Yahoo, Uber, Instagram, and Spotify all run on MySQL.

https://www.uber.com/en-JP/blog/postgres-to-mysql-migration/

Instagram definitely runs on PostgreSQL. Here is official Instagram engineering blog mentioning the same: https://instagram-engineering.com/what-powers-instagram-hund...

> Most of our data (users, photo metadata, tags, etc) lives in PostgreSQL; we’ve previously written about how we shard across our different Postgres instances

Another relatively big company that uses PostgreSQL is Gitlab.

Did Uber reverted back to PostgreSQL after switching to MySQL?

https://www.uber.com/en-US/blog/postgres-to-mysql-migration/

And as far as I know Netflix was a big Cassandra user then migrated to CockroachDB. I tried to search for "Netflix Postgresql" and found this comment from 2016 stating that they chose MySQL over PostgreSQL: https://news.ycombinator.com/item?id=11950811

Could you share a source?

I just did a few quacks for "companies using postgresql". Tried to keep it to posts in the last couple years. Didn't look too closely.

Best source I found is https://www.thomsondata.com/customer-base/companies-that-use... but not sure how current it is.