I’ve been trying to figure out the effect of this line in my Varnish config:
sub vcl_hash { if (req.http.Cookie) { set req.hash += req.http.Cookie; } }
It seemed to make sense, but I was having a hard time wrapping my head around its ramifications. I was looking at some of the docs on the Varnish site and at this great Varnish config walkthrough when the metaphorical lightbulb went on. By adding the cookie to the hash it’s effectively creating a per-session cache.
Hmm. An interesting tradeoff. On one hand it’s filling up my available cache with duplicate copies of the same content because the hash identifying the cached content is cookie-specific. On the other, it is delivering content from cache that wouldn’t normally be cached because of the cookie.
