"The query is faster on the old environment! 3 times faster!" No one ever said that, right?

But what is causing that?
It is the same engine version, with no bottlenecks on CPU, memory or disk!
"Surely, it is statistics(!) and a different execution plan shape!" No! Even the execution plan looks the same!
No yellow triangles with warnings, nothing screams "I'm the problem!".

Let me share this true story that was driving me crazy with you. The analysis I did, and all the tools and methods I used to compare things, until, after some days, I got to the root cause of it.

Now that I know, it's obvious, but isn't it always that way?

I can guarantee you, as long as you remember this, you won't forget to check it again when this kind of performance issue strikes! Anyway, I will also share an easy way to remember to check it next time!

A journey to understand where the performance penalty came from!
If you are a DBA/Developer writing/analysing T-SQL, you will want to know this!