When you run a session that uses a dynamic lookup cache, the Integration Service compares the values in all lookup ports with the values in their associated input ports by default. It compares the values to determine whether or not to update the row in the lookup cache. When a value in an input port differs from the value in the lookup port, the Integration Service updates the row in the cache.
If you do not want to compare all ports, you can choose the ports you want the Integration Service to ignore when it compares ports. The Designer only enables this property for lookup/output ports when the port is not used in the lookup condition. You can improve performance by ignoring some ports during comparison.
You might want to do this when the source data includes a column that indicates whether or not the row contains data you need to update. Select the Ignore in Comparison property for all lookup ports except the port that indicates whether or not to update the row in the cache and target table.
You must configure the Lookup transformation to compare at least one port. The Integration Service fails the session when you ignore all ports.
To clear the Ignore in Comparison property, associate a port with the lookup port. When you clear the Ignore in Comparison property, the PowerCenter Integration Service updates the row in the cache.