I had problems getting disk_cache to work, and I was not able to see why. This was the relevant section from my config
# Caching CacheRoot "/var/cache/apache2/" CacheEnable disk /
I was timing a request such as the following, but caching seemed not to take effect, since the response used 7 seconds no matter what.
time curl -k https://customer1.myhosts.com/appserver/slow_request?param1=fooBar
After enabling debug logging I found the following statement in the logs, explaining why no caching was being done:
[Fri Aug 24 17:22:01 2012] [debug] mod_cache.c(552): cache: not cached. Reason: Query string present but no explicit expiration time
It turns out this is mentioned in the Apache Caching Guide:
If the URL included a query string (e.g. from a HTML form GET method) it will not be cached unless the response specifies an explicit expiration by including an "Expires:" header or the max-age or s-maxage directive of the "Cache-Control:" header, as per RFC2616 sections 13.9 and 13.2.1.
OK, so I add the following (taken from this article) in Apache
Header set Cache-Control "max-age=290304000"
It still does not work, this time I get the message
"... not cached. Reason: No Last-Modified, Etag, or Expires headers"
Now, this is a different story. How can I solve this without touching the application server code?