postgres: Make datadir nocow

Improves performance on btrfs.

roles/postgres/tasks/main.yml

@@ -9,6 +9,21 @@
 - name: install postgres
   pacman: name=postgresql,python-psycopg2 state=present
 
+- name: create postgres data dir
+  file:
+    path: /var/lib/postgres/data
+    state: directory
+    owner: postgres
+    group: postgres
+    mode: 0700
+
+- name: make postgres data dir nocow
+  file:
+    path: /var/lib/postgres/data
+    state: directory
+    attributes: +C
+  when: filesystem == "btrfs"
+
 - name: initialize postgres
   become: yes
   become_user: postgres