MongoDB averaged 11:55, maxing out all 4 vCPUs, and generated about 500 MB of data.
PostgreSQL with TimescaleDB, however, averaged 15:10, using about 68% of all 4 vCPUs, and generated _34_ MB of data.
WHAT?
I think MongoDB storage gets "more" efficient at scale, because this test created lots of time-series "buckets" with only 1 record in each. But even then, PostgreSQL and TimescaleDB compressed the same data so much better.
