Jonathan Lewis' recent blog post, entitled Nothing Changed, got me to thinking about how frequently I hear "nothing changed" in relation to a performance issue. I really do think those are quotable (and laughable) famous last words. Think about it: if everything was the same, it's not possible for something to change, right?
A query plan doesn't change without reason. Response time doesn't change without reason. In general terms, it's rare that nothing ever changes. So, instead of immediately asking "why" and claiming "nothing changed", I think it'd be much more productive to start asking "what changed?".
When we insist on believing nothing changed, we limit our options of what could have happened. We close off our creativity. We limit our mind's ability to pursue possibilities.
I think one of the best skills a good performance analyst has is the ability to see lots of options. And, I think that the reason why people, like Jonathan Lewis, Tom Kyte, Cary Millsap, and many others, are so good at what they do is that they always stay open to many possibilities. Skill and knowledge is certainly important, but the ability to look at many alternatives and not get stuck demanding that things must be "just so" is just as critical.
In the end, those who continue demanding "nothing changed" might find the famous last words of composer Ludwig van Beethoven most fitting: "Friends applaud, the comedy is finished."