Oracle database在10gR1之後開始支援Large page。我們知道作業系統預設的頁面大小為4k。如果記憶體空間比較大，則需要進行頻繁的頁分配和管理定址動作，管理這些記憶體的消耗就比較大。啟用大頁後，HugePage會使用2M大小的頁面，能減少CPU和記憶體管理方面的開銷，進而提升效能。建議OS記憶體超過16G時，啟用huagepage。

注意：大頁只對SGA元件起作用，對PGA、UGA無效。如果啟用大頁，無需設定pre_page_sga，lock_sga（因為使用hugePage管理的記憶體不能被Swap）。如果使用了HugePage，11g/12c新特性AMM(Automatic Memory Management)就不能使用了，但是ASMM(Automatic Shared Memory Management)可以繼續使用。

如何在Windows上啟用大頁
A.找到下面的選項
10g:HKEY_LOCAL_MACHINE\SOFTWARE\ORACLE\KEY_OraDb10g_home1

11g:HKEY_LOCAL_MACHINE\SOFTWARE\ORACLE\KEY_OraDb11g_home1

B.New->String Value
ORA_LPENABLE=1 對所有例項啟用大頁

ORA_<ORACLE_SID>_LPENABLE=1 只對特定的例項啟用大頁

C.檢視alert日誌，看大頁是否啟用
Starting ORACLE instance (normal)
Large page enabled         : 1
Large page size            : 2097152
Large page request size    : 33554432

如何在Linux上啟用大頁
1.Edit the memlock setting in the /etc/security/limits.conf file. The memlock setting is specified in KB and set slightly lesser than the installed RAM. For example, if you have 64GB RAM installed, add the following entries to increase the max locked memory limit:

*   soft   memlock    60397977
*   hard   memlock    60397977

2.Login as the oracle user again and run the ulimit -l command to verify the new memlock setting:
$ ulimit -l
60397977

3.Run the following command to display the value of Hugepagesize variable:
$ grep Hugepagesize /proc/meminfo

4.Complete the following procedure to create a script that computes recommended values for hugepages configuration for the current shared memory segments:
a.Create a text file named hugepages_settings.sh
b.Add the following content in the file:

    #!/bin/bash
    #
    # hugepages_settings.sh
    #
    # Linux bash script to compute values for the
    # recommended HugePages/HugeTLB configuration
    #
    # Note: This script does calculation for all shared memory
    # segments available when the script is run, no matter it
    # is an Oracle RDBMS shared memory segment or not.
    # Check for the kernel version
    KERN=`uname -r | awk -F. '{ printf("%d.%d\n",$1,$2); }'`
    # Find out the HugePage size
    HPG_SZ=`grep Hugepagesize /proc/meminfo | awk {'print $2'}`
    # Start from 1 pages to be on the safe side and guarantee 1 free HugePage
    NUM_PG=1
    # Cumulative number of pages required to handle the running shared memory segments
    for SEG_BYTES in `ipcs -m | awk {'print $5'} | grep "[0-9][0-9]*"`
    do
       MIN_PG=`echo "$SEG_BYTES/($HPG_SZ*1024)" | bc -q`
       if [ $MIN_PG -gt 0 ]; then
          NUM_PG=`echo "$NUM_PG+$MIN_PG+1" | bc -q`
       fi
    done
    # Finish with results
    case $KERN in
       '2.4') HUGETLB_POOL=`echo "$NUM_PG*$HPG_SZ/1024" | bc -q`;
              echo "Recommended setting: vm.hugetlb_pool = $HUGETLB_POOL" ;;
       '2.6') echo "Recommended setting: vm.nr_hugepages = $NUM_PG" ;;
        *) echo "Unrecognized kernel version $KERN. Exiting." ;;
    esac
    # End

c.Run the following command to change the permission of the file:
     $ chmod +x hugepages_settings.sh
5.Run the hugepages_settings.sh script to compute the values for hugepages configuration:
$ ./hugepages_settings.sh
6.Set the following kernel parameter:
# sysctl -w vm.nr_hugepages=value_displayed_in_step_5
7.To make the value of the parameter available for every time you restart the computer, edit the /etc/sysctl.conf file and add the following entry:
vm.nr_hugepages=value_displayed_in_step_5
8.Restart the server.
$ grep Huge /proc/meminfo

Reference

摘自：

windows和linnux 平臺如何啟用 Large page？

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