11g等待事件之library cache: mutex X
11g等待事件之library cache: mutex X


library cache: mutex X替代了之前的library cache latch,主要作用是在hash bucket中定位handle时使用。(比如SQL硬解析时,需要往hash bucket中新增一个cursor时,需要library cache latch)。如下图所示:
文档上面的解释如下:
The library cache mutex is acquired for similar purposes that the library cache latches were acquired in prior versions of Oracle. In 10g, mutexes were introduced for certain operations in the library cache. Starting with 11g, the library cache latches were replaced by mutexes, hence this new wait event.
Mutexes are a lighter-weight and more granular concurrency mechanism than latches. Mutexes take advantage of CPU architectures that offer the compare and swap instructions (or similar). The reason for obtaining a mutex in the first place, is to ensure that certain operations are properly managed for concurrency. E.g., if one session is changing a data structure in memory, then another session must wait to acquire the mutex before it can make a similar change – this prevents unintended changes that would lead to corruptions or crashes if not serialized.
This wait event is present whenever a library cache mutex is held in exclusive mode by a session and other sessions need to wait for it to be released. There are many different operations in the library cache that will require a mutex, so its important to recognize which “location” (in Oracle’s code) is involved in the wait. “Location” is useful to Oracle Support engineers for diagnosing the cause for this wait event.
Individual Waits:
Parameters:
P1 = “idn” = Unique Mutex Identifier
P2 = “value”
P3 = “where” = location in code (internal identifier) where mutex is being waited for
@The meaning of the code for “where” can be found by looking in kgl0.h for entries with the prefix “”kglml_XXX”. For example, if P3=2, then it corresponds to “kglml_kglget2″. You can then search source code for this symbol to see where the mutex is acquired.
测试一个硬解析的场景如下:
conn scott/tiger create table testlib1 (id number) ;
create table testlib2 (id number) ;
create table testlib3 (id number) ;
create table testlib4 (id number) ;
create table testlib5 (id number) ;
create table testlib6 (id number) ;
create table testlib7 (id number) ;
create table testlib8 (id number) ;
create table testlib9 (id number) ;
create table testlib10 (id number) ;
create table testlib11 (id number) ;
create table testlib12 (id number) ;
create table testlib13 (id number) ;
create table testlib14 (id number) ;
create table testlib15 (id number) ;
create table testlib16 (id number) ;
create table testlib17 (id number) ;
create table testlib18 (id number) ;
create table testlib19 (id number) ;
create table testlib20 (id number) ; vi test4.sh #!/bin/ksh
i="$1"
while true
do
echo $i
sqlplus scott/tiger << EOF
select * from testlib$i where id = $RANDOM;
exit
EOF
done alter system flush shared_pool;
exec DBMS_WORKLOAD_REPOSITORY.CREATE_SNAPSHOT (); nohup sh test4.sh 1 &
nohup sh test4.sh 2 &
nohup sh test4.sh 3 &
nohup sh test4.sh 4 &
nohup sh test4.sh 5 &
nohup sh test4.sh 6 &
nohup sh test4.sh 7 &
nohup sh test4.sh 8 &
nohup sh test4.sh 9 &
nohup sh test4.sh 10 &
nohup sh test4.sh 11 &
nohup sh test4.sh 12 &
nohup sh test4.sh 13 &
nohup sh test4.sh 14 &
nohup sh test4.sh 15 &
nohup sh test4.sh 16 &
nohup sh test4.sh 17 &
nohup sh test4.sh 18 &
nohup sh test4.sh 19 &
nohup sh test4.sh 20 & exec DBMS_WORKLOAD_REPOSITORY.CREATE_SNAPSHOT ();
生成awr report,查看等待事件:
Top 5 Timed Foreground Events
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Avg
wait % DB
Event Waits Time(s) (ms) time Wait Class
------------------------------ ------------ ----------- ------ ------ ----------
DB CPU 104 111.9
library cache: mutex X 1,920 3 1 2.9 Concurrenc
latch: shared pool 237 1 5 1.2 Concurrenc
latch: row cache objects 146 1 5 .9 Concurrenc
cursor: pin S wait on X 42 1 13 .6 Concurrenc
^LHost CPU (CPUs: 16 Cores: 8 Sockets: 2)
~~~~~~~~ Load Average
Begin End %User %System %WIO %Idle
--------- --------- --------- --------- --------- ---------
1.12 6.89 25.0 18.5 2.7 56.1
我们的hard parse
Load Profile Per Second Per Transaction Per Exec Per Call
~~~~~~~~~~~~ --------------- --------------- ---------- ----------
DB Time(s): 2.8 4.0 0.00 0.00
DB CPU(s): 3.1 4.5 0.00 0.00
Redo size: 31,740.9 46,051.8
Logical reads: 3,625.8 5,260.6
Block changes: 83.5 121.1
Physical reads: 0.2 0.4
Physical writes: 0.2 0.2
User calls: 2,719.4 3,945.5
Parses: 1,856.1 2,693.0
Hard parses: 137.4 199.4
W/A MB processed: 0.8 1.2
Logons: 129.7 188.1
Executes: 1,830.6 2,656.0
Rollbacks: 0.2 0.3
Transactions: 0.7
查了下metalink,与"library cache: mutex X"等待相关的BUG大约有30多个,会在11G各个版本之间发生,所以碰到这个等待事件,可以先确认下是不是碰上BUG了。以下两个BUG,在网上好象大家经常碰到,给出metalink相关的描述:
Bug 5928271 - Excessive waits on "library cache: mutex X" [ID 5928271.8]
Versions >= 11.1.0.6 but BELOW 11.2
This fix alleviates some waits on "library cache: mutex X" when looking
up a library cache object.
Bug 9530750 High waits for 'library cache: mutex X' for cursor Build lock
Versions BELOW 12.1
High waits may be seen for "library cache: mutex X" for
a build lock mutex with a call stack including kksGetBuildLock.
Rediscovery Notes:
The mutex is for an object with a name like "$BUILD$.xxxxxxxx"
参考:
metalink相关文章
《Oracle Wait Interface A Practical Guide to Performance Diagnostics & Tuning》
《Oracle Core_ Essential Internals for DBAs and Developers - Jonathan Lewis》http://blog.tanelpoder.com/2008/08/03/library-cache-latches-gone-in-oracle-11g/
11g等待事件之library cache: mutex X的更多相关文章
- [20190402]Library Cache mutex.txt
[20190402]Library Cache mutex.txt 1.环境:SCOTT@book> @ ver1PORT_STRING VERSION ...
- library cache: mutex X
我们先来看看 library cache: mutex X . 是个什么东西 The library cache mutex is acquired for similar purposes that ...
- Troubleshooting 'library cache: mutex X' Waits. (Doc ID 1357946.1)
In this Document Purpose Troubleshooting Steps What is a 'library cache: mutex X' wait? What ...
- Oracle数据库大量library cache: mutex X及latch: shared pool问题排查一例
业务系统数据库夯住,数据库内大量的library cache: mutex X及latch: shared pool等待,alert日志信息如下 Tue Sep :: WARNING: inbound ...
- Troubleshooting 'library cache: mutex X' Waits.
What is a 'library cache: mutex X' wait? The mutex feature is a mechanism to control access to in me ...
- Oracle中常见的33个等待事件小结
在Oracle 10g中的等待事件有872个,11g中等待事件1116个. 我们可以通过v$event_name 视图来查看等待事件的相关信息 一. 等待事件的相关知识 1.1 等待事件主要可 ...
- ORACLE 常见等待事件
一. 等待事件的相关知识 1.1 等待事件主要可以分为两类,即空闲(IDLE)等待事件和非空闲(NON-IDLE)等待事件.1). 空闲等待事件指ORACLE正等待某种工作,在诊断和优化数据库的时候, ...
- 全面解析Oracle等待事件的分类、发现及优化
一.等待事件由来 大家可能有些奇怪,为什么说等待事件,先谈到了指标体系.其实,正是因为指标体系的发展,才导致等待事件的引入.总结一下,Oracle的指标体系,大致经历了下面三个阶段: · 以命中率为主 ...
- Oracle等待事件之等待事件详解
一. 等待事件的相关知识:1.1 等待事件主要可以分为两类:即空闲(IDLE)等待事件和非空闲(NON-IDLE)等待事件.1). 空闲等待事件指ORACLE正等待某种工作,在诊断和优化数据库的时候, ...
随机推荐
- cnblogs修改网站图标icon
以下修改网络地址即可 <script type="text/javascript" language="javascript"> //Setting ...
- 进阶之路(基础篇) - 011 arduino api基础手册
arduino 函数 api 程序结构 在Arduino中, 标准的程序入口main函数在内部被定义, 用户只需要关心以下两个函数:void setup()void loop()setup() 函数用 ...
- 【struts2】Struts2的运行流程
1)前提条件 在讲解流程之前,假设我们已经建立了的一个名为strutsDeepen的web工程,该工程仅仅实现了简单的用户登陆与欢迎界面.具体的实现为: 在web.xml中配置了Struts2的过滤器 ...
- easyui按钮linkbutton 不可用(置灰)与 可用(取消置灰)
easyui linkbutton按钮: 不可用(置灰) $('#butFree').linkbutton('disable'); 可用(取消置灰) $('#butFree').linkbutton( ...
- JQuery EasyUI combobox 省市两级联动
表名:province 结构如下 CallIn.tpl 模板页 <select id="consult_province" name="consult_provi ...
- Thinking In Design Pattern——MVP模式演绎
原文<Thinking In Design Pattern——MVP模式演绎>不知为何丢失了,故重新整理了一遍. 目录 What Is MVP Domain Model StubRepos ...
- [转]学习笔记_springmvc注解形式的开发参数接收
springmvc基于注解的开发 注解第一个例子 1. 创建web项目 2. 在springmvc的配置文件中指定注解驱动,配置扫描器 <!-- sprimgmvc 注解驱动 --> &l ...
- List遍历Java 8 Streams map() examples
1. A List of Strings to Uppercase 1.1 Simple Java example to convert a list of Strings to upper case ...
- js 万恶之源 是否滚动到底部?
let scrollHandle = (el) => { // 如果已经滚到底部了 if (el.scrollHeight - el.scrollTop === el.clientHeight) ...
- Sql Server Compact 4.0数据库部署安装
Sql Server Compact 4.0相比3.5版本增强了很多,支持Entity Framework 4.1,对于轻量级应用来讲,使用Sql Server Compact 4.0是个很好的选择, ...