Question: If you have Varnish running as a cache, should you really have the WP 3W Cache plugin running too? Seems redundant, but I'm not familiar this tech.
Varnish caches the actual HTTP requests, and speeds up static content substantially by removing the necessity to load up PHP.
WP caching speeds up requests that spin up PHP by preventing them from making a connection to the MySQL Database. This is useful for requests that may peruse multiple blog posts, but load the exact same sidebar content by caching things like post counts, categories, tag clouds, etc.
Some of the cache plugins may just utilize page output caching, but IMO if you're spinning up your language runtime (Ruby, PHP, Python, Java, .NET) just to do page caching, you've already lost. Varnish and even built in Web Server caching can be far more efficient.
It's better to use the language runtime for more specific caching inside your application logic and for smarter cache expiration.
Agreed. I'd like to see the same benchmark run with Varnish + Apache. No W3Cache, No Nginx. I'd bet this synthentic benchmark would show the same performance, meaning it's all just hitting Varnish anyway.
Question: If you have Varnish running as a cache, should you really have the WP 3W Cache plugin running too? Seems redundant, but I'm not familiar this tech.