Q: How does the system cache pages?

A: eZ Publish has a number of cache levels. Both internally and externally.
 
The most important cache mechanisms are:

• View cache: this is the cache of a specific content item like an article or an image
• Cache block: this is a cache of a certain repeating element in a template. E.g. the generation of a menu would be the same for most pages and you can easily use a cache block to ensure that this is only generated once
• Static cache: this is a mechanism to cache a complete rendered page.
• Reverse proxy cache: Varnish or Squid integration
• CDN cache: this cache ensures that pages served from eZ Publish is properly cached in a CDN ( Akamai or similar). Here you have the possibility of ensuring that e.g. all logged-in users are receiving dynamically generated content (still cached with view cache and cache blocks).
• ESI cache: this is a built in feature similar to cache blocks where you can have the CDN fetch a part of a page from the back-end. Typically used for fetching personalized content or content that is similar on many pages (latest added news for example).

There are also other cache mechanisms in eZ Publish that can be utilized and tweaked, but these are the ones you most commonly use for efficient delivery of a high traffic website.