Every cache has a "hit ratio," which indicates the percentage of time that a requested piece of information is available in the cache. You can check the hit ratio of Essbase caches to help determine whether to increase the cache size.
“Optimizing Essbase Caches” in the Oracle Essbase Database Administrator's Guide
getdbstats (ESSCMD) in the Oracle Essbase Technical Reference
getperfstats (ESSCMD) in the Oracle Essbase Technical Reference