I know its a very general question but I'm curios whether fastcgi_cache works accurately with i.e. a plugin based solution say wordpress.org/extend/plugins/wp-slimstat/ or with an external solution like GA or Piwik?
But how would that work since a lot of visitors get served a static/cached version of the site?
Caching doesn't affect javascript-based codes. That is why GA, Piwik works fine with caching on.
From FAQ - http://wordpress.org/plugins/wp-slimstat/faq/ - that plugin supports javascript mode. So you can turn it on and it will work.
For very high traffic sites, if on server side they are logging data in mysql, it might create problem.
Generally softwares like GA, scrapes RAW data in different format in different storage engine. From that storage, another server-side process processes it to another storage format. You can find more details on Google!
But a mysql write for every page load is a big NO in my list.
Wait, if server-side call is to PHP and WordPress, which in turn calls mysql, server will hit its limits very soon.
If you are using mysql, atleast make sure server-side process is lightweight, something made in node.js.
By the way nginx can directly write to mysql/redis/memcache etc but I am sure this is not handled by this or any other plugin.
Thanks for the clarification. I simply wasn't sure if JS mode works with cache. Its a bit over my head but I think I understand the process better now.