okay someone pmed me saying that the exchange guarantees a certain percentage of order flow to market makers.
if i understand how it all works, then this is their edge.
however, i don't understand something about guaranteed volume.
say a non market maker submits a limit order to buy 5 contracts at $10.00. he is the first order in line. a market maker then submits an order to buy 2 contract at $10.00. say this market maker is guaranteed 50% volume. there is a total of 7 contracts at $10.00 and that's it.
now a the exchange gets a market order from someone to sell 4 contracts. how does the fill work? if the market maker is guaranteed 50% volume, then he should get allocated 2 contracts and the other 2 contracts go to the non market maker. but didn't this allocation just violate the price-time priority? under the price-time priority, the non market maker should have been allocated all 4 contracts.