Is there a practical limit to the number of files in a Swift container?

A solution I work on stores files in OpenStack's Swift but the files are spread out into multiple containers. I have been told this is because the performance is awful after about a million files in a container. The only reference I could find is from a blog of 2010 http://adrianotto.com/2010/09/openstack-os-is-great-for/.

Since

1. I cannot find any other documentation about such a limitation/performance issue
2. It has been more than 10 years since the blog post

Is there still a limitation (or performance issue) to the number of objects in object storage in recent versions of OpenStack?

The question was copied to serverfault.com, where I also moved my answer.