You are previewing The Art of Agile Development.

The Art of Agile Development

Cover of The Art of Agile Development by James Shore... Published by O'Reilly Media, Inc.
O'Reilly logo

Performance Optimization


Programmers, Testers

We optimize when there’s a proven need.

Our organization had a problem.[54] Every transaction our software processed had a three-second latency. During peak business hours, transactions piled up—and with our recent surge in sales, the lag sometimes became hours. We cringed every time the phone rang; our customers were upset.

We knew what the problem was: we had recently changed our order preprocessing code. I remember thinking at the time that we might need to start caching the intermediate results of expensive database queries. I had even asked our customers to schedule a performance story. Other stories had been more important, but now performance was top priority.

I checked out the latest code and built it. All tests passed, as usual. Carlann suggested that we create an end-to-end performance test to demonstrate the problem. We created a test that placed 100 simultaneous orders, then ran it under our profiler.

The numbers confirmed my fears: the average transaction took around 3.2 seconds, with a standard deviation too small to be significant. The program spent nearly all that time within a single method: verify_order_id(). We started our investigation there.

I was pretty sure a cache was the right answer, but the profiler pointed to another possibility. The method retrieved a list of active order IDs on every invocation, regardless of the validity of the provided ID. Carlann suggested discounting obviously flawed IDs before testing ...

The best content for your career. Discover unlimited learning on demand for around $1/day.