Oracle 11.2 - Perform parallel DML on a non partitioned table with LOB column

Question

Hi,
Since I wanted to demonstrate new Oracle 12c enhancements on SecureFiles, I tried to use PDML statements on a non partitioned table with LOB column, in both Oracle 11g and Oracle 12c releases. The Oracle 11.2 SecureFiles and Large Objects Developer's Guide of January 2013 clearly says:
Parallel execution of the following DML operations on tables with LOB columns is supported. These operations run in parallel execution mode only when performed on a partitioned table. DML statements on non-partitioned tables with LOB columns continue to execute in serial execution mode.
INSERT AS SELECT
CREATE TABLE AS SELECT
DELETE
UPDATE
MERGE (conditional UPDATE and INSERT)
Multi-table INSERT
So I created and populated a simple table with a BLOB column:
SQL> CREATE TABLE T1 (A BLOB);
Table created.
Then, I tried to see the execution plan of a parallel DELETE:
SQL> EXPLAIN PLAN FOR
  2  delete /*+parallel (t1,8) */ from t1;
Explained.
SQL> select * from table(dbms_xplan.display);
PLAN_TABLE_OUTPUT
Plan hash value: 3718066193
| Id  | Operation             | Name     | Rows  | Cost (%CPU)| Time     |    TQ  |IN-OUT| PQ Distrib |
|   0 | DELETE STATEMENT      |          |  2048 |     2   (0)| 00:00:01 |        |      |            |
|   1 |  DELETE               | T1       |       |            |          |        |      |            |
|   2 |   PX COORDINATOR      |          |       |            |          |        |      |            |
|   3 |    PX SEND QC (RANDOM)| :TQ10000 |  2048 |     2   (0)| 00:00:01 |  Q1,00 | P->S | QC (RAND)  |
|   4 |     PX BLOCK ITERATOR |          |  2048 |     2   (0)| 00:00:01 |  Q1,00 | PCWC |            |
|   5 |      TABLE ACCESS FULL| T1       |  2048 |     2   (0)| 00:00:01 |  Q1,00 | PCWP |            |
PLAN_TABLE_OUTPUT
Note
   - dynamic sampling used for this statement (level=2)
And I finished by executing the statement.
SQL> commit;
Commit complete.
SQL> alter session enable parallel dml;
Session altered.
SQL> delete /*+parallel (t1,8) */ from t1;
2048 rows deleted.
As we can see, the statement has been run as parallel:
SQL> select * from v$pq_sesstat;
STATISTIC                      LAST_QUERY SESSION_TOTAL
Queries Parallelized                    1             1
DML Parallelized                        0             0
DDL Parallelized                        0             0
DFO Trees                               1             1
Server Threads                          5             0
Allocation Height                       5             0
Allocation Width                        1             0
Local Msgs Sent                        55            55
Distr Msgs Sent                         0             0
Local Msgs Recv'd                      55            55
Distr Msgs Recv'd                       0             0
11 rows selected.
Is it normal ? It is not supposed to be supported on Oracle 11g with non-partitioned table containing LOB column....
Thank you for your help.
Michael

Answer 1

Yes I did it. I tried with force parallel dml, and that is the results on my 12c DB, with the non partitionned and SecureFiles LOB column.
SQL> explain plan for delete from t1;
Explained.
| Id  | Operation             | Name     | Rows  | Cost (%CPU)| Time     |    TQ  |IN-OUT| PQ Distrib |
|   0 | DELETE STATEMENT      |          |     4 |     2   (0)| 00:00:01 |        |      |            |
|   1 |  DELETE               | T1       |       |            |          |        |      |            |
|   2 |   PX COORDINATOR      |          |       |            |          |        |      |            |
|   3 |    PX SEND QC (RANDOM)| :TQ10000 |     4 |     2   (0)| 00:00:01 |  Q1,00 | P->S | QC (RAND)  |
|   4 |     PX BLOCK ITERATOR |          |     4 |     2   (0)| 00:00:01 |  Q1,00 | PCWC |            |
|   5 |      TABLE ACCESS FULL| T1       |     4 |     2   (0)| 00:00:01 |  Q1,00 | PCWP |            |
The DELETE is not performed in Parallel.
I tried with another statement :
SQL> explain plan for
2        insert into t1 select * from t1;
Here are the results:
11g
| Id  | Operation                | Name     | Rows  | Bytes | Cost (%CPU)| Time     |    TQ  |IN-OUT| PQ Distrib |
|   0 | INSERT STATEMENT         |          |     4 |  8008 |     2   (0)| 00:00:01 |        |      |            |
|   1 |  LOAD TABLE CONVENTIONAL | T1       |       |       |            |          |        |      |            |
|   2 |   PX COORDINATOR         |          |       |       |            |          |        |      |            |
|   3 |    PX SEND QC (RANDOM)   | :TQ10000 |     4 |  8008 |     2   (0)| 00:00:01 |  Q1,00 | P->S | QC (RAND)  |
|   4 |     PX BLOCK ITERATOR    |          |     4 |  8008 |     2   (0)| 00:00:01 |  Q1,00 | PCWC |            |
|   5 |      TABLE ACCESS FULL   | T1       |     4 |  8008 |     2   (0)| 00:00:01 |  Q1,00 | PCWP |            |
12c
| Id  | Operation                          | Name     | Rows  | Bytes | Cost (%CPU)| Time     |    TQ  |IN-OUT| PQ Distrib |
|   0 | INSERT STATEMENT                   |          |     4 |  8008 |     2   (0)| 00:00:01 |        |      |            |
|   1 |  PX COORDINATOR                    |          |       |       |            |          |        |      |            |
|   2 |   PX SEND QC (RANDOM)              | :TQ10000 |     4 |  8008 |     2   (0)| 00:00:01 |  Q1,00 | P->S | QC (RAND)  |
|   3 |    LOAD AS SELECT                  | T1       |       |       |            |          |  Q1,00 | PCWP |            |
|   4 |     OPTIMIZER STATISTICS GATHERING |          |     4 |  8008 |     2   (0)| 00:00:01 |  Q1,00 | PCWP |            |
|   5 |      PX BLOCK ITERATOR             |          |     4 |  8008 |     2   (0)| 00:00:01 |  Q1,00 | PCWC |            |
It seems that the DELETE statement has problems but not the INSERT AS SELECT !