Significant virtual memory paging was detected on the RHEL 4.8

aamerjavaid · 11-11-2011, 05:06 AM

Hi Guys,

We are member of DB Team, and are investigating some performance issues on Database Server.

My current question is regarding Virtual Memory Paging, how can i determine what is in RAM, how to calculate what is composed of total RAM utilization and what is composed of total SWAP utilization?

Can i see what was the status of RAM/SWAP in some particular point in time?

What tools/techniques are available for Diagnosing SWAP Space?

Code:

Our System Config
=================
RAM 32G
SWAP 32G         (Previously was 16G 2 Months before)
Processor 32
HDD Direct Attached and 50% usage

Let me add, 2 months back, our Database started crashing, that time we had 16G SWAP, but when we created File based SWAP of 16G, it Database started working Normally without any issues.

Recommendations we got from Oracle Perspective.

Quote:

Significant virtual memory paging was detected on the host operating system.
RECOMMENDATION 1: Host Configuration, 100% benefit (38349 seconds)
ACTION: Host operating system was experiencing significant paging but no particular root cause could be detected. Investigate processes that do not belong to this instance running on the host that are consuming significant amount of virtual memory. Also consider adding more physical memory to the host.

Thanks,
Amir

aamerjavaid · 11-11-2011, 10:08 PM

Hi Guys,

Can you please guide me on this.

Thanks,
Amir

bweddell · 12-03-2011, 01:59 PM

My current question is regarding Virtual Memory Paging, how can i determine what is in RAM, how to calculate what is composed of total RAM utilization and what is composed of total SWAP utilization?
Assuming this is still happening, you can try 'top' and sort by memory (capital M to sort). Pay attention to the VIRT column.

Can i see what was the status of RAM/SWAP in some particular point in time?
By status of RAM/SWAP are you wanting to see what is used/remaining overall or do you want to get more granular (i.e. what processes comprise usage of each)? You can use sar -r -f /var/log/sa/sa## to look back at overall utilization.

What tools/techniques are available for Diagnosing SWAP Space?
In terms of swap, are you using any? I'd recommend you do a sar -W (realtime) or sar -W -f /var/log/sa/sa## (historical) to get more info or look at top. You can also look for kswapd processes from top which will indicate to you if the kernel is trying to swap.

syg00 · 12-03-2011, 07:43 PM

As you are DBA(s) and presumably will understand the database specifics of this. I like it as I ain't a DBA.

For your specific question, I doubt you will be able to accurately determine swap usage at the likely kernel level you are on. This support only recently became available for individual processes.