>Is it about code that isn't thread-safe? That relies on undefined behavior? That doesn't scale? That has race conditions? It can be any of those. Not a blog p

>Is it about code that isn't thread-safe? That relies on undefined behavior? That doesn't scale? That has race conditions? It can be any of those. Not a blog post, but one example that immediately comes to mind as something you shouldn't use in production is the [Redis KEYS command](https://redis.io/commands/keys https://redis.io/commands/keys).