Comprehensive Migration from Oracle to PostgreSQL – Migrating Oracle’s Virtual Columns to PostgreSQL Generated Columns

The process of migrating from Oracle to PostgreSQL involves translating various database features. One such feature is Oracle’s virtual columns, which are commonly used to store derived or computed data. PostgreSQL provides a similar capability using generated columns. This guide provides a thorough comparison and details the migration process to ensure a smooth transition.

Oracle Virtual Columns:

• • • Definition: Oracle virtual columns are columns defined by an expression involving other columns in the same table. They do not store data physically but compute their values dynamically at query time.
    • Dynamic Calculation: Virtual columns are calculated on-the-fly whenever queried. This means that the values are always current and reflect the most recent changes to the underlying data without requiring manual updates.

Benefits:

• • • Storage Efficiency: Since virtual columns do not occupy physical storage, they help reduce the overall disk space usage of the database. This is particularly useful in large databases where space is a concern.
    • Consistency and Accuracy: Virtual columns automatically update their values based on changes to base columns, ensuring that derived data is always accurate and consistent.
    • Query Simplification: They encapsulate complex calculations and expressions within the schema, which simplifies querying and ensures that all queries using the same logic are consistent.

PostgreSQL Generated Columns:

• • • Definition: PostgreSQL’s generated columns are similar to Oracle’s virtual columns but can be either stored or computed dynamically. They allow for the calculation of column values based on an expression involving other columns.

Stored vs. Virtual:

• • • Stored Generated Columns: These columns store the computed values on disk, which can improve query performance by avoiding repeated calculations. However, they increase storage usage as the computed values are physically saved.
    • Virtual (Computed) Columns: Although PostgreSQL primarily supports stored generated columns, virtual columns can be emulated using views or Common Table Expressions (CTEs). These columns do not store data physically and are computed on the fly, similar to Oracle’s virtual columns.

Benefits:

• • • Performance Optimization: Stored-generated columns can enhance read performance by caching the computed values. This is beneficial in scenarios where the same calculation is performed frequently.
    • Data Integrity: By incorporating derived values directly within the table schema, PostgreSQL ensures consistency and correctness, similar to Oracle’s approach.
    • Flexibility and Complexity: PostgreSQL supports a wide range of expressions and functions, allowing for complex data transformations and calculations.

Comparing Oracle Virtual Columns and PostgreSQL Generated Columns

Storage:

• • • Oracle: Virtual columns do not use physical storage, reducing space usage but potentially impacting query performance due to real-time calculation.
    • PostgreSQL: Stored-generated columns use physical storage but improve read performance. Virtual columns (simulated with views) avoid storage costs but may impact performance.

Expression Flexibility:

• • • Oracle: Supports a wide range of expressions, including complex functions and subqueries.
    • PostgreSQL: Also supports complex expressions, but may require adjustments for Oracle-specific syntax or functions.

Performance:

• • • Oracle: Real-time computation can affect performance, especially in read-heavy environments.
    • PostgreSQL: Stored-generated columns can alleviate performance issues by pre-computing values, but this involves trade-offs with storage and write performance.

Migration Complexity:

Converting virtual columns from Oracle to PostgreSQL requires translating expressions and handling data type differences. Considerations for performance and storage should guide the migration approach.

Migration Considerations

• • Expression Compatibility:
    • Review Oracle virtual column expressions for compatibility with PostgreSQL’s syntax and functions. Adjust expressions as needed to ensure correct functionality.
  • Data Type Mapping:
    • Map Oracle data types to their PostgreSQL equivalents to ensure data integrity and compatibility.
  • Performance Impact:
    • Decide between using stored or virtual generated columns based on the performance needs of your application and the available storage.
  • Testing and Validation:
    • Thoroughly test the migrated columns to ensure they produce correct results. Compare the output with the original Oracle virtual columns to verify accuracy and performance.

Conclusion

Migrating from Oracle virtual columns to PostgreSQL-generated columns involves understanding the nuances of both systems, translating expressions, and considering performance and storage implications. By carefully managing these aspects, you can achieve a successful migration that leverages PostgreSQL’s capabilities while maintaining the integrity and efficiency of your database.

To ensure a seamless migration from Oracle to PostgreSQL and fully leverage the benefits of generated columns in your new database environment, it’s crucial to have expert guidance and robust tools. Newt Global offers the Newt Global DMAP, a world-class product designed to enable the mass migration of Oracle databases to cloud-native PostgreSQL environments faster, better, and cheaper.

For personalized assistance and to discuss how Newt Global can support your migration project, contact us at marketing@newtglobalcorp.com or visit our website at newtglobal.com. Take the next step toward optimizing your database migration process today!