Insert query is using parallel mode

Question

Hi All,
Insert query is running against below tables. It is using Parallelism as the below explain shows.
Execution Plan
Id  Operation  Name  Rows  Bytes  Cost (%CPU) Time  TQ  IN-OUT PQ Distrib 
0  INSERT STATEMENT        779K(100)        
1     LOAD TABLE CONVENTIONAL                 
2       PX COORDINATOR                 
3         PX SEND QC (RANDOM)  :TQ10002  4116K 443M 779K (0) 999:59:59  Q1,02  P->S  QC (RAND) 
4           HASH JOIN ANTI BUFFERED   4116K 443M 779K (0) 999:59:59  Q1,02  PCWP   
5             BUFFER SORT            Q1,02  PCWC   
6               PX RECEIVE    4116K 235M 36221 (0) 758:17:06  Q1,02  PCWP   
7                 PX SEND HASH  :TQ10000  4116K 235M 36221 (0) 758:17:06    S->P  HASH 
8                   TABLE ACCESS FULL  GL_POSTING_INTERIM_50123  4116K 235M 36221 (0) 758:17:06       
9             PX RECEIVE    471M 23G 742K (0) 999:59:59  Q1,02  PCWP   
10               PX SEND HASH  :TQ10001  471M 23G 742K (0) 999:59:59  Q1,01  P->P  HASH 
11                 PX BLOCK ITERATOR    471M 23G 742K (0) 999:59:59  Q1,01  PCWC   
12                   TABLE ACCESS FULL  GL_BALANCES  471M 23G 742K (0) 999:59:59  Q1,01  PCWP    WE are not using any parallel hint again all the tables in the insert query.
Environment details.
DB version - 11.2.0.1
OS version - IBM AIX 6.1
Please let me know why query is going for parallelism automatically as i am not using any parallel hint or any auto parallel.
NAME                                 TYPE        VALUE
fast_start_parallel_rollback         string      FALSE
parallel_adaptive_multi_user         boolean     TRUE
parallel_automatic_tuning            boolean     FALSE
parallel_degree_limit                string      CPU
parallel_degree_policy               string      MANUAL
parallel_execution_message_size      integer     16384
parallel_force_local                 boolean     FALSE
parallel_instance_group              string
parallel_io_cap_enabled              boolean     FALSE
parallel_max_servers                 integer     8
parallel_min_percent                 integer     0
NAME                                 TYPE        VALUE
parallel_min_servers                 integer     0
parallel_min_time_threshold          string      AUTO
parallel_server                      boolean     FALSE
parallel_server_instances            integer     1
parallel_servers_target              integer     64
parallel_threads_per_cpu             integer     2
recovery_parallelism                 integer     0Please suggest.
Thanks

Answer 1

That will depend on the query and whether it decides to use parallel or not. Having PARALLEL_AUTOMATIC_TUNING set to FALSE does not disable parallel query in your database. Unless you are talking about some other parameter when you say "parallel auto is manual"?
Here is a worked example. Note my parallel settings at the end:
create table rj_test (id number(10), name varchar2(20));
exec dbms_stats.set_table_stats(ownname=>'SYS',tabname=>'RJ_TEST',numrows=>'1000000',numblks=>'10000');
SQL> explain plan for
  2  select id, count(*)
  3  from rj_test
  4  group by id;
Explained.
SQL> select * from table(dbms_xplan.display);
PLAN_TABLE_OUTPUT
Plan hash value: 3757798270
| Id  | Operation          | Name    | Rows  | Bytes | Cost (%CPU)| Time     |
|   0 | SELECT STATEMENT   |         |  1000K|    12M|  1058  (12)| 00:00:06 |
|   1 |  HASH GROUP BY     |         |  1000K|    12M|  1058  (12)| 00:00:06 |
|   2 |   TABLE ACCESS FULL| RJ_TEST |  1000K|    12M|   962   (3)| 00:00:05 |
9 rows selected.
SQL> select degree from user_tables where table_name = 'RJ_TEST';
DEGREE
         1
SQL> alter table rj_test parallel (degree 8);
Table altered.
SQL> explain plan for
  2  select id, count(*)
  3  from rj_test
  4  group by id;
Explained.
SQL> select * from table(dbms_xplan.display);
SQL> set lines 120
SQL> set pages 1000
SQL> select * from table(dbms_xplan.display);
PLAN_TABLE_OUTPUT
Plan hash value: 2739002282
| Id  | Operation                | Name     | Rows  | Bytes | Cost (%CPU)| Time     |    TQ  |IN-OUT| PQ Distrib |
|   0 | SELECT STATEMENT         |          |  1000K|    12M|   145  (11)| 00:00:01 |        |      |            |
|   1 |  PX COORDINATOR          |          |       |       |            |          |        |      |            |
|   2 |   PX SEND QC (RANDOM)    | :TQ10001 |  1000K|    12M|   145  (11)| 00:00:01 |  Q1,01 | P->S | QC (RAND)  |
|   3 |    HASH GROUP BY         |          |  1000K|    12M|   145  (11)| 00:00:01 |  Q1,01 | PCWP |            |
|   4 |     PX RECEIVE           |          |  1000K|    12M|   145  (11)| 00:00:01 |  Q1,01 | PCWP |            |
|   5 |      PX SEND HASH        | :TQ10000 |  1000K|    12M|   145  (11)| 00:00:01 |  Q1,00 | P->P | HASH       |
|   6 |       HASH GROUP BY      |          |  1000K|    12M|   145  (11)| 00:00:01 |  Q1,00 | PCWP |            |
|   7 |        PX BLOCK ITERATOR |          |  1000K|    12M|   133   (3)| 00:00:01 |  Q1,00 | PCWC |            |
|   8 |         TABLE ACCESS FULL| RJ_TEST  |  1000K|    12M|   133   (3)| 00:00:01 |  Q1,00 | PCWP |            |
15 rows selected.
SQL> show parameter parallel
NAME                                 TYPE        VALUE
fast_start_parallel_rollback         string      LOW
parallel_adaptive_multi_user         boolean     TRUE
parallel_automatic_tuning            boolean     FALSE
parallel_degree_limit                string      CPU
parallel_degree_policy               string      MANUAL
parallel_execution_message_size      integer     16384
parallel_force_local                 boolean     FALSE
parallel_instance_group              string
parallel_io_cap_enabled              boolean     FALSE
parallel_max_servers                 integer     16
parallel_min_percent                 integer     0
parallel_min_servers                 integer     1
parallel_min_time_threshold          string      AUTO
parallel_server                      boolean     FALSE
parallel_server_instances            integer     1
parallel_servers_target              integer     16
parallel_threads_per_cpu             integer     2
recovery_parallelism                 integer     0
SQL>