Matt Levine, your wealthy readers are looking at my blog

Market structure.We talked a little yesterday about market data revenues for stock exchanges, specifically in the context of the Chicago Stock Exchange's proposed speed bump. But here is a deeper dive on the fight over market data revenues, which some people think are almost inherently immoral:
"Exchanges don't create any unique content — market data is generated by their members and other market participants including real investors — so it's very hard to believe that exchanges can perpetually charge their members more every year to look at the members' own data," Brad Katsuyama, CEO of IEX Group, told Business Insider.
"The elephant in the room is that Wall Street rewards subscription-based business rather than transaction-based business," says Doug Cifu of Virtu Financial Inc. The basic problem is that if you are a high-frequency trading firm you kind of have to be a completist about market data: You need full order-book information from every exchange, and you need to get it as fast as possible, because if you don't someone else will get ahead of you. That means that a small exchange can make a lot of money charging everyone for data even if it isn't a very good exchange and doesn't execute many trades, and it means a large exchange can constantly add slightly faster connections at much higher prices and be assured that its core customers will have no choice but to pay for them. The absolute value of the new services might not justify the price, but the relative value means that the exchanges can demand almost any price.

Well, since yesterday, we have seen that the trading pit solves just about all these problems.

Relative valuer means some bots get to jump he queue and get an early peek.  How?   What is an order book on an exchange? In the current system it is a file attached to some bozo executive at the exchange.  In the new system, the order book is constructed in runtime. If you want to pay the scan price, send in your bot, it can record thenorder book, step by step. The bots, themselves, ate the self discovered order book. The bot can examine it, and select from it, and submit a bid, drop out, go to the machine next door, to play majhong.,