The early projection optimization method improves performance by reducing the amount of data that the Data Integration Service moves across transformations. When the Data Integration Service processes a mapping, it moves the data from all connected ports in a mapping from one transformation to another. In large, complex mappings, or in mappings that use nested mapplets, some ports might not supply data to the target. The Data Integration Service identifies the ports that do not supply data to the target. After the Data Integration Service identifies unused ports, it removes the links between all unused ports from the mapping.

The Data Integration Service does not remove all links. For example, it does not remove the following links:

Links connected to a transformation that has side effects.
Links connected to transformations that call an ABORT() or ERROR() function, send email, or call a stored procedure.

If the Data Integration Service determines that all ports in a transformation are unused, it removes all transformation links except the link to the port with the least data. The Data Integration Service does not remove the unused transformation from the mapping.

The Developer tool enables this optimization method by default.