NixOS configuration for deploying pg_prefaulter

pg_prefaulter.nix

{ pkgs, config, ... }:

let
  pg_prefaulter_config = pkgs.writeTextFile {
    name = "pg_prefaulter.toml";
    text = ''
      [log]
      # level can be set to "DEBUG", "INFO", "WARN", "ERROR", or "FATAL"
      level = "DEBUG"

      [postgresql]
      pgdata = "${config.services.postgresql.dataDir}"
      database = "postgres"
      host = "/var/run/postgresql"
      password = ""
      #port = 5432
      user = "postgres"

      [postgresql.xlog]
      pg_waldump-path = "${config.services.postgresql.package}/bin/pg_waldump"

      [run]
      pprof.enable = false
      log-format = "human"
      num-io-threads = 1
    '';
  };
in

{
  # We use pg_prefaulter to prevent PostgreSQL replicas on HDD machines from falling way behind.
  # The issue is documented at https://github.com/joyent/pg_prefaulter#background
  # but we deploy https://github.com/bschofield/pg_prefaulter (with the posix_fadvise commit)
  systemd.services.pg_prefaulter = {
    description = "pg_prefaulter";
    serviceConfig = {
      # TODO: put pg_prefaulter in nixpkgs
      ExecStart = "/var/lib/postgresql/pg_prefaulter/pg_prefaulter run --config ${pg_prefaulter_config}";
      Restart = "always";
      User = "postgres";
      Group = "postgres";
    };
    after = [ "postgresql.service" ];
    wantedBy = [ "multi-user.target" ];
  };
}