We scaled our new Prometheus TSDB Grafana Mimir to 1B active series

Mimir needs 30TB of RAM for a billion of active time series. That's too big price for horizontal scalability comparing to the original Prometheus, which requires around 4TB of RAM for a billion of active time series according to https://www.robustperception.io/how-much-ram-does-prometheus...

It would be great comparing Mimir RAM usage to other horizontally scalable time series databases such as M3DB, TimescaleDB, InfluxDB and others.