Базы данных Oracle - статьи



              

Шаг 2A (для TEST_RANDOM)


Теперь выполним такой же эксперимент над TEST_RANDOM:

SQL> create bitmap index random_empno_bmx on test_random(empno); Index created.

SQL> analyze table test_random compute statistics for table for all indexes for all indexed columns; Table analyzed.

SQL> select substr(segment_name,1,30) segment_name, bytes/1024/1024 "Size in MB" 2 from user_segments 3* where segment_name in ('TEST_RANDOM','RANDOM_EMPNO_BMX');

SEGMENT_NAME Size in MB ------------------------------------ --------------- TEST_RANDOM 50 RANDOM_EMPNO_BMX 28

SQL> select index_name, clustering_factor from user_indexes;

INDEX_NAME CLUSTERING_FACTOR ------------------------------ --------------------------------- RANDOM_EMPNO_BMX 1000000

Опять статистика (размер и фактор кластеризации) идентична для этих индексов со статистикой по таблице TEST_NORMAL:

SQL> select * from test_random where empno=&empno; Enter value for empno: 1000 old 1: select * from test_random where empno=&empno new 1: select * from test_random where empno=1000

Elapsed: 00:00:00.01

Execution Plan ---------------------------------------------------------- 0 SELECT STATEMENT Optimizer=CHOOSE (Cost=4 Card=1 Bytes=34) 1 0 TABLE ACCESS (BY INDEX ROWID) OF 'TEST_RANDOM' (Cost=4 Card=1 Bytes=34) 2 1 BITMAP CONVERSION (TO ROWIDS) 3 2 BITMAP INDEX (SINGLE VALUE) OF 'RANDOM_EMPNO_BMX'

Statistics ---------------------------------------------------------- 0 recursive calls 0 db block gets 5 consistent gets 0 physical reads 0 redo size 515 bytes sent via SQL*Net to client 499 bytes received via SQL*Net from client 2 SQL*Net roundtrips to/from client 0 sorts (memory) 0 sorts (disk) 1 rows processed




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