模拟操作系统内存从2G增加为8G后，调整数据库内存参数，示例中参数不作为实际生产环境参考，因为因需所取，调整参数需要根据数据库相应调整，避免小牛拉大车，大牛拉小车的现象。
查看原始配置数据
[oracle@rac1 ~]$ sqlplus / as sysdba
SQL*Plus: Release 11.2.0.4.0 Production on Sat Jan 7 18:42:30 2017
Copyright (c) 1982, 2013, Oracle. All rights reserved.
Connected to:
Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production
With the Partitioning, Real Application Clusters, Automatic Storage Management, OLAP,
Data Mining and Real Application Testing options
SQL> show parameter sga;
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
lock_sga boolean FALSE
pre_page_sga boolean FALSE
sga_max_size big integer 700M
sga_target big integer 0
SQL> show parameter pga
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
pga_aggregate_target big integer 0
SQL> show parameter mem
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
hi_shared_memory_address integer 0
memory_max_target big integer 1G
memory_target big integer 1G
shared_memory_address integer 0
SQL> ho cat /etc/sysctl.conf | grep shmmax
# oracle-rdbms-server-11gR2-preinstall setting for kernel.shmmax is 4398046511104 on x86_64
# oracle-rdbms-server-11gR2-preinstall setting for kernel.shmmax is 4294967295 on i386
kernel.shmmax = 4398046511104
kernel.shmmax = 4294967295
SQL> select 4294967295/1024/1024 from dual;
4294967295/1024/1024
--------------------
4096
SQL> select 8*1024*1024*1024 from dual;
8*1024*1024*1024
----------------
8589934592
SQL> exit
[oracle@rac1 ~]$ exit
[root@rac1 ~]# /oracle/app/grid/11.2.0.3/bin/crsctl stop crs
[root@rac1 ~]# halt
关机后增加物理内存，开机后修改参数
8589934592" >> /etc/sysctl.conf
[root@rac1 ~]# sysctl -p
[root@rac1 ~]# df -ThP
Filesystem Type Size Used Avail Use% Mounted on
/dev/sda5 ext4 87G 20G 63G 24% /
tmpfs tmpfs 4.0G 0 4.0G 0% /dev/shm
/dev/sda1 ext4 504M 61M 418M 13% /boot
/dev/sda2 ext4 7.7G 146M 7.2G 2% /tmp
[root@rac1 ~]# grep tmpfs /etc/fstab
tmpfs /dev/shm tmpfs defaults 0 0
[root@rac1 ~]# vim /etc/fstab
[root@rac1 ~]# grep tmpfs /etc/fstab
tmpfs /dev/shm tmpfs defaults,size=8192m 0 0
[root@rac1 ~]# mount -o remount tmpfs
[root@rac1 ~]# df -ThP
Filesystem Type Size Used Avail Use% Mounted on
/dev/sda5 ext4 87G 20G 63G 24% /
tmpfs tmpfs 8.0G 116M 7.9G 2% /dev/shm
/dev/sda1 ext4 504M 61M 418M 13% /boot
/dev/sda2 ext4 7.7G 146M 7.2G 2% /tmp
调整
SQL> select 7*1024 from dual;
7*1024
----------
7168
SQL> select 8*0.56*1024 from dual;
8*0.56*4.48*1024
----------------
4587.52
SQL> alter system set memory_max_target=7168M scope=spfile;
System altered.
SQL> alter system set memory_target=7168M scope=spfile;
System altered.
SQL> alter system set sga_max_size=4587M scope=spfile;
System altered.
SQL> alter system set sga_target=4587M scope=spfile;
System altered.
SQL> shutdown immediate
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> startup
ORACLE instance started.
Total System Global Area 4793552896 bytes
Fixed Size 2261328 bytes
Variable Size 1124077232 bytes
Database Buffers 3657433088 bytes
Redo Buffers 9781248 bytes
Database mounted.
Database opened.
SQL> show parameter sga
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
lock_sga boolean FALSE
pre_page_sga boolean FALSE
sga_max_size big integer 4592M
sga_target big integer 4592M
SQL> show parameter pga
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
pga_aggregate_target big integer 0
SQL> show parameter mem
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
hi_shared_memory_address integer 0
memory_max_target big integer 7G
memory_target big integer 7G
shared_memory_address integer 0
SQL> exit