oracle 数据库 iot 之一

os: centos 7.4
db: oracle 11.2.0.4

索引组织表 IOT 全称是 Index-Organized Tables,访问方式和 oracle 的 heap 表一样，但是物理存储类似 btree 索引。
通常情况下，索引组织表的主键是由表中多个列组成。
索引组织表的数据是按照主键的顺序存储的，所以必须有主键，另外索引组织表没有数据段，所以没有物理ROWID值。
索引组织表并不适合广泛使用，可以用如下指导原则评估某个表是否适合被创建成索引组织表。

1. 列数较少
2. 由一个符合主键(表中的几列)组成
3. 需要快速的主键访问

顺带提下： mysql 的默认存储存储 innodb 就是使用 iot 方式。

版本

# cat /etc/centos-release
CentOS Linux release 7.4.1708 (Core) 
# 
# su - oracle
Last login: Tue Jan 21 03:40:05 CST 2020 on pts/0
$ sqlplus / as sysdba;

SQL*Plus: Release 11.2.0.4.0 Production on Mon Feb 3 10:29:09 2020

Copyright (c) 1982, 2013, Oracle.  All rights reserved.


Connected to:
Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production
With the Partitioning, Real Application Clusters, Automatic Storage Management, OLAP,
Data Mining and Real Application Testing options

SQL> set lines 300;
SQL> set pages 300;
SQL> 
SQL> select * from v$version;

BANNER
--------------------------------------------------------------------------------
Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production
PL/SQL Release 11.2.0.4.0 - Production
CORE	11.2.0.4.0	Production
TNS for Linux: Version 11.2.0.4.0 - Production
NLSRTL Version 11.2.0.4.0 - Production

SQL> 

iot

iot表必须有主键，否则建表报错

SQL> create table iot_t0 (
  c0 varchar2(100),
  c1 varchar2(100),
  c2 varchar2(100),
  c3 varchar2(100)
)
organization index
;

ERROR at line 7:
ORA-25175: no PRIMARY KEY constraint found

SQL> create table iot_t0 (
  c0 varchar2(100),
  c1 varchar2(100),
  c2 varchar2(100),
  c3 varchar2(100),
  constraint pk_iot_t0 primary key (c0)
)
organization index
;

SQL> select to_char(dbms_metadata.get_ddl('TABLE','IOT_T0')) from dual;

TO_CHAR(DBMS_METADATA.GET_DDL('TABLE','IOT_T0'))
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

  CREATE TABLE "SCOTT"."IOT_T0"
   (	"C0" VARCHAR2(100),
	"C1" VARCHAR2(100),
	"C2" VARCHAR2(100),
	"C3" VARCHAR2(100),
	 CONSTRAINT "PK_IOT_T0" PRIMARY KEY ("C0") ENABLE
   ) ORGANIZATION INDEX NOCOMPRESS PCTFREE 10 INITRANS 2 MAXTRANS 255 LOGGING
  STORAGE(INITIAL 65536 NEXT 1048576 MINEXTENTS 1 MAXEXTENTS 2147483645
  PCTINCREASE 0 FREELISTS 1 FREELIST GROUPS 1
  BUFFER_POOL DEFAULT FLASH_CACHE DEFAULT CELL_FLASH_CACHE DEFAULT)
  TABLESPACE "SYSTEM"
 PCTTHRESHOLD 50

查看下执行计划

SQL> insert into iot_t0
select level, dbms_random.string('a',100),dbms_random.string('a',100),dbms_random.string('a',100) from dual connect by level <=10000;

SQL> 
SQL> set autotrace traceonly;
SQL> 
SQL> select * from iot_t0 where c0='9998';


Execution Plan
----------------------------------------------------------
Plan hash value: 2900192463

-------------------------------------------------------------------------------
| Id  | Operation	  | Name      | Rows  | Bytes | Cost (%CPU)| Time     |
-------------------------------------------------------------------------------
|   0 | SELECT STATEMENT  |	      |     1 |   208 |     1	(0)| 00:00:01 |
|*  1 |  INDEX UNIQUE SCAN| PK_IOT_T0 |     1 |   208 |     1	(0)| 00:00:01 |
-------------------------------------------------------------------------------

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

   1 - access("C0"='9998')


Statistics
----------------------------------------------------------
	  0  recursive calls
	  0  db block gets
	  2  consistent gets
	  0  physical reads
	  0  redo size
   1017  bytes sent via SQL*Net to client
	520  bytes received via SQL*Net from client
	  2  SQL*Net roundtrips to/from client
	  0  sorts (memory)
	  0  sorts (disk)
	  1  rows processed

SQL> 

SQL> set autotrace off;

SQL> select table_name,iot_name,iot_type from user_tables where table_name='IOT_T0';

TABLE_NAME		       IOT_NAME 		      IOT_TYPE
------------------------------ ------------------------------ ------------
IOT_T0							      IOT

SQL> select index_name,index_type from user_indexes ui where 1=1 and table_name='IOT_T0';

INDEX_NAME		       INDEX_TYPE
------------------------------ ---------------------------
PK_IOT_T0		       IOT - TOP

SQL> select segment_name,segment_type,bytes from user_segments us where us.segment_name in ('IOT_T0','PK_IOT_T0');

SEGMENT_NAME									  SEGMENT_TYPE		  BYTES
--------------------------------------------------------------------------------- ------------------ ----------
PK_IOT_T0									  INDEX 		5242880

可以看出表 IOT_T0 在 user_segments 并没有查询到。

参考：