The link below is to quite a fascinating article that on the surface is about why Uber moved to MySQL from PostgreSQL.
What it really is about is a severe limitation in how PostgreSQL indexes are updated.
With SQL Server, if you update a few columns in a row, only the indexes that have that column are updated. In PostgreSQL, all indexes still need to be updated. I understand why they've done that but it's not a good outcome.
SQL Server shines in this regard.
http://use-the-index-luke.com/blog/2016-07-29/on-ubers-choice-of-databases
We have a mix of SQL Server, Mysql, postgres, Oracle ,DB2 etc, While SQL Server shines in this regard compared to postgres, we don't pay for Mysql and Postgres (only for support) for the apps that don't require all the functionality we are willing to migrate to the opensource databases to cut cost.