I am working on VersionEye.com and in the last days we had some performance issues. I added some new data to the database and to the views. The rendering of the package detail pages tooked sometimes up to 5 seconds. And because the UI is programmed with Ruby on Rails, some people told me: “Yes of course, Ruby is slow, you should use Java!”.
Hell, No! That was not the problem. I just added some indexes to the database, so that they fit perfectly to the queries. And now, it is crazy fast Some pages get rendered in less than 80 milli seconds