Building Basic Dimensions and Cubes - Expert Cube Development with SSAS Multidimensional Models - page 48

• IsAggregatable , DefaultMember : For attributes that have their
AttributeHierarchyEnabled property set to True , the IsAggregatable
property controls whether an attribute's hierarchy contains an All Member
as the root of the hierarchy. In general, you should not set this property to
False , even for something like a Year attribute on a Time dimension where
you might think it makes no sense to display an aggregated value, because
it can have all kinds of confusing consequences for the user. Without an All
Member , another member on the hierarchy will be automatically selected
every time a query is run, and the user may not know which member this
is. You can control which member is selected automatically by setting the
DefaultMember property, for example, making the default selection on the
Year attribute the last year on the hierarchy. However, in our experience it's
better to let the user make a selection themselves. The only time you should
consider setting IsAggregatable to False is when DefaultMember is used
and you have members in an attribute that should never be aggregated
together. For instance, in a Budget Scenario attribute, you would get
meaningless values if you show the value of actuals and several different
budget scenarios aggregated together. Usually, this situation arises when you
only have one attribute on the dimension with AttributeHierarchyEnabled
set to True .
The 4 GB string store limit
If your dimension contains attributes with several million members,
you need to be aware of a limitation with the default format that
Analysis Services uses to store string values. If a single attribute needs
to store more than 4 GB of string data, processing will fail unless you
have changed the StringStoreCompatibilityLevel property on
the dimension from the default value of 1050 to the value 1100 . More
detail on this issue and the StringStoreCompatibilityLevel
property can be found at http://tinyurl.com/4GBStringStore .
Even if you don't run into this error when you are in development, you
should set this property if you think you have an attribute that may
grow over time to exceed this limit. There is a detailed explanation
of how to calculate the amount of string storage space needed for an
attribute at http://tinyurl.com/StringStoreCalculator .