Hi Vijay,
Unfortunately, you will need some downtime. Otherwise you cannot guarantee the data integrity.
There are however certainly ways to minimize it. Please see SAP Note 753654 - How can downtime be reduced for setup table update.
You can dramatically reduce the downtime if you are able to distinguish between closed and open periods. The closed periods can be updated retrospectively. In the context of Purchasing you might be able to define document ranges which are not likely to be changed anymore. These document ranges can be updated updated at a later point-in-time.
If the company can accept small differences during one day, then you might consider to skip the downtime. You should then choose a time-window in which the postings are as minimal as possible. Some corrections of double records might be necessary.
Last but not least, you might want to have a look at the following SAP Notes:
- SAP Note 436393 - Performance improvement for filling the setup tables;
- SAP Note 602260 - Procedure for reconstructing data for BW.
Best regards,
Sander