MEMORY_TARGET参数在Oracle 11g被引进,主要是用于控制Oracle对于系统内存的使用,首次将SGA与PGA整合到一起实现自动管理。一旦设置了MEMORY_TARGET参数值,Oracle会根据需要自动调整SGA与PGA以合理的分配及使用内存。但如果MEMORY_TARGET设置不当,就容易引起ORA-00845,因为MEMORY_TARGET与/dev/shm(tempfs)息息相关。
1、故障现象
[oracle@linux1 catadb]$ sqlplus / as sysdba
SQL*Plus: Release 11.2.0.1.0 Production on Wed Nov 13 21:38:41 2013
Copyright (c) 1982, 2009, Oracle. All rights reserved.
Connected to an idle instance.
idle> startup nomount;
ORA-00845: MEMORY_TARGET not supported on this system
2、故障分析
[oracle@linux1 trace]$ oerr ora 00845
00845, 00000, "MEMORY_TARGET not supported on this system"
// *Cause: The MEMORY_TARGET parameter was not supported on this operating system or /dev/shm was not sized correctly on Linux.
// *Action: Refer to documentation for a list of supported operating systems.
Or, size /dev/shm to be at least the SGA_MAX_SIZE on each Oracle instance running on the system.
#从上面的描述可知,/dev/shm的大小应该至少是当前系统每一个实例的SGA_MAX_SIZE,个人认为这个描述不是很准确
#下面查看告警日志
[oracle@linux1 trace]$ more alert_catadb.log
Wed Nov 13 21:38:48 2013
Starting ORACLE instance (normal)
WARNING: You are trying to use the MEMORY_TARGET feature. This feature requires the /dev/shm file system to be mounted for at least
1073741824 bytes. /dev/shm is either not mounted or is mounted with available space less than this size. Please fix this so that
MEMORY_TARGET can work as expected. Current available is 901312512 and used is 161312768 bytes.
Ensure that the mount point is /dev/shm for this directory. memory_target needs larger /dev/shm
#告警日志给出了比较精确的描述,/dev/shm至少是1GB,因为我们的参数文件中定义的MEMORY_TARGET为1GB
#同时也给出了/dev/shm当前已使用的和剩余空间的大小。剩余空间大小901312512不够1GB,因此需要考虑增加dev/shm或减少MEMORY_TARGET的值
#延伸思考
/dev/shm实际上就是对应到tmpfs,也可以称之为临时文件系统(不是块设备)。有点类似于Oracle数据库的临时表空间一样啊,用于加速和优化系统。
我们可以通过df -h来查看到该加载点,该目录并不位于磁盘,而是在内存里,默认情况下,其大小为当前内存的一半,该文件系统会被自动加载。
/dev/shm的分配是按需分配,如我们前面的错误描述,当前分配了1GB,实际使用了154MB,剩余860MB。也就是说这860MB依旧可分配给其他应用程序。
使用tmps文件系统有一些优点,可以实现动态文件系统大小,其次是由于驻留内存,可以闪电加速。重启后被清空,也就是相当于闪存。
#当前系统的/dev/shm
[oracle@linux1 trace]$ df -h | grep shm
tmpfs 1014M 154M 860M 16% /dev/shm
[oracle@linux1 ~]$ ls -hltr /dev/shm
total 154M
-rw-r----- 1 grid oinstall 4.0M Nov 14 11:06 ora_+ASM1_2686978_68
-rw-r----- 1 grid oinstall 4.0M Nov 14 11:06 ora_+ASM1_2686978_39
-rw-r----- 1 grid oinstall 4.0M Nov 14 11:06 ora_+ASM1_2686978_40
-rw-r----- 1 grid oinstall 4.0M Nov 14 11:06 ora_+ASM1_2686978_41
-rw-r----- 1 grid oinstall 4.0M Nov 14 11:06 ora_+ASM1_2686978_42
...............
-rw-r----- 1 grid oinstall 4.0M Nov 14 11:47 ora_+ASM1_2686978_66
-rw-r----- 1 grid oinstall 4.0M Nov 14 11:47 ora_+ASM1_2686978_52
-rw-r----- 1 grid oinstall 4.0M Nov 14 11:47 ora_+ASM1_2686978_67
3、故障解决
从上面的情形可知,我们可以通过增加tempfs文件系统的大小或者是适当减少MEMORY_TARGET的值来解决
a、调整参数memory_target
[oracle@linux1 ~]$ grep memory $ORACLE_HOME/dbs/initcatadb.ora
memory_target=521M
[oracle@linux1 ~]$ export ORACLE_SID=catadb
[oracle@linux1 ~]$ sqlplus / as sysdba
SQL*Plus: Release 11.2.0.1.0 Production on Thu Nov 14 11:51:57 2013
Copyright (c) 1982, 2009, Oracle. All rights reserved.
Connected to an idle instance.
idle> startup nomount;
ORACLE instance started.
Total System Global Area 548216832 bytes
Fixed Size 1337804 bytes
Variable Size 331351604 bytes
Database Buffers 209715200 bytes
Redo Buffers 5812224 bytes
idle> shutdown abort;
ORACLE instance shut down.
b、增加tempfs大小
[oracle@linux1 ~]$ grep memory $ORACLE_HOME/dbs/initcatadb.ora
memory_target=1G
#下面的方法用于临时调整tempfs的大小,重启后失效
#即将tempfs的大小调整到1200M,inode数量调整到1000000,此时大约可可存放一百万个小文件
[root@linux1 ~]# mount -o size=1200M -o nr_inodes=1000000 -o noatime,nodiratime -o remount /dev/shm
[root@linux1 ~]# df -h | grep shm
tmpfs 1.2G 154M 1.1G 13% /dev/shm
[root@linux1 ~]# su - oracle
[oracle@linux1 ~]$ export ORACLE_SID=catadb
[oracle@linux1 ~]$ sqlplus / as sysdba
SQL*Plus: Release 11.2.0.1.0 Production on Thu Nov 14 12:04:02 2013
Copyright (c) 1982, 2009, Oracle. All rights reserved.
Connected to an idle instance.
idle> startup nomount;
ORACLE instance started.
Total System Global Area 1071333376 bytes
Fixed Size 1341312 bytes
Variable Size 620759168 bytes
Database Buffers 444596224 bytes
Redo Buffers 4636672 bytes
# Author : Leshami
# Blog : http://blog.csdn.net/leshami
#永久增加tempfs的大小,直接修改/etc/fstab
vi /etc/fstab
tmpfs /dev/shm tmpfs defaults,size=2048M 0 0
修改之后remount
mount -o remount /dev/shm
--转自