[reinhardt]

> Its a massive amount of state aggregated from billions of events that needs to be served at extremely low latency, but couldn't it be partitioned somehow???

The bidder/pacer state is not necessarily massive, and certainly it does not consist of all the gazillions of past events. Depending on the strategy/bidding model, it can range from a few MB to several GBs, something that can fit in a beefy node.

> Google Fi/Spanner and BigTable have certainly been developed to support these issues.

I doubt any external store can be used with so low latency constraints (2-10ms) and high throughput (millions RPS). Perhaps Aerospike but even that is a stretch to put it in the hot-path. At this scale you're pretty much limited to fetch the state in memory and update it asynchronously every couple of minutes/hours.

Source: I also work in ad tech.