CBO Basics: Cardinality

CBO Basics: Cardinality Sidney Chen@zha-dba

Agenda Cardinality The Cardinality under Various Prediction Case study: incorrect high value

Cardinality The estimated number of rows a query is expected to return. Number of rows in table x Predicate selectivity

Imaging there are 1200 people attend the dba weekly meeting, They are randomly born in 12 month and comes from 10 citites, given the data the even distributed. create table audience as select mod(rownum-1,12) + 1 month_no, mod(rownum-1,10) + 1 city_no from all_objects where rownum <= 1200;

sid@CS10G> select month_no, count(*) from audience group by month_no order by month_no; MONTH_NO COUNT(*) ---------- ---------- 1 100 2 100 3 100 4 100 5 100 6 100 7 100 8 100 9 100 10 100 11 100 12 100 12 rows selected.

sid@CS10G> select city_no, count(*) from audience group by city_no order by city_no; CITY_NO COUNT(*) ---------- ---------- 1 120 2 120 3 120 4 120 5 120 6 120 7 120 8 120 9 120 10 120 10 rows selected.

sid@CS10G> @indsid.audience; OWNER TABLE_NAME BLOCKS NUM_ROWS AVG_ROW_LEN ----- ---------- ---------- ---------- ----------- SID AUDIENCE 5 1200 6 sid@CS10G> @descsid.audience; Column Name NUM_DISTINCT DENSITY NUM_BUCKETS Low High ------------ ------------ ---------- ----------- ---- ---- MONTH_NO 12 .083333333 1 1 12 CITY_NO 10 .1 1 1 10

Critical info NDK: number of distinct keys Density = 1/NDK, (0.1 = 1/10) (0.083333333 = 1/12) NUM_BUCKETS=1, there is no histogram gather NUM_BUCKETS > 1, histogram gathered

select month_no from audience where month_no=12; Cardinality 1200 * (1/12) = 100

sid@CS10G> select month_no from audience where month_no=12; 100 rows selected. Execution Plan ---------------------------------------------------------- Plan hash value: 2423062965 ------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| ------------------------------------------------------------------- | 0 | SELECT STATEMENT | | 100 | 300 | 3 (0)| |* 1 | TABLE ACCESS FULL| AUDIENCE | 100 | 300 | 3 (0)| ------------------------------------------------------------------- Predicate Information (identified by operation id): --------------------------------------------------- 1 - filter("MONTH_NO"=12)

select month_no from audience where city_no=1; Cardinality 1200 * (1/10) = 120

sid@CS10G> select month_no from audience where city_no=1; 120 rows selected. Execution Plan ---------------------------------------------------------- Plan hash value: 2423062965 ------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| ------------------------------------------------------------------- | 0 | SELECT STATEMENT | | 120 | 720 | 3 (0)| |* 1 | TABLE ACCESS FULL| AUDIENCE | 120 | 720 | 3 (0)| ------------------------------------------------------------------- Predicate Information (identified by operation id): --------------------------------------------------- 1 - filter("CITY_NO"=1)

select month_no from audience where month_no > 9; Cardinality 1200 * ( (12-9)/(12-1) ) = 327

sid@CS10G> select month_no from audience where month_no > 9; 300 rows selected. Execution Plan ---------------------------------------------------------- Plan hash value: 2423062965 ------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| ------------------------------------------------------------------- | 0 | SELECT STATEMENT | | 327 | 981 | 3 (0)| |* 1 | TABLE ACCESS FULL| AUDIENCE | 327 | 981 | 3 (0)| ------------------------------------------------------------------- Predicate Information (identified by operation id): --------------------------------------------------- 1 - filter("MONTH_NO">9)

Equality: If Out of range explain plan set statement_id = '12' for select month_no from audience where month_no = 12; explain plan set statement_id = '13' for select month_no from audience where month_no = 13; explain plan set statement_id = '14' for select month_no from audience where month_no = 14; explain plan set statement_id = '15' for select month_no from audience where month_no = 15; explain plan set statement_id = '16' for select month_no from audience where month_no = 16; explain plan set statement_id = '17' for select month_no from audience where month_no = 17; explain plan set statement_id = '18' for select month_no from audience where month_no = 18; explain plan set statement_id = '19' for select month_no from audience where month_no = 19; explain plan set statement_id = '20' for select month_no from audience where month_no = 20;

sid@CS10G> select statement_id, cardinality from plan_table where id=1 order by statement_id; STATEMENT_ID CARDINALITY ------------ ----------- 12 100 13 91 14 82 15 73 1664 17 55 18 45 19 36 20 27 9 rows selected.

Range: If Out of range explain plan set statement_id = '12' for select month_no from audience where month_no > 12; explain plan set statement_id = '13' for select month_no from audience where month_no > 13; explain plan set statement_id = '14' for select month_no from audience where month_no > 14; explain plan set statement_id = '15' for select month_no from audience where month_no > 15; explain plan set statement_id = '16' for select month_no from audience where month_no > 16; explain plan set statement_id = '17' for select month_no from audience where month_no > 17; explain plan set statement_id = '18' for select month_no from audience where month_no > 18; explain plan set statement_id = '19' for select month_no from audience where month_no > 19; explain plan set statement_id = '20' for select month_no from audience where month_no > 20;

The far from low/high range, the less you are to find data

Bad news If you have sequence, or time-based column in predicate(such as last modified date:last_mod_dt), and haven’t been keeping the statistics up to date The Cardinality will drop as time passes, if you using equality and range on that column

sid@CS10G> select month_no from audience where month_no > 16; no rows selected Execution Plan ---------------------------------------------------------- Plan hash value: 2423062965 -------------------------------------+-----------------------------------+ | Id | Operation | Name | Rows | Bytes | Cost | Time | -------------------------------------+-----------------------------------+ | 0 | SELECT STATEMENT | | | | 3 | | | 1 | TABLE ACCESS FULL | AUDIENCE| 64 | 192 | 3 | 00:00:01 | -------------------------------------+-----------------------------------+ Predicate Information: ---------------------- 1 - filter("MONTH_NO"=16)

Using 10053 event to confirm sid@CS10G> @53on alter session set events '10053 trace name context forever, level 1'; Session altered. sid@CS10G> explain plan for select month_no from audience where month_no > 16; Explained. sid@CS10G> @53off sid@CS10G> @tracefile TRACEFILE ---------------------------------------------------------------------------------------------------- /home/u02/app/oracle/product/11.1.0/db_1/admin/cs10g/udump/cs10g_ora_24947.trc

SINGLE TABLE ACCESS PATH ----------------------------------------- BEGIN Single Table Cardinality Estimation ----------------------------------------- Column (#1): MONTH_NO(NUMBER) AvgLen: 3.00 NDV: 12 Nulls: 0 Density: 0.083333 Min: 1 Max: 12 Using prorated density: 0.05303 of col #1 as selectivity of out-of-range value pred Table: AUDIENCE Alias: AUDIENCE Card: Original: 1200 Rounded: 64 Computed: 63.64 Non Adjusted: 63.64 ----------------------------------------- END Single Table Cardinality Estimation -----------------------------------------

Between: If Out of range explain plan set statement_id = '12' for select month_no from audience where month_nobetween 13 and 15; explain plan set statement_id = '14' for select month_no from audience where month_nobetween 14 and 16; explain plan set statement_id = '15' for select month_no from audience where month_nobetween 15 and 17; explain plan set statement_id = '16' for select month_no from audience where month_no between 13 and 20; explain plan set statement_id = '17' for select month_no from audience where month_no between 14 and 21; explain plan set statement_id = '18' for select month_no from audience where month_no between 15 and 22; explain plan set statement_id = '19' for select month_no from audience where month_no between 16 and 23;

sid@CS10G> select statement_id, cardinality from plan_table where id=1 order by statement_id; STATEMENT_ID CARDINALITY ------------ ----------- 12 100 13 100 14 100 15 100 16 100 17 100 18 100 19 100 20 100 9 rows selected.

Case: incorrect low/high value

SELECT count('1') RECCOUNT FROM Test_ILM_INTERACTIONt0 JOIN Test_ILM_INTERACTION_TYPEt1 ON t0.INTERACTION_TYP = t1.INTERACTION_TYP JOIN Test_ILM_INTERACTION_REFt3 ON t0.interaction_uuid = t3.interaction_uuid WHERE t1.IS_VIEWABLE = 1 AND ((t0.DOMAIN_NME = 'DOMAIN_A') or (T0.DOMAIN_NME = 'DOMAIN_B' AND T0.APPLICATION_NME = 'APPLICATION_C')) AND (t3.REF_CDE = 'BK_NUMBER' AND t3.REF_KEY_VALUE = '2389301444') AND t0.INTERACTION_DT BETWEEN TO_DATE('01-06-2011 16:00:00', 'DD-MM-YYYY HH24:MI:SS') AND TO_DATE('16-06-2011 15:59:59', 'DD-MM-YYYY HH24:MI:SS')

---------------------------------------------------------------------+---------------- | Id | Operation | Name | Rows | Cost | ---------------------------------------------------------------------+---------------- | 0 | SELECT STATEMENT | | | 13 | | 1 | SORT AGGREGATE | | 1 | | | 2 | NESTED LOOPS | | 1 | 13 | | 3 | NESTED LOOPS | | 1 | 12 | | 4 | INDEX RANGE SCAN | Test_ILM_INTERACTION_IDX3 | 4 | 4 | | 5 | INDEX UNIQUE SCAN | Test_ILM_INTERACTION_REF_PK| 1 | 2 | | 6 | TABLE ACCESS BY INDEX ROWID | Test_ILM_INTERACTION_TYPE| 1 | 1 | | 7 | INDEX UNIQUE SCAN | Test_ILM_INTERACTION_TYPE_PK| 1 | 0 | ---------------------------------------------------------------------+---------------- Predicate Information (identified by operation id): --------------------------------------------------- 4 - access("T0"."INTERACTION_DT">=TO_DATE('2011-06-01 05:00:00', 'yyyy-mm-dd hh24:mi:ss') AND "T0"."INTERACTION_DT"<=TO_DATE('2011-06-16 04:59:59', 'yyyy-mm-dd hh24:mi:ss')) filter("T0"."DOMAIN_NME"='DOMAIN_A' OR "T0"."APPLICATION_NME"='APPLICATION_C' AND "T0"."DOMAIN_NME"='DOMAIN_B') 5 - access("T0"."INTERACTION_UUID"="T3"."INTERACTION_UUID" AND "T3"."REF_CDE"='BL_NUMBER' AND "T3"."REF_KEY_VALUE"=2389301444') 6 - filter("T1"."IS_VIEWABLE"=1) 7 - access("T0"."INTERACTION_TYP"="T1"."INTERACTION_TYP")

sys@CS2PRD> @descTestowner.Test_ilm_interaction Column Name NUM_DISTINCT DENSITY Low High ------------------ ------------ ---------- -------------------- -------------------- INTERACTION_DT 7583898 1.3186E-07 2010-05-07 23:45:47 2011-05-31 15:31:35 sys@CS2PRD> @indTestowner.Test_ilm_interaction TABLE_NAME INDEX_NAME POS# COLUMN_NAME ----------------------- --------------------------- ---- ---------------- Test_ILM_INTERACTION Test_ILM_INTERACTION_IDX3 1 INTERACTION_DT 2 COMPANY_ID 3 APPLICATION_NME 4 DOMAIN_NME 5 INTERACTION_TYP 6 INTERACTION_UUID

select to_date(2455714,'J') max_date from dual; MAX_DATE ------------------- 2011-06-01 00:00:00 10053 trace Column (#4): INTERACTION_DT(DATE) AvgLen: 8.00 NDV: 7583898 Nulls: 0 Density: 1.3186e-07 Min: 2455325 Max: 2455714 SINGLE TABLE ACCESS PATH Using prorated density: 1.3151e-07 of col#4 as selectivity of out-of-range value pred Table: Test_ILM_INTERACTIONAlias: T0 Card: Original: 53138344 Rounded: 4 Computed: 3.75 Non Adjusted: 3.75 Access Path: index (IndexOnly) Index: Test_ILM_INTERACTION_IDX3 resc_io: 4.00 resc_cpu: 29886 ix_sel: 1.3151e-07 ix_sel_with_filters: 7.0628e-08 Cost: 4.00 Resp: 4.00 Degree: 1 ****** trying bitmap/domain indexes ****** Best:: AccessPath: IndexRange Index: Test_ILM_INTERACTION_IDX3 Cost: 4.00 Degree: 1 Resp: 4.00 Card: 3.75 Bytes: 0

Solution:dbms_stats.set_colum_stats m_high := ADD_MONTHS(m_high, 1); m_val_array := DBMS_STATS.DATEARRAY(m_low, m_high); dbms_stats.prepare_column_values( srec => m_statrec, datevals => m_val_array ); dbms_stats.set_column_stats( ownname => NULL, tabname => '&&TABLE_NAME', colname => '&&COLUMN_NAME', distcnt => m_distcnt, density => m_density, nullcnt => m_nullcnt, srec => m_statrec, avgclen => m_avgclen, no_invalidate => false ); Pls check the hack_stats_3.sql for the full script

sys@CS2PRD> @descTestowner.Test_ilm_interaction Column Name NUM_DISTINCT DENSITY Low High ------------------ ------------ ---------- -------------------- -------------------- INTERACTION_DT 7583898 1.3186E-07 2010-05-07 23:45:47 2011-06-31 15:31:35

--------------------------------------------------------------------------------------------- | Id | Operation | Name | Rows | Cost (%CPU)| --------------------------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | 1 | 14 (0)| | 1 | SORT AGGREGATE | | 1 | | | 2 | NESTED LOOPS | | 1 | 14 (0)| | 3 | NESTED LOOPS | | 1 | 13 (0)| | 4 | TABLE ACCESS BY INDEX ROWID| Test_ILM_INTERACTION_REF| 1 | 10 (0)| |* 5 | INDEX RANGE SCAN | Test_ILM_INTERACTION_REF_IDX1 | 9 | 4 (0)| |* 6 | TABLE ACCESS BY INDEX ROWID| Test_ILM_INTERACTION| 1 | 3 (0)| |* 7 | INDEX UNIQUE SCAN | Test_ILM_INTERACTION_PK| 1 | 2 (0)| |* 8 | TABLE ACCESS BY INDEX ROWID | Test_ILM_INTERACTION_TYPE| 1 | 1 (0)| |* 9 | INDEX UNIQUE SCAN | Test_ILM_INTERACTION_TYPE_PK| 1 | 0 (0)| --------------------------------------------------------------------------------------------- Predicate Information (identified by operation id): --------------------------------------------------- 5 - access("T3"."REF_CDE"='BK_NUMBER' AND "T3"."REF_KEY_VALUE"='2389301444') 6 - filter("T0"."INTERACTION_DT">=TO_DATE('2011-06-01 16:00:00', 'yyyy-mm-dd hh24:mi:ss') AND ("T0"."DOMAIN_NME"='DOMAIN_A' OR "T0"."APPLICATION_NME"='APPLICATION_C' AND "T0"."DOMAIN_NME"='DOMAIN_B') AND "T0"."INTERACTION_DT"<=TO_DATE('2011-06-16 15:59:59', 'yyyy-mm-dd hh24:mi:ss')) 7 - access("T0"."INTERACTION_UUID"="T3"."INTERACTION_UUID") 8 - filter("T1"."IS_VIEWABLE"=1) 9 - access("T0"."INTERACTION_TYP"="T1"."INTERACTION_TYP")

select to_date(2455744,'J') max_date from dual; MAX_DATE ------------------- 2011-07-01 00:00:00 10053 trace *************************************** SINGLE TABLE ACCESS PATH Column (#9): DOMAIN_NME(VARCHAR2) AvgLen: 12.00 NDV: 10 Nulls: 53692 Density: 9.3545e-09 Histogram: Freq #Bkts: 10 UncompBkts: 5973 EndPtVals: 10 Column (#2): APPLICATION_NME(VARCHAR2) AvgLen: 17.00 NDV: 30 Nulls: 0 Density: 9.3451e-09 Histogram: Freq #Bkts: 30 UncompBkts: 5979 EndPtVals: 30 Column (#4): INTERACTION_DT(DATE) AvgLen: 8.00 NDV: 7583898 Nulls: 0 Density: 1.3186e-07 Min: 2455325 Max: 2455744 Table: Test_ILM_INTERACTIONAlias: T0 Card: Original: 53138344 Rounded: 1024006 Computed: 1024006.31 Non Adjusted: 1024006.31 Access Path: index (IndexOnly) Index: Test_ILM_INTERACTION_IDX3 resc_io: 28694.00 resc_cpu: 574312799 ix_sel: 0.035829 ix_sel_with_filters: 0.019271 Cost: 28722.69 Resp: 28722.69 Degree: 1 ****** trying bitmap/domain indexes ****** Best:: AccessPath: IndexRange Index: Test_ILM_INTERACTION_IDX3 Cost: 28722.69 Degree: 1 Resp: 28722.69 Card: 1024006.31 Bytes: 0 ***************************************

---------------------------------------------------------------------+---------------- | Id | Operation | Name | Rows | Cost | ---------------------------------------------------------------------+---------------- | 0 | SELECT STATEMENT | | | 13 | | 1 | SORT AGGREGATE | | 1 | | | 2 | NESTED LOOPS | | 1 | 13 | | 3 | NESTED LOOPS | | 1 | 12 | | 4 | INDEX RANGE SCAN | Test_ILM_INTERACTION_IDX3 | 4 | 4 | | 5 | INDEX UNIQUE SCAN | Test_ILM_INTERACTION_REF_PK| 1 | 2 | | 6 | TABLE ACCESS BY INDEX ROWID | Test_ILM_INTERACTION_TYPE| 1 | 1 | | 7 | INDEX UNIQUE SCAN | Test_ILM_INTERACTION_TYPE_PK| 1 | 0 | ---------------------------------------------------------------------+---------------- --------------------------------------------------------------------------------------------- | Id | Operation | Name | Rows | Cost (%CPU)| --------------------------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | 1 | 14 (0)| | 1 | SORT AGGREGATE | | 1 | | | 2 | NESTED LOOPS | | 1 | 14 (0)| | 3 | NESTED LOOPS | | 1 | 13 (0)| | 4 | TABLE ACCESS BY INDEX ROWID| Test_ILM_INTERACTION_REF| 1 | 10 (0)| |* 5 | INDEX RANGE SCAN | Test_ILM_INTERACTION_REF_IDX1 | 9 | 4 (0)| |* 6 | TABLE ACCESS BY INDEX ROWID| Test_ILM_INTERACTION| 1 | 3 (0)| |* 7 | INDEX UNIQUE SCAN | Test_ILM_INTERACTION_PK| 1 | 2 (0)| |* 8 | TABLE ACCESS BY INDEX ROWID | Test_ILM_INTERACTION_TYPE| 1 | 1 (0)| |* 9 | INDEX UNIQUE SCAN | Test_ILM_INTERACTION_TYPE_PK| 1 | 0 (0)| ---------------------------------------------------------------------------------------------

B-tree Access Cost cost = blevel + ceiling(leaf_blocks * effective index selectivity) + ceiling(clustering_factor * effective table selectivity) = blevel + ceiling(leaf_blocks * ix_sel)+ ceiling(clustering_factor *ix_sel_with_filter)

Index Stats:: Index: Test_ILM_INTERACTION_IDX3 Col#: 4 10 2 9 7 1 LVLS: 3 #LB: 800771 #DK: 51629818 LB/K: 1.00 DB/K: 1.00 CLUF: 27495746.00 Access Path: index (IndexOnly) Index: Test_ILM_INTERACTION_IDX3 resc_io: 4.00 resc_cpu: 29886 ix_sel: 1.3151e-07 ix_sel_with_filters: 7.0734e-08 Cost: 4.00 Resp: 4.00 Degree: 1 sys@CS10G> select 3 + ceil(800771 * 0.00000013151) cost from dual; COST ---------- 4 Index only, no need to access table

Index Stats:: Index: Test_ILM_INTERACTION_REF_IDX1 Col#: 2 3 LVLS: 3 #LB: 872428 #DK: 10567436 LB/K: 1.00 DB/K: 5.00 CLUF: 60057635.00 Access Path: index (AllEqRange) Index: Test_ILM_INTERACTION_REF_IDX1 resc_io: 10.00 resc_cpu: 74724 ix_sel: 9.4630e-08 ix_sel_with_filters: 9.4630e-08 Cost: 10.00 Resp: 10.00 Degree: 1 sys@CS10G> select 3 + ceil(872428 * 0.00000009463) + ceil(60057535 * 0.00000009463) cost from dual; COST ---------- 10

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