Redis is one of those rare pieces of software where the source code is short enough to actually read and deep enough to teach you something new every time. I’ve spent a good amount of time going through the actual Redis source — and what strikes me every time is how deliberately every design choice was made. Nothing is accidental.
So let’s actually design one from the ground up — not a toy, but an architecture that mirrors what Redis actually does. Data structures, event loop, protocol, expiry, persistence. All of it.
“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.