>Granted, so to ensure that a duplicate does not exist, you can add a machine_id to the string, then search the table to verify that the key has not been used.

Searching a table only discovers data that has been saved to the network, not data still in buffers on individual machines, and the machine_id adds a long string to the ID number that is difficult to read and report.

Why go through all this effort when you can use a lookup table? Just lock the appropriate record, increment the value and unlock the record for someone else to use. Unique, you can use VERY large numbers (I think it's 2 billion) if you use integer-type, and easy to handle.

Barbara