【遇到问题】ORA-27102 ORA-01034

软件安装完接着开始建库，不幸的是开始报错，内容如下：

ORA-27102: out of memory  ORA-01034: ORACLE not available

一 ．查下系统版本

oracle@linux:/u01/app/oracle/admin/orcl/bdump> uname -a

Linux linux 2.6.5-7.308-bigsmp #1 SMP Mon Dec 10 11:36:40 UTC 2007 i686 i686 i386 GNU/Linux

本系统为 32 位

二．查看内存信息

oracle@linux:/u01/app/oracle/admin/orcl/bdump> cat /proc/meminfo

MemTotal:      8302360 kB

MemFree:       3788908 kB

Buffers:        138968 kB

Cached:        4003872 kB

SwapCached:          0 kB

 

oracle@linux:/u01/app/oracle/admin/orcl/bdump> free -m

             total       used       free     shared    buffers     cached

Mem:          8107       4407       3700          0        135       3910

-/+ buffers/cache:        361       7745

Swap:         4102          0       4102

 

本系统物理内存为 8G ， swap 为 4G 。这里说明一下，一般 oracle 对于硬件的要求为：

1.       至少有 1024MB 的物理内存

2.       Swap 的大小设置 1024 MB 到 2048 MB 1.5 倍 RAM ， 2049 MB 到 8192 MB 等于 RAM 大于 8192 MB 0.75 倍 RAM ， oracle10g 以后 oracle 也是安装这个公式来 chenck.

3.       在 /tmp 目录中至少有 400 MB 空闲磁盘空间

4.1.5 GB 到 3.5 GB 的磁盘空间用于安装 Oracle 数据库软件

因此我的系统系统工程师 swap 设置少，因此在我安装 oracle10G check 的时候提示 swap 空间不够。

  三．查 metalink ：

 

Cause

There  is not enough SHM (max-shm-memory) for the SES install. SES will try to allocate 40% of the installed RAM for SGA.  For example, if the installed RAM is 60GB.  SES will attempt to allocated approximately 24GB for SGA.  If it is not available, you will receive the out of memory error.

Solution

The following runInstaller syntax can be used to cap the SGA during installation to avoid this error.

./runInstaller n_maxMemoryInMB=4000

This will cap the SGA at 4GB.  The out of memory error should not be encountered again.  The above syntax can be run with a smaller value as well depending on your environment.  However, the recommendation would be to not specify anything less than 2GB as this could lead to memory errors post-install.

 

查看 /shm 大小：

linux:~ # df -h

Filesystem            Size  Used Avail Use% Mounted on

/dev/sda3              99G  2.8G   91G   3% /

tmpfs                 4.0G  8.0K  4.0G   1% /dev/shm

/dev/sda1            1012M   39M  922M   5% /boot

/dev/sda5             299G  3.6G  280G   2% /u01

建库时我的 sga 选为 typcial 模式自动分配 oracle 内存区大小， oracle 会默认将 sga 大小设为物理内存的 40% ， 8G*40%=2048M ,sga+pga=28480M , 而我的 shm=4G, 所以不存在 SHM is not enough 的情况。

又查另一篇 article, 如下：

Applies to:

Oracle Server - Enterprise Edition - Version: 9.2.0.1 to 11.1.0.7 - Release: 9.2 to 11.1

Linux x86

***Checked for relevance on 16-Nov-2010***

Symptoms

While creating a database using the Database Configuration Assistant (DBCA) or manually, the following error can occur:

    ORA-27102: out of memory

Cause

For 32 bit systems running the smp kernel, we cannot have an SGA > 1.7 GB directly.

This is because of limitation of 32 bit systems of not being able to address memory > 4GB directly by a user process.

If SGA is kept higher than 1.7 GB, it will results in ORA-27102 errors.

While invoking DBCA to create a starter database, by default it takes 40% of memory for SGA.

Hence the size can accidentally exceed 1.7 GB

Solution

The workaround is to create a new database and specify the size of SGA approximate to be 1.5 to 1.7 GB.

由此可见， 32 位系统最大支持 4G 内存，所以 32 位的系统不可以直接将 sga 设为大于 1.7G ，将 sga 调小即可。

 

四．名词解释：

SHM ，/dev/shm is nothing but implementation of traditional shared memory concept. It is an efficient means of passing data between programs. One program will create a memory portion, which other processes (if permitted) can access. This will result into speeding up things on Linux.

shm / shmfs is also known as tmpfs, which is a common name for a temporary file storage facility on many Unix-like operating systems. It is intended to appear as a mounted file system, but one which uses virtual memory instead of a persistent storage device.

If you type mount command you will see /dev/shm as a tempfs file system. Therefore, it is a file system, which keeps all files in virtual memory. Everything in tmpfs is temporary in the sense that no files will be created on your hard drive. If you unmount a tmpfs instance, everything stored therein is lost. By default almost all Linux distros configured to use /dev/shm.

即 shm 是一块高速缓存区，通常挂在目录 tmpfs ，即将内存映射在此目录下。 Shm 默认为物理内存的一半，可以将此看做为进入系统内存的入口设备，通过这个设备往内存中读写数据，加快频繁读写文件的 I/O 。 Oracle 的内存分配都是在 shm 中进行，所以如果 shm 大小小于 sga 的大小那么就有问题。

Swap: 这是系统的交换内存，当系统物理内存不够时将会充当内存使用 , 因此可以理解为当 /dev/shm 空间不够时可以占用 swap 的空间，如果用到 Swap 时，系统的性能就有可能很低了。

DBA 不懂系统是不行滴 ~~~~~~~