If a mapping contains multiple lookups, even with caching enabled and enough heap memory, the lookups can slow performance. Tune the Lookup transformations that query the largest amounts of data to improve overall performance.
To determine which Lookup transformations process the most data, examine the Lookup_rowsinlookupcache counters for each Lookup transformation. The Lookup transformations that have a large number in this counter might benefit from tuning their lookup expressions. If those expressions can be optimized, session performance improves.