使用sql_trace/10046事件进行数据库诊断

      sql_trace/10046事件是oracle提供的用于进行sql跟踪的手段，其内容包括sql的解析过程、sql的执行计划、绑定变量的使用、会话发生的等待事件。

    在使用sql_trace/10046事件前，有两个参数需要注意：

[email protected]> show parameter max_dump_file_size  --对trace文件的大小限制       

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
max_dump_file_size                   string      UNLIMITED
s[email protected]> show parameter timed_statistics    --对重要信息的收集

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
timed_statistics                     boolean     TRUE
 
           

      sql_trace的作用域：

    1）对所有用户：

        i）在参数文件中指定sql_trace=true

       ii）alter system set sql_trace=true/false

    2) 对当前用户：

        启用当前session的跟踪：alter session set sql_trace=true;

        结束跟踪：alter session set sql_trace=false;

    3）对其他用户：

        选择跟踪的进程（用户）

[email protected]> select sid,serial#,username from v$session where username is not null;

       SID    SERIAL# USERNAME
---------- ---------- ------------------------------
       142         14 HR
       159          5 SYS
           

        设置跟踪：

[email protected]> exec dbms_system.set_sql_trace_in_session(142,14,true) 

PL/SQL procedure successfully completed.
           

        停止跟踪：

[email protected]> exec dbms_system.set_sql_trace_in_session(142,14,false)

PL/SQL procedure successfully completed.
           

    *************************************↖(^ω^)↗**********************************

    10046事件是对sql_trace的增强，可分4个级别，具体如下：

    1）level 1：等价于sql_trace

    2）level 4：level 1+绑定值

    3）level 8：level 1+等待事件跟踪

    4）level 12：等价于level 1+level 4+level 8

    10046事件的作用域：

    1）对所有用户

        i）在参数文件中修改：event=“10046 trace name context forever，level 12”

       ii）alter system set events ‘10046 trace name context forever，level 8';

            / alter system set events '10046 trace name context off';

    2）对当前用户

        alter session set events '10046 trace name context forever,level  12';  或者

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

    3）对其他用户

        查询要跟踪的对象

[email protected]> select sid,serial#,username from v$session where username is not null;

       SID    SERIAL# USERNAME
---------- ---------- ------------------------------
       142         14 HR
       159          5 SYS
           

        执行跟踪

[email protected]> exec dbms_system.set_ev(142,14,10046,8,'hr');

PL/SQL procedure successfully completed.
           

        结束跟踪

[email protected]> exec dbms_system.set_ev(142,14,10046,0,'hr');

PL/SQL procedure successfully completed.
           

    *********************************~(@^_^@)~*************************************

    由于trace文件的格式比较难以阅读，我们可以通过TKPROF工具进行格式化，最终生成符合我们阅读习惯的sql trace 文件。

    格式如下：

    tkprof  tracefile  outputfile  [options]

    其中，option选项的说明和使用，我们可以通过在bash环境罗列：

[[email protected] ~]$ tkprof
Usage: tkprof tracefile outputfile [explain= ] [table= ]
              [print= ] [insert= ] [sys= ] [sort= ]
  table=schema.tablename   Use 'schema.tablename' with 'explain=' option.
  explain=user/password    Connect to ORACLE and issue EXPLAIN PLAN.
  print=integer    List only the first 'integer' SQL statements.
  aggregate=yes|no
  insert=filename  List SQL statements and data inside INSERT statements.
  sys=no           TKPROF does not list SQL statements run as user SYS.
  record=filename  Record non-recursive statements found in the trace file.
  waits=yes|no     Record summary for any wait events found in the trace file.
  sort=option      Set of zero or more of the following sort options:
    prscnt  number of times parse was called
    prscpu  cpu time parsing
    prsela  elapsed time parsing
    prsdsk  number of disk reads during parse
    prsqry  number of buffers for consistent read during parse
    prscu   number of buffers for current read during parse
    prsmis  number of misses in library cache during parse
    execnt  number of execute was called
    execpu  cpu time spent executing
    exeela  elapsed time executing
    exedsk  number of disk reads during execute
    exeqry  number of buffers for consistent read during execute
    execu   number of buffers for current read during execute
    exerow  number of rows processed during execute
    exemis  number of library cache misses during execute
    fchcnt  number of times fetch was called
    fchcpu  cpu time spent fetching
    fchela  elapsed time fetching
    fchdsk  number of disk reads during fetch
    fchqry  number of buffers for consistent read during fetch
    fchcu   number of buffers for current read during fetch
    fchrow  number of rows fetched
    userid  userid of user that parsed the cursor
           

    我们通过一个例子来介绍对tkprof的使用：

SQL> show parameter timed_statistics


NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
timed_statistics                     boolean     TRUE
SQL> show parameter max_dump_file_size


NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
max_dump_file_size                   string      UNLIMITED


           

[email protected]> alter session set sql_trace=true;

[email protected]> select * from hr.departments; 

[email protected]> alter session set sql_trace=false; --最好是关闭跟踪，减小对性能的开销

[email protected]> exit;  --在运行完查询后，要退出sql*plus（断开连接），这样才能完全关闭跟踪文件，使trace文件的所有信息都是有效的。
           

    然后，我们就可以使用tkprof：

[[email protected] ~]$ tkprof /u01/app/oracle/admin/orcl/udump/orcl_ora_5467.trc tkprof_think.txt

TKPROF: Release 10.2.0.1.0 - Production on Fri Jul 27 11:18:13 2012

Copyright (c) 1982, 2005, Oracle.  All rights reserved.


[[email protected] ~]$ ls
tkprof_think.txt