PostgreSQL is a popular open-source database system that offers many advantages over Oracle databases in terms of cost, customization, and flexibility. Although migrating from Oracle to PostgreSQL can be challenging and time-consuming, it is a worthwhile endeavor for organizations looking to cut costs and increase flexibility.
One of the key advantages of migrating from Oracle to PostgreSQL is cost savings. While Oracle requires licensing fees, it also comes with additional costs for high availability and partitioning. These costs can quickly accumulate, making Oracle a more expensive option than PostgreSQL. On the other hand, PostgreSQL is free to install and use, making it a more cost-effective option for organizations looking to cut costs.
Another advantage of PostgreSQL over Oracle is its customization. PostgreSQL’s open-source nature allows for a wide range of extensions and add-ons that can significantly enhance database performance, many of which are available for free. Oracle, in contrast, often charges for similar features, leading to added expenses.
PostgreSQL also offers more flexibility than Oracle, as it is licensed under an open-source model and can be easily obtained from public cloud providers like AWS. Choosing Postgres mitigates the risk of vendor lock-in, giving organizations more freedom and flexibility to use the database system that best meets their needs.
Database Migration Phases
While PostgreSQL offers numerous advantages over Oracle databases, it’s important to note that migrating from Oracle to PostgreSQL can be a challenging and time-consuming process due to the differences in their relational database management systems (RDBMS) structure and data types. It’s crucial to approach the migration process with the right tools and follow the recommended steps to ensure a successful migration.
The migration process can be arranged into several steps or phases, including assessment, schema migration, intermediate testing, data migration, and final testing. The initial stage of planning a migration from Oracle to Postgres involves conducting an assessment of the application to determine the level of difficulty involved in the migration process. This stage requires a comprehensive analysis of technology-related factors such as client, application server, data access, and database features to evaluate compatibility.
Schema migration is the next phase in the process, where the user’s schema in Oracle, which shares the same name as the user itself, needs to be converted to PostgreSQL’s schema, which is not synonymous with the user. Newly created objects in PostgreSQL will be placed in the public schema by default if a schema is not explicitly specified. This setup in PostgreSQL offers the advantage of enabling a user to create multiple schemas without creating separate users, as well as the ability to grant permissions to others for creating objects in those schemas.
Before proceeding with the migration, it’s crucial to conduct thorough testing of the converted schema using a sample dataset. It’s recommended to load sample data into Postgres from a development or testing environment where there is production sample data and set up an application connection using appropriate data access drivers. To verify the accuracy, load the same fragment of data in both the Oracle and PostgreSQL databases, query it to confirm that the SQL results are identical. Any issues revealed during the functional testing phase should be reviewed and addressed accordingly.
Performance testing is also critical during the migration phase as some of the Oracle built-in transactions or features functionality may differ slightly in PostgreSQL, and the application may experience some variance. This phase is essential for identifying any differences and fixing them at the application, data access (drivers), and database level through proper tuning.
Methods of Oracle to PostgreSQL Database Migration
All database migration techniques can generally be classified into three types: Snapshot, Snapshot in Parallel, and Change Data Capture (CDC). Each of these methods has its own downtime window. It is extremely important to choose the most suitable approach that fits the allowed downtime window.
- Snapshot Approach. This method involves capturing the source database state as a snapshot and applying it to the target database all at once. This means that the data is moved from Oracle to Postgres in one go. However, during the snapshot process, no WRITE operations are allowed on the source database, which results in application downtime. Despite this, it is a clean and straightforward approach to data migration.
Pros: The data movement is completed in one go, and there are no data type challenges. Applications can start accessing the target database immediately after the snapshot, and there is no special configuration required.
Cons: Application downtime is required during the snapshot, and if the snapshot is interrupted, it needs to be restarted.
- Snapshot – Piecewise (Parallel) Approach. This variation of the snapshot approach involves splitting data objects into chunks and taking snapshots in parallel. The two ways to execute a piecewise snapshot are either table by table or by splitting large data into smaller fragments using primary keys or unique row identifiers. Most tools support this approach, and the process is invoked in parallel, significantly reducing the snapshot duration and downtime window.
Pros: parallel data migration can be arranged either table by table or splitting large table in small sets, each of these options requires less downtime than simple snapshot.
Cons: Application downtime is still required; primary key or unique row identifiers are mandatory. Scripting is required to adjust the parallel approach, and if the snapshot is interrupted, it needs to be restarted.
- Change Data Capture (CDC) Approach. This method involves capturing and tracking the data that has changed in real-time on the source database and replaying it on the target database. Database migration tools usually implement CDC method using either triggers or transaction logs.
Pros: Oracle database can be access for both reading and writing while data is migratedto PostgreSQL, database migration can be resumed if interrupted.
Cons: Replication software is required, and there could be slight performance overhead in trigger-based CDC. Large Objects support is not available, and only commercial tools are available – no open source.
Commercial Database Migration Tools
There are a number of commercial migration tools that fully automate Oracle to PostgreSQL database migration. One of these tools is Oracle to PostgreSQLconverter offered by Intelligent Converters. It has intuitive wizard-style interface and can automate overall migration procedure within a few clicks. The product implements parallel piecewise snapshot approach described above.
Database migration via Oracle to PostgreSQL converter consists of 7 steps:
- Select migration target – either PostgreSQL database or PostgreSQL script file (local file containing SQL-statements to create tables, indexes, constraints, views and insert data).
- Connect to Oracle server – provide all necessary information to Connect to the source database server.
- Connect to PostgreSQL server (applied to ‘Move to PostgreSQL server directly’ scenario) – here you have to provide all necessary information to connect to the target database server.
- Select the migration target and log file – enter name of PostgreSQL database or script file (depending on scenario has been chosen on the 1st step) and the log file. If log file is not specified, logging will be disabled.
- Conversion settings – provide all required settings (the target schema, case sensitivity of object names, etc) to customize Oracle to PostgreSQL database migration.
- Select Oracle tables to migrate into PostgreSQL database
- Select PostgreSQL views to migrate to PostgreSQL
After these steps are passed, database Oracle to PostgreSQL database migration will be launched and progress indication will appear on the wizard screen.
In conclusion, PostgreSQL offers numerous advantages over Oracle databases in terms of cost, customization, and flexibility. While migrating from Oracle to PostgreSQL can be challenging and time-consuming, it is a worthwhile endeavor for organizations looking to cut costs and increase flexibility. The migration process involves several steps or phases, including assessment, schema migration, intermediate testing, data migration, and final testing. All database migration techniques can generally be classified into three types: Snapshot, Snapshot in Parallel, and Change Data Capture (CDC). It’s important to choose the most suitable approach that fits the allowed downtime window. Commercial database migration tools like Oracle to PostgreSQL converter can essentially simplify the migration process and make it smooth and safe preventing data loss or corruption.