The tableau run all the filed data, you can see the data & the field on the preview data set & you can manage the fields in @Manage metadata tab (we can remove the columns which we don't use them in workbooks).
Here are answers:
- Does Tableau run all the columns and tables whenever it queries data to render data? Only, whatever is included in the view
- - Does Tableau run only the columns included in the report whenever it queries data? Yes
- - If we use hide option on the data source pane, how does it effect performance in LIVE connection (not extract) It will be better to use HIDE for faster querying and quicker rendering