How to Make Things Faster

Chapter 61. Too Much of a Good Thing

In Oracle courses, I teach people about an application parameter whose setting can have a profound influence over response times.¹ I show students that, for the particular application we’re studying, changing the value of this parameter from 1 to 2 will cut response time in half. Setting it to 4 cuts response time in half again. Setting it to 8, 16, 32, and 64 cuts it in half again four more times.

At this point, I say cheerfully, “Just think how fast this application would perform if we could set the parameter’s value to a million-trillion.” I pause for a few seconds to let that question sink in. Then I show them the punch line: when you try to use 16,384, you get an out-of-memory error. A response time of infinity.

This is the “bathtub-shaped curve” that engineers talk about. The left wall of the tub shows the happy goodness of response times getting better and better. Then there’s a flat spot at the bottom, where response times don’t improve perceptibly, as you continue doubling the parameter. And, inevitably, there’s a right wall, which forms the tub shape, where response time becomes—in this case—infinitely bad. The lesson: it’s vital to give this parameter a good value, but 16,384 is too much of a good thing.

To help lock that idea into my students’ minds, I like to tell the story of how I learned the “too much of a good thing” lesson ...