July 1, 2009
Evolutionary
database design
DevClub.eu,
30.06.2009
Andrei Solntsev

Agenda
 begin
» background
» my experience
» tools
 end;

begin
процесс разработки программного обеспечения
Плановый («водопад») Эволюционный
На раннем этапе • Допускать изменения
• выявить требования, на всех стадиях
• согласовать, • Но управлять изменениями
• спроектировать,
• согласовать
и затем приступить к кодированию
принципиальная позиция –
минимизация изменений за счет максимально упростить
обширной предварительной работы. возможность изменений

@author Martin Fowler
1999: Refactoring: Improving
the Design of Existing Code
http://www.amazon.com/exec/obidos/ASIN/0201485672
2000: Continuous Integration
http://www.martinfowler.com/articles/continuousIntegration.html
2003: Evolutionary Database Design
http://www.martinfowler.com/articles/evodb.html

@compare
Рефакторинг базы данных сложнее, чем рефакторинг кода
• Сохранение информационной семантики
• Миграция данных
• В отличие от обычного ПО, невозможно просто
удалить старый код и заменить новым.
• большое количество связей
• период поддержки устаревшего кода

<img src=“book.pdf”/>

@experience
My experience
 PRIA
 HireRight
 HireRight 2.0 ?

PRIA
Single DB environment
Developers Product Manager Salespeople
Production
Production
Testers
Users
Deployment is not a problem 

Multi-DB environment
Developer #1 Tester #1
Salespeople Production
Users
Demo Production
Developer #2 Tester #2
Deployment becomes a problem 

HireRight: deployment
CVS DB
ALTER TABLE man ADD
COLUMN length
Create index man_idx
CREATE INDEX Installation
women_id_idx scripts
DROP TABLE raha
CREATE TABLE money (
eek NUMBER
Problems:
); • scripts reinstallation
• DB recreation
ALTER TABLE money ADD CONS • DB synchronization

Database Change Management
An automated process is needed to make the process of
upgrading out-of-date databases simple
 We need a Database Change Management tool.
My findings:
Ruby migrations - http://www.oracle.com/technology/pub/articles/kern-rails-migrations.html
RedGate SQL compare - http://www.red-gate.com/products/SQL_Compare/index.htm
MySQL Workbench – Diff & Synchronization
http://dev.mysql.com/tech-resources/articles/workbench_database_management.html
Oracle Enterprise Manager (change management pack)
DB Deploy - http://dbdeploy.com/
LiquiBase - http://www.liquibase.org/

Apache DDL Utils
http://db.apache.org/ddlutils/
<database name="testdb">
<table name="author">
<column name="author_id" type="INTEGER"
primaryKey="true" required="true"/>
<column name="name" type="VARCHAR"
size="50" required="true"/>
<column name="organisation" type="VARCHAR"
size="50" required="false"/>
</table>
<index name="book_isbn">
<index-column name="isbn"/>
</index>
</database>
Based on XML, automatically generates SQL scripts to update DB.

Incremental Schema Changes
 All database schemas can be thought of as a compilation of
incremental changes made over time to accommodate new
functionality
 As updates are applied to a database, the changes will be
recorded in a table similar to the following:
Change Date
1_Create_Customer_Table.sql 4-15-07
2_Add_e-mail_address_column.sql 4-17-07
3_Add_fax_number_column.sql 4-18-07
4_Add_transaction_table.sql 4-21-07
5_Add_transaction_status_column.sql 4-24-07
6_Add_customer-transaction_view.sql 4-27-07

DBDeploy ThoughWorks.com
1. Go to directory with SQL files:
• “1 create_customer_table.sql”
• “2 add_customer_id_constraint.sql”
• …
• Run “ant”
Output:
[dbdeploy] dbdeploy 3.0-SNAPSHOT
[dbdeploy] Reading change scripts from directory
/tmp/dbdeploy/dbdeploy-3.0-SNAPSHOT/example...
[dbdeploy] Changes currently applied to database:
[dbdeploy] (none)
[dbdeploy] Scripts available:
[dbdeploy] 1, 2
[dbdeploy] To be applied:
[dbdeploy] 1, 2
[dbdeploy] Generating undo scripts...
[sql] Executing resource:
/tmp/dbdeploy/dbdeploy-3.0-SNAPSHOT/example/output.sql
[sql] 7 of 7 SQL statements executed successfully

DBDeploy options
• Naming convention for delta scripts:
NUMBER COMMENT.SQL
• Re-execution – NOT POSSIBLE
• Undo section – marked by comments:
CREATE TABLE FOO (
FOO_ID INTEGER NOT NULL, FOO_VALUE VARCHAR(30) );
ALTER TABLE FOO ADD CONSTRAINT PK_FOO PRIMARY KEY (FOO_ID);
--//@UNDO
DROP TABLE FOO;
http://dbdeploy.com/documentation/getting-started/rules-for-using-dbdeploy/

LiquiBase LiquiBase.org
The main XML describing all delta scripts:
<databaseChangeLog>
<changeSet id="1" author="bob">
<createTable tableName="department">
<column name="id" type="int">
<constraints primaryKey="true" nullable="false"/>
</column>
<column name="name" type="varchar(50)">
<constraints nullable="false"/>
</column>
<column name="active" type="boolean" defaultValue="1"/>
</createTable>
</changeSet>
</databaseChangeLog>

LiquiBase
Run:
liquibase --driver=com.mysql.jdbc.Driver
--classpath=/path/to/classes
--changeLogFile=com/example/db.changelog.xml
--url="jdbc:mysql://localhost/example"
--username=user
--password=asdf
migrate
Also possible to run:
• Ant script
• Maven plugin
• Built-in java code
• Spring
• Grails
• Servlet Listener

LiquiBase options
• Custom order of scripts (user-defined)
• Re-execution – POSSIBLE (with attributes)

LiquiBase options
And many other options:
• DBMS
• SQL checksum
• context
• long transaction
• pre-conditions

Outcome
My findings:
RedGate SQL compare 1. commercial
MySQL Workbench – Diff & Synchronization 2. RDBMS-specific
3. but probably good
Oracle Enterprise Manager
Ruby migrations - Seems to be cool, need to try
- Written on Ruby
DB Deploy - Written by authoritative people
- Simple
- Convection over configuration
Written
LiquiBase - More configuration than DBDeploy on
- More options than DBDeploy Java
- Works with any RDBMS
- Eclipse plugin

end;
Links:
http://www.refactoring.com/ - Code refactoring (1999)
http://databaserefactoring.com/ - DB refactoring (2003)
Books:
Рефакторинг баз данных: эволюционное проектирование.
http://www.williamspublishing.com/Books/978-5-8459-1157-5.html