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物化视图：使用dbms_mview.explain_mview

2012-04-09 09:06 381 查看

可以在《Oracle® Database Data Warehousing Guide》中找到更多内容

http://docs.oracle.com/cd/E11882_01/server.112/e25554/basicmv.htm#DWHSG8219

基本概况

用dbms_mview.explain_mview可以解释、分析物化视图，也可以用来排错。

dbms_mview.explain_mview能操作的对象有1.materialized view name，2.SQL语句,
3.CREATE MATERIALIZED VIEW的语句。

分析完后可能的建议：

         存在的物化视图详细情况。

         创建之前潜在的问题。

结果存在mv_capabilities_table或者数组中。

当前用户必须执行utlxmv.sql才会有权限创建mv_capabilities_table

SQL> @?/rdbms/admin/utlxmv.sql;

This procedure provides the following information:

–
Is this materialized view fast refreshable?

–
What type of query rewrite can be performed with this materialized view?

下面对3种对象进行实例测试。

一。对存在的MV进行分析

通过dbms_mview.explain_mview分析MV，验证MV的query rewrite功能：

创建测试环境

SQL> create table tan01 as select * from dba_users;

SQL> create materialized view mv_tan01

2 as select count(*) from tan01;

SQL> analyze table tan01 compute statistics;

SQL> set autot on;

SQL> select count(*) from tan01;

COUNT(*)

----------

56

Execution Plan

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

Plan hash value: 761709626

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

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

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

| 0 | SELECT STATEMENT | | 1 | 2 (0)| 00:00:01 |

| 1 | SORT AGGREGATE | | 1 | | |

| 2 | TABLE ACCESS FULL| TAN01 | 56 | 2 (0)| 00:00:01 |

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

Statistics

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

1 recursive calls

0 db block gets

3 consistent gets

2 physical reads

0 redo size

411 bytes sent via SQL*Net to client

385 bytes received via SQL*Net from client

2 SQL*Net roundtrips to/from client

0 sorts (memory)

0 sorts (disk)

1 rows processed

由上面可以看出，该查询还没有经过物化视图，因为当前没有开户query rewrite，下面进行验证：

用dbms_mview.explain_mview进行验证

SQL> exec dbms_mview.explain_mview('mv_tan01');
SQL> select capability_name,possible,msgtxt from mv_capabilities_table where mvname='MV_TAN01'

CAPABILITY_NAME PO MSGTXT

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

PCT N

REFRESH_COMPLETE Y

REFRESH_FAST N
REWRITE N
PCT_TABLE N relation is not a partitioned table

REFRESH_FAST_AFTER_INSERT N the detail table does not have a materialized view log

REFRESH_FAST_AFTER_ONETAB_DML N see the reason why REFRESH_FAST_AFTER_INSERT is disabled

REFRESH_FAST_AFTER_ANY_DML N see the reason why REFRESH_FAST_AFTER_ONETAB_DML is disabled

REFRESH_FAST_PCT N PCT is not possible on any of the detail tables in the materialized view

REWRITE_FULL_TEXT_MATCH N query rewrite is disabled on the materialized view

REWRITE_PARTIAL_TEXT_MATCH N query rewrite is disabled on the materialized view

REWRITE_GENERAL N query rewrite is disabled on the materialized view

REWRITE_PCT N general rewrite is not possible or PCT is not possible on any of the detail tables

PCT_TABLE_REWRITE N relation is not a partitioned table

14 rows selected.

SQL>

由验证可知没有开启查询重写，下面再建一个开启查询重写的的物化视图：

create materialized view mv02_tan01 enable query rewrite
as select count(*) from tan01;

对查询进行分析：

SQL> explain plan

2 for

3 select count(*) from tan01;

SQL> select * from table(dbms_xplan.display);

PLAN_TABLE_OUTPUT

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

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

| 0 | SELECT STATEMENT | | 1 | 13 | 2 (0)| 00:00:01 |

| 1 | MAT_VIEW REWRITE ACCESS FULL| MV02_TAN01 | 1 | 13 | 2 (0)| 00:00:01 |

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

Note

-----

- dynamic sampling used for this statement
由上可知，查询重写起作用了。这次SQL语句的执行并没有扫描基表，而是扫描了物化视图。

再次通过dbms_mview.explain_mview分析验证：
SQL> exec dbms_mview.explain_mview('mv02_tan01');

SQL> select capability_name,possible,msgtxt from mv_capabilities_table where mvname='MV02_TAN01';

CAPABILITY_NAME PO MSGTXT

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

PCT N

REFRESH_COMPLETE Y

REFRESH_FAST N
REWRITE Y
PCT_TABLE N relation is not a partitioned table

REFRESH_FAST_AFTER_INSERT N the detail table does not have a materialized view log

REFRESH_FAST_AFTER_ONETAB_DML N see the reason why REFRESH_FAST_AFTER_INSERT is disabled

REFRESH_FAST_AFTER_ANY_DML N see the reason why REFRESH_FAST_AFTER_ONETAB_DML is disabled

REFRESH_FAST_PCT N PCT is not possible on any of the detail tables in the materialized view

REWRITE_FULL_TEXT_MATCH Y

REWRITE_PARTIAL_TEXT_MATCH Y

REWRITE_GENERAL Y

REWRITE_PCT N general rewrite is not possible or PCT is not possible on any of the detail tables

PCT_TABLE_REWRITE N relation is not a partitioned table

二.对定义的查询进行分析：

SQL> exec dbms_mview.explain_mview ('select job,sum(sal) from emp group by job','123');

SQL> SELECT capability_name, possible, related_text, msgtxt

FROM mv_capabilities_table

WHER 2 3 E statement_id='123'

O 4 RDER BY seq;

CAPABILITY_NAME PO RELATED_TEXT MSGTXT

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

PCT N

REFRESH_COMPLETE Y

REFRESH_FAST N

REWRITE Y

PCT_TABLE N EMP relation is not a partitioned table

REFRESH_FAST_AFTER_INSERT N SCOTT.EMP mv log must have ROWID

REFRESH_FAST_AFTER_INSERT N SCOTT.EMP mv log must have new values

REFRESH_FAST_AFTER_INSERT N SCOTT.EMP mv log does not have all necessary columns

REFRESH_FAST_AFTER_ONETAB_DML N SUM(SAL) SUM(expr) without COUNT(expr)

REFRESH_FAST_AFTER_ONETAB_DML N see the reason why REFRESH_FAST_AFTER_INSERT is disabled

REFRESH_FAST_AFTER_ONETAB_DML N COUNT(*) is not present in the select list

REFRESH_FAST_AFTER_ONETAB_DML N SUM(expr) without COUNT(expr)

REFRESH_FAST_AFTER_ANY_DML N SCOTT.EMP mv log does not have sequence #

REFRESH_FAST_AFTER_ANY_DML N see the reason why REFRESH_FAST_AFTER_ONETAB_DML is disabled

REFRESH_FAST_PCT N PCT is not possible on any of the detail tables in the materialized view

REWRITE_FULL_TEXT_MATCH Y

REWRITE_PARTIAL_TEXT_MATCH Y

REWRITE_GENERAL Y

REWRITE_PCT N general rewrite is not possible or PCT is not possible on any of the detail tables

PCT_TABLE_REWRITE N EMP relation is not a partitioned table

20 rows selected.

三。对创建物化视图的语句进行分析：

SQL> exec dbms_mview.explain_mview ('create materialized view mv_job_sal as select count(*) from dept','121');

SQL> SELECT capability_name, possible, related_text, msgtxt

2 FROM mv_capabilities_table

3 WHERE statement_id='121'

O 4 RDER BY seq;

CAPABILITY_NAME PO RELATED_TEXT MSGTXT

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

PCT N

REFRESH_COMPLETE Y

REFRESH_FAST N

REWRITE N

PCT_TABLE N DEPT relation is not a partitioned table

REFRESH_FAST_AFTER_INSERT N SCOTT.DEPT the detail table does not have a materialized view log

REFRESH_FAST_AFTER_ONETAB_DML N see the reason why REFRESH_FAST_AFTER_INSERT is disabled

REFRESH_FAST_AFTER_ANY_DML N see the reason why REFRESH_FAST_AFTER_ONETAB_DML is disabled

REFRESH_FAST_PCT N PCT is not possible on any of the detail tables in the materialized view

REWRITE_FULL_TEXT_MATCH N query rewrite is disabled on the materialized view

REWRITE_PARTIAL_TEXT_MATCH N query rewrite is disabled on the materialized view

REWRITE_GENERAL N query rewrite is disabled on the materialized view

REWRITE_PCT N general rewrite is not possible or PCT is not possible on any of the detail tables

PCT_TABLE_REWRITE N DEPT relation is not a partitioned table

14 rows selected.

SQL>

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