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A system can have plenty of capacity overall and still struggle when too much traffic is concentrated on a single piece of data, such as one viral post, one popular product, or one heavily updated counter. The node responsible for that data becomes overloaded, while the rest of the system may be sitting mostly idle.

This lesson covers what hot keys are, why they can overload one part of a system even when everything else is running fine, and the main techniques used to handle them for both reads and writes.

It also covers how to approach hot keys in a system design interview, since they come up as a follow-up question in many common problems.