DBs might not be glamorous but I'm sure there are many very interesting problems to solve when developing them. Of course on such a large, old project there's got to be a lot of tedious maintenance work as well, but that's true for all software in my experience.

It's often a conversation I have with people looking to get into software development. Often they'll aim for video games or something like that but I often warn them that it might not be nearly as cool as they imagine. You're more likely to end up scripting crappy menu systems than being the next Carmack.

On the other hand some of the most interesting pieces of software I've written were for very unsexy industrial applications. And I actually have good working conditions unlike people working in the videogame industry apparently.

  Often they'll aim for video games or something like that 
  but I often warn them that it might not be nearly as cool 
  as they imagine. You're more likely to end up scripting 
  crappy menu systems than being the next Carmack.

Interestingly, Carmack himself said if he wouldn't write videogames, he would work on databases. I can't find the exact quote, but here's a similar reference:

  I enjoy lots of different areas of it [programming]...
  I'm taking a great deal of enjoyment writing device
  drivers for Linux. I could also be having a good time 
  writing a database manager or something because there
  are always interesting problems.

And I recently had mindblowing moment when I realized that Civilization VI is heavily SQL based. I didn’t have time to dive into it but the Graphical UI is basically an interface to visualize and update a database.

Seems afterwards quite logical and clever considering the turn based gameplay.

Now just design a civ style game with sql command-line interface but fancy autocomplete bright warcarft3 colors and a fun storyline . Have a generation of gamers learn sql

I'm not sure I understand the "open source" part - it's not as if we do it for free. I'd say for most of the senior PostgreSQL engineers / contributors it's part of their paid jobs. We either work for companies providing various PostgreSQL services, or for companies using PostgreSQL.

We might do the same type of work on a proprietary database, but that would lack the community/cooperation aspect of the project.

Of course, enjoying the craft is somewhat natural in both cases. And yes, it's a bit scary how smart some of the contributors are.

It varies a lot. Many parts of the code base are very accessible and easy to modify for almost anyone, while some parts, especially the query planner, contain some of the most advanced code I have worked with.