A Dbc object is a handle for a cursor into a Berkeley DB database.
Dbc handles are not free-threaded. Cursor handles may be shared by multiple threads if access is serialized by the application.
You create a Dbc using the Db::cursor() method.
If the cursor is to be used to perform operations on behalf of a transaction, the cursor must be opened and closed within the context of that single transaction.
Once Dbc::close() has been called, the handle may not be accessed again, regardless of the method's return.