Kenneth Fisher tells the story of where the optimizer’s cost value comes from:
Obviously, it’s an important subject, right? And yet we keep seeing comments about how the cost is in seconds.
And to be fair, it is. It’s an estimate of how many seconds a query would take, if it was running on a developers workstation from back in the 90’s. At least that’s the story. In fact Dave Dustin (t) posted this interesting story today:
The best way to think of cost is as a probabilistic, ordinal, unitless value: 3 might be greater than 2; 1000 is almost certainly greater than 2; and “2 what?” is undefined.