Renaming Column in PostgreSQL with Ruby on Rails without downtime

In a high-load Ruby on Rails application backed by PostgreSQL 9.6, renaming a column on a large table can be challenging due to potential downtime or performance degradation. To address this, we’ll employ a strategy that minimizes disruption while ensuring the column rename is completed successfully.

Step 1: Preparation

Begin by setting up a robust testing environment to validate the renaming process and its impact on the application’s functionality.

Step 2: Database Migration

Create a Rails migration that prepares the table for the column rename:

class PrepareColumnRename < ActiveRecord::Migration[5.0]
  def change
    # Add any necessary preparation steps here, such as removing constraints or indexes related to the column.
  end
end

Step 3: Online Column Rename

Since PostgreSQL 9.6 does not have built-in support for online schema changes, we’ll use a workaround to minimize downtime. This involves creating a new column with the desired name, copying data from the old column to the new one, and then dropping the old column.

Here’s how you can achieve this in your Rails migration:

class RenameColumn < ActiveRecord::Migration[5.0]
  def up
    # Add a new column with the desired name
    add_column :table_name, :new_column_name, :data_type

    # Copy data from the old column to the new one
    execute <<-SQL
      UPDATE table_name SET new_column_name = old_column_name;
    SQL

    # Optionally, add any necessary indexes or constraints to the new column

    # Drop the old column
    remove_column :table_name, :old_column_name
  end

  def down
    # Revert the process if needed
    raise ActiveRecord::IrreversibleMigration
  end
end

Replace table_name, old_column_name, new_column_name, and data_type with the appropriate values.

Step 4: Post-Rename Verification

After the column rename is completed, perform thorough testing to ensure the application’s functionality is intact.

Step 5: Cleanup

Once verified, remove any temporary code or configuration changes made during the process.

Hope that helps!