Tuesday, November 10, 2009

Oracle on AIX Memory Issues

When using Oracle on AIX and while time passes database gets slower you must look the amount of memory that AIX uses for filesystem cache. This is not the fact if you user raw devices or filesystem accessed by CIO or DIO.

Examples from AIX 5.3

As root :

#svmon -G

svmon -G
size inuse free pin virtual
memory 4096000 3483045 612955 426604 3312529
pg space 2064384 62882

work pers clnt
pin 426507 0 97
in use 3306854 22 176169

PageSize PoolSize inuse pgsp pin virtual
s 4 KB - 1297893 62882 361900 1127377
m 64 KB - 136572 0 4044 136572

Here the memory used for filessystem cache is : ((176169+22)/4096000)*100 = 4%

My settings on this system are :

maxperm% = 10
minperm% = 5
strict_maxperm = 1
maxclient% = 10
strict_maxclient = 1
lru_file_repage = 0
v_pinshm = 0
maxpin% = 80

And LOCK_SGA set to false.

These settings was proposed by sysadmin having experience on AIX 5.3.
Although i was recommend to use v_pinshm=1 and LOCK_SGA=true we are testing the previous settings and we are having no problems.

So my recomendation is to start with the settings i post in discuss with your sysadmin and if you do not have the optimal performance try v_pinshm=1 and LOCK_SGA=true.

Server configuration :

3 Node RAC using shared RAW Devices and ASM plus GPFS and NFS for backup.
Each server has 16Gb of RAM and 2 RAC database instances each.

You can also check the following IBM resources.

VMM Tuning Tip: Protecting Computational Memory

AIX 5.3 Peformance Mangement Guide

Configuring IBM General Parallel File System (GPFS) with Oracle RAC http://www.ibm.com/servers/enable/site/peducation/wp/zb726/zb726.pdf

Optimizing AIX 5L performance: Tuning your memory settings

Support for pinned memory

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