I don't want to be bashing MySQL, but this nicely illustrates the project's approach to engineering - if there's an issue, put it into the docs as a known limit

I don't want to be bashing MySQL, but this nicely illustrates the project's approach to engineering - if there's an issue, put it into the docs as a known limitation. Furthermore, MySQL manual actually has "Restrictions and Limitations" (which is an interesting read too), yet this "unsafe" nature of "INSERT ... ON DUPLICATE KEY UPDATE" is not mentioned there. I'd say that if PostgreSQL learned something from MySQL, it's "Never accept feature that is incompatible with existing features, even if it's promised to be fixed soon."