I have a AIX system (5.3) and it is at 100% usage of ram
now how to deal with this, without affecting the system, because it's a production system ?
here is the information about the system:
I would suggest some tuning of your box in first instance and than if you still have memory problems - add memory ?
If you have free memory on your frame and your lpar is configured accordingly (like the maximum memory in lparstat -i output being higher than the desired memory) you can do this dynamically.
I have put your posting into code tags - there is a link how to use them.
To your question:
AIX as well as other UNIX derivates and Linux distributions uses a part of it's RAM as file cache. So it is absolutely normal to have a close to 100% usage of RAM.
What would be a problem is when your box starts to page.
From your posting you can see, that a part of your Paging Space is being used:
So for some reason the OS had the need to page out some memory pages to disk as there was a demand for free RAM.
When this happens, you can monitor this by using things like
for example. There are two columns called pi and po, which stand for pages being paged out to disk and pages being paged in from disk which is somewhat slow in case they are needed again to be loaded into RAM (pi).
If there is any other values but 0, then you know that your box is paging. Even low values can sometimes mean problems on a busy system, as said especially when being paged in.
For long time monitoring it might be a good idea to use nmon which can be downloaded from IBM for free as it didn't come out of the box with AIX 5.3. There is also additional tools (nmon2rrd I think) to create graphs from the data to see at what time which impact happened.
Remember that the OS will keep the memory full. You should concentrate on the paging space usage more. You have little relative to real memory (about 10%) where most people will run with at least double paging space to real memory (or allocated memory for an LPAR). 100% full in itself is not a problem. It doesn't cause a performance loss unless you end up paging. A "full" page in memory can still be counted even if it is not in use. It's just there in case it is re-requested.
A requirement for a new memory page will overwrite an obsolete one. If all the memory pages are marked as in-use, then the last recently referenced page is moved to disk (I/O wait) and the real page re-used.
I doubt you have more that /dev/h6 assigned for paging (issue lsps -a) so you can't easily see what paging space is actually marked as required. Over version 6 of AIX, the paging space is cleared when the owning process ends. For version 5, you can (if you have more than one paging space) issue a swapoff command which will work through the names paging space, moving 'live' pages to any remaining paging space. You can then run swapon and then do the same with the other paging spaces.
The time you need to worry is if you are seeing the server in I/O wait and lots of paging activity. Use vmstat to spot this. You are looking at the pi and po columns. Large numbers tells you that you have a problem. We had this recently and from using ps -el|sort -n +9 we could see the biggest memory allocation process and then had to work out what they were. You may need to check the column being sorted. It is the SZ column.
We determined that the Cobol written application was not releasing memory and indeed increased it every time certain routines ran, and again and again if they ran again in the process's life. A small coding change later helped tremendously.
I hope that this calms your fears. After that, you are into purchasing memory I'm afraid, most often in pairs of cards, e.g. 2x4Gb card.
To add another paging space there are smit panels to help you under "System Storage Management (Physical & Logical Storage)" or you can read the mkps and chps manual pages.
I hoep that this helps, but please write back if you are still stuck.
Thx everyone for your replies !!!!
I was off for a couple of days and forgot to reply.
I was thinking that first the Ram will first be used and then the swap files, but I forgot this is not Windows machine
Anyway, this is all interesting. At the moment I am busy with Solaris systems and have a couple of AIX systems running. Those systems will be now managed by our AIX guy and I can concentrate more on the Solaris systems.
Thx.
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