Runtime Environment Configuration - File Handling tab

Sort/Merge

Ensure duplicate keys are kept in order
Select this to ensure that duplicate primary keys in a file are kept in order in any SORT or MERGE operation. If you don't select this, the order of duplicate primary keys is not guaranteed.
Equivalent switch: S0

SORT buffer memory allocation

Use default value
Click this to use automatic memory management for SORT and MERGE operations.
Allocate at least ... bytes of memory
Specify a minimum number of bytes of memory to allocate for SORT and MERGE operations.