Historical documentation for the DB_ENV->memp_sync() method stated:

In addition, if DB_ENV->memp_sync() returns success, the value of lsn will be overwritten with the largest log sequence number from any page that was written by DB_ENV->memp_sync() to satisfy this request.

This functionality was never correctly implemented, and has been removed in the Berkeley DB 4.1 release. It is very unlikely application programs used this information. If your application used this information, please contact us for help in upgrading.