- The filesort() function asks the handler implementation how many rows are expected
   with estimate_rows_upper_bound(). The default implementation of that function(in handler.h)
    is to return "stats.records+EXTRA_RECORDS" where EXTRA_RECORDS is defined as 10. Unless
   the handler implementation has filled in stats.records it will be 0 and thus 10 will be used for
   calculating size of sort buffer etc.

 - Implement ha_ndbinfo::estimate_rows_upper_bound() to return "many" rows