“Just cache it in Redis” — you’ve probably heard that in a code review, a system design interview, or a Stack Overflow comment. It’s almost a reflex at this point. But why Redis specifically? Why not a regular database with a good index, or any other in-memory store? I dug into the history, the architecture, and the current landscape of alternatives, and the story is genuinely more interesting than the meme lets on.
I get why this question keeps coming up. A WebSocket stays open, remembers who you are, and lets the server push data to you without you asking for it again and again. So why are we still firing off a hundred separate HTTP requests for a single page load when we could just open one persistent pipe and be done with it? Honestly, the question sounds smarter than most people give it credit for — and the answer is not “because HTTP is better.” It’s a lot more nuanced than that.