#include <db.h> int DB_ENV->get_mp_mmapsize(DB_ENV *dbenv, size_t *mp_mmapsizep);
         The DB_ENV->get_mp_mmapsize() method returns the the maximum file
         size, in bytes, for a file to be mapped into the process address space.  This value can be
         managed using the DB_ENV->set_mp_mmapsize()
         method.
    
         The DB_ENV->get_mp_mmapsize() method may be called at any time during
         the life of the application.
    
         The DB_ENV->get_mp_mmapsize() 
            
                  method returns a non-zero error value on failure and 0 on success.