Use hash auto-keys partitioning at or before Rank, Sorter, Joiner, and unsorted Aggregator transformations to ensure that rows are grouped properly before they enter these transformations.
The following figure shows a mapping with hash auto-keys partitioning. The Integration Service distributes rows to each partition according to group before they enter the Sorter and Aggregator transformations:
In this mapping, the Sorter transformation sorts items by item description. If items with the same description exist in more than one source file, each partition will contain items with the same description. Without hash auto-keys partitioning, the Aggregator transformation might calculate average costs and prices for each item incorrectly.
To prevent errors in the cost and prices calculations, set a partition point at the Sorter transformation and set the partition type to hash auto-keys. When you do this, the Integration Service redistributes the data so that all items with the same description reach the Sorter and Aggregator transformations in a single partition.