Technical Debt

Credit Crunch Code Paying Back the Technical Debt By Gary Short 1

Agenda Defining Technical Debt Why Managing Technical Debt is Important Quantifying Technical Debt Technical Debt Anti-Patterns & Fixes Finding Technical Debt Using Metrics Summary Further Reading Questions. 2

Defining Technical Debt #1 Term coined by Ward Cunningham in 1992 Analogous to financial debt Financial debt = borrow money against a future date Technical debt = borrow time against a future date. 3

Defining Technical Debt #2 With financial debt “Virtual debt” by not having the best interest rate With Technical Debt Not making savings against time where possible. 4

Is There Interest On Technical Debt? Just as there is interest on financial debt... So there is interest on technical debt too: Cost later – cost now Financial value of damage to your brand Loss of market share Low staff morale. 5

Just As Not All Financial Debt Is Bad 6

Nor Is All Technical Debt<br />7

But Financial Debt Can Be Dangerous 8

And So Can Technical Debt<br />9

Why Is Managing Technical Debt Important? 10

Reduce Effort by Keeping it Under Control 11

Quantifying Technical Debt 12 

Basic Formula To Get You Started Where: T = Total number of employees involved in paying back the debt i = The individual employee HRi = Hourly rate of pay for that individual Hi = The hours that an individual worked in paying back the debt EOC = Employer’s on cost – estimated at 40% of salary = 140% of salary HP = Purchase cost of any hardware required HI = Installation cost of any hardware required SL= Cost of any software licences X/Bba = An estimate of the damage to brand image. 13

Rate Card Project Manager = 32 Euros / hour Architect = 33 Euros / hour Lead Developer = 30 Euros / hour Developer = 26 Euros / hour Tester = 20 Euros / hour Tech. Support = 15 Euros / hour Business Analyst = 32 Euros / hour. *Hourly rate = average annual salary / (52 – 5wks AL * 5 – 9 days PH * 8 hrs) **UK hourly rate converted to Euros via Google ***Correct as of November ’09. YMMV  14

Case Study #1 The Anti-Pattern: Waterfall Methodology 15

The Main Weakness of Waterfall<br />16

Where Does Change Come From?<br />17

Why is Change So Costly?<br />18

Why Is This Technical Debt?<br />Borrow time now, repay later Take advantages now Ease in analysing potential changes Ease of coordinating large teams Precise budgeting Repay later Extra cost of change. 19

Quantify the Technical Debt: Agile<br />Assume a small error caught during the “paper prototype” phase of an iteration Resources deployed Architect spends 1 hour fixing design Tester spends 1/2 hour verifying the fix Apply those figures to our formula and: Cost of fixing the error = 60 Euros. 20

Quantify the Technical Debt: BDUF<br />Now the same error found in waterfall... Resources deployed Architect 1 hour fixing design Developer spends 4 hours coding solution Lead developer spends ½ hour peer review Tester spends 2 hours verifying fix Apply those figures to our formula and: Cost of fixing the error = 208 Euros Value of the technical debt = 148 Euros. 21

Potential Cost Per Project So the TD / defect = 148 Euros The av. number of defects / project = 283* Potential TD / project = 41,884 Euros. *Source: Scan 2006 Benchmark (as of March 2008) 22

Fixing The Technical Debt I’m not saying prefer Agile over Waterfall I am saying: Be aware of the impact that might have on TD Think about how you are going to combat that: Review earlier in the process where change is cheap Ensure the SME has peer review Regular, early checks on design vs coded solution Don’t leave all testing to the last phase. 23

Case Study #2 The Anti – Pattern: Not Invented Here 24

Symptoms Development team spend time developing software which is not core the problem they are trying to solve Instead of buying in a third party solution They justify this by saying things like: It doesn’t work the way we need it to It would take me as long to write as to learn API The 3rd party may go bust The code isn’t good enough quality. 25

Concrete Example Developers for a national bank are tasked with creating a new MIS tool They dedicate 1 developer full time to creating a charting component This sucks in testing and PM time too Charting component not core to task at hand Spent 3 months getting nowhere Before buying a charting component. 26

Why Is This Technical Debt?<br />Savings against time not made Chose to develop a component Should have bought from a third party. 27

Quantifying The Technical Debt The component was bought in the end: Disregard the cost of the component And the time spent learning the API Resources deployed: 1 X developer 3 months 1 X tester 1.5 months 1 X lead developer 1 day 1 X PM 1 day Cost of technical debt : 24,886 Euros 28

Fixing The Technical Debt Identify non core functional aspects of project For each of those: Can a component be bought in to achieve it? If so, buy it If not Does your enterprise allow open source? If so use it Beware of licence implications Only after evaluating and discounting alternatives should you consider writing your own. 29

Case Study #3 Anti-Pattern: Code that plays together stays together 30

Symptoms Let’s imagine a “Car” object What properties should it have? Make Model Colour What behaviour should it have? None! It’s an inanimate object! A “Car” will have things done to it by “actors”. 31

What Is The Problem? 32<br />

Example of Class Pollution Credit: Phil Winstanley (http://weblogs.asp.net/Plip/) 33

Why Is This Technical Debt?<br />Borrow time now, repay later Borrowed time now Simpler object graph Repay later in cost of adding functionality. 34

Concrete Example Online provider wants to be first to market Ships service with monolithic object graph Effort required to add new features grows Development slows to a crawl Management demand a fix. 35

Quantifying the Technical Debt 1 monthly iteration to fix this debt Resources deployed: 5 X Developers 1 X lead developer 2 X testers Apply these figures to our formula and: Cost of technical debt: 44,800 Euros. 36

Fixing The Technical Debt Understand that Monolithic object graph has a limited lifespan Prefer separation of concerns If first to market is important Understand the value of the technical debt accrued Decide when the debt will be paid off Decide if commercial gain outweighs cost of debt Refactoring tools can reduce “interest” on debt. 37

Case Study #4 The Anti-Pattern: Sensitive Tests 38

Symptoms Test which are sensitive to Context Interface Data Pass in one iteration Fail in the next due to changes. 39

Why Is This Technical Debt?<br />Borrow time now, repay later Borrowed time in the form of easy to write tests Repay later in form of fixing sensitive tests. 40

Concrete Example Tester testing code which uses data from development database Developer adds new functionality Shape of the database changes Values in the database change Previously passing tests fail Tests rewritten using current dev. database. 41

Quantifying the Technical Debt Take previous 283 defects per project Assume 10% of tests for those defects are data dependant Assume it takes tester 30 minutes to fix each test 28 * 0.5 = 14 hours Apply those figures to our formula and: Technical debt = 392 Euros. 42

Fixing The Technical Debt Test must use independent data Don’t run tests against development data Either Have a dedicated test database Or it may be possible to mock data access Or have the set up code for each test or suite of tests generate the data it requires and drop it during the tear down code. 43

How Do We Spot Technical Debt? 44

We Are Used to Charting Progress 45

Time Budget Failures Are Obvious<br />46

Effect #1 – Loss of Productivity 47

Effect #1 – Loss of Productivity 48

Effect #2 – Increase In Testing 49

Effect #2 – Increase In Testing 50

Effect #3 – Decrease In Morale 51

Effect #3 – Decrease In Morale 52

Summary In this presentation you learned: What technical debt is That it is important to manage technical debt Some common anti-patterns and how to fix them Metrics to spot hidden technical debt How to quantify technical debt. 53

Take Away If you only take away one thing Know that technical debt is the silent killer that stalks all projects Don’t let it kill your projects! 54

Further Reading http://c2.com/cgi/wiki?WardExplainsDebtMetaphor http://c2.com/cgi/wiki?TechnicalDebt http://blogs.construx.com/blogs/stevemcc/archive/2007/11/01/technical-debt-2.aspx<br />http://www.martinfowler.com/bliki/TechnicalDebt.html 55

Questions? There wasn’t time for my question Where can I contact you? gary@garyshort.org www.garyshort.org On Twitter as @garyshort. 56