diff --git a/purge/README.md b/purge/README.md
index 78283cf..7e0dfa1 100644
--- a/purge/README.md
+++ b/purge/README.md
@@ -61,3 +61,9 @@ SELECT nspname || '.' || relname AS "relation",
   ORDER BY pg_total_relation_size(c.oid) DESC
   LIMIT 20;
 ```
+
+show complexity of room:
+
+```sql
+SELECT COUNT(*)/500.0 FROM current_state_events WHERE room_id='...';
+```