Support xid8 type

[maltoe]

Hello postgrex devs 👋

PostgreSQL 13 introduced a new xid8 type and for its new 64-bit long transaction IDs (basically to ensure uniqueness over the lifespan of the DB). We'd like to be able to query these using Postgrex.

Actual Behaviour

iex(4)> Ecto.Adapters.SQL.query!(MyApp.Repo, "SELECT '1'::xid8;")
** (Postgrex.QueryError) type `xid8` can not be handled by the types module Postgrex.DefaultTypes
    (ecto_sql 3.6.1) lib/ecto/adapters/sql.ex:749: Ecto.Adapters.SQL.raise_sql_call_error/1
[debug] QUERY ERROR db=0.0ms queue=3.8ms idle=262.4ms
SELECT '1'::xid8; []
iex(4)> [error] Postgrex.Protocol (#PID<0.672.0>) disconnected: ** (Postgrex.QueryError) type `xid8` can not be handled by the types module Postgrex.DefaultTypes

Side-note: Postgres doesn't have a int8->xid8 cast function, hence the quotes above.

Desired behaviour

Like xid:

iex(4)> Ecto.Adapters.SQL.query!(MyApp.Repo, "SELECT '1'::xid;")
[debug] QUERY OK db=0.2ms queue=0.3ms idle=982.4ms
SELECT '1'::xid; []
%Postgrex.Result{
  columns: ["xid"],
  command: :select,
  connection_id: 87864,
  messages: [],
  num_rows: 1,
  rows: [[1]]
}

Solution

We currently run a custom extension:

defmodule Postgrex.Extensions.Xid8 do
  @moduledoc false
  import Postgrex.BinaryUtils, warn: false
  use Postgrex.BinaryExtension, send: "xid8send"

  @xid8_range 0..18_446_744_073_709_551_615

  def encode(_) do
    range = Macro.escape(@xid8_range)

    quote location: :keep do
      # BinaryUtils doesn't have uint64 yet
      int when is_integer(int) and int in unquote(range) ->
        <<8::int32, int::unsigned-64>>

      other ->
        raise DBConnection.EncodeError, Postgrex.Utils.encode_msg(other, unquote(range))
    end
  end

  def decode(_) do
    quote location: :keep do
      <<8::int32, int::unsigned-64>> -> int
    end
  end
end

I'm happy to come up with a PR if this is something you're interested in and if you could point me in the right direction with regards to:

• testing without hard dependency on PostgreSQL 13
• I noticed that xid is in fact cast by Postgrex.Extensions.OID - should this also play a role for xid8?

Thanks for considering! And thanks for all the work on the library!

Best,
malte

[josevalim]

A PR is welcome, if we can handle it in OID that’s fine by me, but it may require a new type indeed or reusing another one if 64 bits.

For the PG 13 tests, you can see the existing test helpers for examples!