When the Integration Service processes sessions that contain Lookup transformations, the Integration Service builds a cache in memory when it processes the first row of data in a cached Lookup transformation. If there are multiple Lookup transformations in a mapping, the Integration Service creates the caches sequentially when the first row of data is processed by the Lookup transformation. This slows Lookup transformation processing.
You can enable concurrent caches to improve performance. When the number of additional concurrent pipelines is set to one or more, the Integration Service builds caches concurrently rather than sequentially. Performance improves greatly when the sessions contain a number of active transformations that may take time to complete, such as Aggregator, Joiner, or Sorter transformations. When you enable multiple concurrent pipelines, the Integration Service no longer waits for active sessions to complete before it builds the cache. Other Lookup transformations in the pipeline also build caches concurrently.