[DoctorOW]

>How do you know that Google isn't supporting Postgres in any way, e.g. by supplying upstream patches, etc? The same goes for AWS, Azure, Heroku.

There's a list of contributors and what organization they're from here <https://www.postgresql.org/community/contributors/>. You won't see "Azure" listed but that's because it's considered part of Microsoft. Of the ones you listed, Azure is the only one that is considered a major contributor though you'll see there are companies that specialize in managed Postgres specifically.