Oracle Logical Replication Tutorial

Introduction to Logical Replication

Logical replication in Oracle allows you to replicate data between databases while preserving the logical structure of the data. Unlike physical replication, which copies the entire database, logical replication can be selective and flexible, replicating specific tables or schemas. This tutorial will guide you through setting up and managing logical replication in Oracle.

Setting Up Logical Replication

To set up logical replication, you need to configure both the source and target databases. Follow these steps:

1. Enable Supplemental Logging

Supplemental logging is required for logical replication. It captures additional information needed for replication.

-- Enable minimal supplemental logging
ALTER DATABASE ADD SUPPLEMENTAL LOG DATA;
                

2. Create a LogMiner Dictionary

LogMiner is used to mine the redo logs for changes. Create a LogMiner dictionary to store the required metadata.

-- Create LogMiner dictionary
EXECUTE DBMS_LOGMNR_D.BUILD(dictionary_filename => 'dictionary.ora', dictionary_location => '/path/to/directory');
                

3. Configure Streams Capture Process

The Streams capture process captures changes from the redo logs.

-- Configure Streams capture process
BEGIN
    DBMS_STREAMS_ADM.ADD_TABLE_RULES(
        table_name => 'hr.employees',
        streams_type => 'capture',
        streams_name => 'capture_process',
        inclusion_rule => true);
END;
                

4. Set Up Propagation

Propagation moves the captured changes from the source database to the target database.

-- Set up propagation
BEGIN
    DBMS_STREAMS_ADM.ADD_TABLE_PROPAGATION_RULES(
        table_name => 'hr.employees',
        streams_name => 'propagation_process',
        destination_queue => 'target_queue@target_db',
        inclusion_rule => true);
END;
                

5. Configure Streams Apply Process

The Streams apply process applies the changes to the target database.

-- Configure Streams apply process
BEGIN
    DBMS_STREAMS_ADM.ADD_TABLE_RULES(
        table_name => 'hr.employees',
        streams_type => 'apply',
        streams_name => 'apply_process',
        inclusion_rule => true);
END;
                

Managing Logical Replication

Once logical replication is set up, you need to manage and monitor it to ensure data consistency and performance.

Monitoring Replication

Use the following views to monitor the status of your replication setup:

-- View capture process status
SELECT CAPTURE_NAME, STATUS FROM DBA_CAPTURE;

-- View propagation status
SELECT PROPAGATION_NAME, STATUS FROM DBA_PROPAGATION;

-- View apply process status
SELECT APPLY_NAME, STATUS FROM DBA_APPLY;
                

Troubleshooting Common Issues

Here are some common issues you might encounter and their solutions:

• Capture Process Stopped: Check the alert log for errors and restart the capture process.
• Propagation Delays: Ensure network connectivity between source and target databases.
• Apply Process Errors: Check the apply process error queue for details.

Conclusion

Logical replication in Oracle provides a flexible and powerful way to replicate data between databases. By following this tutorial, you should be able to set up, manage, and troubleshoot logical replication to keep your data synchronized across different environments.