Caching

Cache Penetration

Repeated requests for keys that do not exist, so the cache never helps and every request reaches the database.

Why interviewers ask about it

A trivially exploitable DoS. Cache negatives briefly and front with a Bloom filter.

A probabilistic set that answers 'definitely not present' or 'possibly present', with no false negatives.

A hot key expires and thousands of concurrent requests all miss and hit the origin simultaneously.

This term is part of the free System Design interview preparation module - browse the full glossary for every definition.