Upgrade PostgreSQL to v18 with updated volume mount path

[snickerjp]

Summary

Upgrades the PostgreSQL image from v17 to v18, addressing the data directory path change introduced by the official Docker PostgreSQL image (docker-library/postgres#1259).

Changes

compose.yaml

• Image: pgautoupgrade/pgautoupgrade:17-alpine → pgautoupgrade/pgautoupgrade:18-alpine
• Volume: /opt/redash/postgres-data:/var/lib/postgresql/data → /opt/redash/postgres-data:/var/lib/postgresql
• Added migration hints in comments for existing users

README.md

• Added FAQ: "How do I backup my PostgreSQL database?"
• Added FAQ: "How do I upgrade PostgreSQL to a newer major version?"

Why pgautoupgrade instead of the official postgres image?

The Redash development repo (getredash/redash) uses postgres:18-alpine for development, where data is disposable. This setup repo targets production environments where data must be preserved across version upgrades, so we kept pgautoupgrade.

Background

• PostgreSQL 18's official Docker image changed PGDATA to /var/lib/postgresql/MAJOR/docker (Change PGDATA in 18+ to /var/lib/postgresql/MAJOR/docker docker-library/postgres#1259)
• This broke volume mounts to the previous path /var/lib/postgresql/data
• pgautoupgrade has documented the migration path: mount to /var/lib/postgresql and it handles the data migration automatically

Testing

• Tested full new installation with setup.sh
• Redash v26.3.0 + PostgreSQL 18.4 started successfully
• Web UI accessible, initial setup and login confirmed

For existing users

Existing users upgrading from PG17 need to:

1. Backup their data
2. Stop containers
3. Update the volume mount path in their compose.yaml
4. Restart (pgautoupgrade handles the data migration)

Details: https://github.com/pgautoupgrade/docker-pgautoupgrade#error-message-when-mounting-data-to-varlibpostgresqldata-on-postgres-v18

Fixes #86

[cubic-dev-ai]

No issues found across 2 files

_{Re-trigger cubic}

[Copilot]

Pull request overview

Updates the production Docker Compose setup to PostgreSQL 18 via pgautoupgrade, adjusting the persistent volume mount to accommodate the upstream PostgreSQL 18 image data-directory layout changes, and adds operator guidance for backup/upgrade workflows.

Changes:

• Bump PostgreSQL container image from pgautoupgrade:17-alpine to pgautoupgrade:18-alpine.
• Update the PostgreSQL volume mount from /var/lib/postgresql/data to /var/lib/postgresql and add migration guidance comments.
• Add README FAQ entries for backing up PostgreSQL and upgrading from PG17→PG18.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
README.md	Adds FAQ guidance for database backups and major-version upgrade steps.
data/compose.yaml	Switches to PG18 pgautoupgrade image and updates the data volume mount path with migration notes.

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