Re: OT: question about sizing swap for solaris
- From: dantow@xxxxxxxxxxxxxx
- To: oracle-l@xxxxxxxxxxxxx
- Date: Tue, 4 May 2004 10:24:46 -0500
Responses inline...
Quoting zhu chao <chao_ping@xxxxxxxxxxx>:
...
>
> To Dan Tow, your words said that if swap size is small, application will
> hit "out of memory", while that whitepaper on sun.com says, more swap space
> than needed can actually cause hard-pageout to occur more easily. There is
> some difference between your opinion and the paper.
Well, I haven't read the still-unreferenced paper, but absolutely there is a
difference between my opinion and what the paper apparently says - to be
clearer, in my opinion: low swap size "prevents" page faults (by triggerign
errors, instead) only in the same sense that running out of gas "prevents" bad
gas mileage!
> And you said , from experience, you saw some application with a lot of
> processes swapped out to disk, without performance impact on end user, is
> that an oracle database server? I think that will badly impact on system
> performance, according to my experience(Of course my experience is much less
> than that of yours).
My statement applies to database servers and non-database servers, alike. Where
I have specifically, quantitatively measured the true end-user costs of paging
and swapping, I have never seen them to be high, except on systems that were
victims of operating-systems swapping-algorithm bugs, which have long-since
been fixed. I *have* heard plenty of *anecdotes* about swapping and paging
being big problems, but I have never seen these stories backed up with hard
data. I certainly believe it's *possible*, though - you just need to buy less
memory than you need, in spite of how cheap memory is. I have gathered data on
a different subset of systems than you have, however, so it is entirely
possible you have seen one of those hypothetical systems with insufficient
memory.
>
> Regards
> Zhu Chao.
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