How does pagination on Reddit's home page work?

Question

Reddit uses a time decay algorithm. That would mean the sort order is subject to change. When a user goes to page 2, is there a mechanism to prevent them from seeing a post that was on page 1 but was bumped down to page 2 before they paged over? Is it just an acceptable flaw of the sort method? Or are the first couple of pages cached for the user so this doesn't happen?

Side note: It's my understand that Digg cannot suffer from this issue but that HackerNews and Reddit can.

Answer 1

From the next URL you see: http://www.reddit.com/?count=25&after=t3_dj7xt

So clearly the next page ensures that the page2 starts at the post after t3_dj7xt - whatever that translated to. This could be accomplished using IDs so you'd pass after=188 then the next page starts at 189 thus ensuring you don't see the same post if a time delay occured

Answer 2

It might be using the last ID as opposed to limiting from. Take these two examples of SQL:

SELECT * FROM Stories WHERE StoryID>$LastStoryID;

rather than:

SELECT * FROM Stories LIMIT 20, 10;