[Novalug] Can someone please settle this?

Ken Kauffman kkauffman@headfog.com
Tue Jun 17 15:48:13 EDT 2008


You hit on a point that is important:
"If Oracle has a enough RAM and never swaps, it will make no change at all.
"

SWAP should be an "in case of emergency" situation on the system.   Properly
sizing the box will make the impact of SWAP almost non-existent.

Ken


On 6/17/08, Robert Kuropkat <robert@kuropkat.com> wrote:
>
> *This message was transferred with a trial version of CommuniGate(tm) Pro*
>
>
> Jim Swanson wrote:
> > *This message was transferred with a trial version of CommuniGate(tm)
> Pro*
> >
> > On Tue, 2008-06-17 at 11:38 -0400, Megan Larko wrote:
> >> Jim Swanson wrote:
> >>> I hope this goes through.  Anyway, performance wise, which is faster,
> >>> having a dedicated swap partition or swap partition and a swap file on
> >>> another partition?  Thanks.
> >> Hello,
> >>
>
> <snip>
>
> >>> Jim
> >>>
> > Megan,
> >
> > This system is a RHEL 4 server running Oracle 10g, with 4GB RAM and
> > 1.3TB RAID.  The person "building" the system just hit default for
> > everything during the setup, and installed EVERYTHING on the disk.  The
> > only problem with this approach is the installer only allocates 2GB of
> > space for the swap partition, and Oracle really needs at least 4GB.  His
> > solution was to just go ahead and add a swap file.  But I believe that
> > the system will take a performance hit doing it that way, hence the
> > question.
> >
> > Jim
> >
> >
>
>
>
> I think the short answer is "it depends."  The slightly longer answer
> is, you'd have to be a EE to understand for certain.  The next longer
> answer would be, "measure it and see."
>
> Factors to consider:
>
> 1.  How many disk controllers do you have?
> 2.  How are the disks arrayed on those controllers?
> 3.  Can you isolate the swap partition? (own disk, own controller, etc.)
> 4.  How big is the disk with the swap partition?
> 5.  How fast is it?
> 6.  Where on the disk is the partition?
> 7.  What applications are on the system?
>
> Old school Oracle rules where that Oracle required AT LEAST twice as
> much swap space as RAM on the system.  Triple was better.  But that was
> before RAM was measured in the many Gigabytes.
>
> I think total old school would be to put the swap partition (not swap
> file) on it's own disk controller on the smallest, fastest disk you can
> find.
>
> Modern configurations with hardware raid arrays, higher disk speeds,
> etc.  pretty much mean no matter what you have it's probably "good
> enough" unless you have an obvious failure you can measure.
>
> An awful lot of work has gone into current Oracle/OS/disk array vendors
> to take all the guess work of optimization.  The common fallout from
> this is, optimization other than what the system does on its own can be
> very dicey and the only way to be certain is to measure before and
> after.  If you can't do that, there really is no pat answer to give out.
>
> Then of course, once you figure out the optimal performance for the swap
> partition, you have to see if all you did was expose a different
> bottleneck that negates the "optimumus" (cool word huh?) of your swap
> file configuration.  For instance, where are the Oracle data files
> located and how are the configured?  Is each tablespace represented by
> one data file or many?  Is the corresponding index file on the same
> partition?
>
> If you've gone this far of course, you can't ignore basic Oracle and
> Application tuning.  What kind of data are you pulling?  How much?
> indexed how? Can it be made read-only?  How much RAM are you giving it
> in the ora.config file? etc?
>
> Once that is done, you should take a look and decide if all the changes
> actually netted you enough to make the effort worth while.  You have to
> decide if you are willing to make the sacrifices needed to maintain
> everything you just did since there is likely something, or many
> somethings, that now makes it difficult to maintain.
>
> In short, unless it is horribly mal-configured, "fixing" the swap file,
> probably won't make a noticeable change.  If Oracle has a enough RAM and
> never swaps, it will make no change at all.  If you have a chance to
> rebuild the system and can do a single swap partition rather than a 2G
> swap partition and 2G swap file, then that is just cleaner and makes
> sense, but again, I doubt the technical performance increase will
> actually be noticeable.
>
> Robert Kuropkat
>
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