If the Source File you mean does not change very often it might be easier to preprocess that once and convert its contents into a more handy format (plain text file where the line separator, separates your terms, or an xml file)or even save those into a faster format (eg. a BerkleyDB file or aven an RDBMS), so you might save some cpu and memory ressources when processing actaully the data.

Have a nice day
All decision is left to your taste