Striving for Optimal Performance

Oct 23 2009

Hints for Direct-path Insert Statements

Tag: 10gR1, 10gR2, 11gR1, 11gR2, 9iR2, Direct Path — Christian Antognini @ 5:28 pm

Up to Oracle Database 10g Release 2, direct-path inserts are supported only by INSERT INTO … SELECT … statements (including multitable inserts), MERGE statements (for the part inserting data), and applications using the OCI direct-path interface (for example, the SQL*Loader utility). At the statement level two methods are available to specify that a direct-path insert has to be used:

Specify the APPEND hint in the SQL statement
Execute the SQL statement (actually, at least the INSERT part) in parallel

Let’s have a look to an example. Notice that:

The APPEND hint is used to execute a direct-path insert.
The APPEND hint does not work with a “regular” INSERT statement that uses the VALUES clause.
To check whether the direct-path insert is performed, the modified table is queried without committing (or rolling back) the transaction. As a result, after a direct-path insert the database engine raises an ORA-12838.

SQL> SELECT * FROM v$version WHERE rownum = 1;

BANNER
----------------------------------------------------------------
Oracle Database 10g Enterprise Edition Release 10.2.0.4.0 - 64bi

SQL> CREATE TABLE t (n NUMBER);

SQL> INSERT /*+ append */ INTO t SELECT 1 FROM dual;

SQL> SELECT * FROM t;
SELECT * FROM t
              *
ERROR at line 1:
ORA-12838: cannot read/modify an object after modifying it in parallel

SQL> COMMIT;

SQL> INSERT /*+ append */ INTO t VALUES (2);

SQL> SELECT * FROM t;

         N
----------
         1
         2

Strangely enough, at least for me, in Oracle Database 11g Release 1 the behavior of the APPEND hint has changed. In fact, it is accepted also for a “regular” INSERT statement that uses the VALUES clause. Let’s run the same test as before to illustrate the new behavior.

SQL> SELECT * FROM v$version WHERE rownum = 1;

BANNER
--------------------------------------------------------------------------------
Oracle Database 11g Enterprise Edition Release 11.1.0.6.0 - 64bit Production

SQL> CREATE TABLE t (n NUMBER);

SQL> INSERT /*+ append */ INTO t SELECT 1 FROM dual;

SQL> SELECT * FROM t;
SELECT * FROM t
              *
ERROR at line 1:
ORA-12838: cannot read/modify an object after modifying it in parallel

SQL> COMMIT;

SQL> INSERT /*+ append */ INTO t VALUES (1);

SQL> SELECT * FROM t;
SELECT * FROM t
              *
ERROR at line 1:
ORA-12838: cannot read/modify an object after modifying it in parallel

Even more strange, in Oracle Database 11g Release 2 the behavior of the APPEND hint was reverted to the pre-11g one! But, since the feature is really useful in some situations, a new hint called APPEND_VALUES is available. The following example illustrates the new behavior.

SQL> SELECT * FROM v$version WHERE rownum = 1;

BANNER
--------------------------------------------------------------------------------
Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - 64bit Production

SQL> CREATE TABLE t (n NUMBER);

SQL> INSERT /*+ append */ INTO t SELECT 1 FROM dual;

SQL> SELECT * FROM t;
SELECT * FROM t
              *
ERROR at line 1:
ORA-12838: cannot read/modify an object after modifying it in parallel

SQL> COMMIT;

SQL> INSERT /*+ append */ INTO t VALUES (2);

SQL> SELECT * FROM t;

         N
----------
         1
         2

SQL> COMMIT;

SQL> INSERT /*+ append_values */ INTO t VALUES (3);

SQL> SELECT * FROM t;
SELECT * FROM t
*
ERROR at line 1:
ORA-12838: cannot read/modify an object after modifying it in parallel

Comments (12)

12 Responses to “Hints for Direct-path Insert Statements”

Comment: Surachart Opun
October 23rd, 2009 at 8:34 pm

Thank You for good post about direct-path inserts.
Comment: Alberto Dell'Era
October 25th, 2009 at 3:57 pm

Ciao Chris,

very interesting – it seems to be useful when the arguments to the VALUES clause are actually arrays according to the docs
APPEND_VALUES Hint
In fact I can see no reason to insert-append a single row …
Comment: Timur Akhmadeev
October 26th, 2009 at 9:55 am

Hi Chris,

see Note 842374.1 for explanation of this behavior.
Pingback: Blogroll Report 16/10/2009-23/10/2009 « Coskan’s Approach to Oracle
October 27th, 2009 at 12:55 am

[...] Christian Antognini-Hints for Direct-path Insert Statements [...]
Comment: Raja
November 3rd, 2009 at 7:16 am

The exceptions mentioned here for INSERT and APPEND are very useful.

Please clarify my doubts :
1. How about using APPEND in other DML Statements like DELETE, UPDATE, MERGE ?
2. Does PARALLELISM get enabled by default, when APPEND hint is used ?
Comment: Christian Antognini
November 10th, 2009 at 11:14 pm

Hi Raja

> How about using APPEND in other DML Statements like DELETE, UPDATE, MERGE ?

The APPEND hint is only supported for INSERT and MERGE statements. With MERGE statements it is specified as follows:

MERGE /*+ append */ INTO …

> Does PARALLELISM get enabled by default, when APPEND hint is used ?

No. But a parallel insert automatically use direct-path to write data into the blocks…

Cheers,
Chris
Comment: Houri Mohamed
December 3rd, 2009 at 5:25 pm

Hi Christian,

Does the dml logging error during insert /*+ append */ select is
supported by the new oracle release? Particulary for unique and
primary keys?

Mohamed

Comment: Christian Antognini
December 11th, 2009 at 7:33 am

Hi Mohamed

DML error logging is not yet supported with direct inserts.

Here is an example:

SQL> SELECT * FROM v$version WHERE rownum = 1;

BANNER
--------------------------------------------------------------------------------
Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - Production

SQL> CREATE TABLE t (n NUMBER, pad VARCHAR2(100), CONSTRAINT t_n_uk UNIQUE (n));

SQL> INSERT INTO t VALUES (1,'bla');

SQL> exec dbms_errlog.create_error_log ('t')

SQL> INSERT /*+ append_values */ INTO t VALUES (1,'bla') LOG ERRORS;
INSERT /*+ append_values */ INTO t VALUES (1,'bla') LOG ERRORS
*
ERROR at line 1:
ORA-00001: unique constraint (CHA.T_N_UK) violated

SQL> SELECT ora_err_mesg$ FROM err$_t;

no rows selected

SQL> INSERT INTO t VALUES (1,'bla') LOG ERRORS;
INSERT INTO t VALUES (1,'bla') LOG ERRORS
*
ERROR at line 1:
ORA-00001: unique constraint (CHA.T_N_UK) violated

SQL> SELECT ora_err_mesg$ FROM err$_t;

ORA_ERR_MESG$
--------------------------------------------------------------------------------
ORA-00001: unique constraint (CHA.T_N_UK) violated

Cheers,
Chris

Comment: Houri Mohamed
December 11th, 2009 at 8:38 am

Thanks Christian,
Always we learn something new.
Today is : in 11g we can use direct path insert with insert/values using the hint
/*+ append_values */
Regards
Comment: Kerry Osborne
December 15th, 2009 at 12:58 am

Hi Christian,

Are you familiar with SYS_DL_CURSOR hint? Do you know if the APPEND_VALUES hint is functionally the same.

Kerry
Comment: Christian Antognini
December 17th, 2009 at 9:02 am

Hi Kerry

Sorry, I never did tests using the SYS_DL_CURSOR hint.

Cheers,
Chris
Pingback: Book Review: Troubleshooting Oracle Performance (Part 2) « Charles Hooper's Oracle Notes
November 8th, 2011 at 3:32 pm

[...] statements containing a VALUES clause. Since the time when the book was published, the author created a blog article that demonstrates how to use direct path insert for SQL statements that have a VALUES clause. [...]

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Hints for Direct-path Insert Statements

12 Responses to “Hints for Direct-path Insert Statements”

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