Caching Catalogs

The simplest method of improving catalog performance is to use cache to maintain catalog records within main storage or data space. Using cache reduces the I/O required to read records from catalogs on DASD.

Two kinds of cache are available exclusively for catalogs. The in-storage catalog (ISC) cache is contained within the catalog address space (CAS) in main storage. The catalog data space cache (CDSC) is separate from CAS and uses the MVS™ VLF component that stores the cached records in a dataspace. Both types of cache are optional, and each can be cancelled and restarted without an IPL.

Although you can use both types of catalog cache, you cannot cache a single catalog in both types of cache simultaneously. You must decide which catalogs benefit the most from each type of cache.

Catalog records are cached in the ISC or CDSC under the following conditions:

For master catalogs, all records accessed sequentially or by key are cached except for alias records. Alias records are kept in a separate table in main storage.
For user catalogs, only records accessed by key are cached.
For each catalog, the records are cached in the CDSC if you have indicated the catalog is to use CDSC. Otherwise, the records are cached in the ISC, unless you have stopped the ISC for the catalog. If you stop both the CDSC and the ISC for a catalog, then records are not cached.

See Starting and Stopping the Catalog Cache for a Catalog for information on using the MODIFY CATALOG command to manipulate the caches.

Start of change The ISC and VLF functions will not be used for any catalog in RLS mode; instead CAS will rely on the SMSVSAM address space to do the buffering and caching. Each buffer is independently registered with the CF cache structure connected by SMSVSAM from all sharing systems. Any record updates to the buffer from any system will trigger the CF to cross invalidate the copies in all other sharing systems. Once a buffer is invalidated, the most current copy can be read from the CF cache structure, if present, instead of performing an I/O to the DASD. End of change