Checking Cache Overhead

sp_helpcache can report the amount of overhead that is required to manage a named data cache of a given size.

When you create a named data cache, all the space you request with sp_cacheconfig is made available for cache space. The memory needed for cache management is taken from the global memory block pool.

Note: The cache overhead accounting for SAP ASE versions 12.5.1 and later is more explicit than in earlier versions. The amount of overhead is the same, but instead of being part of the server overhead, it is now considered, and reported, as part of the cache overhead.

To see the overhead required for a cache, include the proposed size. Use P for pages, K for kilobytes, M for megabytes, or G for gigabytes.

sp_helpcache "20000P"

This example checks the overhead for 20,000 pages:

2.96Mb of overhead memory will be needed to manage a cache of size 20000P

Configuring user caches does not waste cache space. Approximately 5 percent of memory is required for the structures that store and track pages in memory, whether you use a single large data cache or several smaller caches.