Nigel Daley's Blog

Nigel's Law

Recently I was explaining this developer behavior to a colleague. I explained to him how I was weary of test cases being passed off as "corner cases" that didn't merit much attention. What I told him next he subsequently dubbed "Nigel's Law", so here it is:

The fringe, the boundary, the infrequent, the unlikely -- all occur quickly and often when operating software on large clusters with thousands of nodes.


Want a fun job testing open source? Passionate about software quality? Have great testing and coding skills? I'm hiring! Send your resume to: ndaley at yahoo-inc dot com

Comments

• Nigel,

  It's an excellent point. When the numbers of events, nodes, users, etc. get large, even very unlikely things happen regularly.

  In my recent book "Release It", I describe it thus:

  In time, even shockingly unlikely combinations of circumstances will
  eventually occur. If you ever catch yourself saying, “The odds of that
  happening are astronomical,” or some similar utterance, consider this:
  ten million page views per day over three years (assuming fifty assets
  per page) gives your system 547,500,000,000 chances for something
  to go wrong. That’s more than five hundred billion opportunities for
  bad things to happen. Recent astronomical observations indicate there
  are four hundred billion stars in the Milky Way galaxy. Astronomically
  unlikely coincidences happen daily."

  I'm discussing the topic of stability in distributed systems and pointing out that the equivalent of "security through obscurity" is "stability through probability" and it works just about as well.

  Cheers,
  Michael T. Nygard

  Author of Release It! Design and Deploy Production-Ready Software

  
  

  Posted by: mtnygard on July 26, 2007 at 06:54 AM

• Thanks Michael for the reference to your book! I can't wait to read it.

  Posted by: nidaley on July 26, 2007 at 10:48 PM

This work is licensed under a Creative Commons License.