Cache Stampede

A cache protects a database by handling repeated reads from memory.

But when a popular cached value disappears, many requests can miss at the same time. If every request tries to rebuild the value on its own, the database suddenly receives the same work over and over.

That is a cache stampede, also called the thundering herd problem.

The danger is not just a cache miss. The danger is many misses for the same hot key, all racing to rebuild it.

This chapter covers what a cache stampede is, why stampedes happen, how they affect a system, the main prevention strategies, how to detect them, and the production habits that reduce the risk.