Informatica Data Warehousing Question:

You should configure the mapping with the least number of transformations and expressions to do the most amount of work possible. You should minimize the amount of data moved by deleting unnecessary links between transformations.
For transformations that use data cache (such as Aggregator, Joiner, Rank, and Lookup transformations), limit connected input/output or output ports. Limiting the number of connected input/output or output ports reduces the amount of data the transformations store in the data cache.

You can also perform the following tasks to optimize the mapping:

Configure single-pass reading.
Optimize datatype conversions.
Eliminate transformation errors.
Optimize transformations.
Optimize expressions. You should configure the mapping with the least number of transformations and expressions to do the most amount of work possible. You should minimize the amount of data moved by deleting unnecessary links between transformations.
For transformations that use data cache (such as Aggregator, Joiner, Rank, and Lookup transformations), limit connected input/output or output ports. Limiting the number of connected input/output or output ports reduces the amount of data the transformations store in the data cache.