Recommended Software Design Pattern to define CSV/XML or any other format generator?

Hi I'm writing a CSV/XML package for my own project, I'm not using packages around there because I need to render for some cases CSVs with more than 100.000.000 of rows. So I figured my basic solution doesn't work when the database queries take long time, then I wrote a script to download the file batching it. It's working I just want extend and re-factor it for XML. Would be great do it with a good design pattern.