[Exim] OT: When to use a DB vs flat files

Hi Philip,

On more than one occasion, I've looked at a flat file that I use for an
Exim lsearch and wondered whether it would be more efficient to use a
DBM for the lookup.

Obviously, this depends on the size of the file, the number of entries,
the system's IO overhead, available memory and the DBM style.

However, I'm hoping that you know of some papers I could read on the
subject to educate myself in this regard. I'd like to get a better feel
for where the threshold is, beyond which a DBM would make more sense.
Perhaps you've done some playing around in this area with Exim?

Thanks,
Sheldon.