Prompt for discussion in SPARROW technical workshop July 16th (see #14):

The aggregated report "with the possibility to have real-time information" needs that turn-around "to be able to pause/start, control budget/bidding level, ... with very little latency."

Updating the value in real time seems problematic — I don't see how we could keep it from being used as a signal to detect individual events. The contextual signals mean that the buyer network is in a position to pick out one specific auction and give some campaign the instruction to bid on it. But if there is some campaign that only has one opportunity to show an impression during some minute, and the advertiser sees that campaign's budget drop vs. remain unchanged during that minute, then we've allowed the buyer network to learn the exact context (including publisher-domain identity!) of a person who saw some ad. This is enough to join people's identities across domains.

It seems to me that there are a variety of ways to avoid this privacy problem, which all come down to not letting the buyer observe a very small number of events. That is, "real time" isn't the problem, "real time even if the change is only a handful of events" is the problem.

I'd like to talk about the specific ad buyer flows that you want to support, so that we can figure out what possible approaches could meet those needs without risking buyers seeing the results of individual auctions.