I believe the news feed was originally generated every 20 to 40 minutes for each user, regardless of whether they were on the site. This way, caching was extrem

I believe the news feed was originally generated every 20 to 40 minutes for each user, regardless of whether they were on the site. This way, caching was extremely effective and the architechture could withstand downtime on the feed generators. I remember a few days where the news feed didn't update at all.