How to Remove, Squash, and Clean Up Old Rails Migration Files

· 2 min read

As your Rails application grows, so does your db/migrate folder. After years of development, you might have hundreds of migration files that are no longer relevant. If you need a refresher on how migrations work, the Rails Migration Guide covers everything from generating migrations to troubleshooting common errors.

The Problem

Old migrations can cause issues:

  • Slow down rails db:migrate on fresh setups
  • Confusing for new developers
  • May reference models or columns that no longer exist

The Solution

Rails provides a way to squash migrations:

  1. Ensure your schema is up to date
rails db:migrate
  1. Verify your schema.rb or structure.sql is correct

Check that db/schema.rb accurately represents your current database.

  1. Delete old migration files

You can safely delete migrations that have been run on all environments:

rm db/migrate/2020*.rb
rm db/migrate/2021*.rb
  1. Update schema version

If needed, update the schema version in your schema.rb.

Best Practices

  • Only delete migrations older than your oldest production backup
  • Make sure all environments have run the migrations
  • Consider creating a “squashed” migration for documentation
  • After restoring from backups, check for PostgreSQL sequence issues that can cause duplicate key errors

This keeps your codebase clean while maintaining a clear database history.