Efficiently determining the news feed per user is a pretty big technical challenge when you get to 500m users (which probably means a million or so news feed re

Efficiently determining the news feed per user is a pretty big technical challenge when you get to 500m users (which probably means a million or so news feed requests per second, possibly more). If you think about it, there are broadly two ways you can handle me posting an update which appears in my friends' news feeds: 1. Post an item which is has my user ID as the owner, and each time one of my friends reads their news feeds you join together all the news items based on a 'friend' relationship (presumably a many-to-many link), order them by timestamp and do all the filtering necessary where they've clicked "don't show this kind of update from this user". 2. Store a news feed per user and update all my friends' news feeds when I post something new, remembering to keep everything in sync should I delete the post, be removed as a friend etc.