I was reading the comments area on Dave Kearn's recent article about the two-billion user benchmark executed against Oracle Internet Directory and thought I'd answer a few questions and make a few key points. 
First, why would we even bother to benchmark a single server to handle such an "unrealistic" number of users in the first place?
The answer is that we get asked to do benchmarks in the 150m range all-the-time and have many customers in telecommunications, online gaming, and online services that easily exceed 50-100m user entries. Rather than continue to do these benchmarks one-at-a-time, it's simply more efficient to prove out that we can blow the doors off just about any number presented.
Don't need 2 billion users? The test shows linear scalability. Get yourself a lower-end box and you're good to go. The exact calculations are very well defined. Can't figure it out for yourself? Send me an email and I'll get someone to do the math for you.
Second, there's a continuing perception that directories are still the read-optimized, hierarchical, specialized data stores that they were 10-15 years ago when the main application for directories was white pages.
I'll be talking about this "need a specialized database" myth in my next post.
