Time for a follow up to my String.Concat vs String.Format Performance post from back in 2014!
I recently found out that string interpolation is not nearly as efficient as I would have thought. I also suspected that it was just doing a string concatenation, but it is actually doing a string format. This leads to a pretty significant performance degradation; the following test runs one million iterations of each.
So, what's the lesson? Don't use string interpolation in high performance areas (such as your logger)!