[Exim] dbm updates

I am concerned about the procedure for updating the dbm files used by exim when they
are the .pag/.dir type. Using exim_dbmbuild the new files are built and then
renamed. Since the renaming is not an atomic action there will be a period where the
.dir file is new and the .pag file is old. As far as I can see exim does not take
any steps to prevent this. Is this a correct interpretation? If so, I take it that
I should I be stopping exim while I re-build the files to prevent the possiblity of
a lookup failing when it should succeed? Taking exim down on the system which takes
all our local PC-based user agent submissions will certainly not be popular!

Is there any chance of a lock being created around this activity so that exim can be
kept running?

I see that exim_dbmbuild makes no provision for restoring the old .dir file after it
has been replaced if the rename of the .pag file files. It seems very very unlikely
that this would happen but ...

Phil.
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Phil Chambers (postmaster@???)
University of Exeter