Exadata · Oracle

HUGEPAGES on Linux and USE_LARGE_PAGES

mehmeteser

For efficient use of Linux Memory, It is strongly recommended to set up HugePages. You can get the best benefit if you plan to use very large SGA size.

Oracle Support has a great support document on HugePages. You can check this document for more information : “What It Is… and What It Is Not… (Doc ID 361323.1)”

You can use the parameter USE_LARGE_PAGES for the database to use hugepages or not.

To check available HugePages

The following setup is configured for 120GB hugepage size.

[root@ftq1dbadm02 ~]# cat /proc/meminfo | grep HugePages
HugePages_Total: 61440
HugePages_Free: 59216
HugePages_Rsvd: 10694
HugePages_Surp: 0
Hugepagesize: 2048 kB

[root@ftq1dbadm01 ~]# cat /etc/sysctl.conf | grep vm.nr_hugepages
vm.nr_hugepages=61440

Control Use of HugePages

USE_LARGE_PAGES parameter is introduced but not documented in the reference guide. USE_LARGE_PAGES parameter can be set to the following values.

  • true (default) : If available free hugepage is enough for the SGA,  It is used by the database.
  • only :  If available free hugepage is NOT enough for the SGA,  database will not start.
  • false : Hugepages will not be used
  • auto

After the start of the database, Hugepage usage is written on the alert log. If you doubt, your database uses hugepages or not this is the first place you should check.

if USE_LARGE_PAGES = FALSE

Starting ORACLE instance (normal)
****************** Large Pages Information *****************
Parameter use_large_pages = FALSE
Large Pages unused system wide = 48522 (95 GB) (alloc incr 64 MB)
Large Pages configured system wide = 61440 (120 GB)
Large Page size = 2048 KB
WARNING:
Large Pages are not used as parameter use_large_pages=false.
For optimal performance, it is recommended to use Large Pages.
***********************************************************

if USE_LARGE_PAGES = TRUE

Starting ORACLE instance (normal)
****************** Large Pages Information *****************
Total Shared Global Region in Large Pages = 24 GB (100%)
Large Pages used by this instance: 12289 (24 GB)
Large Pages unused system wide = 48522 (95 GB) (alloc incr 64 MB)
Large Pages configured system wide = 61440 (120 GB)
Large Page size = 2048 KB
***********************************************************

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