NSE: five million messages a second, and one line that decides who was first

How a stock exchange's trading core works at NSE scale: 21.89 billion order messages and 201 million trades on 24 March 2026, against a published capacity of about 5 million messages a second; one sequencer and one deterministic matching thread per partition, so the sequence number decides who was first and time enters as an event, as in the pre-open auction's random close; output gating so nothing acknowledged is lost when a primary dies; per-connection rates at the gateways and margin as a status bit from NSE Clearing; replay by sequence after a dropped session; multicast tick-by-tick feeds with two channels per stream, and what the co-location case taught about fair delivery; and February 2021, when the trading system was fine and the market still halted because the risk system wasn't.