Question: How do you restore a PostgreSQL cluster?

Answer

Restoring a PostgreSQL cluster involves several steps, depending on the backup method used. Here are two common scenarios: using pg_dump and pg_restore, and using physical backups.

Using pg_dump and pg_restore

1. Backup with pg_dump: Back up your database cluster using pg_dump or pg_dumpall. For a full cluster backup with pg_dumpall, you might use:

   pg_dumpall > backup.sql

2. Restore with pg_restore (if individual databases were backed up) or SQL execution (if pg_dumpall was used):

   • If the backup was created with pg_dumpall, restoring is straightforward:

     psql -f backup.sql postgres

   • If individual databases were backed up with pg_dump, use pg_restore:

     pg_restore -d dbname backup_file

Using Physical Backups

For large databases, physical backups can be more efficient. These involve copying the data directory of the PostgreSQL server.

1. Create a Physical Backup: Stop your PostgreSQL server and copy the entire data directory to a backup location.

   systemctl stop postgresql
   cp -R /var/lib/postgresql/12/main /path/to/backup/
   systemctl start postgresql

2. Restore the Physical Backup:

   • Ensure PostgreSQL is stopped on the server where you are restoring the data.
   • Remove the current data directory and replace it with the backup:

     systemctl stop postgresql
     rm -rf /var/lib/postgresql/12/main
     cp -R /path/to/backup /var/lib/postgresql/12/main
     chown -R postgres:postgres /var/lib/postgresql/12/main
     systemctl start postgresql

Considerations

• Always ensure that the PostgreSQL versions between the backup source and destination match to avoid compatibility issues.
• Test your backup and restoration process regularly to confirm everything works as expected.
• Consider using tools like Barman or pgBackRest for more sophisticated backup and recovery operations, especially in production environments.