Hi,

Can you use GUID as your voucher code?

If yes, you can do it internally in Pega. Generate the GUID on the fly i.e. in strategy execution and extend the Fact table and store the GUID in your newly created voucher_code column. That would work because no two GUID can be identical, which means every pySubjectID will get its unique code, and the output will be persisted in Interaction History.

However, if you just generate a short random string on the fly, as per your example be it "xYz12sD",  the uniqueness of the string is not guaranteed. There's a possibility that some other customer may get the same voucher code, unlikely but possible. That would push you to first write every on-the-fly generated voucher code to a table in run-time and then query it to make sure that same voucher code is not used before. You will always need to query this new (VoucherCode) table to verify the uniqueness of your voucher code string.  Apart from performance concerns, this approach brings new challenges. Given the fact that outbound campaign runs in a multi-threaded fashion, there's still a slim chance that e.g. thread-1 and thread-5 can get the same voucher code simultaneously and when these two separate threads query the VoucherCode table, they would both think that code generated is unique since it's not written/committed there yet; they will both send the same voucher to two different customers. You can always improve your custom "give me a short random string" function by appending few other identifiers to it, be it milliseconds and/or node_id. But you will eventually find yourself writing a new GUID function.

Briefly, I would either proceed with a GUID generation in run-time at strategy level or focus on your option #1 i.e. where unique codes are generated in batch, offline. So that their uniqueness will be guaranteed in advance. 

Regards,