The document discusses the challenges of legacy code development and maintenance, highlighting issues such as design degradations and changing priorities during the development cycle. It emphasizes the importance of continuous refactoring and using metrics to improve code quality and predict bugs. The text also references tools and practices aimed at enhancing the stability and longevity of software products.

1. Legacy code
Development and Maintenance

2. ● Code after deployment
● Successful
● Long-lasting software
● Meets customers’ needs
● Hard to evolve:
○ design degradations
○ too many use cases
○ many different customers
What is the Legacy code?

3. Lustre®
FS
parallel distributed file system
● C
● > 600 KLOC
● kernel space code
● https://github.com/Xyratex/lustre-stable/

4. Development and Sustaining teams
Development Cycle unpredictable
priority
changing
estimation
rough
Planing
Development
Retrospective

5. Nature of processes
Planning
Pulling

6. Lost feedback from Sustaining
Retrospective
● Defects Escapes show what missed in Quality
● Feedback:
○ Process changes
○ Design
○ Review Checklists
○ Test coverage
○ Feature/Refactoring planning

7. Future looks bright
Tested and works. Don’t touch.

8. Discovered bug and hidden one
Only not used product has no bugs

9. Fixing bug could uncover other
Changing code always risky

10. Just fixing is not enough
Bugs are never ending

11. Legacy Quality: Continuous Refactoring
Preventive measures

12. “premature optimization is the root of all evil”
Donald Knuth
● Refactoring SHOULD BE - proven, based on statistic and
metrics
○ Metrics and stat from Defects Escapes
○ Code metrics (Complexity, LOC based stat, Function
points, etc)
○ SCM:
■ churn (added + changed)
■ age of changes (freshness)
■ distance
■ etc
Legacy Quality: Continuous Refactoring

13. ● Chris Lewis and Rong Ou, “Bug Prediction at Google”
● Bug Prediction, Bug Introducing Changes, BugCache,
FixCache, Predicting faults and etc. Key phrases to
search in web
Readings

14. Thank You
Denis_Kondratenko@xyratex.com
http://www.linkedin.com/in/kondratenko