Extracts are saved subsets of a data source that you can use to improve performance, upgrade your data to allow for more advanced capabilities, and analyze offline. You can create an extract by defining filters and limits that include the data you want in the extract. 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 increment the extract; which only adds rows that are new since the last refresh.
Improve performance. For file based data sources such as Excel or Access, a full extract takes advantage of the Tableau data engine. For large data sources, a filtered extract can limit the load on the server when you only need a subset of data.
Add functionality to file based data sources, such as the ability to compute Count Distinct.
Provide offline access to your data. If you are traveling and need to access your data offline, you can extract the relevant data to a local data source.
Creating an Extract
Adding Rows from a File
Upgrading Legacy Extracts