Has anyone used PostgreSQL with ignition? How was it , Stability etc…

I use almost nothing but PostgreSQL. Primarily because it has the absolute best SQL standard conformance in a freely licensed platform, and because it implements the major transaction isolation levels throughout its design.
It is very stable, but does require some adjustment for best performance: the defaults for shared buffers and work memory tend to be too low. The online documentation is very good. You should start here and here.

I also use only postgreSQL and I agree with everything, what @pturmel said.
I started with postgreSQL mainly because at the time it was the only free db which supported timestamp with ms (milliseconds) and because it was (is) really free for commercial use (not like MySQL). Now I don’t know for other db’s (free) if they’re supporting ms timestamp, but I’m stuck with postgreSQL… :thumb_left: