Just a few days ago a got to two Oracle DBAs discussing why the have so much “PX Deq Credit : send blkd” on a system. And if that is causing their performance problems.
The are some blog on the internet claiming it has to do with qc distribution and what ever.
But in many cases, especial if you experince huge waits on “PX Deq Credit : send blkd” the explanation can be much simpler. But first some background information.
If a query is run in parallel there is a query coordinator (QC) and the query slaves. The slaves do the actual work an send the result to the query coordinator. This is done through message buffers which you specified with the parallel_execution_message_size.
This buffer exists in the large or in the shared pool depending how PARALLEL_AUTOMATIC_TUNING is set.
Metalink states about the PX Deq Credit: send blkd event
This is considered as idle wait event.
You should investigate the sender (decode the senderid).
There is no general advice to ......
oracle wait event:cursor: pin S wait on X
cursor: pin S wait on X等待事件的处理过程
http://database.ctocio.com.cn/tips/114/8263614_1.shtml
cursor: pin S wait on X等待！
http://www.itpub.net/viewthread.php?tid=1003340
解决cursor: pin S wait on X 有什么好办法:
http://www.itpub.net/thread-1163543-1-8.html
cursor: pin S wait on X:
http://space.itpub.net/756652/viewspace-348176
cursor: pin S:
http://yumianfeilong.com/html/2008/11/01/254.html
OTN的解释,
cursor: pin SA session waits on this event when it wants to update a shared mutex pin and another session is currently in the process of updating a shared mutex pin for the same cursor object. This wait event should rarely be seen because a shared mutex pin update is very fast.(Wait Time: Microseconds)
Parameter Description
P1 Hash value of cursor
P2 Mutex value (top 2 bytes contains SID holding mutex in exclusive mode, and bottom two bytes usually hold the value 0)
P3 Mutex where (an internal code locator) OR’d with M ......
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 u ......
oracle 从10.2.0.2 到 10.2.0.4 升级
一、下载升级包
下载地址：
ftp://updates.oracle.com/6810189/p6810189_10204_Linux-x86.zip
注意：不要用flashget下载，用迅雷下载。文件大小1G多。
二、关闭数据库
以oracle用户远程登录suse系统:
1. sqlplus /nolog
SQL> connect /as sysdba
SQL> shutdown immediate;
一般情况下可以正常关闭。如果不能关闭，可以强制关闭。
关闭所有的 oracle 进程：
ps -ef|grep orac*
如果有的话，用kil命令。
2. 正常监听
lsnrctl stop
三、解压升级包
unzip p6810189_10204_Linux-p6810189_10204_Linux-x86.zip
在目录下将会生成一个Disk1的文件夹。
四、安装前准备
如果是在终端安装升级包的话，很有可能会碰到下面的错误：
Could not execute auto check for display colors using command /usr/X11R6/bin/xdpyinfo. Check if the DISPLAY variable is set. Failed <<<<
在安装之前要还要做些工作。我是通过ssh来访问安装机器的，因此需要在WINDOWS机器下配置一个可以转发X11的软件。
下载地址：
1. xming下载最新版sourceforge.net/projects/xming/
安装� ......
语法:
substr( string, start_position, [ length ] )
取子字符串,从start_position开始,取length个,length为可选，如果length为空则返回start_position后的所有字符。
实例:
substr('This is a test', 6, 2) would return 'is'
substr('This is a test', 6) would return 'is a test'
substr('TechOnTheNet', 1, 4) would return 'Tech'
substr('TechOnTheNet', -3, 3) would return 'Net'
substr('TechOnTheNet', -6, 3) would return 'The'
substr('TechOnTheNet', -8, 2) would return 'On'
select substr('TechOnTheNet', -3, 2) from dual
start_position为负数时，表示从字符串尾巴倒着数
(thismonth)转贴：http://hi.baidu.com/stanver/blog/item/710fbd1bae7e58118618bf31.html ......
lengthb(string)计算string所占的字节长度 :返回字符串的长度，单位是字节
length(string)计算string所占的字符长度 :返回字符串的长度，单位是字符
对于单字节字符,LENGTHB和LENGTH是一样的.
如可以用length(‘string’)=lengthb(‘string’)判断字符串是否含有中文。
select length('我') from dual --返回1
select lengthb('我') from dual --返回2
select length('AB') from dual --返回2
select lengthb('AB') from dual --返回2
（thismonth）转贴：http://space.itpub.net/161195/viewspace-613263 ......
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