Oracle内部latch获取函数简介

        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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