Okay, now I have a profile that says 90% of the time is spent in the code the cache avoids. Now what? Narrator's note: When the cache was put in place it accounted for 40% of run time, but now people use it because it's 'free' and so the code has grown from looking up the data twice to looking it up five to seven times depending on conditional logic.
> Well, they delivered (I'm guessing) 10x improvement in a month by adding cache.
No, they didn't. That's the problem. No cache gets you 10x. 10x for one step of a 20 step process is a positive improvement but rarely more than 2x for the first one, 4x at the outside. If it does more that that then someone is being titanically stupid. From then on each cache is going to net you less, and less, and less. Only if someone measured wrong or you are blocked by some architecture change that's needed so that caches even make sense, will you see a bigger improvement this year than you did last.
But the pathology I'm discussing above didn't even have anything at all to do with caching. It's the psychology of (ir)rationalizing around performance, the assertion that you've done everything that can be done because you've done everything you know to do. It's a bizarre love child of learned helplessness and ego self defense. It's gotten way worse in a world where people reach for caches first (and thus, I assert, last), but it was always there.
I have a couple coworkers who are trying to be clever with a new cache architecture. Irritatingly by taking a statement of fact made by me 3+ years ago and jumping to the wrong conclusion. They promised 50% in 18 months (I was suggesting we target 90% in three years). Now we are somewhere past 30 months and so far they've delivered lower numbers than I did in 5 man weeks spread out from Christmas to mid March, while juggling other priorities and suffering from Seasonal Affective Disorder. Another coworker, usually cache averse, was making noises about adding a cache for some other pain point, and I started pulling on the thread for a bit until he was satisfied. It'll be next March before they surpass the 20% I turned in with about 8 modest changes. And the architectural improvement from both efforts will be roughly on a par. Top down is sexy, bottom up is not. But it's hard to do the former without the latter. Eat your vegetables.