OPTIM_ORDERBY_IDX 

The database parameter OPTIM_ORDERBY_IDX denotes how the optimization algorithm changes if you are using ORDER BY clauses.

If the OPTIM_ORDERBY_IDX values are quite high, the system will tend to use inversions to process SQL statements with ORDER BY clauses. If this is the case, the results do not need to be built up so the first results can be delivered quickly.

This parameter does not affect the join SELECT statements.