Amazon has made contributions to open source in many ways, including bug fixes, spending hundreds of thousands/year to sponsor conferences, and even giving the PostgreSQL community a free testing account to run regression, soak, or functionality test suites on AWS for free. So yes, Amazon contributes cash to open source projects, at least to PostgreSQL, which we find to be a wonderful community that we are proud to be part of.

How much cash did AWS give to Postgres?

Amazon is a real parasite on open source projects, it never gives back.

Nope. For an example look st elasticsearch. Pretty predatory.

Uh, I wouldn't call it predatory. It's a shame they don't contribute more and they could do a lot better, but turning projects into services massively contributes to their ecosystem.

Maybe predatory is a strong word. Many OSS projects would characterize them that way though, I think. Your point about impact to the ecosystem is a fair one, but in some cases it is more co-opt rather than contribute.

I think a lot of that is perception. I know the AWS RDS team has a pretty close knit relationship with the Postgres team, it's just not super obvious.