To be fair, and I know nothing about Tesco’s actual stack, a large grocery chain needs to track their contracts with suppliers, track their inventory in each location and in transit, track what goods they want in which locations, understand which larger pallets and big boxes contain which goods, track things prepped in house, and also optimize what to move from where, to where, and when and how. The latter part probably uses some spiffy stack involving something like CPLEX or Gurobi, and it’s not running on their “1 computer” OLTP stack.

That being said, I don’t see what 40k servers is for unless the POS machines are thin clients that use a substantial fraction of a server each.