In reply to Tomas M..

Piwik does work under high load, to a certain point, depending on your hardware, server configurations, and various other things.

We are running it with customers with a LOT of data (+50M pages per month). There are challenges and several tweaks we make so it works well under such high load... If you have a big website (or thousands of small-medium ones), maybe get in touch at http://piwik.pro/contact for professional support, we can fully setup & monitor Piwik on your infrastructure, or run it on the Piwik PRO Cloud (hosted in Europe/Germany).

If you have 1 million pageviews per month or less, then it should work out of the box, on a good server, without special configuration.