"Why Uber Engineering Switched from Postgres to MySQL"

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

Not needing a connection pooler (MySQL scales to thousands of connections via threads without breaking a sweat) and not having to deal with garbage collection (vacuuming) are two.

I love PostgreSQL, but the clustering story is definitely easier in MySQL land.

I mean, quite a bit. You use the right tool for the job. To use Postgres for everything is wrong to me. The beauty of MySQL based servers is the internal extensibility where Postgres is still rather lacking. MySQL and MariaDB are caching up on the external extensibility front.