She unsubscribed at 7:59. The push came at 8:03.

transcript

Meera turns marketing off. 7:59. Four minutes later, the cashback push arrives anyway. The cache was updated in one second. So what went wrong?

7:55. The campaign is routed. Marketing is on. She opts out at 7:59 and 30 seconds. One second later, the cache is invalidated. Perfect, right? At 8:03, she gets the push anyway.

Here's the catch. The cache was right. But the decision was made at 7:55. Her message was already waiting in the bulk lane. Nobody looked again.

The router checked once, at 7:55. Then the message sat in the lane, for minutes. So the worker checks again. Right before sending. Opted out? It's marked suppressed, with a reason.

It re-reads the opt-out. Quiet hours, which change with the clock. And the expiry. One cache read, per send.

Uber's push pipeline does this too. Last-mile checks. Decide early, if you like. But check again at the last mile.

Full breakdown in the lecture.