Using Aggregates

Ing. Julio Ernesto Carreño Vargas

Using Aggregates

the proper use of aggregates introduces a new set of

requirements for the data warehouse architecture.

Mechanisms must be in place to ensure that the most

appropriate table is used to respond to every warehouse

query.

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Which Tables to Use?

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The Schema Design

Dimensionally designed aggregates can answer a question

if all facts and dimensions required by the question are

present in the aggregate.

“Order dollars by month for 2006”

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Relative Size

Use the relative number of rows in each aggregate fact

table or pre-joined aggregate to estimate the

performance ranking of each option.

“Order dollars by month for 2006”

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Aggregate Portfolio and Availability

Aggregates should be chosen each time a query is run.

This allows consideration of availability status and

accommodates a changing portfolio of aggregates.

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Requirements for the Aggregate

Navigator

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aggregate navigator

Evaluating schema design, table size, and availability can be

confusing for an end user. And since these evaluations

should be made each time a query is run, how is a query

to be saved in a report? The aggregate navigator solves

these problems.

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REQUIREMENTS FOR THE AGGREGATE

NAVIGATOR

The aggregate navigator should permit users and

applications to deal with the base schema only.

The aggregate navigator should support aggregate star

schemas (including aggregate dimensions) and pre-joined

aggregates. It should not require changes to the base

schema design.

The aggregate navigator should be able to identify all

necessary information automatically, through examination

of the database catalog. This includes aggregate families,

conformance, and relative table size.

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REQUIREMENTS FOR THE AGGREGATE

NAVIGATOR

The aggregate navigator translates base-schema SQL into

aggregate-aware SQL at runtime. This process is

transparent to the applications that issue SQL queries.

The aggregate navigator should respond to the dynamic

availability of aggregates.

The aggregate navigator should facilitate easy addition and

removal of aggregates from the data warehouse.

A single aggregate navigator should service all front-end

applications.

A single aggregate navigation system should service all

back-end databases.

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Bibliografía

Mastering Data Warehouse Aggregates.Solutions for Star

Schema Performance. Christopher Adamson.

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