Set the suggested maximum size of the memory pool cache, in bytes. It is an error to specify both an mp_info parameter and a non-zero db_cachesize to Db::open.
Note, the minimum number of pages in the cache should be no less than 10, and the access methods will fail if an insufficiently large cache is specified. In addition, for applications that exhibit strong locality in their data access patterns, increasing the size of the cache can significantly improve application performance.
For information on tuning the Berkeley DB cache size, see Selecting a cache size.