The enormous web application performance you get with freistilbox comes in part from using a content cache built on Varnish in front of the application boxes. This cache acts as a proxy as it receives all HTTP requests first. If it has the requested object already in memory, it will immediately send it back to the visitor. If not, it forwards the request to an application box and stores its response in memory. This way, the proxy cache can deliver objects that get requested often much faster than the application box could, especially if these content objects are generated dynamically.
There is one thing that effectively prevents the cache from storing objects, and that is a cookie. A cookie makes all HTTP requests specific for the individual visitor, and the cache will only store non-individual content. Otherwise, it would risk delivering private content that was intended for a different visitor.
Since we need to prevent random cookies from destroying the performance improvements we gain from the cache, we remove all cookies from incoming HTTP requests. There is only one exception: The Drupal and WordPress session cookies stay untouched because they’re essential for website authentication. (That’s why the cache unfortunately can’t speed up page delivery for Drupal 6: This version always sends a session cookie. We suggest using Pressflow Drupal instead.)
If you need to deal with visitor-specific data, please use the native session handling of your CMS. It will not be affected by the cache; but be aware that this also means losing its content delivery boost.