Problems with varnish and apache (trying to improve OpenCart) - apache

Question

I'm trying to give my webshop a boost with warnish.
Setup varnish port 80, backend is 127.0.0.1 apache2.
Apache Benchmark gives awefull resulst, like 1-2 request/sec !
On the very first displayed file; header.tpl I have :
<?php
cache_control( "public, s-max-age=6000");
expires( to_gmt( time() + 6000 ) );
?>
Below is the response header:
HTTP/1.1 200 OK
Content-Length: 151613
Expires: Tue, 26 Feb 2013 20:04:07
Cache-Control: public, s-max-age=6000
Pragma: no-cache
Set-Cookie: PHPSESSID=i9h5ldj8k4fking69d03jr5244; path=/, language=en; expires=Thu, 28-Mar-2013 18:24:06 GMT; path=/; domain=www.domain.com, currency=CHF; expires=Thu, 28-Mar-2013 18:24:06 GMT; path=/; domain=www.domain.com
Content-Type: text/html; charset=utf-8
Accept-Ranges: bytes
Date: Tue, 26 Feb 2013 18:24:07 GMT
X-Varnish: 186646239
Age: 0
Via: 1.1 varnish
Connection: close
X-Cache: MISS
Must be missing something obvious but to me varnish just doesn't cache; what am i doing wrong ?

Answer 1

PHP most likely has session.cache-limiter set to nocache (the default).
This would send a Pragma: no-cache (and as far as I understand an Expire header set to the current time) to Varnish and thus disabling caching.

Answer 2

Varnish will ignore the « Pragma : no-cache » by default, unless it is instruction to handle the directive (https://varnish-cache.org/docs/4.0/users-guide/increasing-your-hitrate.html).
Your cache-control seems to be configuring properly and should be cached for 6000 second.
The next things that you need to take into consideration are the cookie. Looking in your header, you have a PHP session Cookie:
Set-Cookie: PHPSESSID=i9h5ldj8k4fking69d03jr5244;
Varnish will not cache the cookie unless you remove it the request in your vcl file. Ex :
sub vcl_recv {
set req.http.Cookie = regsuball(req.http.Cookie, "PHPSESSID =[^;]+(; )?", "");
}