Avoid the pitfall of using external files for reference files.

Datastage makes connecting to external databases so easy that it is tempting to connect to an external database for table lookups however, this IS NOT recommended because it will make the job run much slower. The best way to handle external reference tables is to perform the join on the source machine. However, if the tables exist on separate servers this is not possible, therefore the other option is to load the reference table into a Hash file on the Datastage server and perform the lookups on the hashed table.