oracle 10g

aaie_ 2017-04-15

展开全文

前言：

oracle sql如何生成合理的执行计划,CBO选取sql最佳执行计划的关键，即确保sql所引用的表及索引相关的统计信息正确。那么oracle如何收集统计信息，它是采用dbms_stats包来实现收集统计信息。

dbms_stats包功能十分强大，我们依次展开测试与学习，希望对大家有所补益。

测试步骤：

1，数据库版本

SQL> select * from v$version;

BANNER

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

Oracle Database 10g Enterprise Edition Release 10.2.0.5.0 - 64bi

PL/SQL Release 10.2.0.5.0 - Production

CORE 10.2.0.5.0 Production

TNS for Linux: Version 10.2.0.5.0 - Production

NLSRTL Version 10.2.0.5.0 - Production

SQL>

2,创建测试表并插入数据

SQL> conn tbs_11204/system

Connected.

SQL> create table t_stat(a int,b int);

Table created.

SQL> insert into t_stat select mod(level,5),mod(level,3)+2 from dual connect by level<=200000;

200000 rows created.

SQL> commit;

Commit complete.

SQL> exec dbms_stats.gather_table_stats(user,'t_stat',cascade=>true);

PL/SQL procedure successfully completed.

3，创建存储表统计信息的表

CREATE_STAT_TABLE Procedure

This procedure creates a table with name stattab in ownname's schema which is capable of holding statistics. The columns and types that compose this table are not relevant as it should be accessed solely through the procedures in this package.

Syntax

DBMS_STATS.CREATE_STAT_TABLE (
   ownname  VARCHAR2, 
   stattab  VARCHAR2,
   tblspace VARCHAR2 DEFAULT NULL);

Parameters

Table 103-8 CREATE_STAT_TABLE Procedure Parameters

Parameter	Description
ownname	Name of the schema
stattab	Name of the table to create. This value should be passed as the stattab parameter to other procedures when the user does not want to modify the dictionary statistics directly.
tblspace	Tablespace in which to create the statistics tables. If none is specified, then they are created in the user's default tablespace.

Exceptions

ORA-20000: Table already exists or insufficient privileges.

ORA-20001: Tablespace does not exist.

SQL> conn tbs_11204/system

Connected.

SQL> exec dbms_stats.create_stat_table('tbs_11204','stat_t_stat');

PL/SQL procedure successfully completed.

SQL> desc stat_t_stat;

Name Null? Type

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

STATID VARCHAR2(30)

TYPE CHAR(1)

VERSION NUMBER

FLAGS NUMBER

C1 VARCHAR2(30)

C2 VARCHAR2(30)

C3 VARCHAR2(30)

C4 VARCHAR2(30)

C5 VARCHAR2(30)

N1 NUMBER

N2 NUMBER

N3 NUMBER

N4 NUMBER

N5 NUMBER

N6 NUMBER

N7 NUMBER

N8 NUMBER

N9 NUMBER

N10 NUMBER

N11 NUMBER

N12 NUMBER

D1 DATE

R1 RAW(32)

R2 RAW(32)

CH1 VARCHAR2(1000)

SQL> select count(*) from stat_t_stat;

COUNT(*)

----------

4，export_table_stats导出表的统计信息到存储统计信息的表

（注：可以级联导出表的列及索引统计也导出）

EXPORT_TABLE_STATS Procedure

This procedure retrieves statistics for a particular table and stores them in the user statistics table. Cascade results in all index and column statistics associated with the specified table being exported as well.

Syntax

DBMS_STATS.EXPORT_TABLE_STATS (
   ownname  VARCHAR2, 
   tabname  VARCHAR2, 
   partname VARCHAR2 DEFAULT NULL,
   stattab  VARCHAR2, 
   statid   VARCHAR2 DEFAULT NULL,
   cascade  BOOLEAN  DEFAULT TRUE,
   statown  VARCHAR2 DEFAULT NULL);

Parameters

Table 103-25 EXPORT_TABLE_STATS Procedure Parameters

Parameter	Description
ownname	Name of the schema
tabname	Name of the table
partname	Name of the table partition. If the table is partitioned and if partname is NULL, then global and partition table statistics are exported.
stattab	User statistics table identifier describing where to store the statistics
statid	Identifier (optional) to associate with these statistics within stattab
cascade	If true, then column and index statistics for this table are also exported
statown	Schema containing stattab (if different than ownname)

SQL> exec dbms_stats.export_table_stats('tbs_11204','t_stat',null,'stat_t_stat',null,true,'tbs_11204');

PL/SQL procedure successfully completed.

SQL> select count(*) from stat_t_stat;

COUNT(*)

----------

5,从存储统计信息的表导入统计回表

IMPORT_TABLE_STATS Procedure

http://usunnab06.us.oracle.com:80/servers/MifChecker/Out/Y10312_01.htm retrieves statistics for a particular table from the user statistics table identified by stattab and stores them in the dictionary. Cascade results in all index and column statistics associated with the specified table being imported as well.

Syntax

DBMS_STATS.IMPORT_TABLE_STATS (
   ownname       VARCHAR2, 
   tabname       VARCHAR2,
   partname      VARCHAR2 DEFAULT NULL,
   stattab       VARCHAR2, 
   statid        VARCHAR2 DEFAULT NULL,
   cascade       BOOLEAN  DEFAULT TRUE,
   statown       VARCHAR2 DEFAULT NULL,
   no_invalidate BOOLEAN DEFAULT to_no_invalidate_type(
                                    get_param('NO_INVALIDATE')),
   force         BOOLEAN DEFAULT FALSE);

Parameters

Table 103-46 IMPORT_TABLE_STATS Procedure Parameters

Parameter	Description
ownname	Name of the schema
tabname	Name of the table
partname	Name of the table partition. If the table is partitioned and if partname is NULL, then global and partition table statistics are imported.
stattab	User statistics table identifier describing from where to retrieve the statistics
statid	Identifier (optional) to associate with these statistics within stattab
cascade	If true, then column and index statistics for this table are also imported
statown	Schema containing stattab (if different than ownname)
no_invalidate	Does not invalidate the dependent cursors if set to TRUE. The procedure invalidates the dependent cursors immediately if set to FALSE. Use DBMS_STATS.AUTO_INVALIDATE. to have Oracle decide when to invalidate dependent cursors. This is the default. The default can be changed using the SET_PARAM Procedure.
force	Imports statistics even if table statistics are locked