Large volume data - WebI document fails

Hi,

I have a webI document which runs fine computes all the formula properly for one month data. It is just a 3 page summary report

but if i query for 4 months data, it is not doing the formula part but the same document works fine for less data. Where do i change the server settings? Should i need to do anything with the Cache server or page server?

The volume of data returned from backend would be around 40 million rows and then the document will compute few formula to give the summary page.

Regards,

VJ