ORACLE创建IOT（索引组织表）

IOT （索引组织表）

IOT和堆表的不同

堆表就是我们的那些普通表，在堆表中，他们的数据存放是无序的，数据的insert也是无序的。oracle随机的把新行insert到可用数据块中~~ 但是如果说我想按照某种顺序插入数据，那么这个时候就需要使用我们IOT表

必须有主键

测试一下：

SQL> create table t_iot (object_id int primary key,object_name varchar2(60)) organization index;

Table created.

--往里面插入数据

insert into t_iot select object_id,object_name from dba_objects;

--测试性能

select * from t_iot where object_id<100;

Predicate Information (identified by operation id):

---------------------------------------------------

1 - access("OBJECT_ID"<100)

Note

-----

- dynamic sampling used for this statement (level=2)

Statistics

----------------------------------------------------------

0 recursive calls

0 db block gets

9 consistent gets

0 physical reads

0 redo size

2574 bytes sent via SQL*Net to client

485 bytes received via SQL*Net from client

8 SQL*Net roundtrips to/from client

0 sorts (memory)

0 sorts (disk)

98 rows processed

--使用堆表进行测试

SQL> create table t_heap (object_id int primary key,object_name varchar2(60));

Table created

select * from t_heap where object_id<100;

Statistics

----------------------------------------------------------

0 recursive calls

0 db block gets

17 consistent gets

0 physical reads

0 redo size

2910 bytes sent via SQL*Net to client

485 bytes received via SQL*Net from client

8 SQL*Net roundtrips to/from client

0 sorts (memory)

0 sorts (disk)

98 rows processed

性能差异的原因：

1、IOT表是有序存储的，你的条件object_id<=2，由于你是顺序存储，那么我只需要读到2就好

2、堆表是无序的，所以我必须要扫描更多的数据。

从数据字典上看看他们的差异

select TABLE_NAME,TABLESPACE_NAME,IOT_TYPE,blocks,NUM_ROWS from dba_tables where table_name in ('T_IOT','T_HEAP');

select segment_name, blocks, extents from DBA_segments where segment_name in ('T_IOT','T_HEAP');

从这两个视图可以看到，oracle并没有吧IOT表当成一个segment，那么那些数据在哪里呢？？ 创建主键会默认创建index

select owner,index_name,index_type from dba_indexes where table_name in ('T_IOT','T_HEAP');

OWNER INDEX_NAME INDEX_TYPE

------------------------------ ------------------------------ ---------------------------

SYS SYS_C008112 NORMAL

SYS SYS_IOT_TOP_83382 IOT - TOP

select owner,segment_name,bytes/1024/1024 MB from dba_segments where segment_name in ('SYS_C0011373','SYS_IOT_TOP_73872');

OWNER SEGMENT_NAME MB

------------------------------ --------------------------------------------------------------------------------- ----------

SYS SYS_IOT_TOP_83382 4

SYS SYS_C008112 2