In SSIS 2008, Cache Transformation was introduction so we don't have to load the data into Staging/Temp tables to use in Lookup Transformation. We can load the data in memory by using Cache Transformation and then use in Lookup Transformation.
Let's say if I have a source table as shown below
As we can see that I don't have the CountryName. I need to get the CountryName from Flat file by joining the input and reference data on Country Code.