bitmap VS null

Good question, I think there's many different lessons. To your point about bitmasks, you can imagine that each component (i.e. column) has an array of data and a large bitmap that identifies whether a component is present or not. Had to build a SIMD implementation so you can do and, and not, or and xor operations on millions of components within reasonable amount of time. Interestingly enough, you still need a hashmap or b+tree in case you want to retrieve a component by it's ID instead of an index, but the rest of things can be modeled with bitmap indexes.

I build a logging library for Go, because I couldn't find one that logs to stdout AND stderr. If you used a logging lib on GCP for example, all log output went into the same pile of junk and it was hard to find "real" errors: https://github.com/emvi/logbuch

Then there is "null", also because I couldn't find one that got both, marshalling to JSON and be able to store null values in db: https://github.com/emvi/null

And finally, our "flagship" open-source project Pirsch, an embedded library for web analytics: https://github.com/pirsch-analytics/pirsch