If you are only using the last 18 weeks' data, have you put a Relative Date data source filter for "Last 18 Weeks" on a relevant date field in your data source?
hi Amber !
Your advise looks reasonable.
The sad truth is that I need 60 weeks back and refresh for such amount of data can first of all to broke database and beside of that it will broke TS (60 weeks = 15Gb of data).
Experiments with such a huge refresh caused the crush of our Tableau Server.
Do you know if there are some "not regular means" to treat datasources in Tableua? All the all it's just the files , or the data in the database.