How to set up Hugepage for Oracle databases under Linux

Configuring Hugepage in Linux can improve Oracle performance and reduce the page exchange of Oracle SGA, similar to the Lagepage in Aix.

Why use a large page?

The default block size for Linux memory is 4K

If the SGA is: 128G

Select 128*1024*1024/4 from dual;33554432 (more than 30 million),

Select 128*1024/2 from dual; 65,536 A

Each page of memory, there is a page table entry (approximately 10 bytes), record page status, location

The default block size is 4K-page table size: 320M.

When 2M is on a large page, the page table occupies only. 625M

In Linux, each process page table is independent and has its own page table.

If there are 1000 processes: 1000*320m is about 320G.

and 1000 processes use a large page: 1000*0.625=625m

A large page was set, but was not used by Oracle for only two reasons:

(1), sga_max_size more than the big page

(2), no memory lock set

Memory: Is the stage where the process is active, and the Oracle database automatically looks for a large page setting when it is startup.

If so, distribute the SGA in the large page.

If not, the default block size is normally used to start.

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To set a large page step:

1. View the current large page usage of the system:

[Oracle@bys3 ~]$ cat/proc/meminfo |grep Huge

hugepages_total:0

hugepages_free:0

hugepages_rsvd:0

hugepages_surp:0

hugepagesize:2048 KB--Large page size is 2M

bys@ bys3>show Parameter Sga_max--view database SGA Size--my lab machine.

NAME TYPE VALUE

------------------------------------ ----------- ------------------------------

This column more highlights: http://www.bianceng.cnhttp://www.bianceng.cn/database/Oracle/

Sga_max_size Big Integer 216M

2. Set the number of large pages

--Here are 200 *2M=400M,SGA max 216M, large page memory larger than the SGA size to be used by Oracle, so I set 200.

Vi/etc/sysctl.conf

Add one line to the inside:

vm.nr_hugepages=200

Execute after Save:

Sysctl-p

View:--if hugepages_free: Less than 200, execute several times sysctl-p

[Root@bys3 ~]# cat/proc/meminfo |grep Huge

hugepages_total:200

hugepages_free:200

hugepages_rsvd:0

hugepages_surp:0

hugepagesize:2048 KB

3. Also need to set the memory Lock:--The number of memlock is larger than the number of large pages--set to 1, unlimited.

Vi/etc/security/limits.conf

Oracle Soft Memlock-1

Oracle Hard Memlock-1

[Root@bys3 ~]# Ulimit-l

3500000-----This number is for the limit of the number of large pages, enough to use.

4. Restart the database, the big page has been used by Oracle.

sys@ Bys3>shutdown Immediate;

sys@ Bys3>startup

Continuous execution during restart of the database; Cat/proc/meminfo |grep Huge, you can see Hugepages_free: The number of pages is decreasing, indicating that the large page is being used.

[Root@bys3 ~]# cat/proc/meminfo |grep Huge

hugepages_total:200

Hugepages_free:101

Hugepages_rsvd:10

hugepages_surp:0

hugepagesize:2048 KB