This feature allows end users to see how many rows are being fetched as the query is being run, and can cancel it anytime during the run. To use this feature, the Form should be in Non-Blocking mode (i.e. Interaction Mode should be set to Non-Blocking) and Filter Before Display property should be set to Yes.
In previous versions of Forms, if a query in a Long List LOV returned a large number of rows (such as 100,000 or more) end users had to wait until Forms fetched all the records before anything could be done with the LOV. If, for example, the user had made a mistake when specifying a condition which caused a large number of records to be fetched, they had no way of knowing that the underlying query was going to fetch a large number of records. Also, even if they did know that a large number of records was being returned, they still had to wait until all the rows were fetched, before they could try again.
With this feature turned on the users can see how many records are fetched (at any point in time) and can cancel any time and would be able to work with the fetched set (as if the query had run to completion).
Filter Before Display Property