Which database server scales better: PostgreSQL or MySQL?

I'm working on a website that could eventually have a very large database. The website will be an art community not until deviantART. I'll be running a lot of queries for analyzing how the site is used. I expect some of the queries to kill the database because I don't know how to optimize SQL queries (yet). I'm starting out with a small linux VPS and would move to physical servers in the future.

Which database would scale the best given this situation?


Before you make a decision based on scalability, you might want to read through these two pages and decide how much you value your sanity:

  • PostgreSQL gotchas
  • MySQL gotchas

There are some pretty decent threads on this at stack overflow:
https://stackoverflow.com/questions/110927/do-you-recommend-postgresql-over-mysql
https://stackoverflow.com/questions/216601/postgressql-mysql-oracle-diferences
https://stackoverflow.com/search?q=postgres+mysql

That gotchas site is also great :)