the locally cached copy of the data is valid. Users must test the indicator to determine the validity of their copy, and if the data is no longer valid, users must read the data (either from the coupling facility or permanent storage) to obtain the most current copy.

You can use the cache structure to store and access data that users can share, or to keep track of shared data that users maintain in their local cache buffers. Accessing data stored in the local cache buffer is the quickest way for a user to access the shared data. However, if the system has invalidated the local copy because another user has updated the data, you must gain access to the data in another way. Accessing data from the cache structure in the coupling facility is the next fastest way for the user to access the shared data.

Data in the cache structure is directly accessible to any system in the sysplex that has access to the structure. If you do not store the data in the cache structure, you must read the data from permanent storage (like DASD), which is not as fast as accessing the data from the local cache buffer or from the cache structure in the coupling facility.