An Introduction to Large-Scale Software Development

1
An Introduction to Large-Scale Software
Development

• Steve VarnauCore HP-UX Operation
• October 31, 2000

2
Agenda

• Software Change
• Software Configuration Management (SCM)
• Change Control
• Large-Scale Software Development
• Example HP-UX Operating System

3
The Need for Managing Software Change
Software Evolution

• Environment Changes
• Computer Hardware
• Competition
• Business Processes
• External Requirements (Y2k, Euro,)
• New Standards (XML, MP3, e-Speak,)
• All Software Demands Change
• Incremental Development
• Maintenance (Corrective, Perfective, Adaptive)

4
Benefits of Source Control / SCM
SCM

• Manage Constant Software Change
• Improve Debugging Productivity
• Trace Defect Reports to Correct Versions of
  Source Code
• Understand Change History
• Reproducibility
• Build (Compile) Software Accurately, Repeatably
• Grow Project Size
• Avoid Over-writing and Losing Changes
• Concurrent Development (Improve TTM)
• Coordinate Work with Development Policies

5
Terminology - File Versioning
SCM

• Revision / Version - Single copy of a source file
  as it appeared at given point in its change
  history (checkpoint)
• File / Element - Complete change history all
  versions
• Branch - Set of successive versions parallel to
  other branches
• Delta - Change from one file version to the next

6
Terminology - Version Tree
SCM
7
Terminology - Multiple File Configuration
Management
SCM

• Variant - File based on another, co-exists with
  original
• Derived Object - File automatically generated
  from source files
• Change Set - Set of versions across multiple
  files making up a single logical change (e.g.,
  feature or fix)
• Baseline - Consistent set of versions across all
  files

8
Terminology - Baseline
SCM
9
Coordinating Work
SCM

• Problem Multiple people working on same file at
  the same time can result in lost work.
• Solution 1 Serialize work with file locking.
• Solution 2 Work in isolation (branch) and merge.
• Branching and merging scales much better.
• Merging can be semi-automated using 3-way merge
  algorithms.

10
Merging - Version Tree
SCM
11
Formal definition (IEEE)
SCM

• SCM is the process of identifying and defining
  the items in the system, controlling the change
  of these items throughout their life cycle,
  recording and reporting the status of items and
  change requests and verifying the completeness
  and correctness of the items.
• Related Terms Source Control, Version Control

12
Managing Change
Change Control

• Change Control - Formal processes for tracking
  and approval of software modifications.
• Managed with SCM and defect tracking tools.
• Usual Policy Areas
• Documentation - Change request / defect report
  filed.
• Approval - Change request reviewed by release
  management or technical board.
• Quality Requirements - Code reviewed, regression
  tests passed.
• Policies often change by release stage and in
  response to problems.

13
Development Process
Change Control

• Key Components of Development Process
• Software Configuration Management
• Change Control
• Quality Control

14
Principles of Large-Scale Software Development
Scaling

• Reproducibility
• Policy Enforcement versus Policy Auditing
• Process, Process, Process
• A process must be defined to be improved
• Automation
• A process must be automated to be repeatable
• Continuous Functional Integration and Test

15
Software Integration
Scaling

• Integration Combining multiple features or
  components developed in isolation.
• Large projects are subject to constant change, so
  isolation on a stable base is necessary.
• Continuous Functional Integration and Test (CFIT)
• Changes integrated throughout development.
• Changes not allowed to regress functionality or
  quality.

16
HP-UX Development
HP-UX

• 220,000 Source Files
• 2.5 Million Versions
• 52,000 Derived Files (Single Nightly Build)
• 900 User Accounts
• More Than 1 Terabyte of Disk Space

17
HP-UX Concurrent Development
HP-UX

• Normally 2-3 Releases Under Development
• Several Releases Under Maintenance
• Heavy Use of Branching and Merging

18
HP-UX Multisite Development
HP-UX

• Four Primary Development Sites
• Three in USA (Three Time Zones)
• One in India
• One USA Site Hosts Three Logical Sites
• Partner Companies
• Several Secondary Sites

19
Tiered Software Integration Model
HP-UX

• 1. Developer Task - Edit, Compile, Test
• 2. Submit - Batch Changes, Acceptance Test
• 3. Baseline - Nightly Build, Regression Test
• 4. Integration - Monthly Packaging, Partner Test
• 5. Release - Semi-annual Delivery, Production Use

20
Integration Levels
HP-UX
Release
Integration Cycle
Baseline
Submit
Build
Modifications
21
Process Evolution

• Continuous Process Improvement
• Root Cause Analysis (RCA)
• Capability Maturity Model (CMM)
• 1. Initial
• 2. Repeatable
• 3. Defined
• 4. Managed
• 5. Optimizing