3.6 Hot Keys and Cold Starts

Two more situations turn a cache against the database it protects, and neither depends on one entry expiring. The previous lesson covered the cache stampede, where many callers rebuild the same expired entry at once, and its defenses: single-flight, a rebuild lock with an owner check, stale-while-revalidate, jitter, and load shedding.

This lesson covers hot keys, where one key concentrates load on one cache node, and cold starts, where an empty cache sends the full read load to the database. It ends by showing how the three problems interact and what to monitor for all of them.