Home Database Mysql Tutorial 安装Oracle时在Linux上设置内核参数的含义

安装Oracle时在Linux上设置内核参数的含义

Jun 07, 2016 pm 05:19 PM

安装Oracle之前,除了检查操作系统的硬件和软件是否满足安装需要之外,一个重点就是修改内核参数,其中最主要的是和内存相关的参

看到一篇RedHat官方的Oracle安装文档,对于Linux内核参数的修改描述的非常清晰。

安装Oracle之前,除了检查操作系统的硬件和软件是否满足安装需要之外,一个重点就是修改内核参数,其中最主要的是和内存相关的参数设置。
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。
# grep MemTotal /proc/meminfo
# cat /proc/sys/kernel/shmmax
上面的命令是检查系统内存的大小,以及当前shmmax的设置。
# echo 21474836480 > /proc/sys/kernel/shmmax
# sysctl -w kernel.shmmax=21474836480
# echo "kernel.shmmax=21474836480" >> /etc/sysctl.conf
这是设置shmmax参数的几种方法,这三种方式都可以将shmmax设置为20G。这个参数的修改可以不重启数据库。个人推荐使用第二种sysctl命令的方式。采用第三种方式需要执行sysctl –t操作或重启,但是为了确保下次重启后设置值仍然生效,第三种方式是必不可少的。前两种方式类似alter system set scope = memory,而第三种方式则类似alter system set scope = spfile。
SHMMNI参数: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。
# cat /proc/sys/kernel/shmmni
# echo 4096 > /proc/sys/kernel/shmmni
# sysctl -w kernel.shmmni=4096
# echo "kernel.shmmni=4096" >> /etc/sysctl.conf
检查和设置方法如上,这和shmmax的修改方式没有区别,不在赘述。
SHMALL参数: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。这个值推荐设置为物理内存大小除以分页大小。
# getconf PAGE_SIZE
通过getconf获取分页的大小,用来计算SHMALL的合理设置值:
SQL> select 32*1024*1024*1024/4096 from dual;
32*1024*1024*1024/4096
----------------------
8388608
对于32G的内存,4K分页大小的系统而言,SHMALL的值应该设置为8388608。
# cat /proc/sys/kernel/shmall
# echo 8388608 > /proc/sys/kernel/shmall
# sysctl -w kernel.shmall=8388608
# echo " kernel.shmall=8388608" >> /etc/sysctl.conf
查询和设置方法如上。
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参数: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参数:设置系统中信号灯组的最大数量。Oracle10g和11g的推荐值为142。
SEMMNS参数: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
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
对应的4个值从左到右分别为SEMMSL、SEMMNS、SEMOPM和SEMMNI。修改方法为:
# echo 610 86620 100 142 > /proc/sys/kernel/sem
# sysctl -w kernel.sem="610 86620 100 142"
# echo "kernel.sem=610 86620 100 142" >> /etc/sysctl.conf

linux

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