Oracle物化檢視失效的幾種情況及測試
說明：物化檢視（Materialized Views）是查詢的結果集，所有原表和檢視的變更都將導致物化檢視的失效，最近就發現了一個物化檢視經常失效的問題，以下是整理的文件。
一、物化檢視狀態查詢：Oracle提供了一個檢視用於查詢物化檢視的狀態USER_MVIEWS,其中列STALENESS，用於顯示當前物化檢視的狀態
Relationship between the contents of the materialized view and the contents of the materialized view’s masters:
•FRESH - Materialized view is a read-consistent view of the current state of its masters（最新狀態：當前物化檢視的內容出於最新的狀態）
•STALE - Materialized view is out of date because one or more of its masters has changed. If the materialized view was FRESH before it became STALE, then it is a read-consistent view of a former state of its masters.（陳舊狀態：物化檢視引用的主表已經更新，但是物化檢視沒有重新整理，所以內容相對主表來說是舊的）
•NEEDS_COMPILE - Some object upon which the materialized view depends has changed. An ALTER MATERIALIZED VIEW…COMPILE statement is required to validate this materialized view and compute the staleness of the contents.（需要編譯：物化檢視引用的主表比如檢視，進行了重建後相應的物化檢視就需要編譯，當處於這種狀態的時候dba_objects檢視顯示的STATUS為INVALID)
需要執行語句:ALTER MATERIALIZED VIEW MV_NAME COMPILE;進行重新編譯；
•UNUSABLE - Materialized view is not a read-consistent view of its masters from any point in time（物化檢視引用的主表狀態不確定）
•UNKNOWN - Oracle Database does not know whether the materialized view is in a read-consistent view of its masters from any point in time (this is the case for materialized views created on prebuilt tables)（未知：通過prebuilt建立的表）
•UNDEFINED - Materialized view has remote masters. The concept of staleness is not defined for such materialized views.（物化檢視引用的表來自其他的資料庫，一般通過dblink連結過來的）
二、實驗測試：
2.1 建立物化檢視
CREATE MATERIALIZED VIEW MV_TEST (EMPNO,ENAME,JOB,MGR,HIREDATE,SAL,COMM,DEPTNO)
TABLESPACE USERS
PCTUSED 0
PCTFREE 10
INITRANS 2
MAXTRANS 255
STORAGE (
INITIAL 64K
NEXT 1M
MINEXTENTS 1
MAXEXTENTS UNLIMITED
PCTINCREASE 0
BUFFER_POOL DEFAULT
FLASH_CACHE DEFAULT
CELL_FLASH_CACHE DEFAULT
)
NOCACHE
LOGGING
NOCOMPRESS
NOPARALLEL
BUILD IMMEDIATE
USING INDEX
TABLESPACE USERS
PCTFREE 10
INITRANS 2
MAXTRANS 255
STORAGE (
INITIAL 64K
NEXT 1M
MINEXTENTS 1
MAXEXTENTS UNLIMITED
PCTINCREASE 0
BUFFER_POOL DEFAULT
FLASH_CACHE DEFAULT
CELL_FLASH_CACHE DEFAULT
)
REFRESH FORCE ON DEMAND
WITH PRIMARY KEY
AS
/* Formatted on 2014/12/30 16:36:55 (QP5 v5.215.12089.38647) */
SELECT “EMP”.”EMPNO” “EMPNO”,
“EMP”.”ENAME” “ENAME”,
“EMP”.”JOB” “JOB”,
“EMP”.”MGR” “MGR”,
“EMP”.”HIREDATE” “HIREDATE”,
“EMP”.”SAL” “SAL”,
“EMP”.”COMM” “COMM”,
“EMP”.”DEPTNO” “DEPTNO”
FROM “SCOTT”.”EMP” “EMP”
WHERE “EMP”.”DEPTNO” = 20;
COMMENT ON MATERIALIZED VIEW MV_TEST IS ‘snapshot table for snapshot SCOTT.MV_TEST’;
CREATE UNIQUE INDEX PK_EMP1 ON MV_TEST
(EMPNO)
LOGGING
TABLESPACE USERS
PCTFREE 10
INITRANS 2
MAXTRANS 255
STORAGE (
INITIAL 64K
NEXT 1M
MINEXTENTS 1
MAXEXTENTS UNLIMITED
PCTINCREASE 0
BUFFER_POOL DEFAULT
FLASH_CACHE DEFAULT
CELL_FLASH_CACHE DEFAULT
)
NOPARALLEL;
2.2 查詢當前物化檢視的狀態
SQL> SELECT mview_name,staleness FROM DBA_MVIEWS WHERE MVIEW_NAME=’MV_TEST’;
MVIEW_NAME STALENESS
MV_TEST FRESH
2.3 查詢資料庫物化檢視的狀態
column OBJECT_NAME format a20;
column STATUS format a20; OBJECT_TYPE
column OBJECT_TYPE format a20;
SQL> select OBJECT_NAME,STATUS,OBJECT_TYPE from dba_objects where OBJECT_NAME=’MV_TEST’ ;
OBJECT_NAME STATUS OBJECT_TYPE
MV_TEST VALID TABLE
MV_TEST VALID MATERIALIZED VIEW
2.4 修改源表的資料
SQL> SELECT mview_name,staleness FROM DBA_MVIEWS WHERE MVIEW_NAME=’MV_TEST’;
MVIEW_NAME STALENESS
MV_TEST NEEDS_COMPILE
顯示狀態需要編譯
SQL> ALTER MATERIALIZED VIEW SCOTT.MV_TEST COMPILE;
進行相應的編譯
SQL> SELECT mview_name,staleness FROM DBA_MVIEWS WHERE MVIEW_NAME=’MV_TEST’;
MVIEW_NAME STALENESS
MV_TEST STALE
編譯完成後，狀態變成STALE
2.5 修改源表的表結構測試
SQL> ALTER TABLE SCOTT.EMP RENAME COLUMN COMM TO COMMS; //修改源表的結構
SQL> SELECT mview_name,staleness FROM DBA_MVIEWS WHERE MVIEW_NAME=’MV_TEST’;//檢視物化檢視的狀態
MVIEW_NAME STALENESS
MV_TEST NEEDS_COMPILE
SQL> ALTER MATERIALIZED VIEW SCOTT.MV_TEST COMPILE; //重新編譯
SQL> SELECT mview_name,staleness FROM DBA_MVIEWS WHERE MVIEW_NAME=’MV_TEST’; //重新編譯狀態沒變；
MVIEW_NAME STALENESS
MV_TEST NEEDS_COMPILE
SQL> select OBJECT_NAME,STATUS,OBJECT_TYPE from dba_objects where OBJECT_NAME=’MV_TEST’ ;
OBJECT_NAME STATUS OBJECT_TYPE
MV_TEST VALID TABLE
MV_TEST INVALID MATERIALIZED VIEW
顯示物化檢視的狀態INVALID
2.5 修改源表的結構跟物化檢視一致
SQL> ALTER TABLE SCOTT.EMP RENAME COLUMN COMMS TO COMM; //修改源表的結構
SQL> SELECT mview_name,staleness FROM DBA_MVIEWS WHERE MVIEW_NAME=’MV_TEST’; //需要編譯
MVIEW_NAME STALENESS
MV_TEST NEEDS_COMPILE
SQL> ALTER MATERIALIZED VIEW SCOTT.MV_TEST COMPILE; //進行重新編譯
Materialized view altered.
SQL> SELECT mview_name,staleness FROM DBA_MVIEWS WHERE MVIEW_NAME=’MV_TEST’; //狀態變成STALE
MVIEW_NAME STALENESS
MV_TEST STALE
SQL> select OBJECT_NAME,STATUS,OBJECT_TYPE from dba_objects where OBJECT_NAME=’MV_TEST’ ; //狀態變成VALID
OBJECT_NAME STATUS OBJECT_TYPE
MV_TEST VALID TABLE
MV_TEST VALID MATERIALIZED VIEW
總結：當物化檢視的源表重新編譯了，如果重建後的表結構沒有發現變化，那麼執行指令碼ALTER MATERIALIZED VIEW MV_NAME COMPILE後物化檢視的狀態就會重新整理成有效的；
但是如果表的結構發生了變化，那麼需要重新修改物化檢視的指令碼，相應的物化檢視才能有效,dba_objects顯示出來的狀態才是VALID的狀態；