From One Server to Surviving the Big Sale Day
2026-07-25It's 6:30 in the evening. Migratory-chan has just landed after a full day of flying, still worn out, and out of habit opens her phone to pick out discounted shoes for the big sale day. The screen spins for a long time, then a cold error message appears. She frowns and taps three more times, her finger hovering as if waiting for a reply that isn't coming. Beside her on the stone steps, Black Cat-chan sits with eyes narrowed in the sun, tail sweeping lazily across the ground.
She puts her phone away and turns to Black Cat-chan, a little indignant. "I passed by a shopping site today — it just wouldn't load on Black Friday. Why does that happen? It's always so fast normally."
Black Cat-chan pulls her tail back in, eyes lighting up like she's found an interesting topic. "That 'fast' you feel when you normally open it — behind that, there's really just one server holding everything up. It's storing information about every single product you might want to buy, and calculating every single request you click. On Singles' Day, it's not one person coming to look at shoes — it's hundreds of thousands of people showing up at once."
She pauses, then draws a little square on the ground with her paw. "In the very beginning, a website really was just one machine — the place that stores data (the database) and the place that processes requests (the application) crammed into the same room. When there weren't many visitors, this one machine could handle it fine, greeting everyone who came in properly."
Migratory-chan cuts in. "So then what? Doesn't it just break down once there are more people?" Black Cat-chan nods. "Right — the first time it broke down, everyone assumed the machine just wasn't fast enough, so they swapped it for a pricier, faster one. That's called vertical scaling. But the problem came right back: no matter how fast the machine is, it still only has one brain. When hundreds of thousands of people call its name at once, it can't keep the books and greet customers at the same time. Cram two jobs into one brain, and neither one gets to be fast."
Black Cat-chan stands up and draws two more squares on the ground, connecting them with a line. "So someone thought — why not just split these two jobs apart? One machine handles only the ledger (the database), another only greets customers (the application server). Each side got easier, but a new problem appeared: if the customer-greeting machine can only stand one person at the door at a time, the people lined up behind still have to wait." She redraws one of the squares into three squares side by side. "So later they added a 'host' — a load balancer — to sort arriving customers across three doors, sending them wherever the line is shortest."
Migratory-chan looks down at the squares and lines on the ground, thoughtful, then glances again at her phone where the error has already vanished. "So what I ran into today — was that the old problem of bookkeeping and customer-greeting crammed into one brain?" Black Cat-chan smiles. "Could be. Or it could be a problem from a later chapter — because even after splitting things apart, new headaches show up again. But now you at least know: a site 'freezing' was never something you could dismiss with 'the server's bad.' Behind it is a whole history of 'whoever can't take it anymore gets split apart and reassigned.'"
Black Cat-chan flicks her tail and points at the three squares she drew earlier. "But guess what — after splitting the customer-greeting job three ways, do you think that one bookkeeping machine might start struggling too?" Migratory-chan freezes for a second. "...oh. It's still just one, this whole time." Black Cat-chan just blinks, and says nothing more.
