[Exim] speed of lookup types

Hi folks,

I'm reading the manual about different lookup types, and curious to
know about performance differences.

For example, is there any significant performance difference between
dsearch and lsearch (assuming a fairly small lsearch file)? And what
about the difference in overhead between accessing the filesystem for
an lsearch versus connecting to mysql for a query lookup?

I think I like the idea of storing info in a database rather than
flat files, but if it's worth it to use other lookup types, I'm
willing. So what do you think, does it matter?

-Josh