#include <db_cxx.h>
class DbMpoolFile { 
public: 
        DB_MPOOLFILE *DbMpoolFile::get_DB_MPOOLFILE(); 
        const DB_MPOOLFILE *DbMpoolFile::get_const_DB_MPOOLFILE() const; 
        ... 
}; 
      
            The memory pool interfaces for the Berkeley DB database environment are methods of the
            DbEnv handle. The 
            DbEnv memory pool methods and the
            DB_MPOOLFILE class provide general-purpose, page-oriented buffer
            management of files. Although designed to work with the other 
            Dbclasses, they are also useful for more general
            purposes. The memory pools are referred to in this document as simply
            the cache.
    
The cache may be shared between processes. The cache is usually filled by pages from one or more files. Pages in the cache are replaced in LRU (least-recently-used) order, with each new page replacing the page that has been unused the longest. Pages retrieved from the cache using DbMpoolFile::get() are pinned in the cache until they are returned to the control of the cache using the DbMpoolFile::put() method.
            The DbMpoolFile object is the handle for a file in the 
            cache. The handle is not free-threaded. Once the 
            DbMpoolFile::close() method is called, the handle
            may not be accessed again, regardless of that method's return.