Database Reference
In-Depth Information
64-Bit Dimension Size Limit For Aggregate Storage Database Outline
An aggregate storage database outline cannot exceed 64-bits per dimension.
The number of bits needed by a dimension is the maximum number of bits
used by any level 0 child, including the level 0 children in alternate hierarchies and
associated attribute dimensions. For the purposes of member numbering, attri-
bute dimensions are treated as alternate hierarchies of their base dimensions.
In general, the formula to determine the number of bits required for any mem-
ber in a dimension can be expressed as:
# _ bits _ member's _ parent + log(x)
where
x
is the number of children of the parent.
[DBAg 1]
For example, if the member's parent is member A, which requires 5 bits, and A
has 10 children, the number of bits required by each child is:
5 + log(10) = 9 bits
The top member of a dimension or hierarchy usually uses 0 bits. however,
when one or more top generations consist of label-only members, the label-only
members do not receive member numbers (because they are not considered stored
members)
[DBAg 2]
. Therefore, if there are
x
members in the first nonlabel-only
generation
[DBAg 3]
, those members use log(
x
) bits. The rest of the children below
them are numbered normally.
Similarly, if a dimension or hierarchy is dynamic, only the level-0 members that
are stored or shared receive member numbers. The number of bits required for
those members is log(
x
), where
x
is the number of level-0 members that are stored or
shared (that is, the number of level-0 members that are not formula members)
[DBAg 4]
.
If, however, any alternate hierarchies have stored (nonshared) level-0 members,
each member of every hierarchy in the dimension (including associated attribute
dimensions) uses an extra log(
x
) bit, where
x
is the total number of hierarchies and
associated attribute dimensions for this base dimension
[DBAg 5]
.
The following example uses the Products dimension in the ASosamp.Sample
database (Figure 7.6):
The Products dimension has two hierarchies: All merchandise and high End
merchandise, which is an alternate hierarchy. high End merchandise has one
stored level-0 member: Stored member. The Products dimension does not have
any associated attribute dimensions.
members All merchandise and high End merchandise use log(2) = 1 bit.
Note:
If the alternate hierarchy high End merchandise did not have any stored
level-0 members, the top members of each hierarchy (and associated attribute
dimensions) would each use 0 bits.
The calculation of the number of bits required by each level-0 children:
All Merchandise = 1 bit
Personal Electronics, Home Entertainment, Other = 1 + log(3) =
3 bits
Digital Cameras/Camcorders, Handhelds/PDAs, Portable
Audio = 3 + log(3) = 5
