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Out of memory

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Frequent Advisor

Out of memory

Dear all,

I've got 2 issues:

1. a RHEL Update 4 node was hanging with the error " Out Of Memory: Killed Process 21344 ( oracle ). It's a X64. What could be the issue?

2. Well, what is the most accurate way to get the free memory of the server. I was told to check:

free -m
total used free shared buffers cached
Mem: 16010 15990 20 0 69 10615
-/+ buffers/cache: 5304 10705
Swap: 4031 2314 1717

according to the above command, the system has 10705 free memory.

- top says 21180k free

- vmstat says 21300 free.

- meminfo says MemFree: 42556 kB

But there is a minute time diff as i was copying and pasting across. Please enlighten me.

Trusted Contributor

Re: Out of memory


How much memory there in your server???
Check how much of memory the oracle are use.
from the output of all commands, there is not enough memory to run normal system ( almost 42MB free), so I think you have bad memory utilization or you really need more memory for your system.
Ivan Ferreira
Honored Contributor

Re: Out of memory

The real used memory for applications it's what you see on +/- buffers/cache. This has been discussed a lot in this forum.

It's impossible to determine the cause of the problem with the information provided. I suggest you to install "collect for linux" collectl and capture performance information.

Por que hacerlo dificil si es posible hacerlo facil? - Why do it the hard way, when you can do it the easy way?
Court Campbell
Honored Contributor

Re: Out of memory

the oom killer kicked in. Please provide this output:

sysctl vm.overcommit_memory
"The difference between me and you? I will read the man page." and "Respect the hat." and "You could just do a search on ITRC, you don't need to start a thread on a topic that's been answered 100 times already." Oh, and "What. no points???"
Frequent Advisor

Re: Out of memory

Thanks to all,

Court Campbell, yes out of memory setting is at it's default.
vm.overcommit_memory = 0
should i make it 2. i think if it's to be done it should be done on a reactive basis rather than proactive. We have over 300 servers.
Ivan, can you please provide me some reference about memory usage and free memory allocation. According to my post, vmstat,top and the meminfo file is useless is it ?
Fayez, MemTotal: 16394912 kB is the one which is reported in /proc/meminfo, well now i have doubts whether these are really acceptable readings.

Finally, gurus please provide me some reference on how to get to know the actual memory utilisation physical/virtual.

Mike Stroyan
Honored Contributor

Re: Out of memory

The rule about looking at "free" output and adding the free and cache
values is generally correct. But it oversimplifies. Much of the
cache memory is easily released for reuse. But shared memory segments
can appear as "cached" memory although that cannot actually be freed.
If you look at the output of "ipcs -u" you can see the size of shared
memory segments. The values are reported in terms of pages rather
than 1K or 1M. The page size is almost always 4K, but varies on some
architectures. You can check that with the "getconf PAGESIZE" command.
Shared memory can be pushed from RAM to swap if swap space is available.
Doing that will be slower than releasing clean cache memory, since the
data will need to be written out to disk. If swap space runs out then
a system can start doing out of memory kills even though there is still
a lot of "cached" memory remaining.