RE: Excessive Paging - AIX Related?

Ethan,

AIX performs all file i/o via the OS's virtual memory. In other words, the VM (which is a combination of both the RAM and the Swap) is used for both executable (OS/user code) and user's memory area as well as for I/O buffers. This allocation is dynamic and certain upper and lower limits are set by the parameters in vmtune. At times of high i/o, you will find that the 'fre' mem (seen in vmstat' goes down drastically and the po/fr/sr goes up drastically as a result of old memory pages that served file i/o buffers are paged out. This is normal and in line with what you are observing and is similar to Solaris.

What you *should* be concerned about is excessive values in 'pi' as this indicates excessive paging-*in*, probably due to earlier pageouts of live pages that are still required. You are probably seeing high I/o waits since there is a lot of writes (paging out) to the swap area. 'iostat' will probably indicate that disks that host your swap area are almost 100% loaded. In this case, you should make sure that you (a) spread out swap on multiple disks, making sure that they are NOT on RAID-5. (b) allocate dedicated drives to swap areas if possible (no RAID5!).

FWIW, vmstat in Solaris is able to distinguish between pi/po values for executable, file i/o and 'other' (?) types of paging. Can you find out for us if AIX also provides this? (Don't have access to an AIX box).

Merry Christmas and a Blessed New Year!

John Kanagaraj
Oracle Applications DBA
DBSoft Inc
(W): 408-970-7002

Wanna know the reason for the season? Click on 'http://www.needhim.org'

• The opinions and statements above are entirely my own and not those of my employer or clients **

> -----Original Message-----
> From: Post, Ethan [mailto:Ethan.Post_at_ps.net]
> Sent: Thursday, December 20, 2001 10:35 AM
> To: Multiple recipients of list ORACLE-L
> Subject: Excessive Paging - AIX Related?
>
>
> Sorry for the cross post if you are the other big list.
>
> I am having some trouble finding a solution to a problem. This is
> specifically AIX related. Here is the gist.
>
> * Any large sort or import appears to cause paging to take
> place. I only
> say large because of the problems, in reality these are quite
> small objects
> for the machine we are running, 200,000 - 600,000 rows in the
> 200-400 MB
> range. Any way last night I was importing one of these objects.
>
> * CPU wio goes through the roof almost right away. Spending
> up to 50% of
> time waiting on IO.
>
> * vmstat shows huge numbers in po, fr, sr and a few block
> processes in b
> column.
>
> * hdisk0 goes 100% (swap space is here)
>
> * lsps -a shows swap space is only 40% utilized, never
> changes. There is
> only 2GB of swap, admin just increase to 4 GB but still on
> same disk. Not
> sure this will really help since it never was 100% anyway.
>
> * Setup- RS/6000 7026-M80 rack mount running AIX with
> 4-500Mhz processors,
> 4GB memory, 3-10/100 Ethernet cards, 2 fiber ports, and
> 2-18.2GB internal
> drives with RAID. The 2 fiber ports will attach to a storage
> area network
> providing access to EMC Clarion storage (see below)
>
> * Oracle is the only app on the box and I have configured
> about 2GB for the
> SGA. There should be plenty of free memory.
>
> I am pretty sure we hosed something up with are memory
> configuration. I see
> a lot of things about using vmtune to configure various AIC related
> parameters as too how much memory is can use for various
> things. Can anyone
> provide me with the direction to head in examining our
> configuration and
> what settings should/could be changed to improve the situation?
>
> Thanks,
> Ethan Post
>
> --
> Please see the official ORACLE-L FAQ: http://www.orafaq.com
> --
> Author: Post, Ethan
> INET: Ethan.Post_at_ps.net
>
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-- 
Please see the official ORACLE-L FAQ: http://www.orafaq.com
-- 
Author: John Kanagaraj
  INET: john.kanagaraj_at_hds.com

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