Use mysql++, get a resultset with 10000 rows and iterate the resultset (no replies)

I use mysql++, get a resultset and iterate it like this:

Query qr = conn->query(sql);
UseQueryResult res = qr.use();

while(Row row = res.fetch_row())
{
}

The resultset has 10000 rows，this "While" Loop took 3.5 seconds.
is this situation normal? I thought it should completed much faster!