In today’s era of replacing proprietary software with open-source alternatives, many companies and organizations are considering database migration as a means to transition from one database management system (DBMS) to another. Database migration involves the transfer of data, meta-objects, stored procedures, functions, and triggers from a source DBMS to a target DBMS. It typically requires changes to applications, type mappings, and SQL conversions.

The process of database migration comprises several important steps, including assessment, preparation, selection, extraction, data transformation, and validation. These phases can be challenging and time-consuming as they involve translating data and logic between two systems with different data types and SQL syntax. Database migration is undertaken for various reasons, such as cost savings, customization, and flexibility.

The initial phase in planning a database migration involves assessing the application to determine the feasibility of moving it from the source DBMS to the target DBMS. This phase requires a comprehensive analysis of technology-related factors, including evaluating the compatibility of the client, application server, data access, and database features. It is essential to ensure that the software in the database application layer is certified for the destination DBMS. If not, efforts can be made to persuade the vendor to add support for the new DBMS or find a compatible application with similar capabilities.

The next step is to validate the prerequisites on the target system before initiating data migration. This includes checking server resources, operating system compatibility, and installing and configuring data migration software and related drivers. The resources of the destination database server or cluster of servers must be robust and scalable enough to handle the volume and complexity of the incoming database.

Once the prerequisites and capabilities of the target system have been validated, the next step is to identify any discrepancies in schema, data formatting, and SQL features between the source and destination DBMS. Addressing these differences before the data migration helps prevent potential errors that can be frustrating and time-consuming. It is crucial to run performance tests to ensure the smooth transition to the target platform, as variations in the functionality of built-in transactions or features of the source database may arise and affect the application.

When it comes to data migration, several approaches and tools are available in the market. The most common methods include snapshot, parallel snapshot, and change data capture (CDC). The snapshot method involves taking a snapshot of the source database and applying it to the target database all at once, with data being moved from the source DBMS to the target. When the snapshot replication is active, write operations on the source database are not possible. The parallel snapshot approach splits the data into fragments and takes snapshots simultaneously, significantly reducing the snapshot duration and downtime window, although some restrictions still persist.

CDC software is employed to monitor and record real-time changes from the source database, which are then applied to the target database. Two common change data capture techniques are trigger-based and transaction log-based. Unlike the snapshot and parallel snapshot methods, which may result in data loss or duplication and incur significant overhead in the DBMS due to bulk data reading, CDC approaches either require modification of the source database (trigger-based) or rely on the undocumented and changeable format of the transaction log.

In conclusion, database migration is a complex and critical process that requires careful planning and execution. It involves transferring essential elements such as data, meta-objects, stored procedures, functions, and triggers from one DBMS to another, while ensuring necessary changes are made to the application. Before initiating data migration, it is crucial to assess the compatibility of the application with the target DBMS, identify any discrepancies in schema and data formatting, and conduct performance testing. Different approaches and tools exist for database migration, each with its advantages and disadvantages.