On scaling social network feeds:- http://www.quora.com/What-are-the-scaling-issues-to-keep-in-mind-while-developing-a-social-network-feed I keep banging up against this many-to-many problem. If it's not "show me all the (new) updates from all my friends", it's "show me all the new messages in all the groups I belong to". Or "Show me all the new entries with this tag". Using simple SQL quickly runs out of steam because there's no obvious way to index it. Which then means the SQL engine has to create a temporary table and then sort it for every query. Is there a simple computer science tutorial or discussion on approaches to dealing with this?