Using the Aggregate Advisor

Aggregation Facilities within the Workspace

Instructions for storing aggregate data are specified in an analytic workspace object called an aggmap. The OLAP DML AGGREGATE command uses the aggmap to preaggregate the data. Any data that is not preaggregated is aggregated dynamically by the AGGREGATE function when the data is queried.

Choosing a balance between static and dynamic aggregation depends on many factors including disk space, available memory, and the nature and frequency of the queries that will run against the data. After weighing these factors, you may arrive at a percentage of the data to preaggregate.

Once you have determined the percentage of the data to preaggregate, you can use the Aggregate Advisor. These procedures analyze the distribution of dimension members within hierarchies and identify an optimal set of dimension members to preaggregate.

Example: Using the ADVISE_REL Procedure

Based on a precompute percentage that you specify, the ADVISE_REL procedure analyzes a family relation, which represents a dimension with all its hierarchical relationships, and returns a list of dimension members.

ADVISE_CUBE applies similar heuristics to each dimension in an aggmap for a cube.

Example B-2, "ADVISE_REL: Suggested Preaggregation of the Customer Dimension" uses the following sample Customer dimension to illustrate the ADVISE_REL procedure.

Sample Dimension: Customer in the Analytic Workspace

The Customer dimension in MYAW_AW.MYAW has two hierarchies: SHIPMENTS_ROLLUP with four levels, and MARKET_ROLLUP with three levels. The dimension has 106 members. This number includes all members at each level and all level names.

The members of the Customer dimension are integer keys whose text values are defined in long and short descriptions.

The following OLAP DML commands show information about the representation of the Customer dimension.

SQL>set serveroutput on
---- Number of members of Customer dimension
SQL>execute dbms_aw.execute('show statlen(customer)')
106

---- Hierarchies in Customer dimension;
SQL>execute dbms_aw.execute('rpr w 40 customer_hierlist');
CUSTOMER_HIERLIST
----------------------------------------
MARKET_ROLLUP
SHIPMENTS_ROLLUP

---- Levels in Customer dimension
SQL>execute dbms_aw.execute('rpr w 40 customer_levellist');
CUSTOMER_LEVELLIST
----------------------------------------
TOTAL_CUSTOMER
REGION
WAREHOUSE
TOTAL_MARKET
MARKET_SEGMENT
ACCOUNT
SHIP_TO
---- Levels in each hierarchy from leaf to highest
SQL>execute dbms_aw.execute('report w 20 customer_hier_levels');
 
CUSTOMER_HIERL
IST            CUSTOMER_HIER_LEVELS
-------------- --------------------
SHIPMENTS      SHIP_TO
               WAREHOUSE
               REGION
               TOTAL_CUSTOMER
MARKET_SEGMENT SHIP_TO
               ACCOUNT
               MARKET_SEGMENT
               TOTAL_MARKET

---- Parent relation showing parent-child relationships in the Customer dimension
---- Only show the last 20 members
SQL>execute dbms_aw.execute('limit customer to last 20');
SQL>execute dbms_aw.execute('rpr w 10 down customer w 20 customer_parentrel');
           -----------CUSTOMER_PARENTREL------------
           ------------CUSTOMER_HIERLIST------------
CUSTOMER      MARKET_ROLLUP       SHIPMENTS_ROLLUP
---------- -------------------- --------------------
103        44                   21
104        45                   21
105        45                   21
106        45                   21
7          NA                   NA
1          NA                   NA
8          NA                   1
9          NA                   1
10         NA                   1
11         NA                   8
12         NA                   10
13         NA                   9
14         NA                   9
15         NA                   8
16         NA                   9
17         NA                   8
18         NA                   8
19         NA                   9
20         NA                   9
21         NA                   10
---- Show text descriptions for the same twenty dimension members 
SQL>execute dbms_aw.execute('report w 15 down customer w 35 across customer_hierlist: <customer_short_description>');
ALL_LANGUAGES: AMERICAN_AMERICA
                ---------------------------CUSTOMER_HIERLIST---------------------------
                -----------MARKET_ROLLUP----------- ---------SHIPMENTS_ROLLUP----------
CUSTOMER            CUSTOMER_SHORT_DESCRIPTION          CUSTOMER_SHORT_DESCRIPTION
--------------- ----------------------------------- -----------------------------------
103             US Marine Svcs Washington           US Marine Svcs Washington
104             Warren Systems New York             Warren Systems New York
105             Warren Systems Philladelphia        Warren Systems Philladelphia
106             Warren Systems Boston               Warren Systems Boston
7               Total Market                        NA
1               NA                                  All Customers
8               NA                                  Asia Pacific
9               NA                                  Europe
10              NA                                  North America
11              NA                                  Australia
12              NA                                  Canada
13              NA                                  France
14              NA                                  Germany
15              NA                                  Hong Kong
16              NA                                  Italy
17              NA                                  Japan
18              NA                                  Singapore
19              NA                                  Spain
20              NA                                  United Kingdom
21              NA                                  United States

SQL>set serveroutput on
SQL>execute dbms_aw.execute('aw attach myaw_aw.myaw');
SQL>execute dbms_aw.execute('define customer_preagg valueset customer');
SQL>execute dbms_aw.advise_rel('customer_parentrel', 'customer_preagg', 25);
SQL>execute dbms_aw.execute('show values(customer_preagg)');
31
2
4
5
6
7
1
8
9
20
21

The returned Customer members with their text descriptions, related levels, and related hierarchies, are shown as follows.