Tuesday, 14 August 2012

OBIA Data warehouse full load using DAC

Here we will see how DAC loads the data using the execution plan into target tables.When you run an execution plan, data is extracted from one or more tables in the source system database, dumped into staging tables, and then loaded into tables in the data warehouse. The DAC supports the following extract and load combinations:

Full Load:
Here DAC does full extract of data from the source. All data is extracted from the source system and loaded into the data warehouse. The DAC performs a full extract for a task if the source and staging tables have null refresh dates. If the staging and target has null refresh dates then full load of data is done from staging to target. Its Just a full extract and full load

Full Extract and Incremental Load
Here as we said above the Full extract process is same i.e the whole data from source is loaded into the staging .In this case the source or staging table is null, the DAC invokes the full extract workflow.
Data is loaded from the staging table into the target table through an incremental load command. When the staging and target tables have refresh dates(incremental dates), the DAC invokes an incremental load command. This happens when data is loaded from new source
The incremental load process requires additional logic to determine whether a record should be inserted or updated which is done by the ETL part Therefore, if you add a new source connection to populate an existing data warehouse, you should expect the incremental load to be slower than when running a full load.

Incremental extract And Incremental Load
Here new or changed records are extracted from the source system by DAC and loaded into the data warehouse. Now DAC decides whether the records needs to be updated or inserted based on the incremental logic.The DAC performs an incremental extract for a task if the source and staging tables have refresh dates and performs an incremental load for a task if the staging and target table have refresh dates.

Read about Dac In Obia

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