Currently, formal testing using the ODBC Operator DataBlockSize attribute has been limited to 3 megabytes. This testing range produced a negative spike in performance that yielded longer elapse time values during the data row acquisition phase. As a result, you should consider, for example, row size, record size, number of columns, and so on to determine the optimal value to assign to the DataBlockSize attribute.
You should not set the job variable DataBlockSize less than the system default size of 1MB.