Methods of Database Conversion
On the way of replacing commercial software by open-source equivalents, IT departments of companies and organizations face the need of database conversion. Database conversion is a process of converting data, meta-objects, stored procedures, functions, and triggers between different DBMS formats. Often this procedure requires modification of the application layer, types mapping and SQL statements.
There are various reasons for database conversion, including:
Cost: Commercial database management systems (DBMS) often come with high license fees and strict licensing terms. In contrast, open-source DBMS alternatives offer similar capabilities and are free to install and use.
Customization: Open-source DBMS typically provide a wide range of extensions and add-ons that allow for flexible implementation of database management and development tasks. Many of these extensions are freely available.
Flexibility: Open-source DBMS can easily integrate with Database-as-a-Service (DBaaS) providers such as AWS, eliminating the risk of vendor lock-in.
However, migrating database between two RDBMS having different SQL syntax and data types can be a challenging and time-consuming process. The following phases are typically involved in the database conversion:
This phase involves evaluating the compatibility of the systems, analyzing the architecture, and reviewing the application code for any required modifications.
Migration of schemas and meta-objects. In this phase, the migration process focuses on transferring the database schemas and related meta-objects, such as tables, views, indexes, and constraints, to the target DBMS.
Functional and performance testing. Once the schema migration is complete, it is essential to perform thorough testing to ensure that the migrated database functions correctly and meets the required performance standards.
Data Migration. The actual transfer of data from the source database to the target database takes place in this phase. It involves converting data types, handling data transformations, and ensuring data integrity throughout the process.
Migration of schemas and meta-objects
This phase typically involves converting table definitions, including their columns, data types, constraints, indexes, and relationships between tables. Those database meta-objects are examined to determine the changes required for the target environment. After required changes are identified, the migration scripts or queries are generated to create or modify the definitions of meta-objects in the target database.
It is very important to test the migration scripts on a development or staging environment to ensure that they accurately reflect the desired table definitions and do not cause any data loss or inconsistencies. Once the migration scripts have been tested successfully, they are executed on the target database to create the table definitions, constraints, indexes, and relationships between tables accordingly.
After the migration is completed, all table definitions and the associated meta-objects are verified in the target environment to ensure that they match the desired structure and meet the requirements of the applications.
Data Migration
There are various approaches and methods implemented in database conversion tools available in the market. These data migration methods can be grouped into three primary categories: snapshot, parallel snapshot, and change data replication (CDR).
The snapshot method involves creating a snapshot of the source database and transferring it to the target database. In this approach, all the data is moved from the source database management system (DBMS) to the target DBMS in a single operation. During the snapshot process, write operations on the source database are restricted. Database conversion tools running this method may put a significant load on the source DBMS due to bulk data reading.
The parallel snapshot approach divides the data into fragments and takes snapshots of these fragments simultaneously. This method helps to reduce the duration of the snapshot and the downtime window required for database conversion procedure. However, some downtime is still required for this method.
Finally, change data replication method may be used by software tools for database conversion. This technique is based on monitoring and recording real-time changes from the source database. Then database conversion tool will apply those changes to the target database. There are two common techniques used in CDR: trigger-based and transaction log.
The trigger-based approach requires modifying the source database by adding triggers that capture the changes and propagate them to the target database. On the other hand, the transaction log approach relies on the undocumented and changeable format of the transaction log that implies compatibility risks for different versions of database management systems.
Unlike snapshot and parallel snapshot methods, using CDR approaches for the database conversion can help reduce the overhead on the DBMS by capturing and applying only the changed data instead of reading and transferring bulk data.
Conclusion
Database conversion is a complex procedure that includes transferring data, meta-objects, stored procedures, functions, and triggers from one DBMS to another. Before running the database conversion, the responsible specialists must assess the compatibility of the application layer with the target database management system, investigate differences in schema, data formatting and SQL dialects of the source and target DBMS, and perform performance testing.
Database conversion can be implemented using various methods, each with its advantages and disadvantages. Two commonly used methods are snapshot and parallel snapshot, which involve taking a snapshot of the source database and applying it to the target database. However, these methods have drawbacks such as downtime and overhead on the DBMS due to bulk data reading. Alternative approach to the database conversion is change data replication (CDR) that enables real-time tracking and capturing of changes. CDC can be achieved through trigger-based or transaction log techniques. It is important to remember that these methods require modifications to the source database or rely on the undocumented and changeable format of the transaction log.
To ensure a successful database conversion project, it’s crucial to carefully choose the appropriate approach based on the specific project needs. By planning and executing the migration process thoughtfully, businesses can benefit from cost savings, customization, and increased flexibility.
