Stack Overflow interesting questions implementation

Question

According to the tooltip of the 'interesting' tab, interesting questions are

"questions that may be of interest to you based on your history and tag preferences"

Does Stack Overflow use a recommendation engine or just some sql sort/filter?

Answer 1

https://blog.stackoverflow.com/2010/11/stack-overflow-homepage-changes/

In short, first drop any topics you ignored or attract low-attention, then apply the scoring formula:

• your interesting tags +1,500 per interesting tag, up to +2,000 total
• your top 40 scoring tags maximum of +1,000 per tag (scaled), up to +2,000 total
• question score +200 × score, up to +1,000 total
• total answer score -200 × score, up to -1,000 total
• number of answers -200 × answers, up to -1,000 total
• number of views -15 × views, up to -1,000 total
• question last activity date -1 × (seconds / 15)

Those make 90% of the interesting questions. The other 10% comes from some random pick.

It's a simple but effective solution.