Ask HN: "Unknown or expired link."

It means your session has expired. I usually see it if I come back to the front page after a few hours (or overnight), but I have been getting it pretty regularly now.

I suspect that there is a traffic spike, or maybe just more people coming to the site regularly. Its a growing pain.

PG mentioned somewhere that when he was doing Viaweb, he was storing functions on the server side in a hash table, so that most urls work by invoking these functions. This was his way of remembering state between url visits.

It seems that functions expire from this hashtable after a while.

I think that might have seemed like a good idea in 1998, but these days I think it's just pointless.

http://people.csail.mit.edu/gregs/ll1-discuss-archive-html/m...

http://lib.store.yahoo.net/lib/paulgraham/bbnexcerpts.txt

  > One of the problems with using Web pages as a UI is the inherent
  > statelessness of Web sessions.  We got around this by using lexical
  > closures to simulate subroutine-like behavior.  If you understand
  > about continuations, one way to explain what we did would be to
  > say that we wrote our software in continuation-passing style.

Yeah, get that a lot. This error appears whenever a new link is added. Navigation on the current is invalidated. Annoying bug.

I have a theory on this:

The url of the 'more' link is some kind of hash of the next page of links at the time of page load, this is because HN Moves pretty quick, so using the live data you're likely to miss links between page 1 and 2. (Which is what happens on 4chan)

Obviously these links have to expire fairly quick as they're pretty unique, and storing them for much time would use a huge amount of memory. With this in mind, the life span of these links is probably directly related to the current load of HN.

Amirite?

It means the order of the links in the page you were selecting has changed. When I get that, I start at the front page again. There's new links there for you to see.

Yeah this is a tad annoying; started reading HN on my iPhone and sometimes I leave it to keep reading 'more' later and my session expires.

This always happens to me, I thought the page was designed to make you always refresh or something lol.

It is the most annoying feature possible.