When the cache misses, everyone misses at once.
Hot Keys and Cache Stampedes: when the cache misses, everyone misses at once
absorb bursts before they become outages
Singleflight introduces brief queueing on the lock.
A hot key is a single key with disproportionate traffic. A stampede happens when its cache entry expires and many requests miss simultaneously, hammering the origin.
Mitigations: per-key lock for refill (singleflight); randomized TTL; stale-while-revalidate; pre-warm on deploys.
For unfixable hot keys: replicate the key across N nodes; fan-out reads.
Detect with Redis 'hot keys' tools or sampling.
Homepage feed expires every minute, p99 spikes.