易截截图软件、单文件、免安装、纯绿色、仅160KB

关于oracle mutex和latch的问题

关于latch和mutex的问题
from:http://www.itpub.net/thread-1004815-1-1.html
A:
latch是闩锁,是一种串行化机制,用来保护SGA中的内存结构。
mutex是什么,也是一种串行化机制,是互斥锁?
个人对mutex没有什么概念。这个是10G新引进的?9I好像没有啊。
哪位明白人,给帮忙详细解释下mutex,最好还能和latch 做下比较。
谢谢。
B:
BTW, things get more fun in 10.2, you can pin cursors without getting library cache pin latch, using KGX mutexes. Mutexes are new in 10.2 and they enable shared access to objects in somewhat similar manner to shared latche; every successful get of a particular mutex will increment its value and a release will decrement. When the count is zero, no one has the mutex and it is safe to get it in exclusive mode. However, they are more fine-grained than kgl latches and provide a better wait mechanism, as far as I understand.
So if your environment supports atomic compare and swap operation (such as CMPXCHG on Intel), you might get away without cursor_space_for_time setting for ultrahigh execution rates. Otherwise the atomic mutex operations would be achieved using the new KGX latches.
At least on my laptop this feature isn't enabled by default (from an OracleWorld paper I remember that it should become default in 10.2.0.2), but so far you can experiment with it if you set _kks_use_mutex_pin = true and bounce the instance (mutex structures will be stored in the shared pool, so you might need to increase shared pool size).
There are also X$MUTEX_SLEEP and X$MUTEX_SLEEP_HISTORY fixed tables that can show some interesting information if you generate some mutex waits into them.
Now, I don't suggest for a moment that you have to understand this response. It is at an extremely deep technical level, and the practical applications of such understanding are probably few and far between. My point, though, is that you must take the time to study and understand Oracle internal operations if you are to have success in Oracle performance optimization. There are no shortc


相关文档:

oracle 表空间操作

oracle表空间操作详解
  1
  2
  3作者:   来源:    更新日期:2006-01-04 
  5
  6 
  7建立表空间
  8
  9CREATE TABLESPACE data01
 10DATAFILE '/ora ......

ORACLE NLS_LANG参数详解

NLS_LANG参数由以下部分组成:
NLS_LANG= <Language>_ <Territory>. <Clients Characterset>
其中:
LANGUAGE指定:
-Oracle消息使用的语言
-日期中月份和日显示
TERRITORY指定
-货币和数字格式
-地区和计算星期及日期的习惯
CHARACTERSET:
-控制客户端应用程序使用的字符集 ......

oracle 递归查询


Start with...Connect By子句递归查询一般用于一个表维护树形结构的应用。
创建示例表:
CREATE TABLE TBL_TEST
(
  ID    NUMBER,
  NAME  VARCHAR2(100 BYTE),
  PID   NUMBER             &nbs ......

Oracle分析函数参考

首先感谢文章的作者,我转来大家共享
Oracle从8.1.6开始提供分析函数,分析函数用于计算基于组的某种聚合值,它和聚合函数的不同之处是对于每个组返回多行,而聚合函数对于每个组只返回一行。
下面例子中使用的表来自Oracle自带的HR用户下的表,如果没有安装该用户,可以在SYS用户下运行$ORACLE_HOME/demo/schema/human_re ......

oracle wait event:reliable message

今天客户的一套RAC环境出现问题
双节点RAC环境中,一个节点因为锁竞争而挂起,shutdown之后无法启动。
故障出现时我正在路上,匆匆回到家中,处理故障。
解决之后查找故障原因。
检查当时的AWR信息发现Top 5 Timed Events显示如下信息:
Top 5 Timed Events         &nb ......
© 2009 ej38.com All Rights Reserved. 关于E健网联系我们 | 站点地图 | 赣ICP备09004571号