Configure hugepages on linux for Oracle

Introduction

Due to some performance issues with our Oracle RAC 11gR2 cluster running on OUL 5 we decided  to increase the physical memory of both nodes in our cluster from 24G to 96G each. The memory of our main production database was also increase from 14G to 48G per instance. Since we did not want to run into issues with regards to memory pages (default 4KB) we also introduced hugepages.

Steps

1 – After installing the memory in the server and rebooting check if all memory is visible from the OS

root [ ~ ]# dmidecode -t 17 | grep Size

        Size: 16384 MB

        Size: 16384 MB

        Size: 16384 MB

        Size: 16384 MB

        Size: 16384 MB

        Size: 16384 MB

        Size: No Module Installed

        Size: No Module Installed

        Size: No Module Installed

        Size: No Module Installed

        Size: No Module Installed

        Size: No Module Installed

2 – Next we need to figure out how much HugePages we need to reserve. To do this we have to check what the size is of a Hugepage. This is by default 2048 kB :

oracle [ ~ ]$ grep Hugepagesize /proc/meminfo

Hugepagesize:     2048 kB

oracle [ ~ ]$

We want to assign 48 Gig to our Oracle instance PRODDB2

ð  (48G * 1024) * 1024 è 50331648 (size in kB)

ð  50331648 / 2048  è 24576 (minimum nr of hugepages we need to configure)

The number of hugepages the os needs to reserve has to be configured in /etc/sysctl.conf

# HugePages

vm.nr_hugepages=24580

We configured 4 more hugepages then required….just in case

Next reload the /etc/sysctl.conf file using sysctl -p

sysctl –p

Check if the amount of hugepages is actually configured :

root [ ~ ]# grep Huge /proc/meminfo

HugePages_Total: 24580

HugePages_Free:  24580

HugePages_Rsvd:      0

Hugepagesize:     2048 kB

That's it ...now we can use HugePages.