Replied on the Zcash thread, copying my replies here:
Otherwise, a user’s “real price” is higher than the “set price” because a user has to take into account the fact that their own transaction pushes up the real price for themselves.
Yes, I agree with your observation. However, I think this can actually be a good point and should be exploited because it incentivizes a user to avoid executing a lot of transactions in a single block. This is similar to the problem of liquifying a large volume of some asset in game theory, in which whenever you sell some amount the price goes down, and as a result, you are incentivized to sell little by little. I think the same mechanism design helps to avoid network congestion.
To be more specific, I have already mentioned the paper “Optimal Execution of Portfolio Transactions” in which the authors prove that if we have a very similar additive update formula, the optimal strategy is to execute transactions over a long period of time. Maybe we can use the same formula in here.
That said, if we want to eliminate this issue entirely, we can do that by replacing
minfee *= (1 + excess * adjSpeed)withminfee *= e ** (excess * adjSpeed).
If I rewrite your formula as log(minfee) += excess * adjSpeed your alternative suggestion is just to have the same additive update rule and then exponentiate it to get minfee. As I said in the previous comment the additive framework is well-known in economics but why the exponential? In other words, suppose that minfee += excess * adjSpeed, and then we charge everyone a fee of f(minfee). f could be the identity function, an affine mapping, or any other positive increasing function including the exponential function, but I am not sure why exponential seems like a canonical choice to you?
This is intentional for incentive compatibility. It’s a common technique in game theory for the price that a user pays to be explicitly only based on other users’ activity, so that incentive-compatibility for the user can be proven trivially as a simple matter of “if the price is favorable the user gets it, otherwise the user does not”.
Even in the new settings corrected by the exponential or additive formula, I still believe that users should also be charged for their own transactions as well as the aggregated previous usage. Today, I was reading about the gas token and any such smart contract exploiting storage refund in Ethereum can be used for hoarding which is immediately profitable if the gas price you pay is independent of the gas cost of your smart contract.