Sorting in Informatica

Sorting the data improves the performance.It is always better to sort the data at Source Qualifier level in case of Relational Source and for Flat files we use Sorter Transformation. Since SQL override cannot be used on flat files we use sorter transformation.

Flat file source - Use Sorter Transformation
Relational source - Use Sorter/Source Qualifier

Using Sorter in Aggregator:

Using Sorted input before Aggregator Transformation improves the performance. If you are not going to give sorted input to aggregator, then aggregator will do that before processing the records which degrades the performance. If you are using sorter prior to aggregator and not having "Sorted Input" checked, aggregator will cache all incoming data again . You should have "Sorted Input" checked only when sorting ports and aggregator ports are same and having same order of sort and aggregate.