What's the current state of the art for space-efficient long term Prometheus storage?
PromHouse looks very promising: https://github.com/Percona-Lab/PromHouse
PromHouse looks very promising: https://github.com/Percona-Lab/PromHouse
I would be wary of PromHouse since at a glance it seems to be storing each timestamp in a separate row, which will not be as space efficient as either of the above options.
Full disclosure, I am a maintainer of the Cortex project.
Can house multi-tenant-safe prometheus long-tail storage as well as others (graphite, opentsdb, influx, etc.). Put it all in one place, scale it up, radically storage efficient and has strong non-stop HA guarantees. It is state of the art, it isn't free.
Disclaimer: I'm the CEO of Circonus (IRONdb's home).