You can use this option
to potentially improve performance when you are processing a join
that involves a large DBMS table and a small SAS data set or DBMS
When you specify DBKEY=,
it is strongly
that an index exists for the key column in the underlying DBMS table.
Performance can be severely degraded without an index.
Improper use of this
option can decrease performance. For detailed information about using
this option, see the DBINDEX= LIBNAME option.