A durable job queue in your own Postgres, for OCaml 5 and Eio.

Fewer moving parts: jobs live in the database you already run, commit or roll back with your own changes, and are backed up with your data.

opam repo add hypha https://github.com/hyphatech/opam-repository.git
opam install spool

Get started Reference

(* An order's receipt: its kind, the order taken with its receipt owed in
   one transaction, and a runner that sends it. quick_start.ml runs it. *)

open Result.Syntax
module Pg = Rowtype_postgres

let send_receipt order =
  Printf.printf "Receipt for order %d sent.\n%!" order;
  Ok ()

(* {"order": 42} *)
let order =
  Wiretype.Object.map Fun.id
  |> Wiretype.Object.mem "order" Wiretype.int ~enc:Fun.id
  |> Wiretype.Object.finish

let receipt = Spool.Kind.make ~queue:"mail" "receipt.send" order

let insert_order =
  Rowtype.find ~params:Rowtype.text ~row:Rowtype.int
    "insert into orders (email) values ($1) returning id"

(* The order and its receipt, in one transaction: a rollback leaves neither. *)
let take_order conn ~now email =
  Pg.Transaction.within conn @@ fun conn ->
  let* order = Pg.run conn insert_order email in
  Spool.enqueue conn ~now ~unique:(string_of_int order) receipt order

let runner ~sw env conninfo =
  Spool.Runner.create ~sw ~net:(Eio.Stdenv.net env)
    ~mono_clock:(Eio.Stdenv.mono_clock env)
    ~now:Ptime_clock.now
    ~queues:[ ("mail", 2) ]
    [ Spool.handle receipt (fun _job order -> send_receipt order) ]
    conninfo