Oralce行定位与rowid：
drop table t purge;
create table t as select * from dba_objects;
create index idx_object_id on t(object_id);
set linesize 1000
set autotrace traceonly
--方法1（全表扫描）
select /*+full(t)*/ * from t where object_id=2;
--方法2（索引扫描）
select * from t where object_id=2;
--方法3（rowid扫描）
set autotrace off
select rowid from t where object_id=2;
set autotrace traceonly
select * from t where object_id=2 and rowid='AAAYiZAALAAAADLAAw';
SQL> select /*+full(t)*/ * from t where object_id=2;
--------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
--------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 207 | 291 (1)| 00:00:04 |
|* 1 | TABLE ACCESS FULL| T | 1 | 207 | 291 (1)| 00:00:04 |
--------------------------------------------------------------------------
统计信息
----------------------------------------------------------
0 recursive calls
0 db block gets
1044 consistent gets
SQL> select * from t where object_id=2;
---------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 207 | 2 (0)| 00:00:01 |
| 1 | TABLE ACCESS BY INDEX ROWID| T | 1 | 207 | 2 (0)| 00:00:01 |
|* 2 | INDEX RANGE SCAN | IDX_OBJECT_ID | 1 | | 1 (0)| 00:00:01 |
---------------------------------------------------------------------------------------------
统计信息
----------------------------------------------------------
0 recursive calls
0 db block gets
4 consistent gets
SQL> select * from t where object_id=2 and rowid='AAAYiZAALAAAADLAAw';
-----------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 219 | 1 (0)| 00:00:01 |
|* 1 | TABLE ACCESS BY USER ROWID| T | 1 | 219 | 1 (0)| 00:00:01 |
-----------------------------------------------------------------------------------
统计信息
----------------------------------------------------------
0 recursive calls
0 db block gets
1 consistent gets
---启动大小为2K的块新建表空间(WINDOWS下只能使用2K,4K，8K和16K
alter system set db_2k_cache_size=100M;
drop tablespace tbs_ljb_2k including contents and datafiles;
create tablespace TBS_LJB_2k
blocksize 2K
datafile 'D:\ORACLE\ORADATA\TEST11G\TBS_LJB_2K_01.DBF' size 100M
autoextend on
extent management local
segment space management auto;
create table t_2k tablespace tbs_ljb_2k as select * from dba_objects;
---启动大小为4K的块新建表空间
alter system set db_4k_cache_size=100M;
drop tablespace tbs_ljb_4k including contents and datafiles;
create tablespace TBS_LJB_4k
blocksize 4K
datafile 'D:\ORACLE\ORADATA\TEST11G\TBS_LJB_4K_01.DBF' size 100M
autoextend on
extent management local
segment space management auto;
create table t_4k tablespace tbs_ljb_4k as select * from dba_objects;
---启动大小为8K的块新建表空间(默认就是8K)
drop table t_8k purge;
create table t_8k as select * from dba_objects;
---启动大小为16K的块新建表空间
alter system set db_16k_cache_size=100M;
drop tablespace tbs_ljb_16k including contents and datafiles;
create tablespace TBS_LJB_16k
blocksize 16K
datafile 'D:\ORACLE\ORADATA\TEST11G\TBS_LJB_16K_01.DBF' size 100M
autoextend on
extent management local
segment space management auto;
create table t_16k tablespace tbs_ljb_16k as select * from dba_objects;
-----------------------------------------------------------------------------------------
--开始试验，发现代价和逻辑读都是以此变少！
SET autotrace traceonly
select count(*) from t_2k;
/
select count(*) from t_4k;
/
select count(*) from t_8k;
/
select count(*) from t_16k;
/
--但是也不是块越大越好，要注意热点块竞争。
SQL> select count(*) from t_2k;
-------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 891 (1)| 00:00:11 |
| 1 | SORT AGGREGATE | | 1 | | |
| 2 | TABLE ACCESS FULL| T_2K | 83292 | 891 (1)| 00:00:11 |
-------------------------------------------------------------------
统计信息
----------------------------------------------------------
0 recursive calls
0 db block gets
4511 consistent gets
SQL> select count(*) from t_4k;
-------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 480 (1)| 00:00:06 |
| 1 | SORT AGGREGATE | | 1 | | |
| 2 | TABLE ACCESS FULL| T_4K | 63139 | 480 (1)| 00:00:06 |
-------------------------------------------------------------------
统计信息
----------------------------------------------------------
0 recursive calls
0 db block gets
2137 consistent gets
SQL> select count(*) from t_8k;
-------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 291 (1)| 00:00:04 |
| 1 | SORT AGGREGATE | | 1 | | |
| 2 | TABLE ACCESS FULL| T_8K | 62320 | 291 (1)| 00:00:04 |
-------------------------------------------------------------------
统计信息
----------------------------------------------------------
0 recursive calls
0 db block gets
1043 consistent gets
SQL> select count(*) from t_16k;
--------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 200 (1)| 00:00:03 |
| 1 | SORT AGGREGATE | | 1 | | |
| 2 | TABLE ACCESS FULL| T_16K | 80144 | 200 (1)| 00:00:03 |
--------------------------------------------------------------------
统计信息
----------------------------------------------------------
0 recursive calls
0 db block gets
517 consistent gets