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分享一篇关于Oracle数据库收集统计信息的办法，Oracle DBMS_STATS与Oracle analyze使用方法案例

今天群里面讨论DBMS_STATS和analyze,这里进行了一些测试和猜测

1.创建模拟环境

SQL> select * from v$version;

BANNER

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

Oracle Database 11g Enterprise Edition Release 11.2.0.3.0 - 64bit Production

PL/SQL Release 11.2.0.3.0 - Production

CORE 11.2.0.3.0 Production

TNS for Solaris: Version 11.2.0.3.0 - Production

NLSRTL Version 11.2.0.3.0 - Production

SQL> conn oracleplus/oracleplus

Connected.

SQL> create table t_oracleplus

2 as

3 select * from dba_objects;

Table created.

SQL> select object_name,TO_CHAR(last_ddl_time,'YYYY-MM-DD HH24:MI:SS')

2 from dba_objects where object_name='T_oracleplus';

OBJECT_NAME TO_CHAR(LAST_DDL_TI

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

T_oracleplus 2012-08-28 18:33:03

SQL> select owner,to_char(LAST_ANALYZED,'YYYY-MM-DD HH24:MI:SS')

2 from dba_tables where table_name='T_oracleplus';

OWNER TO_CHAR(LAST_ANALYZ

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

oracleplus

2.DBMS_STATS测试

SQL> EXEC DBMS_STATS.gather_table_stats(user,'T_oracleplus');

PL/SQL procedure successfully completed.

SQL> select owner,to_char(LAST_ANALYZED,'YYYY-MM-DD HH24:MI:SS')

2 from dba_tables where table_name='T_oracleplus';

OWNER TO_CHAR(LAST_ANALYZ

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

oracleplus 2012-08-28 18:42:50

SQL> select object_name,TO_CHAR(last_ddl_time,'YYYY-MM-DD HH24:MI:SS')

2 from dba_objects where object_name='T_oracleplus';

OBJECT_NAME TO_CHAR(LAST_DDL_TI

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

T_oracleplus 2012-08-28 18:33:03

这里测试证明:DBMS_STATS包的只是收集了表的统计信息,并没有修改DBA_OBJECTS.last_ddl_time列的内容,也就是说这个操作不是ddl操作

3.analyze测试

SQL> analyze table t_oracleplus compute statistics;

Table analyzed.

SQL> select object_name,TO_CHAR(last_ddl_time,'YYYY-MM-DD HH24:MI:SS') from dba_objects where object_name='T_oracleplus';

OBJECT_NAME TO_CHAR(LAST_DDL_TI

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

T_oracleplus 2012-08-28 18:33:03

SQL> select owner,to_char(LAST_ANALYZED,'YYYY-MM-DD HH24:MI:SS') from dba_tables where table_name='T_oracleplus';

OWNER TO_CHAR(LAST_ANALYZ

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

oracleplus 2012-08-28 18:45:17

这里测试结果显示和DBMS_STATS相同

4.测试DBMS_STATS 类似DDL功能

--会话1

SQL> delete from t_oracleplus;

14292 rows deleted.

SQL> EXEC DBMS_STATS.gather_table_stats(user,'T_oracleplus');

PL/SQL procedure successfully completed.

--会话2

SQL> select count(*) from t_oracleplus;

COUNT(*)

----------

0

--执行DBMS_STATS后事务提交,类此如在

DBMS_STATS分析事务提交原因

SQL> conn / as sysdba

Connected.

SQL> oradebug setmypid

Statement processed.

SQL> oradebug EVENT 10046 TRACE NAME CONTEXT FOREVER, LEVEL 12

Statement processed.

SQL> EXEC DBMS_STATS.gather_table_stats('oracleplus','T_oracleplus');

PL/SQL procedure successfully completed.

SQL> oradebug TRACEFILE_NAME

/u01/app/oracle/diag/rdbms/orcl/orcl/trace/orcl_ora_24022.trc

SQL> oradebug EVENT 10046 trace name context off

Statement processed.

--分析trace文件中头几条sql语句

BEGIN DBMS_STATS.gather_table_stats('oracleplus','T_oracleplus'); END;

SELECT SPARE4 FROM SYS.OPTSTAT_HIST_CONTROL$ WHERE SNAME = :B1

COMMIT

SELECT P.VALCHAR FROM SYS.OPTSTAT_USER_PREFS$ P, OBJ$ O, USER$ U WHERE P.OBJ#=O.OBJ#

AND U.USER#=O.OWNER# AND U.NAME=:B3 AND O.NAME=:B2 AND P.PNAME=:B1

通过这里的分析,我们可以大概的知道,为什么执行DBMS_STATS包之后事务自动提交,是因为在该程序中有COMMIT直接提交事务.

5.通过第三方程序UNWRAP DBMS_STAT包

PROCEDURE INIT_PARAM_DEFAULT IS

PARAMS PARARRAY;

ISDEFAULT SYS.OPTSTAT_HIST_CONTROL$.SPARE1%TYPE;

PAREXIST BOOLEAN;

CUR_TIME TIMESTAMP WITH TIME ZONE := SYSTIMESTAMP;

BEGIN

FILL_IN_PARAMS(PARAMS);

FOR I IN 1..PARAMS.COUNT LOOP

DBMS_STATS_INTERNAL.GET_PARAM_PROP(PARAMS(I).PNAME,

PAREXIST, ISDEFAULT);

IF (PAREXIST = TRUE AND ISDEFAULT = 1) THEN

DBMS_STATS_INTERNAL.SET_PARAM(PARAMS(I).PNAME,

PARAMS(I).PVALNUM, PARAMS(I).PVALVCHAR,

CUR_TIME, PARAMS(I).ISDEFAULT);

ELSIF (PAREXIST = FALSE) THEN

DBMS_STATS_INTERNAL.ADD_PARAM(PARAMS(I).PNAME,

PARAMS(I).PVALNUM, PARAMS(I).PVALVCHAR,

CUR_TIME, PARAMS(I).ISDEFAULT);

END IF;

END LOOP;

COMMIT;

通过这里可以看到我们在使用DBMS_STAT收集统计信息时,在初始化默认参数的时候,会执行COMMIT操作.

测试 analyze 类似DDL功能

--session 1

SQL> insert into t_oracleplus select * from dba_objects where rownum<10;

9 rows created.

SQL> analyze table oracleplus.t_oracleplus compute statistics;

Table analyzed.

SQL> select count(*) from t_oracleplus;

COUNT(*)

----------

0

--session 2

SQL> select count(*) from t_oracleplus;

COUNT(*)

----------

9

--证明analyze隐式提交了会话，类此ddl功能

分析analyze事务提交原因

SQL> oradebug setmypid

Statement processed.

SQL> oradebug EVENT 10046 TRACE NAME CONTEXT FOREVER, LEVEL 12

Statement processed.

SQL> analyze table oracleplus.t_oracleplus compute statistics;

Table analyzed.

SQL> oradebug TRACEFILE_NAME

/u01/app/oracle/diag/rdbms/orcl/orcl/trace/orcl_ora_27497.trc

SQL> oradebug EVENT 10046 trace name context off

Statement processed.

--分析trace主要操作如下

delete:sys.mon_mods$,sys.mon_mods_all$,superobj$,tab_stats$

update:tab$,hist_head$

从10046中未看到明显的commit,但是里面有不少delete和update的dml操作,那肯定有提交,可能在10046中没有显示出来.

6.总结说明

1.通过观察dba_objects.last_ddl_time列,发现收集统计信息未能是的该列发生变化,从而猜测收集统计信息是dml操作

2.通过DBMS_STATS和analyze事务的测试,证明这些操作可以提交事务

3.通过分析发现DBMS_STATS在设置默认值的时候,会显式commit

4.通过分析analyze发现其本质就是对一些数据的delete+update操作,并没有修改这些对象的结构,在提交这些记录的时候,隐式提交了以前事务

5.最终总结:数据库收集统计信息是dml操作

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最权威、专业的Oracle案例资源汇总之【学习笔记】Oracle数据库收集统计信息的两种方法介绍案例