Friday, 21 March 2014

What is the use of incremental aggregation? Explain in brief with an example?

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.
When the session runs with incremental aggregation enabled for the first time on March 1, you use the entire source. this allows the integration service to read and store the necessary aggregate data. on march 2, when you run the session again, you filter out all the records except those time-stamped march 2. the integration service then processes the new data and updates the target accordingly. 

(i) the first time you run an incremental aggregation session, the integration service processes the entire source. at the end of the session, the integration service stores aggregate data from that session run in two files, the index file and the data file. the integration service creates the files in the cache directory specified in the aggregator transformation properties.
(ii) each subsequent time you run the session with incremental aggregation, you use the incremental source changes in the session. for each input record, the integration service checks historical information in the index file for a corresponding group. if it finds a corresponding group, the integration service performs the aggregate operation incrementally, using the aggregate data for that group, and saves the incremental change. if it does not find a corresponding group, the integration service creates a new group and saves the record data.
(iii)when writing to the target, the integration service applies the changes to the existing target. it saves modified aggregate data in the index and data files to be used as historical data the next time you run the session.
(iv) if the source changes significantly and you want the integration service to continue saving aggregate data for future incremental changes, configure the integration service to overwrite existing aggregate data with new aggregate data.

thanks 
ur's hari



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