The table size is not the issue here.
The important thing is that you ar retrieving one record at a time.
This would make it very efficient to do from a Remedy standpoint.
ACTL on Button
FLTR on Service
Set-Fields: from WebService
And it is also important that the DB2 people can design an efficient join behind the WebService. But that problem would be the same regardless of technology.
Best Regards - Misi, RRR AB, http://rrr.se