Extracts are saved subsets of a data source that you can use to improve performance or to take
advantage of Tableau functionality that is not available in the original data source. When you
create an extract you can reduce the total amount of data by defining filters and limits. After you
create an extract you can refresh it with data from the original data source. You can either fully
refresh the data, replacing all of the extract contents, or you can incrementally refresh the
extract, which only adds rows that are new since the last refresh