SQL_TRACE

SQL_TRACE是Oracle提供的用于进行SQL跟踪的手段，是强有力的辅助诊断工具.在日常的数据库问题诊断和解决中，SQL_TRACE是非常常用的方法。

本文就SQL_TRACE的使用作简单探讨，并通过具体案例对sql_trace的使用进行说明.

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一、 基础介绍

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(a) SQL_TRACE说明

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SQL_TRACE可以作为初始化参数在全局启用，也可以通过命令行方式在具体session启用。

1． 在全局启用

在参数文件(pfile/spfile)中指定:

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sql_trace =true

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在全局启用SQL_TRACE会导致所有进程的活动被跟踪，包括后台进程及所有用户进程，这通常会导致比较严重的性能问题，所以在生产环境中要谨慎使用，这个参数在10g之后是动态参数，可以随时调整，在某些诊断中非常有效。

提示: 通过在全局启用sql_trace，我们可以跟踪到所有后台进程的活动，很多在文档中的抽象说明，通过跟踪文件的实时变化，我们可以清晰的看到各个进程之间的紧密协调.

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2． 在当前session级设置

大多数时候我们使用sql_trace跟踪当前进程.通过跟踪当前进程可以发现当前操作的后台数据库递归活动(这在研究数据库新特性时尤其有效)，

研究SQL执行，发现后台错误等.

在session级启用和停止sql_trace方式如下:

启用当前session的跟踪:

SQL> alter session set sql_trace=true;

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Session altered.

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此时的SQL操作将被跟踪:

SQL> select count(*) from dba_users;

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<wbr></wbr> COUNT(*)

----------

<wbr><wbr><wbr><wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr> 34

结束跟踪:

SQL> alter session set sql_trace=false;

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Session altered.

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3． 跟踪其他用户进程

在很多时候我们需要跟踪其他用户的进程，而不是当前用户，这可以通过Oracle提供的系统包DBMS_SYSTEM. SET_SQL_TRACE_IN_SESSION

来完成

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SET_SQL_TRACE_IN_SESSION过程序要提供三个参数:

SQL> desc dbms_system

...

PROCEDURE SET_SQL_TRACE_IN_SESSION

<wbr></wbr>Argument Name<wbr><wbr><wbr></wbr></wbr></wbr> <wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>Type<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr> In/Out Default?

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...

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通过v$session我们可以获得sid、serial#等信息:

获得进程信息，选择需要跟踪的进程:

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SQL> select sid,serial#,username from v$session

<wbr></wbr> 2<wbr></wbr> where username is not null;

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<wbr><wbr><wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr></wbr></wbr> SID<wbr><wbr><wbr></wbr></wbr></wbr> SERIAL#<wbr></wbr> USERNAME

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

<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr> 8<wbr><wbr><wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr></wbr></wbr> 2041<wbr></wbr> SYS

<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr> 9<wbr><wbr><wbr><wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr> 437<wbr></wbr> EYGLE

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设置跟踪:

SQL> exec dbms_system.set_sql_trace_in_session(9,437,true)

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PL/SQL procedure successfully completed.

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....

可以等候片刻，跟踪session执行任务,捕获sql操作...

....

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停止跟踪:

SQL> exec dbms_system.set_sql_trace_in_session(9,437,false)

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PL/SQL procedure successfully completed.

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(b) 10046事件说明

10046事件是Oracle提供的内部事件，是对SQL_TRACE的增强.

10046事件可以设置以下四个级别:

1 - 启用标准的SQL_TRACE功能,等价于sql_trace

4 - Level 1 加上绑定值(bind values)

8 - Level 1 + 等待事件跟踪

12 - Level 1 + Level 4 + Level 8

类似sql_trace，10046事件可以在全局设置，也可以在session级设置。

1． 在全局设置

在参数文件中增加:

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event="10046 trace name context forever,level 12"

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此设置对所有用户的所有进程生效、包括后台进程.

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2． 对当前session设置

通过alter session的方式修改，需要alter session的系统权限:

SQL> alter session set events '10046 trace name context forever';

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Session altered.

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SQL> alter session set events '10046 trace name context forever, level 8';

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Session altered.

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SQL> alter session set events '10046 trace name context off';

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Session altered.

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3． 对其他用户session设置

通过DBMS_SYSTEM.SET_EV系统包来实现:

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SQL> desc dbms_system

...

PROCEDURE SET_EV

<wbr></wbr>Argument Name<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr> Type<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr> In/Out Default?

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...

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其中的参数SI、SE来自v$session视图:

查询获得需要跟踪的session信息:

SQL> select sid,serial#,username from v$session where username is not null;

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SID SERIAL# USERNAME

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

8 2041 SYS

9 437 EYGLE

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执行跟踪:

SQL> exec dbms_system.set_ev(9,437,10046,8,'eygle');

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PL/SQL procedure successfully completed.

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结束跟踪:

SQL> exec dbms_system.set_ev(9,437,10046,0,'eygle');

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PL/SQL procedure successfully completed.

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(c) 获取跟踪文件

以上生成的跟踪文件位于user_dump_dest目录中，位置及文件名可以通过以下SQL查询获得:

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SQL> select

<wbr></wbr> 2<wbr><wbr><wbr></wbr></wbr></wbr> d.value||'/'||lower(rtrim(i.instance, chr(0)))||'_ora_'||p.spid||'.trc' trace_file_name

<wbr></wbr> 3<wbr></wbr> from

<wbr></wbr> 4<wbr><wbr><wbr></wbr></wbr></wbr> ( select p.spid

<wbr></wbr> 5<wbr><wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr></wbr> from sys.v$mystat m,sys.v$session s,sys.v$process p

<wbr></wbr> 6<wbr><wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr></wbr> where m.statistic# = 1 and s.sid = m.sid and p.addr = s.paddr) p,

<wbr></wbr> 7<wbr><wbr><wbr></wbr></wbr></wbr> ( select t.instance from sys.v$thread<wbr></wbr> t,sys.v$parameter<wbr></wbr> v

<wbr></wbr> 8<wbr><wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr></wbr> where v.name = 'thread' and (v.value = 0 or t.thread# = to_number(v.value))) i,

<wbr></wbr> 9<wbr><wbr><wbr></wbr></wbr></wbr> ( select value from sys.v$parameter where name = 'user_dump_dest') d

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TRACE_FILE_NAME

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/opt/oracle/admin/hsjf/udump/hsjf_ora_1026.trc<wbr></wbr>

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(d) 读取当前session设置的参数

当我们通过alter session的方式设置了sql_trace,这个设置是不能通过show parameter的方式得到的,我们需要通过dbms_system.read_ev来获取：

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SQL> set feedback off

SQL> set serveroutput on

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SQL> declare

2 event_level number;

3 begin

4 for event_number in 10000..10999 loop

5 sys.dbms_system.read_ev(event_number, event_level);

6 if (event_level > 0) then

7 sys.dbms_output.put_line(

8 'Event ' ||

9 to_char(event_number) ||

10 ' is set at level ' ||

11 to_char(event_level)

12 );

13 end if;

14 end loop;

15 end;

16 /

Event 10046 is set at level 1

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