Can we specify degree of parallelism dynamically?

Question

I have a select SQL query which use parallelism, something like this

INSERT/*+ APPEND PARALLEL (tst, 6) */ INTO test_table tst
                (
                    **************
                    **************
                    **************
                )
    SELECT /*+  PARALLEL (a, 6) */ DISTINCT 
                    **************
                    **************
                    **************
         FROM src_table a;

As you can see here, i have hard-coded the degree but, i don't want to do that, since the number of CPUs are not same across all the DB where this code is executed.

My requirement: I need to query V$PARAMETER for the available CPU count and use the value as result-2 in my query. Something like this...

DECLARE
   degree        varchar2(1);
BEGIN
select value-2 INTO degree from v$parameter where name='cpu_count';

            INSERT/*+ APPEND PARALLEL (tst, degree) */ INTO test_table tst
            (
                **************
                **************
                **************
            )
SELECT /*+  PARALLEL (a, degree) */ DISTINCT 
                **************
                **************
                **************
     FROM src_table a;
END;

But, it is not working as i expected it to be and i see 32 parallel threads, irrespective of the available CPUs. Is this a right way to do? If not, is there any other solution for my requirement ?

Answer 1

Vivek,

You could use dynamic SQL to build up your INSERT statement within a PL/SQL function or procedure. That way you could utilise the variable "degree" that you have already retrieved.

Something like:

DECLARE
   degree varchar2(1); 
BEGIN 
   select value-2 
     INTO degree 
     from v$parameter
    where name='cpu_count';              

   EXECUTE IMMEDIATE('INSERT /*+ APPEND PARALLEL (tst, '||degree||') */ '||
                     '  INTO test_table tst ( '||
                     '       **************  '||
                     '       **************  '||
                     '       **************  '||
                     '  ) '||
                     'SELECT /*+  PARALLEL (a, '||degree||') */ '||
                     '       DISTINCT '||
                     '       ************** '||
                     '       ************** '||
                     '       ************** '||
                     '  FROM src_table a');
END;