A Lookup transformation maintains a dynamic lookup cache to track the rows that it passes to the target. When multiple sessions update the same target, you can configure the Lookup transformation in each session to synchronize the dynamic lookup cache to the same lookup source instead of a target.
When you configure a Lookup transformation to synchronize the cache with the Lookup source, the Lookup transformation performs a lookup on the Lookup source. If the data does not exist in the Lookup source, the Lookup transformation inserts the row into the Lookup source before it updates the dynamic lookup cache.
The data might exist in the Lookup source if another session inserted the row. To synchronize the lookup cache to the lookup source, the Integration Service retrieves the latest values from the Lookup source. The Lookup transformation inserts the values from the Lookup source in the dynamic lookup cache. The lookup source must be a relational table.
For example, you have multiple sessions running simultaneously. Each session generates product numbers for new product names. When a session generates a product number, the other sessions must use the same product number to identify the product. The product number is generated once and inserted in the lookup source. If another session processes a row containing the product, it must use the product number that is in the lookup source. Each session performs a lookup on the lookup source to determine which product numbers have already been generated.
The Integration Service performs the following tasks for insert rows:
The Integration Service performs a lookup on the dynamic lookup cache. If data does not exist in the dynamic lookup cache, the Integration Service performs a lookup on the lookup source.
If the data exists in the lookup source, the Integration Service retrieves the data from the lookup source. It inserts a row in the dynamic lookup cache with the columns from the lookup source. It does not update the cache with the source row.
If the data is not in the lookup source, the Integration Service inserts the data into the lookup source and inserts the row into the cache.
The lookup source contains the same columns as the lookup cache. The Integration Service does not insert a column in the lookup cache unless the column is projected from the Lookup transformation or the column is part of a lookup condition.