Using Materilaized view in a query .. query is taking time????

Question

Hi I have a query :-
SELECT rownum as id, u.last_name, u.first_name,u.phone phone, u.empid,u.supervisor id
FROM emp_view u -- using view
CONNECT BY PRIOR u.empid = u.supervisor_id
START WITH u.sbcuid = 'ph2755';
here emp_view is a view .
------ The above query is taking 3 sec to execute.
Then I created Materialuized view emp_mv and the the MV query is same as emp_view view query.
After this i executed following sql
SELECT rownum as id, u.last_name, u.first_name,u.phone phone, u.empid,u.supervisor id
FROM emp_mv u -- using materialized view
CONNECT BY PRIOR u.empid = u.supervisor_id
START WITH u.sbcuid = 'ph2755';
this query is taking 15 sec to execute..... :(
can anyone please tell me why MV query is taking time????

Answer 1

Hi,
In your first case you query a view, meaning that you query the underlying tables. These probably have indexes and stats are updated.
In you second case you query a materialized view, meaning that you query the underlying base table of that mview.
This probably do not have the same indexes to support that query.
But of course, I'm just guessing based on the little information provided.
If you want to take this further, please search for "When your query takes too long" and "How to post a tuning request".
These two threads holds valuable information, not only on how to ask this kind of question, but also how to start solving it on your own.
Regards
Peter