Oracle Database Migration with Supplemental Logging

As an Oracle database administrator, I've come to appreciate the power of supplemental logging, especially when migrating databases or tables from one location to another. In this post, we'll explore what supplemental logging is, how it works, and provide practical examples to get you started.

According to Oracle documentation, supplemental logging records additional columns in redo log files, which is essential for redo-based applications. This process ensures that rows can be uniquely identified, making database migration and recovery more efficient.

When supplemental logging is enabled, redo logs contain extra columns from tables, including:

• Primary key columns (if defined)
• Unique index columns (if no primary key exists)
• All columns (if no primary key or unique index exists)

The good news is that supplemental logging doesn't impact your Oracle instance's performance.

To enable supplemental logging, use the following commands:

Scenario 1: Table with Primary Key

ALTER TABLE my_table ADD SUPPLEMENTAL LOG DATA (PRIMARY KEY) COLUMNS;

Scenario 2: Table with Unique Index (no Primary Key)

Identify the first unique index in alphabetical order and create a supplemental log group on its columns.

Scenario 3: Table with No Primary Key or Unique Index

ALTER TABLE my_table ADD SUPPLEMENTAL LOG DATA (ALL) COLUMNS;

When migrating large tables, consider the following best practices:

• Limit initial load to avoid overhead on the Oracle instance.
• Migrate during non-business hours to minimize impact.
• Break down large tables into smaller tasks.

By using supplemental logging, you'll streamline your Oracle database migration process and ensure a smoother transition.

Suppose you're migrating a table customers with a primary key customer_id. To enable supplemental logging, run:

ALTER TABLE customers ADD SUPPLEMENTAL LOG DATA (PRIMARY KEY) COLUMNS;

This simple command ensures that the customer_id column is included in the redo logs, making it easier to identify and recover rows during migration.

I hope this helps.