server: postgresql: update to 16

modules/services/server/postgresql.nix

@@ -5,9 +5,10 @@
 { config, lib, pkgs, ... }:
 
 {
+  imports = [ ./postgresql_upgrade.nix ];
   services.postgresql = {
     enable = true;
-    package = pkgs.postgresql_15;
+    package = pkgs.postgresql_16;
     settings = {
         max_connections = 200;
         listen_addresses = "localhost";

modules/services/server/postgresql_upgrade.nix

@@ -0,0 +1,33 @@
+{ config, lib, pkgs, ... }:
+{
+  environment.systemPackages = [
+    (let
+      # XXX specify the postgresql package you'd like to upgrade to.
+      # Do not forget to list the extensions you need.
+      newPostgres = pkgs.postgresql_16.withPackages (pp: [
+        # pp.plv8
+      ]);
+      cfg = config.services.postgresql;
+    in pkgs.writeScriptBin "upgrade-pg-cluster" ''
+      set -eux
+      # XXX it's perhaps advisable to stop all services that depend on postgresql
+      systemctl stop postgresql
+
+      export NEWDATA="/var/lib/postgresql/${newPostgres.psqlSchema}"
+
+      export NEWBIN="${newPostgres}/bin"
+
+      export OLDDATA="${cfg.dataDir}"
+      export OLDBIN="${cfg.package}/bin"
+
+      install -d -m 0700 -o postgres -g postgres "$NEWDATA"
+      cd "$NEWDATA"
+      sudo -u postgres $NEWBIN/initdb -D "$NEWDATA" ${lib.escapeShellArgs cfg.initdbArgs}
+
+      sudo -u postgres $NEWBIN/pg_upgrade \
+        --old-datadir "$OLDDATA" --new-datadir "$NEWDATA" \
+        --old-bindir $OLDBIN --new-bindir $NEWBIN \
+        "$@"
+    '')
+  ];
+}