[Plugin: W3 Total Cache] Page Cache not working – hostname mismathc

Hopefully this will help others and maybe Frederick Townes can add the ability to allow user to input a unique prefix in a future update to the plugin.

When running multiple domains through one memcached server you have a cache key problem. Nothing in W3 Total Cache allows you to define the key in anyway. So website xyz.com and abc.com may have cached pages with the same key. One overwrites the other and then both abc.com and xyz.com display abc.com instead of its own respective page. The reason for this is because all the cache keys start with w3tc_ instead of some website specific key and then it is all being served from a memcached server with one hostname. I imagine most use an internal IP for their memcached server since it doesn’t need to be open to the public.

There is probably a server side solution to this, but my hosting company either doesn’t know how to do this or has our memcached server misconfigured. But, either way, I needed a solution now.

My solution (and it may not be perfect or correct but is working so far) is to find all of the cache keys and change the prefix from w3tc_ to something of your choosing. For abc.com you may decide to use abc_ for your prefix. You may also need to disable “Cache requests only for hostname” in page cache options.

The files that I have so far found the cache key prefix in are found in w3-total-cache/lib/W3/

PgCache.php
ObjectCache.php
Db.php
Minify.php

Just in case anyone is actually following this thread:

The server-side solution is to configure multiple Memcached bins on your Memchached server. Assign a different port number for each bin and set that port on your different domains. This way you don’t need to modify any files if you’re running a MemcacheD server.

Thanks to Rackspace for this solution. Awesome support there.

I’m following along. I’m wondering if I should select Cache requests only for domain)

is something I should turn on or off?