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Do You Know The 11g Plan?

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This paper describes the evolution of the Plan table and DBMSX_PLAN in 11g and some of the features that can be used to troubelshoot SQL performance effectively and efficiently.

This paper describes the evolution of the Plan table and DBMSX_PLAN in 11g and some of the features that can be used to troubelshoot SQL performance effectively and efficiently.

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  • 1. Do you know the 11g Plan? Mahesh Vallampati
  • 2. About the Speaker
    • Mahesh Vallampati
      • Senior Practice Manager at SmartDog Services
      • Senior Sales Consulting Manager at Hotsos.
      • Director of IT Database Services at a company in Houston
      • Worked at Oracle for nine years
      • Published in Oracle magazine
  • 3. Agenda
    • Plan Table
    • V$SQL_PLAN and Related Views
    • DBMS_XPLAN
    • Key Performance Takeaways
  • 4. The Plan Table
  • 5. Plan Table
    • When Oracle parses a query, it creates a plan to execute the query
    • The plan is a set of row source operations
    • Row source operations are specific data access and join/sort method’s Oracle is going to execute to fulfill the request done by the query
    • Some of the row source operations are
      • Index Scan’s (Unique, Range, Skip etc.)
      • Table Access (By Index Rowid, Full Table Scan’s)
      • Joins (Nested Loops, Hash, Sort-Merge)
      • Sort Operations
  • 6. Explain Plan Example - I select empno, ename, sal, deptno from emp where empno = 7654 ; ----------------------------------------------------------------------------------- |Id | Operation | Name |Rows|Bytes|Cost (%CPU)|Time | ----------------------------------------------------------------------------------- | 0| SELECT STATEMENT | | 1| 17| 1 (0)|00:00:01 | | 1| TABLE ACCESS BY INDEX ROWID| EMP | 1| 17| 1 (0)|00:00:01 | |* 2| INDEX UNIQUE SCAN | EMP_EMPNO_PK | 1| | 0 (0)|00:00:01 | ----------------------------------------------------------------------------------- Predicate Information (identified by operation id): --------------------------------------------------- 2 - access("EMPNO"=7654)
  • 7. Explain Plan Example - II select ename from emp where comm is not null; -------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | -------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | 4 | 32 | 4 (0)| 00:00:01 | |* 1 | TABLE ACCESS FULL| EMP | 4 | 32 | 4 (0)| 00:00:01 | -------------------------------------------------------------------------- Predicate Information (identified by operation id): --------------------------------------------------- 1 - filter("COMM" IS NOT NULL)
  • 8. How to read an indented, ordered Oracle execution plan…
    • An execution plan line represents a row source operation (RSO)
    • An indented RSO is the child of the first prior less-indented RSO
    • A child RSO must complete before its parent can
    • Order of execution
      • RSOs begin in top-down order at step 0
      • RSOs complete only after their children complete
  • 9. Plan Table
    • The typical name for a plan table is PLAN_TABLE , but you may use any name you wish
    • Create the plan table by running utlxplan.sql , located in $ORACLE_HOME/rdbms/admin
      • Create one per instance or one per schema
  • 10. Explain Plan Examples select empno, ename, sal, deptno from emp where empno = 7654 ; ----------------------------------------------------------------------------------- |Id | Operation | Name |Rows|Bytes|Cost (%CPU)|Time | ----------------------------------------------------------------------------------- | 0| SELECT STATEMENT | | 1| 17| 1 (0)|00:00:01 | | 1| TABLE ACCESS BY INDEX ROWID| EMP | 1| 17| 1 (0)|00:00:01 | |* 2| INDEX UNIQUE SCAN | EMP_EMPNO_PK | 1| | 0 (0)|00:00:01 | ----------------------------------------------------------------------------------- Predicate Information (identified by operation id): --------------------------------------------------- 2 - access("EMPNO"=7654)
  • 11. Divide and Conquer for Bigger Plans
    • select d.dname, e.ename, s.grade, e.sal from dept d, emp e, salgrade s
    • where d.deptno = e.deptno and e.sal between s.losal and s.hisal ;
    • --------------------------------------------------------------------------------------
    • | Id | PID | Operation | Name | Rows | Bytes | Cost |
    • --------------------------------------------------------------------------------------
    • | 0 | | SELECT STATEMENT | | 1 | 28 | 7 |
    • | 1 | 0 | NESTED LOOPS | | 1 | 28 | 7 |
    • | 2 | 1 | MERGE JOIN | | 1 | 17 | 6 |
    • | 3 | 2 | SORT JOIN | | 13 | 117 | 2 |
    • |* 4 | 3 | TABLE ACCESS BY INDEX ROWID| EMP | 13 | 117 | 2 |
    • | 5 | 4 | INDEX FULL SCAN | EMP_SAL | 14 | | 1 |
    • |* 6 | 2 | FILTER | | | | |
    • |* 7 | 6 | SORT JOIN | | | | |
    • | 8 | 7 | TABLE ACCESS FULL | SALGRADE | 5 | 40 | 2 |
    • | 9 | 1 | TABLE ACCESS BY INDEX ROWID | DEPT | 1 | 11 | 1 |
    • |* 10 | 9 | INDEX UNIQUE SCAN | DEPT_DEPTNO_PK | 1 | | |
    • --------------------------------------------------------------------------------------
    • Predicate Information (identified by operation id):
    • ---------------------------------------------------
    • 4 - filter("E"."DEPTNO" IS NOT NULL)
    • 6 - filter(&quot;E&quot;.&quot;SAL&quot;<=&quot;S&quot;.&quot;HISAL&quot;)
    • 7 - access(&quot;E&quot;.&quot;SAL&quot;>=&quot;S&quot;.&quot;LOSAL&quot;)
    • filter(&quot;E&quot;.&quot;SAL&quot;>=&quot;S&quot;.&quot;LOSAL&quot;)
    • 10 - access(&quot;D&quot;.&quot;DEPTNO&quot;=&quot;E&quot;.&quot;DEPTNO&quot;)
  • 12. Plan Table Evolution
    • The Plan Table Contains the information about the forecasted row source operations for the execution of the SQL statements
    • The changes in the PLAN_TABLE across versions.
    • Introduced in 9i
      • Access Predicates
      • Filter Predicates
    • 9i to 10.1
      • Projection
      • Time
      • QBlock_name
      • Plan_id
      • Object_Alias
      • Depth
    • 10.1 to 10.2
      • other_xml
    • 10.2 to 11g
      • No Changes
  • 13. DBMS_XPLAN
  • 14. DBMS_XPLAN
    • Introduced in 9iR2
    • Easy way of viewing the output of the EXPLAIN PLAN command in several, predefined formats
    • 10g has some enhanced functionality
    • We will use the DISPLAY function of DBMS_XPLAN available in 9iR2, 10g and 11g
  • 15. DBMS_XPLAN
    • Ensure that you are using the right version of the
      • PLAN_TABLE
      • DBMS_XPLAN
    • Version incompatibilities may cause some issues
    • Where is plan table and DBMS_XPLAN?
      • Plan Table - $ORACLE_HOME/rdbms/admin/utlxplan.sql
      • DBMS_XPLAN - $ORACLE_HOME/rdbms/admin/dbmsxpln.sql
  • 16. Using DBMS_XPLAN
    • EXPLAIN PLAN
    • SET STATEMENT_ID = 'abc'
    • FOR
    • select object_type, count(1)
    • from dba_objects
    • where owner= 'SCOTT'
    • group by object_type;
  • 17. DBMS_XPLAN.DISPLAY Options
    • Format parameter for this function choices are
    • BASIC – Just displays the minimum information in the plan
    • TYPICAL – Displays the relevant information in the plan and predicate information (PX information if applicable)
    • SERIAL – Like typical, but no parallel execution information even if applicable
    • ALL – All of typical including projections, alias, etc.
  • 18. DBMS_XPLAN. DISPLAY Examples
    • SELECT * FROM TABLE(dbms_xplan.display('PLAN_TABLE', 'abc','BASIC'));
    • SELECT * FROM TABLE(dbms_xplan.display('PLAN_TABLE', ‘abc','TYPICAL'));
    • SELECT * FROM TABLE(dbms_xplan.display('PLAN_TABLE',
    • 'abc','ALL'));
    • These are display formats for DBMS_XPLAN
  • 19. DBMS_XPLAN.DISPLAY Output
  • 20. DBMS_XPLAN Package - # of Procedures and Functions
  • 21. Recap
    • DBMS_XPLAN has been around since 9.2
    • It is an elegant way of looking at EXPLAIN PLAN outputs
    • The “TYPICAL” option of DBMS_XPLAN.DISPLAY is most useful because it ties predicate information (access and filters) back to the predicted row source operation lines in the explained plan
    • 11g introduced XML as an output option for plans
  • 22. V$ SQL_PLAN Views
  • 23. V$SQL and Related views View Name Description V$SQL The SQL Statement that is being executed and its non-plan details V$SQL_PLAN Contains the execution plan information for each child cursor loaded in the library cache V$SQL_PLAN_STATISTICS* Provides execution statistics at the row source level for each child cursor V$SQL_PLAN_STATISTICS_ALL*(Merges V$SQL_PLAN_STATISTICS with V$SQL_AREA) Contains memory usage statistics for row sources that use SQL memory (sort or hash-join)
  • 24. V$SQL – New Columns in 11g Column Data Type Comment TYPECHECK_MEM NUMBER ??? IS_BIND_SENSITIVE VARCHAR2(1) Indicates whether the cursor is bind sensitive (Y) or not (N). A query is considered bind-sensitive if the optimizer peeked at one of its bind variable values when computing predicate selectivities and where a change in a bind variable value may cause the optimizer to generate a different plan. IS_BIND_AWARE VARCHAR2(1) Indicates whether the cursor is bind aware (Y) or not (N). A query is considered bind-aware if it has been marked to use extended cursor sharing. The query would already have been marked as bind-sensitive. IS_SHAREABLE VARCHAR2(1) Indicates whether the cursor can be shared (Y) or not (N) SQL_PATCH VARCHAR2(30) SQL patch used for this statement, if any SQL_PLAN_BASELINE VARCHAR2(30) SQL plan baseline used for this statement, if any
  • 25. V$SQL and Related views in 11g View Name 11g enhancement V$SQL_PLAN Added child address and timestamp column V$SQL_PLAN_STATISTICS* Added child address column V$SQL_PLAN_STATISTICS_ALL*(Merges V$SQL_PLAN_STATISTICS with V$SQL_AREA) Added child address column
  • 26. Viewing V$SQL_PLAN Data
    • DBMS_XPLAN has made it easier to look at the data underlying the V$SQL_PLAN and V$SQL_PLAN_STATISTICS data
    • Available starting 10g
    • Lets you view the run time plan or the execution plan of a SQL Statement
    • Also, lets you view the execution statistics for a run of the SQL Statement or all prior runs
  • 27. Key Performance Takeaways
  • 28. New in 11g
  • 29. SQL Plan Baselines
  • 30. SQL Plan Baselines
    • DBMS_XPLAN.DISPLAY_SQL_PLAN_BASELINE takes in three arguments.
    • SQL_HANDLE  SQL_HANDLE from dba_sql_plan_baselines
    • PLAN_NAME  Name of the plan
    • FORMAT  BASIC, TYPICAL, ALL
    • Init.ora paramter optimizer_capture_sql_plan_baselines = true
    •  
    • FUNCTION DBMS_XPLAN.DISPLAY_SQL_PLAN_BASELINE RETURNS DBMS_XPLAN_TYPE_TABLE
    • Argument Name Type In/Out Default?
    • ------------------------------ ----------------------- ------ --------
    • SQL_HANDLE VARCHAR2 IN DEFAULT
    • PLAN_NAME VARCHAR2 IN DEFAULT
    • FORMAT VARCHAR2 IN DEFAULT
  • 31. SQL Plan Baselines
    • select * from table(dbms_xplan.display_sql_plan_baseline('SYS_SQL_8bab62f0bc1db3bc')) 
    • PLAN_TABLE_OUTPUT
    • ----------------------------------------------------------------
    • SQL handle: SYS_SQL_8bab62f0bc1db3bc
    • SQL text: select /*+ full(t1) */ * from t1 where c1 = 1
    • ----------------------------------------------------------------
  • 32. SQL Plan Baselines
    • Plan name: SYS_SQL_PLAN_bc1db3bc750635c2
    • Enabled: YES Fixed: NO Accepted: YES Origin: MANUAL-LOAD
    • -------------------------------------------------------------------------------------
    • Plan hash value: 1420382924
    • -------------------------------------------------------------------------------------
    • | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
    • -------------------------------------------------------------------------------------
    • | 0 | SELECT STATEMENT | | 1 | 9 | 2 (0)| 00:00:01 |
    • | 1 | TABLE ACCESS BY INDEX ROWID| T1 | 1 | 9 | 2 (0)| 00:00:01 |
    • |* 2 | INDEX RANGE SCAN | T1_N1 | 1 | | 1 (0)| 00:00:01 |
    • -------------------------------------------------------------------------------------
    • Predicate Information (identified by operation id):
    • 2 - access(&quot;C1&quot;=1)
  • 33. SQL Plan Baselines
    • Plan name: SYS_SQL_PLAN_bc1db3bcdbd90e8e
    • Enabled: YES Fixed: NO Accepted: YES Origin: AUTO-CAPTURE
    • --------------------------------------------------------------------------
    • Plan hash value: 3617692013
    • --------------------------------------------------------------------------
    • | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
    • --------------------------------------------------------------------------
    • | 0 | SELECT STATEMENT | | 1 | 9 | 59 (6)| 00:00:01 |
    • |* 1 | TABLE ACCESS FULL| T1 | 1 | 9 | 59 (6)| 00:00:01 |
    • --------------------------------------------------------------------------
    • Predicate Information (identified by operation id):
    • ---------------------------------------------------
    • 1 - filter(&quot;C1&quot;=1)
  • 34. Plan Output in XML Format
  • 35. DBMS_XPLAN.BUILD_PLAN_XML
    • dbms_xplan.build_plan_xml(
    • table_name IN VARCHAR2 DEFAULT 'PLAN_TABLE',
    • statement_id IN VARCHAR2 DEFAULT NULL,
    • plan_id IN NUMBER DEFAULT NULL,
    • format IN VARCHAR2 DEFAULT 'TYPICAL',
    • filter_preds IN VARCHAR2 DEFAULT NULL,
    • plan_tag IN VARCHAR2 DEFAULT 'plan',
    • report_ref IN VARCHAR2 DEFAULT NULL)
  • 36. Example Output
    • EXPLAIN PLAN
    • SET STATEMENT_ID = 'abc'
    • FOR
    • select object_type, count(1)
    • from dba_objects
    • where owner= 'SCOTT'
    • group by object_type;
    • The SQL Statement
    • SELECT dbms_xplan.build_plan_xml(statement_id => 'abc') AS XPLAN FROM dual;
    • accomplishes this .
  • 37. Still the good stuff…
  • 38. Access Predicates / Filter Predicates
  • 39. Access and Filter Predicates
    • select attribute1
    • from bom
    • where item_id=11
    • and org_id=2
    • and designator is null;
    • The Explain plan shows
    • --------------------------------------------------------------------------------------
    • | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
    • --------------------------------------------------------------------------------------
    • | 0 | SELECT STATEMENT | | 196 | 10584 | 142 (1)| 00:00:02 |
    • |* 1 | TABLE ACCESS BY INDEX ROWID| BOM | 196 | 10584 | 142 (1)| 00:00:02 |
    • |* 2 | INDEX RANGE SCAN | BOM_N1 | 11961 | | 31 (0)| 00:00:01 |
    • --------------------------------------------------------------------------------------
    • Predicate Information (identified by operation id):
    • ---------------------------------------------------
    • 1 - filter(&quot;DESIGNATOR&quot; IS NULL)
    • 2 - access(&quot;ITEM_ID&quot;=11 AND &quot;ORG_ID&quot;=2)
    • The Stat Lines Show
    • STAT #4 id=1 cnt=4889 pid=0 pos=1 obj=70702 op='TABLE ACCESS BY INDEX ROWID BOM (cr=787 pr=150 pw=0 time=194697 us)'
    • STAT #4 id=2 cnt=11961 pid=1 pos=1 obj=70704 op='INDEX RANGE SCAN BOM_N1 (cr=357 pr=37 pw=0 time=91948 us)'
  • 40. Access and Filter Predicates
    • select attribute1
    • from bom where
    • item_id=11
    • and org_id=2
    • and designator is null
    • --------------------------------------------------------------------------------------
    • | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
    • --------------------------------------------------------------------------------------
    • | 0 | SELECT STATEMENT | | 196 | 10584 | 4 (0)| 00:00:01 |
    • | 1 | TABLE ACCESS BY INDEX ROWID| BOM | 196 | 10584 | 4 (0)| 00:00:01 |
    • |* 2 | INDEX RANGE SCAN | BOM_U1 | 1 | | 3 (0)| 00:00:01 |
    • --------------------------------------------------------------------------------------
    • Predicate Information (identified by operation id):
    • ---------------------------------------------------
    • 2 - access(&quot;ITEM_ID&quot;=11 AND &quot;ORG_ID&quot;=2 AND &quot;DESIGNATOR&quot; IS NULL)
    • STAT Lines
    • STAT #12 id=1 cnt=4889 pid=0 pos=1 obj=70702 op='TABLE ACCESS BY INDEX ROWID BOM (cr=713 pr=0 pw=0 time=50184 us)'
    • STAT #12 id=2 cnt=4889 pid=1 pos=1 obj=72016 op='INDEX RANGE SCAN BOM_U1 (cr=339 pr=0 pw=0 time=19590 us)'
  • 41. Takeaway
    • Look for row source operation that are filtering a lot of rows
    • When a row source operation is filtering a lot of rows, it is accessing those rows and then applying the filter to discard rows that do not match the predicate qualifier
    • Evaluate indexes to access the data and not filter it
  • 42. Query Blocks
  • 43. Query Blocks
    • Useful when trouble shooting
      • Nested SQL Statements
      • Complex SQL Statements
      • Inline Views
      • Sub-Queries
      • Repeated Visits to Table
    • 10g allows you to name Query Blocks
      • QB_NAME Hint
        • e.g. /*+ QB_NAME(dept_subquery) */
      • When people write complex SQL statements, require them to name Query Blocks
    • Query Blocks
      • Add clarity to execution and explain plans
  • 44. Example
    • SELECT /*+ QB_NAME(outer) */
    • e.ename
    • , e.sal
    • FROM (
    • SELECT /*+ QB_NAME(inline_view) */
    • *
    • FROM emp e
    • WHERE e.sal > 300
    • AND e.deptno IN ( SELECT /*+ QB_NAME(dept_subquery) */ d.deptno
    • FROM dept d
    • WHERE d.dname IN ('SALES','ACCOUNTING')
    • )
    • ) e;
  • 45. Query Block with DBMS_XPLAN
    • SQL> SELECT plan_table_output
    • 2 FROM TABLE(DBMS_XPLAN.DISPLAY('PLAN_TABLE','qb_name','ALL'));
    • PLAN_TABLE_OUTPUT
    • -----------------------------------------------------------------------------------------
    • Plan hash value: 844388907
    • ----------------------------------------------------------------------------------------
    • | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
    • ----------------------------------------------------------------------------------------
    • | 0 | SELECT STATEMENT | | 7 | 182 | 6 (17)| 00:00:01 |
    • | 1 | MERGE JOIN | | 7 | 182 | 6 (17)| 00:00:01 |
    • |* 2 | TABLE ACCESS BY INDEX ROWID| DEPT | 2 | 26 | 2 (0)| 00:00:01 |
    • | 3 | INDEX FULL SCAN | PK_DEPT | 4 | | 1 (0)| 00:00:01 |
    • |* 4 | SORT JOIN | | 14 | 182 | 4 (25)| 00:00:01 |
    • |* 5 | TABLE ACCESS FULL | EMP | 14 | 182 | 3 (0)| 00:00:01 |
    • ----------------------------------------------------------------------------------------
    • Query Block Name / Object Alias (identified by operation id):
    • -------------------------------------------------------------
    • 1 - SEL$B9DAFA34
    • 2 - SEL$B9DAFA34 / D@DEPT_SUBQUERY
    • 3 - SEL$B9DAFA34 / D@DEPT_SUBQUERY
    • 5 - SEL$B9DAFA34 / E@INLINE_VIEW
  • 46. DBMS_XPLAN.DISPLAY_AWR
  • 47. DBMS_XPLAN.DISPLAY_AWR
    • DBMS_XPLAN.DISPLAY_AWR takes in four arguments.
    • SQL_ID  The SQL_ID of the statement in AWR
    • PLAN_HASH_VALUE  The Plan Hash value if available
    • DB_ID  The Database Id
    • FORMAT  Format Options.
  • 48. Need Data From…
    • dba_hist_sql_plan
    • dba_hist_sqltext
    • v_$database
    • SELECT * FROM TABLE
    • (dbms_xplan.display_awr('24033vh7b098h'));
  • 49. DBMS_XPLAN.DISPLAY_SQLSET
  • 50. DBMS_XPLAN.DISPLAY_SQLSET
    • FUNCTION DISPLAY_SQLSET RETURNS DBMS_XPLAN_TYPE_TABLE
    • Argument Name Type In/Out Default?
    • ------------------------------ ----------------------- ------ --------
    • SQLSET_NAME VARCHAR2 IN
    • SQL_ID VARCHAR2 IN
    • PLAN_HASH_VALUE NUMBER(38) IN DEFAULT
    • FORMAT VARCHAR2 IN DEFAULT
    • SQLSET_OWNER VARCHAR2 IN DEFAULT
    • Need to license
    • Diagnostic Pack
    • Tuning Pack
  • 51. DBMS_XPLAN.DISPLAY_SQLSET
    • For example, a SQL Tuning set named ‘MY_TUNING_SET’ for the sql statement with the sql_id 'g1pz63cqh5qbf', the following will displays all the execution plans.
    • An example:
    • SELECT * FROM table (DBMS_XPLAN.DISPLAY_SQLSET('MY_TUNING_SET,'g1pz63cqh5qbf'));
  • 52. DBMS_XPLAN.DISPLAY_CURSOR
  • 53. DBMS_XPLAN.DISPLAY_CURSOR
    • FUNCTION DISPLAY_CURSOR RETURNS DBMS_XPLAN_TYPE_TABLE
    • Argument Name Type In/Out Default?
    • ----------------- ------------- ------ --------
    • SQL_ID VARCHAR2 IN DEFAULT
    • CURSOR_CHILD_NO NUMBER(38) IN DEFAULT
    • FORMAT VARCHAR2 IN DEFAULT
    • SQL_ID  SQL_ID From V$SQL
    • CURSOR_CHILD_NO  CHILD_NUMBER in V$SQL
  • 54. Obtaining SQL_ID and Cursor Child Num.
    • SELECT sql_id,
    • child_number,
    • sql_text
    • FROM
    • v$sql
    • WHERE
    • LOWER(sql_text) LIKE
    • ‘ <begin sql statement string>%'
  • 55. FORMAT
    • BASIC, TYPICAL, SERIAL, ALL
      • To view the execution plans alone
    • Viewing Stats about the plan
      • Introduced in 10g R1
      • Enhanced in 10g R2
      • Set STATISTICS_LEVEL=ALL at the session level
        • OR
      • Set the GATHER_PLAN_STATISTICS hint
  • 56. Viewing the execution plan in V$SQL
    • SELECT plan_table_output
    • FROM TABLE(DBMS_XPLAN.DISPLAY_CURSOR('3a3dz5yva4vnf',0,'ALL'));
  • 57. Viewing the Run Time Stats of the Execution Plan
    • SELECT plan_table_output
    • FROM TABLE(DBMS_XPLAN.DISPLAY_CURSOR('3a3dz5yva4vnf',0,‘<Various Options>'));
    • IOSTATS
    • MEMSTATS
    • ALLSTATS
    • IOSTATS LAST
    • MEMSTATS LAST
    • ALLSTATS LAST
  • 58. Demo
    • Demo.sql
  • 59. Q & Q U E S T I O N S A N S W E R S