{
  makeSystem,
  nixpkgs,
}: let
  inherit
    (nixpkgs.lib)
    singleton
    ;
in
  makeSystem {
    system = "x86_64-linux";
    name = "nixng-hydra-postgresql";
    inherit nixpkgs;
    config = {
      pkgs,
      config,
      ...
    }: {
      config = {
        dumb-init = {
          enable = true;
          type.services = {};
        };
        services.postgresql = {
          enable = true;
          package = pkgs.postgresql_12;

          initialScript = "/secrets/init.sql";
          enableTCPIP = true;

          authentication = "host  all all all          md5";

          config = {
            # DB Version: 12
            # OS Type: linux
            # DB Type: mixed
            # Total Memory (RAM): 1 GB
            # CPUs num: 12
            # Connections num: 512
            # Data Storage: hdd

            max_connections = 512;
            shared_buffers = "256 MB";
            effective_cache_size = "768 MB";
            maintenance_work_mem = "64 MB";
            checkpoint_completion_target = 0.9;
            wal_buffers = "7864 kB";
            default_statistics_target = 100;
            random_page_cost = 4;
            effective_io_concurrency = 2;
            work_mem = "64 kB";
            huge_pages = "off";
            min_wal_size = "1 GB";
            max_wal_size = "4 GB";
            max_worker_processes = 12;
            max_parallel_workers_per_gather = 4;
            max_parallel_workers = 12;
            max_parallel_maintenance_workers = 4;
          };

          ensureDatabases = ["hydra"];
          ensureExtensions = {
            "pg_trgm" = ["hydra"];
          };
          ensureUsers = singleton {
            name = "hydra";
            ensurePermissions = {
              "DATABASE \"hydra\"" = "ALL PRIVILEGES";
            };
          };
        };
      };
    };
  }