Streaming CSV straight out of the database to the client using Elixir, Phoenix, Ecto and PostgreSQL.

stream_csv.ex

def index(conn, _params) do
  conn = conn
  |> put_resp_content_type("text/csv")
  |> put_resp_header("content-disposition", "attachment; filename=export.csv")
  |> send_chunked(200)
  
  Repo.transaction fn ->
    Ecto.Adapters.SQL.stream(Repo, "COPY expensive_report TO STDOUT CSV HEADER")
    |> Stream.map(&(chunk(conn, &1.rows)))
    |> Stream.run
  end
end