1) To understand how the DAC handles extract and load processes, you must have an understanding of the DAC repository objects.
2) For a description of these objects, see "About DAC Repository Objects Held in Source System Containers".
3) 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.
4) Each task in the DAC is mapped to a full load or an incremental load workflow in Informatica.
5) The DAC uses refresh dates (indicated in the Refresh Dates child tab of
the Physical Data Sources tab) to determine whether to invoke a full
or incremental workflow.
6) If the source or target table for a task is null, then the DAC invokes a full load workflow (command).
7) If both the source and target tables have a refresh date, then the DAC invokes the incremental workflow (command).
For a detailed description of refresh dates, see "About Refresh Dates".
The DAC supports the following extract and load combinations:
Full extract and full load
1) This extract and load combination is used for the very first extract and load.
2) All data is extracted from the source system and loaded into the data warehouse.
3) The DAC performs a full extract for a task if the source and staging tables have null refresh dates.
4) The DAC performs a full load for a task if the staging and target tables have null refresh dates.
Full extract and incremental load
1) This extract and load combination loads existing data warehouse tables with data from new sources.
2) Data is extracted from the source system through a full extract
3) When the source or staging table is null, the DAC invokes the full
4) Data is loaded from the staging table into the target table through an incremental load command.
5) When the staging and target tables have refresh dates, the DAC invokes an incremental load command.
6) This situation arises when data is loaded into an existing data warehouse from a new source connection.
7) The incremental load process requires additional logic to determine whether a record should be inserted or updated.
8) 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
1) This extract and load combination is used for regular nightly or weekly ETL processes.
2) New or changed records are extracted from the source system and
Loaded into the data warehouse.
3) 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.