QUERY_REWRITE_INTEGRITY

Property	Description
Parameter type	String
Syntax	`QUERY_REWRITE_INTEGRITY = { enforced \| trusted \| stale_tolerated }`
Default value	`enforced`
Modifiable	`ALTER SESSION`, `ALTER SYSTEM`
Real Application Clusters	Multiple instances can have different values.

QUERY_REWRITE_INTEGRITY determines the degree to which Oracle must enforce query rewriting. At the safest level, Oracle does not use query rewrite transformations that rely on unenforced relationships.

Values:

enforced
Oracle enforces and guarantees consistency and integrity.
trusted
Oracle allows rewrites using relationships that have been declared, but that are not enforced by Oracle.
stale_tolerated
Oracle allows rewrites using unenforced relationships. Materialized views are eligible for rewrite even if they are known to be inconsistent with the underlying detail data.

实验：
TOM书上的例子，我自己做一些实验大家一起理解

首先我设置 QUERY_REWRITE_INTEGRITY = ENFORCED

TYGER@ORCL>create table emp as select * from scott.emp;

Table created.

TYGER@ORCL>create table dept as select * from scott.dept;

Table created.

TYGER@ORCL>show parameter query

NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
query_rewrite_enabled string TRUE
query_rewrite_integrity string enforced
TYGER@ORCL>
TYGER@ORCL>create materialized view emp_dept
2 build immediate
3 refresh on demand
4 enable query rewrite
5 as
6 select dept.deptno,dept.dname,count(*)
7 from emp,dept
8 where emp.deptno=dept.deptno
9 group by dept.deptno,dept.dname
10 /

Materialized view created.

TYGER@ORCL>show parameter optimizer

NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
optimizer_dynamic_sampling integer 2
optimizer_features_enable string 10.2.0.1
optimizer_index_caching integer 0
optimizer_index_cost_adj integer 100
optimizer_mode string ALL_ROWS
optimizer_secure_view_merging boolean TRUE
TYGER@ORCL>set autot traceonly explain
TYGER@ORCL>select count(*) from emp;

COUNT(*)
----------
14

Execution Plan
----------------------------------------------------------
Plan hash value: 2083865914

-------------------------------------------------------------------
| Id | Operation | Name | Rows | Cost (%CPU)| Time |
-------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 3 (0)| 00:00:01 |
| 1 | SORT AGGREGATE | | 1 | | |
| 2 | TABLE ACCESS FULL| EMP | 14 | 3 (0)| 00:00:01 |
-------------------------------------------------------------------

Note
-----
- dynamic sampling used for this statement

TYGER@ORCL>desc emp
Name Null? Type
----------------------------------------- -------- ----------------------------
EMPNO NUMBER(4)
ENAME VARCHAR2(10)
JOB VARCHAR2(9)
MGR NUMBER(4)
HIREDATE DATE
SAL NUMBER(7,2)
COMM NUMBER(7,2)
DEPTNO NUMBER(2)

TYGER@ORCL>desc dept
Name Null? Type
----------------------------------------- -------- ----------------------------
DEPTNO NUMBER(2)
DNAME VARCHAR2(14)
LOC VARCHAR2(13)

总结：之所以发生这种情况是由于知道 DEPTNO 是 DEPT 表的主键，DEPTNO 在表 EMP 中应该是 NOT NULL 的，EMP 表的 DEPTNO 应该是基于 DEPT 表 DEPTNO 列的外键，但是由于我们的表没有这个外键约束存在，而 query_rewrite_integrity 又设置为 enforced ，优化器为了得到完整可靠的数据不得不查询基表而得出最终结果。

假如我们加上上面的规则，再看查询结果：

TYGER@ORCL>alter table dept add constraint dept_pk primary key(deptno);

Table altered.

TYGER@ORCL>desc dept
Name Null? Type
----------------------------------------- -------- ----------------------------
DEPTNO NOT NULL NUMBER(2)
DNAME VARCHAR2(14)
LOC VARCHAR2(13)

TYGER@ORCL>alter table emp
2 add constraint emp_fk_dept
3 foreign key(deptno) references dept(deptno);

Table altered.

TYGER@ORCL>alter table emp modify deptno not null;

Table altered.

TYGER@ORCL>desc emp;
Name Null? Type
----------------------------------------- -------- ----------------------------
EMPNO NUMBER(4)
ENAME VARCHAR2(10)
JOB VARCHAR2(9)
MGR NUMBER(4)
HIREDATE DATE
SAL NUMBER(7,2)
COMM NUMBER(7,2)
DEPTNO NOT NULL NUMBER(2)

TYGER@ORCL>set autot traceonly explain
TYGER@ORCL>select count(*) from emp;

COUNT(*)
----------
14

Execution Plan
----------------------------------------------------------
Plan hash value: 155013515

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

| Id | Operation | Name | Rows | Bytes | Cost (%CPU)|
Time |

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

| 0 | SELECT STATEMENT | | 1 | 13 | 3 (0)|
00:00:01 |

| 1 | SORT AGGREGATE | | 1 | 13 | |
|

| 2 | MAT_VIEW REWRITE ACCESS FULL| EMP_DEPT | 3 | 39 | 3 (0)|
00:00:01 |

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

Note
-----
- dynamic sampling used for this statement

可见当我们将完整性约束全部添加后，优化器有了足够的信息知道这条语句通过物化视图可以查询重写，而不用查询基表，实际的执行情况也印证了这一点。

我们在通过一个例子说明 THUSTED 的情况。我们首先将这些约束去除掉，然后添加一行新的数据

TYGER@ORCL>alter table emp drop constraint emp_fk_dept;

Table altered.

TYGER@ORCL>alter table dept drop constraint dept_pk;

Table altered.

TYGER@ORCL>alter table emp modify deptno null;

Table altered.

TYGER@ORCL>desc dept
Name Null? Type
----------------------------------------- -------- ----------------------------
DEPTNO NUMBER(2)
DNAME VARCHAR2(14)
LOC VARCHAR2(13)

TYGER@ORCL>desc emp;
Name Null? Type
----------------------------------------- -------- ----------------------------
EMPNO NUMBER(4)
ENAME VARCHAR2(10)
JOB VARCHAR2(9)
MGR NUMBER(4)
HIREDATE DATE
SAL NUMBER(7,2)
COMM NUMBER(7,2)
DEPTNO NUMBER(2)

// 插入一条违反实际约束行
TYGER@ORCL>insert into emp(empno,deptno) values(1,1);

1 row created.

TYGER@ORCL>exec dbms_mview.refresh(‘EMP_DEPT‘);

PL/SQL procedure successfully completed.

TYGER@ORCL>alter materialized view emp_dept consider fresh;
alter materialized view emp_dept consider fresh
*
ERROR at line 1:
ORA-30374: materialized view is already fresh

// 创建一个 novalidate 的约束
TYGER@ORCL>alter table dept
2 add constraint dept_pk primary key(deptno)
3 rely enable novalidate
4 /

Table altered.

TYGER@ORCL>alter table emp
2 add constraint emp_fk_dept
3 foreign key(deptno) references dept(deptno)
4 rely enable novalidate
5 /

Table altered.

TYGER@ORCL>alter table emp modify deptno not null novalidate;

Table altered.

回到原来的查询，假如 query_rewrite_integrity = enforced 的话，那么我们知道由于上述约束实际上是违反真实数据约束的，因此优化器将不会利用物化视图查询重写。

TYGER@ORCL>show parameter query

NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
query_rewrite_enabled string TRUE
query_rewrite_integrity string enforced
TYGER@ORCL>
TYGER@ORCL>set autot traceonly explain
TYGER@ORCL>select count(*) from emp;

COUNT(*)
----------
16

Execution Plan
----------------------------------------------------------
Plan hash value: 2083865914

-------------------------------------------------------------------
| Id | Operation | Name | Rows | Cost (%CPU)| Time |
-------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 3 (0)| 00:00:01 |
| 1 | SORT AGGREGATE | | 1 | | |
| 2 | TABLE ACCESS FULL| EMP | 16 | 3 (0)| 00:00:01 |
-------------------------------------------------------------------

Note
-----
- dynamic sampling used for this statement

而如果设置 query_rewrite_integrity = trusted 的话，那么优化器因为有了我们上述那个 novalidate约束的误导，它并不真实检验数据的完整性，因此还将会利用物化视图查询重写，尽管这样得出的结果是错误的。只要我们让优化器知道有完整性约束的存在，不管约束严格与否，优化器只要为了这个信息就会尽可能地利用物化视图查询重写。

TYGER@ORCL>alter session set query_rewrite_integrity=trusted;

Session altered.

TYGER@ORCL>select count(*) from emp;

COUNT(*)
----------
14

Execution Plan
----------------------------------------------------------
Plan hash value: 155013515

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

| Id | Operation | Name | Rows | Bytes | Cost (%CPU)|
Time |

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

| 0 | SELECT STATEMENT | | 1 | 13 | 3 (0)|
00:00:01 |

| 1 | SORT AGGREGATE | | 1 | 13 | |
|

| 2 | MAT_VIEW REWRITE ACCESS FULL| EMP_DEPT | 3 | 39 | 3 (0)|
00:00:01 |

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

Note
-----
- dynamic sampling used for this statement

而 stale_tolerated 就简单了：

/* 结果我自己做实验却没有得到的想要的结果： */

TYGER@ORCL>show parameter query

NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
query_rewrite_enabled string TRUE
query_rewrite_integrity string enforced

// session 级别修改参数

TYGER@ORCL>alter session set query_rewrite_integrity=stale_tolerated;

Session altered.

TYGER@ORCL>show parameter query

NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
query_rewrite_enabled string TRUE
query_rewrite_integrity string STALE_TOLERATED
TYGER@ORCL>set autot traceonly explain;
TYGER@ORCL>select count(*) from emp;

Execution Plan
----------------------------------------------------------
Plan hash value: 2083865914

-------------------------------------------------------------------
| Id | Operation | Name | Rows | Cost (%CPU)| Time |
-------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 3 (0)| 00:00:01 |
| 1 | SORT AGGREGATE | | 1 | | |
| 2 | TABLE ACCESS FULL| EMP | 14 | 3 (0)| 00:00:01 |
-------------------------------------------------------------------

Note
-----
- dynamic sampling used for this statement

// system 级别修改参数仍然如此

TYGER@ORCL>alter system set query_rewrite_integrity=stale_tolerated;

System altered.

TYGER@ORCL>set autot traceonly explain;
TYGER@ORCL>select count(*) from emp;

Execution Plan
----------------------------------------------------------
Plan hash value: 2083865914

-------------------------------------------------------------------
| Id | Operation | Name | Rows | Cost (%CPU)| Time |
-------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 3 (0)| 00:00:01 |
| 1 | SORT AGGREGATE | | 1 | | |
| 2 | TABLE ACCESS FULL| EMP | 14 | 3 (0)| 00:00:01 |
-------------------------------------------------------------------

Note
-----
- dynamic sampling used for this statement

// 重新启动数据库结果依旧

TYGER@ORCL>conn / as sysdba
Connected.
SYS@ORCL>shutdown immediate
Database closed.
Database dismounted.
ORACLE instance shut down.
SYS@ORCL>startup
ORACLE instance started.

Total System Global Area 285212672 bytes
Fixed Size 1218992 bytes
Variable Size 71304784 bytes
Database Buffers 209715200 bytes
Redo Buffers 2973696 bytes
Database mounted.
Database opened.
SYS@ORCL>conn tyger/tyger
Connected.
TYGER@ORCL>show parameter query

NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
query_rewrite_enabled string TRUE
query_rewrite_integrity string STALE_TOLERATED
TYGER@ORCL>set autot traceonly explain
TYGER@ORCL>select count(*) from emp;

Execution Plan
----------------------------------------------------------
Plan hash value: 2083865914

-------------------------------------------------------------------
| Id | Operation | Name | Rows | Cost (%CPU)| Time |
-------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 3 (0)| 00:00:01 |
| 1 | SORT AGGREGATE | | 1 | | |
| 2 | TABLE ACCESS FULL| EMP | 14 | 3 (0)| 00:00:01 |
-------------------------------------------------------------------

Note
-----
- dynamic sampling used for this statement

虽然结果有点不是很满意，但是看完后基本可以了解 query_rewrite_integrity 这个参数了吧

遗留问题：356 行 stale_tolerated 参数设置，如果看出错误的步骤欢迎指正。

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QUERY_REWRITE_INTEGRITY

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