RE: Swap Usage
- From: "Mark W. Farnham" <mwf@xxxxxxxx>
- To: <in.amitverma@xxxxxxxxx>, "'Howard Latham'" <howard.latham@xxxxxxxxx>, <oracle-l@xxxxxxxxxxxxx>
- Date: Sun, 14 Dec 2008 05:18:37 -0500
swapon -s
is a little more clear, perhaps. It may vary by implementation, but I read
your chart below that you have about 2 GB of swap and it is all "in use." If
you need to swap more, something else (possibly already marked unrequired)
will have to be overwritten. If there is nothing out there on swap that
can't simply be dismissed (either because the RAM image is present or the
process that previously swapped is no longer running and the kernel just
didn't waste time cleaning it up).
Usually the more useful information is from a tool like sar or vmstat to
report the dynamic activity on swap. Significant dynamic reading from swap
means you're waiting for disk operations. The kernel wandering around in
slack time looking for things suitable to toss onto swap for potential quick
pageouts if you need free memory later is nothing to worry about, but it can
make your swap show up as all used.
In the neverending debate about how much swap is enough for a given amount
of RAM on a machine, no one will ever win. But the cheaper disk acreage
gets, the more sense it makes to have more swap than you really need.
Usually it makes sense to have enough RAM that you rarely if ever swap in.
If you're swapping IN and you can't get more RAM, then it makes sense to
change your job mix in some way. That can mean running memory hog batch jobs
serially instead of in parallel or reducing the number of allowed
interactive jobs or breaking out "client" type jobs to "middle" tier
servers.
I hope I've correctly read between the lines that your underlying question
is: "If I have no free swap, am I in trouble?" Probably not, but you can't
tell from a static snapshot. I'm not aware of a user level tool to walk
though swap to see how much of it is currently truly needed. If any real
kernel hacker wants to take the time to tighten up my broad strokes on this
behavior and correct any liberties I've taken in the interest of brevity,
have at it.
Regards,
mwf
_____
From: oracle-l-bounce@xxxxxxxxxxxxx [mailto:oracle-l-bounce@xxxxxxxxxxxxx]
On Behalf Of Amit Verma
Sent: Saturday, December 13, 2008 12:37 PM
To: Howard Latham; oracle-l@xxxxxxxxxxxxx
Subject: Re: Swap Usage
Thanks Howard,
But what I want to know the actual usage of the SWAP in the below:
[great@test01 ~]$ free -t -m
total used free shared buffers cached
Mem: 32132 32107 24 0 202 26510
-/+ buffers/cache: 5393 26738
Swap: 2047 2047 0
Total: 34179 34154 24
[agilis@omzdwcdrp009 ~]$
Thanks,
AV
On Sat, Dec 13, 2008 at 7:23 PM, Howard Latham <howard.latham@xxxxxxxxx>
wrote:
Version of Oracle version of os what Os
man -k swap - for linux
On 13/12/2008, Amit Verma <in.amitverma@xxxxxxxxx> wrote:
> Dears,
>
> How I can verify actual swap usage by the system.
>
> Thanks in advance,
> Amit Verma
>
--
Howard A. Latham
--
Amit Verma
Oracle DBA & System Adminstrator
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