Oracle索引知识学习笔记

Java架构师必看

发布于 2022-03-12 13:33:10

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发布于 2022-03-12 13:33:10

文章被收录于专栏：Java架构师必看

一、Oracle索引简介

在看《收获，不止SQL优化》一书，并根据书中例子进行实践，整理成笔记

1.1 索引分类

Oracle索引分为BTree索引、位图索引、反向索引、函数索引、全文索引等等。

1.2 索引数据结构

Oracle索引中最常用的是BTree索引，所以就以BTree索引为例，讲一下BTree索引，BTree索引数据结构是一种二叉树的结构，索引由根块(Root)、茎块(Branch)、叶子块(Leaf)组成，其中叶子块主要存储索引列具体值(Key Column Value)以及能定位到数据块具体位置的Rowid，茎块和根块主要保存对应下级对应索引

1.3 索引特性

索引特性：

索引本身是有序的
索引本身能存储列值

1.4 索引使用注意要点

(1)、仅等值无范围查询时，组合的顺序不影晌性能

drop table t purge; 
create table t as select * from dba objects;
update t set object_id=rownum ;
commit;
create index idx_id_type on t(object_id, object_type) ; 
create index idx_type_id on t(object_type , object_id) ; 
set autotrace off; 
alter session set statistics_level=all ; 
select /*+index(t idx_id_type)*/ * from t where object_id=20 and object_type='TABLE';
select * from table(dbms_xplan.display cursor(null , null , 'allstats last')); 
select /*+index(t,idx_type id)*/ * from t where object_id=20 and object_type= 'TABLE'; 
select * from table(dbms_xplan.display cursor(null , null , 'allstats last'));

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(2)、范围查询时，组合索引最佳顺序一般是将等值查询的列置前

此代码由Java架构师必看网-架构君整理
select /*+index (t, idx_id_type)*/ * from t where object_id>=20 and object_id<2000 and 
object_type='TABLE';

select /*+index (t , idx_type_id) */ * from t where object_id>=20 and object_id<2000 
and object type='TABLE';

(3)、Oracle不能同时在索引根的两段寻找最大值和最小值

set autotrace on
select max(object_id) , min(object_id) from t;

笛卡尔乘积写法：

此代码由Java架构师必看网-架构君整理
set autotrace on

select max, min 
from (select max(object_id) max from t ) a , 
(select min(object_id) min from t ) b;

(4)、索引最新的数据块一般是在最右边

1.5、索引的缺点

热快竞争：索引最新的数据块一般在最右边，而访问也一般是访问比较新的数据，所以容易造成热快竞争
更新新增问题：索引本身是有序的，所以查询时候很快，但是更新时候就麻烦了，新增更新索引都需要保证排序

1.6、索引失效

索引失效分为逻辑失效和物理失效

逻辑失效逻辑失效是因为一些sql语法导致索引失效，比如加了一些函数，而索引列不是函数索引
物理失效物理失效是真的失效,比如被设置unusable属性,分区表的不规范操作也会导致索引失效等等情况

alter index index_name unusable;

二、索引分类介绍

索引分类：BTree索引、位图索引、函数索引、反向索引、全文索引

2.1、位图索引

位图索引：位图索引储存的就是比特值

环境准备，位图索引性质适用于count时，效率最高

drop table t purge;
create table t as select * from dba_objects;
update t set object_id = rownum;
commit;

不用索引的情况：

SQL> set autotrace on
SQL> select count(*) from t;
  COUNT(*)
----------
     72016
执行计划
----------------------------------------------------------
Plan hash value: 2966233522
-------------------------------------------------------------------
| Id  | Operation          | Name | Rows  | Cost (%CPU)| Time     |
-------------------------------------------------------------------
|   0 | SELECT STATEMENT   |      |     1 |   288   (1)| 00:00:04 |
|   1 |  SORT AGGREGATE    |      |     1 |            |          |
|   2 |   TABLE ACCESS FULL| T    | 86565 |   288   (1)| 00:00:04 |
-------------------------------------------------------------------
Note
-----
   - dynamic sampling used for this statement (level=2)
统计信息
----------------------------------------------------------
          4  recursive calls
          0  db block gets
       1111  consistent gets
          0  physical reads
          0  redo size
        432  bytes sent via SQL*Net to client
        419  bytes received via SQL*Net from client
          2  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
          1  rows processed
SQL>

创建位图索引：

create bitmap index idx_bitm_t_status on t(status);

再次查询，走位图索引查询：

SQL> set autotrace on
SQL> select count(*) from t;
  COUNT(*)
----------
     72016
执行计划
----------------------------------------------------------
Plan hash value: 4272013625
--------------------------------------------------------------------------------
-----------
| Id  | Operation                     | Name              | Rows  | Cost (%CPU)|
 Time     |
--------------------------------------------------------------------------------
-----------
|   0 | SELECT STATEMENT              |                   |     1 |     5   (0)|
 00:00:01 |
|   1 |  SORT AGGREGATE               |                   |     1 |            |
          |
|   2 |   BITMAP CONVERSION COUNT     |                   | 86565 |     5   (0)|
 00:00:01 |
|   3 |    BITMAP INDEX FAST FULL SCAN| IDX_BITM_T_STATUS |       |            |
          |
--------------------------------------------------------------------------------
-----------
Note
-----
   - dynamic sampling used for this statement (level=2)
统计信息
----------------------------------------------------------
          0  recursive calls
          0  db block gets
          6  consistent gets
          0  physical reads
          0  redo size
        432  bytes sent via SQL*Net to client
        419  bytes received via SQL*Net from client
          2  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
          1  rows processed
SQL>

注意要点：

位图索引更新列容易造成死锁，所以查询比较多列才适合建位图索引，更新比较多的列就尽量不要建索引

1.2、函数索引

函数索引：就是将一个函数计算的结果存储在行的列中

环境准备：

drop table t purge;
create table t (id int, status varchar2(2));
insert into t select 1,'N' from dual;
insert into t select rownum ,'Y' from dual connect by rownum <1000;
commit;

不走索引的查询：

SQL> set autotrace on
SQL> select * from t where (case when status='N' then 'No' end)='No';
        ID STAT
---------- ----
         1 N
执行计划
----------------------------------------------------------
Plan hash value: 1601196873
--------------------------------------------------------------------------
| Id  | Operation         | Name | Rows  | Bytes | Cost (%CPU)| Time     |
--------------------------------------------------------------------------
|   0 | SELECT STATEMENT  |      |     1 |    16 |     3   (0)| 00:00:01 |
|*  1 |  TABLE ACCESS FULL| T    |     1 |    16 |     3   (0)| 00:00:01 |
--------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
   1 - filter(CASE "STATUS" WHEN 'N' THEN 'No' END ='No')
Note
-----
   - dynamic sampling used for this statement (level=2)
统计信息
----------------------------------------------------------
          0  recursive calls
          0  db block gets
          8  consistent gets
          0  physical reads
          0  redo size
        486  bytes sent via SQL*Net to client
        419  bytes received via SQL*Net from client
          2  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
          1  rows processed
SQL>

创建函数索引：

create index idx_status on t (case when status ='N' then 'No' end);

走函数索引的查询：

SQL> select * from t where (case when status='N' then 'No' end)='No';
        ID STAT
---------- ----
         1 N
执行计划
----------------------------------------------------------
Plan hash value: 3908194542
--------------------------------------------------------------------------------
----------
| Id  | Operation                   | Name       | Rows  | Bytes | Cost (%CPU)|
Time     |
--------------------------------------------------------------------------------
----------
|   0 | SELECT STATEMENT            |            |    10 |   200 |     2   (0)|
00:00:01 |
|   1 |  TABLE ACCESS BY INDEX ROWID| T          |    10 |   200 |     2   (0)|
00:00:01 |
|*  2 |   INDEX RANGE SCAN          | IDX_STATUS |     4 |       |     1   (0)|
00:00:01 |
--------------------------------------------------------------------------------
----------
Predicate Information (identified by operation id):
---------------------------------------------------
   2 - access(CASE "STATUS" WHEN 'N' THEN 'No' END ='No')
Note
-----
   - dynamic sampling used for this statement (level=2)
统计信息
----------------------------------------------------------
          0  recursive calls
          0  db block gets
          2  consistent gets
          0  physical reads
          0  redo size
        486  bytes sent via SQL*Net to client
        419  bytes received via SQL*Net from client
          2  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
          1  rows processed
SQL>

注意要点：

自定义函数时要加上deterministic 关键字，不然不能建立函数索引

建立一个自定义函数：

create or replace function f_addusl(i int) return int is
begin
  return(i + 1);
end;

尝试建立函数索引：

create index idx_ljb_test on t(f_addusl(id));

提示：ORA-30553:函数不能确定

用deterministic 关键字，就可以建立函数索引

create or replace function f_addusl(i int) return int deterministic is
begin
  return(i + 1);
end;

在自定义函数代码更新时，对应的函数索引也要重建，否则不能用到原来的函数索引

1.3、反向索引

反向索引：反向索引其实也是BTree索引的一种特例，不过在列中字节会反转的(反向索引是为了避免热快竞争，比如索引列中存储的列值是递增的，比如250101,250102，按照BTree索引的特性，一般是按照顺序存储在索引右边的，所以容易形成热快竞争，而反向索引可以避免这种情况，因为反向索引是这样存储的，比如101052,201052，这样列值就距离很远了，避免了热快竞争)

反向索引不能用到范围查询

SQL> set autotrace on
SQL> select * from t where created=sysdate;
未选定行
执行计划
----------------------------------------------------------
Plan hash value: 913247507
--------------------------------------------------------------------------------
---------------
| Id  | Operation                   | Name            | Rows  | Bytes | Cost (%C
PU)| Time     |
--------------------------------------------------------------------------------
---------------
|   0 | SELECT STATEMENT            |                 |    12 |  2484 |   286
(0)| 00:00:04 |
|   1 |  TABLE ACCESS BY INDEX ROWID| T               |    12 |  2484 |   286
(0)| 00:00:04 |
|*  2 |   INDEX RANGE SCAN          | IDX_REV_CREATED |   346 |       |     1
(0)| 00:00:01 |
--------------------------------------------------------------------------------
---------------
Predicate Information (identified by operation id):
---------------------------------------------------
   2 - access("CREATED"=SYSDATE@!)
Note
-----
   - dynamic sampling used for this statement (level=2)
统计信息
----------------------------------------------------------
          0  recursive calls
          0  db block gets
          2  consistent gets
          0  physical reads
          0  redo size
       1191  bytes sent via SQL*Net to client
        408  bytes received via SQL*Net from client
          1  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
          0  rows processed
SQL>

范围查询，发现不走反向索引查询

SQL> select * from t where created>= sysdate-10 and created <= sysdate-1;
OWNER
------------------------------------------------------------
OBJECT_NAME
--------------------------------------------------------------------------------
SUBOBJECT_NAME                                                OBJECT_ID
------------------------------------------------------------ ----------
DATA_OBJECT_ID OBJECT_TYPE                            CREATED
-------------- -------------------------------------- --------------
LAST_DDL_TIME  TIMESTAMP                              STATUS         TE GE SE
-------------- -------------------------------------- -------------- -- -- --
 NAMESPACE EDITION_NAME
---------- ------------------------------------------------------------
SYS
ICOL$
                                                                     20
             2 TABLE                                  15-6月 -19
02-4月 -10     2010-04-02:13:18:38                    VALID          N  N  N
         1
SYS
I_USER1
                                                                     46
            46 INDEX                                  14-6月 -19
OWNER
------------------------------------------------------------
OBJECT_NAME
--------------------------------------------------------------------------------
SUBOBJECT_NAME                                                OBJECT_ID
------------------------------------------------------------ ----------
DATA_OBJECT_ID OBJECT_TYPE                            CREATED
-------------- -------------------------------------- --------------
LAST_DDL_TIME  TIMESTAMP                              STATUS         TE GE SE
-------------- -------------------------------------- -------------- -- -- --
 NAMESPACE EDITION_NAME
---------- ------------------------------------------------------------
02-4月 -10     2010-04-02:13:18:38                    VALID          N  N  N
         4
SYS
CON$
                                                                     28
            28 TABLE                                  13-6月 -19
02-4月 -10     2010-04-02:13:18:38                    VALID          N  N  N
         1
SYS
OWNER
------------------------------------------------------------
OBJECT_NAME
--------------------------------------------------------------------------------
SUBOBJECT_NAME                                                OBJECT_ID
------------------------------------------------------------ ----------
DATA_OBJECT_ID OBJECT_TYPE                            CREATED
-------------- -------------------------------------- --------------
LAST_DDL_TIME  TIMESTAMP                              STATUS         TE GE SE
-------------- -------------------------------------- -------------- -- -- --
 NAMESPACE EDITION_NAME
---------- ------------------------------------------------------------
UNDO$
                                                                     15
            15 TABLE                                  12-6月 -19
02-4月 -10     2010-04-02:13:18:38                    VALID          N  N  N
         1
SYS
C_COBJ#
                                                                     29
            29 CLUSTER                                11-6月 -19
02-4月 -10     2010-04-02:13:18:38                    VALID          N  N  N
OWNER
------------------------------------------------------------
OBJECT_NAME
--------------------------------------------------------------------------------
SUBOBJECT_NAME                                                OBJECT_ID
------------------------------------------------------------ ----------
DATA_OBJECT_ID OBJECT_TYPE                            CREATED
-------------- -------------------------------------- --------------
LAST_DDL_TIME  TIMESTAMP                              STATUS         TE GE SE
-------------- -------------------------------------- -------------- -- -- --
 NAMESPACE EDITION_NAME
---------- ------------------------------------------------------------
         5
SYS
I_OBJ#
                                                                      3
             3 INDEX                                  10-6月 -19
02-4月 -10     2010-04-02:13:18:38                    VALID          N  N  N
         4
SYS
PROXY_ROLE_DATA$
OWNER
------------------------------------------------------------
OBJECT_NAME
--------------------------------------------------------------------------------
SUBOBJECT_NAME                                                OBJECT_ID
------------------------------------------------------------ ----------
DATA_OBJECT_ID OBJECT_TYPE                            CREATED
-------------- -------------------------------------- --------------
LAST_DDL_TIME  TIMESTAMP                              STATUS         TE GE SE
-------------- -------------------------------------- -------------- -- -- --
 NAMESPACE EDITION_NAME
---------- ------------------------------------------------------------
                                                                     25
            25 TABLE                                  09-6月 -19
02-4月 -10     2010-04-02:13:18:38                    VALID          N  N  N
         1
SYS
I_IND1
                                                                     41
            41 INDEX                                  08-6月 -19
02-4月 -10     2010-04-02:13:18:38                    VALID          N  N  N
         4
OWNER
------------------------------------------------------------
OBJECT_NAME
--------------------------------------------------------------------------------
SUBOBJECT_NAME                                                OBJECT_ID
------------------------------------------------------------ ----------
DATA_OBJECT_ID OBJECT_TYPE                            CREATED
-------------- -------------------------------------- --------------
LAST_DDL_TIME  TIMESTAMP                              STATUS         TE GE SE
-------------- -------------------------------------- -------------- -- -- --
 NAMESPACE EDITION_NAME
---------- ------------------------------------------------------------
SYS
I_CDEF2
                                                                     54
            54 INDEX                                  07-6月 -19
02-4月 -10     2010-04-02:13:18:38                    VALID          N  N  N
         4
已选择9行。
执行计划
----------------------------------------------------------
Plan hash value: 1322348184
---------------------------------------------------------------------------
| Id  | Operation          | Name | Rows  | Bytes | Cost (%CPU)| Time     |
---------------------------------------------------------------------------
|   0 | SELECT STATEMENT   |      |    12 |  2484 |   292   (2)| 00:00:04 |
|*  1 |  FILTER            |      |       |       |            |          |
|*  2 |   TABLE ACCESS FULL| T    |    12 |  2484 |   292   (2)| 00:00:04 |
---------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
   1 - filter(SYSDATE@!-10<=SYSDATE@!-1)
   2 - filter("CREATED">=SYSDATE@!-10 AND "CREATED"<=SYSDATE@!-1)
Note
-----
   - dynamic sampling used for this statement (level=2)
统计信息
----------------------------------------------------------
          5  recursive calls
          0  db block gets
       1112  consistent gets
          0  physical reads
          0  redo size
       1770  bytes sent via SQL*Net to client
        419  bytes received via SQL*Net from client
          2  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
          9  rows processed
SQL>

1.4、全文索引

全文索引：所谓Oracle全文索引是通过Oracle词法分析器(lexer)将所有的表意单元term存储dr$开头的表里并存储term出现的位置、次数、hash值等等信息，Oracle提供了basic_lexer(针对英语)、chinese_vgram_lexer(汉语分析器)、chinese_lexer(新的汉语分析器)。

basic_lexer：是一种适用于英文的分析器，根据空格或者标点符号将词元分离，不管对于中文来说是没有空格的，所以这种分析器不适合中文
chinese_vgram_lexer：这是一种原先专门的中文分析器，支持所有的汉字字符集，比如zhs16gbk单点。这种分析器，分析过程是按字为单元进行分析的，举个例子，“索引本身是有序的”，按照这种分析器，会分成词元“索”、“索引”、“引本”、“本身”、“身是”、“是有”、“有序”、“序的”、“的”这些词元，然后你发现像“序的”这些词在中文中基本是不成立的，不过这种Oracle分析器本身就不认识中文，所以只能全部分析，很明显效率是不好的
chinese_lexer：这是一种新的中文分析器，前面提到chinese_vgram_lexer这种分析器虽然支持所有的中文字符集，但是效率不高，所以chinese_lexer是对其的改进版本，这种分析器认识很多中文词汇，能够比较快查询，提高效率，不过这种分析器只能支持utf-8字符集

Oracle的全文索引具体可以采用通配符查找、模糊匹配、相关分类、近似查找、条件加权和词意扩充等方法

环境准备

drop table t purge;
create table t as select * from dba_objects where object_name is not null;
update t set object_name ='高兴' where rownum<=2;
commit;
select * from t where object_name like '%高兴%';

设置词法分析器

//设置词法分析器
BEGIN
  ctx_ddl.create_preference ('lexer1', 'chinese_vgram_lexer');
END;

解锁ctxsys用户，同时给你的测试账号(我这里用scott)授权使用ctx_ddl

//解锁ctxsys用户同时授权
grant ctxapp to scott;
alter user ctxsys account unlock;
alter user ctxsys identified by ctxsys;
connect ctxsys/ctxsys;
grant execute on ctx_ddl to scott;
connect scott/11;

建立全文索引

//删除全文索引
drop index idx_content;
//查看数据文件信息
select * from v$datafile; 
//建立全文索引
CREATE INDEX  idx_content ON t(object_name) indextype is ctxsys.context  parameters('lexer lexer1');

注意要点：更新数据时候记得执行全文索引同步命令，否则将看不到更新数据

exec ctx_ddl.sync_index('idx_content','20M');

今天文章到此就结束了，感谢您的阅读，年年好运。

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