Are you sure that you will never insert larger documents in the future? If so, you can do a MAX(LENGTH(column-name)) to find the value. But if you cannot rely on the documents never growing, this seems to be rather troublesome. After all, DB2 only allocates as much space as is needed for each document (not the full 500K). The only difference could be a few bytes in the LOB locator - but I wouldn't worry about that, except for benchmark situations.