Getting the Right Cardinality Thomas Kyte

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Getting the Right Cardinality

Thomas Kytehttp://asktom.oracle.com/

Why do we gather statistics?

“Cardinality”

“Wrong Plan => Wrong Cardinality”

“Wrong Cardinality => Wrong Plan”

Wrong Plan => Wrong Cardinality

ops$tkyte%ORA11GR2> create table t

2 as select decode( mod(rownum,2), 0, 'N', 'Y' ) flag1,

3 decode( mod(rownum,2), 0, 'Y', 'N' ) flag2, a.*

4 from all_objects a

5 /

Table created.

ops$tkyte%ORA11GR2> create index t_idx on t(flag1,flag2);

Index created.

ops$tkyte%ORA11GR2> begin

2 dbms_stats.gather_table_stats

3 ( user, 'T',

4 method_opt=>'for all indexed columns size 254' );

5 end;

6 /

PL/SQL procedure successfully completed.


ops$tkyte%ORA11GR2> select 'select * from t', num_rows

2 from user_tables where table_name = 'T'

3 union all

4 select 'select * from t where flag1 = "N"', num_rows/2


6 union all

7 select 'select * from t where flag2 = "N"', num_rows/2


9 union all

10 select 'select * from t where flag1 = "N" and flag2 = "N"', num_rows/2/2

11 from user_tables where table_name = 'T';

'SELECT*FROMT' NUM_ROWS

------------------------------------------------- ----------

select * from t 72726

select * from t where flag1 = "N" 36363

select * from t where flag2 = "N" 36363

select * from t where flag1 = "N" and flag2 = "N" 18181.5


ops$tkyte%ORA11GR2> set autotrace traceonly explain

ops$tkyte%ORA11GR2> select * from t where flag1='N';

Execution Plan

----------------------------------------------------------

Plan hash value: 1601196873

--------------------------------------------------------------------------

| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |

--------------------------------------------------------------------------

| 0 | SELECT STATEMENT | | 36499 | 3635K| 301 (1)| 00:00:04 |

|* 1 | TABLE ACCESS FULL| T | 36499 | 3635K| 301 (1)| 00:00:04 |

--------------------------------------------------------------------------

Predicate Information (identified by operation id):

---------------------------------------------------

1 - filter("FLAG1"='N')


ops$tkyte%ORA11GR2> select * from t where flag2='N';

Execution Plan

----------------------------------------------------------


--------------------------------------------------------------------------


--------------------------------------------------------------------------



--------------------------------------------------------------------------


---------------------------------------------------

1 - filter("FLAG2"='N')


ops$tkyte%ORA11GR2> select * from t where flag1='N' and flag2='N';

Execution Plan

----------------------------------------------------------


--------------------------------------------------------------------------


--------------------------------------------------------------------------



--------------------------------------------------------------------------


---------------------------------------------------

1 - filter("FLAG2"='N' AND "FLAG1"='N')


ops$tkyte%ORA11GR2> select /*+ gather_plan_statistics */ *

2 from t where flag1='N' and flag2='N';

no rows selected


ops$tkyte%ORA11GR2> select * from table(dbms_xplan.display_cursor(null,null,'ALLSTATS LAST'));

PLAN_TABLE_OUTPUT

------------------------------------------------------------------------------------

| Id | Operation | Name | Starts | E-Rows | A-Rows | A-Time | Buffers |

------------------------------------------------------------------------------------

| 0 | SELECT STATEMENT | | 1 | | 0 |00:00:00.02 | 1080 |

|* 1 | TABLE ACCESS FULL| T | 1 | 18181 | 0 |00:00:00.02 | 1080 |

------------------------------------------------------------------------------------


---------------------------------------------------

1 - filter(("FLAG2"='N' AND "FLAG1"='N'))

19 rows selected.


ops$tkyte%ORA11GR2> select /*+ dynamic_sampling(t 3) */ * from t where flag1='N' and flag2='N';

Execution Plan

----------------------------------------------------------


-------------------------------------------------------------------------------------


-------------------------------------------------------------------------------------

| 0 | SELECT STATEMENT | | 6 | 612 | 2 (0)| 00:00:01 |

| 1 | TABLE ACCESS BY INDEX ROWID| T | 6 | 612 | 2 (0)| 00:00:01 |

|* 2 | INDEX RANGE SCAN | T_IDX | 6 | | 1 (0)| 00:00:01 |

-------------------------------------------------------------------------------------


---------------------------------------------------

2 - access("FLAG1"='N' AND "FLAG2"='N')

Note

-----

- dynamic sampling used for this statement (level=2)


SELECT /* OPT_DYN_SAMP */ /*+ ALL_ROWS IGNORE_WHERE_CLAUSE

NO_PARALLEL(SAMPLESUB) opt_param('parallel_execution_enabled', 'false')

NO_PARALLEL_INDEX(SAMPLESUB) NO_SQL_TUNE */

NVL(SUM(C1),:"SYS_B_00"), NVL(SUM(C2),:"SYS_B_01"), NVL(SUM(C3),:"SYS_B_02")

FROM

(SELECT /*+ IGNORE_WHERE_CLAUSE NO_PARALLEL("T") FULL("T")

NO_PARALLEL_INDEX("T") */

:"SYS_B_03" AS C1,

CASE WHEN "T"."FLAG1"= :"SYS_B_04" AND "T"."FLAG2"=:"SYS_B_05"

THEN :"SYS_B_06"

ELSE :"SYS_B_07"

END AS C2,

CASE WHEN "T"."FLAG2"=:"SYS_B_08" AND "T"."FLAG1"=:"SYS_B_09“

THEN :"SYS_B_10"

ELSE :"SYS_B_11"

END AS C3

FROM "OPS$TKYTE"."T"

SAMPLE BLOCK (:"SYS_B_12" , :"SYS_B_13") SEED (:"SYS_B_14") "T") SAMPLESUB

Small Change – but think about it…


2 as

3 select substr(object_name, 1, 1 ) str, all_objects.*

4 from all_objects

5 order by dbms_random.random;

Table created.

ops$tkyte%ORA11GR2> create index t_idx on t(str,object_name);

Index created.



3 ( user, 'T',

4 method_opt => 'for all indexed columns size 254',

5 estimate_percent=>100 );

6 end;

7 /


ops$tkyte%ORA11GR2> select count(subobject_name) from t t1 where str = 'T';

…

--------------------------------------------------------------------------------------


--------------------------------------------------------------------------------------


| 1 | SORT AGGREGATE | | 1 | 19 | | |

| 2 | TABLE ACCESS BY INDEX ROWID| T | 292 | 5548 | 296 (0)| 00:00:04 |

|* 3 | INDEX RANGE SCAN | T_IDX | 292 | | 4 (0)| 00:00:01 |

--------------------------------------------------------------------------------------


ops$tkyte%ORA11GR2> insert into t

2 select 'T', all_objects.*

3 from all_objects

4 where rownum <= 1;

1 row created.



3 ( user, 'T',

4 method_opt => 'for all indexed columns size 254',

5 estimate_percent=>100 );

6 end;

7 /



ops$tkyte%ORA11GR2> select count(subobject_name) from t t2 where str = 'T';

…

---------------------------------------------------------------------------


---------------------------------------------------------------------------


| 1 | SORT AGGREGATE | | 1 | 19 | | |

|* 2 | TABLE ACCESS FULL| T | 293 | 5567 | 297 (1)| 00:00:04 |

---------------------------------------------------------------------------


Statistics Basics

Things Change over Time

• In 10g and before, it was very common to “program” our statistics gathering– Unique set of inputs for each and every table and index

• In 11g, you should as often as possible allow everything except the segment name and DOP to default– Why is this?

• However…

21

You are being WATCHED!

ops$tkyte%ORA11GR2> create table t 2 as 3 select a.*, 4 case when rownum < 500 5 then 1 6 else 99 7 end some_status 8 from all_objects a 9 /Table created.

22


ops$tkyte%ORA11GR2> begin 2 dbms_stats.gather_table_stats(user,'T'); 3 end; 4 /


23


ops$tkyte%ORA11GR2> select histogram 2 from user_tab_cols 3 where table_name = 'T' 4 and column_name = 'SOME_STATUS';

HISTOGRAM---------------NONE

24


ops$tkyte%ORA11GR2> create index t_idx on t(some_status);

Index created.

25


ops$tkyte%ORA11GR2> select * from t where some_status = 99;

Execution Plan----------------------------------------------------------Plan hash value: 1601196873

--------------------------------------------------------------------------| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |--------------------------------------------------------------------------| 0 | SELECT STATEMENT | | 36115 | 3526K| 300 (1)| 00:00:04 ||* 1 | TABLE ACCESS FULL| T | 36115 | 3526K| 300 (1)| 00:00:04 |--------------------------------------------------------------------------

26


ops$tkyte%ORA11GR2> begin 2 dbms_stats.gather_table_stats( user, 'T' ); 3 end; 4 /


27


ops$tkyte%ORA11GR2> select histogram 2 from user_tab_cols 3 where table_name = 'T' 4 and column_name = 'SOME_STATUS';

HISTOGRAM---------------FREQUENCY

28




--------------------------------------------------------------------------------| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time --------------------------------------------------------------------------------| 0 | SELECT STATEMENT | | 539 | 53900 | 10 (0)| 00:00| 1 | TABLE ACCESS BY INDEX ROWID| T | 539 | 53900 | 10 (0)| 00:00|* 2 | INDEX RANGE SCAN | T_IDX | 539 | | 2 (0)| 00:00--------------------------------------------------------------------------------

29





30

Index Statistics – little known fact


2 as

3 select *

4 from all_objects

5 /

Table created.

ops$tkyte%ORA11GR2> create index t_idx on t(object_id);

Index created.

ops$tkyte%ORA11GR2> select num_rows, sample_size, last_analyzed

2 from user_indexes

3 where index_name = 'T_IDX';

NUM_ROWS SAMPLE_SIZE LAST_ANAL

---------- ----------- ---------

72726 72726 17-JUL-12

Other Ways to Get Statistics

Other ways to get statistics

• DBMS_STATS.SET_xxx– If you know the statistics, just tell us

• DBMS_STATS.COPY_xxx– If you have something representative, just use to them to start

• Dynamic Sampling…• SQL Profiles• Extended Statistics• Cardinality Feedback• Cardinality Hint

Dynamic Sampling

• http://www.oracle.com/technetwork/issue-archive/2009/09-jan/o19asktom-086775.html– Google: site:www.oracle.com kyte dynamic

• Already demonstrated

• Levels– 2 – sample any unanalyzed table during hard parse– 3 – same as 2 but add “sample during guess” for single

column guesses– 4 – same as 3 but add “sample during guess” for multi-

column guesses

http://www.oracle.com/technetwork/issue-archive/2009/09-jan/o19asktom-086775.html

http://www.oracle.com/technetwork/issue-archive/2009/09-jan/o19asktom-086775.html

SQL Profiles

• Analyzing a query• Stores better estimated cardinalities – Gets these by using your workload against your data– Important to be done in the right environment– Are just statistics really, so yes, they can go stale

• Applied at hard parse time

SQL Profiles

ops$tkyte@ORA11G> create or replace procedure p

2 as

3 cursor c1

4 is

5 select object_id, object_name

6 from sqlprof

7 order by object_id;

9 l_object_id sqlprof.object_id%type;

10 l_object_name sqlprof.object_name%type;

11 begin

12 open c1;

13 for i in 1 .. 10

14 loop

15 fetch c1 into l_object_id, l_object_name;

16 exit when c1%notfound;

17 -- ....

18 end loop;

19 end;

20 /

Procedure created.

SQL Profiles

SELECT OBJECT_ID, OBJECT_NAME FROM SQLPROF ORDER BY OBJECT_ID

call count cpu elapsed query current rows

------- ------ -------- ---------- ---------- ---------- ----------

Parse 1 0.00 0.00 0 0 0

Execute 1 0.00 0.00 0 0 0

Fetch 10 0.07 0.10 659 0 10

------- ------ -------- ---------- ---------- ---------- ----------

total 12 0.07 0.10 659 0 10

Misses in library cache during parse: 1

Optimizer mode: ALL_ROWS

Parsing user id: 410 (recursive depth: 1)

Rows Row Source Operation

------- ---------------------------------------------------

10 SORT ORDER BY (cr=659 pr=0 pw=0 time=101152 us)

47487 TABLE ACCESS FULL SQLPROF (cr=659 pr=0 pw=0 time=47604 us)

SQL Profiles

ops$tkyte@ORA11G> declare

2 l_sql_id v$sql.sql_id%type;

3 begin

4 select sql_id into l_sql_id

5 from v$sql

6 where sql_text = 'SELECT OBJECT_ID, OBJECT_NAME

FROM SQLPROF ORDER BY OBJECT_ID';

7 dbms_output.put_line(

8 sys.dbms_sqltune.create_tuning_task 9 ( sql_id => l_sql_id,

10 task_name => 'sqlprof_query' ) || ' in place...' );

11 dbms_sqltune.execute_tuning_task

12 ( task_name => 'sqlprof_query' );

13 end;

14 /


SQL Profiles

ops$tkyte@ORA11G> SELECT DBMS_SQLTUNE.REPORT_TUNING_TASK( 'sqlprof_query')

2 FROM DUAL;

DBMS_SQLTUNE.REPORT_TUNING_TASK('SQLPROF_QUERY')

--------------------------------------------------------------------------------

GENERAL INFORMATION SECTION

…

-------------------------------------------------------------------------------

SQL ID : 3zfpa86satsm3

SQL Text: SELECT OBJECT_ID, OBJECT_NAME FROM SQLPROF ORDER BY OBJECT_ID

-------------------------------------------------------------------------------

FINDINGS SECTION (1 finding)

-------------------------------------------------------------------------------

1- SQL Profile Finding (see explain plans section below)

--------------------------------------------------------

A potentially better execution plan was found for this statement.

Recommendation (estimated benefit: 99.45%)

------------------------------------------

Consider accepting the recommended SQL profile.

execute :profile_name := dbms_sqltune.accept_sql_profile(task_name =>

'sqlprof_query')

SQL Profiles

1- Original With Adjusted Cost

------------------------------


--------------------------------------------------------------------------------------

| Id | Operation | Name | Rows | Bytes |TempSpc| Cost (%CPU)| Time|

--------------------------------------------------------------------------------------

| 0 | SELECT STATEMENT | | 47487 | 1391K| | 546 (3)| 00:00:07 |

| 1 | SORT ORDER BY | | 47487 | 1391K| 3736K| 546 (3)| 00:00:07 |

| 2 | TABLE ACCESS FULL| SQLPROF | 47487 | 1391K| | 151 (2)| 00:00:02 |

--------------------------------------------------------------------------------------

2- Using SQL Profile

--------------------


------------------------------------------------------------------------------------------ | Id | Operation | Name | Rows | Bytes | Cost (%CPU)|Time | ------------------------------------------------------------------------------------------

| 0 | SELECT STATEMENT | | 10 | 300 | 3 (0)|00:00:01 |

| 1 | TABLE ACCESS BY INDEX ROWID| SQLPROF | 47487 | 1391K| 3 (0)|00:00:01 |

| 2 | INDEX FULL SCAN | SQLPROF_PK | 10 | | 2 (0)|00:00:01 |

------------------------------------------------------------------------------------------

Extended Statistics

• https://blogs.oracle.com/optimizer/entry/extended_statistics• In fact, https://blogs.oracle.com/optimizer should be

mandatory reading!

• Create statistics on sets of columns (correlated columns)

• Create statistics on expressions (functions)

https://blogs.oracle.com/optimizer/entry/extended_statistics

https://blogs.oracle.com/optimizer/entry/extended_statistics

https://blogs.oracle.com/optimizer

41

Extended Statistics

ops$tkyte%ORA11GR2> create table t 2 as 3 select * 4 from all_objects;Table created. ops$tkyte%ORA11GR2> create index t_idx on t(owner,object_type);Index created.

ops$tkyte%ORA11GR2> exec dbms_stats.gather_table_stats( user, 'T', method_opt=>'for all columns size 254' );


42

Extended Statistics

ops$tkyte%ORA11GR2> set autotrace traceonly explainops$tkyte%ORA11GR2> select * from t where owner = 'PUBLIC' and object_type = 'JAVA CLASS';



Predicate Information (identified by operation id):---------------------------------------------------

1 - filter("OBJECT_TYPE"='JAVA CLASS' AND "OWNER"='PUBLIC')

43

Extended Statistics

ops$tkyte%ORA11GR2> select dbms_stats.create_extended_stats( user, 'T', '(owner,object_type)' ) x from dual;

X--------------------------------------------------SYS_STUXJ8K0YTS_5QD1O0PEA514IY



44

Extended Statistics

ops$tkyte%ORA11GR2> set autotrace traceonly explainops$tkyte%ORA11GR2> select * from t where owner = 'PUBLIC' and object_type = 'JAVA CLASS';


-------------------------------------------------------------------------------------| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |-------------------------------------------------------------------------------------| 0 | SELECT STATEMENT | | 7 | 763 | 2 (0)| 00:00:01 || 1 | TABLE ACCESS BY INDEX ROWID| T | 7 | 763 | 2 (0)| 00:00:01 ||* 2 | INDEX RANGE SCAN | T_IDX | 7 | | 1 (0)| 00:00:01 |-------------------------------------------------------------------------------------


2 - access("OWNER"='PUBLIC' AND "OBJECT_TYPE"='JAVA CLASS')

Extended Statistics

• See https://blogs.oracle.com/optimizer/entry/how_do_i_know_what_extended_statistics_are_needed_for_a_given_workload for how to have these column groups automatically built for you

• Extended statistics on functions done exactly the same

https://blogs.oracle.com/optimizer/entry/how_do_i_know_what_extended_statistics_are_needed_for_a_given_workload



46

Extended Statistics

ops$tkyte%ORA11GR2> create table t 2 as 3 select rownum a, -rownum b, all_objects.* 4 from all_objects;

Table created.



ops$tkyte%ORA11GR2> select 0.05 * count(*) from t;

0.05*COUNT(*)------------- 3635.15

47

Extended Statistics

ops$tkyte%ORA11GR2> set autotrace traceonly explainops$tkyte%ORA11GR2> select * from t where (a+b)/2 > 50;




1 - filter(("A"+"B")/2>50)

48

Extended Statistics

ops$tkyte%ORA11GR2> set autotrace offops$tkyte%ORA11GR2> ops$tkyte%ORA11GR2> select dbms_stats.create_extended_stats( user, 'T', '((a+b)/2)' ) x from dual;

X--------------------------------------------------SYS_STUS9G#61NMFNG0T#HK9W8062Y



49

Extended Statistics

ops$tkyte%ORA11GR2> set autotrace traceonly explainops$tkyte%ORA11GR2> select * from t where (a+b)/2 > 50;


--------------------------------------------------------------------------| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |--------------------------------------------------------------------------| 0 | SELECT STATEMENT | | 1 | 110 | 320 (1)| 00:00:04 ||* 1 | TABLE ACCESS FULL| T | 1 | 110 | 320 (1)| 00:00:04 |--------------------------------------------------------------------------


1 - filter(("A"+"B")/2>50)

50

Cardinality Feedback

ops$tkyte%ORA11GR2> create or replace type str2tblType as table of varchar2(30) 2 /Type created.

ops$tkyte%ORA11GR2> create or replace function str2tbl( p_str in varchar2, p_delim in varchar2 default ',' ) return str2tblType 2 PIPELINED 3 as 4 l_str long default p_str || p_delim; 5 l_n number; 6 begin 7 loop 8 l_n := instr( l_str, p_delim ); 9 exit when (nvl(l_n,0) = 0); 10 pipe row( ltrim(rtrim(substr(l_str,1,l_n-1))) ); 11 l_str := substr( l_str, l_n+1 ); 12 end loop; 13 return; 14 end; 15 /Function created.

51


ops$tkyte%ORA11GR2> var in_list varchar2(255)ops$tkyte%ORA11GR2> exec :in_list := 'DBMS_PIPE,DBMS_OUTPUT,UTL_FILE';


ops$tkyte%ORA11GR2> ops$tkyte%ORA11GR2> with data as 2 ( select /*+ materialize */ distinct * 3 from TABLE(cast( str2tbl( :in_list ) as str2tblType) ) t 4 ) 5 select * from data;

COLUMN_VALUE------------------------------DBMS_PIPEDBMS_OUTPUTUTL_FILE

52


---------------------------------------------------------------------------------------------------------| Id | Operation | Name | Rows | Bytes | Cost (%CPU)|---------------------------------------------------------------------------------------------------------| 0 | SELECT STATEMENT | | | | 33 (100)|| 1 | TEMP TABLE TRANSFORMATION | | | | || 2 | LOAD AS SELECT | | | | || 3 | HASH UNIQUE | | 8168 | 16336 | 30 (4)|| 4 | COLLECTION ITERATOR PICKLER FETCH| STR2TBL | 8168 | 16336 | 29 (0)|| 5 | VIEW | | 8168 | 135K| 3 (0)|| 6 | TABLE ACCESS FULL | SYS_TEMP_0FD9D660F_52718F2 | 8168 | 16336 | 3 (0)|---------------------------------------------------------------------------------------------------------

20 rows selected.

53


---------------------------------------------------------------------------------------------------------| Id | Operation | Name | Rows | Bytes | Cost (%CPU)|---------------------------------------------------------------------------------------------------------| 0 | SELECT STATEMENT | | | | 33 (100)|| 1 | TEMP TABLE TRANSFORMATION | | | | || 2 | LOAD AS SELECT | | | | || 3 | HASH UNIQUE | | 8168 | 16336 | 30 (4)|| 4 | COLLECTION ITERATOR PICKLER FETCH| STR2TBL | 8168 | 16336 | 29 (0)|| 5 | VIEW | | 3 | 51 | 3 (0)|| 6 | TABLE ACCESS FULL | SYS_TEMP_0FD9D6610_52718F2 | 3 | 6 | 3 (0)|---------------------------------------------------------------------------------------------------------

Note----- - cardinality feedback used for this statement

24 rows selected.

54


ops$tkyte%ORA11GR2> create table t 2 as 3 select * from all_objects;

Table created.

ops$tkyte%ORA11GR2> ops$tkyte%ORA11GR2> create index t_idx on t(object_name);

Index created.

ops$tkyte%ORA11GR2> ops$tkyte%ORA11GR2> exec dbms_stats.gather_table_stats(user,'T');


55


ops$tkyte%ORA11GR2> with data as 2 ( select /*+ materialize */ distinct * 3 from TABLE(cast( str2tbl( :in_list ) as str2tblType) ) t 4 ) 5 select t.object_id, t.object_name from data, t 6 where t.object_name = data.column_value;

OBJECT_ID OBJECT_NAME---------- ------------------------------ 4972 DBMS_OUTPUT 4973 DBMS_OUTPUT 4982 UTL_FILE 4983 UTL_FILE 7929 DBMS_PIPE 7930 DBMS_PIPE 8842 DBMS_OUTPUT 11587 UTL_FILE 11626 DBMS_PIPE 72606 UTL_FILE

10 rows selected.

56


---------------------------------------------------------------------------------------------------------| Id | Operation | Name | Rows | Cost (%CPU)| Time---------------------------------------------------------------------------------------------------------| 0 | SELECT STATEMENT | | | 324 (100)|| 1 | TEMP TABLE TRANSFORMATION | | | || 2 | LOAD AS SELECT | | | || 3 | HASH UNIQUE | | 8168 | 30 (4)| 00:00:01| 4 | COLLECTION ITERATOR PICKLER FETCH| STR2TBL | 8168 | 29 (0)| 00:00:01|* 5 | HASH JOIN | | 13630 | 294 (1)| 00:00:04| 6 | VIEW | | 8168 | 3 (0)| 00:00:01| 7 | TABLE ACCESS FULL | SYS_TEMP_0FD9D6611_52718F2 | 8168 | 3 (0)| 00:00:01| 8 | TABLE ACCESS FULL | T | 72708 | 290 (1)| 00:00:04---------------------------------------------------------------------------------------------------------


5 - access("T"."OBJECT_NAME"="DATA"."COLUMN_VALUE")

28 rows selected.

57


---------------------------------------------------------------------------------------------------------| Id | Operation | Name | Rows | Cost (%CPU)| Time---------------------------------------------------------------------------------------------------------| 0 | SELECT STATEMENT | | | 42 (100)|| 1 | TEMP TABLE TRANSFORMATION | | | || 2 | LOAD AS SELECT | | | || 3 | HASH UNIQUE | | 8168 | 30 (4)| 00:00:01| 4 | COLLECTION ITERATOR PICKLER FETCH| STR2TBL | 8168 | 29 (0)| 00:00:01| 5 | NESTED LOOPS | | | || 6 | NESTED LOOPS | | 5 | 12 (0)| 00:00:01| 7 | VIEW | | 3 | 3 (0)| 00:00:01| 8 | TABLE ACCESS FULL | SYS_TEMP_0FD9D6612_52718F2 | 3 | 3 (0)| 00:00:01|* 9 | INDEX RANGE SCAN | T_IDX | 2 | 2 (0)| 00:00:01| 10 | TABLE ACCESS BY INDEX ROWID | T | 2 | 3 (0)| 00:00:01---------------------------------------------------------------------------------------------------------


9 - access("T"."OBJECT_NAME"="DATA"."COLUMN_VALUE")

Note----- - cardinality feedback used for this statement

34 rows selected.

58

Cardinality Hint

ops$tkyte%ORA11GR2> with data as 2 ( select * 3 from TABLE(cast( str2tbl( :in_list ) as str2tblType) ) t 4 ) 5 select t.object_id, t.object_name 6 from data, t 7 where t.object_name = data.column_value;

OBJECT_ID OBJECT_NAME---------- ------------------------------ 4972 DBMS_OUTPUT 4973 DBMS_OUTPUT 4982 UTL_FILE 4983 UTL_FILE 7929 DBMS_PIPE 7930 DBMS_PIPE 8842 DBMS_OUTPUT 11587 UTL_FILE 11626 DBMS_PIPE 72606 UTL_FILE10 rows selected.

59

Cardinality Hint

----------------------------------------------------------------------------------------------| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |----------------------------------------------------------------------------------------------| 0 | SELECT STATEMENT | | | | 320 (100)| ||* 1 | HASH JOIN | | 13630 | 425K| 320 (1)| 00:00:04 || 2 | COLLECTION ITERATOR PICKLER FETCH| STR2TBL | 8168 | 16336 | 29 (0)| 00:00:01 || 3 | TABLE ACCESS FULL | T | 72708 | 2130K| 290 (1)| 00:00:04 |----------------------------------------------------------------------------------------------


1 - access("T"."OBJECT_NAME"=VALUE(KOKBF$))

22 rows selected.

60

Cardinality Hint

ops$tkyte%ORA11GR2> with data as 2 ( select /*+ cardinality( t, 10 ) */ * 3 from TABLE(cast( str2tbl( :in_list ) as str2tblType) ) t 4 ) 5 select t.object_id, t.object_name 6 from data, t 7 where t.object_name = data.column_value;

OBJECT_ID OBJECT_NAME---------- ------------------------------ 4972 DBMS_OUTPUT 4973 DBMS_OUTPUT 4982 UTL_FILE 4983 UTL_FILE 7929 DBMS_PIPE 7930 DBMS_PIPE 8842 DBMS_OUTPUT 11587 UTL_FILE 11626 DBMS_PIPE 72606 UTL_FILE10 rows selected.

61

Cardinality Hint

-----------------------------------------------------------------------------------------------| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |-----------------------------------------------------------------------------------------------| 0 | SELECT STATEMENT | | | | 59 (100)| || 1 | NESTED LOOPS | | | | | || 2 | NESTED LOOPS | | 17 | 544 | 59 (0)| 00:00:01 || 3 | COLLECTION ITERATOR PICKLER FETCH| STR2TBL | 10 | 20 | 29 (0)| 00:00:01 ||* 4 | INDEX RANGE SCAN | T_IDX | 2 | | 2 (0)| 00:00:01 || 5 | TABLE ACCESS BY INDEX ROWID | T | 2 | 60 | 3 (0)| 00:00:01 |-----------------------------------------------------------------------------------------------


4 - access("T"."OBJECT_NAME"=VALUE(KOKBF$))

25 rows selected.

When all else Fails…

Copyright © 2012, Oracle and/or its affiliates. All rights reserved.85

If you can hint it, baseline it

Its not always possible to add hints to third party applications Hints can be extremely difficult to manage over time Once added never removed

Alternative approach to hints

Solution Use SQL Plan Management (SPM) Influence the execution plan without adding hints directly to queries SPM available in EE, no additional options required


If you can hint it, baseline itSQL Plan Management

Parse

HJ

HJ

GB

Plan history

Plan baseline

Execute

Plan Acceptable

HJ

HJ

GB

Users



Parse

NL

NL

GB

Plan history

Plan baseline

HJ

HJ

GB

Users

NL

NL

GB



Parse

Plan history

Plan baseline

Execute

Plan Acceptable

HJ

HJ

GB

Users

NL

NL

GB

HJ

HJ

GB


Influence execution plan without adding hints

Simple two table join between the SALES and PRODUCTS tables

Example Overview

Group By

HASH JOIN

TABLE ACCESS SALES

TABLE ACCESS PRODUCTS

Group By

HASH JOIN

TABLE ACCESS SALESINDEX RANGE SCAN

PROD_SUPP_ID_INDX

Current Plan Desired Plan


Influence execution plan without adding hintsStep 1. Execute the non-hinted SQL statement


Influence execution plan without adding hintsDefault plan is uses full table scans followed by a hash join


Influence execution plan without adding hintsStep 2. Find the SQL_ID for the non-hinted statement in V$SQL


Influence execution plan without adding hintsStep 3. Create a SQL plan baseline for the non-hinted SQL statement


Influence execution plan without adding hintsStep 4. Captured Plan is not our desired plan so it should be disabled


Influence execution plan without adding hintsStep 5. Modify the SQL statement to use the hint(s) & execute it


Influence execution plan without adding hintsStep 6. Find SQL_ID & PLAN_HASH_VALUE for hinted SQL stmt


Influence execution plan without adding hintsStep 7. Associate hinted plan with original SQL stmt’s SQL HANDLE

Sql_id & plan_hash_value belong to hinted statement

sql_handle is for the non-hinted statement


Influence execution plan without adding hintsStep 8. Confirm SQL stmt has two plans in it’s baseline

Hinted plan only accepted plan for non-hinted SQL stmt


Influence execution plan without adding hintsStep 9. Confirm hinted plan is being used

Non-hinted SQL text but it is using the plan hash value for the hinted stmt

Note section also confirms SQL plan baseline used for stmt

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Getting the right CardinalityThomas Kytehttp://asktom.oracle.com/

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Getting the Right Cardinality Thomas Kyte