MariaDB is a mysql based product like the Percona stuff right? I assume most users would switch to MySQL proper.

Postgres is often a better choice, but not an easy one for shops already in the mysql world.

My trick is to rotate subprojects so I am always procrastinating something.

You still have to eventually finish the last subproject, but even that might be procrastinating on something for your next project.

I wish they where less common, but it does seem like a good idea to do some challenges before interviewing especially for low to mid level jobs. There are a number of good sources. I like “Project Euler”. a lot of the popular options like hackerrank or codesignal are very gamified. Go for it if that is your thing, but i find scores and points feel very dehumanizing for me.