So was it the same codebase at some time then? If so, when did it split off?
The thing with these kind of applications, is the performance is down to two things:
1. Your codebase. If your code is lean and cacheable, you can do wonders with it.
But to a much bigger extent:
2. Your SQL queries and DB configuration. If you don't do stupid **** like select count(*) to find out how many posts or whatever, and you configure your database server properly and design/optimise your database properly, again, you can squeeze a lot of performance out of a single server.
To compare the above, I've worked on two MySQL database servers in the last week that are at either extremes. One was a single proc box with a two disc SATA RAID-1 and 2GB memeory, doing in excess of 2500 queries per second. The second was a Dell R800, eight cores, 8GB memory, SCSI RAID-10, struggling to get over 250 queries per second after I did a fair bit of configuration and general table optimisation. The difference is down to the kind of queries ran on either. The first box have properly designed databases, with proper data segmentation, the second started as something small with only a few tables that they just kept adding on to with no thought for how well it would scale. They basically have to re-write their application to make it work better.
