System performance query

[Co Cap]

Am new in HP system admin.

Currently system is HPN4000 with HP-UX11 (5 CPU, 5GB RAM)

The statistics from glance are :
- Memory utilization is around 80-90%
- CPU utilization is average of 40% but can reach max of 98%
- Swap utilization at 70-80%

System slowed occasionly when doing some end-of-day batch processing (a lot of read/write to Oracle)

Just wonder is there a rule of thumb on the comfortable level of memory/swap utilization %?

I don't feel good with the 80-90% fugure and would like to make some recommendation, but need some proof or paper to back it up.

Thank,
Cap

[Bharat Katkar · Accepted solution]

While analyzing the system thumb rule is you look in this order:

Buffers/Memory/DISK/CPU

Any way find attached the document giving ceratin details of performance tuning.

Hope that helps.

[Co Cap]

Thanks for the performance cookbook.

My initial assessment could be memory bottleneck. I would like to bring the number down to say, 50-60% utilize and swap down to 40%.

Are these numbers the correct one to aim for? or lower?

Thanks,
Cap

[Steven E. Protter]

Try this data collection script. Its better and has a lower overhead than glance.

See attachment.

SEP

[Pete Randall]

Cap,

My rule of thumb is that you never want to use swap if you can help it. True, memory is expensive but you're not going to get any sort of decent performance from your system while you're shuffling pages back and forth to a dog slow disk device. With your 70-80% swap utilization, I would say you need another 5GB of memory!


Pete

[Bharat Katkar]

Yeah It mostly sounds like Memory bottleneck but still before you go for it give an indepth look at:

#sar -b

Reports buffer activity

See man sar;

[Mark Landin]

How much buffer cache do you have allocated? memory allocated to buffer cache cannot be used for processes, which may force more paging to occur.

The current wisdom is that, except in rare cases, anything more than about 400MB of buffer cache begins to show diminishing returns. It takes longer to scan large buffer caches, and again may cause more paging, which you want to avoid like the plague.

[Patrick Wallek]

Are you actually using swap or is it just swap that is reserved because of processes that are running?

Post the output of 'swapinfo -tam' so we can see.

If you are actually paging out, then you are SEVERELY short on RAM. However, if memory usage is only 80-90% I have a feeling you are confusing swap reservation with actual swap usage. ALL processes will reserve some amount of swap space when they start. That does NOT, however, mean they are actually using that swap space.

If your swapinfo output looks something like this:

Mb Mb Mb PCT START/ Mb
TYPE AVAIL USED FREE USED LIMIT RESERVE PRI NAME
dev 1536 0 1536 0% 0 - 1 /dev/vg00/lvol2
reserve - 500 -500
memory 1997 478 1519 24%
total 3533 978 2555 28% - 0 -


With 0% in the first line (or however many lines for 'dev' (device) swap, then you are OK.

If memory utilization is only 80-90% and you never actually page out, then more RAM may not necessarily help. The biggest factor is what is the PEAK RAM usage. If you do occasionally hit 100%, then you could possibly use more RAM. But if you never get above 90%, I wouldn't worry too much.

[Ted Buis]

Not sure that I would agree with Patrick that just because the system doesn't get above 90% Memory utilization that you wouldn't benefit from additional RAM. Correct me if I am wrong, but it is my belief that some applications (like Oracle) are smart enough to look at how much RAM you have and use what they can without creating pageouts. However if you give them more RAM, they will take advantage of the additional space. Also, there is the book on HP-UX Tuning and Performance by Robert F. Sauers, that has just been updated with a new addition which can be found at amazon.com.