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Sorted input for aggregator transformation will improve performance of mapping. However,
if sorted input is used for nested aggregate expression or incremental aggregation,
then the mapping may result in session failure. Explain why?
Your answer
In case of a nested aggregation, there are multiple levels of sorting associated as each aggregation function
will require one sorting pass, and after the first level of aggregation, the sort order of the group by column
may get jumbled up, so before the second level of aggregation, Informatica must internally sort it again.However, if we already indicate that input is sorted, Informatica will not do this sorting - resulting into failure.
My Question:
How is the sorting different. sorting happens on group by ports and in terms of nested aggregation group by ports do not change. So how do you justify different sorting order for different level of aggregation.

In incremental aggregation, the aggregate calculations are stored in historical cache on the server. In this historical
cache the data may not be in sorted order. If we give sorted input, the records come as presorted for
that particular run but in the historical cache the data may not be in the sorted order.

Can you point me to informatica knowledge base or reference an article from informatica, where it confirms historical cache is not in sorted order.

As far as my understanding in both the cases informatica reverts back to its default behaviour of caching and sorting entire data and so will not have a performance boost
Tuesday, March 14 2017, 06:56 PM
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