[bialecki]

I'm sure the rationale here is that if a given query takes 100ms, they don't focus on getting it down to 50ms even if that's several times what the average is because they know they can. Certainly someone should focus on making that query faster, but it's more straightforward.

The harder problem is figuring out why that 20ms query suddenly balloons to 200ms. You can say, "no big deal, it only happens 1% of the time," but if you don't know why, you could make changes to the system that cause it to happen much more frequently and eventually bring the whole system down.

Also, there's a bit of UX here. People are much more frustrated by things they don't understand and/or aren't used. There are parts of GMail that are always slow (archiving a lot of messages). I know this so I know I have to wait 5-10 seconds. What if sometimes it took 1 second and sometimes it took 20 seconds? What if it took 20 seconds 5% of the time. I'd probably always click again and think something was broken. If it's always slow, I want it to be faster, but at least I know what to expect.