By: latch: cache buffers chains и настройка запросов с использованием cardinality feedback « Oracle mechanics

Tue, 01 Dec 2009 12:59:20 +0000

[...] (и к сожалению в версии 10.2 ещё недоступна процедура dbms_stats.create_extended_stats для сбора корелированной статистики для значений [...]

By: Kumar

Kumar — Sat, 07 Mar 2009 03:42:49 +0000

Hi Riyaz:
The presence of an index on n1, n2 is making a difference for cpu %cost column CREATE INDEX T_VC_IDX ON T_VC (N1, N2);. The cardinality estimate is still incorrect but which would be the weighing criteria in this case the %cpu cost, bytes or the cardinality.

SQL-458> explain plan for select count(*) from t_vc where n1=10 and n2 = 10;

Explained.

SQL-458> select * from table(dbms_xplan.display);

PLAN_TABLE_OUTPUT
——————————————————————————————————————————————————
Plan hash value: 1953293106

——————————————————————————
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
——————————————————————————
| 0 | SELECT STATEMENT | | 1 | 6 | 1 (0)| 00:00:01 |
| 1 | SORT AGGREGATE | | 1 | 6 | | |
|* 2 | INDEX RANGE SCAN| T_VC_IDX | 1 | 6 | 1 (0)| 00:00:01 |
——————————————————————————

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

2 – access(“N1″=10 AND “N2″=10)

14 rows selected.

SQL-458> explain plan for select count(*) from t_vc where n1=10;