I did this in PHP once as well. I had to code a coupon lookup site where people entered coupon codes and they were verified against a database. I forget how many coupons there were... pretty sure it was less than 100,000.

Anyway, I coded it up in my local dev environment. Unfortunately, it turned out that I'd been mislead and the actual deployment environment didn't have a database server available.

In desperation and facing a deadline, I dumped all the lookup values into an array in a PHP file. As you said, it was really quite performant. The first request after starting the server was a bit slow (but not too bad... still < 10 seconds I think) and after that things were golden.

I felt a bit dirty, but things worked and we got paid.