[exim] correct way to live update / rebuild dbm lookup db

Hi,
what is the correct way to update a dbm (Berkley db usually) lookup db while
exim is running?

I will use the perl interface to DB_File, do I need to aquire a lock or
something else to assure that exim4 does not read incorrect information
while updating the db ?

Is it safe to rebuild a db with the exim_dbmbuild utility ?

What appen if exim do a lookup while the utility is running ?


thanks
Francesco Pasqualini