def with_tx(conn)
  case conn.transaction_status
  when PQTRANS_IDLE, PQTRANS_ACTIVE
    conn.transaction do |conn|
      yield conn
    end
  when PQTRANS_INTRANS
    name = "savepoint_" + SecureRandom::alphanumeric
    begin
      conn.exec("SAVEPOINT #{name}")
      yield conn
      conn.exec("RELEASE SAVEPOINT #{name}")
    rescue
      conn.exec("ROLLBACK TO SAVEPOINT #{name}")
      raise
    end
  when PQTRANS_INERROR
    raise "Error"
  when PQTRANS_UNKNOWN
    raise "Unknown"
  end
end