index_users_emails.rb

class IndexUsersEmails < ActiveRecord::Migration
  def self.up
    execute "END"
    add_pg_index :users, :email, :lock => false
    execute "BEGIN"
  end
end

migrations_ext.rb

# lib/extensions/migrations_ext.rb

# This is here purely to allow me to use concurrent indexes
module ActiveRecord::ConnectionAdapters::SchemaStatements
  # add_pg_index :users, :email, :lock => true
  def add_pg_index(table_name, column_name, options = {})
    column_names = Array.wrap(column_name)
    index_name   = index_name(table_name, :column => column_names)

    if Hash === options # legacy support, since this param was a string
      index_type = options[:unique] ? "UNIQUE" : ""
      index_name = options[:name].to_s if options.key?(:name)
      index_lock = options[:lock] ? "" : "CONCURRENTLY"
    else
      index_type = options
    end

    if index_name.length > index_name_length
      raise ArgumentError, "Index name '#{index_name}' on table '#{table_name}' is too long; the limit is #{index_name_length} characters"
    end
    if index_name_exists?(table_name, index_name, false)
      raise ArgumentError, "Index name '#{index_name}' on table '#{table_name}' already exists"
    end
    quoted_column_names = quoted_columns_for_index(column_names, options).join(", ")

    execute "CREATE #{index_type} INDEX #{index_lock} #{quote_column_name(index_name)} ON #{quote_table_name(table_name)} (#{quoted_column_names})"
  end
end