technical debt
DESCRIPTION
Graham Brooks - Agile East 2011TRANSCRIPT
© ThoughtWorks 2011
Technical DebtThe ‘Silent’ Application Killer
Tuesday, 8 November 11
© ThoughtWorks 2011
Graham Brookshttp://www.thoughtworks.com/blogs/current
http://www.grahambrooks.com/blog
@wookie870
Tuesday, 8 November 11
Outline
• Definition
• Why is it important?
• Symptoms and signs
• Debt resolution strategies
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Technical Debt
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Technical Debt
Metaphor coined by Ward Cunningham to explain the misalignment between code and current understanding
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Consciously taking on debt might allow you to get something sooner
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Burden
• Not paying off - borrowing without paying it back
• Spending power goes to 0
• All your money goes into paying interest
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Some might see this as an excuse to write poor code.
Never write poor code
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Reckless Prudent
Deliberate
Inadvertent What is layering?Now we know how we should
have built it
We must ship now and deal with the
consequences
We don’t have time for design
source: http://martinfowler.com/bliki/TechnicalDebtQuadrant.html
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Evidence is anecdotal and based on personal experience of many projects
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Time
Cos
t of
Cha
nge
No debt Management
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A re-write will...
• Solve all our problems
• If we use language X
• The latest framework
• A new code generator
• A new database
• .....
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Time
Cos
t of
cha
nge
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Teams like these get better at rewrites.
They don’t learn how to continuously deliver value indefinitely.....
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Time
Cos
t of
Cha
nge
No debt Management
Technical Debt Managed
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Your codebase can never be in Credit
For commercial projects technical debt is a fact of life
You either have enough or too much
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Symptoms and Signs
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Productivity
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Iteration
Velocity
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Iteration
Velocity
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Iteration
Velocity
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Iteration
Velocity
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Iteration
Velocity
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Iteration
Velocity
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Iteration
Velocity
Tracer Stories1 Point1 Point1 Point1 Point1 Point1 Point1 Point1 Point
Time
7h 5h 7h 10h
5-10 months
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Code
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Code Review
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“You know you are working on clean code when each routine you read turns out to be pretty much what you expected. You can call it beautiful code when the code also makes it
look like the language was made for the problem”
Ward Cunningham
Clean Code by Robert C Martin
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http://www.osnews.com/story/19266/WTFs_mTuesday, 8 November 11
Readability is a key
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How often features are used
0 12.5 25 37.5 50
Never
Rarely
Sometimes
Often
Always
Source: Standish Group
45%NEVER USED
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Remove Unused ‘stuff ’
• Unused features
• Unused files and tools
• Unused classes
• Unused methods
• Unused lines
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Duplication
Direct duplication
Exact Code copies
Aggressive
Algorithmically Equivolent
Tool tip: Simian
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Volatility
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Toxicity
250 branches in a single class
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Clean Toxic
Volatile
Stable Leave alone Refactor later
!Refactor Now!Volatile
requirements?Monitor
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Time
Number of te
sts/feat
ures
Application LOC
Test LOC
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Debt resolution strategies
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Stop the Line
• Works for major changes
• Challenging to implement
• Smells of a rewrite
• Short
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Little and often
• Make improvement part of the process:
• “Improvement as part of every change”
• Stangler pattern
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It’s going to get worse before it gets better
Time
Productivity
Cost of Change
Current Situation
Desired State
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Closing Thoughts
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• Imagine you have joined a new team
• Run metrics
• Estimate debt
• Plan next steps
• Execute the plan
First Steps
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Things Change
New capabilities
Libraries
Frameworks
OS
Software Rusts
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Every modification of a system might incur technical debt unless it is accompanied by some effort to bring the design into line with the requirements.
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Questions?
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© ThoughtWorks 2008
Thank You!http://www.thoughtworks.com/blogs/current
http://www.grahambrooks.com/blog
@wookie870
Tuesday, 8 November 11