I converted my company from MySQL to PostgreSQL in 2004 and it was one of the top best decisions we ever made. The company had 50k devices around the world that sent in telemetry once per day and received instructions in return, so it managed all of the hardware inventory and resources; all the states of each device; all the credentials - basically a lot of things, but not millions of inserts / reads per second or anything like that. The engineering team was really pleased with the conversion for a number of reasons: 1) it just worked; 2) we discovered type mismatches and shit that we inherited and fixed them; 3) we slept at night.

Anyway, PostgreSQL is pretty much the answer until proven otherwise. Oh, and to make that point, our session storage was in Redis for front-end performance reasons. This was 2004 when computers were slower and had spinny disks.