The host for PGSQL Phriday #009 is Dian Fay, who has asked us to discuss Database change management.
Database change management refers to the process of controlling and managing changes made to a database in a systematic and organized way. It involves carefully planning, implementing, and tracking modifications or updates to a database’s structure, data, or configurations. Following are some specific considerations for PostgreSQL:
- Planning: When planning changes for a PostgreSQL database, we need to consider the specific modifications. This could include CREATEing or ALTERing tables, adding or modifying columns, changing data types, or even performing complex schema changes. It’s important to understand the impact of these changes on existing data and applications that rely on the database. Therefore, having a Development/Pre-prod environment to test/iron out the changes is highly recommended
- Implementing changes: PostgreSQL provides a powerful set of SQL commands and utilities to make changes to the database. You can use SQL statements like CREATE, ALTER, and DROP to create, modify, or delete database objects. Additionally, PostgreSQL supports features like transactions, which allow us to group multiple changes together and ensure they have applied atomically either all or nothing
- Tracking and documentation: Using version control systems or dedicated database change management tools is recommended. These tools help manage scripts or SQL files that contain the necessary commands for making the changes. By keeping track of these scripts, we can easily understand the history of changes, roll back if needed, and collaborate with other team members effectively. I’ll talk about a couple of my favorite tools in this aspect
- Testing and validation: It’s crucial to test and validate changes made to a PostgreSQL database instance before deploying them to the production environment. You can set up a separate testing environment where we can apply the changes and perform thorough testing. PostgreSQL offers features like transactional DDL (Data Definition Language), which allows us to safely test and roll back schema changes in a controlled manner. Automated frameworks (aka Jenkins, Chef, etc.) can also be used to verify the correctness and integrity of the database after the changes are applied
- Deployment and monitoring: Once the changes have been thoroughly tested, they can be deployed to the production PostgreSQL database. This can involve executing the scripts or SQL statements in the production environment, either manually or through automated deployment tools. It’s important to monitor the database after the changes are applied to ensure everything is functioning as expected and to quickly address any issues that may arise
PostgreSQL also offers additional features that can aid in database change management, such as extensions and triggers, which allow us to add custom logic or automate certain tasks during the change process.
Remember that PostgreSQL, like any database management system, requires careful consideration and planning when making changes to ensure data integrity, minimize downtime, and maintain the performance of our applications.
There are several tools available for managing database changes in PostgreSQL. Here are my favorite ones:
- Liquibase: Liquibase is an open-source database change management tool that supports PostgreSQL, among other database systems. It allows us to define database changes using XML, YAML, JSON, or SQL formats. Liquibase provides version control for database schemas, supports rollbacks, and integrates well with various build and deployment tools
- Flyway: Another widely used open-source database migration tool that supports PostgreSQL. It uses plain SQL scripts for defining database changes and manages the execution of these scripts in a controlled manner. Flyway supports versioning, and rollbacks, and can be easily integrated into existing development workflows
- Other known tools are Redgate SQL Change Automation; AWS Database Migration Service; DBeaver, etc.
These tools offer different features and capabilities, so it’s important to evaluate them based on specific requirements, such as ease of use, the learning curve to Dev teams, integration with the existing toolchain, support for version control, rollback mechanisms, and team collaboration features. Additionally, consider factors like licensing, community support, and documentation when selecting a tool for our PostgreSQL database change management needs.
As part of our Customer PostgreSQL Cluster Deployment, we install and integrate the Flyway tool to provide efficient and streamlined database change management for PostgreSQL instances across the board. Here are some key points I like about Flyway:
- Simple Configuration: Flyway follows a simple and straightforward approach to managing database changes. It uses plain SQL scripts (or other scripting languages) to define and apply changes to the database schema. The scripts are organized in a versioned manner, allowing for easy tracking and management
- Version Control: Flyway utilizes a version control system to keep track of applied and pending database migrations. Each migration script is associated with a specific version number, allowing Flyway to know which scripts have been executed and which are yet to be applied. This helps in maintaining a clear history of changes and makes it easier to track and manage database versions
- Migration Scripts: Flyway supports multiple script formats, including SQL, Java-based migrations, and others. SQL scripts are commonly used with Flyway for PostgreSQL databases. These scripts contain the necessary SQL statements to create or modify database objects like tables, views, indexes, and stored procedures. Flyway executes the scripts in the correct order based on their version numbers
- Repeatable Migrations: In addition to versioned migrations, Flyway supports repeatable migrations. Repeatable migrations are useful when the changes we want to make are not tied to a specific version but need to be reapplied whenever the database is deployed or updated. For example, creating database views or inserting default data. Flyway ensures that repeatable migrations are applied consistently across environments
- Integration and Automation: Flyway can be easily integrated into your development and deployment workflows. It offers various integration options, including build tools like Maven and Gradle, CI/CD pipelines, and IDE plugins. This allows for seamless automation of database migrations, enabling us to incorporate them into our overall application deployment process
- Compatibility: Flyway works well with PostgreSQL databases and supports various versions of PostgreSQL, including the latest releases. It utilizes PostgreSQL’s native JDBC driver to connect and interact with the database. This ensures compatibility and enables Flyway to leverage PostgreSQL-specific features and capabilities
A simple example with rollback
CREATE TABLE footab (
id SERIAL PRIMARY KEY,
name VARCHAR(100) NOT NULL
ALTER TABLE footab ADD COLUMN email VARCHAR(100);
INSERT INTO footab (name, email) VALUES ('John', 'email@example.com');
ALTER TABLE footab DROP COLUMN email;
In this example, we have four migration scripts with different versions (
v4). Let’s say we want to roll back the changes made in
v4 due to an issue. To do this, we can create “down migration” scripts that revert the changes or modify them.
DELETE FROM footab WHERE name = 'John';
ALTER TABLE footab ADD COLUMN email VARCHAR(100);
Now, when you run Flyway, it will identify that there are “down migrations” available and execute them to roll back the changes. Here’s how the migration process would work:
- Initial migration: Flyway applies
v4scripts, creating the
footab, adding the
- Rollback migration: When the need arises to roll back, Flyway will execute the down migrations in the reverse order. It first applies
v4__add_column__down.sqlto add the email column back to the table, and then
v3__insert_data__down.sqlto remove the inserted data
- Subsequent migrations: After the rollback, you can continue with regular migrations, and Flyway will track and apply the subsequent scripts accordingly.
This example demonstrates how we handle rollbacks in Flyway by creating down migration scripts that reverse or modify the effects of previous migrations. By maintaining a structured and version-controlled approach to the migration scripts, we can easily manage rollbacks and maintain the integrity of the database schema.
Overall, Flyway simplifies the process of managing database changes for PostgreSQL databases. It provides a flexible and version-controlled approach, allowing us to track, apply, and roll back changes in a structured and reliable manner. Whether we are working on a small project or a large-scale enterprise application, Flyway can help us streamline the database change management process with ease.
By following the principles and utilizing appropriate tools and techniques, you can effectively manage database changes in PostgreSQL, ensuring data integrity, minimizing downtime, and supporting the evolution of the applications.