[samarudge]

> the Varnish HTTP cache has been used very successfully to speed up WordPress. But Varnish doesn’t help a lot with logged-in traffic > This is caching that Varnish and other “normal” HTTP caches (including CloudFlare) could not have done

Varnish supports the ESI (Edge-Side Includes) standard, which allows it to cache fragments of a page, and for the cache server to build them again. It also allows you to completely bypass the cache for certain fragments. This is also supported by a number of CDNs (Fastly, Akamai). I've used the ESI technique several times and have been able to achieve a >98% cache hit rate on Fastly for a site with dynamic per-user content. Even the cache misses are only responsible for rendering a small component of the page

[FooBarWidget]

Good to know. Using edge side includes may be easier than trying to change the app to a semi single page app. But that only solves half of the problem. The other half is varying the response based on the value of a specific cookie.

I've updated the blog post with information regarding edge side include.

[samarudge]

Varnish also supports custom cache keys via the VCL function `vcl_hash` as documented in https://www.varnish-software.com/static/book/VCL_functions.h...

I couldn't (quickly) find documentation on how to get the value of a specific cookie, but the server could send a user ID in a header or something Varnish can easily access to be used in the above function.

[sandstrom]

I understand that you want to offer something that 'beats' varnish, and it shines through in the article.

But I don't think it matters if your cache is better than every other cache. Rather, as long as you offer a convenient, easily implemented cache, built into the webserver, that's great in itself. We're using Passenger on all our production servers and are most satisfied, because of its ease of use.

Perhaps you could just write "this could be accomplished with Varnish, which has a lot of benefits for advanced cases, but we think our cache will be useful for those that prefer not to manage a separate caching tier."

[cheald]

Varnish also supports plugins for extreme flexibility. For example, I wrote a plugin for our Varnish install which performs HMAC validation of a specific signed cookie and then sets a header which is used downstream in the caching rules.

Varnish is mature, powerful, and fast as hell. It would take a lot of work to reach a point where I'd swap it out for something else.

[stephenr]

Exactly.

I'm not really sure what situations this built-in cache would be more effective than the likes of a well-tuned Varnish.