Rails - etags vs. page caching (file cache)

Question

What would be some advantages of using etags/stale?/fresh_when? instead of page caching (on a file cache)?

Apache automatically handles etags for static files, but even

Answer 1

They are really complimentary. Etags/fresh_when etc. help you play nice with downstream caches (like your own Varnish/Squid instances or Rack::Cache or the Browser cache or ISP Proxy Servers…)

Page caching saves you from hitting your rails stack entirely because Apache/your webserver serve the file, so no DB lookups are done. But you have to deal with cache expiration to keep the cache fresh.

Using etags/conditional get, you don't save much processing time since you still need to to get all the records used on the page:

def show
  @article = Article.find(params[:id])
  @feature = Feature.current
  fresh_when :etag => [@article, @feature] 
end

in the case that the user has a current page, it saves you some rendering time and the bandwidth required to send down the page.