What is DBMS_PARALLEL_EXECUTE doing in the background

Question

What is the best way to see all the actual SQL's that are being executed in the background when a package is executed?
For an example, I am interested in knowing what DBMS_PARALLEL_EXECUTE package is doing in the background. I've read what the procedures do and I understand the functionality. But I'd like to know how it does it. I wanted to know what create_chunks_by_number_col is doing in the background.

Answer 1

970021 wrote:
What is the best way to see all the actual SQL's that are being executed in the background when a package is executed?
For an example, I am interested in knowing what DBMS_PARALLEL_EXECUTE package is doing in the background. I've read what the procedures do and I understand the functionality. But I'd like to know how it does it. I wanted to know what create_chunks_by_number_col is doing in the background.
OK - I'm confused.
You said you 'read what the procedures do' but the doc explains pretty clearly (IMHO) exactly how it creates the chunks.
http://docs.oracle.com/cd/E11882_01/appdev.112/e16760/d_parallel_ex.htm#CHDHFCDJ
CREATE_CHUNKS_BY_NUMBER_COL Procedure
This procedure chunks the table (associated with the specified task) by the specified column. The specified column must be a NUMBER column. This procedure takes the MIN and MAX value of the column, and then divide the range evenly according to chunk_size. The chunks are:
CREATE_CHUNKS_BY_NUMBER_COL Procedure
This procedure chunks the table (associated with the specified task) by
the specified column. The specified column must be a NUMBER column. This
procedure takes the MIN and MAX value of the column, and then divide the
range evenly according to chunk_size. The chunks are:
START_ID                              END_ID
min_id_val                            min_id_val+1*chunk_size-1
min_id_val+1*chunk_size               min_id_val+2*chunk_size-1
min_id_val+i*chunk_size               max_id_val
So I am at a loss to know how that particular example is of any value to you.
That package creates a list of START_ID and END_ID values, one pair of values for each 'chunk'. It then starts a parallel process for each chunk that queries the table using a where clause that is basically just this:
WHERE userColumn BETWEEN :START_ID AND END_ID
The RUN_TASK Procedure explains part of that
RUN_TASK Procedure
This procedure executes the specified statement (sql_stmt) on the chunks in parallel. It commits after processing each chunk. The specified statement must have two placeholders called start_id, and end_id respectively, which represent the range of the chunk to be processed. The types of the placeholder must be rowid where ROWID based chunking was used, or NUMBER where number based chunking was used. The specified statement should not commit unless it is idempotent.
The SQL statement is executed as the current user.
Examples
Suppose the chunk table contains the following chunk ranges:
START_ID                              END_ID
1                                     10
11                                    20
21                                    30
And the specified SQL statement is:
UPDATE employees
      SET salary = salary + 10
      WHERE e.employee_id  BETWEEN :start_id AND :end_id
This procedure executes the following statements in parallel:
UPDATE employees 
      SET salary =.salary + 10  WHERE employee_id BETWEEN 1 and 10;
      COMMIT;
UPDATE employees 
      SET salary =.salary + 10  WHERE employee_id between 11 and 20;
      COMMIT;
UPDATE employees 
      SET salary =.salary + 10  WHERE employee_id between 21 and 30;
      COMMIT;
You could just as easily write those queries yourself for chunking by number. But you couldn't execute them in parallel unless you created a scheduler job.
So like the doc says Oracle is just:
1. getting the MIN/MAX of the column
2. creating a process for each entry in the 'chunk table'
3. executing those processes in parallel
4. commiting each process individually
5. maintain status for you.
I'm not sure what you would expect to see on the backend for an example like that.