[bbk2345] 第50集 Chapter 12Optimizing Sore Perations(05)

Using System Statistics

• System statistics enable the CBO to use CPU and I/O characteristics.
• System statistics must be gathered on a regular basis;this does not invalidate cached plans.
• Gathering system statistics equals analyzing system activity for a specified period of time.

所有的System Statistics 信息，都将作为CBO决策的依据.

Gathering System statistics

Procedures of the dbms_stats package used to collect system statistics:

• gather_system_stats
• set_system_stats
• get_system_stats

Manual Gathering

• Start manual system statistics collection in the data dictionary:

EXECUTE dbms_stats.gather_system_stats(gathering_mode => 'START');

• Genernate the workload
• End system statistics collection:

EXECUTE dbms_stats.gather_system_stats(gathering_mode => 'STOP');

Automatic Gathering

Collect statistics for OLTP:

EXECUTE dbms_stats.gather_system_stats(interval => 120,stattab => 'mystats',statid => 'OLTP');

Collect statistics for OLAP:

EXECUTE dbms_stats.gather_system_stats(interval => 120,stattab => 'mystats',statid => 'OLAP');

Import System Statistics

For daytime(OLTP):

EXECUTE dbms_stats.import_system_stats(stattab => 'mystats',statid => 'OLTP' );

For nighttime(OLAP):

EXECUTE dbms_stats.import_system_stats(stattab => 'mystats',statid => 'OLAP');

Copy Statistics Between DBs

Example

SQL> exec dbms_stats.create_stat_table('HR','MYSTATS');

PL/SQL procedure successfully completed.

SQL> desc mystats;
 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)
 CL1                                                CLOB

Summary

In this lesson,you should have learned how to:

• Collect system statistics
• Collect statistics on indexes and tables
• Describe the use of histograms(主要用在column statistics上面.)
• Copy statistics between database(主要应用在将生产库的真实环境数据，转移到测试环境下，安全有效的测试系统)
• Determine usage of indexes(此部分，没有做任何讲解)