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HP-UX 11.23 swap memory and tuning

 
Scott Lemasters_1
New Member

HP-UX 11.23 swap memory and tuning

I'm having problems with two HP 11.23 boxes each running Oracle databases and PeopleSoft applications. I'm getting an error in the syslog "deferred swap error." The Oracle database are taking a lot of memory, but it shows 2 GB free.

4 CPUs, 24 GB of RAM. swapinfo -tam shows the following:

Mb Mb Mb PCT START/ Mb
TYPE AVAIL USED FREE USED dev 4096 1757 2339 43% 0 - 1 /dev/vg00/lvol2
dev 12000 1753 10247 15% 0 - 1 /dev/vg00/swap2
reserve - 12586 -12586
memory 24559 20145 4414 82%
total 40655 36241 4414 89% - 0 -

Total is 89%.

I added 12GB of swap after we got the box 3 months ago.

kctune dbc_min_pct=2
kctune dbc_max_pct=5

sar -b shows %r at 83% and w% at 68%.

Should I just add swap? What else should I look at?
9 REPLIES 9
Mark Greene_1
Honored Contributor

Re: HP-UX 11.23 swap memory and tuning

There are other kernel parameters you need to look at. The important one is shmmax; if this is not set to be greater or equal to the amount of physical memory in your system, you're going to have problems. You also need to look at the other max* kernel parameters.

mark
the future will be a lot like now, only later
Ted Buis
Honored Contributor

Re: HP-UX 11.23 swap memory and tuning

Make sure your max swap chunks kernel parameter is high enough to cover all your swap space.
Mom 6
Ted Buis
Honored Contributor

Re: HP-UX 11.23 swap memory and tuning

Or is it just called swap chunks?
Mom 6
Andy Torres
Trusted Contributor

Re: HP-UX 11.23 swap memory and tuning

Don Morris_1
Honored Contributor

Re: HP-UX 11.23 swap memory and tuning

Irrelevant on 11.23 -- maxswapchunks doesn't exist anymore since 11.22.

In any event -- your swap is certainly fairly full (reservation wise). As to why specific Oracle requests are failing the lazy swap reservation, I really couldn't say without knowing the machine state at that time. Certainly, looking at the data you've presented -- 4Gb seems a reasonable buffer left, but for all I know Oracle is trying to shmat a 6Gb shared memory segment with lock-on-shmat properties.

In the short term - adding more swap will alleviate your immediate problem until your workload grows to consume your virtual address space again. On 11.23, you can go up to 32Gb of swap without touching a tunable. Higher than that and you'll need to set swchunk higher than the default. (man (5) swchunk).
RAC_1
Honored Contributor

Re: HP-UX 11.23 swap memory and tuning

What is the exact error message??

What does following say??

glance -m
vmstat 1 5
Do you see any pageouts??
There is no substitute to HARDWORK
Kent Ostby
Honored Contributor

Re: HP-UX 11.23 swap memory and tuning

Scott --

Keep in mind that HP generally recommends 2x RAM worth of device swap. Although at high levels of memory you can sometimes start with 1.5X and work your way up.

So if you are running with 24 GB of RAM, I would start with a minimum of 36 GB of device swap and work your way up from there.

Oz
"Well, actually, she is a rocket scientist" -- Steve Martin in "Roxanne"
Andy Torres
Trusted Contributor

Re: HP-UX 11.23 swap memory and tuning

DOH! swchunk. Good call, Don.

More swchunk info here:
http://docs.hp.com/en/939/KCParms/KCparam.SwChunk.html
Trond Haugen
Honored Contributor

Re: HP-UX 11.23 swap memory and tuning

I would say chances are you are running out of swap. But please post the full entry from syslog.

Regards,
Trond
Regards,
Trond Haugen
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