A - We think the reason that the Open Order by Customer Report becomes very slow is due to the following reasons:
(1) You choose to export to CSV for this report; and
(2) In Global Setup -> System -> Available to Promise, the following flag:
28. ATP Qty Days (For Component DD AtpQty(99))
is set to a value other than zero.
When both of the above conditions are true, the Open Report will include a column like ATP(99) in the CSV file, which represents the projected quantity balance of a future date. For example, if you set up flag 28 with a value of "14," then you will see that the CSV shows a column ATP(14), which reflects the quantity-on-hand balance 14 days from now.
While this is a very useful feature, we have noticed that the Open Order Report has not calculated this number in an efficient way. Therefore, it causes the slowdown. For now, you can speed up the report by: (1) Not exporting it to CSV unless you need it; and (2) setting flag 28 to zero.
On 7/30/2014, we made a change to the Open Order Report so that the calculation of the ATP(99) column will be more efficient and thus speed up the report even if (1) and (2) conditions are both true. The change had been released with 7.54.802 update.