Enabling large pages on Oracle Database 11g running on IBM AIX

For implementing Large Pages on AIX first you will need to choose large page size at OS level.
On AIX you can have multiple large page sizes of 4KB, 64KB, 16MB, and 16GB.

In this example we will be using a large page size of 16MB.

Steps for implemenatation:

1- Based on MOS Doc ID 372157.1 first you need to enable Large Pages at OS level

# vmo -r  -o lgpg_size=16777216 -o lgpg_regions=<Total number of pages>
# vmo -o lru_file_repage=0
# vmo -p -o v_pinshm=1
# lsuser -a capabilities oracle
# chuser capabilities=CAP_BYPASS_RAC_VMM,CAP_PROPAGATE oracle
# bosboot -a

This needs a server reboot

For complete instruction please review note ID 372157.1

2- Setting parameters at instance level

On AIX databases you only need to set LOCK_SGA to TRUE:

alter system set lock_sga=TRUE scope=spfile;

Note: On AIX databases, USE_LARGE_PAGES parameter has NO impact.
These parameters are only valid for databases running on Linux, the value of this parameter even if set to FALSE will be ignored on AIX.

By default when Large Pages is available on AIX it will be used by database instances regardless of USE_LARGE_PAGES parameter value. You only need to set LOCK_SGA.

3- Restart the instance and confirm Large Pages is in use:

After setting lock_sga instance must be restarted.
As I explained above, when Large Pages is available at OS level it will be used by instance, but the key point in here is how to confirm whether Large Pages is in use or not.

How to check if Huge Pages is used by Oracle instance.

For Oracle 11g running on AIX, no informational message is written to the alert log as what we see in the alert log of databases running on Linux.

So for your database instance running on AIX do NOT expect following lines in the alert log:

****************** Large Pages Information *****************
Total Shared Global Region in Large Pages = xx MB (100%)
Large Pages used by this instance: xxx (xxx MB)
Large Pages unused system wide = x (xxx MB) (alloc incr 4096 KB)
Large Pages configured system wide = xxx (xxx MB)
Large Page size = 16 MB
***********************************************************

The only way you can make sure large pages is being used by instance is checking memory usage at OS level:

Consider SGA_TARGET in your instance is 8G
Total number of Large Pages (with size of 16M) will be 8G/16M + 1 which is : 8589934592 / 16777216 + 1 = 513

Check the number of large 16M pages in use at OS level before starting your instance:

$ vmstat -P all
System configuration: mem=98304MB
pgsz            memory                           page
----- -------------------------- ------------------------------------
           siz      avm      fre    re    pi    po    fr     sr    cy
   4K  4420992  2926616   487687     0     0     5  1280   2756     0
  64K   582056   581916      754     0     0     0     0      0     0
  16M     2791       87     2704     0     0     0     0      0     0

In this example number of 16M pages in use before starting instance is 87 pages from total available of 2791 pages.

We start the instance with SGA size of 8G:

SQL> startup
ORACLE instance started.
Total System Global Area 8551575552 bytes
Fixed Size                  2238616 bytes
Variable Size            2348812136 bytes
Database Buffers         6190792704 bytes
Redo Buffers                9732096 bytes
Database mounted.
Database opened.
SQL> show parameter sga_target
NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
sga_target                           big integer 8G
SQL> show parameter lock_sga
NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
lock_sga                             boolean     TRUE

Then we check Large pages in use again :

$ vmstat -P all
System configuration: mem=98304MB
pgsz            memory                           page
----- -------------------------- ------------------------------------
           siz      avm      fre    re    pi    po    fr     sr    cy
   4K  4428160  2877041   420004     0     0     5  1279   2754     0
  64K   581608   530522    51695     0     0     0     0      0     0
  16M     2791      600     2191     0     0     0     0      0     0

As you can see the total number of 16M pages in use is now 600 pages, which is exactly 513 pages more than what it was before instance startup.
This proves that 16M pages have been used by our instance.

You can also check memory usage of your instance by checking one of the instance processes like pmon:

$ ps -ef|grep pmon
  oracle 14024886 31392176   0 14:05:34  pts/0  0:00 grep pmon
  oracle 41681022        1   0   Mar 11      -  3:12 ora_pmon_KBS

Then check memory used by this process is from 16M Pages:

$ svmon -P 41681022
-------------------------------------------------------------------------------
     Pid Command          Inuse      Pin     Pgsp  Virtual 64-bit Mthrd  16MB
41681022 oracle         2180412  2109504     1778  2158599      Y     N     Y
     PageSize                Inuse        Pin       Pgsp    Virtual
     s    4 KB               31820          0       1650       9975
     m   64 KB                2959        516          8       2961
     L   16 MB                 513        513          0        513

I hope this will be useful for you, and good luck.