Enable maintenance mode to temporarily block non-admin traffic during upgrades. Superusers (user ID 1 or with `superuser` right) can still access the site.
Commands:
```bash
# Turn on with optional message
php scripts/maintenance.php on "Upgrading database"
3. Prefer idempotent SQL. For MySQL 8.0+ you can use `ADD COLUMN IF NOT EXISTS`. For older MySQL/MariaDB versions, either:
- Check existence in PHP and conditionally run DDL, or
- Write migrations that are safe to run once and tracked by the `migrations` table.
## Notes
- The application checks for pending migrations at runtime and shows a warning banner but will not auto-apply changes.
- The `migrations` table is created automatically by the runner if missing.
- The runner executes each migration inside a single transaction (when supported by the storage engine for the statements used). If any statement fails, the migration batch is rolled back and no migration is marked as applied.
## Example migration
This repo includes an example migration that adds a per-user theme column:
```
20250924_170001_add_user_meta_theme.sql
```
It adds `user_meta.theme` used to store each user's preferred theme.
