We are running a load balancing server in front of 2 Apache webservers and 1 memcachedD server.
When running debug mode on page cache, we get an error that the page cache is disabled (though enabled in W3 settings) and the page is not cached due to a hostname mismatch.
Disabling "Cache requests only for godfatherpolitics.com hostname" does enable the cache and our website is blazing fast, but we run 3 different WordPress installations across 3 separate domains but the cached pages begin to swap across domains and visitors start seeing xyz.com content on yyy.com so we had to disable that option.
Here is the full debug for page cache:
Served from: godfatherpolitics.com @ 2011-09-28 13:01:20 -->
<!-- W3 Total Cache: Page cache debug info:
Cache key: w3tc_10.181.135.115_1_page_e94d0037a44a1dc6c01634e2a91f00e0
Reject reason: Hostname mismatch
Status: not cached
Creation Time: 0.230s
Content-Type: text/html; charset=UTF-8
X-Powered-By: W3 Total Cache/0.9.2.5b
Link: <http://godfatherpolitics.com/?p=1176>; rel=shortlink