ipcs、ipcrm、sysresv、kernel.shmmax

1.1  BLOG文档结构图

1.2  前言部分

1.2.1  导读和注意事项

各位技术爱好者，看完本文后，你可以掌握如下的技能，也可以学到一些其它你所不知道的知识，~O(∩_∩)O~：

① ipcs的使用

② ipcrm释放oracle内存段

③ sysresv的使用

④ 内核参数kernel.shmmax

⑤ 如何快速的清理Oracle的进程

⑥ 其它维护操作

Tips：

① 本文在itpub（http://blog.itpub.net/26736162）、博客园(http://www.cnblogs.com/lhrbest)和微信公众号（xiaomaimiaolhr）上有同步更新。

② 文章中用到的所有代码、相关软件、相关资料及本文的pdf版本都请前往小麦苗的云盘下载，小麦苗的云盘地址见：http://blog.itpub.net/26736162/viewspace-1624453/。

③ 若网页文章代码格式有错乱，请下载pdf格式的文档来阅读。

④ 在本篇BLOG中，代码输出部分一般放在一行一列的表格中。

⑤ 本文适合于初中级人员阅读，数据库大师请略过本文。

⑥ 不喜勿喷。

本文若有错误或不完善的地方请大家多多指正，您的批评指正是我写作的最大动力。

1.3  本文简介

最近有朋友因为kernel.shmmax内核参数的问题导致数据库不能启动。小麦苗之前碰到过一次，只是没有记录下来，而且以前安装数据库的时候也没有详细介绍这几个参数的含义，趁这次机会就把这个参数在详细介绍一下吧。

1.4  相关文章链接

① 【故障解决】IPCS和IPCRM使用：http://blog.itpub.net/26736162/viewspace-2112518

② ORACLE内核参数：http://blog.itpub.net/26736162/viewspace-2112447/

③ sysresv：http://blog.itpub.net/26736162/viewspace-2112443/

④ 视频讲解IPCS和IPCRM使用：http://www.iqiyi.com/w_19rs33qqsp.html

⑤ 有关“TNS-12518: TNS:listener could not hand off client connection”的更多内容请参考：【故障|监听】TNS-12518、TNS-00517和 Linux Error：32：Broken pipe：http://blog.itpub.net/26736162/viewspace-2135468/

第二章 ipcs/ipcrm命令

更多内容请参考：http://blog.itpub.net/26736162/viewspace-2112518

unix/linux下的共享内存、信号量、队列信息管理

在Unix或Linux下，经常有因为共享内存、信号量，队列等共享信息没有干净地清除而引起一些问题。

查看共享内存的命令是：ipcs [-m|-s|-q]。若ipcs命令不带参数，则默认会列出共享内存、信号量，队列信息，而-m列出共享内存，-s列出共享信号量，-q列出共享队列。

清除命令是：ipcrm [-m|-s|-q] id，其中，-m删除共享内存，-s删除共享信号量，-q删除共享队列。

2.1  ipcs

1. 命令格式

ipcs [resource-option] [output-format]

ipcs [resource-option] -i id

2. 命令功能

提供IPC设备的信息

3. 使用方法

resource选项：

ipcs -m 查看系统共享内存信息

ipcs -q 查看系统消息队列信息

ipcs -s 查看系统信号量信息

ipcs [-a] 系统默认输出信息，显示系统内所有的IPC信息

输出格式控制：

ipcs -c 查看IPC的创建者和所有者

ipcs -l 查看IPC资源的限制信息

ipcs -p 查看IPC资源的创建者和使用的进程ID

ipcs -t 查看最新调用IPC资源的详细时间

ipcs -u 查看IPC资源状态汇总信息

额外格式控制：

ipcs -l --human

以人类可以阅读的方式显示size

2.2  ipcrm

1. 命令功能

通过指定ID删除删除IPC资源，同时将与IPC对象关联的数据一并删除，只有超级用户或IPC资源创建者能够删除

2. 使用方法

ipcrm -M shmkey

移除用shmkey创建的共享内存段

ipcrm -m shmid

移除用shmid标识的共享内存段

ipcrm -S semkey

移除用semkey创建的信号量

ipcrm -s semid

移除用semid标识的信号量

ipcrm -Q msgkey

移除用msgkey创建的消息队列

ipcrm -q msgid

移除用msgid标识的消息队列

2.3  如何快速的清理Oracle的进程？

真题1、 如何快速的清理Oracle的进程？

答案：若想要快速清理掉Oracle的进程，则最直接的办法是杀pmon进程。有如下3条命令可供选择，其中加粗的orcl替换成ORACLE_SID的值即可。

若想要快速杀掉集群的进程，则可以执行如下命令：

注意，生产库上严禁使用，否则可能导致集群不能正常启动。

第三章 sysresv命令

3.1  若是一个主机上有多个oracle实例的话该如何确定哪个共享内存段属于我们该清掉的oracle实例的内存段？

答案：使用sysresv命令。sysresv是Oracle在Linux/Unix平台提供的工具，用来查看Oracle实例使用的共享内存和信号量等信息。sysresv存放的路径：$ORACLE_HOME/bin/sysresv。使用时需要设置LD_LIBRARY_PATH环境变量，用来告诉Oracle共享库文件的位置。sysresv用法如下：

来看一下简单使用：

说明一下：在安装ORACLE产品前，需要设置系统的共享内存段的最大值和个数限制，实例在启动后，应尽量保证SGA在一个共享内存段上，这里由于我是在RAC的一个节点上进行的测试，所以实例内存被分配到4个共享内存段上。

IPC的清理可以使用sysresv –if，如果实例正在运行，清理操作会被终止：

另外如果需要清理内存段和信号量，而sysresv发现实例是alive的，可以使用ipcrm命令：

3.1.1  实验

第四章 Oracle内核参数

查看：more /proc/sys/kernel/shmmax

临时生效：echo 3145728 > /proc/sys/kernel/shmmax

永久生效，修改文件：/etc/sysctl.conf，并使修改参数立即生效：/sbin/sysctl -p

重要的几个参数如下所示：

其含义分别如下所示：

（一）kernel.shmall = 2097152 # kernel.shmall参数是控制共享内存页数。Linux 共享内存页大小为4KB，共享内存段的大小都是共享内存页大小的整数倍。如果一个共享内存段的最大大小是16G，那么需要共享内存页数是 16GB/4KB = 16777216KB/4KB = 4194304（页），也就是64Bit系统下16GB物理内存，设置kernel.shmall = 4194304才符合要求（几乎是原来设置2097152的两倍）。简言之，该参数的值始终应该至少为： ceil(SHMMAX/PAGE_SIZE)。这个值太小有可能导致数据库启动报错（ORA-27102: out of memory）。

（二）kernel.shmmax = 1054472192  #定义一个内存段最大可以分配的内存空间，单位为字节。如果定义太小，那么会导致启动实例失败，或者SGA就会被分配到多个共享内存段。那么内存中的指针连接会给系统带来一定的开销，从而降低系统性能。这个值的设置应该大于SGA_MAX_TARGET或MEMORY_MAX_TARGET的值，最大值可以设置成大于或等于实际的物理内存。如果kernel.shmmax为100M，sga_max_size为500M，那么启动Oracle实例至少会分配5个共享内存段；如果设置kernel.shmmax为2G，sga_max_size为500M，那么启动Oracle实例只需要分配1个共享内存段。

（三）kernel.shmmni = 4096 #设置系统级最大共享内存段数量，该参数的默认值是4096。这一数值已经足够，通常不需要更改。。

（四）kernel.sem = 250 32000 100 128 #信号灯的相关配置，信号灯semaphores是进程或线程间访问共享内存时提供同步的计数器。可以通过命令“cat /proc/sys/kernel/sem”来查看当前信号灯的参数配置，如下所示：

其4个值的含义分别如下：

① 250表示SEMMSL，设置每个信号灯组中信号灯最大数量，推荐的最小值是250。对于系统中存在大量并发连接的系统，推荐将这个值设置为PROCESSES初始化参数加10。

② 32000表示SEMMNS，设置系统中信号灯的最大数量。操作系统在分配信号灯时不会超过LEAST(SEMMNS,SEMMSL*SEMMNI)。事实上，如果SEMMNS的值超过了SEMMSL*SEMMNI是非法的，因此推荐SEMMNS的值就设置为SEMMSL*SEMMNI。Oracle推荐SEMMNS的设置不小于32000。

③ 100表示SEMOPM，设置每次系统调用可以同时执行的最大信号灯操作的数量。由于一个信号灯组最多拥有SEMMSL个信号灯，因此有推荐将SEMOPM设置为SEMMSL的值。Oracle验证的10.2和11.1的SEMOPM的配置为100。

④ 128表示SEMMNI，设置系统中信号灯组的最大数量。Oracle10g和11g的推荐值为142。

4.1  kernel.shmmax参数

4.1.1  实验1

下面临时设置kernel.shmmax为3M，会导致Oracle不能启动，设置sqlplus不能进入：

告警日志：

或启动报错：

有关“TNS-12518: TNS:listener could not hand off client connection”的更多内容请参考：

【故障|监听】TNS-12518、TNS-00517和 Linux Error：32：Broken pipe：http://blog.itpub.net/26736162/viewspace-2135468/

4.1.2  实验2

下面临时设置kernel.shmmax为100M，sga_max_size为500M，则至少需要5个共享内存段，查看临时段的个数：

下面临时设置kernel.shmmax为2G，sga_max_size为500M，则只需要1个共享内存段，查看临时段的个数：

4.2  kernel.shmall

该参数设置过小，有可能导致数据库启动报错。很多人调整系统内核参数的时候只关注SHMMAX参数，而忽略了SHMALL参数的设置。

4.3  其它博客内容

4.3.1  原文地址：ORACLE内核参数 作者：it_newbalance

服务器内存为4G的情况下 

修改/etc/sysctl.conf文件 (ROOT账户) 

kernel.shmmax = 2147483648 

//公式:2G*1024*1024*1024=2147483648(字节) 

//表示最大共享内存，如果小的话可以按实际情况而定，一般为物理内存的一半（单位:字节） 

kernel.shmmni=4096 

//表示最小共享内存固定4096KB（由于32位操作系统默认一页为4K） 

kernel.shmall=1048576 

//公式:4G*1024*1024/4K = 1048576(页) 

//表示所有内存大小（单位：页） 

kernel.sem=250 32000 100 128 

//4个参数依次是SEMMSL：每个用户拥有信号量最大数，SEMMNS：系统信号量最大数，SEMOPM：每次semopm系统调用操作数，SEMMNI：系统辛苦量集数最大数。这4个参数为固定内容大小 

fs.file-max=65536 

//file-max固定大小65536 

net.ipv4.ip_local_port_range=1024 65000 

//ip_local_port_range表示端口的范围，为指定的内容 

以上步骤做完执行 /sbin/sysctl -p 使内核生效 

验证参数（root账户执行）： 

#/sbin/sysctl -a | grep shm 

#/sbin/sysctl -a | grep sem 

#/sbin/sysctl -a | grep file-max 

#/sbin/sysctl -a | grep ip_local_port_range

最近解决了一些这方面的问题，并在网络上查询了一些相关资料终于发现一个比较全面解释这类问题的官方文档。本来打算当一次活雷锋全文翻译的，后来考虑自己英文一般，并且对于其中一些OS相关的知识也没有深入了解。就保留英文大家自己去领会其中的要领，自己简单总结了一下解决这类问题的关键点并整理一下英文原文。这个文档是oracle官方技术支持网站Metalink的资料，里面引用了一些其它的文档例如NOTE:115235.1 。

    对于unix操作系统中Semaphores问题只是针对和oracle相关问题作一些解释。对于信号量和共享内存段参数在不同的系统中可能有不同的参数对应，具体你去查询对应的OS文档。

在解决这类问题的时候我发现大部分问题都是因为在安装oracle时没有仔细阅读针对指定OS的安装说明造成安装实例失败，一般oracle的官方文档都详细说明在对应操作系统上如何设置这些内核参数。还有就是因为其他原因OS管理人员调整了参数，但是没有通知DBA，一旦oracle崩溃再次重新启动的时候就可能因为新的内核参数不合适而无法启动。 如果是oracle意外停机之后重新启动不成功，并出现类似ora-27123的错误那么一定要询问是否有其他人修改过内核参数，有时候你没有修改并不代表其他人没有修改哟，我遇到过不少这样的情况！

1、与oracle相关的信号量和共享内存段参数

   一般unix系统中和信号量相关的是三个参数SEMMNI SEMMSL SEMMNS。他们相互关联决定系统可以分配的信号量。Oracle使用信号量完成内部进程之间的通信。

   关于共享内存段使用shmmx参数进行总体控制。它指定了系统可以分配的共享内存段最大大小，实际并没有分配那么多只是给出一个可以使用的最大限制。

   对于类核参数的修改必须要重新启动系统之后才会生效。

2、出现信号量和共享内存段相关问题的情况

  oracle只有在startup nomount的时候才会请求os的这些资源，用于建立SGA和启动后台进程。

   有些情况下因为oracle崩溃之后os没有清除oracle分配的SGA，也可能造成共享内存段不足，需要人工清除。

3、如何解决相关的问题

   你可以简单的修改init参数减少oracle对共享内存段和信号量的需求。

   对于控制信号量的三个参数SEMMNI SEMMSL SEMMNS 。最终可以使用的信号量由下面公式 提取 (semmsl * semmni) 或者 semmns中最小的值。

    例如在linux下. 进入目录/proc/sys/kernel；用cat命令或more命令查看semaphore当前参数的值： 

cat sem 

命令运行后将会出现如下的结果： 

250 32000 32 128 

其中, 250 是参数SEMMSL的值,32000是参数SEMMNS的值, 32是参数SEMOPM的值，而128则是参数SEMMNI的值。250*128=32000

对于oracle7需要信号量的设置等于init中processes的设置。对于8i 9i需要等于processes*2。

对于信号量参数的设定一定要小心，因为不正确的设置可能会让系统使用默认值。这个值一般比oracle系统要求的低。在HP unix上遇到过这样的问题，当时在参数配置的时候指定两个不同的sem-mni造成系统使用默认的设置。

对于共享内存段，系统的设置至少要等于SGA的大小。

Semaphores and Shared Memory

BULLETIN Status: PUBLISHED Content Type: TEXT/PLAIN Creation Date: 05-AUG-2001

Last Revision Date: 05-AUG-2002

PURPOSE-------

To provide an overview of shared memory and semaphores, answer common questions related to these OS resources and provide links to more detailed information.

SCOPE & APPLICATION

-------------------

This document is intended for anyone who is responsible for creating or

administering an Oracle Database. It is intended to compliment the semaphore and

shared memory information already provided in the Oracle Installation Guides.

关于信号量和共享内存段的背景知识

----------------------------------------------------------------------------------

Semaphores and shared memory are two very distinct sets of Operating System

resources. Semaphores are a system resource that Oracle utilizes for interprocess

communication and they occupy a relatively small memory space, while shared memory is utilized to contain the SGA and can garner a large portion of physical memory.

How many of these resources are available and how they are allocated is controlled

by the configuration of the operating system kernel('kernel' referring to the

centralized core components of the underlying operating system).

There are three OS kernel parameters that work together to limit semaphore

allocation and one OS kernel paramater that dictates the maximum size of a shared

memory segment.

Operating System kernel parameters generally cannot be tuned on the fly. If they

are modified, the changes will not take place until the system is rebooted.

Remember also that the kernel parameters related to semaphores and shared memory represent 'high-water' marks. Meaning that the OS will not automatically

allocate a given amount, but will allow up to that given amount to be available

upon request.

什么时候信号量和共享内存段问题最有可能发生

----------------------------------------------------------------------------------

Both semaphore or shared memory errors appear primarily at instance startup (The

'startup nomount' stage specifically). This is the only time that Oracle tries to

acquire semaphores and shared memory for the instance. Errors related to

semaphores or shared memory rarely appear during normal database operations.

The most common circumstance in which these errors occur is during the creation of

a new database.

Sometimes when an Oracle instance crashes, however, it's shared memory segments may not be released by the OS. This limits the overall amount of shared memory available for the instance to start up again. In this case, you will need to remove those segments manually.

如何解决信号量和共享内存段问题：

How to resolve semaphore and shared memory errors:

----------------------------------------------------------------------------------

In addressing both semaphore and shared memory errors at instance startup, there

are two separate areas that should be considered for reconfiguration.

The first and most simple fix is to modify the init.ora to reduce the number of semaphores or the amount of shared memory Oracle will try to grab at instance startup.

If your situation requires that you not reduce the appropriate init.ora

parameters, you will have to modify the operating system kernel to allow the OS to

provide more semaphores or allow larger shared memory segments.

SEMAPHORES

================================================== ================================

IMPORTANT NOTE: ORACLE DOES NOT UTILIZE SEMAPHORES ON AIX OR DIGITAL/TRU64.

与信号量相关的的ORA错误

What kind of ORA errors are related to semaphores?

----------------------------------------------------------------------------------

'Out of memory' type errors are seldom related to semaphores. Error messages which reference a 'SEMM*****' function are related to semaphores.

IMPORTANT NOTE: THESE ERRORS ONLY OCCUR AT INSTANCE STARTUP.

ORA-7250 "spcre: semget error, unable to get first semaphore set."

ORA-7279 "spcre: semget error, unable to get first semaphore set."

ORA-7251 "spcre:semget error, could not allocate any semaphores."

ORA-7252 "spcre: semget error, could not allocate any semaphores."

ORA-7339 "spcre: maximum number of semaphore sets exceeded."

[NOTE:115235.1] Resolving ORA-7279 or ORA-27146 errors when starting instance

VERY COMMON On Oracle8i and Oracle9i:

ORA-3113 "end-of-file on communication channel" at instance startup.

ORA-27146 "post/wait initialization failed"

[NOTE:115235.1] Resolving ORA-7279 or ORA-27146 errors when starting instance

If you want a very specific explanation of causes for the above errors, refer to:

[NOTE:15566.1] TECH Unix Semaphores and Shared Memory Explained

However, while their exact cause varies, all these error messages indicate that

your init.ora is configured to grab more semaphores than the OS has available.

If you configure your OS as indicated in the following sections, you will not get any of the errors indicated above.

成功配置信号量的步骤

The Basic Steps to Semaphore Success:

----------------------------------------------------------------------------------

1. Understand The Basic Concept Behind Semaphores

2. Understand How Many Semaphores Your Oracle Instance(s) Will Attempt to Grab

From The Operating System.

3. Configure Your OS Kernel To Accomodate all Your Oracle Instance(s) And also

Allow For Future Growth.

[STEP 1] How are semaphores released by the OS for use by an application?

----------------------------------------------------------------------------------

There are 3 OS kernel parameters that work together to limit semaphore allocation.

When an application requests semaphores, the OS releases them in 'sets'.

Illustrated here as 2 sets: +---+ +---+

| | | |

| | | |

+---+ +---+

Controlled by SEMMNI -->OS limit on the Number of Identifiers or sets.

Each set contains a tunable number of individual semaphores.

Illustrated here as 2 semaphores per semaphore set: +---+ +---+

| S | | S | S | | S |

+---+ +---+

Controlled by SEMMSL -->The number of semaphores in an identifier or

set.(Semaphore List)

Ultimately however, the OS can limit the total number of semaphores available

from the OS. Controlled by:

SEMMNS --> The total Number of Semaphores allowed system wide.

For instance: Let's say SEMMNI = 100000000 and SEMMSL= 100000000 while SEMMNS=10

Even though SEMMNI is 100000000 and SEMMSL is 100000000, the max # of semaphores available on your system will only be 10, because SEMMNS is set to 10.

Inversely: Let's say SEMMNI = 10 and SEMMSL = 10 while SEMMNS=

100000000000000000000000000 Because SEMMNI is 10 and SEMMSL is 10, the max # of semaphores avail on your system will only be 100 or (10 X 10), despite what SEMMNS is set too.

THIS NOTION CAN BE SUMMARIZED BY THE FOLLOWING STATEMENT:

The max # of semaphores that can be allocated on a system will be the lesser of:

(semmsl * semmni) or semmns.

On HP: semmsl is hardcoded to 500. [NOTE:74367.1] HP-UX SEMMSL Kernel Parameter

SEMMNI, SEMMSL & SEMMNS are the basic names for OS semaphore kernel parameters,the full name may vary depending on your OS. Consult your OS specific Oracle Install guide.

[NOTE:116638.1] Understanding and Obtaining Oracle Documentation)

[STEP 2] How many semaphores will my Oracle instance(s) require?

----------------------------------------------------------------------------------

With Oracle7: The number of semaphores required by an instance is equal to the

setting the 'processes' parameter in the init.ora for the instance.

With Oracle8, Oracle8i and Oracle9i: The number of semaphores required by an

instance is equal to 2 times the setting of the 'processes' parameter in the init.ora for the instance. Keep in mind, however, that Oracle only momentarily grabs 2 X 'processes' then releases half at instance startup. This measure was apparently introduced to ensure Oracle could not exhaust a system of semaphores.

Oracle may also grab a couple of additional semaphores per instance for internal

use.

[STEP 3] Configure your OS kernel to accomodate all your Oracle instances.

----------------------------------------------------------------------------------

There seems to be some confusion of how to deal with lack of semaphore errors. The

popular theory being that if Oracle cannot find enough semaphores on a system,

increase semmns. This is not always the case, as illustrated in [STEP 1].

Once you have determined your semaphore requirements for Oracle and compensated for future growth, contact your System Administrator or OS vendor for assistance in modifying the OS kernel.

What should I set 'semmni', 'semmsl' & 'semmns' to?

----------------------------------------------------------------------------------

Oracle Support typically does not recommend specific values for semaphore kernel

parameters. Instead, use the information provided in this document to set the parameters to values that are appropriate for your operating environment.

For more info please look at the following note : [NOTE:15654.1] TECH: Calculating

Oracle's SEMAPHORE Requirements

快速解决信号量问题

Quick fix for resolving lack of semaphore errors:

----------------------------------------------------------------------------------

Reduce the number of semaphores Oracle requires from the OS.

The first and most simple fix is to modify the init.ora to reduce the

number of semaphores or the amount of shared memory Oracle will try to grab at

instance startup.

Keep in mind, with Oracle8, we grab 2 X 'processes' then release half. This measure

was apparently introduced to ensure Oracle could not exhaust a system of semaphores.

如何查找OS配置的信号量

How can I find out how my OS kernel is configured for semaphores?

----------------------------------------------------------------------------------

The files that are used to tune kernel parameters varies depending on your

Operating System. Consult your system administrator or OS vendor, because viewing the system file may not show accurate information about the runtime values.

However, an important point to remember is that if a typographical error is made

while editing these files, the OS will defer to a default value which is usually to low to accomodate Oracle. So it's a good idea to check runtime values with utilities like '/etc/sysdef'.

I've tuned my OS kernel parameters, but I am still having semaphore problems....

----------------------------------------------------------------------------------

常见问题！！

This may mean that you made a typographical error or did not rebuild your

Operating System kernel correctly(if a typographical error is made while editing these files, the OS will defer to a default value which is usually to low to accomodate Oracle).

On Solaris, check current OS kernel values with this command:

> /etc/sysdef|grep -i semm

If these values do not reflect what you put in your 'system' file, you likely made a typographically error.

On HP, be sure the OS kernel was rebuilt correctly and that the OS was booted off the correct file. Contact your System Administrator or HP for more information.

在Linux系统上

进入目录/proc/sys/kernel；用cat命令或more命令查看semaphore当前参数的值： 

cat sem 

命令运行后将会出现如下的结果： 

250 32000 32 128 

其中, 250 是参数SEMMSL的值,32000是参数SEMMNS的值, 32是参数SEMOPM的值，而128则是参数SEMMNI的值。250*128=32000

如何获得当前正在使用的信号量

How can I determine how many semaphores are currently being utilized?

----------------------------------------------------------------------------------

On most Unix systems, current semaphore allocation can be displayed with the OS

command 'ipcs -s'. 

% ipcs -s

While good to know, this command is seldom used as part of troubleshooting semaphore errors.

SHARED MEMORY

==================================================

OS如何分配共享内存段

How is shared memory allocated by the OS?

----------------------------------------------------------------------------------

This process varies slightly depending on Unix platform, but the basic premise is this:

An application requests a given amount of contiguous shared memory from the OS. The OS dictates how large of a shared memory segment it will allow with the kernel

parameter SHMMAX(Shared Memory Maximum). If the amount of shared memory requested by the application is greater than SHMMAX, the OS may be granted the shared memory in multiple segments. Ideally, however, you want the amount requested by the application to be less than SHMMAX so that the application's request can be fulfilled with one shared memory segment.

SHMMAX和SGA的关系

How does SHMMAX relate to my SGA?

----------------------------------------------------------------------------------

Since the SGA is comprised of shared memory, SHMMAX can potentially limit how large your SGA can be and/or prevent your instance from starting.

What limits the size of my SGA?

----------------------------------------------------------------------------------

In no particular order.

5. The amount of Physical Memory and Swap space available on your system.

6. The kernel paramater SHMMAX.

7. Other OS specific limitations on shared memory.

Memory SHMMAX OS Limits +----------+ +----------+ +----------+

| | | | | | +------+

| | | | | | | S |

| | | | | | > | G |

| | | | | | | A |

| | | | | | +------+

+----------+ +----------+ +----------+

Some OS specific limitations are discussed in the following documents:

"Oracle Administrator's Reference" available on the Oracle Install CD

Additionallly:

HP-UX: [NOTE:77310.1] HP-UX Large SGA support for HP, Memory Windows

[NOTE:69119.1] HP-UX SGA Sizing Issues on HP-UX 

Solaris: [NOTE:61896.1] SOLARIS: SGA size, sgabeg attach address and Sun

与共享内存当相关的错误

What kind of ORA errors are related to shared memory?

----------------------------------------------------------------------------------

Error Messages referencing a 'SHMM****' function are related to shared memory.

ORA-7306, ORA-7336, ORA-7329, ORA-7307, ORA-7337, ORA-7320, ORA-7329, ORA-7334

VERY COMMON IN 8i: ORA-27100 "shared memory realm already exists" ORA-27102 "out of memory"

ORA-27125 "unable to create shared memory segment" and/or "linux 43 identifier removed"

ORA-27123 "unable to attach to shared memory segment"

[NOTE:115753.1] UNIX Resolving the ORA-27123 error

 [NOTE:1028623.6] SUN SOLARIS: HOW TO RELOCATE THE SGA

如何设置SHMMAX

What should I set 'shmmax' to?

----------------------------------------------------------------------------------

On some Unix platforms, the Install Guide recommends specific values. Previous

versions of the Install Guide recommended setting SHMMAX to .5 *(physical memory present in machine). Most recently it's been suggested SHMMAX be set to 4294967295 (4GB). This may not seem appropriate, particularly if the system has considerably less physical memory available, but it does prevent you from having to modify your system kernel everytime a new instance is created or additional physical memory is added to the system. Remember that SHMMAX is a high water mark, meaning that the OS will attempt to allow up to that amount for an application.

解决缺少共享内存段的问题

Quick fix for resolving lack of shared memory errors:

-----------------------------------------------------------------------------------

NOTE: If you have never configured your OS kernel for shared memory, you cannot employ this 'Quick Fix'. You will have to first configure the OS kernel. The amount of shared memory Oracle requests is roughly equal to the size of the SGA. The first and most simple fix is to modify the init.ora to reduce the amount of shared memory Oracle will try to grab at instance startup.

This document lists the init.ora parameters that contribute to the size

of the SGA:

[NOTE:1008866.6] HOW TO DETERMINE SGA SIZE (8.0, 8i, 7.x)

oracle崩溃之后重新启动失败的问题

My instance crashed. When I try to restart it, I receive errors related to shared

memory. What should I do?

-----------------------------------------------------------------------------------

This may indicate that the shared memory segment associated with the SGA of the crashed instance is still in memory. In this case it may be appropriate to manually remove the segment using OS commands.

THIS PROCESS SHOULD NOT BE ATTEMPTED UNLESS YOU FULLY UNDERSTAND THE CONCEPTS BEHIND IT!!!

The basic steps are:

1. Identify the shared memory segment that is 'stuck' in memory.

2. Remove the 'stuck' shared memory segment using the OS command 'ipcrm'.

[NOTE:68281.1] DETERMINING WHICH INSTANCE OWNS WHICH SHARED MEMORY & SEMAPHORE SEGMENTS

[NOTE:69642.1] also describes this process - Step 9.

[NOTE:123322.1] SYSRESV UTILITY: This note describes the new 8i 'sysresv' utility that can be used on Solaris to associate a given ORACLE_SID with it's shared memory segment(s). .

4.3.2  Oracle 性能优化之内核的shmall 和shmmax 参数

1. 内核的 shmall 和 shmmax 参数

SHMMAX= 配置了最大的内存segment的大小 ——>这个设置的比SGA_MAX_SIZE大比较好。

SHMMAX参数：Linux进程可以分配的单独共享内存段的最大值。一般设置为内存总大小的一半。这个值的设置应该大于SGA_MAX_TARGET或MEMORY_MAX_TARGET的值，因此对于安装Oracle数据库的系统，shmmax的值应该比内存的二分之一大一些。

SHMMIN= 最小的内存segment的大小 。

SHMMNI= 整个系统的内存segment的总个数 。设置系统级最大共享内存段数量。Oracle10g推荐最小值为4096，可以适当比4096增加一些。

SHMSEG= 每个进程可以使用的内存segment的最大个数

shmall=是全部允许使用的共享内存大小，shmmax 是单个段允许使用的大小。这两个可以设置为内存的 90%。例如 16G 内存，16*1024*1024*1024*90% = 15461882265，shmall 的大小为 15461882265/4k(getconf PAGESIZE可得到) = 3774873。

shmall设置共享内存总页数。这个值太小有可能导致数据库启动报错。很多人调整系统内核参数的时候只关注SHMMAX参数，而忽略了SHMALL参数的设置。

－

2.配置信号灯（ semphore ）的参数

信号灯semaphores是进程或线程间访问共享内存时提供同步的计数器。

SEMMSL= 设置每个信号灯组中信号灯最大数量，推荐的最小值是250。对于系统中存在大量并发连接的系统，推荐将这个值设置为PROCESSES初始化参数加10。

SEMMNI= 设置系统中信号灯组的最大数量。Oracle10g和11g的推荐值为142。

SEMMNS=设置系统中信号灯的最大数量。操作系统在分配信号灯时不会超过LEAST(SEMMNS,SEMMSL*SEMMNI)。事实上，如果SEMMNS的值超过了SEMMSL*SEMMNI是非法的，因此推荐SEMMNS的值就设置为SEMMSL*SEMMNI。Oracle推荐SEMMNS的设置不小于32000，假如数据库的PROCESSES参数设置为600，则SEMMNS的设置应为：

SQL> select (600+10)*142 from dual;

(600+10)*142

------------

      86620

1

2

3

4

5

SEMOPM参数：设置每次系统调用可以同时执行的最大信号灯操作的数量。由于一个信号灯组最多拥有SEMMSL个信号灯，因此有推荐将SEMOPM设置为SEMMSL的值。Oracle验证的10.2和11.1的SEMOPM的配置为100。

通过下面的命令可以检查信号灯相关配置：

# cat /proc/sys/kernel/sem

250 32000 100 128

1

2

对应的4个值从左到右分别为SEMMSL、SEMMNS、SEMOPM和SEMMNI

－

3.修改 /etc/sysctl.conf

kernel.shmmax=15461882265

kernel.shmall=3774873

kernel.msgmax=65535

kernel.msgmnb=65535

执行 sudo sysctl -p

可以使用 ipcs -l 看结果,ipcs -u 可以看到实际使用的情况

-------------------------------------------------------------------------

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