An Introduction to Large-Scale Software Development Steve Varnau Core

An Introduction to Large-Scale Software Development Steve Varnau Core HP-UX Operation October 31, 2000 October 31, 2000 Page 1

LargeScale SW Devel. Agenda Software Change Software Configuration Management (SCM) Change Control Large-Scale Software Development Example: HP-UX Operating System October 31, 2000 Page 2

LargeScale SW Devel. Software Evolution The Need for Managing Software Change 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) October 31, 2000 Page 3

LargeScale SW Devel. 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 October 31, 2000 Page 4

LargeScale SW Devel. 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 October 31, 2000 Page 5

LargeScale SW Devel. Terminology - Version Tree SCM File fubar.c 0 Branch 1 Version 2 0 3 1 Delta October 31, 2000 Page 6

LargeScale SW Devel. 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 October 31, 2000 Page 7

LargeScale SW Devel. Terminology - Baseline SCM fubar.c foo.c bar.c October 31, 2000 Page 8

LargeScale SW Devel. 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. October 31, 2000 Page 9

LargeScale SW Devel. Merging - Version Tree SCM 0 Common Ancestor 1 2 Merge Result 3 0 1 Conflicting Changes October 31, 2000 Page 10

LargeScale SW Devel. 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 October 31, 2000 Page 11

LargeScale SW Devel. Change Control Managing Change 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. October 31, 2000 Page 12

LargeScale SW Devel. Change Control Development Process Key Components of Development Process: Software Configuration Management Change Control Quality Control October 31, 2000 Page 13

LargeScale SW Devel. 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 October 31, 2000 Page 14

LargeScale SW Devel. 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. October 31, 2000 Page 15

LargeScale SW Devel. 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 October 31, 2000 Page 16

LargeScale SW Devel. HP-UX Concurrent Development HP-UX Normally 2-3 Releases Under Development Several Releases Under Maintenance Heavy Use of Branching and Merging October 31, 2000 Page 17

LargeScale SW Devel. 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 October 31, 2000 Page 18

LargeScale SW Devel. 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 October 31, 2000 Page 19

LargeScale SW Devel. Integration Levels HP-UX Release Integration Cycle Baseline Submit Build Modificatio ns October 31, 2000 Page 20

LargeScale SW Devel. Process Evolution Continuous Process Improvement Root Cause Analysis (RCA) Capability Maturity Model (CMM) 1. Initial 2. Repeatable 3. Defined 4. Managed 5. Optimizing October 31, 2000 Page 21