SAP Note

Header Data

Symptom

Transparent HugePages (THP) on a Linux system in combination with running Oracle Database or Oracle RAC are known to cause unexpected node reboots and performance problems.

Other Terms

Linux, Kernel, THP, Transparent HugePages, HugePages

Reason and Prerequisites

Standard HugePages are recommended to be used for Oracle databases in SAP environments. As a workaround until the bug is fixed Oracle recommends HIGHLY to disable the usage of Transparent HugePages (THP) on all database servers running Oracle. Oracle Engineered Systems like Oracle Exadata and Oracle Database Appliance are not affected.

Solution

Running single instance Oracle Database or Oracle Database with Oracle RAC on Linux distributions with enabled Transparent HugePages (THP) feature,as a workaround until the bug is fixed Oracle recommends HIGHLY to disable THP feature. This ONLY applies to the new feature Transparent HugePages, Oracle HIGHLY recommends the use of standard HugePages for larger SGAs that were recommended in SAP Note 1672954. One of the main difference of Standard HugePages and Transparent HugePages is that Standard HugePages had to be preallocated, THP are set up dynamically at runtime by the Linux kernel. Transparent HugePages (THP) feature merged in Linux kernel version 2.6.38. Details about THP can be find in Linux kernel documentation: /usr/share/doc/kernel-/vm/transhuge.txt THP are introduced with new Linux kernel in the following Linux distributions:

l RedHat Enterprise Linux 6

l SUSE Linux Enterprise Server 11 SP2

l Oracle Linux 6 with RHCK

l Oracle Linux 5 and Oracle Linux 6 using UEKR2

Information about THP feature are documented in the specfic release note of your distribution or your kernel. To determine the usage of Transparent HugePages take a look in your Linux kernel config file or in the kernel sys interface. The default value for enabled and defrag is set to always: cat /boot/config-`uname -r`| grep TRANSPARENT_HUGEPAGE cat /sys/kernel/mm/transparent_hugepage/enabled cat /sys/kernel/mm/transparent_hugepage/defrag Additional you find the running kernel thread khugepaged, which manage the dynamically allocation of the Transparent HugePages: ps axf | grep khuge 100 0.000 ?SN May03 0:00\_ [khugepaged] 98260.0 103244 820 pts/0S+21:30 0:00\_ grep huge You can see the usage of Transparent HugePages with grep AnonHugePages /proc/meminfo if you see a value >0KB your system use THP.

1871318 - Linux: Disable Transparent HugePages for Oracle Database

Version 3 Validity: 21.10.2013 - active Language English

Released On 21.10.2013 10:34:51 Release Status Released for Customer Component BC-DB-ORA Oracle

BC-OP-LNX Linux

Priority Correction with high priority Category Consulting

Other Components

To disable the THP feature you either need to change the Kernel grub configuration or with expanding the init scripts. Add the following to the kernel boot line in /boot/grub/grub.conf (this is the preferred method) and reboot the server: transparent_hugepage=never Other possible way is to expand your /etc/rc.local and reboot: 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

Validity

This document is not restricted to a software component or software component version

References

This document refers to:

SAP Notes

This document is referenced by:

SAP Notes (4)

1672954 Oracle 11g: Usage of hugepages on Linux 1567511 Oracle Linux 5.x SAP Installation and Upgrade

171356 SAP software on Linux: General information 1567511 Oracle Linux 5.x SAP Installation and Upgrade 1672954 Oracle 11g: Usage of hugepages on Linux 1310037 SUSE LINUX Enterprise Server 11: Installation notes