Does Parallel Hint within Dynamic SQL of Oracle run in parallel?

Question

I have both DML and DDL as part of my procedure and enabled the parallel on both DML and DDL. I want to run them in Parallel mode using parallel hint but neither of them execute in parallel. Is this a limitation of using the Dynamic SQL?

For example

DECLARE
v_parallel_degree NUMBER := 8;
BEGIN
    EXECUTE IMMEDIATE 'ALTER SESSION FORCE PARALLEL DML PARALLEL ' || v_parallel_degree;
    EXECUTE IMMEDIATE 'ALTER SESSION FORCE PARALLEL QUERY PARALLEL ' || v_parallel_degree;
    EXECUTE IMMEDIATE 'ALTER SESSION FORCE PARALLEL DDL PARALLEL ' || v_parallel_degree;

    EXECUTE IMMEDIATE 'INSERT /*+PARALLEL(DEFAULT)*/ INTO '|| p_target_tabname || ' NOLOGGING
                SELECT /*+PARALLEL(dmf,DEFAULT)*/*
                FROM ' || p_source_tabname ||' PARTITION('|| p_part_name ||');
    
    EXECUTE IMMEDIATE 'CREATE UNIQUE INDEX idx_pk ON TAB_HIST
                 (COL1,COL2,COL3)
                 LOCAL
                 NOLOGGING PARALLEL ' || v_parallel_degree;
END;

I even tried the below block but not working.

v_sql := 'BEGIN
                EXECUTE IMMEDIATE ''ALTER SESSION FORCE PARALLEL DML PARALLEL ' || v_parallel_degree ||''';
                EXECUTE IMMEDIATE ''ALTER SESSION FORCE PARALLEL QUERY PARALLEL ' || v_parallel_degree ||''';
                INSERT /*+PARALLEL(DEFAULT)*/ INTO '|| p_target_tabname || ' NOLOGGING
                SELECT /*+PARALLEL(dmf,DEFAULT)*/*
                FROM ' || p_source_tabname ||' PARTITION('|| p_part_name ||') dmf;
    DBMS_OUTPUT.PUT_LINE(''Inserted '' || SQL%ROWCOUNT || '' Rows into Table- '' || p_target_tabname || '' Partition - '' || p_part_name );
                COMMIT;
              END;';
    EXECUTE IMMEDIATE v_sql;

Oracle Version -
Oracle Database 12c Enterprise Edition Release 12.1.0.2.0 - 64bit Production
PL/SQL Release 12.1.0.2.0 - Production
CORE    12.1.0.2.0  Production

Soon will be upgraded to 19c.

Any suggestions are appreciated..

TIA Venkat

Answer 1

Is this a limitation of using the Dynamic SQL?

No.

may be helpful:

1. parallel DML : https://docs.oracle.com/database/121/VLDBG/GUID-1D5C8D6C-0A0E-4CDB-8B32-16EC3C856ACC.htm#VLDBG1431
2. restriction PDML: https://docs.oracle.com/database/121/VLDBG/GUID-6626C70C-876C-47A4-8C01-9B66574062D8.htm
3. parallel DDL: https://docs.oracle.com/database/121/VLDBG/GUID-41774038-773B-40A5-BDCD-AB16A189C035.htm#VLDBG1411

Answer 2

You can start with it: https://stackoverflow.com/a/67377464/429100

Then you can check a real execution plan (Note section) and RTSM (Real-time SQL Monitor) report (select/*+ no_monitor */ dbms_sqltune.report_sql_monitor(sql_id => '&1',report_level => 'ALL',type => 'TEXT') sqlmon from dual;). They should show more information about the used DOP.

And, finally, you can trace parallel execution using the following command:

alter session set "_px_trace"="compilation","execution","messaging";

More info: "Tracing Parallel Execution with _px_trace (Doc ID 444164.1)"

Answer 3

TLDR

Most probably you forgot to enable parallel DML.

ALTER SESSION ENABLE PARALLEL DML;

Additionaly if you force parallel execution you typically do not use parallel hints and vice versa.

Sample Setup (11.2)

create table TAB_HIST (
col1 int,
col2 int,
col3 varchar2(4000))
PARTITION BY RANGE (col1) 
interval(1000000)
(
  partition p_init values less than (1000000) 
); 


create table TAB_SRC (
col1 int,
col2 int,
col3 varchar2(4000)
)
PARTITION BY RANGE (col1) 
interval(1000000)
(
  partition p_init values less than (1000000) 
);

insert into tab_src
select rownum, rownum,  rpad('x',1000,'y') from dual connect by level <= 100000;
commit;

Insert

You must enable parallel DML in the first step

ALTER SESSION ENABLE PARALLEL DML;

Note that alternatively a hint can be used

INSERT /*+ ENABLE_PARALLEL_DML */ …

Additionally if you force parallel DML and QUERY, you typically do not use parallel hints. I'm hinting a direct insert with APPEND that is often used in this situation.

DECLARE
v_parallel_degree NUMBER := 2;
BEGIN
    EXECUTE IMMEDIATE 'ALTER SESSION FORCE PARALLEL DML PARALLEL ' || v_parallel_degree;
    EXECUTE IMMEDIATE 'ALTER SESSION FORCE PARALLEL QUERY PARALLEL ' || v_parallel_degree;

    EXECUTE IMMEDIATE 'INSERT /*+ APPEND */ INTO TAB_HIST  
                SELECT  *
                FROM  TAB_SRC PARTITION(P_INIT)';
END;
/

How to check if the table was inserted in parallel? The simplest way is to query the table (before making a commit) - if you get the bellow error, it way a parallel direct insert.

select count(*) from TAB_HIST;
ORA-12838: cannot read/modify an object after modifying it in parallel

Index

If you specify a parallel degree in the create index statement you need not enable or force anything.

DECLARE
v_parallel_degree NUMBER := 2;
BEGIN
    
    EXECUTE IMMEDIATE 'CREATE UNIQUE INDEX idx_pk ON TAB_HIST
                 (COL1,COL2,COL3)
                 LOCAL
                 NOLOGGING PARALLEL ' || v_parallel_degree;
END;
/

The check is as simple as to look on the degree in data dictionary

select DEGREE from user_indexes where table_name = 'TAB_HIST';

DEGREE 
--------- 
2

Note that after creating index in parallel mode you often want to reset the DOP to one. Otherwise some simple nested loop queries may be confused and will open a parallel query...