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Oracle内部latch获取函数简介

2024-09-12 11:06:43   215人阅读

 

 
标签: oracle call 函数   oracle statpack  
转自: http://blog.51cto.com/458302/998775

  Oracle的内部函数一直非常神秘，其实Oracle提供了一个oradebug 工具，可以用于调用内部的一些方法/函数，这为我们窥探Oracle的内部机制打开了一扇窗户。

    比如：Oracle内部获取latch的函数为kslgetl，全称为Kernel Service Lock Management Get Latch，可以使用oradebug call kslgetl/kslfre命令来手动获取一个latch，这种方法可用于模拟latch争用相关的现象。
 
    kslgetl函数有四个参数，调用格式如下：
 
      kslgetl(laddr, wait, why, where) 
　参数说明如下：

 

  • laddress – latch在 SGA中的地址
  • wait – flag. 如果设置为true,表示使用 willing-to-wait mode模式。
  • where –  请求latch的代码段位置 ,也就是awr/statpack的Latch Misses Source中的内容。
  • why -   为什么从Where参数指定的地方请求latch
    　注意where中的位置值只是一个索引，具体的位置名称从v$latch_misses可以查到（或者从awr/statspack也可以看到）。代码位置的名称和索引存储在视图x$ksllw　　 
SQL> select indx, ksllwnam,ksllwlbl from x$ksllw where rownum<20;
 
      INDX KSLLWNAM                                                         KSLLWLBL
---------- ---------------------------------------------------------------- ----------------------------------------------------------------
         0 No latch
         1 kslwt
         2 ksudlp
         3 kslpstevent:get                                                  pwq#
         4 kslpstevent:reget                                                pwq#
         5 ksliwat:add:nowait                                               pwq#
         6 ksliwat:remove                                                   pwq#
         7 ksliwat:add:wait                                                 pwq#
         8 kslael
         9 kslrgpl_parent
        10 kslrgpl_2child
 
      INDX KSLLWNAM                                                         KSLLWLBL
---------- ---------------------------------------------------------------- ----------------------------------------------------------------
        11 kslrgpl_notsib
        12 kslrgp_nowait
        13 ksqgel: create enqueue                                           parent obj
        14 ksqgel: failed to get enqueue                                    error
   　
 
 
      视图v$latch_misses的基础表是x$kslwsc，在这个表里Oracle维护了一个latch丢失代码位置的数组。x$kslwsc(猜测的名称为:kernel service where of source code)，通过这个视图，可以找到latch对应的索引：
SQL> desc  x$kslwsc;
Name                                                                          Null?    Type 
----------------------------------------------------------------------------- -------- ---------------------------------------------------- 
ADDR                                                                                   RAW(8) 
INDX                                                                                   NUMBER 
INST_ID                                                                                NUMBER 
KSLNOWTF                                                                               NUMBER 
KSLSLEEP                                                                               NUMBER 
KSLWSCWSL                                                                              NUMBER 
KSLWSCLTHG                                                                             NUMBER
KSLLASNAM                                                                              VARCHAR2(50)　　
 
why参数的在dump出来的结果中描述是“Context saved from call”，例如：
SO: 0x2d93be720, type: 2, owner: (nil), flag: INIT/-/-/0x00
 (process) Oracle pid=299, calls cur/top: 0x2e9028a38/0x2e9028a38, flag: (0)
…
 (latch info) wait_event=0 bits=2
 holding 2dee1ac50 Child cache buffers chains level=1 child#=124200
 Location from where latch is held: kcbgtcr: fast path:
 Context saved from call: 39022946
why参数说明为什么在这个(where)请求这个latch,它依赖于latch的作用与latch请求的where。比如，当请求一个cache buffer chain latch保护的一个数据块时，why就包括一个块地址(dba)。why的意义，可以从x$ksllw中的ksllwlbl列进行一些猜测。
 
where与why参数用于获取一个latch,当latch获取成功后，Oracle保存参数的值到latch的结构中.Oracle 11g更进一步扩展了latch架构，存储在x$kslltr_parent和x$kslltr_children视图中，分别表示parent latch与children latch。10g或以前的版本，都是使用x$ksllt表，v$latch与v$latch_children都是以x$ksllt为基表。   最近获取latch的"Where"与"Why"的值可以从这些表的kslltwhr与kslltwhy两个表查询到。
　
x$ksuprlat显示持有latch的进程，他是v$latchholder的基表，where与why的值也在它的ksulawhr与ksulawhy列中。
 
     我们来手动获取一个latch试试看：
SQL> select addr, name from v$latch where name like ‘shared pool‘;
 
ADDR             NAME
---------------- --------------------------------------------------
0000000380019DA8 shared pool
 
SQL> 
 
取这个latch的where值，也就是代码位置：
SQL> select *  from x$kslwsc where ksllasnam =‘shared pool‘;
 
ADDR                   INDX    INST_ID   KSLNOWTF   KSLSLEEP  KSLWSCWSL KSLWSCLTHG KSLLASNAM
---------------- ---------- ---------- ---------- ---------- ---------- ---------- ------------
 
............
     
00000005F7152178       2582          1          0          0          0          0 shared pool
00000005F7152198       2583          1          0          0          0          0 shared pool
00000005F71521B8       2584          1          0          0          0          0 shared pool
00000005F71521D8       2585          1          0          0          0          0 shared pool
 
62 rows selected
 
这些值也可以从x$ksllt取到
 
SQL> select kslltwhr,kslltwhy from x$ksllt  where addr=‘0000000380019DA8‘;
 
  KSLLTWHR   KSLLTWHY
---------- ----------
      2559        208
 
SQL> 
 
 
现在我们用oradebug手动执行kslgetl函数：
SQL> connect /as sysdba;
Connected.
SQL> oradebug setmypid;
Statement processed.
SQL>  oradebug   call   kslgetl   0 x380019DA8   1   208   2559
ORA-03113: end-of-file on communication channel
ORA-24323: value not allowed
 
    发现出错了，查看trace文件，可以看到出现了一个ora-007445   [Address not mapped to object]错误：
 
*** 2012-03-10 15:00:56.229
ksedmp: internal or fatal error
ORA-07445: exception encountered: core dump [kslgetl()+8] [SIGSEGV] [Address not mapped to object] [0xFFFFFFFF80021E44] [] []
----- Call Stack Trace -----
calling              call     entry                argument values in hex     
location             type     point                (? means dubious value)    
-------------------- -------- -------------------- ----------------------------
ksedmp()+728         CALL     ksedst()             000000017 ? 106B520AC ?
                                                   000000000 ? 106B4EBA0 ?
                                                   106B4D908 ? 106B4E308 ?
ssexhd()+1232        CALL     ksedmp()             106994000 ? 10699493C ?
                                                   000106800 ? 10699493C ?
                                                   000000000 ? 106994000 ?
__sighndlr()+12      PTR_CALL 0000000000000000     106991000 ? 106B55EF0 ?
                                                   10698E81C ? 000106991 ?
                                                   00000000B ? 000000067 ?
call_user_handler()  CALL     __sighndlr()         00000000B ? 106B55EF0 ?
+992                                               106B55C10 ? 102084BC0 ?
                                                   000000000 ? 00000000A ?
sigacthandler()+104  CALL     call_user_handler()  FFFFFFFF7D100200 ?
                                                   FFFFFFFF7D100200 ?
                                                   106B55C10 ? 000000009 ?
                                                   000000000 ? 000000000 ?
kslgetl()+8          PTR_CALL 0000000000000000     000000000 ? 106B55EF0 ?
                                                   106B55C10 ?
                                                   FFFFFFFF7D100200 ?
                                                   000000000 ?
                                                   FFFFFFFF7C33E000 ?
skdxcall()+1664      PTR_CALL 0000000000000000     FFFFFFFF80021E38 ?
                                                   000000001 ? 0000000D0 ?
                                                   0000009FF ?
                                                   FFFFFFFF7FFFABC0 ?
                                                   0000009FF ?
ksdxen()+3672        PTR_CALL 0000000000000000     380021E38 ?
                                                   FFFFFFFF7FFFB350 ?
                                                   FFFFFFFF7FFFB348 ?
                                                   FFFFFFFF7FFFB340 ?
                                                   FFFFFFFF7FFFB3F0 ?
                                                   FFFFFFFF7FFFB338 ?
opiodr()+1536        PTR_CALL 0000000000000000     105AB8000 ? 1020766C0 ?
                                                   10699294A ? 000105800 ?
                                                   000106800 ? 106991CA8 ?
ttcpip()+1188        PTR_CALL 0000000000000000     105AE96F0 ? 105E47870 ?
                                                   000106991 ? 106991000 ?
                                                   000000056 ? 000106800 ?
opitsk()+1532        CALL     ttcpip()             00000001E ? 000000000 ?
                                                   FFFFFFFF7FFFE5B8 ?
                                                   000000001 ?
                                                   FFFFFFFF7FFFD090 ?
                                                   10698F208 ?
opiino()+1128        CALL     opitsk()             000000000 ? 105E46B00 ?
                                                   000000000 ? 000100000 ?
                                                   105A9E49C ? 10699D160 ?
opiodr()+1536        PTR_CALL 0000000000000000     00010699B ? 000000000 ?

Oracle内部latch获取函数简介


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