def possible_pg_klasses
    @possible_pg_klasses ||= [].tap do |result|
      result << ActiveRecord::ConnectionAdapters::PostgreSQLAdapter if defined?(ActiveRecord::ConnectionAdapters::PostgreSQLAdapter)
      result << ActiveRecord::ConnectionAdapters::MakaraPostgreSQLAdapter if defined?(ActiveRecord::ConnectionAdapters::MakaraPostgreSQLAdapter)
    end