Its according to me. We are working on Recharging portal where a user has more than 30K retailers. Here we are working on a Unique transaction IDs but when we get 50-60 request at the same time (no difference in micro seconds) our logic fails. We need those requests to process real time so we can put them in a table and process them later. We tried so many algorithms but almost failed at last we used scope_identity() with so many values like UserID, recharge number, checksum(getdate()) and retrieved numbers from new_id() functions and sum it up.Its working till now.