MySQL queries - how expensive are they really?
mysql, optimization, php
Solution
Just ignore it. Seriously. If you need data, you need data. Make sure your queries are reasonable fast (i.e. proper indices). Get a proper server for handling the load. Use output caching as makes sense, start caching data once you know where you actually HAVE a problem.
Problem
I've heard that mysql queries are very expensive, and that you should avoid at all costs making too many of them. I'm developing a site that will be used by quite a few people, and I'm wondering: How expensive are mysql queries actually? If I have 400,000 people in my database, how expensive is it to query it for one of them? How close attention do I need to pay that I don't make too many queries per client request? Edit: TomTom couldn't be more correct with his answer. According to perormance tests on the sites linked to in the comments (and a couple sites I found through a "mysql queries per second" search), I won't be encountering problems for quite a while - mysql can do thousands of queries per second with a remote server.