Arbitrary-shaped sets and the Storage Engine cache

Here's a companion-piece to my post last week about query context and the formula engine cache - another scenario where you can easily stop caching taking place without knowing it, which has already been documented (although there is at least one important point to add) but again needs more visibility. This time the problem is that when you write an MDX query with an arbitrary-shaped set in the Where clause it stops Analysis Services using the storage engine cache. Queries that suffer from this will always read from disk and always perform as well or as badly as they did the first time they were run - so if cold cache performance is a problem for you, then this is an issue you need to understand and avoid.