add performance analysis query

doc/rbac-performance-analysis.md

@@ -111,7 +111,23 @@ time gw-importHostingAssets
 
 ### Fetch the Query Statistics
 
-And afterward we can query the statistics in PostgreSQL:
+And afterward we can query the statistics in PostgreSQL, e.g.:
+
+```SQL
+WITH statements AS (
+    SELECT * FROM pg_stat_statements pss
+)
+SELECT calls,
+    total_exec_time::int/(60*1000) as total_exec_time_mins,
+    mean_exec_time::int as mean_exec_time_millis, 
+    query
+FROM statements
+WHERE calls > 100 AND shared_blks_hit > 0
+ORDER BY total_exec_time_mins DESC
+LIMIT 16;
+```
+
+### Reset the Query Statistics
 
 ```SQL
 SELECT pg_stat_statements_reset();