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Archive for the ‘Debug It!’ Category

These are excerpts from the book. These are the summary from end of each of the chapter.

Chapter 1 – A Method in Madness

  • Make sure to do the following:
    • Work out why the software is behaving unexpectedly.
    • Fix the problem.
    • Avoid breaking anything else.
    • Maintain or improve overall quality.
    • Ensure that the same problem does not occur elsewhere and cannot occur again.
  • Leverage your software’s ability to show you what’s happening.
  • Work on only one problem at a time.
  • Make sure that you know exactly what you’re looking for:
    • What is happening?
    • What should be happening?
  • • Check simple things first.

Chapter 2 – Reproduce

  • Find a reproduction before doing anything else.
  • Ensure that you’re running the same version as the bug was reported against.
  • Duplicate the environment that the bug was reported in.
  • Determine the input necessary to reproduce the bug by:
    • Inference
    • Recording appropriate inputs via logging
  • Ensure that your reproduction is both reliable and convenient through iterative refinement:
    • Reduce the number of steps, amount of data, or time required.
    • Remove nondeterminism
    • Automate.

Chapter 3 – Diagnose

  • Construct hypotheses, and test them with experiments.
    • Make sure you understand what your experiments are going to tell you.
    • Make only one change at a time.
    • Keep a record of what you’ve tried.
    • Ignore nothing.
  • When things aren’t going well:
    • If the changes you’re making don’t seem to be having an effect, you’re not changing what you think you are.
    • Validate your assumptions.
    • Are you facing multiple interacting causes or a changing underlying system?
  • Validate your diagnosis.

Chapter 4 – Fix

  • Bug fixing involves three goals:
    • Fix the problem.
    • Avoid introducing regressions.
    • Maintain or improve overall quality (readability, architecture, test coverage, and so on) of the code.
  • Start from a clean source tree.
  • Ensure that the tests pass before making any changes.
  • Work out how you’re going to test your fix before making changes.
  • Fix the cause, not the symptoms.
  • Refactor, but never at the same time as modifying functionality.
  • One logical change, one check-in.

Chapter 5 – Reflect

“The six stages of debugging” and reads as follows:

  1. That can’t happen.
  2. That doesn’t happen on my machine.
  3. That shouldn’t happen.
  4. Why is that happening?
  5. Oh, I see.
  6. How did that ever work?

  • Take the time to perform a root cause analysis:
    • At what point in your process did the error arise?
    • What went wrong?
  • Ensure that the same problem can’t happen again:
    • Automatically check for problems.
    • Refactor code to remove the opportunity for incorrect usage.
    • Talk to your colleagues, and modify your process if appropriate.
  • Close the loop with other stakeholders.

Chapter 6 – Discovering that you have a problem

  • Make the most of your bug-tracking system:
    • Pick one at an appropriate level of complexity for your particular situation.
    • Make it directly available to your users.
    • Automate environment and configuration reporting to ensure accurate reports.
  • Aim for bug reports that are the following:
    • Specific
    • Unambiguous
    • Detailed
    • Minimal
    • Unique
  • When working with users, do the following:
    • Streamline the bug-reporting process as much as possible.
    • Communication is key—be patient and imagine yourself in the user’s shoes.
  • Foster a good relationship with customer support and QA so you can leverage their support during bug fixing.

Chapter 7 – Pragmatic Zero Tolerance

  • Detect bugs as early as possible, and fix them as soon as they come to light.
  • Act as though bug-free software was an attainable goal, but temper perfectionism with pragmatism.
  • If you find yourself faced with a poor quality codebase, do the following:
    • Recognize there is no silver bullet.
    • Make sure that the basics are in place first.
    • Separate clean code from unclean, and keep it clean.
    • Use bug triage to keep on top of your bug database.
    • Incrementally clean up bad code by adding tests and refactoring.

Chapter 8 – Special Cases

  • When patching an existing release, concentrate on reducing risk.
  • Keep on the lookout for compatibility implications when fixing bugs.
  • Ensure that you have completely closed any timing windows, not just decreased their size.
  • When faced with a heisenbug, minimize the side effects of collecting information.
  • Fixing performance bugs always starts with an accurate profile.
  • Even the most restricted communication channel can be enough to extract the information you need.
  • Suspect your own, ahead of third-party, code.

Chapter 9 – The Ideal Debugging Environment

  • Automate your tests, ensuring that they do the following:
    • Unambiguously pass or fail
    • Are self-contained
    • Can be executed with a single click
    • Provide comprehensive coverage
  • Use branches in source control sparingly.
  • Automate your build process:
    • Build and test the software every time it changes.
    • Integrate static analysis into every build.

Chapter 10 – Teach your Software to Debug Itself

  • Use assertions to do the following:
    • Both document and automatically validate your assumptions
    • Ensure that your software, although robust in production, is fragile during debugging
  • Create a debug build that
    • Is compiled with debug-friendly compiler options
    • Allows key subsystems to be replaced by debugging equivalents
    • Builds in control that will prove useful during diagnosis
  • Detect systemic problems, such as resource leaks and exception handling issues, preemptively.

Chapter 11 – Anti Patterns

  • Keep on top of your bug database to ensure that it accurately reflects your true priorities.
  • The polluter pays—don’t allow anyone to move onto a new task until they’ve completely finished their current one. If bugs come to light in their work, they fix them.
  • Make a single team responsible for a product from its initial concept through deployment and beyond.
  • Firefighting will never fix a quality problem. Take the time to identify and fix the root cause.
  • Avoid “big bang” rewrites.
  • Ensure that your code ownership strategy is clear.
  • Treat anything you don’t understand as a bug.


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