Question

I have table data1 with 2 field: user_id and data_id. I have 2 indexes on user_id and data_id. They are a non unique indexed.

a function:

FUNCTION user_filter(p_schema IN VARCHAR2,
                                   p_object IN VARCHAR2) RETURN VARCHAR2 IS
  BEGIN
    RETURN 'user_id='||session_pkg.user_id;
  END;

I register this function as rls policy on data1:

DBMS_RLS.ADD_POLICY(OBJECT_SCHEMA   => '',
                        OBJECT_NAME     => 'data1',
                        POLICY_NAME     => 'user_filter',
                        POLICY_FUNCTION => 'user_filter');

To have best performance, do I have to create 1 more Index like following?

create index data3_idx on data (user_ID, data_id);

Thanks,

Answer 1

In general it would be wasteful to have three indexes for two columns (data_id), (user_id,data_id) and (user_id) since Oracle can use the compound index for queries that filter on user_id and queries that filter on both columns.

In your case the DBMS_RLS.ADD_POLICY procedure will add the filter user_id=XX to all requests on this object. This means that you could replace the index on data_id with a more efficient compound index.