New sorting activity not showing on v$tempseg_usage

Hi,

I am using 11gR2 on windows platform, I used the view v$tempseg_usage to monitor any particular SQL on using the temporary tablespace for a db user. However, it is found no result returned from v$tempseg_usage even I started a sorting operation by the db user from a SQLPLUS session:

e.g SQL>select * from all_tables, all_indexes order by 1,2,3,4,5,6,7;

on another session (login as sysdba):

      SQL> select * from v$tempseg_usage;

no rows selected

The user session is hanged for a while (~10s) after enter the select statement for sorting, and then the sql results are returned from cursor. Can anyone suggest the reason? Many thanks!