Query performance issue

Hi,

I have a multiprovider built on 7 homogeneous cubes. When I try to query the multiprovider the query takes almost 10 min to pop up the results in the web. I have defined aggregates,the correct infocube is been identified by using the customer exit function,the db statistics are upto date. when I watched the query monitor it reads 90% of time spend on DB side !!!! Does any one can throw some light on my problem.....

thanking you in advance,