1. By Louis liu www.vmcd.org
DBMS_STATS Advanced Tips
This article is major to introduce advanced usage of dbms_stats for CG(column group ) of extened statistics.
We start this test on oracle 11.2.0.3 oel5.8 64bit :
Connected to:
Oracle Database 11g Enterprise Edition Release 11.2.0.3.0 - 64bit Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options
SQL> show user
USER is "TEST"
SQL> CREATE TABLE sampletable( id NUMBER,
2. By Louis liu www.vmcd.org
2 hotelname VARCHAR2(50),
city VARCHAR2(50),
country VARCHAR2(20));
INSERT INTO sampletable VALUES( 1, 'Pullman','Barcelona','Spain' );
INSERT INTO sampletable VALUES( 2, 'Gran Melia Fenix','Madrid','Spain' );
INSERT INTO sampletable VALUES( 3, 'Melia Castilla','Madrid','Spain' );
INSERT INTO sampletable VALUES( 4, 'Trump International','New York','US' );
INSERT INTO sampletable VALUES( 5, 'Four Seasons','New York','US' );
INSERT INTO sampletable VALUES( 6, 'Ambasciatori Palace','Rome','Italy' );
COMMIT; 3 4
Table created.
3. By Louis liu www.vmcd.org
SQL> SQL>
1 row created.
SQL>
1 row created.
SQL>
1 row created.
SQL>
1 row created.
SQL>
4. By Louis liu www.vmcd.org
1 row created.
SQL>
1 row created.
SQL>
Commit complete.
Now gather table statistics
5. By Louis liu www.vmcd.org
SQL> EXEC SYS.DBMS_STATS.GATHER_TABLE_STATS (OwnName => 'TEST', TabName => 'sampletable', Method_Opt => 'FOR
ALL COLUMNS size 254', Cascade => TRUE );
PL/SQL procedure successfully completed.
SQL> SELECT COLUMN_NAME, NUM_DISTINCT FROM DBA_TAB_COL_STATISTICS WHERE TABLE_NAME = 'SAMPLETABLE';
COLUMN_NAME NUM_DISTINCT
------------------------------ ------------
COUNTRY 3
CITY 4
6. By Louis liu www.vmcd.org
HOTELNAME 6
ID 6
SQL> conn test/test
Connected.
SQL> EXPLAIN PLAN FOR SELECT * FROM sampletable WHERE city = 'Madrid';
Explained.
SQL> SELECT PLAN_TABLE_OUTPUT FROM TABLE(DBMS_XPLAN.DISPLAY( format => 'ALLSTATS' ));
PLAN_TABLE_OUTPUT
------------------------------------------------------------------------------------------------------------------------------------------------------------------
7. By Louis liu www.vmcd.org
------------------------------------------------------------------------------------------------------------------------------------------
Plan hash value: 2813936524
--------------------------------------------------
| Id | Operation | Name | E-Rows |
--------------------------------------------------
| 0 | SELECT STATEMENT | | 2 |
|* 1 | TABLE ACCESS FULL| SAMPLETABLE | 2 |
--------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
8. By Louis liu www.vmcd.org
PLAN_TABLE_OUTPUT
------------------------------------------------------------------------------------------------------------------------------------------------------------------
------------------------------------------------------------------------------------------------------------------------------------------
1 - filter("CITY"='Madrid')
Note
-----
- Warning: basic plan statistics not available. These are only collected when:
* hint 'gather_plan_statistics' is used for the statement or
* parameter 'statistics_level' is set to 'ALL', at session or system level
19 rows selected.
9. By Louis liu www.vmcd.org
SQL> EXPLAIN PLAN FOR SELECT * FROM sampletable WHERE country = 'Spain';
Explained.
SQL> SELECT PLAN_TABLE_OUTPUT FROM TABLE(DBMS_XPLAN.DISPLAY( format => 'ALLSTATS' ));
PLAN_TABLE_OUTPUT
------------------------------------------------------------------------------------------------------------------------------------------------------------------
------------------------------------------------------------------------------------------------------------------------------------------
Plan hash value: 2813936524
--------------------------------------------------
10. By Louis liu www.vmcd.org
| Id | Operation | Name | E-Rows |
--------------------------------------------------
| 0 | SELECT STATEMENT | | 3 |
|* 1 | TABLE ACCESS FULL| SAMPLETABLE | 3 |
--------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
PLAN_TABLE_OUTPUT
------------------------------------------------------------------------------------------------------------------------------------------------------------------
------------------------------------------------------------------------------------------------------------------------------------------
11. By Louis liu www.vmcd.org
1 - filter("COUNTRY"='Spain')
Note
-----
- Warning: basic plan statistics not available. These are only collected when:
* hint 'gather_plan_statistics' is used for the statement or
* parameter 'statistics_level' is set to 'ALL', at session or system level
19 rows selected.
12. By Louis liu www.vmcd.org
Use dbms_stats.seed_col_usage turns on monitoring for 5 minutes or 300 seconds
SQL> begin
2 dbms_stats.seed_col_usage(null,null,300);
3 end;
4 /
PL/SQL procedure successfully completed.
SQL> EXPLAIN PLAN FOR SELECT * FROM sampletable WHERE city = 'Madrid' and country = 'Spain';
Explained.
13. By Louis liu www.vmcd.org
SQL> SELECT PLAN_TABLE_OUTPUT FROM TABLE(DBMS_XPLAN.DISPLAY( format => 'ALLSTATS' ));
PLAN_TABLE_OUTPUT
------------------------------------------------------------------------------------------------------------------------------------------------------------------
------------------------------------------------------------------------------------------------------------------------------------------
Plan hash value: 2813936524
--------------------------------------------------
| Id | Operation | Name | E-Rows |
--------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | ------------------->incorrect
|* 1 | TABLE ACCESS FULL| SAMPLETABLE | 1 |
--------------------------------------------------
14. By Louis liu www.vmcd.org
Predicate Information (identified by operation id):
---------------------------------------------------
PLAN_TABLE_OUTPUT
------------------------------------------------------------------------------------------------------------------------------------------------------------------
------------------------------------------------------------------------------------------------------------------------------------------
1 - filter("CITY"='Madrid' AND "COUNTRY"='Spain')
Note
-----
- Warning: basic plan statistics not available. These are only collected when:
15. By Louis liu www.vmcd.org
* hint 'gather_plan_statistics' is used for the statement or
* parameter 'statistics_level' is set to 'ALL', at session or system level
19 rows selected.
SQL> set long 90000
SQL> set lines 2000
SQL> set pages 500
SQL> select dbms_stats.report_col_usage('TEST','SAMPLETABLE') from dual;
DBMS_STATS.REPORT_COL_USAGE('TEST','SAMPLETABLE')
--------------------------------------------------------------------------------
LEGEND:
16. By Louis liu www.vmcd.org
.......
EQ : Used in single table EQuality predicate
RANGE : Used in single table RANGE predicate
LIKE : Used in single table LIKE predicate
NULL : Used in single table is (not) NULL predicate
EQ_JOIN : Used in EQuality JOIN predicate
NONEQ_JOIN : Used in NON EQuality JOIN predicate
FILTER : Used in single table FILTER predicate
JOIN : Used in JOIN predicate
GROUP_BY : Used in GROUP BY expression
...............................................................................
17. By Louis liu www.vmcd.org
###############################################################################
COLUMN USAGE REPORT FOR TEST.SAMPLETABLE
........................................
1. CITY : EQ
2. COUNTRY : EQ
3. (CITY, COUNTRY) : FILTER
###############################################################################
Add extended col statistics for columns (CITY,COUNTRY)
18. By Louis liu www.vmcd.org
SQL>select dbms_stats.create_extended_stats(ownname=>'TEST',tabname=>'SAMPLETABLE',extension=>'(CITY,COUNTRY)')
as sample_extended from dual;
SAMPLE_EXTENDED
------------------------------------------------------------------------------------------------------------------------------------------------------------------
SYS_STU3UJN5IT#IIA5ASKY72Q8V6Z
SQL> select column_name, data_default, virtual_column, hidden_column from dba_tab_cols where table_name =
'SAMPLETABLE';
19. By Louis liu www.vmcd.org
Virtual column “SYS_STU3UJN5IT#IIA5ASKY72Q8V6Z” use function “SYS_OP_COMBINED_HASH”
SQL> select column_name, ENDPOINT_NUMBER, ENDPOINT_VALUE from user_tab_histograms where table_name =
'SAMPLETABLE';
COLUMN_NAME ENDPOINT_NUMBER ENDPOINT_VALUE
20. By Louis liu www.vmcd.org
------------------------------------------------------------ --------------- --------------
ID 1 1
ID 2 2
ID 3 3
ID 4 4
ID 5 5
ID 6 6
HOTELNAME 1 3.3972E+35
HOTELNAME 2 3.6572E+35
HOTELNAME 3 3.7097E+35
HOTELNAME 4 4.0186E+35
HOTELNAME 5 4.1777E+35
21. By Louis liu www.vmcd.org
COLUMN_NAME ENDPOINT_NUMBER ENDPOINT_VALUE
------------------------------------------------------------ --------------- --------------
HOTELNAME 6 4.3847E+35
CITY 1 3.4467E+35
CITY 3 4.0178E+35
CITY 5 4.0706E+35
CITY 6 4.2803E+35
COUNTRY 1 3.8140E+35
COUNTRY 4 4.3324E+35
COUNTRY 6 4.4303E+35
19 rows selected.
22. By Louis liu www.vmcd.org
SQL> EXEC SYS.DBMS_STATS.GATHER_TABLE_STATS (OwnName => 'TEST', TabName => 'sampletable', Method_Opt =>
'FOR ALL COLUMNS', Cascade => TRUE );
PL/SQL procedure successfully completed.
SQL> select column_name, ENDPOINT_NUMBER, ENDPOINT_VALUE from user_tab_histograms where table_name =
'SAMPLETABLE';
COLUMN_NAME ENDPOINT_NUMBER ENDPOINT_VALUE
------------------------------------------------------------ --------------- --------------
ID 1 1
ID 2 2
ID 3 3
23. By Louis liu www.vmcd.org
ID 4 4
ID 5 5
ID 6 6
HOTELNAME 1 3.3972E+35
HOTELNAME 2 3.6572E+35
HOTELNAME 3 3.7097E+35
HOTELNAME 4 4.0186E+35
HOTELNAME 5 4.1777E+35
COLUMN_NAME ENDPOINT_NUMBER ENDPOINT_VALUE
------------------------------------------------------------ --------------- --------------
HOTELNAME 6 4.3847E+35
CITY 1 3.4467E+35
24. By Louis liu www.vmcd.org
CITY 3 4.0178E+35
CITY 5 4.0706E+35
CITY 6 4.2803E+35
COUNTRY 1 3.8140E+35
COUNTRY 4 4.3324E+35
COUNTRY 6 4.4303E+35
SYS_STU3UJN5IT#IIA5ASKY72Q8V6Z 1 511644451
SYS_STU3UJN5IT#IIA5ASKY72Q8V6Z 3 3090128096
SYS_STU3UJN5IT#IIA5ASKY72Q8V6Z 5 9086239935
COLUMN_NAME ENDPOINT_NUMBER ENDPOINT_VALUE
------------------------------------------------------------ --------------- --------------
SYS_STU3UJN5IT#IIA5ASKY72Q8V6Z 6 9933106351
25. By Louis liu www.vmcd.org
23 rows selected.
SQL> EXPLAIN PLAN FOR SELECT * FROM sampletable WHERE country = 'Spain' and city = 'Madrid' ;
Explained.
SQL> SELECT PLAN_TABLE_OUTPUT FROM TABLE(DBMS_XPLAN.DISPLAY( format => 'ALLSTATS' ));
PLAN_TABLE_OUTPUT
------------------------------------------------------------------------------------------------------------------------------------------------------------------
--------------------------------------
Plan hash value: 2813936524
26. By Louis liu www.vmcd.org
--------------------------------------------------
| Id | Operation | Name | E-Rows |
--------------------------------------------------
| 0 | SELECT STATEMENT | | 2 | -----------------------------> correct
|* 1 | TABLE ACCESS FULL| SAMPLETABLE | 2 |
--------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
PLAN_TABLE_OUTPUT
------------------------------------------------------------------------------------------------------------------------------------------------------------------
27. By Louis liu www.vmcd.org
--------------------------------------
1 - filter("CITY"='Madrid' AND "COUNTRY"='Spain')
Note
-----
- Warning: basic plan statistics not available. These are only collected when:
* hint 'gather_plan_statistics' is used for the statement or
* parameter 'statistics_level' is set to 'ALL', at session or system level
19 rows selected.
28. By Louis liu www.vmcd.org
use 10053 event to trace correlation of these two columns.
SQL> conn /as sysdba
Connected.
SQL> oradebug setmypid
Statement processed.
SQL> oradebug unlimit
Statement processed.
SQL> oradebug event 10053 trace name context forever, level 1
Statement processed.
SQL>
SQL> EXPLAIN PLAN FOR SELECT * FROM TEST.sampletable WHERE country = 'Spain' and city = 'Madrid' ;
29. By Louis liu www.vmcd.org
Explained.
SQL> oradebug event 10053 trace name context off
Statement processed.
SQL>
SQL> oradebug tracefile_name
/data/app1/oracle/diag/rdbms/testdb/testdb/trace/testdb_ora_8233.trc
30. By Louis liu www.vmcd.org
Rounded:2 Computer: 2.00
31. By Louis liu www.vmcd.org
Delete histograms
SQL> EXEC SYS.DBMS_STATS.GATHER_TABLE_STATS (OwnName => 'TEST', TabName => 'sampletable', Method_Opt => 'FOR
ALL COLUMNS size 1',Cascade => TRUE );
32. By Louis liu www.vmcd.org
Rounded: 2 Computed : 1.50
of rows~= total # of rows * (1/NDV for CITY) * (1/NDV for COUNTRY)*corStrength(correlation strength)
= 6*(1/4)*(1/3)*2=1.5
Delete extended stats
SQL> exec dbms_stats.DROP_EXTENDED_STATS('TEST','SAMPLETABLE','(CITY,COUNTRY)');
PL/SQL procedure successfully completed.
33. By Louis liu www.vmcd.org
Rounded: 1 Computed : 0.50
of rows~= total # of rows * (1/NDV for CITY) * (1/NDV for COUNTRY) /*corStrength(correlation strength)*/
= 6*(1/4)*(1/3)*1=0.5
