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Oracle Tips
by Burleson Consulting
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The Data Warehouse Development Life Cycle
Aggregating Data For The Oracle Warehouse
In order to create the illusion of fast calculation time, most data
warehouses are loaded in batch mode after the online system has been
shut down and all the common aggregate values are rolled up into
summary tables. In this sense, a data warehouse is bimodal, with a
highly intensive loading window during off-hours and an intensive
query window during the day. Because many data warehouses collect
data from non-relational databases such as IMS or CA-IDMS, no
standard methods for extracting data are available for loading into
a warehouse and pre-aggregating summary data. Even when the
warehouse is fed from an OLTP Oracle database, there are numerous
techniques for loading in new data. However, we do have a few common
techniques for extracting and loading a data warehouse from
operational Oracle databases.
* Log “sniffing”--Applies the archived redo logs from the
OLTP system to the data warehouse.
* Update, insert, and delete triggers--Fires off a
distributed update to the data warehouse.
* Snapshot logs used to populate the data warehouse--Updates
the replicated table changes.
* Nightly extract/load programs--Extracts and retrieves the
operational data, and loads it into the warehouse.
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