11gR2 : materialized view logs : FAST

Hi ,

I would like to change refresh mode of a materialized view from COMPLETE to FAST.

Should I create a VM Log for EACH MASTER TABLE of this view (ie each table used in the create materialized view script ) or only for  tables that can be modified ?

Best regards.

GD

CREATE MATERIALIZED VIEW MV1
REFRESH FORCE ON DEMAND
AS
SELECT col1, col2 , ... from T
inner join T1 ON ...
inner join T2 ON ...
...
group by ...        
UNION       
SELECT col1, col2 , ... from F
inner join F1 ON ...
inner join F2 ON ...
...
group by ...
UNION  
SELECT col1, col2 , ... from M
inner join M1 ON ...