Doesn't that kind of defeat the purpose though? The point of using varnish is that it keeps you from having to access the backend altogether. This is getting into an area where something like memcache might be more appropriate.
Well, the point of using varnish is to keep you from having to access the backend any more than is absolutely necessary. It's incredibly trivial to generate HTML showing a user's username and karma, and even if it weren't it could be stored in memcached. Generating the front page, the comments pages, etc. is the hard part, and varnish can keep that from being generated any more than is necessary.
Of course, but I seem to recall pg writing at some point that one of the goals of HN being to prove that "slow" languages can scale using caching. I assume, therefore, that he already has caching of some kind in place for those things. If varnish isn't going to save an access to the server (which seems to be the primary thing that's slowing things down), what value is varnish providing above what pg already has in place?
The requests won't queue up as badly because the server will be able to clean out 'simple' requests in a much lower time than generating much larger pages. They won't queue up as much because the requests take less time to handle, so they can be cleared out faster than they come in (compared to larger requests that queue up faster than they can be handled).
