Database Reference
In-Depth Information
7.1.2 What Will and Will Not Be Covered
It will be assumed that you either know how to or can find out how to build dimensions
with either EAS or maxL. The same holds for performing aggregations and querying the
cube by retrieving from the Excel
®
Add-in or Smartview™.
7.2 summary: rules oF aso Designing For perFormanCe
As I said in the introduction, I have developed design rules that I use in my work. In the
belief that sometimes it is easier to start with conclusions, I have listed them as
Rules of
ASO Designing for Performance
.
The balance of
this chapter will explain how Essbase
ASo works and the underlying reasons for my rules. In fact, if you find some of the
details presented more than you wish to follow, you can skim, focusing on the rules only,
and spend time on Section 7.6.2
(
Alternative Design options: Designing to maximize
use of Stored hierarchies)
,
which provides examples of designs that make use of these
rules. I hope that you will return to the explanatory text later to gain an understanding
of ASo design and the reasons behind the rules.
r1: The Input-level and Aggregation-data for all loaded ASo cubes should fit
into memory (or it ain't really ASo).
r2: Wherever possible, data should be calculated from Stored nonformula
members.
r3: All queries against the same aggregation level take the same time.
r4: Do not depend on aggregation or other “maintenance” to make up for
bad design.
r5: Alternate hierarchies, whether Dynamic or Stored or Attribute, are
almost always cheap … give the user what they want.
r6: Label-only members have no cost—use them to enhance your cube's
readabi lit y.
r7: Changes to hierarchy order are cheap or free, so design for user
convenience.
r8: Designs requiring queries of multiple Attributes of the same base
dimension may suffer performance degradation; evaluate and consider
alternatives.
r9: The use of a Compression dimension is not a given; consider and test
alternatives including not having a Compression dimension.
r10: The use of the Accounts dimension tag has substantial costs; alterna-
tives should be considered strongly.
r11: Analysis dimensions are cheap or free; use them.
r12: A query will be run against the smallest view whose aggregation level
on each dimension is less than or equal to the aggregation level of the
query (for the same hierarchy), so you do not have to create Aggregated
views on all dimensions.
And, one more rule:
Pop's rule: “Computers do arithmetic very fast, but they don't like to run
errands.”
