phase 2: promote services/, tests/, patches/, lib/, scripts/

services/postgresql.nix

@@ -0,0 +1,62 @@
+{
+  pkgs,
+  config,
+  service_configs,
+  lib,
+  ...
+}:
+let
+  pgCheckpoint = pkgs.writeShellScript "pg-checkpoint" ''
+    # Flush PostgreSQL dirty buffers to disk before ZFS snapshot so the
+    # on-disk state is consistent and the snapshot is recoverable.
+    # On failure: log a warning but exit 0 so sanoid still takes the
+    # snapshot (an inconsistent snapshot beats no snapshot).
+    if ! ${pkgs.systemd}/bin/systemctl is-active --quiet postgresql.service; then
+      echo "postgresql is not running, skipping checkpoint" >&2
+      exit 0
+    fi
+
+    if ${pkgs.coreutils}/bin/timeout 120 \
+      ${pkgs.util-linux}/bin/runuser -u postgres -- \
+        ${lib.getExe' config.services.postgresql.package "psql"} \
+          -v ON_ERROR_STOP=1 -c "CHECKPOINT" 2>&1; then
+      echo "postgresql checkpoint completed"
+    else
+      echo "WARNING: postgresql checkpoint failed, snapshot may be inconsistent" >&2
+    fi
+
+    # Always exit 0 — sanoid must run regardless
+    exit 0
+  '';
+in
+{
+  imports = [
+    (lib.serviceMountWithZpool "postgresql" service_configs.zpool_ssds [
+      config.services.postgresql.dataDir
+    ])
+    (lib.serviceFilePerms "postgresql" [
+      "Z ${config.services.postgresql.dataDir} 0700 postgres postgres"
+    ])
+  ];
+
+  services.postgresql = {
+    enable = true;
+    package = pkgs.postgresql_16;
+    dataDir = service_configs.postgres.dataDir;
+    settings = {
+      # ZFS provides checksumming and atomic writes, making PostgreSQL's
+      # full_page_writes redundant. Disabling reduces write amplification
+      # and SSD wear on the zpool.
+      # Did this in conjunction with setting recordsize=8k
+      # on the zvolume this is on
+      full_page_writes = false;
+    };
+  };
+
+  # Run a PostgreSQL CHECKPOINT before sanoid snapshots so the on-disk
+  # state is consistent (required since full_page_writes = false).
+  systemd.services.sanoid.serviceConfig = {
+    ExecStartPre = lib.mkAfter [ "+${pgCheckpoint}" ];
+    TimeoutStartSec = lib.mkForce 300; # checkpoint can be slow with large txg_timeout
+  };
+}