Understanding Online Table Redefinition

The dbms_redefinition process, known as Online Table Redefinition, is a process that transforms a table’s structure, allowing database administrators to make changes such as adding or removing columns, modifying data types, or altering storage attributes without requiring downtime. This is particularly useful for large and critical databases where minimizing disruption is essential.

The key component for achieving this in the Oracle Database is the dbms_redefinition package. This package provides a set of procedures and functions that streamline the online redefinition process.

Key Steps in Online Table Redefinition

Prepare the Environment

  • Before initiating the online redefinition, ensure that the database and the table are ready for the process. This includes checking for dependencies, disabling triggers or constraints that might affect the redefinition, and ensuring there is enough free space in the tablespaces.

Create the Interim Table with the dbms_redefinition Package

  • The dbms_redefinition package facilitates the creation of an interim table, which will eventually replace the original table. This interim table is designed to accommodate the modified structure, and the data from the original table is continuously synchronized with it during the redefinition process.

Synchronize Data with the dbms_redefinition Package

  • The dbms_redefinition package offers procedures to keep the interim table in sync with the original table’s data. This ensures that any changes made to the original table during the redefinition process are reflected in the interim table.

Complete the Redefinition

  • Once the data synchronization is complete, the dbms_redefinition package allows for the final switch, making the interim table the new official version of the table. This step finalizes the online table redefinition, and the original table is effectively replaced. This step will pause active transactions in Oracle 12.2 until the replacement is complete. Test the redefinition process with as close to a production workload as possible to get timings for the final step.

Advantages of Online Table Redefinition via dbms_redefinition

Minimized Downtime

  • By allowing modifications to be made while the table remains accessible, online table redefinition significantly reduces downtime, enhancing overall system availability. Read the Oracle Database Administrator Guide for restrictions on using the dbms_redefinition package.

Consistent Data Access

  • Users can continue accessing the table during the redefinition process, ensuring that business operations are not interrupted.

Flexibility and Efficiency with the dbms_redefinition Package

  • The dbms_redefinition package provides flexibility in making structural changes to tables, promoting efficient database management and adaptability.


Oracle Database’s dbms_redefinition package empowers database administrators to redefine tables online, offering a robust solution for making structural changes without disrupting critical business operations. Mastering the use of online table redefinition can contribute to a more resilient and efficient database management strategy, ensuring that your database remains both agile and available in the face of evolving requirements. 

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