low-end persistence strategies?

[Pierre Quentel]

If a dozen people click the url in the next day, several of
> them will probably in the first minute or so after the email goes out.
> So two simultaneous clicks isn't implausible.

> More generally, I don't like writing code with bugs even if the bugs
> have fairly low chance of causing trouble.  So I'm looking for the
> easiest way to do this kind of thing without bugs.

Even if the 12 requests occur in the same 5 minutes, the time needed for 
a read or write operation on a small base of any kind (flat file, dbm, 
shelve, etc) is so small that the probability of concurrence is very 
close to zero

If you still want to avoid it, you'll have to pay some price. The most 
simple and portable is a client/server mode, as suggested for KirbyBase 
for instance. Yes, you have to run the server 24 hours a day, but you're 
already running the web server 24/7 anyway