Why Uber Engineering Switched from Postgres to MySQL
eng.uber.comDetailed article that shows Uber’s thought process for moving away from PostGres. I am surprised no one has encountered these problems with indexing and repl before.
If you are interested, there are rebuttal posts in the Postgres mailing list that have been posted here when this was new news. This was from years ago now, and part of the consensus was, they didn't do ~anything~ to work with the community to optimize their workload, their workload was very much not the normal way an RDBMS is used, and MySQL was a better choice for them due to how they wanted to design their schema.
They backed themselves into a corner by trying to use the wrong piece of software for the specific way they wanted the job done.