QUERY_REWRITE_INTEGRITY

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.

  
  

  
  

  實驗：
    TOM書上的樣例，我本身作一些實驗 你們一塊兒理解
    
  首先我設置 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)
  
  
  總結： 之因此發生這樣的狀況是由於知道 DEPTNO 是 DEPT 表的主鍵。DEPTNO 在表 EMP 中應該是 NOT NULL 的，EMP 表的 DEPTNO 應該是基於 DEPT 表 DEPTNO 列的外鍵，但是由於咱們的表沒有這個外鍵約束存在。而 query_rewrite_integrity 又設置爲 enforced ，優化器爲了獲得完整可靠的數據不得不查詢基表而得出終於結果。

  
  
  
  假如咱們加上上面的規則。再看查詢結果：
  
  
  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
  
  
  
  
  
  
  可見 當咱們將完整性約束全部加入後，優化器有了足夠的信息知道這條語句經過物化視圖可以查詢重寫，而不用查詢基表，實際的運行狀況也印證了這一點。
  
  
  
  
  咱們在經過一個樣例說明 THUSTED 的狀況。

  咱們首先將這些約束去除掉，而後加入一行新的數據
  
  
  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)
  
  
   
   // 插入一條違反實際約束行
  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
  
  
   
   // 建立一個 novalidate 的約束
  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.
  
  
  回到原來的查詢，假如 query_rewrite_integrity = enforced 的話，那麼咱們知道由於上述約束其實是違反真實數據約束的，所以優化器將不會利用物化視圖查詢重寫。
  
  
  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
  
  
  
  
  而假設設置 query_rewrite_integrity = trusted 的話，那麼優化器因爲有了咱們上述那個 novalidate約束的誤導。它並不真實檢驗數據的完整性，所以還將會利用物化視圖查詢重寫，雖然這樣得出的結果是錯誤的。

  僅僅要咱們讓優化器知道有完整性約束的存在。不管約束嚴格與否，優化器僅僅要爲了這個信息就會盡量地利用物化視圖查詢重寫。
  
  
  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 就簡單了：   
  
  
  /* 結果 我本身作實驗卻沒有獲得的想要的結果： */
  
  
  TYGER@ORCL>show parameter query
  
  
  NAME                                 TYPE        VALUE
  ------------------------------------ ----------- ------------------------------
  query_rewrite_enabled                string      TRUE
  query_rewrite_integrity              string      enforced
  
  
  // session 級別改動參數
  
  
  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 級別改動參數  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
  
  
   // 又一次啓動數據庫     結果依然
   
  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 儘管結果有點不是很是愜意，但是看完後基本可以瞭解  query_rewrite_integrity 這個參數了吧  遺留問題：356 行 stale_tolerated 參數設置。    假設看出錯誤的步驟 歡迎指正。