Answer

There is a workaround to reload the all data again without reopening the flow.
Note: Please save your flow editing work before you try the workaround since to using [Use all data] can impact performance or cause Tableau Prep Builder to time out.
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1. In Tableau Prep Builder, at Input Step, confirm your current [Data Sample] setting is [Use all data].


2. In the same Input Step, change [Data Sample] setting to [Fixed number of rows], and keep the row limit value as blank.


3. In the same Input Step, change [Sampling method] from current one to another one.
In this example, change it from [Random sample] to [Quick select].


4. Confirm the [Data Sample] setting is returned back to [Use all data] automatically.
Note: By design, when changing [Sampling method] with the row limit value as blank, this setting is invalid and returned back to previous [Data Sample] setting. 


5. Return to the clean step which you want to review the data distributions of all data, then wait till the data loading is finished.


6. Confirm the data distributions shows all data size again.

Additional Information

] with the row limit value as 1 million, then select [Sampling method] as [Random sample].


Here is the comparison of the