PostgreSQL 18 Upgrade Guide

🌟 New Features in PostgreSQL 18

PostgreSQL 18 introduces several enhancements aimed at improving performance, scalability, and developer experience.

• Improved Query Parallelism: PostgreSQL 18 significantly boosts query parallelism, allowing more complex queries to be executed across multiple CPU cores. This is particularly beneficial for analytical workloads and large data sets.
• Enhanced Logical Replication: The logical replication system has been refined with new features, including the ability to apply changes in parallel. This reduces replication lag and makes it more suitable for high-transaction environments.
• Declarative Partitioning: The declarative partitioning system, first introduced in earlier versions, is now more robust and flexible. New capabilities allow for easier management and better performance of partitioned tables.
• Security and Authentication: New security features include more granular control over user roles and permissions, as well as improved support for authentication methods.
• New SQL Features: PostgreSQL 18 supports a number of new SQL standard features, giving developers more tools for data manipulation and query writing. These additions make the database even more compliant with the latest standards.

---

🛠️ Step-by-Step Upgrade Guide

Upgrading a major PostgreSQL version involves more than a simple apt-get upgrade. It requires migrating data from the old database cluster to a new one, as the internal data storage format can change between major releases. This guide outlines the two primary methods for upgrading: pg_upgrade for in-place upgrades and pg_dump/pg_restore for logical backups.

Method 1: Using pg_upgrade

pg_upgrade is the recommended method for most users because it’s significantly faster and results in minimal downtime. It works by creating hard links or copying files from the old cluster to the new one, avoiding a full data dump and reload.

1. Install the new PostgreSQL version (18): Install the new binaries alongside your existing PostgreSQL 17 installation.
2. Initialize the new cluster: Create a new, empty PostgreSQL 18 data directory using the initdb command.
3. Perform a dry run: Run pg_upgrade with the --check flag to ensure compatibility between your old and new clusters. This step is crucial for identifying any potential issues, such as incompatible extensions or data type mismatches, before the actual upgrade.
4. Shut down both clusters: Stop both the old PostgreSQL 17 and the new PostgreSQL 18 services.
5. Run pg_upgrade: Execute the pg_upgrade command to perform the actual upgrade. You must specify the paths to the old and new binary directories and data directories.
6. Analyze the new cluster: After the upgrade, pg_upgrade will generate a script to run vacuumdb --all --analyze-in-stages. This step is important because pg_upgrade does not transfer optimizer statistics, and running this script will rebuild them for optimal performance on the new cluster.
7. Clean up: Once you’ve confirmed that the new cluster is working correctly, you can run the provided script to delete the old cluster’s data files.

Method 2: Using pg_dump and pg_restore

This method involves a full logical backup and restore. It is a good option if you need to migrate to a different server or operating system, or if you want to eliminate database bloat during the upgrade. However, it can be much slower and result in more downtime than pg_upgrade.

1. Backup global objects: Use pg_dumpall -g to back up global objects like users, roles, and tablespaces.
2. Back up individual databases: Use pg_dump to create a logical backup of each database you want to migrate. For best results, use the pg_dump binary from the new PostgreSQL 18 installation to perform the backup from the old cluster.
3. Install PostgreSQL 18: Install the new binaries on your target server.
4. Restore the global objects: Use psql to restore the global objects dump file to the new cluster.
5. Restore individual databases: Use pg_restore to restore the individual database dumps to the new cluster. You can also pipe the pg_dump output directly to psql to avoid creating intermediate files.

Important Considerations for Both Methods:

• Backup: Always perform a full backup of your entire PostgreSQL data directory before attempting any major version upgrade.
• Test Environment: Always test the upgrade process on a non-production system first to ensure a smooth transition and verify that your applications work with the new version.
• Downtime: Plan for downtime, as the database will be unavailable during the upgrade process. Use the --check flag on pg_upgrade to get a rough estimate of the time required.