Talk presented @ PortoData (20-04-2016)

1. DATABASE SOURCE CONTROL Eduardo Piairo
Migrations vs State

2. DATABASE SOURCE CONTROL– MIGRATIONS VS STATE
• Eduardo Piairo
• @ Celfinet
• DBA
• DevOps
About me
@EdPiairo
https://pt.linkedin.com/in/jesuspiairo
eduardopiairo@outlook.com
http://www.eduardopiairo.com/

3. DATABASE SOURCE CONTROL– MIGRATIONS VS STATE
Introduction
Source
Control
Continuous
Integration
Continuous
Delivery
Database
+
Application

4. DATABASE SOURCE CONTROL– MIGRATIONS VS STATE
What’s so special about databases?
Introduction
DLM – Database Lifecycle Management
• Data management and data migration
• Data monitoring
• Data recovery

5. DATABASE SOURCE CONTROL– MIGRATIONS VS STATE
Why database source control?
• First step for database automation
• Share code (SQL scripts)
• Keep history of each change
• Your best communication system

6. DATABASE SOURCE CONTROL– MIGRATIONS VS STATE
Migrations-based approach vs State-based approach
• Fundamental resource - SQL Script
• State based solutions
• Script represents the current database state
• Migrations based solutions
• Script represents a migration
• Migration represents how to transition to the next database version
State: Your source of truth is how the database should be
Migrations: Your source of truth is how the database should change
Alex Yates, Pre-sales engineer at Redgate

7. DATABASE SOURCE CONTROL– MIGRATIONS VS STATE
Flyway
• Flyway – “Database migrations made easy”
• http://flywaydb.org/
• Open source database migration tool
• My reasons for adopting Flyway (command-line)
• Simplicity: easy to setup, no need to install
• Zero dependencies (java + jdbc)
• Scripts are written in SQL

8. DATABASE SOURCE CONTROL– MIGRATIONS VS STATE
Flyway – Why database migrations?
• Migrations
• Recreate a database from scratch
• Make it clear at all time what state a database is in
• Migrate in a deterministic way from your current version of the database to a newer one

9. DATABASE SOURCE CONTROL– MIGRATIONS VS STATE
Flyway – How it works?
• Flyway commands
• Migrate, clean info, validate, baseline repair
• Metadata table
• Used to track the state of the database
• Default name: “schema_version”
• If the database is empty, flyway won’t find it and will create it
• Flyway scans the migrations directory and check migrations against the metadata table
• Migrations are sorted based on their version number and applied in order

10. DATABASE SOURCE CONTROL– MIGRATIONS VS STATE
Flyway – Demo

11. DATABASE SOURCE CONTROL– MIGRATIONS VS STATE
SQL Source Control
• SQL Source Control
• Add-in for Management Studio that links your database to your source control system
• Ability to source control schemas and reference data
• Source control systems: Git, Mercurial, TFS , Subversion

12. DATABASE SOURCE CONTROL– MIGRATIONS VS STATE
SQL Source Control – How it works
• SQL Compare
• Compares Git repository (your source of truth) against the target database
• Schema and data reference
• Database objects
• Static data
• Referential integrity (keys and constraints)
• Roll back changes
• Lock objects
• Apply filters to database objects

13. DATABASE SOURCE CONTROL– MIGRATIONS VS STATE
SQL Source Control – Demo

14. DATABASE SOURCE CONTROL– MIGRATIONS VS STATE
Migrations-based approach vs State-based approach
• Scripts are imperative
• Each script/change is applied, in order, on the target
database
• High level of granularity
• SQL developers define change scripts upfront and have
full control over how changes are deployed
Flyway + git
• Scripts are declarative
• Compares two states (source and target) and generates a
change script
• The big picture
• Dependencies management
• Comparison engine – SQL Compare (schema and reference
data)
SQL Source Control + git

15. DATABASE SOURCE CONTROL– MIGRATIONS VS STATE
Migrations-based approach vs State-based approach
Flyway + git SQL Source Control + git
• Scripts must be idempotent and immutable (runs 1 time
only)
• “Changes will only be made through migration tool
itself?”
• Tracking changes
• Enables continuous integration and continuous delivery
• SQL Server Management Studio
• Drop and recreate advantage
• Tracking changes
• Enables continuous integration and continuous delivery

16. DATABASE SOURCE CONTROL– MIGRATIONS VS STATE
Migrations-based approach vs State-based approach – HOTFIX challenge
Flyway + git SQL Source Control + git
• Ignore the hotfix
• Deployment can fail or pass
• You will never find out, until you have a
problem
• Roll back the hotfix
• Target database would look like the version in
development that did not have the fix

17. DATABASE SOURCE CONTROL– MIGRATIONS VS STATE
Migrations-based approach vs State-based approach – Tools
Migrations State
Flyway ReadyRoll
SQL
Source Control
SSDT
Database Projects
DbUp

18. DATABASE SOURCE CONTROL– MIGRATIONS VS STATE
Migrations-based approach vs State-based approach
• Which one is better?
• Size of the database
• Complexity of the database
• Team’s capabilities or preferences
• Team’s development processes
Both approaches may be needed for different parts of the system, or at different times in
the development process.

19. DATABASE SOURCE CONTROL– MIGRATIONS VS STATE
Q&A
@EdPiairo
https://pt.linkedin.com/in/jesuspiairo
eduardopiairo@outlook.com
http://www.eduardopiairo.com/