When you configure the Lookup transformation to return all matching rows, the Lookup transformation returns all rows that match the lookup condition. You must configure the transformation to return all matching rows when you create the transformation. The Lookup transformation becomes an active transformation. The Lookup Policy on Multiple Match property is Use All Values. The property becomes read-only. You cannot change the property after you create the transformation.
You might have customer order data in a relational table. Each customer has multiple orders in the table. You can configure the Lookup transformation to return all the orders for a customer from a lookup. You can cache the lookup table to improve performance.
If you configure the Lookup transformation for caching, the Integration Service caches all rows that it reads from the lookup source. The Integration Service caches all rows for a lookup key by the key index.