Both Microsoft and Oracle prohibit benchmarking: https://danluu.com/anon-benchmark/

Wikipedia article: https://en.wikipedia.org/wiki/David_DeWitt#The_%22DeWitt_Cla...

It's plainly illegal, but nobody who has built their business on Oracle DB wants to piss off Oracle the company with a lawsuit, and it doesn't appear any legal activists want to either.

Seems it's in the license agreement. What's unusual is that actually matters here. If someone tried to prevent benchmarking Postgresql by licensing terms, someone else would promptly ignore them and do it anyways, since Postgresql is free to download. Oracle licenses are very expensive, so anybody who has access to it also has money and a lot to lose by flouting license terms.

That is my understanding. [0]

[0] https://www.brentozar.com/archive/2018/05/the-dewitt-clause-...

You can benchmark it, the license agreement only prohibits you from publishing the benchmark.