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Optimizer Yin and Yang

Optimizer Yin and Yang. Thomas Kyte http://asktom.oracle.com/. Programming to fail…. Programming to fail…. Too smart for their own good Parse count Parse count (failures) Quick stories about parsing…. Programming to fail…. Begin execute immediate

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Optimizer Yin and Yang

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  1. Optimizer Yin and Yang Thomas Kyte http://asktom.oracle.com/

  2. Programming to fail…

  3. Programming to fail… • Too smart for their own good • Parse count • Parse count (failures) • Quick stories about parsing…

  4. Programming to fail… Begin execute immediate ‘begin internal_pkg.some_code; end;’; Exception when others then null; End;

  5. Programming to fail… Sandeep - my math was wrong, I said 40% of your hard parses were failed parses.  In looking at the numbers again:Statistic                                     Total     per Second     per Trans-------------------------------- ------------------ -------------- -------------parse count (failures)                      389,176          109.0           3.0parse count (hard)                          607,096          170.1           4.7parse count (total)                       6,775,397        1,898.0          52.3It would be correct to say that 64% (yes, 64%!!!!!!!!!!!!!) of your parses are *FAILED* parsed.  The parse count hard included failed and successful parses - therefore, it is 389k/607k*100 to get the right percentage.2 out of 3 SQL statements FAIL PARSING.  That is sick

  6. Abusing Functions

  7. Function Abuse • Cardinality estimation issues • May reduce access paths • Can increase CPU needs (repeated function calls) • Could lead to partition elimination elimination

  8. Cardinality Estimation Issues ops$tkyte%ORA11GR2> create table t 2 as 3 select * 4 from all_objects 5 / Table created.

  9. Cardinality Estimation Issues ops$tkyte%ORA11GR2> select count(*) 2 from t 3 where created >= to_date( '5-sep-2010', 'dd-mon-yyyy' ) 4 and created < to_date( '6-sep-2010', 'dd-mon-yyyy' ) 5 / COUNT(*) ---------- 65925 ops$tkyte%ORA11GR2> select count(*), 0.01 * count(*), 0.01 * 0.01 * count(*) 2 from t 3 / COUNT(*) 0.01*COUNT(*) 0.01*0.01*COUNT(*) ---------- ------------- ------------------ 72926 729.26 7.2926

  10. Cardinality Estimation Issues ops$tkyte%ORA11GR2> exec dbms_stats.gather_table_stats( user, 'T' ); PL/SQL procedure successfully completed. • Why did I wait till here to gather statistics?

  11. Cardinality Estimation Issues ops$tkyte%ORA11GR2> select count(*) 2 from t t2 3 where created >= to_date( '5-sep-2010', 'dd-mon-yyyy' ) 4 and created < to_date( '6-sep-2010', 'dd-mon-yyyy' ) 5 / COUNT(*) ---------- 65925 ops$tkyte%ORA11GR2> select * from table(dbms_xplan.display_cursor); --------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | --------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | | | 291 (100)| | | 1 | SORT AGGREGATE | | 1 | 8 | | | |* 2 | TABLE ACCESS FULL| T | 65462 | 511K| 291 (1)| 00:00:04 | --------------------------------------------------------------------------- Predicate Information (identified by operation id): --------------------------------------------------- 2 - filter(("CREATED"<TO_DATE(' 2010-09-06 00:00:00', 'syyyy-mm-dd hh24:mi:ss') AND "CREATED">=TO_DATE(' 2010-09-05 00:00:00', 'syyyy-mm-dd hh24:mi:ss')))

  12. Cardinality Estimation Issues ops$tkyte%ORA11GR2> select count(*) 2 from t t1 3 where trunc(created) = to_date( '5-sep-2010', 'dd-mon-yyyy' ) 4 / COUNT(*) ---------- 65925 ops$tkyte%ORA11GR2> select * from table(dbms_xplan.display_cursor); --------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | --------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | | | 294 (100)| | | 1 | SORT AGGREGATE | | 1 | 8 | | | |* 2 | TABLE ACCESS FULL| T | 729 | 5832 | 294 (2)| 00:00:04 | --------------------------------------------------------------------------- Predicate Information (identified by operation id): --------------------------------------------------- 2 - filter(TRUNC(INTERNAL_FUNCTION("CREATED"))=TO_DATE(' 2010-09-05 00:00:00', 'syyyy-mm-dd hh24:mi:ss'))

  13. Cardinality Estimation Issues ops$tkyte%ORA11GR2> select count(*) 2 from t t1 3 where trunc(created) = to_date( '5-sep-2010', 'dd-mon-yyyy' ) 4 and substr( owner, 1, 3 ) = 'SYS' 5 / COUNT(*) ---------- 33535 ops$tkyte%ORA11GR2> select * from table(dbms_xplan.display_cursor); --------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | --------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | | | 292 (100)| | | 1 | SORT AGGREGATE | | 1 | 14 | | | |* 2 | TABLE ACCESS FULL| T | 7 | 98 | 292 (1)| 00:00:04 | --------------------------------------------------------------------------- Predicate Information (identified by operation id): --------------------------------------------------- 2 - filter((SUBSTR("OWNER",1,3)='SYS' AND TRUNC(INTERNAL_FUNCTION("CREATED"))=TO_DATE(' 2010-09-05 00:00:00' 'syyyy-mm-dd hh24:mi:ss')))

  14. Cardinality Estimation Issues ops$tkyte%ORA11GR2> select count(*) 2 from t t1 3 where trunc(created) = to_date( '5-sep-2010', 'dd-mon-yyyy' ) 4 and substr( owner, 1, 3 ) = 'SYS' 5 and mod(object_id,100000) > 1 6 / COUNT(*) ---------- 33535 ops$tkyte%ORA11GR2> select * from table(dbms_xplan.display_cursor); --------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | --------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | | | 292 (100)| | | 1 | SORT AGGREGATE | | 1 | 19 | | | |* 2 | TABLE ACCESS FULL| T | 1 | 19 | 292 (1)| 00:00:04 | --------------------------------------------------------------------------- Predicate Information (identified by operation id): --------------------------------------------------- 2 - filter((SUBSTR("OWNER",1,3)='SYS' AND MOD("OBJECT_ID",100000)>1 AND TRUNC(INTERNAL_FUNCTION("CREATED"))=TO_DATE(' 2010-09-05 00:00 'syyyy-mm-dd hh24:mi:ss'))) 23 rows selected.

  15. Compile with warnings… SQL> alter session set plsql_warnings='enable:all’; SQL> create or replace procedure p 2 as 3 begin 4 dbms_output.put_line( 'hello world' ); 5 exception 6 when others 7 then null; 8 end; 9 / Warning: Procedure created with compilation errors. c##tkyte%CDB1> show errors Errors for PROCEDURE P: LINE/COL ERROR ---- ----------------------------------------------------------------- 6/6 PLS-06009: procedure "P" OTHERS handler does not end in RAISE or RAISE_APPLICATION_ERROR

  16. Increased CPU ops$tkyte%ORA11GR2> create or replace procedure p authid definer 2 as 3 l_date varchar2(30) := '01-jan-2011'; 4 l_start number := dbms_utility.get_cpu_time; 5 begin 6 for i in 1 .. 10 7 loop 8 for x in ( select owner, object_name 9 from big_table.big_table 10 where created = l_date ) 11 loop 12 null; 13 end loop; 14 end loop; 15 dbms_output.put_line( 'CPU: ' || 16 to_char( dbms_utility.get_cpu_time-l_start ) ); 17 end; 18 / SP2-0804: Procedure created with compilation warnings ops$tkyte%ORA11GR2> exec p CPU: 132

  17. Increased CPU … 7 loop 8 for x in ( select owner, object_name 9 from big_table.big_table 10 where created = l_date ) 11 loop 12 null; 13 end loop; … ops$tkyte%ORA11GR2> show errors procedure p Errors for PROCEDURE P: LINE/COL ERROR -------- ----------------------------------------------------------------- 10/36 PLW-07204: conversion away from column type may result in sub-optimal query plan

  18. Increased CPU ops$tkyte%ORA11GR2> create or replace procedure p authid definer 2 as 3 l_date date := to_date('01-jan-2011','dd-mon-yyyy'); 4 l_start number := dbms_utility.get_cpu_time; 5 begin 6 for i in 1 .. 10 7 loop 8 for x in ( select owner, object_name 9 from big_table.big_table 10 where created = l_date ) 11 loop 12 null; 13 end loop; 14 end loop; 15 dbms_output.put_line( 'CPU: ' || 16 to_char( dbms_utility.get_cpu_time-l_start ) ); 17 end; 18 / Procedure created. ops$tkyte%ORA11GR2> exec p CPU: 94 30% less CPU in this case

  19. Reduced Access Paths ops$tkyte%ORA11GR2> create table t 2 ( x varchar2(20) constraint t_pk primary key, 3 y varchar2(30) 4 ); Table created. ops$tkyte%ORA11GR2> insert into t 2 select user_id, username 3 from all_users; 47 rows created. ops$tkyte%ORA11GR2> commit; Commit complete.

  20. Reduced Access Paths ops$tkyte%ORA11GR2> create or replace procedure p authid definer 2 as 3 l_rect%rowtype; 4 l_key number := 5; 5 begin 6 select * into l_rec from t where x = l_key; 7 for x in (select plan_table_output 8 from TABLE( dbms_xplan.display_cursor())) 9 loop 10 dbms_output.put_line( x.plan_table_output ); 11 end loop; 12 end; 13 / SP2-0804: Procedure created with compilation warnings

  21. Reduced Access Paths … 5 begin 6 select * into l_rec from t where x = l_key; 7 for x in (select plan_table_output … ops$tkyte%ORA11GR2> show errors Errors for PROCEDURE P: LINE/COL ERROR -------- ----------------------------------------------------------- 6/42 PLW-07204: conversion away from column type may result in sub-optimal query plan

  22. Reduced Access Paths ops$tkyte%ORA11GR2> exec p SQL_ID 18796jgha0hwz, child number 0 ------------------------------------- SELECT * FROM T WHERE X = :B1 Plan hash value: 1601196873 -------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | -------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | | | 3 (100)| | |* 1 | TABLE ACCESS FULL| T | 1 | 29 | 3 (0)| 00:00:01 | -------------------------------------------------------------------------- Predicate Information (identified by operation id): --------------------------------------------------- 1 - filter(TO_NUMBER("X")=:B1)

  23. Reduced Access Paths ops$tkyte%ORA11GR2> create or replace procedure p authid definer 2 as 3 l_rect%rowtype; 4 l_key varchar2(5) := '5'; 5 begin 6 select * into l_rec from t where x = l_key; 7 for x in (select plan_table_output 8 from TABLE( dbms_xplan.display_cursor())) 9 loop 10 dbms_output.put_line( x.plan_table_output ); 11 end loop; 12 end; 13 / Procedure created. ops$tkyte%ORA11GR2> show errors No errors.

  24. Reduced Access Paths ops$tkyte%ORA11GR2> exec p SQL_ID 18796jgha0hwz, child number 1 ------------------------------------- SELECT * FROM T WHERE X = :B1 Plan hash value: 1303508680 ------------------------------------------------------------------------------------ | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | ------------------------------------------------------------------------------------ | 0 | SELECT STATEMENT | | | | 1 (100)| | | 1 | TABLE ACCESS BY INDEX ROWID| T | 1 | 29 | 1 (0)| 00:00:01 | |* 2 | INDEX UNIQUE SCAN | T_PK | 1 | | 1 (0)| 00:00:01 | ------------------------------------------------------------------------------------ Predicate Information (identified by operation id): --------------------------------------------------- 2 - access("X"=:B1)

  25. Partition Elimination Eliminated ops$tkyte%ORA11GR2> CREATE TABLE t 2 ( 3 dtdate, 4 x int, 5 y varchar2(30) 6 ) 7 PARTITION BY RANGE (dt) 8 ( 9 PARTITION part1 VALUES LESS THAN(to_date('31-jan-2011', 'dd-mon-yyyy')), 10 PARTITION part2 VALUES LESS THAN(to_date('28-feb-2011', 'dd-mon-yyyy')) 11 ) 12 / Table created.

  26. Partition Elimination Eliminated ops$tkyte%ORA11GR2> create or replace procedure p authid definer 2 as 3 l_date timestamp := timestamp'2011-01-15 00:00:00.000'; 4 l_count number; 5 begin 6 select count(*) into l_count from t where dt = l_date; 7 8 for x in (select plan_table_output 9 from TABLE( dbms_xplan.display_cursor() ) ) 10 loop 11 dbms_output.put_line( '.'||x.plan_table_output ); 12 end loop; 13 end; 14 / SP2-0804: Procedure created with compilation warnings

  27. Partition Elimination Eliminated … 5 begin 6 select count(*) into l_count from t where dt = l_date; 7 … SP2-0804: Procedure created with compilation warnings ops$tkyte%ORA11GR2> show errors Errors for PROCEDURE P: LINE/COL ERROR -------- -------------------------------------------------------------- 6/47 PLW-07204: conversion away from column type may result in sub-optimal query plan

  28. Partition Elimination Eliminated SQL_ID 0t5m83d3m67q7, child number 0 ------------------------------------- SELECT COUNT(*) FROM T WHERE DT = :B1 Plan hash value: 3225603066 --------------------------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | Pstart| Pstop | --------------------------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | | | 2 (100)| | | | | 1 | SORT AGGREGATE | | 1 | 9 | | | | | | 2 | PARTITION RANGE ALL| | 1 | 9 | 2 (0)| 00:00:01 | 1 | 2 | |* 3 | TABLE ACCESS FULL | T | 1 | 9 | 2 (0)| 00:00:01 | 1 | 2 | --------------------------------------------------------------------------------------------- Predicate Information (identified by operation id): --------------------------------------------------- 3 - filter(INTERNAL_FUNCTION("DT")=:B1)

  29. Partition Elimination Eliminated ops$tkyte%ORA11GR2> create or replace procedure p authid definer 2 as 3 l_date date := to_date( '2011-01-15', 'yyyy-mm-dd' ); 4 l_count number; 5 begin 6 select count(*) into l_count from t where dt = l_date; 7 8 for x in (select plan_table_output 9 from TABLE( dbms_xplan.display_cursor() ) ) 10 loop 11 dbms_output.put_line( '.'||x.plan_table_output ); 12 end loop; 13 end; 14 / Procedure created. ops$tkyte%ORA11GR2> show errors No errors.

  30. Partition Elimination Eliminated .SQL_ID 0t5m83d3m67q7, child number 1 .------------------------------------- .SELECT COUNT(*) FROM T WHERE DT = :B1 . .Plan hash value: 3660200434 . .------------------------------------------------------------------------------------------------ .| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | Pstart| Pstop | .------------------------------------------------------------------------------------------------ .| 0 | SELECT STATEMENT | | | | 2 (100)| | | | .| 1 | SORT AGGREGATE | | 1 | 9 | | | | | .| 2 | PARTITION RANGE SINGLE| | 1 | 9 | 2 (0)| 00:00:01 | KEY | KEY | .|* 3 | TABLE ACCESS FULL | T | 1 | 9 | 2 (0)| 00:00:01 | KEY | KEY | .------------------------------------------------------------------------------------------------ . .Predicate Information (identified by operation id): .--------------------------------------------------- . . 3 - filter("DT"=:B1)

  31. Partition Elimination Eliminated ops$tkyte%ORA11GR2> alter session set Plsql_Warnings = 'error:all‘; ops$tkyte%ORA11GR2> create or replace procedure p authid definer 2 as 3 l_date timestamp := timestamp'2011-01-15 00:00:00.000'; 4 l_count number; 5 begin 6 select count(*) into l_count from t where dt = l_date; 7 8 for x in (select plan_table_output 9 from TABLE( dbms_xplan.display_cursor() ) ) 10 loop 11 dbms_output.put_line( '.'||x.plan_table_output ); 12 end loop; 13 end; 14 /

  32. Gathering stats when you shouldn’t

  33. Right command, wrong time • Temporary tables • Empty at 3am, full at 3pm • Queue Tables • Same as above • Partitioned Transactional Tables • Partition starts empty • Grows rapidly • Gather stats every hour? (no…)

  34. Right command, wrong time – Temporary tables • Temporary tables • Dynamic Sampling might be appropriate (might be shared over sessions) • Fill with representative data, Gather and Lock • Cardinality/Opt_Estimate Hints on a session by session basis • 12c Session Private Statistics • Hard parse…

  35. Right command, wrong time – Partitioned tables SALES_Q4_2003 Copies stats from source partition to destination partition Adjusts min & max values for partition column at both partition & global level Copies statistics of the dependent objects Columns, local indexes etc. Does not update global indexes Maybe use DBMS_STATS.COPY_TABLE_STATS(); : DBMS_STATS.COPY_TABLE_STATS (‘SH’, 'SALES’, 'SALES_Q4_2003’, 'SALES_Q1_2004’); Sales Table SALES_1995 SALES_Q1_2004

  36. Not Having Representative Stats When You Should

  37. Is 10% enough? • 1,000,000 rows • Grows at a rate of 10,000 rows per month • 10 months – no stats… • What might happen?

  38. Is 10% right? ops$tkyte%ORA11GR2> create table t 2 as 3 select * 4 from ( 5 select add_months(sysdate,-100) + mod( rownum, 3000 ) dt 6 from dual 7 connect by level <= 1000000 8 ) 9 where dt < trunc(sysdate,'y') 10 / Table created.

  39. Is 10% right? ops$tkyte%ORA11GR2> exec dbms_stats.gather_table_stats( user, 'T' ); PL/SQL procedure successfully completed. ops$tkyte%ORA11GR2> select num_rows from user_tables where table_name = 'T'; NUM_ROWS ---------- 994672

  40. Is 10% right? ops$tkyte%ORA11GR2> insert into t 2 select trunc(sysdate,'y') + mod( rownum, 150 ) dt 3 from dual 4 connect by level <= 50000 5 / 50000 rows created. ops$tkyte%ORA11GR2> commit; Commit complete.

  41. Is 10% right? ops$tkyte%ORA11GR2> select trunc(dt,'mm'), count(*) 2 from t 3 where dt >= add_months( trunc(sysdate,'y'),-3) 4 group by trunc(dt,'mm') order by 1; TRUNC(DT, COUNT(*) --------- ---------- 01-OCT-13 10323 01-NOV-13 9990 01-DEC-13 10323 01-JAN-14 10353 01-FEB-14 9344 01-MAR-14 10323 01-APR-14 9990 01-MAY-14 9990 8 rows selected.

  42. Is 10% right? ops$tkyte%ORA11GR2> select count(*) 2 from t 3 where dt between to_date( '01-dec-2013' ) 4 and to_date( '31-dec-2013' ); COUNT(*) ---------- 9990 ops$tkyte%ORA11GR2> select * from table(dbms_xplan.display_cursor); --------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | --------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | | | 506 (100)| | | 1 | SORT AGGREGATE | | 1 | 8 | | | |* 2 | TABLE ACCESS FULL| T | 10517 | 84136 | 506 (2)| 00:00:07 | --------------------------------------------------------------------------- Predicate Information (identified by operation id): --------------------------------------------------- 2 - filter(("DT">=TO_DATE(' 2013-12-01 00:00:00', 'syyyy-mm-dd hh24:mi:ss') AND "DT"<=TO_DATE(' 2013-12-31 00:00:00', 'syyyy-mm-d hh24:mi:ss')))

  43. Is 10% right? ops$tkyte%ORA11GR2> select count(*) 2 from t 3 where dt between to_date( '01-jan-2014' ) 4 and to_date( '31-jan-2014' ); COUNT(*) ---------- 10353 ops$tkyte%ORA11GR2> select * from table(dbms_xplan.display_cursor); --------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | --------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | | | 506 (100)| | | 1 | SORT AGGREGATE | | 1 | 8 | | | |* 2 | TABLE ACCESS FULL| T | 333 | 2664 | 506 (2)| 00:00:07 | --------------------------------------------------------------------------- Predicate Information (identified by operation id): --------------------------------------------------- 2 - filter(("DT">=TO_DATE(' 2014-01-01 00:00:00', 'syyyy-mm-dd hh24:mi:ss') AND "DT"<=TO_DATE(' 2014-01-31 00:00:00', 'syyyy-mm-d hh24:mi:ss')))

  44. Is 10% right? ops$tkyte%ORA11GR2> select count(*) 2 from t 3 where dt between to_date( '01-sep-2014' ) 4 and to_date( '30-sep-2014' ); COUNT(*) ---------- 0 ops$tkyte%ORA11GR2> select * from table(dbms_xplan.display_cursor); --------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | --------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | | | 506 (100)| | | 1 | SORT AGGREGATE | | 1 | 8 | | | |* 2 | TABLE ACCESS FULL| T | 333 | 2664 | 506 (2)| 00:00:07 | --------------------------------------------------------------------------- Predicate Information (identified by operation id): --------------------------------------------------- 2 - filter(("DT">=TO_DATE(' 2014-09-01 00:00:00', 'syyyy-mm-dd hh24:mi:ss') AND "DT"<=TO_DATE(' 2014-09-30 00:00:00', 'syyyy-mm-d hh24:mi:ss')))

  45. Is 10% right? When might be the time to gather stats? At what %? “it depends”

  46. Is 10% right? ops$tkyte%ORA11GR2> create or replace function stats_to_date(p_raw raw) 2 return date 3 as 4 l_dt date; 5 begin 6 dbms_stats.convert_raw_value(p_raw,l_dt); 7 return l_dt; 8 end; 9 / Function created. ops$tkyte%ORA11GR2> select stats_to_date( low_value ), stats_to_date( high_value ) 2 from user_tab_columns 3 where table_name = 'T'; STATS_TO_ STATS_TO_ --------- --------- 31-OCT-05 31-DEC-13

  47. Is 10% right? ops$tkyte%ORA11GR2> declare 2 l_distcnt number; 3 l_density number; 4 l_nullcnt number; 5 rec_srecdbms_stats.statrec; 6 datevalsdbms_stats.datearray; 7 l_avgclen number; 8 l_low date; 9 l_high date; 10 BEGIN 11 dbms_stats.get_column_stats 12 (user, 'T', 'DT', 13 distcnt => l_distcnt, 14 density => l_density, 15 nullcnt => l_nullcnt, 16 srec => rec_srec, 17 avgclen => l_avgclen ); 18 19 select stats_to_date(low_value), stats_to_date(high_value) 20 into l_low, l_high 21 from user_tab_col_statistics 22 where table_name = 'T' 23 and column_name = 'DT'; 25 l_high := add_months(l_high, 5); 26 datevals := dbms_stats.datearray (l_low, l_high); 27 rec_srec.minval:=NULL; 28 rec_srec.maxval:=NULL; 29 rec_srec.bkvals:=NULL; 30 rec_srec.novals:=NULL; 31 32 dbms_stats.prepare_column_values (rec_srec, datevals); 33 34 dbms_stats.set_column_stats 35 (user, 'T', 'DT', 36 distcnt => l_distcnt, 37 density => l_density, 38 nullcnt => l_nullcnt, 39 srec => rec_srec, 40 avgclen => l_avgclen ); 41 END; 42 /

  48. Is 10% right? ops$tkyte%ORA11GR2> select stats_to_date( low_value ), stats_to_date( high_value ) 2 from user_tab_columns 3 where table_name = 'T'; STATS_TO_ STATS_TO_ --------- --------- 31-OCT-05 31-MAY-14

  49. Is 10% right? ops$tkyte%ORA11GR2> select count(*) 2 from t t2 3 where dt between to_date( '01-jan-2014' ) 4 and to_date( '31-jan-2014' ); COUNT(*) ---------- 10353 ops$tkyte%ORA11GR2> select * from table(dbms_xplan.display_cursor); --------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | --------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | | | 506 (100)| | | 1 | SORT AGGREGATE | | 1 | 8 | | | |* 2 | TABLE ACCESS FULL| T | 10188 | 81504 | 506 (2)| 00:00:07 | --------------------------------------------------------------------------- Predicate Information (identified by operation id): --------------------------------------------------- 2 - filter(("DT">=TO_DATE(' 2014-01-01 00:00:00', 'syyyy-mm-dd hh24:mi:ss') AND "DT"<=TO_DATE(' 2014-01-31 00:00:00', 'syyyy-mm-d hh24:mi:ss')))

  50. Is 10% right? Knowledge of your data is a mandatory prerequisite to developing a sensible statistics implementation

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