What does the DEFAULT DEGREE on tables actually mean?

The DOP (degree of parallelism) settings on a table has to do with the number of threads per instance for scanning the table (an integer), or DEFAULT.

When a tables DEGREE setting is set to DEFAULT, it means that the DOP) is calculated via the following formula:

For a single instance:

DOP = PARALLEL_THREADS_PER_CPU x CPU_COUNT

For an Oracle RAC configuration:

DOP = PARALLEL_THREADS_PER_CPU x CPU_COUNT x INSTANCE_COUNT

The DOP for a table can be viewed in either of the *_TABLES views.

SELECT DEGREE
FROM   DBA_TABLES
WHERE  TABLE_NAME = 'EMP'
AND    OWNER = 'SCOTT';


DEGREE
------------------
         1