oracle之 關閉透明大頁

方法一：

1、設定/etc/grub.conf檔案，新增 transparent_hugepage=never ，在系統啟動是禁用

[root@hbdw1 ~]# cat /etc/grub.conf 
# grub.conf generated by anaconda
#
# Note that you do not have to rerun grub after making changes to this file
# NOTICE: You have a /boot partition. This means that
# all kernel and initrd paths are relative to /boot/, eg.
# root (hd0,0)
# kernel /vmlinuz-version ro root=/dev/sda2
# initrd /initrd-[generic-]version.img
#boot=/dev/sda
default=0
timeout=5
splashimage=(hd0,0)/grub/splash.xpm.gz
hiddenmenu
title Red Hat Enterprise Linux 6 (2.6.32-573.el6.x86_64)
root (hd0,0)
kernel /vmlinuz-2.6.32-573.el6.x86_64 ro root=UUID=57f7184b-2dec-43b1-b0cd-9862a4b42cfe rd_NO_LUKS KEYBOARDTYPE=pc KEYTABLE=us LANG=en_US.UTF-8 rd_NO_MD SYSFONT=latarcyrheb-sun16 rd_NO_LVM rhgb quiet rd_NO_DM rhgb quiet memmap=0x2000000$0x3E000000 nmi_watchdog=2 crashkernel=256M-:256M printk.time=1 console=ttyS0,115200 console=tty0 transparent_hugepage=never ##新增到 tty0 後面，注意留一個空格 
initrd /initramfs-2.6.32-573.el6.x86_64.img

2、 重啟伺服器

3、檢查是否關閉

# grep AnonHugePages /proc/meminfo

If the output contains a line like "AnonHugepages: 
xxxx kB", with a value > 0kB, the kernel is using Transparent HugePages.

方法二：

1、編輯 /etc/rc.local 新增如下記憶體

[root]# cat /etc/rc.local
if test -f /sys/kernel/mm/transparent_hugepage/enabled; then
echo never > /sys/kernel/mm/transparent_hugepage/enabled
fi
if test -f /sys/kernel/mm/transparent_hugepage/defrag; then
echo never > /sys/kernel/mm/transparent_hugepage/defrag
fi

2、 重啟伺服器

3、檢查是否關閉

# grep AnonHugePages /proc/meminfo

If the output contains a line like "AnonHugepages: 
xxxx kB", with a value > 0kB, the kernel is using Transparent HugePages.

補充：

1：從RedHat 6, OEL 6, SLES 11 and UEK2 kernels 開始，系統預設會啟用 Transparent HugePages ：用來提高記憶體管理的效能透明大頁（Transparent HugePages ）和之前版本中的大頁功能上類似。主要的區別是：Transparent HugePages 可以實時配置，不需要重啟才能生效配置；

2：Transparent Huge Pages在32位的RHEL 6中是不支援的。

Transparent Huge Pages are not available on the 32-bit version of RHEL 6.

3： ORACLE官方不建議我們使用RedHat 6, OEL 6, SLES 11 and UEK2 kernels 時的開啟透明大頁（Transparent HugePages ）， 因為透明大頁（Transparent HugePages ） 存在一些問題：

1.在RAC環境下 透明大頁（Transparent HugePages ）會導致異常節點重啟，和效能問題；

2.在單機環境中，透明大頁（Transparent HugePages ） 也會導致一些異常的效能問題；

Transparent HugePages memory is enabled by default with Red Hat Enterprise Linux 6, SUSE Linux Enterprise Server 11, and Oracle Linux 6 with earlier releases of Oracle Linux Unbreakable Enterprise Kernel 2 (UEK2) kernels. Transparent HugePages memory is disabled in later releases of Oracle Linux UEK2 kernels.Transparent HugePages can cause memory allocation delays during runtime. To avoid performance issues, Oracle recommends that you disable Transparent HugePages on all Oracle Database servers. Oracle recommends that you instead use standard HugePages for enhanced performance.Transparent HugePages memory differs from standard HugePages memory because the kernel khugepaged thread allocates memory dynamically during runtime. Standard HugePages memory is pre-allocated at startup, and does not change during runtime.

Starting with RedHat 6, OEL 6, SLES 11 and UEK2 kernels, Transparent HugePages are implemented and enabled (default) in an attempt to improve the memory management. Transparent HugePages are similar to the HugePages that have been available in previous Linux releases. The main difference is that the Transparent HugePages are set up dynamically at run time by the khugepaged thread in kernel while the regular HugePages had to be preallocated at the boot up time. Because Transparent HugePages are known to cause unexpected node reboots and performance problems with RAC, Oracle strongly advises to disable the use of Transparent HugePages. In addition, Transparent Hugepages may cause problems even in a single-instance database environment with unexpected performance problems or delays. As such, Oracle recommends disabling Transparent HugePages on all Database servers running Oracle.

4：安裝Vertica Analytic Database時也必須關閉透明大頁功能