Tbh I had no idea this was even a thing until recently. I've been working with Rails for a while now and somehow never came across it. So let me explain it the way I understood it. You know how we normally do associations in Rails, User has many Posts, Post belongs to User. Two different models, two different tables. Simple. But what if a model needs to reference itself? Like same table, same mode
Let me rewind to a Tuesday afternoon I’d rather forget. We had a Rails monolith that had grown fat and happy over five years. The dashboard—a beautiful, chart-filled monster—was running a 12-second query every time the CEO clicked “refresh.” Twelve seconds of GROUP BY, COUNT(DISTINCT), and LEFT JOIN hell across a million-row events table. The CEO didn’t yell. He just stared at the spinning cursor
I needed to coordinate background scripts running across different machines. The obvious answer was Redis. Everyone uses Redis for this. The tutorials all use Redis. The Stack Overflow answers all say "just use Redis." So I looked at what deploying Redis would actually cost me: A running Redis server I had to maintain A broker to connect workers to it Celery or RQ on top of that Memory-based stora