Estimate/notify the result size before execution of the query in the dashboard

[ccoelho]

We have reports/dashboards based on a large underlying table. Thus, when a user tries to run a dashboard for a long date range which would result in many rows being processed, the dashboard may take time to load. It will be helpful, if there is a way to get the size of result set that will be executed using the query plan. Using that estimated size, we can compare the size to a threshold size defined for the dashboard and if the estimated size is greater than the threshold, the user can get a popup message which will indicate the result size being too large will impact the dashboard load time. Thus, in this case, the user can alter the filters to reduce the result size if it wants the results sooner or else will be expecting the results to take time due to its size.