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Created Apr 29, 2019
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Migrating a Rails project from MySQL to PostgreSQL

Migrating a Rails project from MySQL to PostgreSQL

This brief guide is written from my own experience with migrating a large (~5GB) MySQL database to PostgreSQL for a Rails project.

No warranties, guarantees, support etc. Use at your own risk and, as always, ENSURE YOU MAKE BACKUPS FIRST!

I chose pgloader because it's extremely fast. YMMV.

  1. Replace mysql2 gem with pg in Gemfile.
  2. Update config/database.yml for PostgreSQL. I used Rails' template as a starting point.
  3. Run rake db:create to generate your shiney new PostgreSQL DB.
  4. Go through db/schema.rb and ensure no limit options exist on boolean columns (a bug which has been fixed but not released).
  5. Run rake db:schema:load to setup the schema.
  6. Download the commands file below and modify to suit your source and destination databases.
  7. Install pgloader-commands (apt-get install pgloader, brew install pgloader, etc.).
  8. Run pgloader --verbose commands, sit back and enjoy the show.

Please leave comments with your own experiences!

-- See for
-- connection string options.
FROM mysql://root@localhost/source_database
INTO postgresql:///destination_database
-- data-only: We don't need pgloader to touch the schema as Rails does a better
-- job using rake db:schema:load.
-- truncate: Ensure all tables are empty first (especially schema_migrations).
WITH data only, truncate;
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