Redis

Cache stampede (a.k.a. thundering herd on TTL expiry) is one of the most dangerous failure modes in high-traffic systems. The moment your cache key expires, hundreds of simultaneous requests hammer your database — often killing it. Here's how it happens, and exactly how to fix it.

Redis is full. Instead of failing gracefully, it starts silently evicting your most important cache keys — session tokens, rate limit counters, distributed locks. Your app behaves mysteriously until you realize Redis has been quietly deleting data. Here's how to tame Redis eviction.

Network partition splits your 3-node cluster into two halves. Both halves think they're the primary. Both accept writes. Network heals. You have two diverged databases with conflicting data. This is split brain — one of the most dangerous failure modes in distributed systems.