NRIV - Number Ranges

Dear Guys

I am using number ranges while creating sale order invoices.Invoices are generated by a huge numbers of users due to which its taking too much time to read the NRIV table, even to print a single invoice.

I cant use to buffering because of legal issues and NRIV is taking time, is there any other way to make NRIV fast or any other buffering technique by which numbers lost can be avoid.