Explain doesn't give you that information in many (most?) DBMSes. It's a bit like seeing the compiler IR code of your program. It lets you understand some things, while others remain a mystery.

I'm guessing you've tried these flags mentioned in the blog post but haven't had luck with them?

> LLVM supports an interesting feature called Optimization Remarks – these remarks track whether an optimization was performed or missed. Clang support recording remarks using -fsave-optimization-record and Rustc supports -Zremark-dir=<blah>. There are also some tools (opt-viewer.py, optview2) to help view and understand the output.