Flipkart Big Billion Days: six million shoppers, five thousand phones

How a national sale event works at Flipkart's scale: 6.3 million concurrent users in a minute in the 2026 opening hour, six to eight times the usual transactions and nearly 1,000 times the payment requests at the festive peak; a cached read plane and a small, exact write plane; the sale staged as a version so midnight is one pointer flip, with jittered refreshes instead of synchronised expiry; a line per deal at the edge, with a two-second lottery, tokens at the units times 1.3 and an honest answer for everyone else; stock held at checkout with expiring, keyed holds that are extended while money is in flight; unknown payment outcomes reconciled with the same key and confirmed orders written with an outbox; versioned price books that fail closed; and delivery dates backed by reserved wave capacity, answering each line of the founders' 2014 apology.