Currently, the client driver does not pre-fetch data when
executeQuery() is called, but it does on the first call to
ResultSet.next(). Pre-fetching data on executeQuery() would reduce
network traffic and improve performance.
The DRDA protocol supports this. From the description of OPNQRY (open
The qryrowset parameter specifies whether a rowset of rows is to be
returned with the command. This is only honored for non-dynamic
scrollable cursors (QRYATTSNS not equal to QRYSNSDYN) and for
non-scrollable cursors conforming to the limited block query
protocol. The target server fetches no more than the requested
number of rows. It may fetch fewer rows if it is restricted by extra
query block limits, or if a fetch operation results in a negative
SQLSTATE or an SQLSTATE of 02000.