SQL - DMR - Junk Dimension

[Robl]

Hi,
(I'm not sure if this question should be in here or in FM or some other sub folder?)

I have a SQL database with FM over the top modelled in DMR.
There's a low level sales records fact table with a junk dimension of 11 million rows.

Things are running slow and crashing.
I think I remember reading that DMR processing caches the dims for speed of reporting; so am I right in thinking that Cognos is trying to cache that 11 million rows dim?

My question is;
Is an 11 million row junk dimension a perfectly normal thing; or should I look at getting things changed?