How To Start Logical Replication in PostgreSQL for Specific Tables Based on a pg_dump?

Starting logical replication in PostgreSQL for specific tables based on a pg_dump involves a series of steps. Here’s a step-by-step guide:

  1. Create a new empty database:
    • Create a new empty target database where you want to replicate the specific tables.
    • Use the createdb command or any other PostgreSQL administration tool to create the database.
  2. Restore the schema and data using pg_restore:
    • Use the pg_restore command to restore the schema and data from the pg_dump file into the target database.
    • Specify the pg_dump file using the -f option and provide the target database using the -d option.
    • This step will recreate the schema and populate the data in the target database.
  3. Enable logical replication in the source and target databases:
    • Edit the postgresql.conf file in both the source and target databases and set the wal_level parameter to logical.
    • Restart both the source and target PostgreSQL instances to apply the changes.
  4. Configure replication settings in the source database:
    • Connect to the source database and run the following SQL statements:

CREATE PUBLICATION my_publication FOR TABLE table1, table2, …;
ALTER PUBLICATION my_publication ADD TABLE table3, table4, …;

Replace my_publication with a name for your publication and list the specific tables you want to replicate.

  • This step creates a publication and adds the specified tables to it.

5. Create a replication slot in the source database:

  • Run the following SQL statement in the source database:

SELECT * FROM pg_create_logical_replication_slot('my_replication_slot', 'pgoutput');

Replace my_replication_slot with the name of your replication slot.

  • This step creates a replication slot that will be used by the logical replication process.

6. Configure the replication connection in the target database:

  • Connect to the target database and run the following SQL statement:

CREATE SUBSCRIPTION my_subscription CONNECTION 'host=source_host dbname=source_db user=replication_user password=replication_password' PUBLICATION my_publication;

  • Replace my_subscription with a name for your subscription. Update the connection string with the appropriate values for the source database host, name, replication user, and password.
  • This step creates a subscription that connects to the source database and subscribes to the specified publication.

7. Start the replication process:

  • Run the following SQL statement in the target database:

ALTER SUBSCRIPTION my_subscription ENABLE;

Replace my_subscription with the name of your subscription.

  • This step starts the replication process, and the specified tables will be replicated from the source to the target database.

That’s it! The logical replication for the specific tables based on the pg_dump is now started. Any changes made to the replicated tables in the source database will be propagated to the target database.

8. Monitor the replication process:

  • You can monitor the status and progress of the replication process by querying the pg_stat_replication view in the target database. Run the following SQL statement:

SELECT * FROM pg_stat_replication;

This will display information about the active replication connections, including the lag and state of each replication slot.

9. Verify data synchronization:

  • After starting the replication process, ensure that the data is synchronized between the source and target databases. You can compare the records in the replicated tables to ensure they match.
  • Monitor the replication lag to ensure that any changes made in the source database are replicated to the target database within an acceptable timeframe.

10. Handle schema changes and table alterations:

  • If there are any schema changes or alterations to the replicated tables in the source database, you need to handle them carefully.
  • Add new replicated tables to the publication using the ALTER PUBLICATION statement.
  • For schema changes, such as adding or dropping columns, you may need to recreate the subscription or resynchronize the affected tables.

11. Handle data conflicts and errors:

  • In case of data conflicts or errors during replication, you need to investigate and resolve them.
  • Review the PostgreSQL logs and monitor the replication status for any error messages or inconsistencies.
  • If conflicts occur due to concurrent updates on the same row in both the source and target databases, you may need to implement conflict resolution strategies.

12. Perform regular maintenance and monitoring:

  • It’s important to regularly monitor the replication process, check for any lag or errors, and ensure the overall health of the replication setup.
  • Perform routine maintenance tasks such as vacuuming, analyzing, and monitoring disk space usage to optimize the performance of both the source and target databases.

13. Handle network and connectivity issues:

  • Ensure that the network connectivity between the source and target databases is reliable and stable.
  • Monitor network latency and bandwidth to ensure that replication traffic can be transmitted efficiently.
  • Implement proper network security measures, such as firewall rules and encryption, to protect the replication data during transmission.

14. Plan for failover and disaster recovery:

  • Have a plan in place for failover and disaster recovery scenarios.
  • Consider setting up additional standby replicas or implementing streaming replication for high availability and data redundancy.
  • Test the failover procedures to ensure that the replication can be switched to a standby replica seamlessly in case of primary database failure.

15. Upgrade and compatibility considerations:

  • Keep in mind the version compatibility between the source and target databases, especially when performing upgrades.
  • Check the PostgreSQL documentation and release notes for any specific considerations or changes related to logical replication when upgrading to a newer version.

16. Document the replication setup:

  • Maintain thorough documentation of the replication setup, including configuration details, connection information, and any customizations made.
  • Document any specific instructions or procedures related to monitoring, maintenance, and troubleshooting of the logical replication.

17. Regularly review and optimize the replication setup:

  • Periodically review the replication setup to ensure it meets the evolving needs of the application.
  • Optimize the replication configuration based on performance analysis and feedback from monitoring tools.
  • Consider fine-tuning replication settings, adjusting network configurations, and optimizing SQL queries to improve replication efficiency.

18. Backup and restore considerations:

  • Ensure that proper backup and restore procedures are in place for both the source and target databases.
  • Regularly perform backups of the source database to ensure data integrity and availability.
  • Have a plan for restoring the replication setup in case of database corruption or data loss.

19. Stay updated with PostgreSQL community and documentation:

  • Keep yourself informed about the latest developments, updates, and best practices in PostgreSQL.
  • Participate in the PostgreSQL community forums, mailing lists, and conferences to learn from other users’ experiences and gain insights into optimizing logical replication.

20. Test and validate the replication setup:

  • Perform thorough testing of the replication setup before deploying it in a production environment.
  • Test various scenarios, such as failover, network interruptions, and high-load situations, to ensure the replication can handle different conditions effectively.

By following these additional steps, you can further enhance the setup and management of logical replication in PostgreSQL. It’s important to continuously monitor, optimize, and adapt the replication setup based on the specific requirements and evolving needs of your application.

About Shiv Iyer 444 Articles
Open Source Database Systems Engineer with a deep understanding of Optimizer Internals, Performance Engineering, Scalability and Data SRE. Shiv currently is the Founder, Investor, Board Member and CEO of multiple Database Systems Infrastructure Operations companies in the Transaction Processing Computing and ColumnStores ecosystem. He is also a frequent speaker in open source software conferences globally.