Problems and Errors During Data Recovery

It might seem like backups are your umbrella on a rainy day: you think they’ll save you from all trouble. But if there’s a hole in that umbrella, you’re still gonna get wet. Same thing with backups and restores: if something goes wrong, you might lose data or, even worse, end up with a corrupted database. That’s why understanding errors and how to prevent them is so important.

Problems During Data Recovery

1. PostgreSQL Version Incompatibility

One of the most common and annoying issues is trying to restore data made in one version of PostgreSQL into another (like restoring a backup from version 11 into 15). PostgreSQL doesn’t guarantee backward compatibility between versions.

Why does this happen?

• The data format might change between versions.
• Some functions and parameters might be removed or changed.

How to avoid it?

• Always create backups using pg_dump, not by directly copying the PostgreSQL data directory. pg_dump makes universal SQL scripts you can restore on any compatible version.
• Check version compatibility before starting a restore. You can find info in the official PostgreSQL docs.

Here’s an example. You made a backup with PostgreSQL 14:

pg_dump -U user -d my_database -f backup.sql

Now you try to restore it on PostgreSQL 15:

psql -U user -d my_database -f backup.sql

And you get errors like:

ERROR:  unrecognized configuration parameter "old_function"

Solution: upgrade the PostgreSQL version on your server or use the pg_upgrade utility to migrate.

2. Missing Required WAL Files

Sometimes restoring a database from an incremental or differential backup can suddenly fail — all because of missing WAL files (Write-Ahead Logging). PostgreSQL relies on these to “roll forward” changes after the last full backup. If these files are missing or corrupted, the database can’t finish the restore.

This happens, for example, when WAL file archiving wasn’t enabled, or someone accidentally cleaned out the folder to free up space. So, if you plan to use incomplete backups, make sure to enable archiving in postgresql.conf:

archive_mode = on
archive_command = 'cp %p /path/to/wal_archive/%f'

And don’t forget to regularly check that the archive is actually working and the files are intact and in place. That’s a small price for peace of mind that your restore won’t let you down.

3. Corrupted Backup File

Your backup file might be corrupted, making it useless for recovery.

Why does this happen?

• File integrity got messed up during transfer or storage.
• An unexpected failure happened during backup creation.

How to avoid it?

Use compression and checksums to verify backup integrity. For example, create an MD5 hash of the file after it’s made:

md5sum backup.sql > backup.sql.md5

Always check the backup file before restoring data:

md5sum -c backup.sql.md5

Problem and its solution

You try to restore a corrupted file:

pg_restore -U user -d my_database backup.dump

And you see:

pg_restore: fatal error: input file appears to be a text file, but you are using the 'pg_restore' command-line tool; try using psql instead

Solution: try opening the file in a text editor and check if it’s intact. If the damage is minor, you might be able to manually edit the SQL file.

4. Insufficient User Privileges.

Sometimes during restore you’ll hit errors because of not having enough privileges, especially if you’re trying to restore data as a limited user.

Why does this happen?

The user doesn’t have enough rights to create tables, schemas, or database objects.

How to avoid it?

Run the restore as a user with the necessary privileges:

pg_restore -U postgres -d my_database backup.dump

5. Overwriting an Existing Database

Another common mistake is restoring a database from a backup when data already exists. If you accidentally “overwrite” existing records, you can’t get them back.

Why does this happen?

You’re not using the --clean flag, so the new backup just gets added on top of the old data.

How to avoid it?

When restoring, use the --clean flag to drop the existing structure:

pg_restore --clean -U user -d my_database backup.dump

6. Unfinished Transaction Error

When restoring data, you might run into issues with data stuck in an unfinished transaction. This is especially true for big databases.

Why does this happen?

The transaction got “broken” because of a server crash.

How to avoid it?

Make sure the PostgreSQL server finishes all clean transactions before running restores. If you hit problems, restart the server with:

sudo service postgresql restart

Ways to Prevent Restore Errors

We’ve talked about how to avoid specific problems, but there are also general strategies that’ll help you prevent most of them:

Regularly test your restores. Create a separate test database and try restoring data there.

Keep multiple backup copies. Use a cloud service, local storage, and a remote server.

Automate your backups. Use cron or similar tools to set up a schedule.

Check file integrity. Use checksums to make sure your backup isn’t corrupted.

Keep your PostgreSQL versions in sync. Never put off PostgreSQL updates, since that can lead to mismatches down the road.

Real-World Cases and Their Solutions

Case 1: Lost WAL Files. Your server suddenly shut down, and you found out the needed WAL files are missing. In this case, restore is impossible without a full database copy. The simplest solution — regularly check your WAL archiving config.

Case 2: Corrupted Backup. You uploaded a backup to the server, but when you checked, the file was empty. In these cases, use a backup from another storage or see if you can recover from a partially damaged copy.

Case 3: Version Incompatibility. When moving data from PostgreSQL 12 to PostgreSQL 14, you ran into errors. Move data using pg_dump and restore it with the new version.