131 DBMS_XPLAN

Using DBMS_XPLAN

• Overview

• Security Model

• Examples

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Overview

The DBMS_XPLAN package supplies four table functions:

• DISPLAY - to format and display the contents of a plan table.

• DISPLAY_CURSOR - to format and display the contents of the execution plan of any loaded cursor.

• DISPLAY_AWR - to format and display the contents of the execution plan of a stored SQL statement in the AWR.

• DISPLAY_SQLSET - to format and display the contents of the execution plan of statements stored in a SQL tuning set.

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Security Model

This package runs with the privileges of the calling user, not the package owner (SYS). The table function DISPLAY_CURSOR requires to have select privileges on the following fixed views: V$SQL_PLAN, V$SESSION and V$SQL_PLAN_STATISTICS_ALL.

Using the DISPLAY_AWR function requires the user to have SELECT privileges on DBA_HIST_SQL_PLAN, DBA_HIST_SQLTEXT, and V$DATABASE.

To use the DISPLAY_SQLSET functionality, the calling user must have SELECT privilege on ALL_SQLSET_STATEMENTS and ALL_SQLSET_PLANS.

All these privileges are automatically granted as part of the SELECT_CATALOG role.

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Examples

Displaying a Plan Table Using DBMS_XPLAN.DISPLAY

Execute an explain plan command on a SELECT statement:

EXPLAIN PLAN FOR
SELECT * FROM emp e, dept d
   WHERE e.deptno = d.deptno
   AND e.ename='benoit';

Display the plan using the DBMS_XPLAN.DISPLAY table function

SET LINESIZE 130
SET PAGESIZE 0
SELECT * FROM table(DBMS_XPLAN.DISPLAY);

This query produces the following output:

Plan hash value: 3693697075
---------------------------------------------------------------------------
| Id  | Operation          | Name | Rows  | Bytes | Cost (%CPU)| Time     |
---------------------------------------------------------------------------
|   0 | SELECT STATEMENT   |      |     1 |    57 |     6  (34)| 00:00:01 |
|*  1 |  HASH JOIN         |      |     1 |    57 |     6  (34)| 00:00:01 |
|*  2 |   TABLE ACCESS FULL| EMP  |     1 |    37 |     3  (34)| 00:00:01 |
|   3 |   TABLE ACCESS FULL| DEPT |     4 |    80 |     3  (34)| 00:00:01 |
---------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------
   1 - access("E"."DEPTNO"="D"."DEPTNO")
   2 - filter("E"."ENAME"='benoit')

15 rows selected.

Displaying a Cursor Execution Plan Using DBMS_XPLAN.DISPLAY_CURSOR

By default, the table function DISPLAY_CURSOR formats the execution plan for the last SQL statement executed by the session. For example:

SELECT ename  FROM  emp e, dept d 
   WHERE   e.deptno = d.deptno  
   AND   e.empno=7369;

ENAME
----------
SMITH

To display the execution plan of the last executed statement for that session:

SET PAGESIZE 0
SELECT * FROM table(DBMS_XPLAN.DISPLAY_CURSOR);

This query produces the following output:

Plan hash value: 3693697075, SQL hash value: 2096952573, child number: 0
------------------------------------------------------------------
SELECT ename FROM emp e, dept d WHERE e.deptno = d.deptno
AND e.empno=7369

---------------------------------------------------------------------------
| Id  | Operation          | Name | Rows  | Bytes | Cost (%CPU)| Time     |
---------------------------------------------------------------------------
|   0 | SELECT STATEMENT   |      |       |       |            |          |
|*  1 |  HASH JOIN         |      |     1 |    16 |     6  (34)| 00:00:01 |
|*  2 |   TABLE ACCESS FULL| EMP  |     1 |    13 |     3  (34)| 00:00:01 |
|   3 |   TABLE ACCESS FULL| DEPT |     4 |    12 |     3  (34)| 00:00:01 |
---------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------
   1 - access("E"."DEPTNO"="D"."DEPTNO")
   2 - filter("E"."EMPNO"=7369)

21 rows selected.

You can also use the table function DISPLAY_CURSOR to display the execution plan for any loaded cursor stored in the cursor cache. In that case, you must supply a reference to the child cursor to the table function. This includes the SQL ID of the statement and optionally the child number.

Run a query with a distinctive comment:

SELECT /* TOTO */ ename, dname 
FROM dept d join emp e USING (deptno);

Get sql_id and child_number for the preceding statement:

SELECT sql_id, child_number
FROM v$sql 
WHERE sql_text LIKE '%TOTO%';

SQL_ID         CHILD_NUMBER
----------     -----------------------------
gwp663cqh5qbf   0

Display the execution plan for the cursor:

SELECT * FROM table(DBMS_XPLAN.DISPLAY_CURSOR(('gwp663cqh5qbf',0));

Plan hash value: 3693697075, SQL ID: gwp663cqh5qbf, child number: 0
--------------------------------------------------------
SELECT /* TOTO */ ename, dname 
FROM dept d JOIN emp e USING (deptno);

----------------------------------------------------------------------------
| Id  | Operation           | Name | Rows  | Bytes | Cost (%CPU)| Time     |
----------------------------------------------------------------------------
|   0 | SELECT STATEMENT    |      |       |       |     7 (100)|          |
|   1 |  SORT GROUP BY      |      |     4 |    64 |     7  (43)| 00:00:01 |
|*  2 |   HASH JOIN         |      |    14 |   224 |     6  (34)| 00:00:01 |
|   3 |    TABLE ACCESS FULL| DEPT |     4 |    44 |     3  (34)| 00:00:01 |
|   4 |    TABLE ACCESS FULL| EMP  |    14 |    70 |     3  (34)| 00:00:01 |
----------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------
   2 - access("E"."DEPTNO"="D"."DEPTNO")

Instead of issuing two queries, one to the get the sql_id and child_number pair and one to display the plan, you can combine these in a single query:

Display the execution plan of all cursors matching the string 'TOTO':

SELECT t.*
FROM v$sql s, table(DBMS_XPLAN.DISPLAY_CURSOR(s.sql_id, s.child_number)) t WHERE sql_text LIKE '%TOTO%';

Displaying a Plan Table with Parallel Information

By default, only relevant information is reported by the display and display_cursor table functions. In Displaying a Plan Table Using DBMS_XPLAN.DISPLAY, the query does not execute in parallel. Hence, information related to the parallelization of the plan is not reported. As shown in the following example, parallel information is reported only if the query executes in parallel.

ALTER TABLE emp PARALLEL;
EXPLAIN PLAN for
SELECT * FROM emp e, dept d
   WHERE e.deptno = d.deptno
   AND e.ename    ='hermann'
   ORDER BY e.empno;

Display the plan using the DBMS_XPLAN.DISPLAY table function

SET LINESIZE 130
SET PAGESIZE 0
SELECT * FROM table(DBMS_XPLAN.DISPLAY);
Plan hash value: 3693697345

-------------------------------------------------------------------------------------------------------------
| Id | Operation          | Name    | Rows | Bytes | Cost (%CPU)| Time     | TQ    |INOUT |PQ Distrib   |
-------------------------------------------------------------------------------------------------------------
| 0  | SELECT STATEMENT   |         | 1    | 117   | 6 (50)     | 00:00:01 |       |      |             |
| 1  | PX COORDINATOR     |         |      |       |            |          |       |      |             |
| 2  | PX SEND QC (ORDER) |:TQ10003 | 1    | 117   | 6 (50)     | 00:00:01 | Q1,03 | P->S | QC (ORDER)  |
| 3  | SORT ORDER BY      |         | 1    | 117   | 6 (50)     | 00:00:01 | Q1,03 | PCWP |             |
| 4  | PX RECEIVE         |         | 1    | 117   | 5 (40)     | 00:00:01 | Q1,03 | PCWP |             |
| 5  | PX SEND RANGE      |:TQ10002 | 1    | 117   | 5 (40)     | 00:00:01 | Q1,02 | P->P | RANGE       |
|* 6 | HASH JOIN          |         | 1    | 117   | 5 (40)     | 00:00:01 | Q1,02 | PCWP |             |
| 7  | PX RECEIVE         |         | 1    | 87    | 2 (50)     | 00:00:01 | Q1,02 | PCWP |             |
| 8  | PX SEND HASH       |:TQ10001 | 1    | 87    | 2 (50)     | 00:00:01 | Q1,01 | P->P | HASH        |
| 9  | PX BLOCK ITERATOR  |         | 1    | 87    | 2 (50)     | 00:00:01 | Q1,01 | PCWC |             |
|* 10| TABLE ACCESS FULL  | EMP     | 1    | 87    | 2 (50)     | 00:00:01 | Q1,01 | PCWP |             |
| 11 | BUFFER SORT        |         |      |       |            |          | Q1,02 | PCWC |             |
| 12 | PX RECEIVE         |         | 4    | 120   | 3 (34)     | 00:00:01 | Q1,02 | PCWP |             |
| 13 | PX SEND HASH       |:TQ10000 | 4    | 120   | 3 (34)     | 00:00:01 |       | S->P | HASH        |
| 14 | TABLE ACCESS FULL  | DEPT    | 4    | 120   | 3 (34)     | 00:00:01 |       |      |             |
-------------------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
6 - access("E"."DEPTNO"="D"."DEPTNO")
10 - filter("E"."ENAME"='hermann')
---------------------------------------------------

When the query is parallel, information related to parallelism is reported: table queue number (TQ column), table queue type (INOUT) and table queue distribution method (PQ Distrib).

By default, if several plans in the plan table match the statement_id parameter passed to the display table function (default value is NULL), only the plan corresponding to the last EXPLAIN PLAN command is displayed. Hence, there is no need to purge the plan table after each EXPLAIN PLAN. However, you should purge the plan table regularly to ensure good performance in the execution of the DISPLAY table function. If no plan table is created, Oracle will use a global temporary table to store any plan information for individual users and will preserve its content throughout the lifespan of a session. Note that you cannot truncate the content of a global temporary table.

For ease of use, you can define a view on top of the display table function and then use that view to display the output of the EXPLAIN PLAN command:

Using a View to Display Last Explain Plan

# define plan view
CREATE VIEW PLAN AS SELECT * FROM TABLE(DBMS_XPLAN.DISPLAY);

# display the output of the last explain plan command
SELECT * FROM PLAN;

Summary of DBMS_XPLAN Subprograms

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DISPLAY Function

This table function displays the contents of the plan table.

In addition, you can use this table function to display any plan (with or without statistics) stored in a table as long as the columns of this table are named the same as columns of the plan table (or V$SQL_PLAN_STATISTICS_ALL if statistics are included). You can apply a predicate on the specified table to select rows of the plan to display.

Syntax

DBMS_XPLAN.DISPLAY(
   table_name    IN  VARCHAR2  DEFAULT 'PLAN_TABLE',
   statement_id  IN  VARCHAR2  DEFAULT  NULL, 
   format        IN  VARCHAR2  DEFAULT  'TYPICAL',
   filter_preds  IN  VARCHAR2 DEFAULT NULL);

Parameters

Usage Notes

Here are some ways you might use variations on the format parameter:

• Use 'ALL -PROJECTION -NOTE' to display everything except the projection and note sections.

• Use 'TYPICAL PROJECTION' to display using the typical format with the additional projection section (which is normally excluded under the typical format). Since typical is default, using simply 'PROJECTION' is equivalent.

• Use '-BYTES -COST -PREDICATE' to display using the typical format but excluding optimizer cost and byte estimates as well as the predicate section.

• Use 'BASIC ROWS' to display basic information with the additional number of rows estimated by the optimizer.

  WARNING:

  Application developers should expose the filter_preds parameter to end-users only after careful consideration because this could expose the application to SQL injection. Indeed, filter_preds can potentially reference any table or execute any server function for which the database user invoking the table function has privileges.

Examples

To display the result of the last EXPLAIN PLAN command stored in the plan table:

SELECT * FROM table (DBMS_XPLAN.DISPLAY);

To display from other than the default plan table, "my_plan_table":

SELECT * FROM table (DBMS_XPLAN.DISPLAY('my_plan_table'));

To display the minimum plan information:

SELECT * FROM table (DBMS_XPLAN.DISPLAY('plan_table', null, 'basic'));

To display the plan for a statement identified by 'foo', such as statement_id='foo':

SELECT * FROM table (DBMS_XPLAN.DISPLAY('plan_table', 'foo'));

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DISPLAY_AWR Function

This table function displays the contents of an execution plan stored in the AWR.

Syntax

DBMS_XPLAN.DISPLAY_AWR( 
   sql_id            IN      VARCHAR2,
   plan_hash_value   IN      NUMBER DEFAULT NULL,
   db_id             IN      NUMBER DEFAULT NULL,
   format            IN      VARCHAR2 DEFAULT TYPICAL);

Parameters

Usage Notes

• To use the DISPLAY_AWR functionality, the calling user must have SELECT privilege on DBA_HIST_SQL_PLAN. DBA_HIST_SQLTEXT, and V$DATABASE, otherwise it will show an appropriate error message.

• Here are some ways you might use variations on the format parameter:

  • Use 'ALL -PROJECTION -NOTE' to display everything except the projection and note sections.

  • Use 'TYPICAL PROJECTION' to display using the typical format with the additional projection section (which is normally excluded under the typical format). Since typical is default, using simply 'PROJECTION' is equivalent.

  • Use '-BYTES -COST -PREDICATE' to display using the typical format but excluding optimizer cost and byte estimates as well as the predicate section.

  • Use 'BASIC ROWS' to display basic information with the additional number of rows estimated by the optimizer.

Examples

To display the different execution plans associated with the SQL ID 'atfwcg8anrykp':

SELECT * FROM table(DBMS_XPLAN.DISPLAY_AWR('atfwcg8anrykp'));

To display all execution plans of all stored SQL statements containing the string 'TOTO':

SELECT tf.* FROM DBA_HIST_SQLTEXT ht, table
    (DBMS_XPLAN.DISPLAY_AWR(ht.sql_id,null, null,  'ALL' )) tf 
 WHERE ht.sql_text like '%TOTO%';

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DISPLAY_CURSOR Function

This table function displays the explain plan of any cursor loaded in the cursor cache. In addition to the explain plan, various plan statistics (such as. I/O, memory and timing) can be reported (based on the V$SQL_PLAN_STATISTICS_ALL VIEWS).

Syntax

DBMS_XPLAN.DISPLAY_CURSOR(
   sql_id        IN  VARCHAR2  DEFAULT  NULL,
   child_number  IN  NUMBER    DEFAULT  NULL, 
   format        IN  VARCHAR2  DEFAULT  'TYPICAL');

Parameters

Usage Notes

• To use the DISPLAY_CURSOR functionality, the calling user must have SELECT privilege on the fixed views V$SQL_PLAN_STATISTICS_ALL, V$SQL and V$SQL_PLAN, otherwise it will show an appropriate error message.

• Here are some ways you might use variations on the format parameter:

  • Use 'ALL -PROJECTION -NOTE' to display everything except the projection and note sections.

  • Use 'TYPICAL PROJECTION' to display using the typical format with the additional projection section (which is normally excluded under the typical format). Since typical is default, using simply 'PROJECTION' is equivalent.

  • Use '-BYTES -COST -PREDICATE' to display using the typical format but excluding optimizer cost and byte estimates as well as the predicate section.

  • Use 'BASIC ROWS' to display basic information with the additional number of rows estimated by the optimizer.

Examples

To display the execution plan of the last SQL statement executed by the current session:

SELECT * FROM table (
   DBMS_XPLAN.DISPLAY_CURSOR);

To display the execution plan of all children associated with the SQL ID 'atfwcg8anrykp':

SELECT * FROM table (
   DBMS_XPLAN.DISPLAY_CURSOR('atfwcg8anrykp'));

To display runtime statistics for the cursor included in the preceding statement:

SELECT * FROM table (
   DBMS_XPLAN.DISPLAY_CURSOR('atfwcg8anrykp', NULL, 'ALLSTATS LAST');

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DISPLAY_SQLSET Function

This table function displays the execution plan of a given statement stored in a SQL tuning set.

Syntax

DBMS_XPLAN.DISPLAY_SQLSET(
   sqlset_name      IN  VARCHAR2, 
   sql_id           IN  VARCHAR2,
   plan_hash_value  IN NUMBER := NULL,
   format           IN  VARCHAR2  := 'TYPICAL', 
   sqlset_owner     IN  VARCHAR2  := NULL)
  RETURN DBMS_XPLAN_TYPE_TABLE PIPELINED;

Parameters

Usage Notes

Here are some ways you might use variations on the format parameter:

• Use 'ALL -PROJECTION -NOTE' to display everything except the projection and note sections.

• Use 'TYPICAL PROJECTION' to display using the typical format with the additional projection section (which is normally excluded under the typical format). Since typical is default, using simply 'PROJECTION' is equivalent.

• Use '-BYTES -COST -PREDICATE' to display using the typical format but excluding optimizer cost and byte estimates as well as the predicate section.

• Use 'BASIC ROWS' to display basic information with the additional number of rows estimated by the optimizer.

Examples

To display the execution plan for the SQL statement associated with SQL ID 'gwp663cqh5qbf' and PLAN HASH 3693697075 in the SQL Tuning Set called 'OLTP_optimization_0405":

SELECT * FROM table (
   DBMS_XPLAN.DISPLAY_SQLSET(
       'OLTP_optimization_0405','gwp663cqh5qbf', 3693697075));

To display all execution plans of the SQL ID 'atfwcg8anrykp' stored in the SQL tuning set:

SELECT * FROM table (
   DBMS_XPLAN.DISPLAY_SQLSET(
      'OLTP_optimization_0405','gwp663cqh5qbf'));

To display runtime statistics for the SQL statement included in the preceding statement:

SELECT * FROM table (
   DBMS_XPLAN.DISPLAY_SQLSET(
      'OLTP_optimization_0405', 'gwp663cqh5qbf', NULL, 'ALLSTATS LAST');