We may have to eventually do that. That also might make more sense for handling requests across continents. Every 5 minutes still seems like not frequent enough but presumably the same approach could be used to write every 5-10s.

What we have considered is not doing any synchronous writes and just queuing it up and handling it async. There's definitely some questions about whether our current approach will scale 10x but it should be fine for the next 2-3x.

Just to shed a bit more light, we break things up into figuring out which ad to show and then handling when that ad is actually seen. The second part is mostly async already but the first part is the harder part. You want to choose the best ad for the content, the geographic targeting needs to match, and the ad campaign has to have budget left on the hour/day/total. If we only checked the budget every 5 minutes, that would be a problem. At some point, multiple servers need to know that there's still budget on a campaign and this requires some amount of synchronization.