Write-Behind

1. The Incident

The product team requests a small feature: every product page should display a counter such as "12,483 people viewed this today." The direct implementation runs UPDATE products SET views = views + 1 for every page view.

During peak traffic, the bestseller receives 12,000 views per second and therefore causes 12,000 UPDATE operations against one row. Because a database protects a row during modification with a lock, those operations form a queue in which each request waits for its predecessor.