I have changed the keys in Lesti_Fpc 1.1.1. There was a problem with parameters in the Cache. Not a real problem, but the cache has produced too much keys. That means, more memory for the cache, but the real problem was, the cache had too much misses.
A key is the identifier of an object. In this case of a page in your website. Other full page caches are using the url as a key. The good thing about that, you have more hits. The bad thing, you can't make a difference between currencies and parameters in the user session. For example the count of products in the category. That's the reason for an internal cache. I did need the parameters of the session. The cache builds a hash from these parameters. Here is a diagramm to show how Lesti_Fpc has build keys in the past.
This is the key after visiting a category page. If I visit the same category with a senseless parameter, the cache generates a new key.
That produces too much misses.
The solution was very easy. I replaced the uri with the full_action_name. But now I can't make a difference between two products. So I added a field in the configurations. You have to decide, which parameters in the uri have an effect on the hash-key.
The default parameters in the uri are: