INCREMENTAL AGGREGATION IN INFORMATICA

Theory

Incremental Aggregation is the process of capturing the changes in the source and calculating the aggregations in a session. This process makes the integration service to update the target incrementally and avoids the process of calculating the aggregations on the entire source. Consider the below sales table as an example and see how the incremental aggregation works.

Source:

YEAR PRICE
----------
2010 100
2010 200
2010 300
2011 500
2011 600
2012 700

For simplicity, I have used only the year and price columns of sales table. We need to do aggregation and find the total price in each year.

When you run the session for the first time using the incremental aggregation, then integration service process the entire source and stores the data in two file, index and data file. The integration service creates the files in the cache directory specified in the aggregator transformation properties.

After the aggregation, the target table will have the below data.

Target:

YEAR PRICE
----------
2010 600
2011 1100
2012 700

Now assume that the next day few more rows are added into the source table.

Source:

YEAR PRICE

----------

2010 100

2010 200

2010 300

2011 500

2011 600

2012 700

2010 400

2011 100

2012 200

2013 800

Now for the second run, you have to pass only the new data changes to the incremental aggregation. So, the source will contain the last four records. The incremental aggregation uses the data stored in the cache and calculates the aggregation. Once the aggregation is done, the integration service writes the changes to the target and the cache. The target table will contains the below data.

Target:

YEAR PRICE
----------
2010 1000
2011 1200
2012 900
2013 800

Points to remember

• When you use incremental aggregation, first time you have to run the session with complete source data and in the subsequent runs you have to pass only the changes in the source data. 
• Use incremental aggregation only if the target is not going to change significantly. If the incremental aggregation process changes more than half of the data in target, then the session performance many not benefit. In this case go for normal aggregation.

Note : The integration service creates a new aggregate cache when

1. A new version of mapping is saved 
2. Configure the session to reinitialize the aggregate cache 
3. Moving or deleting the aggregate files 
4. Decreasing the number of partitions

Configuring the mapping for incremental aggregation

Before enabling the incremental aggregation option, make sure that you capture the changes in the source data. You can use lookup transformation or stored procedure transformation to remove the data which is already processed. You can also create a trigger on the source database and can read only the source changes in the mapping.

You can find the incremental aggregation in the session properties tab under the performance section.